METTL14 regulates microglia/macrophage polarization and NLRP3 inflammasome activation after ischemic stroke by the KAT3B-STING axis

STING agonist 8803 reprograms the immune microenvironment and increases survival in preclinical models of glioblastoma

STING agonists can reprogram the tumor microenvironment to induce immunological clearance within the central nervous system. Using multiplexed sequential immunofluorescence (SeqIF) and the Ivy Glioblastoma Atlas, STING expression was found in myeloid populations and in the perivascular space. The STING agonist 8803 increased median survival in multiple preclinical models of glioblastoma, including QPP8, an immune checkpoint blockade-resistant model, where 100% of mice were cured. Ex vivo flow cytometry profiling during the therapeutic window demonstrated increases in myeloid tumor trafficking and activation, alongside enhancement of CD8+ T cell and NK effector responses. Treatment with 8803 reprogrammed microglia to express costimulatory CD80/CD86 and iNOS, while decreasing immunosuppressive CD206 and arginase. In humanized mice, where tumor cell STING is epigenetically silenced, 8803 therapeutic activity was maintained, further attesting to myeloid dependency and reprogramming. Although the combination with a STAT3 inhibitor did not further enhance STING agonist activity, the addition of anti-PD-1 antibodies to 8803 treatment enhanced survival in an immune checkpoint blockade-responsive glioma model. In summary, 8803 as a monotherapy demonstrates marked in vivo therapeutic activity, meriting consideration for clinical translation.

SS-31 inhibits mtDNA-cGAS-STING signaling to improve POCD by activating mitophagy in aged mice

BACKGROUND

Neuroinflammation is crucial in the development of postoperative cognitive dysfunction (POCD), and microglial activation is an active participant in this process. SS-31, a mitochondrion-targeted antioxidant, is widely regarded as a potential drug for neurodegenerative diseases and inflammatory diseases. In this study, we sought to explore whether SS-31 plays a neuroprotective role and the underlying mechanism.

METHODS

Internal fixation of tibial fracture was performed in 18-month-old mice to induce surgery-associated neurocognitive dysfunction. LPS was administrated to BV2 cells to induce neuroinflammation. Neurobehavioral deficits, hippocampal injury, protein expression, mitophagy level and cell state were evaluated after treatment with SS-31, PHB2 siRNA and an STING agonist.

RESULTS

Our study revealed that SS-31 interacted with PHB2 to activate mitophagy and improve neural damage in surgically aged mice, which was attributed to the reduced cGAS-STING pathway and M1 microglial polarization by decreased release of mitochondrial DNA (mtDNA) but not nuclear DNA (nDNA). In vitro, knockdown of PHB2 and an STING agonist abolished the protective effect of SS-31.

CONCLUSIONS

SS-31 conferred neuroprotection against POCD by promoting PHB2-mediated mitophagy activation to inhibit mtDNA release, which in turn suppressed the cGAS-STING pathway and M1 microglial polarization.

Arginine Methylation of β-Catenin Induced by PRMT2 Aggravates LPS-Induced Cognitive Dysfunction and Depression-Like Behaviors by Promoting Ferroptosis

Depression is a prevalent and debilitating psychiatric disorder, imposing substantial societal and individual burdens. This study aims to investigate the involvement of ferroptosis and microglial polarization in the pathogenesis of depression, as well as the underlying mechanism. Increased protein arginine methyltransferase 2 (PRMT2) expression was observed in BV2 cells and the hippocampus following lipopolysaccharide (LPS) stimulation. Mechanistically, alkylation repair homolog protein 5 (ALKBH5)-mediated m6A modification enhanced the stability of PRMT2 mRNA. PRMT2 promoted arginine methylation of β-catenin and induced proteasomal degradation of β-catenin proteins, resulting in transcriptional inhibition of glutathione peroxidase 4 (GPX4). The upregulation of PRMT2 further accelerated microglia polarization by activating ferroptosis through the β-catenin-GPX4 axis. Depletion of PRMT2 improved LPS-induced depressive- and anxiety-like behaviors as well as cognitive impairment by inhibiting ferroptosis and M1 polarization of microglia. Our findings underscore the crucial involvement of the ALKBH5-PRMT2-β-catenin-GPX4 axis in ferroptosis and M1 polarization of microglia, thereby offering novel insights into the pathogenesis interventions for depression.

Role of m6A RNA Methylation in Ischemic Stroke

Ischemic stroke is a prominent contributor to global morbidity and mortality rates. The intricate and diverse mechanisms underlying ischemia-reperfusion injury remain poorly comprehended. RNA methylation, an emerging epigenetic modification, plays a crucial role in regulating numerous biological processes, including immunity, DNA damage response, tumorigenesis, metastasis, stem cell renewal, adipocyte differentiation, circadian rhythms, cellular development and differentiation, and cell division. Among the various RNA modifications, N6-methyladenosine (m6A) modification stands as the most prevalent in mammalian mRNA. Recent studies have demonstrated the crucial involvement of m6A modification in the pathophysiological progression of ischemic stroke. This review aims to elucidate the advancements in ischemic stroke-specific investigations pertaining to m6A modification, consolidate the underlying mechanisms implicated in the participation of m6A modification during the onset of ischemic stroke, and deliberate on the potential of m6A modification as a viable therapeutic target for ischemic stroke.

METTL14 contributes to acute lung injury by stabilizing NLRP3 expression in an IGF2BP2-dependent manner

Acute lung injury (ALI) as well as its more severe form, acute respiratory distress syndrome (ARDS), frequently leads to an uncontrolled inflammatory response. N6-methyladenosine (m6A) modification was associated with the progression of several inflammatory diseases. However, the role of methyltransferase-like 14 (METTL14)-mediated m6A methylation in ALI/ARDS remains unclear. Here, we reported an increase in overall expression levels of m6A and METTL14 in circulating monocyte-derived macrophages recruited to the lung following ALI, which is correlated with the severity of lung injury. We further demonstrated the critical function of METTL14 in activating NOD-like receptor pyrin domain-containing protein 3 (NLRP3) inflammasome in vitro and in mouse models of ALI/ARDS, and validated NLRP3 as the downstream target of METTL14 by the m6A RNA immunoprecipitation (MeRIP) and RIP assays. Mechanistically, METTL14-methylated NLRP3 transcripts were subsequently recognized by insulin-like growth factor 2 mRNA-binding protein 2 (IGF2BP2), an m6A reader, which stabilized NLRP3 mRNA. Furthermore, we observed that IGF2BP2 knockdown diminished LPS-induced ALI in mice by downregulating NLRP3 expression. In summation, our study revealed that the molecular mechanism underlying the pathogenesis of ALI/ARDS involves METTL14-mediated activation of NLRP3 inflammasome in an IGF2BP2 dependent manner, thereby demonstrating the potential of METTL14 and IGF2BP2 as promising biomarkers and therapeutic targets for ALI/ARDS treatment.