Abstract Body: Stroke, especially in the aged population, affects the lung health of stroke patients, and this influences the stroke outcome. Blood circulating CC-motif chemokine 11 (CCL11) increases in rodents and humans with age. Under aging-related pathological stress, the lung-modified neutrophils (PMNs) can acquire a ‘damaging’ phenotype. Lungs can release these PMNs into the bloodstream, and these PMNs potentially exacerbate severity upon entering the ICH-affected brains of aged mice. Microglia (MG) are essential for hematoma clearance and brain repair; however, MG exacerbates tissue injury if polarized to a ‘damaging’ type. The aging elevated CCL11 can robustly alter MG function in the aged mouse brains, impacting ICH outcomes.

Methods: Autologous blood injection was used for the mouse ICH model. To simulate aging with an increase of circulating CCL11 level, we intraperitoneally administered the CCL11 once every 4d for 1mo into the middle-aged mice. To examine the effect of lung-targeted delivery of CCL11 on stroke outcome in the young ICH mice, the CCL11 was administered via oropharyngeal injection to the young mice before the ICH onset. To prevent the effect of circulating CCL11 in the aged ICH mice, a CCL11-neutralizing antibody was intraperitoneally administered to the aged mice before ICH onset. Neurological deficit scores (NDS) were measured with a postural reflex test.

Results: We found that chronic exposure to CCL11 in middle-aged mice increased the PMN population in lung tissue and polarized these PMNs to a ‘damaging’ type (n=4-5, p<0.05). We also found that CCL11 infused directly into the lungs of young ICH mice increased PMNs in the lung and aggravated neurological deficits (n=10, p<0.05 on d-7). Moreover, systemic delivery of a CCL11-neutralizing antibody into aged ICH mice reduced NDS (n=13, p<0.01 on d-21) and PMN influx to the ICH-affected brain. In the cultured MG, we found that CCL11 decreased MnSOD expression and phagocytic function by downregulating PPARγ and its target genes, signifying a pro-inflammatory phenotype (n=4, p<0.05).

Conclusions: These data suggest a new target for ICH treatment in elderly people, based on understanding the pathological role of CCL11 through lung-localized polarization of PMNs to a ‘damaging’ phenotype before their transmigration to the brain and augmentation of the injury and through disruption of MG homeostasis.