Early intensive insulin therapy attenuates the p38 pathway in the renal cortex and indices of nephropathy in diabetic rats

Abstract

In this rodent study, we compared the effects of early versus late intensive insulin therapy on diabetic nephropathy and potential causal mechanisms. Diabetes was induced in rats by high-fat diet and low-dose streptozotocin. Intensive insulin therapy was initiated in the early intensive insulin therapy groups as soon as diabetes was confirmed and lasted for 8 (8wEI group) and 16 weeks (16wEI group). In the late insulin therapy group (LI group), intensive insulin treatment was initiated 8 weeks later and lasted for 8 weeks. Age-matched diabetic rats (8wDM group and 16wDM group) and non-diabetic rats (8wNC group and 16wNC group) served as controls. Histological analysis, real-time PCR, and western blot were performed in renal cortex specimens. Glomerular hypertrophy and mesangial matrix expansion were prominent in the 16wDM and LI groups while the EI groups remained normal and similar to the 16wNC group. Western blots revealed that p38 MAPK activities in the EI groups decreased significantly, whereas the level in the LI group was markedly higher than the 16wEI group, and not different from the DM groups. Activities of MKK3/6, CREB and MKP-1 proteins as well as CREB and MKP-1 mRNA showed a similar pattern. Therefore, we concluded that early intensive insulin treatment and attainment of good glycemic control counteracted some renal molecular pathways associated with epigenetic metabolic memory to minimize risk of diabetic nephropathy. However, late insulin therapy did not abrogate the increased renal cortical p38 MAPK pathway activation in diabetic rats and led to glomerular hypertrophy and extracellular matrix expansion.