Glutamate can act as a signaling molecule in mouse preimplantation embryos

• Published in: Biology of reproduction 2022-06, Vol.107 (4), p.916-927
• Main Authors: Špirková, Alexandra, Kovaříková, Veronika, Šefčíková, Zuzana, Pisko, Jozef, Kšiňanová, Martina, Koppel, Juraj, Fabian, Dušan, Čikoš, Štefan
• Format: Article
• Language: English
• Subjects: Amino acids; blastocyst; Blastocysts; Cell activation; Cell membranes; Embryos; Food additives; Gene expression; glutamic acid; Glutamic acid receptors (ionotropic); Glutamic acid receptors (metabotropic); Immunohistochemistry; ionotropic glutamate receptors; Kainic acid receptors; metabotropic glutamate receptors; Monosodium glutamate; oocyte; Oocytes; RESEARCH ARTICLE; Reverse transcription; α-Amino-3-hydroxy-5-methyl-4-isoxazole propionic acid; α-Amino-3-hydroxy-5-methyl-4-isoxazole propionic acid receptors
• ISSN: 0006-3363; 1529-7268
• DOI: 10.1093/biolre/ioac126

Free amino acids are present in the natural environment of the preimplantation embryo, and their availability can influence early embryo development. Glutamic acid is one of the amino acids with the highest concentrations in female reproductive fluids, and we investigated whether glutamic acid/glutamate can affect preimplantation embryo development by acting through cell membrane receptors. Using reverse transcription-polymerase chain reaction, we detected 15 ionotropic glutamate receptor transcripts and 8 metabotropic glutamate receptor transcripts in mouse ovulated oocytes and/or in vivo developed blastocysts. Using immunohistochemistry, we detected the expression of two α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptor subunits, three kainate receptor subunits, and member 5 metabotropic glutamate receptor protein in blastocysts. Extracellular concentrations of glutamic acid starting at 5 mM impaired mouse blastocyst development, and this fact may be of great practical importance since glutamic acid and its salts (mainly monosodium glutamate) are widely used as food additives. Experiments with glutamate receptor agonists (in combination with gene expression analysis) revealed that specific AMPA receptors (formed from glutamate receptor, ionotropic, AMPA3 [GRIA3] and/or glutamate receptor, ionotropic, AMPA4 [GRIA4] subunits), kainate receptors (formed from glutamate receptor, ionotropic, kainate 3 [GRIK3] and glutamate receptor, ionotropic, kainate 4 [GRIK4] or glutamate receptor, ionotropic, kainate 5 [GRIK5] subunits), and member 5 metabotropic glutamate receptor (GRM5) were involved in this effect. The glutamic acid-induced effects were prevented or reduced by pretreatment of blastocysts with AMPA, kainate, and GRM5 receptor antagonists, further confirming the involvement of these receptor types. Our results show that glutamic acid can act as a signaling molecule in preimplantation embryos, exerting its effects through the activation of cell membrane receptors. Summary Sentence Several types of glutamate receptors are expressed in mouse oocytes and blastocysts, and extracellular concentrations of glutamic acid at 5 mM can inhibit blastocyst development by activating glutamate receptors. Graphical Abstract