Introduction: The purpose of this study was to examine the effects of rapamycin on the cardioprotective effect of hypoxic preconditioning (HPC) and on the mammalian target of rapamycin (mTOR)-mediated hypoxia-inducible factor 1 (HIF-1) signaling pathway.
Material and methods: Primary cardiomyocytes were isolated from rat pups and underwent rapamycin and/or HPC, followed by hypoxia/re-oxygenation (H/R) injury. Cell viability and cell injury were determined by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) and lactate dehydrogenase (LDH) assays, and qRT-PCR was used to measure HIF-1α and mTOR mRNA expression. A Langendorff heart perfusion model was conducted to observe the effect of rapamycin.
Results: Rapamycin treatment nearly abolished the cardioprotective effect of HPC in cardiomyocytes, reduced cell viability (p = 0.007) and increased cell damage (p = 0.032). HIF-1α and mTOR mRNA expression increased in cardiomyocytes undergoing I/R injury within 2 h after HPC. After rapamycin treatment, mTOR mRNA expression and HPC-induced HIF-1α mRNA expression were both reduced (p < 0.001). A Langendorff heart perfusion model in rat hearts showed that rapamycin greatly attenuated the cardioprotective effect of HPC in terms of heart rate, LVDP, and dp/dtmax (all, p < 0.029).
Conclusions: Rapamycin, through inhibition of mTOR, reduces the elevated HIF-1α expression at an early stage of HPC, and attenuates the early cardioprotective effect of HPC.
Keywords: hypoxia inducible factor 1α; hypoxic preconditioning; primary neonatal rat cardiomyocytes; rapamycin.