Introduction: Stress is associated with increased risk of stroke and poor prognosis, but the mechanisms through which stress may alter stroke outcome remain elusive. Stress compromises neuronal survival and neuroinflammation following an ischemic attack. Post-ischemic inflammatory response involves the activation of microglia, which can be polarized from a harmful M1 phenotype which expresses pro-inflammatory cytokines, to a protective M2 phenotype which releases neurotrophic factors. We hypothesize that progesterone (PROG) will improve global ischemia outcome by modulating microglial polarization in stressed ischemic animals.
Methods: Adult male rats were exposed to social defeat stress over 8 consecutive days. Then, rats were subjected to 8 min of global ischemia by the four-vessel occlusion model. PROG (8 mg/Kg/b.w.) was administered by intraperitoneal injection at 2 h post-ischemia followed by subcutaneous injections at 6 h and once every 24 h post-injury for 5 days, and then 2 days with progressively halved dosages. Animals were sacrificed at 7 days post-ischemia. Neuronal loss was assessed by Nissl staining, M1/M2 polarization markers were assessed by immunofluorescence, and pro-inflammatory cytokine and growth factor expression were assessed by western blot.
Results: Results revealed extensive neuronal loss and exacerbated microglial activation in hippocampal CA1 region of stressed ischemic rats. Remarkably, both M1 and M2 markers increased. PROG treatment attenuated neuronal loss, robustly reduced M1/M2 markers and significantly increased brain-derived neurotrophic factor expression in the stressed ischemic hippocampus.
Conclusion: Our data demonstrate that PROG can modulate neuroinflammation after global ischemic injury by changing microglial phenotype in certain vulnerable brain areas like the hippocampus. These findings support the therapeutic potential of PROG for treating global ischemia with comorbid stress.