Effects of catecholamine release on cardiac BCKDK expression and its underlying mechanism

  AIM  To explore the mechanism of BCKDK up-regulation in cardiomyocytes under pathological conditions such as ischemia, hypertension and heart failure.

  METHODS  Isoproterenol (ISO) was injected intraperitoneally to simulate the cardiomyopathy model induced by catecholamine. Mice were divided into two groups: control group (Vehicle) and ISO injection group (ISO). Isoproterenol (ISO), hydrogen peroxide (H₂O₂), rotenone (rotenone) and antimycin A (antimycin A) were used to simulate various cardiac pathological stimuli. Western blot was used to detect the expression level of BCKDK, NHLRC1 and Hsp70 and real-time fluorescence quantitative PCR was used to detect the expression level of BCKDK mRNA. Immunofluorescence was used to detect the intracellular localization of BCKDK, NHLRC1 and Hsp70 and immunoprecipitation was used to explore the protein-protein interaction and the ubiquitination level of BCKDK.

  RESULTS  Compared with those in Con group, BCKDK protein level in ISO group was significantly increased (P<0.01), but mRNA level remained unchanged. ISO treatment decreased the binding of BCKDK and NHLRC1 and significantly down-regulated the ubiquitination level of BCKDK. Overexpression of NHLRC1 upregulated the ubiquitination level of BCKDK and decreased its protein expression. Compared with ISO group, Hsp70 knockdown reversed the increase of BCKDK and the decrease of ubiquitination induced by ISO, and reversed the catabolism disorder of BCAA induced by ISO (P<0.01).

  CONCLUSION  ISO exposure reduced the ubiquitination of BCKDK mediated by NHLRC1 by inducing the binding of HSP70 and BCKDK, thus leading to the upregulation of BCKDK and the disorder of BCAA catabolism in cardiomyocytes.