Regulation and actions of activin A and follistatin in myocardial ischaemia–reperfusion injury

• We studied the expression of activin A and follistatin in myocardial ischemia reperfusion injury.
• Activin A promotes, whereas follistatin reduces, myocardial damage following ischemia reperfusion.
• Follistatin reduces myocardial damage by improving myocardial mitochondrial membrane potential.

Activin A, a member of the transforming growth factor-β superfamily, is stimulated early in inflammation via the Toll-like receptor (TLR) 4 signalling pathway, which is also activated in myocardial ischaemia–reperfusion. Neutralising activin A by treatment with the activin-binding protein, follistatin, reduces inflammation and mortality in several disease models. This study assesses the regulation of activin A and follistatin in a murine myocardial ischaemia–reperfusion model and determines whether exogenous follistatin treatment is protective against injury. Myocardial activin A and follistatin protein levels were elevated following 30 min of ischaemia and 2 h of reperfusion in wild-type mice. Activin A, but not follistatin, gene expression was also up-regulated. Serum activin A did not change significantly, but serum follistatin decreased. These responses to ischaemia–reperfusion were absent in TLR4−/− mice. Pre-treatment with follistatin significantly reduced ischaemia–reperfusion induced myocardial infarction. In mouse neonatal cardiomyocyte cultures, activin A exacerbated, while follistatin reduced, cellular injury after 3 h of hypoxia and 2 h of re-oxygenation. Neither activin A nor follistatin affected hypoxia-reoxygenation induced reactive oxygen species production by these cells. However, activin A reduced cardiomyocyte mitochondrial membrane potential, and follistatin treatment ameliorated the effect of hypoxia-reoxygenation on cardiomyocyte mitochondrial membrane potential. Taken together, these data indicate that myocardial ischaemia–reperfusion, through activation of TLR4 signalling, stimulates local production of activin A, which damages cardiomyocytes independently of increased reactive oxygen species. Blocking activin action by exogenous follistatin reduces this damage.