Central daily regulation of splenic macrophage clock: Role of norepinephrine

CARGNELLUTTI E; CASTRO-PASCUAL, I; TOLEDO, F; ANZULOVICH AC

San Luis

Congreso; SAN 2023; 2023

The suprachiasmatic nucleus (SCN) functions as the central clock in mammals, synchronizing endogenous cellular clocks with the day/night alternation. Splenic macrophages (MΦ) play pivotal roles in fundamental immune responses. However, a comprehensive understanding of the central circadian regulation of these cells remains elusive. The SCN and spleen communicate through the sympathetic nervous system (SNS), that release norepinephrine (NE) in regions housing MΦ. To elucidate NE's influence on the molecular clock regulation of spleen MΦ, a rat model of localized sympathetic denervation was developed using guanethidine. Rats received saline or guanethidine injections and were euthanized at 6 zeitgeber times (ZT) across a 24-hour cycle (ZT2, 6, 10, 14, 18, and 22). Spleens were isolated for ex vivo cultures. BMAL1 and ACTIN protein levels were assessed in splenic adherent cells. Control rats' splenic MΦ displayed daily oscillations of BMAL1, with a peak occurring at the midpoint of the light period. Remarkably, ex vivo splenic MΦ from the guanethidine-treated animals showed a loss of the 24-hour BMAL1 oscillation and significantly lower levels, compared to controls. Both control and sympathectomized rats displayed daily Rev-Erbα expression rhythms. However, guanethidine administration induced a phase delay and increased expression of Rev-Erbα. These findings underscore the SCN-mediated regulation of the molecular clock in splenic adherent cells through the NE sympathetic pathway.