Background: The p38 mitogen-activated protein kinase (MAPK) pathway is activated by several stress factors, potentially leading to cellular apoptosis and growth. Little is known about the pattern of glomerular p38 MAPK pathway activation during the course of diabetic nephropathy (DN). We examined the activity and expression of the p38 MAPK pathway members, p38 MAPK, MKK3/6, cAMP-responsive element binding protein (CREB), and MAPK phosphatase-1 (MKP-1), in experimental DN in rats over the course of four months.
Methods: Control (C; N = 16) and diabetic (DM; N = 16) rats were studied. Four rats from each group were sacrificed monthly, and competitive reverse transcription-polymerase chain reaction and Western blot were performed with microdissected and sieved glomeruli, respectively.
Results: Glomerular p38 MAPK mRNA expression was significantly higher in DM than C (P < 0.01) throughout the four-month period. Western blot revealed an average 3.1-fold increase in p38 MAPK protein throughout the study period (P < 0.05). However, p38 MAPK activity was significantly increased only in one- and two-month diabetic glomeruli. Glomerular MKK3/6 and CREB mRNA as well as activity were significantly increased only in one- and two-month DM compared with C. MKP-1 mRNA showed a similar pattern.
Conclusions: Glomerular p38 MAPK activity was increased in early DN. Parallel to this, we also showed, to our knowledge for the first time, that there were increased MKK3/6 and CREB activities and mRNA expression. This activated p38 MAPK pathway in diabetic glomeruli may, in part, play a role in the pathogenesis of early hypertrophy and extracellular matrix accumulation.