Increasing the level of cytoskeletal protein Flightless I reduces adhesion formation in a murine digital flexor tendon model

Jessica E Jackson,Allison J Cowin,Zlatko Kopecki,Peter J Anderson

doi:10.1186/s13018-020-01889-y

Abstract

BackgroundSurgical repair of tendons is common, but function is often limited due to the formation of flexor tendon adhesions which reduce the mobility and use of the affected digit and hand. The severity of adhesion formation is dependent on numerous cellular processes many of which involve the actin cytoskeleton. Flightless I (Flii) is a highly conserved cytoskeletal protein, which has previously been identified as a potential target for improved healing of tendon injuries. Using human in vitro cell studies in conjunction with a murine model of partial laceration of the digital flexor tendon, we investigated the effect of modulating Flii levels on tenocyte function and formation of adhesions.MethodsHuman tenocyte proliferation and migration was determined using WST-1 and scratch wound assays following Flii knockdown by siRNA in vitro. Additionally, mice with normal and increased levels of Flii were subjected to a partial laceration of the digital flexor tendon in conjunction with a full tenotomy to immobilise the paw. Resulting adhesions were assessed using histology and immunohistochemistry for collagen I, III, TGF-β1and -β3ResultsFlii knockdown significantly reduced human tenocyte proliferation and migration in vitro. Increasing the expression of Flii significantly reduced digital tendon adhesion formation in vivo which was confirmed through significantly smaller adhesion scores based on collagen fibre orientation, thickness, proximity to other fibres and crimping. Reduced adhesion formation was accompanied with significantly decreased deposition of type I collagen and increased expression of TGF-β1 in vivo.ConclusionsThese findings suggest that increasing the level of Flii in an injured tendon may be beneficial for decreasing tendon adhesion formation.

Highlights

Surgical repair of tendons is common, but function is often limited due to the formation of flexor tendon adhesions which reduce the mobility and use of the affected digit and hand
The findings suggest that increasing Flightless I (Flii) levels may be beneficial for reducing tendon adhesion formation
We investigated the effect of modulating Flii levels on human tenocyte function and formation of tendon adhesions using a murine model of a partial laceration of the digital flexor tendon

Summary

Introduction

Surgical repair of tendons is common, but function is often limited due to the formation of flexor tendon adhesions which reduce the mobility and use of the affected digit and hand. The function of the restored tendon is highly dependent on the size and severity of adhesions that form during the healing process as a consequence of the significant inflammatory response that occurs after injury [3]. For a tendon to heal effectively with its function intact, there must be a re-establishment of strength and gliding functions with minimal adhesion formation [7]. In order for this to occur, a delicate balance must exist between intrinsic and extrinsic repair processes, allowing migration and proliferation of cells to the site of injury to allow effective tendon repair [7,8,9,10]. The actin cytoskeleton is important in facilitating the cellular migratory and proliferative processes and proteins that regulate the actin cytoskeleton are integral to the repair process [11,12,13]

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