Role of the thioredoxin system in chronic corticosterone treatment- impaired neuronal differentiation and degeneration

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Llanes Cuesta, Maria Alejandra
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During the stress response, the hypothalamic-pituitary-adrenal (HPA) axis releases glucocorticoids into the bloodstream, targeting different organs including the brain. Chronic stress is a major risk factor for depression. Thioredoxin (Trx) is an oxidoreductase that reverses protein cysteine thiol oxidation, inhibits apoptosis signal-regulating kinase 1 (ASK1) and has been shown to promote cAMP response element-binding protein (CREB) activation. Trx reductase (TrxR) maintains Trx in a reduced state, while Trx interacting protein (Txnip) acts as an endogenous Trx inhibitor. Studies from our lab showed that chronic stress and chronic corticosterone (CORT) treatment upregulated Txnip and induced oxidative damage in cultured mouse neurons and mouse brain, suggesting that Trx system mediates CORT-induced neuronal damage. The objective of this work is to investigate the role of Trx system in chronic CORT-impaired neuronal differentiation and CORT-enhanced neurodegeneration. First, we found that Trx and TrxR protein levels increased during differentiation, while Txnip increased during neurodegeneration of primary mouse cortical neurons. Blocking Trx with CRISPR/Cas9 or the Trx inhibitor PX12 reduced neurite outgrowth. PX12 treatment also reduced the expression of synaptic proteins vGLUT1 and PSD95. Second, we found that CREB phosphorylation increased during neuronal differentiation and that blocking Trx reduced CREB phosphorylation in primary cortical neurons. In SH-SY5Y cells, we found that H2O2 reduced CREB phosphorylation and promoted CREB cysteine oxidation, while treatment with Trx mimetic peptide CB3 reversed H2O2 effect. We also found in primary mouse cortical neurons that ASK1 phosphorylation was increased during neurodegeneration and that PX12 increased ASK1 phosphorylation. Third, we found that CORT treatment elevated Txnip protein levels, reduced CREB phosphorylation, enhanced ASK1 phosphorylation, and impaired neurite outgrowth in primary neurons. Knocking down Txnip prevented CORT-impaired neurite outgrowth. Fourth, we found that chronic CORT injections induced depressive-like behaviors in mice, which was reversed by knocking down Txnip in the frontal cortex. Our findings suggest that Trx can facilitate neuronal differentiation by preserving the cellular redox balance, inhibiting CREB cysteine oxidation and maintaining CREB activation. Trx can also inhibit ASK1 apoptotic signaling and produce a neuroprotective effect. Chronic CORT treatment can upregulate Txnip, which may further inhibit Trx activity, inhibiting neurite outgrowth and promoting depressive-like behaviors in mice.
thioredoxin system, neurite outgrowth, neurodegeneration, corticosterone, depressive-like behaviors