GLS hyperactivity causes glutamate excess, infantile cataract and profound developmental delay

Area of Science:

• Biochemistry
• Genetics
• Neuroscience

Background:

• Loss-of-function mutations in glutaminase (GLS) and glutamine synthetase (GS) disrupt glutamate homeostasis, causing neonatal encephalopathy.
• Glutamate is a key neurotransmitter, and its dysregulation can lead to severe neurological disorders.

Purpose of the Study:

• To investigate the pathogenicity of a de novo Ser482Cys gain-of-function variant in GLS.
• To elucidate the molecular mechanisms underlying the observed clinical phenotypes: profound developmental delay and infantile cataract.

Main Methods:

• Functional analysis of the Ser482Cys-GLS variant in vitro.
• Analysis of GLS expression and its counteracting enzyme GS.
• Measurement of glutamate and glutamine levels in patient-derived samples (urine, fibroblasts) and brain tissue using magnetic resonance spectroscopic imaging.
• Zebrafish model to study cataract formation and test therapeutic interventions.

Main Results:

• The Ser482Cys variant causes GLS hyperactivity, leading to compensatory downregulation of GLS and upregulation of GS.
• Elevated glutamate and decreased glutamine levels were observed in patient samples and brain tissue.
• High brain glutamate concentrations correlate with developmental delay.
• The variant induced oxidative stress and cataract formation in zebrafish, which was reversible with GLS inhibition.

Conclusions:

• The Ser482Cys-GLS variant represents a novel inborn error of glutamate metabolism.
• Balanced GLS activity is crucial for maintaining glutamate homeostasis and preventing neurodevelopmental and ocular complications.
• Targeting GLS may offer therapeutic potential for conditions associated with GLS hyperactivity.