Regulatory T cells suppress novel skeletal muscle macrophages identified by single-cell RNA sequencing


Single Cell Analysis Approaches

Poster Number: 198


Gerald Coulis, PhD, Jenna Kastenschmidt, Ali Mannaa, Quy Nguyen, Nicholas Pervolarakis, Jorge Duarte, Melissa Emami, Catherine Yang, Kai Kessenbrock, PhD, Armando Villalta, PhD


1. University of California Irvine, 2. University of California Irvine, 3. University California of Irvine, 4. University California of Irvine, 5. University California of Irvine, 6. University California of Irvine, 7. University California of Irvine, 8. University California of Irvine, 9. University California of Irvine, 10. University California of Irvine

Duchenne muscular dystrophy (DMD) is a lethal X-linked disorder that results from mutations in the dystrophin gene causing necrosis, muscle inflammation and ultimately fibrosis. In DMD, muscle macrophages are multifaceted effector immune cells that regulate multiple pathogenic processes, including myofiber injury, inflammation and fibrosis, but also promote regeneration. In previous work, we demonstrated that regulatory T cells (Tregs) ameliorated the severity of muscular dystrophy by regulating M1-like and M2-like macrophage activation, and more recently, a subset of undefined macrophages. Herein, we used single-cell RNA sequencing (scRNAseq) approaches to define the phenotypic complexity and transcriptional profile of skeletal muscle macrophages in healthy and dystrophic muscle. A T-distributed Stochastic Neighbor Embedding (t-SNE) analysis of gene expression data revealed unexpectedly that, traditional M1 and M2 markers do not distinguish functionally distinct macrophage populations in dystrophic muscle. Rather, we identified that skeletal muscle macrophages clustered into six novel populations defined by unique transcriptional programs. We observed that a population expressing high levels of galectin-3 was largely absent in wildtype and dystrophic muscle before the onset of disease, but was increased at the onset of acute pathology and further expanded when Tregs were depleted in the mdx mouse model of DMD. In light of emerging evidence in the literature suggesting a role for galectin-3 and Tregs in fibrosis, we performed functional assays using various mouse models to underscore the role of the Treg-Macrophages axis in the control of muscle fibrosis in DMD. Our data support a new paradigm, in which unique transcriptional programs define novel macrophage populations likely adapted to the diseased muscle milieu, and suggest that therapies focused on augmenting the function of Tregs in dystrophic muscle may have beneficial effects in treating fibrosis.