Investigating novel roles for exogenous and endogenous Galectin-3 in leukocyte recruitment to the inflamed microcirculation

Abstract

This study uses in vivo and ex vivo imaging to explore the hypothesis that galectin-3 (Gal-3) acts as a positive regulator of leukocyte recruitment to the inflamed microcirculation. In addition to this, due to its localisation both within and outside the cell, the effect of exogenous as well as the role of endogenous Gal-3 was investigated. Leukocyte recruitment in the cremasteric microcirculation of wild-type (C57BL/6), Gal-3-/- and CX3CR1gfp/+ mice was assessed by intravital microscopy following intrascrotal injection of PBS, IL-1β, TNF-α or Gal-3 and intravenous administration of anti-Ly6G to label neutrophils. Concurrently, these responses were investigated further with the use of the parallel plate flow chamber assay, confocal microscopy, flow cytometry, PCR analysis and proteome profile array. Treatment with IL-1β and TNF-α significantly reduced leukocyte rolling velocities in WT mice, an effect that was absent in Gal-3-/- mice. These observations were repeated in the flow chamber where Gal-3-/- leukocytes did not capture to E-selectin and initiate downstream changes in their activation state and cell morphology. Flow cytometric analysis showed that Gal-3-/- neutrophils express reduced PSGL-1 in response to TNFα and that basally both neutrophils and monocytes display reduced HPA and PNA lectin binding – suggesting that the Gal-3-/- leukocytes have an altered glycophenotype. Furthermore, Gal-3-/- neutrophils express reduced CD11b basally and after TNFα treatment, though both Gal-3-/- neutrophils and monocytes express comparable levels of L-selectin.Gal-3 did not increase ICAM-1 or E-selectin expression however, treatment in vivo followed by confocal analysis indicated possible increases in PECAM-1, VCAM-1 and E-selectin expression. These data suggest the mechanisms mediating leukocyte rolling are impaired in Gal-3 null-/- mice and support a role for Gal-3 as a positive regulator of neutrophil and monocyte trafficking. In conclusion, this study unveils novel biology for exogenous and endogenous Gal-3 in controlling vascular inflammation.