MicroRNA29a regulates IL-33-mediated tissue remodelling in tendon disease

Functional tendon regeneration is driven by regulatory T cells and IL-33 signaling

Tendon injuries heal by scar, leading to poor function. To date, the role of immune cells remains underexplored. Using a neonatal mouse model of functional tendon healing compared to adult scar-mediated healing, we identified a regenerative immune profile that is associated with type 1 inflammation followed by rapid polarization to type 2, driven by macrophages and regulatory T cells (Treg cells). Single-cell and bulk RNA sequencing also revealed neonatal Treg cells with an immunomodulatory signature distinct from adult. Neonatal Treg cell ablation resulted in a dysregulated immune response, failed tenocyte recruitment, and impaired regeneration. Adoptive transfer further confirmed the unique capacity of neonatal Treg cells to rescue functional regeneration. We showed that neonatal Treg cells mitigate interleukin-33 (IL-33) to enable tenocyte recruitment and structural restoration, and that adult IL-33 deletion improves functional healing. Collectively, these findings demonstrate that Treg cells and IL-33 immune dysfunction are critical components of failed tendon healing and identify potential targets to drive tendon regeneration.

Reactive oxygen species in tendon injury and repair

Reactive oxygen species (ROS) are chemical moieties that in physiological concentrations serve as fast-acting signaling molecules important for cellular homeostasis. However, their excess either due to overproduction or inability of the antioxidant system to inactivate them results in oxidative stress, contributing to cellular dysfunction and tissue damage. In tendons, which are hypovascular, hypocellular, and composed predominantly of extracellular matrix (ECM), particularly collagen I, ROS likely play a dual role: regulating cellular processes such as inflammation, proliferation, and ECM remodeling under physiological conditions, while contributing to tendinopathy and impaired healing when dysregulated. This review explores the sources of ROS in tendons, including NADPH oxidases and mitochondria, and their role in key processes such as tissue adaptation to mechanical load and injury repair, also in systemic conditions such as diabetes. In addition, we integrate the emerging perspective that calcium signaling-mediated by mechanically activated ion channels-plays a central role in tendon mechanotransduction under daily mechanical loads. We propose that mechanical overuse (overload) may lead to hyperactivation of calcium channels, resulting in chronically elevated intracellular calcium levels that amplify ROS production and oxidative stress. Although direct evidence linking calcium channel hyperactivity, intracellular calcium dysregulation, and ROS generation under overload conditions is currently circumstantial, this review aims to highlight these connections and identify them as critical avenues for future research. By framing ROS within the context of both adaptive and maladaptive responses to mechanical load, this review provides a comprehensive synthesis of redox biology in tendon injury and repair, paving the way for future work, including development of therapeutic strategies targeting ROS and calcium signaling to enhance tendon recovery and resilience.

Craniofacial and Dental Anomalies of a Patient Carrying Two MicroRNA Variants: A Proof-Of-Concept Case Report

Craniofacial and dentofacial anomalies often result from disruptions in embryogenetic processes driven by genetic alterations. Dental development involves complex interactions between coding and non-coding genes, orchestrated by a network of signaling pathways. Next Generation Sequencing (NGS) has identified genes, particularly in the WNT signaling pathway, associated with dental anomalies. MicroRNAs (miRNAs), small non-coding RNA molecules, play a crucial role in post-transcriptional regulation. Variants in miRNAs, such as in MIR146A, have been linked to various craniofacial pathologies. A 10-year-old female with a class II molar malocclusion and maxillary constriction was examined. Clinical and radiographic assessments revealed impacted cuspids (both maxillary canines and the right mandibular canine), odontoma, and root resorption. Genetic analysis showed that the patient carried two variants in MIR146A (rs2910164) and MIR182 (rs76481776). The patient exhibited skeletal anomalies including class II ponticulus posticus and sella turcica bridging. The proof-of-concept study incorporates relevant literature discussing the molecular basis of dental anomalies, suggesting to take into account the potential functional role of miRNAs. Previous research has associated MIR146A polymorphisms with various diseases, highlighting the need for a comprehensive understanding of genetic influences on craniofacial development. This case report presents craniofacial and dental anomalies in a patient carrying two miRNA variants. Understanding the genetic basis of dental anomalies, particularly the role of miRNAs, holds promise for future advancements in orthodontics, enabling personalized diagnostics and prognostics.

Janus hydrogel microrobots with bioactive ions for the regeneration of tendon-bone interface

Regenerating natural gradients of the tendon‒bone interface (TBI) is a major challenge in the reconstruction of rotator cuff tear (RCT). In this study, magnetic Janus hydrogel microrobots to match the TBI orientation during RCT reconstruction surgery are developed via a biofriendly gas-shearing microfluidic platform. Through separate loading of Mg2+ and Zn2+, the microrobots facilitate the immediate restoration and long-term maintenance of the natural mineral gradient in the TBI after implantation and alignment through magnetic manipulation. In vitro studies confirm the spatiotemporal cell phenotype modulation effects of the microrobots. In a rat RCT model, microrobots synchronously promote the bone and tendon regeneration, and the restoration of gradient tendon‒bone transition structures in the TBI. Overall, by rebuilding the Mg2+/Zn2+ mineral gradient, cell phenotype gradient and structural gradient of the TBI, magnetic Janus microrobots loaded with dual bioactive ions represent a promising strategy for promoting TBI healing in RCT reconstruction surgery.

Targeting the IL-17A pathway for therapy in early-stage tendinopathy

OBJECTIVES

Tendinopathy is a frequent clinical problem and represents an extraordinary health economic and socioeconomic burden with high unmet medical needs. Recent clinical evidence suggests blockade of interleukin 17A (IL-17A) for tendinopathy therapy. The present preclinical study elucidates the biological mechanisms of IL-17A pathway stimulation and blockade in tendinopathy.

METHODS

We explored whether IL-17A and other IL-17 family members are differentially expressed in biopsies of healthy, early-stage and late-stage tendinopathic human rotator cuff tendons using RT-qPCR. IL-17 pathway signature genes in healthy human tendon-derived cells were identified following IL-17A stimulation using AmpliSeq RNA. The molecular, structural and functional consequences of IL-17A pathway stimulation were explored in healthy human tendon-derived cells and in a rat tendon fascicle model ex vivo. The effects of IL-17A pathway blockade were investigated in a rat model of rotator cuff tendinopathy in vivo.

RESULTS

We provide evidence of differential expression of IL-17A mRNA (IL17A) versus other IL-17 family members in human rotator cuff early-stage tendinopathy. In human tendon-derived cells, stimulation with IL-17A induced the expression of the selected IL-17A pathway signature genes NFKBIZ, ZC3H12A, CXCL1, IL6, MMP3. Expression was inhibited by IL-17A blockade. In the rat ex vivo and in vivo models, IL-17A blockade alleviated inflammatory immune effector release, tendon structural degeneration, tendon inflammation and impaired tendon function.

CONCLUSION

Our data provide evidence that IL-17A is a key contributor to the pathogenesis of tendinopathy by promoting tendon inflammation and degeneration and that IL-17A blockade may represent a potential therapy in early-stage tendinopathy.

Single-cell RNA sequencing reveals the CRTAC1+ population actively contributes to the pathogenesis of spinal ligament degeneration by SPP1+ macrophage

Degenerative spinal stenosis is a chronic disease that affects the spinal ligaments and associated bones, resulting in back pain and disorders of the limbs among the elderly population. There are few preventive strategies for such ligament degeneration. We here aimed to establish a comprehensive transcriptomic atlas of ligament tissues to identify high-priority targets for pharmaceutical treatment of ligament degeneration. Here, single-cell RNA sequencing was performed on six degenerative ligaments and three traumatic ligaments to understand tissue heterogeneity. After stringent quality control, high-quality data were obtained from 32,014 cells. Distinct cell clusters comprising stromal and immune cells were identified in ligament tissues. Among them, we noted that collagen degradation associated with CTHRC1+ fibroblast-like cells and calcification linked to CRTAC1+ chondrocyte-like cells were key features of ligament degeneration. SCENIC analysis and further experiments identified ATF3 as a key transcription factor regulating the pathogenesis of CRTAC1+ chondrocyte-like cells. Typically, immune cells infiltrate localized organs, causing tissue damage. In our study, myeloid cells were found to be inflammatory-activated, and SPP1+ macrophages were notably enriched in degenerative ligaments. Further exploration via CellChat analysis demonstrated a robust interaction between SPP1+ macrophages and CRTAC1+ chondrocyte-like cells. Activated by SPP1, ATF3 propels the CRTAC1/MGP/CLU axis, fostering ligament calcification. Our unique resource provides novel insights into possible mechanisms underlying ligament degeneration, the target cell types, and molecules that are expected to mitigate degenerative spinal ligament. We also highlight the role of immune regulation in ligament degeneration and calcification, enhancing our understanding of this disease.

CTHRC1 Attenuates Tendinopathy via Enhancing EGFR/MAPK Signaling Pathway

Tendinopathy poses a formidable challenge due to the inherent limitations of tendon regenerative capabilities post-injury. At present, effective curative approaches for tendinopathy are still lacking. Collagen triple helix repeat-containing 1 (CTHRC1) is an extracellular matrix protein with significant roles in both physiological and pathological processes. The present study aims to investigate the function and underlying mechanism of CTHRC1 in tendinopathy. In this study, CTHRC1 is identified as a potential effector in promoting tendon regeneration through multi-proteomic analysis of Achilles tendon tissues in mice. In vitro, CTHRC1 enhances the proliferation, migration, and tenogenic differentiation of tendon stem/progenitor cell (TSPC). In vivo, CTHRC1 deletion impairs tendon healing, while its overexpression reverses the detrimental effects caused by CTHRC1 deficiency. Mechanistically, proteomics on TSPC stimulated with recombinant CTHRC1 reveal that CTHRC1 activates the mitogen-activated protein kinase (MAPK) signaling pathway via binding to epidermal growth factor receptor (EGFR), which in turn promotes the proliferative, migrative, and tenogenic capacities of TSPC to attenuate Achilles tendinopathy. Conversely, inhibiting EGFR reverses the tendon-healing effect of CRHRC1. The study demonstrates that CTHRC1 can promote the proliferative, migrative, and tenogenic capacities of TSPC, ultimately facilitating tendon healing through activating the EGFR/MAPK signaling pathway. CTHRC1 holds promise as a potential intervention for tendinopathy.

Challenges in tendon-bone healing: emphasizing inflammatory modulation mechanisms and treatment

Tendons are fibrous connective tissues that transmit force from muscles to bones. Despite their ability to withstand various loads, tendons are susceptible to significant damage. The healing process of tendons and ligaments connected to bone surfaces after injury presents a clinical challenge due to the intricate structure, composition, cellular populations, and mechanics of the interface. Inflammation plays a pivotal role in tendon healing, creating an inflammatory microenvironment through cytokines and immune cells that aid in debris clearance, tendon cell proliferation, and collagen fiber formation. However, uncontrolled inflammation can lead to tissue damage, and adhesions, and impede proper tendon healing, culminating in scar tissue formation. Therefore, precise regulation of inflammation is crucial. This review offers insights into the impact of inflammation on tendon-bone healing and its underlying mechanisms. Understanding the inflammatory microenvironment, cellular interactions, and extracellular matrix dynamics is essential for promoting optimal healing of tendon-bone injuries. The roles of fibroblasts, inflammatory cytokines, chemokines, and growth factors in promoting healing, inhibiting scar formation, and facilitating tissue regeneration are discussed, highlighting the necessity of balancing the suppression of detrimental inflammatory responses with the promotion of beneficial aspects to enhance tendon healing outcomes. Additionally, the review explores the significant implications and translational potential of targeted inflammatory modulation therapies in refining strategies for tendon-bone healing treatments.

Human Tendon-on-Chip: Unveiling the Effect of Core Compartment-T Cell Spatiotemporal Crosstalk at the Onset of Tendon Inflammation

The lack of representative in vitro models recapitulating human tendon (patho)physiology is among the major factors hindering consistent progress in the knowledge-based development of adequate therapies for tendinopathy.Here, an organotypic 3D tendon-on-chip model is designed that allows studying the spatiotemporal dynamics of its cellular and molecular mechanisms.Combining the synergistic effects of a bioactive hydrogel matrix with the biophysical cues of magnetic microfibers directly aligned on the microfluidic chip, it is possible to recreate the anisotropic architecture, cell patterns, and phenotype of tendon intrinsic (core) compartment. When incorporated with vascular-like vessels emulating the interface between its intrinsic-extrinsic compartments, crosstalk with endothelial cells are found to drive stromal tenocytes toward a reparative profile. This platform is further used to study adaptive immune cell responses at the onset of tissue inflammation, focusing on interactions between tendon compartment tenocytes and circulating T cells.The proinflammatory signature resulting from this intra/inter-cellular communication induces the recruitment of T cells into the inflamed core compartment and confirms the involvement of this cellular crosstalk in positive feedback loops leading to the amplification of tendon inflammation.Overall, the developed 3D tendon-on-chip provides a powerful new tool enabling mechanistic studies on the pathogenesis of tendinopathy as well as for assessing new therapies.

Emerging roles of non-coding RNAs in fibroblast to myofibroblast transition and fibrotic diseases

The transition of fibroblasts to myofibroblasts (FMT) represents a pivotal process in wound healing, tissue repair, and fibrotic diseases. This intricate transformation involves dynamic changes in cellular morphology, gene expression, and extracellular matrix remodeling. While extensively studied at the molecular level, recent research has illuminated the regulatory roles of non-coding RNAs (ncRNAs) in orchestrating FMT. This review explores the emerging roles of ncRNAs, including microRNAs (miRNAs), long non-coding RNAs (lncRNAs), and circular RNAs (circRNAs), in regulating this intricate process. NcRNAs interface with key signaling pathways, transcription factors, and epigenetic mechanisms to fine-tune gene expression during FMT. Their functions are critical in maintaining tissue homeostasis, and disruptions in these regulatory networks have been linked to pathological fibrosis across various tissues. Understanding the dynamic roles of ncRNAs in FMT bears therapeutic promise. Targeting specific ncRNAs holds potential to mitigate exaggerated myofibroblast activation and tissue fibrosis. However, challenges in delivery and specificity of ncRNA-based therapies remain. In summary, ncRNAs emerge as integral regulators in the symphony of FMT, orchestrating the balance between quiescent fibroblasts and activated myofibroblasts. As research advances, these ncRNAs appear to be prospects for innovative therapeutic strategies, offering hope in taming the complexities of fibrosis and restoring tissue equilibrium.

Tumor Necrosis Factor-Alpha Modulates Expression of Genes Involved in Cytokines and Chemokine Pathways in Proliferative Myoblast Cells

Skeletal muscle regeneration after injury is a complex process involving inflammatory signaling and myoblast activation. Pro-inflammatory cytokines like tumor necrosis factor-alpha (TNF-α) are key mediators, but their effects on gene expression in proliferating myoblasts are unclear. We performed the RNA sequencing of TNF-α treated C2C12 myoblasts to elucidate the signaling pathways and gene networks regulated by TNF-α during myoblast proliferation. The TNF-α (10 ng/mL) treatment of C2C12 cells led to 958 differentially expressed genes compared to the controls. Pathway analysis revealed significant regulation of TNF-α signaling, along with the chemokine and IL-17 pathways. Key upregulated genes included cytokines (e.g., IL-6), chemokines (e.g., CCL7), and matrix metalloproteinases (MMPs). TNF-α increased myogenic factor 5 (Myf5) but decreased MyoD protein levels and stimulated the release of MMP-9, MMP-10, and MMP-13. TNF-α also upregulates versican and myostatin mRNA. Overall, our study demonstrates the TNF-α modulation of distinct gene expression patterns and signaling pathways that likely contribute to enhanced myoblast proliferation while suppressing premature differentiation after muscle injury. Elucidating the mechanisms involved in skeletal muscle regeneration can aid in the development of regeneration-enhancing therapeutics.

Reprogramming tendon healing: a guide to novel molecular tools

Tendons are a frequent site of injury, which greatly impairs the movement and locomotion of patients. Regrettably, injuries at the tendon frequently require surgical intervention, which leads to a long path to recovery. Moreover, the healing of tendons often involves the formation of scar tissue at the site of injury with poor mechanical properties and prone to re-injury. Tissue engineering carries the promise of better and more effective solutions to the improper healing of tendons. Lately, the field of regenerative medicine has seen a significant increase in the focus on the potential use of non-coding RNAs (e.g., siRNAs, miRNAs, and lncRNAs) as molecular tools for tendon tissue engineering. This class of molecules is being investigated due to their ability to act as epigenetic regulators of gene expression and protein production. Thus, providing a molecular instrument to fine-tune, reprogram, and modulate the processes of tendon differentiation, healing, and regeneration. This review focuses particularly on the latest advances involving the use of siRNAs, miRNAs, and lncRNAs in tendon tissue engineering applications.

Assessing Bioprinted Functionalized Grafts for Biological Tendon Augmentation In Vitro

Tendinopathy, characterized by inflammatory and degenerative changes, presents challenges in sports and medicine. In addressing the limitations of conservative management, this study focuses on developing tendon grafts using extrusion bioprinting with platelet-rich plasma (PRP)-infused hydrogels loaded with tendon cells. The objective is to understand paracrine interactions initiated by bioprinted tendon grafts in either inflamed or non-inflamed host tissues. PRP was utilized to functionalize methacrylate gelatin (GelMA), incorporating tendon cells for graft bioprinting. Bioinformatic analyses of overexpressed proteins, predictive of functional enrichment, revealed insights into PRP graft behavior in both non-inflamed and inflamed environments. PRP grafts activated inflammatory pathways, including Interleukin 17 (IL-17), neuroinflammation, Interleukin 33 (IL-33), and chemokine signaling. Interleukin 1 beta (IL-1b) in the graft environment triggered p38 mitogen-activated protein kinase (MAPK) signaling, nuclear factor kappa light chain enhancer of activated B cells (NF-kB) canonical pathway, and Vascular Endothelial Growth Factor (VEGF) signaling. Biological enrichment attributed to PRP grafts included cell chemotaxis, collagen turnover, cell migration, and angiogenesis. Acellular PRP grafts differed from nude grafts in promoting vessel length, vessel area, and junction density. Angiogenesis in cellular grafts was enhanced with newly synthesized Interleukin 8 (IL-8) in cooperation with IL-1b. In conclusion, paracrine signaling from PRP grafts, mediated by chemokine activities, influences cell migration, inflammation, and angiogenic status in host tissues. Under inflammatory conditions, newly synthesized IL-8 regulates vascularization in collaboration with PRP.

The Use of Extracellular Vesicles in Achilles Tendon Repair: A Systematic Review

Achilles tendon (AT) pathologies are common musculoskeletal conditions that can significantly impair function. Despite various traditional treatments, recovery is often slow and may not restore full functionality. The use of extracellular vesicles (EVs) has emerged as a promising therapeutic option due to their role in cell signaling and tissue regeneration. This systematic review aims to consolidate current in vivo animal study findings on the therapeutic effects of EVs on AT injuries. An extensive literature search was conducted using the PubMed, Scopus, and Embase databases for in vivo animal studies examining the effects of EVs on AT pathologies. The extracted variables included but were not limited to the study design, type of EVs used, administration methods, efficacy of treatment, and proposed therapeutic mechanisms. After screening, 18 studies comprising 800 subjects were included. All but one study reported that EVs augmented wound healing processes in the AT. The most proposed mechanisms through which this occurred were gene regulation of the extracellular matrix (ECM), the enhancement of macrophage polarization, and the delivery of therapeutic microRNAs to the injury site. Further research is warranted to not only explore the therapeutic potential of EVs in the context of AT pathologies, but also to establish protocols for their clinical application.

Interfacial Tissue Regeneration with Bone

PURPOSE OF REVIEW

Interfacial tissue exists throughout the body at cartilage-to-bone (osteochondral interface) and tendon-to-bone (enthesis) interfaces. Healing of interfacial tissues is a current challenge in regenerative approaches because the interface plays a critical role in stabilizing and distributing the mechanical stress between soft tissues (e.g., cartilage and tendon) and bone. The purpose of this review is to identify new directions in the field of interfacial tissue development and physiology that can guide future regenerative strategies for improving post-injury healing.

RECENT FINDINGS

Cues from interfacial tissue development may guide regeneration including biological cues such as cell phenotype and growth factor signaling; structural cues such as extracellular matrix (ECM) deposition, ECM, and cell alignment; and mechanical cues such as compression, tension, shear, and the stiffness of the cellular microenvironment. In this review, we explore new discoveries in the field of interfacial biology related to ECM remodeling, cellular metabolism, and fate. Based on emergent findings across multiple disciplines, we lay out a framework for future innovations in the design of engineered strategies for interface regeneration. Many of the key mechanisms essential for interfacial tissue development and adaptation have high potential for improving outcomes in the clinic.

MicroRNA-146a gene transfer ameliorates senescence and senescence-associated secretory phenotypes in tendinopathic tenocytes

OBJECTIVE

Tendinopathy is influenced by multiple factors, including chronic inflammation and aging. Senescent cells exhibit characteristics such as the secretion of matrix-degrading enzymes and pro-inflammatory cytokines, collectively known as senescence-associated secretory phenotypes (SASPs). Many of these SASP cytokines and enzymes are implicated in the pathogenesis of tendinopathy. MicroRNA-146a (miR-146a) blocks senescence by targeting interleukin-1β (IL-1β) receptor-associated kinase 4 (IRAK-4) and TNF receptor-associated factor 6 (TRAF6), thus inhibiting NF-κB activity. The aims of this study were to (1) investigate miR-146a expression in tendinopathic tendons and (2) evaluate the role of miR-146a in countering senescence and SASPs in tendinopathic tenocytes.

METHODS

MiR-146a expression was assessed in human long head biceps (LHB) and rat tendinopathic tendons by in situ hybridization. MiR-146a over-expression in rat primary tendinopathic tenocytes was achieved by lentiviral vector-mediated precursor miR-146a transfer (LVmiR-146a). Expression of various senescence-related markers was analyzed by quantitative reverse transcription polymerase chain reaction (qRT-PCR), immunoblotting and immunofluorescence. MiR-146a expression showed a negative correlation with the severity of tendinopathy in human and rat tendinopathic tendons (p<0.001).

RESULTS

Tendinopathic tenocyte transfectants overexpressing miR-146a exhibited downregulation of various senescence and SASP markers, as well as the target molecules IRAK-4 and TRAF6, and the inflammatory mediator phospho-NF-κB. Additionally, these cells showed enhanced nuclear staining of high mobility group box 1 (HMGB1) compared to LVmiR-scramble-transduced controls in response to IL-1β stimulation.

CONCLUSIONS

We demonstrate that miR-146a expression is negatively correlated with the progression of tendinopathy. Moreover, its overexpression protects tendinopathic tenocytes from SASPs and senescence through the IRAK-4/TRAF6/NF-kB pathway.

Small RNA signatures of the anterior cruciate ligament from patients with knee joint osteoarthritis

Introduction: The anterior cruciate ligament (ACL) is susceptible to degeneration, resulting in joint pain, reduced mobility, and osteoarthritis development. There is currently a paucity of knowledge on how anterior cruciate ligament degeneration and disease leads to osteoarthritis. Small non-coding RNAs (sncRNAs), such as microRNAs and small nucleolar RNA (snoRNA), have diverse roles, including regulation of gene expression. Methods: We profiled the sncRNAs of diseased osteoarthritic ACLs to provide novel insights into osteoarthritis development. Small RNA sequencing from the ACLs of non- or end-stage human osteoarthritic knee joints was performed. Significantly differentially expressed sncRNAs were defined, and bioinformatics analysis was undertaken. Results and Discussion: A total of 184 sncRNAs were differentially expressed: 68 small nucleolar RNAs, 26 small nuclear RNAs (snRNAs), and 90 microRNAs. We identified both novel and recognized (miR-206, -365, and -29b and -29c) osteoarthritis-related microRNAs and other sncRNAs (including SNORD72, SNORD113, and SNORD114). Significant pathway enrichment of differentially expressed miRNAs includes differentiation of the muscle, inflammation, proliferation of chondrocytes, and fibrosis. Putative mRNAs of the microRNA target genes were associated with the canonical pathways "hepatic fibrosis signaling" and "osteoarthritis." The establishing sncRNA signatures of ACL disease during osteoarthritis could serve as novel biomarkers and potential therapeutic targets in ACL degeneration and osteoarthritis development.

An Extracellular Vesicle-Cloaked Multifaceted Biocatalyst for Ultrasound-Augmented Tendon Matrix Reconstruction and Immune Microenvironment Regulation

The healing of tendon injury is often hindered by peritendinous adhesion and poor regeneration caused by the accumulation of reactive oxygen species (ROS), development of inflammatory responses, and the deposition of type-III collagen. Herein, an extracellular vesicles (EVs)-cloaked enzymatic nanohybrid (ENEV) was constructed to serve as a multifaceted biocatalyst for ultrasound (US)-augmented tendon matrix reconstruction and immune microenvironment regulation. The ENEV-based biocatalyst exhibits integrated merits for treating tendon injury, including the efficient catalase-mimetic scavenging of ROS in the injured tissue, sustainable release of Zn2+ ions, cellular uptake augmented by US, and immunoregulation induced by EVs. Our study suggests that ENEVs can promote tenocyte proliferation and type-I collagen synthesis at an early stage by protecting tenocytes from ROS attack. The ENEVs also prompted efficient immune regulation, as the polarization of macrophages (Mφ) was reversed from M1φ to M2φ. In a rat Achilles tendon defect model, the ENEVs combined with US treatment significantly promoted functional recovery and matrix reconstruction, restored tendon morphology, suppressed intratendinous scarring, and inhibited peritendinous adhesion. Overall, this study offers an efficient nanomedicine for US-augmented tendon regeneration with improved healing outcomes and provides an alternative strategy to design multifaceted artificial biocatalysts for synergetic tissue regenerative therapies.

Moderate evidence exists for four microRNAs as potential biomarkers for tendinopathies and degenerative tendon ruptures at the upper extremity in elderly patients: conclusion of a systematic review with best-evidence synthesis

PURPOSE

The aim of this systematic review was to investigate tendon-specific microRNAs (miRNAs) as biomarkers for the detection of tendinopathies or degenerative tendon ruptures. Also, their regulatory mechanisms within the tendon pathophysiology were summarized.

METHODS

A systematic literature research was performed using the PRISMA guidelines. The search was conducted in the Pubmed database. The SIGN checklist was used to assess the study quality of the included original studies. To determine the evidence and direction of the miRNA expression rates, a best-evidence synthesis was carried out, whereby only studies with at least a borderline methodological quality were considered for validity purposes.

RESULTS

Three thousand three hundred seventy studies were reviewed from which 22 fulfilled the inclusion criteria. Moderate evidence was found for miR-140-3p and miR-425-5p as potential biomarkers for tendinopathies as well as for miR-25-3p, miR-29a-3p, miR-140-3p, and miR-425-5p for the detection of degenerative tendon ruptures. This evidence applies to tendons at the upper extremity in elderly patients. All miRNAs were associated with inflammatory cytokines as interleukin-6 or interleukin-1ß and tumor necrosis factor alpha.

CONCLUSIONS

Moderate evidence exists for four miRNAs as potential biomarkers for tendinopathies and degenerative tendon ruptures at the upper extremity in elderly patients. The identified miRNAs are associated with inflammatory processes.

MicroRNA expression changes in the development of rotator cuff tendon injuries

Traumatic or degenerative rotator cuff (RC) tendon injuries are a leading cause of persistent shoulder pain and reduction of mobility with associated disability and dysfunction, which require each year more than 250,000 surgical repairs in the United States. MicroRNAs (miRNAs) are small noncoding RNAs, that in the posttranscriptional phase lead to the development and function of tissues. The aim of this review was to identify miRNA expression changes in patients with RC pathologies and to determine their relevance as a potential novel diagnostic and potentially therapeutic tool for RC disorders. Various miRNAs seemed to be key regulators in the muscle architecture, determining several modifications in muscle atrophy, skeletal muscle mechanical adaptation, lipid accumulation, and fibrosis in the presence of RC tears. The search was executed using PubMed, Medline, Scopus, and Cochrane Central. We included studies written in English that evaluated the role of miRNA in diagnosis, physiopathology, and potential therapeutic application of RC tendon injuries. We included 11 studies in this review. Many miRNAs emerged as key regulators in the pathogenesis of RC tears, inflammation, and muscle fatty degeneration. In fact, they are involved in the regulation of myogenesis, inflammatory cytokines, metalloproteases expression, muscle adaptation, adipogenesis, fibrogenic factors, and extracellular matrix synthesis. The gene expression may be altered in the pathological processes of tendon lesions. Therefore, the knowledge of all the gene mechanisms underlying RC tendinopathy should be achieved with future diagnostic and clinical studies.

Platelet-rich plasma in the pathologic processes of tendinopathy: a review of basic science studies

Tendinopathy is a medical condition that includes a spectrum of inflammatory and degenerative tendon changes caused by traumatic or overuse injuries. The pathological mechanism of tendinopathy has not been well defined, and no ideal treatment is currently available. Platelet-rich plasma (PRP) is an autologous whole blood derivative containing a variety of cytokines and other protein components. Various basic studies have found that PRP has the therapeutic potential to promote cell proliferation and differentiation, regulate angiogenesis, increase extracellular matrix synthesis, and modulate inflammation in degenerative tendons. Therefore, PRP has been widely used as a promising therapeutic agent for tendinopathy. However, controversies exist over the optimal treatment regimen and efficacy of PRP for tendinopathy. This review focuses on the specific molecular and cellular mechanisms by which PRP manipulates tendon healing to better understand how PRP affects tendinopathy and explore the reason for the differences in clinical trial outcomes. This article has also pointed out the future direction of basic research and clinical application of PRP in the treatment of tendinopathy, which will play a guiding role in the design of PRP treatment protocols for tendinopathy.

Role of the IL-33/ST2 Activation Pathway in the Development of the Hepatic Fibrosis Induced by Schistosoma mansoni Granulomas in Mice

Schistosoma mansoni eggs retained in host tissues induce innate cytokine release, contributing to the induction of Type-2 immune responses and granuloma formation, important to restrain cytotoxic antigens, but leading to fibrosis. Interleukin(IL)-33 participates in experimental models of inflammation and chemically induced fibrosis, but its role in S. mansoni-induced fibrosis is still unknown. To explore the role of the IL-33/suppressor of the tumorigenicity 2 (ST2) pathway, serum and liver cytokine levels, liver histopathology, and collagen deposition were comparatively evaluated in S. mansoni-infected wild-type (WT) and IL-33-receptor knockout (ST2-/-) BALB/c mice. Our data show similar egg counts and hydroxyproline in the livers of infected WT and ST2-/- mice; however, the extracellular matrix in ST2-/- granulomas was loose and disorganised. Pro-fibrotic cytokines, such as IL-13 and IL-17, and the tissue-repairing IL-22 were significantly lower in ST2-/- mice, especially in chronic schistosomiasis. ST2-/- mice also showed decreased α-smooth muscle actin (α-SMA) expression in granuloma cells, in addition to reduced Col III and Col VI mRNA levels and reticular fibres. Therefore, IL-33/ST2 signalling is essential for tissue repairing and myofibroblast activation during S. mansoni infection. Its disruption results in inappropriate granuloma organisation, partly due to the reduced type III and VI collagen and reticular fibre formation.

Computational Analysis of miR-140 and miR-135 as Potential Targets to Develop Combinatorial Therapeutics for Degenerative Tendinopathy

Background

Degenerative tendinopathy, a condition causing movement restriction due to high pain, highly impacts productivity and quality of life. The healing process is a complex phenomenon and involves a series of intra-cellular and inter-cellular processes. Proliferation and differentiation of the tenocyte is a major and essential process to heal degenerative tendinopathy. The recent development in microRNA (miRNA)-mediated reprogramming of the cellular function through specific pathways opened door for the development of new regenerative therapeutics. Based on information about gene expression and regulation of tendon injury and healing, we attempted to evaluate the combinatorial effect of selected miRNAs for better healing of degenerative tendinopathy.

Methods

The present study was designed to evaluate the combinatorial effect of two miRNAs (has-miR-140 and has-miR-135) in the healing process of the tendon. Publicly available information/data were retrieved from appropriate platforms such as PubMed. Only molecular data, directly associated with tendinopathies, including genes/proteins and miRNAs, were used in this study. The miRNAs involved in tendinopathy were analyzed by a Bioinformatics tools (e.g., TargetScan, miRDB, and the RNA22v2). Interactive involvement of the miRNAs with key proteins involved in tendinopathy was predicted by the Insilco approach.

Results

Based on information available in the public domain, tendon healing-associated miRNAs were predicted to explore their therapeutic potentials. Based on computation analysis, focusing on the potential regulatory effect on tendon healing, the miR-135 and miR-140 were selected for this study. These miRNAs were found as key players in tendon healing through Rho-associated coiled-coil containing protein kinase 1 (ROCK1), IGF-1/PI3K/Akt, PIN, and Wnt signaling pathways. It was also predicted that these miRNAs may reprogram the cells to induce proliferation and differentiation activity. Many miRNAs are likely to regulate genes important for the tendinopathy healing process, and the result of this study allows an approach for miRNA-mediated regeneration of the tenocyte for tendon healing. Based on computational analysis, the role of these miRNAs in different pathways was established, and the results provided insights into the combinatorial approach of miRNA-mediated cell reprogramming.

Conclusions

In this study, the association between miRNAs and the disease was evaluated to correlate the tendinopathy genes and the relevant role of different miRNAs in their regulation. Through this study, it was established that the synergistic effect of more than one miRNA on directed reprogramming of the cell could be helpful in the regeneration of damaged tissue. It is anticipated that this study will be helpful for the design of miRNA cocktails for the orchestration of cellular reprogramming events.

MiRNAs as Potential Regulators of Enthesis Healing: Findings in a Rodent Injury Model

MicroRNAs (miRNAs) are short non-coding RNA sequences with the ability to inhibit the expression of a target mRNA at the post-transcriptional level, acting as modulators of both the degenerative and regenerative processes. Therefore, these molecules constitute a potential source of novel therapeutic tools. In this study, we investigated the miRNA expression profile that presented in enthesis tissue upon injury. For this, a rodent enthesis injury model was developed by creating a defect at a rat's patellar enthesis. Following injury, explants were collected on days 1 (n = 10) and 10 (n = 10). Contra lateral samples (n = 10) were harvested to be used for normalization. The expression of miRNAs was investigated using a "Fibrosis" pathway-focused miScript qPCR array. Later, target prediction for the aberrantly expressed miRNAs was performed by means of the Ingenuity Pathway Analysis, and the expression of mRNA targets relevant for enthesis healing was confirmed using qPCRs. Additionally, the protein expression levels of collagens I, II, III, and X were investigated using Western blotting. The mRNA expression pattern of EGR1, COL2A1, RUNX2, SMAD1, and SMAD3 in the injured samples indicated their possible regulation by their respective targeting miRNA, which included miR-16, -17, -100, -124, -133a, -155 and -182. Furthermore, the protein levels of collagens I and II were reduced directly after the injury (i.e., day 1) and increased 10 days post-injury, while collagens III and X showed the opposite pattern of expression.

Nanosilver-functionalized polysaccharides as a platform for wound dressing

Polysaccharides that are naturally sourced have enormous promise as wound dressings, due to their wider availability and reasonable cost and good biocompatibility. Furthermore, nanosilver extensively applied in wound treatment is attributed to its broad spectrum of antimicrobial effects and lesser drug resistance. Consequently, wound dressings in corporating nanosilver have attracted wide-scale interest in wound healing, and nanosilver-functionalized polysaccharide-based wound dressings present an affordable option for healing of chronic wounds. This review encompasses preparation methods, classification, and antibacterial performances of nanosilver wound dressings. The prospective research arenas of nanosilver-based wound polysaccharide dressings are also elaborated. The review attempts to include a summary of the most recent advancements in silver nanotechnology as well as guidance for the investigation of nanosilver-functionalized polysaccharide-based wound dressings.

TGF-β1 stimulated mesenchymal stem cells-generated exosomal miR-29a promotes the proliferation, migration and fibrogenesis of tenocytes by targeting FABP3

BACKGROUND

Rotator cuff Tear (RCT) causes a lot of inconvenience for patients. In most cases, RCT injury does not heal back to bone after repair, and there is a high chance of retearing. Therefore, there is a need to explore more effective targeted therapies. Bone mesenchymal stem cell-derived exosome (BMSCs-Exo) has been proved to be beneficial to the proliferation of tendon cells, but its specific mechanism remains to be further explored.

METHODS

BMSCs-Exo was isolated and identified by detecting the specific markers using flow cytometry and western blot assays. qRT-PCR and western blot were utilized to determine the gene or protein expressions, respectively. Cell proliferation, and migration in tenocytes were measured by CCK8, EdU and transwell assays. The interaction between miR-29a and FABP3 was analyzed using dual-luciferase reporter assay.

RESULTS

Our findings demonstrated that miR-29a was expressed in BMSCs-Exo and could be significantly enriched after TGF-β1 treatment. Moreover, TGF-β1-modified BMSCs-Exo co-cultured could promote the proliferation, migration and fibrosis of tenocytes by carrying miR-29a. Upon miR-29a was reduced in BMSCs-Exo, the regulatory roles of BMSCs-Exo on tenocytes were reversed. Mechanistically, miR-29a negatively regulated FABP3 via interaction with its 3'-UTR. Enforced expression of FABP3 could reverse the modulation of exosomal miR-29a in tenocytes.

CONCLUSION

Exosomal miR-29a derived from TGF-β1-modified BMSCs facilitated the proliferation, migration and fibrosis of tenocytes through targeting FABP3.

MicroRNA-29a and MicroRNA-124 as novel biomarkers for hepatocellular carcinoma

BACKGROUND

Numerous microRNAs (miRNAs) have been observed to be abnormally expressed in cancer. Therefore, miRNA signatures could be potential noninvasive diagnostic and prognostic biomarkers for hepatocellular carcinoma (HCC).

AIMS

To correlate miRNA-29a and miRNA-124 expression levels with the clinical features and survival rates of HCC patients.

METHODS

Serum miRNA expression in 150 samples (50 patients with HCC, 50 patients with liver cirrhosis, and 50 healthy controls) were quantified using real-time qRT-PCR.

RESULTS

The expression levels of serum miRNA-29a were higher and the levels of miRNA-124 were lower in patients with HCC than in patients with liver cirrhosis and controls. ROC curve analysis showed promising accuracy for both miRNAs in distinguishing patients with HCC from those with liver cirrhosis. Levels of miRNA-29a were related to tumor number, size, stage, and outcome, whereas levels of miRNA-124 were related to vascular invasion. The overall survival rate of patients with low miRNA-29a expression was significantly higher than that of patients with high expression. Additionally, the multivariate analysis identified miRNA-29a as an independent prognostic variable.

CONCLUSIONS

The investigated miRNAs showed acceptable accuracy in the diagnosis of HCC; therefore, both could be utilized as diagnostic biomarkers. Additionally, miRNA-29a could be used as a prognostic biomarker.

Biological and Mechanical Factors and Epigenetic Regulation Involved in Tendon Healing

Tendons are an important part of the musculoskeletal system. Connecting muscles to bones, tendons convert force into movement. Tendon injury can be acute or chronic. Noticeably, tendon healing requires a long time span and includes inflammation, proliferation, and remodeling processes. The mismatch between endogenous and exogenous healing may lead to adhesion causing further negative effects. Management of tendon injuries and complications such as subsequent adhesion formation are still challenges for clinicians. Due to numerous factors, tendon healing is a complex process. This review introduces the role of various biological and mechanical factors and epigenetic regulation processes involved in tendon healing.

Revealing stromal and lymphoid sources of Col3a1-expression during inflammation using a novel reporter mouse

One of the earliest signs of dysregulation of the homeostatic process of fibrosis, associated with pathology in chronic conditions such as rheumatoid arthritis, is the overexpression of collagen type III (COL-3). Critically, there is still relatively little known regarding the identity of the cell types expressing the gene encoding COL-3 (Col3a1). Identifying and characterizing Col3a1-expressing cells during the development of fibrosis could reveal new targets for the diagnosis and treatment of fibrosis-related pathologies. As such, a reporter mouse expressing concomitantly Col3a1 and mKate-2, a fluorescent protein, was generated. Using models of footpad inflammation, we demonstrated its effectiveness as a tool to measure the expression of COL-3 during the repair process and provided an initial characterization of some of the stromal and immune cells responsible for Col3a1 expression.

Dual Immune Regulatory Roles of Interleukin-33 in Pathological Conditions

Interleukin-33 (IL-33), a member of the IL-1 cytokine family and a multifunctional cytokine, plays critical roles in maintaining host homeostasis and in pathological conditions, such as allergy, infectious diseases, and cancer, by acting on multiple types of immune cells and promoting type 1 and 2 immune responses. IL-33 is rapidly released by immune and non-immune cells upon stimulation by stress, acting as an “alarmin” by binding to its receptor, suppression of tumorigenicity 2 (ST2), to trigger downstream signaling pathways and activate inflammatory and immune responses. It has been recognized that IL-33 displays dual-functioning immune regulatory effects in many diseases and has both pro- and anti-tumorigenic effects, likely depending on its primary target cells, IL-33/sST2 expression levels, cellular context, and the cytokine microenvironment. Herein, we summarize our current understanding of the biological functions of IL-33 and its roles in the pathogenesis of various conditions, including inflammatory and autoimmune diseases, infections, cancers, and cases of organ transplantation. We emphasize the nature of context-dependent dual immune regulatory functions of IL-33 in many cells and diseases and review systemic studies to understand the distinct roles of IL-33 in different cells, which is essential to the development of more effective diagnoses and therapeutic approaches for IL-33-related diseases.

Enhanced tendon healing by a tough hydrogel with an adhesive side and high drug-loading capacity

Hydrogels that provide mechanical support and sustainably release therapeutics have been used to treat tendon injuries. However, most hydrogels are insufficiently tough, release drugs in bursts, and require cell infiltration or suturing to integrate with surrounding tissue. Here we report that a hydrogel serving as a high-capacity drug depot and combining a dissipative tough matrix on one side and a chitosan adhesive surface on the other side supports tendon gliding and strong adhesion (larger than 1,000 J m-2) to tendon on opposite surfaces of the hydrogel, as we show with porcine and human tendon preparations during cyclic-friction loadings. The hydrogel is biocompatible, strongly adheres to patellar, supraspinatus and Achilles tendons of live rats, boosted healing and reduced scar formation in a rat model of Achilles-tendon rupture, and sustainably released the corticosteroid triamcinolone acetonide in a rat model of patellar tendon injury, reducing inflammation, modulating chemokine secretion, recruiting tendon stem and progenitor cells, and promoting macrophage polarization to the M2 phenotype. Hydrogels with 'Janus' surfaces and sustained-drug-release functionality could be designed for a range of biomedical applications.

Advances toward transformative therapies for tendon diseases

Approved therapies for tendon diseases have not yet changed the clinical practice of symptomatic pain treatment and physiotherapy. This review article summarizes advances in the development of novel drugs, biologic products, and biomaterial therapies for tendon diseases with perspectives for translation of integrated therapies. Shifting from targeting symptom relief toward disease modification and prevention of disease progression may open new avenues for therapies. Deep evidence-based clinical, cellular, and molecular characterization of the underlying pathology of tendon diseases, as well as therapeutic delivery optimization and establishment of multidiscipline interorganizational collaboration platforms, may accelerate the discovery and translation of transformative therapies for tendon diseases.

Epigenetic Alterations in Sports-Related Injuries

It is a well-known fact that physical activity benefits people of all age groups. However, highly intensive training, maladaptation, improper equipment, and lack of sufficient rest lead to contusions and sports-related injuries. From the perspectives of sports professionals and those performing regular–amateur sports activities, it is important to maintain proper levels of training, without encountering frequent injuries. The bodily responses to physical stress and intensive physical activity are detected on many levels. Epigenetic modifications, including DNA methylation, histone protein methylation, acetylation, and miRNA expression occur in response to environmental changes and play fundamental roles in the regulation of cellular activities. In the current review, we summarise the available knowledge on epigenetic alterations present in tissues and organs (e.g., muscles, the brain, tendons, and bones) as a consequence of sports-related injuries. Epigenetic mechanism observations have the potential to become useful tools in sports medicine, as predictors of approaching pathophysiological alterations and injury biomarkers that have already taken place.

Evaluation of SS-31 as a Potential Strategy for Tendinopathy Treatment: An In Vitro Model

BACKGROUND

Studies in our laboratory have demonstrated mitochondrial dysfunction in human and animal models of supraspinatus tendinopathy. SS-31 (elamipretide) has been reported to improve mitochondrial function and to be effective in clinical trials for several diseases. The potential of SS-31 in treating tendinopathy has not been explored.

HYPOTHESIS

SS-31 would improve mitochondrial function in human tenocytes sampled from patients with tendinopathy.

STUDY DESIGN

Controlled laboratory study.

METHODS

Healthy tenocytes were obtained from normal hamstring tendon biopsy specimens in 9 patients undergoing anterior cruciate ligament reconstruction, and tenocytes were collected from degenerative supraspinatus tendon biopsy specimens in 9 patients undergoing rotator cuff repair. Tenocytes were cultured, used at passage 1, and assigned to 4 groups: healthy tenocytes, healthy tenocytes with 1μM SS-31 treatment for 72 hours, degenerative tenocytes, and degenerative tenocytes with 1μM SS-31 treatment for 72 hours. The outcomes included measurements of mitochondrial potential, mitochondrial morphology by transmission electron microscopy imaging, reactive oxygen species and superoxidative dismutase activity, gene expression, and cell viability.

RESULTS

An increase in the cell fraction with depolarized mitochondria was found in degenerative tenocytes (P = .014), followed by a decrease after SS-31 treatment (P = .018). Transmission electron microscopy images demonstrated morphological changes with a decreased number and size of mitochondria per cell in the degenerative tenocytes (P = .018) and with improvement after SS-31 treatment. There was no significant difference in the level of reactive oxygen species between healthy and degenerative tenocytes in culture, but superoxidative dismutase activity was significantly decreased in the degenerative group (P = .006), which then increased after SS-31 treatment (P = .012). These findings suggested that mitochondrial dysfunction may be reversed by SS-31 treatment. The gene expression of matrix metalloproteinase-1 (matrix remodeling, P = .029) and fatty acid-binding protein 4 (fatty infiltration, P = .046) was significantly upregulated in the degenerative tenocytes and reduced by SS-31 treatment (P = .048; P = .007). Gene expression for hypoxia-inducible factor1 α and the proapoptotic regulator Bcl-2-associated X protein was increased in the degenerative tenocytes. There was a significant decrease in cell viability in degenerative tenocytes as compared with the healthy tenocytes, with small improvement after treatment with SS-31.

CONCLUSION

There are changes in mitochondrial structure and function in tenocytes derived from degenerative tendons, and SS-31, as a mitochondrial protectant, could improve mitochondrial function and promote the healing of tendinopathy.

CLINICAL RELEVANCE

Mitochondrial dysfunction appears to play a role in the development of tendinopathy, and SS-31, as a mitochondrial protective agent, may be a therapeutic agent in the treatment of tendinopathy.

Age-related changes in microRNAs expression in cruciate ligaments of wild-stock house mice

Cruciate ligaments (CL) of the knee joint are injured following trauma or aging. MicroRNAs (miRs) are potential therapeutic targets in musculoskeletal disorders, but there is little known about the role of miRs and their expression ligaments during aging. This study aimed to (1) identify if mice with normal physical activity, wild-stock house mice are an appropriate model to study age-related changes in the knee joint and (2) investigate the expression of miRs in aging murine cruciate ligaments. Knee joints were collected from 6 and 24 months old C57BL/6 and wild-stock house mice (Mus musculus domesticus) for ligament and cartilage (OARSI) histological analysis. Expression of miR targets in CLs was determined in 6-, 12-, 24-, and 30-month-old wild-stock house mice, followed by the analysis of predicted mRNA target genes and Ingenuity Pathway Analysis. Higher CL and knee OARSI histological scores were found in 24-month-old wild-stock house mice compared with 6- and 24-month-old C57BL/6 and 6-month-old wild-stock house mice (p < 0.05). miR-29a and miR-34a were upregulated in 30-month-old wild-stock house mice in comparison with 6-, 12-, and 24-month-old wild-stock house mice (p < 0.05). Ingenuity Pathway Analysis on miR-29a and 34a targets was associated with inflammation through interleukins, TGFβ and Notch genes, and p53 signaling. Collagen type I alpha 1 chain (COL1A1) correlated negatively with both miR-29a (r = -0.35) and miR-34a (r = -0.33). The findings of this study support wild-stock house mice as an appropriate aging model for the murine knee joint. This study also indicated that miR-29a and miR-34a may be potential regulators of COL1A1 gene expression in murine CLs.

Advances in Stem Cell Therapies for Rotator Cuff Injuries

Rotator cuff injury is a common upper extremity musculoskeletal disease that may lead to persistent pain and functional impairment. Despite the clinical outcomes of the surgical procedures being satisfactory, the repair of the rotator cuff remains problematic, such as through failure of healing, adhesion formation, and fatty infiltration. Stem cells have high proliferation, strong paracrine action, and multiple differentiation potential, which promote tendon remodeling and fibrocartilage formation and increase biomechanical strength. Additionally, stem cell-derived extracellular vesicles (EVs) can increase collagen synthesis and inhibit inflammation and adhesion formation by carrying regulatory proteins and microRNAs. Therefore, stem cell-based therapy is a promising therapeutic strategy that has great potential for rotator cuff healing. In this review, we summarize the advances of stem cells and stem cell-derived EVs in rotator cuff repair and highlight the underlying mechanism of stem cells and stem cell-derived EVs and biomaterial delivery systems. Future studies need to explore stem cell therapy in combination with cellular factors, gene therapy, and novel biomaterial delivery systems.

Changes in Physiological Tendon Substrate Stiffness Have Moderate Effects on Tendon-Derived Cell Growth and Immune Cell Activation

Tendinopathy is characterised by pathological changes in tendon matrix composition, architecture, and stiffness, alterations in tendon resident cell characteristics, and fibrosis, with inflammation also emerging as an important factor in tendinopathy progression. The sequence of pathological changes in tendinopathy and the cellular effects of the deteriorating matrix are largely unknown. This study investigated the effects of substrate stiffness on tendon-derived cells (TDCs) and THP-1 macrophages using PDMS substrates representing physiological tendon stiffness (1.88 MPa), a stiff gel (3.17 MPa) and a soft gel (0.61 MPa). Human TDCs were cultured on the different gel substrates and on tissue culture plastic. Cell growth was determined by alamarBlue™ assay, cell morphology was analysed in f-actin labelled cells, and phenotypic markers were analysed by real-time PCR. We found that in comparison to TDCs growing on gels with physiological stiffness, cell growth increased on soft gels at 48 h (23%, p = 0.003). Cell morphology was similar on all three gels. SCX expression was slightly reduced on the soft gels (1.4-fold lower, p = 0.026) and COL1A1 expression increased on the stiff gels (2.2-fold, p = 0.041). Culturing THP-1 macrophages on soft gels induced increased expression of IL1B (2-fold, p = 0.018), and IL8 expression was inhibited on the stiffer gels (1.9-fold, p = 0.012). We also found that culturing TDCs on plastic increased cell growth, altered cell morphology, and inhibited the expression of SCX, SOX9, MMP3, and COL3. We conclude that TDCs and macrophages respond to changes in matrix stiffness. The magnitude of responses measured in TDCs were minor on the range of substrate stiffness tested by the gels. Changes in THP-1 macrophages suggested a more inflammatory phenotype on substrates with non-physiological stiffness. Although cell response to subtle variations in matrix stiffness was moderate, it is possible that these alterations may contribute to the onset and progression of tendinopathy.

Bioinspired bimodal micro-nanofibrous scaffolds promote the tenogenic differentiation of tendon stem/progenitor cells for achilles tendon regeneration

Poor tendon repair remains a clinical problem due to the difficulties in replicating the complex multiscale hierarchical structure of native tendons. In this work, a bioinspired fibrous scaffold with bimodal micro-nanofibers and a teno-inductive aligned topography was developed to replicate microscale collagen fibers and nanoscale collagen fibrils that compose native tendons. The results showed indicated that the combination of micro- and nanofibers enhanced the mechanical properties. Furthermore, their biological performance was assessed using tendon stem/progenitor cells (TSPCs). Micro-nanofibers induced a higher cell aspect ratio and enhanced the tenogenic differentiation of TSPCs compared to micro- and nanocontrols. Interestingly, it was observed that scaffold nanotopography and microstructures promoted tenogenesis via activating the TGF-β/Smad2/3-mediated signaling pathway. The in situ implantation study confirmed that micro-nanofibrous scaffolds promoted the structural and mechanical properties of the regenerated Achilles tendon. Overall, our study shows that the bimodal micro-nanofibrous scaffold developed here presents a promising potential to improve the outcomes of tendon tissue engineering.

Inflammatory mechanisms linking obesity and tendinopathy

Chronic tendinopathy is a debilitating tendon disorder with disappointing treatment outcomes. This review focuses on the potential roles of chronic low-grade inflammation in promoting tendinopathy in obesity. A systematic literature search was performed to identify all clinical studies supporting the actions of obesity-associated inflammatory mediators in the development of tendinopathy. The mechanisms of obesity-induced chronic inflammation in adipose tissue are firstly reviewed. Common inflammatory mediators potentially linking obesity and the development of tendinopathy, and their association with mechanical overuse, are discussed, along with pre-clinical evidences and a systematic literature search on clinical studies. The potential contribution of local adipose tissues in the promotion of inflammation, pain and tendon degeneration is then discussed. The future research directions are proposed.

Translational potential statement

Better understanding of the roles of obesity-associated inflammatory mediators on tendons will clarify the pathophysiological drivers of tendinopathy in patients with obesity and identify possible treatment targets. Further studies on the mechanisms of obesity-induced chronic inflammation on tendon are a promising direction for the treatment of tendinopathy.

Association of COA1 with Patellar Tendonitis: A Genome-wide Association Analysis

PURPOSE

It is unknown why some athletes develop patellar tendinopathy and others do not, even when accounting for similar workloads between individuals. Genetic differences between these two populations may be a contributing factor. The purpose of this work was to screen the entire genome for genetic markers associated with patellar tendinopathy.

METHODS

Genome-wide association (GWA) analyses were performed utilizing data from the Kaiser Permanente Research Board (KPRB) and the UK Biobank. Patellar tendinopathy cases were identified based on electronic health records from KPRB and UK Biobank. GWA analyses from both cohorts were tested for patellar tendinopathy using a logistic regression model adjusting for sex, height, weight, age, and race/ethnicity using allele counts for single nucleotide polymorphisms. The data from the two GWA studies (KPRB and UK Biobank) were combined in a meta-analysis.

RESULTS

There were a total of 1670 cases of patellar tendinopathy and 293,866 controls within the two cohorts. Two single nucleotide polymorphisms located in the intron of the cytochrome c oxidase assembly factor 1 (COA1) gene showed a genome-wide significant association in the meta-analysis.

CONCLUSIONS

Genetic markers in COA1 seem to be associated with patellar tendinopathy and are potential risk factors for patellar tendinopathy that deserve further validation regarding molecular mechanisms.

Tendinopathy and tendon material response to load: What we can learn from small animal studies

Tendinopathy is a debilitating disease that causes as much as 30% of all musculoskeletal consultations. Existing treatments for tendinopathy have variable efficacy, possibly due to incomplete characterization of the underlying pathophysiology. Mechanical load can have both beneficial and detrimental effects on tendon, as the overall tendon response depends on the degree, frequency, timing, and magnitude of the load. The clinical continuum model of tendinopathy offers insight into the late stages of tendinopathy, but it does not capture the subclinical tendinopathic changes that begin before pain or loss of function. Small animal models that use high tendon loading to mimic human tendinopathy may be able to fill this knowledge gap. The goal of this review is to summarize the insights from in-vivo animal studies of mechanically-induced tendinopathy and higher loading regimens into the mechanical, microstructural, and biological features that help characterize the continuum between normal tendon and tendinopathy. STATEMENT OF SIGNIFICANCE: This review summarizes the insights gained from in-vivo animal studies of mechanically-induced tendinopathy by evaluating the effect high loading regimens have on the mechanical, structural, and biological features of tendinopathy. A better understanding of the interplay between these realms could lead to improved patient management, especially in the presence of painful tendon.

The role of MicroRNAs in tendon injury, repair, and related tissue engineering

Tendon injuries are one of the most common musculoskeletal disorders that cause considerable morbidity and significantly compromise the patients' quality of life. The innate limited regenerative capacity of tendon poses a substantial treating challenge for clinicians. MicroRNAs (miRNAs) are a family of small non-coding RNAs that play a vital role in orchestrating many biological processes through post-transcriptional regulation. Increasing evidence reveals that miRNA-based therapeutics may serve as an innovative strategy for the treatment of tendon pathologies. In this review, we briefly present miRNA biogenesis, the role of miRNAs in tendon cell biology and their involvement in tendon injuries, followed by a summary of current miRNA-based approaches in tendon tissue engineering with a special focus on attenuating post-injury fibrosis. Next, we discuss the advantages of miRNA-functionalized scaffolds in achieving sustained and localized miRNA administration to minimize off-target effects, and thus hoping to inspire the development of effective miRNA delivery platforms specifically for tendon tissue engineering. We envision that advancement in miRNA-based therapeutics will herald a new era of tendon tissue engineering and pave a way for clinical translation for the treatments of tendon disorders.

CD146 Delineates an Interfascicular Cell Sub-Population in Tendon That Is Recruited during Injury through Its Ligand Laminin-α4

The interfascicular matrix (IFM) binds tendon fascicles and contains a population of morphologically distinct cells. However, the role of IFM-localised cell populations in tendon repair remains to be determined. The basement membrane protein laminin-α4 also localises to the IFM. Laminin-α4 is a ligand for several cell surface receptors, including CD146, a marker of pericyte and progenitor cells. We used a needle injury model in the rat Achilles tendon to test the hypothesis that the IFM is a niche for CD146+ cells that are mobilised in response to tendon damage. We also aimed to establish how expression patterns of circulating non-coding RNAs alter with tendon injury and identify potential RNA-based markers of tendon disease. The results demonstrate the formation of a focal lesion at the injury site, which increased in size and cellularity for up to 21 days post injury. In healthy tendon, CD146+ cells localised to the IFM, compared with injury, where CD146+ cells migrated towards the lesion at days 4 and 7, and populated the lesion 21 days post injury. This was accompanied by increased laminin-α4, suggesting that laminin-α4 facilitates CD146+ cell recruitment at injury sites. We also identified a panel of circulating microRNAs that are dysregulated with tendon injury. We propose that the IFM cell niche mediates the intrinsic response to injury, whereby an injury stimulus induces CD146+ cell migration. Further work is required to fully characterise CD146+ subpopulations within the IFM and establish their precise roles during tendon healing.

A combined physicochemical approach towards human tenocyte phenotype maintenance

During in vitro culture, bereft of their optimal tissue context, tenocytes lose their phenotype and function. Considering that tenocytes in their native tissue milieu are exposed simultaneously to manifold signals, combination approaches (e.g. growth factor supplementation and mechanical stimulation) are continuously gaining pace to control cell fate during in vitro expansion, albeit with limited success due to the literally infinite number of possible permutations. In this work, we assessed the potential of scalable and potent physicochemical approaches that control cell fate (substrate stiffness, anisotropic surface topography, collagen type I coating) and enhance extracellular matrix deposition (macromolecular crowding) in maintaining human tenocyte phenotype in culture. Cell morphology was primarily responsive to surface topography. The tissue culture plastic induced the largest nuclei area, the lowest aspect ratio, and the highest focal adhesion kinase. Collagen type I coating increased cell number and metabolic activity. Cell viability was not affected by any of the variables assessed. Macromolecular crowding intensely enhanced and accelerated native extracellular matrix deposition, albeit not in an aligned fashion, even on the grooved substrates. Gene analysis at day 14 revealed that the 130 kPa grooved substrate without collagen type I coating and under macromolecular crowding conditions positively regulated human tenocyte phenotype. Collectively, this work illustrates the beneficial effects of combined physicochemical approaches in controlling cell fate during in vitro expansion.

Overexpression of mechanical sensitive miR-337-3p alleviates ectopic ossification in rat tendinopathy model via targeting IRS1 and Nox4 of tendon-derived stem cells

Tendinopathy, which is characterized by the ectopic ossification of tendon, is a common disease occurring in certain population, such as athletes that suffer from repetitive tendon strains. However, the molecular mechanism underlying the pathogenesis of tendinopathy caused by the overuse of tendon is still lacking. Here, we found that the mechanosensitive miRNA, miR-337-3p, had lower expression under uniaxial cyclical mechanical loading in tendon-derived stem cells (TDSCs) and negatively controlled chondro-osteogenic differentiation of TDSCs. Importantly, downregulation of miR-337-3p expression was also observed in both rat and human calcified tendons, and overexpressing miR-337-3p in patellar tendons of rat tendinopathy model displayed a robust therapeutic efficiency. Mechanistically, we found that the proinflammatory cytokine interleukin-1β was the upstream factor of miR-337-3p that bridges the mechanical loading with its downregulation. Furthermore, the target genes of miR-337-3p, NADPH oxidase 4, and insulin receptor substrate 1, activated chondro-osteogenic differentiation of TDSCs through JNK and ERK signaling, respectively. Thus, these findings not only provide novel insight into the molecular mechanisms underlying ectopic ossification in tendinopathy but also highlight the significance of miR-337-3p as a putative therapeutic target for clinic treatment of tendinopathy.

The Role of miRNA in the Pathophysiology of Neuroendocrine Tumors

Neuroendocrine tumors (NETs) represent a tumor group that is both rare and heterogeneous. Prognosis is largely determined by the tumor grading and the site of the primary tumor and metastases. Despite intensive research efforts, only modest advances in diagnostic and therapeutic approaches have been achieved in recent years. For patients with non-respectable tumor stages, prognosis is poor. In this context, the development of novel diagnostic tools for early detection of NETs and prediction of tumor response to therapy as well as estimation of the overall prognosis would greatly improve the clinical management of NETs. However, identification of novel diagnostic molecules is hampered by an inadequate understanding of the pathophysiology of neuroendocrine malignancies. It has recently been demonstrated that microRNA (miRNA), a family of small RNA molecules with an established role in the pathophysiology of quite different cancer entities, may also play a role as a biomarker. Here, we summarize the available knowledge on the role of miRNAs in the development of NET and highlight their potential use as serum-based biomarkers in the context of this disease. We discuss important challenges currently preventing their use in clinical routine and give an outlook on future directions of miRNA research in NET.

Novel self-amplificatory loop between T cells and tenocytes as a driver of chronicity in tendon disease

OBJECTIVES

Increasing evidence suggests that inflammatory mechanisms play a key role in chronic tendon disease. After observing T cell signatures in human tendinopathy, we explored the interaction between T cells and tendon stromal cells or tenocytes to define their functional contribution to tissue remodelling and inflammation amplification and hence disease perpetuation.

METHODS

T cells were quantified and characterised in healthy and tendinopathic tissues by flow cytometry (FACS), imaging mass cytometry (IMC) and single cell RNA-seq. Tenocyte activation induced by conditioned media from primary damaged tendon or interleukin-1β was evaluated by qPCR. The role of tenocytes in regulating T cell migration was interrogated in a standard transwell membrane system. T cell activation (cell surface markers by FACS and cytokine release by ELISA) and changes in gene expression in tenocytes (qPCR) were assessed in cocultures of T cells and explanted tenocytes.

RESULTS

Significant quantitative differences were observed in healthy compared with tendinopathic tissues. IMC showed T cells in close proximity to tenocytes, suggesting tenocyte-T cell interactions. On activation, tenocytes upregulated inflammatory cytokines, chemokines and adhesion molecules implicated in T cell recruitment and activation. Conditioned media from activated tenocytes induced T cell migration and coculture of tenocytes with T cells resulted in reciprocal activation of T cells. In turn, these activated T cells upregulated production of inflammatory mediators in tenocytes, while increasing the pathogenic collagen 3/collagen 1 ratio.

CONCLUSIONS

Interaction between T cells and tenocytes induces the expression of inflammatory cytokines/chemokines in tenocytes, alters collagen composition favouring collagen 3 and self-amplifies T cell activation via an auto-regulatory feedback loop. Selectively targeting this adaptive/stromal interface may provide novel translational strategies in the management of human tendon disorders.

Cell lineage tracing and functional assessment of supraspinatus tendon healing in an acute repair murine model

Rotator cuff supraspinatus tendon injuries are common with high rates of anatomic failure after surgical repair. The purpose of the study was to define clinically relevant features of a mouse model of supraspinatus tendon injury to determine painful, functional, and structural outcomes; we further investigated two cell populations mediating healing using genetic lineage tracing after full detachment and repair of the supraspinatus tendon in mice. The pain was assessed using the mouse grimace scale and function by gait analysis and tensile testing. Histological and microCT analyses were used to determine enthesis/tendon and bone structure, respectively. Lineage tracing was carried out using inducible Cre lines for ScxCreERT2 (tendon cells) and αSMACreERT2 (myofibroblasts and mesenchymal progenitors). Mice only expressed pain transiently after surgery despite long-term impairment of functional and structural properties. Gait, tensile mechanical properties, and bone properties were significantly reduced after injury and repair. Lineage tracing showed relatively few Scx ^lin tendon cells while αSMA ^lin cells contributed strongly to scar formation. Despite surgical reattachment of healthy tendon, lineage tracing revealed poor preservation of supraspinatus tendon after acute injury and loss of tendon structure, suggesting that tendon degeneration is also a key impediment of successful rotator cuff repair. Scar formation after surgery is mediated largely by αSMA ^lin cells and results in permanently reduced functional and structural properties.

Reparative and Maladaptive Inflammation in Tendon Healing

Tendon injuries are common and debilitating, with non-regenerative healing often resulting in chronic disease. While there has been considerable progress in identifying the cellular and molecular regulators of tendon healing, the role of inflammation in tendon healing is less well understood. While inflammation underlies chronic tendinopathy, it also aids debris clearance and signals tissue repair. Here, we highlight recent findings in this area, focusing on the cells and cytokines involved in reparative inflammation. We also discuss findings from other model systems when research in tendon is minimal, and explore recent studies in the treatment of human tendinopathy to glean further insights into the immunobiology of tendon healing.