Assessing scale and predictive diversity in models for single-cell transcriptomics based on Geneformer.

Major depressive disorder (MDD), characterized by enduring low mood, anhedonia and loss of energy, is a prevalent, severely disabling psychiatric disorder [,]. Although conventional monoamine antidepressants are commonly used, they have notable limitations, including delayed onset of efficacy and treatment resistance in approximately one-third of patients []. These limitations underscore the urgency of unraveling the pathophysiological mechanisms of MDD and discovering new therapeutic targets beyond the monoaminergic system. Accumulating evidence implicates ferroptosis in the pathophysiology of depression [,]. Ferroptosis is defined as a distinct form of regulated, iron-dependent cell death driven by lipid peroxidation []. It fundamentally differs from other types of cell death, such as apoptosis, autophagy and pyroptosis, in terms of its physiological, morphological and genetic features []. Dysregulation of iron and lipid metabolism has been observed in patients with depression [,]. Furthermore, our previous study demonstrated the downregulation of the expression of the central ferroptosis regulators glutathione peroxidase 4 (GPX4) and the nuclear factor erythroid 2-related factor 2 (NRF2) in mice subjected to CSDS, supporting the involvement of ferroptosis in depression-related models []. In addition, pharmacological inhibition of ferroptosis with ferrostatin-1 (Fer-1) ameliorated behavioral deficits induced by chronic unpredictable mild stress (CUMS) []. The hippocampus (Hip), a brain area vital for emotion regulation, is particularly vulnerable to ferroptosis []. Quantitative proteomics revealed that protein alterations in the Hip of CUMS mice were primarily enriched in ferroptosis-associated pathways []. Moreover, ferroptosis has intricate interactions with the pathological mechanisms of depression, suggesting that it may serve as a critical node in the pathophysiological network underlying MDD []. Therefore, elucidating the mechanisms that govern ferroptosis may provide novel therapeutic strategies for depression. Recent studies have linked endoplasmic reticulum (ER) stress, triggered by the accumulation of misfolded proteins, to ferroptosis []. To promote ER homeostasis, cells respond by triggering the unfolded protein response (UPR). However, under excessive or prolonged stress, the UPR is overwhelmed and shifts to a maladaptive state, ultimately triggering cell death []. The UPR is orchestrated by three sensors: protein kinase RNA-like ER kinase (PERK), activating transcription factor 6 (ATF6) and inositol-requiring enzyme 1α (IRE1α) []. These sensors detect ER stress and activate adaptive UPR programs that promote protein folding and reduce protein translation. Activated PERK phosphorylates eIF2α, leading to the upregulation of activating transcription factor 4 (ATF4) expression. Activated IRE1α mediates X-box binding protein 1 (XBP1) mRNA splicing, while ATF6 promotes ER chaperone-related adaptive responses []. In addition, UPR signaling has been implicated in the regulation of ferroptosis during ER stress []. Notably, the PERK/ATF4 signaling arm can promote ferroptosis through the transcriptional upregulation of glutathione-specific γ-glutamylcyclotransferase 1 (CHAC1), a downstream effector of ATF4 that promotes ferroptosis by depleting intracellular glutathione (GSH) and thereby impairing GPX4-mediated detoxification of lipid peroxides [,].