Impact of Reactive Oxygen Species and G-Quadruplexes in Telomeres and Mitochondria

Possible formation of G-quadruplex (G4G-quadruplex (G4)) structures in telomereTelomere and mitochondrialMitochondria DNA (mtDNA) are the subjects of intense current research interest. The telomereTelomere, a complex of repetitive nucleotide sequences and binding proteins, is present at the end of chromosomesChromosome to safeguard genomic stability. G4G-quadruplex (G4), a noncanonicalNoncanonical DNA structure, forms in guanine-rich nucleic acid sequences such as immunoglobulin switch regions, telomeresTelomere, promoter regions (especially of oncogenes), and 5′-untranslated regions of genes. G4G-quadruplex (G4) motifs have been recognized as regulatory structures and are associated with genome instability and gene expression defects in the nuclear genome. The mitochondrial genome is a circular double-stranded DNA with significant asymmetry in strand composition. Mitochondrial DNA, especially the heavy (H) strand, is rich in guanine sequences and hence shows a strong propensity to form G4G-quadruplex (G4) structures that have been associated with mtDNA deletion breakpoints. mtDNA deletions are notably observed in various genetic disorders, mitochondrial dysfunctionMitochondrial dysfunction, cancer, and agingAging. TelomeraseTelomerase, which maintains telomereTelomere length, shuttles dynamically between different cellular locations. Under oxidative stressOxidative stress, telomeraseTelomerase localizes to mitochondriaMitochondria; however, little is known about the role of the interaction between the G4G-quadruplex (G4) structures in mtDNA and telomeraseTelomerase in determining mitochondrial function and fate. In this review, we cover the recent evidences supporting the potential of G4G-quadruplex (G4) structures and telomeraseTelomerase to regulate mitochondrial function and mitochondrial fate.