Targeting CD14 to Inhibit Macrophage Senescence and Regulate the Microenvironment for Enhanced Tendon-Bone Healing

Abstract

Background:

To date, no targeted pharmacological agents have been clinically available specifically for postoperative management after anterior cruciate ligament reconstruction (ACLR).

Purpose:

To elucidate the role of macrophage senescence in the tendon-bone interface microenvironment and assess whether targeting CD14 can mitigate senescence, thereby enhancing tendon-bone healing.

Study Design:

Controlled laboratory study.

Methods:

A murine ACLR model was used to evaluate the tendon-bone healing. Healing was assessed 8 weeks postsurgery through histological staining, micro–computed tomography analysis of neoplastic bone formation within bone tunnels, and biomechanical testing of tendon grafts. Cellular senescence was evaluated using β-galactosidase staining, while immunofluorescence and immunohistochemistry were used to analyze protein expression levels. Macrophage heterogeneity at the tendon-bone interface was assessed via t-distributed stochastic neighbor embedding projection, and senescent macrophage characteristics were investigated using CellChat, KEGG, and GO analyses. Alkaline phosphatase and Alizarin Red S staining were used to evaluate osteogenic differentiation of bone marrow mesenchymal stem cells.

Results:

Early inflammatory responses triggered by apoptotic cells at the tendon-bone interface resulted in macrophage senescence, activation of inflammatory pathways, increased secretion of pro-inflammatory factors, and elevated CD14 expression. Targeting CD14 reduced macrophage senescence and the inflammatory response at the tendon-bone interface, thereby increasing tendon-bone healing.

Conclusion:

The findings indicate that excessive inflammation within the tendon-bone interface microenvironment promotes macrophage senescence, thereby impairing tendon-bone healing. Targeting CD14 effectively prevents macrophage senescence, facilitating improved tendon-bone healing.

Clinical Relevance:

Currently, targeted therapeutics to enhance tendon-bone healing post-ACLR are lacking in clinical practice. The findings demonstrate that microenvironmental inflammation leading to macrophage senescence is a critical factor contributing to impaired tendon-bone healing. CD14-targeted therapy may inhibit macrophage senescence, accelerate tendon-bone healing, and offer significant translational potential for clinical application.