2-Aminoethyl diphenyl borinate (2-APB) inhibits TRPM7 channels through an intracellular acidification mechanism

Orthopedic implants containing biodegradable magnesium have been used for fracture repair with considerable efficacy; however, the underlying mechanisms by which these implants improve fracture healing remain elusive. Here we show the formation of abundant new bone at peripheral cortical sites after intramedullary implantation of a pin containing ultrapure magnesium into the intact distal femur in rats. This response was accompanied by substantial increases of neuronal calcitonin gene-related polypeptide-α (CGRP) in both the peripheral cortex of the femur and the ipsilateral dorsal root ganglia (DRG). Surgical removal of the periosteum, capsaicin denervation of sensory nerves or knockdown in vivo of the CGRP-receptor-encoding genes Calcrl or Ramp1 substantially reversed the magnesium-induced osteogenesis that we observed in this model. Overexpression of these genes, however, enhanced magnesium-induced osteogenesis. We further found that an elevation of extracellular magnesium induces magnesium transporter 1 (MAGT1)-dependent and transient receptor potential cation channel, subfamily M, member 7 (TRPM7)-dependent magnesium entry, as well as an increase in intracellular adenosine triphosphate (ATP) and the accumulation of terminal synaptic vesicles in isolated rat DRG neurons. In isolated rat periosteum-derived stem cells, CGRP induces CALCRL-and RAMP1-dependent activation of cAMP-responsive element binding protein 1 (CREB1) and SP7 (also known as osterix), and thus enhances osteogenic differentiation of these stem cells. Furthermore, we have developed an innovative, magnesium-containing intramedullary nail that facilitates femur fracture repair in rats with ovariectomy-induced osteoporosis. Taken together, these findings reveal a previously undefined role of magnesium in promoting CGRP-mediated osteogenic differentiation, which suggests the therapeutic potential of this ion in orthopedics.

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“…30)) or 2-aminoethoxydiphenyl borate (2-APB) (100 µM, inhibiting TRPM7 (ref. 31)), but not by ruthenium red (50 µM, inhibiting TRPM6 (ref. 32)).…”

Section: Resultsmentioning

confidence: 99%

Implant-derived magnesium induces local neuronal production of CGRP to improve bone-fracture healing in rats

Zhang

Ruan

et al. 2016

Nat Med

778

550

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“…Specifically, when using 2-APB, an inhibitor of TRPM7 [22], CNNM2-dependent Mg 2+ transport was abolished in HEK293 cells. Remarkably, in a similar fashion to trpm7 mutants in zebrafish [28]–[29], cnnm2a or cnnm2b morphants showed weaker touch-evoked escape behaviour compared to controls.…”

Section: Discussionmentioning

confidence: 98%

CNNM2 Mutations Cause Impaired Brain Development and Seizures in Patients with Hypomagnesemia

et al. 2014

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Intellectual disability and seizures are frequently associated with hypomagnesemia and have an important genetic component. However, to find the genetic origin of intellectual disability and seizures often remains challenging because of considerable genetic heterogeneity and clinical variability. In this study, we have identified new mutations in CNNM2 in five families suffering from mental retardation, seizures, and hypomagnesemia. For the first time, a recessive mode of inheritance of CNNM2 mutations was observed. Importantly, patients with recessive CNNM2 mutations suffer from brain malformations and severe intellectual disability. Additionally, three patients with moderate mental disability were shown to carry de novo heterozygous missense mutations in the CNNM2 gene. To elucidate the physiological role of CNNM2 and explain the pathomechanisms of disease, we studied CNNM2 function combining in vitro activity assays and the zebrafish knockdown model system. Using stable Mg2+ isotopes, we demonstrated that CNNM2 increases cellular Mg2+ uptake in HEK293 cells and that this process occurs through regulation of the Mg2+-permeable cation channel TRPM7. In contrast, cells expressing mutated CNNM2 proteins did not show increased Mg2+ uptake. Knockdown of cnnm2 isoforms in zebrafish resulted in disturbed brain development including neurodevelopmental impairments such as increased embryonic spontaneous contractions and weak touch-evoked escape behaviour, and reduced body Mg content, indicative of impaired renal Mg2+ absorption. These phenotypes were rescued by injection of mammalian wild-type Cnnm2 cRNA, whereas mammalian mutant Cnnm2 cRNA did not improve the zebrafish knockdown phenotypes. We therefore concluded that CNNM2 is fundamental for brain development, neurological functioning and Mg2+ homeostasis. By establishing the loss-of-function zebrafish model for CNNM2 genetic disease, we provide a unique system for testing therapeutic drugs targeting CNNM2 and for monitoring their effects on the brain and kidney phenotype.

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“…Interestingly, while 2-APB inhibits TRPM7, it activates its paralog TRPM6, making this compound a useful tool in discriminating between currents carried by these two proteins (Li et al 2006). Furthermore, it is now known that 2-APB does not bind directly to TRPM7, but rather inhibits channel activity through an intracellular acidification mechanism (Chokshi et al 2012a). …”

Section: A Biophysical Description Of the Channel Function Permeatmentioning

confidence: 99%

Trpm7

Fleig

Chubanov

2014

Handbook of Experimental Pharmacology

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The channel kinases TRPM6 and TRPM7 are fusion proteins with an ion transport domain and an enzymatically active kinase domain. TRPM7 has been found in every mammalian tissue investigated to date. The two-in-one protein structure, the ubiquitous expression profile, and the protein’s unique biophysical characteristics that enable divalent ion transport involve TRPM7 in a plethora of (patho)physiological processes. With its prominent role in cellular and systemic magnesium homeostasis, TRPM7 emerges as a key player in embryonic development, global ischemia, cardiovascular disease, and cancer.

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2-Aminoethyl diphenyl borinate (2-APB) inhibits TRPM7 channels through an intracellular acidification mechanism

Cited by 85 publications

References 44 publications

Implant-derived magnesium induces local neuronal production of CGRP to improve bone-fracture healing in rats

Implant-derived magnesium induces local neuronal production of CGRP to improve bone-fracture healing in rats

CNNM2 Mutations Cause Impaired Brain Development and Seizures in Patients with Hypomagnesemia

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