Multiple pathogenic proteins implicated in neuronopathic Gaucher disease mice

Abstract

Gaucher disease, a prevalent lysosomal storage disease (LSD), is caused by insufficient activity of acid β-glucosidase (GCase) and the resultant glucosylceramide (GC)/glucosylsphingosine (GS) accumulation in visceral organs (Type 1) and the central nervous system (Types 2 and 3). Recent clinical and genetic studies implicate a pathogenic link between Gaucher and neurodegenerative diseases. The aggregation and inclusion bodies of α-synuclein with ubiquitin are present in the brains of Gaucher disease patients and mouse models. Indirect evidence of β-amyloid pathology promoting α-synuclein fibrillation supports these pathogenic proteins as a common feature in neurodegenerative diseases. Here, multiple proteins are implicated in the pathogenesis of chronic neuronopathic Gaucher disease (nGD). Immunohistochemical and biochemical analyses showed significant amounts of β-amyloid and amyloid precursor protein (APP) aggregates in the cortex, hippocampus, stratum and substantia nigra of the nGD mice. APP aggregates were in neuronal cells and colocalized with α-synuclein signals. A majority of APP co-localized with the mitochondrial markers TOM40 and Cox IV; a small portion co-localized with the autophagy proteins, P62/LC3, and the lysosomal marker, LAMP1. In cultured wild-type brain cortical neural cells, the GCase-irreversible inhibitor, conduritol B epoxide (CBE), reproduced the APP/α-synuclein aggregation and the accumulation of GC/GS. Ultrastructural studies showed numerous larger-sized and electron-dense mitochondria in nGD cerebral cortical neural cells. Significant reductions of mitochondrial adenosine triphosphate production and oxygen consumption (28-40%) were detected in nGD brains and in CBE-treated neural cells. These studies implicate defective GCase function and GC/GS accumulation as risk factors for mitochondrial dysfunction and the multi-proteinopathies (α-synuclein-, APP- and Aβ-aggregates) in nGD.

ADrosophilaModel of Neuronopathic Gaucher Disease Demonstrates Lysosomal-Autophagic Defects and Altered mTOR Signalling and Is Functionally Rescued by Rapamycin

“…Accordingly, we demonstrated mitochondrial abnormalities in dGBA1b Ϫ/Ϫ flies, with giant mitochondria, reduced ATP and hypersensitivity to oxidative stress. Enlarged mitochondria and decreased ATP occur in neuronopathic GD mice (Xu et al, 2014), and giant mitochondria are directly linked to Drosophila autophagy defects (Bouché et al, 2016). Therefore, the accumulation of autophagic substrates and giant mitochondria in dGBA1b Ϫ/Ϫ flies is consistent with autophagy block (Fig.…”

“…Consistent with this, we found that dGBA1b Ϫ/Ϫ flies displayed reduced survival and locomotor ability and brain accumulation of p62/Ref(2)P and polyubiquitinated proteins. Both p62 and ubiquitin accumulate in neurodegenerative diseases, such as Alzheimer's disease and PD (Zatloukal et al, 2002;Bartlett et al, 2011), and multiple pathogenic proteins, including p62 and ␤-amyloid, have been identified in neuronopathic GD mouse brains (Xu et al, 2014).…”

“…Indeed, mitochondrial dysfunction occurs in GD mouse models (Osellame et al, 2013;Xu et al, 2014), likely due to defects in the autophagic removal of damaged mitochondria (Osellame et al, 2013). In keeping with this, the deficiency of the Drosophila autophagy gene atg7 is associated with sensitivity to oxidative stressors (Juhász et al, 2007).…”

Mitochondrial dysfunction and mitophagy defect triggered by heterozygous GBA mutations

“…The link between GBA deficiency and mitochondrial dysfunction is corroborated by decreased MMP in neuronal cultures treated with conduritol B epoxide (CBE), a covalent inhibitor of GBA [11,12]. These findings provided evidence for a loss-of-function mechanism of GBA mutations for mitochondrial dysfunction associated with GD, in which both GBA alleles are mutated, resulting in a reduction in GBA protein levels and lysosomal GBA enzyme activity, probably because GBA mutations often lead to misfolded proteins that are retained in the endoplasmic reticulum (ER) and undergo rapid ER-associated degradation through the ubiquitin-proteasome pathway [9].…”

Ambroxol effects in glucocerebrosidase and α‐synuclein transgenic mice

“…It has been shown in SH‐SY5Y cell cultures, neuronal cultures, conduritol‐β‐epoxide (CβE)‐treated mice, and transgenic Gba1 mouse models that reduced GCase activity results in increased α‐synuclein levels 7, 8, 9, 10, 11, 12, 13, 14. Conversely, it has been demonstrated in cell models that increased α‐synuclein causes a decrease in GCase activity 15.…”