[Immunohistochemical study of the role of mast cells and macrophages in the process of angiogenesis in the atherosclerotic plaques in patients with metabolic syndrome]

Cellular and Molecular Mechanisms of Mast Cells in Atherosclerotic Plaque Progression and Destabilization

Mast cells (MCs) are commonly recognized for their crucial involvement in the pathogenesis of allergic diseases, but over time, it has come to light that they also play a role in the pathophysiology of non-allergic disorders including atherosclerosis. The involvement of MCs in the pathology of atherosclerosis is supported by their accumulation in atherosclerotic plaques upon their progression and the association of intraplaque MC numbers with acute cardiovascular events. MCs that accumulate within the atherosclerotic plaque release a cocktail of mediators through which they contribute to neovascularization, plaque progression, instability, erosion, rupture, and thrombosis. At a molecular level, MC-released proteases, especially cathepsin G, degrade low-density lipoproteins (LDL) and mediate LDL fusion and binding of LDL to proteoglycans (PGs). Through a complicated network of chemokines including CXCL1, MCs promote the recruitment of among others CXCR2+ neutrophils, therefore, aggravating the inflammation of the plaque environment. Additionally, MCs produce extracellular traps which worsen inflammation and contribute to atherothrombosis. Altogether, evidence suggests that MCs actively, via several underlying mechanisms, contribute to atherosclerotic plaque destabilization and acute cardiovascular syndromes, thus, making the study of interventions to modulate MC activation an interesting target for cardiovascular medicine.

Vascular Inflammation in Cardiovascular Disease: Is Immune System Protective or Bystander?

Cardiovascular disease (CVD) is one of the leading causes of death worldwide. Chronic atherosclerosis induced vascular inflammation and perturbation of lipid metabolism is believed to be a major cause of CVD. Interplay of innate and adaptive Immune system has been interwined with various risk factors associated with the initiation and progression of atherosclerosis in CVD. A large body of evidence indicates a correlation between immunity and atherosclerosis. Retention of plasma lipoproteins in arterial subendothelial wall triggers the T helper type 1 (Th1) cells and monocyte-derived macrophages to form atherosclerotic plaques. In the present review, we will discuss the pathogenesis of CVD in relation to atherosclerosis with a particular focus on pro-atherogenic role of immune cells. Recent findings have also suggested anti-atherogenic roles of different B cell subsets. Therapeutic approaches to target atherosclerosis risk factors have reduced the mortality, but a need exists for the novel therapies to treat arterial vascular inflammation. These insights into the immune pathogenesis of atherosclerosis can lead to new targeted therapeutics to abate cardiovascular mortality and morbidity.

Endoglin: An 'Accessory' Receptor Regulating Blood Cell Development and Inflammation

Transforming growth factor-β1 (TGF-β1) is a pleiotropic factor sensed by most cells. It regulates a broad spectrum of cellular responses including hematopoiesis. In order to process TGF-β1-responses in time and space in an appropriate manner, there is a tight regulation of its signaling at diverse steps. The downstream signaling is mediated by type I and type II receptors and modulated by the ‘accessory’ receptor Endoglin also termed cluster of differentiation 105 (CD105). Endoglin was initially identified on pre-B leukemia cells but has received most attention due to its high expression on activated endothelial cells. In turn, Endoglin has been figured out as the causative factor for diseases associated with vascular dysfunction like hereditary hemorrhagic telangiectasia-1 (HHT-1), pre-eclampsia, and intrauterine growth restriction (IUPR). Because HHT patients often show signs of inflammation at vascular lesions, and loss of Endoglin in the myeloid lineage leads to spontaneous inflammation, it is speculated that Endoglin impacts inflammatory processes. In line, Endoglin is expressed on progenitor/precursor cells during hematopoiesis as well as on mature, differentiated cells of the innate and adaptive immune system. However, so far only pro-monocytes and macrophages have been in the focus of research, although Endoglin has been identified in many other immune system cell subsets. These findings imply a functional role of Endoglin in the maturation and function of immune cells. Aside the functional relevance of Endoglin in endothelial cells, CD105 is differentially expressed during hematopoiesis, arguing for a role of this receptor in the development of individual cell lineages. In addition, Endoglin expression is present on mature immune cells of the innate (i.e., macrophages and mast cells) and the adaptive (i.e., T-cells) immune system, further suggesting Endoglin as a factor that shapes immune responses. In this review, we summarize current knowledge on Endoglin expression and function in hematopoietic precursors and mature hematopoietic cells of different lineages.

Flt3 Regulation in the Mononuclear Phagocyte System Promotes Ocular Neovascularization

Fms-like tyrosine kinase 3 (Flt3), a tyrosine kinase receptor expressed in CD34+ hematopoietic stem/progenitor cells, is important for both normal myeloid and lymphoid differentiation. It has been implicated in mice and humans for potential multilineage differentiation. We found that mice deficient in Flt3 or mice that received an Flt3 inhibitor (AC220) showed significantly reduced areas of ischemia-induced retinal neovascularization (RNV) and laser-induced choroidal NV (CNV) (P < 0.05). Increased Flt3 expression at the protein level was detected in retinas of oxygen-induced retinopathy (OIR) mice at P15 and P18 during retinal NV (RNV) progression. We subsequently found that macrophages (Mphi) polarization was regulated at the site of CNV in Flt3-deficient mice. Flow cytometry analysis demonstrated that Flt3 deficiency shifted Mphi polarization towards an M2 phenotype during RNV with significant reduction in M1 cytokine expression when compared to the wild-type controls (P < 0.05). Based on the above findings, we concluded that Flt3 inhibition alleviated ocular NV by promoting a Mphi polarization shift towards the M2 phenotype. Therapies targeting Flt3 may provide a new approach for the treatment of ocular NV.

Inflammation: A Novel Therapeutic Target/Direction in Atherosclerosis

Over the past two decades, the viewpoint of atherosclerosis has been replaced gradually by a lipid-driven, chronic, low-grade inflammatory disease of the arterial wall. Current treatment of atherosclerosis is focused on limiting its risk factors, such as hyperlipidemia or hypertension. However, treatment targeting the inflammatory nature of atherosclerosis is still very limited and deserves further attention to fight atherosclerosis successfully. Here, we review the current development of inflammation and atherosclerosis to discuss novel insights and potential targets in atherosclerosis, and to address drug discovery based on anti-inflammatory strategy in atherosclerotic disease.