Serpine1 Knockdown Enhances MMP Activity after Flexor Tendon Injury in Mice: Implications for Adhesions Therapy

Margaret A T Freeberg,Jacob G Kallenbach,Dominic W Malcolm,Anas Easa,Danielle S W Benoit,Hani A Awad,Youssef M Farhat,Mark R Buckley

doi:10.1038/s41598-018-24144-1

Margaret A T Freeberg, Jacob G Kallenbach + Show 6 more

Open Access

https://doi.org/10.1038/s41598-018-24144-1

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Abstract

Injuries to flexor tendons can be complicated by fibrotic adhesions, which severely impair the function of the hand. Adhesions have been associated with TGF-β1, which causes upregulation of PAI-1, a master suppressor of protease activity, including matrix metalloproteinases (MMP). In the present study, the effects of inhibiting PAI-1 in murine zone II flexor tendon injury were evaluated utilizing knockout (KO) mice and local nanoparticle-mediated siRNA delivery. In the PAI-1 KO murine model, reduced adherence of injured tendon to surrounding subcutaneous tissue and accelerated recovery of normal biomechanical properties compared to wild type controls were observed. Furthermore, MMP activity was significantly increased in the injured tendons of the PAI-1 KO mice, which could explain their reduced adhesions and accelerated remodeling. These data demonstrate that PAI-1 mediates fibrotic adhesions in injured flexor tendons by suppressing MMP activity. In vitro siRNA delivery to silence Serpine1 expression after treatment with TGF-β1 increased MMP activity. Nanoparticle-mediated delivery of siRNA targeting Serpine1 in injured flexor tendons significantly reduced target gene expression and subsequently increased MMP activity. Collectively, the data demonstrate that PAI-1 can be a druggable target for treating adhesions and accelerating the remodeling of flexor tendon injuries.

Highlights

Staining of normal human tendon (A and C) and fibrotic Dupuytren’s contracture tissue (B and D) against TGFβ1 and PAI-1
We observed that TGF-β1 and PAI-1 are abundant in the healing and adhesion tissue developed 14 days following zone II injury to the deep digital flexor tendon in the hind paw of C57Bl/6 J WT mice (Fig. 2)
Gliding space volume decreased significantly over time up to 7 dpi in both WT and PAI-1 KO mice before returning to uninjured levels, but there were no significant differences attributed to PAI-1 deficiency (Fig. 3D)

Summary

Introduction

Staining of normal human tendon (A and C) and fibrotic Dupuytren’s contracture tissue (B and D) against TGFβ1 and PAI-1. Induces downstream mediators of fibrosis, which may include novel therapeutic targets One such target is the protease suppressor, plasminogen activator inhibitor 1 or PAI-1. As a repressor of MMP activity, increased PAI-1 has been implicated in major organ fibrotic conditions including skin, liver, kidney, and lung[12,13,14,15,16,17,18] and strategies to abrogate its effects have demonstrated preclinical proof of efficacy[19,20]. We treated flexor tendon injuries in WT mice using a nanoparticle-mediated localized siRNA delivery strategy[21,22] to inhibit Serpine[1] gene expression in vivo and evaluate repair tissue remodeling

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