Candidate molecules for chemical chaperone therapy of GM1-gangliosidosis.

A growing body of evidence suggests that misfolding of a mutant protein followed by its aggregation or premature degradation in the endoplasmic reticulum is one of the main mechanisms that underlie inherited neurodegenerative diseases, including lysosomal storage diseases. Chemical or pharmacological chaperones are small molecules that bind to and stabilize mutant lysosomal enzyme proteins in the endoplasmic reticulum. A number of chaperone compounds for lysosomal hydrolases have been identified in the last decade. They have gained attention because they can be orally administrated, and also because they can penetrate the blood-brain barrier. In this article, we describe two chaperone candidates for the treatment of GM1-gangliosidosis. We also discuss the future direction of this strategy targeting other lysosomal storage diseases as well as protein misfolding diseases in general.

Reciprocal control of hERG stability by Hsp70 and Hsc70 with implication for restoration of LQT2 mutant stability.

RATIONALE: The human ether-a-go-go-related gene (hERG) encodes the α subunit of the potassium current I(Kr). It is highly expressed in cardiomyocytes and its mutations cause long QT syndrome type 2. Heat shock protein (Hsp)70 is known to promote maturation of hERG. Hsp70 and heat shock cognate (Hsc70) 70 has been suggested to play a similar function. However, Hsc70 has recently been reported to counteract Hsp70. OBJECTIVE: We investigated whether Hsc70 counteracts Hsp70 in the control of wild-type and mutant hERG stability. METHODS AND RESULTS: Coexpression of Hsp70 with hERG in HEK293 cells suppressed hERG ubiquitination and increased the levels of both immature and mature forms of hERG. Immunocytochemistry revealed increased levels of hERG in the endoplasmic reticulum and on the cell surface. Electrophysiological studies showed increased I(Kr). All these effects of Hsp70 were abolished by Hsc70 coexpression. Heat shock treatment of HL-1 mouse cardiomyocytes induced endogenous Hsp70, switched mouse ERG associated with Hsc70 to Hsp70, increased I(Kr), and shortened action potential duration. Channels with disease-causing missense mutations in intracellular domains had a higher binding capacity to Hsc70 than wild-type channels and channels with mutations in the pore region. Knockdown of Hsc70 by small interfering RNA or heat shock prevented degradation of mutant hERG proteins with mutations in intracellular domains. CONCLUSIONS: These results indicate reciprocal control of hERG stability by Hsp70 and Hsc70. Hsc70 is a potential target in the treatment of LQT2 resulting from missense hERG mutations.

Mental retardation, spasticity, basal ganglia calcification, cerebral white matter lesions, multiple endocrine defects, telangiectasia and atrophic skin: a new syndrome?

We report on an 8-year-old boy with mental retardation and spastic tetraparesis associated with atrophic skin on the face and extremities, telangiectasia, and severe dental caries. Basal ganglia calcification and multiple lesions in the subcortical white matter have been present since infancy. The patient has complications of liver dysfunction, multiple endocrine defects, and elevation of blood/cerebrospinal fluid lactate. Extensive laboratory examinations, including skin and muscle biopsies, and UV- and mitomycin C-sensitivity tests on fibroblasts, provided no evidence of a specific disease entity. No deterioration was noted, and supplementation of riboflavin and other vitamins had no apparent effect on the neurodevelopmental status of this patient. This patient may represent a novel disease entity, with unclear pathogenesis.

The Wilson disease protein ATP7B resides in the late endosomes with Rab7 and the Niemann-Pick C1 protein.

Wilson disease is a genetic disorder characterized by the accumulation of copper in the body due to a defect of biliary copper excretion. Although the Wilson disease gene has been cloned, the cellular localization of the gene product (ATP7B) has not been fully clarified. Therefore, the precise physiological action of ATP7B is still unknown. We examined the distribution of ATP7B using an anti-ATP7B antibody, green fluorescent protein (GFP)-ATP7B (GFP-ATP7B) and ATP7B-DsRed in various cultured cells. Intracellular organelles were visualized by fluorescence microscopy. The distribution of ATP7B was compared with that of Rab7 and Niemann-Pick C1 (NPC1), proteins that localize in the late endosomes. U18666A, which induces the NPC phenotype, was used to modulate the intracellular vesicle traffic. GFP-ATP7B colocalized with various late endosome markers including Rab7 and NPC1 but not with Golgi or lysosome markers. U18666A induced the formation of late endosome-lysosome hybrid organelles, with GFP-ATP7B localized with NPC1 in these structures. We have confirmed that ATP7B is a late endosome-associated membrane protein. ATP7B appears to translocate copper from the cytosol to the late endosomal lumen, thus participating in biliary copper excretion via lysosomes. Thus, defective copper ATPase activity of ATP7B in the late endosomes appears to be the main defect of Wilson disease.