8-Oxoguanine accumulation in mitochondrial DNA causes mitochondrial dysfunction and impairs neuritogenesis in cultured adult mouse cortical neurons under oxidative conditions

Abstract

Oxidative stress and mitochondrial dysfunction are implicated in aging-related neurodegenerative disorders. 8-Oxoguanine (8-oxoG), a common oxidised base lesion, is often highly accumulated in brains from patients with neurodegenerative disorders. MTH1 hydrolyses 8-oxo-2′-deoxyguanosine triphosphate (8-oxo-dGTP) to 8-oxo-dGMP and pyrophosphate in nucleotide pools, while OGG1 excises 8-oxoG paired with cytosine in DNA, thereby minimising the accumulation of 8-oxoG in DNA. Mth1/Ogg1-double knockout (TO-DKO) mice are highly susceptible to neurodegeneration under oxidative conditions and show increased accumulation of 8-oxoG in mitochondrial DNA (mtDNA) in neurons, suggesting that 8-oxoG accumulation in mtDNA causes mitochondrial dysfunction. Here, we evaluated the contribution of MTH1 and OGG1 to the prevention of mitochondrial dysfunction during neuritogenesis in vitro. We isolated cortical neurons from adult wild-type and TO-DKO mice and maintained them with or without antioxidants for 2 to 5 days and then examined neuritogenesis. In the presence of antioxidants, both TO-DKO and wild-type neurons exhibited efficient neurite extension and arborisation. However, in the absence of antioxidants, the accumulation of 8-oxoG in mtDNA of TO-DKO neurons was increased resulting in mitochondrial dysfunction. Cells also exhibited poor neurite outgrowth with decreased complexity of neuritic arborisation, indicating that MTH1 and OGG1 are essential for neuritogenesis under oxidative conditions.

Human mitochondrial transcriptional factor A breaks the mitochondria-mediated vicious cycle in Alzheimer’s disease

“…Many studies have shown the role of mitochondria on neuritogenesis through calcium handling and ATP production4344. Recently, we demonstrated that 8-oxoG accumulation in neuronal mtDNA results in mitochondrial dysfunction, and leads to poor neurite outgrowth with decreased complexity of neuritic arborization, using isolated cortical neurons from mice lacking both 8-oxo-dGTP-depleting MTH1 and 8-oxoG excising OGG130, similar to the AD model neurons. In the present study, we showed that rhTFAM efficiently suppresses mitochondrial dysfunction accompanied by reduced accumulation of 8-oxoG and single strand breaks in mtDNA (Fig.…”

“…It is noteworthy that not only ROS production but also intracellular Aβ accumulation is significantly suppressed by hTFAM, probably through increased expression of transthyretin which is known to suppress Aβ aggregation26. Moreover, poor neuritogenesis found in the iPSC-derived AD neuron model which is also likely to be a consequence of mitochondrial dysfunction30, is also efficiently improved by hTFAM (Figs 5a and 7d,e). Inhibition of transthyretin mRNA expression by phenylalanine abolished the improvement in neuritogenesis with a significantly reduced level of transthyretin (Figs 6e and 7f), which is likely to be associated with hTFAM in mitochondria (Fig.…”

“…As shown in the upper panels of Fig. 7e, each neuron was classified into three stages based on the pattern of their neurite outgrowth, as previously described30: stage 1, lacking neurites; stage 2, one or more minor neurites; stage 3, one neurite at least twice as long as any other. In the absence of rhTFAM, wild-type neurons and PS1 P117L neurons were approximately 10% and 0% in stage 3, 70% and 30% in stage 2, and 20% and 70% in stage 1, respectively (Fig.…”

MUTYH promotes oxidative microglial activation and inherited retinal degeneration

“…Sheng et al demonstrated that 3-NP exposure induces nuclear DNA oxidation and PARP activation in striatal microglia; it also induces mitochondrial DNA oxidation and calpain activation in medium spiny neurons (23), whereas isolated neurons from MTH1/OGG1 double-deficient mice accumulated 8-oxoG only in mitochondrial DNA, and the mice thus underwent impaired neuritogenesis in vitro (42). Consistent with these findings, our present in vitro and in vivo experiments showed that nuclear DNA oxidation in microglia is associated with PARP activation, which was reversed by MUTYH deficiency.…”

Oxidative stress and DNA damage induced by spinosad exposure in Spodoptera frugiperda Sf9 cells

“…Among the various types of oxidative lesions, 8-oxoguanine (8-oxoG) is one of the major oxidized base in both nucleotide pools and polymerized DNA, which is strongly mutagenic as it can mispair with adenine residues instead of the cysteine residues, leading to GC to AT transversion mutations (Leon et al, 2016). 8-oxoG-DNA glycosylase (OGG1) excises 8-oxoG paired with cytosine in DNA, and 8-oxoG nucleoside triphosphatase (MTH1) hydrolyzes 8-oxo-dGTP in nucleotide pools, avoid incorporation of 8-oxo-dGMP into DNA, thus preventing the accumulation of oxidative DNA damage (Sheng et al, 2012).…”