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Single cell deconstruction of murine volumetric muscle loss reveals inflammatory imbalances preventing muscle stem cell mediated regeneration

ABSTRACT: Volumetric muscle loss (VML) overwhelms the innate regenerative capacity of mammalian skeletal muscle (SkM), leading to numerous disabilities and reduced quality of life. Immune cells are critical responders to muscle injury and guide tissue resident stem cell and progenitor mediated myogenic repair. However, how immune cell infiltration and inter-cellular communication networks are altered following VML and drive pathological outcomes remains under-explored. Herein, we characterize the cellular and molecular mechanisms of VML injuries that result in fibrotic degeneration or regeneration of SkM. Following degenerative VML injuries, we observe heightened infiltration of a previously uncharacterized population of Natural Killer (NK) cells as well as persistence of neutrophils beyond two weeks post injury. Functional validation of NK cells revealed an antagonistic role on neutrophil accumulation in part via CCR1 mediated chemotaxis. The persistent infiltration of neutrophils in degenerative VML injuries was found to contribute to impairments in muscle stem cell regenerative function, which was also attenuated by transforming growth factor beta 1 (TGFb1). Blocking TGFb signaling antagonized neutrophil accumulation, reduced fibrosis, and improved muscle specific force. Collectively, these results enhance our understanding of immune cell-stem cell crosstalk that drives regenerative dysfunction and provide further insight into possible avenues for fibrotic therapy exploration.

ORGANISM(S): Mus musculus

PROVIDER: GSE163376 | GEO | 2022/04/04

REPOSITORIES: GEO

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Project description:Recent studies using advanced techniques such as single cell RNA sequencing (scRNAseq), high parameter flow cytometry, and proteomics have revealed that neutrophils are more heterogeneous than previously thought. Unique subsets have been identified in the context of bacterial and parasitic infections, cancer and tissue injury and repair. The diversity of subsets that predominate the neutrophil infiltrate in each of these conditions appears dependent on the type of injury and timing of neutrophil involvement in the disease state. We previously described a subpopulation of immature Ly6Glow neutrophils that accumulate in the peritoneal cavity 3 days following intraperitoneal (i.p.) administration of the fungal cell wall extract, zymosan. In contrast, conventional, mature Ly6Ghi neutrophils dominate the peritoneal infiltrate 4 hours following i.p. zymosan injection. The 3 day Ly6Glow, but not 4 hour Ly6Ghi, neutrophils induce neurite outgrowth of explanted neurons in vitro. Furthermore, they drive axon regeneration in the optic nerve (ON) and spinal cord (SC) when adoptively transferred in proximity to the eye after ON crush injury or SC dorsal column transection, respectively. These pro-regenerative effects are mediated in part, by the production of the growth factors insulin-like growth factor-1 (IGF-1) and nerve growth factor (NGF). In the current study, we expand upon on our previous observations by performing an in-depth characterization of the zymosan-modulated neutrophil subsets through scRNAseq and high parameter flow cytometry. Circulating neutrophils, harvested from unmanipulated mice, were analyzed in parallel as a control. We found that each of the unfractionated neutrophil populations is diverse, composed of multiple distinct clusters. Zymosanmodulated 3-day Ly6Glow neutrophils contain a cluster that expresses neuroprotective growth factors in association with markers of alternative activation. Furthermore, the unfractionated neutrophil populations were analyzed by liquid chromatography/ mass spectrometry for proteomic analysis. This new proteomic data identified a wide variety of proteins and pathways that contribute to the alternative activation state of these pro-regenerative 3 day Ly6Glow neutrophils. Collectively, the data generated by the current study constitute another step towards pinpointing the identity and mechanisms of action of pro-regenerative, neuroprotective neutrophil subsets.

Project description:Objective: To identify transcript level differences between traumatic and degenerative tears of subacromial bursal tissues in shoulder joint using RNA-seq. Methods: Bursal tissues were collected from female and male patients with traumatic or degenerative tears during arthroscopic surgery (N=32). Differentially expressed transcript between traumatic and degenerative tears were detected by RNA-seq and biological processes were identified computationally. RNA-seq results were selectively validated by real-time qPCR. Results: We identified 334 protein-coding transcripts differentially expressed between traumatic and degenerative tears in females and 167 in males at a fold-change greater than |2| and a P < 0.05. In females, XIRP2, MYL1, MYBPC1, TNNT1, and LMOD2, were the highly expressed in traumatic tears and TPSD1, CDSN, RCVRN, LTBP4, and PTGS1 were prominently repressed in traumatic tears. Transcripts elevated in traumatic tears represented muscle cell differentiation and development, and muscle contraction whereas those elevated in degenerative tears represented cell activation, neutrophil granulation, immune response, and protein transport. In males, AZGP1, CNTFR, COL9A1, ZNF98 and EREG were highly elevated in traumatic tears whereas MYL2, HOXD11, SLC6A7, CADM1, and MMP17 were most highly repressed in traumatic tears. Transcripts elevated in traumatic tears represented metabolic processes, catabolic processes, and transmembrane protein transport while processes related to cell cycle were mainly repressed in traumatic tears. We also identified a number of novel lncRNAs differentially expressed between traumatic and degenerative tears in both females and males. Conclusions: This study increases our molecular understanding of bursal tissues in patients with rotator cuff tendinopathy based on the nature of disease that is trauma or degeneration. These finding also provide new insights into sex-based transcript differences that could inform clinical decision making in treating patients with traumatic and degenerative shoulder injuries.

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Single cell deconstruction of murine volumetric muscle loss reveals inflammatory imbalances preventing muscle stem cell mediated regeneration

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