Molecular mechanisms of Fam3c cardioprotective activity

Despite the urgent and broad need to develop new treatments for myocardial infarction (MI) and heart failure (HF), drug treatment to revert these pathologies has not evolved significantly over the last two decades. A key aspect underlying the epidemic burden of MI is the incapacity of the cardiac muscle to undergo regeneration in adult life. Damaged cardiac tissue typically results in irreversible loss of cardiomyocytes (CMs) with relative fibrosis and scarring. Although the massive effort so far made in trying and developing cardioprotective therapies, effective treatments have not been identified yet. To systematically identify novel cardioactive biologicals, the Molecular Medicine Laboratory at ICGEB Trieste has generated a library of 1198 barcoded AAV vectors encoding for the mouse secretome and developed cardiac FunSel (cFunSel), a method for their in vivo unbiased selection ranking these factors for efficacy against MI. This strategy is based on the FUNctional SELection of molecules of interest without a priori knowledge on their function. After an iterative selection in mice subjected to MI, this method led to the identification of novel cardioactive proteins for which no information is currently available nor study has been performed relative to cardiac biology. Among the selected hits identified by cFunSel, we focused our attention on Fam3c, a small, secreted protein ubiquitously expressed in all tissues with still unknown cardiac function. In vivo, cardiac Fam3c overexpression protected the heart after MI, preserving cardiomyocyte viability, sustaining ejection fraction, and preventing pathological remodelling. Fam3c overexpression in cardiomyocytes induced protective cardiac autophagy and decreased cardiomyocyte apoptosis in an in vitro model of cardiotoxicity. Moreover, Fam3c induced cardiomyocyte specific STAT3 activation in a Leukemia Inhibitory Factor receptor (LIFR)-complex dependent way. Although STAT3 participates in a well-known cardioprotective pathway, we demonstrate here that Fam3c induced autophagy is not mediated by STAT3 activation. Fam3c, both expressed by cardiomyocytes and cardiac fibroblasts, was upregulated in an engineered heart tissue (EHT) model of cryoinjury and in the early phases after MI in mice. Fam3c upregulation upon cardiac injury is consequent to the upstream activation of TGF-β pathway and may reveal a new physiological mechanism to protect myocytes against acute ischemic damage, which can be exploited for therapeutic purposes.