The effect of all-trans retinoic acid on the mitochondrial function and survival of cardiomyoblasts exposed to local photodamage.

Using H9C2 cardiomyoblasts, we have shown that all-trans retinoic acid (ATRA), the biologically active metabolite of vitamin A, affects mitochondrial dynamics and functions. The low dose (10 nM) ATRA stimulates the expression of nuclear retinoid receptors and induces mechanisms that are protective against severe local damage caused by laser irradiation at the mitochondrial level. These changes include increased density of the mitochondrial network, higher number of mitochondrial junctions, and enhanced mitochondrial velocity. Moreover, the treated cells had lower basal level of reactive oxygen species (ROS) and could maintain mitochondrial potential (ΔΨ m ) after photodamage. Cells treated with 10 nM ATRA had significantly better survival rate after photodamage in comparison to control cells. Cells treated with pharmacological concentration of ATRA (1 µM) expressed higher mitochondrial connectivity without increased motility, which did not lead to better survival or decreased ROS level as was in the case of low-dose ATRA. The proteomics analysis showed changes in proteins related to cellular metabolism (glycolysis) and respiration in ATRA-treated cells. The l-lactate assay confirmed the shift to anaerobic glycolysis in cells treated with 1 µm ATRA, whereas the 10 nM ATRA decreased the level of lactate in medium. The increased levels of cytochrome c or peroxiredoxins 5 level and also lower expression of retinoid and rexinoid receptors were observed in cells treated with 1 µM ATRA. The effect of ATRA is concentration-dependent; the increased mitochondrial dynamics and slower metabolism at 10 nM ATRA contributed significantly to the chance of survival of the cells after photodamage whereas the higher concentration of ATRA overrode the protective effect and led to the unfavorable ones.