Role of Sensory Neuropeptides in the Regulation of Biliary Function
Human liver is innervated by a dense network of extrinsic and intrinsic nerves that regulate liver regeneration. Cholangiocyte differentiation and biliary remodeling are critical for the maintenance of biliary mass, and the functional recovery during the pathogenesis of cholestatic liver diseases such as primary biliary cirrhosis (PBC) and primary sclerosing cholangitis (PSC). With regard to the plasticity of intrahepatic cholangiocytes,it has been postulated that terminally differentiated cells of one lineage may directly differentiae into another lineage or undergo trans-differentiation. Therefore, specific subpopulations of cells,such as small cholangiocytes that express known biliary progenitor cell markers, can be hypothesized to contain a multipotent cell population that may be activated when exposed to certain pathological conditions. We have previously demonstrated a direct role for the parasympathetic and sympathetic innervation in the regulation of biliary mass and cholangiocyte functional activity. Although sensory innervation is present in the liver as dense neural networks in the fibromuscular layer of the biliary epithelium, little information exists regarding its role n the regulation of biliary proliferation and function in normal and diseased states. Our preliminary studies have indicated that small cholangiocytes possess functional pluripotent characteristics under conditions that large more senescent cholangiocytes are damaged or lost. During the damage of large cholangoicytes, this pluripotent cell population is activated by the sensory neuropeptides to repopulate damaged bile ducts and livers. Based on these compelling data, we propose the central hypothesis that small murine cholangiocytes contribute to the recovery of biliary injury through acquiring the sensory neuropeptides regulated phenotypes of large cholangiocytes under diseased conditions. The central hypothesis will be evaluated by the following three specific aims: (1) substance P (SP)-dependent sensory innervation involved in the regulation of tissue repair-related cellular functions in small and large cholangoicytes will b identified, (2) the functional role of SP- dependent miRNAs involved in differentiation-related cellular functions in biliary committed progenitors will be defined, (3) the effects of SP-associated mRNAs and miRNAs on accelerating the morphologic and functional recovery of biliary damage during chronic cholestatic liver injury in vivo. Therefore, a systematic evaluation of substance P-regulated pluripotent genes and microRNAs as markers in small cholangiocytes with the therapeutic potentials for cholestatic liver injury is proposed in this application. In addition, the translational role of the selective manipulation of gene/miRNA on biliary cell differentiation will be evaluated. The completion of the proposed studies may lead to alternative therapeutic strategies for human biliary injury. Novel insights into the mechanisms of sensory neuropeptides regulate heterogeneity in human biliary tree will be obtained. This newly acquired fundamental knowledge about regulation of differentiation by sensory neuropeptide-regulated mRNAs and miRNAs in biliary progenitors will advance the general field of cholangiocyte biology.