Regulation of the Mg2+ transporter TRPM7 by growth factors-implications in vascular function in health and disease

Zou, Zhiguo (2020) Regulation of the Mg2+ transporter TRPM7 by growth factors-implications in vascular function in health and disease. PhD thesis, University of Glasgow.

Abstract

Transient receptor potential melastatin 7 (TRPM7) is a ubiquitously expressed bi-functional protein (chanzyme, channel + kinase) comprising a cation channel and a C-terminal α-kinase domain. As an ion channel, TRPM7 conducts primarily divalent cations such as Mg2+, Ca2+ and Zn2+. The kinase domain has been found to influence activity of downstream target proteins including calpain-2, annexin-1, myosin IIA, phospholipase Cγ2 (PLCγ2) and eukaryotic elongation factor 2-kinase (eEF2-k). The relevance of TRPM7 in the cardiovascular system has been demonstrated by an increasing number of studies. Our group has previously identified TRPM7 as a key regulator of Mg2+ homeostasis and growth in vascular smooth muscle cells (VSMCs). We show that TRPM7 exerts protective effects against Ang II-induced hypertension, endothelial dysfunction and cardiac hypertrophy and that vasoactive agent bradykinin regulates TRPM7 and its downstream target annexin-1, playing an important role in VSMC Mg2+ homeostasis, cell migration and invasion. The implication of TRPM7 in regulating blood pressure was also highlighted recently with a study showing that leptin induces hypertension through TRPM7 in carotid body.
Growth factors, such as vascular endothelial growth factor (VEGF) and epidermal growth factor (EGF), through activating their receptors VEGF receptor (VEGFR) and EGF receptor (EGFR) respectively, which belong to the receptor tyrosine kinase (RTK) family, trigger a variety of downstream signalling including PLCγ/protein kinase C (PKC), RAS/RAF/mitogen-activated protein kinase kinase (MEK)/mitogen-activated protein kinase (MAPK), phosphoinositide 3-kinase (PI3K)/protein kinase B (AKT)/mammalian target of rapamycin (mTOR), Janus kinase (JAK)/signal transducer and activator of transcription (STAT) and Src family kinases (SFKs). The activation of RTK exerts significant biological effects on many cellular processes including cell division, proliferation, migration, differentiation and ion homeostasis, and plays a pivotal role in embryo development, wound healing and tumour biology.
There is a paucity of information about the relationship between growth factors and TRPM7 in the vasculature, and whether the interaction has a role in vascular health and disease. We hypothesize that in VSMCs VEGF and EGF exert regulatory effects on TRPM7 activity, and the process mediates ion homeostasis and the activation of cellular signalling, which consequently influences cell function and vessel health. While under pathological conditions such as hypertension, the growth factor-RTK-TRPM7 axis could be aberrantly expressed and result in deleterious consequences.
This study identified novel roles of growth factors (VEGF and EGF) in VSMCs which is specifically mediated by TRPM7. We demonstrate that VEGF and EGF through activating the RTKs (VEGFR and EGFR respectively) upregulate TRPM7 expression and phosphorylation in VSMCs and consequently regulate ion homeostasis (Mg2+ and Ca2+) through TRPM7 channel activation. With regards to the downstream effects, we show the crucial involvement of TRPM7 in the effects mediated by EGF, including activation of extracellular signal-regulated kinase 1/2 (ERK1/2) and migration and proliferation in VSMCs, processes that are associated with vessel morphology. We also show that the VEGF-regulated TRPM7 plays an important role in the endothelium-independent vascular relaxation.
Our study demonstrates that the Growth Factor/RTK system is both upstream and downstream of TRPM7 in the vasculature. Taking advantage of different approaches, we identify the direct interaction between EGFR and TRPM7 in VSMCs and the interaction is enhanced by EGF in a c-Src dependent manner. Our experiments provide visible evidence that the interaction between EGFR and TRPM7 occurs at cell membrane, confirming that TRPM7 functions as a cell surface protein. Importantly, our data indicate that TRPM7 acts as an upstream regulator of RTK, since TRPM7 kinase is indispensable for EGFR expression and c-Src activation in VSMCs and lack of TRPM7 kinase activity is associated with reduced EGFR phosphorylation in the vessels. Our data also highlight that the property of TRPM7 as a kinase is specifically involved in these vascular effects.
We explored the potential clinical relevance of the RTK-TRPM7 crosstalk. First, we show that the EGFR-TRPM7-ERK1/2 pathway is enhanced in VSMCs from hypertensive rats, which is associated with increased intracellular Ca2+ and cell migration, suggesting that aberrant activity of this pathway might be involved in the pathophysiology of hypertension. Secondly, this study takes advantage of placental tissues from two different animal models of preeclampsia and show that dysregulation of VEGFR and TRPM7 is present in the placenta under preeclamptic conditions. Our experiments suggest that the VEGFR-TRPM7 crosstalk might be important for future studies aimed at pathophysiological mechanisms and therapeutic targets of preeclampsia.
Taken together our findings identify TRPM7 as a novel signalling target of growth factors EGF and VEGF in the vascular system. Importantly TRPM7 is differentially regulated by EGF and VEGF, which likely contributes to diverse vascular functional consequences of RTK-TRPM7 signalling. Data from our studies advance the field of TRMP7, Mg2+ regulation and vascular biology and delineate new molecular mechanisms whereby growth factors impact vascular function in health and disease.

• Item Type: Thesis (PhD)
• Qualification Level: Doctoral
• Additional Information: Supported by funding from China Scholarship Council.
• Keywords: Growth factor, RTK, magnesium transporter, TRPM7, vascular health, vascular disease.
• Colleges/Schools: College of Medical Veterinary and Life Sciences > School of Cardiovascular & Metabolic Health
• Funder's Name: China Scholarship Council
• Supervisor's Name: Touyz, Professor Rhian
• Date of Award: 2020
• Depositing User: Mr Zhiguo/ZG Zou
• Unique ID: glathesis:2020-81556
• Copyright: Copyright of this thesis is held by the author.
• Date Deposited: 04 Aug 2020 13:16
• Last Modified: 10 Apr 2024 13:19
• URI: https://theses.gla.ac.uk/id/eprint/81556

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