2026-08-05 | In vitro and in silico characterization of competitive inhibition and repression of DUX4 target gene activation as a therapeutic approach for facioscapulohumeral muscular dystrophy (FSHD)
ABSTRACT Facioscapulohumeral muscular dystrophy (FSHD) is a rare neuromuscular disease caused by aberrant re-expression of the embryonic transcription factor DUX4 in skeletal muscle, which activates a toxic transcriptional program that drives progressive muscle wasting. No approved disease-modifying therapies currently exist. Prior work in mammalian and zebrafish models has shown that a truncated form of DUX4 retaining only its DNA-binding domain (DBD) lacks transactivation capacity and can suppress DUX4-FL-driven pathology; separately, dCas9/KRAB-based epigenetic repressors have demonstrated efficacy in silencing DUX4 expression, though CRISPR-based strategies face challenges from the repetitive nature of the D4Z4 locus, the immunogenicity associated with bacterial Cas proteins, and the payload limitations of gene delivery vehicles. Building on these findings, we corroborate that the DUX4 DBD, comprising both homeodomains, acts as a non-toxic competitive inhibitor of full-length DUX4 (DUX4-FL) at its genomic target sites, and extend this strategy by fusing the DBD to a human KRAB(ZNF10) domain, converting DUX4 from a transcriptional activator into a fully humanized epigenetic silencer of its own targets. Using a fluorescent DUX4-responsive reporter, we show that DBD alone produces dose-dependent repression of DUX4-FL transcriptional activity in HEK293T cells (200-fold at the highest inducible dose tested), while a constitutively expressed DBD-KRAB fusion produces significantly greater repression than DBD alone (949-fold versus 17-fold at a 25x molar ratio), with a similar trend observed in C2C12 myoblasts (47-fold versus 3.3-fold knockdown). To contextualize these findings and explore dosing considerations, we developed three complementary computational models – a transcription factor competitive binding model, a myotube diffusion model, and an ordinary differential equation (ODE) compartmental model – that illustrate how DBD concentration, intracellular diffusion, and population-level cell state transitions may relate to therapeutic efficacy. Together, these results corroborate and extend existing approaches into a single, fully humanized construct that may help circumvent the immunogenicity and delivery limitations of Cas-based systems.
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2026-07-31 | Metformin enhances differentiation and function of skeletal muscle in models of Facioscapulohumeral Muscular Dystrophy (FSHD)
Abstract Facioscapulohumeral muscular dystrophy (FSHD) is one of the most prevalent inherited muscular dystrophies, for which there are no disease-modifying therapies. Metabolic perturbation, mitochondrial dysfunction, and oxidative stress are key contributors to FSHD pathology. Here, the effects of the metabolic regulator and anti-diabetic drug Metformin on myogenesis and muscle function in human and murine models of FSHD were investigated. Metformin did not affect the proliferation rate of human control or patient-derived FSHD myoblasts but promoted their myogenic differentiation, increasing myotube formation and maturation. Metformin also enhanced the metabolic health and viability of myotubes. Mechanistic interrogation revealed reduced levels of mitochondrial reactive oxygen species and modified mitochondrial turnover. These cellular investigations were complemented with in vivo functional assessment in a murine model of FSHD, in which Metformin treated mice exhibited significantly improved muscle strength. Collectively, these findings identify metabolic regulation as a therapeutically tractable feature of FSHD and demonstrate that Metformin improves muscle function in multiple models of FSHD via reduction of oxidative stress and augmentation of cellular metabolic fitness. These results provide insight into the therapeutic actions of Metformin and pre-clinical data to support its testing for repurposing in FSHD.
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2026-07-29 | Targeted DUX4 base editing improves muscle function in an iPSC-derived model of childhood-onset FSHD
Abstract Facioscapulohumeral muscular dystrophy (FSHD) is one of the most common dominant muscular dystrophies and remains without an approved disease modifying therapy. Caused by the aberrant expression of the cytotoxic gene DUX4, FSHD is typically diagnosed in adulthood, however clinical onset in children (<18 years of age) is often associated with a more severe and rapid disease. While clinical trials are underway, a lack of human-specific pre-clinical models limit effective testing of potential therapies, particularly in children. To fill this gap, we describe here the development of induced pluripotent stem cell-derived 2-and 3-dimensional skeletal muscle models of children with clinically defined mild, moderate, and severe FSHD. These iPSC-derived muscle models replicate key features of FSHD, including aberrant DUX4 mRNA expression, muscle atrophy, and weakness, which correlate with the individuals’ specific disease severity. Next, we assessed the efficacy of adenine base editing (ABE) as a potential gene therapy approach to treat FSHD. DUX4 -targeted ABE reduced DUX4 mRNA expression, improved muscle area and force generation in the most severe individual. Together this work supports the use of iPSC-derived skeletal muscle models as a less invasive method to study childhood-onset FSHD and establishes targeted DUX4 gene editing therapies as a potential treatment approach.
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2026-07-28 | Impaired Myogenic Differentiation Is a Shared Feature Across Genetic Myopathies.
There is a shared hallmark of defective differentiation across genetic myopathies, a process that has been extensively described in Duchenne muscular dystrophy and also observed in Emery-Dreifuss muscular dystrophy. In this article, we broaden the discussion on myopathies associated with differentiation defects, examining their implications in less characterized muscle conditions that can have onset in adulthood, including facioscapulohumeral muscular dystrophy (FSHD), oculopharyngeal muscular dystrophy (OPMD), and myotonic dystrophies (DM), as well as myopathies caused by genetic variants in FHL1, GNE, DES, CAPN3, and members of the HNRNP family. Muscle damage can result from injury, exercise, or disease, necessitating a highly coordinated repair process to restore normal strength and function. Resident satellite cells are activated, differentiate, and fuse with the damaged tissue to facilitate this repair. This overview emphasizes the importance of muscle differentiation in the pathogenesis of myopathies with diverse etiologies and a broad range of underlying molecular mechanisms. These insights highlight differentiation as a potential convergent therapeutic target.
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2026-07-09 | Epigenetic editing approaches maturity: AI-driven precision design, delivery innovation, and the road to clinical translation.
Epigenetic editing achieves durable gene silencing through targeted modification of chromatin and DNA methylation states without altering the genomic sequence-modifications that remain fundamentally reversible compared with genome editing. Long constrained by transient efficacy, insufficient precision, and delivery bottlenecks, the field reached a critical inflection point in 2024-2025, measurable through three quantifiable criteria: (1) mechanistic durability-silencing maintained across ≥ 450 cell divisions in vitro and ≥ 12 months in vivo without continued editor expression; (2) delivery competence-tissue-selective transduction at > 50% efficiency in liver, muscle, and whole brain via engineered lipid nanoparticle and AAV platforms; and (3) clinical validation-advancement of multiple first-in-human trials. The inaugural trial in epigenetic editing was OTX-2002 (targeting MYC-driven malignancies, MYCHELANGELO study), initiated in October 2022, followed by TUNE-401 for chronic hepatitis B (Phase Ib, November 2024) and EPI-321 for facioscapulohumeral muscular dystrophy (Phase I/II, first patient dosed August 2025). Artificial intelligence contributes at distinct levels: deep learning platforms have directly accelerated clinical-stage LNP formulation screening and AAV capsid prediction; AlphaFold3 has optimized protein-DNA interaction validation without yet entering clinical programs; and the 2025 de novo design of DNA-binding proteins smaller than 65 amino acids represents a proof-of-concept breakthrough with zero clinical precedent. This review comprehensively analyzes epigenetic editing's technological maturation, provides a tiered assessment of AI's realized and anticipated contributions, critically evaluates the emerging clinical landscape, and identifies decisive unresolved challenges-including long-term stability in non-dividing cells, the lack of monitoring systems and intervention protocols needed to implement reversibility in clinical practice, and manufacturing access barriers. We argue that epigenetic editing is progressively establishing itself as a distinctive therapeutic modality characterized by durable efficacy and sequence-independent safety-reversibility as a theoretical safety mechanism has been validated preclinically, but the monitoring and intervention infrastructure required for its clinical implementation remains to be established. Long-term human validation remains the outstanding core question.
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