The C-domain of the cerebral dopamine neurotrophic factor (CDNF) is responsible for its cardioprotective activity by binding to the KDEL receptor relocated to the plasma membrane under endoplasmic reticulum stress conditions.

Cerebral dopamine neurotrophic factor (CDNF) has emerged as a key cytoprotective molecule, with well-documented neuroprotective effects in Parkinson's disease models and, more recently, demonstrated cardioprotective properties. In this study, we investigated the protective role of CDNF and its isolated domains (CDNF-N and CDNF-C) in isolated hearts subjected to ischemia/reperfusion (I/R) injury. Our data showed that the infarct area at risk decreased from approximately 40% in untreated hearts to about 20% in the presence of CDNF or CDNF-C, but not CDNF-N, indicating that CDNF-C is the principal mediator of CDNF's cardioprotective activity. This effect is mediated by activation of the PI3K/AKT signaling pathway, as the cardioprotective action of CDNF-C was abolished by wortmannin, a PI3K/AKT inhibitor. The study also examined the interaction between CDNF and the KDEL receptor (KDEL-R) at the plasma membrane using cardiomyocytes (H9c2 cells, neonatal primary cardiomyocytes, and human induced pluripotent stem cell-derived cardiomyocytes - hiPSC-dCM) exposed to endoplasmic reticulum (ER) stress induced by thapsigargin. Confocal microscopy revealed that KDEL-R translocates to the plasma membrane under ER stress, where it binds to both full-length CDNF and CDNF-C. However, only the full-length protein undergoes internalization by cardiomyocytes, suggesting that the N-domain is critical for CDNF endocytosis. Following internalization, CDNF traffics primarily to lysosomes, with a minor fraction localizing to mitochondria and the ER. Collectively, these findings identify exogenous CDNF - through its C-domain - as a novel cardiomyokine and highlight its therapeutic potential in cardiac injury and ER stress-related disorders via KDEL-R-mediated PI3K/AKT activation.