High-fat diet-induced obesity exacerbated collagenase-induced tendon injury with upregulation of interleukin-1beta and matrix metalloproteinase-1.

Aims: Obesity increases tendinopathy's risk, but its mechanisms remain unclear. This study examined the effect of high-fat diet (HFD)-induced obesity on the outcomes and inflammation of collagenase-induced (CI) tendon injury.

Methods: Mice were fed with standard chow (SC) or HFD for 12 weeks. Bacterial collagenase I or saline was injected over the patellar tendons of each mouse. At weeks 2 and 8 post-injection, the patellar tendons were harvested for histology, immunohistochemical staining, and gait analysis. The difference (Δ) of limb-idleness index (LII) at the time of post-injury and pre-injury states was calculated. Biomechanical test of tendons was also performed at week 8 post-injection.

Results: HFD aggravated CI tendon injury with an increase in vascularity and cellularity compared to SC treatment. The histopathological score (week 2:  = 0.025; week 8:  = 0.013) and ΔLII (week 2:  = 0.012; week 8:  = 0.005) were significantly higher in the HFD group compared to those in the SC group after CI tendon injury. Stiffness (saline:  = 0.003; CI:  = 0.010), ultimate stress (saline:  < 0.001; CI:  = 0.006), and Young's modulus (saline:  = 0.017; CI:  = 0.007) were significantly lower in the HFD group compared to the SC group at week 8 after saline or collagenase injection. HFD induced higher expression of IL-1β (week 2:  = 0.010; week 8:  = 0.025) and MMP-1 (week 2:  = 0.010; week 8:  = 0.004) compared to SC treatment after CI tendon injury at both time points.

Conclusions: HFD-induced obesity exacerbated histopathological, functional, and biomechanical changes in the CI tendon injury model, which was associated with an upregulation of IL-1β and MMP-1.