University of Iowa Institute for Vision Research, Iowa City, Iowa, USA.
Department of Ophthalmology and Visual Sciences and.
JCI Insight. 2023 Jul 24;8(14):e165937. doi: 10.1172/jci.insight.165937.
Variants within the high copy number mitochondrial genome (mtDNA) can disrupt organelle function and lead to severe multisystem disease. The wide range of manifestations observed in patients with mitochondrial disease 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 nonrandom distribution of a pathogenic mtDNA variant across a complex tissue using single-cell RNA-Seq, mitochondrial single-cell ATAC sequencing, and multimodal single-cell sequencing. We profiled 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 from healthy control donors. Utilizing the retina as a model for complex multilineage 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 WT 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 nonrandom nature of mitochondrial variant partitioning in human mitochondrial disease and underscore its implications for mitochondrial disease pathogenesis and treatment.
高拷贝数线粒体基因组（mtDNA）内的变体可能会破坏细胞器的功能，并导致严重的多系统疾病。患有线粒体疾病的患者表现出广泛的症状，这是由于不同细胞和组织中异常 mtDNA 分子的比例不同，这种现象称为异质性。然而，组织内不同细胞类型的异质性分布及其对受影响患者表型表达的影响在很大程度上仍未得到探索。在这里，我们使用单细胞 RNA-Seq、线粒体单细胞 ATAC 测序和多模态单细胞测序，鉴定了一种致病性 mtDNA 变体在复杂组织中的非随机分布。我们对线粒体脑肌病伴高乳酸血症和卒中样发作（MELAS）患者和健康对照供体的眼睛细胞的转录组、染色质可及性状态和异质性进行了分析。利用视网膜作为复杂多谱系组织的模型，我们发现致病性 m.3243A>G 等位基因的比例在不同细胞类型中既不均匀也不随机分布。所有神经外胚层衍生的神经细胞均表现出高比例的突变变体。然而，一部分中胚层衍生的谱系，即脉络膜的血管，WT 等位基因近乎同质。具有高比例和低比例 m.3243A>G 的细胞类型的基因表达和染色质可及性谱表明 mTOR 信号通路参与了细胞对异质性的反应。我们通过视网膜色素上皮细胞的多模态单细胞测序进一步发现，高比例的致病性 mtDNA 变体与转录和形态异常的细胞有关。总之，这些发现表明人类线粒体疾病中线粒体变体分配的非随机性，并强调了其对线粒体疾病发病机制和治疗的影响。
