Background/Purpose: Galectin-9 (Gal-9) is a mammalian lectin which contributes to T-cell autoimmunity and tumor biology. Here, we examined the contribution of Gal-9 in angiogenesis and inflammatory arthritis, two critical components involved in the pathogenesis of rheumatoid arthritis (RA).

Methods: To determine the role of Gal-9 in angiogenesis in vitro, we performed human dermal microvascular endothelial cell (HMVEC) chemotaxis in modified Boyden chambers and Matrigel tube formation assays. We employed the mouse Matrigel plug angiogenesis assay to examine the involvement of Gal-9 in angiogenesis in vivo. Inhibitors and siRNA to signaling molecules for Gal-9 were also tested in these assays. We performed a local model of inflammation by injecting Gal-9 in the knees of C57/Bl6 wild type (wt) mice. HMVECs were stimulated with Gal-9 in the presence or absence of chemical inhibitors and Western blots were performed to investigate the phosphorylation of signaling molecules. We also examined the expression of Gal-9 in RA synovial tissue (ST) sections by performing immunohistochemistry.

Results: Gal-9 significantly induced HMVEC migration at 1µg/mL and 2µg/mL (P < 0.05), while signaling inhibitors of Erk1/2, p38, and c-Jun inhibited Gal-9-mediated HMVEC migration (P < 0.05). Gal-9 increased HMVEC Matrigel tube formation in vitro, another facet of angiogenesis, which was significantly reduced by the signaling inhibitors of Erk1/2, c-Jun, and p38 (P < 0.05). We confirmed our data by using siRNA directed against signaling intermediates. To examine the role of Gal-9 in angiogenesis in vivo, we performed Matrigel plug angiogenesis assays in mice. Gal-9 induced significantly higher (P < 0.05) hemoglobin, an indirect measure of angiogenesis, compared to phosphate buffered saline (PBS) injected plugs. Gal-9-mediated angiogenesis was attenuated in the plugs containing Jnk inhibitor, suggesting the importance of Jnk in Gal-9 induced angiogenesis in vivo. We found a marked increase in inflammation when wt mouse knees were injected with Gal-9 compared to PBS, suggesting that Gal-9 is a potent proinflammatory mediator. Gal-9-stimulated HMVECs showed a time-dependent increase in Jnk and Erk1/2 phosphorylation. We also found that Jnk is upstream of Erk1/2, as siRNA directed against Jnk decreased Gal-9-activated Erk1/2 phosphorylation in HMVECs. Immunohistochemical staining showed markedly higher expression of Gal-9 in blood vessels in RA compared to osteoarthritis ST sections.

Conclusion: Gal-9 mediates angiogenesis in vitro and in vivo via Erk1/2 and Jnk pathways. Gal-9 increases mouse knee circumference when injected intraarticularly. Our data suggest a novel role of Gal-9 in angiogenesis and inflammatory arthritis. Gal-9 may be a potential therapeutic target for angiogenesis-dependent diseases such as RA.

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/a-unique-role-for-galectin-9-in-angiogenesis-and-inflammatory-arthritis/