Type 2 diabetes mellitus (T2DM) is a major cause of premature morbidity and mortality in the US and many emerging nations. There is an increasing appreciation that the underlying mechanism leading to T2DM is inadequate insulin secretion in response to insulin resistance, the latter most commonly secondary to a lifestyle with high calorie fat enriched food intake in excess of physical activity requirements. The failure to adequately increase insulin secretion in T2DM is accompanied by a specific islet pathology, with an approximate 60% deficit in beta cell mass and islet amyloid derived from islet amyloid polypeptide (IAPP). There is an increasing appreciation that diseases with this pathological phenotype can be at least in part attributed to the formation of intracellular toxic oligomers of the amyloidogenic diseases. The cellular process designated to clear intracellular oligomers and damaged organelles in long lived cells, such as beta-cells, is autophagy. By definition, since damaged organelles and intracellular IAPP aggregates are present in T2DM, autophagy is inadequate. In the proposed studies we plan to address that in health autophagy adaptively increases under conditions of insulin resistance to maintain cellular integrity, but fails to do so in the development and progression of T2DM.
In Specific Aim One, we will seek to establish that formation of toxic h-IAPP oligomers in pancreatic beta-cells disrupts autophagy. We will determine the extent of autophagy activity by analyzing western blots for increases in proteins associated with autophagy (i.e. LC3II, p62, and Atg7) and use of the gold standard in the field, electron microscopy.
In Specific Aim Two, we will test the postulate that autophagy provides protection against formation of toxic h-IAPP oligomers. We will determine whether autophagy is protective by knocking down autophagy in INS cells and islets of mice overexpressing h-IAPP with siRNA against a critical component of the autophagy pathway, Atg7, and monitoring cell death. Moreover, we will cross- breed transgenic mice overexpressing h-IAPP with mice deficient in autophagy (Atg7 knock out mice) and monitor them for diabetes progression. Finally, we will attempt to rescue autophagy impairment by inducing autophagy with rapamycin.
In Specific Aim Three, we will test the postulate that toxic h-IAPP oligomers cause impaired disposal of autophagocytosed cellular debris. We hypothesize that h-IAPP toxic oligomers disrupt the integrity of lysosome and/or autophagosome membranes thereby preventing the fusion of the autophagosome with the lysosome. We will utilize fluorescently-labeled proteins that localize to autophagosomes or lysosomes to visualize transport and fusion abnormalities in real time experiments by confocal microscopy (live cell imaging).
Type 2 diabetes now affects more than 25 million people in the USA and is increasing rapidly in prevalence worldwide. In people with type 2 diabetes there is a shortened life expectancy through vascular complications as well as an increased risk of several cancers. The present application requests training funds to support the career development of a new islet investigator in studies designed to address the underlying mechanisms that lead to type 2 diabetes at the level of the pancreatic beta cell in the hope that such an approach can help establish novel methods to prevent and or treat the disease.
|Rivera, Jacqueline F; Costes, Safia; Gurlo, Tatyana et al. (2014) Autophagy defends pancreatic ? cells from human islet amyloid polypeptide-induced toxicity. J Clin Invest 124:3489-500|