Welander Distal Myopathy (WDM) Cell Models for Research

Welander Distal Myopathy (WDM) is a rare autosomal dominant disorder primarily affecting the hands, with onset typically in the fourth to sixth decade. Prevalence is estimated at 1-9 per 1,000,000 in Scandinavian populations, but exact global incidence is unknown due to underdiagnosis. The disease is progressive, leading to distal muscle weakness and wasting, but life expectancy is generally normal. There is no cure; management focuses on symptomatic relief and physical therapy. Research is crucial to understand the molecular mechanisms and develop targeted therapies.

WDM is an ideal model for studying distal myopathies and the role of RNA-binding proteins in muscle degeneration. The disease is linked to mutations in the TIA1 gene, which encodes a stress granule protein. This provides a clear genetic target for gene editing. Public datasets, such as those from NCBI and ClinVar, offer mutation information. Open questions include the precise mechanism of TIA1 toxicity and the role of stress granules in muscle pathology. Gene-edited cell models can help answer these questions.

• • The primary pathway involves TIA1 mutations leading to aberrant stress granule dynamics. Steps include:
• • TIA1 mutation (e.g., p.Glu384Lys) increases the propensity of TIA1 to aggregate.
• • Aggregated TIA1 sequesters RNA and proteins, disrupting stress granule assembly/disassembly.
• • This leads to chronic stress granule formation, impairing cellular stress response.
• • Ultimately, muscle cells undergo apoptosis or necrosis, causing distal muscle wasting.

Additionally, impaired autophagy and proteostasis may contribute to the pathology.

Data from ClinVar and NCBI Gene.

• • Key networks involved:
• • Stress granule signaling: TIA1, G3BP1, eIF2α, and other RNA-binding proteins.
• • Autophagy pathway: mTOR, ULK1, LC3, p62.
• • Apoptosis: Caspase-3, Bcl-2 family.
• • Inflammatory response: NF-κB, TNF-α.

These networks interact to mediate muscle degeneration.

Organoids derived from patient iPSCs can recapitulate muscle development and are useful for studying TIA1 mutations in a 3D context.

• • Transgenic mice expressing human TIA1 with the p.Glu384Lys mutation.
• • Knock-in mice with the equivalent mutation in the endogenous Tia1 gene.
• • Induced models using AAV-mediated delivery of mutant TIA1 to muscle.
• • PDX models are not typical for WDM due to its non-cancerous nature.

CRISPR-Cas9 technology enables the creation of isogenic cell lines with specific TIA1 mutations. For example, a knock-in line with the p.Glu384Lys mutation in a wild-type myoblast background can be used to study the disease mechanism. Conversely, a knockout line lacking TIA1 can help elucidate its normal function. These sequence-verified models are commercially available and accelerate research by providing consistent, reproducible systems. They are essential for drug screening and functional studies.

Knockout and knock-in lines are used to validate the role of TIA1 in WDM. For example, knocking out TIA1 in myoblasts can reveal its impact on stress granule formation and cell viability. Knock-in lines with patient-specific mutations allow for the study of mutant protein behavior in a controlled environment.

Isogenic pairs (wild-type vs. mutant) are used in high-throughput screens to identify compounds that rescue the mutant phenotype. These models can also be used to study drug resistance mechanisms, although WDM is not a cancer, so resistance is less relevant. However, they are valuable for testing potential therapeutics.

CRISPR synthetic lethality screens can identify genes that are essential in mutant TIA1 cells but not in wild-type cells. This can reveal novel therapeutic targets and biomarkers for disease progression.