Autism spectrum disorder (ASD) is a complex disorder that is underpinned by numerous dysregulated biological pathways, including pathways that affect mitochondrial function. Epigenetic mechanisms contribute to this dysregulation and DNA methylation is an important factor in the etiology of ASD. We measured DNA methylation of peroxisome proliferator-activated receptor-gamma coactivator-1 alpha (PGC-1α), as well as five genes involved in regulating mitochondrial homeostasis to examine mitochondrial dysfunction in an ASD cohort of South African children. Using targeted Next Generation bisulfite sequencing, we found differential methylation (p < 0.05) at six key genes converging on mitochondrial biogenesis, fission and fusion in ASD, namely PGC-1α, STOML2, MFN2, FIS1, OPA1, and GABPA. PGC-1α, the transcriptional regulator of biogenesis, was significantly hypermethylated at eight CpG sites in the gene promoter, one of which contained a putative binding site for CAMP response binding element 1 (CREB1) (p = 1 × 10–6). Mitochondrial DNA (mtDNA) copy number, a marker of mitochondrial function, was elevated (p = 0.002) in ASD compared to controls and correlated significantly with DNA methylation at the PGC-1α promoter and there was a positive correlation between methylation at PGC-1α CpG#1 and mtDNA copy number (Spearman’s r = 0.2, n = 49, p = 0.04) in ASD. Furthermore, DNA methylation at PGC-1α CpG#1 and mtDNA copy number correlated significantly (p < 0.05) with levels of urinary organic acids associated with mitochondrial dysfunction, oxidative stress, and neuroendocrinology. Our data show differential methylation in ASD at six key genes converging on PGC-1α-dependent regulation of mitochondrial biogenesis and function. We demonstrate that methylation at the PGC-1α promoter is associated with elevated mtDNA copy number and metabolomic evidence of mitochondrial dysfunction in ASD. This highlights an unexplored role for DNA methylation in regulating specific pathways involved in mitochondrial biogenesis, fission and fusion contributing to mitochondrial dysfunction in ASD.

BackgroundAutism Spectrum Disorder (ASD) is a complex disorder that is underpinned by numerous dysregulated biological pathways, including canonical mitochondrial pathways. Epigenetic mechanisms contribute to this dysregulation and DNA methylation is an important factor in the aetiology of ASD. We examined the relationship between DNA methylation of peroxisome proliferator-activated receptor gamma coactivator-1 alpha (PGC-1α), an essential transcriptional regulator of mitochondrial homeostasis, and mitochondrial dysfunction in an ASD cohort of South African children.ResultsUsing targeted Next Generation bisulfite sequencing, we found 12 highly variable CpG sites in PGC-1α that were significantly differentially methylated (p<0.05) between ASD (n = 55) and controls (n = 44). In ASD, eight CpG sites were hypermethylated in the PGC-1α promotor with a putative binding site for CAMP response binding element 1 (CREB1) spanning one of these CpG sites (p = 1 × 10−6). Mitochondrial DNA (mtDNA) copy number, a marker of mitochondrial function, was elevated (p = 0.002) in ASD compared to controls and correlated significantly with DNA methylation at the PGC-1α promoter. There was a positive correlation between methylation at PGC-1α at CpG#1 and mtDNA copy number (Spearman’s r = 0.2, n = 49, p = 0.04) in ASD, but a negative correlation between methylation at PGC-1α at CpG#4 promoter and mtDNA copy number in controls (Spearman’s r = −0.4, n = 42, p = 0.045). While there was no relationship between mtDNA deletions and PGC-1α methylation in ASD, mtDNA deletions correlated negatively with methylation at PGC-1α at CpG#4 (Spearman’s r = −0.4, n = 42, p = 0.032) in controls. Furthermore, levels of urinary organic acids associated with mitochondrial dysfunction correlated significantly (p<0.05) with DNA methylation at PGC-1α CpG#1 and mtDNA copy number in ASD (n= 20) and controls (n= 13) with many of these metabolites involved in altered redox homeostasis and neuroendocrinology.ConclusionsThese data show an association between PGC-1α promoter methylation, elevated mtDNA copy number and metabolomic evidence of mitochondrial dysfunction in ASD. This highlights an unexplored link between DNA methylation and mitochondrial dysfunction in ASD.

The increased awareness of autism spectrum disorders (ASD) is accompanied by burgeoning ASD research, and concerted research efforts are trying to elucidate the molecular ASD aetiology. However, much of this research is concentrated in the Global North, with recent reviews of research in Sub-Saharan Africa (SSA) highlighting the significant shortage of ASD publications from this region. The most limited focus area was molecular research with only two molecular studies ever published from SSA, both being from South Africa (SA). We examine the molecular ASD research publications from 2016 to 2021 from all African countries, with a special focus on SA. The SSA publications are compared to Brazil and India, two non-African, low-to-middle-income countries (LMICs), and to the UK and USA, two high-income countries (HICs). There were 228 publications across all regions of interest; only three publications were from SA. Brazil (n=29) and India (n=27) had almost 10 times more publications than SA. The HICs had more publications than the LMICs, with the UK (n=62) and the USA (n=74) having approximately 20 to 25 times more publications than SA, respectively. Given that SA has substantial research capacity as demonstrated by its recent research on SARS-CoV-2, we explore potential reasons for this deficit in molecular ASD publications from SA. We compare mental health research outputs, GDP per capita, research and development expenditure, and the number of psychiatrists and child psychiatrists per 100,000 people across all regions. The UK and the USA had significantly higher numbers for all these indicators, consistent with their higher publication output. Among the LMICs, SA can potentially produce more molecular ASD research, however, there are numerous barriers that need to be addressed to facilitate increased research capacity. These include cultural stigmas, challenges in accessing mental healthcare, shortages of specialists in the public sector, and the unreliability of ASD diagnostic tools across the 11 official SA languages. The unique genetic architecture of African populations presents an untapped reservoir for finding novel genetic loci associated with ASD. Therefore, addressing the disparity in molecular ASD research between the Global North and SSA is integral to global advancements in ASD research.

Mitochondrial dysregulation is implicated in numerous neurological disorders. Mitochondrial dynamics, including biogenesis, fusion and fission, are essential components of mitostasis which is modulated by complex regulatory mechanisms. Although expression studies are often used to investigate mitochondrial dynamics, these studies may be limited by the interdependent and temporal nature of mitostasis. Transmission electron microscopy (TEM) and cryogenic preparation methods provide a direct approach to examine mitochondrial ultrastructure in neurons. We investigated the utility of TEM to visualize mitochondrial morphological changes in SH-SY5Y cells treated with propionic acid (PPA). We examined whether morphological alterations were associated with differences in membrane potential or expression of biogenesis, fusion and fission genes. PPA induced a significant decrease in mitochondrial area (p&lt;0.01 5mM), Feret's diameter and perimeter (p&lt;0.05 5mM), and in area2 (p&lt;0.05 3mM, p&lt;0.01 5mM) &ndash; consistent with a shift towards fission. Morphological changes were not associated with significant differences in mitochondrial membrane potential. However, we observed decreased gene expression of NRF1 (p&lt;0.01), TFAM (p&lt;0.05), and STOML2 (p&lt;0.0001). These data support a disruption of the balance in dynamics to preserve function under stress. This demonstrates the utility of TEM to provide insight into mitochondrial dynamics and function which can inform targeted mechanistic investigations into neuropathology.

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