A mechanistic model for thiol redox dynamics in the organogenesis stage rat conceptus

Precise control of the glutathione/glutathione disulfide (GSH/GSSG) redox balance is vital for the developing embryo, but regulatory mechanisms are poorly understood. We developed a novel, mechanistic mass-balance model for GSH metabolism in the organogenesis stage (gestational day 10.0-11.13) rat conceptus predicting the dynamics of 8 unique metabolites in 3 conceptal compartments: the visceral yolk sac (VYS), the extra-embryonic fluid (EEF) and the embryo proper (EMB). Our results show that thiol concentrations in all compartments are well predicted by the model. Protein synthesis is predicted to be a major efflux pathway for all amino acid precursors of GSH synthesis and an essential model element. Our model provides quantitative insights in the transport fluxes and enzymatic fluxes needed to maintain thiol redox balances under normal physiological conditions. This is crucial to further elucidate the mechanisms through which chemical exposure can perturb redox homeostasis, causing oxidative stress, and potentially birth defects.

Characterizing thiol redox dynamics in the organogenesis stage rat embryo

Precise control of the glutathione (GSH): glutathione disulfide (GSSG) balance is vital for the developing embryo, but it is not yet well understood how GSH levels and the GSH redox state are regulated, maintained, and modulated over the course of mammalian embryonic development. In this study, we characterize and connect thiol redox dynamics, protein synthesis, volumetric growth and net cysteine fluxes over the course of early organogenesis (gestational day (GD) 10-GD11.13) in the rat embryo. Our results show that despite a significant exponential growth of conceptal volumes and protein mass, the GSH: GSSG redox balance is remarkably stable during early organogenesis, with distinct redox potentials for the visceral yolk sac (VYS) (- 218mV) and the embryo proper (EMB) (- 222mV). The yolk sac was found to play a key role in maintaining GSH levels and the GSH: GSSG redox balance in the developing embryo. Based on an overall cysteine (Cys) mass-balance, we show that until GD10.6, yolk sac supply of Cys, the rate-limiting precursor for GSH synthesis, is sufficient to sustain embryonic demands for its GSH synthesis and protein synthesis needs. After GD10.6, the EMB maintains the amino acid intake flux, resulting in a significant depletion of most thiols in the amniotic fluid and the yolk sac fluid. Cysteine, was found to be predominantly used for de novo protein synthesis in the developing embryo (approximately 90% of total Cys). Protein synthesis (rates) should thus be included in any quantitative assessment of GSH redox dynamics in the developing embryo. Our time-course dataset of thiol dynamics, developed exponential relationships for protein synthesis and volumetric growth, and yolk sac surface area-mediated protein influx, provide important quantitative insights in GSH redox dynamics during embryonic development and are a prerequisite to further develop quantitative 'systems biology' models for GSH metabolism in the developing embryo.