Inhibition of MAP-kinase cascade normalizes the proliferation rate of fibroblasts from patients with Type 1 diabetes and nephropathy

Faster proliferation rate characterizes human skin fibroblasts from patients with Type 1 diabetes and nephropathy (DN), but the reason of this phenomenon is still unknown. Growth factors control cell proliferation through an intracellular mitogen-activated protein (MAP) kinase cascade. We have examined the effect of the inhibition of MAP kinase/ERK kinase (MEK), a key point of the MAP kinase cascade, on the proliferation rate of fibroblasts from 40 patients with Type 1 diabetes (20 with and 20 without DN) and from 10 nondiabetic participants. Proliferation rate was measured by cell count in the presence or absence of 30 μmol/l of the MEK inhibitor PD 098059. In normal cultural conditions, proliferation rate was faster in fibroblasts from patients with (0.175±0.009×10⁵ cells day^-1, mean±S.E.M.) than without DN (0.110±0.009) and in nondiabetic participants (0.094±0.008; ANOVA P5 cells day^-1; 55% of reduction) than without DN (0.068±0.006; 38% of reduction) and in nondiabetic participants (0.064±0.006; 32% of reduction), and differences among groups were lost. In parallel, PD 098059 induced a greater reduction of MEK-dependent phosphorylation in lysates of fibroblasts from patients with (73%) than without (40%) DN. In conclusion, the inhibition of MEK normalizes the proliferation rate of fibroblasts from patients with DN, suggesting that the MAP kinase cascade could be involved in this cellular dysfunction.