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Aggouras AN, Stowe EJ, Mlawer SJ, Connizzo BK. Aged Tendons Exhibit Altered Mechanisms of Strain-Dependent Extracellular Matrix Remodeling. J Biomech Eng 2024; 146:071009. [PMID: 38584416 PMCID: PMC11080950 DOI: 10.1115/1.4065270] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/20/2023] [Revised: 04/02/2024] [Accepted: 04/03/2024] [Indexed: 04/09/2024]
Abstract
Aging is a primary risk factor for degenerative tendon injuries, yet the etiology and progression of this degeneration are poorly understood. While aged tendons have innate cellular differences that support a reduced ability to maintain mechanical tissue homeostasis, the response of aged tendons to altered levels of mechanical loading has not yet been studied. To address this question, we subjected young and aged murine flexor tendon explants to various levels of in vitro tensile strain. We first compared the effect of static and cyclic strain on matrix remodeling in young tendons, finding that cyclic strain is optimal for studying remodeling in vitro. We then investigated the remodeling response of young and aged tendon explants after 7 days of varied mechanical stimulus (stress deprivation, 1%, 3%, 5%, or 7% cyclic strain) via assessment of tissue composition, biosynthetic capacity, and degradation profiles. We hypothesized that aged tendons would show muted adaptive responses to changes in tensile strain and exhibit a shifted mechanical setpoint, at which the remodeling balance is optimal. Interestingly, we found that 1% cyclic strain best maintains native physiology while promoting extracellular matrix (ECM) turnover for both age groups. However, aged tendons display fewer strain-dependent changes, suggesting a reduced ability to adapt to altered levels of mechanical loading. This work has a significant impact on understanding the regulation of tissue homeostasis in aged tendons, which can inform clinical rehabilitation strategies for treating elderly patients.
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Affiliation(s)
- Anthony N. Aggouras
- Department of Biomedical Engineering, Boston University, 44 Cummington Mall, Boston, MA 02115
- Boston University
| | - Emma J. Stowe
- Department of Biomedical Engineering, Boston University, 44 Cummington Mall, Boston, MA 02115
| | - Samuel J. Mlawer
- Department of Biomedical Engineering, Boston University, 44 Cummington Mall, Boston, MA 02115
- Boston University
| | - Brianne K. Connizzo
- Department of Biomedical Engineering, Boston University, 44 Cummington Mall, Boston, MA 02115
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Aggouras AN, Stowe EJ, Mlawer SJ, Connizzo BK. Aged Tendons Exhibit Altered Mechanisms of Strain-Dependent Extracellular Matrix Remodeling. BIORXIV : THE PREPRINT SERVER FOR BIOLOGY 2024:2024.01.26.577397. [PMID: 38352312 PMCID: PMC10862756 DOI: 10.1101/2024.01.26.577397] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Indexed: 02/19/2024]
Abstract
Aging is a primary risk factor for degenerative tendon injuries, yet the etiology and progression of this degeneration is poorly understood. While aged tendons have innate cellular differences that support a reduced ability to maintain mechanical tissue homeostasis, the response of aged tendons to altered levels of mechanical loading has not yet been studied. To address this question, we subjected young and aged murine flexor tendon explants to various levels of in vitro tensile strain. We first compared the effect of static and cyclic strain on matrix remodeling in young tendons, finding that cyclic strain is optimal for studying remodeling in vitro. We then investigated the remodeling response of young and aged tendon explants after 7 days of varied mechanical stimulus (stress-deprivation, 1%, 3%, 5%, or 7% cyclic strain) via assessment of tissue composition, biosynthetic capacity, and degradation profiles. We hypothesized that aged tendons would show muted adaptive responses to changes in tensile strain and exhibit a shifted mechanical setpoint, at which the remodeling balance is optimal. Interestingly, we found 1% cyclic strain best maintains native physiology while promoting ECM turnover for both age groups. However, aged tendons display fewer strain-dependent changes, suggesting a reduced ability to adapt to altered levels of mechanical loading. This work has significant impact in understanding the regulation of tissue homeostasis in aged tendons, which can inform clinical rehabilitation strategies for treating elderly patients.
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Affiliation(s)
- Anthony N. Aggouras
- Department of Biomedical Engineering, Boston University, Boston, Massachusetts, USA., 44 Cummington Mall, Boston, Massachusetts, USA, 02115
| | - Emma J. Stowe
- Department of Biomedical Engineering, Boston University, Boston, Massachusetts, USA., 44 Cummington Mall, Boston, Massachusetts, USA, 02115
| | - Samuel J. Mlawer
- Department of Biomedical Engineering, Boston University, Boston, Massachusetts, USA., 44 Cummington Mall, Boston, Massachusetts, USA, 02115
| | - Brianne K. Connizzo
- Department of Biomedical Engineering, Boston University, Boston, Massachusetts, USA., 44 Cummington Mall, Boston, Massachusetts, USA, 02115
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Korcari A, Przybelski SJ, Gingery A, Loiselle AE. Impact of aging on tendon homeostasis, tendinopathy development, and impaired healing. Connect Tissue Res 2023; 64:1-13. [PMID: 35903886 PMCID: PMC9851966 DOI: 10.1080/03008207.2022.2102004] [Citation(s) in RCA: 6] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 01/18/2022] [Accepted: 07/11/2022] [Indexed: 02/03/2023]
Abstract
Aging is a complex and progressive process where the tissues of the body demonstrate a decreased ability to maintain homeostasis. During aging, there are substantial cellular and molecular changes, with a subsequent increase in susceptibility to pathological degeneration of normal tissue function. In tendon, aging results in well characterized alterations in extracellular matrix (ECM) structure and composition. In addition, the cellular environment of aged tendons is altered, including a marked decrease in cell density and metabolic activity, as well as an increase in cellular senescence. Collectively, these degenerative changes make aging a key risk factor for the development of tendinopathies and can increase the frequency of tendon injuries. However, inconsistencies in the extent of age-related degenerative impairments in tendons have been reported, likely due to differences in how "old" and "young" age-groups have been defined, differences between anatomically distinct tendons, and differences between animal models that have been utilized to study the impact of aging on tendon homeostasis. In this review, we address these issues by summarizing data by well-defined age categories (young adults, middle-aged, and aged) and from anatomically distinct tendon types. We then summarize in detail how aging affects tendon mechanics, structure, composition, and the cellular environment based on current data and underscore what is currently not known. Finally, we discuss gaps in the current understanding of tendon aging and propose key avenues for future research that can shed light on the specific mechanisms of tendon pathogenesis due to aging.
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Affiliation(s)
- Antonion Korcari
- Department of Orthopaedics & Rehabilitation, Center for Musculoskeletal Research, University of Rochester Medical Center, Rochester, NY, USA
- Department of Biomedical Engineering, University of Rochester, Rochester, NY, USA
| | | | - Anne Gingery
- Division of Orthopedic Surgery Research, Mayo Clinic, Rochester, MN, USA
- Department of Biochemistry and Molecular Biology, Mayo Clinic, Rochester, MN, USA
| | - Alayna E Loiselle
- Department of Orthopaedics & Rehabilitation, Center for Musculoskeletal Research, University of Rochester Medical Center, Rochester, NY, USA
- Department of Biomedical Engineering, University of Rochester, Rochester, NY, USA
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Lai F, Wang J, Tang H, Huang P, Liu J, He G, Zhou M, Tao X, Tang K. VEGF promotes tendon regeneration of aged rats by inhibiting adipogenic differentiation of tendon stem/progenitor cells and promoting vascularization. FASEB J 2022; 36:e22433. [PMID: 35867348 DOI: 10.1096/fj.202200213r] [Citation(s) in RCA: 4] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/11/2022] [Revised: 05/23/2022] [Accepted: 06/13/2022] [Indexed: 11/11/2022]
Abstract
Studies have shown that the stem cell microenvironment is a key factor for stem cell maintenance or differentiation. In this study, we compared the expression of 23 cytokines such as IL-6, IL-10, and TNFα between young and aged rats during patellar tendon repair by cytokine microarray, and found that significant difference between IL-10, G-CSF, and VEGF at 3, 7, or 14 days post-operatively. The effects of these factors on adipogenic differentiation of TPSCs were examined through western blot and oil red O experiments. It was shown that VEGF had an inhibitive effect on the adipogenic differentiation of TPSCs. SPP-1 was figured out as our target by RNA sequencing and confirmed by western blot in vitro. Further in vivo studies showed that adipocyte accumulation was also decreased in the tendons of aged rats after injection of VEGF and the histological score and biomechanical property were also improved via targeting SPP-1. Furthermore, histochemical results showed that vascularization of the injury sites was significantly elevated. In conclusion, VEGF not only plays an important role in decreasing adipocyte accumulation but also improves vascularization of the tendon during aged tendon healing. We believe active regulation of VEGF may improve the treatment of age-related tendon diseases and tendon injuries.
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Affiliation(s)
- Fan Lai
- Department of Sports Medicine Center, Southwest Hospital, Army Medical University, Chongqing, China
| | - Jingjing Wang
- Department of Blood Transfusion, Xinqiao Hospital, Army Medical University, Chongqing, China
| | - Hong Tang
- Department of Sports Medicine Center, Southwest Hospital, Army Medical University, Chongqing, China
| | - Pan Huang
- Department of Sports Medicine Center, Southwest Hospital, Army Medical University, Chongqing, China
| | - Juan Liu
- Department of Sports Medicine Center, Southwest Hospital, Army Medical University, Chongqing, China
| | - Gang He
- Department of Sports Medicine Center, Southwest Hospital, Army Medical University, Chongqing, China
| | - Mei Zhou
- Department of Sports Medicine Center, Southwest Hospital, Army Medical University, Chongqing, China
| | - Xu Tao
- Department of Sports Medicine Center, Southwest Hospital, Army Medical University, Chongqing, China
| | - Kanglai Tang
- Department of Sports Medicine Center, Southwest Hospital, Army Medical University, Chongqing, China
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