Specific alterations in levels of mannose 6-phosphorylated glycoproteins in different neuronal ceroid lipofuscinoses

Abstract

Mannose 6-phosphate (Man-6-P) is a carbohydrate modification that is generated on newly synthesized lysosomal proteins. This modification is specifically recognized by two Man-6-P receptors that direct the vesicular transport of the lysosomal enzymes from the Golgi to a prelysosomal compartment. The Man-6-P is rapidly removed in the lysosome of most cell types; however, in neurons the Man-6-P modification persists. In this study we have examined the spectrum of Man-6-P-containing glycoproteins in brain specimens from patients with different neuronal ceroid lipofuscinoses (NCLs), which are progressive neurodegenerative disorders with established links to defects in lysosomal catabolism. We find characteristic alterations in the Man-6-P glycoproteins in specimens from late-infantile (LINCL), juvenile (JNCL) and adult (ANCL) patients. Man-6-P glycoproteins in LINCL patients were similar to controls, with the exception that the band corresponding to CLN2, a recently identified lysosomal enzyme whose deficiency results in this disease, was absent. In an ANCL patient, two Man-6-P glycoproteins were elevated in comparison with normal controls, suggesting that this disease also results from a perturbation in lysosomal hydrolysis. In JNCL, total levels of Man-6-P glycoproteins were 7-fold those of controls. In general this was reflected by increased lysosomal enzyme activities in JNCL but three Man-6-P glycoproteins were elevated to an even greater degree. These are CLN2 and the unidentified proteins that are also highly elevated in the ANCL.

Neuronal Ceroid Lipofuscinosis: A Common Pathway?

“…The NCL share clinical manifestations, biochemistry, and pathology, hence their classification together (5)(6)(7)(8)(9)(10)(11)(12)(13)(14). It is probable that all of the NCL genes belong to a common metabolic pathway (15).…”

“…They are implicated in the pathogenesis of neurodegenerative diseases such as Alzheimer's and prion diseases (14). NCL protein deficiencies result in similar cell biologic phenotypes including dysregulated cell growth, apoptosis, and abnormal sphingolipid/phospholipid levels in CLN1-, CLN2-, CLN3-, CLN6-, and CLN8-deficient cells and neurodegeneration (1).…”

A Knock-In Reporter Model of Batten Disease

“…Measurement of TPP1 activity was used as an indicator of compensatory upregulation of lysosomal enzyme activity, typical of many lysosomal storage disorders. TPP1 is deficient in the infantile form of NCL (Sleat et al, 1997), and TPP-1 activity was found previously to be enhanced in Cln3 ⌬ex1-6 mice (Mitchison et al, 1999) and in JNCL patients (Sleat et al, 1998). Cerebellar lysates from 1-and 6-month-old mice were analyzed for TPP1 activity (Fig.…”

Metabolic changes in the lower esophageal sphincter influencing the result of anti-reflux surgical interventions in chronic gastroesophageal reflux disease

“…Glycosidase activities were measured using 4-methylumbelliferyl (4-MU) substrates described by Sleat et al [6] Protease assays using amino-4-methylcoumarin (AMC) substrates have been described by Sleat et al [7] and Sohar et al [8] Reactions were initiated by adding 40 L substrate (various concentration 20 mol/L), buffer (100 mmol/ L) solution to 5 L (CB) or 10 L (other enzymes) of sample (after centrifugation, supernatants were diluted 2-, 4-and 8-fold in homogenization buffer in duplicate), incubated at 37 ℃, and terminated by the addition of 100 L of 0.5 mol/L glycine, pH10.5 (at 4-MU substrates) or 0. 1 mol/L monochloroacetic acid in 0.1 mol/L acetate, pH4.3 (AMC substrates).…”