Galectin-1 Modulates Cell Adhesions, Caveolae, and Vascular Permeability in Kidney Endothelial Cells – Insights from Proteomics, Phosphoproteomics, and Functional Studies

ABSTRACT Microvascular inflammation and endothelial injury, triggered by interferon-gamma (IFNγ), are hallmarks of antibody-mediated rejection (ABMR), the leading cause of premature kidney allograft loss. Glomerular extracellular matrix (ECM) remodeling and endothelial caveolae formation are important aspects of chronic ABMR. We found galectin-1, an immunomodulatory protein that interacts with the ECM, to be increased in the glomeruli of patients with ABMR, while its gene ( LGALS1 ) expression was decreased by IFNγ stimulation in glomerular endothelial cells. Mechanisms underlying endothelial dysfunction in ABMR, its links to ECM remodeling, and the role of immunomodulatory proteins such as galectin-1 remain incompletely understood. Here we studied the effects of galectin-1 modulation in glomerular microvascular endothelial cells (GMECs) in vitro . We demonstrated that galectin-1 was mainly expressed by glomerular endothelial cells in ABMR kidneys. To model key aspects of endothelial injury in ABMR, we knocked down LGALS1 in GMECs, followed by stimulation with IFNγ and performed label-free quantitative proteomic and phosphoproteomic profiling of GMECs. Proteomic analysis identified 5446 proteins (FDR<0.01), of which 236, 827, and 267 were differentially expressed in response to LGALS1 knockdown, IFNγ treatment, and their interaction, respectively (FDR<0.05). Both LGALS1 knockdown and the interaction between treatments significantly altered expression of adhesion proteins (FDR<0.01), particularly integrin subunit β5, which was validated. Phosphoproteomic profiling identified 2727 phosphopeptides (FDR<0.01), with 28 that were differentially expressed across LGALS1 knockdown, IFNγ treatment, and their interaction (P<0.01). Phosphorylation of CAVN1 and co-localization with its partner CAV1, critical for caveolar formation, were decreased in GMECs upon LGALS1 knockdown, IFNγ stimulation, or both. In a microfluidic model of the glomerular microvasculature, addition of recombinant galectin-1 increased both endothelial permeability and secretion of proinflammatory cytokines, in LGALS1 -silenced GMECs. Thus, endothelial signaling pathways regulated by inflammatory cues and galectin-1 contribute to endothelial injury and caveolae formation, highlighting galectin-1 as a potential therapeutic target in ABMR. Synopsis Galectin-1 is expressed by kidney glomerular endothelium. This study reveals that modifying galectin-1 in endothelial cells, in the presence of IFNγ perturbs cytoskeletal, adhesion and caveolar proteins resulting in altered endothelial permeability. LGALS1 knockdown increased ECM proteins and decreased interferon-induced proteins. LGALS1 knockdown and IFNγ treatment perturbed cell adhesion proteins such as ITGB5. CAVN1 phosphorylation and colocalization with CAV1 decreased upon LGALS1 knockdown. Extracellular galectin-1 increased microvascular permeability in response to IFNγ.