Aspirin promotes tenogenic differentiation of tendon stem cells and facilitates tendinopathy healing through regulating the GDF7/Smad1/5 signaling pathway

Tendinopathy is a common musculoskeletal system disorder in sports medicine, but regeneration ability of injury tendon is limited. Tendon stem cells (TSCs) have shown the definitive treatment evidence for tendinopathy and tendon injuries due to their tenogenesis capacity. Aspirin, as the representative of nonsteroidal anti-inflammatory drugs for its anti-inflammatory and analgestic actions, has been commonly used in treating tendinopathy in clinical, but the effect of aspirin on tenogenesis of TSCs is unclear. We hypothesized that aspirin could promote injury tendon healing through inducing TSCs tenogenesis. The aim of the present study is to make clear the effect of aspirin on TSC tenogenesis and tendon healing in tendinopathy, and thus provide new treatment evidence and strategy of aspirin for clinical practice. First, TSCs were treated with aspirin under tenogenic medium for 3, 7, and 14 days. Sirius Red staining was performed to observe the TSC differentiation. Furthermore, RNA sequencing was utilized to screen out different genes between the induction group and aspirin treatment group. Then, we identified the filtrated molecules and compared their effect on tenogenesis and related signaling pathway. At last, we constructed the tendinopathy model and compared biomechanical changes after aspirin intake. From the results, we found that aspirin promoted tenogenesis of TSCs. RNA sequencing showed that growth differentiation factor 6 (GDF6), GDF7, and GDF11 were upregulated in induction medium with the aspirin group compared with the induction medium group. GDF7 increased tenogenesis and activated Smad1/5 signaling. In addition, aspirin increased the expression of TNC, TNMD, and Scx and biomechanical properties of the injured tendon. In conclusion, aspirin promoted TSC tenogenesis and tendinopathy healing through GDF7/Smad1/5 signaling, and this provided new treatment evidence of aspirin for tendinopathy and tendon injuries.     

The Effects of Mechanical Loading on Tendons - An In Vivo and In Vitro Model Study

Mechanical loading constantly acts on tendons, and a better understanding of its effects on the tendons is essential to gain more insights into tendon patho-physiology. This study aims to investigate tendon mechanobiological responses through the use of mouse treadmill running as an in vivo model and mechanical stretching of tendon cells as an in vitro model. In the in vivo study, mice underwent moderate treadmill running (MTR) and intensive treadmill running (ITR) regimens. Treadmill running elevated the expression of mechanical growth factors (MGF) and enhanced the proliferative potential of tendon stem cells (TSCs) in both patellar and Achilles tendons. In both tendons, MTR upregulated tenocyte-related genes: collagen type I (Coll. I ∼10 fold) and tenomodulin (∼3–4 fold), but did not affect non-tenocyte-related genes: LPL (adipocyte), Sox9 (chondrocyte), Runx2 and Osterix (both osteocyte). However, ITR upregulated both tenocyte (Coll. I ∼7–11 fold; tenomodulin ∼4–5 fold) and non-tenocyte-related genes (∼3–8 fold). In the in vitro study, TSCs and tenocytes were stretched to 4% and 8% using a custom made mechanical loading system. Low mechanical stretching (4%) of TSCs from both patellar and Achilles tendons increased the expression of only the tenocyte-related genes (Coll. I ∼5–6 fold; tenomodulin ∼6–13 fold), but high mechanical stretching (8%) increased the expression of both tenocyte (Coll. I ∼28–50 fold; tenomodulin ∼14–48 fold) and non-tenocyte-related genes (2–5-fold). However, in tenocytes, non-tenocyte related gene expression was not altered by the application of either low or high mechanical stretching. These findings indicate that appropriate mechanical loading could be beneficial to tendons because of their potential to induce anabolic changes in tendon cells. However, while excessive mechanical loading caused anabolic changes in tendons, it also induced differentiation of TSCs into non-tenocytes, which may lead to the development of degenerative tendinopathy frequently seen in clinical settings.     

Sodium butyrate inhibits aerobic glycolysis of hepatocellular carcinoma cells via the c‐myc/hexokinase 2 pathway

Aerobic glycolysis is a well‐known hallmark of hepatocellular carcinoma (HCC). Hence, targeting the key enzymes of this pathway is considered a novel approach to HCC treatment. The effects of sodium butyrate (NaBu), a sodium salt of the short‐chain fatty acid butyrate, on aerobic glycolysis in HCC cells and the underlying mechanism are unknown. In the present study, data obtained from cell lines with mouse xenograft model revealed that NaBu inhibited aerobic glycolysis in the HCC cells in vivo and in vitro. NaBu induced apoptosis while inhibiting the proliferation of the HCC cells in vivo and in vitro. Furthermore, the compound inhibited the release of lactate and glucose consumption in the HCC cells in vitro and inhibited the production of lactate in vivo. The modulatory effects of NaBu on glycolysis, proliferation and apoptosis were related to its modulation of hexokinase 2 (HK2). NaBu downregulated HK2 expression via c‐myc signalling. The upregulation of glycolysis in the HCC cells induced by sorafenib was impeded by NaBu, thereby enhancing the anti‐HCC effect of sorafenib in vitro and in vivo. Thus, NaBu inhibits the expression of HK2 to downregulate aerobic glycolysis and the proliferation of HCC cells and induces their apoptosis via the c‐myc pathway.     

Extracorporeal Shock Wave Treatment (ESWT) Improves In Vitro Functional Activities of Ruptured Human Tendon-Derived Tenocytes

In vitro models of human tenocytes derived from healthy as well as from ruptured tendons were established, characterized and used at very early passage (P1) to evaluate the effects of Extracorporeal Shock Wave Treatment (ESWT). The molecular analysis of traditional tenocytic markers, including Scleraxis (Scx), Tenomodulin (Tnm), Tenascin-C (Tn-C) and Type I and III Collagens (Col I and Col III), permitted us to detect in our samples the simultaneous expression of all these genes and allowed us to compare their levels of expression in relationship to the source of the cells and treatments. In untreated conditions, higher molecular levels of Scx and Col I in tenocytes from pathological compared to healthy samples have been detected, suggesting – in the cells from injured tendon – the natural trigger of an early differentiation and repairing program, which depends by Scx and requires an increase in collagen expression. When ESWT (at the dose of 0.14 mJ/mm²) was applied to cultured tenocytes explanted from injured source, Scx and Col I were significantly diminished compared to healthy counterpart, indicating that such natural trigger maybe delayed by the treatment, in order to promote cellular repair. Herein, we show for the first time that ESWT enhances in vitro functional activities of ruptured tendon-derived tenocytes, such as proliferation and migration, which could probably contributes to tendon healing in vivo.     

The effects of some natural products compared to synthetic products on the metabolic activity,proliferation, viability,migration, and wound healing in sheep tenocytes

BackgroundTendinopathy or tendon injuries can affect many people, causing a huge impact on their movements and maintaining standing posture. Treatment options include physiotherapy, anti-inflammatory drugs, and alternative medicine. The use of physiotherapy or anti-inflammatory drugs may cause some side effects like pain and liver failure, respectively, therefore, alternative medicine will be a better choice.MethodTenocytes were isolated from sheep Achilles tendon and used in Alamar blue assay to assess the metabolic activity, proliferation, and viability of tenocytes over 24 hrs. and 48 hrs., using natural and synthetic products [i.e., olive oil, oleic acid, corn oil, Inula viscosa oil, Inula viscosa extract, Nigella sativa oil, naproxen sodium, and paracetamol and LED photobiomodulation]. Furthermore, tenocytes viability was assessed by FDA/PI stain. For migration and healing of a wound, the scratch assay was used.ResultsAlamar blue assay over 24 hrs. showed that Nigella sativa oil increased the metabolic activity, proliferation, and viability of tenocytes significantly, while Alamar blue over 48 hrs. showed that oleic acid, LED, and their combination increased these parameters for tenocytes significantly. Olive oil increased the viability of tenocytes significantly using FDA/PI stains. Scratch assay revealed that Inula viscosa oil, Inula viscosa extract, and paracetamol increased tenocyte migration and healing significantly.ConclusionNigella sativa oil, olive oil, oleic acid, Inula viscosa oil, and Inula viscosa extract may be used as an alternative therapy for tendinopathy with less side effects.     

Lipid storage and lipophagy regulates ferroptosis

The synthesis, storage, and degradation of lipids are highly regulated processes. Impaired lipid metabolism is implicated in inflammation and cell death. Although ferroptosis is a recently described form of regulated cell death driven by lipid peroxidation, the impact of lipid droplets on ferroptosis remains unidentified. Here, we demonstrate that lipophagy, the autophagic degradation of intracellular lipid droplets, promotes RSL3-induced ferroptotic cell death in hepatocytes. Lipid droplet accumulation is increased at the early stage but decreased at the late stage of ferroptosis in mouse or human hepatocytes. Importantly, either genetically enhancing TPD52-dependent lipid storage or blocking ATG5-and RAB7A-dependent lipid degradation prevents RSL3-induced lipid peroxidation and subsequent ferroptosis in vitro and in vivo. These studies support an antioxidant role for lipid droplets in cell death and suggest novel strategies for the inhibition of ferroptosis by targeting the lipophagy pathway.     

Experimental Diabetes Induces Structural,Inflammatory and Vascular Changes of Achilles Tendons

This study aims to demonstrate how the state of chronic hyperglycemia from experimental Diabetes Mellitus can influence the homeostatic imbalance of tendons and, consequently, lead to the characteristics of tendinopathy. Twenty animals were randomly divided into two experimental groups: control group, consisting of healthy rats and diabetic group constituted by rats induced to Diabetes Mellitus I. After twenty-four days of the induction of Diabetes type I, the Achilles tendon were removed for morphological evaluation, cellularity, number and cross-sectional area of blood vessel, immunohistochemistry for Collagen type I, VEGF and NF-κB nuclear localization sequence (NLS) and nitrate and nitrite level. The Achilles tendon thickness (µm/100g) of diabetic animals was significantly increased and, similarly, an increase was observed in the density of fibrocytes and mast cells in the tendons of the diabetic group. The average number of blood vessels per field, in peritendinous tissue, was statistically higher in the diabetic group 3.39 (2.98) vessels/field when compared to the control group 0.89 (1.68) vessels/field p = 0.001 and in the intratendinous region, it was observed that blood vessels were extremely rare in the control group 0.035 (0.18) vessels/field and were often present in the tendons of the diabetic group 0.89 (0.99) vessels/field. The immunohistochemistry analysis identified higher density of type 1 collagen and increased expression of VEGF as well as increased immunostaining for NFκB p50 NLS in the nucleus in Achilles tendon of the diabetic group when compared to the control group. Higher levels of nitrite/nitrate were observed in the experimental group induced to diabetes. We conclude that experimental DM induces notable structural, inflammatory and vascular changes in the Achilles tendon which are compatible with the process of chronic tendinopathy.     

Attenuation of SARS‐CoV‐2 replication and associated inflammation by concomitant targeting of viral and host cap 2'‐O‐ribose methyltransferases

The SARS‐CoV‐2 infection cycle is a multistage process that relies on functional interactions between the host and the pathogen. Here, we repurposed antiviral drugs against both viral and host enzymes to pharmaceutically block methylation of the viral RNA 2''‐O‐ribose cap needed for viral immune escape. We find that the host cap 2''‐O‐ribose methyltransferase MTr1 can compensate for loss of viral NSP16 methyltransferase in facilitating virus replication. Concomitant inhibition of MTr1 and NSP16 efficiently suppresses SARS‐CoV‐2 replication. Using in silico target‐based drug screening, we identify a bispecific MTr1/NSP16 inhibitor with anti‐SARS‐CoV‐2 activity in vitro and in vivo but with unfavorable side effects. We further show antiviral activity of inhibitors that target independent stages of the host SAM cycle providing the methyltransferase co‐substrate. In particular, the adenosylhomocysteinase (AHCY) inhibitor DZNep is antiviral in in vitro, in ex vivo, and in a mouse infection model and synergizes with existing COVID‐19 treatments. Moreover, DZNep exhibits a strong immunomodulatory effect curbing infection‐induced hyperinflammation and reduces lung fibrosis markers ex vivo. Thus, multispecific and metabolic MTase inhibitors constitute yet unexplored treatment options against COVID‐19.     

CoCrMo‐Nanoparticles induced peri‐implant osteolysis by promoting osteoblast ferroptosis via regulating Nrf2‐ARE signalling pathway

ObjectivesAseptic loosening (AL) is the most common reason of total hip arthroplasty (THA) failure and revision surgery. Osteolysis, caused by wear particles released from implant surfaces, has a vital role in AL. Although previous studies suggest that wear particles always lead to osteoblast programmed death in the process of AL, the specific mechanism remains incompletely understood and osteoblast ferroptosis maybe a new mechanism of AL.Materials and MethodsCoCrMo nanoparticles (CoNPs) were prepared to investigate the influence of ferroptosis in osteoblasts and calvaria resorption animal models. Periprosthetic osteolytic bone tissue was collected from patients who underwent AL after THA to verify osteoblast ferroptosis.ResultsOur study demonstrated that CoNPs induced significant ferroptosis in osteoblasts and particles induced osteolysis (PIO) animal models. Blocking ferroptosis with specific inhibitor Ferrostatin‐1 dramatically reduced particle‐induced ferroptosis in vitro. Moreover, in osteoblasts, CoNPs significantly downregulated the expression of Nrf2 (nuclear factor erythroid 2‐related factor 2), a core element in the antioxidant response. The overexpression of Nrf2 by siKeap1 or Nrf2 activator Oltipraz obviously upregulated antioxidant response elements (AREs) and suppressed ferroptosis in osteoblasts. Furthermore, in PIO animal models, the combined utilization of Ferrostatin‐1 and Oltipraz dramatically ameliorated ferroptosis and the severity of osteolysis.ConclusionsThese results indicate that CoNPs promote osteoblast ferroptosis by regulating the Nrf2‐ARE signalling pathway, which suggests a new mechanism underlying PIO and represents a potential therapeutic approach for AL.

CoCrMo‐Nanoparticles induced peri‐implant osteolysis by promoting osteoblast ferroptosis via regulating Nrf2‐ARE signalling pathway. Blocking ferroptosis with Ferrostatin‐1 and Oltipraz significantly ameliorated osteolysis induced by implanted particles, which suggests a new mechanism underlying particle‐induced osteolysis and represents a potential therapeutic approach for aseptic loosening.     

PPARα alleviates iron overload‐induced ferroptosis in mouse liver

Ferroptosis is an iron‐dependent form of non‐apoptotic cell death implicated in liver, brain, kidney, and heart pathology. How ferroptosis is regulated remains poorly understood. Here, we show that PPARα suppresses ferroptosis by promoting the expression of glutathione peroxidase 4 (Gpx4) and by inhibiting the expression of the plasma iron carrier TRF. PPARα directly induces Gpx4 expression by binding to a PPRE element within intron 3. PPARα knockout mice develop more severe iron accumulation and ferroptosis in the liver when fed a high‐iron diet than wild‐type mice. Ferrous iron (Fe²⁺) triggers ferroptosis via Fenton reactions and ROS accumulation. We further find that a rhodamine‐based "turn‐on" fluorescent probe(probe1) is suitable for the in vivo detection of Fe²⁺. Probe1 displays high selectivity towards Fe²⁺, and exhibits a stable response for Fe²⁺ with a concentration of 20 μM in tissue. Our data thus show that PPARα activation alleviates iron overload‐induced ferroptosis in mouse livers through Gpx4 and TRF, suggesting that PPARα may be a promising therapeutic target for drug discovery in ferroptosis‐related tissue injuries. Moreover, we identified a fluorescent probe that specifically labels ferrous ions and can be used to monitor Fe²⁺ in vivo.     

Ferulic acid (FA) protects human retinal pigment epithelial cells from H2O2‐induced oxidative injuries

The aim of present study is to investigate whether Ferulic acid (FA), a natural polyphenol antioxidant, was able to protect ARPE‑19 cells from hydrogen peroxide (H₂O₂)‑induced damage, and elucidate the underlying mechanisms. Our results revealed that FA pre‐treatment for 24 hours can reverse cell loss of H₂O₂‐induced ARPE‐19 cells via the promotion of cell proliferation and prevention of apoptosis, as evidenced by 5‐ethynyl‐2′‐deoxyuridine (EdU) incorporation and terminal deoxynucleotidyl transferase‐mediated dUTP nick end‐labelling (TUNEL) assay, respectively. Moreover, the addition of FA (5 mM) can decrease Bax and cleaved caspase‐3 protein expression, but increase Bcl‐2 protein expression in ARPE‐19 cells. Furthermore, H₂O₂‐induced oxidative stress in ARPE‐19 cells was significantly alleviated by FA, illustrated by reduced levels of ROS and MDA. In addition, the attenuated antioxidant enzymes activities of (SOD, CAT and GPX) and GSH level were reversed almost to the normal base level by the pre‐addition of FA for 24 hours. In all assays, FA itself did not exert any effect on the change of the above parameters. These novel findings indicated that FA effectively protected human ARPE‐19 cells from H₂O₂‐induced oxidative damage through its pro‐proliferation, anti‐apoptosis and antioxidant activity, suggesting that FA has a therapeutic potential in the prevention and treatment of AMD.     

Marked innervation but also signs of nerve degeneration in between the Achilles and plantaris tendons and presence of innervation within the plantaris tendon in midportion Achilles tendinopathy

Objectives:

The plantaris tendon is increasingly recognised as an important factor in midportion Achilles tendinopathy. Its innervation pattern is completely unknown.

Methods:

Plantaris tendons (n=56) and associated peritendinous tissue from 46 patients with midportion Achilles tendinopathy and where the plantaris tendon was closely related to the Achilles tendon were evaluated. Morphological evaluations and stainings for nerve markers [general (PGP9.5), sensory (CGRP), sympathetic (TH)], glutamate NMDA receptor and Schwann cells (S-100β) were made.

Results:

A marked innervation, as evidenced by evaluation for PGP9.5 reactions, occurred in the peritendinous tissue located between the plantaris and Achilles tendons. It contained sensory and to some extent sympathetic and NMDAR1-positive axons. There was also an innervation in the zones of connective tissue within the plantaris tendons. Interestingly, some of the nerve fascicles showed a partial lack of axonal reactions.

Conclusion:

New information on the innervation patterns for the plantaris tendon in situations with midportion Achilles tendinopathy has here been obtained. The peritendinous tissue was found to be markedly innervated and there was also innervation within the plantaris tendon. Furthermore, axonal degeneration is likely to occur. Both features should be further taken into account when considering the relationship between the nervous system and tendinopathy.     

GSTZ1 sensitizes hepatocellular carcinoma cells to sorafenib-induced ferroptosis via inhibition of NRF2/GPX4 axis

Increasing evidence supports that ferroptosis plays an important role in tumor growth inhibition. Sorafenib, originally identified as an inhibitor of multiple oncogenic kinases, has been shown to induce ferroptosis in hepatocellular carcinoma (HCC). However, some hepatoma cell lines are less sensitive to sorafenib-induced ferroptotic cell death. Glutathione S-transferase zeta 1 (GSTZ1), an enzyme in the catabolism of phenylalanine, suppresses the expression of the master regulator of cellular redox homeostasis nuclear factor erythroid 2-related factor 2 (NRF2). This study aimed to investigate the role and underlying molecular mechanisms of GSTZ1 in sorafenib-induced ferroptosis in HCC. GSTZ1 was significantly downregulated in sorafenib-resistant hepatoma cells. Mechanistically, GSTZ1 depletion enhanced the activation of the NRF2 pathway and increased the glutathione peroxidase 4 (GPX4) level, thereby suppressing sorafenib-induced ferroptosis. The combination of sorafenib and RSL3, a GPX4 inhibitor, significantly inhibited GSTZ1-deficient cell viability and promoted ferroptosis and increased ectopic iron and lipid peroxides. In vivo, the combination of sorafenib and RSL3 had a synergic therapeutic effect on HCC progression in Gstz1^−/− mice. In conclusion, this finding demonstrates that GSTZ1 enhanced sorafenib-induced ferroptosis by inhibiting the NRF2/GPX4 axis in HCC cells. Combination therapy of sorafenib and GPX4 inhibitor RSL3 may be a promising strategy in HCC treatment.Subject terms: Cancer therapeutic resistance, Cancer therapeutic resistance     

Sorafenib attenuates liver fibrosis by triggering hepatic stellate cell ferroptosis via HIF‐1α/SLC7A11 pathway

ObjectivesEvidences demonstrate that sorafenib alleviates liver fibrosis via inhibiting HSC activation and ECM accumulation. The underlying mechanism remains unclear. Ferroptosis, a novel programmed cell death, regulates diverse physiological/pathological processes. In this study, we aim to investigate the functional role of HSC ferroptosis in the anti‐fibrotic effect of sorafenib.Materials and MethodsThe effects of sorafenib on HSC ferroptosis and ECM expression were assessed in mouse model of liver fibrosis induced by CCl₄. In vitro, Fer‐1 and DFO were used to block ferroptosis and then explored the anti‐fibrotic effect of sorafenib by detecting α‐SMA, COL1α1 and fibronectin proteins. Finally, HIF‐1α siRNA, plasmid and stabilizers were applied to assess related signalling pathway.ResultsSorafenib attenuated liver injury and ECM accumulation in CCl₄‐induced fibrotic livers, accompanied by reduction of SLC7A11 and GPX4 proteins. In sorafenib‐treated HSC‐T6 cells, ferroptotic events (depletion of SLC7A11, GPX4 and GSH; accumulation iron, ROS and MDA) were discovered. Intriguingly, these ferroptotic events were not appeared in hepatocytes or macrophages. Sorafenib‐elicited HSC ferroptosis and ECM reduction were abrogated by Fer‐1 and DFO. Additionally, both HIF‐1α and SLC7A11 proteins were reduced in sorafenib‐treated HSC‐T6 cells. SLC7A11 was positively regulated by HIF‐1α, inactivation of HIF‐1α/SLC7A11 pathway was required for sorafenib‐induced HSC ferroptosis, and elevation of HIF‐1α could inhibit ferroptosis, ultimately limited the anti‐fibrotic effect.ConclusionsSorafenib triggers HSC ferroptosis via HIF‐1α/SLC7A11 signalling, which in turn attenuates liver injury and fibrosis.     

The mitochondrial Ca2+ uptake regulator,MICU1, is involved in cold stress‐induced ferroptosis

Ferroptosis has recently attracted much interest because of its relevance to human diseases such as cancer and ischemia‐reperfusion injury. We have reported that prolonged severe cold stress induces lipid peroxidation‐dependent ferroptosis, but the upstream mechanism remains unknown. Here, using genome‐wide CRISPR screening, we found that a mitochondrial Ca²⁺ uptake regulator, mitochondrial calcium uptake 1 (MICU1), is required for generating lipid peroxide and subsequent ferroptosis under cold stress. Furthermore, the gatekeeping activity of MICU1 through mitochondrial calcium uniporter (MCU) is suggested to be indispensable for cold stress‐induced ferroptosis. MICU1 is required for mitochondrial Ca²⁺ increase, hyperpolarization of the mitochondrial membrane potential (MMP), and subsequent lipid peroxidation under cold stress. Collectively, these findings suggest that the MICU1‐dependent mitochondrial Ca²⁺ homeostasis‐MMP hyperpolarization axis is involved in cold stress‐induced lipid peroxidation and ferroptosis.     

Creating an Animal Model of Tendinopathy by Inducing Chondrogenic Differentiation with Kartogenin

Previous animal studies have shown that long term rat treadmill running induces over-use tendinopathy, which manifests as proteoglycan accumulation and chondrocytes-like cells within the affected tendons. Creating this animal model of tendinopathy by long term treadmill running is however time-consuming, costly and may vary among animals. In this study, we used a new approach to develop an animal model of tendinopathy using kartogenin (KGN), a bio-compound that can stimulate endogenous stem/progenitor cells to differentiate into chondrocytes. KGN-beads were fabricated and implanted into rat Achilles tendons. Five weeks after implantation, chondrocytes and proteoglycan accumulation were found at the KGN implanted site. Vascularity as well as disorganization in collagen fibers were also present in the same site along with increased expression of the chondrocyte specific marker, collagen type II (Col. II). In vitro studies confirmed that KGN was released continuously from KGN-alginate in vivo beads and induced chondrogenic differentiation of tendon stem/progenitor cells (TSCs) suggesting that chondrogenesis after KGN-bead implantation into the rat tendons is likely due to the aberrant differentiation of TSCs into chondrocytes. Taken together, our results showed that KGN-alginate beads can be used to create a rat model of tendinopathy, which, at least in part, reproduces the features of over-use tendinopathy model created by long term treadmill running. This model is mechanistic (stem cell differentiation), highly reproducible and precise in creating localized tendinopathic lesions. It is expected that this model will be useful to evaluate the effects of various topical treatments such as NSAIDs and platelet-rich plasma (PRP) for the treatment of tendinopathy.     

Differential expression of Tenomodulin and Chondromodulin-1 at the insertion site of the tendon reflects a phenotypic transition of the resident cells

The insertion site of the tendon to the skeletal element is hypovascular and is one of the most common sites of dysfunction in the musculoskeletal system. However, the resident cells have been poorly defined due to a lack of a specific marker for tenocytes. We previously reported that Tenomodulin (Tnmd) and Chondromodulin-1 (Chm1) are homologous angiogenesis inhibitors and predominantly expressed in the avascular region of tendons and cartilage, respectively. In this study, we analyzed the expression of Tnmd, Chm1, alpha 1 chain of the type I collagen (Col1a1) and alpha 1 chain of the type II collagen (Col2a1) at the insertion site of the Achilles, patellar, or rotator cuff tendons of 1-week-old rabbits by in situ hybridization analysis. Tnmd was co-expressed with Col1a1 in tenocytes of these tendons, while Chm1 and Col2a1 were detected in chondrocytes of the hyaline cartilage. Interestingly, the cell population between Tnmd/Col1a1 positive tenocytes and Chm1/Col2a1 positive chondrocytes expressed Col1a1 but none of the other markers (Tnmd, Chm1, and Col2a1). Red blood cells were exclusively present at the interface between the tendon substance and cartilage in the insertion site of the Achilles tendon. Lack of Tnmd and Chm1 in this newly characterized cell population may allow the transitional zone between the poorly vascularized tendon and cartilage to establish the unique vascular pattern for blood supply.