Protective role of Uncoupling Protein 3 under hypoxic conditions in vitro and in the pathogenesis of post-ischemic cardiac remodelling in vivo

Uncoupling protein 3 (UCP3) is a member of the mitochondrial anion carrier superfamily, uncoupling mitochondrial respiration and thus decreasing the energy status. In this study we investigated the effects of UCP3 genetic deletion on mitochondrial function, cell survival and cardiac remodelling in vivo. In order to test whether UCP3 deletion was associated with mitochondrial damage, increased reactive oxygen species (ROS) production and apoptotic cell death, murine embryonic fibroblasts (MEFs) were isolated from WT and UCP3 knockout mice (ucp3–/–). Compared to WT, under both normoxic and hypoxic conditions, ucp3–/– MEFs exhibited significantly reduced mitochondrial dehydrogenase activity (WT: 1.2±0.02, ucp3–/–: 0.3±0.02, p<0.05) and increased mitochondrial ROS generation assayed by mitosox staining. Furthermore, apoptotic cell death was significantly increased in ucp3–/– MEFs as shown by TUNEL assay under basal conditions (WT: 8.5±0.15, ucp3–/–: 12.6±0.29, p<0.05) and annexin-propidium iodide double staining under normoxic or hypoxic conditions (normoxia, WT: 0.3±0.1, ucp3–/–: 3.0±0.2; 30 min hypoxia, WT: 0.99±0.3, ucp3–/–: 2.9±0.6; p<0.05). In order to test the role of UCP3 on cardiac remodelling in vivo, physiological hypertrophy by swimming and acute myocardial infarction (MI) by surgical coronary ligation were induced in wild-type (WT) and ucp3–/– mice. After 5 weeks of swimming training, cardiac structure and function in ucp3–/– mice was not statistically different from WT mice. In contrast, 8 weeks after MI, cardiac function was significantly decreased in ucp3–/– mice compared to the WT (% fractional shortening, WT: 42.7±3; ucp3–/–: 24.4±3, p<0.05; infarct size cm2, WT: 0.19±0.03; ucp3–/–: 0.21±0.2, not significant), and this was associated with increased fibrosis. Importantly, survival rates of ucp3–/– mice after MI were significantly lower than WT (p<0.05; {chi}2=4.35). Taken together, our data indicate for the first time the protective role of UCP3 under hypoxic conditions, and suggest that UCP3 might represent a novel important player in the pathogenesis of post-ischemic cardiac remodelling in vivo