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Effects of chronic intermittent hypoxia on left cardiac function in young and aged mice.

Obstructive sleep apnea (OSA) is an independent risk factor for cardiovascular disease that is characterized by chronic intermittent hypoxia (CIH), and its impact is related to age. This study aims to assess the age-related impact of CIH on cardiac function and to further explore the mechanism. After 8 weeks of severe CIH exposure, the hearts of young mice showed slight physiological hypertrophy, decreased diastolic function, and collagen I accumulation but no obvious change in contractile function. However, the contractile function of the hearts of aged mice was severely decreased. CIH exposure promoted the fragmentation of mitochondria in the hearts of aged mice and decreased the mitochondrial membrane potential of cardiomyocytes, but these effects were not observed in young mice exposed to the same conditions. CIH induced significant decreases in basal respiration, maximum respiration and ATP production in cardiac mitochondria of aged mice compared to those of young mice. The assessment of mitochondrial-related proteins showed that young mouse hearts had upregulated adaptive nuclear respiratory factors (Nrf)1/2 sirtuin (SIRT)1/3 and transcription factor A (TFAM) expression that stabilized mitochondrial function in response to CIH exposure. Aged mouse hearts exhibited maladaptation to CIH exposure, and downregulation of SIRT1 and TFAM expression resulted in mitochondrial dysfunction.