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Since the discovery of adipokines, the adipose tissue is no longer considered to be an inactive fat storage. It secretes a variety of bioactive molecules, which regulate body metabolism and energy homeostasis. One of these molecules is the adipokine adiponectin. In different tissues, adiponectin triggers metabolic effects through the adenosine monophosphate-activated protein kinase (PRKA), which is a master regulator in glucose and lipid metabolism. Recent studies point to a role for adiponectin in reproduction. Adiponectin and its receptors are present in female reproductive tract during pregnancy, and the preimplantation embryo is fully equipped with adiponectin. Here, we show that both receptor isoforms, ADIPOR1 and ADIPOR2, are expressed in 6-day-old rabbit blastocysts. To investigate the signaling pathway of adiponectin in preimplantation embryos, rabbit blastocysts were cultured in vitro and stimulated with adiponectin. Supplementation of adiponectin (1 μg/ml) enhanced PRKA alpha 1/2 (PRKAA1/2) phosphorylation and decreased expression of phosphoenolpyruvate carboxykinase 2 (PCK2), a key regulator of gluconeogenesis. Inhibition of PRKAA1/2 by Compound C (10 μM) restored PCK2 transcription. Adiponectin enhanced embryonic glucose uptake and led to a translocation of solute carrier family 2 (facilitated glucose transporter), member 4 (SLC2A4), previously known as GLUT4. We conclude that adiponectin influences the glucose metabolism of rabbit blastocysts via the phosphorylation of PRKAA1/2, which in turn results in a decrease of gluconeogenesis and an increase in glycolysis. The regulatory influence of adiponectin on glucose metabolism of blastocysts may be of specific interest in pathophysiological situations, such as obesity during pregnancy.

The peptidyl-prolyl cis/trans isomerase (PPIase) activity and the expression of cyclophilins were studied in 6-day-old rabbit preimplantation embryos cultured under physiological and increased oxygen concentrations of 5% and 20% O(2), respectively. The PPIase activity was completely inhibited by cyclosporin A (CsA). The inhibitor of FK506-binding proteins, rapamycin, had no effect on the PPIase activity, indicating that the PPIase activity in rabbit blastocysts originates from cyclophilins. Using CsA affinity chromatography, only one cyclophilin with a molecular mass of about 17.8 kDa was separated. The cDNA of rabbit cyclophilin was cloned and sequenced. Analysis of the 682-base pair cDNA revealed an open reading frame coding for a polypeptide of 164 amino acid residues with a molecular weight of 17.83 kDa. Homologies of 90% and 96% for the cDNA and amino acid sequence, respectively, to the human CyP18 were found, suggesting that the novel rabbit cyclophilin is a member of the CyP18 family (rabCyP18). The transcription level of rabCyP18 mRNA was 8.3 +/- 0.6 pg in 100 ng total RNA in noncultured blastocysts. In vitro culture with moderate oxygen stress (20% O(2)) resulted in a 1.5-fold increase in rabCyP18 transcription and an increased PPIase activity compared to that of blastocysts cultured with 5% O(2). Increase in transcription rate and PPIase activity by oxygen stress suggests an involvement of CyP18 in oxygen defense in rabbit preimplantation embryos.

Since the discovery of adipokines, the adipose tissue is no longer considered to be an inactive fat storage. It secretes a variety of bioactive molecules, which regulate body metabolism and energy homeostasis. One of these molecules is the adipokine adiponectin. In different tissues, adiponectin triggers metabolic effects through the adenosine monophosphate-activated protein kinase (PRKA), which is a master regulator in glucose and lipid metabolism. Recent studies point to a role for adiponectin in reproduction. Adiponectin and its receptors are present in female reproductive tract during pregnancy, and the preimplantation embryo is fully equipped with adiponectin. Here, we show that both receptor isoforms, ADIPOR1 and ADIPOR2, are expressed in 6-day-old rabbit blastocysts. To investigate the signaling pathway of adiponectin in preimplantation embryos, rabbit blastocysts were cultured in vitro and stimulated with adiponectin. Supplementation of adiponectin (1 μg/ml) enhanced PRKA alpha 1/2 (PRKAA1/2) phosphorylation and decreased expression of phosphoenolpyruvate carboxykinase 2 (PCK2), a key regulator of gluconeogenesis. Inhibition of PRKAA1/2 by Compound C (10 μM) restored PCK2 transcription. Adiponectin enhanced embryonic glucose uptake and led to a translocation of solute carrier family 2 (facilitated glucose transporter), member 4 (SLC2A4), previously known as GLUT4. We conclude that adiponectin influences the glucose metabolism of rabbit blastocysts via the phosphorylation of PRKAA1/2, which in turn results in a decrease of gluconeogenesis and an increase in glycolysis. The regulatory influence of adiponectin on glucose metabolism of blastocysts may be of specific interest in pathophysiological situations, such as obesity during pregnancy.