Abstract
<title>Abstract</title> <p> Background Duchenne muscular dystrophy (DMD) results from loss of full-length dystrophin (DP427), but many patients retain expression of the short isoform DP71. While DP71 is abundant in proliferating muscle cells and early differentiation stages, its contribution to cellular adaptation in dystrophin-deficient muscle remains poorly understood. Methods We analysed <italic>DP71</italic> expression, alternative splicing and promoter activity in human and murine muscle models, and examined the consequences of selective DP427 depletion, complete dystrophin loss, and combined utrophin depletion in differentiating human myotubes. Functional assays were used to assess cell morphology, viability, reactive oxygen species (ROS), intracellular calcium, membrane integrity, and mitochondrial status, while transcriptomic profiling and rescue experiments with individual DP71 splice variants were performed to define isoform-specific mechanisms. Results DP71 was enriched in proliferating cells and early myogenic stages and displayed greater splice diversity in human than in murine models. In DP427-deficient myotubes, <italic>DP71</italic> expression increased through enhanced promoter activity rather than increased transcript stability. Retention of DP71 under DP427-deficient conditions was associated with larger myotube areas, improved viability, reduced ROS production, and lower intracellular calcium levels during early differentiation. In contrast, cells lacking all dystrophin isoforms showed more pronounced structural disruption and stress-associated phenotypes. Transcriptomic profiling showed that selective DP427 depletion in cells retaining DP71 produced a state distinct from complete dystrophin deficiency. This state was characterized by weaker induction of structural, extracellular-matrix and stress-responsive genes, together with relative preservation of ribosomal, mitochondrial and proteostasis-related programmes. Functional studies of DP71 splice variants showed differential subcellular localisation and distinct effects on membrane-associated proteins, mitochondrial activity, calcium homeostasis, and cell survival. Conclusions DP71 functions as a transcriptionally induced and splice-sensitive modulator of early adaptation in dystrophin-deficient muscle cells. By supporting membrane–cytoskeletal homeostasis and attenuating oxidative and calcium-associated stress, DP71 promotes early cellular resilience but does not restore full structural maturation. These findings identify retained short dystrophin isoforms as determinants of a distinct early adaptive state and highlight isoform-specific regulation of cellular homeostasis in DMD. </p>