Systemic EP4 Inhibition Increases Adhesion Formation in a Murine Model of Flexor Tendon Repair

Abstract

Flexor tendon injuries are a common clinical problem, and repairs are frequently complicated by post-operative adhesions forming between the tendon and surrounding soft tissue. Prostaglandin E2 and the EP4 receptor have been implicated in this process following tendon injury; thus, we hypothesized that inhibiting EP4 after tendon injury would attenuate adhesion formation. A model of flexor tendon laceration and repair was utilized in C57BL/6J female mice to evaluate the effects of EP4 inhibition on adhesion formation and matrix deposition during flexor tendon repair. Systemic EP4 antagonist or vehicle control was given by intraperitoneal injection during the late proliferative phase of healing, and outcomes were analyzed for range of motion, biomechanics, histology, and genetic changes. Repairs treated with an EP4 antagonist demonstrated significant decreases in range of motion with increased resistance to gliding within the first three weeks after injury, suggesting greater adhesion formation. Histologic analysis of the repair site revealed a more robust granulation zone in the EP4 antagonist treated repairs, with early polarization for type III collagen by picrosirius red staining, findings consistent with functional outcomes. RT-PCR analysis demonstrated accelerated peaks in F4/80 and type III collagen (Col3a1) expression in the antagonist group, along with decreases in type I collagen (Col1a1). Mmp9 expression was significantly increased after discontinuing the antagonist, consistent with its role in mediating adhesion formation. Mmp2, which contributes to repair site remodeling, increases steadily between 10 and 28 days post-repair in the EP4 antagonist group, consistent with the increased matrix and granulation zones requiring remodeling in these repairs. These findings suggest that systemic EP4 antagonism leads to increased adhesion formation and matrix deposition during flexor tendon healing. Counter to our hypothesis that EP4 antagonism would improve the healing phenotype, these results highlight the complex role of EP4 signaling during tendon repair.

Effect of aging on the tendon structure and tendon‑associated gene expression in mouse foot flexor tendon

“…Picrosirius red staining is utilized for evaluating the differential distribution of the structurally distinct collagen types I and III (13)(14)(15). Picrosirius red-stained sections were illuminated with polarized light, allowing the visualization of collagen fiber organization; type I collagen appears red, while type III collagen appears yellow/green (16). Digital images of all specimens were captured and analyzed with a custom-built spectral template (red or yellow/green) using the Nuance multispectral imaging system (Nuance 3.0.2; PerkinElmer, Inc., Waltham, MA, USA).…”

Obesity/Type II Diabetes Alters Macrophage Polarization Resulting in a Fibrotic Tendon Healing Response

“…Mmp9 is associated with increased adhesion formation (17, 20, 21), while Mmp2 expression is up-regulated during the remodeling phase of tendon repair (20). Peak Mmp9 expression occurred day 7 in LFD repairs, while the HFD group demonstrated a delayed and significantly elevated expression pattern at 10 and 14 days (D10-LFD: 0.44 ± 0.14; HFD: 2.27 ± 0.47, p<0.0001) (D14- LFD: 0.25 ± 0.01; HFD: 2.66 ± 0.35, p<0.0001) (Figure 5C).…”

“…Data are presented as mean ± SEM. Sample sizes were based on post-hoc power analyses of previous studies (17, 20, 21). Body weight and fasting BG levels were compared using one-way analysis of variance (ANOVA) with Bonferroni’s multiple comparisons test, with a single pooled variance.…”

Non-invasive ultrasound quantification of Scar Tissue Volume predicts functional changes during tendon healing

“…However, we typically observe only slight differences in gliding function metrics between these time-points 4 . Importantly, the real utility of end-point metrics of gliding function is in identifying differences between genetically different strains of mice 10,16 , or between pharmacological treatment groups 11 at a given timepoint. Taken together, these data strongly suggest that longitudinal US based quantification of scar tissue volume may be utilized as a corollary to predict tendon ROM and gliding function during healing.…”