Identification of Small Molecule Compounds for Pharmacological Chaperone Therapy of Aspartylglucosaminuria

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.

Optical coherence tomography features in brothers with aspartylglucosaminuria

“…A missense variant of Cys163Ser is responsible for 98% of Finnish AGU cases. This variant destabilizes the precursor protein and prevents proper cleavage and rearrangement of the subunits via disruption of intramolecular disulfide bonds 13. The maternally inherited deletion in our patients is predicted to not produce any protein, while the Thr122Lys mutation is likely to have an impact on the assembly of tetrameric ( αβ ) 2 AGA 13.…”

“…The maternally inherited deletion in our patients is predicted to not produce any protein, while the Thr122Lys mutation is likely to have an impact on the assembly of tetrameric ( αβ ) 2 AGA 13. Thr122 is located on the α chain at the interface between the α and β dimers, and the Thr122Lys replacement is predicted to alter conformations and interactions within this hydrophobic core 13. It is likely that the misfolding induced by the Thr122Lys mutation is milder than that of AGU‐Fin, based on studies in human fibroblasts 13…”

“…AGA is synthesized as a single precursor protein that undergoes autocatalytic rearrangement into the active molecule with an (αβ) 2 tetrameric conformation 13. A missense variant of Cys163Ser is responsible for 98% of Finnish AGU cases.…”

“…This variant destabilizes the precursor protein and prevents proper cleavage and rearrangement of the subunits via disruption of intramolecular disulfide bonds 13. The maternally inherited deletion in our patients is predicted to not produce any protein, while the Thr122Lys mutation is likely to have an impact on the assembly of tetrameric ( αβ ) 2 AGA 13. Thr122 is located on the α chain at the interface between the α and β dimers, and the Thr122Lys replacement is predicted to alter conformations and interactions within this hydrophobic core 13.…”

White Matter Microstructure and Subcortical Gray Matter Structure Volumes in Aspartylglucosaminuria; a 5-Year Follow-up Brain MRI Study of an Adolescent with Aspartylglucosaminuria and His Healthy Twin Brother

“…Mouse model studies investigating virus-mediated gene therapy and enzyme replacement therapy in AGU have shown some promise (Dunder et al 2000;Virta et al 2006). Also, small molecule compounds which may be suitable for chaperone therapy of AGU have been identified in a recent study (Banning et al 2016). At the moment, objective modalities are needed for indexing illness stage and monitoring response to emerging treatment.…”