A circadian clock in macrophages controls inflammatory immune responses

Abstract

Time of day-dependent variations of immune system parameters are ubiquitous phenomena in immunology. The circadian clock has been attributed with coordinating these variations on multiple levels; however, their molecular basis is little understood. Here, we systematically investigated the link between the circadian clock and rhythmic immune functions. We show that spleen, lymph nodes, and peritoneal macrophages of mice contain intrinsic circadian clockworks that operate autonomously even ex vivo. These clocks regulate circadian rhythms in inflammatory innate immune functions: Isolated spleen cells stimulated with bacterial endotoxin at different circadian times display circadian rhythms in TNF-␣ and IL-6 secretion. Interestingly, we found that these rhythms are not driven by systemic glucocorticoid variations nor are they due to the detected circadian fluctuation in the cellular constitution of the spleen. Rather, a local circadian clock operative in splenic macrophages likely governs these oscillations as indicated by endotoxin stimulation experiments in rhythmic primary cell cultures. On the molecular level, we show that >8% of the macrophage transcriptome oscillates in a circadian fashion, including many important regulators for pathogen recognition and cytokine secretion. As such, understanding the cross-talk between the circadian clock and the immune system provides insights into the timing mechanism of physiological and pathophysiological immune functions.adrenalectomy ͉ LPS ͉ IL-6 ͉ microarray ͉ TNF-␣ A 24-h periodicity in the environment has led to the evolution of molecular circadian clocks in organisms ranging from cyanobacteria to humans. Circadian rhythms display a near 24-h period and persist even in the absence of external timing information. In mammals, a small hypothalamic region, the suprachiasmatic nucleus (SCN), has been identified as the master pacemaker regulating circadian rhythms in physiology, metabolism, and behavior (1). Recent evidence shows that also peripheral organs such as liver, heart, kidney, skin, and even cultured cell lines contain circadian oscillators. Although the SCN probably sets the phase of these peripheral clocks (by as yet unknown means), recent reports implicate peripheral clocks in the regulation of local physiology (2-4). The fundamental mechanism of rhythm generation is cell autonomous and highly conserved in SCN and peripheral cells: Interlocked transcriptional/translational feedback loops involving clock genes, such as Per1-3, Cry1-2, Clock, Bmal1, and Rev-Erb␣ create oscillations on the molecular level (reviewed in ref. 2).In the immune system, many functions and parameters have been described to be time-of-day dependent, e.g., lymphocyte proliferation (5), natural killer (NK) cell activity (6), humoral immune response (7), rhythms in absolute and relative numbers of circulating white blood cells and their subsets (8), cytokine levels (9), and serum cortisol (10) (reviewed in ref. 11). In addition, time-of-day variation in susceptibility to infection (12), cour...

Depression in Autoimmune Diseases

“…For example the macrophage response to Salmonella is decreased in mice with an inactive clock gene (Bellet et al, 2013), and the extent of secretion of TNF and IL-6 by LPS stimulated macrophages follows a circadian rhythm (Keller et al, 2009). Besides effects of the circadian system on the immune response, the immune system also influences the circadian clock.…”

A pilot study on temporal changes in IL-1β and TNF-α serum levels after spinal cord injury: the serum level of TNF-α in acute SCI patients as a possible marker for neurological remission

“…Authors have shown that macrophages secrete cytokines based on a circadian clock in mice. 20 A circadian-dependent secretion could have influenced the levels found in SCI patients and account for the variability of our results, although more investigation of this topic in humans is needed.…”

Diurnal and seasonal changes in <i>IL-6</i> and <i>IL-18</i> gene expression in blood leukocytes of male chickens with experimental peritonitis: the impact of lighting conditions and melatonin

“…This last point raises the role of circadian clock mechanisms in rhythmic immune functions that are now the subject of extensive investigation. Recent studies have shown that in mice, an endogenous clock can influence the daily oscillations in innate immune functions, like bacterial endotoxin-stimulated TNF-α and IL-6 secretion by isolated spleen cells (Keller et al, 2009) or phagocytosis in macrophages (Hayashi et al, 2007). These circadian clock mechanisms, which can operate autonomously even ex vivo in the spleen and lymph nodes, are based on the expression of major clock genes, like Bmal, Per, Clock and Rev-erb α (Keller et al, 2009).…”

“…Recent studies have shown that in mice, an endogenous clock can influence the daily oscillations in innate immune functions, like bacterial endotoxin-stimulated TNF-α and IL-6 secretion by isolated spleen cells (Keller et al, 2009) or phagocytosis in macrophages (Hayashi et al, 2007). These circadian clock mechanisms, which can operate autonomously even ex vivo in the spleen and lymph nodes, are based on the expression of major clock genes, like Bmal, Per, Clock and Rev-erb α (Keller et al, 2009). Moreover, clock gene expression in human immune cells seems to be very sensitive to a damaging challenge, since a single injection with endotoxin was found to suppress the expression of these genes in the PBLs of healthy humans volunteers (Haimovich et al, 2010).…”

“…However, the experimental protocols employed in these two studies differ in several aspects, including induction of inflammation, melatonin treatment and, most importantly, the source of the immune cells examined. Circulating PBLs represent a highly heterogeneous population of cells that move between the marginal zones and the site of inflammation, and they probably differ in their sensitivity to regulatory/synchronizing humoral factors (Keller et al, 2009).…”