MON-252 - Monocytes Chemotaxis to MCP-1 Is Enhanced by Thyroid Hormone-Signaling through ΑVβ3 Integrin

Introduction: Monocyte chemoattractant protein-1 (MCP-1/CCL1) is a chemotactic cytokine (chemokine) that regulates the recruitment of monocytes to sites of inflammation by acting through the cell surface receptor CCR2. Thyroid hormone effects can be mediated through the αvβ3 integrin, a non-classical thyroid hormone receptor also present on the surface of monocytes. This signaling represents a recently identified system that can influence cell recruitment and drive tumor growth and angiogenesis in tumors. We asked if T3/T4 signaling through αvβ3 integrin could impact monocyte recruitment by MCP-1/CCL1.

Methods: Transendothelial migration assay was performed using confluent endothelial monolayers on 3µm pore inserts. Monocytes were treated with T3 (1-100 nM) or T4 (100-1000 nM), with or without tetrac (100 nM), a specific inhibitor of αvβ3 integrin-mediated thyroid hormone action, and allowed to migrate toward a solution containing MCP-1 (10ng/ml). Migrated cells were quantified by flow cytometry. In a modified Boyden chamber assay, monocytes were fluorescence-labeled and treated with T3 or T4 with or without tetrac. Similar to the prior assay, MCP-1 had been used as chemoattractant added to the lower chamber only. The fluorescence of transmigrated monocytes in the lower chamber was measured at different time points. Finally, using a 3D chemotaxis migration assay, monocytes treated with T3 or T4 with or without tetrac were subjected to a gradient between serum-free medium and MCP-1 medium. Cells randomly selected were manually tracked using an ImageJ plug-in Manual Tracking.

Results: Monocytes showed a significantly increased transmigration towards MCP-1 compared to medium only. In all assays, the migratory behaviour of monocytes was significantly enhanced upon treatment with T3 or T4. Treatment with tetrac inhibited the effects of T3 and T4 on MCP-1-driven monocyte migration in the transendothelial, modified Boyden chamber and 3D chemotaxis assays, suggesting that this effect is mediated through αvβ3 integrin signaling.

Conclusion: By working with two distinct monocytes signalling pathways (CCR2 and αvβ3) and selectively inhibiting only one of them, we were able to analyse the real impact of thyroid hormones on the migratory behaviour of monocytes. Our results suggest that thyroid hormones T3 and T4, and the thyroid hormone metabolite tetrac acting through αvβ3 can directly interact with chemokine signalling through the G protein coupled receptor CCR2 to influence the ability of monocytes to undergo transendothelial and chemotaxis migration. This suggests a potential role for non-genomic, integrin αvβ3-mediated thyroid hormone action on monocyte recruitment with implications for inflammatory responses.

*Unless otherwise noted, all abstracts presented at ENDO must not be released to the press or the public until the date and time of presentation. For oral presentations, the abstracts are embargoed until the session begins. The Endocrine Society reserves the right to lift the embargo on specific abstracts that are selected for promotion prior to or during ENDO.*