The Interfascicular Matrix of Energy Storing Tendons Houses Heterogenous Cell Populations Disproportionately Affected by Aging

Zamboulis, DE; Marr, N; Lenzi, L; Birch, HL; Screen, HRC; Clegg, PD; Thorpe, CT

Abstract

Energy storing tendons such as the human Achilles and equine superficial digital flexor tendon (SDFT) are prone to injury, with incidence increasing with aging, peaking in the 5th decade of life in the human Achilles tendon. The interfascicular matrix (IFM), which binds tendon fascicles, plays a key role in energy storing tendon mechanics, and aging alterations to the IFM negatively impact tendon function. While the mechanical role of the IFM in tendon function is well-established, the biological role of IFM-resident cell populations remains to be elucidated. Therefore, the aim of this study was to identify IFM-resident cell populations and establish how these populations are affected by aging. Cells from young and old SDFTs were subjected to single cell RNA sequencing, and immunolabelling for markers of each resulting population used to localise cell clusters. Eleven cell clusters were identified, including tenocytes, endothelial cells, mural cells, and immune cells. One tenocyte cluster localised to the fascicular matrix, whereas nine clusters localised to the IFM. Interfascicular tenocytes and mural cells were preferentially affected by aging, with differential expression of genes related to senescence, dysregulated proteostasis and inflammation. This is the first study to establish heterogeneity in IFM cell populations, and to identify age-related alterations specific to IFM-localised cells.

Citation

Zamboulis, D., Marr, N., Lenzi, L., Birch, H., Screen, H., Clegg, P., & Thorpe, C. (2023). The Interfascicular Matrix of Energy Storing Tendons Houses Heterogenous Cell Populations Disproportionately Affected by Aging. Aging and Disease, https://doi.org/10.14336/AD.2023.0425-1

• Journal Article Type: Article
• Acceptance Date: Apr 25, 2023
• Online Publication Date: May 22, 2023
• Publication Date: 2023
• Deposit Date: Jul 3, 2023
• Publicly Available Date: Jul 3, 2023
• Publisher: International Society on Aging and Disease
• Peer Reviewed: Peer Reviewed
• DOI: https://doi.org/10.14336/AD.2023.0425-1
• Keywords: interfascicular matrix; tendon aging; single cell sequencing; tendon cell populations; proteostasis; senescence; ACHILLES-TENDON; MECHANICAL-PROPERTIES; PROTEIN; FASCICLES; MUSCLE; INJURY