SCA-1 micro-heterogeneity in the fate decision of dystrophic fibro/adipogenic progenitors

Abstract

The term micro-heterogeneity refers to non-genetic cell to cell variability observed in a bell-shaped distribution of the expression of a trait within a population. The contribution of micro-heterogeneity to physiology and pathology remains largely uncharacterised. To address such an issue, we investigated the impact of heterogeneity in skeletal muscle fibro/adipogenic progenitors (FAPs) isolated from an animal model of Duchenne muscular dystrophy (DMD), the mdx mouse. FAPs play an essential role in muscle homoeostasis. However, in pathological conditions or ageing, they are the source of intramuscular infiltrations of fibrotic or adipose tissue. By applying a multiplex flow cytometry assay, we characterised and purified from mdx muscles two FAP cell states expressing different levels of SCA-1. The two cell states are morphologically identical and repopulate each other after several growth cycles. However, they differ in their in vitro behaviour. Cells expressing higher levels of SCA-1 (SCA1-High-FAPs) differentiate more readily into adipocytes while, when exposed to a fibrogenic stimulation, increase the expression of Col1a1 and Timp1 mRNA. A transcriptomic analysis confirmed the adipogenic propensity of SCA1-High-FAPs. In addition, SCA1-High-FAPs proliferate more extensively ex vivo and display more proliferating cells in dystrophic muscles in comparison to SCA1-Low-FAPs. Adipogenesis of both FAP cell states is inhibited in vitro by leucocytes from young dystrophic mice, while leucocytes isolated from aged dystrophic mice are less effective in limiting the adipogenesis of SCA1-High-FAPs suggesting a differential regulatory effect of the microenvironment on micro-heterogeneity. Our data suggest that FAP micro-heterogeneity is modulated in pathological conditions and that this heterogeneity in turn may impact on the behaviour of interstitial mesenchymal cells in genetic diseases.

Duchenne muscular dystrophy trajectory in R-DMDdel52 preclinical rat model identifies COMP as biomarker of fibrosis

“…We thus decided to focus our analysis on this cell population that we found overrepresented in DMD muscles compared to WT. In comparison, such a large increase in cell number has never been observed in the mdx mouse model, in which the FAP number was reported to be only slightly increased [ 20 ]. Next, we targeted the scRNAseq analysis by focusing on the transcriptomic changes between WT and R-DMDdel52 samples, and identified COMP as a crucial extracellular matrix protein that could be used as a specific biomarker of muscle fibrosis, as previously done for liver, lung, and skin diseases follow-up [ 4 , 17 , 66 ].…”

Evolving Roles of Muscle-Resident Fibro-Adipogenic Progenitors in Health, Regeneration, Neuromuscular Disorders, and Aging

“…Fibrosis is a common hallmark of several congenital muscular dystrophies, and notably, FAPs are pathologically dysregulated in most of them (Figure 4). These include mouse models of Collagen VI- (Noguchi et al, 2017;Mohassel et al, 2018), human DMD (Uezumi et al, 2014) and mouse models of DMD (Box 1) (Uezumi et al, 2011;Mozzetta et al, 2013;Lemos et al, 2015;Contreras et al, 2016Contreras et al, , 2020Ieronimakis et al, 2016;Kopinke et al, 2017;Mázala et al, 2020;Reggio et al, 2020;Giuliani et al, 2021), Facioscapulohumeral dystrophy (FSHD) (Bosnakovski et al, 2017(Bosnakovski et al, , 2020, Limb-girdle muscular dystrophy (LGMD) (Hogarth et al, 2019), and ALS neuromuscular disease (Gonzalez et al, 2017;Madaro et al, 2018). Increased muscle fibrosis and FAP expansion also occur after single and repeated cycles of intramuscular BaCl 2 , notexin, cardiotoxin, or glycerol administrations (Uezumi et al, 2010;Dadgar et al, 2014;Pessina et al, 2014;Contreras et al, 2016Contreras et al, , 2020Theret et al, 2021), vastus medialis muscles of compromised knee osteoarthritis patients (Ikemoto- Uezumi et al, 2017), human anterior cruciate ligament injuries (Fry et al, 2017), induced hindlimb ischemia (Santini et al, 2020), degenerated muscles of type 2 diabetic patients (Farup et al, 2020), obesity-mediated diaphragm dysfunction of chronic high-fat diet-fed mice (Buras et al, 2019), and surgical muscle traumas including denervation and laceration (Brandan et al, 1992;Pessina et al, 2014;Contreras et al, 2016;…”

Fibro-adipogenic progenitors in skeletal muscle homeostasis, regeneration and diseases

“…FAPs cultured in vitro can spontaneously differentiate into fibroblasts or adipocytes [ 15 , 17 ]. Their fibrogenic differentiation can be stimulated by adding transforming growth factor-β (TGF-β) to the medium, while their adipogenic differentiation can be promoted by a medium containing insulin, 3-isobutyl-1-methylxanthine and dexamethasone [ 33 – 35 ]. Lineage tracing experiments confirmed that this multipotent capacity is also observed in vivo .…”

“…Two subpopulations of FAPs, the Sca1-low/CD34-low and Sca1-high/CD34-high subsets, which are predominantly found in non-injured and injured wild-type muscles, respectively, are both found alongside within mdx muscles [ 34 ]. The Sca1-high subpopulation proliferate faster than the Sca1-low subpopulation and are predisposed to differentiate into adipocytes [ 33 ]. Similarly, there is the emergence of a subpopulation of PDGFRα-low FAPs expressing high levels of fibroblast associated genes ( TGFb1 , Col1a1 and CTGF ) in the skeletal muscles of mdx mice [ 66 ].…”