Taurine attenuates hepatic steatosis in a genetic model of fatty liver disease.

Mice lacking the farnesoid X receptor (FXR) are used as a genetic model for nonalcoholic fatty liver disease because their livers exhibit hepatic steatosis and inflammation. The influence of taurine drinking on disrupted hepatic function was investigated using female Fxr-null mice. Significant decreases in the levels of hepatic damage-associated diagnostic markers, hepatic triglycerides, non-esterified fatty acids, and total bile acids were found in Fxr-null mice that had drunk water containing 0.

Extracellular low pH affects circadian rhythm expression in human primary fibroblasts.

Circadian rhythm is a fundamental biological system involved in the regulation of various physiological functions. However, little is known about a nature or function of circadian clock in human primary cells. In the present study, we have applied in vitro real time circadian rhythm monitoring to study human clock properties using primary skin fibroblasts.

Selective serotonin reuptake inhibitors and raft inhibitors shorten the period of Period1-driven circadian bioluminescence rhythms in rat-1 fibroblasts.

Alterations in circadian rhythm generation may be related to the development of mood disorders. Although it has been reported that the most popular antidepressant, selective serotonin reuptake inhibitors (SSRIs) affect circadian phase, no data are available that describe the effects of SSRIs on other circadian parameters (period, amplitude and damping rate) in dissociated cells. In the present study we used real-time monitoring of bioluminescence in rat-1 fibroblasts expressing the Period1-luciferase transgene, and that in Period1-luciferase transgenic mouse suprachiasmatic nucleus (SCN) explants, in order to characterize the effects of SSRI on circadian oscillator function in vitro.

Analysis of daily and circadian gene expression in the rat pineal gland.

The mammalian pineal gland is an important component of the circadian system. In the present study, we examined the expression of roughly 8000 genes in the rat pineal gland as a function of time of day under light-dark (LD) cycles and in constant dark (DD) using oligo DNA microarray technique. We identified 47 and 13 genes that showed higher levels at night and day, respectively, under LD.

Localization of a circadian clock in mammalian photoreceptors.

Several studies have demonstrated that the mammalian retina contains an autonomous circadian clock. Dopaminergic and other inner retinal neurons express many of the clock genes, whereas some of these genes seem to be absent from the photoreceptors. This observation has led to the suggestion that in mammalian retina the circadian pacemaker driving retinal rhythms is located in the inner nuclear layer.

Light and GABA)(A) receptor activation alter period mRNA levels in the SCN of diurnal Nile grass rats.

We examined Period (Per) mRNA rhythms in the suprachiasmatic nucleus (SCN) of a diurnal rodent and assessed how phase-shifting stimuli acutely affect SCN Per mRNA using semiquantitative in situ hybridization. First, Per1 and Per2 varied rhythmically in the SCN over the course of one circadian cycle in constant darkness: Per1 mRNA was highest in the early to mid-subjective day, while Per2 mRNA levels peaked in the late subjective day. Second, acute light exposure in the early subjective night significantly increased both Per1 and Per2 mRNA.

Role of calcium in the gating of isoproterenol-induced arylalkylamine N-acetyltransferase gene expression in the mouse pineal gland.

Melatonin and its autonomic regulation serve important physiological functions. We recently demonstrated that stimulation of beta-adrenergic receptors only increases nighttime arylalkylamine N-acetyltransferase (Aa-Nat, the rate-limiting enzyme in melatonin synthesis) mRNA levels in mouse pineal gland in vitro, which suggests that pineal clocks may gate Aa-Nat gene expression. In the present study, our data reveal that cAMP analog increased Aa-Nat at any time of day but only in the presence of ionomycin.

Effect of long-term exposure to constant dim light on the circadian system of rats.

The newly discovered multi-oscillatory nature of the mammalian circadian clock system and the cloning of the genes involved in the molecular mechanism that generates circadian rhythmicity have opened new approaches for understanding how mammals are temporally organized and how the mammalian circadian system reacts to the lack of normal synchronization cues. In the present study we investigated the effects of long-term exposure to constant red dim light on the pattern of the expression of Period 1 in the suprachiasmatic nuclei of the hypothalamus and of Arylalkylamine N-acetyltransferase(Aa-nat) in the retina and pineal gland. Our data demonstrate that Period 1 mRNA expression in the suprachiasmatic nuclei of the hypothalamus was not affected by exposure to constant red dim light for 60 days, whereas Aa-nat mRNA expression in the retina and in the pineal gland was significantly affected, since in some animals (20-30%) Aa-nat mRNA levels were found to be higher during the subjective day.

Regulation of cAMP-induced arylalkylamine N-acetyltransferase, Period1, and MKP-1 gene expression by mitogen-activated protein kinases in the rat pineal gland.

In rodent pineal glands, sympathetic innervation, which leads to norepinephrine release, is a key process in the circadian regulation of physiology and certain gene expressions. It has been shown that gene expression of the rate-limiting enzyme in the melatonin synthesis arylalkylamine N-acetyltransferase (Aa-Nat), circadian clock gene Period1, and mitogen-activated protein kinase (MAPK) phosphtase-1 (MKP-1), is controlled mainly by a norepinephrine-beta-adrenergic receptor-cAMP signaling cascade in the rat pineal gland. To further dissect the signaling cascades that regulate those gene expressions, we examined whether MAPKs are involved in cAMP-induced gene expression.

AMPA/kainate receptor antagonist DNQX blocks the acute increase of Per2 mRNA levels in most but not all areas of the SCN.

The daily light:dark cycle synchronizes the circadian timing system by resetting the phase of the circadian pacemaker on a daily basis. Light acutely increases mRNA levels of the clock genes Per1 and Per2 in the suprachiasmatic nucleus (SCN), the site of the primary circadian pacemaker in mammals. Light is conveyed to the SCN through the retinohypothalamic tract (RHT), an efferent projection from retinal ganglion cells that releases the excitatory amino acid (EAA) neurotransmitter glutamate in the SCN.

Pineal circadian clocks gate arylalkylamine N-acetyltransferase gene expression in the mouse pineal gland.

In mammals it has been thought that the circadian clock localizes only in the suprachiasmatic nucleus of the hypothalamus. Recent studies have revealed that certain brain regions and peripheral tissues may also have intrinsic circadian clocks. However, the roles played by 'peripheral circadian clocks' have not been fully elucidated.

Effect of dark exposure in the middle of the day on Period1, Period2, and arylalkylamine N-acetyltransferase mRNA levels in the rat suprachiasmatic nucleus and pineal gland.

The suprachiasmatic nucleus (SCN) of the mammalian hypothalamus contains a central circadian pacemaker, which adjusts circadian rhythms within the body to environmental light-dark cycles. It has been shown that dark exposure in the day causes phase shifts in circadian rhythms, but it does not induce changes in the melatonin levels in the pineal gland. In this study, we examined the effect of dark exposure on two "circadian clock" genes Period1 and Period2 mRNA levels in the rat SCN, and on Period1, Period2, and arylalkylamine N-acetyltransferase (Aa-Nat, the rate-limiting enzyme in melatonin synthesis) gene expression in the pineal gland.

Diurnal rhythms of tryptophan hydroxylase 1 and 2 mRNA expression in the rat retina.

Tryptophan hydroxylase is the first of four enzymes in the melatonin biosynthetic pathway. Recent studies have shown that there are two genes, Tph1 and Tph2, that encode tryptophan hydroxylase in mammals. In this study, we investigated which of the two genes is expressed in the rat retina.

Tetrodotoxin administration in the suprachiasmatic nucleus prevents NMDA-induced reductions in pineal melatonin without influencing Per1 and Per2 mRNA levels.

The suprachiasmatic nucleus (SCN) of the anterior hypothalamus contains a light-entrainable circadian pacemaker. Neurons in the SCN are part of a circuit that conveys light information from retinal efferents to the pineal gland. Light presented during the night acutely increases mRNA levels of the circadian clock genes Per1 and Per2 in the SCN, and acutely suppresses melatonin levels in the pineal gland.

Gating of the cAMP signaling cascade and melatonin synthesis by the circadian clock in mammalian retina.

Melatonin is synthesized in retinal photoreceptor cells and acts as a neuromodulator imparting photoperiodic information to the retina. The synthesis of melatonin is controlled by an ocular circadian clock and by light in a finely tuned mechanism that ensures that melatonin is synthesized and acts only at night in darkness. Here we report that the circadian clock gates melatonin synthesis in part by regulating the expression of the type 1 adenylyl cyclase (AC1) and the synthesis of cAMP in photoreceptor cells.

Localization of Aa-nat mRNA in the rat retina by fluorescence in situ hybridization and laser capture microdissection.

Arylalkylamine N-acetyltransferase (AA-NAT) is the key regulatory enzyme in the melatonin biosynthetic pathway. Previous investigations have reported that Aa-nat mRNA in rat is only detected in a sub-population of photoreceptor cells that resemble cones in shape and size. In the present study, we investigated Aa-nat expression in the rat retina by using in situ hybridization and laser capture microdissection combined with the reverse transcription/polymerase chain reaction technique.

Analysis of gene expression following norepinephrine stimulation in the rat pineal gland using DNA microarray technique.

Several studies have demonstrated that norepinephrine (NE) is the critical neurotransmitter for the regulation of gene expression in the pineal gland. We studied the acute effect of NE stimulation in cultured rat pineal glands using Affymetrix rat genome microarray GeneChip probe arrays. Our data demonstrate that NE stimulation affects regulation of several genes; 44 and 29 genes were up- or down-regulated more than 2.

Induction of photosensitivity in cultured rat pineal affects Aa-nat regulation.

In a previous investigation we have demonstrated that neonatal rat pineal may become photosensitive if removed from the animal at post-natal day 1 and cultured for 7 days. In the present study we demonstrated that Aa-nat mRNA, the key enzyme in melatonin biosynthetic pathway, is affected by illumination in photosensitive pineal, and Aa-nat transcription in photosensitive pineal, but not in adult or non photosensitive pineals, is up-regulated by BMAL1:CLOCK.

Peripheral circadian oscillators and their rhythmic regulation.

Most of the organisms living on earth show 24 hour (circadian) rhythms that are endogenously controlled by biological clocks. In mammals, these rhythms are generated by the circadian pacemaker located in the suprachiasmatic nucleus (SCN) of the hypothalamus. However, recent studies have demonstrated that circadian oscillators can be found in many organs and tissues, and it appears that the circadian oscillators in the periphery are not self-sustained, since, in vitro, the oscillation disappears after a few cycles.

The mammalian retina as a clock.

Many physiological, cellular, and biochemical parameters in the retina of vertebrates show daily rhythms that, in many cases, also persist under constant conditions. This demonstrates that they are driven by a circadian pacemaker. The presence of an autonomous circadian clock in the retina of vertebrates was first demonstrated in Xenopus laevis and then, several years later, in mammals.

Regulation of period 1 expression in cultured rat pineal.

The aim of the present study was to investigate the in vitro expression of Period 1 (Per1), Period 2 (Per2) and arylalkylamine N-acetyltransferase (AA-NAT) genes in the rat pineal gland to understand the mechanism(s) regulating the expression of these genes in this organ. Pineals, when maintained in vitro for 5 days, did not show circadian rhythmicity in the expression of any of the three genes monitored. Norepinephrine (NE) induced AA-NAT and Per1, whereas its effect on Per2 was negligible.