Proteomic analysis of amniotic fluid of pregnant rats with spina bifida aperta.

Congenital spina bifida aperta is a common congenital malformation in children and has an incidence of 1‰ to 5‰ in China. However, we currently lack specific biomarkers for screening or prenatal diagnosis and there is no method to entirely cure or prevent such defects. In this study, we used two-dimensional gel electrophoresis (2-DE)/mass spectrometry (MS) to characterize differentially expressed proteins in amniotic-fluid samples (AFSs) of embryonic day (E) 17.5 rat fetuses with spina bifida aperta induced by retinoic acid (RA). We identified five proteins differentially expressed in AFSs of spina bifida aperta, including three upregulated proteins (transferrin, alpha-1 antiproteinase and signal recognition particle receptor, B subunit [SRPRB] 55 kDa), two downregulated proteins (apolipoprotein A IV [APO A4] and Srprb 77 kDa). Specifically, we found 11 alpha-1 fetoprotein (AFP) fragments that were downregulated and 35 AFP fragments that were upregulated in AFSs from embryos with spina bifida aperta. Of the downregulated AFP fragments, 72.7% (8/11) were confined to the AFP N-terminus (amino acids [aas] 25-440) and 77.1% (27/35) of upregulated AFP fragments were confined to the AFP C-terminus (aas 340-596). We also confirmed APO A4 and AFP by immunoblot analysis. This is the first comparative proteomic study of AFSs from rat fetuses with spina bifida aperta. We demonstrate proteomic alterations in the AFS of spina bifida aperta, which may provide new insights in neural tube defects and contribute to the prenatal screening.