Excess ASNS links neuronal stress to Angelman syndrome features in mice

Lowering excess asparagine synthetase in a mouse model of Angelman syndrome restored neuronal protein synthesis, corrected microcephaly and improved many behavioural deficits, according to a study that combined biochemical screening, mouse genetics and analyses of human neurons. The researchers identified asparagine synthetase, abbreviated ASNS, as a target of UBE3A, the gene whose loss causes the severe neurodevelopmental disorder. Their results indicate that UBE3A loss can leave neurons in a persistent stress state that suppresses protein production and limits development.

The rescue was substantial but incomplete, showing that ASNS is an important contributor to the disorder rather than a full explanation for every feature. Angelman syndrome results from loss of UBE3A function in the brain. UBE3A encodes an E3 ubiquitin ligase, but the study was designed around a more specific unresolved problem: which proteins affected by loss of this protein contribute to particular disease phenotypes?

The investigators combined disease-linked UBE3A mutations that gain or lose function with unbiased proteomics, then examined candidate substrates in a mouse model and in neurons derived from patient cell lines. The human cell lines included one carrying a large maternal deletion spanning UBE3A and another carrying a premature truncating mutation in the maternal UBE3A allele. ASNS emerged from the proteomic screen as a strong candidate.

The protein was more abundant in the brains of Ube3a-null mice and in human neurons with Angelman syndrome. Its expression was concentrated mainly in neurons, paralleling the neuron-specific imprinting pattern of Ube3a in the mouse. ASNS makes asparagine, a non-essential amino acid that can be obtained through the diet but must be transported across the blood–brain barrier to enter the central nervous system.

The study’s authors proposed that neurons may rely on ASNS for most or all of the asparagine they require, making changes in its abundance a potential point of vulnerability during development. Experimental manipulation linked excess ASNS to stress signalling. Overexpressing ASNS in neurons was sufficient to increase phosphorylated eIF2α and levels of HRI, the kinase encoded by Eif2ak1.

Phosphorylated eIF2α and HRI are associated with integrated stress responses, and HRI is induced in neurons during proteostatic stress. The investigators therefore examined whether altered ASNS contributed to the reduced protein synthesis observed when UBE3A was absent. The central measured defect was a global decline in neuronal protein synthesis, detected through amino-acid labelling in mouse brain and cultured neurons, together with a reduction in polysome fractions.

Monosome fractions were not reduced. The pattern of lower polysomes and unchanged monosomes is important because it distinguishes aspects of translation affected by the model. Polysomes are complexes in which several ribosomes translate the same messenger RNA, whereas previous work cited by the researchers indicates that monosomes are predominantly located in neuronal processes and can synthesize proteins from at least a subset of transcripts.

Whether monosome-dependent translation remains preserved in Ube3a-null neurons requires further study. The investigators also found elevated free amino acids in Angelman mouse brains, a result consistent with the observed reduction in protein synthesis, although the amino acid result alone does not identify the mechanism responsible. Genetic reduction of Asns expression in the mouse model restored protein synthesis, corrected microcephaly and rescued many aberrant behavioural phenotypes.

The experiments included assessments of brain weight, movement and motor performance, open-field behaviour, marble burying, hindlimb clasping, and sleep and circadian activity. The reported finding was not that every behavioural or anatomical outcome returned to normal; rather, reducing ASNS improved many of the abnormal phenotypes while leaving some pathology unresolved. That partial rescue indicates that additional UBE3A substrates probably contribute to Angelman syndrome.

It also means that the results support ASNS as a major disease-relevant target without establishing it as the sole target. It was the only integrated stress response–associated gene found to be upregulated in Angelman mice and rescued through Asns modulation. HRI is involved in mitochondrial maintenance and protein synthesis, both closely connected to the findings in this study.

The researchers did not detect activation of the amino acid response pathway that they had originally expected to accompany the increased brain amino acids. It remains unresolved whether ASNS drives stress signalling through increased asparagine production or through another, unidentified activity. The study therefore establishes a mechanistic connection among UBE3A loss, excess ASNS, altered stress signalling and reduced protein synthesis, while leaving the precise route from ASNS activity to HRI unresolved.

The direction of ASNS change in Angelman syndrome contrasts with established asparagine synthetase deficiency. Homozygous loss of ASNS causes a rare congenital condition characterized by microcephaly, global developmental delay, hypotonia, spastic quadriplegia and intractable seizures. In the Angelman model investigated here, ASNS protein abundance increased rather than decreased, and genetic correction of the overabundance improved disease-related outcomes.

This does not mean that reduced ASNS is beneficial in every context. It indicates that insufficient and excessive ASNS can be associated with different neurological problems. Gain-of-function mutations in ASNS have not yet been established as causes of neurodevelopmental disorders, so the mouse results do not establish a new human genetic condition.

Several limitations qualify the study’s scope and therapeutic implications. The main rescue was achieved by genetically reducing Asns in mice, while the human evidence came from proteomic data and neurons derived from patient cell lines rather than a clinical treatment trial. The proteomic workflow also had restricted coverage.

Affinity purification of ubiquitinated proteins can underrepresent low-abundance or rapidly degraded substrates, and the researchers could not completely exclude competition between endogenous UBE3A and overexpressed UBE3A for binding to substrate proteins. The broader landscape of UBE3A substrates relevant to Angelman syndrome therefore remains incompletely defined. The incomplete behavioural and anatomical rescue also cautions against assuming that correcting one upstream imbalance will normalize the entire disorder.

Even with those limitations, the results identify ASNS, HRI and the wider integrated stress response as possible intervention points that could complement genetically targeted approaches. The work provides a testable rationale for investigating whether reducing excess ASNS activity or modifying stress signalling can relieve part of the abnormal protein-synthesis and growth program associated with UBE3A loss. The clearest conclusion from the present study is not that a therapy has been demonstrated, but that persistent neuronal stress signalling is a central feature of the Angelman mouse model: correcting one major molecular imbalance restored protein synthesis and improved microcephaly and many behavioural deficits, while the residual phenotypes show why more than one target may be needed.

Subject of Research: Neuronal stress signalling and asparagine synthetase in Angelman syndrome

Article Title: Persistent neuronal stress signalling underlies Angelman syndrome phenotypes

Article References: Kim, K.-S., Gardner, C., Cullen, A., Stelzer, J. A., Cho, K., Sharma, A., Nemera, M. T., Law, T., Naz, H., Zhao, G., Gabel, H. W., Patti, G. J., Musiek, E. S., Ahn, T.-H., & Yi, J. J. (2026). Persistent neuronal stress signalling underlies Angelman syndrome phenotypes. Nature. https://doi.org/10.1038/s41586-026-11165-4

Image Credits: AI Generated

DOI: 10.1038/s41586-026-11165-4

Keywords: Angelman syndrome, UBE3A, asparagine synthetase, ASNS, neuronal stress, protein synthesis, neurodevelopmental disorder, mouse model, human neurons, proteostasis, Persistent, neuronal