Elucidating the mechanism of action of a small molecule proteostasis regulator with potential relevance for treatment of the lysosomal storage disease, mucopolysaccharidosis I

The lysosomal storage disease Mucopolysaccharidosis I, involving lysosomal deficiency of α-L-iduronidase (IDUA), is often characterized by extensive ER-associated degradation (ERAD) of missense mutant IDUAs, folding variants which often retain residual activity. Compound X-372, identified from a plant cell-based screen of 1,040 FDA-approved drugs, enhanced the post-ER transport of ERAD-prone P533R-IDUA. Here, dose response studies of compound treatment on Nicotiana tabacum BY2 protoplasts, expressing human wild-type and ERAD-prone R383H-IDUA, not only validated the rescuing effect of X-372, but also indicated this effect occurred via augmenting a general cellular process. Microarray analysis and subsequent quantitative PCR validation of candidate genes showed that the therapeutic effect of X-372 was linked to augmented sulfur assimilation. Reduced glutathione - a product of the sulfur assimilation pathway that is also a potent cellular antioxidant – is a target for future studies to identify the specific means by which X-372 enhances the post-ER transport of ERAD-prone folding mutants.