Mitochondrial dysfunction and DNA damage accompany enhanced levels of formaldehyde in cultured primary human fibroblasts
Authors: Samuel H Wilson
Donna F Stefanick
Ming-Lang Zhao
Jack D Griffith
Ashley M Brooks
Cristina A Nadalutti
Julie K Horton
Rajendra Prasad
Journal: Scientific Reports (2020)
Discipline: Multidisciplinary
Keywords: Formaldehyde; Mitochondrial dysfunction; Primary human fibroblasts; Cytotoxicity; Gene expression
Affiliations: Genome Integrity and Structural Biology Laboratory, National Institute of Environmental Health Sciences, NIH, Research Triangle Park, NC, 27709, USA., Center for Integrative Bioinformatics, National Institute of Environmental Health Sciences, NIH, Research Triangle Park, NC, 27709, USA., Lineberger Comprehensive Cancer Center, University of North Carolina at Chapel Hill, Chapel Hill, NC, USA., Genome Integrity and Structural Biology Laboratory, National Institute of Environmental Health Sciences, NIH, Research Triangle Park, NC, 27709, USA. .

Abstract:  Formaldehyde (FA) is a simple biological aldehyde that is produced inside cells by several processes such as demethylation of DNA and proteins, amino acid metabolism, lipid peroxidation and one carbon metabolism (1-C). Although accumulation of excess FA in cells is known to be cytotoxic, it is unknown if an increase in FA level might be associated with mitochondrial dysfunction. We choose to use primary human fibroblasts cells in culture (foreskin, FSK) as a physiological model to gain insight into whether an increase in the level of FA might affect cellular physiology, especially with regard to the mitochondrial compartment. FSK cells were exposed to increasing concentrations of FA, and different cellular parameters were studied. Elevation in intracellular FA level was achieved and was found to be cytotoxic by virtue of both apoptosis and necrosis and was accompanied by both G2/M arrest and reduction in the time spent in S phase. A gene expression assessment by microarray analysis revealed FA affected FSK cells by altering expression of many genes including genes involved in mitochondrial function and electron transport. We were surprised to observe increased DNA double-strand breaks (DSBs) in mitochondria after exposure to FA, as revealed by accumulation of γH2A.X and 53BP1 at mitochondrial DNA foci. This was associated with mitochondrial structural rearrangements, loss of mitochondrial membrane potential and activation of mitophagy. Collectively, these results indicate that an increase in the cellular level of FA can trigger mitochondrial DNA double-strand breaks and dysfunction. 

Retracted: No

PubPeer comments:
 I found the title highly interesting, but I was immediately stunned by the following statement in the Abstract and similar sentences in the main text: u201cWe were surprised to observe increased DNA double-strand breaks (DSBs) in mitochondria after exposure to FA, as revealed by accumulation of u03b3H2A.X and 53BP1 at mitochondrial DNA foci.u201d The consensus is that histones are not involved in the packaging of mitochondrial DNA (mtDNA). Therefore, there are no H2Ax for phosphorylation to yield u03b3H2A.X (serine 139-phosphorylated u03b3H2A.X) upon mtDNA DSBs. u03b3H2A.X is a standard marker of DSBs in nuclear DNA not in mtDNA. Neither has 53BP1 been reported to take part in mtDNA damage response. The shady immunofluorescence overlays suggesting colocalization are not sufficient to prove that u03b3H2A.X would mark mtDNA DSBs. Considering the lack of literature references validating the u03b3H2A.X and 53BP1 foci as markers of mtDNA DSBs and the lack direct demonstration of DSBs, some of the main conclusions are highly questionable. I am also curious what does the anti-DNA antibody (catalogue number?) stain when there is such a poor overlap with the DAPI signalu2026. ,