GlcCer accumulation causes
Gaucher disease where GlcCer breakdown is inhibited due to a hereditary deficiency in
glucocerebrosidase.
Glycolipids are endocytosed and targeted to the Golgi apparatus in normal cells but in
Gaucher disease they are mistargeted to lysosomes. To better understand the role of GlcCer in endocytic sorting RAW macrophages were treated with
Conduritol B-epoxide to inhibit GlcCer breakdown.
Lipid analysis found increases in GlcCer led to accumulation of both
triacylglycerol and
cholesterol consistent with increased lysosomal pH. Ratio imaging of macrophages using both
acridine orange and
lysosensor yellow/blue to measure endolysosomal pH revealed increases in
Conduritol B-epoxide treated RAW macrophages and Gaucher patient lymphoblasts. Increased endolysosomal pH was restricted to Gaucher lymphoblasts as no significant increases in pH were seen in Fabry, Krabbe, Tay-Sachs and GM1-gangliosidosis lymphoblasts. Substrate reduction
therapy utilises inhibitors of
GlcCer synthase to reduce storage in
Gaucher disease. The addition of inhibitors of GlcCer synthesis to RAW macrophages also led to increases in
cholesterol and
triacylglycerol and an endolysosomal pH increase of up to 1 pH unit. GlcCer modulation appears specific since
glucosylsphingosine but not
galactosylsphingosine reversed the effects of GlcCer depletion. Although no acute effects on
glycolipid trafficking were observed using
bafilomycin A the results are consistent with a multistep model whereby increases in pH lead to altered trafficking via
cholesterol accumulation. GlcCer modulates endolysosomal pH in lymphocytes suggesting an important role in normal lysosomes which may be disrupted in
Gaucher disease.