Axonopathy and Reduction of Membrane Resistance: Key Features in a New Murine Model of Human G M1 -Gangliosidosis.

G _M1 -gangliosidosis is caused by a reduced activity of β-galactosidase ( Glb1 ), resulting in intralysosomal accumulations of G _M1 . The aim of this study was to reveal the pathogenic mechanisms of G _M1 -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 G _M1 , G _A1 , 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.