Proliferating Reactive Astrocytes Are Regulated by Notch-1 in the Peri-Infarct Area After Stroke

Abstract

Background and Purpose The formation of reactive astrocytes is common following CNS injuries such as stroke. However, the signaling pathway(s) that control reactive astrocyte formation or functions are poorly defined. Here we assess the affects of Notch 1 signaling in peri-infarct reactive astrocytes after stroke. Methods We examined reactive astrocyte formation in the peri-infarct area 3 days following distal Middle Cerebral Artery Occlusion (dMCAO), with or without Gamma-secretase inhibitor (GSI) treatment. To directly study the effects of inhibiting a GS cleavage target in reactive astrocytes, we generated GFAP-CreER™∷Notch 1 conditional knock out (GN) mice. Results GSI treatment after stroke decreased the number of proliferative GFAP-positive reactive astrocytes and RC2-positive reactive astrocytes directly adjacent to the infarct core. The decrease in reactive astrocytes correlated with an increased number of CD45-positive cells that invaded into the peri-infarct area. To study the influence of reactive astrocytes on immune cell invasion, ex vivo immune cell invasion studies were performed. We found that a gamma-secretase mediated pathway in astrocytes affected Jurkat cell invasion. Following Tamoxifen (TM) treatment, GN mice had a significantly decreased number of proliferating reactive astrocytes and RC2-positive reactive astrocytes. TM treatment also led to an increased number of CD45-positive cells that invaded the peri-infarct area. Conclusions Our results demonstrate that proliferating and RC2-positive reactive astrocytes are regulated by Notch 1 signal transduction and control immune cell invasion after stroke.

Alterations in sulfated chondroitin glycosaminoglycans following controlled cortical impact injury in mice

“…The immunogen for this antibody is GFAP derived from cow spinal cord. On western blot, this antibody detects a single band around 50kDa (Shimada et al, 2011). Staining of mouse brain sections with this antibody shows positive labeling of cells typical of astrocytes.…”

The 3 Rs of Stroke Biology: Radial, Relayed, and Regenerative

“…The border of the stroke is formed by reactive astrocytes that have evolved into a bipolar morphology from their normal multipolar state and secrete large amounts of chondroitin sulfate proteoglycans [18]. This zone close to the infarct appears to be the only region where there is true astrocyte proliferation after stroke [72,73]. Ablation of these border astrocytes after stroke and other injuries results in increased inflammation and worsening lesion size [74].…”

Effect of Ilexonin A on the Notch signaling pathway following cerebral ischemia-reperfusion in rats

“…Glial scar can inhibit axonal regeneration and astrocytes have been considered a barrier to neural repair. However, emerging studies suggest that glia suppress the invasion of immune cells into the peri-infarct region [22], suggesting that they are not only protecting neurons in the acute phase of cerebral ischemia, but also promoting neurogensis and angiogenesis in the chronic phase [23,24]. Reactive astrocytes in peri-ischemic cortex may promote neurovascular remodeling, which becomes useful for the functional recovery after stroke [25].…”