Myodegeneration in EDA-A2 Transgenic Mice Is Prevented by XEDAR Deficiency

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Abstract
EDA-A1 and EDA-A2 are members of the tumor necrosis factor family of ligands. The products of alternative splicing of the ectodysplasin (EDA) gene, EDA-A1 and EDA-A2 differ by an insertion of two amino acids and bind to distinct receptors. The longer isoform, EDA-A1, binds to EDAR and plays an important role in sweat gland, hair, and tooth development; mutations in EDA, EDAR, or the downstream adaptor EDARADD cause hypohidrotic ectodermal dysplasia. EDA-A2 engages the receptor XEDAR, but its role in the whole organism is less clear. We have generated XEDAR-deficient mice by gene targeting and transgenic mice expressing secreted forms of EDA-A1 or EDA-A2 downstream of the skeletal muscle-specific myosin light-chain 2 or skin-specific keratin 5 promoter. Mice lacking XEDAR were indistinguishable from their wild-type littermates, but EDA-A2 transgenic mice exhibited multifocal myodegeneration. This phenotype was not observed in the absence of XEDAR. Skeletal muscle in EDA-A1 transgenic mice was unaffected, but their sebaceous glands were hypertrophied and hyperplastic, consistent with a role for EDA-A1 in the development of these structures. These data indicate that XEDAR-transduced signals are dispensable for development of ectoderm-derived organs but might play a role in skeletal muscle homeostasis.