Splenectomy may be a prophylactic treatment for cerebral ischemia?

Conditional ablation of myeloid TNF increases lesion volume after experimental stroke in mice, possibly via altered ERK1/2 signaling

Microglia are activated following cerebral ischemia and increase their production of the neuro- and immunomodulatory cytokine tumor necrosis factor (TNF). To address the function of TNF from this cellular source in focal cerebral ischemia we used TNF conditional knock out mice (LysMcreTNF^fl/fl) in which the TNF gene was deleted in cells of the myeloid lineage, including microglia. The deletion reduced secreted TNF levels in lipopolysaccharide-stimulated cultured primary microglia by ~93%. Furthermore, phosphorylated-ERK/ERK ratios were significantly decreased in naïve LysMcreTNF^fl/fl mice demonstrating altered ERK signal transduction. Micro-PET using ¹⁸[F]-fluorodeoxyglucose immediately after focal cerebral ischemia showed increased glucose uptake in LysMcreTNF^fl/fl mice, representing significant metabolic changes, that translated into increased infarct volumes at 24 hours and 5 days compared to littermates (TNFfl/fl). In naïve LysMcreTNF^fl/fl mice cytokine levels were low and comparable to littermates. At 6 hours, TNF producing microglia were reduced by 56% in the ischemic cortex in LysMcreTNF^fl/fl mice compared to littermate mice, whereas no TNF⁺ leukocytes were detected. At 24 hours, pro-inflammatory cytokine (TNF, IL-1β, IL-6, IL-5 and CXCL1) levels were significantly lower in LysMcreTNF^fl/fl mice, despite comparable infiltrating leukocyte populations. Our results identify microglial TNF as beneficial and neuroprotective in the acute phase and as a modulator of neuroinflammation at later time points after experimental ischemia, which may contribute to regenerative recovery.

Peripheral to central: Organ interactions in stroke pathophysiology

Stroke is associated with a high risk of disability and mortality, and with the exception of recombinant tissue-type plasminogen activator for acute stroke, most treatments have proven ineffective. Clinical translation of promising experimental therapeutics is limited by inadequate stroke models and a lack of understanding of the mechanisms underlying acute stroke and how they affect outcome. Bidirectional communication between the ischemic brain and peripheral immune system modulates stroke progression and tissue repair, while epidemiological studies have provided evidence of an association between organ dysfunction and stroke risk. This crosstalk can determine the fate of stroke patients and must be taken into consideration when investigating the pathophysiological mechanisms and therapeutic options for stroke. This review summarizes the current evidence for interactions between the brain and other organs in stroke pathophysiology in basic and clinic studies, and discusses the role of these interactions in the progression and outcome of stroke and how they can direct the development of more effective treatment strategies.