Oral Presentation ESA-SRB-ANZBMS 2024 in conjunction with ENSA

Mitochondrial complex I deficiency in fetal growth restriction is programmed by single nucleotide polymorphisms (#226)

Joshua J Fisher 1 2 , Heather Murray 3 4 , Veronica B Botha 1 2 , Siddarth Acharya 1 2 , John Schjenken 5 6 , Roger Smith 1 2
  1. Mothers and Babies Research Program, Hunter Medical Research Institute, Newcastle, New South Wales, Australia
  2. School of Medicine and Public Health, College of Health, Medicine and Wellbeing, The University of Newcastle, Newcastle, NSW, Australia
  3. School of Biomedical Sciences and Pharmacy, College of Health, Medicine and Wellbeing, The University of Newcastle, Newcastle, NSW, Australia
  4. Precision Medicine Research Program, Hunter Medical Research Institute, Newcastle, NSW, Australia
  5. School of Environmental and Life Science, College of Engineering, Science and Environment, The University of Newcastle, Newcastle, NSW, Australia
  6. Infertility and Reproduction Research Program, Hunter Medical Research Institute, Newcastle, NSW, Australia

Fetal growth restriction (FGR) occurs when the fetus fails to reach its predetermined growth potential.  FGR placenta are smaller than healthy term placentae, and display a reduced number of underdeveloped placental villi. A finding suggested to arise from poor cytotrophoblast function, although the underlying mechanisms remain unknown. Mitochondrial dysfunction has been established as a contributing factor to placental insufficiency, and identified in the placenta of gestational diabetes mellitus and preeclamptic pregnancies. However, links between FGR and mitochondrial dysfunction are less established. We hypothesise that single nucleotide polymorphisms (SNPs) cause dysregulation of nuclear genes which encode mitochondrial structure, leading to impaired mitochondrial function, limiting the growth and development of the placenta, and in turn the fetus.

Sanger sequencing was performed to identify SNPs within nuclear genes encoding subunits of mitochondrial complex I in FGR (n=10) placentae and compared to a control consensus genome (n=8) before validation against the human genome reference database. Subsequent investigation examined the effect of SNPs on gene expression and protein levels via PCR, proteomics and immunoblotting.

We identified 8 SNPs within the nuclear genes that encode complex I, with NDUFA5, NDUFS3, and NDUFS6 found at a disproportionally greater percentage compared to their expected population prevalence. NDUFA5 was increased in FGR placentae at the gene and protein level (P=<0.05), while NDUFS3 and NDUFS6 were decreased at the protein level (P=<0.001) compared to healthy controls. Moreover, we observed a 30% reduction in NDUFS6 levels in cytotrophoblast mitochondria from FGR compared to control.

This data demonstrates that SNPs found within nuclear gene regions encoding complex I assembly and the transfer of electrons result in altered gene and protein levels in FGR. We suggest that this programs mitochondrial dysfunction in complex I, predominantly within the cytotrophoblast cell lineage of FGR, resulting in placental insufficiencies, decreased placental weight, and reduced birth weight.