Investigating the role of Galectin-9 in monocytes associated with atherosclerosis

Cardiovascular disease is the number one cause of death worldwide. They are most often caused by atherosclerotic plaques, formed by lipid depositions in the vessel wall of major blood vessels which cause an inflammatory immune response. While it has been long accepted that the immune response is a driving factor in atherosclerotic plaque progression, no suitable therapeutics have been developed so far to successfully target inflammation and reduce the risk of cardiovascular events. Therefore the identification of new therapeutic targets involved in the progression of atherosclerosis and their mechanism of action is required in order to develop successful therapies. Monocyte recruitment and migration into the vessel wall and their differentiation into macrophages, which release pro-inflammatory factors, and lipid-laden foam cells are driving forces of atherosclerosis. Many major proteins involved in the multistep adhesion cascade of leukocyte recruitment have been well characterised, however there are still gaps in knowledge. Galectin-9 is a ß-galactoside binding protein and has been shown to have a wide range of functions. More recently, various studies have demonstrated its role in the modulation of leukocyte trafficking. However, its role in monocyte recruitment and migration remains elusive. The aim of this study is to characterise the role of Galectin-9 in monocyte migration and atherosclerotic plaque progression. The results show that Galectin-9 is expressed and released by human monocytes, macrophages and endothelial cells and its upregulation is induced by pro-inflammatory environments. Soluble Galectin-9 was demonstrated to induce human monocyte activation and the release of pro-inflammatory cytokines and chemokines by human monocyte derived macrophages. Additionally, it was observed that Galectin-9 upregulation by the endothelium is required for monocyte adhesion in vitro while PBMCs of peripheral arterial patients adhere to immobilised Galectin-9 with higher frequency compared to healthy young and aged controls. These inflammation-specific modes of function of Galectin-9 were confirmed in vivo: Galectin-9 induced monocyte and neutrophil migration into tissue during inflammation but not during homeostasis. Finally, the role of Galectin-9 in atherosclerotic plaque progression was demonstrated, since it was shown that ApoE-/- Gal-9-/- mice had a reduced plaque burden as well as a reduced macrophage and collagen content in aortic root plaques in a model of dietinduced atherosclerosis compared to ApoE-/- mice. In conclusion this study demonstrates that inflammation-induced expression of Galectin-9 modulates atherosclerotic plaque progression in two ways: i) by facilitating monocyte recruitment and ii) through inducing a pro-inflammatory macrophage phenotype. These findings suggest that Galectin-9 is a novel therapeutic target in the prevention of atherosclerotic plaque progression

Triggering the resolution of immune mediated inflammatory diseases:can targeting leukocyte migration be the answer?

Leukocyte recruitment is a pivotal process in the regulation and resolution of an inflammatory episode. It is vital for the protective responses to microbial infection and tissue damage, but is the unwanted reaction contributing to pathology in many immune mediated inflammatory diseases (IMIDs). Indeed, it is now recognized that patients with IMIDs have defects in at least one, if not multiple, check-points regulating the entry and exit of leukocytes from the inflamed site. In this review, we will explore our understanding of the imbalance in recruitment that permits the accumulation and persistence of leukocytes in IMIDs. We will highlight old and novel pharmacological tools targeting these processes in an attempt to trigger resolution of the inflammatory response. In this context, we will focus on cytokines, chemokines, known pro-resolving lipid mediators and potential novel lipids (e.g., sphingosine-1-phosphate), along with the actions of glucocorticoids mediated by 11-beta hydroxysteroid dehydrogenase 1 and 2

The interplay of galectins-1, -3, and -9 in the immune-inflammatory response underlying cardiovascular and metabolic disease

Galectins are β-galactoside-binding proteins that bind and crosslink molecules via their sugar moieties, forming signaling and adhesion networks involved in cellular communication, differentiation, migration, and survival. Galectins are expressed ubiquitously across immune cells, and their function varies with their tissue-specific and subcellular location. Particularly galectin-1, -3, and -9 are highly expressed by inflammatory cells and are involved in the modulation of several innate and adaptive immune responses. Modulation in the expression of these proteins accompany major processes in cardiovascular diseases and metabolic disorders, such as atherosclerosis, thrombosis, obesity, and diabetes, making them attractive therapeutic targets. In this review we consider the broad cellular activities ascribed to galectin-1, -3, and -9, highlighting those linked to the progression of different inflammatory driven pathologies in the context of cardiovascular and metabolic disease, to better understand their mechanism of action and provide new insights into the design of novel therapeutic strategies

Galectin-9 mediates neutrophil capture and adhesion in a CD44 and β2 integrin-dependent manner.

Neutrophil trafficking is a key component of the inflammatory response. Here, we have investigated the role of the immunomodulatory lectin Galectin-9 (Gal-9) on neutrophil recruitment. Our data indicate that Gal-9 is upregulated in the inflamed vasculature of RA synovial biopsies and report the release of Gal-9 into the extracellular environment following endothelial cell activation. siRNA knockdown of endothelial Gal-9 resulted in reduced neutrophil adhesion and neutrophil recruitment was significantly reduced in Gal-9 knockout mice in a model of zymosan-induced peritonitis. We also provide evidence for Gal-9 binding sites on human neutrophils; Gal-9 binding induced neutrophil activation (increased expression of β2 integrins and reduced expression of CD62L). Intra-vital microscopy confirmed a pro-recruitment role for Gal-9, with increased numbers of transmigrated neutrophils following Gal-9 administration. We studied the role of both soluble and immobilized Gal-9 on human neutrophil recruitment. Soluble Gal-9 significantly strengthened the interaction between neutrophils and the endothelium and inhibited neutrophil crawling on ICAM-1. When immobilized, Gal-9 functioned as an adhesion molecule and captured neutrophils from the flow. Neutrophils adherent to Gal-9 exhibited a spread/activated phenotype that was inhibited by CD18 and CD44 neutralizing antibodies, suggesting a role for these molecules in the pro-adhesive effects of Gal-9. Our data indicate that Gal-9 is expressed and released by the activated endothelium and functions both in soluble form and when immobilized as a neutrophil adhesion molecule. This study paves the way for further investigation of the role of Gal-9 in leukocyte recruitment in different inflammatory settings