WNT10B was first discovered by the Leder group in the mammary gland of mice in 1995 (Lee et al., 1995). Since then, WNT10B has been shown to play important roles in many tissue types in normal development (including bone, adipocytes, teeth, skin, hair, immune system, muscle, placenta, and heart) and diseases [including cancer, obesity, osteoporosis, and split-hand/foot malformation (SHFM)]. WNT10B was reviewed a decade ago (Wend et al., 2012). Here, we provide an update on the current understanding of WNT10B in normal development and disease from 2012 to 2022.

WNT ligands (e.g., WNT1, WNT3A, and WNT10B) can activate signal transduction in a β-catenin-dependent manner, referred to as “canonical” WNT/β-catenin signaling, and/or in a β-catenin-independent manner (e.g., WNT5A, WNT5B, and WNT7A), referred to as “non-canonical” WNT/β-catenin signaling. WNT10B is considered a “canonical”/β-catenin-dependent WNT ligand. Many WNT signaling reviews have summarized the signaling pathway with data combined from a variety of species and WNT ligands (MacDonald et al., 2009; Rim et al., 2022). Here, we will specifically summarize what is known for WNT10B (Figure 1).

Canonical WNTs bind to LRP5 and/or LRP6 and a frizzled (FZD) co-receptor to initiate signaling. WNT10B has been shown to interact with both LRP5 and LRP6 in different tissue-specific contexts. In the prostate cancer cell line PC3, WNT10B was shown by proximal ligation assay (PLA) to co-localize with FZD6 and LRP6 and then induce nuclear β-catenin in 5 min (Neuhaus et al., 2021). In osteoblasts, WNT10B upregulates the transcription of fatty acid metabolism genes via LRP5 (but not LRP6) (Frey et al., 2015). In addition, WNT10B expression is often correlated with LRP5 expression (Belaya et al., 2018; Li Z. et al., 2021). LRP5 and LRP6 are both required for WNT signaling reporter assay activity in response to WNT10B in mouse embryonic fibroblasts (Goel et al., 2012).

A molecular docking simulation study was performed to predict the binding affinity of WNTs with various human FZDs, and it predicted that human WNT10B has the highest binding affinity with human FZD3, 4, 5, 6, 7, 8, and 9 (Agostino et al., 2017). Tissue-specific receptor and co-receptor expression may determine ligand binding. Specifically in acute myeloid leukemia (AML), WNT10B signals through FZD4 and FZD5, while in T-cell acute lymphoblastic leukemia, WNT10B signals through FZD6 (Lazzaroni et al., 2016; Cassaro et al., 2021). WNT10B also interacted with FZD6 in a T-cell acute lymphoblastic leukemia cell line and HEK293T cells, as demonstrated by immunoprecipitation and PLA (Lu et al., 2019; Cassaro et al., 2021). In BeWo choriocarcinoma cells, WNT10B signaling requires FZD7 for migration but not the other expressed FZD family members (FZD1, FZD3, FZD5, and FZD10) (Wang et al., 2019).

The signaling output of the canonical WNT pathway is determined by the level of cytosolic β-catenin, which is under the strict control of the “destruction complex.” The core destruction complex is composed of AXIN, APC, and two constitutively active kinases [casein kinase 1 (CK1) and glycogen synthase kinase 3 (GSK3α/β)], which associate with β-catenin and promote its polyubiquitination by phosphorylating the degron motif of β-catenin (Stamos and Weis, 2013). Phosphorylated β-CATENIN is presented to the proteasome through its interaction with the F-box/WD-repeat containing E3-ligase protein β-TrCP, an adaptor protein that forms a complex with the SKP1/Cullin machinery, to facilitate assembly of K48-linked polyubiquitin chains on β-catenin, leading to it proteasome-dependent degradation (Kitagawa et al., 1999).

WNT ligands, including WNT10B (Lee et al., 2013), lead to the phosphorylation of GSK3β, which inhibits the destruction complex. Therefore, WNT10B stabilizes and activates β-catenin, as demonstrated by analysis of β-catenin (Abiola et al., 2009; Lei et al., 2015). Increased cytoplasmic β-catenin then translocates into the nucleus where it binds to members of the T cell factor/lymphoid enhancer factor (TCF/LEF) transcription factor family to drive transcription of WNT/β-catenin target genes, such as MYC, CCND1, and AXIN2. WNT10B activates the TOPFLASH reporter, a canonical WNT signaling reporter with TCF/LEF binding sites, which has been widely used as a readout of activated WNT10B signaling (Christodoulides et al., 2006; Suthon et al., 2022a).

WNT binding to FZD helps recruit DVL to the plasma membrane. Recruitment of DVL to the membrane provides a platform for AXIN and GSK3β to bind and phosphorylate LRP5/6, thereby preventing constitutive degradation of β-catenin (Sharma et al., 2018). In several studies, WNT10B was shown to induce DVL2 and/or DVL3 phosphorylation (Chen et al., 2008; Golestaneh et al., 2009; Lee and Heur, 2015).

WNT10B signals through RAC1, which is part of the canonical and non-canonical pathways. WNT10B can signal via FZD7 to activate RAC1 in placental extravillous trophoblasts to mediate migration (Wang et al., 2019). In corneal endothelial cells, WNT10B treatment caused an activation of RAC1 and an association of RAC1 and β-catenin in the nucleus. In contrast, WNT10B inhibited RHOA (a member of the same GTPase family as RAC1) activity (Lee and Heur, 2015).

WNT10B, which was first identified in the mammary gland, plays a very fundamental role in mammary gland development. It is the earliest (E11.5) expressed WNT ligand in the mammary anlagen and is a characteristic of the definitive mammary line (Veltmaat et al., 2004). However, research in the past decade has not focused on WNT10B in the normal mammary gland but on its role in breast cancer and other tissues (discussed in following sections).

WNT signaling is an important regulator of bone. Human mutations in LRP5 and SOST (sclerostin) alter WNT signaling and cause osteoporosis-pseudoglioma syndrome (OPPG) and van Buchem disease. Romosozumab (EVENITY), an antibody to sclerostin which activates WNT signaling, is an FDA-approved therapy for osteoporosis. In mice, knockouts of LRP5, LRP6, β-catenin, and many WNT ligands each have skeletal phenotypes (Maupin et al., 2013). In the previous decade, WNT10B-knockout mice and transgenic mice demonstrated the importance of WNT10B in bone and bone marrow-derived mesenchymal stem cells (Bennett et al., 2005; Bennett et al., 2007; Stevens et al., 2010). More recently, studies have focused on the regulation of WNT10B in bone and the therapeutic applications of WNT10B in bone.

Analysis of WNT10B single nucleotide polymorphisms (SNPs) has also supported a role for WNT10B in bone. A 2009 study demonstrated an association of two SNPs (rs1051886 and rs3741627) in the WNT10B gene with high hip bone-mass density and increased bone size in Afro-Caribbean men (Zmuda et al., 2009). A study on Danish men also showed a correlation of SNP rs10875902 (which is in high linkage disequilibrium with rs1051886) with bone mineral density (Van Camp et al., 2013). However, WNT10B-targeted studies in Spanish (Perez-Castrillon et al., 2009) and Chinese (Zheng et al., 2016) populations, as well as large GWAS (Estrada et al., 2012; Liu et al., 2020c), did not identify any correlations between WNT10B SNPs and bone properties.

WNT10B affects mesenchymal stem cells (MSCs), osteoblasts, osteoclasts, and T cells, which contribute to bone homeostasis. The effects of WNT10B from T cells affecting the bone are discussed later in the review (see Section 5: WNT10B and the immune system).

MSCs differentiate into osteoblasts, adipocytes, chondrocytes, myocytes, and other mesenchymal tissues. Osteoblasts and adipocytes have an inverse relationship; factors that increase osteoblastogenesis tend to decrease adipogenesis and vice versa. WNT10B is considered a master negative regulator of adipocyte differentiation (see Section 8). Thus, WNT10B is often used as a marker of increased osteoblastogenesis, decreased adipogenesis, or both (Liu et al., 2016; Matsushita et al., 2016; Yi et al., 2019; Palmieri et al., 2021), for example in bone marrow adipocytes (Georgiou et al., 2015; Lee et al., 2019).

An interesting model to study bone biology is the scales of goldfish. Teleost scales are formed by intramembranous ossification and comprise osteoblasts and osteoclasts. Tazaki et al. (2018) detected WNT10B by qPCR and in situ hybridization in multinucleated osteoclasts in fish scales. Furthermore, the inhibition of WNT10B with an anti-WNT10B antibody increased RANKL expression, increasing osteoclast differentiation (Tazaki et al., 2018), thereby supporting the role of WNT10B in increasing bone mineral density.

The majority of studies on WNT10B in the bone have focused on osteoblasts, and WNT10B is also expressed in osteoclasts. It is hypothesized that the WNT10B produced from osteoclasts links the coupling of osteoclasts and osteoblasts in the resorption cycle, inducing paracrine signaling to osteoblasts from the osteoclasts (Ota et al., 2013; Zheng et al., 2019). A loss-of-function mutation of c-kit in mice led to an increase in osteoclast expression of WNT10B and an increase in osteoblast differentiation and mineralization that could be blocked with a WNT10B neutralizing antibody or addition of recombinant DKK1 (Lotinun and Krishnamra, 2016). In the studies on WNT10B expression in osteoclasts, no direct effect of WNT10B on osteoclasts is shown, only the effect on osteoblasts. Therefore, it is unknown if WNT10B affects the osteoclast directly. Wnt10b-knockout mice or Wnt10b overexpressing mice (osteocalcin-Cre) have no differences in osteoclast numbers compared to wild-type mice (Bennett et al., 2007; Stevens et al., 2010), although the Wnt10b overexpressing mice have an increase in the bone resorption marker CTX (a collagen metabolite produced by type I collagen degradation due to osteoclast activity).

WNT signaling has been shown to regulate a vast array of biological functions in the immune system, including hematopoietic stem cells (HSCs), normal and malignant hematopoiesis, self-renewal, proliferation, and terminal differentiation of immune cells (Roozen et al., 2012; Bigas et al., 2020; Roo and Staal, 2020). The transcription factors downstream of WNT signaling, T cell factor 1 (TCF1) (Falk et al., 1983), and lymphoid enhancing factor-1 (LEF1) (Castrop et al., 1995) were first identified in immune cells. Of the 19 WNT family members, 12 play a role in immune cells, notably WNT2B, WNT3A, WNT5A, WNT5B, and WNT10B (Wend et al., 2012).

WNT10B’s main functions in the immune system have been shown to arise from T cells. The thymus is the primary organ for T-cell development. As the cells develop, they undergo a negative and positive selection to ensure appropriate T-cell function and the prevention of autoimmune or autoreactive T cells. This is an intricate and complex procedure by which both thymic stromal cells, most notably dendritic cells, and the thymus epithelia play critical roles in normal T-cell lymphopoiesis. Wnt10b mRNA has been detected in embryonic thymic development at day 13 (E13) (Balciunaite et al., 2002). The mouse hematopoietic progenitors have migrated to the bone marrow at this stage, but thymic development has not been completed. Since our last review, important new findings on the role of WNT10B in immune cells are discussed in the following paragraphs.

Parathyroid hormone (PTH) regulates calcium and phosphate homeostasis, which has an impact on bone turnover. Primary hyperparathyroidism (PHP) manifests into an increased risk for bone fractures due to its catabolic effects on bone. In contrast, iPTH therapies using amino acids 1–34 of PTH are used clinically to treat post-menopausal osteoporosis. In 2009, the Pacifici Lab demonstrated that iPTH increases the production of WNT10B in bone marrow CD8⁺ T cells, increasing trabecular bone density (Terauchi et al., 2009), previously reviewed in Wend et al. (2012). A follow-up paper from the Pacifici Lab demonstrated that the ability of iPTH to induce WNT10B expression in T cells is dependent on the parathyroid hormone receptor (PPR). A T-cell-specific PPR disruption (T-cell PPR^{T-cells−/−} mice) was generated by crossing PPR^flx/flx mice with mice expressing Cre under the control of a T-cell-specific promoter (Lck). Comparisons of PPRflx/flx versus PPR^{T-cells−/−} with or without iPTH therapies revealed that the PPR^{T-cells−/−} mice had no increase in bone marrow density in response to iPTH and iPTH failed to induce the production of Wnt10b. The results argued that the iPTH influence on T cells to secrete WNT10B protein depends on T cells expressing PPR (Bedi et al., 2012).

Furthermore, iPTH treatment expands hematopoietic stem and progenitor cells (HSPCs), but the underlining mechanism has been unknown. Li et al. (2012) demonstrated that T cells were required for the expansion of short-term HPSC (ST-HPSCs) mediated by iPTH, as this effect was abrogated by the disruption of PPR signaling. Mechanistically, secretion of WNT10B was required from the T cells to expand ST-HPSCs. Concurrently, WNT10B also activated WNT signaling in bone marrow stromal cells (BM-SCs). In the absence of WNT10B expression in T cells, several bone marrow stromal cell genes (Ahr, Axin2, Cyr61, Nkd2, Tagin, Tgfβ3, Thhbs1, Twist1, and Wisp1) were not induced by iPTH therapies. These data prove that WNT10B secretion from the T cell is necessary for ST-HSPC expansion after iPTH therapies (Li et al., 2012).

In a follow-up manuscript, Li et al. (2013) showed that ovariectomized (OVX, mice lacking ovaries and consequently, estrogen production) female mice expanded ST-HPSCs, which was dependent on the T-cell costimulatory molecule CD40 ligand (CD40L). T-cell production of WNT10B required the expression of CD40L for OVX mice to expand ST-HPSCs and activate bone marrow stromal cells. This model would suggest that the use of antiestrogens would expand ST-HPSC function. Moreover, this activity requires CD40L expression on the T cells for the secretion of WNT10B (Li J. Y. et al., 2013). Robinson et al. (2015) demonstrated that T-cell expression of CD40L potentiated the activity of iPTH bone anabolic activity. CD40L^−/− mice had decreased secretion of WNT10B from T cells, thus causing iPTH to be unable to increase trabecular bone density. Moreover, bone marrow stromal cells devoid of CD40L failed to upregulate the WNT10B-dependent WNT targets after iPTH therapy. This paper argues that CD40L expression is required for iPTH to induce the secretion of WNT10B from T cells (Robinson et al., 2015).

D’Amelio et al. (2015) evaluated the role of WNT10B production in T cells after iPTH therapy in a randomized trial of 82 women diagnosed with either osteoporosis or PHP. The randomized group included women treated with vitamin D and calcium alone (n = 22), 1–84 PTH (n = 42), or bisphosphonate ibandronate (n = 18). The results from the randomized trial indicated that patients with PHP did not increase WNT10B compared to healthy controls. In contrast, iPTH therapy increased WNT10B expression in T cells, compared to ibandronate treatment (D'Amelio et al., 2015). This was the first time it was shown that in humans, iPTH treatment increases WNT10B production in T cells but not in B cells or monocytes.

Cyclic adenosine monophosphate (cAMP) is generated following the engagement of the T-cell receptor (TCR) with antigen presented by antigen-presenting cells. cAMP-dependent phosphodiesterase (PDE) inhibitors such as pentoxifylline (PTX) can activate cAMP signaling. PTX, which activates cAMP signaling to downstream effectors PKA, had been recognized to increase bone formation, the mechanism of which was unknown. In a preclinical model, Roser-Page et al. (2022) used PTX to investigate bone turnover to determine if the mechanism of action was through T cells secreting WNT10B. PTX induced WNT10B production in CD3- and CD28-activated T cells. Suppression of cAMP mediator protein kinase A (PKA) decreased Wnt10b expression in the T cells. The increase in bone mass mediated by PTX occurs when T cells are activated.

WNT10B has differential expression in male and female immune cells. In wild-type CB57L/6 mice, the percentage of WNT10B-positive myeloid cells was higher in females than males. In contrast, males had higher levels of WNT10B-positive cells in lymphoid cells. Specifically in males, the absence of TNFα increased bone marrow WNT10B expression but significantly reduced the number of WNT10B-positive dendritic cells, CD4⁺ T cells, CD8⁺ T cells, macrophages, and granulocytes. These results suggest a possible role for TNFα activity in regulating the expression of WNT10B-positive immune cells. In contrast, ovariectomy reduced the expression of WNT10B in bone marrow cells, further demonstrating a role for estrogen and sex-specific regulation of WNT10B (Collins et al., 2017).

Periodontal disease (PDD) is a gum disease of the surrounding bone that supports the teeth and is mostly seen in adults. Wolf et al. (2016) used human periodontal ligament (hPDL) cells, which can exhibit osteoblastic properties, to model inflammatory PDD (Wolf et al., 2016). hPDL cells from the third molar, isolated from healthy subjects aged 12–14 years with no signs of periodontitis, and enriched CD8⁺ T cells, isolated from matched individuals, were either cultured alone or in combination and exposed to PTH (1–34). WNT10B expression was observed only in the T cells when PTH was added. hPDL cells were treated with recombinant WNT10B (rWNT10B) to measure the direct effects of WNT10B on the hPDL cells. rWNT10B marginally increased the proliferation of the primary hPDL cells, and over 3 days, the hPDL cells had increased osteoblast differentiation markers (alkaline phosphatase and osteocalcin protein levels). A co-culturing system with both the T cells and hPDL plus PTH (1–34) increased alkaline phosphatase and osteocalcin relative to control. A WNT10B neutralizing antibody reversed the effects mediated by PTH.

In addition to affecting bone mineral density, probiotics have been shown to prevent obesity and modulate the immune system. The probiotic bacterium Clostridium butyricum (CB) produces butyrate, which is known to inhibit pro-inflammatory cytokines. Li H. et al. (2022) evaluated the effects of CB on fat deposition (Li H. et al., 2022). CB administration increased blood butyrate suppressing adipogenic markers and size distribution of inguinal white adipocyte tissue (iWAT) and epididymal WAT (eWAT). Butyrate effectively increased anti-inflammatory peripheral regulatory FoxP3⁺ T cells (Arpaia et al., 2013). Li et al. (2022) showed an increased number of FoxP3⁺CD4⁺ Tregs after CB administration in iWAT tissue. FACS-sorted Tregs had an increase in Wnt10b mRNA levels. CB administration had no effects on fat accumulation in Wnt10bKO mice. These results determined that CB’s ability to block fat accumulation requires the secretion of WNT10B protein from Tregs. The role of WNT10B in adipocytes is further described in Section 8.

Rheumatoid arthritis (RA) is an inflammatory autoimmune disease that causes crippling disabilities in over 1.3–1.5 million people affected by this disease in the United States. RA-associated bone loss, and cartilage destruction is mediated by autoantigen autoreactive T cells (Fournier, 2005). In RA, T cells infiltrate the synovial membranes and initiate macrophages and synovial fibroblasts to transform into a tissue-destructive force. CD3 and CD28 mediate T-cell activation. A CD28-costimulatory pharmacological inhibitor abatacept (CTLA-4Ig), which is FDA-approved for intractable RA, causes T-cell dormancy (T-cell anergy), a form of perpetual tolerance after antigen interaction. Roser-Page et al. (2014) determined that abatacept increases bone mass in young (3 months) and mature (6 months) mice. Abatacept-treated mice had 200-fold higher Wnt10b mRNA in total bone marrow cells compared to the Ig control, and in vitro isolated T cells had a sixfold increase in Wnt10b expression compared to control-treated cells. Isolated T cells, activated by CD3, increased Wnt10b mRNA. In contrast, when CD3 and CD28 were co-activated, the increase in the Wnt10b mRNA expression was reversed. An antigen-presenting cell (APC) assay was conducted with isolated CD11C dendritic cells cultured with ovalbumin-specific peptide to serve as the APC. The challenged DCs were then co-cultured with CD8⁺ T cells expressing ovalbumin-specific TCR cells. A combination of both cell types increased Wnt10b mRNA levels over those of the two cell types alone. When abatacept was added to the APC assay, a 20-fold increase in Wnt10b mRNA was observed. These results suggest a novel role of antigen-presenting dendritic cells in increasing the levels of Wnt10b expression (Roser-Page et al., 2014). Roser-Page et al. (2018) paradoxically determined that, in the absence of Wnt10b, there was a decrease in bone mass rather than no change in response to abatacept (Roser-Page et al., 2018). The authors attribute this to an increase in sclerostin (a WNT inhibitor) in the bone marrow stroma of wild-type mice, but this is not shown in the Wnt10bKO mice, so this is not convincing.

Asthma is a chronic inflammatory disease that is very common among children and is often associated with the activation of CD4⁺ T-helper 2 cells (CD4^Th2). Trischler et al. (2016) used an in vivo house dust mite (HDM) asthma model. The HDM-treated mice demonstrate upregulation of Wnt10b mRNA in the lung and splenocyte-enriched T cells. The Wnt10bKO mice were challenged with HDM resulting in an increased number of eosinophils, EMBP protein expression (a marker of activated eosinophils), and Il4, Il13, Arg1, and Ccl2 mRNA expression over wild-type mice. This signature is consistent with either Th2 polarization or macrophage activation. Subsequently, splenic T cells were isolated from wild-type and Wnt10bKO mice, activated via CD3/CD28, and cocultured in the presence or absence of IL4 and IL12. Wnt10bKO T cells in the presence of IL4 increased GATA3 and IL4. GATA3 and IL4 expression levels are known to be produced from activated Th2. In contrast, Wnt10bKO T cells cultured in the presence of IL12 did not upregulate the Th1-promoting marker T-bet mRNA. Moreover, Wnt10bKO HDM-challenged mice increased effector T cells (CD4⁺CD44^hiCD62L^lo, CD4⁺CD69^hiCD11a^hi, and CD8⁺CD44^hiCD62L^lo). The results suggest that WNT10B expression regulates type 2 inflammation and the activation of a Th2 response in HDM-challenged mice.

Post-traumatic stress disorder (PTSD) frequently occurs in the aftermath of a psychologically traumatic event. PTSD is associated with a heightened inflammation that can be assessed by determining the levels of the inflammatory chemokines IL17A and interferon-gamma (IFNγ) in a patient’s peripheral blood mononuclear cells (PBMC). Bam et al. (2020) demonstrated increased levels of WNT10B in PTSD patients compared to healthy controls. miR-7113-5p was identified by microRNA expression analysis to be downregulated in PTSD patients and decreased the levels of WNT10B protein expression in a monocyte cell line (Table 1). rWNT10B treatment in human PBMCs in combination with PMA increased IFNγ expression significantly, relative to PMA treatment alone (Bam et al., 2020). In a follow-up study to determine how WNT10B is upregulated in PTSD, Bam et al. (2022) conducted RNA-sequencing on PBMCs of PTSD patients and determined that LINC008926 was upregulated compared to controls (Table 1). An increase in the open chromatin mark H3K4me3 at the promoter of WNT10B is due to LINC00896 recruiting a histone methyltransferase (MML1) onto the promoter of WNT10B. Knockdown experiments of MML1 showed a loss of WNT10B transcripts and a subsequent reduction in IFNγ. Conversely, the authors knocked down KDM5B (a histone demethylase) and increased the levels of the WNT10B transcript. rWNT10B added to preactivated PBMCs from healthy donors increased IL17A and IFNγ expression. ICG-001, which blocks CBP-mediated acetylation of β-catenin preventing active gene expression, significantly reduced the IL17A and IFNγ expression levels. Knockdown of LINC008926 in PBMCs and the lymphoblastic cell line TALL-107 decreased the WNT10B and IFNγ expression levels (Bam et al., 2022).

Severe infection elicits an inflammatory response, which causes an estimated 20,000 deaths worldwide, even when antibiotics are used. To better understand humans with sepsis, whole blood was analyzed for the correlation of inflammatory cytokines and WNT ligands. WNT10B correlated with the number of monocytes and expression of IL6 and TNFα, but not IL10, in patients with sepsis but not in healthy patients. In comparison, mice were administered LPS to induce endotoxemia, a model for human sepsis. In splenocytes, Wnt10b expression was significantly associated with Tnfα, Il12b, and Il10 after 1.5 h of LPS treatment. They further showed that canonical TLR4 signaling events via MYD88 mediated Wnt10b mRNA expression in response to LPS. Inhibition of WNT signaling by either ICG-001 or IWP-2 (a porcupine inhibitor, thereby inhibiting WNT secretion) reversed the cytokine signatures. Therefore, WNT ligands, including WNT10B, are part of the immune response during septic shock (Gatica-Andrades et al., 2017).

In 1998, WNT10B was shown to be expressed at the beginning of tooth development in epithelial cells, signaling to the mesenchyme (Dassule and McMahon, 1998). In the past decade, polymorphisms and mutations in WNT10B have been associated with tooth abnormalities.

Tooth agenesis is a developmental absence of certain teeth. Up to 20% of people are missing their third molar. An SNP (rs833843) in the 5’ promoter of WNT10B correlates with tooth agenesis (Magruder et al., 2018). The T allele at rs833843 was shown to have less transcriptional activation activity in a luciferase reporter assay compared to the C allele (Williams et al., 2021), suggesting that WNT10B levels are critical for tooth formation in humans.

Oligodontia is a severe form of tooth agenesis in which at least six teeth are missing. Four different coding mutations in WNT10B (p.Arg211Gln, p.Pro190Arg, p.Trp262^∗, and p.Phe284Cys) have been detected in families with oligodontia (Yu et al., 2016). In vitro expression of the mutant ligands decreased the activation of the TCF-luciferase reporter gene and decreased endothelial differentiation of dental pulp stem cells. The p.Arg211Gln mutation is predicted to decrease the binding affinity of the WNT10B ligand to FZD8, p.Trp262^∗ is a truncating mutation, and the other two mutations have unknown consequences (Yu et al., 2016). In a second study, Kantaputra et al. (2018) found that WNT10B mutations are associated with oligodontia, microdontia (small teeth), short tooth roots, dental pulp stones, and taurodontism (elongation of the pulp chamber of the tooth) (Kantaputra et al., 2018). Mutations in other components of WNT signaling (WNT10A, LRP6, and KREMEN1) have also been shown to lead to tooth agenesis (Chu et al., 2021).

SHFM is a congenital limb malformation characterized by the absence of certain digits, leading to a claw-like hand or foot. Mutations in WNT10B and several other genes have been shown to cause SHFM, with WNT10B mutations associated with SHFM type 6. WNT signaling plays a role in many stages of limb development during embryogenesis, and specifically, WNT10B is expressed in the limb bud at all stages (Wang and Shackleford, 1996). Mutations in WNT10B in patients with SHFM were first identified in a Turkish family in 2008 (c.994C→T, p.R332W) (Ugur and Tolun, 2008). Since then, several other case studies have shown a variety of WNT10B mutations in SHFM individuals (Khan et al., 2012; Ullah et al., 2018; Khan et al., 2019; Al Ghamdi et al., 2020; Bilal et al., 2020; Elalaoui et al., 2021). Many of these result in frameshifts or premature stop codons.

Interestingly, the patients with SHFM do not have tooth abnormalities and have different mutations than those with tooth agenesis (Yu et al., 2016). Individuals with tooth agenesis have mutations in amino acids between 190 and 284, and those with SHFM have mutations between 329 and 388, in addition to non-sense and frame-shift mutations. Furthermore, the knockout of Wnt10b in mice does not lead to an SHFM phenotype. Wnt10b knockout mice are obese and have low bone mineral density, which has not been reported in SHFM patients. Therefore, a mutated WNT10B is functionally different from the absence of WNT10B, or there are species-specific differences.

WNT10B is expressed in muscle cells. Myoblasts can differentiate into myocytes or adipocytes, and WNT10B signaling regulates this process. Wnt10b knockout mice have increased adipogenesis in actively regenerating myofibers (Vertino et al., 2005). This balance between myocytes and adipocytes was also demonstrated in the rotator cuff. There is increased adipogenesis in muscle tissue near a torn rotator cuff, and this is a prognostic factor for poor recovery after rotator cuff surgery. The expression of WNT10B is decreased in the muscle, corresponding with increased adipogenesis, after rotator cuff injury in a rabbit model and human patients (Shah et al., 2017; Kuwahara et al., 2019).

Additional evidence that showed the inverse biology between adipose and muscle was presented in a study comparing patients with high insulin sensitivity (IS) to patients with low IS. Adipose tissue from the high-IS group had a higher expression of WNT10B than the low-IS group. In contrast, the skeletal muscle from the high-IS had lower WNT10B expression than the low-IS group (Karczewska-Kupczewska et al., 2016).

Intramuscular fat (IMF) is an important characteristic of beef quality and taste, and castration increases the fat content. The muscle of castrated cows had a decrease in WNT10B expression compared to intact bulls. In castrated cows, there was an inverse correlation between WNT10B (and β-catenin) expression and fat content (Jeong et al., 2013). Therefore, Jeong et al. (2013) suggested that the WNT10B/β-catenin signaling pathway could be used to predict beef quality. Another study showed that WNT10B is higher in the longissimus thoracis muscle (used for ribeye steaks) compared to subcutaneous fat in an age-dependent manner (Soret et al., 2016). WNT10B expression did not vary between four different muscles with different IMF levels (Martinez Del Pino et al., 2017). Therefore, further work on the level of WNT10B and other genes in muscle and the relationship to IMF should be performed to optimize beef quality.

IMF is also a consideration in donkey meat. Guangling donkeys are raised in China for consumption. RNA-sequencing was performed on high- and low-fat Guangling donkey muscles. One of the most important regulated genes, based on co-expression networks, was WNT10B. WNT10B had increased expression in the high-fat group, in contrast to the expected inverse correlation in studies on humans and cows (Li W. et al., 2022) (see Section 8).

Wnt10b in muscle has also been studied in the zebrafish model. Wnt10b signaling inhibits the synthesis of fatty acids in zebrafish myocytes (Liu D. et al., 2019). Knockdown of Wnt10b mRNA led to an increase in triglyceride, total cholesterol, and non-esterified fatty acids in the muscle and corresponding increases in the expression of fatty acid synthetase, acetyl-CoA carboxylase, and ATP-citrate lyase. Wnt10b signaling is activated by vitamin E, an antioxidant, and Wnt10b regulates the activities of antioxidant enzymes (superoxide dismutase, peroxidase, and glutathione peroxidase) in the muscle of zebrafish (Liu et al., 2020b).

Fibrosis is the development of fibrous connective tissue as a reparative response to injury or damage. It is characterized by chronic inflammation, excessive accumulation of mesenchymal proteins [e.g., α-smooth muscle actin (α-SMA), vimentin, fibronectin, and fibroblast-specific protein 1 (FSP-1)], and an increase in the extracellular matrix that disrupts the normal tissue function. WNT signaling plays a role in fibrosis (Hu et al., 2020). In 2011, it was reported that the ectopic expression of Wnt10b in skin fibroblasts caused enhanced dermal fibrosis. In addition, in the past decade, further work in systemic sclerosis (SSc) and fibrosis in additional tissues [heart (see Section 12), lungs, liver, and penis] demonstrate a function for WNT10B, specifically in fibrosis.

WNT10B expression correlates with lung fibrosis. The addition of WNT10B increased the expression of mesenchymal markers and epithelial-to-mesenchymal transition. Conversely, the reduction of WNT10B by siRNA decreased mesenchymal markers and pulmonary fibrosis (Yang Z. et al., 2021). Furthermore, a reduction in WNT10B levels by miR-16 and miR-148a (Table 1), found in extracellular vesicles from the bronchial epithelium, decreased myofibroblast differentiation (Kadota et al., 2021).

WNT pathway genes (including Wnt10b) are upregulated in activated hepatic stellate cells leading to liver fibrosis. The mechanism includes repression of PPARγ and liver adipogenesis (Cheng et al., 2008). MSCs reduce liver fibrosis, and the treatment of liver fibrosis in rats with exosomes from MSCs decreased Wnt10b expression (Rong et al., 2019). A WNT antagonist also reduced liver fibrosis. In addition to WNT10B, other WNTs, including WNT1, WNT3/3A, WNT4A, and WNT5A, are implicated in liver fibrosis (Cheng et al., 2008).

Fibrosis is also present in penile cavernous tissue from diabetic mice and correlates with erectile dysfunction. This tissue has an increase in Wnt10b expression, along with an increase in the expression of four other WNT ligands. TGFβ also increased the expression of Wnt10b (Shin et al., 2014). Because the downregulation of Wnt10b with small interfering RNA did not decrease the production of extracellular matrix proteins in the fibroblasts, additional research on the role of WNT10B in this system should be performed.

The skin is the largest organ in the body and consists of appendages that include hair follicles, sebaceous glands, sweat glands, and nails. Many WNT ligands are expressed in the skin and the hair follicle (Wend et al., 2012). Importantly, the earliest and highest expressed WNT ligand in hair follicle development and hair cycle induction is Wnt10b (Reddy et al., 2001). Hair follicles have periodic stages: the anagen (growth stage), catagen (regression), and telogen (resting) stages. Wnt10b is only expressed in the anagen stage (Li Y. H. et al., 2013; Bai et al., 2021). Specifically, Wnt10b is restricted to follicular epithelial cells overlying the dermal condensate (Reddy et al., 2001; Hawkshaw et al., 2020). Overexpression of Wnt10b induces the telogen hair follicle to proceed into anagen earlier (Li Y. H. et al., 2013). Adenoviral Wnt10b increased the number of proliferating cells and, subsequently, the size of the anagen hair follicle (Lei et al., 2014). Increased proliferating CD34⁺ stem cells were also observed in the bulge region and the outer root sheath of the hair follicle.

Dermal papilla cells are specialized fibroblasts located in hair follicles that work as a signaling center for hair growth. WNT10B promotes the proliferation of cultured dermal papilla cells from mice, Angora rabbits, and Rex rabbits in vitro (Ouji et al., 2012; Bai et al., 2019; Wu et al., 2020). Cultured dermal papilla cells with WNT10B had the greatest hair follicle induction in skin reconstitution assays (Ouji et al., 2013). Together these papers demonstrate that WNT10B is produced by the epithelial cells, acting upon the fibroblasts in a paracrine manner. AXIN2, the canonical WNT target gene, while expressed in the epithelial cells, is highest in the mesenchymal cells in the early anagen (Hawkshaw et al., 2020).

WNT10B also plays a role in the differentiation of melanocytes (melanin-producing cells) of the hair bulbs during the anagen stage. Intradermal injections of adenoviral Wnt10b in a mouse led to more melanocytes with more pigmentation. Similar results were obtained when whisker follicles were treated with adenoviral Wnt10b. Adenoviral Wnt10b also increased the differentiation of a melanocyte cell line in culture (Ye et al., 2013).

WNT10B is potentially involved in the development of apocrine sweat glands. Apocrine sweat glands are found in hairy regions such as the axilla and secrete nutrients to the opening of hair follicles. While mice and chickens do not have these, sheepskin sweat glands show some similarities to human glands. Examining the complex network of development and maturation of apocrine sweat glands has shown that WNT10B has decreased expression in the gland budding stage, compared to the pre-gland stage, as determined by RNA-sequencing. In contrast, WNT16, WNT5A, and β-catenin are upregulated in the gland budding stage (Li S. et al., 2018). Functional studies were not performed.

The role of WNT10B in the skin is further elucidated by examining skin pathologies, such as SSc and psoriasis. SSc is a chronic connective tissue disorder causing fibrosis of the skin and other organs due to overactive fibroblasts. Fibroblasts of those with SSc contain higher levels of nuclear β-catenin, which correlates with increased expression of Wnt1 and Wnt10b (Beyer et al., 2012). Transgenic mice in which Wnt10b is expressed from the fatty acid binding protein 4 (FABP4) promoter have increased skin thickness and are used to study SSc and anti-fibrotic therapies (Wei et al., 2011). For example, inhibition of the X-linked inhibitor of apoptosis protein (XIAP) reduced the skin thickness of Wnt10b transgenic mice (Bergmann and Distler, 2016).

Psoriasis is a chronic inflammatory skin condition causing patches of itchy, flaky skin with scales (lesions). Samples from the lesional skin of psoriasis patients show significantly decreased WNT10B gene expression compared to the non-lesional skin of patients and skin from healthy individuals. WNT7B showed a similar gene expression pattern, and TCF7L2, a transcription factor downstream of WNT signaling, decreased in the lesional skin compared to non-lesional skin. The gene expression of WNT10B and WNT7B increases after treatment with narrowband UV, which is a therapy for psoriasis. IL-17 acts on keratinocytes and releases inflammatory mediators that lead to psoriasis symptoms. IL-17A inhibits WNT signaling in bone (osteopenia and osteoporosis have been associated with psoriasis). Although this has to be shown in the skin yet, psoriasis patients have increased IL-17, which could explain the low WNT expression in lesional skin. Current psoriasis therapy incudes IL-17 inhibitors, which not only reduce IL-17 signaling but also may help increase downstream WNT signaling to reduce inflammation (Assarsson et al., 2019).

Agents to increase hair growth could be used to treat various conditions, such as alopecia. Increasing the expression of WNT10B either directly or indirectly could induce hair growth. Several hormones and growth factors have been shown to regulate WNT10B, including androgens, melatonin, hepatocyte growth factor (HGF), vitamin D, and bone morphogenic protein 6 (BMP6).

Androgenetic alopecia is the most common type of hair loss in men. The androgen DHT decreases WNT10B expression in dermal papilla cells while increasing DKK1 expression. DHT decreases hair follicle stem cell differentiation in vitro, and the addition of rWNT10B reverses this effect (Leiros et al., 2017).

HGF from dermal white adipose tissue induces WNT10B expression in dermal papilla cells (Nicu et al., 2021). The topical application of small-molecule antagonists to c-Met (the receptor for HGF) for excessive hair growth has been suggested. This is clinically possible as c-Met antagonists have been approved for cancer.

Aoi et al. (2012) showed that vitamin D3 increased WNT10B expression in dermal papilla cells; however, vitamin D decreased their proliferation, and WNT10B has been previously shown to increase their proliferation. These conflicting results need to be clarified. All-trans retinoic acid upregulated WNT10B expression in a screen of 20 growth factors (Aoi et al., 2012).

Furthermore, BMP6 regulates the hair cycle and is expressed at the highest level in early anagen. BMP6 was shown to repress WNT10B expression and decrease the proliferation of hair follicle stem cells, and conversely, WNT10B repressed BMP6 expression and increased the number of proliferating hair follicle stem cells (Wu P. et al., 2019).

The promoter of WNT10B is DNA methylated in the catagen and telogen stages, whereas there is a decrease in methylation at the anagen stage, correlating with WNT10B expression. Furthermore, there is an increase in histone H3 acetylation, a marker of open chromatin, only during the anagen stage (Bai et al., 2021). The transcription factors that regulate the expression of WNT10B at the WNT10B promoter in hair follicles remain unknown.

In dermal papilla stem cells, WNT10B mRNA expression is downregulated by miR-329 (Table 1). The long non-coding RNA PCAT1 sponges miR-329 to allow the expression of WNT10B. The upregulation of PCAT1 or a decrease in miR-329 corresponded with enhanced WNT10B expression and increased the proliferation of the dermal papilla stem cells (Nicu et al., 2021).

WNT10B is also regulated by miR-15b-5p in dermal papilla cells, which in turn is sponged by lncRNA-599547 (Table 1). This long non-coding RNA was shown to be expressed in the secondary hair follicles of cashmere goats at anagen, thus allowing for the expression of WNT10B at anagen (Leiros et al., 2017).

WNT10B expression can be increased by melatonin, a hormone induced in the brain in response to light and dark. Seasonally, there are changes in the length of the day and, subsequently, the amount of melatonin released. Interestingly, the administration of melatonin can increase WNT10B mRNA and protein levels and improve the cashmere yields from cashmere goats, which produce it seasonally (Liu et al., 2021). While melatonin increased the expression of WNT10B, it remains unclear if this is a direct or indirect effect.

WNT10B expression in the heart was detected along with the cloning of the human gene in 1997. In fact, the tissues with the highest expression levels of WNT10B included the heart (Hardiman et al., 1997). Only in the past decade has there been functional data about the role of WNT10B in the heart, along with an association with fibrosis and disease.

WNT10B is expressed in the intercalated discs of normal cardiomyocytes, and in ischemic cardiomyopathy patients, WNT10B accumulates along the lateral borders of cardiomyocytes. Furthermore, WNT10B protein is increased in cardiomyocytes after experimental myocardial infarction in mice. Overexpression of Wnt10b in cardiomyocytes led to improved cardiac function. After injury, Wnt10b overexpression led to increased neovascularization and endothelial cell recruitment. WNT10B in the cardiomyocytes induced canonical WNT signaling (β-catenin accumulation in the nucleus and AXIN2 expression) in the endothelial cells but not in the cardiomyocytes, demonstrating paracrine signaling. The authors show that Wnt10b overexpression led to decreased fibrosis (decreased scar formation and decreased collagen deposition after cardiac repair) (Paik et al., 2015). This contrasts with other studies (described here) on fibrosis in the heart and the other tissues presented in Section 10.

Kamimura et al. (2016) demonstrated that WNT10B expression levels in the left ventricle increased in heart failure, which was correlated with fibrosis. Pioglitazone, a PPARγ agonist used for type 2 diabetes mellitus, has cardiac antifibrotic effects in animals and human patients. Pioglitazone inhibited WNT signaling and prevented the development of left ventricle fibrosis (Kamimura et al., 2016). WNT10B has been shown to suppress PPARγ in adipose tissue (see Section 8).

Fibrosis is also observed in autoimmune myocarditis. In a mouse model of autoimmune myocarditis, the angiotensin II/angiotensin receptor (Agtr1a) pathway is activated. Wnt10b and Wnt1 are lower in Agtr1a knockout cells with lower fibrosis. The authors state that reduced WNT signaling explains the reduced profibrotic response of Agtr1a^−/− cells (Czepiel et al., 2022).

Adipose tissue is also found in the heart, and its accumulation contributes to atrial fibrillation. Multipotent mesenchymal epicardium-derived cells, which can differentiate into adipocytes, express WNT10B. WNT10B expression is associated with repressed adipogenesis in these cells, as is seen in other MSCs (Suffee et al., 2017).

Only one study has shown a role for WNT10B in the nervous system (Tassew et al., 2017). In that work, WNT10B was shown to promote axonal regeneration. WNTs have previously been shown to be in exosomes. Tassew et al. (2017) showed that while fibroblast-derived exosomes are needed for axonal regeneration, WNT10B is not in the exosomes. Instead, WNT10B requires the exosomes for activity. What was present in the exosomes and affected WNT10B activity was not described. However, after the addition of exosomes, WNT10B re-localized to lipid rafts for endocytosis. Exosome-WNT10B induction of neurite outgrowth did not affect β-catenin. Instead, it led to mTOR activation and phosphorylation of S6 ribosomal protein (pS6K), indicating WNT signaling through the non-canonical pathway in neurons (Tassew et al., 2017).

WNT signaling is involved in angiogenesis (Olsen et al., 2017). In particular, a role for WNT10B in angiogenesis and endothelial cells has become apparent. Vascular endothelial growth factor (VEGF) is a key angiogenic growth factor. WNT10B regulates VEGFA in umbilical cord mesenchymal stem cells (Liu et al., 2020g) and vascular endothelial growth factor receptor 2 (VEGFR2) in endothelial cells ((Paik et al., 2015). Furthermore, the expression of WNT10B and VEGFA genes correlate in the subcutaneous white adipose tissue of 80 individuals, and hypoxia increases WNT10B and VEGFA in adipocytes (Pourdashti et al., 2022).

The vasculature plays a critical role in bone physiology and fracture healing (Owen-Woods and Kusumbe, 2022). Human umbilical cord mesenchymal stem cells transfected with WNT10B accelerated bone healing and induced endothelial cells to migrate and form capillary-like structures in a tube formation assay (Hu et al., 2022).

Treatment of corneal endothelial cells with IL-1β resulted in the activation of WNT10B expression and cellular proliferation. NFκB and c-Jun bound to the proximal promoter of WNT10B after IL-1β induction. Then, WNT10B stimulated proliferation by upregulating cyclin D1 expression. Co-treatment with a secreted frizzled-related peptide (sFRP), the β-catenin antagonist XAV939, or a disheveled-PDZ domain inhibitor blocked WNT10B signaling and proliferation. The modulation of WNT10B could treat vision loss secondary to corneal endothelial dysfunction (Lee and Heur, 2015).

The biology of WNT10B in the ovary beyond gene expression has not been determined. Single-cell RNA-sequencing was performed on normal mouse ovaries and ovaries from mice exposed to cigarette smoke, as cigarette smoke affects fertility. Nine different cell types were identified, including oocytes. WNT10B was specifically expressed only in the granulosa cells, and WNT signaling pathway genes were enriched. Cigarette smoke increased the expression of WNT10B mRNA (Li F. et al., 2022). Others have identified WNT10B expression in the full-grown oocyte, ovulated oocyte, zygote, and two-cell stage embryo (Harwood et al., 2008). WNT10B expression was downregulated in a mouse model of premature ovulatory failure (Ruohonen et al., 2022). Further studies should be carried out to assess the functional implications of WNT10B expression in the ovaries.

Dysfunctional placental development is associated with several pregnancy complications, including fetal growth restriction, which impacts 3%–7% of pregnancies in the United States. Several key steps are required for the formation of a functional placenta, including implantation in the maternal endometrium, formation of a syncytium for the exchange of food and waste, generation of villi, and remodeling of the maternal spiral arteries. These steps are accomplished by different subtypes of mature, differentiated trophoblasts, such as syncytiotrophoblasts (STBs), proliferating villous cytotrophoblasts (vCTBs), and invasive extravillous cytotrophoblasts (EVTs). Early work from Sonderegger et al. (2007), using differential gene expression analyses of WNT expression, showed that WNT10B expression is the highest in first-trimester trophoblasts but not detected in third-trimester samples. Interestingly, examination of human trophoblast cell lines showed the highest WNT10B expression in the EVT-like SGHPL-5 cells and in JEG-3 cells derived from choriocarcinoma (Sonderegger et al., 2007). These findings are supported by more recent studies from Takahashi et al. (2021), who found high WNT10B expression in EVT-like cell lines and primary EVT (Takahashi et al., 2021).

Recent work has identified functional roles for WNT10B in the CTB, STB, and EVT. Treatment of EVT cell lines with WNT10B induced CD44 and MMP9 expression and invasiveness, whereas knockdown of WNT10B decreased CD44 expression and invasiveness. In primary EVT, WNT10B treatment also increased invasiveness (Takahashi et al., 2021). This work is consistent with Wang et al. (2019), showing that the transcription factor glial cells missing 1 (GCM1) binds the WNT10B promoter and induces WNT10B expression. Secreted WNT10B binds FZD7, inducing EVT migration (Wang et al., 2019). These data suggest an important role for WNT10B in promoting the invasiveness of EVT. Takahashi et al. (2021) claimed activation of the canonical pathway by WNT10B. In contrast, Wang et al. (2019) claimed non-canonical signaling induced by WNT10B, showing no effect of WNT10B on the expression of AXIN2 and the failure of WNT10B to affect the expression from a β-catenin/TCF luciferase reporter (Wang et al., 2019). Furthermore, they showed the activation of RAC1 by WNT10B stimulation of trophoblast cell lines. In support of these studies, β-catenin transcript expression is reduced in first-trimester EVT compared to CTB (DaSilva-Arnold et al., 2015). Canonical versus non-canonical pathway induction by WNT10B in the regulation of EVT remains an open question.

In addition to playing an important role in the invasiveness of EVT, WNT10B regulates the cell fusion of STBs to form a syncytium. STBs are formed through the process of cell fusion of cytotrophoblasts. Forskolin treatment of BeWo trophoblast cells increased cAMP production, PKA phosphorylation, and CREB phosphorylation, which induced cell fusion to form the syncytium. Forskolin also selectively induced WNT10B expression, as other WNTs were unaffected (Malhotra et al., 2015). Forskolin induced WNT10B expression in JEG3 cells, a different trophoblast cell line (Wang et al., 2019). Interestingly, forskolin induced total β-catenin expression, suggesting a canonical role for WNT10B in cell fusion (Malhotra et al., 2017).

The hormone human chorionic gonadotrophin (hCG) is critical for the maintenance of pregnancy. hCG binds to the G protein-coupled receptor LHCGR to induce cAMP production. Treatment of BeWo trophoblasts with hCG induced the expression of WNT10B and cell fusion. Knockdown of WNT10B in BeWo trophoblasts reduced cell fusion, formation of active β-catenin, and the expression of syncytin-1, a key cell fusion protein (Malhotra et al., 2017). These data suggest that hCG induction of WNT10B promotes the fusion of the epithelial cytotrophoblast cells to form the syncytium for the exchange of food and oxygen. Therefore, WNT10B plays key roles in human differentiated trophoblasts that form the functional placenta. Interestingly, the role for WNT10B in murine placental development and function has not been examined. Based on studies in the human placenta, we predict that Wnt10bKO mice may be an important tool for understanding the role of WNT10B in the placenta.

Many WNT10B polymorphisms have been identified in various conditions across species. Thus far, we have discussed polymorphisms in the WNT10B locus associated with obesity, dental anomalies, SFHM, and bone mineral density in humans. Additionally, the G607C polymorphism in the WNT10B promoter is associated with the Yin Deficiency pattern (a type of stroke in traditional Korean medicine that results from a deficiency of yin fluid and essence, incapable of restraining yang) and a phenomenon called bi-sup (a kind of body shape in Korean medicine) in Korean cerebral infarction patients (Ko et al., 2012; Ko et al., 2015). In cows, WNT10B polymorphisms in different breeds associate with body height, body length, body weight, and chest circumference (Zhao et al., 2012). In pigs, a polymorphism in the promoter of WNT10B is associated with litter size, as do two other WNT pathway genes [TCF12 and catenin alpha-like protein 1 (CTNNAL1)] (Tao et al., 2013). In Bernese mountain dogs, an SNP near WNT10B is associated with elbow dysplasia (Pfahler and Distl, 2012).

The knowledge and understanding of WNT10B have been greatly enhanced in the last decade. Interestingly, WNT10B has been studied not only in human, rodent, and zebrafish model systems, but also in goats, rabbits, sheep, cows, pigs, donkeys, and dogs. WNT10B is an oncogene in over 15 cancer types. WNT10B plays a role in cancer and has been implicated in the pathogenesis of osteoporosis, obesity, oligodontia, tooth agenesis, SHFM, fibrosis, PTSD, asthma, and rheumatoid arthritis (Figure 2).

WNT ligands regulate stem cell biology, and WNT10B has been ascribed roles in mesenchymal, mammary, prostate, skin, hematopoietic, dental pulp, and cancer stem cells. WNT10B expression correlates with stem cell proliferation or differentiation, but the mechanism of action of WNT10B in stem cells is not well defined. This is an important area for future studies in regenerative medicine and anti-cancer therapies.

Although several WNT-signaling inhibitors are in early clinical trials for various cancer types, no WNT-specific drugs have been FDA-approved for cancer to date (Harb et al., 2019). In contrast, the WNT signaling activator (the anti-sclerostin antibody EVENITY) is approved for osteoporosis. However, this may not be through the activation of WNT10B signaling, as there remains an increase in bone mineral density in the WNT10B knockout mice treated with the anti-sclerostin antibody. Nevertheless, targeting WNT10B signaling could lead to therapies for many conditions.

The past decade has focused on WNT10B regulation. Numerous miRNAs, lncRNAs, and a circRNA regulate WNT10B (Table 1). miR-148a, the most studied of the RNAs, regulates WNT10B in adipocytes, lung fibrosis, pancreatic cancer, oral squamous cell carcinoma, colon adenocarcinoma, endometrial carcinoma, and thyroid cancer. In addition, many transcription factors and chemicals (such as butyrate from probiotics) regulate WNT10B.

In addition to therapeutics and understanding more about WNT10B regulation in different cell types, emerging areas for WNT10B studies may include fetal growth restriction and placenta biology, immune-oncology, and the tumor microenvironment in various cancer types. The work in the last decade on understanding the role of WNT10B in a variety of normal and disease processes is fascinating and holds exciting promise for enhancing our future understanding of normal development, pathogenesis, and treatment.