Mechanisms of Coronary Arteriolar Dysfunction in Type 2 Diabetes

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DESCRIPTION (provided by applicant): Coronary arteriolar function is highly dependent on the integrity of endothelial cells (EC) and vascular smooth muscle cells (VSMC). Type 2 diabetes is associated with increased prevalence of ischemic heart disease, generally related to coronary artery disease that is associated with increased morbidity and death in diabetic patients. Epidermal growth factor receptor (EGFR) tyrosine kinase, of the many factors involved in cell growth and migration has been shown to be critical in the development of microvascular myogenic tone expressed as microvascular constriction in response to pressure increases. Our studies show an exacerbation of EGFR tyrosine kinase phosphorylation in coronary arteriolar from type 2 diabetic mice (db-/db- mice lacking leptin receptor gene) associated with coronary arteriolar dysfunction characterized by a reduced endothelial-dependent relaxation and potentiation of myogenic tone. Interestingly, in vivo inhibition of EGFR tyrosine kinase in db-/db- mice significantly improves coronary arteriolar function. Thus, enhanced EGFR tyrosine kinase in diabetes could be a critical up stream signal leading to a myriad of downstream signaling including oxidative stress, NFkB and PARP-1. More importantly, oxidative stress, nuclear factor kappa Beta (NFkB-transcriptional and nuclear factor) and poly(ADP-ribose)polymerase (PARP-1 nuclear factor), which are highly implicated in the etiology and progression of type 2 diabetes, could be critical in coronary arteriolar dysfunction in diabetes. Our preliminary data indicate an increase in oxidative stress (superoxide; O2.-), p65- NFkB activity and PARP-1 activity in coronary arterioles from db-/db- mice. Despite these connections, there has been no link determined between the coronary arteriolar pathology of diabetes with EGFR tyrosine kinase, oxidative stress, NFkB and PARP-1 pathway. Therefore, our central hypothesis is that exacerbation of EGFR tyrosine kinase phosphorylation leads to the increased ROS, NFkB and PARP activity, which in turn are responsible for coronary arteriolar dysfunction in type 2 diabetes. We will determine that: Aim 1. EGFR tyrosine kinase inhibition reduces O2.-, p65-NFkB and PARP activity, and improves coronary arteriolar function in db-/db- mice; Aim 2. Inhibition of O2.- production or scavenging of O2.- in db-/db- mice improves coronary arteriolar EC and VSMC dysfunction; Aim 3. Increased p65-NFkB and PARP-1 activities are critical in coronary arteriolar dysfunction in db-/db- mice. The successful completion of this project will determine the mechanisms how exacerbation of EGFR tyrosine kinase leads to the increased oxidative stress, NFkB and PARP-1 activity, which in turn are responsible for coronary arteriolar dysfunction, and will provide new insight into the vasculopathy mechanisms in diabetes.