Genetic loss of the muscarinic M 3 receptor markedly alters bile formation and cholestatic liver injury in mice.

Aim: Hepatic innervation represents a potentially underestimated regulator of liver function and regeneration. The muscarinic 3 receptor (M-3-R) is the primary cholangiocyte receptor for the afferent parasympathetic innervation of bile ducts. We aimed to determine the specific role of the M-3-R in bile formation and models for cholestatic liver disease in mice. Methods: We compared bile flow and composition in M-3-R knock-out mice (M-3-R-/-) and wild type littermates (WT). Furthermore, we compared liver inury of M-3-R-/- and WT mice after 3,5-diethoxycarbonyl-1,4-dihydrocollidine (DDC) feeding, a well-characterized preclinical model of cholestatic liver disease. To analyze the possible role of the M-3-R as a therapeutic target, we treated 4-week-old Mdr2(-/-) mice, a preclinical model for sclerosing cholangitis, with the M-3-R agonist bethanechol for 4 weeks. Results: M-3-R-/- mice showed significantly reduced bile flow compared to WT mice, most likely due to decreased biliary HCO3- secretion. However, even aged M-3-R-/- mice did not spontaneously develop liver injury or cholestasis. Challenging M-3-R-/- and WT littermates with DDC feeding showed substantially aggravated liver injury in M-3-R-/- mice. After 4 weeks bethanechol treatment, Mdr2(-/-) mice showed less liver injury compared to controls. Conclusion: Our experimental findings suggest that M-3-R-signalling significantly influences bile formation. Loss of the M-3-R increases susceptibility to cholestatic injury in DDC-fed mice. Since treatment of Mdr2(-/-) mice with a M-3-R agonist decreases liver injury, M3-R signaling may represent a therapeutic target in specific cholangiopathies.