Diurnal rhythms in gene expression in the prefrontal cortex in schizophrenia

Genome-wide studies of time of day in the brain: Design and analysis

Transcriptome profiling at different times of day is powerful for studying circadian regulation in model organisms and humans. To date, 24 h profiles from many tissue types suggest that about half of all genes are circadian-expressed somewhere in the body. However, few of these studies focused on the brain. Thus, despite known links between circadian disruption and neurological disease, we have virtually no mechanistic understanding. In the coming decade, we expect more genome-wide studies of time of day in different brain diseases, regions, and cell types. We expect just as many different approaches to the design and analysis of these studies. This review considers key principles of circadian tran scriptomics, with the goal of maximizing utility and reproducibility of future studies in the nervous system.

Circadian Rhythms of Perineuronal Net Composition

Perineuronal nets (PNNs) are extracellular matrix (ECM) structures that envelop neurons and regulate synaptic functions. Long thought to be stable structures, PNNs have been recently shown to respond dynamically during learning, potentially regulating the formation of new synapses. We postulated that PNNs vary during sleep, a period of active synaptic modification. Notably, PNN components are cleaved by matrix proteases such as the protease cathepsin-S. This protease is diurnally expressed in the mouse cortex, coinciding with dendritic spine density rhythms. Thus, cathepsin-S may contribute to PNN remodeling during sleep, mediating synaptic reorganization. These studies were designed to test the hypothesis that PNN numbers vary in a diurnal manner in the rodent and human brain, as well as in a circadian manner in the rodent brain, and that these rhythms are disrupted by sleep deprivation. In mice, we observed diurnal and circadian rhythms of PNNs labeled with the lectin Wisteria floribunda agglutinin (WFA+ PNNs) in several brain regions involved in emotional memory processing. Sleep deprivation prevented the daytime decrease of WFA+ PNNs and enhances fear memory extinction. Diurnal rhythms of cathepsin-S expression in microglia were observed in the same brain regions, opposite to PNN rhythms. Finally, incubation of mouse sections with cathepsin-S eliminated PNN labeling. In humans, WFA+ PNNs showed a diurnal rhythm in the amygdala and thalamic reticular nucleus (TRN). Our results demonstrate that PNNs vary in a circadian manner and this is disrupted by sleep deprivation. We suggest that rhythmic modification of PNNs may contribute to memory consolidation during sleep.

Sleep and Microbiome in Psychiatric Diseases

Objectives: Disturbances in the gut–brain barrier play an essential role in the development of mental disorders. There is considerable evidence showing that the gut microbiome not only affects digestive, metabolic and immune functions of the host but also regulates host sleep and mental states through the microbiota–gut–brain axis. The present review summarizes the role of the gut microbiome in the context of circadian rhythms, nutrition and sleep in psychiatric disorders. Methods: A PubMed search (studies published between April 2015–April 2020) was conducted with the keywords: “sleep, microbiome and psychiatry”; “sleep, microbiome and depression”; “sleep, microbiome and bipolar disorder”, “sleep, microbiome and schizophrenia”, “sleep, microbiome and anorexia nervosa”, “sleep, microbiome and substance use disorder”, “sleep, microbiome and anxiety”; “clock gene expression and microbiome”, “clock gene expression and nutrition”. Only studies investigating the relationship between sleep and microbiome in psychiatric patients were included in the review. Results: Search results yielded two cross-sectional studies analyzing sleep and gut microbiome in 154 individuals with bipolar disorder and one interventional study analyzing the effect of fecal microbiota transplantation in 17 individuals with irritable bowel syndrome on sleep. In patients with bipolar disorder, Faecalibacterium was significantly associated with improved sleep quality scores and a significant correlation between Lactobacillus counts and sleep. Conclusion: Translational research on this important field is limited and further investigation of the bidirectional pathways on sleep and the gut microbiome in mood disorders is warranted.

Dopamine Receptor Subtypes, Physiology and Pharmacology: New Ligands and Concepts in Schizophrenia

Dopamine receptors are widely distributed within the brain where they play critical modulator roles on motor functions, motivation and drive, as well as cognition. The identification of five genes coding for different dopamine receptor subtypes, pharmacologically grouped as D1- (D1 and D5) or D2-like (D2S, D2L, D3, and D4) has allowed the demonstration of differential receptor function in specific neurocircuits. Recent observation on dopamine receptor signaling point at dopamine-glutamate-NMDA neurobiology as the most relevant in schizophrenia and for the development of new therapies. Progress in the chemistry of D1- and D2-like receptor ligands (agonists, antagonists, and partial agonists) has provided more selective compounds possibly able to target the dopamine receptors homo and heterodimers and address different schizophrenia symptoms. Moreover, an extensive evaluation of the functional effect of these agents on dopamine receptor coupling and intracellular signaling highlights important differences that could also result in highly differentiated clinical pharmacology. The review summarizes the recent advances in the field, addressing the relevance of emerging new targets in schizophrenia in particular in relation to the dopamine - glutamate NMDA systems interactions.

Disrupted Sleep and Circadian Rhythms in Schizophrenia and Their Interaction With Dopamine Signaling

Sleep and circadian rhythm disruption (SCRD) is a common feature of schizophrenia, and is associated with symptom severity and patient quality of life. It is commonly manifested as disturbances to the sleep/wake cycle, with sleep abnormalities occurring in up to 80% of patients, making it one of the most common symptoms of this disorder. Severe circadian misalignment has also been reported, including non-24 h periods and phase advances and delays. In parallel, there are alterations to physiological circadian parameters such as body temperature and rhythmic hormone production. At the molecular level, alterations in the rhythmic expression of core clock genes indicate a dysfunctional circadian clock. Furthermore, genetic association studies have demonstrated that mutations in several clock genes are associated with a higher risk of schizophrenia. Collectively, the evidence strongly suggests that sleep and circadian disruption is not only a symptom of schizophrenia but also plays an important causal role in this disorder. The alterations in dopamine signaling that occur in schizophrenia are likely to be central to this role. Dopamine is well-documented to be involved in the regulation of the sleep/wake cycle, in which it acts to promote wakefulness, such that elevated dopamine levels can disturb sleep. There is also evidence for the influence of dopamine on the circadian clock, such as through entrainment of the master clock in the suprachiasmatic nuclei (SCN), and dopamine signaling itself is under circadian control. Therefore dopamine is closely linked with sleep and the circadian system; it appears that they have a complex, bidirectional relationship in the pathogenesis of schizophrenia, such that disturbances to one exacerbate abnormalities in the other. This review will provide an overview of the evidence for a role of SCRD in schizophrenia, and examine the interplay of this with altered dopamine signaling. We will assess the evidence to suggest common underlying mechanisms in the regulation of sleep/circadian rhythms and the pathophysiology of schizophrenia. Improvements in sleep are associated with improvements in symptoms, along with quality of life measures such as cognitive ability and employability. Therefore the circadian system holds valuable potential as a new therapeutic target for this disorder.

Are Circadian Disturbances a Core Pathophysiological Component of Schizophrenia?

Schizophrenia is a multifactorial disorder caused by a combination of genetic variations and exposure to environmental insults. Sleep and circadian rhythm disturbances are a prominent and ubiquitous feature of many psychiatric disorders, including schizophrenia. There is growing interest in uncovering the mechanistic link between schizophrenia and circadian rhythms, which may directly affect disorder outcomes. In this review, we explore the interaction between schizophrenia and circadian rhythms from 2 complementary angles. First, we review evidence that sleep and circadian rhythm disturbances constitute a fundamental component of schizophrenia, as supported by both human studies and animal models with genetic mutations related to schizophrenia. Second, we discuss the idea that circadian rhythm disruption interacts with existing risk factors for schizophrenia to promote schizophrenia-relevant behavioral and neurobiological abnormalities. Understanding the mechanistic link between schizophrenia and circadian rhythms will have implications for mitigating risk to the disorder and informing the development of circadian-based therapies.

Increased interleukin 18 activity in adolescents with early-onset psychosis is associated with cortisol and depressive symptoms

OBJECTIVE

Evidence indicates that the pathophysiology of adult psychosis involves immune dysregulation, but its associations with stress are often not considered. The inflammatory cytokine interleukin (IL)-18, which is elevated in adult schizophrenia, is suggested to be sensitive to stress. We compared the associations of IL-18 with cortisol and clinical variables in adolescents with early-onset psychosis (EOP) aged 12-18 years and age-matched healthy controls (HC).

METHOD

We measured serum IL-18, IL-18 binding protein (IL-18BP), IL-18 receptor accessory protein (IL-18RAP), IL-18 receptor 1 (IL-18R1) and cortisol, and calculated the IL-18/IL-18BP ratio in patients (n = 31) and HC (n = 60). Psychotic symptoms were assessed using the Positive and Negative Syndrome Scale and depressive symptoms by the Mood and Feelings Questionnaire-Child version (MFQ-C). Bivariate correlation analysis was used to explore relationships between IL-18/IL-18BP ratio and cortisol, depression and other clinical characteristics. Hierarchical multiple linear regression analysis was used to assess their individual contributions to the variance of the IL-18/IL-18BP ratio.

RESULTS

Patients had significantly higher IL-18 levels and IL-18/IL-18BP ratios than HC, but similar IL-18BP, IL-18RAP and IL-18R1. Both cortisol (R² change = 0.05) and the MFQ-C score (R² change = 0.09) contributed significantly to the variance in IL-18/IL-18BP ratios after controlling for confounders.

CONCLUSION

We found increased IL-18 system activity in adolescents with EOP. Cortisol and depressive symptoms each contributed to the variance in the IL-18/IL-18BP ratio. Our findings support activation of inflammatory pathways in adolescent psychosis and suggest interactions between stress, inflammation and depressive symptoms in EOP.

Circadian rhythm disruption and mental health

Circadian rhythms are internal manifestations of the solar day that permit adaptations to predictable environmental temporal changes. These ~24-h rhythms are controlled by molecular clockworks within the brain that are reset daily to precisely 24 h by exposure to the light-dark cycle. Information from the master clock in the mammalian hypothalamus conveys temporal information to the entire body via humoral and neural communication. A bidirectional relationship exists between mood disorders and circadian rhythms. Mood disorders are often associated with disrupted circadian clock-controlled responses, such as sleep and cortisol secretion, whereas disruption of circadian rhythms via jet lag, night-shift work, or exposure to artificial light at night, can precipitate or exacerbate affective symptoms in susceptible individuals. Evidence suggests strong associations between circadian rhythms and mental health, but only recently have studies begun to discover the direct interactions between the circadian system and mood regulation. This review provides an overview of disrupted circadian rhythms and the relationship to behavioral health and psychiatry. The focus of this review is delineating the role of disruption of circadian rhythms on mood disorders using human night shift studies, as well as jet lag studies to identify links. We also review animal models of disrupted circadian rhythms on affective responses. Lastly, we propose low-cost behavioral and lifestyle changes to improve circadian rhythms and presumably behavioral health.

Alternative rhythms in schizophrenia

A distinct set of rhythmically expressed genes related to mitochondrial function is identified in the brains of patients with schizophrenia.