TGFβ signaling in the brain increases with aging and signals to astrocytes and innate immune cells in the weeks after stroke

Background: TGF beta is both neuroprotective and a key immune system modulator and is likely to be an important target for future stroke therapy. The precise function of increased TGF-beta 1 after stroke is unknown and its pleiotropic nature means that it may convey a neuroprotective signal, orchestrate glial scarring or function as an important immune system regulator. We therefore investigated the time course and cell-specificity of TGFb signaling after stroke, and whether its signaling pattern is altered by gender and aging. Methods: We performed distal middle cerebral artery occlusion strokes on 5 and 18 month old TGFb reporter mice to get a readout of TGF beta responses after stroke in real time. To determine which cell type is the source of increased TGF beta production after stroke, brain sections were stained with an anti-TGF beta antibody, colocalized with markers for reactive astrocytes, neurons, and activated microglia. To determine which cells are responding to TGF beta after stroke, brain sections were double-labelled with anti-pSmad2, a marker of TGF beta signaling, and markers of neurons, oligodendrocytes, endothelial cells, astrocytes and microglia. Results: TGF beta signaling increased 2 fold after stroke, beginning on day 1 and peaking on day 7. This pattern of increase was preserved in old animals and absolute TGF beta signaling in the brain increased with age. Activated microglia and macrophages were the predominant source of increased TGF beta after stroke and astrocytes and activated microglia and macrophages demonstrated dramatic upregulation of TGF beta signaling after stroke. TGF beta signaling in neurons and oligodendrocytes did not undergo marked changes. Conclusions: We found that TGF beta signaling increases with age and that astrocytes and activated microglia and macrophages are the main cell types that undergo increased TGF beta signaling in response to post-stroke increases in TGF beta. Therefore increased TGF beta after stroke likely regulates glial scar formation and the immune response to stroke.