Target formation in muscle fibres indicates reinnervation - A proteomic study in muscle samples from peripheral neuropathies

Neuropathol Appl Neurobiol. 2023 Feb;49(1):e12853. doi: 10.1111/nan.12853. Epub 2022 Oct 17.

Abstract

Aims: Target skeletal muscle fibres - defined by different concentric areas in oxidative enzyme staining - can occur in patients with neurogenic muscular atrophy. Here, we used our established hypothesis-free proteomic approach with the aim of deciphering the protein composition of targets. We also searched for potential novel interactions between target proteins.

Methods: Targets and control areas were laser microdissected from skeletal muscle sections of 20 patients with neurogenic muscular atrophy. Samples were analysed by a highly sensitive mass spectrometry approach, enabling relative protein quantification. The results were validated by immunofluorescence studies. Protein interactions were investigated by yeast two-hybrid assays, coimmunoprecipitation experiments and bimolecular fluorescence complementation.

Results: More than 1000 proteins were identified. Among these, 55 proteins were significantly over-represented and 40 proteins were significantly under-represented in targets compared to intraindividual control samples. The majority of over-represented proteins were associated with the myofibrillar Z-disc and actin dynamics, followed by myosin and myosin-associated proteins, proteins involved in protein biosynthesis and chaperones. Under-represented proteins were mainly mitochondrial proteins. Functional studies revealed that the LIM domain of the over-represented protein LIMCH1 interacts with isoform A of Xin actin-binding repeat-containing protein 1 (XinA).

Conclusions: In particular, proteins involved in myofibrillogenesis are over-represented in target structures, which indicate an ongoing process of sarcomere assembly and/or remodelling within this specific area of the muscle fibres. We speculate that target structures are the result of reinnervation processes in which filamin C-associated myofibrillogenesis is tightly regulated by the BAG3-associated protein quality system.

Keywords: Filamins; LIMCH1; laser microdissection; mass spectrometry; proteomics; reinnervation; skeletal muscle; target fibre.

MeSH terms

  • Actins / analysis
  • Actins / metabolism
  • Adaptor Proteins, Signal Transducing / metabolism
  • Apoptosis Regulatory Proteins / analysis
  • Apoptosis Regulatory Proteins / metabolism
  • Humans
  • Muscle Fibers, Skeletal / chemistry
  • Muscle Fibers, Skeletal / metabolism
  • Muscle Proteins / metabolism
  • Muscle, Skeletal / metabolism
  • Muscular Atrophy / metabolism
  • Peripheral Nervous System Diseases* / metabolism
  • Proteomics

Substances

  • Actins
  • Muscle Proteins
  • BAG3 protein, human
  • Adaptor Proteins, Signal Transducing
  • Apoptosis Regulatory Proteins