Identification of Thioredoxin1 interacting proteins in neuronal cytoskeletal organization during autophagy

Thioredoxin1 (Trx1) is a major cytoplasmic thiol oxidoreductase protein involved in redox signaling. This function is rendered by a rapid electron transfer reaction during which Trx1 reduces its substrate and itself becomes oxidized. In this reaction, Trx1 forms a transient disulfide bond with the substrate which is unstable and therefore identification of Trx1 substrates is technically challenging. This process maintains the cellular proteins in a balanced redox state and ensures cellular homeostasis. Trx1 levels are reduced in some neurodegenerative diseases; therefore, understanding the interactions between Trx1 and its substrates in neurons could have significant therapeutic implications. We utilized a transgenic mouse model expressing a Flag-tagged mutant form of Trx1 that can form stable disulfide bonds with its substrates allowing identification of the Trx1 interacting proteins. The involvement of Trx1 has been suggested in autophagy, we aimed to investigate Trx1 substrate after pharmacologic induction of autophagy in primary hippocampal neurons. Treatment of primary neurons by rapamycin, a standard autophagy inducer, caused significant reduction of neurite outgrowth and alterations in the cytoskeleton. Through immunoprecipitation and mass spectrometry, we have identified 77 Trx1 interacting proteins which were associated with a wide range of cellular functions including a major impact on cytoskeletal organization. The results were confirmed in Trx1 knocked-down cells and in nucleofected primary neurons. Our study suggests a novel role for Trx1 in regulation of neuronal cytoskeleton organization, marking the first investigation of Trx1-interacting proteins in primary neurons and confirming the multifaceted role of Trx1 in physiological and pathological states.