Pauline Po Yee Lui

Effect of In Vitro Passaging on the Stem Cell-Related Properties of Tendon-Derived Stem Cells—Implications in Tissue Engineering

This study aimed to compare clonogenicity, proliferation, stem cell-related marker expression, senescence, and differentiation potential of rat patellar tendon-derived stem cells (TDSCs) at early (P5), mid (P10), and late (P20, P30) passages. The clonogenicity of the cells was assessed by colony-forming assay and their proliferative potential was assessed by bromodeoxyuridine assay. The surface expression of CD90 and CD73 was assessed by flow cytometry. The cellular senescence was assessed by β-galactosidase activity. The adipogenic, chondrogenic, and osteogenic differentiation potentials of TDSCs were assessed by standard assays after induction. The mRNA expression of tendon-related markers, scleraxis (Scx) and tenomodulin (Tnmd), was measured by quantitative real-time reverse transcription-polymerase chain reaction. Both the colony numbers and proliferative potential of TDSCs increased with passaging. Concomitantly, there was significant upregulation of β-galactosidase activity with TDSC passaging. The subculture of TDSCs downregulated the expression of CD90 and CD73. Lipid droplets were formed in the early and mid passages of TDSCs upon adipogenic induction, but were absent in the late passages. The expression of peroxisome proliferator activator receptor gamma 2 (PPARγ2) and CCAAT/enhancer binding protein alpha (C/EBPα) in TDSCs after adipogenic induction decreased with passaging. Chondrogenesis, proteoglycan deposition, collagen type II protein expression, collagen type 2A1 (Col2AI), and aggrecan (Acan) mRNA expression were less in pellets formed with later passages of TDSCs after chondrogenic induction. The expression of Scx and Tnmd was lower in the late, compared with early and mid, passages of TDSCs. However, matrix mineralization and expression of alkaline phosphatase (Alpl) and osteocalcin (Bglap) mRNA after osteogenic induction increased with TDSC passaging. Researchers and clinicians should consider the changes of stem cell-related properties of TDSCs when multiplying them in vitro for tissue engineering.

Application of Tendon-Derived Stem Cell Sheet for the Promotion of Graft Healing in Anterior Cruciate Ligament Reconstruction

Background: Both osteointegration and remodeling of graft midsubstance (collectively called graft healing) are slow processes after anterior cruciate ligament (ACL) reconstruction. Tendon-derived stem cells (TDSCs) form a cell sheet after treatment with connective tissue growth factor (CTGF) and ascorbic acid, which exhibits higher tenogenic and maintains high chondro-osteogenic gene expression of TDSCs. No external scaffold is required for cell delivery. Hypothesis: Wrapping the TDSC sheet around the ACL graft would promote early graft healing in a rat model. Study Design: Controlled laboratory study. Methods: Green fluorescent protein (GFP) rat TDSCs were treated with connective tissue growth factor and ascorbic acid to promote cell sheet formation. Rats undergoing unilateral ACL reconstruction were divided into a control group and a TDSC group. The tendon graft was wrapped with the GFP-TDSC sheet before graft insertion in the TDSC group. At weeks 2, 6, and 12 after reconstruction, the samples were harvested for computed tomography imaging and histologic or biomechanical testing. The fate of the transplanted cell sheet was examined by immunohistochemical staining of GFP. Results: There were significantly higher tunnel bone mineral density (BMD) (42.3% increase, P = .047) and bone volume/total volume (BV/TV) (625% increase, P = .009) at the metaphyseal region of the tibial tunnel at week 2 and at the femoral tunnel at week 6 (BMD: 30.8% increase, P = .014; BV/TV: 100% increase, P = .014) in the TDSC group compared with the control group. Only the TDSC group showed a time-dependent increase in tunnel BMD (overall P = .038) and BV/TV (overall P = .015) at the epiphyseal region of the tibial tunnel. Semiquantitative image analysis showed better graft osteointegration and higher intra-articular graft integrity with lower cellularity and vascularity, better cell alignment, and higher collagen birefringence in the TDSC group. The ultimate load at week 2 (52.5% increase, P = .027) and stiffness at week 6 (62% increase, P = .008) were significantly higher in the TDSC group. Cells positive for GFP were observed in all samples in the TDSC group at week 2 but became reduced with time after reconstruction. Conclusion: The TDSC sheet improved early graft healing after ACL reconstruction in the rat model. Clinical Relevance: The TDSC sheet could potentially be used for the promotion of graft healing in ACL reconstruction.

Altered fate of tendon-derived stem cells isolated from a failed tendon-healing animal model of tendinopathy.

We hypothesized that altered fate of tendon-derived stem cells (TDSCs) might contribute to chondro-ossification and failed healing in the collagenase-induced (CI) tendon injury model. This study aimed to compare the yield, proliferative capacity, immunophenotypes, senescence, and differentiation potential of TDSCs isolated from healthy (HT) and CI tendons. TDSCs were isolated from CI and healthy Sprague-Dawley rat patellar tendons. The yield, proliferative capacity, immunophenotypes, and senescence of TDSCs (CI) and TDSCs (HT) were compared by colony-forming unit assay, BrdU assay, flow cytometry, and β-galactosidase activity assay, respectively. Their osteogenic and chondrogenic differentiation potentials and mRNA expression of tendon-related markers were compared using standard assays. More TDSCs, which showed a lower proliferative potential and a higher cellular senescence were present in the CI patellar tendons compared to HT tendons. There was a higher alkaline phosphatase activity and mineralization in TDSCs (CI) in both basal and osteogenic media. More chondrocyte-like cells and higher proteoglycan deposition, Sox9 and collagen type II expression were observed in TDSCs (CI) pellets upon chondrogenic induction. There was a higher protein expression of Sox9, but a lower mRNA expression of Col1a1, Scx, and Tnmd in TDSCs (CI) in a basal medium. In conclusion, TDSCs (CI) showed altered fate, a higher cellular senescence, but a lower proliferative capacity compared to TDSCs (HT), which might contribute to pathological chondro-ossification and failed tendon healing in this animal model.

In Vivo Identity of Tendon Stem Cells and the Roles of Stem Cells in Tendon Healing

We investigated the spatial distribution of stem cells in tendons and the roles of stem cells in early tendon repair. The relationship between tendon-derived stem cells (TDSCs) isolated in vitro and tendon stem cells in vivo was also explored. Iododeoxyuridine (IdU) label-retaining method was used for labeling stem cells in rat patellar tendons with and without injury. Co-localization of label-retaining cells (LRCs) with different markers was done by immunofluorescent staining. TDSCs were isolated from patellar tendon mid-substance after IdU pulsing, and the expression of different markers in fresh and expanded cells was done by immunofluorescent staining. More LRCs were found at the peritenon and tendon-bone junction compared with the mid-substance. Some LRCs at the peritenon were located at the perivascular niche. The LRC number and the expression of proliferative, tendon-related, pluripotency, and pericyte-related markers in LRCs in the window wound increased. Most of the freshly isolated TDSCs expressed IdU, and some TDSCs expressed pericyte-related markers, which were lost during expansion. Both freshly isolated and subcultured TDSCs expressed pluripotency markers, which were absent in LRCs in intact tendons. In conclusion, we identified LRCs at the peritenon, mid-substance, and tendon-bone junction. There were both vascular and non-vascular sources of LRCs at the peritenon, while the source of LRCs at the mid-substance was non-vascular. LRCs participated in tendon repair via migration, proliferation, activation for tenogenesis, and increased pluripotency. Some LRCs in the window wound were pericyte like. Most of the mid-substance TDSCs were LRCs. The pluripotency markers and pericyte-related marker in LRCs might be important for function after injury.

BMP-2 stimulated non-tenogenic differentiation and promoted proteoglycan deposition of tendon-derived stem cells (TDSCs) in vitro.

We hypothesized that BMP‐2 might induce non‐tenocyte differentiation and increase production of proteoglycans of tendon‐derived stem cells (TDSCs). This study investigated the effects of BMP‐2 on the differentiation and production of proteoglycans in TDSCs in vitro. Rat patellar TDSCs were treated without or with BMP‐2. The osteogenic, adipogenic, chondrogenic, and tenogenic differentiation of TDSCs were assessed by (1) Alizarin red‐S staining assay; (2) Oil Red‐O staining assay; (3) haematoxylin–eosin staining, Safranin‐O staining, immunohistochemical staining of Sox9, and collagen type II; and (4) qRT‐PCR analysis of lineage‐specific markers. The production of glycoaminoglycans (GAG) in the BMP‐2‐treated TDSCs was assessed by alcian blue staining. The mRNA expression of aggrecan (Acan), decorin (Dcn), biglycan (Bgn), and fibromodulin (Fmod) in TDSCs after BMP‐2 treatment was assessed by qRT‐PCR. BMP‐2 promoted the osteogenic, adipogenic, and chondrogenic differentiation but inhibited tenogenic marker expression of TDSCs. GAG production and Acan increased while Dcn, Bgn, and Fmod decreased in TDSCs after BMP‐2 stimulation. In conclusion, BMP‐2 promoted GAG deposition, aggrecan expression, and enhanced non‐tenocyte differentiation of TDSCs in vitro. The effect of BMP‐2 on TDSCs might provide insights into the histopathological changes of tendinopathy.

Scx-transduced tendon-derived stem cells (tdscs) promoted better tendon repair compared to mock-transduced cells in a rat patellar tendon window injury model.

We hypothesized that the transplantation of Scx-transduced tendon-derived stem cells (TDSCs) promoted better tendon repair compared to the transplantation of mock-transduced cells. This study thus aimed to investigate the effect of Scx transduction on the expression of lineage markers in TDSCs and the effect of the resulting cell line in the promotion of tendon repair. Rat non-GFP or GFP-TDSCs were transduced with Scx or empty lentiviral vector (Mock) and selected by blasticidin. The mRNA expressions of Scx and different lineage markers were examined by qRT-PCR. The effect of the transplantation of GFP-TDSC-Scx on tendon repair was then tested in a rat unilateral patellar tendon window injury model. The transplantation of GFP-TDSC-Mock and scaffold-only served as controls. At week 2, 4 and 8 post-transplantation, the repaired patellar tendon was harvested for ex vivo fluorescent imaging, vivaCT imaging, histology, immunohistochemistry and biomechanical test. GFP-TDSC-Scx consistently showed higher expressions of most of tendon- and cartilage- related markers compared to the GFP-TDSC-Mock. However, the effect of Scx transduction on the expressions of bone-related markers was inconclusive. The transplanted GFP-TDSCs could be detected in the window wound at week 2 but not at week 4. Ectopic mineralization was detected in some samples at week 8 but there was no difference among different groups. The GFP-TDSC-Scx group only statistically significantly improved tendon repair histologically and biomechanically compared to the Scaffold-only group and the GFP-TDSC-Mock group at the early stage of tendon repair. There was significant higher expression of collagen type I in the window wound in the GFP-TDSC-Scx group compared to the other two groups at week 2. The transplantation of GFP-TDSC-Scx promoted healing at the early stage of tendon repair in a rat patellar tendon window injury model.

Transplantation of tendon-derived stem cells pre-treated with connective tissue growth factor and ascorbic acid in vitro promoted better tendon repair in a patellar tendon window injury rat model

BACKGROUND AIMSnTreatment of tendon-derived stem cells (TDSCs) with connective tissue growth factor (CTGF) and ascorbic acid promoted their tenogenic differentiation. We investigated the effects of TDSCs pre-treated with CTGF and ascorbic acid on tendon repair in a patellar tendon window injury rat model.nnnMETHODSnGreen fluorescent protein-TDSCs (GFP-TDSCs) were pre-treated with or without CTGF and ascorbic acid for 2 weeks before transplantation. The patellar tendons of rats were injured and divided into three groups: fibrin glue-only group (control group), untreated and treated TDSC group. The rats were followed up until week 16.nnnRESULTSnThe treated TDSCs accelerated and enhanced the quality of tendon repair compared with untreated TDSCs up to week 8, which was better than that in the controls up to week 16 as shown by histology, ultrasound imaging and biomechanical test. The fibrils in the treated TDSC group showed better alignment and larger size compared with those in the control group at week 8 (P = 0.004). There was lower risk of ectopic mineralization after transplantation of treated or untreated TDSCs (all P ≤ 0.050). The transplanted cells proliferated and could be detected in the window wound up to weeks 2 to 4 and week 8 for the untreated and treated TDSC groups, respectively.nnnCONCLUSIONSnThe transplantation of TDSCs promoted tendon repair up to week 16, with CTGF and ascorbic acid pre-treatment showing the best results up to week 8. Pre-treatment of TDSCs with CTGF and ascorbic acid may be used to further enhance the rate and quality of tendon repair after injury.

Histopathological changes in tendinopathy—potential roles of BMPs?

The pathogenesis of tendinopathy remains unclear. Chondro-osteogenic BMPs such as BMP-2, BMP-4 and BMP-7 have been reported in clinical samples and animal models of tendinopathy. As chondrocyte-like cells and ossified deposits have been observed in both clinical samples and animal models of failed tendon healing tendinopathy, chondro-osteogenic BMPs might contribute to tissue metaplasia and other histopathological changes in tendinopathy. In this review I have summarized the current evidence supporting the roles of chondro-osteogenic BMPs in the histopathological changes of tendinopathy. The potential targets, effects and sources of these BMPs are discussed. I have also provided directions for future studies about the potential roles of BMPs in the pathogenesis of tendinopathy. Better understanding of the roles of these BMPs in the histopathological changes of tendinopathy could provide new options for the prevention and treatment of this disabling tendon disorder.

Expression of Wnt pathway mediators in metaplasic tissue in animal model and clinical samples of tendinopathy

OBJECTIVEnTissue metaplasia is observed in both ossified failed healing animal model and clinical samples of tendinopathy. The Wnt signalling pathway plays a vital role in pathological calcification. We hypothesized that the Wnt signalling pathway might contribute to tissue metaplasia and failed healing in tendinopathy. This study aimed to examine the spatial-temporal expression of Wnt pathway mediators in an ossified failed tendon healing animal model and clinical samples of tendinopathy. The effect of Wnt3a on the osteogenic differentiation of tendon-derived stem cells (TDSCs) was also examined.nnnMETHODSnOssified failed tendon healing was induced by the injection of collagenase into the patellar tendon of rats. At various times the tendons were harvested for immunohistochemical staining of Wnt3a, β-catenin, Lrp5 and Tcf1. Patellar tendon samples were obtained from 13 patients with patellar tendinopathy (11 unossified and 2 ossified) and 10 controls. Immunohistochemical staining of Wnt3a, β-catenin, Lrp5 and Tcf1 was similarly performed. Rat patellar TDSCs were treated with Wnt3a. The osteogenic differentiation of TDSCs was examined by ALP activity, alizarin red S staining and mRNA expression of osteogenic markers.nnnRESULTSnThere was increased expression of Wnt3a, β-catenin, Lrp5 and Tcf1 in the healing fibroblast-like cells, chondrocyte-like cells and ossified deposits in the animal model and in some clinical samples of tendinopathy. Wnt3a increased ALP activity, calcium nodule formation and expression of osteogenic markers in TDSCs.nnnCONCLUSIONnActivation of the Wnt signalling pathway and its effect on TDSCs might contribute to tissue metaplasia and failed healing in some cases of tendinopathy.

Local administration of alendronate reduced peri-tunnel bone loss and promoted graft-bone tunnel healing with minimal systemic effect on bone in contralateral knee

Continued systemic administration of alendronate was reported to reduce peri‐tunnel bone resorption and promoted graft‐bone tunnel healing at the early stage post‐anterior cruciate ligament (ACL) reconstruction. However, systemic increase in bone mineral density (BMD) in the contralateral intact knee was observed. We tested if single local administration of alendronate into the bone tunnel during ACL reconstruction could achieve similar benefits yet without the systemic effect on bone. Seventy‐two rats with unilateral ACL reconstruction were divided into three groups: saline, low‐dose (6u2009μg/kg) and mid‐dose (60u2009μg/kg) alendronate. For local administration, alendronate was applied to the bone tunnels for 2u2009min before graft insertion and repair. At weeks 2 and 6, the reconstructed complex was harvested for high‐resolution computed tomography (vivaCT) imaging followed by biomechanical test or histology. Our results showed that local administration of low‐dose alendronate showed comparable benefits on the reduction of peri‐tunnel bone loss, enhancement of bone tunnel mineralization, tunnel graft integrity, graft osteointegration and mechanical strength of the reconstructed complex at early stage post‐reconstruction, yet with minimal systemic effect on mineralized tissue at the contralateral intact knee. A single local administration of alendronate at the low‐dose therefore might be used to promote early tunnel graft healing post‐reconstruction.