Progranulin deficiency-induced lysosomal dysfunction drives maladaptive myeloid cell states through the MITF/TFE...

Lysosomal dysfunction in myeloid cells is increasingly implicated in neurodegenerative diseases. To examine the interplay between lysosomal health and cellular state, we performed multi-omic profiling of myeloid cells from brains of aged mice lacking progranulin (Grn^-/- mice), a lysosomal protein linked to neurodegeneration. Single-cell RNA sequencing identified a microglial subpopulation defined by GPNMB expression, which displays hallmarks of lysosomal stress, including altered lysosomal protein expression, lipofuscinosis, and metabolic and lipid dysregulation. Epigenetic profiling of Grn^-/- microglia revealed an enrichment of MITF/TFE transcription factor motifs at active enhancers, and deletion of these factors reversed the Grn^-/--specific myeloid cell transcriptional signature. Diverse lysosomal perturbations drove a common transcriptional and functional signature, with conditions that induce lysosomal deacidification closely phenocopying progranulin deficiency. Finally, compensatory GPNMB induction in Grn^-/- myeloid cells promoted lysosomal acidification, and loss of myeloid cell GPNMB exacerbated neurotoxicity. Our findings link lysosomal health with epigenetic, transcriptional, and functional myeloid cell states associated with neurodegeneration.