The role of circadian clock proteins in innate and adaptive immunity

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ABSTRACT Within each mammalian cell is a core set of circadian clock proteins that regulate the cellular biology supporting more complex organ physiologies. The central nervous system, entrained by the principle environmental cue – light, synchronizes these peripheral cellular ‘clocks’ across the entire organism, which enables the host organism to anticipate and prepare for the stresses of the active day (e.g., metabolic demands, septic threat). The current evidence, including data derived from our own research program, highlight the profound influence individual clock proteins have on the physiologic capacity with which an organism responds to stress. We first identified that the spectrum of light is a critical determinant of its effects on mammalian biology, and that the short wavelength visible blue spectrum favorably modifies the biology and outcome of sepsis. In murine models of intraabdominal sepsis and Klebsiella pneumoniae (KP) pneumonia, exposure to blue light after sepsis enhanced immune competence, as evidenced by more efficient clearance of bacteria from the septic focus, reduced bacterial dissemination, and attenuated systemic inflammation. The mechanism involved an optic-cholinergic pathway that induced the clock protein Rev-Erba in immune tissues of the spleen and Mj. A Rev-Erba agonist similarly enhance immune function in both in vitro and in vivo studies. Our overarching hypothesis is that the cellular state of the clock protein Rev-Erba is a critical determinant of immune competence and can be modulated to improve the outcome of sepsis. We specifically hypothesize that Rev-Erba regulates the protein machinery supporting the immune phenotype of the mononuclear phagocyte and B cell and is vital to an efficient immune response to microbial threat. In Aim 1 we will study the physiologic and cellular mechanisms by which blue light and the clock protein Rev-Erba regulate monocyte recruitment to the spleen and peripheral tissues and differentiation into a type of monocyte highly efficient in bacterial clearance, using a model of KP pneumonia. In Aim 2, we will explore the mechanisms by which blue light and Rev-Erba modulate B cell PI3K-AKT-mTOR signaling and actin assembly to mediate B cell differentiation, activation, MHC II antigen presentation, and antibody production. As these mechanisms are metabolically demanding and ATP-dependent, we will (Aim 3) determine the mechanisms by which Rev-Erba modulates mitochondrial dynamics to support oxidative metabolism and thereby the phenotype of immune cells during sepsis. The ramifications of light on health and disease remain to be convincingly defined. This proposal will define the biological mechanisms through which circadian clock proteins beneficially alter the host response to acute infectious insult. We will define the dimensions of light and state of clock proteins that are optimally protective and examine their biological relevance and potential therapeutic value in studies of patients with pneumonia.