Microglia play a critical role in neuroinflammation, a key secondary injury mechanism following traumatic brain injury (TBI). The colony-stimulating factor 1 receptor (CSF-1R) inhibitor PLX5622 has shown promise in suppressing neuroinflammation by depleting microglia, but it lacks specificity in targeting microglia at the injury site. To overcome this limitation, we developed PLX5622 nanoparticles functionalized with the CAQK peptide for lesion-specific targeting and combined them with a hydrogel (GelMA-PPS) that possesses potent reactive oxygen species (ROS) scavenging capabilities. This nanoparticle-hydrogel drug delivery system (GelMA-PPS/P) significantly enhanced the delivery efficiency and therapeutic efficacy of PLX5622 in TBI treatment. Localized administration of this system effectively depleted microglia at the injury site, suppressed neuroinflammation, and reduced the release of inflammatory cytokines. Its ROS scavenging ability was also validated in vitro and in vivo. Together, these effects synergistically improved neurological function recovery in TBI mouse models. This innovative strategy offers a comprehensive and targeted approach to managing neuroinflammation after TBI, providing a promising avenue for advancing TBI therapies.
Purpose Optic nerve injury (ONI) causes neuroinflammation and neurodegeneration leading to visual deficits. The response of microglia has emerged as an impactful component of etiology in neurodegeneration. This study aimed to investigate the effect of SIRT1-mTORC1 signaling pathway in microglia regulation after ONI. Methods Cx3Cr1-Cre ERT2 / Raptor F/F and Cx3Cr1-Cre ERT2 / Sirt1 F/F mice were used to delete Raptor and Sirt1 in microglia, respectively. Optic nerve crush (ONC) model was established to mimic ONI. PLX5622, a highly specific inhibitor of the colony-stimulating factor 1 receptor (CSF1R), is used to eliminate microglia in optic nerve. Ionized calcium binding adaptor molecule 1 (Iba1) immunostaining was used to detect microglial activation. Retinal ganglion cells (RGCs) were quantified by Nissl staining and retinal whole-mount immunostaining with RNA-binding protein with multiple splicing (RBPMS). Axonal damage was valued by transmission electron microscopy (TEM). Results Microglial activation emerged on day 3 post ONC and was earlier than RGCs loss which occurred at day 5 after injury. Depleting microglia with PLX5622 could attenuate the loss of RGCs and axon damage after ONC. Gain- and loss-of-function studies revealed that SIRT1 determined the activation of microglia in optic nerve. In addition, microglia-specific deletion of Raptor resulted in decreased microglial activation. Interestingly, activating mTORC1 with CCT007093 could reverse the function of SIRT1 in regulating the process of microglial activation mediated RGCs loss. Conclusion Our study reveals a potential novel mechanism of SIRT1-mTORC1 pathway in microglia regulation, and indicates a therapeutic potential for the protection of RGCs in ONI.
Depression is one of the most prevalent psychiatric disorders worldwide, yet its pathogenesis remains unclear. Here, we aimed to investigate the effects of formyl peptide receptor 2 (FPR2), a key regulator of innate immunity and inflammation, on lipopolysaccharide (LPS)-induced depression-related behaviors in mice after intraperitoneal administration, and to elucidate its regulatory mechanisms in microglia. FPR2 knockout (Fpr2 -/- ) significantly attenuated LPS-induced depressive and anxiety-like behaviors in mice. LPS markedly increased FPR2 expression in microglia of the prefrontal cortex (PFC) and hippocampus, while only a minimal increase was observed in neurons. FPR2 deficiency alleviated LPS-induced microglial activation and reduced neuronal synaptic alterations. RNA sequencing and validation experiments confirmed that FPR2 deletion substantially decreased LPS-induced microglial NLRP3 inflammasome activation and IL-1β levels in the brain. Mechanistically, FPR2 regulated downstream NLRP3 activation by modulating CSF1, and FPR2/CSF1 activation was governed by its upstream ligand, serum amyloid A (SAA). Analysis of public clinical datasets revealed that SAA1 levels were significantly upregulated in the orbital ventral PFC of patients with major depressive disorder (MDD) and in the plasma of patients with late-life depression. These findings demonstrate that the SAA/FPR2/CSF1/NLRP3 pathway mediates LPS-induced depressive-like behaviors by regulating microglial activation and neuroinflammation.
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