Aims/hypothesis: To verify whether individual susceptibility to diabetic nephropathy resides in an intrinsic difference in Protein Kinase C (PKC) activity.
Methods: We compared the effect of different glucose concentrations on PKC activity, PKC isoform expression and diacylglycerol (DAG) content in cultured fibroblasts from 14 Type 1 diabetic patients who developed nephropathy with those in cells from 14 patients without nephropathy. We recruited 14 normal subjects as control patients. Forearm skin fibroblasts were cultured in either normal (5 mmol/l) or high (20 mmol/l) glucose concentrations.
Results: In normal glucose, in situ PKC activity was higher in Type 1 patients with nephropathy (10.1+/-1.4 pmol/min/mg protein; p<0.01) than in those without (6.8+/-0.8) and the normal control subjects (6.3+/-0.5). This difference was due to increased concentrations of PKCalpha isoform in the membrane fraction of fibroblasts from patients with nephropathy. DAG content was also higher in cells from Type 1 patients with nephropathy. Incubation in high glucose concentration caused a further increase in PKC activity and DAG content in quiescent fibroblasts from patients with diabetic nephropathy, with no significant changes in cells from diabetic patients without nephropathy and normal control subjects.
Conclusion/interpretation: Differences in PKC activation could contribute to the individual susceptibility to renal damage in Type 1 diabetic patients.