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

Inflammatory Cell Interactions in the Rotator Cuff Microenvironment: Insights From Single-Cell Sequencing

Rotator cuff injuries are a common cause of shoulder pain and dysfunction, with chronic inflammation complicating recovery. Recent advances in single-cell RNA sequencing (scRNA-seq) have provided new insights into the immune cell interactions within the rotator cuff microenvironment during injury and healing. This review focuses on the application of scRNA-seq to explore the roles of immune and nonimmune cells, including macrophages, T-cells, fibroblasts, and myofibroblasts, in driving inflammation, tissue repair, and fibrosis. We discuss how immune cell crosstalk and interactions with the extracellular matrix influence the progression of healing or pathology. Single-cell analyses have identified distinct molecular signatures associated with chronic inflammation, which may contribute to persistent tissue damage. Additionally, we highlight the therapeutic potential of targeting inflammation in rotator cuff repair, emphasizing personalized medicine approaches. Overall, the integration of scRNA-seq in studying rotator cuff injuries enhances our understanding of the cellular mechanisms involved and offers new perspectives for developing targeted treatments in regenerative medicine.

Mesenchymal Stem Cell Secretome Effectiveness in Healing Chronic Tendon Injury: Procollagen Analysis and Histopathology in Rat Tendons

Background

Chronic tendon injuries often lead to diminished healing capacity, necessitating innovative treatments. Mesenchymal stem cells (MSCs) secretome has emerged as a promising option for enhancing tendon repair through paracrine signaling. This study evaluates the effectiveness of MSC secretome, derived from tendon-derived stem cells (TDSCs) and adipose-derived stem cells (ASCs) in healing chronic Achilles tendon injuries in a rat model. The focus is on Procollagen Type I N-Terminal Peptide (PINP) and Procollagen Type III N-Terminal Peptide (PIIINP) levels, and histopathological changes.

Methods

Fourteen adult male rats were divided into four groups: Group I (TDSC secretome), Group II (ASC secretome), Group III (combination of TDSC and ASC secretome), and Group IV (control). The healing response was assessed through PINP and PIIINP immunoserological markers, and histopathological changes were analyzed. The study adhered to ARRIVE and ICLAS guidelines and followed the National Institutes of Health (NIH) Guide for the Care and Use of Laboratory Animals.

Results

The combination group showed significantly higher PINP levels compared to the control group (p = 0.004), suggesting enhanced Type I collagen synthesis. However, no significant differences in PIIINP levels were observed among the groups. Histopathological analysis showed no significant differences in collagen alignment or angiogenesis between treatment and control groups.

Conclusion

The MSC secretome, particularly the combination of TDSCs and ASCs, may accelerate collagen Type I synthesis and improve tendon microstructure. This suggests their potential for treating chronic tendon injuries. However, further research with longer observation periods and clinical trials is crucial to confirm these findings and advance our understanding of tendon healing.

Urolithin A attenuates apoptosis and ferroptosis in hyperlipidemic tenocytes through PPARδ/ALDH2-mediated antioxidative signaling

Urolithin A (URA), a product of the gut microflora from foods rich in ellagitannins found in berries and nuts, has demonstrated anti-inflammatory and antioxidative stress properties in various disease models. Ferroptosis, an iron-dependent form of cell death, is considered a pathogenic cause of tendinopathy. However, the effects of URA on hyperlipidemic tenocytes and the related molecular mechanisms for the treatment of tendinopathy have not been elucidated. The expression of various proteins in human primary tenocytes was assessed via Western blot analysis. Tenocyte reactive oxygen species (ROS) were detected via DCFDA staining. Apoptotic tenocytes were visualized via TUNEL staining. The activities of antioxidant enzymes and caspase 3 were measured via activity assays. Cell viability was examined via the MTT assay. In this study, we found that URA treatment blocked ferroptosis and apoptosis and improved oxidative stress in palmitate-treated tenocytes. Moreover, URA treatment reversed the changes in the expression of extracellular matrix (ECM) markers and impaired cell migration. siRNA targeting PPARδ or ALDH2 abrogated the effects of URA on tenocytes treated with palmitate. Additionally, treatment of tenocytes with URA increased SOD and catalase activities. These results suggest that URA ameliorates tenocyte ferroptosis and apoptosis through PPARδ/ALDH2 signaling-mediated suppression of oxidative stress. By utilizing natural bioactive compounds derived from renewable dietary sources, this study highlights a potential therapeutic avenue for treating obesity-related tendinopathy while emphasizing the importance of sustainable, health-promoting interventions.

Multifaceted roles of IL-17 in bone and tendon health

The interleukin-17 (IL-17) family, encompassing IL-17A to IL-17F, plays pivotal roles across various biomedical fields. IL-17A, a prominent cytokine, has garnered significant attention. However, the pathological effects of IL-17 can often be unpredictable. This review delves into the multifaceted roles of IL-17 family members in bone healing, tendon ossification, and aging. IL-17 is central in modulating the inflammatory response during bone healing, influencing osteoblast and osteoclast activities, and promoting bone regeneration. In the context of tendon ossification, IL-17 orchestrates the proliferation, differentiation, and apoptosis of fibroblasts, instigating inflammatory responses. It also impacts the functionality of tendon stem cells and the composition of the extracellular matrix, correlating with indicators of tendon senescence. By understanding these dynamic changes, we gain deeper insights into IL-17's crucial function in bone and tendon tissues, highlighting its potential in modulating inflammatory responses. As research continues to evolve, promising therapeutic interventions targeting IL-17 are on the horizon, addressing disease challenges and paving the way for new, effective treatments.

Hydrogels empowered mesenchymal stem cells and the derived exosomes for regenerative medicine in age-related musculoskeletal diseases

As the population ages, musculoskeletal diseases (MSK) have emerged as a significant burden for individuals, healthcare systems, and social care systems. Recently, regenerative medicine has exhibited vast potential in age-related MSK, with mesenchymal stromal cells (MSCs) and their derived exosomes (Exos) therapies showing distinct advantages. However, these therapies face several limitations, including issues related to ensuring stability and effective distribution within the body. Hydrogels, acting as an ideal carrier, can enhance the therapeutic effects and application range of MSCs and Exos derived from MSCs (MSC-Exos). Therefore, this review comprehensively summarizes the application progress of MSCs and MSC-Exos combined with hydrogels in age-related MSK disease research. It aims to provide a detailed perspective, showcasing the functional enhancement of MSCs and MSC-Exos when incorporated into hydrogels. Additionally, this review explores their potential and challenges in treating age-related MSK diseases, offering references for future research directions and potential innovative strategies.

Decorin Knockdown Improves Aged Tendon Healing by Enhancing Recovery of Viscoelastic Properties, While Biglycan May Not

The objective of the study was to determine the specific roles of decorin and biglycan in the early and late phases of tendon healing in aged mice. Aged (300 day-old) female wildtype (WT), Dcnflox/flox (I-Dcn-/-), Bgnflox/flox (I-Bgn-/-), and compound Dcnflox/flox/Bgnflox/flox (I-Dcn-/-/Bgn-/-) mice with a tamoxifen (TM) inducible Cre underwent a bilateral patellar tendon injury (PT). Cre excision of the conditional alleles was induced at 5 days (samples collected at 3 and 6 weeks) or 21 days post-injury (samples collected at 6 weeks). Scar tissue area, collagen architecture, gene expression and mechanical properties were assessed during re-establishment of tendon architecture after injury. Fibril diameter distribution was impacted by both decorin and biglycan knockdown at 3 and 6 weeks compared to WT. Although early healing appeared to be delayed in the I-Bgn-/- tendons (larger scar tissue area at 3 weeks), no differences in failure properties were detected. By 6 weeks, in the I-Dcn-/- tendons, we observed a better recovery of viscoelastic properties compared to the WT tendons (reduced stress relaxation and increased dynamic modulus) when the knockdown was induced early. This could be explained by the increased expression of other matrix proteins, such as elastin whose gene expression was increased at 3 weeks in the I-Dcn-/- tendons. Despite an impact on collagen fibrillogenesis, decorin and/or biglycan knockdown did not produce a detectable effect on quasi-static properties after patellar tendon injury. However, early decorin knockdown resulted in better recovery of viscoelastic properties. Mechanisms underlying this result remained to be clarified in further studies.

Viscoelastic Mechanics: From Pathology and Cell Fate to Tissue Regeneration Biomaterial Development

Viscoelasticity is the mechanical feature of living tissues and the cellular extracellular matrix (ECM) and has been recognized as an essential biophysical cue in cell function and fate regulation, tissue development and homeostasis maintenance, and disease progression. These findings provide new insights for the development of biomaterials with comparable viscoelastic properties as native ECMs and the tissue matrix, displaying promising applications in regeneration medicine. In this review, the relationship between matrix viscoelasticity and tissue functions (e.g., development and regeneration) in physiological conditions and disease progression (e.g., aging, degenerative, fibrosis, and tumor) in pathological conditions will be especially highlighted to figure out the potential therapeutic target for disease treatment and inspiration for tissue regeneration related biomaterial development. Furthermore, findings and an understanding of the cell response to ECM viscoelasticity and the mechanism behind it are comprehensively summarized to provide a pathophysiological basis for viscoelastic biomaterials design. The advances of viscoelastic biomaterials on defect tissue repair are also reviewed, suggesting the significance of the native matrix matchable microenvironment on tissue regeneration. Although challenging, tunable viscoelastic biomaterials that match the mechanical properties of native tissues and ECMs show great promise. They could promote tissue regeneration, treat degenerative diseases, and support the development of organoids and artificial organs.

Loss of Cochlin drives impairments in tendon structure and function

Aging tendons undergo disruptions in homeostasis, increased susceptibility to injury, and reduced capacity for healing. Exploring the mechanisms behind this disruption in homeostasis is essential for developing therapeutics aimed at maintaining tendon health through the lifespan. We have previously identified that the extracellular matrix protein, Cochlin, which is highly expressed in healthy flexor tendon, is consistently lost during both natural aging and upon depletion of Scleraxis-lineage cells in young animals, which recapitulates many aging-associated homeostatic disruptions. Therefore, we examined the effects of Cochlin-/- on tendon maturation and hypothesized that loss of Cochlin would disrupt normal tendon maturation and recapitulate phenotypes associated with disrupted adult tendon homeostasis, including alterations in collagen fibril organization, and impaired tendon mechanics. By 3-months of age, Cochlin-/- flexor tendons exhibited altered collagen structure, with these changes persisting through at least 9-months. In addition, Cochlin -/- tendons demonstrated significant declines in structural and material properties at 6-months, and structural properties at 9-months. While Cochlin-/- did not drastically change the overall tendon proteome, consistent decreases in proteins associated with RNA metabolism, extracellular matrix production and the cytoskeleton were observed in Cochlin -/-. Interestingly, disrupted tendon maturation via Cochlin-/- did not impair the tendon healing process. Taken together, these data define a critical role for Cochlin in facilitating physiological tendon maturation.

Smaller Width Quadriceps Tendon Grafts Maintain Advantageous Biomechanical Properties for ACL Reconstruction

Background

Despite clinical evidence of risks in knee arthrofibrosis and graft impingement with larger grafts, the optimal size for quadriceps tendon (QT) autografts in anterior cruciate ligament reconstruction (ACLR) has not been established.

Purpose/Hypothesis

This study aimed to evaluate the mechanical properties of full-thickness 6-mm and 8-mm wide QT grafts compared with 10-mm patellar tendon (PT) and 10-mm QT grafts. The hypothesis was that both the 6- and 8-mm QT grafts would exhibit similar or superior ultimate tensile strength compared with the 10-mm PT graft.

Study Design

Controlled laboratory study.

Methods

A total of 18 matched pairs of cadaveric knees were used in this study. From each pair, a 10-mm wide full-thickness QT was harvested from 1 knee. Based on randomization, a 6-mm wide or 8-mm wide full-thickness QT along with a 10-mm wide PT were harvested from the contralateral knee. Each tendon was clamped, tensioned, and cycled on a servohydraulic testing machine before final loading to failure.

Results

The ultimate failure load was 1286 ± 237.3 N for the 10-mm QT, 1056 ± 226.7 N for the 8-mm QT, 935.1 ± 283.8 N for the 6-mm QT, and 816 ± 192.7 N for the 10-mm PT. Ultimate tensile strength differed significantly between the 10-mm and 8-mm QT (P = .004), 10-mm and 6-mm QT (P < .001), 10-mm QT and 10-mm PT (P < .001), and 8-mm QT and 10-mm PT grafts (P < .001), but not between the 6-mm QT and 10-mm PT grafts (P = .152).

Conclusion

The 8-mm QT had higher ultimate tensile strength than the 10-mm PT, and the 6-mm QT was comparable to the 10-mm PT. Full-thickness QT grafts <10 mm in width may maintain sufficient tensile strength for ACLR.

Clinical Relevance

Given these biomechanical properties, smaller QT graft sizes may be advantageous in minimizing arthrofibrosis risk while maintaining graft strength.

Coordination of Glucose and Glutamine Metabolism in Tendon is Lost in Aging

Tendinopathy is an age-associated degenerative disease characterized by a loss in extracellular matrix (ECM). Since glucose and glutamine metabolism is critical to amino acid synthesis and known to be altered in aging, we sought to investigate if age-related changes in metabolism are linked to changes in ECM remodeling. We exposed young and aged tendon explants to various concentrations of glucose and glutamine to observe changes in metabolic processing (enzyme levels, gene expression, etc.) and matrix biosynthesis. Interestingly, we found that glutamine processing is affected by glucose levels, but this effect was lost with aging. ECM synthesis was altered in a protein-dependent manner by increased glucose and glutamine levels in young tendons. However, these changes were not conserved in aged tendons. Overall, our work suggests that glucose and glutamine metabolism is important for ECM homeostasis, and age-related changes in nutrient metabolism could be a key driver of tendon degeneration.

Comparative study on muscle-tendon stiffness and balance impairment in postmenopausal women: a focus on osteosarcopenia and osteoporosis

BACKGROUND AND AIMS

This study set out to examine the stiffness of the gastrocnemius medialis (GM) and Achilles tendon across postmenopausal women with osteosarcopenia (OS), osteoporosis (OP), and normal bone mineral density. Furthermore, we explored the relationship between muscle-tendon stiffness and postural sway during a curve-tracking task in both sagittal (AP) and frontal (ML) planes.

METHODS

Seventy-three women volunteered to participate in this study. The participants were classified into OS (T-score ≤ - 2.5 and muscle mass below 5.5 kg/m2), OP (T-score ≤ - 2.5), and healthy (T-score >-1) groups. The shear wave elastography was used to determine GM and Achilles tendon stiffness during rest and activation. The postural sway was recorded using a force plate during the performance-based curve tracking (CT) task.

RESULTS

The stiffness of the GM and Achilles tendon was found to be significantly lower in the OS group compared to the OP and healthy groups (P < 0.05). In the CT task, the OS group exhibited a significant decrease in the mean absolute (P = 0.011) and RMS error (P = 0.022) in the ML direction compared to the OP group. Additionally, a positive correlation was found between the ML mean absolute error and both GM and Achilles's stiffness during rest and activation (P < 0.05).

DISCUSSION AND CONCLUSION

The OS group exhibited the lowest muscle-tendon stiffness. The GM and Achilles stiffness was positively correlated with poor performance-based balance, particularly in the ML direction. This may increase the risk of falls and subsequent hip fractures during simple daily weight- shifting activities in women with osteosarcopenia.

Physiological and Psychological Differences Between 20% Grade Incline Walking and Level-Grade Jogging at Isocaloric Intensity

High-incline walking is a relatively new trend with little comparative information. This study compared physiological and psychological differences between high-incline walking at 20% grade (HIW) and level-grade jogging (LGJ) at isocaloric intensities in young adults. Twenty-two participants (M = 11, F = 11) aged 19-31 years completed the study. Participants completed HIW and LGJ on a treadmill for twenty minutes on two separate occasions and matched at isocaloric intensities. Rating of perceived exertion (RPE), maintainability (HCM), and affective valence using the Feeling Scale (FS) were measured at minutes 2, 10, and 20. Gas exchange and heart rate (HR) were continuously recorded. Post-exercise, participants completed the Physical Activity Enjoyment Scale (PACES) and 0-100 Likelihood scale. Relative oxygen uptake between LGJ and HIW (24.25 ± 3.53; 24.11 ± 3.63 mL/kg/min; p = .570, d = -.12), total calories (LGJ = 169.78 ± 35.80; HIW = 171.07 ± 35.09 kcal; p = .504), RER (LGJ = .86 ± .03; HIW = .88 ± .04; p = .137), and HR (LGJ = 146.28 ± 18.29; HIW = 143.94 ± 21.26 bpm; p = .146) was not different. LGJ (96.82 ± 15.76) had significantly higher total PACES (96.82 ± 15.76) and Likelihood scores (75.86 ± 18.30) than HIW (85.14 ± 15.08, p < .001; 65.09 ± 25.45, p = .032) respectively. RPE for both LGJ and HIW increased significantly with time (p < .001), but not between tests (p = .312). FS for LGJ and HIW increased significantly between tests (p = .008), but not between time (p = .083). At isocaloric intensities, young adults preferred and enjoyed LGJ relative to HIW.

Loss of Cochlin drives impairments in tendon structure and function

Aging tendons undergo disruptions in homeostasis, increased susceptibility to injury, and reduced capacity for healing. Exploring the mechanisms behind this disruption in homeostasis is essential for developing therapeutics aimed at maintaining tendon health through the lifespan. We have previously identified that the extracellular matrix protein, Cochlin, which is highly expressed in healthy flexor tendon, is consistently lost during both natural aging and upon depletion of Scleraxis-lineage cells in young animals, which recapitulates many aging-associated homeostatic disruptions. Therefore, we hypothesized that loss of Cochlin would disrupt tendon homeostasis, including alterations in collagen fibril organization, and impaired tendon mechanics. By 3-months of age, Cochlin -/- flexor tendons exhibited altered collagen structure, with these changes persisting through at least 9-months. In addition, Cochlin-/- tendons demonstrated significant declines in structural and material properties at 6-months, and structural properties at 9-months. While Cochlin -/- did not drastically change the overall tendon proteome, consistent decreases in proteins associated with RNA metabolism, extracellular matrix production and the cytoskeleton were observed in Cochlin -/-. Interestingly, homeostatic disruption via Cochlin -/- did not impair the tendon healing process. Taken together, these data define a critical role for Cochlin in maintaining tendon homeostasis and suggest retention or restoration of Cochlin as a potential therapeutic approach to retain tendon structure and function through the lifespan.

Tenascin-C-Matrix Metalloproteinase-3 Phenotype and the Risk of Tendinopathy in High-Performance Athletes: A Case-Control Study

Background/Objectives: Tendon structure is predominantly composed of the extracellular matrix (ECM), and genetic variants in non-collagenous ECM components may influence susceptibility to tendinopathy. We investigated the potential influence of single nucleotide polymorphisms (SNPs) in fibrillin-2 (FBN2), tenascin-C (TNC), and matrix metalloproteinase-3 (MMP3) on the tendon regeneration failure phenotype and impact on the susceptibility to tendinopathy in Brazilian high-performance athletes. Methods: This case-control study was conducted with 397 high-performance athletes from different sports modalities (197 tendinopathy cases and 200 controls), and they were analyzed by validated TaqManTM SNP genotyping assays of the SNPs FBN2 (rs331079), TNC (rs2104772), and MMP3 (rs591058). Results: Out of the 197 tendinopathy cases, 63% suffered from chronic tendon pain and 22% experienced more than three episodes of disease manifestation. The TNC-rs2104772-A allele was significantly associated with tendinopathy (OR: 1.4; 95% CI: 1.1-1.8), while athletes carrying the MMP3-rs591058-T allele were linked to an increased risk of more episodes of disease manifestation (OR: 1.7; 95% CI: 1.1-2.8). The TNC-MMP3 tendon regeneration failure phenotype (TNC-A/MMP3-T) was associated with an increased risk of tendinopathy (OR: 1.4; 95% CI: 1.1-2.0) and episodes of disease manifestation (OR: 2.0; 95% CI: 1.2-3.5). Athletes with tendinopathy who had the TNC-A/MMP3-T interaction were more prone to experiencing more than three disease exacerbations (OR: 4.3; 95% CI: 1.8-10.5) compared to TNC-A/TNC-C. Conclusions: This study suggests that rs2104772 and rs591058 SNPs could be involved in the tendon regeneration failure phenotype and may influence the molecular mechanism related to the regulation of the tendon ECM during training workload.

Mitochondrial destabilization in tendinopathy and potential therapeutic strategies

Tendinopathy is a prevalent aging-related disorder characterized by pain, swelling, and impaired function, often resulting from micro-scarring and degeneration caused by overuse or trauma. Current interventions for tendinopathy have limited efficacy, highlighting the need for innovative therapies. Mitochondria play an underappreciated and yet crucial role in tenocytes function, including energy production, redox homeostasis, autophagy, and calcium regulation. Abnormalities in mitochondrial function may lead to cellular senescence. Within this context, this review provides an overview of the physiological functions of mitochondria in tendons and presents current insights into mitochondrial dysfunction in tendinopathy. It also proposes potential therapeutic strategies that focus on targeting mitochondrial health in tenocytes. These strategies include: (1) utilizing reactive oxygen species (ROS) scavengers to mitigate the detrimental effects of aberrant mitochondria, (2) employing mitochondria-protecting agents to reduce the production of dysfunctional mitochondria, and (3) supplementing with exogenous normal mitochondria. In conclusion, mitochondria-targeted therapies hold great promise for restoring mitochondrial function and improving outcomes in patients with tendinopathy. The translational potential of this article: Tendinopathy is challenging to treat effectively due to its poorly understood pathogenesis. This review thoroughly analyzes the role of mitochondria in tenocytes and proposes potential strategies for the mitochondrial treatment of tendinopathy. These findings establish a theoretical basis for future research and the clinical translation of mitochondrial therapy for tendinopathy.

Oral Corticosteroids for Skin Disease in the Older Population: Minimizing Potential Adverse Effects

Corticosteroids play a crucial role as anti-inflammatory and immunomodulatory agents in dermatology and other medical specialties; however, their therapeutic benefits are accompanied by significant risks, especially in older adults. This review examines the broad spectrum of adverse effects (AEs) associated with oral corticosteroid therapy and offers strategies to prevent, monitor, and manage these issues effectively in older adults. AEs associated with systemic corticosteroids include immune suppression, gastrointestinal problems, hyperglycemia, insulin resistance, weight gain, cardiovascular complications, ocular issues, osteoporosis, osteonecrosis, muscle weakness, collagen impairment, psychiatric symptoms, and adrenal suppression. To minimize these AEs, tailored dosing and duration, frequent monitoring, and additional preventative measures can be employed to optimize corticosteroid treatment. By customizing management plans to the specific needs and risk factors associated with each patient, clinicians can promote the safe and effective use of oral corticosteroids, ultimately improving outcomes and quality of life in patients with inflammatory dermatologic disorders.

Neural and muscular contributions to the age-related differences in peak power of the knee extensors in men and women

The mechanisms for the loss in limb muscle power output in old (60-79 yr) and very old (≥80 yr) adults and whether the mechanisms differ between men and women are not well understood. We compared maximal peak power of the knee extensor muscles between young, old, and very old men and women and identified the neural and muscular factors contributing to the age-related differences in power. Thirty-one young (22.9 ± 3.0 yr, 15 women), 82 old (70.3 ± 4.9 yr, 38 women), and 16 very old adults (85.8 ± 4.2 yr, 9 women) performed maximal isokinetic contractions at 14 different velocities (30-450°/s) to identify peak power. Voluntary activation (VA) and contractile properties were assessed with transcranial magnetic stimulation to the motor cortex and electrical stimulation of the femoral nerve. The age-related loss in peak power was ∼6.5 W·yr-1 for men (R2 = 0.62, P < 0.001), which was a greater rate of decline (P = 0.002) than the ∼4.2 W·yr-1 for women (R2 = 0.77, P < 0.001). Contractile properties were the most closely associated variables with peak power for both sexes, such as the rate of torque development of the potentiated twitch (men: R2 = 0.69, P < 0.001; women: R2 = 0.57, P < 0.001). VA was weakly associated with power in women (R2 = 0.13, P = 0.012) but not in men (P = 0.191). Similarly, neuromuscular activation [rates of electromyography (EMG) rise] during the maximal power contraction was associated with power in women (R2 = 0.07, P = 0.042) but not in men (P = 0.456). These data suggest that the age-related differences in maximal peak power of the knee extensor muscles are due primarily to factors within the muscle for both sexes, although neural factors may play a minor role in older women.NEW & NOTEWORTHY The greater age-related loss in power relative to the loss in muscle mass of the knee extensors was primarily due to factors altering the contractile properties of the muscle for both old and very old (≥80 yr) adults. The mechanisms for the decrements in power with aging appear largely similar for men and women, although neural factors may play more of a role in older women.

Growth on stiffer substrates impacts animal health and longevity in C. elegans

Mechanical stress is a measure of internal resistance exhibited by a body or material when external forces, such as compression, tension, bending, etc. are applied. The study of mechanical stress on health and aging is a continuously growing field, as major changes to the extracellular matrix and cell-to-cell adhesions can result in dramatic changes to tissue stiffness during aging and diseased conditions. For example, during normal aging, many tissues including the ovaries, skin, blood vessels, and heart exhibit increased stiffness, which can result in a significant reduction in function of that organ. As such, numerous model systems have recently emerged to study the impact of mechanical and physical stress on cell and tissue health, including cell-culture conditions with matrigels and other surfaces that alter substrate stiffness and ex vivo tissue models that can apply stress directly to organs like muscle or tendons. Here, we sought to develop a novel method in an in vivo model organism setting to study the impact of altering substrate stiffness on aging by changing the stiffness of solid agar medium used for growth of C. elegans. We found that greater substrate stiffness had limited effects on cellular health, gene expression, organismal health, stress resilience, and longevity. Overall, our study reveals that altering substrate stiffness of growth medium for C. elegans has only mild impact on animal health and longevity; however, these impacts were not nominal and open up important considerations for C. elegans biologists in standardizing agar medium choice for experimental assays.

Extracellular Vesicle-Contained Thrombospondin 1 Retards Age-Related Degenerative Tendinopathy by Rejuvenating Tendon Stem/Progenitor Cell Senescence

Advanced age is a major risk factor for age-related degenerative tendinopathy. During aging, tendon stem/progenitor cell (TSPC) function declines owing to the transition from a normal quiescent state to a senescent state. Extracellular vesicles (EVs) from young stem cells are reported to possess anti-aging functions. However, it remains unclear whether EVs from young TSPCs (TSPC-EVs) can rejuvenate senescent TSPCs to delay age-related degeneration. Here, this study finds that TSPC-EVs can mitigate the aging phenotypes of senescent TSPCs and maintain their tenogenic capacity. In vitro studies reveal that TSPC-EVs can reinstall autophagy in senescent TSPCs to alleviate cellular senescence, and that the re-establishment of autophagy is mediated by the PI3K/AKT pathway. Mechanistically, this study finds that thrombospondin 1, a negative regulator of the PI3K/AKT pathway, is enriched in TSPC-EVs and can be transported to senescent TSPCs. Moreover, in vivo studies show that the local delivery of TSPC-EVs can rejuvenate senescent TSPCs and promote their tenogenic differentiation, thereby rescuing tendon regeneration in aged rats. Taken together, TSPC-EVs as a novel cell-free approach have promising therapeutic potential for aging-related degenerative tendinopathy.

Anterior cruciate ligament reconstruction in the elderly: 5-Year follow-up study

BACKGROUND

Older adults remain active for longer and continue sports and activities that require rotation on one leg later in life. The rate of anterior cruciate ligament (ACL) tears is therefore increasing in those over 40 years old, with an associated increase in the rate of surgical reconstruction (ACLR), but there is limited literature on its effectiveness. Our aim was to compare the outcomes of elderly patients who have undergone ACLR with those of a younger group of patients.

MATERIALS AND METHODS

Patients who underwent ACLR with bone-patella tendon-bone grafting (BPTB) at a level I trauma center between 2015 and 2017 were included in the study with a 5-year follow-up. Patients were divided into 4 groups: below 40 years, 40-49 years, 50-59 years and over 60 years. The graft function was evaluated by the International Knee Documentation Committee (IKDC) Objective Score, the anteroposterior (AP) displacement was measured by arthrometer (KT-1000; MEDMetric) and the Lysholm scale was used for subjective evaluation.

RESULTS

195 patients were included in the final analysis. The IKDC score showed significantly poorer scores in the 50-59 years and over 60 years group than in the younger groups, however in 83 % and 66 % of cases reached normal or nearly normal grades, respectively. A significant difference was found in the knee AP displacement (measured in mm) between the below 40 years group and 50-59 years as well as over 60 years old groups; however, the number of graft failure (laxity >5 mm) and elongation (>3 mm) did not increased in these senior groups. The patient-reported Lysholm scores in the 40-49 years, 50-59 years and 60 years groups was lower than in the below 40 years group, but the average score was "good".

CONCLUSIONS

The long-term results of ACL reconstruction in older athletes are comparable to those of younger patients, both in terms of knee function and patient satisfaction. Furthermore, there is no difference in outcomes for older patients over the age of 40 compared to those in their 50 s or even 60 s. There is still insufficient published evidence to define an upper age limit for ACL reconstruction in older athletes.

Chronic Adaptation of Achilles Tendon Tissues upon Injury to Rotator Cuff Tendon in Hyperlipidemic Swine

The biomechanical properties of the tendon are affected due to the changes in composition of the tendon extracellular matrix (ECM). Age, overuse, trauma and metabolic disorders are a few associated conditions that contribute to tendon abnormalities. Hyperlipidemia is one of the leading factors that contribute to the compromised biomechanical. Injury was made on infraspinatus tendon of hyperlipidemic swines. After 8 weeks (i) infraspinatus tendon from the injury site, (ii) infraspinatus tendon from the contralateral side and (iii) Achilles tendon, were collected and analyzed for ECM components that form the major part in biomechanical properties. Immunostaining of infraspinatus tendon on the injury site had higher staining collagen type-1 (COL1A1), biglycan, prolyl 4-hydroxylase and mohawk but lower staining for decorin than the control group. The Achilles tendon of the swines that had injury on infraspinatus tendon showed a chronic adaptation towards load which was evident from a more organized ECM with increased decorin, mohawk and decreased biglycan, scleraxis. The mechanism behind the collagen turnover and chronic adaptation to load need to be studied in detail with the biomechanical properties.

Mechanical stress through growth on stiffer substrates impacts animal health and longevity in C. elegans

Mechanical stress is a measure of internal resistance exhibited by a body or material when external forces, such as compression, tension, bending, etc. are applied. The study of mechanical stress on health and aging is a continuously growing field, as major changes to the extracellular matrix and cell-to-cell adhesions can result in dramatic changes to tissue stiffness during aging and diseased conditions. For example, during normal aging, many tissues including the ovaries, skin, blood vessels, and heart exhibit increased stiffness, which can result in a significant reduction in function of that organ. As such, numerous model systems have recently emerged to study the impact of mechanical and physical stress on cell and tissue health, including cell-culture conditions with matrigels and other surfaces that alter substrate stiffness and ex vivo tissue models that can apply stress directly to organs like muscle or tendons. Here, we sought to develop a novel method in an in vivo, model organism setting to study the impact of mechanical stress on aging, by increasing substrate stiffness in solid agar medium of C. elegans. To our surprise, we found shockingly limited impact of growth of C. elegans on stiffer substrates, including limited effects on cellular health, gene expression, organismal health, stress resilience, and longevity. Overall, our studies reveal that altering substrate stiffness of growth medium for C. elegans have only mild impact on animal health and longevity; however, these impacts were not nominal and open up important considerations for C. elegans biologists in standardizing agar medium choice for experimental assays.

Optimizing tendon repair and regeneration: how does the in vivo environment shape outcomes following rupture of a tendon such as the Achilles tendon?

Risk for rupture of the Achilles tendon, and other tendons increases with age. Such injuries of tissues that function in high load environments generally are believed to heal with variable outcome. However, in many cases, the healing does not lead to a good outcome and the patient cannot return to the previous level of participation in active living activities, including sports. In the past few years, using proteomic approaches and other biological techniques, reports have appeared that identify biomarkers that are prognostic of good outcomes from healing, and others that are destined for poor outcomes using validated criteria at 1-year post injury. This review will discuss some of these recent findings and their potential implications for improving outcomes following connective tissue injuries, as well as implications for how clinical research and clinical trials may be conducted in the future where the goal is to assess the impact of specific interventions on the healing process, as well as focusing the emphasis on regeneration and not just repair.