The Role of Dysfunctional CCK-1R in Cholelithogenesis

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DESCRIPTION (provided by applicant): The long-term objectives of this laboratory are to identify, localize, and estimate the lithogenic effects of pathophysiologically relevant gallstone (LITH) genes; understand at a fundamental level the genetic mechanisms of cholesterol gallstones; and explore the genotypes and phenotypes of LITH genes in mice and eventually in humans. Studies on both humans and mice have clearly demonstrated that a complex genetic basis determines the individual predisposition to develop cholesterol gallstones in response to environmental factors. A powerful genetic technique, quantitative trait locus (QTL) analysis can identify primary, usually rate- limiting genetic defects and discriminate them from secondary downstream pathophysiologic effects caused by mutations of the primary genes. We performed a QTL analysis in intercross progeny of gallstone-susceptible 129S3/SvlmJ mice and resistant AKR/J mice, and determined the subset of gallstone susceptibility genes possessed in the susceptible strain. Our molecular and genetic data from these mouse studies support the notion that dysfunctional cholecystokinin-1 receptor (CCK-1R) in the gallbladder plays a critical role in the formation of cholesterol gallstones in 129S3/SvlmJ mice challenged to a lithogenic diet. Furthermore, abnormalities in gallbladder emptying function in response to exogenously administered CCK-8 have been observed in patients with cholesterol gallstones, suggesting that altered structure and function of the gallbladder CCK-1R gene could be involved in the formation of cholesterol gallstones in humans. However, the identification of the lithogenic mechanisms of the mutated CCK-1R gene still remains a challenging task. This application will be focused on identifying the lithogenic effects of dysfunctional CCK-1R by systematically studying its pathophysiological functions in some "manufactured" mouse strains such as CCK-1R congenic mice and CCK-1R knockout mice. Also, we will investigate pathophysiological effects of gallbladder stasis on cholesterol crystallization and gallstone formation, as well as gene therapy of gallbladder dysmotility in these mice. In this application, the applicant proposes to (i) elucidate whether the mutated CCK-1R results in gallbladder stasis due to a defect in receptor-G protein coupling; (ii) determine the alterations induced by gallbladder hypomotility that account for rapid cholesterol crystallization and gallstone formation in mice with the mutated CCK-1R; and (iii) explore whether lentivirus-mediated transfer of the mouse CCK-1R gene prevents cholesterol gallstone formation in mice with gallbladder hypomotility. Due to the close homology between human and mouse genomes, the identification of lithogenic effects of dysfunctional CCK-1R in mice may elucidate previously unknown but pathophysiologically relevant genetic determinants of cholesterol cholelithiasis in humans.