TNF-α acts to prevent occurrence of malformed fetuses in diabetic mice

Activation of apoptosis in embryos is thought to be a key event in the pathogenesis of diabetes-induced embryopathies such as early embryonic death and inborn structural anomalies. TNF-alpha can activate apoptotic and anti-apoptotic signalling cascades, indicating its ability to contribute to and counteract diabetes-induced maldevelopment. To investigate how TNF-alpha regulates the response of embryos to diabetes-induced embryopathic stress, we used streptozotocin-induced diabetic TNF-alpha knockout mice. To evaluate the reproductive performance, mated diabetic female mice were examined on days 4 and 8 of pregnancy for the presence of blastocysts or embryos in uterine horns. To evaluate the teratogenic effect, the female mice were killed on day 18 of pregnancy and fetuses were examined for gross external anomalies. In addition, apoptotic nuclei were localised by the TUNEL assay and DNA-binding activity of the transcription factor NF-kappaB was evaluated by electrophoretic mobility shift assay in 10- and 11-day-old embryos respectively. Severely diabetic TNF-alpha(+/+) female mice had a much greater decrease in pregnancy rate but a lower incidence of malformed fetuses in litters than severely diabetic TNF-alpha(-/-) female mice. Also, the intensity of excessive apoptosis was higher, but the amount of active NF-kappaB complexes was lower in malformed TNF-alpha(-/-) embryos than in TNF-alpha(+/+) embryos. TNF-alpha contributes to death of peri-implantation embryos and possibly protects postimplantation embryos exposed to diabetes-induced teratogenic stimuli via activation of NF-kappaB-mediated anti-apoptotic signalling. It seems that TNF-alpha prevents the birth of malformed offspring in severely diabetic mice.