M1 Macrophage Vesicles Protect Joint Cartilage by Triggering Cellular Cleanup

Osteoarthritis of the temporomandibular joint (TMJ-OA) affects 8–16% of the global population and is characterized by synovial inflammation, cartilage breakdown, and bone remodeling. Current therapies suppress symptoms but do not repair damage. Understanding how cells in the inflamed joint communicate is critical to finding new treatments.

This study focused on migrasomes — vesicular organelles ranging 0.5–3 µm in diameter that form at the trailing edges of migrating cells. Unlike exosomes, migrasomes arise specifically during cell migration and carry distinct cargo. The researchers first confirmed migrasomes exist in human TMJ-OA synovial tissue and fluid using transmission electron microscopy and immunofluorescence. Using a publicly available single-cell RNA sequencing dataset (GEO: GSE267942) from a mouse arthritis model, they computed a 'Migrasome Score' based on seven key biogenesis genes and identified infiltrating M1 macrophages as a primary source of synovial migrasomes in the inflamed joint.

In vitro experiments showed that M1 macrophage-derived migrasomes, when co-cultured with TNF-α-stressed rat condylar chondrocytes, reduced apoptosis, preserved proteoglycan content, and suppressed catabolic enzyme expression (MMPs). Proteomic analysis revealed the migrasomes were enriched in autophagy-related proteins, suggesting a mechanistic link. The team then built a 'Mini-TMJ' model — a synovium-cartilage organoid co-culture system — and found that blocking migrasome transfer from synovial organoids to cartilage organoids under monosodium iodoacetate (MIA)-induced inflammatory stress reduced autophagy markers in cartilage. Adding exogenous M1 macrophage migrasomes restored autophagy activity, confirming the transfer-dependent mechanism.

In a rat TMJ-OA model, intra-articular injection of purified M1 macrophage migrasomes attenuated cartilage degradation and promoted autophagy activation in vivo. These converging lines of evidence — human tissue confirmation, single-cell transcriptomics, organoid modeling, and animal validation — collectively support the conclusion that M1 macrophage migrasomes ameliorate TMJ-OA progression by delivering autophagy-activating cargo to chondrocytes.

The findings are notable for reframing M1 macrophages — classically viewed as pro-inflammatory drivers of joint damage — as also capable of delivering chondroprotective signals via migrasomes. Caveats include the use of THP-1-derived macrophages rather than primary human macrophages for migrasome production, reliance on a rodent TMJ-OA model that may not fully replicate human disease, and limited characterization of the specific molecular cargo responsible for autophagy induction.