MULTIOMIC PROFILING OF RAPID ANTIDEPRESSANT MECHANISMS IN A RAT MODEL OF DEPRESSION

Abstract Background The stress response is a physiological event finely orchestrated by the brain and aimed at restoring the homeostasis lost in case of environmental changes perceived as dangerous for survival. Most subjects successfully activate an adaptive stress response however, when the exposure to stressful stimuli is prolonged over time or overwhelming, some individuals may fail in activating coping strategies. This condition refers to stress vulnerability and increases the risk of developing systemic diseases, particularly psychiatric disorders. Accordingly, stress is considered a key risk factor in the onset of depression, and most preclinical models of psychopathologies are based on the exposure of animals to validated stress protocols [1]. Chronic Mild Stress (CMS) is one of the most widely used animal models of depression to study both etiopathogenetic and antidepressant mechanisms. Recently, the NMDA receptor antagonist ketamine has emerged as the first rapid-acting antidepressant drug effective in patients with treatment resistant depression (TRD) [2]. The study of the mechanisms underlying ketamine antidepressant response are crucial to identify the molecular underpinnings of the rapid antidepressant effect, thus making a step forward in the development of novel antidepressants. Aims & Objectives The aim of the study was to draw a multiomic picture of rapid antidepressant mechanisms in the hippocampus of an animal model of depression. Methods Male rats were exposed to CMS for 5 weeks, sucrose preference test was used to measure the anhedonic phenotype and acute subanesthetic ketamine (10 mg/kg) was intraperitoneally injected 24 h before sacrifice [3]. Sucrose preference test was used to classify the rats stress resilient and vulnerable and ketamine responder/non-responder. The hippocampi were collected to obtain DNA, RNA, and protein extracts (both total extract and synaptic terminals). Genome-Wide DNA methylation was assessed by RBBS, transcriptional changes were evaluated by RNA-seq analysis, and DIA-PASEF label free analysis was used for proteomics. Bioinformatic enrichment analysis was performed with WebGestaltR v.4.0.3 and the Gene Set Enrichment Analysis (GSEA) method. Results Starting from 3 weeks of CMS, stress vulnerable rats developed depressive-like behavior. Acute ketamine induced antidepressant-like behavior in most of the animals but some of them (about 30%) were non-responders remaining anhedonic. Our omic analyses revealed several effectors differentially regulated among the groups (FDR<0.05). Enrichment analysis showed differences between control and vulnerable rats and between ketamine responders and non- responders particularly in pathways involved in synaptic plasticity. Discussion & Conclusion Overall, our results highlighted several pathways affected by stress and potentially involved in the rapid antidepressant effect of ketamine. Future studies will better elucidate how these changes may contribute to ketamine antidepressant mechanism of action and resistance. References 1. Sanacora G, Yan Z, Popoli M. The stressed synapse 2.0: pathophysiological mechanisms in stress- related neuropsychiatric disorders. Nat Rev Neurosci. 2022;23:86–103. 2. Kadriu B, Musazzi L, Henter ID, Graves M, Popoli M, Zarate CA. Glutamatergic Neurotransmission: Pathway to Developing Novel Rapid- Acting Antidepressant Treatments. Int J Neuropsychopharmacol. 2019;22:119–135. 3. Derosa S, Misztak P, Mingardi J, Mazzini G, Mü ller HK, Musazzi L. Changes in neurotrophic signaling pathways in brain areas of the chronic mild stress rat model of depression as a signature of ketamine fast antidepressant response/non-response. Prog Neuropsychopharmacol Biol Psychiatry. 2023 Oct 2;128:110871. doi: 10.1016/j.pnpbp.2023.110871.