Diabetes mellitus is characterized by impaired glucose homeostasis resulting from insufficiency or functional failure of insulin-producing ??cells, alone or in association with insulin resistance. Therefore, restoring ?-cell mass and function is essential to reverse the development of diabetes. Utilizing small molecule inducers of ?-cell proliferation is a particularly promising strategy with numerous valuable features such as their oral bioavailability and target specificity. However, the slow rate of ?-cell proliferation in adult humans is a major hurdle to overcome to use this approach. Through a chemical genetic screen for small molecule enhancers of ?-cell regeneration in zebrafish, we identified several TBK1/IKK? inhibitors (TBK1/IKK?-Is). TBK1/IKK?-Is promoted ?-cell regeneration by markedly increasing proliferation of ?-cells. Mammalian target of rapamycin (mTOR) inhibitor rapamycin eliminated the effect of TBK1/IKK?-Is on regenerating ?-cells, whereas TBK1/IKK?-Is augmented mTOR activity. Interestingly, treatment with TBK1/IKK?-Is led to pronounced increase in cAMP levels. The proliferation effect of TBK1/IKK?-Is was verified in primary mammalian islets including human islets. The goal of this application is to delineate the mechanisms and the strategies of how to increase functional ?-cell mass with suppression of TBK1/IKK?. First, we will design and investigate the potency of novel TBK1/IKK?-Is on ?-cell regeneration. Using (E)-3-(3-phenylbenzo[c]isoxazol-5-yl)acrylic acid (abbreviated as PIAA), which markedly increases ?-cell regeneration, as a lead compound, we will perform structure-activity relationship (SAR) analyses of TBK1/IKK?-PIAA interaction. Furthermore, we will use the PIAA as a scaffold to design new molecular architectures that exhibit potent and selective TBK1/IKK? inhibition activities with minimum toxicity on ?-cell regeneration. Second, we will elucidate underlying mechanisms of TBK1/IKK?-mediated ?-cell regeneration. Given that rapamycin treatment abolished the effect of TBK1/IKK? suppression on ?-cell regeneration and TBK1/IKK?-Is enhanced mTOR activity and cAMP levels, we will test whether TBK1/IKK? suppression promotes ?-cell regeneration via modulating the cAMP-mTOR signaling cascade. We will perform biochemical and functional analyses to characterize the TBK1/IKK?-cAMP-mTOR interplay on ?-cell regeneration in vitro and in vivo. Third, we will investigate the efficacy of TBK1/IKK?-Is on expanding functional ?-cell mass in mammalian systems. We will use primary pancreatic islets to examine the potency of PIAA and its newly synthesized analogs on ?-cell replication. Furthermore, we will evaluate the ability of PIAA and its analogs to promote ?-cell expansion and enhance glycemic control in mice including a mouse model of streptozotocin (STZ)-induced diabetes.
We will delineate the mechanisms and the strategies of how to augment functional ?-cell mass by repressing TBK1/IKK? function. The outcomes of the proposed study will make a significant breakthrough to prevail over the current bottleneck of enhancing human ?-cell proliferation in treating diabetes.
| Xu, Jin; Jia, Yun-Fang; Tapadar, Subhasish et al. (2018) Inhibition of TBK1/IKK? Promotes Regeneration of Pancreatic ?-cells. Sci Rep 8:15587 |
