Axonopathy and Reduction of Membrane Resistance: Key Features in a New Murine Model of Human GM1-Gangliosidosis

Abstract

GM1-gangliosidosis is caused by a reduced activity of β-galactosidase (Glb1), resulting in intralysosomal accumulations of GM1. The aim of this study was to reveal the pathogenic mechanisms of GM1-gangliosidosis in a new Glb1 knockout mouse model. Glb1−/− mice were analyzed clinically, histologically, immunohistochemically, electrophysiologically and biochemically. Morphological lesions in the central nervous system were already observed in two-month-old mice, whereas functional deficits, including ataxia and tremor, did not start before 3.5-months of age. This was most likely due to a reduced membrane resistance as a compensatory mechanism. Swollen neurons exhibited intralysosomal storage of lipids extending into axons and amyloid precursor protein positive spheroids. Additionally, axons showed a higher kinesin and lower dynein immunoreactivity compared to wildtype controls. Glb1−/− mice also demonstrated loss of phosphorylated neurofilament positive axons and a mild increase in non-phosphorylated neurofilament positive axons. Moreover, marked astrogliosis and microgliosis were found, but no demyelination. In addition to the main storage material GM1, GA1, sphingomyelin, phosphatidylcholine and phosphatidylserine were elevated in the brain. In summary, the current Glb1−/− mice exhibit a so far undescribed axonopathy and a reduced membrane resistance to compensate the functional effects of structural changes. They can be used for detailed examinations of axon–glial interactions and therapy trials of lysosomal storage diseases.

GM1 Gangliosidosis—A Mini-Review

“…With the development of new gene editing approaches, additional β-gal deficient mouse models have been more recently generated using either TALEN or CRISPR/Cas9 technologies (Przybilla et al, 2019;Eikelberg et al, 2020;Liu et al, 2021). Using CRISPR/Cas9 Przybilla et al (2019) engineered a knockout mouse model by introducing a deletion in exon 8 of the Glb1 gene.…”

“…Phenotypic alterations in these mice were evaluated using behavioral tests that showed profound neurocognitive impairment (Przybilla et al, 2019). In Eikelberg et al (2020) described a knock-out model using TALENs to target exon 15 of Glb1. These mice display brain and spinal cord pathology, characterized by swelling of axons and loss of myelin, leading to abnormal electrophysiological activity of neurons (Eikelberg et al, 2020).…”

“…In Eikelberg et al (2020) described a knock-out model using TALENs to target exon 15 of Glb1. These mice display brain and spinal cord pathology, characterized by swelling of axons and loss of myelin, leading to abnormal electrophysiological activity of neurons (Eikelberg et al, 2020). This is the first electrophysiological study performed in a mouse model of the disease, showing abnormalities TABLE 1 | Overview of developed GM1 gangliosidosis mouse models: characteristics and therapies tested.…”

GM1 Gangliosidosis: Mechanisms and Management

“…GM1 gangliosidosis mouse models have been generated through knockout of the glb1 gene and complete loss of β-gal activity. [50][51][52][53] Gross abnormalities are absent in mice until about 4-5 months of age, at which point, affected mice develop severe clinical signs including tremor, ataxia, and abnormal gait. 50,52 In the recent literature, a CRISPR/Cas-generated 20 bp deletion in exon 8 of glb1 produces a GM1 mouse that reaches humane endpoint at 7-10 months with no detectable β-gal activity.…”

Phenotypical changes of satellite glial cells in a murine model of GM1‐gangliosidosis

“…Consequently, G M1 ‐gangliosides and related glycoconjugates are deposited in several tissues but especially within neurons 37 . This leads to distension with subsequent death of neurons within both, CNS and PNS 37,40,41 . Studying murine models for G M1 ‐gangliosidosis, it was observed that Glb1‐deficient mice, despite increasing accumulations of G M1 ‐ganglioside, did not show clinical abnormalities up to the age of 4–5 months 35,42 …”