Mechanisms underlying dampened ischemic tolerance in type 2 diabetes

Tolerance to cerebral ischemia can be induced by exposure to brief ischemia or pharmacological agents including the Toll-like receptor (TLR) agonists, a phenomenon known as the ischemic preconditioning (IPC). Established evidence suggests that innate immune pathways such as TLRs and type 1 interferon (IFN) signaling are involved in IPC-mediated neuroprotection. Although it is well known that tolerance to ischemia or the effect of IPC declines with age and pathological conditions including metabolic diseases, the underlying mechanism for this damping effect is not well understood. Using single cell RNA sequencing, we have recently found that monocytes in the peripheral blood of T2DM mice db/db are defective in type 1 and type 2 IFN signaling pathways, rendering them incapable of producing interferon stimulus genes (ISGs) that are known to be immunomodulatory and anti- inflammatory. Given the premise of the defective IFN responses in the db/db mice, we hypothesize that they should show attenuated tolerance against cerebral ischemia following TLR-mediated preconditioning compared to db/+ mice. To test hypothesis, we will compare the effect of preconditioning with TLR agonists CpG or LPS in T2DM and control mice subjected to MCAO by stroke outcome, blood flow imaging, coagulation. We will determine the effect of TLR- mediated preconditioning on leukocyte trafficking to the meninges and brain parenchyma by comparing phenotypes and transcriptome profile of leukocytes in each compartment. We will also determine how the altered native immune responses in db/db mice predispose them to post stroke immunosuppression and exacerbated vascular damage and BBB leakage compared to control mice. The knowledge gained in this study will be insightful in identifying potential therapeutic targets to circumvent age and metabolic disease-associated decline in ischemic tolerance in multiple organs.