Iron Deficiency Reprograms Phosphorylation Signaling and Reduces O-GlcNAc Pathways in Neuronal Cells

Micronutrient sensing is critical for cellular growth and differentiation. Deficiencies in essential nutrients such as iron strongly affect neuronal cell development and may lead to defects in neuronal function that cannot be remedied by subsequent iron supplementation. To understand the adaptive intracellular responses to iron deficiency in neuronal cells, we developed and utilized a Stable Isotopic Labeling of Amino acids in Cell culture (SILAC)-based quantitative phosphoproteomics workflow. Our integrated approach was designed to comprehensively elucidate the changes in phosphorylation signaling under both acute and chronic iron-deficient cell models. In addition, we analyzed the differential cellular responses between iron deficiency and hypoxia (oxygen-deprived) in neuronal cells. Our analysis identified nearly 16,000 phosphorylation sites in HT-22 cells, a hippocampal-derived neuronal cell line, more than ten percent of which showed at least 2-fold changes in response to either hypoxia or acute/chronic iron deficiency. Bioinformatic analysis revealed that iron deficiency altered key metabolic and epigenetic pathways including the phosphorylation of proteins involved in iron sequestration, glutamate metabolism, and histone methylation. In particular, iron deficiency increased glutamine-fructose-6-phosphate transaminase (GFPT1) phosphorylation, which is a key enzyme in the glucosamine biosynthesis pathway and a target of 5' AMP-activated protein kinase (AMPK), leading to reduced GFPT1 enzymatic activity and consequently lower global O-GlcNAc modification in neuronal cells. Taken together, our analysis of the phosphoproteome dynamics in response to iron and oxygen deprivation demonstrated an adaptive cellular response by mounting post-translational modifications that are critical for intracellular signaling and epigenetic programming in neuronal cells.