Transforming Growth Factor Beta-Activated Kinase 1-Dependent Microglial and Macrophage Responses Aggravate Long-Term Outcomes After Ischemic Stroke

Background and Purpose-Microglia/macrophages (Mi/M Phi) can profoundly influence stroke outcomes by acquiring functionally dominant phenotypes (proinflammatory or anti-inflammatory; deleterious or salutary). Identification of the molecular mechanisms that dictate the functional status of Mi/M Phi after brain ischemia/reperfusion may reveal novel therapeutic targets for stroke. We hypothesized that activation of TAK1 (transforming growth factor beta-activated kinase 1), a key MAP3K upstream of multiple inflammation-regulating pathways, drives Mi/M Phi toward a proinflammatory phenotype and potentiates ischemia/reperfusion brain injury. Methods-Young adult mice were subjected to 1 hour of middle cerebral artery occlusion (MCAO) followed by reperfusion. TAK1 was targeted by tamoxifen-induced Mi/M Phi-specific knockout or administration of a selective inhibitor 5Z-7-Oxozeaenol after MCAO. Neurobehavioral deficits and long-term gray matter and white matter injury were assessed up to 35 days after MCAO. Mi/M Phi functional status and brain inflammatory profiles were assessed 3 days after MCAO by RNA-seq, flow cytometry, and immunohistochemistry. Results-TAK1 Mi/M Phi-specific knockout markedly ameliorated neurological deficits in the rotarod and cylinder tests for at least 35 days after MCAO. Mechanistically, RNA-seq of purified brain Mi/M Phi demonstrated that proinflammatory genes and their predicted biological functions were downregulated or inhibited in microglia and macrophages from TAK1 Mi/M Phi-specific knockout mice versus WT mice 3 days after MCAO. Consistent with the anti-inflammatory phenotype of Mi/M Phi-specific knockout, oxozeaenol treatment mitigated neuroinflammation 3 days after MCAO, manifested by less Iba1(+)/CD16(+) proinflammatory Mi/M Phi and suppressed brain invasion of various peripheral immune cells. Oxozeaenol treatment beginning 2 hours after MCAO improved long-term sensorimotor and cognitive functions in the foot fault, rotarod, and water maze tests. Furthermore, Oxozeaenol promoted both gray matter and white matter integrity 35 days after MCAO. Conclusions-TAK1 promotes ischemia/reperfusion-induced inflammation, brain injury, and maladaptive behavior by enhancing proinflammatory and deleterious Mi/M Phi responses. Therefore, TAK1 inhibition is a promising therapy to improve long-term stroke outcomes.