Alternatively-spliced extra domain a of fibronectin promotes acute inflammation and brain injury after cerebral ischemia in mice

Abstract

Background and Purpose-The fibronectin isoform containing the alternatively spliced extra domain A (EDA +-FN) is normally absent from the circulation, but plasma levels of EDA +-FN can become markedly elevated in several human pathological conditions associated with inflammation including ischemic stroke. It remains unknown whether EDA +-FN contributes to stroke pathogenesis or is simply an associative marker. Several in vitro studies suggest that EDA +-FN can activate Toll-like receptor 4, an innate immune receptor that triggers proinflammatory responses. We undertook a genetic approach in mice to investigate the ability of EDA +-FN to mediate inflammatory brain damage in a focal cerebral ischemia/reperfusion injury model. Methods-We used genetically modified EDA + mice, which constitutively express EDA +-FN. Extent of injury, neurological outcome, and inflammatory mechanisms were assessed after 1-hour cerebral ischemia/23-hour reperfusion injury and compared with wild-type mice. Results-We found that EDA + mice developed significantly larger infarcts and severe neurological deficits that were associated with significant increased neutrophil and macrophage infiltration as quantitated by immunohistochemistry. Additionally, we found upregulation of nuclear factor-κB, cyclo-oxygenase-2, and inflammatory cytokines tumor necrosis factor-α, interleukin-1β, and interleukin-6 in the EDA + mice compared with wild-type mice. Interestingly, increased brain injury and neurological deficits were largely abrogated in EDA + mice by treatment with a specific Toll-like receptor 4 inhibitor. Conclusions-These findings provide the first evidence that EDA +-FN promotes inflammatory brain injury after ischemic stroke and suggest that the elevated levels of plasma EDA +-FN observed in chronic inflammatory conditions could worsen injury and outcome in patients after acute stroke. © 2012 American Heart Association, Inc.