Colangioids to Define the Genetic Factors Involved in Atypical Primary Sclerosing Cholangitis

Overview

Primary sclerosing cholangitis (PSC) is a rare, progressive and often fatal disease of the intrahepatic or extrahepatic bile ducts, with an estimated prevalence in Western countries of 1/10,000. Biliary disease in PSC is represented by cholestasis, chronic inflammation of the bile ducts, the small tubes through which bile passes, progressive concentric fibrosis around the bile ducts2. This results in an obstruction to the passage of bile, which can lead to the development of cirrhosis with complications related to portal hypertension, cholangitis and often progress to bile duct cancer (cholangiocarcinoma). The only curative therapy in patients with PSC is liver transplantation, since no drug has been shown to be effective in preventing disease progression. The etiology is most likely multifactorial immune-mediated, where the onset of PSC is triggered by environmental factors in a genetically susceptible host2Genome-wide association studies (GWAS) have identified variations at the human leukocyte antigen (HLA) complex on chromosome 6 and several other loci, but these explain only a small part of the heritability of PSC. In most cases, PSC occurs in men in their 30s and 40s who have inflammatory bowel disease (IBD) suggesting a key role of altered intestinal permeability and inflammation. However, approximately 30% of patients do not present colonic inflammation, which is consistent with the heterogeneity of the disease. Preliminary data obtained in our laboratory analyzing a cohort of Italian individuals with atypical PSC (aPSC), identified a suggestive enrichment of rare variants in genes involved in cilia morphogenesis (CEP120 and AHI1). These data are consistent with previous findings, showing the correlation between gene variants involved in ciliopathies, including the DCDC26 gene, and chronic cholestatic disorders that can mimic PSC. Primary cilia are organelles present on the outer membrane of ductal cells, called cholangiocytes. These organelles function as antennas that detect stimuli from bile and transmit information to cells by regulating various signaling pathways involved in secretion, proliferation and apoptosis. Therefore, the alteration of primary cilia plays an important role in the de-differentiation of cholangiocytes and therefore in the development of cholangiopathies, in the invasion of inflammatory cells and in the fibrotic process. However, to date little is known about the contribution of genetic variants to the severity and progression of PSC, perhaps also due to the lack of a reliable model of bile duct. Recently, three-dimensional cell cultures, called organoids, have been proposed as a revolutionary tool in the field of cell biology, as they are able to mimic the corresponding organ in vivo.Organoids can be derived from either induced pluripotent stem cells (iPSCs) or tissue-resident adult stem cells. Compared to conventional 2D cultures and animal models, organoids allow to reproduce the genetic background of the patient in the model, recapitulating in vitro structures and functions similar to in vivo tissues. For this reason, organoids have been exploited in different applications, including drug discovery and testing, precision medicine and cell therapy 9311. However, organoids still show several limitations to model liver diseases. Indeed, they are only able to recapitulate the hepatic epithelial component, cholangiocytes and/or hepatocytes and above all they lack the 3D hepatic microenvironment, such as stromal and immune cells, which play an important role in the pathogenesis of several liver diseases. The present study is part of a project funded by the Regional Foundation for Biomedical Research (FRRB) whose general objective is to generate three-dimensional models of primary sclerosing cholangitis (PSC), called assemblyloids, and to study the cellular and molecular mechanisms through which genetic variants associated with genes involved in ciliopathies accelerate the progression of PSC. Our hypothesis is that the loss of function of cilia in cholangiocytes may represent a link between cellular senescence, development of inflammation, fibrosis and finally liver cancer. The variants related to ciliopathies could lead to an incomplete maturation of cholangiocytes with consequent malfunction that can therefore lead to a chronic inflammation of ductal cells and therefore to a persistent and uncontrolled activation of stromal cells and infiltration of immune cells. Furthermore, the generation of assemblyloids capable of reproducing native tissue as faithfully as possible will provide a new in vitro model for testing new pharmacological approaches aimed at correcting genetic mutations for improved precision medicine.