A MATTER OF NUTRIENT EXCESS AND SHEAR STRESS

Abstract: The metabolic syndrome is a clustering of several risk factors associated with diabetes and cardiovascular disease. Diabetes is a global problem with 90% of patients suffering from type 2 diabetes (T2D), which is attributable to various factors including genetic predispositions and lifestyle. In T2D, there is a reduction in β cell mass and function, and impaired glucose homeostasis. It is often associated with insulin resistance in target tissues and has a profound influence on vascular health. This, thesis investigates the novel role of cocaine and amphetamine regulated transcript (CART) in the pancreatic β cells and purinergic signaling mechanisms in the vascular endothelial cells. Using rat pancreatic clonal β cell lines (INS-1 832/13) and rat islets, we provide evidence for a novel role of CART in β cell survival and proliferation. Exogenous addition of CART 55-102 attenuated glucotoxicity-induced β cell death. This effect of CART was likely due to the activation of signaling molecules important for cell survival, namely, CREB, IRS-2, PKB, FoxO1, p44/42-MAPK, and p90RSK. Furthermore, the pharmacological inhibition of the kinases blocked the proliferative effect of CART on β cells. In conclusion, CART 55-102 protects β cells against glucotoxicity and promotes proliferation and may thereby contribute to the preservation of β cell mass. Physical inactivity and metabolic risk factors together form a continuum that over time negatively affects endothelial function. The vascular endothelium is exposed to fluid shear stress from flowing blood and maintains vascular homeostasis. The resident endothelial cells express a repertoire of specialized purinergic receptors that respond to extracellular nucleotides mediating various physiological responses. In human vascular endothelial cells, both ATPγS and shear stress increased KLF2, a transcription factor important for atheroprotection, in part via the P2X4 receptor. Additionally, shear stress-induced endothelial cell alignment and cytoskeletal remodeling, as seen in atheroprotective regions of the vascular tree, was found to be P2Y2 receptor-dependent. Using pharmacological inhibitors of P2X7 and P2X4, we observed differential effects of these receptors in inhibiting inflammatory genes, reactive oxygen species, and leukocyte adhesion in endothelial cells exposed to high glucose and palmitate. In addition, we demonstrate a novel role of UTP and ATP in regulating miR-22 transcription that inhibits ICAM-1 and leukocyte-endothelial adhesion, an effect possibly mediated by P2Y2 receptors. In conclusion, this thesis provides a molecular basis for treatment strategies, albeit at a cellular level, aiming at (i) preserving β cell mass and function and (ii) enhancing vascular health that range from lifestyle interventions to specific pharmacological therapies.