Overexpression of endothelial SIRT1 prevents the development of hypertension in PER2 mutant mice

The circadian clock and rhythmicity regulate cardiovascular function and energy homeostasis. Mice with selective mutation of the Per2 protein (a circadian regulator) in the hypothalamus (PER2 Brdm1 ) were established to investigate blood pressure regulation through the circadian clock. We hypothesize that disruption of the circadian rhythm adversely affects blood pressure regulation which can be restored by overexpression of SIRT1 in the vascular endothelium. To investigate this, radio transmitter telemetry was implanted in PER2 Brdm1 , Per2 mutant mice with selective overexpression of SIRT1 in the endothelium (PER2 Brdm1 /eSIRT1), as well as in wild type (WT) littermates. At 12‐weeks old, a telemetry catheter was surgically inserted into the left carotid artery and extended into the aorta and a transmitter device was placed under the skin along the animal's flank. Mice were allowed free access to water and diet, as well as normal housing conditions post recovery. Twenty‐four (24)‐hour blood pressure recording was taken at 16‐, 20‐ and 24‐weeks for four consecutive days. Quantitative PCR (qPCR) and western blotting were performed to evaluate mRNA levels of SIRT1 and expressions of key enzymes involved in leucine metabolism respectively. The mean systolic and diastolic pressures (147 ± 9.3 mmHg; 123 ± 7.3 mmHg) were found to be higher in PER2 Brdm1 when compared to PER2 Brdm1 /eSIRT1(118 ± 3.4 mmHg; 90 ± 2.6 mmHg) and WT (121 ± 2.2 mmHg; 90.7 ± 2.1 mmHg) respectively. Day and night blood pressure oscillation in PER2 Brdm1 at the age of 16, 20 & 24‐weeks showed a loss of in circadian rhythmicity as day and night blood pressures were not significantly different. The circadian rhythm was however restored in PER2 Brdm1 /eSIRT1 mice as blood pressure was significantly higher during the night when compared to during the day. The mean differences in day and night systolic pressure in WT, PER2 Brdm1 and PER2 Brdm1 /eSIRT1 were found to be: 9.7 ± 0.7 mmHg vs 1.74 ± 0.5 mmHg vs 5.62 ± 1.5 mmHg, respectively. Similarly, the diastolic differences in day and night were 9.2 ± 0.5 mmHg vs 0.06 ± 1.3 mmHg vs 4.45 ± 2.0 mmHg, respectively. The non‐dipping pattern of day/night blood pressure changes in PER2 Brdm1 was restored to normal dipping in PER2 Brdm1 /eSIRT1 mice. SIRT1 mRNA levels in skeletal muscles were found to be significantly lower in PER2 Brdm1 mice when compared to WT and PER2 Brdm1 /eSIRT1. Also, protein levels of enzymes involved in leucine metabolism were significantly lower in PER2 Brdm1 when compared with the controls. In summary, mutation of Per2 in the hypothalamus induces dysregulation of leucine metabolism, resulting in increased blood pressure and loss of diurnal blood pressure oscillation. However, increased endothelial SIRT1 expression attenuates the hypertensive phenotype of Per2 mutation and restores day and night blood pressure rhythmicity.