CD44-mediated cyclooxygenase-2 expression and thromboxane A2 production in RAW 264.7 macrophages

Abstract.

Objective and design: CD44 is the major cell surface receptor for hyaluronan (HA) on macrophages. Stimulation of macrophages via the HA-CD44 pathway leads to the enhanced expression of inflammatory gene products, including cytokines, chemokines, and adhesion molecules. We have examined whether activation of CD44 by crosslinking is capable of activating the cyclooxygenase (COX) and prostaglandin (PG)/thromboxane (TX) pathway in cultured macrophages.¶Materials and methods: CD44 was crosslinked on RAW 264.7 mouse macrophages using specific rat anti-mouse CD44 monoclonal antibodies and anti-rat IgG. Total RNA was extracted and subjected to RT-PCR analysis for genes of the PG/TX synthetic pathway. Supernatants were analyzed for PGE₂ and TXB₂ using specific ELISAs.¶Results: Transcripts for COX-1, COX-2, TX synthase (TXS), and PGE₂ synthase (PGES) were all constitutively expressed in the mouse macrophage cell line RAW 264.7. Crosslinking of CD44 markedly enhanced COX-2 and weakly increased TXS mRNA, whereas COX-1 and PGES mRNA did not change significantly in these cells. Crosslinking of CD44 selectively increased the production of TXB₂ but not PGE₂.¶Conclusions: These findings suggest that the activation of the CD44 pathway plays a unique role in PG synthesis. Activation of this pathway results in enhanced TXA₂ but not PGE₂ production. This leads to an imbalance of the TXA₂/PGE₂ profile which favors a proinflammatory and vasoconstrictory response.