Introduction: Middle-aged female rats sustain larger strokes than younger female rats. This may be due to age-related loss of circulating and parenchymal brain levels of insulin like growth factor-1 (IGF-1). With age, IGF-1 synthesis is decreased in astrocytes, a critical cell type for post-stroke recovery. Here we tested the hypothesis that replenishing IGF-1 in aging astrocytes will improve stroke outcomes by influencing the type and extent of immune cells infiltration into the brain post-stroke.
Methods: Middle-aged (10-12 mo old, acyclic) female rats were injected into the striatum and cortex with adeno-associated virus serotype 5 (rAAV5) packaged with the coding sequence of the hIGF-1 gene downstream of an astrocyte-specific promoter (GFAP). The rAAV-control consisted of an identical shuttle vector construct without the hIGF-1 gene. Three to four weeks later, animals underwent 90 minute transient middle cerebral artery occlusion via intraluminal suture. At 2d post stroke, flow cytometry was used to determine the type and extent of peripheral immune cells trafficked into the brain. In parallel studies, animals were tested for performance on sensory motor tasks at 2d and 5 days after MCAo.
Results: rAAV-mediated IGF-1 expression was confirmed in astrocytes with RT-PCR. Flow cytometry analysis of immune cells in the brain at 24h post-stroke found that proportion of Treg cells was greater in animals with rAAV-IGF-1 as compared to rAAV-controls. Additionally, while there was no difference in the proportion of M2 microglia, rAAV-IGF-1 enhanced M2 infiltrating macrophages. At 2d and 5d post stroke, stroke-induced sensory motor impairment was reduced in animals with rAAV-IGF-1 as compared to rAAV-controls.
Conclusion: Targeted enhancement of IGF-1 in astrocytes of middle-aged females improved stroke-induced behavioral impairment concomitant with recruitment of anti-inflammatory cell types to the ischemic brain.