Aspartylglucosaminuria (AGU) Cell Models for Research

Aspartylglucosaminuria (AGU) is a rare autosomal recessive lysosomal storage disorder caused by mutations in the AGA gene, leading to deficiency of aspartylglucosaminidase. The disease is most prevalent in Finland, with an incidence of approximately 1 in 18,000 live births, but cases are reported worldwide. Patients typically present in early childhood with developmental delay, progressive intellectual disability, coarse facial features, and skeletal abnormalities. The disease is chronic and progressive, with most patients surviving into adulthood but with significant morbidity. There is no cure, and current management is symptomatic. The global burden is substantial for affected families, and research is critical for developing therapies. (Source: WHO, Orphanet)

AGU is an ideal model for studying lysosomal dysfunction, protein misfolding, and neurodegeneration. The monogenic nature of the disease simplifies genetic manipulation, making it a prime candidate for gene editing studies. Public datasets, such as those in ClinVar and UniProt, provide extensive information on AGA mutations. Open questions include the molecular mechanisms linking enzyme deficiency to cognitive decline and the potential for enzyme replacement or gene therapy. Gene-edited cell models are essential for screening therapeutic compounds and understanding disease pathogenesis.

The primary pathway involves the lysosomal degradation of N-linked glycoproteins. Deficiency of aspartylglucosaminidase leads to accumulation of aspartylglucosamine and other glycoasparagines in lysosomes, causing cellular dysfunction. This accumulation triggers secondary pathways:

• • Lysosomal dysfunction: Impaired autophagy and accumulation of undegraded substrates.
• • Neuroinflammation: Activation of microglia and astrocytosis in the brain.
• • Oxidative stress: Increased reactive oxygen species due to lysosomal overload.
• • Apoptosis: Neuronal cell death in affected brain regions.

Data from ClinVar and NCBI Gene.

Although AGU is a monogenic disease, secondary signaling pathways are affected:

• • mTORC1 signaling: Altered due to lysosomal dysfunction, affecting cell growth and autophagy.
• • Unfolded protein response (UPR): Endoplasmic reticulum stress due to mutant AGA protein.
• • Neurotrophin signaling: Impaired BDNF/TrkB signaling in neurons.
• • Inflammatory pathways: NF-κB activation in microglia.

Organoids derived from patient iPSCs recapitulate neuronal and glial differentiation, providing a more physiologically relevant model for studying AGU pathology.

• • AGA knockout mouse: Generated by homologous recombination; exhibits lysosomal storage and behavioral deficits.
• • Patient-derived xenograft (PDX) models: Not applicable for AGU as it is not a cancer; however, xenografts of patient cells can be used for in vivo studies.
• • Genetically engineered mouse models (GEMM): Knock-in mice carrying specific AGA mutations (e.g., R161*) are used to study genotype-phenotype correlations.
• • Induced models: Chemical induction of lysosomal storage in wild-type mice using inhibitors.

CRISPR-based gene editing enables the creation of isogenic cell lines with precise AGA mutations. These models are invaluable for studying the effects of specific mutations in a controlled genetic background. Examples include:

• • AGA knockout cell lines: Complete loss of function to model null mutations.
• • AGA knock-in cell lines: Introduction of patient-specific point mutations (e.g., R161*) to study protein misfolding and enzyme activity.
• • Reporter cell lines: Tagged AGA to track protein localization and degradation.

Commercially available, sequence-verified gene-edited cell lines accelerate research by providing reliable and reproducible models. These are available from commercial sources and are essential for drug screening and functional studies.

Gene-edited cell lines are used to validate the function of AGA and its mutations. For example:

• • Knockout of AGA in HEK293 cells confirms the enzyme's role in glycoasparagine metabolism.
• • Knock-in of patient mutations allows assessment of residual enzyme activity and protein stability.
• • CRISPR screens can identify genetic modifiers that rescue the phenotype, providing new therapeutic targets.

Isogenic cell line pairs (wild-type vs. mutant) are ideal for high-throughput screening of potential therapies:

• • Enzyme replacement therapy (ERT) efficacy can be tested by measuring enzyme uptake and activity.
• • Pharmacological chaperones that stabilize mutant AGA can be identified.
• • Substrate reduction therapy (SRT) can be evaluated by measuring glycoasparagine accumulation.
• • Resistance models are less relevant for AGU, but gene-edited cells can be used to study drug toxicity and off-target effects.

CRISPR-engineered cells are used to discover biomarkers for disease progression and treatment response:

• • Synthetic lethality screens: Identify genes that, when knocked out, are lethal only in AGA-deficient cells, revealing potential drug targets.
• • Secreted proteins: Conditioned media from mutant cells can be analyzed for novel biomarkers.
• • Transcriptomic and proteomic profiling: Compare wild-type and mutant cells to identify differentially expressed genes and proteins.