Protein Kinase C-β Contributes to Impaired Endothelial Insulin Signaling in Humans With Diabetes Mellitus

Abstract

Background Abnormal endothelial function promotes atherosclerotic vascular disease in diabetes. Experimental studies indicate that disruption of endothelial insulin signaling through the activity of protein kinase C-β (PKCβ) and nuclear factor κB (NFκB) reduces nitric oxide availability. We sought to establish whether similar mechanisms operate in the endothelium in human diabetes mellitus. Methods and Results We measured protein expression and insulin response in freshly isolated endothelial cells from patients with Type 2 diabetes mellitus (n=40) and non-diabetic controls (n=36). Unexpectedly, we observed 1.7-fold higher basal endothelial nitric oxide synthase (eNOS) phosphorylation at serine 1177 in patients with diabetes (P=0.007) without a difference in total eNOS expression. Insulin stimulation increased eNOS phosphorylation in non-diabetic subjects but not in diabetic patients (P=0.003) consistent with endothelial insulin resistance. Nitrotyrosine levels were higher in diabetic patients indicating endothelial oxidative stress. PKCβ expression was higher in diabetic patients and was associated with lower flow-mediated dilation (r=−0.541, P=0.02) Inhibition of PKCβ with LY379196 reduced basal eNOS phosphorylation and improved insulin-mediated eNOS activation in patients with diabetes. Endothelial NFκB activation was higher in diabetes and was reduced with PKCβ inhibition. Conclusions We provide evidence for the presence of altered eNOS activation, reduced insulin action and inflammatory activation in the endothelium of patients with diabetes. Our findings implicate PKCβ activity in endothelial insulin resistance.

Liraglutide Treatment Reduces Endothelial Endoplasmic Reticulum Stress and Insulin Resistance in Patients With Diabetes Mellitus

“…GLP‐1 analogues have been described previously to induce a transient phosphorylation of eNOS at Ser1177 31. As shown in Figure S4, and concordant with our previous reports, patients with DM had higher basal levels of activated eNOS at Ser1177 32. We found that liraglutide treatment induced an increase in eNOS phosphorylation at its activation residue (Ser1177) in endothelial cells isolated from patients without DM.…”

“…As shown in Figure 4 and consistent with our previous reports, insulin stimulation did not induce eNOS phosphorylation in patients with DM 32. Pretreatment with liraglutide for 15 minutes before insulin stimulation (10 nmol/L, 30 minutes) restored eNOS activation and endothelial function in endothelial cells isolated from patients with DM (n=10; P =0.019).…”

Targeting Vascular Endothelial Cell Insulin Resistance in Type 2 Diabetes Mellitus

“…13,14 Consistent with these in vitro findings, the study by Tabit et al 11 reports that endothelial cells from diabetic patients compared with control subjects demonstrate a trend for higher expression of NFκB p65 and intracellular adhesion molecule-1 (ICAM-1), and reduced expression of the inhibitor protein of NFκB (IκBα) (Figure). This is significant because ICAM-1 is responsible for leukocyte adhesion to the endothelium during the development of atherosclerosis and endothelial dysfunction.…”

“…In summary, the study by Tabit et al 11 demonstrates for the first time in humans that PKCβ and NFκB are key integrative mechanisms involved in mediating endothelial cell insulin resistance in patients with type 2 diabetes mellitus. Given the disappointing results of clinical studies using PKCβ inhibitors, targeting NFκB with salsalate or newly developed more selective NFκB inhibitors may be the new therapeutic bullseye for reducing vascular risk in patients with type 2 diabetes mellitus.…”

Endothelial Nitric Oxide Synthase (eNOS) Glu298Asp Gene Polymorphism (G894T) as a Risk Factor for Type 2 Diabetes Mellitus in the Tunisian Population

“…The decreased eNOS activation by insulin was greatly attenuated in endothelial cells from diabetic patients indicates the presence of the endothelial insulin resistance [24].…”