ALG13 deficiency impairs cortical development via suppression of the PI3K/AKT/mTOR pathway.

ALG13 mutations cause congenital disorders of glycosylation and neurodevelopmental deficits, but how asparagine-linked glycosylation 13 (ALG13) deficiency impairs brain development remains unclear. This study aimed to elucidate the underlying mechanisms in Alg13 knockout (ALG13KO) mice. We first confirmed neurodevelopmental delays and abnormal cortical neuron distribution in ALG13KO mice. Quantitative proteomic analysis of the postnatal day 7 cerebral cortex revealed widespread protein abundance changes. Subsequent bioinformatic and protein-protein interaction net-work analyses pinpointed the phosphatidylinositol-3-kinase (PI3K)/protein kinase B (AKT)/ mammalian target of rapamycin (mTOR) pathway. Pathway as a central hub. Parallel reaction monitoring validated the downregulation of key upstream regulators Laminin γ-1 (LAMC1), Focal Adhesion Kinase (FAK), and Integrin α6 (ITGA6). Western blot confirmed the inhibition of PI3K/AKT/mTOR phosphorylation. Our findings demonstrate that ALG13 deficiency disrupts cortical development, likely via suppression of the PI3K/AKT/mTOR pathway through the LAMC1-ITGA6-FAK axis. This study reveals a critical, early-developmental suppression of mTOR signaling, contrasting with its reported hyperactivation in adult epileptic ALG13KO mice, highlighting a stage-dependent role. SIGNIFICANCE: This study provides the first proteomic evidence of early postnatal suppression of the PI3K/AKT/mTOR pathway in a mouse model of ALG13-congenital disorder of glycosylation (ALG13-CDG). By integrating unbiased quantitative proteomics, targeted validation, and phenotyping, we identify the LAMC1-ITGA6-FAK axis as a novel upstream regulator mediating this suppression, linking a glycosylation defect directly to a key neurodevelopmental signaling hub. Importantly, our finding contrasts with reported mTOR hyperactivation in adult epileptic mice, revealing a critical, previously unrecognized stage-dependent duality of mTOR signaling in ALG13-CDG pathophysiology. This work not only advances the mechanistic understanding of neurodevelopmental deficits in CDG but also showcases the power of a focused, early time-point proteomic strategy to disentangle primary developmental pathophysiology from secondary disease states.