Regional molecular and cellular differences in the female rabbit Achilles tendon complex: potential implications for understanding responses to loading

Abstract

The aim of this study was: (i) to analyze the morphology and expression of extracellular matrix genes in six different regions of the Achilles tendon complex of intact normal rabbits; and (ii) to assess the effect of ovariohysterectomy (OVH) on the regional expression of these genes. Female New Zealand White rabbits were separated into two groups: (i) intact normal rabbits (n = 4); and (ii) OVH rabbits (n = 8). For each rabbit, the Achilles tendon complex was dissected into six regions: distal gastrocnemius (DG); distal flexor digitorum superficialis; proximal lateral gastrocnemius (PLG); proximal medial gastrocnemius; proximal flexor digitorum superficialis; and paratenon. For each of the regions, hematoxylin and eosin staining was performed for histological evaluation of intact normal rabbit tissues and mRNA levels for proteoglycans, collagens and genes associated with collagen regulation were assessed by real-time reverse transcription-quantitative polymerase chain reaction for both the intact normal and OVH rabbit tissues. The distal regions displayed a more fibrocartilaginous phenotype. For intact normal rabbits, aggrecan mRNA expression was higher in the distal regions of the Achilles tendon complex compared with the proximal regions. Collagen Type I and matrix metalloproteinase-2 expression levels were increased in the PLG compared to the DG in the intact normal rabbit tissues. The tendons from OVH rabbits had lower gene expressions for the proteoglycans aggrecan, biglycan, decorin and versican compared with the intact normal rabbits, although the regional differences of increased aggrecan expression in distal regions compared with proximal regions persisted. The tensile and compressive forces experienced in the examined regions may be related to the regional differences found in gene expression. The lower mRNA expression of the genes examined in the OVH group confirms a potential effect of systemic estrogen on tendon.

Influence of repetitive mechanical loading on MMP2 activity in tendon fibroblasts

“…Tendon tissues of the LG, MG, and FDS region were taken 3 cm proximal of the calcaneus; this is the location that was anticipated to be most affected by the repetitive motion . The paratenon was collected separately followed by splitting the Achilles tendon complex in the LG, MG, and FDS as described previously . The tissues from each region were divided; samples for mRNA expression and protein level analysis were snap frozen using liquid nitrogen and stored at −80°C until further analysis, and samples for histological analysis were fixed in 10% formalin in phosphate‐buffered saline.…”

“…The four regions of the rabbit Achilles tendon complex assessed in this study; FDS, flexor digitorum superficialis; LG, lateral gastrocnemius; MG, medial gastrocnemius; P, paratenon. Original art by Gustav Andersson, reproduced and adapted with permission.…”

Impact of oestrogen deficiency and aging on tendon: concise review

“…Bridgeman et al observed both ERα and ERβ in normal and disease tendon of male and female patients, without any statistically significant difference. On the other hand the impact of ovariohysterectomy (OVH) on gene expression in rabbit resulted different in various tendons that may indicate variances in number and distribution of oestrogen receptors 43,44 . Oestrogen level has a direct effect on collagenous tissue in severalpreclinical studies.…”

The absence of oestrogen receptor beta disturbs collagen I type deposition during Achilles tendon healing by regulating the IRF5‐CCL3 axis

“…36,37 It should be noted that oestrogen might exert different effects on the biomechanical properties of tendons due to disparities in the loading profile and differences in the relative distribution and numbers of oestrogen receptors. 38,39 Our recent study demonstrated that the absence of ERβ leads to abnormalities in Achilles tendon healing at the early stage and that these are mainly characterized by increased adipocyte accumulation. 6 However, whether and how ERβ affects Achilles tendon repair after the early healing stage.…”