SPATA2 Attenuates Inflammatory Injury Through CYLD-Related Regulation of Microglial Inflammatory Responses After Focal Cerebral Ischemia/Reperfusion in Rats

Background: Post-ischemic inflammation is strongly influenced by interactions between neurons and microglia. We previously observed that spermatogenesis-associated protein 2 (SPATA2) alleviates inflammatory injury following cerebral ischemia/reperfusion; however, the relationship between SPATA2, cylindromatosis (CYLD)-associated inflammatory signaling, and microglial inflammatory responses remains incompletely understood. Methods: Adult Sprague-Dawley (SD) rats were subjected to transient middle cerebral artery occlusion followed by reperfusion. SPATA2 expression was knocked down in vivo via intracerebroventricular lentiviral delivery. Neurological function and infarct volume were evaluated after reperfusion. Selected pro-inflammatory and anti-inflammatory/reparative markers were assessed by immunofluorescence, real-time quantitative polymerase chain reaction (RT-qPCR), and enzyme-linked immunosorbent assay (ELISA). Double immunofluorescence staining of SPATA2 with neuronal nuclei (NeuN), ionized calcium-binding adapter molecule 1 (Iba1), or glial fibrillary acidic protein (GFAP) was performed to examine the cellular localization of SPATA2 in the peri-ischemic cortex. To further assess neuron-to-microglia regulation, primary neurons and microglia were cultured in a Transwell system and exposed to oxygen-glucose deprivation/reperfusion. SPATA2 knockdown and overexpression, together with CYLD knockdown in SPATA2-overexpressing cells, were used to investigate CYLD-associated signaling. Co-immunoprecipitation (Co-IP) was performed to assess CYLD-heme-oxidized IRP2 ubiquitin ligase 1L-like interacting protein (HOIP) association. Results: SPATA2 knockdown exacerbated neurological deficits and increased infarct volume following middle cerebral artery occlusion (MCAO). In peri-ischemic cortex tissue, SPATA2 knockdown increased the proportion of Iba1+/cluster of differentiation 86 (CD86)+ cells while reducing the proportion of Iba1+/CD206+ cells. Representative double-immunofluorescence images showed that SPATA2 immunoreactivity predominantly overlapped with NeuN-positive neurons, with relatively limited overlap with Iba1-positive microglia or GFAP-positive astrocytes. In the Transwell-based neuron–microglia system, depletion of SPATA2 in neurons shifted microglia toward a stronger inflammatory profile, as reflected by elevated secretion of interleukin-1 beta (IL-1β), IL-6, tumor necrosis factor alpha (TNF-α), and soluble C-X-C motif 3 chemokine ligand 1 (CX3CL1). By contrast, neuronal SPATA2 overexpression attenuated these inflammatory changes. At the mechanistic level, SPATA2 overexpression strengthened the association between CYLD and HOIP, together with reduced nuclear factor-κB (NF-κB) p65 expression and decreased soluble CX3CL1 release. When CYLD was silenced, the suppressive influence of SPATA2 overexpression on NF-κB p65 expression and soluble CX3CL1 release was partly weakened, indicating that CYLD contributes to this regulatory process. Conclusion: SPATA2 attenuates inflammatory injury following focal cerebral ischemia/reperfusion and modulates selected microglial inflammatory markers. In vitro results further support the role of neuron-derived SPATA2 in regulating microglial inflammatory responses in a Transwell co-culture system. Based on these observations, SPATA2 may be involved in CYLD-related inflammatory signaling and the regulation of CX3CL1/CX3C chemokine receptor 1 (CX3CR1) pathway activity.