Effects of small molecule therapies on lysosomal function in Gaucher disease

Gaucher disease (GD), the deficiency of the lysosomal enzyme glucocerebrosidase (GCase), is caused by the mutations in GBA. Most mutations lead to misfolding of GCase in the endoplasmic reticulum and altered protein trafficking to the lysosome. The accumulated substrate, glucosylceramide in the lysosomes is also suggested to alter autophagy-lysosome pathway (ALP) functions. Enzyme replacement therapy successfully treats hematologic manifestation, however has lessor no effect on other end organs, such as brain, lungs, and bones. Small molecule therapies haves the potential for better tissue distribution and nervous system penetration. Eliglustat hemitartrate (EGT), a substrate reducing agent, works by inhibiting UDP-glucosylceramide synthase, the first enzyme that catalyzes the biosynthesis of glycosphingolipids, thus reducing the load of glucosylceramide influx into the lysosome. Ambroxol (ABX), is a pharmacologic chaperone shown to partially recover the mutated GCase. The effects of both molecules on ALP are yet to be studied. The effects of EGT and ABX on autophagy-lysosomal pathways were examined in various primary cells derived from patients with GD. Overall, both compounds increased GCase activity, but this effect was only observed in some patients. GCase expression analysis demonstrated elevated protein but not mRNA levels after ABX and EGT treatments. There was also an increase in autophagic vesicle formation and autophagosome accumulation as evidenced by changing levels of LC3A/BII. There was an increase in LysoTracker signal and mitochondria levels, but RT-PCR demonstrated no change in LC3 and LAMP1 in primary fibroblasts, PBMC and macrophages. Decreasing RNA levels of pro-inflammatory cytokines CCL17, IL10, IFNγ were observed in macrophages following both treatments, while ABX particularly inhibited CCL2 levels. While the small molecules, EGT and ABX have completely different mechanisms of action, they both lead to ALP activation and decreased pro-inflammatory cytokine levels that could be among the reasons for improved GCase activity in select cell lines.