Enhanced monocyte influx to the injured heart at dark phase exacerbates cardiac hypertrophy in a mouse model of Takotsubo cardiomyopathy

While circadian rhythms are critical regulators of cardiovascular physiopathology, their role in Takotsubo Syndrome (TTS) remains poorly understood. This study aimed to investigate the influence of time-of-day on cardiac hypertrophy and inflammation in a mouse model of TTS induced by isoproterenol (ISO) administration. Female mice were injected with saline (Sal) or ISO at the beginning of the light (ZT0) or dark phase (ZT12). Our data show that mice treated with ISO at ZT12 developed more prominent cardiac hypertrophy and exhibited worse cardiomyocyte calcium handling. This was accompanied by an enhanced accumulation of leukocytes in the hearts of ISO/ZT12 compared with ISO/ZT0 mice. Flow cytometry analysis revealed an exacerbation in the number CD64 ^hi/int Ly6C ^hi/lo CCR2 ⁺ monocytes/macrophages at ZT12 indicating a time-of-day influence on the inflammatory response following ISO administration. Of note, these differences were not secondary to differences in initial tissue injury as assessed by Evans Blue uptake by necrotic cells. However, cardiac expression of Ccl2/7 was significantly higher in the hearts of ISO/ZT12 in comparison to ISO/ZT0, suggesting the involvement of the CCL2/CCR2 signaling axis in the enhanced recruitment of monocytes. Finally, pharmacological and genetic strategies used to prevent CCR2-dependent recruitment of monocytes ameliorated the cardiac hypertrophy induced by ISO at ZT12, indicating that the CCL2/CCR2 signaling axis is crucial to the temporal dependent effects of ISO. Taken together, our data show a previously unrecognized role of the time-of-day on cardiac inflammation following adrenergic overload.