Partial Restoration of Mutant Enzyme Homeostasis in Three Distinct Lysosomal Storage Disease Cell Lines by Altering Calcium Homeostasis

Abstract

A lysosomal storage disease (LSD) results from deficient lysosomal enzyme activity, thus the substrate of the mutant enzyme accumulates in the lysosome, leading to pathology. In many but not all LSDs, the clinically most important mutations compromise the cellular folding of the enzyme, subjecting it to endoplasmic reticulum–associated degradation instead of proper folding and lysosomal trafficking. A small molecule that restores partial mutant enzyme folding, trafficking, and activity would be highly desirable, particularly if one molecule could ameliorate multiple distinct LSDs by virtue of its mechanism of action. Inhibition of L-type Ca2+ channels, using either diltiazem or verapamil—both US Food and Drug Administration–approved hypertension drugs—partially restores N370S and L444P glucocerebrosidase homeostasis in Gaucher patient–derived fibroblasts; the latter mutation is associated with refractory neuropathic disease. Diltiazem structure-activity studies suggest that it is its Ca2+ channel blocker activity that enhances the capacity of the endoplasmic reticulum to fold misfolding-prone proteins, likely by modest up-regulation of a subset of molecular chaperones, including BiP and Hsp40. Importantly, diltiazem and verapamil also partially restore mutant enzyme homeostasis in two other distinct LSDs involving enzymes essential for glycoprotein and heparan sulfate degradation, namely α-mannosidosis and type IIIA mucopolysaccharidosis, respectively. Manipulation of calcium homeostasis may represent a general strategy to restore protein homeostasis in multiple LSDs. However, further efforts are required to demonstrate clinical utility and safety.

Defects in calcium homeostasis and mitochondria can be reversed in Pompe disease

“…Interestingly, diltiazem (another Ca 2C channel blocker) and verapamil are effective in restoring partial cellular folding, trafficking, and function to mutant lysosomal enzymes in fibroblasts from patients with Gaucher disease, Sanfilippo A or a-mannosidosis. 82,83 Therefore, Ca 2C channel blockers might serve as chaperones to boost the activity of the mutant GAA in some Pompe patients as an added bonus to their ability to restore Ca 2C homeostasis.…”

Ultrastructural and functional abnormalities of mitochondria in cultivated fibroblasts from α-mannosidosis patients

“…Overall aspects of disbalance in calcium homeostasis due to changes in mitochondrial buffering ability and relation between mitochondria and ER (with respect to particular cell type and impacts to cell signalling) were reviewed by Duszynski et al (2006). Interestingly, it has been shown recently (Mu et al 2008) that increasing ER calcium level appears to be a relatively selective strategy to partial restoration of mutant lysosomal enzyme homeostasis in diseases caused by the misfolding and degradation of non-homologous mutant enzymes, as is the case of α-mannosidosis. A possibility of pharmacological influence of ER calcium homeostasis as a new approach for treatment of lysosomal disorders was thus suggested (Mu et al 2008).…”

“…Interestingly, it has been shown recently (Mu et al 2008) that increasing ER calcium level appears to be a relatively selective strategy to partial restoration of mutant lysosomal enzyme homeostasis in diseases caused by the misfolding and degradation of non-homologous mutant enzymes, as is the case of α-mannosidosis. A possibility of pharmacological influence of ER calcium homeostasis as a new approach for treatment of lysosomal disorders was thus suggested (Mu et al 2008).…”

Glucocerebrosidase Mutations in Parkinson Disease

“…Abnormally folded GCase has been found to accumulate in the ER which results in reduced levels of GCase in the lysosome as well as triggers the unfolded protein response and ER-associated degradation (ERAD) [43][44][45]. Markers of ERAD were indeed found to be increased in the PD-GBA brains (Gegg Ann Neurol 2012).…”