Cystic fibrosis transmembrane conductance regulator mediates tenogenic differentiation of tendon-derived stem cells and tendon repair: accelerating tendon injury healing by intervening in its downstream signaling

Nanoparticle-Driven Tendon Repair: Role of Vasoactive Intestinal Peptide in Immune Modulation and Stem Cell Enhancement

Tendon repair remains challenging owing to the limited capacity for endogenous repair. Vasoactive intestinal peptide (VIP) promotes bone tissue regeneration; however, its role in tendon repair remains unclear. In the present study, we demonstrated that VIP stimulated M2 polarization of macrophages and facilitated tendon regeneration by regulating immune homeostasis and maintaining the function of tendon stem/progenitor cells (TSPCs). Additionally, we established GelMa-loaded VIP@PLGA@ZIF-8 (VPZ) nanoparticles (VPZG) to enable the sustained and localized release of VIP at the site of patellar tendon injury in SD rats. The results of the in vitro experiments demonstrated that VPZG regulated the homeostasis of macrophage polarization by downregulating the NF-κB axis. VPZG also promoted efferocytosis and suppressed the release of proinflammatory factors. Additionally, VPZG enhanced the tenogenic differentiation of TSPCs when cocultured with macrophages. In vivo, we implanted VPZG at the site of patellar tendon injury, where it released VIP sustainably and slowly to promote tendon regeneration. This effect was achieved through the downregulation of the expression levels of various inflammatory factors, as well as the regulation of local immune homeostasis. In conclusion, our results demonstrated that VPZG facilitated tendon injury repair by regulating immune homeostasis and enhancing TSPC function. These findings suggest that VPZG is a promising avenue for the clinical improvement of tendon injury treatment.

Role of tendon-derived stem cells in tendon and ligament repair: focus on tissue engineer

This review offered a comprehensive analysis of tendon and ligament injuries, emphasizing the crucial role of tendon-derived stem cells (TDSCs) in tissue engineering as a potential solution for these challenging medical conditions. Tendon and ligament injuries, prevalent among athletes, the elderly, and laborers, often result in long-term disability and reduced quality of life due to the poor intrinsic healing capacity of these avascular structures. The formation of biomechanically inferior scar tissue and a high rate of reinjury underscore the need for innovative approaches to enhance and guide the regenerative process. This review delved into the complexities of tendon and ligament structure and function, types of injuries and their impacts, and the limitations of the natural repair process. It particularly focused on the role of TDSCs within the context of tissue engineering. TDSCs, with their ability to differentiate into tenocytes, are explored in various applications, including biocompatible scaffolds for cell tracking, co-culture systems to optimize tendon-bone healing, and graft healing techniques. The review also addressed the challenges of immunoreactivity post-transplantation, the importance of pre-treating TDSCs, and the potential of hydrogels and decellularized matrices in supporting tendon regeneration. It concluded by highlighting the essential roles of mechanical and molecular stimuli in TDSC differentiation and the current challenges in the field, paving the way for future research directions.

Metabolic Syndrome and Tendon Disease: A Comprehensive Review

Metabolic syndrome (MS) is a multifaceted pathological condition characterized by the atypical accumulation of various metabolic components such as central obesity or excess weight, hyperlipidemia, low-density lipoprotein (LDL), hypertension, and insulin resistance. Recently, MS has been recognized as a notable contributor to heart and circulatory diseases. In addition, with increasing research, the impact of MS on tendon repair and disease has gradually emerged. Recent studies have investigated the relationship between tendon healing and diseases such as diabetes, dyslipidemia, obesity, and other metabolic disorders. However, diabetes mellitus (DM), hypercholesterolemia, obesity, and various metabolic disorders often coexist and together constitute MS. At present, insulin resistance is considered the major pathological mechanism underlying MS, central obesity is regarded as the predominant factor responsible for it, and dyslipidemia and other metabolic diseases are known as secondary contributors to MS. This review aims to evaluate the current literature regarding the impact of various pathological conditions in MS on tendon recovery and illness, and to present a comprehensive overview of the effects of MS on tendon recovery and diseases, along with the accompanying molecular mechanisms.

TRIM54 alleviates inflammation and apoptosis by stabilizing YOD1 in rat tendon-derived stem cells

Tendinopathy is a disorder of musculoskeletal system that primarily affects athletes and the elderly. Current treatment options are generally comprised of various exercise and loading programs, therapeutic modalities, and surgical interventions and are limited to pain management. This study is to understand the role of TRIM54 (tripartite motif containing 54) in tendonitis through in vitro modeling with tendon-derived stem cells (TDSCs) and in vivo using rat tendon injury model. Initially, we observed that TRIM54 overexpression in TDSCs model increased stemness and decreased apoptosis. Additionally, it rescued cells from tumor necrosis factor α-induced inflammation, migration, and tenogenic differentiation. Further, through immunoprecipitation studies, we identified that TRIM54 regulates inflammation in TDSCs by binding to and ubiquitinating YOD1. Further, overexpression of TRIM54 improved the histopathological score of tendon injury as well as the failure load, stiffness, and young modulus in vivo. These results indicated that TRIM54 played a critical role in reducing the effects of tendon injury. Consequently, these results shed light on potential therapeutic alternatives for treating tendinopathy.

Enhancing cartilage repair with optimized supramolecular hydrogel-based scaffold and pulsed electromagnetic field

Functional tissue engineering strategies provide innovative approach for the repair and regeneration of damaged cartilage. Hydrogel is widely used because it could provide rapid defect filling and proper structure support, and is biocompatible for cell aggregation and matrix deposition. Efforts have been made to seek suitable scaffolds for cartilage tissue engineering. Here Alg-DA/Ac-β-CD/gelatin hydrogel was designed with the features of physical and chemical multiple crosslinking and self-healing properties. Gelation time, swelling ratio, biodegradability and biocompatibility of the hydrogels were systematically characterized, and the injectable self-healing adhesive hydrogel were demonstrated to exhibit ideal properties for cartilage repair. Furthermore, the new hydrogel design introduces a pre-gel state before photo-crosslinking, where increased viscosity and decreased fluidity allow the gel to remain in a semi-solid condition. This granted multiple administration routes to the hydrogels, which brings hydrogels the ability to adapt to complex clinical situations. Pulsed electromagnetic fields (PEMF) have been recognized as a promising solution to various health problems owing to their noninvasive properties and therapeutic potentials. PEMF treatment offers a better clinical outcome with fewer, if any, side effects, and wildly used in musculoskeletal tissue repair. Thereby we propose PEMF as an effective biophysical stimulation to be 4th key element in cartilage tissue engineering. In this study, the as-prepared Alg-DA/Ac-β-CD/gelatin hydrogels were utilized in the rat osteochondral defect model, and the potential application of PEMF in cartilage tissue engineering were investigated. PEMF treatment were proven to enhance the quality of engineered chondrogenic constructs in vitro, and facilitate chondrogenesis and cartilage repair in vivo. All of the results suggested that with the injectable self-healing adhesive hydrogel and PEMF treatment, this newly proposed tissue engineering strategy revealed superior clinical potential for cartilage defect treatment.

Cyclic mechanical stretch regulates the AMPK/Egr1 pathway in tenocytes via Ca2+-mediated mechanosensing

PURPOSE

Mechanical stimuli are essential for the maintenance of tendon tissue homeostasis. The study aims to elucidate the mechanobiological mechanisms underlying the maintenance of tenocyte homeostasis by cyclic mechanical stretch under high-glucose (HG) condition.

MATERIALS AND METHODS

Primary tenocytes were isolated from rat Achilles tendon and 2D-cultured under HG condition. The in vitro effects of a single bout, 2-h cyclic biaxial stretch session (1 Hz, 8%) on primary rat tenocytes were explored through Flexcell system. Cell viability, tenogenic gene expression, intracellular calcium concentration, focal adhesion kinase (FAK) expression, and signaling pathway activation were analyzed in tenocytes with or without mechanical stretch.

RESULTS

Mechanical stretch increased tenocyte proliferation and upregulated early growth response protein 1 (Egr1) expression. An increase in intracellular calcium was observed after 30 min of stretching. Mechanical stretch phosphorylated FAK, calmodulin-dependent protein kinase kinase 2 (CaMKK2), and 5' adenosine monophosphate-activated protein kinase (AMPK) in a time-dependent manner, and these effects were abrogated after blocking intracellular calcium. Inhibition of FAK, CaMKK2, and AMPK downregulated the expression of Egr1. In addition, mechanical stretch reinforced cytoskeletal organization via calcium (Ca2+)/FAK signaling.

CONCLUSIONS

Our study demonstrated that mechanical stretch-induced calcium influx activated CaMKK2/AMPK signaling and FAK-cytoskeleton reorganization, thereby promoting the expression of Egr1, which may help maintain tendon cell characteristics and homeostasis in the context of diabetic tendinopathy.

Challenges and perspectives of tendon-derived cell therapy for tendinopathy: from bench to bedside

Tendon is composed of dense fibrous connective tissues, connecting muscle at the myotendinous junction (MTJ) to bone at the enthesis and allowing mechanical force to transmit from muscle to bone. Tendon diseases occur at different zones of the tendon, including enthesis, MTJ and midsubstance of the tendon, due to a variety of environmental and genetic factors which consequently result in different frequencies and recovery rates. Self-healing properties of tendons are limited, and cell therapeutic approaches in which injured tendon tissues are renewed by cell replenishment are highly sought after. Homologous use of individual’s tendon-derived cells, predominantly differentiated tenocytes and tendon-derived stem cells, is emerging as a treatment for tendinopathy through achieving minimal cell manipulation for clinical use. This is the first review summarizing the progress of tendon-derived cell therapy in clinical use and its challenges due to the structural complexity of tendons, heterogeneous composition of extracellular cell matrix and cells and unsuitable cell sources. Further to that, novel future perspectives to improve therapeutic effect in tendon-derived cell therapy based on current basic knowledge are discussed.

The role of the Wnt signalling pathway in the energy metabolism of bone remodelling

OBJECTIVES

Bone remodelling is necessary to repair old and impaired bone caused by aging and its effects. Injury in the process of bone remodelling generally leads to the development of various bone diseases. Energy metabolism plays crucial roles in bone cell formation and function, the disorder of which will disrupt the balance between bone formation and bone resorption.

MATERIALS AND METHODS

Here, we review the intrinsic interactions between bone remodelling and energy metabolism and the role of the Wnt signalling pathway.

RESULTS

We found a close interplay between metabolic pathways and bone homeostasis, demonstrating that bone plays an important role in the regulation of energy balance. We also discovered that Wnt signalling is associated with multiple biological processes regulating energy metabolism in bone cells.

CONCLUSIONS

Thus, targeted regulation of Wnt signalling and the recovery of the energy metabolism function of bone cells are key means for the treatment of metabolic bone diseases.

Small Leucine-Rich Proteoglycans in Tendon Wound Healing

Significance: Tendon injury possesses a high morbidity rate and is difficult to achieve a satisfying prognosis with currently available treatment strategies. Current approaches used for tendon healing always lead to the formation of fibrovascular scar tissue, which significantly compromises the biomechanics of the healed tendon. Moreover, the related functional deficiency deteriorates over time with an increased injury recurrence risk. Small leucine-rich proteoglycans (SLRPs) link and interact with collagen fibrils to regulate tendon structure and biomechanics, which can provide a new and promising method in the field of tendon injury management. Recent Advances: The effect of SLRPs on tendon development has been extensively investigated. SLRP deficiency impairs tendon collagen fibril structure and biomechanic properties, while administration of SLRPs generally benefits tendon wound healing and regains better mechanical properties. Critical Issues: Current knowledge on the role of SLRPs in tendon development and regeneration mostly comes from uninjured knockout mice, and mainly focuses on the morphology description of collagen fibril profile and mechanical properties. Little is known about the regulatory mechanism on the molecular level. Future Directions: This article reviews the current knowledge in this highly translational topic and provides an evidence-based conclusion, thereby encouraging in-depth investigations of SLRPs in tendons and the development of SLRP-based treatments for desired tendon healing.

A Hyperglycemic Microenvironment Inhibits Tendon-to-Bone Healing through the let-7b-5p/CFTR Pathway

Background

Tendon-to-bone healing is a difficult process in treatment of rotator cuff tear (RCT). In addition, diabetes is an important risk factor for poor tendon-to-bone healing. Therefore, we investigated the specific mechanisms through which diabetes affects tendon-to-bone healing by regulating the Cystic Fibrosis Transmembrane Conductance Regulator (CFTR).

Methods

Tendon-derived stem cells (TDSCs) were extracted from rats after which their proliferative capacities were evaluated by the MTT assay. The expression levels of CFTR and tendon-related markers were determined by qRT-PCR. Then, bioinformatics analyses and dual luciferase reporter gene assays were used to identify miRNAs with the ability to bind CFTR mRNA. Finally, CFTR was overexpressed in TDSCs to validate the specific mechanisms through which the high glucose microenvironment inhibits tendon-to-bone healing.

Results

The high glucose microenvironment downregulated mRNA expression levels of tendon-related markers and CFTR in TDSCs cultured with different glucose concentrations. Additionally, bioinformatics analyses revealed that let-7b-5p may be regulated by the high glucose microenvironment and can regulate CFTR levels. Moreover, a dual luciferase reporter gene assay was used to confirm that let-7b-5p targets and binds CFTR mRNA. Additional experiments also confirmed that overexpressed CFTR effectively reversed the negative effects of the hyperglycaemic microenvironment and upregulation of let-7b-5p on TDSC proliferation and differentiation. These findings imply that the hyperglycemic microenvironment inhibits CFTR transcription and, consequently, proliferation and differentiation of TDSCs in vitro by upregulating let-7b-5p.

Conclusions

A hyperglycemic microenvironment inhibits TDSC proliferation in vitro via the let-7b-5p/CFTR pathway, and this is a potential mechanism in diabetes-induced poor tendon-to-bone healing.

Nonwoven-based gelatin/polycaprolactone membrane loaded with ERK inhibitor U0126 for treatment of tendon defects

BACKGROUND

Tendon is a major component of musculoskeletal system connecting the muscles to the bone. Tendon injuries are very common orthopedics problems leading to impeded motion. Up to now, there still lacks effective treatments for tendon diseases.

METHODS

Tendon stem/progenitor cells (TSPCs) were isolated from the patellar tendons of SD rats. The expression levels of genes were evaluated by quantitative RT-PCR. Immunohistochemistry staining was performed to confirm the presence of tendon markers in tendon tissues. Bioinformatics analysis of data acquired by RNA-seq was used to find out the differentially expressed genes. Rat patellar tendon injury model was used to evaluate the effect of U0126 on tendon injury healing. Biomechanical testing was applied to evaluate the mechanical properties of newly formed tendon tissues.

RESULTS

In this study, we have shown that ERK inhibitor U0126 rather PD98059 could effectively increase the expression of tendon-related genes and promote the tenogenesis of TSPCs in vitro. To explore the underlying mechanisms, RNA sequencing was performed to identify the molecular difference between U0126-treated and control TSPCs. The result showed that GDF6 was significantly increased by U0126, which is an important factor of the TGFβ superfamily regulating tendon development and tenogenesis. In addition, NBM (nonwoven-based gelatin/polycaprolactone membrane) which mimics the native microenvironment of the tendon tissue was used as an acellular scaffold to carry U0126. The results demonstrated that when NBM was used in combination with U0126, tendon healing was significantly promoted with better histological staining outcomes and mechanical properties.

CONCLUSION

Taken together, we have found U0126 promoted tenogenesis in TSPCs through activating GDF6, and NBM loaded with U0126 significantly promoted tendon defect healing, which provides a new treatment for tendon injury.

Tendon and multiomics: advantages, advances, and opportunities

Tendons heal by fibrosis, which hinders function and increases re-injury risk. Yet the biology that leads to degeneration and regeneration of tendons is not completely understood. Improved understanding of the metabolic nuances that cause diverse outcomes in tendinopathies is required to solve these problems. 'Omics methods are increasingly used to characterize phenotypes in tissues. Multiomics integrates 'omic datasets to identify coherent relationships and provide insight into differences in molecular and metabolic pathways between anatomic locations, and disease stages. This work reviews the current literature pertaining to multiomics in tendon and the potential of these platforms to improve tendon regeneration. We assessed the literature and identified areas where 'omics platforms contribute to the field: (1) Tendon biology where their hierarchical complexity and demographic factors are studied. (2) Tendon degeneration and healing, where comparisons across tendon pathologies are analyzed. (3) The in vitro engineered tendon phenotype, where we compare the engineered phenotype to relevant native tissues. (4) Finally, we review regenerative and therapeutic approaches. We identified gaps in current knowledge and opportunities for future study: (1) The need to increase the diversity of human subjects and cell sources. (2) Opportunities to improve understanding of tendon heterogeneity. (3) The need to use these improvements to inform new engineered and regenerative therapeutic approaches. (4) The need to increase understanding of the development of tendon pathology. Together, the expanding use of various 'omics platforms and data analysis resulting from these platforms could substantially contribute to major advances in the tendon tissue engineering and regenerative medicine field.

MicroRNA engineered umbilical cord stem cell-derived exosomes direct tendon regeneration by mTOR signaling

Background

Exosomes are extracellular vesicles of nano-structures and represent an emerging nano-scale acellular therapy in recent years. Tendon regeneration is a sophisticated process in the field of microsurgery due to its poor natural healing ability. To date, no successful long-term solution has been provided for the healing of tendon injuries. Functional recovery requires advanced treatment strategies. Human umbilical cord mesenchymal stem cell-derived exosomes (HUMSC-Exos) are considered as promising cell-free therapeutic agents. However, few studies reported their potential in the tendon repair previously. In this study, we explored the roles and underlying mechanisms of HUMSC-Exos in the tendon regeneration.

Results

Expression of tendon‐specific markers in, and collagen deposition by, tendon-derived stem cells (TDSCs) treated with HUMSC-Exos increased in vitro. In a rat Achilles tendon injury model, treatment with HUMSC-Exos improved the histological structure, enhanced tendon-specific matrix components, and optimized biomechanical properties of the Achilles tendon. Findings in miRNA sequencing indicated a significant increase in miR-29a-3p in HUMSC-Exo-treated Achilles tendons. Next, luciferase assay in combination with western blot identified phosphatase and tensin homolog (PTEN) as the specific target of miR-29a-3p. Furthermore, we applied a miR-29a-3p-specific agonist to engineer HUMSC-Exos. These HUMSC-Exos overexpressing miR-29a-3p amplified the gain effects of HUMSC-Exos on tendon healing in vivo. To explore the underlying mechanisms, a transforming growth factor-β1 (TGF-β1) inhibitor (SB-431542), mTOR inhibitor (rapamycin), and engineered HUMSC-Exos were employed. The results showed that TGF-β1 and mTOR signaling were involved in the beneficial effects of HUMSC-Exos on tendon regeneration.

Conclusion

The findings in our study suggest that PTEN/mTOR/TGF-β1 signaling cascades may be a potential pathway for HUMSC-Exos to deliver miR-29a-3p for tendon healing and implicate a novel therapeutic strategy for tendon regeneration via engineered stem cell-derived exosomes.

Graphic abstract

Interplay of Forces and the Immune Response for Functional Tendon Regeneration

Tendon injury commonly occurs during sports activity, which may cause interruption or rapid decline in athletic career. Tensile strength, as one aspect of tendon biomechanical properties, is the main parameter of tendon function. Tendon injury will induce an immune response and cause the loss of tensile strength. Regulation of mechanical forces during tendon healing also changes immune response to improve regeneration. Here, the effects of internal/external forces and immune response on tendon regeneration are reviewed. The interaction between immune response and internal/external forces during tendon regeneration is critically examined and compared, in relation to other tissues. In conclusion, it is essential to maintain a fine balance between internal/external forces and immune response, to optimize tendon functional 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.

Tendon Stem/Progenitor Cell Subpopulations and Their Implications in Tendon Biology

Tendon harbors a cell population that possesses stem cell characteristics such as clonogenicity, multipotency and self-renewal capacity, commonly referred to as tendon stem/progenitor cells (TSPCs). Various techniques have been employed to study how TSPCs are implicated in tendon development, homeostasis and healing. Recent advances in single-cell analysis have enabled much progress in identifying and characterizing distinct subpopulations of TSPCs, which provides a more comprehensive view of TSPCs function in tendon biology. Understanding the mechanisms of physiological and pathological processes regulated by TSPCs, especially a particular subpopulation, would greatly benefit treatment of diseased tendons. Here, we summarize the current scientific literature on the various subpopulations of TSPCs, and discuss how TSPCs can contribute to tissue homeostasis and pathogenesis, as well as examine the key modulatory signaling pathways that determine stem/progenitor cell state. A better understanding of the roles that TSPCs play in tendon biology may facilitate the development of novel treatment strategies for tendon diseases.

Zinc Finger Protein CTCF Regulates Extracellular Matrix (ECM)-Related Gene Expression Associated With the Wnt Signaling Pathway in Gastric Cancer

Gastric cancer (GC), a leading cause of cancer-related death, is a heterogeneous disease. We aim to describe clinically relevant molecular classifications of GC that incorporate heterogeneity and provide useful clinical information. We combined different gene expression datasets and filtered a 7-gene signature related to the extracellular matrix (ECM), which also exhibited significant prognostic value in GC patients. Interestingly, putative CCCTC-binding factor (CTCF) regulatory elements were identified within the promoters of these ECM-related genes and were confirmed by chromatin immunoprecipitation sequencing (ChIP-Seq). CTCF binding sites also overlapped with histone activation markers, indicating direct regulation. In addition, CTCF was also correlated with the Wnt signaling pathway. A comparison of human GC cell lines with high or low expression of ECM-related genes revealed different levels of tumor aggressiveness, suggesting the cancer development-promoting functions of ECM-related genes. Furthermore, CTCF regulated COL1A1 and COLA31 expression in vitro. Silencing CTCF or COL1A1/COL1A3 markedly inhibited cell growth and migration in the metastatic GC cell line BGC823. Collectively, this ECM-related 7-gene signature provides a novel insight for survival prediction among GC patients. The zinc finger protein CTCF regulates ECM-related genes, thereby promoting GC cell growth and migration.

Mechanotransduction of stem cells for tendon repair

Tendon is a mechanosensitive tissue that transmits force from muscle to bone. Physiological loading contributes to maintaining the homeostasis and adaptation of tendon, but aberrant loading may lead to injury or failed repair. It is shown that stem cells respond to mechanical loading and play an essential role in both acute and chronic injuries, as well as in tendon repair. In the process of mechanotransduction, mechanical loading is detected by mechanosensors that regulate cell differentiation and proliferation via several signaling pathways. In order to better understand the stem-cell response to mechanical stimulation and the potential mechanism of the tendon repair process, in this review, we summarize the source and role of endogenous and exogenous stem cells active in tendon repair, describe the mechanical response of stem cells, and finally, highlight the mechanotransduction process and underlying signaling pathways.

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.

AQP1 modulates tendon stem/progenitor cells senescence during tendon aging

The link between tendon stem/progenitor cells (TSPCs) senescence and tendon aging has been well recognized. However, the cellular and molecular mechanisms of TSPCs senescence are still not fully understood. In present study, we investigated the role of Aquaporin 1 (AQP1) in TSPCs senescence. We showed that AQP1 expression declines with age during tendon aging. In aged TSPCs, overexpression of AQP1 significantly attenuated TSPCs senescence. In addition, AQP1 overexpression also restored the age-related dysfunction of self-renewal, migration and tenogenic differentiation. Furthermore, we demonstrated that the JAK-STAT signaling pathway is activated in aged TSPCs, and AQP1 overexpression inhibited the JAK-STAT signaling pathway activation which indicated that AQP1 attenuates senescence and age-related dysfunction of TSPCs through the repression of JAK-STAT signaling pathway. Taken together, our findings demonstrated the critical role of AQP1 in the regulation of TSPCs senescence and provided a novel target for antagonizing tendon aging.

CFTR deletion affects mouse osteoblasts in a gender-specific manner

Advancements in research and care have contributed to increase life expectancy of individuals with cystic fibrosis (CF). With increasing age comes a greater likelihood of developing CF bone disease, a comorbidity characterized by a low bone mass and impaired bone quality, which displays gender differences in severity. However, pathophysiological mechanisms underlying this gender difference have never been thoroughly investigated. We used bone marrow-derived osteoblasts and osteoclasts from Cftr^+/+ and Cftr^-/- mice to examine whether the impact of CF transmembrane conductance regulator (CFTR) deletion on cellular differentiation and functions differed between genders. To determine whether in vitro findings translated into in vivo observations, we used imaging techniques and three-point bending testing. In vitro studies revealed no osteoclast-autonomous defect but impairment of osteoblast differentiation and functions and aberrant responses to various stimuli in cells isolated from Cftr^-/- females only. Compared with wild-type controls, knockout mice exhibited a trabecular osteopenic phenotype that was more pronounced in Cftr^-/- males than Cftr^-/- females. Bone strength was reduced to a similar extent in knockout mice of both genders. In conclusion, we find a trabecular bone phenotype in Cftr^-/- mice that was slightly more pronounced in males than females, which is reminiscent of the situation found in patients. However, at the osteoblast level, the pathophysiological mechanisms underlying this phenotype differ between males and females, which may underlie gender differences in the way bone marrow-derived osteoblasts behave in absence of CFTR.

Biology of Tendon Stem Cells and Tendon in Aging

Both tendon injuries and tendinopathies, particularly rotator cuff tears, increase with tendon aging. Tendon stem cells play important roles in promoting tendon growth, maintenance, and repair. Aged tendons show a decline in regenerative potential coupled with a loss of stem cell function. Recent studies draw attention to aging primarily a disorder of stem cells. The micro-environment (“niche”) where stem cells resided in vivo provides signals that direct them to metabolize, self-renew, differentiate, or remain quiescent. These signals include receptors and secreted soluble factors for cell-cell communication, extracellular matrix, oxidative stress, and vascularity. Both intrinsic cellular deficits and aged niche, coupled with age-associated systemic changes of hormonal and metabolic signals can inhibit or alter the functions of tendon stem cells, resulting in reduced fitness of these primitive cells and hence more frequent injuries and poor outcomes of tendon repair. This review aims to summarize the biological changes of aged tendons. The biological changes of tendon stem cells in aging are reviewed after a systematic search of the PubMed. Relevant factors of stem cell aging including cell-intrinsic factors, changes of microenvironment, and age-associated systemic changes of hormonal and metabolic signals are examined, with findings related to tendon stem cells highlighted when literature is available. Future research directions on the aging mechanisms of tendon stem cells are discussed. Better understanding of the molecular mechanisms underlying the functional decline of aged tendon stem cells would provide insight for the rational design of rejuvenating therapies.

A novel knitted scaffold made of microfiber/nanofiber core–sheath yarns for tendon tissue engineering

PCL-SF/PLCL microfiber/nanofiber yarns with core-sheath architecture were fabricated and knitted into a 3D scaffold for tendon tissue engineering.

Lgr5-overexpressing mesenchymal stem cells augment fracture healing through regulation of Wnt/ERK signaling pathways and mitochondrial dynamics

Fracture remains one of the most common traumatic conditions in orthopedic surgery. The use of mesenchymal stem cells (MSCs) to augment fracture repair is promising. Leucine-rich repeat-containing GPCR 5 (Lgr5), a transmembrane protein, has been identified as a novel adult stem cell marker in various organs and tissues. However, the roles of Lgr5 in MSCs are not fully understood. In this study, we investigated cellular functions of Lgr5 in MSCs and its potential implications in treating fracture. Lgr5-overexpressing MSCs (MSCLgr5) were established in murine SV40 promoter-driven luciferase reporter MSC line through virus transfection. Results of real-time quantitative PCR and Western blot analysis confirmed the increased expression of Lgr5 in MSCLgr5. MSCLgr5 exhibited increased osteogenic capacity, which may result from elevated expression of β-catenin and phosphorylated ERK1/2 within the nuclear region of cells. In contrast, inhibition of Lgr5 expression decreased the osteogenic differentiation ability of MSCs, accompanied with increased mitochondrial fragmentation and reduced expression of β-catenin. Local transplantation of MSCLgr5 at fracture sites accelerated fracture healing via enhanced osteogenesis and angiogenesis. MSCLgr5 stimulated the tube formation capacity of HUVECs in a Matrigel coculture system in vitro significantly. Taken together, results suggest that Lgr5 is implicated in the cellular processes of osteogenic differentiation of MSCs through regulation of Wnt and ERK signaling pathways and mitochondrial dynamics in fusion and fission. Inhibition of Lgr5 expression induced increased mitochondrial fragmentation and suppression of osteogenesis. MSCLgr5 exhibited enhanced therapeutic efficacy for fracture healing, which may serve as a superior cell source for bone tissue repair.-Lin, W., Xu, L., Pan, Q., Lin, S., Feng, L., Wang, B., Chen, S., Li, Y., Wang, H., Li, Y., Wang, Y., Lee, W. Y. W., Sun, D., Li, G. Lgr5-overexpressing mesenchymal stem cells augment fracture healing through regulation of Wnt/ERK signaling pathways and mitochondrial dynamics.

-Book-shaped decellularized tendon matrix scaffold combined with bone marrow mesenchymal stem cells-sheets for repair of achilles tendon defect in rabbit

Tissue-engineering approaches have great potential to improve the treatment of tendon injuries which are major musculoskeletal disorders. The purpose of this study was to assess the tissue engineering potential of a novel multilayered decellularized tendon "book" scaffold with bone marrow mesenchymal stem cells (BMSCs) sheets for repair of an Achilles tendon defect in a rabbit model. In this study, we developed a novel book-shaped decellularized scaffold derived from the extracellular matrix of tendon tissues from New Zealand white rabbits. Hematoxylin and eosin (H&E) staining, 4', 6-diamidino-2-phenylindole (DAPI) staining, DNA quantitation, and scanning electron microscopy (SEM) confirmed the efficiency of decellularization. After culturing BMSCs on decellularized scaffolds, 3-(4, 5-dimethylthiazol-2-yl)-2, 5-diphenyltetrazolium bromide (MTT) assay, SEM, quantitative real time polymerase chain reaction (qRT-PCR), and immunofluorescence analysis demonstrated that decellularized scaffolds have the capacity to yield homogeneous distribution and alignment of BMSCs, as well as support their differentiation into tendon. Tenomodulin and Alpha-1 collagen type I are important indicators for evaluating tenogenic differentiation of BMSCs. When decellularized "book" scaffolds with BMSCs sheets were used to repair a 1 mm Achilles tendon defect, histomorphological analysis, immunohistochemical assessment, and biomechanical testing showed that the book-shaped decellularized tendon matrix scaffold and BMSCs sheets could promote the regeneration of type I collagen at the wound site during healing, and improve the mechanical properties of the repaired tendon. Therefore, the results of this study suggest that the novel decellularized "book" tendon scaffolds combined with BMSCs sheets have therapeutic effects on improving the healing quality of the Achilles tendon. © 2019 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 9999:1-11, 2019.

MiR-378a suppresses tenogenic differentiation and tendon repair by targeting at TGF-β2

Background

Tendons are a crucial component of the musculoskeletal system and responsible for transmission forces derived from muscle to bone. Patients with tendon injuries are often observed with decreased collagen production and matrix degeneration, and healing of tendon injuries remains a challenge as a result of limited understanding of tendon biology. Recent studies highlight the contribution of miR-378a on the regulation gene expression during tendon differentiation.

Methods

We examined the tendon microstructure and tendon repair with using miR-378a knock-in transgenic mice, and the tendon-derived stem cells were also isolated from transgenic mice to study their tenogenic differentiation ability. Meanwhile, the expression levels of tenogenic markers were also examined in mouse tendon-derived stem cells transfected with miR-378a mimics during tenogenic differentiation. With using online prediction software and luciferase reporter assay, the binding target of miR-378a was also studied.

Results

Our results indicated miR-378a impairs tenogenic differentiation and tendon repair by inhibition collagen and extracellular matrix production both in vitro and in vivo. We also demonstrated that miR-378a exert its inhibitory role during tenogenic differentiation through binding at TGFβ2 by luciferase reporter assay and western blot.

Conclusions

Our investigation suggests that miR-378a could be considered as a new potential biomarker for tendon injury diagnosis or drug target for a possible therapeutic approach in future clinical practice.

Electronic supplementary material

The online version of this article (10.1186/s13287-019-1216-y) contains supplementary material, which is available to authorized users.

Identification of an Anti-Inflammation Protein, Annexin A1, in Tendon Derived Stem Cells (TDSCs) of Cystic Fibrosis Mice: A Comparative Proteomic Analysis

PURPOSE

A previous study reported an elevated inflammation during tendon injury in mice with cystic fibrosis (CF), indicating the inadequate management of inflammation due to dysfunction of the cystic fibrosis transmembrane conductance regulator (CFTR). The objective of this study is to identify the targets of CFTR that contribute to the abnormal inflammation during tendon injury.

EXPERIMENTAL DESIGN

A 2D gel electrophoresis and mass-spectrometry-based comparative proteomics is performed to find the molecular targets of CFTR. And the targeted protein is further confirmed at both mRNA and protein levels.

RESULTS

It is identified that 14 proteins are differentially expressed, with annexin A1 being one of the most significantly downregulated protein. Further confirmation shows that annexin A1 is significantly decreased in TDSCs isolated from DF508 mice. As an essential anti-inflammation mediator, it is also downregulated in the injured tendon tissue of DF508 mice when compared with WT mice.

CONCLUSIONS AND CLINICAL RELEVANCE

Decreased annexin A1 expression can contribute to the elevated inflammation in DF508 mice during tendon injury. Therefore, annexin A1 can be considered as a new potential biomarker or drug target for a possible therapeutic approach in clinical practice.

3D uniaxial mechanical stimulation induces tenogenic differentiation of tendon-derived stem cells through a PI3K/AKT signaling pathway

The tendon is a mechanosensitive tissue, but little is known about how mechanical stimulation selectively signals tenogenic differentiation and neo-tendon formation. In this study, we compared the impact of uniaxial and biaxial mechanical loading on tendon-derived stem cells (TDSCs). Our data show that there are variations in cell signaling and cell differentiation of mouse TDSCs in response to uniaxial and biaxial loading in monolayer culture. Whereas uniaxial loading induced TDSCs toward tenogenic and osteogenic differentiation, biaxial loading induced osteogenic, adipogenic, and chondrogenic differentiation of TDSCs. Furthermore, by applying uniaxial loading on 3-dimensional (3D) TDSC constructs, tenogenic-specific differentiation and neo-tendon formation were observed, results that were replicated in human TDSCs. We also showed that uniaxial loading induced PKB (AKT) phosphorylation (pAKT), whereas biaxial loading induced pERK. Most importantly, we found that inhibition of the PI3K/AKT signaling pathway could attenuate tenogenic differentiation and tendon formation in 3D TDSC constructs subjected to uniaxial loading. Taken together, our study highlights the importance of appropriate mechanobiological stimulation in 3D cell niches on tendon-like tissue formation and demonstrates that uniaxial mechanical loading plays an essential role in tenogenic differentiation and tendon formation by activating the PI3K/AKT signaling pathway.-Wang, T., Thien, C., Wang, C., Ni, M., Gao, J., Wang, A., Jiang, Q., Tuan, R. S., Zheng, Q., Zheng, M. H. 3D uniaxial mechanical stimulation induces tenogenic differentiation of tendon-derived stem cells through a PI3K/AKT signaling pathway.

In vitro loading models for tendon mechanobiology

Tendons are the connective tissue responsible for transferring force from muscles to bones. A key factor in tendon development, maturation, repair, and degradation is its biomechanical environment. Understanding tendon mechanobiology is essential for the development of injury prevention strategies, rehabilitation protocols and potentially novel treatments in tendon injury and degeneration. Despite the simple overall loading on tendon tissue, cells within the tissue in vivo experience a much more complex mechanical environment including tension, compression and shear forces. This creates a substantial challenge in the establishment of in vitro loading models of the tendon. This article reviews multiple loading models used for the study of tendon mechanobiology and summarizes the main findings. Although impressive progress has been achieved in the functionality and mimicry of in vitro loading models, an ideal platform is yet to be developed. Multidisciplinary approaches and collaborations will be the key to unveiling the tendon mechanobiology. © 2017 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 36:566-575, 2018.