Ectodysplasin A (EDA), a trimeric ligand of the TNF super-family, is implicated in the em- bryonic development of ectodermal appendages such as hairs, teeth, sweat glands and other types of glands. Inactivating mutations in the EDA gene located on the X-chromosome cause X-linked hypohidrotic ectodermal dysplasia (XLHED), a disease characterized by the absence or malformation of structures derived from the ectoderm. Although EDA is synthetized as a membrane-bound protein, it can be cleaved and released in a soluble form, but it is not known whether soluble EDA can be detected.
Stimulation of EDA receptor (EDAR) during development in EDA-deficient animals can cor- rect the phenotype of EDA deficiency. It is however unknown whether EDAR stimulation in adult mice might affect exocrine glands in the nasal cavity, eyes and ears.
Objectives:
1. One aim was to develop a method for the detection of endogenous EDA.
2. A second aim was to localize exocrine glands in the nasal cavity, eyes and ears of wild- type and EDA-deficient adult mice and to evaluate the impact on these glands of a chronic, post-developmental stimulation of EDAR.
Methods:
1. A sandwich ELISA was used to detect EDA in sera of different species (human, foetal calf, mouse). Serum pre-depletions were performed to address the nature of the signal detected. For this purpose, EDA-binding reagents distinct from the pair of anti-EDA antibodies used in the sandwich ELISA were used.
2. Adult EDA-deficient mice were treated for 12 weeks by intraperitoneal injections of an EDAR agonist. Localization, size and morphology of exocrine glands in the nasal cavity, eye and ear were monitored in histology sections.
Results: Endogenous levels of circulating EDA were detected in human and bovine, but not in mouse sera. Pre-depletion on recombinant EDAR could remove about half of the signal, confirming the presence of receptor-binding competent EDA in the serum.
A variety of exocrine glands were localized by histology in the nasal cavity, eyes and ears of WT and EDA-deficient mice. Differences were noticed across genotypes, but no obvious effect of treatment on the presence or morphology of these glands was detected.
Importance: A clinical trial for the orphan disease XLHED based on neonatal administration of an EDAR agonist is currently on-going. In this context, the detection of endogenous EDA in serum is relevant. Indeed, this could be exploited to establish a diagnostic screen for EDA-deficiency.