Thesis title: The interplay between β-adrenergic receptors signaling and clock genes in cardiac tissue physiology
Rationale: The cardiac circadian clock is responsible for the modulation of different myocardial processes, and its dysregulation has been linked to disease development. β-adrenergic receptors signaling regulate several aspects of cardiac physiology during the day but how the signaling is coordinated to circadian cardiac response is not completely elucidated, and the specific contribution of β1- and β2-AR in clock genes regulation remains an open question.
Aims:To provide a systematic circadian analysis of β-ARs signaling components in physiological environment and to investigate the specific role of β-ARs subtypes in cardiac clock genes modulation.
Methods and Results: Hearts collected every 4 hours from C57BL/6, β1-AR-/- and β2-AR -/- mouse exposed to 12:12 light-dark cycle were analyzed for β-ARs signaling components and clock genes expression. Cardiac tissue shows functioning circadian rhythms with Clock/Bmal1 acrophase correspond to the transition from the active to the resting phase, and display an antiphase rhythm oscillation respect to Per genes (Per1, Per2, Per3) and Rev-erbα. The analysis of clock genes expression in β1-AR-/- and β2-AR -/- mouse revealed that β1-AR plays a central role in the maintenance of Clock and Bmal1 genes amplitude, whereas β2-AR is involved in the control of Clock and Per genes circadian rhythmicity. Moreover, β1-and β2-AR display a 12-hours cyclic expression, with a peaks at 8AM and 8PM, corresponding respectively to the onset of the resting phase and with the transition from resting phase to active one. Interestingly the cAMP- and cGMP-dependent kinases (PKA and PKG respectively) which modulate cardiac inotropy, chronotropy and lusitropy, and the phosphodiesterases (PDEs) responsible for cAMP and cGMP availability, display a circadian expression. Furthermore, we revealed a daily modulation in the activity of specific PDEs (PDE4, PDE2 and PDE5) with the maximum peak of cAMP and cGMP hydrolysis that occurs in the middle of light and dark phases.
Conclusions: Overall our results strengthen the hypothesis of a tight relationship between β-ARs signaling and cardiac clock genes oscillation, providing a new framework for understanding the physiological mechanism involved in modulation of cardiac clock genes and highlighting an additional time-of-day dependent regulation of β-ARs signaling components.