Defective Atypical Protein Kinase C (PKC) Activation in Diabetes and Metabolic Syndrome

We have provided clear evidence that insulin activation of all three signaling components, Viz., IRS-1-dependent PI 3-Kinase, atypical protein kinase C (aPKC) and PKB/Akt is defective in diabetic muscle. These defects are best seen when insulin activation is conducted at both half-maximal and maximal stimulation. Moreover, whereas previous studies had shown that treatment with metformin (Met) alone improves aPKC activation, or that treatment with thiazolidinedione (TZD) alone produces increases in activation of IRS-1/PI3K and aPKC when evaluated at maximal insulin stimulation, we have recently found that combined treatment with Met plus TZD for 6 weeks provokes marked increases in insulin effects on all three signaling factors at both half-maximal and maximal insulin stimulation. This work is being prepared for submission for publication.

We have also evaluated the improvement in insulin signaling in diabetic muscle 4 hours after acute endurance (one-legged) exercise and found that the responsiveness of aPKC to the lipid PI3K-derived activator, PIP3, was improved. Also increased was the activation by insulin of IRS-2-dependent PI3K, ERK1/2, and downstream protein synthesis machinery, viz., p70S6 kinase and eukaryotic elongation factor eEF2. These effects of exercise would be expected to enhance glucose transport and utilization by muscle, and promote protein synthesis, i.e., an anabolic response.

Inclusion criteria

• Stable uncomplicated type 2 diabetes
• Able to be off oral treatments for 2 months

Exclusion criteria

• Diabetic complications related to heart, eye, nerve problems
• Renal impairment
• Cardiovascular disease
• Hepatic disease
• Prior history of other disorders or complications caused by diseases
• Insulin therapy needed