In the next 35 years, the global population of individuals above 60 years of age will double to approximately 2 billion. In the aged population, cardiovascular diseases are known to occur at a higher prevalence ultimately leading to increased mortality. G protein-coupled receptors (GPCRs) have been identified as vital regulators of cardiac function. GPCR kinases (GRKs) are important in cardiac GPCR regulation through desensitization of these receptors. GRK2 is highly expressed in the heart, and has been widely characterized due to its upregulation in heart failure. Studies from our lab have shown that elevated GRK2 levels in ischemia-reperfusion (I/R) injury result in a pro-death phenotype. Interestingly, cardio-protection can be inferred via S-nitrosylation of GRK2 at cysteine 340. Further, we have generated a knock-in GRK2 340S mouse, in which cysteine 340 was mutated to block dynamic GRK2 S-nitrosylation. GRK2 340S mice are more susceptible to I/R injury. Given that GRK2 340S mice are more susceptible to oxidative stress, and there is a nitroso-redox imbalance in senescence, it is possible that these mice are more likely to exhibit decreased cardiac performance as they age. Therefore, we hypothesize that with age GRK2 340S knockin mice will develop an overall worsened cardiac phenotype compared to control wild-type (WT) mice. To test this hypothesis, 340S and WT mice were aged for a year, and cardiac function was evaluated via echocardiography. Aged 340S mice exhibited significantly decreased ejection fraction and fraction shortening relative to aged WT controls. Prior to tissue harvesting, in-vivo hemodynamics was conducted via Millar catheterization. At baseline, aged 340S mice exhibited increased systolic blood pressure compared to aged WT mice. At the conclusion of this protocol, mice were sacrificed and heart weight (HW), body weight (BW), and tibia length (TL) measured to evaluate cardiac hypertrophy. Aged 340S mice exhibited significantly increased HW/BW and HW/TL ratios, indicative of cardiac hypertrophy, relative to aged WT controls. Taken together, these data suggest that with age, loss of the cardio protection inferred by S-nitrosylation of GRK2 at leads to decreased cardiac performance, and an overall worsened cardiac phenotype.
The Impact of a Non-Functional Thyroid Receptor Beta upon Triiodotironine-Induced Cardiac Hypertrophy in Mice