Transient Receptor Potential Melastatin 7 Ion Channels Regulate Magnesium Homeostasis in Vascular Smooth Muscle Cells

Abstract

Abstract-Magnesium modulates vascular smooth muscle cell (VSMC) function. However, molecular mechanisms regulating VSMC Mg 2ϩ remain unknown. Using biochemical, pharmacological, and genetic tools, the role of transient receptor potential membrane melastatin 7 (TRPM7) cation channel in VSMC Mg 2ϩ homeostasis was evaluated. Rat, mouse, and human VSMCs were studied. Reverse transcriptase polymerase chain reaction and immunoblotting demonstrated TRPM7 presence in VSMCs (membrane and cytosol). Angiotensin II (Ang II) and aldosterone increased TRPM7 expression. Gene silencing using small interfering RNA (siRNA) against TRPM7, downregulated TRPM7 (mRNA and protein). Basal [1][2][3][4] Mg 2ϩ also influences growth processes associated with remodeling and fibrosis, characteristic features of vascular damage in hypertension, atherosclerosis, and diabetes. 5,6 At the subcellular level, these effects occur, at least in part, through Mg 2ϩ -dependent regulation of mitogen-activated protein (MAP) kinases, tyrosine kinases, and reactive oxygen species, important signaling molecules involved in VSMC proliferation, fibrosis, and inflammation. [7][8][9] Microarray studies demonstrated that changes in [Mg 2ϩ ] i have potent modulatory actions on expression of various growth signaling molecules. 10 polypeptides with dual-function ion channel/ protein kinases, characterized by six transmembrane spanning domains with an adjacent coiled coil region, a long, highly conserved cytoplasmic N-terminal region, and a cytoplasmic C terminus, which has enzymatic activity. 22-24 TRPM6 and TRPM7, which have an overall amino acid sequence homology of 52%, harbor serine/threonine kinase domains in their C termini. 21,25,26 TRPM6 is preferentially expressed in small intestine, colon, and kidney, participating in gastrointestinal and renal Mg 2ϩ absorption. 21,27,28 Mutations in TRPM6 cause hypomagnesemia with secondary hypocalcemia. 27,29,30 Expression of TRPM7 is widespread with transcripts in brain, spleen, lung, kidney, heart, and liver. 22,[31][32][33] It is also expressed in lymphoid-derived cell lines, hematopoietic cells, granulocytes, leukemia cells, and microglia. 20,25 In various cell lines, TRPM7 is regulated by intracellular levels of Mg-ATP and is strongly activated when Mg-ATP falls below 1 mmol/L. 32,34 Studies in microglial and HEK293-transfected cells demonstrated that TRPM7 activity is also modulated through its endogenous kinase in a cAMP-, PKA-, and Src-dependent manner 25,35 and is inactivated by PIP2 hydrolysis in cardiac fibroblasts. 36 To our knowledge nothing is known about the status of TRPM7 in the vasculature. It is unclear whether this cation channel influences Mg 2ϩ transport in vascular cells and whether vasoactive agents regulate TRPM7. To gain insights into the putative role of TRPM7 in vascular Mg 2ϩ homeostasis, we used a combination of biochemical, pharmacological, molecular and genetic approaches to investigate the presence and functional significance of TRPM7 in VSMCs. Our data demonstrate that VSMCs poss...

Dysregulation of Vascular TRPM7 and Annexin-1 Is Associated With Endothelial Dysfunction in Inherited Hypomagnesemia

“…We showed that, in vascular cells, magnesium influx is driven mainly through TRPM7-sensitive pathways and that an altered cellular magnesium homeostasis and abnormal vascular smooth muscle cell function in hypertension may be, in part, related to defective TRPM7 expression/activity. 15,16 To further explore the pathophysiological significance of these findings, we used a model of inherited hypomagnesemia to investigate the effects of chronic magnesium deficiency on microvascular structure and function, magnesium transporter (TPRM7) expression, and vascular inflammatory status. Using bidirectional selective breeding, mice from a heterogenous population were selected for low (MgL) and normal-high (MgH) levels of erythrocyte magnesium.…”

Imbalance and dysfunction of transient receptor potential channels contribute to the pathogenesis of hypertension

“…Altered cellular Mg 2+ homeostasis and abnormal VSMC function in hypertension may be related to defective TRPM7 expression/ activity [65,66]. Touyz et al [67] demonstrated that TRPM7 was present and functionally active in human, mouse and rat VSMCs. Furthermore, they found that TRPM6 was unaltered in SHR, but expression of TRPM7 was blunted.…”

Vascular Responses to Shear Stress: The Involvement of Mechanosensors in Endothelial Cells

“…TRPM7 or TRP-PLIK (transient receptor potentialphospholipase interacting kinase) is widely expressed in tissues including vascular smooth muscle and endothelium [31]. It is a 105pS outward rectifier and is permeable to Na + and Ca 2+ .…”