Achilles Tendons Display Region-Specific Transcriptomic Signatures Associated With Distinct Mechanical Properties

Abstract

Background: Previous studies have examined the transcriptomes and mechanical properties of whole tendons in different regions of the body. However, less is known about these characteristics within a single tendon. Purpose: To develop a regional transcriptomic atlas and evaluate the region-specific mechanical properties of Achilles tendons. Study Design: Descriptive laboratory study. Methods: Achilles tendons from 2-month-old male Sprague Dawley rats were used. Tendons were isolated and divided into proximal, middle, and distal thirds for RNA sequencing (n = 5). For mechanical testing, the Achilles muscle-tendon-calcaneus unit was mounted in a custom-designed materials testing system with the unit clamped over the musculotendinous junction (MTJ) and the calcaneus secured at 90° of dorsiflexion (n = 9). Tendons were stretched to 20 N at a constant speed of 0.0167 mm/s. Cross-sectional area, strain, stress, and Young modulus were determined in each tendon region. Results: An open-access, interactive transcriptional atlas was generated that revealed distinct gene expression signatures in each tendon region. The proximal and distal regions had the largest differences in gene expression, with 2596 genes significantly differentially regulated at least 1.5-fold ( q < .01). The proximal tendon displayed increased expression of genes resembling a tendon phenotype and increased expression of nerve cell markers. The distal region displayed increases in genes involved in extracellular matrix synthesis and remodeling, immune cell regulation, and a phenotype similar to cartilage and bone. There was a 3.72-fold increase in Young modulus from the proximal to middle region ( P < .01) and an additional 1.34-fold increase from the middle to distal region ( P = .027). Conclusion: Within a single tendon, there are region-specific transcriptomic signatures and mechanical properties, and there is likely a gradient in the biological and functional phenotype from the proximal origin at the MTJ to the distal insertion at the enthesis. Clinical Relevance: These findings improve our understanding of the underlying biological heterogeneity of tendon tissue and will help inform the future targeted use of regenerative medicine and tissue engineering strategies for patients with tendon disorders.

Spatial gene expression in the adult rat patellar tendon

“…The average number of UMIs per spot was 40,312 for rat #1 and 64,438 for rat #2 ( Table 1 ). The percentage of reads mapped to the genome was 93.8 % and 83.7 %, respectively, which is similar to mapping rates reported in other studies [11] , [12] . There was a strong correlation (R 2 = 0.97) between the number of genes per spot and number of UMIs per spot ( Fig.…”

Current and emerging technologies for defining and validating tendon cell fate

“…Studies have uncovered dysregulation of tendon gene expression and signaling pathways in Achilles and patellar tendons from mouse models of recessive osteogenesis imperfecta 35 . Whereas others have reported differences in gene expression along the axis of the Achilles tendon with proximal regions enriched for tendon and nerve cell markers and distal regions enriched for extracellular matrix remodeling, immune cell regulation, and cartilage‐/bone‐related genes 36 …”

“…35 Whereas others have reported differences in gene expression along the axis of the Achilles tendon with proximal regions enriched for tendon and nerve cell markers and distal regions enriched for extracellular matrix remodeling, immune cell regulation, and cartilage-/bone-related genes. 36 In addition to bulk RNA-seq analyses, which examine the transcriptomes of pooled cell populations or whole tissues, single-cell (sc) RNA-seq has permitted unprecedented resolution of cell diversity and tissue composition. As bulk RNA-seq combines transcripts from all cells in the tissue, differential gene expression between samples (e.g., between control and mutant tendons) could, therefore, result from changes in the composition of the cells in the tissue or to changes in the gene expression within the same cells in that tissue, confounding some interpretations of gene expression changes and requiring further validation.…”

Equine tendon mechanical behaviour: Prospects for repair and regeneration applications

“…The tensile forces at enthesis may be four times more powerful than mid-substance (Kaya, 2020). Moreover, regional differences in mechanical properties of rat AT were reported by Disser et al (2022), which showed a 3.72-fold increase in the Young modulus from the proximal origin (at the MTJ) to middle region and an additional 1.34-fold increase from the middle to distal region (at the enthesis).…”