FSHD muscle shows perturbation in fibroadipogenic progenitor cells, mitochondrial function and alternative splicing independently of inflammation

Abstract

Facioscapulohumeral muscular dystrophy (FSHD) is a prevalent, incurable myopathy. FSHD is highly heterogeneous, with patients following a variety of clinical trajectories, complicating clinical trials. Skeletal muscle in FSHD undergoes fibrosis and fatty replacement that can be accelerated by inflammation, adding to heterogeneity. Well controlled molecular studies are thus essential to both categorise FSHD patients into distinct subtypes and understand pathomechanisms. Here, we further analysed RNA-sequencing data from 24 FSHD patients, each of whom donated a biopsy from both a non-inflamed (TIRM−) and inflamed (TIRM+) muscle, and 15 FSHD patients who donated peripheral blood mononucleated cells (PBMCs), alongside non-affected control individuals. Differential gene expression analysis identified suppression of mitochondrial biogenesis and up-regulation of fibroadipogenic progenitor (FAP) gene expression in FSHD muscle, which was particularly marked on inflamed samples. PBMCs demonstrated suppression of antigen presentation in FSHD. Gene expression deconvolution revealed FAP expansion as a consistent feature of FSHD muscle, via meta-analysis of 7 independent transcriptomic datasets. Clustering of muscle biopsies separated patients in an unbiased manner into clinically mild and severe subtypes, independently of known disease modifiers (age, sex, D4Z4 repeat length). Lastly, the first genome-wide analysis of alternative splicing in FSHD muscle revealed perturbation of autophagy, BMP2 and HMGB1 signalling. Overall, our findings reveal molecular subtypes of FSHD with clinical relevance and identify novel pathomechanisms for this highly heterogeneous condition.

Meta-analysis towards FSHD reveals misregulation of neuromuscular junction, nuclear envelope, and spliceosome

“…Furthermore, skeletal muscle regeneration in FSHD was found to correlate with disease severity 63 . A recently published study also showed that FSHD muscle exhibits disruption of fibroadipogenic progenitor cells, mitochondrial function and alternative splicing independent of inflammation 64 . The latter underpins the results of our meta-analysis and shows the great importance of these aspects for the disease course in FSHD.…”

Transcriptomic gene signatures measure satellite cell activity in muscular dystrophies

“…2023 28 and Engquist et al. 2024, 32 each FSHD patient donated biopsies from two muscles selected on turbo inversion recovery magnitude (TIRM) imaging: one from the non-inflamed vastus lateralis (23/24) muscle (TIRM – ) and one from an inflamed (TIRM + ) muscle, and the healthy individuals donated a single biopsy from the vastus lateralis ( Figure 4 A). These biopsies were then used for bulk RNA-Sequencing and cutting muscle sections ( Figure 4 A).…”

Muscle stem cells in Duchenne muscular dystrophy exhibit molecular impairments and altered cell fate trajectories impacting regenerative capacity

“…We examined the "genuine quiescence" and "primed core" expression signatures established from bulk RNA-sequencing of Cd34 High and Cd34 Low satellite cells 8 . Additionally, we used "satellite cell", "myoblasts/myocytes", and "myonuclei" gene signatures recently generated from murine scRNA-seq data 56 . We also validated the early activated MuSC clusters using the "core stress signature" determined from tissue dissociation-induced transcriptomic changes 24 and the immunomyoblast cluster from an "immunomyoblast" score generated from scRNA-seq data of regenerating muscle 26 .…”