Murine Model of the Ehlers-Danlos Syndrome: col5a1 HAPLOINSUFFICIENCY DISRUPTS COLLAGEN FIBRIL ASSEMBLY AT MULTIPLE STAGES

Richard J Wenstrup,Jane B Florer,Jeffrey M Davidson,Charlotte L Phillips,Brent J Pfeiffer,Diana W Menezes,Inna Chervoneva,David E Birk

doi:10.1074/jbc.m511528200

Abstract

The most commonly identified mutations causing Ehlers-Danlos syndrome (EDS) classic type result in haploinsufficiency of proalpha1(V) chains of type V collagen, a quantitatively minor collagen that co-assembles with type I collagen as heterotypic fibrils. To determine the role(s) of type I/V collagen interactions in fibrillogenesis and elucidate the mechanism whereby half-reduction of type V collagen causes abnormal connective tissue biogenesis observed in EDS, we analyzed mice heterozygous for a targeted inactivating mutation in col5a1 that caused 50% reduction in col5a1 mRNA and collagen V. Comparable with EDS patients, they had decreased aortic stiffness and tensile strength and hyperextensible skin with decreased tensile strength of both normal and wounded skin. In dermis, 50% fewer fibrils were assembled with two subpopulations: relatively normal fibrils with periodic immunoreactivity for collagen V where type I/V interactions regulate nucleation of fibril assembly and abnormal fibrils, lacking collagen V, generated by unregulated sequestration of type I collagen. The presence of the aberrant fibril subpopulation disrupts the normal linear and lateral growth mediated by fibril fusion. Therefore, abnormal fibril nucleation and dysfunctional fibril growth with potential disruption of cell-directed fibril organization leads to the connective tissue dysfunction associated with EDS.

Highlights

Type V collagen is a quantitatively minor fibril-forming collagen
Disruption of [␣1(V)]2 [␣2(V)] heterotrimer synthesis using a dominant negative approach (24) or utilizing fibroblasts from EDS patients with characterized mutations in COL5A1 have demonstrated that heterotypic collagen I/V interactions are involved in regulation of fibril diameter and fibril number in vitro (25)
Heterozygous animals are haploinsufficient for col5a1 with a 50% reduction in the col5a1 mRNA and tissue type V collagen compared with wild-type animals

Summary

Introduction

Type V collagen is a quantitatively minor fibril-forming collagen. Several isoforms of type V collagen exist, differing in the type and ratios of constituent ␣ chains, including heterotrimeric molecules containing type XI collagen chains. The most abundant and most widely distributed isoform of type V collagen is the [␣1(V)]2 ␣2(V)] heterotrimer that co-assembles with type I collagen as heterotypic fibrils (20). This isoform of type V collagen retains a non-collagenous, N-terminal domain that is present on the fibril surface, and this domain has been demonstrated to have regulatory functions (21–23). Mice heterozygous for a col5a1 mutation show a 50% reduction in type V collagen and recapitulate many of the clinical, biomechanical, morphologic, and biochemical features of the Ehlers-Danlos syndrome, classic type and are excellent models for the classic form of EDS for use in further studies in the regulation of collagen biogenesis and for potential therapeutic interventions. Structurally abnormal fibrils from dermis of col5a1-haploinsufficient mice provides insights into the mechanisms by which collagen fibrillogenesis is regulated and the mechanism of abnormal connective biosynthesis underlying the Ehlers-Danlos syndrome

Methods

Results

Conclusion