Date Published: September 12, 2017
Publisher: Impact Journals LLC
Author(s): Jose F. Moruno-Manchon, Edward C. Koellhoffer, Jayakrishnan Gopakumar, Shashank Hambarde, Nayun Kim, Louise D. McCullough, Andrey S. Tsvetkov.
The G-quadruplex is a non-canonical DNA secondary structure formed by four DNA strands containing multiple runs of guanines. G-quadruplexes play important roles in DNA recombination, replication, telomere maintenance, and regulation of transcription. Small molecules that stabilize the G-quadruplexes alter gene expression in cancer cells. Here, we hypothesized that the G-quadruplexes regulate transcription in neurons. We discovered that pyridostatin, a small molecule that specifically stabilizes G-quadruplex DNA complexes, induced neurotoxicity and promoted the formation of DNA double–strand breaks (DSBs) in cultured neurons. We also found that pyridostatin downregulated transcription of the Brca1 gene, a gene that is critical for DSB repair. Importantly, in an in vitro gel shift assay, we discovered that an antibody specific to the G-quadruplex structure binds to a synthetic oligonucleotide, which corresponds to the first putative G-quadruplex in the Brca1 gene promoter. Our results suggest that the G-quadruplex complexes regulate transcription in neurons. Studying the G-quadruplexes could represent a new avenue for neurodegeneration and brain aging research.
Understanding the mechanisms of aging is a problem of paramount importance. Brain aging is a complex phenomenon, and its mechanisms are poorly under-stood. In physiological aging, as neurons become older, they exhibit changes in synaptic plasticity, gene transcription, and DNA methylation, and are less capable of degrading oxidized material and accumulate lipofuscin. These changes are observed in the absence of significant neurological phenotypes. In unsuccessful neuronal aging, there are multiple dramatic events, including abnormally enhanced DNA damage, accumulation of impaired organelles, and protein aggregates [1, 2]. Neurons lose their synapses, processes, and degenerate. These changes are associated with neurological symptoms. It is not always clear why some age successfully and some do not [3, 4].
Our results revealed a potentially new mechanism of neurodegeneration and transcriptional regulation in neurons (Fig. 7). Pyridostatin, a G-quadruplex-stabilizing small molecule, causes neurite retraction, synaptic loss, and dose-dependent neuronal death. In cultured primary neurons, pyridostatin induces the formation of DNA DSBs. Remarkably, the drug downregulates the BRCA1 protein, a protein that guards and repairs the neuronal genome, at the transcriptional level. Using an in vitro gel shift experiment, we demonstrated that an antibody developed against the G-quadruplex structures binds to a synthetic oligo-nucleotide, which was synthesized to correspond to the first putative G-quadruplex sequence in the Brca1 gene promoter. Our results suggest that small molecules with pyridostatin-like properties promote neurodegeneration and identify a novel mechanism of transcriptional regulation in neurons.