Cellular and biochemical response to chaperone versus substrate reduction therapies in neuropathic Gaucher disease

Abstract

Gaucher disease (GD) is caused by the deficiency of the lysosomal membrane enzyme glucocerebrosidase (GCase), and the subsequent accumulation of its substrate, glucosylceramide substrate (GC). Mostly missense mutations of the glucocerebrosidase gene ( GBA ) lead to GCase misfolding and inhibiting the lysosome's proper trafficking. The accumulated GC leads to lysosomal dysfunction and impairs the autophagy pathway. GD types 2 and 3 (GD 2-3), or the neuronopathic forms, affect not only the Central Nervous System (CNS) but also have severe systemic involvement and progressive bone disease. Enzyme replacement therapy (ERT) successfully treats the hematologic manifestations; however, due to the lack of equal distribution of the recombinant enzyme in different organs, it has no impact on the nervous system and has minimal effect on bone involvement. Small molecules have the potential for better tissue distribution. Ambroxol (AMB) is a pharmacologic chaperone that partially recovers the mutated GCase activity and crosses the blood-brain barrier. Eliglustat (EGT) works by inhibiting UDP-glucosylceramide synthase, an enzyme that catalyzes the GC biosynthesis, reducing a GC influx load into the lysosome. Substrate reduction therapy (SRT) using EGT is associated with improvement in GD bone marrow burden score and bone mineral density. The effects of EGT and ABX on GCase activity and autophagy-lysosomal pathway (ALP) were assessed in primary cell lines derived from patients with GD2-3 and compared to cell lines from healthy controls. While both compounds enhanced GCase activity in control cells, an individualized response was observed in cells from patients with GD2-3 that varied with GBA mutations. EGT and AMB enhanced the formation of lysosomal/ late endosomal compartments and autophagy, and this effect was independent of GBA mutations. Both AMB and EGT increased mitochondrial mass and density in GD2-3 fibroblasts, suggesting enhancement of the mitochondrial function by activating the mitochondrial membrane potential. These results suggest that EGT and ABX may have different molecular mechanisms of action, but both enhance GCase activity, improve autophagy-lysosome dynamics and mitochondrial functions.

Exploring the efficacy and safety of Ambroxol in Gaucher disease: an overview of clinical studies

“…Using patients' derived cells, cellular assessment of ABX's chaperoning activity demonstrated positive enhancement in mutated GCase expression, residual activity, and/or glucosylceramide accumulation for different GD disease-causing variants, including N370S, L444P, N227S, F213I, G232W, R159W, and G241R (Maegawa et al, 2009;Bendikov-Bar et al, 2011;Narita et al, 2016;Kim et al, 2020). In GD3 fibroblast cells with L444P (the second most prevalent following F213I) variant, ABX helps to release ER-retained enzymes to lysosomes, resulting in a noticeable increase in residual activity (Ivanova et al, 2021). Notably, the observed impact was not universally present in cells derived from L444P homozygous patients, with some displaying no discernible positive response (Bendikov-Bar et al, 2011).…”

“…ABX's capability of crossing the BBB was further supported in healthy nonhuman primates (Migdalska-Richards et al, 2017). Besides its chaperoning effect, ABX also affects lysosomal biogenesis, autophagy, secretory pathways, and mitochondrial function (Ambrosi et al, 2015;Fois et al, 2015;Magalhaes et al, 2018;Ivanova et al, 2021;Kopytova et al, 2021). ABX has been discovered to boost lysosomal activity and facilitate the removal of protein aggregates in different neurological-related disorders including GD (Bonam et al, 2019).…”

“…ABX facilitates lysosomal-autophagosomal fusion, enhancing protein degradation and potentially reducing ER stress and lysosomal dysfunction for improved protein folding and clearance (Magalhaes et al, 2018). Additionally, ABX induces mitochondrial activation, evidenced by an augmentation in both mitochondrial mass and density, along with the activation of mitochondrial membrane potential as demonstrated in GD2-3 fibroblast cells (Ivanova et al, 2021). Mitochondrial content and lysosomal biogenesis are also enhanced by ABX through peroxisome proliferator-activated receptor gamma coactivator 1-alpha (PGC1α) and TFEB, respectively (Magalhaes et al, 2018).…”