Production of TNF-␣ and IL-1 in infectious and autoimmune diseases is associated with fever, fatigue, and sleep disturbances, which are collectively referred to as sickness behavior syndrome. In mice TNF-␣ and IL-1 increase nonrapid eye movement sleep. Because clock genes regulate the circadian rhythm and thereby locomotor activity and may alter sleep architecture we assessed the influence of TNF-␣ on the circadian timing system. TNF-␣ is shown here to suppress the expression of the PAR bZip clockcontrolled genes Dbp, Tef, and Hlf and of the period genes Per1, Per2, and Per3 in fibroblasts in vitro and in vivo in the liver of mice infused with the cytokine. The effect of TNF-␣ on clock genes is shared by IL-1␤, but not by IFN-␣, and IL-6. Furthermore, TNF-␣ interferes with the expression of Dbp in the suprachiasmatic nucleus and causes prolonged rest periods in the dark when mice show spontaneous locomotor activity. Using clock reporter genes TNF-␣ is found here to inhibit CLOCK-BMAL1-induced activation of E-box regulatory elements-dependent clock gene promoters. We suggest that the increase of TNF-␣ and IL-1␤, as seen in infectious and autoimmune diseases, impairs clock gene functions and causes fatigue.behavior ͉ circadian rhythms ͉ cytokines ͉ innate immunity

A 24-h treatment with the cytokine tumor necrosis factor-alpha (TNF-alpha) suppresses transcription of E-box-driven clock genes (D-site albumin promoter binding protein, Dbp; Tyrotroph embryonic factor, Tef ; Hepatic leukemia factor, Hlf; Period homolog to Drosophila 1/2/3, Per1, Per2, and Per3) by yet unknown molecular mechanisms. The attenuation of clock genes has been suggested as a putative cause for the development of sickness behavior syndrome in infectious and autoimmune diseases. Here, the authors studied the effect of TNF-alpha at early time points (<3 h) on intracellular signaling events and clock gene expression in fibroblasts. Interaction of TNF-alpha with TNFR1 (Tnfrsf1a , CD120a, p55), but not TNFR2 (Tnfrsf1b, CD120b , p75), leads to fast downregulation of gene expression of Dbp and upregulation of negative regulators of the molecular clock, Per1 and Per2, Cryptochrome-1 (Cry1), and Differentiated embryo chondrocytes-1 (Dec1). Since the decrease of Dbp is also observed in cells deficient for Per1/Per2, Cry1/Cry2 , or Dec1, these genes are unlikely to be responsible for inhibition of Dbp. The early effect of TNF-alpha on the clock gene Per1 is dependent on p38, mitogen-activated protein kinase (MAPK), and/or calcium signaling, whereas the effect on Dbp is independent of p38 MAPK, but also involves calcium signaling. Both genes remain unaffected by the NF-kappaB and AP-1 pathway. Taken collectively these data show p38 MAPK- and calcium-dependent TNFR1-mediated transient increase of the negative regulator Per1 and an independent decrease of Dbp.

Disturbances of sleep-wake rhythms are an important problem in Alzheimer's disease (AD). Circadian rhythms are regulated by clock genes. Transforming growth factor-beta (TGF-β) is overexpressed in neurons in AD and is the only cytokine that is increased in cerebrospinal fluid (CSF). Our data show that TGF-β2 inhibits the expression of the clock genes Period (Per)1, Per2, and Rev-erbα, and of the clock-controlled genes D-site albumin promoter binding protein (Dbp) and thyrotroph embryonic factor (Tef). However, our results showed that TGF-β2 did not alter the expression of brain and muscle Arnt-like protein-1 (Bmal1). The concentrations of TGF-β2 in the CSF of 2 of 16 AD patients and of 1 of 7 patients with mild cognitive impairment were in the dose range required to suppress the expression of clock genes. TGF-β2-induced dysregulation of clock genes may alter neuronal pathways, which may be causally related to abnormal sleep-wake rhythms in AD patients.

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