Sooyoung Chung

Adrenal peripheral clock controls the autonomous circadian rhythm of glucocorticoid by causing rhythmic steroid production

Glucocorticoid (GC) is an adrenal steroid with diverse physiological effects. It undergoes a robust daily oscillation, which has been thought to be driven by the master circadian clock in the suprachiasmatic nucleus of the hypothalamus via the hypothalamus–pituitary–adrenal axis. However, we show that the adrenal gland has its own clock and that the peripheral clockwork is tightly linked to steroidogenesis by the steroidogenic acute regulatory protein. Examination of mice with adrenal-specific knockdown of the canonical clock protein BMAL1 reveals that the adrenal clock machinery is required for circadian GC production. Furthermore, behavioral rhythmicity is drastically affected in these animals, together with altered expression of Period1, but not Period2, in several peripheral organs. We conclude that the adrenal peripheral clock plays an essential role in harmonizing the mammalian circadian timing system by generating a robust circadian GC rhythm.

Maternal Stress Produces Learning Deficits Associated with Impairment of NMDA Receptor-Mediated Synaptic Plasticity

Stress in adulthood can have a profound effect on physiology and behavior, but the extent to which prolonged maternal stress affects the brain function of offspring when they are adult remains primarily unknown. In the present work, chronic immobilization stress to pregnant mice affected fetal growth and development. When pups born from stressed mice were reared to adulthood in an environment identical to that of nonstressed controls, several physiological parameters were essentially unaltered. However, spatial learning and memory was significantly impaired in the maternally stressed offspring in adulthood. Furthermore, electrophysiological examination revealed a significant reduction in NMDA receptor-mediated long-term potentiation in the CA1 area of hippocampal slices. Subsequent biochemical analysis demonstrated a substantial decrease in NR1 and NR2B subunits of the NMDA receptor in synapses of the hippocampus, and the interaction between these two subunits appeared to be reduced. These results suggest that prolonged maternal stress leads to long-lasting malfunction of the hippocampus, which extends to and is manifested in adulthood.

Circadian rhythm of adrenal glucocorticoid: its regulation and clinical implications.

Glucocorticoid (GC) is an adrenal steroid hormone that controls a variety of physiological processes such as metabolism, immune response, cardiovascular activity, and brain function. In addition to GC induction in response to stress, even in relatively undisturbed states its circulating level is subjected to a robust daily variation with a peak around the onset of the active period of the day. It has long been believed that the synthesis and secretion of GC are primarily regulated by the hypothalamus-pituitary-adrenal (HPA) neuroendocrine axis. However, recent chronobiological research strongly supports the idea that multiple regulatory mechanisms along with the classical HPA neuroendocrine axis underlie the diurnal rhythm of circulating GC. Most notably, recent studies demonstrate that the molecular circadian clockwork is heavily involved in the daily GC rhythm at multiple levels. The daily GC rhythm is implicated in various human diseases accompanied by abnormal GC levels. Patients with such diseases frequently show a blunted GC rhythmicity and, more importantly, circadian rhythm-related symptoms. In this review, we focus on recent advances in the understanding of the circadian regulation of adrenal GC and its implications in human health and disease.

Impact of Circadian Nuclear Receptor REV-ERBα on Midbrain Dopamine Production and Mood Regulation

The circadian nature of mood and its dysfunction in affective disorders is well recognized, but the underlying molecular mechanisms are still unclear. Here, we show that the circadian nuclear receptor REV-ERBα, which is associated with bipolar disorder, impacts midbrain dopamine production and mood-related behavior in mice. Genetic deletion of the Rev-erbα gene or pharmacological inhibition of REV-ERBα activity in the ventral midbrain induced mania-like behavior in association with a central hyperdopaminergic state. Also, REV-ERBα repressed tyrosine hydroxylase (TH) gene transcription via competition with nuclear receptor-related 1 protein (NURR1), another nuclear receptor crucial for dopaminergic neuronal function, thereby driving circadian TH expression through a target-dependent antagonistic mechanism. In conclusion, we identified a molecular connection between the circadian timing system and mood regulation, suggesting that REV-ERBα could be targeting in the treatment of circadian rhythm-related affective disorders.

The adrenal peripheral clock: glucocorticoid and the circadian timing system.

The mammalian circadian timing system is organized in a hierarchy, with the master clock residing in the suprachiasmatic nucleus (SCN) of the hypothalamus and subsidiary peripheral clocks in other brain regions as well as peripheral tissues. Since the local oscillators in most cells contain a similar molecular makeup to that in the central pacemaker, determining the role of the peripheral clocks in the regulation of rhythmic physiology and behavior is an important issue. Glucocorticoids (GCs) are a class of multi-functional adrenal steroid hormones, which exhibit a robust circadian rhythm, with a peak linked with the onset of the daily activity phase. It has long been believed that the production and secretion of GC is primarily governed through the hypothalamus-pituitary-adrenal (HPA) neuroendocrine axis in mammals. Growing evidence, however, strongly supports the notion that the periodicity of GC involves the integrated activity of multiple regulatory mechanisms related to circadian timing system along with the classical HPA neuroendocrine regulation. The adrenal-intrinsic oscillator as well as the central pacemaker plays a pivotal role in its rhythmicity. GC influences numerous biological processes, such as metabolic, cardiovascular, immune and even higher brain functions, and also acts as a resetting signal for the ubiquitous peripheral clocks, suggesting its importance in harmonizing circadian physiology and behavior. In this review, we will therefore focus on the recent advances in our understanding of the circadian regulation of adrenal GC and its functional relevance.

Adrenal peripheral oscillator in generating the circadian glucocorticoid rhythm

The mammalian circadian timing system is organized into hierarchical structures with a central clock in the suprachiasmatic nucleus (SCN) and subsidiary peripheral oscillators. After the discovery of the local clockwork in peripheral organs and tissues, which have a molecular makeup similar to the central pacemaker SCN, uncovering the roles of the peripheral clock in the rhythmic physiology has been an emerging goal in chronobiology. Glucocorticoid (GC) is a multifunctional adrenal steroid hormone that shows a robust circadian rhythm. The daily GC rhythm has long been thought to be governed by the SCN via the hypothalamus–pituitary–adrenal neuroendocrine axis. Recent findings, however, indicate that multiple regulatory mechanisms, including the adrenal intrinsic mechanism by the peripheral clock, are also involved. GC regulates diverse physiological processes and acts as a signal for resetting peripheral clocks, which suggests the importance of the GC rhythm in harmonizing overall circadian physiology and behavior. Therefore, in this review, we will discuss the important role of the adrenal peripheral clockwork in the circadian regulation of GC and its physiological relevance in the circadian timing system.

Impairment of Fear Memory Consolidation in Maternally Stressed Male Mouse Offspring: Evidence for Nongenomic Glucocorticoid Action on the Amygdala

The environment in early life elicits profound effects on fetal brain development that can extend into adulthood. However, the long-lasting impact of maternal stress on emotional learning remains largely unknown. Here, we focus on amygdala-related learning processes in maternally stressed mice. In these mice, fear memory consolidation and certain related signaling cascades were significantly impaired, though innate fear, fear memory acquisition, and synaptic NMDA receptor expression in the amygdala were unaltered. In accordance with these findings, maintenance of long-term potentiation (LTP) at amygdala synapses, but not its induction, was significantly impaired in the maternally stressed animals. Interestingly, amygdala glucocorticoid receptor expression was reduced in the maternally stressed mice, and administration of glucocorticoids (GCs) immediately after fear conditioning and LTP induction restored memory consolidation and LTP maintenance, respectively, suggesting that a weakening of GC signaling was responsible for the observed impairment. Furthermore, microinfusion of a membrane-impermeable form of GC (BSA-conjugated GC) into the amygdala mimicked the restorative effects of GC, indicating that a nongenomic activity of GC mediates the restorative effect. Together, these findings suggest that prenatal stress induces long-term dysregulation of nongenomic GC action in the amygdala of adult offspring, resulting in the impairment of fear memory consolidation. Since modulation of amygdala activity is known to alter the consolidation of emotionally influenced memories allocated in other brain regions, the nongenomic action of GC on the amygdala shown herein may also participate in the amygdala-dependent modulation of memory consolidation.

Identification and Validation of Cryptochrome Inhibitors That Modulate the Molecular Circadian Clock

Circadian rhythms, biological oscillations with a period of about 24 h, are maintained by a genetically determined innate time-keeping system called the molecular circadian clockwork. Despite the physiological and clinical importance of the circadian clock, the development of small molecule modulators that directly target the core clock machinery has only been recently initiated. In the present study, we aimed to identify novel small molecule modulators influencing the molecular feedback loop of the circadian clock by applying our two-step cell-based screening strategy based on E-box-mediated transcriptional activity to test more than 1000 drug-like compounds. A derivative of 2-ethoxypropanoic acid designated as compound 15 was selected as the most promising candidate in terms of both efficacy and potency. We then performed pull-down assays with the biotinylated compound and find out that both cryptochrome (CRY)1 and 2 (CRY1/2), key negative components of the mammalian circadian clock, as molecular targets of compound 15. In accordance with the binding property, compound 15 enhanced E-box-mediated transcription in a CRY1/2-dependent manner, and more importantly, it attenuated the circadian oscillation of Per2-Luc and Bmal1-dLuc activities in cultured fibroblasts, indicating that compound 15 can functionally inhibit the effects of CRY1/2 in the molecular circadian clockwork. In conclusion, the present study describes the first novel chemical inhibitor of CRY1/2 that inhibits the repressive function of CRY1/2, thereby activating CLOCK-BMAL1-evoked E-box-mediated transcription. Further optimizations and subsequent functional studies of this compound may lead to development of efficient therapeutic strategies for a variety of physiological and metabolic disorders with circadian natures.

Advanced Circadian Phase in Mania and Delayed Circadian Phase in Mixed Mania and Depression Returned to Normal after Treatment of Bipolar Disorder.

Disturbances in circadian rhythms have been suggested as a possible cause of bipolar disorder (BD). Included in this study were 31 mood episodes of 26 BD patients, and 18 controls. Circadian rhythms of BD were evaluated at admission, at 2-week intervals during hospitalization, and at discharge. All participants wore wrist actigraphs during the studies. Saliva and buccal cells were obtained at 8:00, 11:00, 15:00, 19:00, and 23:00 for two consecutive days. Collected saliva and buccal cells were used for analysis of the cortisol and gene circadian rhythm, respectively. Circadian rhythms had different phases during acute mood episodes of BD compared to recovered states. In 23 acute manic episodes, circadian phases were ~ 7 hour advanced (equivalent to ~ 17 hour delayed). Phases of 21 out of these 23 cases returned to normal by ~ 7 hour delay along with treatment, but two out of 23 cases returned to normal by ~ 17 hour advance. In three cases of mixed manic episodes, the phases were ~ 6–7 hour delayed. For five cases of depressive episodes, circadian rhythms phases were ~ 4–5 hour delayed. After treatment, circadian phases resembled those of healthy controls. Circadian misalignment due to circadian rhythm phase shifts might be a pathophysiological mechanism of BD.

Class-C SOX Transcription Factors Control GnRH Gene Expression via the Intronic Transcriptional Enhancer

GnRH is a pivotal hypothalamic neurohormone governing reproduction and sexual development. Because transcriptional regulation is crucial for the spatial and temporal expression of the GnRH gene, a region approximately 3.0 kb upstream of the mammalian GnRH promoter has been extensive studied. In the present study, we demonstrate a transcription-enhancer located in the first intron (intron A) region of the GnRH gene. This transcriptional enhancer harbors putative sex-determining region Y-related high-mobility-group box (SOX) family transcription factor-binding sites, which are well conserved across many mammalian species. The class-C SOX member proteins (SOX-C) (SOX4 and SOX11) specifically augment this transcriptional activation by binding to these SOX-binding sites. In accordance, SOX11 is highly enriched in immortalized GnRH-producing GT1-1 cells, and suppression of its expression significantly decreases GnRH gene expression as well as GnRH secretion. Chromatin immunoprecipitation shows that endogenous SOX-C factors recognize and bind to the intronic enhancer in GT1-1 cells and the hypothalamus. Accompanying immunohistochemical analysis demonstrates that SOX4 or SOX11 are highly expressed in the majority of hypothalamic GnRH neurons in adult mice. Taken together, these findings demonstrate that SOX-C transcription factors function as important transcriptional regulators of cell type-specific GnRH gene expression by acting on the intronic transcriptional enhancer.