Collagen V expression is crucial in regional development of the supraspinatus tendon

Abstract

Manipulations in cell culture and mouse models have demonstrated that reduction of collagen V results in altered fibril structure and matrix assembly. A tissue-dependent role for collagen V in determining mechanical function was recently established, but its role in determining regional properties has not been addressed. The objective of this study was to define the role(s) of collagen V expression in establishing the site-specific properties of the supraspinatus tendon. The insertion and midsubstance of tendons from wild type, heterozygous and tendon/ligament-specific null mice were assessed for crimp morphology, fibril morphology, cell morphology, as well as total collagen and pyridinoline cross-link (PYD) content. Fibril morphology was altered at the midsubstance of both groups with larger, but fewer, fibrils and no change in cell morphology or collagen compared to the wild type controls. In contrast, a significant disruption of fibril assembly was observed at the insertion site of the null group with the presence of structurally aberrant fibrils. Alterations were also present in cell density and PYD content. Altogether, these results demonstrate that collagen V plays a crucial role in determining region-specific differences in mouse supraspinatus tendon structure. © 2016 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 34:2154-2161, 2016.

Keywords: EDS; collagen; fibril; supraspinatus; tendon.

Figure 1

(A) Crimp frequency was decreased in the null tendons compared to both other groups at the insertion site. (B) Crimp amplitude was decreased in the heterozygous and null groups at the insertion site. No differences between groups were detected in crimp frequency or amplitude at the midsubstance.

Figure 2

Representative micrographs of fibrils from insertion site (top) and midsubstance (bottom) in wild type (left), heterozygous (middle) and null (right) tendons.

Figure 3

TEM analysis of fibril diameter distribution (n = 20/genotype) for (A/B) wild type, (C/D) heterozygous, and (E/F) null tendons for both insertion site (left column) and midsubstance (right column).

Figure 4

Quantitative analysis confirmed that (A) fibril diameter was larger in the heterozygous groups at both regions but only in the null group at the midsubstance. (B) Fibril density was decreased in both groups at both regions. (C) Fibril irregularity was quantified and was significantly increased in the null group at the insertion site.

Figure 5

(A) Cell density in tendon proper was slightly decreased (trend) at the insertion site of the null group compared to the wild type group. (B) There were no differences in cell shape between groups in either region.

Figure 6

Biochemical analysis of tendon proper and associated sheaths showed no differences in collagen content in either region.

Figure 7

Biochemical analysis of tendon proper and associated sheaths showed increased pyridinoline crosslinks in the heterozygous group at the insertion site and in the null group at both regions when compared to the wild type.