Citations

Cholangiocytes are specialized epithelial cells that line the intrahepatic and extrahepatic biliary tree and play a critical role in bile modification, liver homeostasis, and response to injury. Cholangiocytes exhibit notable heterogeneity and plasticity, and their dysfunction is central to a spectrum of diseases targeting the bile ducts, collectively called cholangiopathies. These disorders include genetic, infectious, immune-mediated, and malignant diseases, with primary sclerosing cholangitis (PSC) representing one of the most complex and enigmatic of these disorders. PSC is a progressive, fibro-inflammatory disease of the bile ducts that is closely linked to inflammatory bowel disease, carries a heightened risk of cancer, and lacks any approved therapies. This review explores the biology of cholangiocytes, including their development, functional plasticity, and roles in secretion, absorption, and cellular signaling. We provide a detailed examination of cholangiopathies, particularly PSC, a complex cholangiopathy characterized by a paradoxical state of cholangiocyte senescence and hyperproliferation. We describe how immune cell dysfunction, the gut microbiome, genetic predispositions, and environmental factors converge to mediate PSC pathogenesis. We revisit the foundational technologies that empowered early discoveries and shaped the field as we know it today. We also explore how newer techniques such as organoid cultures, single-cell transcriptomics, epigenomics, and spatialomics have transformed our modern understanding of biliary pathophysiology. Finally, we provide an overview of existing rodent models of cholangiopathies and discuss their relevance to human disease. PSC remains therapeutically unaddressed, and thus ongoing multidisciplinary efforts are essential to developing targeted interventions. This review serves as a comprehensive resource for researchers and clinicians navigating the rapidly evolving landscape of cholangiocyte-centered liver disease research.

Liver macrophages are central in maintaining hepatic homeostasis and mediating immune responses during liver injury, including fibrosis. Macrophages may have proinflammatory or antiinflammatory properties, but which properties influence fibrosis remains unclear. To explore the role of macrophages in liver fibrosis, we performed single-cell RNA-seq in a mouse model of liver injury and found that macrophage diversity was increased. Marco was among the most significantly upregulated genes, and a population of Marco hi macrophages increased with injury and spatially segregated to nonfibrotic areas. The macrophage receptor with collagenous structure (MARCO) protein is a scavenger receptor expressed by specific subsets of macrophages, and its role in liver fibrosis is unclear. In vitro induction of Marco in bone marrow–derived macrophages decreased proinflammatory gene expression, increased antiinflammatory and antifibrotic gene expression, and enhanced phagocytosis, indicating a restorative phenotype. Adoptive transfer of MARCO + macrophages in a mouse model of liver fibrosis reduced the expression of extracellular matrix–associated (ECM-associated) genes in hepatic stellate cells (HSCs) and reduced collagen deposition, which did not occur with the transfer of MARCO – macrophages. Therefore, MARCO + macrophages have a tissue restorative role in the liver and attenuate fibrogenesis through interaction with HSCs, thereby providing a potential therapeutic pathway for liver fibrosis.

Objectives/Goals: Primary sclerosing cholangitis (PSC) manifests with an inflammatory milieu that leads to fibrotic scarring of the liver. Human PSC liver bile ducts are enriched with neutrophils; however, their infiltration and functional role is unexplored. Our goal is to investigate the mechanism and impact of peribiliary neutrophil infiltration observed in PSC. Methods/Study Population: Primary cholangiocytes (bile duct cells) isolated from WT and mouse models of PSC (3,5-diethoxycarbonyl-1,4-dihydrocollidine (DDC)-fed mice and Mdr2-/- mice) were analyzed by RNA-sequencing. Immunofluorescence (IF) was performed on liver tissues from PSC patients and mouse models of PSC for markers of bile ducts and neutrophils (KRT19 and MPO). Intrahepatic leukocytes (IHL) isolated from mice livers were evaluated for neutrophil abundance and activation state. Anti-Ly6G antibody-mediated neutrophil depletion in Mdr2-/- mice was analyzed by IF, histology, and cytometry by time-of-flight (CyTOF). Cholangiocytes stimulated with TNFα (to induce an inflammatory phenotype) were analyzed for neutrophil chemoattractants with genetic and pharmacological interventions. Results/Anticipated Results: RNA-seq analysis of primary cholangiocytes from PSC mouse models revealed enrichment in inflammatory and neutrophil degranulation pathways. Flow cytometry and RT-PCR analysis revealed an increase in the neutrophil population in PSC mice with activated phenotype. Peripheral depletion of neutrophils in Mdr2-/- mice alleviated liver injury and inflammation, along with a reduction in peribiliary neutrophil infiltration and attenuated bridging fibrosis. CyTOF analysis showed a significant reduction in CD8+ T cells upon neutrophil depletion, implying neutrophils sustain CD8+ T cells in PSC liver. Mechanistically in cholangiocytes, TNFα mediates expression of neutrophil chemoattractants, CXCL1 and CXCL8, through the cyclic GMP-AMP synthase stimulator of interferon genes (cGAS-STING) pathway. Discussion/Significance of Impact: Our findings suggest that activation of the STING pathway in cholangiocytes in cholestatic liver disease triggers an immune response resulting in peri-portal neutrophil infiltration via CXC chemokines. The sustained presence of these activated neutrophils engages the adaptive immune system to perpetuate the inflammation and fibrosis seen in PSC.

The field of ribonucleic acid (RNA) biology has revealed an array of noncoding RNA species, particularly long noncoding RNAs (lncRNAs), which play crucial roles in liver disease pathogenesis. This review explores the diverse functions of lncRNAs in liver pathology, including metabolic-associated steatotic liver disease, hepatocellular carcinoma, alcohol-related liver disease, and cholangiopathies such as primary sclerosing cholangitis and cholangiocarcinoma. We highlight key lncRNAs that regulate lipid metabolism, inflammation, fibrosis, and oncogenesis in the liver, demonstrating their diagnostic and therapeutic potential. Emerging RNA-based therapies, such as mRNA therapy, RNA interference, and antisense oligonucleotides, offer approaches to modulate lncRNA activity and address liver disease at a molecular level. Advances in sequencing technologies and bioinformatics pipelines are simultaneously enabling the identification and functional characterization of novel lncRNAs, driving innovation in personalized medicine. In conclusion, this review highlights the potential of lncRNAs as biomarkers and therapeutic targets in liver disease and emphasizes the need for further research into their regulatory mechanisms and clinical applications.

Portal hypertension (PHTN) is a severe complication of liver cirrhosis and is associated with intrahepatic sinusoidal remodeling induced by sinusoidal resistance and angiogenesis. Collagen type IV (COL4), a major component of basement membrane, forms in liver sinusoids upon chronic liver injury. However, the role, cellular source, and expression regulation of COL4 in liver diseases are unknown. Here, we examined how COL4 is produced and how it regulates sinusoidal remodeling in fibrosis and PHTN. Human cirrhotic liver sample RNA sequencing showed increased COL4 expression, which was further verified via immunofluorescence staining. Single-cell RNA sequencing identified liver sinusoidal endothelial cells (LSECs) as the predominant source of COL4 upregulation in mouse fibrotic liver. In addition, COL4 was upregulated in a TNF-α/NF-κB–dependent manner through an epigenetic mechanism in LSECs in vitro. Indeed, by utilizing a CRISPRi-dCas9-KRAB epigenome-editing approach, epigenetic repression of the enhancer-promoter interaction showed silencing of COL4 gene expression. LSEC-specific COL4 gene mutation or repression in vivo abrogated sinusoidal resistance and angiogenesis, which thereby alleviated sinusoidal remodeling and PHTN. Our findings reveal that LSECs promote sinusoidal remodeling and PHTN during liver fibrosis through COL4 deposition.

Cellular senescence and biliary fibrosis are prototypical features of obliterative cholangiopathies, such as primary sclerosing cholangitis (PSC). Telomere dysfunction can lead to senescence either through telomere erosion or damaged telomeres. Our goal was to investigate a mechanistic relationship between telomere damage and biliary fibrosis in PSC. Telomere attrition was observed in the bile ducts of patients with PSC along with a reduction in telomerase reverse transcriptase (TERT) expression, compared with that in normal livers. Similarly, liver tissue from mouse models of biliary fibrosis showed telomere attrition with increased damage at telomeres measured as telomere-associated foci (TAF). Cellular models of senescence induction increased the TAF in cholangiocytes. This coincided with decreased TERT expression and increased senescence, which was rescued by modulating TERT levels. Epigenetic analysis revealed increased acquisition of repressive histone methylation at the TERT promoter, which correlated with decreased TERT transcription. Cholangiocyte-selective deletion of TERT in mice exacerbated fibrosis, whereas androgen therapy toward telomerase rescued liver fibrosis and liver function in a genetic mouse model of PSC. Our results demonstrate a mechanistic role for telomere dysfunction in cellular senescence and fibrosis that characterize PSC. This suggests that PSC may be, in part, a telomere biology disorder, and identifies TERT as a potential therapeutic target.