Role of STING complex in differential retrograde signaling in cybrids with K versus H haplogroup mtDNA

Mitochondrial (mt) DNA haplogroups, defined by specific single nucleotide polymorphism (SNPs) patterns, represent populations of diverse geographic origins and may play a role in disparate disease susceptibilities found in different ethnic/racial populations. The most common European haplogroup is H, while the K haplogroup is highly associated with Ashkenazi Jewish populations. Studies using transmitochondrial cybrids (cell lines with identical nuclei but mitochondria from either H or K haplogroup subjects) demonstrated significant molecular and biological differences but mechanisms for these disparities are unclear. In this study, we hypothesized that there is differential retrograde signaling occurring between the Stimulator of Interferon Genes (STING) pathway and H versus K mtDNA haplogroups. Results showed that K cybrids exhibit increased levels of cytoplasmic mtDNA fragments. After STING Knock-Down, H cybrids had lower expression levels for EGFR, BRCA1, DNMT3A, DNMT3B, HDAC1, and IFNα genes, but upregulated DNMT3A compared to control H cybrids. The STING-KD K cybrids showed downregulation of EGFR, DNMT3A, HDAC1, HCAD9, CFH, and CHI, along with upregulation of DNMT1 and IL-6 compared to control K cybrids. Since all cybrids have identical nuclei, the STING DNA sensor system interacts differently with K haplogroup mtDNA compared to H mtDNA for genes related to cancer (EGFR, BRCA1), methylation (DNMT1, DNMT3A, DNMT3B), acetylation (HDAC1, HDCA9), complement (CFH, CHI) and inflammation (IFNα, IL-6). In summary, in non-pathologic conditions, (a) STING is an important retrograde signaling mechanism(s) and (b) cybrids possessing Ashkenazi Jewish mtDNA (K haplogroup) interact with the STING complex differently compared to H cybrids which affects various disease-related pathways.