Mariutti, G. | bioRxiv Science

bioRxiv2025

Gpnmb Defines a Phagocytic State of Microglia Linked to Neuronal Loss in Prion Disease

Neurodegenerative conditions can induce the region-specific emergence of cell states relevant to their pathogenesis. To identify such phenomena, we generated a spatiotemporal transcriptomic atlas of mice infected with the RML prion strain. Thalamus and cerebellum experienced severe neuronal loss, developed intense microgliosis and, starting from 30 weeks post-inoculation, accumulated a novel microglial subpopulation characterized by strong expression of Glycoprotein non-metastatic melanoma protein B (Gpnmb). Elevated GPNMB levels were detected in the cerebrospinal fluid of sCJD patients, suggesting its possible usefulness as a biomarker of disease progression. The transcriptional profile of Gpnmb+ microglia reflected a state of enhanced phagocytic activity with upregulation of genes associated with lysosomal function, including vacuolar ATPase V0 domain subunit d2 (Atp6v0d2) and Galectin-3 (Lgals3). In microglia-like murine BV2 cells, Gpnmb upregulation was induced by soluble find-me signals released during apoptosis, but not by apoptotic bodies or prion accumulation. Likewise, human iPSC-derived microglia showed marked upregulation of GPNMB when co-cultured with apoptotic human neurons. Gpnmb ablation impaired the ability of BV2 cells to clear apoptotic cells, underscoring its role in maintaining microglial phagocytosis. Our findings define Gpnmb microglia as a distinct, apoptosis-driven phagocytic state, linking neuronal loss to microglial activation and positioning it as a key regulator of microglial responses to prion propagation.

neuroscience↗

bioRxiv2024

TFAP2C and HNRNPK control mTOR cell metabolism and prion propagation

Heterogeneous Nuclear Ribonucleoprotein K (hnRNP K) is a limiting factor for prion propagation. However, little is known about the function of hnRNP K except that it is essential to cell survival. Here, we performed a synthetic-viability CRISPR ablation screen to identify epistatic interactors of HNRNPK. We found that deletion of Transcription Factor AP-2{gamma} (TFAP2C) suppressed the death of hnRNP K-depleted LN-229 and U-251 MG cells, whereas its overexpression hypersensitized cells to hnRNP K loss. HNRNPK ablation decreased cellular ATP, downregulated genes related to lipid and glucose metabolism, and enhanced autophagy. Co-occurrent deletion of TFAP2C reversed these effects, restoring transcriptional balance and alleviating energy deficiency. We linked HNRNPK and TFAP2C interaction to mTOR signaling, observing that HNRNPK ablation inhibited mTORC1 activity through downregulation of mTOR and Rptor, while TFAP2C overexpression enhanced mTORC1 downstream functions. In prion-infected cells, TFAP2C activation reduced prion levels and countered the increased prion propagation caused by HNRNPK suppression. Short-term pharmacological inhibition of mTOR also elevated prion levels and partially mimicked the effects of HNRNPK silencing. Our study identifies TFAP2C as a genetic interactor of HNRNPK, implicates their roles in mTOR metabolic regulation, and establishes a causative link between these activities and prion propagation.

cell biology↗