The Delta Opioid Peptide DADLE Represses Hypoxia-Reperfusion Mimicked Stress Mediated Apoptotic Cell Death in Human Mesenchymal Stem Cells in Part by Downregulating the Unfolded Protein Response and ROS along with Enhanced Anti-Inflammatory Effect

Hypoxia-reperfusion (H/R) emblems a plethora of pathological conditions which is potent in contributing to the adversities encountered by human mesenchymal stem cells (hMSCs) in post-transplant microenvironment, resulting in transplant failure. D-Alanine 2, Leucine 5 Enkephaline (DADLE)-mediated delta opioid receptor (DOR) activation is well-known for its recuperative properties in different cell types like neuronal and cardiomyocytes. In the current study its effectiveness in assuaging hMSC mortality under H/R-like insult has been delineated. The CoCl2 mimicked H/R conditions in vitro was investigated upon DOR activation, mediated via DADLE. hMSCs loss of viability, reactive oxygen species (ROS) production, inflammatory responses and disconcerted unfolded protein response (UPR) were assessed using AnnexinV/PI flow cytometry, fluorescence imaging, mitochondrial complex 1 assay, quantitative PCR, immunoblot analysis and ELISA. H/R like stress induced apoptosis of hMSCs was significantly mitigated by DADLE via modulation of the apoptotic regulators (Bcl-2/Bax) along with significant curtailment of ROS and mitochondrial complex 1 activity. DADLE concomitantly repressed the misfolded protein aggregation, alongside the major UPR sensors: PERK/BiP/IRE-1 alpha /ATF-6, evoked due to the H/R mimicked endoplasmic reticulum stress. Undermined phosphorylation of the Akt signalling pathway was observed, which concerted its effect onto regulating both the pro and anti-inflammatory cytokines, actuated as a response to the H/R-like insult. The effects of DADLE were subdued by naltrindole (specific DOR antagonist) reaffirming the involvement of DOR in the process. Taken together these results promulgate the role of DADLE-induced DOR activation on improved hMSC survival, which signifies the plausible implications of DOR-activation in cell-transplantation therapies and tissue engineering aspect.