Abstract 218: TRPM7 Kinase - A Novel Signaling Pathway for Ang II-induced MAPK Activation in Vascular Smooth Muscle Cells.
Transient receptor potential melastatin 7 (TRPM7) cation channel is a unique protein, which regulates transmembrane magnesium (Mg2+) transport through its channel domain, and intracellular signaling through its kinase domain. We previously demonstrated that TRPM7, is expressed on vascular smooth muscle cells (VSMC), controls Mg2+ influx, and is regulated by angiotensin II (Ang II). Low Mg2+ levels are among the many factors leading to hypertension, where intracellular Mg2+ deficiency and TRPM7 downregulation is observed. Despite the advancement in the understanding of Mg2+ and TRPM7 biology, the role of TRPM7, and its kinase, in hypertension remains elusive. In this study, we investigated whether deletion of TRPM7 kinase domain alters Ang II-induced Mg2+ influx and signaling in VSMCs. Cultured VSMCs from mesenteric arteries obtained from heterozygous mice for the TRPM7 kinase deletion (+/-) and WT mice were used. Mg2+ influx was assessed by fluorescence microscopy. Activation of MAP kinases was evaluated by immunoblotting. Ang II (10-7M) increase in Mg2+ influx was similar in VSMC from both, WT and TRPM7+/- mice (2.5-fold; p<0.001). Ang II increased phosphorylation of JNK (10-fold), p38MAPK (4-fold) and ERK1/2 (6.4-fold) in VSMC from WT mice (p<0.001). Ang II-induced MAPK activation was blunted in TRPM7+/- VSMC. Moreover, Ang II treatment induced PDGF-R (2-fold) and Akt phosphorylation (3-fold) in VSMC from WT mice (p<0.05), an effect that was also blunted in TRPM+/- VSMC. Ang II induced SMAD2/3 activation in VSMC from WT (1.5-fold; p<0.05) and, with a greater extent, TRPM7+/- mice (3.5-fold; p<0.05). To understand whether the blunted effects of Ang II on intracellular signaling in VSMC from TRPM7+/- mice could be attributed to downregulation of Ang II receptors, AT1R and AT2R expression was assessed. No differences in receptor expression were observed between VSMC from WT and TRPM+/-. In conclusion, our findings identify that TRPM7 kinase domain is not necessary for Mg2+ influx, but it seems to be a novel and important player in Ang II-induced signaling in VSMCs.
- © 2012 by American Heart Association, Inc.