LIMP-2 deficiency-associated glycolipid abnormalities in mice

Glucocerebrosidase (GCase) catalyzes the lysosomal degradation of glucosylceramide (GlcCer). GCase deficiency results in Gaucher disease (GD), a lysosomal storage disorder with characteristic hepatosplenomegaly. Transport of GCase to lysosomes is mediated by the lysosomal integral membrane protein type 2 (LIMP-2). Deficiency of LIMP-2 leads to reduced cellular GCase levels and manifests as Action Myoclonic Renal Failure Syndrome (AMRF). We investigated the cause for the markedly different symptomatology of GD and AMRF. In tissues of Limp2 -/- mice no prominent abnormalities in lysosomal enzymes were noted except for variable deficiency of GCase, as measured with enzymatic activity assay and detection of active GCase molecules with an activity-based probe. Noteworthy, in LIMP-2-deficient mice, residual GCase is remarkably high in leukocytes. GCase deficiency in tissues does not correlate with increases in GlcCer, but rather with increases in glucosylsphingosine (GlcSph) and glucosylated cholesterol (GlcChol), both glucosylated metabolites derived from GlcCer. Isolated lysosomes from hepatocytes of Limp2 -/- mice revealed no prominent abnormalities in lysosomal matrix proteins except GCase. The Limp2 -/- tritosomes showed clear increases in GlcSph and GlcChol but not in GlcCer. In conclusion, our data imply a critical role of LIMP-2 in glycosphingolipid homeostasis. Despite low GCase levels striking GlcCer accumulation is avoided in tissues of LIMP-2 deficient mice.