The Role of Hyaluronan/RHAMM Interactions in the Modulation of Macrophage Polarization and Cartilage Repair.

Hyaluronan (HA), a negatively charged linear glycosaminoglycan, is a key macromolecular component of the articular cartilage extracellular matrix. The differential effects of HA are determined by a spatially/temporally regulated display of HA receptors, such as CD44 and Receptor for Hyaluronan Mediated Motility (RHAMM). HA signaling through CD44 with RHAMM has been shown to stimulate inflammation and fibrotic processes. This study shows an increased expression of RHAMM in pro-inflammatory macrophages. Interfering with HA/RHAMM interactions using a 15mer RHAMM-mimetic, HA binding peptide (P15-1) together with high molecular weight (HMW)HA reduced the expression and release of inflammatory markers and increased the expression of anti-inflammatory markers in pro-inflammatory macrophages. Interfering with HA/RHAMM interactions in vivo during the regeneration of a full thickness cartilage defect after microfracture surgery in rabbits using three intra-articular injections of P15-1 together with HMWHA reduced the number of pro-inflammatory macrophages and increased the number of anti-inflammatory macrophages in the injured knee joint and greatly improved the repair of the cartilage defect compared to intra-articular injections of HMWHA alone. These findings suggest that HA/RHAMM interactions play a key role in cartilage repair/regeneration via stimulating inflammatory and fibrotic events, including increasing the ratio of pro-inflammatory to anti-inflammatory macrophages. Interfering with these interactions reduced inflammation and greatly improved cartilage repair.

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