Muscle fibre-resolved spatial transcriptomics of regeneration, necrosis and border zones in human paraspinal muscle

Focal necrotizing lesion fields in human skeletal muscle contain a mosaic of necrotic fibres, regenerative fibres, and morphologically preserved neighbouring fibres, but their fibre-resolved molecular organisation remains poorly defined. We applied targeted Xenium spatial transcriptomics to a human lumbar paraspinal muscle biopsy with toxic myopathy and integrated the analysis with serial post-run hematoxylin and eosin stain, adult and neonatal myosin heavy-chain isoforms, immunostaining for membrane attack complex of complement (C5b9) and manual fibre-level region-of-interest segmentation. Distant normal type 1 and type 2 fibres, necrotic fibres, regenerative fibres, and intact type 1 and type 2 fibres immediately adjacent to necrosis or regeneration were compared. Baseline transcriptional differences between distant normal type 1 and type 2 fibres were modest, whereas lesion-associated contrasts were substantially broader, indicating that pathological state outweighed basal fibre identity within this targeted panel. Necrotic fibre regions were enriched for immune/myeloid-associated transcripts, including PLA2G7 , TREM2 , FCGR3A , MS4A4A , CD163 , MRC1 , and PTPRC , whereas regenerative fibres preferentially expressed structural and calcium-handling genes, including MYBPC1 , DES , MEF2C , S100A1 , and PVALB . Despite preserved morphology, fibres bordering necrosis displayed a pronounced border-zone signature that largely overlapped the necrotic programme, whereas neighbourhood effects around regeneration were weaker and fibre-type dependent. These findings define necrosis, regeneration, and their border zones as distinct spatial states within a focal human muscle lesion and indicate that fibres adjacent to necrosis, despite being morphologically normal, are unsuitable internal comparators.