Biology subjects

Sondheimer, N.

Publications and source records attributed to Sondheimer, N..

3 recordsLinked to original sources

bioRxiv2020

Characterization of mitochondrial health from human peripheral blood mononuclear cells to cerebral organoids derived from induced pluripotent stem cells

Mitochondrial health plays a crucial role in human brain development and diseases. However, the evaluation of mitochondrial health in the brain is not incorporated into clinical practice due to ethical and logistical concerns. As a result, the development of targeted mitochondrial therapeutics remains a significant challenge due to the lack of appropriate patient-derived brain tissues. To address these unmet needs, we developed cerebral organoids (COs) from induced pluripotent stem cells (iPSCs) derived from human peripheral blood mononuclear cells (PBMCs) and monitored mitochondrial health from the primary, reprogrammed and differentiated stages. Our results show preserved mitochondrial genetics, function and treatment responses across PBMCs to iPSCs to COs, and measurable neuronal activity in the COs. We expect our approach will serve as a model for more widespread evaluation of mitochondrial health relevant to a wide range of human diseases using readily accessible patient peripheral (PBMCs) and stem-cell derived brain tissue samples.

neuroscience↗

bioRxiv2018

G-quadruplex dynamics contribute to epigenetic regulation of mitochondrial function

Single-stranded DNA or RNA sequences rich in guanine (G) can adopt non-canonical structures known as G-quadruplexes (G4). Predicted G4-forming sequences in the mitochondrial genome are enriched on the heavy-strand and have been associated with formation of deletion breakpoints that cause mitochondrial disorders. However, the functional roles of G4 structures in regulating mitochondrial respiration in non-cancerous cells remain unclear. Here, we demonstrate that RHPS4, previously thought to be a nuclear G4-ligand, localizes primarily to mitochondria in live cells by mechanisms involving mitochondrial membrane potential. We find that RHPS4 exposure causes an acute inhibition of mitochondrial transcript elongation, leading to respiratory complex depletion. At higher ligand doses, RHPS4 causes mitochondrial DNA (mtDNA) replication pausing and genome depletion. Using these different levels of RHPS4 exposure, we describe discrete nuclear gene expression responses associated with mitochondrial transcription inhibition or with mtDNA depletion. Importantly, a mtDNA variant with increased anti-parallel G4-forming characteristic shows a stronger respiratory defect in response to RHPS4, supporting the conclusion that mitochondrial sensitivity to RHPS4 is G4-structure mediated. Thus, we demonstrate a direct role for G4 perturbation in mitochondrial genome replication, transcription processivity, and respiratory function in normal cells and describe the first molecule that differentially recognizes G4 structures in mtDNA.

molecular biology↗

bioRxiv2018

Targeted Reduction of Pathogenic Heteroplasmy Through Binding of G-Quadruplex DNA

Pathogenic mitochondrial DNA (mtDNA) variants are typically heteroplasmic, with coexistence of variant and wild type genomes. Because heteroplasmy dictates phenotype, the reduction of heteroplasmy is potentially therapeutic. We identified pathogenic variants that increased the potential for formation of non-canonical G-quadruplexes (GQ) within mtDNA. The Leigh Syndrome (LS)-associated mt.10191T>C variant has a high probability of local GQ formation that was enhanced by the variant. Structural studies of mt.10191C-containing oligonucleotides confirmed the formation of GQ, and its interaction with the small molecule GQ-binding agent berberine increased GQ stability. The GQ formed at mt.10191 impeded polymerase processivity, and inhibition was enhanced by the mt.10191C variant. We applied a cyclical treatment of two GQ binding compounds, berberine or RHPS4, to primary fibroblasts from LS patients with heteroplasmic mt.10191T>C mutation. This treatment induced alternating mtDNA depletion and repopulation and was effective in shifting heteroplasmy towards the nonpathogenic allele, leading to an increase in complex I protein levels. This study demonstrates the potential for using small-molecule GQ-binding agents to induce beneficial shifts in mitochondrial heteroplasmy.

genetics↗