PHLPP1/2 phosphatases as new target for beta-cell-directed therapy in diabetes

• Applicant: Amin Ardestani, Ph.D.
• Subject Area: Endocrinology, Diabetology, Metabolism
• Term: from 2014 to 2022
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 260745940

Both type 1 diabetes (T1D) and type 2 diabetes (T2D) result from a decline in pancreatic beta-cell function and/or mass. There is a critical need to develop therapeutic approaches to restore beta-cell mass in patients with diabetes. Apoptosis as well as impaired function of insulin producing beta-cell are hallmarks of beta-cell failure and the fundamental cause of diabetes. Modulation of beta-cell apoptosis and/or enhancement of regenerative capacity represent an attractive therapeutic approach to the treatment of diabetes. Serine-threonine phosphatases (STPs) such as PHLPP1/2 (PH domain leucine-rich repeat protein phosphatase-1/2) regulate cell death and serve as potential targets for drug development. Our understanding of the function of PHLPPs in beta-cell death regulation has important biological and clinical significance. We show that PHLPP1 and PHLPP2 are highly up-regulated in beta-cells under diabetogenic conditions in vitro, in human T1D and T2D and in mouse models of diabetes. PHLPP1/2 overexpression impairs beta-cell survival and function. PHLPP1/2 induced beta-apoptosis is mediated through the inactivation of AKT pro-survival signaling and the activation of pro-apoptotic MST1 kinase, two well-established PHLPP substrates. During the initial DFG-funded period, we have found: (i) PHLPP, AKT and MST1 form an auto-inhibitory triangle that controls beta-cell apoptosis. (ii) mTORC1 hyper-activation regulates PHLPPs up-regulation, MST1 activation and beta-cell death under diabetic conditions. (iii) Genetic and pharmacological inhibition of PHLPP restores beta-cell survival and insulin secretion in vitro and in in vivo mouse models of diabetes.In the present proposal, we continue to fully discover the mechanism of PHLPP upregulation under diabetic conditions by assessing how PHLPP is upregulated in the -cell and whether mTORC1 controls PHLPPs at the translation level. We will also perform islet transplantation studies; islets from PHLPP1-KO mice and wild-type controls are transplanted into diabetic mice in order to uncover and distinguish an islet specific action and a systemic metabolic benefit of PHLPP1 deletion in vivo. Ultimately, we will investigate the utility, pharmacokinetics and MALDI-based drug localization of specific chemical PHLPP inhibitors available in the lab, and subsequently test their efficacy to restore beta-cell survival and function in vitro and to normalize glycemia, beta-cell survival and function in vivo in a mouse model of diabetes within a preclinical study. The purpose of this application is to further elucidate the cellular and molecular mechanisms of PHLPP regulation and action in pancreatic islets in order to move our initial highly promising results forward into translational research; to establish the previously uncharacterized PHLPP1/2 signaling pathway as a novel target for beta-cell curative pharmacological intervention to restore a functional pancreatic beta-cell mass in diabetes.

• DFG Programme: Research Grants