The BMAL1/HIF2A heterodimer modulates circadian variations of myocardial injury (human)
Cardiac injury following myocardial infarction exhibits a circadian pattern, yet the underlying mechanism remains unclear. To elucidate genes governing circadian variation of myocardial injury, we conducted transcriptomic profiling of left-ventricular tissues from mice or humans experiencing myocardial injury at different daytimes. Through comprehensive analyses, including transgenic mouse models and functional studies, we identified BMAL1 as a pivotal transcription factor modulating diurnal variation of myocardial injury. Remarkably, we discovered that BMAL1 regulates circadian-dependent cardiac injury by forming a transcriptionally active heterodimer with HIF2A. Substantiating this finding, we determined the cryo-EM structure of the BMAL1/HIF2F/DNA complex, revealing a previously unknown capacity for structural rearrangement within BMAL1. Furthermore, we confirmed amphiregulin (AREG) as a transcriptional target of the BMAL1/HIF2A heterodimer, critical for modulating circadian variation of myocardial injury. Finally, targeting the BMAL1/HIF2A-AREG pathway via timed AREG administration or enhancing circadian rhythm pharmacologically offered significant cardioprotection, implicating this pathway in treating ischemic heart disease. Overall design: We examined samples from a prospective study of myocardial injury in humans during cardiac surgery (clinicaltrials.gov: NCT00281164). The study population consisted of consecutive patients (aged =20 years) with aortic stenosis referred to our cardiovascular surgery department at Brigham and Women's Hospital (MA, USA) for aortic valve replacement (with or without coronary artery bypass graft) between Jan 1, 2009, and Dec 31, 2014. Patients enrolled in a concurrent drug or device trial were excluded. This ongoing study involved 56 patients in the morning (samples collected between 8:00 am-12:00 pm, median time 10:32 am) and 17 patients who underwent the same procedure in the afternoon (samples collected between 3:00-9:00 pm, median time 5:15 pm). Patients whose surgery fell between our outside of these time periods were excluded from the analysis. The ethics committee of our institution approved the protocol, and written informed consent was obtained from all patients. Patients underwent aortic valve replacement either in the morning or in the afternoon by the same senior surgeon. Anesthesia, cardiopulmonary bypass, cardioplegia, and surgical procedures were done according to standard guidelines. Anesthesia was induced with intravenous fentanyl or sufentanil and propofol (0.5-1.5 mg/kg) and maintained with isoflurane. Surgery was done using normothermic cardiopulmonary bypass and repeated antegrade and retrograde cold blood cardioplegia. Left ventricular biopsy samples from the morning and afternoon patient cohorts were obtained after approximately 80 minutes of aortic cross-clamping at the site of the routinely placed left ventricular vent.