While everyone loves hearing about a scientific controversy, clearing the air can also provide a sense of satisfaction. So, sit back and take a breath of the fresh air that an environmentally conscious team brings to the controversy surrounding mitochondrial (mt)DNA methylation through their examination of prenatal exposure to environmental stressors such as air pollution on the placenta.
To settle this epigenetic controversy, myth-busting environmentalists led by Bram G Janssen (Hasselt University, Hasselt, Belgium) followed-up on their previous research (See here and here!) through their analysis of stratified individuals from the ENVIRONAGE birth cohort. Using bisulfite pyrosequencing, the team evaluated mtDNA methylation levels of linearized mtDNA from the placentas of 60 infants prenatally exposed to varying levels of environmental stressors (maternal smoking or air pollution) and explored the resulting phenotypes in the newborns. Further upgrades included controlling for incomplete bisulfite conversion and the presence of nuclear mtDNA, two of the major compounding factors identified in previous studies.
So, let’s set aside the squabbles and take a breather from the bickering and let Vos and colleagues cut through the smog with their fresh new findings:
- Prenatal exposure to environmental stressors increases methylated mtDNA in the placenta
- Higher mtDNA methylation correlates with lower placental mtDNA content
- Significantly lower mtDNA content in the placentas of the infants correlates to prenatal exposure to cigarette smoke
- Higher mtDNA methylation correlates with lower DNA methylation at the promoter of a nuclear-encoded mitochondrial maintenance gene (PINK1), with lower methylation of the PINK1 promoter observed in mother exposed to high levels of air pollution
- Importantly, elevated placental mtDNA methylation associates with a significantly lower birth weight in newborns
These findings support the conclusions of previous studies using bisulfite pyrosequencing but note a probable overestimation of the effect. While the air is still clearing, the authors note study limitations to confront in their future research, including small sample size, the evaluation of a small DNA region, the involvement of methylation of non-CpG sites, and the heterogeneous nature of the placenta.
To see how these environmentalists cut through the smog and underscored the importance of mtDNA methylation, head to Epigenetics, July 2020!