The effects of circadian rhythms on Toll-like receptor responses in murine macrophages (INM7P.357)

Abstract

Abstract Circadian rhythms refer to the endogenous oscillations of biological processes with 24-hour periodicity in response to environmental cues. On a molecular level, circadian rhythms are accomplished through positive and negative feedback loops among the core Clock genes: Clock, Period, Cryptochrome and Bmal. These oscillations in gene expression regulate a myriad of cellular functions and activities. Recently, circadian rhythms have been found to promote comparable oscillations in components of the innate and adaptive immune system. Synchronization of the circadian clock can be induced in vitro via a process known as serum shock. Here, we took advantage of this model to investigate the effects of circadian oscillations on Toll-like receptor (TLR) responses in murine macrophages. Serum shock induced a 24h oscillation in mRNA expression for the clock gene Period 2, as well as for a period2-luciferase fusion reporter gene, confirming synchronization of the circadian clock. Serum-shocked cells were then stimulated with a panel of TLR agonists and cytokine secretion was quantified over time to investigate the impact of circadian rhythms on TLR responses. Our findings suggest circadian oscillation with regard to interleukin (IL)-12p40 production upon stimulation of TLR2 and TLR7. Suggestive oscillations were also observed with regard to IL-6 production upon stimulation of TLR2. These data suggest that circadian rhythms control TLR responses at the cellular level.