MICROGLIAL COMPLEMENT-DEPENDENT SYNAPTIC PRUNING UNDERLIES CEREBELLAR SPONGIFORM DEGENERATION IN CHRONIC HYPERAMMONEMIA

Hepatic encephalopathy associated with chronic hyperammonemia leads to profound neurological alterations, including cerebellar spongiform degeneration, motor impairment, and metabolic dysfunction. In the portacaval anastomosis (PCA) rat model, previous studies have described cerebellar cell loss, microglial activation, oxidative stress, and mitochondrial network fragmentation. However, the molecular mechanisms linking metabolic stress to synaptic dysfunction and tissue remodeling remain poorly understood. Here, we performed bulk RNA sequencing of the cerebellum from PCA rats at 13 weeks post-surgery to identify molecular pathways underlying spongiform neurodegeneration. Differential expression analysis revealed that only 2.6% of expressed genes were significantly altered, with a predominance of upregulated genes related to microglial activity and innate immune signaling. Notably, genes associated with homeostatic and reparative microglia (P2ry12, Cx3cr1, Csf1r), complement-mediated synaptic tagging (C1qa, C3, Trem2), and regulated phagocytosis (Mertk, Lgals3) were robustly upregulated. In contrast, downregulated genes were primarily linked to axonal transport, cytoskeletal organization, energy metabolism, and extracellular matrix components, suggesting increased synaptic vulnerability. Gene network and functional enrichment analyses supported the activation of pathways related to synaptic pruning, gliogenesis, and structural remodeling rather than classical pro-inflammatory responses. Consistently, protein analyses showed no increase in IL-1β or pyroptosis-associated markers, alongside reduced levels of caspase-1 and gasdermin D, indicating the absence of a cytotoxic inflammatory profile. Together, these findings identify a transcriptional signature consistent with a non-proinflammatory, reparative microglial state that actively promotes complement-dependent synaptic pruning and structural reorganization. This adaptive response may represent a compensatory mechanism aimed at preserving cerebellar homeostasis under chronic metabolic stress induced by hyperammonemia.