Glucose deprivation, oxidative stress and peroxisome proliferator-activated receptor-α (PPARA) cause peroxisome proliferation in preimplantation mouse embryos

Abstract

Ex vivo two-cell mouse embryos deprived of glucose in vitro can develop to blastocysts by increasing their pyruvate consumption; however, zygotes when glucose-deprived cannot adapt this metabolic profile and degenerate as morulae. Prior to their death, these glucose-deprived morulae exhibit upregulation of the H C -monocarboxylate co-transporter SLC16A7 and catalase, which partly co-localize in peroxisomes. SLC16A7 has been linked to redox shuttling for peroxisomal b-oxidation. Peroxisomal function is unclear during preimplantation development, but as a peroxisomal transporter in embryos, SLC16A7 may be involved and influenced by peroxisome proliferators such as peroxisome proliferator-activated receptor-a (PPARA). PCR confirmed Ppara mRNA expression in mouse embryos. Zygotes were cultured with or without glucose and with the PPARA-selective agonist WY14643 and the developing embryos assessed for expression of PPARA and phospho-PPARA in relation to the upregulation of SLC16A7 and catalase driven by glucose deprivation, indicative of peroxisomal proliferation. Reactive oxygen species (ROS) production and relationship to PPARA expression were also analysed. In glucose-deprived zygotes, ROS was elevated within 2 h, as were PPARA expression within 8 h and catalase and SLC16A7 after 12-24 h compared with glucose-supplied embryos. Inhibition of ROS production prevented this induction of PPARA and SLC16A7. Selective PPARA agonism with WY14643 also induced SLC16A7 and catalase expression in the presence of glucose. These data suggest that glucose-deprived cleavage stage embryos, although supplied with sufficient monocarboxylate-derived energy, undergo oxidative stress and exhibit elevated ROS, which in turn upregulates PPARA, catalase and SLC16A7 in a classical peroxisomal proliferation response.

Metabolism of the preimplantation embryo: 40 years on

“…It was then discovered that glucose was required for morulae to express the glucose transporter GLUT3, essential for blastocyst formation and that glucose was also responsible for expression of the monocarboxylate transporters Jansen et al (2006Jansen et al ( , 2008 responsible for coupled transport of a proton with an anion such as pyruvate and lactate; which as well as being involved in the transport of these nutrients, plays a role in [pH]i regulation (Fitzharris & Baltz 2009); indirect evidence for which had earlier been obtained by Gibb et al (1997) and Butcher et al (1998). Exploration of the molecular details of this intriguing story has revealed a ROSmediated stress response leading to peroxisomal proliferation (Jansen et al 2009). In other words, glucose plays a role as a cell-signaling agent as well as potential metabolic substrate.…”

The peroxisome: an update on mysteries

“…In addition to PPARa-induced peroxisome proliferation, several other PPARa-independent stimuli were found to augment peroxisome abundance in vitro and in vivo in mammals (Baumgart et al 1990;Schrader et al 1998a;Jansen et al 2009). Thus, other regulatory pathways must influence peroxisome abundance.…”

The Role of Hexosamine Biosynthesis and Signaling in Early Development

“…Thus, zygotes cultured under these conditions display reduced proliferative capacity and higher levels of apoptosis ). Moreover they undergo oxidative stress and exhibit elevated levels of reactive oxygen species (ROS) despite a supply of sufficient monocarboxylates (Jansen et al 2009). This suggests that in the complete absence of glucose the embryo is unable to respond to environmental stress, making it more susceptible to developmental arrest and cell death.…”

“…This is because in the absence of glucose, glucosamine may activate additional stress response pathways as a result of oxidative stress (Jansen et al 2009), independently of effects through O-GlcNAcylation. Glucosamine enters cells and is readily phosphorylated to GlcN-6-P and thus enters the HSP downstream of entry into the PPP at F-6-P as discussed earlier (Fig.…”

“…3.1). In the absence of glucose, flux through the PPP is attenuated reducing NADPH production and increasing oxidative stress (Jansen et al 2009). Moreover, GlcN-6-P is a potent inhibitor of the first enzyme of the PPP glucose-6-P-dehydrogenase (G6PDH) (Wu et al 2001) and this high Glcn-6-P concentration arising from glucosamine supplementation may also limit PPP flux arising from any gluconeogenic activity, should this be occuring.…”