Age-related changes in diurnal expression of inflammatory mediators in the brain and peripheral blood of male and female mice

Several molecules in human body exhibit light-dependent diurnal expression rhythms, and their disruption impairs physiological functions and health. Normal aging alters these rhythms, contributing to aging processes and age-related brain disorders. Chronic low-grade inflammation is a hallmark of aging (inflammaging), and age-related changes in the diurnal expression of proinflammatory cytokines have been reported in the suprachiasmatic nucleus (SCN) and peripheral blood. However, it remains unclear which genes show diurnal expression changes in brain with the SCN regions removed (extra-SCN) and whether these changes are reflected in peripheral blood. To address this, we analyzed the diurnal expression of genes in extra-SCN brain regions and cytokines in the peripheral blood of young and aged male and female mice. Samples were collected during the light (10 AM) and the dark (10 PM) phases and analyzed using RNA sequencing and cytokine array analysis. In the aged brain, the number of genes displaying diurnal variation in expression was reduced, whereas genes related to inflammation and immune responses, especially Ccl21, were upregulated regardless of phase, suggesting age-associated immune dysregulation. However, peripheral blood levels of CCL21 protein did not differ between age groups. Instead, CXCL13 and IGFBP1 showed age-related diurnal alterations in the blood, but their expression patterns in the aged brain differed from those in the blood. These findings indicate that diurnal expression of inflammation-related molecules is altered with aging in both the brain and blood, with differences observed. These diurnal changes may contribute to the underlying mechanism of inflammaging and age-related diseases.