Heffner, C. M. | Search bioRxiv

bioRxiv2024

The ALS- and FTD-associated proteins Annexin A11 and CHMP2B act sequentially in membrane repair

Maintenance of plasma membrane and organellar integrity is essential for cell viability. Cells must recognise damaged membranes and orchestrate repair programmes to preserve compartmentalisation. A variety of cellular factors including ESCRTs, Annexins, stress granules, lipids and proteins allowing vesicle and organelle fusion with damaged membranes have been reported to contribute to membrane repair. However, whether these factors operate independently or together to repair membranes is unclear. Here, we expose temporal differences and interdependencies in the recruitment of ESCRT-III and Annexin proteins to sites of membrane damage. We show that while Annexins are recruited immediately to sites of damage, ESCRT-III assembles only after membrane sealing. We show that ESCRT-III acts to shed damaged membranes from the cell and that FTD-and ALS-associated mutations in CHMP2B and ANXA11 compromise the repair process. These data present an integrated sealing and healing model of events allowing membrane repair and restoration of membrane integrity. One-Sentence Summary: A rubric of sealing and healing for ESCRT-mediated membrane repair

cell biology↗

bioRxiv2024

Lysosomes cell autonomously regulate myeloid cell states and immune responses

Myeloid cells maintain tissue homeostasis via the recognition, engulfment, and lysosomal clearance of dying cells and cellular debris, which is often accompanied by changes from homeostatic to reactive states. While a role for phagocytic receptors in gating these transitions has been described1,2, less is known about if and how lysosomes can contribute to transcriptional and functional plasticity. To determine how lysosomal health impacts myeloid cell states, we evaluated microglia and macrophages deficient for progranulin (encoded by Grn), a lysosomal protein with pleiotropic functions whose loss is associated with several neurodegenerative diseases3-8. Single-cell RNA-sequencing of the aged mouse brain identified a Grn knockout (KO)-specific microglial subpopulation marked by high GPNMB expression that displays hallmarks of lysosomal dysfunction, including lipofuscin accumulation. Epigenetic analysis of aged microglia revealed MITF/TFE transcription factors as key mediators of the transcriptional states associated with Grn deficiency. In addition to identifying a core myeloid cell transcriptional response to diverse lysosomal stressors, targeted perturbations of various lysosomal properties in vitro uncovered a cell autonomous, TREM2- independent, response to lysosomal deacidification (via v-ATPase or VPS34 loss of function) that overlaps with Grn KO microglia phenotypes, including the induction of a lysosomal gene program, increased proliferation, and secretion of pro-inflammatory cytokines. Compound loss-of-function approaches established GPNMB upregulation upon lysosomal stress is required for the compensatory response to enhance lysosomal function via promoting acidification. Finally, pharmacological endolysosomal reacidification through sodium/proton exchanger inhibition partially rescued Grn KO microglia phenotypes. Overall, these data establish a fundamental link between lysosomal health and myeloid cell epigenetic, transcriptional, and functional states observed in neurodegeneration models.

neuroscience↗