Mechanisms of gallbladder smooth muscle dysfunction

Gallbladder disease is one of the most common digestive disorders, and hallmark properties include decreased contractility, inflammation, and gallstone formation. Three features are consistently associated with gallstone disease: (1) elevated cholesterol hydrophobic salt and triglyceride (TG) levels in the bile; (2) inflammation of the gallbladder; and (3) impairments in gallbladder tone and contractility. Nevertheless, the interrelationships between decreased gallstone formation, inflammation, and contractility are not understood, and this reflects our lack of understanding of the cellular events that lead to decreased resting tone and postprandial contractions in gallbladder disease. This grant application proposes to address these fundamental gaps in our knowledge. The overall objectives of this grant application are to: (1) elucidate the cellular and ionic mechanisms by which gallbladder smooth muscle (GBSM) contractility is disrupted in gallstone disease; (2) determine the role of inflammation in smooth muscle dysfunction and associated biliary stasis in gallstone disease; and (3) explore the utility of hydrophilic bile salts in the protection of gallbladder function by preventing or reversing these disruptions to GBSM. We will use wild type and transgenic mice fed a lithogenic (gallstone forming) diet to evaluate the functional changes that occur in GBSM and interstitial cells of Cajal (ICC) during the progression of gallstone disease in normal mice and mice that do not develop gallbladder inflammation. We will also evaluate GBSM function in mice fed a lithogenic diet while being treated with a cyclooxygenase inhibitor, or the protective hydrophilic bile salt, ursodeoxycholic acid (UDCA). The second model involves evaluation of the effects of cholesterol and hydrophobic bile salts applied in vitro to gallbladder muscularis preparations, with or without prior application of UDCA. This approach allows us to examine the actions of these compounds, individually or together, on GBSM and ICC in a controlled environment. This grant proposal involves an integrated approach using state-of-the-art techniques to investigate gallbladder pathophysiology from single molecules to intact tissue during the progression of disease in the animal. Techniques to be used include optogenetic Ca2+ imaging of GBSM cells and ICC in intact muscle bundles, intracellular and patch clamp recording from intact and isolated GBSM cells, respectively, and muscularis tension measurements. Together with our previous studies on smooth muscle function, we will provide insights on how gallbladder motor function is disrupted leading to biliary stasis, and the interrelationship between disrupted motor function and inflammation. Furthermore, these studies will elucidate the therapeutic potential of UDCA to prevent or reverse cellular changes in GBSM/ICC that underlie decreased gallbladder contractility, and uncover the cellular mechanisms that mediate their actions in the gallbladder.