MAGNESIUM AND ENDOTHELIAL FUNCTION: COMPARATIVE STUDIES IN MACRO AND MICROVASCULAR ENDOTHELIAL CELLS

Mg is referred to as the intracellular divalent cation par excellence. Its biological role is extremely versatile as it can serve structural functions as well as dynamic functions. Accordingly, Mg deficiency has been reported to be involved in the pathogenesis of cardiovascular diseases and, in particular, in atherogenesis. 1)Mg in macrovascular endothelial cells. In cultured macrovascular endothelial cells, low Mg increases tha adhesion of monocytes to the monolayer via upregulation of vascular cell adhesion molecule (VCAM), induces plasminogen activator inhibitor (PAI)1, augments the levels of the pro-inflammatory cytokine interleukin (IL)-1α, impairs endothelial proliferation and promotes cellular senescence (Killilea DW and Ames BN, 2008). Recently, endothelial function has been shown significantly impaired in a model of inherited hypomagnesemia in mice (MgL mice) (Mazur A et al., 2007). All these results point to the fact that low Mg promotes the acquisition of an inflammatory phenotype in endothelium. Since NFkB transcription factors control the inflammatory response and are activated by free radicals, I investigated whether culture in low Mg promotes oxidative stress and activates NFkB in human umbilical vein endothelial cells (HUVEC). Because NFkB activation correlates with marked alterations of the cytokine network, I also studied the secretion profile of inflammatory molecules in cells grown in low Mg. My results highlight molecular events that contribute to the pro-atherogenic effect of Mg deficiency. 2)Mg in microvascular endothelial cells. MEC contribute to inflammation by elaborating cytokines, synthesizing chemical mediators and expressing adhesion molecules which bind leukocytes, thus facilitating their passage in the nearby tissues. In addition, also in the microvasculature the endothelium itself is sensitive to cytokines which profoundly affect its behavior. Low extracellular Mg affects also microvascular endothelial cells. In murine microvascular cells, it has been reported that low Mg induces the synthesis of vascular cell adhesion molecule (VCAM), a marker of inflammation which binds the integrin VLA-4 (very late activation antigen-4) expressed by monocytes and most of the lymphocytes. Focal adhesion of leukocytes to the microvasculature is a key step in inflammation and immune response. In addition, Mg deficiency upregulates IL-1α and IL-6, pleiotropic cytokines implicated in acute phase response and inflammation (Bernardini D. et al, 2005). Because MEC are important players in inflammation and angiogenesis, I asked whether different concentrations of Mg could affect the behavior of human MEC in vitro. My results demonstrate that culture in low Mg affects human MEC with some differences in respect to HUVEC. 3)TRPM7, a Mg transport channel. The novel Mg transporter TRPM7, a ubiquitously expressed protein with the feature of being both a functional ion channel and kinase, is a critical regulator of Mg homeostasis in vascular cells. Because endothelial cells are very sensitive to extracellular concentrations of Mg, we have investigated the expression and the role of TRPM7 in human macro- and microvascular endothelial cells. I show that the regulation of TRPM7 expression is very different in human MEC vs HUVEC. By siRNA I also demonstrate completely different effects of TRPM7 silencing in HUVEC vs MEC.