Altered emotion regulation and low mood states in major depressive disorder (MDD) are thought to reflect altered corticolimbic structure and function in affected individuals, and involve the dorsolateral prefrontal cortex (DLPFC), the subgenual anterior cingulate cortex (sgACC) and the amygdala. Specifically, low GABA-related inhibition may underlie inadequate sensing and relaying of emotionally-salient stimuli by the amygdala and deficient integration of this relayed information by the sgACC with higher DLPFC processing. However, primary cellular and molecular evidence for these proposals are sparse. We have now identified a selective downregulation of somatostatin (SST), an inhibitory neuropeptide expressed in a subset of GABA neurons, in the DLPFC, sgACC and amygdala of subjects with MDD. Low SST was confirmed across cohorts, affected female subjects more robustly, and moderately correlated with the severity of the illness. At the microcircuitry level, SST GABA neurons target the distal dendrites of pyramidal neurons, but different subsets of SST neurons display different anatomical localizations and physiological properties, potentially mediating different information processing. Together, this lead us to hypothesize that low SST levels in specific cortical layers and amygdala nuclei are critical risk factors for MDD, and that additional factors determine the severity of the illness. Accordingly, we further hypothesize that, under challenging conditions, suboptimal SST function may trigger cellular and molecular maladaptive changes that lead to altered emotion regulation and low mood states, changes that will provide leads for the future development of novel therapeutics. Hence, to investigate the contribution of SST in mood regulation, we will first characterize the anatomical and microcircuitry specificity of changes in the human postmortem brains of MDD subjects (cortical layer &amygdala nuclei) (Aim 1). We will then test the """"""""low SST - risk factor"""""""" hypothesis in a rodent model, and predict that mice with low SST (heterozygous mutant) will display increased vulnerability to develop high anxiety-like/depressive-like behaviors (defined as """"""""emotionality"""""""") after unpredictable chronic mild stress (Aim 2). Finally, we will use mice expressing green fluorescent protein in the SST interneuron subtype(s), which most closely corresponds to the subtype affected in MDD, to investigate low SST- and stress-associated cell-specific maladaptive molecular changes (Aim 3). In summary, low SST in MDD provide a cellular and molecular lead to investigate mechanisms of the illness, and a potential molecular link between foremost hypotheses for biological disturbances in MDD (neural network dysfunction and reduced GABA-related function). However, SST also assumes several central and peripheral functions, and pharmacological manipulation has multiple (side-)effects, so it is essential to identify maladaptive molecular changes in SST GABA neurons, as potential mediators of the phenotype and as novel and potentially selective targets for the future investigation and development of novel therapeutics aimed at relieving the burden of MDD.
Major Depressive Disorder (MDD) is a severe mental illness, the leading cause of disability and of years of productivity lost worldwide in men and women, and a significant contributor to the development and progression of systemic and organ diseases. We have now identified in the human postmortem brain of depressed subjects, a specific downregulation in somatostatin (SST), a signaling molecule, which affects three brain regions known to be critical in the illness. The characterization of the cellular context of these changes and of their potential causal role in MDD, using both human postmortem samples and a validated rodent model, will provide new insight into mechanisms of the disease and reveal potential selective targets for novel therapeutic strategies aimed at relieving the burden of MDD.
|Begum, Ferdouse; Sharker, Monir H; Sherman, Stephanie L et al. (2016) Regionally Smoothed Meta-Analysis Methods for GWAS Datasets. Genet Epidemiol 40:154-60|
|Oh, Hyunjung; Lewis, David A; Sibille, Etienne (2016) The Role of BDNF in Age-Dependent Changes of Excitatory and Inhibitory Synaptic Markers in the Human Prefrontal Cortex. Neuropsychopharmacology 41:3080-3091|
|Douillard-Guilloux, Gaelle; Lewis, David; Seney, Marianne L et al. (2016) Decrease in somatostatin-positive cell density in the amygdala of females with major depression. Depress Anxiety :|
|Chen, Cho-Yi; Logan, Ryan W; Ma, Tianzhou et al. (2016) Effects of aging on circadian patterns of gene expression in the human prefrontal cortex. Proc Natl Acad Sci U S A 113:206-11|
|McKinney, Brandon C; Lin, Chien-Wei; Oh, Hyunjung et al. (2015) Hypermethylation of BDNF and SST Genes in the Orbital Frontal Cortex of Older Individuals: A Putative Mechanism for Declining Gene Expression with Age. Neuropsychopharmacology 40:2604-13|
|Seney, Marianne L; Tripp, Adam; McCune, Samuel et al. (2015) Laminar and cellular analyses of reduced somatostatin gene expression in the subgenual anterior cingulate cortex in major depression. Neurobiol Dis 73:213-9|
|Lin, L C; Sibille, E (2015) Somatostatin, neuronal vulnerability and behavioral emotionality. Mol Psychiatry 20:377-87|
|Ding, Ying; Chang, Lun-Ching; Wang, Xingbin et al. (2015) Molecular and Genetic Characterization of Depression: Overlap with other Psychiatric Disorders and Aging. Mol Neuropsychiatry 1:1-12|
|Lin, L C; Sibille, E (2015) Transcriptome changes induced by chronic psychosocial/environmental or neuroendocrine stressors reveal a selective cellular vulnerability of cortical somatostatin (SST) neurons, compared with pyramidal (PYR) neurons. Mol Psychiatry 20:285|
|Guilloux, Jean-Philippe; Bassi, Sabrina; Ding, Ying et al. (2015) Testing the predictive value of peripheral gene expression for nonremission following citalopram treatment for major depression. Neuropsychopharmacology 40:701-10|
Showing the most recent 10 out of 43 publications