Glucose and diabetes: Effects on podocyte and glomerular p38MAPK, heat shock protein 25, and actin cytoskeleton

Phosphorylated p38 (pp38) mitogen-activated protein kinase ( MAPK) regulates heat shock protein 25 (HSP25), stabilizing fibrillar actin (FA) and preventing cleavage to G-actin (GA). Cultured podocytes ( Pods) were exposed to glucose (5.5 - 50 mM) +/- p38MAPK inhibitor SB202190 (SB) or control SB202474 to assess the effects on FA/GA and Pod structure. The relationship of p38MAPK with in vivo Pod structure and albuminuria (Ualb) was assessed in rats with streptozotocin (SZ)- induced diabetes (DM) for 1 week, 1 month, and 4 months. High glucose induced concentration-dependent increases in pp38MAPK and phosphorylated HSP25 (pHSP25) maintained actin cytoskeleton. Inhibition by SB diminished pp38MAPK and pHSP25, decreased FA/GA, and altered FA and GA immunohistochemical appearance. In SZ-DM, glomerular pp38MAPK and biphosphorylated HSP25 were increased after 1 week, declining at 1 month, and at or below C values at 4 months. Glomerular FA/GA in DM was normal at 1 week, declining at 1 month, and low at 4 months. Ualb/creatinine was similar in DM vs C at 1 week, and increased at 1 and 4 months. Morphometry demonstrated progressively diminishing slit pore density in DM over time, denoting evolving effacement. There were strong correlations between slit membrane density and both glomerular biphosphorylated HSP25 and lnUalb/ cr ratio. The data suggest that increased pp38MAPK and pHSP25 comprise an acute adaptation to glycemic stress. Later depletion of DM may contribute to Pod structural alterations and Ualb.