Primary biliary cholangitis (previously named primary biliary cirrhosis, PBC) is a chronic cholestatic liver disease characterized by a female predominance, production of specific anti-mitochondrial antibodies (AMAs), and immunological destruction of small- and medium-sized bile ducts (Kaplan and Gershwin, 2005; Gulamhusein and Hirschfield, 2020). Untreated PBC is progressive and may lead to fibrosis and cirrhosis and even liver failure and hepatocellular carcinoma (HCC) (Tanaka, 2021). Globally, the prevalence and incidence of PBC vary greatly and have been increasing. Approximately 1 in 1000 women over the age of 40 years live with PBC (Jepsen et al., 2015). Only ursodeoxycholic acid (UDCA) and obeticholic acid (OCA) have been approved by the United States Food and Drug Administration for treating PBC. However, ∼40% of patients with PBC respond inadequately to UDCA (Carey et al., 2015), and OCA was reported to increase the risk of liver failure (Chascsa and Lindor, 2020; Eaton et al., 2020). Therefore, a more in-depth understanding of the molecular mechanism involved in the development and progression of PBC is urgently needed to facilitate the development of therapeutic targets.

The pathogenesis of PBC is complex, involving multiple factors, such as environmental factors and epigenetic regulation. The loss of tolerance to biliary epithelial cells, driven by the dysregulation of the innate and adaptive immune pathways, is the initiating event of PBC (Gulamhusein and Hirschfield, 2020). However, because obtaining clinical samples of PBC is challenging and suitable animal models of PBC are lacking, the pathophysiology of PBC is unclear. High-throughput sequencing technologies and bioinformatic analysis have been widely used to study gene networks and identify key genes involved in various diseases; however, their application in PBC is limited.

In this study, microarray gene expression profiles (GSE61260)—from the liver tissues of patients with PBC—were obtained from the Gene Expression Omnibus (GEO) database. The limma package in R was used to screen out differentially expressed genes (DEGs) between patients with PBC and healthy controls (HCs). Subsequently, Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment analysis, and protein–protein interaction (PPI) network analysis were performed to elucidate the molecular function and interaction of the DEGs. In addition, integrative regulatory networks of transcription factors–DEGs–microRNAs were constructed to reveal the regulatory mechanisms of key genes in PBC. Finally, a hub gene aldo-keto reductase family 1 member B10 (AKR1B10), which has not been reported to be related to PBC, was identified. The expression of AKR1B10 and its correlation with the severity of PBC in clinical samples were analyzed. This study identified a potential gene involved in PBC, enhanced the understanding of the molecular mechanisms involved in the progression of the disease, and may provide insights for the development of therapeutic interventions for patients with PBC.

Although mortality due to PBC has reduced, its prevalence has increased (Lu et al., 2018). The management of PBC is limited. Current therapeutic methods cannot help in achieving a “cure” for patients with PBC, and the patients must take medicines life-long. For patients that show incomplete response to UDCA and second-line treatment, such as OCA, liver transplantation is the only treatment option (Shah and Kowdley, 2020). These unresolved needs underscore the urgency to improve our understanding of the pathogenesis and molecular mechanisms of disease progression.

This study highlights the following major findings: 1) AKR1B10 was identified as a key gene in the progression of PBC using bioinformatics analysis; 2) high expression of hepatic AKR1B10 might promote the progression of PBC to HCC; 3) increase in hepatic AKR1B10 expression was associated with PBC severity; 4) levels of hepatic AKR1B10 were positively correlated with the circulatory parameters associated with hepatic function in patients with PBC.

AKR1B10 is a member of the aldo-keto reductase superfamily, a multifunctional nicotinamide adenine dinucleotide phosphate (NADPH)-dependent oxidoreductase that metabolizes endogenous carbonyl compounds and xenobiotics (Barski et al., 2008). This function is critical for protecting host cells from DNA damage induced by electrophilic carbonyl compounds (Zu et al., 2017). Growing evidence supports that AKR1B10 is involved in the occurrence and progression of many cancers, such as HCC (Ye et al., 2019), breast cancer (Qu et al., 2021), non-small cell lung cancer (Fukumoto et al., 2005), and pancreatic cancer (Chung et al., 2012). Because of its role as an effective retinal reductase, AKR1B10 is considered to have an inhibitory effect on retinoic acid signaling, which results in cellular proliferation (Gallego et al., 2007). Therefore, the up-regulation of AKR1B10 is believed to play a key role in promoting the tumor phenotype of cancer cells (Ruiz et al., 2012). In addition, AKR1B10 may be upregulated by the activation of some signal transduction pathways, such as MAPK (Nishinaka et al., 2015), Nrf2 (Nishinaka et al., 2017), and AP-1 (Cheng et al., 2018) pathways, and promote the proliferation and migration of cancer cells. Moreover, given its role in detoxification, AKR1B10 was shown to contribute to the chemoresistance acquisition against some anti-cancer drugs, such as daunorubicin, and idarubicin (Zhong et al., 2011) (Morikawa et al., 2015), and cisplatin (Matsunaga et al., 2016).

AKR1B10 was shown to be upregulated not only in cancers but also in some preneoplastic conditions, such as Barrett’s esophagus (Breton et al., 2008) and squamous metaplasia (Li et al., 2008). Importantly, AKR1B10 was reportedly upregulated in some chronic liver diseases that are thought to be preneoplastic diseases of HCC. Two similar studies have demonstrated that patients with chronic hepatitis B (Li et al., 2008) and chronic hepatitis C (Murata et al., 2016) expressed high levels of AKR1B10 and its expression acted as an independent risk factor for HCC development. AKR1B10 expression was reported to be significantly increased in nonalcoholic steatohepatitis, where it promotes the progression of nonalcoholic steatohepatitis to HCC through several mechanisms, such as by contributing to lipogenesis and facilitating the detoxification of reactive carbonyl species derived from lipid peroxidation (Bitter et al., 2015; Endo et al., 2021). Over the past decade, AKR1B10 has emerged as a promising biomarker for HCC. Although the molecular mechanisms underlying hepatocarcinogenesis remain poorly clarified, AKR1B10 may play a pivotal role in HCC through several mechanisms, including lipogenesis, oxidative stress, detoxification of cytotoxic reactive carbonyls, and regulation of sphingosine-1 phosphate and retinoic acid (DiStefano and Davis, 2019). Considering that higher expression of AKR1B10 is correlated with increased survival rate and lower metastatic incidence, AKR1B10 acts as a useful biomarker for the prognosis of HCC (Liu et al., 2015) (Jin et al., 2016).

In addition to improvements in long-term outcomes for patients with PBC, the development of HCC is not a rare event. A previous meta-analysis, with a larger sample size and stronger evidence, demonstrated an increased risk of HCC in PBC patients, which was more than 18.8-fold higher than that of the general population (Liang et al., 2012). Male sex, advanced histological stage, and non-response to UDCA are defined as high-risk factors that contribute to the development of HCC from PBC (Tanaka, 2021). The findings of this study demonstrate for the first time that AKR1B10 is a hub gene that is highly expressed in patients with PBC. GSEA analysis in the AKR1B10 high- and low-expression groups revealed that AKR1B10 may promote the progression of PBC to HCC. However, PBC predominantly occurs in women, which is contrary to HCC. The incidence rates of HCC are up to 2-3 fold higher in men compared to women (Yang et al., 2020). One of the reasons for the gender disparity is that hepatitis B virus (HBV) is the major etiology for HCC. As the sixth most commonly diagnosed cancer and the fourth leading cause of cancer death worldwide, the etiologies for HCC are diverse, in which HBV plays a dominant role (the percentage of HCC by HBV is 41%) (Liu et al., 2022). Chronic HBV infection is more common in men compared to in women (10.7% vs. 4.4%) among those who receive vaccination at birth and are followed up for over 18 years (Su et al., 2007). Furthermore, the progression of HBV occurs faster in men than in women, which also leads to HBV-related HCC being much more common in men compared to women (with a ratio of 5–7:1) (Lee et al., 1999; Zheng et al., 2017). The above reports suggested that men have a greater risk of developing HCC than women worldwide. Another reason for the gender disparity is that PBC is a relatively rare disease, so it is difficult for PBC-derived HCC to affect the gender distribution of HCC. Moreover, high levels of AKR1B10 protein in PBC livers was verified in the present study, and the increase of ARR1B10 was found to be associated with the severity of PBC. Thus, the expression of hepatic AKR1B10 is closely related to the development of PBC and affects the prognosis of patients with PBC. These findings may provide a new mechanism for the pathogenesis and progression of PBC and shed light on strategies for therapeutic intervention for patients with PBC.

Multiple studies have reported the regulatory mechanism of AKR1B10 in many diseases especially tumors. The present results revealed the regulatory network of AKR1B10 preliminarily via constructing the TF–AKR1B10–miRNA network. Interestingly, many TFs that potentially regulate the expression of AKR1B10 according to our analysis, such as KDM5B (Wang et al., 2016; Gong et al., 2018), TRIM28 (Zhang et al., 2021; Han et al., 2022; Zhang et al., 2022), and PHF8(Zhou et al., 2018), had been previously identified to promote the development of HCC. Considering AKR1B10 is suggested to facilitate the progression of PBC to HCC, we speculate that AKR1B10 may be regulated by these TFs during this process. Furthermore, miRNA plays another significant role in regulating the expression of targeted genes. A previous study suggested that miR-98, a miRNA also predicted in our analysis, could regulate AKR1B10–ERK signaling (Cong et al., 2019). Importantly, ERK signaling plays a pivotal role in cholestatic liver diseases including PBC (Jones et al., 2015; Chen L. et al., 2021; Chen X. et al., 2021; Wang et al., 2022). Therefore, miR-98–AKR1B10–ERK signaling is probably also involved in PBC. However, further research needs to be performed to elucidate the contribution of these potential genes to AKR1B10 in PBC. In addition to the genes discussed above, it is also worth exploring whether other regulators may interact with AKR1B10 in PBC.

This study has some limitations. First, the microarray data were obtained from public datasets and not generated by the authors. Second, the levels of AKR1B10 in the blood samples of patients with PBC have not been confirmed. This will be an area for further research because it may provide rapid, accessible strategies for the diagnosis and prognosis of PBC. Finally, the function and molecular mechanisms involving AKR1B10 in the development and progression of PBC remain unclear. In the future, in-depth analysis using in vivo and in vitro experiments is warranted.

In summary, this study identifies AKR1B10 as a key gene that correlates with the progression of PBC, using bioinformatics analysis combined with clinical validation. The findings of this study provide an insight into gene expression and molecular mechanisms involved in the development and progression of PBC. In the future, experiments at the cellular and molecular levels are required to verify the biological function of AKR1B10 in PBC.