Dynamic bile flow modelling and cellular pressure sensing in primary sclerosing cholangiti (DYNAFLOW)

Primary sclerosing cholangitis (PSC) is a progressive liver disease characterized by destruction of the intra- and/or extra-hepatic bile ducts, leading to advanced stages of liver disease such as cirrhosis and hepatobiliary cancer. There is no effective medical therapy for PSC, and the majority of patients will eventually require liver transplantation or even die from liver disease or cancer. Following a primary immunological insult to the bile duct, biliary flow obstruction leads to pressure damage to the biliary epithelium and drives disease progression. To date the medical treatment options are very limited. In this project we aim to identify targets for the utterly needed pharmacological intervention to prevent biliary pressure damage and pave the way for personalized pharmacological biliary pressure optimization in affected patients. To this purpose we will use an approach to model the hydrodynamic and signalling consequences of altered biliary flow in murine mouse models of PSC and well characterized long-term followed patients with PSC. Intriguingly, biliary flow dynamics, pressure sensing and the signalling consequences are as yet very poorly understood. Thus, the current consortium unites established liver research with novel mechanosensing and modelling expertise that has never been systematically applied in a PSC context. Specifically, the consortium unites renowned liver research centres from Norway (clinical PSC research) and Austria (experimental PSC research) with fluid dynamics (Israel), high- definition 3D tissue reconstruction, functional genomics (Germany) and mechanosensing (France). The results of this project can be expected to improve our future medical management of PSC as one ot the last remaing black boxes in Hepatology.

Primary sclerosing cholangitis (PSC) is a chronic inflammatory bile duct disease that can progress to liver cirrhosis and cancer. To date no established drug treatment for PSC is available. Ursodeoxycholic acid (UDCA) is well tolerated in medium doses and improves liver enzymes but has not been shown to improve survival of PSC patients and can be even detrimental at higher dosage which may increase biliary pressure into a dangerous range. Therefore, its use in PSC is still highly controversial. In this project we modeled the hydrodynamic and signaling consequences of altered bile flow which should allow to identify new targets for utterly needed pharmacological interventions. To test whether personalized application of UDCA may improve the therapeutic response to UDCA the effects of different dosages were tested in a mouse model of PSC (Mdr2-/- mice). Furthermore, co-treatment with norUDCA (a side chain-shortened derivative of UDCA undergoing cholehepatic shunting instead of enterohepatic circulation) was explored. The interactions of UDCA and norUDCA are of utmost importance, since norUDCA as novel emerging therapy for PSC is combined with UDCA as an add-on strategy in ongoing studies. Therefore, a dose ranging experiment for UDCA was performed in Mdr2-/- mice (0,01%; 0,1%; 0,25% or 0,5% UDCA (w/w)) for 4 weeks. Only 0,1%UDCA feeding improved liver injury. These observations are in line with bioinformatical modeling results, which anticipated the need for personalized UDCA concentration adjustments in treated patients. Based on this observation, combination of 0,1%UDCA and 0,5%norUDCA was tested in Mdr2-/- mice. Animals treated with this combination showed improved cholestatic liver and bile duct injury. Although combination of UDCA and norUDCA was not superior to 0,5% norUDCA monotherapy, a positive modulation of cholangiocyte-specific mechano- and osmosensing genes was observed in the combination group. Hence, our data support norUDCA as a promising new therapeutic strategy for PSC, while strongly recommending personalized UDCA dosage adjustments until norUDCA may become the new standard therapy. To further explore the role of altered bile formation in the development of sclerosing cholangitis, a mouse model lacking the key canalicular bile salt export pump (Bsep) was crossed with the Mdr2-/- mouse model of PSC. Notably, absence of Bsep, and subsequent changes in bile flow and biliary pressure together with a more hydrophilic bile acid pool composition protected these mice from development of sclerosing cholangitis. These finding point towards a crucial role of biliary pressure in addition to bile composition in the pathogenesis and treatment of cholestatic liver disease. Overall, we demonstrate dose-dependent modification of bile formation and composition as novel therapy strategies for bile duct diseases such as PSC.