The functional role of AC6 N-terminus in the heart

• Main Authors: Wu, Yu-Shuo, 吳育碩
• Other Authors: Chern, Yijuang
• Format: Others
• Language: en_US
• Published: 2017
• Online Access: http://ndltd.ncl.edu.tw/handle/99383392389032264595

博士 === 國防醫學院 === 生命科學研究所 === 105 === Adenylyl cyclase type VI (AC6) is one of the major adenylyl cyclase (AC) isoforms in the heart. AC6 protects the heart from failure in heart disease while the mechanism beneath remains to be elucidated. Meanwhile, another major AC isoform, AC5, increase cardiac remodeling in response to stress in the heart. AC6 and AC5 share similar properties such as inhibited activity by Ca2+ and similar sequences except for their N-terminus. The N-terminus of AC6 (AC6-N) contributes the major difference of AC6 from AC5. In order to investigate the mechanism beneath the beneficial role of AC6, an N-terminus deleted AC6 (AC6-ΔN) knockin mouse model (AC6ΔN/ΔN) was created. The enzyme activity producing cAMP of AC6ΔN/ΔN was unaffected as previously reported. Interestingly, the basal protein kinase A (PKA) activity of AC6ΔN/ΔN heart was increased while the basal cAMP content was unaffected. Immunocytochemistry revealed that AC6ΔN/ΔN was out from sarcolemma membrane onto sarcoplasmic reticulum (SR) and co-localized with PKA. Coincident with increased basal PKA activity, the PKA mediated phosphorylation of phospholamban (PLN), E-C coupling efficiency, and Ca2+ storage were increased. Removal of compensatory effect from parasympathetic activity by muscarinic antagonist revealed the increased basal cardiac function of AC6ΔN/ΔN mice. To evaluate the AC6 function on sarcolemmal membrane, the phenomenon of AC6ΔN/ΔN mice was next compared to WT and AC6-/- mice. Using a β-agonist isoproterenol (ISO), the β-stimulated cAMP and PKA activity were both reduced in AC6ΔN/ΔN and AC6-/- hearts. Immunoblot revealed the β-stimulation increased STAT3 phosphorylation was reduced in AC6ΔN/ΔN and AC6-/- hearts compared to WT. Blockage of PKA, Src, and STAT3 revealed that AC6 regulates a PKA/Src/ STAT3 pathway, protected cardiomyocytes from cell death induced by ISO stimulation. Furthermore, the AC6ΔN/ΔN and AC6-/- mice showed more sever cardiac hypertrophy and fibrosis after serial ISO injection comparing to WT, indicating the importance of AC6/PKA/Src/STAT3 pathway during catecholamine stress. In summary, the AC6-N controls it cellular distribution and couples a pro-survival PKA/Src/STAT3 pathway in the heart.