Regulatory role of collagen V in establishing mechanical properties of tendons and ligaments is tissue dependent.

Patients with classic (type I) Ehlers-Danlos syndrome (EDS), characterized by heterozygous mutations in the Col5a1 and Col5a2 genes, exhibit connective tissue hyperelasticity and recurrent joint dislocations, indicating a potential regulatory role for collagen V in joint stabilizing soft tissues. This study asked whether the contribution of collagen V to the establishment of mechanical properties is tissue dependent. We mechanically tested four different tissues from wild type and targeted collagen V-null mice: the flexor digitorum longus (FDL) tendon, Achilles tendon (ACH), the anterior cruciate ligament (ACL), and the supraspinatus tendon (SST). Area was significantly reduced in the Col5a1(ΔTen/ΔTen) group in the FDL, ACH, and SST. Maximum load and stiffness were reduced in the Col5a1(ΔTen/ΔTen) group for all tissues. However, insertion site and midsubstance modulus were reduced only for the ACL and SST. This study provides evidence that the regulatory role of collagen V in extracellular matrix assembly is tissue dependent and that joint instability in classic EDS may be caused in part by insufficient mechanical properties of the tendons and ligaments surrounding each joint.