Biology subjects

Nagel-Wolfrum, K.

Publications and source records attributed to Nagel-Wolfrum, K..

4 recordsLinked to original sources

bioRxiv2025

Lost in communication: How Mueller glia cells fail to maintain retinal integrity in USH1C retinal organoids

Usher syndrome type 1, caused by pathogenic variants in the USH1C gene, leads to congenital deafness and progressive retinal degeneration resulting in vision loss. While auditory deficits can be compensated by cochlea implants and hearing aids, no treatment exists to prevent retinal degeneration. Here, we generated retinal organoids from induced pluripotent stem cells of two USH1C patients to elucidate the cellular and molecular mechanisms driving ocular pathogenesis. Single-cell RNA sequencing of both healthy and USH1C retinal organoids identified differential expression of genes related to phototransduction in photoreceptors, as well as alterations in cell adhesion and canonical Wnt signaling in Muller glia cells. Analysis of intercellular communication revealed an overall reduced signaling efficiency, particularly affecting Muller glia-mediated retinal adhesion processes. Morphological characterization of organoids confirmed transcriptome changes by showing degeneration of the outer limiting membrane and loss of adherens junction architecture. Moreover, photoreceptors revealed increased susceptibility to morphological and functional changes related to phototransduction. These results demonstrate that disruption of Muller glia signaling contributes to a loss of retinal integrity, providing novel insights into USH1C pathogenesis and offering targets for therapeutic interventions.

cell biology↗

bioRxiv2024

The adhesion GPCR ADGRV1 controls glutamate homeostasis in hippocampal astrocytes supporting neuron development: First insights into to pathophysiology of ADGRV1-associated epilepsy

ADGRV1 is the largest member of adhesion G protein-coupled receptor (aGPCR) family. In the cell, aGPCRs have dual roles in cell adhesion and signal transduction. Mutations in ADGRV1 have been linked not only to Usher syndrome (USH), which causes deaf-blindness, but recently also to various forms of epilepsy. While the USH defects are attributed to the loss of fiber links between membranes formed by the extracellular domain of ADGRV1, the pathomechanisms leading to epilepsy remain elusive to date. Here, we study the specific functions of ADGRV1 in astrocytes where it is highest expressed in the nervous system. Affinity proteomics showed the interaction of ADRGV1 with proteins enriched in astrocytes. Dysregulations of cellular processes important in astrocyte function were indicated by the different transcriptomes of patient-derived cells and Adgrv1-deficent mouse hippocampi compared to appropriate controls. Alteration in morphology and reduced numbers of astrocytes in the hippocampus of Adgrv1-deficent mice. Monitoring the glutamate uptake in colorimetric assay and by live cell imaging of a genetic glutamate reporter consistently showed that glutamate uptake from the extracellular environment is significantly reduced in Adgrv1-deficent astrocytes. Expression analyses of key enzymes of the glutamate-glutamine cycle in astrocytes and the glutamate metabolism indicated imbalanced glutamate homeostasis in Adgrv1-deficient astrocytes. Finally, we provide evidence that the supportive function of astrocytes in neuronal development also relies on ADGRV1 expression in astrocytes. Our data collectively provides first insights into the molecular pathophysiology underlying the development of epilepsy associated with mutations in ADGRV1. HighlightsO_LIADGRV1 deficiency reduces the number of astrocytes in CA1 and changes the morphology of astrocytes in the hippocampus. C_LIO_LIADGRV1 interacts with numerous proteins enriched in astrocytes. C_LIO_LIDifferential transcriptomes revealed differential expression of genes related to glutamate homeostasis and epilepsy in ADGRV1 deficient models. C_LIO_LIADGRV1 controls glutamate uptake and regulates homeostasis in astrocytes. C_LIO_LIADGRV1 in astrocytes is vital for neuron morphogenesis. C_LIO_LIFirst insights into the molecular pathophysiology underlying the development of epilepsy associated with mutations in ADGRV1. C_LI Graphical Abstract O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=197 SRC="FIGDIR/small/591120v1_ufig1.gif" ALT="Figure 1"> View larger version (54K): org.highwire.dtl.DTLVardef@1f1f749org.highwire.dtl.DTLVardef@a1ea01org.highwire.dtl.DTLVardef@a0be1org.highwire.dtl.DTLVardef@191f96a_HPS_FORMAT_FIGEXP M_FIG C_FIG

neuroscience↗

bioRxiv2021

Characterization of USH1C/harmonin in the human retina provides insights into pathophysiology and therapy options for Usher syndrome

Usher syndrome (USH) is the most common form of hereditary deafness-blindness in humans. USH is a complex genetic disorder, assigned to three clinical subtypes differing in onset, course, and severity, with USH1 being the most severe. Rodent USH1 models do not reflect the ocular phenotype observed in human patients to date; hence, little is known about the pathophysiology of USH1 in the human eye. One of the USH1 genes, USH1C, exhibits extensive alternative splicing and encodes numerous harmonin protein isoforms that function as scaffolds for organizing the USH interactome. RNA-seq analysis of human retinas uncovered harmonin_a1 as the most abundant transcript of USH1C. Bulk RNA-seq analysis and immunoblotting showed abundant expression of harmonin in Muller glia cells (MGCs) and retinal neurons. Furthermore, harmonin was localized in the terminal endfeet and apical microvilli of MGCs, presynaptic region (pedicle) of cones, and outer segments of rods as well as at adhesive junctions of MGCs and photoreceptors in the outer limiting membrane (OLM). Our data provide evidence for the interactions of harmonin with OLM molecules in photoreceptors (PRCs) and MGCs and rhodopsin in PRCs. Subcellular expression and colocalization of harmonin correlate with the clinical phenotype observed in USH1C patients. In addition, primary cilia defects in USH1C patient-derived fibroblasts could be reverted by the delivery of harmonin_a1 transcript isoform. Our data provide novel insights into PRC cell biology, USH1C pathophysiology, and for developing gene therapy treatment.

molecular biology↗

bioRxiv2021

Early Disruption of Photoreceptor Cell Architecture and Loss of Vision in a Humanized Pig Model of Usher Syndrome

Usher syndrome (USH) is the most common form of monogenic deaf-blindness. Loss of vision is untreatable and, so far, there are no suitable animal models for testing therapeutic strategies. By introducing a human mutation into the harmonin-encoding USH1C gene in pigs, we generated the first translational animal model for USH type 1 with characteristic hearing defect, vestibular dysfunction and visual impairment. Changes in photoreceptor architecture, quantitative motion analysis and electroretinography were characteristics of the reduced retinal virtue in USH1C pigs. Primary cells from those animals and USH1C patients showed significantly elongated primary cilia, compared to wild-type, confirming the nature of USH as a true and general ciliopathy and proving the therapeutic capacity of gene supplementation and gene repair approaches.

genetics↗