REGULATORY MECHANISM DRIVING ΑB-CRYSTALLIN INDUCTION IN SKELETAL MUSCLE CELLS UPON REDOX IMBALANCE

The cytoprotective and antioxidant role of αB-crystallin (αB-cry) is mediated by the ability to upregulate itself, but the molecular pathway driving αB-cry expression in muscle cells during oxidative stress still remains unknown. We analyzed changes in αB-cry expression in C2C12 myogenic cells at different time post-treatment (0, 2, 6 and 18 hours) with two distinct oxidative stress inducers: sodium meta-arsenite NaAsO2 (50 μM) and hydrogen peroxide H2O2 (100 μM). A significant and rapid increase in αB-cry mRNA and protein levels was observed in NaAsO2 treated cells. On the contrary, H2O2 treatment showed a slight increase, at 18 hours only. Activation of JNK and AKT were evident for both oxidants. The AKT phosphorylation induced by NaAsO2 was always much less intense than that resulting by H2O2, while a stronger activation of p38 kinase was observed after NaAsO2 compared to H2O2 treatment. Only NaAsO2 exposure induced an almost complete oxidation of both Thioredoxin-1 and Thioredoxin-2, with a complete recovery of their redox status at 6 hours from treatment. To get a further insight into this regulatory mechanism, we searched for putative redox-sensitive transcription factors (RSTFs) that could drive the αB-cry mRNA induction. Interestingly, the RSTFs c-jun and Nrf2 were found specifically up-regulated after NaAsO2 treatment. Moreover, our data regarding their binding activity on αB-cry promoter strongly support the direct role for c-jun and Nrf2 in the regulation of this gene upon NaAsO2-induced redox imbalance in skeletal muscle cells.