Time-restricted feeding reveals a role for neural respiratory clocks in optimizing daily ventilatory-metabolic coupling in mice

Jun 5, 2024American journal of physiology. Endocrinology and metabolism

Time-restricted feeding shows brain breathing clocks help match breathing and metabolism daily in mice

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Abstract

Mice fed exclusively during the day exhibited an approximately 8.5-hour advance in carbon dioxide production rhythm, disrupting the daily ventilation rhythm.

Daily rhythms in oxygen consumption, carbon dioxide production, and minute ventilation in night-fed mice align with the master circadian clock's organization.
Shifting feeding times to the day separated metabolic and ventilatory rhythm timings, indicating conflicting influences on ventilation.
Mice lacking the BMAL1 protein in specific respiratory cells displayed a consistent daily ventilation rhythm during day feeding, unlike wild-type mice.
Results suggest that both daily changes in carbon dioxide output and intrinsic circadian mechanisms within respiratory cells significantly contribute to regulating the daily rhythm in ventilation.

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The master circadian clock, located in the suprachiasmatic nuclei (SCN), organizes the daily rhythm in minute ventilation (V̇e). However, the extent that the daily rhythm in V̇e is secondary to SCN-imposed Oand COcycles (i.e., metabolic rate) or driven by other clock mechanisms remains unknown. Here, we experimentally shifted metabolic rate using time-restricted feeding (without affecting light-induced synchronization of the SCN) to determine the influence of metabolic rate in orchestrating the daily V̇e rhythm. Mice eating predominantly at night exhibited robust daily rhythms in Oconsumption (V̇o), COproduction (V̇co), and V̇e with similar peak times (approximately ZT18) that were consistent with SCN organization. However, feeding mice exclusively during the day separated the relative timing of metabolic and ventilatory rhythms, resulting in an approximately 8.5-h advance in V̇coand a disruption of the V̇e rhythm, suggesting opposing circadian and metabolic influences on V̇e. To determine if the molecular clock of cells involved in the neural control of breathing contributes to the daily V̇e rhythm, we examined V̇e in mice lacking BMAL1 in Phox2b-expressing respiratory cells (i.e., BKOP mice). The ventilatory and metabolic rhythms of predominantly night-fed BKOP mice did not differ from wild-type mice. However, in contrast to wild-type mice, exclusive day feeding of BKOP mice led to an unfettered daily V̇e rhythm with a peak time aligning closely with the daily V̇corhythm. Taken together, these results indicate that both daily V̇cochanges and intrinsic circadian time-keeping within Phox2b respiratory cells are predominant orchestrators of the daily rhythm in ventilation.The master circadian clock organizes the daily rhythm in ventilation; however, the extent that this rhythm is driven by SCN regulation of metabolic rate versus other clock mechanisms remains unknown. We report that metabolic rate alone is insufficient to explain the daily oscillation in ventilation and that neural respiratory clocks within Phox2b-expressing cells additionally optimize breathing. Collectively, these findings advance our mechanistic understanding of the circadian rhythm in ventilatory control. 2 2 2 2 2 2 2 2 2NEW & NOTEWORTHY

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Time-restricted feeding reveals a role for neural respiratory clocks in optimizing daily ventilatory-metabolic coupling in mice

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