Osteopontin attenuates early brain injury after subarachnoid hemorrhage by promoting macrophage M2 polarization through the PI3K/Akt signaling pathway
Year: 2026
Type: article
Abstract: Background Subarachnoid hemorrhage (SAH) is a devastating cerebrovascular event associated with high mortality and disability. Early brain injury (EBI), which occurs shortly after SAH onset, is a major determinant of neurological outcome. Neuroinflammation is a central mechanism underlying EBI progression. In this process, macrophages exhibit marked phenotypic plasticity and can polarize toward either the pro-inflammatory M1 phenotype or the anti-inflammatory M2 phenotype. Osteopontin (OPN), a multifunctional phosphoglycoprotein involved in inflammation and tissue remodeling, has been implicated in immune regulation; however, its role in macrophage polarization after SAH remains unclear. Objective To investigate whether OPN alleviates early brain injury after SAH by promoting macrophage M2 polarization through activation of the PI3K/Akt signaling pathway. Methods An in vivo SAH model was established in male Sprague-Dawley rats using the endovascular perforation technique. Brain tissues were collected at 2, 6, 8, 12, 24, 48, and 72 h after SAH induction, and OPN expression was assessed by Western blotting. In vitro, RMa-bm macrophages were stimulated with oxyhemoglobin (OxyHb) to mimic the SAH microenvironment. Cells were assigned to a control group, an OPN inhibitor group, a PI3K agonist group, and a combination treatment group. Western blotting and double immunofluorescence staining were used to evaluate OPN expression and macrophage polarization markers, including CD86, iNOS, TNF-α, and IL-1β for M1 polarization and CD206, Arg-1, and TGF-β for M2 polarization. A Transwell co-culture system of RMa-bm macrophages and SH-SY5Y cells was established, and wound-healing assays were performed to examine neuronal cellular motility and in vitro recovery capacity. Results OPN protein expression was significantly increased in rat brain tissue after SAH in a time-dependent manner. OPN was also upregulated in OxyHb-stimulated RMa-bm macrophages. Pharmacological inhibition of OPN significantly increased the expression of M1-associated markers while decreasing the expression of M2-associated markers. Double immunofluorescence confirmed increased CD86 and decreased Arg-1 fluorescence in the inhibitor group. In the macrophage-neuron co-culture model, inhibition of OPN significantly impaired SH-SY5Y cellular motility and in vitro recovery capacity, whereas PI3K agonist treatment reversed this effect. These findings indicate that OPN promotes macrophage polarization toward the anti-inflammatory M2 phenotype and exerts neuroprotective effects through the PI3K/Akt pathway. Conclusions OPN is upregulated after SAH and acts as an endogenous protective factor in early brain injury. OPN promotes macrophage M2 polarization and attenuates neuroinflammation after SAH, at least in part through activation of the PI3K/Akt signaling pathway.
Source: Discover Neuroscience
Language: English
Subfield: Clinical Neurology
Field: Medicine
Domain: Health Sciences
Open Access status: diamond
OpenAlex ID: W7225801083