Human Rotator Cuff Tears Reveal an Age-Dependent Increase in Markers of Cellular Senescence and Selective Removal of Senescent Cells With Dasatinib + Quercetin Increases Genetic Expression of COL1A1 In Vitro

Cellular senescence impairs tendon extracellular matrix remodeling in response to mechanical unloading

Musculoskeletal injuries, including tendinopathies, present a significant clinical burden for aging populations. While the biological drivers of age-related declines in tendon function are poorly understood, it is well accepted that dysregulation of extracellular matrix (ECM) remodeling plays a role in chronic tendon degeneration. Senescent cells, which have been associated with multiple degenerative pathologies in musculoskeletal tissues, secrete a highly pro-inflammatory senescence-associated secretory phenotype (SASP) that has potential to promote ECM breakdown. However, the role of senescent cells in the dysregulation of tendon ECM homeostasis is largely unknown. To assess this directly, we developed an in vitro model of induced cellular senescence in murine tendon explants. This novel technique enables us to study the isolated interactions of senescent cells and their native ECM without interference from age-related systemic changes. We document multiple biomarkers of cellular senescence in induced tendon explants including cell cycle arrest, apoptosis resistance, and sustained inflammatory responses. We then utilize this in vitro senescence model to compare the ECM remodeling response of young, naturally aged, and induced-senescent tendons to an altered mechanical stimulus. We found that both senescence and aging independently led to alterations in ECM-related gene expression, reductions in protein synthesis, and tissue compositional changes. Furthermore, MMP activity was sustained, thus shifting the remodeling balance of aged and induced-senescent tissues towards degradation over production. Together, this demonstrates that cellular senescence plays a role in the altered mechano-response of aged tendons and likely contributes to poor clinical outcomes in aging populations.

Role of oxidative stress in the concurrent development of osteoporosis and tendinopathy: Emerging challenges and prospects for treatment modalities

Both osteoporosis and tendinopathy are widely prevalent disorders, encountered in diverse medical contexts. Whilst each condition has distinct pathophysiological characteristics, they share several risk factors and underlying causes. Notably, oxidative stress emerges as a crucial intersecting factor, playing a pivotal role in the onset and progression of both diseases. This imbalance arises from a dysregulation in generating and neutralising reactive oxygen species (ROS), leading to an abnormal oxidative environment. Elevated levels of ROS can induce multiple cellular disruptions, such as cytotoxicity, apoptosis activation and reduced cell function, contributing to tissue deterioration and weakening the structural integrity of bones and tendons. Antioxidants are substances that can prevent or slow down the oxidation process, including Vitamin C, melatonin, resveratrol, anthocyanins and so on, demonstrating potential in treating these overlapping disorders. This comprehensive review aims to elucidate the complex role of oxidative stress within the interlinked pathways of these comorbid conditions. By integrating contemporary research and empirical findings, our objective is to outline new conceptual models and innovative treatment strategies for effectively managing these prevalent diseases. This review underscores the importance of further in-depth research to validate the efficacy of antioxidants and traditional Chinese medicine in treatment plans, as well as to explore targeted interventions focused on oxidative stress as promising areas for future medical advancements.

Biologic Adjuvants to Rotator Cuff Repairs Induce Anti-inflammatory Macrophage 2 Polarization and Reduce Inflammatory Macrophage 1 Polarization In Vitro

PURPOSE

To examine the effect of various biologic adjuvants on the polarization of macrophages in an in vitro model for rotator cuff tears.

METHODS

Tissue was harvested from 6 patients undergoing arthroscopic rotator cuff repair. An in vitro model of the supraspinatus and subacromial bursa was created and treated with control, platelet-rich plasma (PRP), autologous activated serum (AAS), or a combination of PRP+AAS. The effect of treatment on macrophage polarization between M1 proinflammatory macrophages or M2 anti-inflammatory macrophages was measured using gene expression, protein expression, flow cytometry, and nitric oxide production.

RESULTS

Tendon and bursa treated with PRP, AAS, and PRP+AAS significantly decreased the gene expression of M1 markers interleukin (IL)-12 and tumor necrosis factor-alpha while significantly increasing the expression of M2 markers arginase, IL-10, and transforming growth factor-β (P < .05) compared with treatment with control. Enzyme-linked immunosorbent assay analysis of protein production demonstrated that, compared with control, coculture treated with PRP, AAS, and PRP+AAS significantly decreased markers of M1-macrophages (IL-6, IL-12, and tumor necrosis factor-alpha) while significantly increasing the expression of markers of M2-macrophages (arginase, IL-10, and transforming growth factor-beta) (P < .05). Flow cytometry analysis of surface markers demonstrated that compared with control, tendon and bursa treated with PRP, AAS, and PRP+AAS significantly decreased markers of M1-macrophages (CD80, CD86, CD64, CD16) while significantly increasing the expression of markers of M2-macrophages (CD163 and CD206) (P < .05). Treatment of the coculture with PRP, AAS, and PRP+AAS consistently demonstrated a decrease in nitric oxide production (P < .05) compared with control. AAS and PRP+AAS demonstrated an increased macrophage shift to M2 compared with PRP alone, whereas there was not as uniform of a shift when comparing PRP+AAS with AAS alone.

CONCLUSIONS

In an in vitro model of rotator cuff tears, the treatment of supraspinatus tendon and subacromial bursa with PRP, AAS, and PRP+AAS demonstrated an increase in markers of anti-inflammatory M2-macrophages and a concomitant decrease in markers of proinflammatory M1-macrophages. AAS and PRP+AAS contributed to a large shift to macrophage polarization to the anti-inflammatory M2 compared with PRP.

CLINICAL RELEVANCE

The mechanism of biologic adjuvant effects on the rotator cuff remains poorly understood. This study suggests that they may contribute to polarization of macrophages for their proinflammatory (M1) state to the anti-inflammatory (M2) state.

Editorial Commentary: Dasatinib With Quercetin Shows Promise in Decreasing Age-Related Senescence in the Rotator Cuff Tendon-Can It Work Elsewhere?

Cellular senescence is a fundamental mechanism seen in all age-related diseases. Human supraspinatus tendon and adjacent bursal specimens evaluated for cellular senescence by immunohistochemistry and gene expression show more senescent cells in older patients. This confirms the observation that older patients are more likely to have rotator cuff pathology, and older age is associated with lower rates of rotator cuff healing and more frequent tendon retears. Senolytic drugs can selectively eliminate senescent cells without a localized or systemic impact. Tendon and bursal specimens co-cultured and then incubated with dasatinib and quercetin for 48 hours show a significant decrease in senescent cells. This suggests that these drugs may slow biological aging in rotator cuff tendons and offer the possibility of a clinically effective treatment for the aging rotator cuff tendon. Moreover, this concept is promising for the development of future effective therapies addressing tissue senescence.