Biology subjects

Karpen, S. J.

Publications and source records attributed to Karpen, S. J..

3 recordsLinked to original sources

bioRxiv2026

Cholangiocyte RUNX1 Orchestrates Fibrogenic and Inflammatory Signaling to Drive Biliary Fibrosis

IntroductionBiliary fibrosis and inflammation are central to the pathogenesis of cholangiopathies such as primary sclerosing cholangitis (PSC) and primary biliary cholangitis (PBC). Inflammatory and fibrogenic stimuli, such as transforming growth factor-{beta} (TGF{beta}) and lipopolysaccharide (LPS) signaling, drive these processes, but their underlying transcriptional mechanisms in cholangiocytes remain incompletely defined. We investigated the role of Runt-related transcription factor 1 (RUNX1) as a transcriptional co-regulator of fibroinflammatory signaling in cholangiocytes. MethodsHuman PSC-derived cholangiocytes (PSC-Cs) and mouse large biliary epithelial cells (MLEs) were subjected to RUNX1 knockdown or pharmacologic inhibition (Ro5-3335 or AI-10-104). Cytokine secretion was profiled by Luminex multiplexing; RUNX1 genomic binding and protein interactome were assessed by ChIP-qPCR, ChIP-seq, and LC-MS/MS. In vivo, Mdr2-/- mice received Ro5-3335, and cholangiocyte-selective Runx1 knockout mice (Krt19-CreERT) were challenged with a DDC diet, followed by evaluation of fibrosis and inflammation. ResultsRUNX1 expression was significantly increased in cholangiocytes from PSC and PBC patients, and Mdr2-/- mice. RUNX1 knockdown or inhibition reduced IL6, TNF, and other proinflammatory cytokines in PSC-Cs and attenuated TGF{beta}-, LPS-, and TNF-induced Il6 and Ccl2 expression in MLEs. ChIP-qPCR and ChIP-seq revealed TGF{beta}-induced RUNX1 binding to the Il6 promoter and 727 additional genomic sites enriched for fibrosis and inflammatory pathways; predicted upstream regulators included TGF{beta}, TNF, and NF{kappa}B signaling. Proteomic analysis identified TGF{beta}-induced RUNX1 interactions with SMAD2 and NF{kappa}B2. In vivo, Ro5-3335 treatment in Mdr2-/- mice reduced hepatic collagen, ECM gene expression, immune cell infiltration, and serum liver injury markers and bile acids. Similarly, cholangiocyte-specific Runx1 deletion mitigated fibrosis, inflammation, and liver injury in DDC-fed mice. ConclusionRUNX1 is a central transcriptional hub integrating TGF{beta} and inflammatory signals in cholangiocytes. Its inhibition attenuates biliary fibrosis and inflammation in cholestatic models, supporting RUNX1 as a potential therapeutic target in fibroinflammatory cholangiopathies.

physiology↗

bioRxiv2024

Quantifying forms and functions of intestinal bile acid pools in mice

Bile acids (BAs) are gastrointestinal metabolites that serve dual functions in lipid absorption and cell signaling. BAs circulate actively between the liver and distal small intestine (i.e., ileum), yet the dynamics through which complex BA pools are absorbed in the ileum and interact with intestinal cells in vivo remain ill-defined. Through multi-site sampling of nearly 100 BA species in individual wild type mice, as well as mice lacking the ileal BA transporter, Asbt/Slc10a2, we calculate the ileal BA pool in fasting C57BL/6J mice to be [~]0.3 moles/g. Asbt-mediated transport accounts for [~]80% of this pool and amplifies size, whereas passive absorption explains the remaining [~]20%, and generates diversity. Accordingly, ileal BA pools in mice lacking Asbt are [~]5-fold smaller than in wild type controls, enriched in secondary BA species normally found in the colon, and elicit unique transcriptional responses in cultured ileal explants. This work quantitatively defines ileal BA pools in mice and reveals how BA dysmetabolism can impinge on intestinal physiology.

physiology↗

bioRxiv2021

Active Enterohepatic Cycling is Not Required for the Choleretic Actions of 24-norUrsodeoxycholic Acid in Mice

The superior ability of norursodeoxycholic acid (norUDCA) to induce a bicarbonate-rich hypercholeresis has been attributed to its ability to undergo cholehepatic shunting and norUDCA is currently being evaluated as a therapeutic for forms of liver disease. The goal of this study was to use mouse models to investigate contributions of bile acid transporters to the choleretic actions of norUDCA. Here, we show that the apical sodium-dependent bile acid transporter (ASBT) and Organic solute transporter-alpha (OST) are dispensable for norUDCA-stimulation of bile flow and biliary bicarbonate secretion in mice. Analysis of the liver transcriptome revealed that norUDCA induced hepatic expression of a limited number of transporter genes, particularly organic anion transporting polypeptide 1a4 (Oatp1a4). However, norUDCA potently stimulated a bicarbonate-rich hypercholeresis in Oatp1a/1b-deficient mice. Blocking intestinal bile acid reabsorption by co-administration of an ASBT inhibitor or bile acid sequestrant did not impact the ability of norUDCA to induce bile flow in wildtype mice. The results support the concept that these major bile acid transporters are not directly involved in the absorption, cholehepatic shunting, or choleretic actions of norUDCA. Additionally, the findings support further investigation of the therapeutic synergy between norUDCA and ASBT inhibitors or bile acid sequestrants for cholestatic liver disease.

cell biology↗