In the liver, hepatic stem/progenitor cells (HPCs) represent a facultative stem/progenitor cell compartment located within canals of Hering and bile ductules. HPCs are bipotent stem cells characterized by the capability to differentiate towards mature hepatocytes and cholangiocytes. In human Non Alcoholic Fatty Liver Disease (NAFLD), HPCs can activate and proliferate as a consequence of impaired proliferation of mature hepatocyes due to lipotoxicity. Recently, a niche of stem cells endowed within peribiliary glands (PBGs) has been described along extrahepatic and large intrahepatic bile ducts. This heterogeneous population of stem and progenitor cells has been collectively named Biliary Tree Stem Cells (BTSCs) and is implicated in the pathogenesis of human cholangiopathies.
The general aim of the present project will be to define the role and the activation mechanisms of HPCs and BTSCs in human liver diseases. Specific objectives of the present project will be: i) to investigate the activation of HPCs in the progression of NAFLD and the relationship with levels of Lipopolysaccharide (LPS), platelets and macrophage activation; ii) to study the signaling pathways driving the BTSC activation in human Primary Sclerosing Cholangitis (PSC) and Non anastomotic strictures (NAS) in transplanted livers; iii) to individuate the role of peribiliary glands (PBGs) in biliary regeneration and in the pathogenesis of biliary damage by a lineage tracing approach in mice.
Data obtained from this project will lead i) to understand cellular mechanisms at the basis of NAFLD progression; ii) to characterize the anatomy and physiology of PBG stem cell niche, its behavior in regenerative response, and the signals involved in niche activation; iii) to clarify the pathogenesis of cholangiopathies and biliary fibrosis; iv) to individuate novel molecular tools and therapeutic approaches targeting stem cell niches.
The present project will clarify important aspects on the activation of hepatic progenitor cells (HPCs) within the liver and the relevant pathways implicated in the activation of stem/progenitor cell niches along the biliary tree. This project will examine regenerative pathways in several human pathologies and will examine their role in the response to pathologic conditions, including diseases of liver and biliary tract.
The objective #1 of the present project will characterize cellular cross-talks which can influence the development of NASH and the progression to fibrosis and cirrhosis. In particular, the results coming from this specific objective will assess the contribution of macrophage activation in the evolution of NASH and its relationship with Escherichia Coli-derived LPS levels. There is a growing body of experimental and clinical evidence suggesting that gut microbiota may be implicated in the pathogenesis of NAFLD. Recent experimental studies in animals drew the attention on the role of LPS from gut microbiota in favoring the occurrence of NASH. However, the interplay between LPS and NAFLD in humans is less clear. Therefore, our study would test whether NAFLD is associated with enhanced LPS uptake by hepatic cells with potential deleterious effects in terms of inflammation and eventually hepatic fibrosis. Moreover, we will evaluate the role of platelets and their activation on NASH progression and fibrosis. Finally, our experimental study will elucidate whether treatment with aspirin would be able to reduce the progression to fibrosis. This part of the study will have important implications regarding the clinical association between liver-gut axis and NAFLD and will individuate possible therapeutic target. In general, the correlation of histological aspects with serum levels of LPS will furnish relevant insight, and data obtained from this part of the project will be useful to understand cellular mechanisms at the basis of NAFLD progression and could individuate novel molecular tools and cellular target for therapeutic approaches.
The objectives #2 and #3 of the present project will further clarify the regenerative pathways involved in biliary regeneration during cholangiopathies. In particular, the eventual activation of PBG niche due to cholangiocyte loss will be established both in a rodent experimental model and in human diseases. Using an innovative linage tracing approach, we will be able to characterize the putative role and contribution of Biliary Tree Stem Cells (BTSCs) within PBGs during induction of biliary damage. Moreover, signaling pathways, such as Notch and Wnt pathways, will be studied during the regenerative response and in the restitutio ad integrum of diseased duct. Furthermore, the eventual disarrangement of these pathways during human Primary Sclerosing Cholangitis (PSC) will be assessed to test the hypothesis that such alterations could represent a main mechanism at the basis of defective regenerative response and biliary fibrosis progression in this disease.
Then, our project will further characterize pathogenetic mechanisms underlying biliary complications in transplanted organs and assess whether they are related to ischemia. In this setting, the role of VEGF system will be studied to unravel possible mechanism at the basis of biliary defects. Biliary complications after liver transplantation, including non-anastomotic strictures (NAS), represent a major cause for re-transplantation, with a reported incidence varying between 5% and 30%; therefore, the study of their pathogenesis would be crucial to individuate possible prognostic and clinical target. Thus, our results would clarify whether the pathogenesis of NAS is associated with PBG niche and whether VEGF system is activated and participate in this process. Finally, the correlation of histological study with clinical and surgical parameters will unravel whether a proper activation of PBG niche both in term of degree and mature fate commitment would be necessary for regenerating surface epithelium defects due to transplantation procedure.
Therefore, the results coming from objectives #2 and #3 would be crucial to understand anatomy and physiology of PBG stem cell niche, physiological behavior and signals within the niche, and their involvement in biliary disease. In general, data obtained from this part of the project will be useful to clarify the pathogenesis of cholangiopathies and biliary fibrosis and to individuate possible cellular target for therapeutic approaches.