Circadian clock component PER2 negatively regulates CD4⁺ T cell IFN-γ production in ulcerative colitis

Period circadian clock 2 (PER2) is involved in the pathogenesis of various inflammatory and autoimmune diseases. However, there are gaps in our understanding of the role of PER2 in regulating CD4⁺ T cells beyond its time-keeping function in ulcerative colitis (UC) pathogenesis. Our findings revealed PER2 was predominantly expressed in CD4⁺ T cells, while it was significantly decreased in the inflamed mucosa and peripheral blood CD4⁺ T cells of UC patients compared with that in Crohn's disease (CD) patients and healthy controls (HC). Notably, PER2 expression was significantly recovered in UC patients in remission (R-UC) compared to that in active UC patients (A-UC) but not in CD patients. It was negatively correlated with the Ulcerative Colitis Endoscopic Index of Severity (UCEIS), Crohn's Disease Activity Index (CDAI), Simple Endoscopic Score for Crohn's disease (SES-CD), and C-reactive protein (CRP), respectively. Overexpression of PER2 markedly inhibited IFN-γ production in UC CD4⁺ T cells. RNA-seq analysis showed that overexpression of PER2 could repress the expression of a disintegrin and metalloproteinase 12 (ADAM12), a costimulatory molecule that determines Th1 cell fate. Mechanistically, cleavage under targets and tagmentation (CUT&Tag) analysis revealed that PER2 down-regulated ADAM12 expression by reducing its binding activity, thereby suppressing IFN-γ production in UC CD4⁺ T cells. Additionally, our data further demonstrated that ADAM12 was upregulated in CD4⁺ T cells and inflamed mucosa of A-UC patients compared to HC. Our study reveals a critical role of PER2 in regulating CD4⁺ T cell differentiation and highlights its potential as a therapeutic target for UC treatment.