Circadian clock protein cryptochrome regulates the expression of proinflammatory cytokines

Abstract

Chronic sleep deprivation perturbs the circadian clock and increases susceptibility to diseases such as diabetes, obesity, and cancer. Increased inflammation is one of the common underlying mechanisms of these diseases, thus raising a hypothesis that circadianoscillator components may regulate immune response. Here we show that absence of the core clock component protein cryptochrome (CRY) leads to constitutive elevation of proinflammatory cytokines in a cell-autonomous manner. We observed a constitutive NF-κB and protein kinase A (PKA) signaling activation in Cry1 −/− ; Cry2 −/− cells. We further demonstrate that increased phosphorylation of p65 at S276 residue in Cry1 −/− ;Cry2 −/− cells is due to increased PKA signaling activity, likely induced by a significantly high basal level of cAMP, which we detected in these cells. In addition, we report that CRY1 binds to adenylyl cyclase and limits cAMP production. Based on these data, we propose that absence of CRY protein(s) might release its (their) inhibition on cAMP production, resulting in elevated cAMP and increased PKA activation, subsequently leading to NF-κB activation through phosphorylation of p65 at S276. These results offer a mechanistic framework for understanding the link between circadian rhythm disruption and increased susceptibility to chronic inflammatory diseases.biological clock | immune system I n response to the rotation of the earth, many of the mammalian physiological processes such as sleep-wake cycle and feeding pattern undergo an ∼24-h oscillation referred as the circadian clock. Circadian oscillation helps organisms anticipate and adapt to predictable daily changes in the environment. The hypothalamic suprachiasmatic nucleus (SCN) functions as a master circadian oscillator, which controls behaviors. At molecular level, the circadian oscillator is based on a cell-autonomous transcription-translation feedback loop, in which transcriptional activators circadian locomotor output cycles kaput (CLOCK)/brain and muscle aryl hydrocarbon receptor nuclear translocator (ARNT)-like (BMAL)1 activate the expression of Cryptochrome (Cry) and Period (Per), in turn their protein products repress BMAL1 and CLOCK activity, thus producing Cry and Per expression rhythms (1, 2). Reverse orientation c-erb (REV-ERB)s and RAR-related orphan receptor (ROR)s also participate in the rhythmic transcriptional activity of the molecular oscillator (3). Molecular components of the circadian clock network are conserved in the SCN and also in peripheral cells. The oscillator uses direct and indirect mechanisms to impose rhythms and regulate several physiological processes, such as rest-activity cycle, endocrine system, and metabolism (4).Sleep loss or chronic sleep deprivation disrupts the circadian rhythm. It has been reported that people exposed to constant circadian disruption, such as shift-workers, show increased incidence of chronic diseases such as diabetes, obesity, and also cancer (5-7). Chronic inflammation is one of the important pathogenic features of these di...

Immunometabolism: Is it under the eye of the clock?

“…By ectopically expressing CRY1 in MEFs isolated from Cry1/Cry2 −/-mice, activation of a TNF␣ luciferase promoter was vastly decreased. This could possibly be due to CRY1 limiting NF-B activation as has previously been demonstrated [147]. Absence of CRY1 and CRY2 in fibroblasts and BMDMs leads to a basal increase in mRNA levels of Cxcl1, Il-6 and Tnf˛.…”

“…Il-6 and Tnf˛ RNA. Lower NF-B activation [147] Cry1 (AP-Tg) Global • Elevated glucose levels in serum and urine [161] • Common symptoms of diabetes mellitus, polydipsia and polyuria [161] Per2 Global • Reduced levels of triacylglycerol and non-sterified fatty acids [139] • Enhanced adipocyte differentiation [139] • Increased plasma insulin and impaired gluconeogenesis [142,143] • Protected from sepsis-induced death [144] • Lower IL-1␤ and IFNϒ in serum [144] • Lower Tlr9 expression [82] Per3 Global • Enhanced adipogenesis [139] • Increased adipose tissue and decreased muscle tissue mass [139] Rev-erb˛ Global • Increased adiposity and mild hyperglycemia [119] • Altered lipid and glucose metabolism [119] • Increase in G6Pase and PEPCK [120] • Increased IL-6 in serum [124] ROR˛ sg/sg Global • Reduced adiposity and protection from obesity [128] • Lower serum and liver triglyceride levels [128] • Impaired Th17 cell development [133] • Highly susceptible to LPS induced sepsis [136] ROR Global • Enhanced production of insulin sensitive adipocytes.…”

Circadian rhythm‐related genes: implication in autoimmunity and type 1 diabetes

“…Many other examples have been published since, some of which concern highly specific immune functions. Recent studies showed for example that Th17 differentiation is controlled by the circadian clock [18], that the circadian gene Bmal1 regulates diurnal oscillations of Ly6C(hi) inflammatory monocytes [19], or that the circadian clock protein CRY regulates the expression of proinflammatory cytokines [8].…”

“…Many other examples have been published since, some of which concern highly specific immune functions. Recent studies showed for example that Th17 differentiation is controlled by the circadian clock [18], that the circadian gene Bmal1 regulates diurnal oscillations of Ly6C(hi) inflammatory monocytes [19], or that the circadian clock protein CRY regulates the expression of proinflammatory cytokines [8].In this context, it does not seem surprising that autoimmune disease is influenced by the circadian rhythm. This observation has particularly been made in rheumatoid arthritis, where patients suffer more from stiffness and pain in the morning than during other times of the day.…”

“…The major circadian pacemaker ARNTL1 has in addition been associated with susceptibility to gestational diabetes mellitus [7]. CRY, another component of the core clock, is required for the regulation of inflammatory cytokines via the NF-kappaB pathway [8]. Absence of this key circadian clock component leads to the activation of this signalling system and elevated levels of inflammatory molecules in the body.…”