Analysis GPNMB + Macrophages in Skeletal Muscle Aging

National Institute On Aging

Investigators

Abstract

Our lab recently characterized macrophage populations in aging mouse SKM by scRNA-sequencing and flow cytometry, identifying 11 distinct MΦ clusters and observing a generalized increase of inflammatory MΦs in aged SKM. We also identified several specific subpopulations whose abundance shifted in aged SKM. Of particular interest, cluster 6 (Cl6) increased from 2.5% of the total MΦ population in young mice (3 months old, m.o.) to 13% in old (23 m.o.) mice. This subpopulation of MΦs was enriched in mRNAs encoding candidate senescence proteins including GPNMB, SPP1, CTSD and GDF15. Targeted systemic ablation of GPNMB+ cells by diphtheria toxin (DT) or GPNMB vaccination has been shown to attenuate tissue senescence, improve age-associated phenotypes and extend the lifespan of male progeroid mice4. We hypothesize that this cluster of GPNMB+ MΦs represent senescent SKM macrophages that may contribute to age-related SKM phenotypes. GPNMB is a transmembrane protein expressed in various cell types, including MΦs. GPNMB was originally shown to be associated with cancer progression, but recent studies have unveiled a contrasting role for GPNMB as a marker of cellular senescence, playing an “anti-senescence” role. Here, we propose to study the role of GPNMB+ MΦ cluster (Cl6), rather than GPNMB itself, in SKM injury response and aging using an inducible GPNMB+ MΦ ablation mouse model. We aim to (1) generate a Cre-inducible Gpnmb-diphtheria toxin receptor (DTR) knock-in (KI) mice to enable specific elimination of GPNMB+ MΦs via DT. We will then (2) elucidate the role of GPNMB+ MΦs in injury repair performing acute-injury experiments on both WT and KI mice. Finally, we propose to (3) explore the role of GPNMB+ MΦs in SKM aging by analyzing phenotypic and molecular shifts in young and old KI mice.