CCR2 Knockout Reduces Early Inflammation in Mouse Rotator Cuff Injury Model

A commentary in The Journal of Bone and Joint Surgery discusses research by Covello et al. on the timing of macrophage responses in rotator cuff tendinopathy. Using a mouse subacromial impingement model, investigators compared wild-type mice with mice lacking the CCR2 gene. Outcomes included macrophage activation, gene expression, histology, and tendon biomechanics; the supplied commentary does not report sample size.

Macrophage activation, assessed indirectly using gallium-68 folate receptor–targeted microPET/CT at 3, 7, 21, and 42 days after injury, peaked at days 3 and 7 in wild-type mice. CCR2-knockout mice showed significantly lower activation at these early time points and less severe tendinopathic changes. Gene expression in wild-type mice shifted from early pro-inflammatory, M1-associated signaling toward later anti-inflammatory, M2-associated markers. However, CCR2 knockout did not confer superior biomechanical properties at day 42.

The findings support further investigation of CCR2 as a target for early inflammation, rather than establishing a treatment for patients. Histology and biomechanics were assessed only at day 42, and PET signals may vary with macrophage phenotype and tissue environment. The commentary also hypothesizes that corticosteroid effects could depend on inflammatory phase, but the described study does not establish corticosteroid efficacy or optimal treatment timing in humans.