Chemistry of heparitin sulfate and heparin from normal tissues and from patients with Hunter syndrome

Cathepsin B-associated Activation of Amyloidogenic Pathway in Murine Mucopolysaccharidosis Type I Brain Cortex

Mucopolysaccharidosis type I (MPS I) is caused by genetic deficiency of α-l-iduronidase and impairment of lysosomal catabolism of heparan sulfate and dermatan sulfate. In the brain, these substrates accumulate in the lysosomes of neurons and glial cells, leading to neuroinflammation and neurodegeneration. Their storage also affects lysosomal homeostasis-inducing activity of several lysosomal proteases including cathepsin B (CATB). In the central nervous system, increased CATB activity has been associated with the deposition of amyloid plaques due to an alternative pro-amyloidogenic processing of the amyloid precursor protein (APP), suggesting a potential role of this enzyme in the neuropathology of MPS I. In this study, we report elevated levels of protein expression and activity of CATB in cortex tissues of 6-month-old MPS I (Idua -/- mice. Besides, increased CATB leakage from lysosomes to the cytoplasm of Idua -/- cortical pyramidal neurons was indicative of damaged lysosomal membranes. The increased CATB activity coincided with an elevated level of the 16-kDa C-terminal APP fragment, which together with unchanged levels of β-secretase 1 was suggestive for the role of this enzyme in the amyloidogenic APP processing. Neuronal accumulation of Thioflavin-S-positive misfolded protein aggregates and drastically increased levels of neuroinflammatory glial fibrillary acidic protein (GFAP)-positive astrocytes and CD11b-positive activated microglia were observed in Idua -/- cortex by confocal fluorescent microscopy. Together, our results point to the existence of a novel CATB-associated alternative amyloidogenic pathway in MPS I brain induced by lysosomal storage and potentially leading to neurodegeneration.

Impaired sulphated glycosaminoglycan metabolism in a patient with GM-2 gangliosidosis (Tay-Sachs disease)

An abnormal urinary excretion of sulphated glycosaminoglycans in a patient with GM-2 gangliosidosis (Tay-Sachs disease) is described. Besides the accumulation of GM-2 ganglioside in liver and lack of hexosaminidase A, the patient shows an abnormal urinary excretion of an iduronic acid-rich low molecular weight heparan sulphate. Also, no dermatan sulphate could be detected in the urine, whereas this compound was the main sulphated glycosaminoglycan in the liver of the patient. Heparan sulphate was the main glycosaminoglycan of normal liver. The total amount of sulphated glycosaminoglycans in the urine and liver of the patient did not differ significantly from the amounts found in the liver and urine of normal subjects. Several plasma glycosidases have been assayed and the activities did not differ significantly from the values obtained for the plasma of normal subjects.

Isolation and characterization of peptidoglycans in urine from patients with mucopolysaccharidoses

Urinary dermatan sulfate (DS) and heparan sulfate (HS) were purified from mucopolysaccharidosis patients. DS shows average mol. wt 8600-12,000 (approx. one half of tissue DS), iduronic acid content 99.1-99.6% (81.8% in tissue DS), core peptide mostly di- or tri-peptide (--Ser--Gly--or--Ser--Gly--Glu--). Molecular weight of HS ranged from 2500 to 20,000, averaging about 5000. Highly sulfated HS was found in the low molecular weight fraction, and no bound core peptide. By contrast, HS in the high molecular weight fraction bound one sulfate per repeating unit, which include core peptide.