ABSTRACT
Aberrant aggregation of the RNA-binding protein TDP-43 in neurons is a hallmark of frontotemporal lobar degeneration caused by haploinsufficiency in the gene encoding progranulin1,2. However, the mechanism leading to TDP-43 proteinopathy remains unclear. Here we use single-nucleus RNA sequencing to show that progranulin deficiency promotes microglial transition from a homeostatic to a disease-specific state that causes endolysosomal dysfunction and neurodegeneration in mice. These defects persist even when Grn-/- microglia are cultured ex vivo. In addition, single-nucleus RNA sequencing reveals selective loss of excitatory neurons at disease end-stage, which is characterized by prominent nuclear and cytoplasmic TDP-43 granules and nuclear pore defects. Remarkably, conditioned media from Grn-/- microglia are sufficient to promote TDP-43 granule formation, nuclear pore defects and cell death in excitatory neurons via the complement activation pathway. Consistent with these results, deletion of the genes encoding C1qa and C3 mitigates microglial toxicity and rescues TDP-43 proteinopathy and neurodegeneration. These results uncover previously unappreciated contributions of chronic microglial toxicity to TDP-43 proteinopathy during neurodegeneration.
Subject(s)
Microglia/metabolism , Microglia/pathology , Neurons/metabolism , Neurons/pathology , Progranulins/deficiency , TDP-43 Proteinopathies/metabolism , TDP-43 Proteinopathies/pathology , Aging/genetics , Aging/pathology , Animals , Cell Nucleus/genetics , Cell Nucleus/pathology , Complement Activation/drug effects , Complement Activation/immunology , Complement C1q/antagonists & inhibitors , Complement C1q/immunology , Complement C3b/antagonists & inhibitors , Complement C3b/immunology , Culture Media, Conditioned/chemistry , Culture Media, Conditioned/pharmacology , DNA-Binding Proteins/metabolism , Disease Models, Animal , Female , Male , Mice , Nuclear Pore/metabolism , Nuclear Pore/pathology , Progranulins/genetics , RNA-Seq , Single-Cell Analysis , TDP-43 Proteinopathies/drug therapy , TDP-43 Proteinopathies/genetics , Thalamus/metabolism , Thalamus/pathology , TranscriptomeABSTRACT
Under mating conditions, yeast cells adopt a characteristic pear-shaped morphology, called a "shmoo," as they project a cell extension toward their mating partners. Mating partners make contact at their shmoo tips, dissolve the intervening cell wall, and fuse their plasma membranes. We identified mutations in ERG4, encoding the enzyme that catalyzes the last step of ergosterol biosynthesis, that impair both shmoo formation and cell fusion. Upon pheromone treatment, erg4Delta mutants polarized growth, lipids, and proteins involved in mating but did not form properly shaped shmoos and fused with low efficiency. Supplementation with ergosterol partially suppressed the shmooing defect but not the cell fusion defect. By contrast, removal of the Erg4 substrate ergosta-5,7,22,24(28)-tetraenol, which accumulates in erg4Delta mutant cells and contains an extra double bond in the aliphatic chain of the sterol, restored both shmooing and cell fusion to wild-type levels. Thus, a two-atom change in the aliphatic moiety of ergosterol is sufficient to obstruct cell shape remodeling and cell fusion.