Cardiomyocyte beta2AR mediates cardiac fibrosis via maintaining Ca2+ homeostasis in the heart

Objective: Cardiac beta2-adrenoceptor (β 2 AR) has been suggested functions a protective role in defending myocyte apoptosis and cardiac damage induced by various stress. Our recent studies indicate divergent roles of cardiac β 2 AR in cardiomyocytes and myofibroblasts in regulating high fat diet (HFD) induced cardiac remodeling and dysfunction. While β 2 AR in cardiomyocytes attenuates HFD-induced cardiac fibrosis, myofibroblast β 2 AR facilitates cardiac fibrosis. Cell-specific actions of β 2 AR has been suggested in mediating cardiac fibrosis in the heart. This study is aimed to further determine the role of cardiomyocyte-specific β 2 AR in cardiac function and cardiac fibrosis. Hypothesis: Cardiomyocyte-specific β 2 AR regulates cardiac fibrosis via maintaining Ca 2+ homeostasis in the heart. Results and Methods: 2-3-month-old mice with cardiomyocyte-specific deletion of β 2 AR (β 2 AR-cKO) and β 2 AR-flox mice were used. While echocardiography showed a comparable cardiac function between cKO and flox mice, the expression of both inflammatory and fibrotic marker proteins, NLR family pyrin domain containing 3 (NLRP3) and connective tissue growth factor (CTGF), was elevated in cKO hearts. As β 2 AR has been suggested to restrict excessive adrenergic insults, the activities of major molecules in β-adrenergic signaling were examined. Notably, western blot showed the phosphorylation level of Calcium/calmodulin-dependent kinase II (CaMKII) was significantly upregulated in cKO heart which implies a higher level of cytosolic Ca 2+ . Consequently, the CaMKII phosphorylation site (serine 1700) on L-type Ca 2+ channel (LTCC) was also upregulated. To further examine the LTCC activity, whole cell currents (ICa) were recorded from freshly isolated ventricular myocytes, which indicated a higher LTCC activity after isoproterenol stimulation (peak ICa: cKO, -12.87 vs. flox, -10.40, p<0.05). Moreover, cKO and flox were subjected to LTCC blocker (nifedipine,10mg/kg/day) treatment to confirm the effect of Ca 2+ activity on cardiac inflammatory and fibrotic response. Two weeks of nifedipine injection completely attenuated over-elevated CaMKII activity and NLRP3 and CTGF expression in cKO hearts. Overall, these results indicate that deletion of β 2 AR in cardiomyocytes facilitates cardiac fibrosis by altering cytosolic Ca 2+ homeostasis via LTCC activity. Conclusion: This study elucidates that cardiomyocyte β 2 AR is essential to maintain normal cardiac function and plays a protective role against the development of cardiac fibrosis. National Institutes of Health grants R01-HL147263, Veteran Affair Merit grant 01BX002900, American Heart Association postdoctoral fellowship This is the full abstract presented at the American Physiology Summit 2023 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.