Cyclophilins are induced by hypoxia and heat stress in myogenic cells

This is a novel study demonstrating that cyclophilins are heat and stress inducible proteins in eukaryotic myogenic cells. We investigated the expression of cyclophilins in embryonal rat heart derived H9c2 myocytes following heat stress and chronic hypoxia. We report here that cyclophilins, the proteins capable of catalysing the interconversion of cis and trans isomers (PPIses) in proteins and peptides, are heat and stress inducible, and are involved in the complex stress response, as their level is significantly elevated after heat stress and hypoxia. A time course analysis showed the gradual increase in expressed levels of cyclophilin after heat stress of cells, with maximal expression as measured by Western blot at 48 hours after the actual treatment. Rat myogenic cells exposed to chronic hypoxia followed by 5 hours reoxygenation resulted in approximately threefold expression of PPI-ases. The results showing that cyclophilins are heat and stress inducible suggest a multiple role for cyclophilins in ischemia: a potential functional association with the different heat shock proteins, with the established protective role in ischaemic injury, as well as the possible involvement of cyclophilins in the protein folding in cooperation with molecular chaperones.