(3-cell failure in obesity-associated type 2 diabetes (T2DM) is believed to correlate with chronic hyperlipidemia and hyperglycemia that leads to defects in insulin secretion and growth factor signaling necessary to maintain p-cell mass. However, lipids also have a role in the compensatory growth and proliferation of (3-cells that precedes the development of T2DM. Mammalian target of rapamycin (mTOR) is a serine/threonine protein kinase that integrates signals from growth factors and nutrients to regulate cell growth and proliferation. Our overall objective is to appropriately regulate mTOR by nutrients to enhance the growth and proliferative capacity of adult (3-cells. Preliminary data demonstrate that free fatty acids (FFAs), ketones and glucose activate mTOR and enhance DNA synthesis as a prerequisite for (3-cells to enter the cell cycle and progress to mitosis.
In specific aim 1. we will characterize the physiological processes affected by mTOR in response to FFAs, ketones and glucose that include: A) S6K1 phosphorylation and DNA synthesis, B) cell cycle progression and cell proliferation, and C) evaluate these nutrients on mTORmediated defects in growth factor signaling. It is hypothesized that mitochondrial oxidative metabolism represents a means by which cells take multiple nutrient inputs and convert them to diverse regulatory signals.
In specific aim 2. we will further establish the role of the mitochondrial transition pore (MTP) in linking mitochondrial factors to mTOR-mediated events by: A) identifying mitochondrial factors that influence transient MTP opening in response to FFAs and ketones, B) determining if FFAs and ketones affect the MTP by similar or different mechanisms and the potential role for endogenous ketone production in mTOR signaling, and C) defining links between MTP opening and retrograde communication involving mTORdependent signaling to transcriptional factors for metabolic adaptation, mitochondrial biogenesis, and cell proliferation. Based on our findings that FFAs and ketones (acetoacetate) are regulators of mTOR in human and rodent islets, in specific aim 3 we will determine whether elevated plasma ketones and FFAs in a setting of normoglycemia, promote (3-cell growth and proliferation in a rapamycin-sensitive manner by studying rats consuming either A) a ketogenic or B) a calorie-restricted diet ? rapamycin, and C) evaluate the ability of acetoacetate to promote islet graft survival and improve blood glucose regulation by 24-96 h pre-culture of islets with acetoacetate prior to transplanting a """"""""marginal dose"""""""" of islets to STZ-diabetic SCID mice. It is anticipated that completion of these objectives involving our novel findings of the regulation of mTOR by FFAs, ketones and glucose will provide significant strategies to enhance growth and proliferation of adult pcells applicable to treatments for both T1DM and T2DM and provide basic knowledge of the mechanisms by which nutrients affect the mTOR pathway.
