In vitro and In vivo Neuroinflammatory Responses to LPS in Plcg2-Deficient Mice 2259976

Introduction PLCG2, a critical immune regulator, has emerged as a key factor in Alzheimer’s disease, with genetic variants conferring both risk and protection. In the brain, PLCG2 is predominantly expressed in microglia, influencing cellular functions including calcium signaling and inflammatory responses. Methods We investigated PLCG2’s role in neuroinflammation using constitutive knockout mouse models subjected to lipopolysaccharide (LPS)-induced acute inflammation. Calcium imaging, transcriptomic profiling, and protein analyses were performed, followed by behavioral assessment. Results In primary microglia, PLCG2 loss blunted LPS-induced calcium responses and reduced calcium release even after ionomycin stimulation, indicating impaired intracellular Ca²+ handling or signaling capacity. I vivo, systemic LPS treatment induced over 200 differentially expressed genes in the brain, altering pathways related to innate and adaptive immune responses, inflammatory signaling, and microglial function. Knockout mice exhibited a distinct gene signature characterized by upregulated interleukin, prostaglandin, and interferon pathways. Consistent with the transcriptomic data, protein analysis confirmed elevated brain levels of the chemokine CCL2 (MCP-1), a key mediator of monocyte recruitment during inflammation, in LPS-treated knockout mice. Interferon-responsive genes were markedly upregulated in homozygote knockout mice post-LPS, a phenotype associated with white matter pathology and inflammaging. Principal component analysis of myelin-enriched genes revealed LPS-treated homozygote knockout samples clustering separately from other genotypes. Behaviorally, LPS-treated knockout mice displayed reduced locomotion in open-field tests, correlating with expression of sickness behavior-related genes. Conclusion These findings suggest that PLCG2 deficiency enhances interferon responses, potentially driving behavioral changes and myelin-related pathology. Funding Source This research was supported by the Alzheimer’s Association (AARG-21-846012, SH and JPP); the William & Ella Owens Medical Research Foundation (JPP); and intramural funding (SH and JPP).