The development of a broad-spectrum retaining β-exo-galactosidase activity-based probe

Acid β-galactosidase (GLB1) and galactocerebrosidase (GALC) are retaining exo-β-galactosidases involved in lysosomal glycoconjugate metabolism. Deficiency of GLB1 may result in the lysosomal storage disorders GM1 gangliosidosis, Morquio B syndrome, and galactosialidosis, and deficiency of GALC may result in Krabbe disease. Activity-based protein profiling (ABPP) is a powerful technique to assess the activity of retaining glycosidases in relation to health and disease. This work describes the use of fluorescent and biotin-carrying activity-based probes (ABPs) to assess the activity of both GLB1 and GALC in cell lysates, culture media, and tissue extracts. The reported ABPs, which complement the growing list of retaining glycosidase ABPs based on configurational isomers of cyclophellitol, should assist in fundamental and clinical research on various β-galactosidases, whose inherited deficiencies cause debilitating lysosomal storage disorders.

Brain Targeted AAV1-GALC Gene Therapy Reduces Psychosine and Extends Lifespan in a Mouse Model of Krabbe Disease

Krabbe disease (KD) is a progressive and devasting neurological disorder that leads to the toxic accumulation of psychosine in the white matter of the central nervous system (CNS). The condition is inherited via biallelic, loss-of-function mutations in the galactosylceramidase (GALC) gene. To rescue GALC gene function in the CNS of the twitcher mouse model of KD, an adeno-associated virus serotype 1 vector expressing murine GALC under control of a chicken β-actin promoter (AAV1-GALC) was administered to newborn mice by unilateral intracerebroventricular injection. AAV1-GALC treatment significantly improved body weight gain and survival of the twitcher mice (n = 8) when compared with untreated controls (n = 5). The maximum weight gain after postnatal day 10 was significantly increased from 81% to 217%. The median lifespan was extended from 43 days to 78 days (range: 74-88 days) in the AAV1-GALC-treated group. Widespread expression of GALC protein and alleviation of KD neuropathology were detected in the CNS of the treated mice when examined at the moribund stage. Functionally, elevated levels of psychosine were completely normalized in the forebrain region of the treated mice. In the posterior region, which includes the mid- and the hindbrain, psychosine was reduced by an average of 77% (range: 53-93%) compared to the controls. Notably, psychosine levels in this region were inversely correlated with body weight and lifespan of AAV1-GALC-treated mice, suggesting that the degree of viral transduction of posterior brain regions following ventricular injection determined treatment efficacy on growth and survivability, respectively. Overall, our results suggest that viral vector delivery via the cerebroventricular system can partially correct psychosine accumulation in brain that leads to slower disease progression in KD.

Clinical and immunopathologic alterations in rhesus macaques affected with globoid cell leukodystrophy

Globoid cell leukodystrophy, or Krabbe's disease, is a severe disorder of the central and peripheral nervous system caused by the absence of galactocerebrosidase (GALC) activity. Herein, we describe the clinical, neuropathological, histochemical, and immunohistological features observed in rhesus macaques affected with Krabbe's disease. Clinical signs included pronounced muscle tremors of head and limbs, difficulty ambulating, ataxia, hypermetria, proprioceptive deficits, and respiratory abnormalities. Histopathologically, all animals presented with evidence of demyelination in the peripheral and central nervous systems and accumulation of mononuclear and multinuclear globoid cells in the cerebral and cerebellar white matter associated with severe gliosis. Using immunohistochemistry and multi-label confocal microscopy, it was determined that globoid cells were CD68+, HAM56+, LN5+, CD163+, IBA-1+, and Glut-5+, suggesting that both peripheral blood-derived monocytes/macrophages and resident parenchymal microglia gave rise to globoid cells. Interestingly, many of the globoid cells and parenchymal microglia with a more ameboid morphology expressed HLA-DR, indicating immune activation. Increased expression of iNOS, TNF-alpha, and IL-1 beta were observed in the affected white matter, colocalizing with globoid cells, activated microglia, and astrocytes. Cytokine mRNA levels revealed markedly increased gene expression of CCL2 in the brain of affected macaques. CCL2-expressing cells were detected throughout the affected white matter, colocalizing with GFAP+ cells and astrocytes. Collectively, these data suggest that dysregulation of monocyte/macrophage/microglia and up-regulation of certain cytokines may contribute to the pathogenesis of Krabbe's disease.

Absence of MHC class II molecules reduces CNS demyelination, microglial/macrophage infiltration, and twitching in murine globoid cell leukodystrophy

Globoid cell leukodystrophy (GLD) is a severe genetic demyelinating disorder with an increased number of Ia (immune response antigen) positive brain microglia/macrophages. To assess the role of aberrant Ia expression in the central nervous system (CNS), twitcher mice, which represent the murine model for GLD, were mated with Ia- transgenic mice. Compared with the Ia+ controls, Ia- twitcher mice showed a profound reduction in the severity of demyelinating lesions correlated with significantly fewer microglia/macrophages. Most importantly, Ia- twitcher mice showed significantly reduced twitching compared with ia+ twitcher mice. In contrast with experimental allergic encephalomyelitis (EAE), there was no significant amount of inflammatory T cell infiltrates, implying that T cells may not play a predominant role in this disease. These findings may have broad therapeutic implications for Alzheimer's disease, Parkinson's disease, and Huntington's disease, which display enhanced Ia expression in the CNS without obvious T cell infiltrates.

GM1 ganglioside beta-galactosidases from bovine liver

Two GM1 ganglioside beta-galactosidases, multimeric form (enzyme I) and monomeric form (enzyme IV), have been purified from bovine liver by the procedures comprising Sephadex G-100 gel filtration, affinity chromatographies on Concanavalin A (Con A)-Sepharose and p-aminophenyl thio-beta-galactoside-CH-Sepharose (PATG-Sepharose) and Sephadex G-200 gel filtration. The multimeric form of the enzyme was purified 13,000-fold and monomeric form was 68,700-fold. On sodium dodecyl sulfate poly acrylamide gel electrophoresis, the monomeric form of the enzyme gave a single protein band with a molecular weight of 65,000, while the multimeric form gave two minor protein bands with molecular weights of 32,000 and 20,000 in addition to the major band at 65,000. Both enzymes liberated the terminal galactose from GM1 ganglioside and lactosylceramide. Enzyme I showed a broad pH optimum between pH 4.3 and 5.0, while enzyme IV was most active at pH 4.75. The pI values of beta-galactosidases I and IV were 4.6 and 5.8, respectively. Both enzymes were quite stable upon preincubation at 45 degrees C under acidic condition (pH 4.5), but rapidly lost their activities under neutral condition (pH 7.0). The apparent Km values for GM1 ganglioside of beta-galactosidases I and IV were calculated to be 2.0 x 10(-4) M and 3.3 x 10(-4) M, respectively.

Multiplicity of bovine liver GM1 ganglioside beta-galactosidase

The multiplicity of bovine liver acid beta-galactosidase was investigated. Acid beta-galactosidase activity was measured in the presence of glucono-delta-lactone, which inhibited the neutral beta-galactosidase activity but not the acid beta-galactosidase activity in bovine liver. Three forms of acid beta-galactosidase were separated by Sephadex G-200 gel filtration and the elution pattern of the 4-methylumbelliferyl-beta-galactosidase activity coincided with that of the GM1-beta-galactosidase activity. These forms were relatively stable under acidic conditions (pH 4.5), but the two high molecular weight forms were inclined to dissociate into the low molecular weight form under neutral conditions (pH 7.0). The three forms of the enzyme showed similar pH-optima and apparent Michaelis constants for GM1 ganglioside.

Glycosphingolipid levels in an unusual neurovisceral storage disease characterized by lactosylceramide galactosyl hydrolase deficiency: lactosylceramidosis

The glycosphingolipid composition of brain and visceral tissue from a patient with an unusual neurovisceral lipid storage disease, characterized by a lactosylceramide galactosyl hydrolase deficiency, was determined. Analyses of erythrocytes, plasma, bone marrow cells, urine sediment, and liver biopsy from the patient were compared with those of normal infantile controls. Abnormally high levels of lactosylceramide (GL-2a) were found in these samples. Subsequent studies on spleen, liver, kidney, lymph nodes, and adrenal gland confirmed this finding and clearly showed that the metabolism of hematoside (Gm3) and glucosylceramide (GL-1a) was also affected. The accumulation of GL-1a and Gm3 was most pronounced in spleen, but it was not of the order seen in the spleens of patients with Gaucher's disease that were studied for comparison. Since the disease was primarily neurological in nature, fresh-frozen brain was also studied. The level of GL-2a in gray matter was equal to that of galactosylceramide (GL-1b), and elevated amounts of GL-1a, asialo-Gm2, Gm2, and Gm3 were also found; the only major abnormality in white matter was the accumulation of GL-2a and lesser amounts of the gangliosides Gm3 and Gm2. Chemical and enzymic evidence suggests the use of the term "lactosylceramidosis" for this disease.