A p.C217R Mutation in Fibulin-5 from Cutis Laxa Patients Is Associated with Incomplete Extracellular Matrix Formation in a Skin Equivalent Model

Abstract

Cutis laxa (CL) is a rare genodermatosis, which is clinically and genetically heterogeneous. It is characterized by redundant, loose, sagging, and inelastic skin. In a consanguineous family from Lebanon with autosomal-recessive transmission, we identified a homozygous missense mutation (c.649T --> C; p.C217R) in the fibulin-5 gene (FBLN5), which was, to our knowledge, previously unreported. Small skin biopsies were performed, which permitted isolation of skin fibroblasts harboring this FBLN5 mutation; they exhibited a deficit in cell growth. A CL skin equivalent (CL-SE) model compared with control SE was successfully developed to define the behavior of CL fibroblasts in a three-dimensional model. There was increased cell death and a global extracellular matrix deficiency in the dermis of this CL-SE model, and a low level of the main elastic fiber expression. There was no basement membrane evident at the ultrastructural level, and type-VII collagen could not be detected at the histological level. This model reproduced some defects of the extracellular matrix and highlighted other defects, which occurred at the time of the basement membrane formation, which were not evident in skin from patients. This CL-SE model could be adapted to screen for therapeutically active molecules.

Cutis laxa: A review

“…34 Patients with FBLN5 mutations commonly have supravalvular aortic stenosis. 24,29,30 In contrast, patients with FBLN4/EFEMP2 mutations do not have supravalvular aortic stenosis but can have aortic aneurysms. [31][32][33][34] Based on this distinct cardiovascular presentation, we recommend calling FBLN4/EFEMP2-related CL ''autosomal recessive cutis laxa type IA'' and calling FBLN5-related CL ''autosomal recessive cutis laxa type IB.…”

“…22,27,28 Etiology. Some cases of ARCL-I result from FBLN5 24,29,30 interacts with tropoelastin, fibrillin-1, and lysyl oxidase-like-1, [35][36][37] and facilitates the deposition of tropoelastin onto a scaffold of fibrillin-1 microfibrils. 4 Fibulin-4 is also required for mature elastic fiber formation, and can bind tropoelastin, lysyl oxidase, and fibrillin-1.…”

Fibulins: Multiple roles in matrix structures and tissue functions

“…In most subjects, the disease manifests as yellowish accumulations of drusen beneath the RPE and within the elastin-containing structure (known as Bruch membrane). In cutis laxa, the missense mutations in fibulin-5 gene S227P and C217R result in misfolding and decreased secretion and interactions of fibulin-5 with elastin and fibrillin-1 [77,78]. There is impaired elastic fiber development, suggesting that fibulin-5 is necessary for the proper elastic fiber formation [79].…”

Biophysical Characterisation of Fibulin-5 Proteins Associated with Disease

“…5,8 Mutations in the fibulin-5 gene (FBLN5) (GenBank accession number AJ133490) have been found in patients suffering from autosomal-recessive cutis laxa (CL) and age-related macular degeneration (AMD). [10][11][12][13][14][15][16][17] Genetic forms of CL, which may be dominant or recessive depending on the gene affected, are characterised by loose inelastic skin, developmental emphysema and major defects in the systemic and pulmonary arteries. 18 The underlying molecular defect is the disruption of elastic fibres due to impaired elastogenesis during late embryonic development.…”