Expression of chondro‐osteogenic BMPs in ossified failed tendon healing model of tendinopathy

Abstract

Chondrocytes phenotype/markers were expressed in clinical samples of tendinopathy and calcifying tendinopathy. This study examined the spatial-temporal expression of chondro-osteogenic Bone Morphogenetic Proteins (BMPs), which might contribute to ectopic chondro-osteogenesis and failed healing process in tendinopathy. Collagenase was injected into patellar tendon of rats to induce ossified failed tendon healing. At week 2, 4, 8, 12, and 16, the patella tendon was harvested for immunohistochemical staining and analysis of BMP-2/ 4/7. BMP-4/7 showed similar expression patterns, which was different from BMP-2. The expression of BMP-2 in the tendon matrix increased at week 2 and was reduced to nearly undetectable level afterwards except at the chondro-ossification sites. However, the expression of BMP-4/7 in the healing tendon fibroblast-like cells and matrix increased at week 2, reduced at week 4 and 8 and increased again at week 12 and 16, consistent with transient healing at week 8 in this animal model. There was increasing strong expression of BMP-4/7 in the chondrocyte-like cells in the un-ossified and ossified areas from week 8-16. BMP-4/7, besides BMP-2, might also contribute to ectopic chondro-osteogenesis and failed healing in tendon injuries. BMP-4/7, but not BMP-2, might be involved in regulating late events in ossified failed tendon healing. Keywords: tendinopathy; failed tendon healing; BMP-2/4/7; ectopic chondrogenesis; ectopic ossificationChronic tendinopathy refers to a broad spectrum of pathological conditions in tendons and their insertion, with symptoms including activity-related chronic pain, which is prevalent among athletes and sedentary subjects. Despite its prevalence, its underlying pathogenesis is poorly understood and treatment is usually symptomatic. Failed healing was suggested as the pathological mechanism of tendinopathy. 1 Chondrocyte phenotype/ markers were expressed in clinical samples of tendinopathy and calcifying tendinopathy. 2,3 We reported the presence of chondrocyte phenotype and ectopic ossification in our collagenase-induced failed tendon healing model. 4 We have shown this collagenase animal model to reproduce many key histopathological features of clinical tendinopathy and can be used to study the ossified failed healing process in tendinopathy. 5 We further reported the expression of bone morphogenetic protein-2 (BMP-2) protein, an osteogenic growth factor, around the chondrogenic and ossifying sites in the same animal model, 6 suggesting that BMP-2 might be involved in the pathogenesis. This was further supported by ectopic over-expression of BMPs in the subacromial bursa of patients with chronic degeneration of the rotator cuff. 7 Our result also showed that repetitive cyclic loading could increase the expression of BMP-2 in tendonderived stem cells (TDSCs) and that BMP-2 could induce the osteogenic differentiation of TDSCs in vitro. 8 To date, more than 20 BMPs have been identified and many of them were chondro-osteogenic. We hypothesized that other chondro-...

Higher BMP/Smad sensitivity of tendon-derived stem cells (TDSCs) isolated from the collagenase-induced tendon injury model: possible mechanism for their altered fate in vitro

“…No expression of BMP-2, BMP-4 and BMP-7 was observed in the intact tendons [9,11]. By exploring the mechanisms of the altered fate of TDSCs (CI), the present study added further support for the role of BMPs and the BMP/Smad signaling pathway in the pathogenesis of tendinopathy.…”

“…There was ectopic expression of BMP-2, BMP-4 and BMP-7 in clinical samples of tendinopathy [9,10] and collagenase-induced tendon injury rat model [11]. No expression of BMP-2, BMP-4 and BMP-7 was observed in the intact tendons [9,11].…”

“…Ectopic expression of BMP-2, -4 and -7 were observed in clinical samples of tendinopathy [9,10] and collagenase-induced (CI) tendon injury rat model which showed failed healing and ectopic chondro-ossification in tendons [11]. These BMPs were reported to promote osteogenic, chondrogenic and adipogenic differentiation of mesenchymal stem cells (MSCs) including tendon-derived stem cells (TDSCs) isolated from healthy tendons in vitro [12-16].…”

Biology and mechano‐response of tendon cells: Progress overview and perspectives

“…40 Indeed, TSPCs isolated from the biglycan and fibromodulin double knock-out animal model displayed higher sensitivity to BMP-2 signaling. 3 Besides, healing tendon cells in animal models and clinical samples of tendinopathy displayed an increase in the expression of chondroosteogenic BMPs and Wnt3a, chondrocyte-like cells and ossified deposits leading to “in-tendon ossification.” 3; 41; 42 These findings provide the first insight into the role the molecular niche in the appropriate maintenance of TPSCs. The importance of tendon ECM in the maintenance of TSPC stemness was further supported by a recent study showing that rabbit TDSCs cultured on decellularized tendon matrix proliferated at a higher rate and had better stemness properties than TDSCs cultured on plastic tissue culture surface.…”

Identity of tendon stem cells – how much do we know?

“…TDSCs isolated from the biglycan and fibromodulin double knock-out animal model displayed higher sensitivity to BMP-2 signalling [1]. There was increased expression of chondro-osteogenic BMPs and Wnt3a in the healing tendon cells, chondrocyte-like cells and ossified deposits in the animal model and clinical samples of tendinopathy [15, 59, 60]. Wnt3a promoted the osteogenic differentiation of TDSCs in vitro 60, whereas BMP-2 promoted non-tenocyte differentiation and proteoglycan deposition of TDSCs in vitro [55, 61].…”