Elevated Glucosylsphingosine in Gaucher Disease induced Pluripotent Stem Cell Neurons Deregulates Lysosomal Compartment through Mammalian Target of Rapamycin Complex 1

Abstract

Gaucher disease (GD) is a lysosomal storage disorder caused by mutations in GBA1, the gene that encodes lysosomal β-glucocerebrosidase (GCase). Mild mutations in GBA1 cause type 1 non-neuronopathic GD, whereas severe mutations cause types 2 and 3 neuronopathic GD (nGD). GCase deficiency results in the accumulation of glucosylceramide (GlcCer) and glucosylsphingosine (GlcSph). GlcSph is formed by deacylation of GlcCer by the lysosomal enzyme acid ceramidase. Brains from patients with nGD have high levels of GlcSph, a lipid believed to play an important role in nGD, but the mechanisms involved remain unclear. To identify these mechanisms, we used human induced pluripotent stem cell-derived neurons from nGD patients. We found that elevated levels of GlcSph activate mammalian target of rapamycin (mTOR) complex 1 (mTORC1), interfering with lysosomal biogenesis and autophagy, which were restored by incubation of nGD neurons with mTOR inhibitors. We also found that inhibition of acid ceramidase prevented both, mTOR hyperactivity and lysosomal dysfunction, suggesting that these alterations were caused by GlcSph accumulation in the mutant neurons. To directly determine whether GlcSph can cause mTOR hyperactivation, we incubated wild-type neurons with exogenous GlcSph. Remarkably, GlcSph treatment recapitulated the mTOR hyperactivation and lysosomal abnormalities in mutant neurons, which were prevented by coincubation of GlcSph with mTOR inhibitors. We conclude that elevated GlcSph activates an mTORC1-dependent pathogenic mechanism that is responsible for the lysosomal abnormalities of nGD neurons. We also identify acid ceramidase as essential to the pathogenesis of nGD, providing a new therapeutic target for treating GBA1-associated neurodegeneration.

Substrate Reduction Therapy Reverses Mitochondrial, mTOR, and Autophagy Alterations in a Cell Model of Gaucher Disease

“…Our finding is consistent with studies in nGD iPSC-derived neurons, in which elevated GS levels were implicated in the pathological activation of mTOR [ 18 ]. In previous studies, inhibition of glucosylceramide synthase and acid ceramidase, the lysosomal enzyme that deacylates elevated GC to GS, also reduced mTOR kinase activity [ 19 ]. Overall, our results suggest that the mTOR pathway may be a potential new target for treating nGD.…”

“…Furthermore, mitochondrial dysfunction is a well-documented pathological feature in chemically induced cell and genetic mouse models of nGD [ 14 , 15 , 16 , 17 ]. Recently, mTOR pathway hyperactivity has also been implicated in nGD iPSC-derived neurons [ 18 , 19 ]. Accumulations of GC and GS have been considered a primary insult leading to GD manifestations, particularly in nGD, and may directly alter cellular functions [ 3 ].…”

Xylose‐Configured Cyclophellitols as Selective Inhibitors for Glucocerebrosidase

“…[5][6][7] Recently, it has been recognized that carriers of mutations in the GBA gene are at an increased risk for developing Parkinson's disease (PD), [8] in which excessive GlcSph is speculated to promote harmful α-synuclein aggregation. [9,10] The current therapies for the treatment of GD are enzyme supplementation based on chronic intravenous administration of macrophage-targeted recombinant human GBA (rhGBA), also known as "enzyme replacement therapy", and "substrate reduction therapy" founded on the inhibition of GlcCer synthesis. [11] Gene therapy approaches are presently actively studied in pre-clinical and clinical settings.…”

“…[ 5 , 6 , 7 ] Recently, it has been recognized that carriers of mutations in the GBA gene are at an increased risk for developing Parkinson's disease (PD), [8] in which excessive GlcSph is speculated to promote harmful α‐synuclein aggregation. [ 9 , 10 ]…”

C5a Activates a Pro-Inflammatory Gene Expression Profile in Human Gaucher iPSC-Derived Macrophages

“…Other leukocytes are also affected in GD, leading to chronic inflammation and in some cases, development of B-cell and T-cell lymphomas [ 7 , 8 , 9 , 10 , 11 ]. The accumulation of GluCer and its deacylated derivative glucosylsphingosine (GluSph) has also been reported in iPSC-neuronal cells derived from GD patients [ 12 , 13 ]. The abnormal elevation of glucosylsphingolipids in type 1 GD results in anemia, excessive bruising, hepato-splenomegalia, and bone pathologies including reduced bone mineral density, avascular necrosis, and bone infarctions [ 14 , 15 ].…”