Identification of Small Molecule Compounds for Pharmacological Chaperone Therapy of Aspartylglucosaminuria

Antje Banning,Juha Rouvinen,Ritva Tikkanen,Steven J Gray,Christina Gülec

doi:10.1038/srep37583

Abstract

Aspartylglucosaminuria (AGU) is a lysosomal storage disorder that is caused by genetic deficiency of the enzyme aspartylglucosaminidase (AGA) which is involved in glycoprotein degradation. AGU is a progressive disorder that results in severe mental retardation in early adulthood. No curative therapy is currently available for AGU. We have here characterized the consequences of a novel AGU mutation that results in Thr122Lys exchange in AGA, and compared this mutant form to one carrying the worldwide most common AGU mutation, AGU-Fin. We show that T122K mutated AGA is expressed in normal amounts and localized in lysosomes, but exhibits low AGA activity due to impaired processing of the precursor molecule into subunits. Coexpression of T122K with wildtype AGA results in processing of the precursor into subunits, implicating that the mutation causes a local misfolding that prevents the precursor from becoming processed. Similar data were obtained for the AGU-Fin mutant polypeptide. We have here also identified small chemical compounds that function as chemical or pharmacological chaperones for the mutant AGA. Treatment of patient fibroblasts with these compounds results in increased AGA activity and processing, implicating that these substances may be suitable for chaperone mediated therapy for AGU.

Highlights

The AGA enzyme is synthesized as a single precursor molecule of 346 amino acids
We here identify potential small molecular substances that are capable of functioning as pharmacological chaperone (PC) for the mutated AGA enzyme, and show that these compounds result in increased AGA activity and improved lysosomal morphology in patient fibroblasts with two different mutations
We show that specific compounds that are likely to act as pharmacological chaperones can facilitate the activation and cleavage into subunits of the mutated AGA enzyme, and provide a potential therapy for AGU

Summary

Introduction

The AGA enzyme is synthesized as a single precursor molecule of 346 amino acids. After removal of the signal peptide, AGA precursor becomes N-glycosylated in two Asn residues[4]. No treatment for AGU is available, several preclinical studies aiming at enzyme replacement (ERT)[10,11] or gene therapy[12,13] have been published. We here identify potential small molecular substances that are capable of functioning as PCs for the mutated AGA enzyme, and show that these compounds result in increased AGA activity and improved lysosomal morphology in patient fibroblasts with two different mutations. These findings pave way for a PC-based therapy for AGU

Methods

Results

Conclusion