Significance: Cardiovascular disease is more prevalent in diabetic patients than non-diabetic patients, and is often more extensive and more rapidly progressive.1,2 Diabetes is associated with changes in vascular endothelial function and vasomotor control as well as with increased morbidity and mortality in patients with ischemic heart diseases. Thus, maintaining coronary-arteriolar endothelial function during cardiac surgery can reduce the incidence of morbidity and mortality of diabetic patients. The mechanism behind the alteration in endothelial dysfunction in diabetic coronary microvasculature is incompletely understood, but may involve modification of electrical signaling in the coronary arteriolar endothelium. This electrical signaling, endothelium-dependent hyper-polarization and vascular relaxation is mediated by small and intermediate conductance of calcium-activated potassium (KCa) (SKCa/IKCa) channels. We have found that the SKCa/IKCa channels are largely responsible for endothelium-dependent relaxation of human coronary microcirculation of non-diabetic patients. Further investigation into endothelial IKCa/SK¬Ca activity, channel current density, and gene/protein expression/localization of SKCa/IKCa will improve our understanding of these alteration and will hopefully lead to novel therapies for endothelial protection for diabetic and non-diabetic patients with ischemic heart diseases.

The goal of this pilot project is to elucidate the role of SKCa/IKCa in coronary-arteriolar endothelial dysfunction of diabetic patients. Recently we observed that microvascular response of diabetic patients to the SKCa/IKCa channel activators was significantly impaired compared to the respective response of non-diabetic vessels at baseline, suggesting that diabetes is associated with down-regulation of SKCa/IKCa.

Thus, we hypothesize that diabetes may affect: 1) SKCa/IKCa gene/protein expression/localization, 2) SKCa/IKCa-mediated microvascular endothelium-dependent relaxation/function, and 3)SKCa/IKCa channels activity, current density and hyper-polarization of human coronary endothelial cells. Using in vitro human coronary arterioles and endothelial cells harvested from diabetic and non-diabetic patients, we will specifically investigate how diabetes affects SKCa/IKCa gene/protein expression/localization, SKCa/IKCa-mediated endothelium-dependent relaxation and SKCa/IKCa current density and endothelium hyper-polarization.
To address these issues, multiple approaches will be employed, such as, the in-vitro human microvessel preparation, RT-PCR, western blotting and immuno-histochemistry and whole cell patch-clamp methods.

We anticipate that diabetes will significantly down-regulate SKCa/IKCa expression/localization, SKCa/IKCa-mediated endothelium-dependent hyper-polarization/relaxation, SKCa/IKCa activity and channel density. Therefore, based on the findings of current project, we expect to submit a proposal to NIH (R01) on May, 2015 to further investigate into the molecular mechanisms responsible for diabetes related down-regulation of SKCa/IKCa. In the R01 proposal, we will specifically investigate: a) the role of reactive oxygen species signaling in diabetes-related down-regulation of SKCa/IKCa of human endothelial cells and diabetes-related endothelial dysfunction; b) the role PKC signaling in diabetes-related down-regulation of SKCa/IKCa of human endothelial cells and diabetic endothelial function; c) the role of integrins and extra cellular matrix in diabetes-related down-regulation of human-endothelial-cells SKCa/IKCa and endothelial function.

Our long-term goal is to develop novel therapeutic strategies for coronary-arteriolar endothelium repair for diabetic or non-diabetic patients with coronary artery diseases. PI has long term, extensive experience, and excellent-publication track records in microvascular and endothelial research. We are one of only a few laboratories in the United States to examine the human microcirculation with our very unique in vitro methods. The mentor Dr. Frank Sellke is a well-known cardiac surgeon and surgeon scientist in microvascular research. The co-investigator Dr. An Xie is an established electro-physiologist and patch clamp expert at Cardiovascular Research Center of Rhode Island Hospital.