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Bi-allelic Alterations in AEBP1 Lead to Defective Collagen Assembly and Connective Tissue Structure Resulting in a Variant of Ehlers-Danlos Syndrome.

ABSTRACT: AEBP1 encodes the aortic carboxypeptidase-like protein (ACLP) that associates with collagens in the extracellular matrix (ECM) and has several roles in development, tissue repair, and fibrosis. ACLP is expressed in bone, the vasculature, and dermal tissues and is involved in fibroblast proliferation and mesenchymal stem cell differentiation into collagen-producing cells. Aebp1-/- mice have abnormal, delayed wound repair correlating with defects in fibroblast proliferation. In this study, we describe four individuals from three unrelated families that presented with a unique constellation of clinical findings including joint laxity, redundant and hyperextensible skin, poor wound healing with abnormal scarring, osteoporosis, and other features reminiscent of Ehlers-Danlos syndrome (EDS). Analysis of skin biopsies revealed decreased dermal collagen with abnormal collagen fibrils that were ragged in appearance. Exome sequencing revealed compound heterozygous variants in AEBP1 (c.1470delC [p.Asn490_Met495delins(40)] and c.1743C>A [p.Cys581?]) in the first individual, a homozygous variant (c.1320_1326del [p.Arg440Serfs?3]) in the second individual, and a homozygous splice site variant (c.1630+1G>A) in two siblings from the third family. We show that ACLP enhances collagen polymerization and binds to several fibrillar collagens via its discoidin domain. These studies support the conclusion that bi-allelic pathogenic variants in AEBP1 are the cause of this autosomal-recessive EDS subtype.

SUBMITTER: Blackburn PR

PROVIDER: S-EPMC5985336 | biostudies-literature | 2018 Apr

REPOSITORIES: biostudies-literature

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Bi-allelic Alterations in AEBP1 Lead to Defective Collagen Assembly and Connective Tissue Structure Resulting in a Variant of Ehlers-Danlos Syndrome.

Blackburn Patrick R PR Xu Zhi Z Tumelty Kathleen E KE Zhao Rose W RW Monis William J WJ Harris Kimberly G KG Gass Jennifer M JM Cousin Margot A MA Boczek Nicole J NJ Mitkov Mario V MV Cappel Mark A MA Francomano Clair A CA Parisi Joseph E JE Klee Eric W EW Faqeih Eissa E Alkuraya Fowzan S FS Layne Matthew D MD McDonnell Nazli B NB Atwal Paldeep S PS

American journal of human genetics 20180329 4

AEBP1 encodes the aortic carboxypeptidase-like protein (ACLP) that associates with collagens in the extracellular matrix (ECM) and has several roles in development, tissue repair, and fibrosis. ACLP is expressed in bone, the vasculature, and dermal tissues and is involved in fibroblast proliferation and mesenchymal stem cell differentiation into collagen-producing cells. Aebp1<sup>-/-</sup> mice have abnormal, delayed wound repair correlating with defects in fibroblast proliferation. In this stu ...[more]

PMID: 29606302

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Project description:Ehlers-Danlos syndromes (EDS) represent a group of rare genetic disorders affecting connective tissues. Globally, approximately 1.5 million individuals suffer from EDS, with 10,000 reported cases in Canada alone. Understanding the histological properties of collagen in EDS has been challenging, but advanced techniques like atomic force microscopy (AFM) have opened up new possibilities for label-free skin imaging. This approach, which explores Type I collagen fibrils at the nanoscale, could potentially enhance EDS diagnosis and our knowledge of collagen type I-related connective tissue disorders. In the current study, we have employed AFM to examine ex-vivo skin biopsies from four individuals: one with classical EDS (cEDS), one with hypermobile EDS (hEDS), one with hEDS and Scleroderma (hEDS-Scleroderma), and one healthy control. Picrosirius red (PS) staining was used to highlight collagen differences in the samples. For each case, 14 images and 1400 force curves were obtained, with seven images and 700 force curves representing healthy collagen (PS-induced red staining) and the rest showcasing disrupted collagen (yellow staining). The results showed that PS staining was uniform throughout the control section, while cEDS and hEDS displayed localized areas of yellow staining. In the case of hEDS-Scleroderma, the yellow staining was widespread throughout the section. AFM images revealed irregular collagen fibrils in the disrupted, yellow-stained areas, contrasting with aligned and well-registered collagen fibrils in healthy, red-stained regions. Additionally, the study assessed the ability of non-AFM specialists to differentiate between healthy and disrupted collagen in AFM images, yielding substantial agreement among raters according to Fleiss's and Cohen's kappa scores (0.96 and 0.79±0.1, respectively). Biomechanical analysis revealed that normal healthy collagen exhibited a predominant population at 2.5 GPa. In contrast, EDS-affected collagen displayed subpopulations with lower compressive elastic modulus, indicating weaker collagen fibrils in EDS patients. Although these findings pertain to a limited number of cases, they offer valuable insights into the nanoscale collagen structure and biomechanics in individuals with EDS. Over time, these insights could be developed into specific biomarkers for the condition, improving diagnosis and treatment for EDS and related connective tissue disorders.

Project description:Ehlers-Danlos syndrome type IV, the vascular type of Ehlers-Danlos syndromes (EDS), is an inherited connective tissue disorder defined by characteristic facial features (acrogeria) in most patients, translucent skin with highly visible subcutaneous vessels on the trunk and lower back, easy bruising, and severe arterial, digestive and uterine complications, which are rarely, if at all, observed in the other forms of EDS. The estimated prevalence for all EDS varies between 1/10,000 and 1/25,000, EDS type IV representing approximately 5 to 10% of cases. The vascular complications may affect all anatomical areas, with a tendency toward arteries of large and medium diameter. Dissections of the vertebral arteries and the carotids in their extra- and intra-cranial segments (carotid-cavernous fistulae) are typical. There is a high risk of recurrent colonic perforations. Pregnancy increases the likelihood of a uterine or vascular rupture. EDS type IV is inherited as an autosomal dominant trait that is caused by mutations in the COL3A1 gene coding for type III procollagen. Diagnosis is based on clinical signs, non-invasive imaging, and the identification of a mutation of the COL3A1 gene. In childhood, coagulation disorders and Silverman's syndrome are the main differential diagnoses; in adulthood, the differential diagnosis includes other Ehlers-Danlos syndromes, Marfan syndrome and Loeys-Dietz syndrome. Prenatal diagnosis can be considered in families where the mutation is known. Choriocentesis or amniocentesis, however, may entail risk for the pregnant woman. In the absence of specific treatment for EDS type IV, medical intervention should be focused on symptomatic treatment and prophylactic measures. Arterial, digestive or uterine complications require immediate hospitalisation, observation in an intensive care unit. Invasive imaging techniques are contraindicated. Conservative approach is usually recommended when caring for a vascular complication in a patient suffering from EDS type IV. Surgery may, however, be required urgently to treat potentially fatal complications.

Dataset Information

Bi-allelic Alterations in AEBP1 Lead to Defective Collagen Assembly and Connective Tissue Structure Resulting in a Variant of Ehlers-Danlos Syndrome.

Publications

Bi-allelic Alterations in AEBP1 Lead to Defective Collagen Assembly and Connective Tissue Structure Resulting in a Variant of Ehlers-Danlos Syndrome.

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