TGF[beta] 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 TGF[beta] 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 TGF[beta] 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.