Adiponectin up-regulates the decrease of myocardial autophagic flux induced by β1-adrenergic receptor antibody partly dependent on AMPK

Abstract

BackgroundCardiomyocyte autophagy is essential for maintaining cardiac function. Our previous studies have found that β1-adrenergic receptor autoantibody (β1-AA) induced the decreased myocardial autophagic flux, which resulted in cardiomyocytes death and cardiac dysfunction. And other studies demonstrated that β1-AA induced the decrease of AMPK phosphorylation, the key hub of autophagy pathway, while adiponectin up-regulated autophagic flux mediated by AMPK. However, it is not clear whether adiponectin improves the inhibition of myocardial autophagic flux induced by β1-AA by up-regulating the level of AMPK phosphorylation.MethodAPN-KO and WT mice were subcutaneously injected withthe peptide of the second extracellular loop of β1-adrenergic receptor (β1-AR-ECII) as antigen to establish β1-AA active immunization model. The OD value of β1-AA in serum of mice was detected by SA-ELISA to ensure the successful construction of active immunization model. The changes of cardiac function and myocardial fibrosis were detected by small animal ultrasound and Masson trichrome staining. The cardiomyocytes viability was assessed using a Cell Counting Kit-8. The mRNA levels of LC3B and Beclin1 in cardiomyocytes were measured by Real-time PCR. The protein levels of LC3 II, p62, AMP dependent protein kinase (AMP) - activated protein kinase (AMPK) and phosphorylated AMP dependent protein kinase (p-AMPK) in cardiomyocytes were detected by Western blotting.ResultsIn this study, it has been confirmed that β1-AA induced the decrease of AMPK phosphorylation level in both vivo and vitro. Moreover, pretreatment of cardiomyocytes with AMPK inhibitor Compound C could further reduce the autophagic flux induced by β1-AA. Adiponectin deficiency could aggravate the decrease of myocardial AMPK phosphorylation level, autophagic flux and cardiac function induced by β1-AA. Further, exogenous adiponectin could reverse the decline of AMPK phosphorylation level and autophagic flux induced by β1-AA, and even reduce cardiomyocytes death. While pre-treated with the Compound C, the adiponectin treatment did not improve the decreased autophagosome formation, but still improved the decreased autophagosome clearance induced by β1-AA in cardiomyocytes, suggesting that adiponectin up-regulated β1-AA-induced decreased autophagic flux of cardiomyocytes partly depended on the AMPK.ConclusionThis study is the first time to confirm that β1-AA could inhibit myocardial autophagic flux by down regulating AMPK phosphorylation level. Adiponectin could improve the inhibition of myocardial autophagic flux induced by β1-AA partly dependent on AMPK, so as to provide an experimental basis for the treatment of patients with β1-AA-positive cardiac dysfunction.

Mechanisms of autophagy regulation by adiponectin

“…Adiponectin deficiency could aggravate the downregulation of myocardial AMPK phosphorylation, autophagic flux, and cardiac function. By contrast, exogenous administration of adiponectin reverses the decline of AMPK phosphorylation and autophagic flux and eventually reduce cardiomyocyte death [26]. AdipoRon, as an adiponectin receptor agonist, inhibits myeloma cell proliferation and induces apoptosis, and AMPK/autophagy pathway may be one of its mechanisms [9].…”