Role of pH-mediated metabolic reprogramming in β cell failure in Type 2 Diabetes Mellitus

DEI Supplement R01-DK128844: Supplement abstract Type 2 diabetes mellitus (T2DM) manifests through the development of fasting and postprandial hyperglycemia the etiology of which can be distilled to failure of pancreatic β cells to maintain appropriate glucose-stimulated insulin secretion (i.e., β cell function) to compensate for the decline in insulin action (i.e. insulin resistance). Part of our ongoing studies indicate that SLC4A4 and its protein product (electrogenic Na+ -coupled HCO3- cotransporter, NBCe1) in β cells contributes to β cell functional decline in T2DM. As this NBCe1 protein is inappropriately activated in T2D and should elicit changes of intracellular buffering and intracellular pH (pHi) regulation, this Supplement training vehicle seeks to directly measure pHi in β cells that have NBCe1 knocked out or overexpressed. This work should not only reveal the metabolic state of the β cells but also allow us to more directly determine if altered intracellular pH-regulation, intracellular buffering or some other aspect of NBCe1 physiology changes the β cell phenotype to a T2D-state. To address this hypothesis, we will focus on parts of the original Specific Aims 2 (cellular pH regulation with genetic gain-of-function tools) and 3 (utilize novel genetic loss-of-function animal models) to test therapeutic potential of inhibiting SLC4A4/NBCe1 expression/activity in β cells as means to attenuate β cell failure and improve overall glucose metabolism under diabetogenic conditions. From Specific Aim 2, INS1 cells with a genetically encoded pH-sensor will be evaluated with and without NBCe1 genetic gain-of-function to document pH-changes and determine if pHi changes per se leads to β cell functional failure through impairment of mitochondrial metabolism and function. Similarly for Specific Aim 3, novel genetic loss-of-function animal models (NBCe1-loss in β cells) will be crosses with a novel pH-sensor mouse to determine pH and buffering of β cells within intact pancreatic islets. The current project will uncover novel molecular/physiological mechanisms underlying induction of β cell dysfunction and test a potentially novel therapeutic strategy to attenuate of β cell failure in T2DM. Parent PROJECT SUMMARY/ABSTRACT Type 2 diabetes mellitus (T2DM) manifests through the development of fasting and postprandial hyperglycemia the etiology of which can be distilled to failure of pancreatic β cells to maintain appropriate glucose-stimulated insulin secretion (i.e. β cell function) to compensate for the decline in insulin action (i.e. insulin resistance). Thus preservation of β cell function has been identified as a critical barrier for the development of successful preventative and treatment strategies to combat the rise in T2DM prevalence. Studies suggest that β cell dysfunction in T2DM is associated with metabolic reprogramming/shift toward increased non-oxidative glucose metabolism and reduced mitochondrial function similar to an adaptive features observed in cancer cells. Accordingly, cancer cells facilitate increased glycolytic flux and subsequent rise in metabolic acid production by upregulating expression of ion pumps/transporters that enhance cellular buffering capacity and promote cellular alkalinization (increased pHi), such as SLC4 family of bicarbonate transporters. Although, previous studies have confirmed importance of pHi for proper β cell functionality, it is unknown whether intracellular alkalinization or increased pHi buffering contributes to β cell functional decline in T2DM. Thus, the key objective of the current proposal is to test the hypothesis that aberrant induction of a novel T2DM gene SLC4A4 and its protein product (electrogenic Na+ -coupled HCO3- cotransporter, NBCe1) in β cells contributes to β cell functional decline in T2DM. To address this hypothesis, Specific Aim 1 will 1) perform detailed examination of SLC4A4/NBCe1 expression using our unique collection of autopsy-derived human pancreas from patients with obesity, pre-diabetes and T2DM and 2) elucidate molecular mechanisms mediating aberrant β cell induction of SLC4A4/NBCe1 in response to diabetogenic stressors. Specific Aim 2 will utilize novel genetic gain-of-function tools to test the hypothesis that intracellular alkalinization mediated by increased β cell expression of SLC4A4/NBCe1 leads to β cell functional failure through impairment of mitochondrial metabolism and function. Finally, Specific aim 3 will utilize novel genetic loss-of-function animal models and T2DM human islets to test therapeutic potential of inhibiting SLC4A4/NBCe1 expression/activity in β cells as means to attenuate β cell failure and improve overall glucose metabolism under diabetogenic conditions. The current project will uncover novel molecular/physiological mechanisms underlying induction of β cell dysfunction and test a potentially novel therapeutic strategy to attenuate of β cell failure in T2DM.