Submitted on September 16, 2004
Accepted on May 25, 2005
HYPOXIC STRESS IN DIABETIC PREGNANCY CONTRIBUTES TO IMPAIRED EMBRYO GENE EXPRESSION AND DEFECTIVE DEVELOPMENT BY INDUCING OXIDATIVE STRESS
Rulin Li1, Martha Chase2, Sung-Kwon Jung3, Peter J.S. Smith3, and Mary R. Loeken1*
1 Section on Developmental and Stem Cell Biology, Joslin Diabetes Center, Boston, MA, USA; Department of Medicine, Harvard Medical School, Boston, MA, USA
2 Section on Developmental and Stem Cell Biology, Joslin Diabetes Center, Boston, MA, USA
3 BioCurrents Research Center, Marine Biological Laboratory, Woods Hole, MA, USA
* To whom correspondence should be addressed. E-mail: mary.loeken{at}joslin.harvard.edu.
We have shown that neural tube defects (NTD) in a mouse model of diabetic embryopathy are associated with deficient expression of Pax3, a gene required for neural tube closure. Hyperglycemia-induced oxidative stress is responsible.
Prior to organogenesis, the avascular embryo is physiologically hypoxic (2-5% O2). Here we hypothesized that, since O2 delivery is limited at this stage of development, excess glucose metabolism could accelerate the rate of O2 consumption, thereby exacerbating the hypoxic state. Since hypoxia can increase mitochondrial superoxide production, excessive hypoxia may contribute to oxidative stress.
To test this, we assayed O2 flux, an indicator of O2 availability, in embryos of glucose-injected hyperglycemic or saline-injected mice. O2 flux was reduced by 30% in embryos of hyperglycemic mice. To test whether hypoxia replicates, and hyperoxia suppresses, the effects of maternal hyperglycemia, pregnant mice were housed in controlled O2 chambers on embryonic day 7.5. Housing pregnant mice in 12% O2, or induction of maternal hyperglycemia (>250 mg/dl), decreased Pax3 expression 5-fold, and increased NTD 8-fold. Conversely, housing pregnant diabetic mice in 30% O2 significantly suppressed the effect of maternal diabetes to increase NTD. These effects of hypoxia appear to be due to increased production of mitochondrial superoxide, as indicated by assay of lipid peroxidation, reduced glutathione, and H2O2. Further support of this interpretation was the effect of antioxidants, which blocked the effects of maternal hypoxia, as well as hyperglycemia, on Pax3 expression and NTD.
These observations suggest that maternal hyperglycemia depletes O2 in the embryo and that this contributes to oxidative stress and the adverse effects of maternal hyperglycemia on embryo development.
