Abstract
Introduction: Irisin, a muscle-derived hormone released during exercise, improves ischemic stroke outcomes, though the mechanisms remain unclear. The current study tests the hypothesis that post-stroke recombinant irisin therapy attenuates neuroinflammation, assessed by inflammasome complex protein levels and microglial reactivity.
Methods: Middle-aged female Sprague-Dawley rats underwent transient middle cerebral artery occlusion (tMCAO; 90 min) and were divided into two cohorts. One cohort received saline or irisin (PeproTech, 0.2 µg/g BW) treatment at 4.5 h post-surgery and was survived 1 or 3 days for cortical tissue collection followed by Western blotting for apoptosis-associated speck-like protein containing a caspase recruitment domain (ASC) and caspase-1. A second cohort received saline or irisin treatment at 4.5 h post-tMCAO and weekly for 1 month. Following treatment, brains were collected for histological analysis of microglial activation. Two-dimensional morphometric analysis was performed using ImageJ, and Sholl analysis was conducted with the NIH ImageJ Sholl Analysis Plugin (v1.0).
Results: Western blotting revealed significantly (p<0.05) reduced ASC and caspase-1 levels in irisin-treated rats at 3 days post-tMCAO compared to saline controls, suggesting that irisin suppresses ASC expression or promotes its degradation to limit inflammasome assembly. Sholl analysis demonstrated that irisin-treated rats exhibited significantly (p<0.05) greater branching complexity at distal radii consistent with a more ramified state. Morphometric analysis also revealed 21% smaller soma areas in irisin-treated animals compared to saline. Together, our results indicate that irisin reduces microglial activation into an amoeboid, pro-inflammatory phenotype characterized by retracted processes and enlarged somas.
Conclusion: The current findings suggest that irisin promotes neuroprotection by limiting inflammasome complex protein levels and microglial activation, though further studies are needed to clarify the underlying mechanisms.