Single-cell transcriptome reveals diversity of Müller cells with different metabolic-mitochondrial signatures in normal and degenerated macula

Abstract

Müller cell is the most abundant glial cell in mammalian retina, supporting the functions of photoreceptors and other retinal neurons via maintaining environmental homeostasis. In response to injury and/or neuronal degeneration, Müller cells undergo morphological and functional alternations, known as reactive gliosis documented in multiple retinal diseases, including age-related macular degeneration (AMD), retinitis pigmentosa, diabetic retinopathy, and traumatic retinal detachment. But the functional consequences of Müller glia cell reactivation or even the regulatory networks of the retinal gliosis are still controversial. In this study, we reveal different subpopulations of Müller cells with distinct metabolic-mitochondrial signatures by integrating single cell transcriptomic data from Early AMD patients and healthy donors. Our results show that a portion of Müller cells exhibits low mitochondrial DNA (mtDNA) expressions, reduced protein synthesis, impaired homeostatic regulation, decreased proliferative ability but enhanced proangiogenic function. Interestingly, the major alternation of Müller cells in Early AMD retina is the change of subpopulation abundance, rather than generation of new subcluster. Transcription factor enrichment analysis further highlights the key regulators of metabolic-mitochondrial states of Müller glias in Early AMD patients especially. Our study demonstrates new characteristics of retinal gliosis associated with Early AMD and suggests the possibility to prevent degeneration by intervening mitochondrial functions of Müller cells.

Spatial detection of mitochondrial DNA and RNA in tissues

“…In the example of the retina, photoreceptors are just part of a tissue comprised of around 100 cell types, making it difficult to discern their contribution to changes in mitochondrial gene expression above the retinal milieu. Recent advances in single-cell RNA sequencing have enabled the study of mtDNA in retinal cell subpopulations ( Liu et al, 2022 ), but some neuron types are not represented. Further, tissue digestion and cell sorting conditions can induce stress-related changes to gene expression ( Denisenko et al, 2020 ).…”

Retinal gliosis and phenotypic diversity of intermediate filament induction and remodeling upon acoustic blast overpressure (ABO) exposure to the rat eye

“…The acute retinal glial responses we observe in our rodent TBI model are heterogeneous, with potential further divergence of established subtypes; these may adapt to local neurotoxic stress and damage. In age-related macular degeneration and injury models, Müller glia also diverge into varied adaptive subsets, expressing new transcriptomes—with either maladaptive, or compensatory profiles ( Liu et al, 2022 ; Tomita et al, 2021 ). While beyond the scope of the current study, single cell transcriptomics has emerged as important tool for analyzing Müller cell heterogeneity—we now view these principal glia as complex populations of cells capable of varied responses to disease states ( Lamas and Martinez-Colin, 2022 ).…”

Müller Glial Cells in the Macula: Their Activation and Cell-Cell Interactions in Age-Related Macular Degeneration

“…40 This interdependent nature of the metabolic ecosystem can rapidly deteriorate due to insult and disease, 41 and damage or pathology to one cell type in this ecosystem may lead to the dysregulation of the entire system. Relevant to this concept, recent studies have identified different Müller cell clusters with distinct metabolic signatures, 42,43 suggesting that their metabolism across the retina may vary. These metabolic adaptations may be critical in protecting the retina from oxidative stress, a significant risk factor in the pathogenesis of AMD.…”

“… 62 These results challenge the existing dogma that the expression of AMD risk genes is associated only with RPE and photoreceptors as they reveal an association of Müller glia with AMD genetic risk. Additionally, a single-cell transcriptome analysis from human macular samples indicates the prevalence of a subcluster of Müller cells with reduced mitochondrial (mt) DNA 42 in samples from patients with early AMD. These changes in mtDNA in Müller cells are similar to those in the RPE, where reduced mt DNA copy number and increased mt DNA mutational load have been strongly associated with AMD.…”