Neuronopathic Gaucher disease in the mouse: viable combined selective saposin C deficiency and mutant glucocerebrosidase (V394L) mice with glucosylsphingosine and glucosylceramide accumulation and progressive neurological deficits

Abstract

Gaucher disease is caused by defective acid β-glucosidase (GCase) function. Saposin C is a lysosomal protein needed for optimal GCase activity. To test the in vivo effects of saposin C on GCase, saposin C deficient mice (C−/−) were backcrossed to point mutated GCase (V394L/V394L) mice. The resultant mice (4L;C*) began to exhibit CNS abnormalities ∼30 days: first as hindlimb paresis, then progressive tremor and ataxia. Death occurred ∼48 days due to neurological deficits. Axonal degeneration was evident in brain stem, spinal cord and white matter of cerebellum accompanied by increasing infiltration of the brain stem, cortex and thalamus by CD68 positive microglial cells and activation of astrocytes. Electron microscopy showed inclusion bodies in neuronal processes and degenerating cells. Accumulation of p62 and Lamp2 were prominent in the brain suggesting the impairment of autophagosome/lysosome function. This phenotype was different from either V394L/V394L or C−/− alone. Relative to V394L/V394L mice, 4L;C* mice had diminished GCase protein and activity. Marked increases (20- to 30-fold) of glucosylsphingosine (GS) and moderate elevation (1.5- to 3-fold) of glucosylceramide (GC) were in 4L;C* brains. Visceral tissues had increases of GS and GC, but no storage cells were found. Neuronal cells in thick hippocampal slices from 4L;C* mice had significantly attenuated long-term potentiation, presumably resulting from substrate accumulation. The 4L;C* mouse mimics the CNS phenotype and biochemistry of some type 3 (neuronopathic) variants of Gaucher disease and is a unique model suitable for testing pharmacological chaperone and substrate reduction therapies, and investigating the mechanisms of neuronopathic Gaucher disease.

Acid β‐glucosidase mutants linked to gaucher disease, parkinson disease, and lewy body dementia alter α‐synuclein processing

“…37 Ultimately, it is necessary to delineate the temporal sequence and causal relationship between GCase activity loss, regional GC and GS accumulation, altered ubiquitylation of target proteins, axonal transport changes, and the dysregulation of proteases (such as cathepsins), all of which may facilitate the formation of intracellular aggregates. 37 With that in mind, it will also be important to quantify the GC, GS, ceramide, and GSL content in our cellular models of mtGBA overexpression, as has been done for the murine models that we employed here, 23,36 and to discern any secondary effects on proteolytic activities in the cell (such as by ceramide levels on cathepsin proteases).…”

“…This 2-hit model results in GCase activity of 10% in the brain leading to accumulation of GC in cerebellum and forebrain (elevation, 10-and 4-fold, respectively) and an even greater rise in GS (>20-fold), thereby replicating important neurochemical aspects of human type 3 Gaucher disease. 36 Neurological dysfunction in these mice usually begins after 10 weeks of age and includes ataxia, tremor, postural instability, and progressive immobility, resulting in death at age 22 weeks. 37 When we analyzed tissue extracts from forebrain and cerebellum from 12-week-old V394Lgbaþ/þ//prosaposin-null//ps-tg mice, we recorded greater variability-but no convincing rise-in total Snca concentrations of Tris/saline, membrane-associated, and SDS-extracted fractions compared with their age-matched littermates (n ¼ 3 each; Fig 4A, B).…”

Multi-system disorders of glycosphingolipid and ganglioside metabolism

“…Unlike galactosylsphingosine in Krabbe disease, glucosylsphingosine has not been proven in vivo as a direct cause of CNS Gaucher disease. However, a recent glucosylsphingosine storage disease mouse model supports this concept ( 205 ). The correlations between disease progression and age-dependent GSL levels also occur in NPC disease ( 206 ), Tay-Sachs disease ( 207 ), and GM1 gangliosidosis mice ( 156 ).…”

Glucocerebrosidase, a new player changing the old rules in Lewy body diseases

“…However, LC3 and beclin-1, markers of macroautophagy, do not change following starvation of fibroblasts from patients with GD (Pacheco et al , 2007 ). LAMP-2 and p62 accumulate in the thalamus, brain stem, and basal ganglia in a mouse model of neuropathic GD, which has a saposin C (an activator of GCase) deficiency and is homozygous for the GBA1 V394L mutation, suggesting impaired macroautophagy (Sun et al , 2010 ). Additionally, overexpression of GBA1 mutant D409V in a PC12 cell model results in α -synuclein accumulation, which is rescued by rapamycin (Cullen et al , 2011 ).…”