Circadian Control of Brain-peripheral Immune Response After Stroke

Circadian control of brain-peripheral immune response after stroke Aging and circadian rhythm are strong modulators of the immune system, and the immune response is a major contributor to stroke pathophysiology. But how aging and circadian rhythm interacts to influence immune response after stroke remains poorly understood. In this project, we will focus on the brain-to-cervical lymph node signaling pathway (Esposito et al, Nat Commun 2019). Because lymphatic drainage is regulated by circadian rhythm, and circadian rhythm is altered in aging, we hypothesize that this pathway may provide a novel integrating mechanism that connects these 3 major factors in stroke pathophysiology: immune response, circadian phase, and aging. Pilot data (some published in Esposito et al, Nat Commun 2019 and Nature 2020) suggest that (i) circadian phase significantly influences the progression of injury after cerebral ischemia; (ii) Bmal1 expression in brain and HO1 in astrocytes are higher after active phase vs inactive phase strokes; (iii) higher brain HO1 draining into CLN in active phase stroke may decrease oxidative stress 4-Hydroxynonenal (4HNE) in CLN lymphatic endothelium; (iv) higher brain HO1 draining into CLN in active phase stroke may reduce cytotoxic CD8+ T cells (TLR4+) in spleen; (v) CD8+ T cell infiltration and brain endothelial Cxcl10 and Hmgb1 may be lower in active phase stroke; (vi) CSF drainage from brain to CLN is affected by both circadian phase and aging; (vii) aging alters HO1 brain-to-CLN drainage in active phase stroke. We will test this overall hypothesis: Astrocytic HO1 in active phase stroke (ZT13) amplifies endogenous anti-oxidative stress response in CLN, reduces splenic inflammation, and decreases brain endothelial inflammation, whereas aging alters circadian genes and HO1 drainage in the CNS, thus weakening this endogenous protective response in active phase stroke. In Aim 1, we will dissect circadian effects in brain-cervical lymph node signaling after focal cerebral ischemia. In Aim 2, we will investigate the effects of circadian rhythm in post-stroke brain endothelial inflammation. In Aim 3, we will investigate effects of aging in circadian rhythm- mediated systemic response after focal cerebral ischemia. This project should define new mechanisms that connect the stroke immune response with circadian biology and aging, thus provide a new conceptual framework for seeking targets and biomarkers for day-time vs night- time strokes in aging patients.