A Combination of Oxo-M and 4-PPBP as a potential regenerative therapeutics for tendon injury

Pharmacological modulation of gp130 signalling enhances Achilles tendon repair by regulating tenocyte migration and collagen synthesis via SHP2-mediated crosstalk of the ERK/AKT pathway

Tendon injuries typically display limited reparative capacity, often resulting in suboptimal outcomes and an elevated risk of recurrence or rupture. While cytokines of the IL-6 family are primarily recognised for their inflammatory properties, they also have multifaceted roles in tissue regeneration and repair. Despite this, studies examining the association between IL-6 family cytokines and tendon repair remained scarce. gp130, a type of glycoprotein, functions as a co-receptor for all cytokines in the IL-6 family. Its role is to assist in the transmission of signals following the binding of ligands to receptors. RCGD423 is a gp130 modulator. Phosphorylation of residue Y759 of gp130 recruits SHP2 and SOCS3 and inhibits activation of the STAT3 pathway. In our study, RCGD423 stimulated the formation of homologous dimers of gp130 and the phosphorylation of Y759 residues without the involvement of IL-6 and IL-6R. Subsequently, the phosphorylated residues recruited SHP2, activating the downstream ERK and AKT pathways. These mechanisms ultimately promoted the migration ability of tenocytes and matrix synthesis, especially collagen I. Moreover, RCGD423 also demonstrated significant improvements in collagen content, alignment of collagen fibres, and biological and biomechanical function in a rat Achilles tendon injury model. In summary, we demonstrated a promising gp130 modulator (RCGD423) that could potentially enhance tendon injury repair by redirecting downstream signalling of IL-6, suggesting its potential therapeutic application for tendon injuries.

Engineered Microenvironmental Cues from Fiber-Reinforced Hydrogel Composites Drive Tenogenesis and Aligned Collagen Deposition

Effective tendon regeneration following injury is contingent on appropriate differentiation of recruited cells and deposition of mature, aligned, collagenous extracellular matrix that can withstand the extreme mechanical demands placed on the tissue. As such, myriad biomaterial approaches have been explored to provide biochemical and physical cues that encourage tenogenesis and template aligned matrix deposition in lieu of dysfunctional scar tissue formation. Fiber-reinforced hydrogels present an ideal biomaterial system toward this end given their transdermal injectability, tunable stiffness over a range amenable to tenogenic differentiation of progenitors, and capacity for modular inclusion of biochemical cues. Here, tunable and modular, fiber-reinforced, synthetic hydrogels are employed to elucidate salient microenvironmental determinants of tenogenesis and aligned collagen deposition by tendon progenitor cells. Transforming growth factor β3 drives a cell fate switch toward pro-regenerative or pro-fibrotic phenotypes, which can be biased toward the former by culture in softer microenvironments or inhibition of the RhoA/ROCK activity. Furthermore, studies demonstrate that topographical anisotropy in fiber-reinforced hydrogels critically mediates the alignment of de novo collagen fibrils, reflecting native tendon architecture. These findings inform the design of cell-free, injectable, synthetic hydrogels for tendon tissue regeneration and, likely, that of a range of load-bearing connective tissues.

Circ_0005736 promotes tenogenic differentiation of tendon-derived stem cells through the miR-636/MAPK1 axis

BACKGROUND

Tendon-derived stem cells (TDSCs) are one of stem cells characterized by greater clonogenicity, tenogenesis, and proliferation capacity. Circ_0005736 has been shown to be decreased in Rotator cuff tendinopathy. Here, we investigated the function and relationship of circ_0005736 in TDSC tenogenic differentiation.

METHODS

Transforming growth factor β1 (TGF-β1) was used to induce the tenogenic differentiation in TDSC. Cell proliferation, invasion and migration were evaluated by Cell Counting Kit-8, 5-Ethynyl-2'-deoxyuridine, transwell, and wound healing assays, respectively. The detection of the levels of genes and proteins was performed by qRT-PCR and Western blot. The binding between miR-636 and circ_0005736 or MAPK1 (Mitogen-Activated Protein Kinase 1) was verified using dual-luciferase reporter assay and RIP assays.

RESULTS

TGF-β1 induced tenogenic differentiation by enhancing the production of tendon-specific markers and TDSC proliferation, invasion and migration. TGF-β1 treatment promoted circ_0005736 expression, knockdown of circ_0005736 abolished TGF-β1-induced tenogenic differentiation in TDSCs. Mechanistically, circ_0005736 acted as a sponge for miR-636 to up-regulate the expression of MAPK1, which was confirmed to be a target of miR-636 in TDSCs. Further rescue assays showed that inhibition of miR-636 could rescue circ_0005736 knockdown-induced suppression on TGF-β1-caused tenogenic differentiation in TDSCs. Moreover, forced expression of miR-636 abolished TGF-β1-caused tenogenic differentiation in TDSCs, which was rescued by MAPK1 up-regulation.

CONCLUSION

Circ_0005736 enhanced TGF-β1-induced tenogenic differentiation in TDSCs via increasing the production of tendon-specific markers and TDSC proliferation, invasion and migration through miR-636/MAPK1 axis.

The use of connective tissue growth factor mimics for flexor tendon repair

Intrasynovial flexor tendon lacerations of the hand are clinically problematic, typically requiring operative repair and extensive rehabilitation. The small-molecule connective tissue growth factor (CTGF) mimics, oxotremorine M (Oxo-M) and 4-PPBP maleate (4-PPBP), have been shown to improve tendon healing in small animal models by stimulating the expansion and differentiation of perivascular CD146+ cells. To enhance intrasynovial flexor tendon healing, small-molecule CTGF mimics were delivered to repaired canine flexor tendons via porous sutures. In vitro studies demonstrated that Oxo-M and 4-PPBP retained their bioactivity and could be released from porous sutures in a sustained manner. However, in vivo delivery of the CTGF mimics did not improve intrasynovial tendon healing. Histologic analyses and expression of tenogenic, extracellular matrix, inflammation, and remodeling genes showed similar outcomes in treated and untreated repairs across two time points. Although in vitro experiments revealed that CTGF mimics stimulated robust responses in extrasynovial tendon cells, there was no response in intrasynovial tendon cells, explaining the lack of in vivo effects. The results of the current study indicate that therapeutic strategies for tendon repair must carefully consider the environment and cellular makeup of the particular tendon for improving the healing response.

The combination of BMP12 and KY02111 enhances tendon differentiation in bone marrow-derived equine mesenchymal stromal cells (BM-eMSCs)

The Wingless and Int-1 (WNT) and bone morphogenic protein/growth differentiation factor (BMP/GDF) signalling pathways contribute significantly to the development of the musculoskeletal system. The mechanism by which they contribute is as follows: BMP/GDF signalling usually promotes tendon differentiation, whereas WNT signalling inhibits it. We hypothesised that inhibiting WNT and subsequently stimulating BMP signalling may enhance the tenogenic differentiation of stem cells. The objective of this study was to determine whether a combination of WNT inhibitor (KY02111) and BMP12/GDF7 protein could enhance the differentiation of bone marrow-derived equine mesenchymal stromal cells (BM-eMSCs) into tenocytes. Cells were cultured in five treatments: control, BMP12, and three different combinations of BMP12 and KY02111. The results indicated that a 1-day treatment with KY02111 followed by a 13-day treatment with BMP12 resulted in the highest tenogenic differentiation score in this experiment. The effect of KY02111 is dependent on the incubation time, with 1 day being better than 3 or 5 days. This combination increased tenogenic gene marker expression, including SCX, TNMD, DCN, and TNC, as well as COL1 protein expression. In conclusion, we propose that a combination of BMP12 and KY02111 can enhance the in vitro tenogenic differentiation of BM-eMSCs more than BMP12 alone. The findings of this study might be useful for improving tendon differentiation protocols for stem cell transplantation and application to tendon regeneration.

Oxo-M and 4-PPBP Delivery via Multi-Domain Peptide Hydrogel Toward Tendon Regeneration

We have recently identified novel small molecules, Oxo-M and 4-PPBP, which specifically stimulate endogenous tendon stem/progenitor cells (TSCs), leading to potential regenerative healing of fully transected tendons. Here, we investigated an injectable, multidomain peptide (MDP) hydrogel providing controlled delivery of the small molecules for regenerative tendon healing. We investigated the release kinetics of Oxo-M and 4-PPBP from MDP hydrogels and the effect of MDP-released small molecules on tenogenic differentiation of TSCs and in vivo tendon healing. In vitro, MDP showed a sustained release of Oxo-M and 4-PPBP and a slower degradation than fibrin. In addition, tenogenic gene expression was significantly increased in TSC with MDP-released Oxo-M and 4-PPBP as compared to the fibrin-released. Invivo, MDP releasing Oxo-M and 4-PPBP significantly improved tendon healing, likely associated with prolonged effects of Oxo-M and 4-PPBP on suppression of M1 macrophages and promotion of M2 macrophages. Comprehensive analyses including histomorphology, digital image processing, and modulus mapping with nanoindentation consistently suggested that Oxo-M and 4-PPBP delivered via MDP further improved tendon healing as compared to fibrin-based delivery. In conclusion, MDP delivered with Oxo-M and 4-PPBP may serve as an efficient regenerative therapeutic for in situ tendon regeneration and healing.

The glucagon-like peptide 1 receptor agonist Exendin-4 induces tenogenesis in human mesenchymal stem cells

Tendon injuries are common and account for up to 50% of musculoskeletal injuries in the United States. The poor healing nature of the tendon is attributed to poor vascularization and cellular composition. In the absence of FDA-approved growth factors for tendon repair, engineering strategies using bioactive factors, donor cells, and delivery matrices to promote tendon repair and regeneration are being explored. Growth factor alternatives in the form of small molecules, donor cells, and progenitors offer several advantages and enhance the tendon healing response. Small drug molecules and peptides offer stability over growth factors that are known to suffer from relatively short biological half-lives. The primary focus of this study was to assess the ability of the exendin-4 (Ex-4) peptide, a glucagon-like peptide 1 (GLP-1) receptor agonist, to induce tenocyte differentiation in bone marrow-derived human mesenchymal stem cells (hMSCs). We treated hMSCs with varied doses of Ex-4 in culture media to evaluate proliferation and tendonogenic differentiation. A 20 nM Ex-4 concentration was optimal for promoting cell proliferation and tendonogenic differentiation. Tendonogenic differentiation of hMSCs was evaluated via gene expression profile, immunofluorescence, and biochemical analyses. Collectively, the levels of tendon-related transcription factors (Mkx and Scx) and extracellular matrix (Col-I, Dcn, Bgn, and Tnc) genes and proteins were elevated compared to media without Ex-4 and other controls including insulin and IGF-1 treatments. The tendonogenic factor Ex-4 in conjunction with hMSCs appear to enhance tendon regeneration.

Characterization of Tendon-Derived Stem Cells and Rescue Tendon Injury

The natural healing ability of tendon is limited, and it cannot restore the native structure and function of tendon injuries. Tendon-derived stem cells (TDSCs) are a new type of pluripotent stem cells with multi-directional differentiation potential and are expected to become a promising cell-seed for the treatment of tendon injuries in the future. In this review, we outline the latest advances in the culture and identification of TDSCs. In addition, the influencing factors on the differentiation of TDSCs are discussed. Moreover, we aim to discuss recent studies to enhance TDSCs treatment of injured tendons. Finally, we identify the limitations of the current understanding of TDSCs biology, the main challenges of using their use, and potential therapeutic strategies to inform cell-based tendon repair.

Effect of local anesthetics on viability and differentiation of various adult stem/progenitor cells

BACKGROUND

Local anesthetics (LAs) are widely used to control pain during various clinical treatments. One of the side effects of LAs, cytotoxicity, has been investigated in various cells including stem/progenitor cells. However, our understanding of the effects of LAs on the differentiation capacity of stem/progenitor cells still remains limited. Therefore, a comparative study was conducted to investigate the effects of multiple LAs on viability and multi-lineage differentiation of stem/progenitor cells that originated from various adult tissues.

METHOD

Multiple types of stem/progenitor cells, including bone marrow mesenchymal stem/progenitor cells (MSCs), dental pulp stem/progenitor cells (DPSCs), periodontal ligament stem/progenitor cells (PDLSCs), and tendon-derived stem/progenitor cells, were either obtained from a commercial provider or isolated from adult human donors. Lidocaine (LD) and bupivacaine (BP) at various doses (1×, 0.75×, 0.5×, and 0.25× of each physiological dose) were applied to the different stem/progenitor cells for an hour, followed by induction of fibrogenic, chondrogenic, osteogenic, and adipogenic differentiation. Live/dead and MTT assays were performed at 24 h after the LD or BP treatment. At 2 weeks, qRT-PCR was conducted to evaluate the gene expressions associated with differentiation. After 4 weeks, multiple biochemical staining was performed to evaluate matrix deposition.

RESULTS

At 24 h after LD or BP treatment, 1× and 0.75× physiological doses of LD and BP showed significant cytotoxicity in all the tested adult stem/progenitor cells. At 0.5×, BP resulted in higher viability than the same dose LD, with variance between cell types. Overall, the gene expressions associated with fibrogenic, chondrogenic, osteogenic, and adipogenic differentiation were attenuated in LD or BP pre-treated stem/progenitor cells, with notable dose-effect and dependence on types. In contrast, certain doses of LD and/or BP were found to increase specific gene expression, depending on the cell types.

CONCLUSION

Our data suggest that LAs such as LD and BP affect not only the viability but also the differentiation capacity of adult stem/progenitor cells from various anatomical sites. This study sheds light on stem cell applications for tissue regeneration in which isolation and transplantation of stem cells frequently involve LA administration.

High-Strength Fiber-Reinforced Composite Hydrogel Scaffolds as Biosynthetic Tendon Graft Material

The development of suitable synthetic scaffolds for use as human tendon grafts to repair tendon ruptures remains a significant engineering challenge. Previous synthetic tendon grafts have demonstrated suboptimal tissue ingrowth and synovitis due to wear particles from fiber-to-fiber abrasion. In this study, we present a novel fiber-reinforced hydrogel (FRH) that mimics the hierarchical structure of the native human tendon for synthetic tendon graft material. Ultrahigh molecular weight polyethylene (UHMWPE) fibers were impregnated with either biosynthetic polyvinyl alcohol/gelatin hydrogel (FRH-PG) or with polyvinyl alcohol/gelatin + strontium-hardystonite (Sr-Ca₂ZnSi₂O₇, Sr-HT) composite hydrogel (FRH-PGS). The scaffolds were fabricated and assessed to evaluate their suitability for tendon graft applications. The microstructure of both FRH-PG and FRH-PGS showed successful impregnation of the hydrogel component, and the tendon scaffolds exhibited equilibrium water content of ∼70 wt %, similar to the values reported for native human tendon, compared to ∼50 wt % water content retained in unmodified UHMWPE fibers. The tensile strength of FRH-PG and FRH-PGS (77.0-81.8 MPa) matched the range of human Achilles' tendon tensile strengths reported in the literature. In vitro culture of rat tendon stem cells showed cell and tissue infiltration into both FRH-PG and FRH-PGS after 2 weeks, and the presence of Sr-HT ceramic particles influenced the expression of tenogenic markers. On the other hand, FRH-PG supported the proliferation of murine C2C12 myoblasts, whereas FRH-PGS seemingly did not support it under static culture conditions. In vivo implantation of FRH-PG and FRH-PGS scaffolds into full-thickness rat patellar tendon defects showed good collagenous tissue ingrowth into these scaffolds after 6 weeks. This study demonstrates the potential viability for our FRH-PG and FRH-PGS scaffolds to be used for off-the-shelf biosynthetic tendon graft material.

Upregulation of HSP72 attenuates tendon adhesion by regulating fibroblast proliferation and collagen production via blockade of the STAT3 signaling pathway

The proliferation of fibroblasts creates an environment favoring post-operative tendon adhesion, but targeted therapy of this pathology remains in its infancy. In this study, we explored the effect of heat shock protein 72 (HSP72), a major inducible member of the heat shock protein family that can protect cells against many cellular stresses including heat shock, on fibroblast proliferation in tendon adhesion, with its underlying mechanisms investigated. HSP72 expression was examined in an established rat model of tendon injury using RT-qPCR and immunoblot analysis. After conducting ectopic expression and depletion experiments in fibroblast NIH3T3 cells, we determined the effects of HSP72 on the expression of α-SMA and STAT3 signaling pathway-related genes, fibroblast proliferation, as well as collagen production. The mRNA (65.46%) and protein (63.65%) expression of HSP72 was downregulated in the rat model of tendon injury. The in vitro experiments revealed that overexpression of HSP72 inhibited fibroblast proliferation (42.57%) and collagen production (45.60%), as well as reducing α-SMA expression (42.49%) and the extent of STAT3 phosphorylation (55.46%). Moreover, we observed that HSP72 overexpression reduced inflammation as well as the number of inflammatory cell infiltration and fibroblasts in vivo. Furthermore, the inhibited extent of STAT3 phosphorylation contributed to the impaired fibroblast proliferation and collagen production evoked by upregulated HSP72. In summary, the present study unveils an inhibitory role of HSP72 in tendon adhesion via inactivation of the STAT3 signaling pathway. This finding may enable the development of new therapeutic strategies for the prevention against tendon adhesion.