[Regulation of heat shock protein 27/activating transcription factor-5 complex and its implication in podocyte apoptosis induced by high glucose].

OBJECTIVE: To investigate the regulation of heat shock protein (HSP)27/activating transcription factor (ATF)-5 complex in podocytes induced by high glucose and relevant mechanisms.

METHODS: Mice kidney podocytes were cultured in culture fluid with D-glucose at normal concentration (5.5 mol/L) (Group NG) or with D-glucose at high concentration (30 mmol/L) (Group HG) cells of these 2 groups were collected at different time points after glucose stimulation to detect the cell apoptosis by Hoechst 33342 staining and fluorescence microscopy and flow cytometry. Western blotting was used to analyze the activation of extracellular signal-regulated kinase (ERK = MAPK) and p38 signaling pathway. The HSP27/ATF5 complex was assessed by co-immunoprecipitation. ERK pathway blocker PD98059 and p38 signal pathway blocker SB203580 were added into the culture fluid of Group HG and Group NG respectively, and then the podocytes were collected at different time points to detect the high glucose-induced HSP27/ATF5 complex and cell apoptosis.

RESULTS: The apoptotic rate of the podocytes of Group HG 24 hours after high glucose incubation was 14.3% +/- 6.2%, and that 48 h after was 27.2% +/- 8.9%, significantly higher than that of Group NG (10.6% +/- 2.7%, P < 0.05). HSP27/ATF5 complex could detected in the cells of Group NG too, however, the level of HSP27/ATF5 complex in Group HG 12 hours after incubation was 195% +/- 36% that of Group NG (P < 0.05). Both the ERK signal pathway and p38 signal pathway of Group HG began to be activated 10 min after incubation, peaked 30 min after, remained at the highest level till 1 hour after, and returned almost to the baseline level 2 hours after. No activation of these 2 pathways was observed in Group NG. The HSP27/ATF5 complex level of the PD98059 + high glucose group was 109% +/- 19% that of Group NG, significantly lower than that of Group HG (211% +/- 46% that of Group NG, P < 0.05). The apoptotic rate of the PD98059 + high glucose group was 51% +/- 4%, significantly higher than that of PD98059 + normal glucose group (16% +/- 3%, P < 0.05) and that of Group HG (27% +/- 9%, P < 0.05). The apoptotic rate of the SB203580 + HG group was 16% +/- 6%, significantly lower than that of Group HG (27% +/- 9%, P < 0.05). The HSP27/ATF5 complex level of the SB230580 + HG group was 290% +/- 43% that of Group NG, not significantly different from that of Group HG (231% +/- 20% that of Group NG, P > 0.05).

CONCLUSION: High glucose stimulates the formation of HSP27/ATF5 complex in podocytes through ERK signaling pathway but not P38 signaling pathway, and the HSP27/ATF5 complex may have a regulatory effect in podocyte apoptosis induced by high glucose.