Mitochondrial Oxidative Stress Enhances Vasoconstriction by Altering Calcium Homeostasis in Cerebrovascular Smooth Muscle Cells under Simulated Microgravity.

OBJECTIVE

Exposure to microgravity results in postflight cardiovascular deconditioning in astronauts. Vascular oxidative stress injury and mitochondrial dysfunction have been reported during this process. To elucidate the mechanism for this condition, we investigated whether mitochondrial oxidative stress regulates calcium homeostasis and vasoconstriction in hindlimb unweighted (HU) rat cerebral arteries.

METHODS

Three-week HU was used to simulate microgravity in rats. The contractile responses to vasoconstrictors, mitochondrial fission/fusion, Ca distribution, inositol 1,4,5-trisphosphate receptor (IP R) abundance, and the activities of voltage-gated K channels (K ) and Ca -activated K channels (BK ) were examined in rat cerebral vascular smooth muscle cells (VSMCs).

RESULTS

An increase of cytoplasmic Ca and a decrease of mitochondrial/sarcoplasmic reticulum (SR) Ca were observed in HU rat cerebral VSMCs. The abundance of fusion proteins (mitofusin 1/2 [MFN1/2]) and fission proteins (dynamin-related protein 1 [DRP1] and fission-mitochondrial 1 [FIS1]) was significantly downregulated and upregulated, respectively in HU rat cerebral VSMCs. The cerebrovascular contractile responses to vasoconstrictors were enhanced in HU rats compared to control rats, and IP R protein/mRNA levels were significantly upregulated. The current densities and open probabilities of K and BK decreased and increased, respectively. Treatment with the mitochondrial-targeted antioxidant mitoTEMPO attenuated mitochondrial fission by upregulating MFN1/2 and downregulating DRP1/FIS1. It also decreased IP R expression levels and restored the activities of the K and BK channels. MitoTEMPO restored the Ca distribution in VSMCs and attenuated the enhanced vasoconstriction in HU rat cerebral arteries.

CONCLUSION

The present results suggest that mitochondrial oxidative stress enhances cerebral vasoconstriction by regulating calcium homeostasis during simulated microgravity.