Auxiliary proteins that facilitate formation of collagen‐rich deposits in the posterior knee capsule in a rabbit‐based joint contracture model

Abstract

Post-traumatic joint contracture is a debilitating consequence of trauma or surgical procedures. It is associated with fibrosis that develops regardless of the nature of initial trauma and results from complex biological processes associated with inflammation and cell activation. These processes accelerate production of structural elements of the extracellular matrix, particularly collagen fibrils. Although the increased production of collagenous proteins has been demonstrated in tissues of contracted joints, researchers have not yet determined the complex protein machinery needed for the biosynthesis of collagen molecules and for their assembly into fibrils. Consequently, the purpose of our study was to investigate key enzymes and protein chaperones needed to produce collagen-rich deposits. Using a rabbit model of joint contracture, our biochemical and histological assays indicated changes in the expression patterns of heat shock protein 47 and the a-subunit of prolyl 4-hydroxylase, key proteins in processing nascent collagen chains. Moreover, our study shows that the abnormal organization of collagen fibrils in the posterior capsules of injured knees, rather than excessive formation of fibril-stabilizing cross-links, may be a key reason for observed changes in the mechanical characteristics of injured joints. This result sheds new light on pathomechanisms of joint contraction, and identifies potentially attractive anti-fibrotic targets. ß

Blocking collagen fibril formation in injured knees reduces flexion contracture in a rabbit model

“…All animal studies were approved by the TJU Institutional Animal Care and Use Committee. The following attributes make rabbits a relevant model to study post‐traumatic joint contracture: (i) the critical α2Ct epitope recognized by the ACA in rabbits is identical with its human counterpart and (ii) the rabbit model employed here adequately represents clinical features associated with post‐traumatic joint contractures in human patients …”

“…We employed an established rabbit model of post‐traumatic joint contracture . In brief, knee injury is caused by intra‐articular fracture and mechanical disruption of the posterior capsule (PC).…”

“…Following euthanasia, flexion contracture was measured using a custom‐made instrument (Test Resources, Inc., Shakopee, MN), as described (Fig. S3) . Flexion contracture was defined as the difference between the angles recorded at 0.2 Nm torque for the control limb and for the injured limb .…”

“…Since the PC is the main contributor to the knee contracture in the rabbit model employed here, the PCs were dissected from the limbs, as described (Fig. S4) . While one part of the PC was processed for histology, another part was processed for assays of collagen content and composition.…”

“…The fibrotic deposits in stiff joints consist mainly of fibril‐forming collagen I and collagen III . The formation of these collagen fibrils is needed for proper wound healing in response to joint injury, but excessive fibrillogenesis causes unwanted fibrosis and results in post‐traumatic joint contracture .…”