Non-alcoholic steatohepatitis is characterized by inflammation and hepatocellular injury; it plays a central role in the development of liver fibrosis, with a 40% incidence, making it the second leading cause of liver transplantation in the United States (Carter and Friedman, 2022; Noureddin et al., 2018). As the main fibrogenic cell type in the liver, the excess of the extracellular matrix via the activation of HSCs is a hallmark feature in the prognosis of patients with non-alcoholic fatty liver disease (NAFLD) (Hagström et al., 2017). Single-cell RNA-sequencing analysis (scRNASeq) of HSCs has identified a specific transcriptome signature in NASH patients (He et al., 2023). Sixty-one genes were enriched in the cell cluster of activated HSCs but not in the population of inactivated HSCs (He et al., 2023). Specifically, the expression of genes essential in cell-mediated immunity and anti-viral activity, such as interferon-induced transmembrane protein 1 (IFITM1) and macrophage migration inhibitory factor (MIF), is upregulated. Genes relevant for cell adhesion, cell proliferation, and cell-cell communication- such as collagen type 1 alpha 1 chain (Col1A1) and 2 chain (Col1a2), S100 calcium-binding protein A11 (S100a11), alpha-actinin-2-associated LIM protein (Pdlim3), galectin 3 (Lgals3), spondin 2 (Spon2), nicotinamide N-methyltransferase (Nnmt) and collagen triple helix repeat containing 1 (Cthrc1)- are augmented and correlated with the severity of fibrosis in NASH (Azevedo Foinquinos et al., 2020; Feng et al., 2021; He et al., 2023; Heinrichs et al., 2021; Hou et al., 2018; Qi et al., 2017; Shin et al., 2018; Sun J. et al., 2024; Teng et al., 2021; Wu C. et al., 2021; Younossi et al., 2009) (see Table 1). Moreover, epidermal growth factor (EGF), platelet derived growth factor (PDGF), and transforming growth factor beta (TGF-ß)-mediate HSCs activation (Ahmed et al., 2022; Bhushan et al., 2019; Wiering et al., 2023; Table 1). Tamoxifen-induced expression of PDGF subunit B (PDGF-B) in the liver of transgenic mice acts as a proliferative and profibrogenic stimulus, inducing transdifferentiation of HSCs; additionally, expression levels of MMP-2, MMP-9, and TIMP-1 are upregulated, with no significant changes in TGF-ß (Czochra et al., 2006; Table 1). This suggests a TGF-ß-independent mechanism in PDGF-B transgenic mice and highlights the importance of the specific markers across transition to activated HSCs in different models of liver disease. For example, the expression of PDGF can be up-regulated in response to Il-1α as well (Andrae et al., 2008). Interestingly, the gene encoding the expression of the PDGF receptor beta shows upregulation in inactivated HSCs in NASH but not in quiescent HSCs in healthy cell-clusters (He et al., 2023), suggesting a PDGF-dependent mechanism in the early stages of NASH followed by activation of HSCs and transition to fibrotic states.

The transcriptional signature of qHSCs differentiation into myofibroblasts shows high activity of the transcription factors FOS like 1 (FOSL1) and FOSL2, members of the activator protein-1 complex (AP-1) (Kim et al., 2024; Rippe and Brenner, 2004; Taha et al., 2023). Overexpression of Fosl1 promotes spontaneous liver fibrosis in mouse models and is associated with the progression of liver tumors and worse prognosis in patients with hepatocellular carcinoma (HCC) (Taha et al., 2023). Members of the Nuclear Factor-kß- (NF-kß) family, such as NF-kB1, NF-kB2, and RELB, are highly active at early stages of HSCs activation. NF-kß plays a key role in hepatic injury, particularly in the transition of fibrosis to HCC (Luedde and Schwabe, 2011; Shen et al., 2014; Wu Y. J. et al., 2021). The mammalian NF-kß family dimers comprise the interaction of five subunits: p50, p52, cRel, p65 (also known as RelA) and RelB, encoded by NF-κB1, NF-κB2, REL, RELA, and RELB, respectively (Ghosh and Hayden, 2008; Hoffmann et al., 2003). NF-kß activation may occur via canonical and non-canonical pathways. The canonical NF-kß pathway is activated in response to inflammatory stimuli and is related to the activation of HSCs (Elsharkawy et al., 2010). Various drugs including Sofosbuvir and Velpatasvir display antifibrotic effects in carbon tetrachloride (CCl₄)-induced fibrosis rat model; these effects are not dependent on their antiviral activity but are mediated through the suppression of HSCs via regulation of TNF-α levels and its downstream NF-κB pathway (Yasmeen et al., 2023). The activity patterns of the transcription factor WT1, the paired related homeobox protein 1 (PRRX1), and the transcription factor myocyte enhancer factor 2 (MEF2) demonstrate high activation in myofibroblasts in both mouse and human cells (Kendall et al., 2019; Merens et al., 2025; Wang et al., 2004). For example, Prrx1 is involved in PDGF-dependent HSCs migration via modulation of metalloproteinases MMP2 and MMP9 expression. Moreover, administration of an adenoviral-mediated Prrx1 shRNA attenuates liver fibrosis induced by thioacetamide in rats (Gong et al., 2017). Similarly, Mef2 interference RNA significantly inhibits the expression of smooth muscle- α (α-SMA), COL1A1, and proliferating cell nuclear antigen, all markers in liver fibrogenesis. Collectively, these findings suggest that the upregulation of these genes is conserved between humans and mice and that they play pivotal roles in HSCs activation across different liver injury models (Table 1).

In the last two decades, the HCC mortality rate has increased globally (Singal et al., 2023). In both primary and metastatic liver cancers, HSCs are the main source of activated myofibroblast-like cells (Cogliati et al., 2023). The scRNASeq data from fibrotic mouse liver (GSE1326620), human cell populations of patients with NAFLD (GSE49541), and patients with liver fibrosis during HBV infection (GSE89632, GSE84044), were retrieved from the Gene Expression Omnibus (GEO) dataset. The in-silico reconstruction of a single-lineage pseudo-time trajectory of HSCs activation identified three pseudotime-dependent differentiation stages. After the quiescent cell type (stage 1), HSCs display two diverse stages (stages 2 and 3) during in vitro transdifferentiation process (Wang H. et al., 2022). The downregulation of qHSCs markers such Lrat, Reln, and Rgs5, along with high expression levels of Acta2, Ccn2, and Mmp10- markers of activated HSCs- are characteristic of the early stages of HSCs-to-myofibroblast transition (state 2). For example, LRAT encodes the main enzyme in retinyl esters production in qHSCs, specifically lecithin: retinol acyltransferase (LRAT). The loss of retinyl esters is characteristic of activated HSCs; this disruption in retinyl ester metabolism is mediated by reduced levels of Lrat, loss of LRAT activity, and enhanced breakdown of retinyl esters (Haaker et al., 2024; Wang H. et al., 2022). Reelin, an extracellular matrix protein, has been studied in silico and in vivo, demonstrating lower levels of reelin in activated HCSs compared to qHSCs. Meanwhile, reelin expression is not detectable in rat liver myofibroblasts, indicating reelin as a key protein for distinguishing the transdifferentiation states of HSCs (Kobold et al., 2002; Wang H. et al., 2022). The regulator of G-protein signaling-5 (RGS5) is encoded by Rgs5. RGS5 controls contraction, migration, and fibrosis in HSCs by regulating G-protein coupled receptor (GPCR)-mediated signaling, via endothelin-1 (ET-1) and angiotensin II (AngII) (Bahrami et al., 2014; Wang H. et al., 2022). Interestingly, the levels of activated HSC markers show an increased pattern at the early stages of differentiation (state 2). Smooth muscle α actin (Act2) is undetectable in qHSCs isolated from normal livers but is abundant in activated HSCs, where it reduces cell motility and contraction (Rockey et al., 2013; Wang H. et al., 2022). The cellular communication network factor 2 (Ccn2)/connective tissue growth factor (Ctgf) (CCN2/CTGF), an extracellular signaling modulator, and the Slit2 ligand synergistically mediate HSC activation and fibrotic response in CCl₄-induced liver injury by activating phosphatidylinositol 3-kinase (PI3K) and AKT signaling pathways. In vitro studies suggest that the production of CTGF/CCN2 is primarily regulated by TGF-β (Pi et al., 2023; Rachfal and Brigstock, 2003; Wang H. et al., 2022). The matrix metalloproteinase 10 (Mmp10) is also involved in fibrosis progression in the liver. The increase of MMP10 expression can be detected after acute liver damage, for example, following a single dose of CCl₄; the secretion of MMPs degrades the normal extracellular matrix, leading to the activation of HSCs (Han, 2006; Knittel et al., 2000; Wang H. et al., 2022; Table 1).

Genes involved in liver carcinogenesis are upregulated in stage 3, when HSCs are predominantly differentiated into myofibroblasts (Wang H. et al., 2022). Interestingly, Npm1, Rack1, Mif, Cstb, Arpc2, and Krtcap2, crucial in cell proliferation, differentiation and migration, fibrogenesis, immune response, cell-cell junction, and HCC metastasis (Bourd-Boittin et al., 2008; Ding et al., 2023; Huang et al., 2021; Liu et al., 2015; Moles et al., 2009; Qin et al., 2021; Sun et al., 2023; Wang H. et al., 2022), are expressed at much higher levels in activated HSCs derived from cancer-associated fibroblasts than in diet biliary fibrosis or mice biliary fibrosis model (Wang H. et al., 2022), highlighting these specific genes as possible early indicators of the liver tumor microenvironment (Table 1). Moreover, genes associated with the regulation of signal transduction by p53 class mediators- essential for DNA damage response, intrinsic apoptotic signal, and regulation of protein ubiquitination- constitute more than 30% of the genes overexpressed in clusters of activated HSCs (Wang H. et al., 2022).

The etiology of AD remains unclear, but hallmark lesions in AD are characterized by abnormal folding and aggregation of amyloid-ß (Aß) and Tau proteins (Breijyeh and Karaman, 2020; Cummings et al., 1998). Astrocytes are involved in the pathophysiology of AD (Breijyeh and Karaman, 2020; Cai et al., 2017; Verkhratsky et al., 2010). Early studies on AD have shown an abundant population of glial cells at the neuritic plaques. It is now well established that reactive astrogliosis at the late stages of AD is a pathological modification observed in both the human brain and tissues isolated from AD animal models (Verkhratsky et al., 2010). Sequencing of single-nucleus RNA from astrocytes in brain regions representing the hierarchical spreading of pTau neurofibrillary tangles (NFB) along neural networks (i.e., using the Braak NFT staging system: entorhinal region, inferior temporal gyrus, dorsolateral prefrontal cortex, secondary and primary visual cortex), reveals transcriptomic changes in astrocytes throughout the temporal progression of AD in human brains (Serrano-Pozo et al., 2024). The expression of relevant genes in cell energy metabolism (Aldh2, Ckb, Pfkb), lipid metabolism (Apoe, Lrp4), cell-cell communication and mitochondrial function (Gjal1), and intracellular transport (Atp2b4, Slc27a1, Slc38a2, Slc39a11, Slc39a12, Trak1) is low at early and intermediate stages, peaks at the late stages of AD, and then decreases expression without returning to baseline at the end of the stage characterized by moderate NPs (Bhalla et al., 2023; Lv et al., 2015; Ren et al., 2020; Serrano-Pozo et al., 2024; Sun et al., 2016; Wilson et al., 1997; Zheng et al., 2024; Table 2). However, specific genes are upregulated in astrocytes at late stages of AD. These include genes that encode heat shock proteins (HSP90AA1, HSP90AB1, HSPA1A, HSPA1B, HSPA4, HSPA4L, HSPA8, HSPA9, HSPB1, HSPD1, HSPH1), antioxidant response (NFE2L2, PRDX1, SOD1, SOD2), inflammatory response (IL17RB, NFAT5), translation factors (EEF1A1, EIF1, EIF2S2), cytoskeleton and extracellular matrix proteins (CLIP2, MAP2, VIM, MMP16, PLOD2 and 3, SERPINH1, ST6GALNAC6), and glutamate metabolism (GS, Glt-1) (Escartin et al., 2021; Geisert et al., 1990; Nakano-Kobayashi et al., 2023; Serrano-Pozo et al., 2024; Szeliga, 2020; Table 2). These findings demonstrate that astrocytes exhibit a strong response to various types of stress in AD.

A pathological feature of PD is the degeneration and loss of dopaminergic neurons in the substantia nigra pars compacta (Booth et al., 2017). However, it has been demonstrated that astrocyte dysfunction may also be involved in the pathogenesis of PD (Booth et al., 2017; Kam et al., 2020). Specific genes have been shown to have higher expression in astrocytes from postmortem human brain tissue, such as Park7, which is involved in the response to oxidative stress. Deletion or mutations in Park7 increase sensitivity to oxidative stress and proinflammatory responses, disrupt extracellular matrix interaction, increase microglial activation, and impair glutamate uptake via EAAT2 (Slc1a2) (De Miranda et al., 2018; Helgueta et al., 2024; Kam et al., 2020; Kim et al., 2016; Table 2). The gene that encodes to α-synuclein protein, Snca, is considered a key player in PD. Mutations in the Snca gene may lead to early onset of PD. The neuropathological characteristics observed in postmortem brain samples from patients with Snca duplication mutations reveal histopathological damage in the locus ceruleus, the dorsal motor nucleus of the vagus, and the basal nucleus of Meynert, with aggregation of α-synuclein in the form of Lewy bodies and Lewy neurites, as well as a loss of dopaminergic neurons in the substantia nigra, amygdala and hippocampus, which are hallmarks of PD (Konno et al., 2016). Importantly, the aggregation of α-synuclein through phagocytic uptake, secretion of exosomes, transfer via tunneling nanotubules, and de novo aggregation has been reported in astrocytes (Ozoran and Srinivasan, 2023). This leads to chronic inflammation, astrocyte reactivity, and a reduction in their functional activity related to glutamate uptake, which correlates with the exacerbation of PD pathology (An et al., 2021; Gu et al., 2010). Recently, scRNA-seq profiles within the substantia nigra of PD samples identified that Gfap, Serpina3, Aqp4, and Chi3l1 genes were upregulated in astrocyte populations with PD (Gong et al., 2025; Table 2). The water channel aquaporin-4 (AQP4) encoded by the Aqp4 gene (Jung et al., 1994), is the most abundant aquaporin and is highly expressed in astrocytes endfoot, facilitating the bidirectional flow of water, cerebrospinal fluid, and small uncharged solutes from the brain parenchyma, making it a key player in water homeostasis in the CNS (Jung et al., 1994; Salman et al., 2022; Simon and Iliff, 2016). Intriguingly, changes or loss of AQP4 in perivascular locations have been reported not only in PD but also in AD, traumatic brain injury and epilepsy (Binder et al., 2012; Ren et al., 2013; Simon and Iliff, 2016). Although oligodendrocytes are considered the primary source of SERPINA3N protein, dysregulation of the Serpina3 gene in astrocytes has been identified as a gene signature in AD and schizophrenia (Akbor et al., 2021; Zattoni et al., 2022). The role of SERPINA3 in neurological diseases is still not fully understood. It displays a cell-specific molecular mechanism but modulates blood-brain barrier integrity and neuronal cell death, and it is involved in the inflammatory response (Zhu et al., 2024). Interestingly, the glycoprotein Chitinase-3-like 1 protein (CHI3L1) is differentially expressed in the pseudotime trajectory in PD. This pattern is associated with astrocyte activation (Gong et al., 2025). CHI3L1 has been identified as a biomarker for the progression of neurocognitive disorders such as PD and multiple sclerosis (Gong et al., 2025; Song et al., 2024; Talaat et al., 2023; Yeo et al., 2019). It is secreted in response to immune activation, mainly by activated astrocytes in the CNS and its high expression is also related to glioma invasion and patient survival prognosis (Chen A. et al., 2021; Ku et al., 2011). In PD, CHI3L1 is highly expressed in astrocyte populations in the middle of the differentiation trajectory toward reactive astrocytes (Gong et al., 2025). The specific molecular mechanism of CHI3L1 in PD is not yet fully understood; however, it has been demonstrated that the intrinsic pathway of CHI3L1 in glioma involves the PI3K/AKT/mTOR pathway (Chen A. et al., 2021). CHI3L1 binds to the Receptor for Advanced Glycation End products (RAGE), activating the downstream ERK1/2-MAPK pathway, which is associated with cancer cell proliferation (Yeo et al., 2019). It has been suggested that CHI3L1 promotes the activation of the NF-κB pathway, leading to an inflammatory response and PD progression (Gong et al., 2025).

Hepatic encephalopathy (HE) is a brain dysfunction caused by acute or chronic liver insufficiency and/or portal-systemic shunting (Lu, 2023; Rose et al., 2020). HE is characterized by a spectrum of neurological and/or psychiatric abnormalities that may include acute changes in mental state, cognitive disturbances, motor impairment, sleep abnormalities, and, in severe cases, dementia, or a comatose state (Vilstrup et al., 2014). The pathophysiology of HE has not been fully elucidated; however, the elevation of toxins such as ammonia in the blood following liver disease- followed by the accumulation of neurotoxins (e.g., ammonia, manganese, inflammatory cytokines and glutamate) and metabolic impairment- contribute to the pathogenesis of HE (Lu, 2023). Interestingly, glial cells are a key target in HE. Early changes observed in experimental models of HE demonstrated cytoplasmic hypertrophy in astrocytes. Additionally, Alzheimer type II astrocyte change has been reported as a distinctive histopathological feature during the later phases of HE in human brain tissue (Norenberg, 1987).

Significative changes in astrocytic genes such as Gfap, Aqp4, Tnfα, and Kir 4.1 have been reported in the cerebral cortex in a HE rat model induced by thioacetamide (Elsherbini et al., 2022; Table 2). Similar to other neurocognitive diseases, the expression of Gfap, Aqp4 and Tnfα genes increased in the brain tissue in HE, leading to gliosis, astrocyte swelling with enlarged nuclei, neuropil vacuolation, nuclear pyknosis in neurons, and an increase in brain water content (Elsherbini et al., 2022). Hyperammonemia, a hallmark in HE, increases the levels of TNFα through the activation and nuclear translocation of NF-κB in microglia, astrocytes and Purkinje neurons in both postmortem and rat cerebellar tissues (Balzano et al., 2020). This is correlated with an increase in GABAergic neurotransmission mediated by the activation of the TNFR1 receptor (Balzano et al., 2020; Cabrera-Pastor et al., 2018). The administration of cGMP reduces glial activation, neuroinflammation, and normalizes extracellular glutamate and GABA levels in the cerebellum, leading to the restoration of motor coordination in hyperammonemia and HE (Cabrera-Pastor et al., 2018). The cortical transcriptome profile in a mouse model of HE induced by bile duct ligation demonstrated an increase in genes that code for proteins related to iron transport (Rp110), energy expenditure, and insulin sensitivity (Mc4r). Meanwhile, proteins such as the low-density lipoprotein receptor-related protein 8 (Lrp8), MAPK8 mitogen-activated protein kinase 8 (Mapk8), brain-derived neurotrophic factor (Bdnf) are significantly decreased in HE (Kim et al., 2022; Table 2). Importantly, these protein expression patterns are closely related to AD and PD pathology. For example, LRP8, as a receptor of apolipoprotein E (ApoE) and Reelin, may initiate signal pathways crucial for synaptic plasticity through the tyrosine phosphorylation of the adaptor protein Dab1/2, followed by the activation of PI3K, ERK1/2, Src-family kinases and protein kinase B/Akt signaling cascades (Passarella et al., 2022). Moreover, ApoE, specifically the isoform ApoE4, is considered a genetic risk factor for sporadic AD. APOE4 induces a proinflammatory response by regulating Transgelin 3 expression and, ultimately, NF-kB activation in human astrocytes (Arnaud et al., 2022).

Critical cell signaling pathways involved in the activation of HSCs and the progression of liver fibrosis- such as Wnt/ß-catenin, NF-κB, TGF-ß/Smad, Hedgehog, and Notch- are modulated by lncRNAs and miRNAs (Li et al., 2023; Wu Z. et al., 2021). As described in Section “2 Physiological basis of brain-liver axis, after liver injury,” qHSCs differentiate into activated HSCs. In this phase, it has been demonstrated that the microRNAs- namely miR-31, miR-17-5p, miR-19, miR-27b, miR-503, miR-103-3p, miR-130a/b, and miR-942- are highly expressed in liver fibrosis tissue and in vitro models of liver injury (Chen et al., 2020; Hu et al., 2015; Lu et al., 2015; Tao et al., 2020; Xie X. et al., 2021; Yu et al., 2015; Zhang et al., 2016; Zhu et al., 2018). These miRNAs promote the phenotypic differentiation of qHSCs into activated HSCs via TGF-ß, PI3K/AKT, and PPAR-_γ pathways (Li et al., 2023; Table 3). Interestingly, several studies have reported the downregulation of specific microRNAs in various fibrotic murine models, and inducing the expression of these microRNAs may lead to the suppression of HSC activation. miR-98, miR-30, miR-130a-3p, miR-146a-5p, miR-200a, miR-489-3p, miR-708, sja-miR-71a inhibit HSC activation via TGF-ß, PI3K/AKT, Wnt/ß-catenin, PPAR-_γ, JAG1/Notch3, and Hedgehog signaling pathways (Du et al., 2015; Li L. et al., 2020; Li et al., 2021; Liu et al., 2021; Tu et al., 2015; Wang H. et al., 2020; Wang Q. et al., 2020; Yang et al., 2020; Table 3). After phenotypic differentiation, activated HSCs highly express α-SMA, collagen alpha 1 (COL1A), and GFAP, modifying the architecture of the extracellular matrix (Cequera, 2014; Zhao et al., 2024). During this phase, sja-miR-1, miR-140-3p, miR-195-3p up-regulate the expression of α-SMA and accumulation of extracellular matrix through the regulation of Wnt/ß-catenin and PI3K/AKT signaling (Li et al., 2023; Wang Y. et al., 2020; Wang A. et al., 2022; Wu et al., 2019). On the other hand, the role of LncRNAs has been reported in the development of liver cirrhosis and HCC progression by activating HSCs (Wu Z. et al., 2021). LncRNA-ATB competitively binds to the common miRNA responsive element of miR-425-5p with TGF-ß type II receptor (TGFBR2) and SMAD2, leading to activated HSCs and increased Col1A1 and α-SMA production (Fu et al., 2016). The upregulation of the lncRNA HOXA transcript at the distal tip (HOTTIP) has been described in human liver samples with liver fibrosis and cirrhosis as well as in liver tissue and HSC of CCl₄ -treated mouse. HOTTIP negatively regulates miR-148a in a sequence-specific manner (Li Z. et al., 2018). miR-148a is involved in hepatocytic differentiation of progenitor cells (Jung et al., 2016). The downregulation of miR-148a-3p through direct interaction with HOTTIP (Han L. et al., 2020) leads to high levels of mRNA and protein expression of TGFBR1, TGFBR2, Smad2 and Smad3- regulators of HSC activation via the TGF-ß/SMAD pathways (Li Z. et al., 2018). The lncRNA small nucleolar RNA host gene 7 (SNHG7) and lncRNA plasmacytoma variant translocation 1 (PVT1) are considered potential oncogenes in HCC (Cui et al., 2017; Xie et al., 2020; Yang et al., 2019). Similar to HOTTIP, SNHG7 functions as a competing endogenous RNA (ceRNA). It has been reported that SNHG7 interacts with various miRNAs, including miR-9-5p, miR-29b, miR-122-5p, miR-216b, and miR-425. For example, SNHG7 binds to miR-29b and inhibits its expression. This event affects the expression of DNA methyltransferase 3A (DNMT3A), a downstream target gene of miR-29b, and induces HSC activation evidenced by increased levels of α-SMA, Collα1 and autophagy-related factors (Xie Z. et al., 2021). Moreover, SNHG7 knockdown increased the levels of miR-122-5p and reduced the mRNA and protein levels of the ribosomal protein L4 (RPL4) diminishing cell proliferation, migration, and invasion in HCC (Yang et al., 2019).

It has been reported that downregulation of PVT1 inhibits HSC activation and proliferation in vitro and attenuates collagen deposits in vivo by rescuing demethylation and overexpression of Patched1 (PTCH1) caused by miR-152 (Zheng et al., 2016).

Human cirrhotic liver and murine models of cirrhosis show a marked reduction in the long intergenic non-coding RNA-p21 (lincRNA-p21) (Jiang et al., 2024). Particularly, lentivirus-mediated lincRNA-p21 transfer into mice decreased the severity of liver fibrosis in vivo; the enhancement of p21 mRNA and protein expression inhibits proliferation, and reverses the activation of HSCs to their quiescent phenotype, reducing α-SMA and Col1A1 expression (Zheng et al., 2015). The suggested mechanism is that lincRNA-p21 suppresses HSC activation via suppression of the miR-17-5p-mediated-Wnt/β-catenin pathway (Yu et al., 2017; Table 3).

Astrocytic activation is also regulated by post-transcriptional modulators. The upregulated levels of miRNA-125b have been reported in human astrocytes in an in vitro model of astrogliosis induced by interleukin-6 treatment. High levels of miRNA-125b are positively correlated with the glial cell markers, GFAP, and meanwhile exogenous treatment with anti-miRNA-125b attenuates glial proliferation by increasing the expression of the cyclin-dependent kinase inhibitor 2A (CDKN2A) (Pogue et al., 2010; Table 4). The p16^INK4A protein, encoded by the CDKN2A, is inactivated by promoter methylation in astrocytomas and gliomas (Alves et al., 2013; Fueyo et al., 1996), which is related to the age and sex of patients, showing a predominance of methylated CDKN2A in astrocytic tumor tissue of young female patients (Alves et al., 2013). Another study in normal human astrocytes but stimulated with lipopolysaccharide (LPS) reported that miR-211 inhibited the brain-derived neurotrophic factor (BDNF) expression by binding to the 3′-UTR of BDNF. miR-211 significantly downregulates BDNF mRNA and protein expression, thereby suppressing reactive astrocytic proliferation via the PI3K/AKT pathway (Zhang et al., 2017). Similarly, BDNF is a direct target of miR-140, which binds to the 3′-UTR of BDNF and attenuates the effects of LPS-induced injury in human astroglial cultures. Furthermore, ectopic miR-140 expression may lead to a restoration of the expression of IL-6 and TGF-α (Tu et al., 2017; Table 4). A negative regulation in astrogliosis has been reported following the induced overexpression of miR-145, achieved through a lentivirus-mediated pre-miRNA delivery system utilizing the promoter of GFAP. Astrocyte-specific overexpression of miR-145 also attenuates the morphological changes of reactive astrocytes, as well as cell proliferation and migration (Table 4). Since overexpression of miR-145 suppresses the maturation of astrocytes derived from glial progenitors, GFAP and c-myc have been suggested as potential targets of miR-145 to reduce hypertrophic reactivity through the p38 MAPK and ERK1/2 signaling pathways (Wang et al., 2015). The upregulation of GFAP, hypertrophy of the cell body, astrogliosis, and deficits in dendritic spine formation have been reported in the lateral septal nucleus and cortex in Dicer-null transgenic mice. The molecular mechanism involves the downregulation of miRNA-324-5p, followed by elevated astrocytic secretion of chemokine ligand 5 (CCL5) and downstream inhibition of the MAPK/CREB signaling pathway, leading to dysfunction in astrocyte-neuron crosstalk in a long-lasting manner (Sun et al., 2019; Table 4).

It has been reported that lncRNAs play a role in the regulation of inflammatory responses, microglial apoptosis, microglial pyroptosis, microglial activation, neuronal damage, and neuronal apoptosis in neurocognitive diseases (Chen M. et al., 2021). In this section, we describe the regulatory mechanisms of lncRNAs related to astrocyte dysfunction, mainly reactive astrogliosis.

The overexpression of the lncRNA H19 has been observed in glioblastoma tissue, and it is associated with glioma angiogenesis and invasion of glioma cells (Jia et al., 2016; Jiang et al., 2016). Overexpression of H19 through an adeno-associated viral vector delivery system in a rat epilepsy model induced the activation of hippocampal astrocytes and the release of proinflammatory cytokines, including IL-1ß, IL-6, and TNF-α by promoting the expression of Stat3 and c-Myc via JAK/STAT signaling (Han et al., 2018). Moreover, H19 may act as ceRNA and competitively bind to miRNA let-7 and suppress its expression (Kallen et al., 2013) promoting changes in the morphology and proliferation of hippocampal astrocytes and epileptic seizures by targeting Stat3. This suggests the involvement of JAK/STAT signaling pathway during the activation of astrocytes in epileptogenesis (Han C. L. et al., 2020; Table 4). Importantly, the overexpression of miR-1-3p attenuates proliferation and activation of normal human astrocytes in an in vitro model of spinal cord injury induced by LPS treatment; miR-1-3p directly binds to H19 and CCL2 3’UTR, reducing the levels of IL-6, and TNF-α (Li P. et al., 2020).

The lncRNA PRDM16-DT has emerged as a key regulator of astrocytes homeostasis. PRDM16-DT in human and Prdm16os in murine models are downregulated in AD. The knockdown of PRDM16-DT in human iPSC-derived astrocytes leads to functional deficits in astrocytes and induces astrogliosis downregulating central molecules of the glutamatergic neurotransmission, such as the glutamate transporter (GLAST) and lactate transporter (MCT4) correlated with disruption in glutamate uptake and lactate release. Prdm16os and PRDM16-DT exert their effects functioning as a decoy for RE1-Silencing Transcription factor (Rest) in conjunction with the methyltransferase Polycomb Repressive Complex 2 (PRC2) (Schröder et al., 2024). Induced overexpression of the lncRNA urothelial cancer-associated 1 (UCA1) shows a protective effect on neuronal injury induced by kainic acid in rats; UCA1 inhibited KA-induced abnormal elevation of GLAST, astrocyte activation via JAK/STAT signaling pathway, moreover, cognitive deficits in epilepsy rats (Wang H. et al., 2020; Table 4).

Although the expression of GFAP in human-activated HSCs remains debated, various studies suggest GFAP as a hallmark in the differentiation of HSCs into myofibroblast and in astrogliosis (Schachtrup et al., 2011). Since GFAP is the main protein in the intermediate filaments of astrocytes, it has been recognized as a prototypical marker of reactive astrocytes. However, in rat hepatic tissue, GFAP displays different expression patterns depending on the time course of liver injury; for example, GFAP is highly expressed during acute injury but decreases in chronic responses. Particularly, GFAP expression has been correlated with the fraction volume of fibrosis at early stages in human cirrhotic tissue, when GFAP-positive HSCs are still negative to α-SMA, a marker of activated HSCs (Carotti et al., 2008). In this context, no relationship has been observed between α-SMA expression and fibrosis stage in patients with chronic hepatitis infection, but a correlation between GFAP and the fibrotic score (Levy et al., 2002). Moreover, GFAP immunoreactivity was positively correlated with fibrosis progression in post-transplant recurrent hepatitis C (Carotti et al., 2008). These clinical studies suggest GFAP as an early marker of activated HSCs. However, further studies are necessary to understand (1) whether GFAP-positive cells are precursors of activated HSCs (α-SMA-positive), (2) if similar GFAP expression patterns occur in liver injury with different etiologies, and (3) whether GFAP-positive cells are confined to specific areas within the liver across different stages of disease.

The small non-coding miR-455-3p has been described as a potential biomarker and therapeutic candidate for AD and liver fibrosis (Islam et al., 2024; Wei et al., 2019). MiR-455-3p is one of the two isoforms of mirR-455; its precursor sequence is transcribed from intron 10 of the human Col27a1 gene (collagen type XXVII alpha chain). However, the regulation of AD-related genes and hepatic fibrosis-related genes by miR-455-3p genes display opposite regulation patterns. Upregulation of miR455-3p has been observed in serum and postmortem cerebral cortex and hippocampus from AD patients. Although its molecular mechanism in reactive astrocytes is still not well understood, it has been reported that miR-455-3p knockout mice exhibit increased activity in astrocytes and microglia (Islam et al., 2024).

During HSCs activation, miR455-3p is significantly downregulated. Its reduction has been linked to liver fibrosis in various mouse models of liver injury such as bile duct ligation, high-fat diet, and CCl₄ administration (Wei et al., 2019). Ectopic overexpression of miR455-3p inhibits HSC activation by suppressing heat shock factor 1 (HSF1), which is involved in the Hsp47/TGF-β/Smad4 signaling pathway in liver tissue (Wei et al., 2019). Although miR455-3p has potential as a therapeutic target, further studies are needed to elucidate its specific role in astrocytes/HSCs activation across different etiologies, in order to determine its potential as a biomarker for scar formation and neuronal and hepatic regeneration.

The axis miR-140/BDNF has been suggested as a promising target to ameliorate reactive human astrocyte proliferation after spinal cord injury (Tu et al., 2017). MiR-140 binds to the 3′UTR of BDNF and inhibits its expression. Since BDNF upregulation regulates astrocyte proliferation and differentiation, ectopic expression of miR-140 restores BDNF and pro-inflammatory cytokine levels, thereby ameliorating astrogliosis after nerve fiber damage (Tu et al., 2017). The miR140-3p belongs to the miR-140 cluster and has been linked to liver fibrosis. Upregulation of miR-140-3p is correlated with activation of rat HSCs (HSC-T6) through silencing of the tumor suppressor, phosphatase and tensin homolog deleted on chromosome 10 (PTEN), which enhances activated HSC proliferation and reduces apoptosis via AKT/mTOR signaling pathway. Meanwhile, miR-140-3p knockdown results in downregulation of α-SMA and desmin levels (Wu et al., 2019), demonstrating the potential of miR140-3p to suppress the fibrotic role of TGF-β1.

Clinical data showed that miRNA-140 is significantly downregulated in liver tissues of patients with HCC and might stimulate metastasis and HCC progression (Kong et al., 2021), analog to reported in HCC mouse models (Ghafouri-Fard et al., 2021). The molecular mechanism has been described by in vitro studies that demonstrated miRNA-140 overexpression inhibits cell proliferation, migration and invasion in HCC through PI3K Akt signaling pathway, TGF-β signaling pathway, and MAPK signaling pathway (Kong et al., 2021; Lu et al., 2020). Importantly, studies in tumor xenograft mice model indicated that the downregulation of miRNA-140 leads to sorafenib resistant and poor prognosis in HCC, this chemoresistance might be regulated through the small nucleolar RNA host gene 16, this lncRNA is overexpressed and its directly interacting with miRNA-14, which targets the pregnane X receptor resulted in the modulation of downstream genes involved in drug-resistant during HCC (Li J. et al., 2018; Ye et al., 2019).

The prognostic role of miRNA-140 has been identified in cancerous brain tumor as well. Downregulation of miRNA-140 has been inversely associated with the cysteine protease, cathepsin B expression in glioblastoma multiforme (Ho et al., 2019). In this case, miRNA-140 might regulate mesenchymal transition and response to temozolomide, the first-line antineoplastic against glioblastoma multiforme via cathepsin B (Ho et al., 2019; Palizkaran Yazdi et al., 2024). Additionally, treatment with cathepsin B inhibitors such as E64D and CA074Me reduces glioma cell proliferation, reduces amyloid plaques deposition, protects against astrocytic apoptosis, rescues motor and cognitive dysfunction in animal models (Cawley et al., 2014; Xu et al., 2014). Cathepsin B is an important mediator of NLR family protein domain containing 3 inflammasome activation, which have implications in a variety of neurodegenerative diseases such as Parkinson and AD but in the progression of liver diseases by inflammatory response-mediated HSC activation and fibrogenesis (Charan et al., 2023).

The miR-148a-3p has been associated with neuroprotection by the inhibition of proinflammatory factors (Ramírez et al., 2022). Qian et al. (2024) demonstrated that miR-148a-3p from astrocytes-derived exosomes stimulates phenotype transition of microglia in vitro and in traumatic brain injury model in rats. The transfection of miR-148a-3p induces the polarization into the pro-inflammatory M1 phenotype to the anti-inflammatory M2 phenotype in pre-microglia cultures. Additionally, miR-148a-3p attenuates lipopolysaccharide-mediated inflammatory response in vitro and improves the modified neurological severity score after traumatic brain injury in rat model, this neurological restoration occurs via the inhibition of the nuclear factor kß pathway (Qian et al., 2024).

Similarly, the role of miR-148a-3p in HCC progression has been demonstrated in xenograft liver cancer model (Zhang et al., 2022). miR-148a-3p is downregulated in the transformation process from qHSCs to activate HSCs, in vitro co-cultures showed that decreased exosomal miR-148a-3p may be uptake by HCC cells leading to tumorigenesis and HCC progression, this data is correlated with the result from clinical samples that show the downregulation of miR-148a-3p in patients with primary HCC tumor (Cheng et al., 2017; Gailhouste et al., 2013; Zhang et al., 2022). In healthy microenvironment, miR-148a-3p displays high expression in hepatic satellite cells and HSCs, thus miR-148a-3p overloaded exosomes might be a promising approach to regulate the proliferation and invasion of tumor microenvironment via ITGA5/PI3K/Akt pathway and improve prognosis (Zhang et al., 2022).

As previously discussed in Section “4 The atlas of astrocytes in nervous system diseases,” the LncRNA HOTTIP mediates HSCs activation. Interestingly, aberrant HOTTIP down-regulation has been demonstrated in various glioma cell lines isolated from human brain tissue such as A172, U251, U-118 MG and U-87 MG (Xu et al., 2016). Although the specific role of HOTTIP in astrocytes has not been described, its role by regulating microglia-mediated inflammation and neuronal damage has been reported (Lun et al., 2022). The overexpression of HOTTIP in an intro model of PD using 1-Methyl-4-phenylpyridium showed microglial activation, exacerbating proinflammatory cytokine expression such as IL-lβ, IL-6, IL-18, TNF-α, iNOS, COX2, and phosphorylated NF-κB. Similarly, an induced PD mouse model combined with HOTTIP knockdown confirmed the suppression of MPTP-induced NLRP3-ASC-Caspase-1 inflammasome activation and microglial activation in substantia nigra, additionally, HOTTIP knockdown rescues the dopamine content in striatal brain region and improvement in motor and cognitive function (Lun et al., 2022). Future studies are needed to address the possible role of HOTTIP in astroglia and its clinical significance to ameliorate another neurocognitive disease.