Mitochondria and Lipid Defects in Hereditary Progranulin-Related Frontotemporal Dementia

Frontotemporal dementia (FTD) is a neurodegenerative disorder predominantly affecting individuals under 65 years of age, characterized by significant behavioral and language disabilities. Despite extensive research efforts, effective treatments for FTD remain elusive. Familial cases of FTD have been linked to genetic mutations in several key genes, among these, mutations in granulin (GRN) account for 5-20% of cases, leading to haploinsufficiency of progranulin (PGRN), a multifunctional glycoprotein. This study investigates the cellular pathology associated with GRN insufficiency by using fibroblasts derived from FTD patients carrying the c.709-1G>A GRN mutation (FTD-GRN). These fibroblasts exhibited pathological hallmarks of FTD, including lysosomes, autophagosomes, and lipofuscin accumulation, mirroring observations in affected patient tissues. Notably, we report mitochondrial abnormalities, characterized by mitochondrial swelling which is associated with decreased mitochondrial respiration, and lipid droplet accumulation, reflecting altered lipid metabolism. Experimental supplementation with recombinant human progranulin (rhPGRN) was associated with recovery of lysosomal acidification and attenuation of mitochondrial and lipid abnormalities in vitro. This study reveals that GRN haploinsufficiency induces mitochondrial and lipid dysfunctions, suggesting that these pathways may contribute to FTD-GRN pathogenesis and could be of interest for therapeutic development.