PTH1R Mutants Found in Patients with Primary Failure of Tooth Eruption Disrupt G-Protein Signaling

Abstract

AimPrimary failure of tooth eruption (PFE) is causally linked to heterozygous mutations of the parathyroid hormone receptor (PTH1R) gene. The mutants described so far lead to exchange of amino acids or truncation of the protein that may result in structural changes of the expressed PTH1R. However, functional effects of these mutations have not been investigated yet.Materials and MethodsIn HEK293 cells, PTH1R wild type was co-transfected with selected PTH1R mutants identified in patients with PFE. The effects on activation of PTH-regulated intracellular signaling pathways were analyzed by ELISA and Western immunoblotting. Differential effects of wild type and mutated PTH1R on TRESK ion channel regulation were analyzed by electrophysiological recordings in Xenopus laevis oocytes.ResultsIn HEK293 cells, activation of PTH1R wild type increases cAMP and in response activates cAMP-stimulated protein kinase as detected by phosphorylation of the vasodilator stimulated phosphoprotein (VASP). In contrast, the PTH1R mutants are functionally inactive and mutant PTH1R/Gly452Glu has a dominant negative effect on the signaling of PTH1R wild type. Confocal imaging revealed that wild type PTH1R is expressed on the cell surface, whereas PTH1R/Gly452Glu mutant is mostly retained inside the cell. Furthermore, in contrast to wild type PTH1R which substantially augmented K+ currents of TRESK channels, coupling of mutated PTH1R to TRESK channels was completely abolished.ConclusionsPTH1R mutations affect intracellular PTH-regulated signaling in vitro. In patients with primary failure of tooth eruption defective signaling of PTH1R mutations is suggested to occur in dento-alveolar cells and thus may lead to impaired tooth movement.

Zahneruption und Zahnbewegung bei kongenitaler Retention mit Mutation des PTH1-Rezeptor-Gens

“…Dutzende verschiedene Mutationen des PTH1-Rezeptor-Gens (OMIM 168 468) wurden beschrieben [10]. Problematisch sind v. a. Mutationen, welche Strukturveränderungen und dadurch eine Funktionsänderung des PTH1-Rezeptors verursachen [11]. Je nach phänotypischer Expression des mutierten Gens kann Funktionsverlust, normale Funktion oder auch Überaktivierung resultieren.…”

“…Eine homozygote Mutation des PTH1-Rezeptor-Gens verursacht schwere Entwicklungs-und Wachstumsstörungen (Murk-Jansen-Metaphysenchondrodysplasie, Blomstrand-Chondrodysplasie und Eiken-Syndrom), welche entweder auf Überaktivierung oder Funktionsverlust des Rezeptors zurückzuführen sind und eine abnorme enchondrale Knochenreifung zur Folge haben [12]. Bei menschlichen embryonalen Nierenzellen konnte eine veränderte intrazelluläre Signalgebung auf Grund mutierter PTH1-Rezeptoren nachgewiesen werden [11].…”

“…Wiederholt wurde beschrieben, dass die nicht eruptierten Zähne auch nicht bewegt werden können, obwohl primär keine Ankylose besteht [1,6,14]. Die molekularen funktionalen Effekte der PTH1R-Mutation wurden aber bisher noch nicht erforscht [11].…”

Shedding new light on the mysteries of tooth eruption

“…1, do not affect signaling within the enamel organ but may result in a loss of function specifically in the dental follicle. Functional analysis of some of the human PTH1R heterozygous variants suggests that they may act in a dominantnegative fashion to inhibit the wild-type receptor (10). Some variants result in a loss of function or haploinsufficiency in the G protein-coupled receptor (10).…”

“…Functional analysis of some of the human PTH1R heterozygous variants suggests that they may act in a dominantnegative fashion to inhibit the wild-type receptor (10). Some variants result in a loss of function or haploinsufficiency in the G protein-coupled receptor (10). In either case, the result of most human variants is a decrease in signal transduction mediated by PTH1R.…”