Chronic stress is a major risk factor in the aetiology of several psychiatric disorders, including depression, which affects around 5.7% of the adult population worldwide -around 332 million people- according to the World Health Organization. Despite the availability of pharmacological treatments, therapeutic efficacy remains limited. Nearly two thirds of patients fail to respond adequately to the first antidepressant prescribed, and among these, approximately 30% are considered treatment-resistant, showing insufficient response to two or more antidepressant trials. Given the marked heterogeneity in clinical manifestations and treatment responses, multiple components of its pathophysiology have been extensively studied in an effort to improve disease management. In this context, recent studies highlight the key role of astrocytes in stress-related disorders. Beyond providing metabolic support to neurons, astrocytes actively regulate neuronal function by maintaining neurotransmitter homeostasis, for example through the clearance of excess glutamate -known to be aberrantly elevated in depression- via specific transporters. In addition, the astrocyte–neuron lactate shuttle supplies lactate as an energy substrate to active neurons, while it can also act as a signalling molecule with reported antidepressant-like effects. Consistent with this, postmortem studies of patients with depression report reduced astrocyte density and decreased expression of astrocytic markers, suggesting that astrocyte dysfunction is implicated in disease pathology. However, the contribution of astrocytic metabolic impairment to stress-induced behavioural phenotypes remains incompletely understood.
The aim of this study is to evaluate the effects of chronic mild stress on astrocytic metabolic pathways. To this end, we employed a 10-week Unpredictable Chronic Mild Stress (UCMS) protocol consisting of seven mild stressors applied once a day for 2 hours in random order and at variable times. Control (n=8) and UCMS-exposed (n=12) C57BL/6J male mice were phenotyped longitudinally using body weight monitoring, nest building assessment, sucrose preference and elevated plus maze tests. All animal procedures were performed according to the UK Animal Scientific Procedures Act 1986, and the Animal Welfare and Ethics Review Board, University of Bristol (PPL PP5495972). Interestingly, UCMS-exposed animals showed a significant reduction in nest building behaviour (-23%) and body weight gain (-24%) compared to controls. However, rather than focusing on group-level behaviour, we integrated behavioural and physiological measures across tests by calculating a global z-score for each animal. This approach enabled the identification of extreme phenotypes, from which 4 mice of each group displaying the most representative control or UCMS-exposed profiles were selected for further molecular analyses. Blood and limbic brain regions were collected 24 hours after the end of the UCMS paradigm for corticosterone quantification and bulk RNA sequencing, with subsequent identification of astrocyte-enriched transcripts.
Our experimental approach combines behavioural phenotyping–based animal selection with transcriptomic profiling to identify stress-related transcriptional alterations in astrocytic metabolic pathways, with particular emphasis on genes previously reported to be involved in astrocyte metabolism and stress response. Together, this work seeks to refine the relationship between chronic stress, behavioural phenotype expression, and astrocyte metabolic dysfunction, thus providing insights into glial contributions to stress-related neuropsychiatric disorders.