Biology subjects

Mullins, R. F.

Publications and source records attributed to Mullins, R. F..

3 recordsLinked to original sources

bioRxiv2022

Non-random distribution of mitochondrial m.3243A>G heteroplasmy in human retina and its impact on cellular phenotype

Variants within the high copy number mitochondrial genome (mtDNA) can disrupt organelle function and lead to severe multi-system disease. The wide range of manifestations observed in mitochondrial disease patients results from varying fractions of abnormal mtDNA molecules in different cells and tissues, a phenomenon termed heteroplasmy. However, the landscape of heteroplasmy across cell types within tissues and its influence on phenotype expression in affected patients remains largely unexplored. Here, we identify non- random distribution of a pathogenic mtDNA variant across a complex tissue using single-cell RNA sequencing, mitochondrial single-cell ATAC sequencing, and multimodal single-cell sequencing. We profile the transcriptome, chromatin accessibility state, and heteroplasmy in cells from the eyes of a patient with mitochondrial encephalopathy, lactic acidosis, and stroke-like episodes (MELAS) and healthy control donors. Utilizing the retina as a model for complex multi-lineage tissues, we found that the proportion of the pathogenic m.3243A>G allele was neither evenly nor randomly distributed across diverse cell types. All neuroectoderm- derived neural cells exhibited a high percentage of the mutant variant. However, a subset of mesoderm- derived lineage, namely the vasculature of the choroid, was near homoplasmic for the wildtype allele. Gene expression and chromatin accessibility profiles of cell types with high and low proportions of m.3243A>G implicate mTOR signaling in the cellular response to heteroplasmy. We further found by multimodal single-cell sequencing of retinal pigment epithelial cells that a high proportion of the pathogenic mtDNA variant was associated with transcriptionally and morphologically abnormal cells. Together, these findings show the non- random nature of mitochondrial variant partitioning in human mitochondrial disease and underscore its implications for mitochondrial disease pathogenesis and treatment. GRAPHICAL ABSTRACT O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=155 SRC="FIGDIR/small/496449v2_ufig1.gif" ALT="Figure 1"> View larger version (49K): org.highwire.dtl.DTLVardef@10b1c41org.highwire.dtl.DTLVardef@6c2d7corg.highwire.dtl.DTLVardef@1e4d09org.highwire.dtl.DTLVardef@153a5a0_HPS_FORMAT_FIGEXP M_FIG C_FIG

genetics↗

bioRxiv2022

Genetic modifiers of Cep290-mediated retinal degeneration

Mutations in CEP290 cause up to 30% of cases of Leber congenital amaurosis (LCA), a severe childhood blindness resulting from abnormalities in the photoreceptor connecting cilia that lead to rapid retinal degeneration. Like many genetic diseases, CEP290-LCA has considerable variable expressivity, indicating the presence of other factors that influence phenotypic outcome. Here, we have undertaken a phenotype-driven approach in mice to identify genetic modifiers of CEP290-mediated retinal degeneration through backcrosses and intercrosses between BXD24-Cep290rd16 mice and the genetically distinct inbred CAST strain to introduce genetic variation. Optical coherence tomography was used to quantitatively measure retinal thickness as a surrogate indication of photoreceptor degeneration in the resulting rd16-mutant mice. It was readily apparent that CEP290-mediated retinal degeneration in the resulting mice is sensitive to genetic background, with some mice exhibiting relatively thick laminated retinas and others having thin retinas with advanced disease. Quantitative trait locus (QTL) analysis identified multiple genomic loci capable of influencing the retinal degeneration phenotype in Cep290-mutant mice that together account for 71.7% of the phenotypic variation in retinal thickness observed in our population. Following the QTL analysis, two suppressor loci were studied in detail through a combination of physical and molecular approaches to narrow the critical region for each QTL and identify the probable causative genetic variations.

genetics↗

bioRxiv2020

The SWELL1-LRRC8 complex regulates endothelial AKT-eNOS-mTOR signaling and vascular function

The endothelium responds to a multitude of chemical and mechanical factors in regulating vascular tone, angiogenesis, blood pressure and blood flow. The endothelial volume regulatory anion channel (VRAC) has been proposed to be mechano-sensitive, to activate in response to fluid flow/hydrostatic pressure and putatively regulate vascular reactivity and angiogenesis. Here, we show that the Leucine Rich Repeat Containing Protein 8a, LRRC8a (SWELL1) functionally encodes VRAC in human umbilical vein endothelial cells (HUVECs). Endothelial SWELL1 (SWELL1) expression positively regulates AKT-eNOS signaling while negatively regulating mTOR signaling, via a SWELL1-GRB2-Cav1-eNOS signaling complex. Endothelium-restricted SWELL1 KO (SWELL1 KO) mice exhibit enhanced tube formation from ex-vivo aortic ring explants in matrigel angiogenesis assays, develop hypertension in response to chronic angiotensin II infusion and have impaired retinal blood flow with both diffuse and focal blood vessel narrowing in the setting of Type 2 diabetes (T2D). These data demonstrate that SWELL1 antithetically regulates AKT-eNOS and mTOR signaling in endothelium and is required for maintaining vascular function, particularly in the setting of T2D.

cell biology↗