BioProject

Background: The disruption of the circadian clock is associated with inflammatory and immunological disorders. More...

Background: The disruption of the circadian clock is associated with inflammatory and immunological disorders. BMAL2, a critical circadian protein, forms a dimer with CLOCK, activating transcription. Extracellular cold-inducible RNA-binding protein (eCIRP), released during sepsis, can induce macrophage endotoxin tolerance. We hypothesized that eCIRP modulates BMAL2 expression and promotes macrophage endotoxin tolerance through triggering receptor expressed on myeloid cells-1 (TREM-1). Methods: C57BL/6 wild-type (WT) male mice were subjected to sepsis by cecal ligation and puncture (CLP). Serum was collected 20 hours post-CLP to assess eCIRP levels. Peritoneal macrophages (PerM) and immortalized bone marrow-derived macrophages (iBMDMs) were seeded into plates and treated with recombinant mouse (rm) CIRP (eCIRP) at various doses. Induction of BMAL2 activation in iBMDM was performed by transfection of BMAL2 CRISPR activation plasmid. Circadian gene expression profiles in eCIRP-treated macrophages were determined by PCR array and confirmed by qPCR. Cytokine levels in the culture supernatants were assessed by ELISA. The interaction of BMAL2 in the PD-L1 promoter was determined by computational modeling and confirmed by the BIAcore assay. Results: PCR array screening of circadian clock genes in peritoneal macrophages treated with eCIRP revealed the elevated expression of BMAL2, CRY1, and PER2. eCIRP serum levels were increased in septic mice. In eCIRP-treated macrophages, TREM-1 deficiency prevented the upregulation of these circadian genes. Macrophages pre-treated with eCIRP exhibited reduced TNFá and IL-6 release upon LPS challenge, indicating macrophage endotoxin tolerance. In addition, eCIRP increased the expression of PD-L1, IL-10, and STAT3, markers of immune tolerance. Interestingly, TREM-1 deficiency reversed eCIRP-induced macrophage endotoxin tolerance. In macrophages, inducible BMAL2 expression correlated with increased PD-L1 expression. In septic human patients, blood monocytes exhibited increased expression of BMAL2 and PD-L1 in comparison to healthy subjects. Computational modeling and BIAcore assay identified a putative binding region of BMAL2 in the PD-L1 promoter, suggesting BMAL2 positively regulates PD-L1 expression in macrophages. Conclusion: eCIRP upregulates BMAL2 expression via TREM-1, leading to macrophage endotoxin tolerance in sepsis. Targeting eCIRP to maintain circadian rhythm may correct endotoxin tolerance and enhance host resistance to bacterial infection. Overall design: Peritoneal macrophages (PerM) were isolated from WT C57BL/6 male mice and TREM-1-/- (triggering receptor expressed on myeloid cells-1) male mice. After cultured overnight, these cells were treated with PBS or rmCIRP (recombinant mouse cold-inducible RNA-binding protein) at concentration 1 μg/ml for 24 h. We used Qiagen mouse circadian rhythms RT2 Profiler PCR Array panel to evaluate the gene expression. qPCR gene expression profiling. Equal amount total RNA from each sample was used for gene expression analysis. Less...