Targeting Senescent Tendon Stem/Progenitor Cells to Prevent or Treat Age-Related Tendon Disorders

Platelet-derived exosomes alleviate tendon stem/progenitor cell senescence and ferroptosis by regulating AMPK/Nrf2/GPX4 signaling and improve tendon-bone junction regeneration in rats

BACKGROUND

Tendon stem/progenitor cell (TSPC) senescence contributes to tendon degeneration and impaired tendon repair, resulting in age-related tendon disorders. Ferroptosis, a unique iron-dependent form of programmed cell death, might participate in the process of senescence. However, whether ferroptosis plays a role in TSPC senescence and tendon regeneration remains unclear. Recent studies reported that Platelet-derived exosomes (PL-Exos) might provide significant advantages in musculoskeletal regeneration and inflammation regulation. The effects and mechanism of PL-Exos on TSPC senescence and tendon regeneration are worthy of further study.

METHODS

Herein, we examined the role of ferroptosis in the pathogenesis of TSPC senescence. PL-Exos were isolated and determined by TEM, particle size analysis, western blot and mass spectrometry identification. We investigated the function and underlying mechanisms of PL-Exos in TSPC senescence and ferroptosis via western blot, real-time quantitative polymerase chain reaction, and immunofluorescence analysis in vitro. Tendon regeneration was evaluated by HE staining, Safranin-O staining, and biomechanical tests in a rotator cuff tear model in rats.

RESULTS

We discovered that ferroptosis was involved in senescent TSPCs. Furthermore, PL-Exos mitigated the aging phenotypes and ferroptosis of TSPCs induced by t-BHP and preserved their proliferation and tenogenic capacity. The in vivo animal results indicated that PL-Exos improved tendon-bone healing properties and mechanical strength. Mechanistically, PL-Exos activated AMPK phosphorylation and the downstream nuclear factor erythroid 2-related factor 2 (Nrf2)/glutathione peroxidase 4 (GPX4) signaling pathway, leading to the suppression of lipid peroxidation. AMPK inhibition or GPX4 inhibition blocked the protective effect of PL-Exos against t-BHP-induced ferroptosis and senescence.

CONCLUSION

In conclusion, ferroptosis might play a crucial role in TSPC aging. AMPK/Nrf2/GPX4 activation by PL-Exos was found to inhibit ferroptosis, consequently leading to the suppression of senescence in TSPCs. Our results provided new theoretical evidence for the potential application of PL-Exos to restrain tendon degeneration and promote tendon regeneration.

Injectable self-assembled GDF5-containing dipeptide hydrogels for enhanced tendon repair

Owing to the tissue characteristics of tendons with few blood vessels and cells, the regeneration and repair of injured tendons can present a considerable challenge, which considerably affects the motor function of limbs and leads to serious physical and mental pain, along with an economic burden on patients. Herein, we designed and fabricated a dipeptide hydrogel (DPH) using polypeptides P11-4 and P11-8. This hydrogel exhibited self-assembly characteristics and could be administered in vitro. To endow the hydrogel with differentiation and regeneration abilities, we added different concentrations of growth differentiation factor 5 (GDF5) to form GDF5@DPH. GDF5@DPH promoted the aggregation and differentiation of tendon stem/progenitor cells and promoted the regeneration and repair of tendon cells and collagen fibers in injured areas. In addition, GDF5@DPH inhibited inflammatory reactions in the injured area. Owing to its injectable properties, DPH can jointly inhibit adhesion and scar hyperplasia between tissues caused by endogenous inflammation and exogenous surgery and can provide a favorable internal environment for the regeneration and repair of the injured area. Overall, the GDF5@DPH system exhibits considerable promise as a novel approach to treating tendon injury.

Heterotopic mineralization (ossification or calcification) in aged musculoskeletal soft tissues: A new candidate marker for aging

Aging can lead to various disorders in organisms and with the escalating impact of population aging, the incidence of age-related diseases is steadily increasing. As a major risk factor for chronic illnesses in humans, the prevention and postponement of aging have become focal points of research among numerous scientists. Aging biomarkers, which mirror molecular alterations at diverse levels in organs, tissues, and cells, can be used to monitor and evaluate biological changes associated with aging. Currently, aging biomarkers are primarily categorized into physiological traits, imaging characteristics, histological features, cellular-level alterations, and molecular-level changes that encompass the secretion of aging-related factors. However, in the context of the musculoskeletal soft tissue system, aging-related biological indicators primarily involve microscopic parameters at the cellular and molecular levels, resulting in inconvenience and uncertainty in the assessment of musculoskeletal soft tissue aging. To identify convenient and effective indicators, we conducted a comprehensive literature review to investigate the correlation between ectopic mineralization and age-related changes in the musculoskeletal soft tissue system. Here, we introduce the concept of ectopic mineralization as a macroscopic, reliable, and convenient biomarker for musculoskeletal soft tissue aging and present novel targets and strategies for the future management of age-related musculoskeletal soft tissue disorders.

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.

HPF1 regulates tendon stem/progenitor cell senescence and tendon repair via PARP1-mediated poly-ADP ribosylation of HuR

BACKGROUND

Tendon stem/progenitor cells (TSPCs) play a vital role in tendon repair, regeneration and homeostasis. However, the specific mechanism of TSPCs aging is still unclear.

OBJECTIVE

This study aims to explore the role and molecular mechanism of HPF1 in the aging of TSPCs.

METHODS

Young and aged TSPCs (Y-TSPCs and A-TSPCs) were acquired from 3 to 4 and 24-26-month-old Sprague-Dawley male rats, TSPCs (Y-TSPCs and A-TSPCs) were subjected to senescence-associated β-galactosidase (SA-β-Gal))staining and telomerase activity detection, p16, p21, Scx, Tnmd, Col1, Col3HPF1 and PAPR1 expression levels were detected by Western blot or Reverse Transcription-quantitative Polymerase Chain Reaction (RT-qPCR), Reciprocal co-immunoprecipitation (co-IP) was used to explore the interaction between HPF1 and PARP1. Ribonucleoprotein immunoprecipitation (RNP-IP) was used to analyze the binding of HuR to the senescence marker gene mRNAs, IP was used to perform HPF1 to the PARylation of HuR, and the half-life of p16 and p21 were detected. Finally, we established an in vivo model, and the tendon tissue was used to perform hematoxylin and eosin (HE) and masson's trichrome staining, as well as the immunohistochemical analysis of Col I and TNMD.

RESULTS

Compared with Y-TSPCs, A-TSPCs had significantly enhanced cell senescence and significantly reduced tendon differentiation ability, and significantly increased the expression of HPF1 and PARP1. In addition, HPF1 and PARP1 interacted and coordinated the senescence and differentiation of TSPCs, HPF1 could also regulate the expression of p21 and p21, the interaction of p16 or p21 with HuR, and the poly-ADP ribosylation of PARP1 to HuR. HPF1 overexpression and siHuR co-transfection significantly reduced the half-life of p16 and p21, and HPF1 and PARP1 regulated the mRNA levels of p16 and p21 through HuR. Finally, in vivo experiments have shown that HPF1 or PARP1 overexpression could both inhibit the ability of tendon differentiation and promote cell senescence.

CONCLUSIONS

HPF1 promoted the senescence of TSPCs and inhibits the tendon differentiation of TSPCs through PARP1-mediated poly-ADP ribosylation of HuR.

Effect of Aging on Tendon Biology, Biomechanics and Implications for Treatment Approaches

Tendon aging is associated with an increasing prevalence of tendon injuries and/or chronic tendon diseases, such as tendinopathy, which affects approximately 25% of the adult population. Aged tendons are often characterized by a reduction in the number and functionality of tendon stem/progenitor cells (TSPCs), fragmented or disorganized collagen bundles, and an increased deposition of glycosaminoglycans (GAGs), leading to pain, inflammation, and impaired mobility. Although the exact pathology is unknown, overuse and microtrauma from aging are thought to be major causative factors. Due to the hypovascular and hypocellular nature of the tendon microenvironment, healing of aged tendons and related injuries is difficult using current pain/inflammation and surgical management techniques. Therefore, there is a need for novel therapies, specifically cellular therapy such as cell rejuvenation, due to the decreased regenerative capacity during aging. To augment the therapeutic strategies for treating tendon-aging-associated diseases and injuries, a comprehensive understanding of tendon aging pathology is needed. This review summarizes age-related tendon changes, including cell behaviors, extracellular matrix (ECM) composition, biomechanical properties and healing capacity. Additionally, the impact of conventional treatments (diet, exercise, and surgery) is discussed, and recent advanced strategies (cell rejuvenation) are highlighted to address aged tendon healing. This review underscores the molecular and cellular linkages between aged tendon biomechanical properties and the healing response, and provides an overview of current and novel strategies for treating aged tendons. Understanding the underlying rationale for future basic and translational studies of tendon aging is crucial to the development of advanced therapeutics for tendon regeneration.

HMGB1: a potential new target for tendinopathy treatment

Tendinopathy describes a complex pathology of the tendon characterized by abnormalities in the microstructure, composition, and cellularity of the tendon, leading to pain, limitation of activity and reduced function. Nevertheless, the mechanism of tendinopathy has not been fully elucidated, and the treatment of tendinopathy remains a challenge. High mobility group box 1 (HMGB1), a highly conserved and multifaceted nuclear protein, exerts multiple roles and high functional variability and is involved in many biological and pathological processes. In recent years, several studies have suggested that HMGB1 is associated with tendinopathy and may play a key role in the pathogenesis of tendinopathy. Therefore, this review summarizes the expression and distribution of HMGB1 in tendinopathy, focuses on the roles of HMGB1 and HMGB1-based potential mechanisms involved in tendinopathy, and finally summarizes the findings on HMGB1-based therapeutic approaches in tendinopathy, probably providing new insight into the mechanism and further potential therapeutic targets of tendinopathy.