Circadian Rhythm Signaling Research Articles

Circadian modulation of hepatic transcriptome in transgenic rats expressing human growth hormone

The secretory profile of growth hormone (GH) is sexually dimorphic in rats. In male transgenic (TG) rats expressing human GH (hGH) that we generated, the circulating levels of both hGH and endogenous GH are flattened with no male-type pulsatility. To elucidate the regulatory role of episodic GH profile on the liver, the hepatic transcriptome of male TG rats at the middle of the light and dark phases was characterized by genome-wide analyses as compared with that of male wild-type (WT) rats. Transcripts commonly up- or down-regulated regardless of the lighting conditions in TG rats were mainly enriched in the metabolism of xenobiotics. In TG rats, the gene expression profile was functionally feminized, verifying that the sexually dimorphic profile of GH rather than genetic sexuality is a stronger sex-determining factor on the hepatic transcriptome. The common transcripts which fluctuated during the day in both TG and WT rats were enriched in circadian rhythm signaling, and physiological rhythmicity was considered to be finely interconnected with liver metabolism via sexually dimorphic GH secretion. In contrast, some genes were differentially regulated in TG rats at only one of two time points measured, and others were fluctuated daily in only one genotype. In particular, some genes involved in the GH signaling pathway were included, suggesting the signal transduction is circadian-modulated depending upon the GH profile. Our transcriptome analyses clarified the regulatory role of episodic GH profile on the liver and strengthen the functional link between sexually dimorphic GH secretion, liver metabolism, and its circadian regulation.

Investigation of post-transcriptional gene regulatory networks associated with autism spectrum disorders by microRNA expression profiling of lymphoblastoid cell lines

BackgroundAutism spectrum disorders (ASD) are neurodevelopmental disorders characterized by abnormalities in reciprocal social interactions and language development and/or usage, and by restricted interests and repetitive behaviors. Differential gene expression of neurologically relevant genes in lymphoblastoid cell lines from monozygotic twins discordant in diagnosis or severity of autism suggested that epigenetic factors such as DNA methylation or microRNAs (miRNAs) may be involved in ASD.MethodsGlobal miRNA expression profiling using lymphoblasts derived from these autistic twins and unaffected sibling controls was therefore performed using high-throughput miRNA microarray analysis. Selected differentially expressed miRNAs were confirmed by quantitative reverse transcription-polymerase chain reaction (qRT-PCR) analysis, and the putative target genes of two of the confirmed miRNA were validated by knockdown and overexpression of the respective miRNAs.ResultsDifferentially expressed miRNAs were found to target genes highly involved in neurological functions and disorders in addition to genes involved in gastrointestinal diseases, circadian rhythm signaling, as well as steroid hormone metabolism and receptor signaling. Novel network analyses of the putative target genes that were inversely expressed relative to the relevant miRNA in these same samples further revealed an association with ASD and other co-morbid disorders, including muscle and gastrointestinal diseases, as well as with biological functions implicated in ASD, such as memory and synaptic plasticity. Putative gene targets (ID3 and PLK2) of two RT-PCR-confirmed brain-specific miRNAs (hsa-miR-29b and hsa-miR-219-5p) were validated by miRNA overexpression or knockdown assays, respectively. Comparisons of these mRNA and miRNA expression levels between discordant twins and between case-control sib pairs show an inverse relationship, further suggesting that ID3 and PLK2 are in vivo targets of the respective miRNA. Interestingly, the up-regulation of miR-23a and down-regulation of miR-106b in this study reflected miRNA changes previously reported in post-mortem autistic cerebellum by Abu-Elneel et al. in 2008. This finding validates these differentially expressed miRNAs in neurological tissue from a different cohort as well as supports the use of the lymphoblasts as a surrogate to study miRNA expression in ASD.ConclusionsFindings from this study strongly suggest that dysregulation of miRNA expression contributes to the observed alterations in gene expression and, in turn, may lead to the pathophysiological conditions underlying autism.

Interaction of Singlet Molecular Oxygen with Melatonin and Related Indoles¶

Singlet molecular oxygen (1O2) is one of the major agents responsible for (photo)oxidative damage in biological systems including human skin and eyes. It has been reported that the neural hormone melatonin (MLT) can abrogate 1O2-mediated cytotoxicity through its purported high antioxidant activity. We studied the interaction of MLT with 1O2 in deuterium oxide (D2O), acetonitrile and methanol by measuring the phosphorescence lifetime of 1O2 in the presence of MLT and related indoles for comparison. Rose bengal (RB) was used as the main 1O2 photosensitizer. The rate constant (kq) for the total (physical and chemical) quenching of 1O2 by MLT was determined to be 4.0 x 10(7) M(-1) s(-1) in D2O (pD 7), 6.0 x 10(7) M(-1) s(-1) in acetonitrile, and 6.1 x 10(7) M(-1) s(-1) in methanol-d1. The related indoles, tryptophan, 5-hydroxyindole, 5-methoxytryptamine, 5-hydroxytryptamine (5-OH-T, serotonin), 6-hydroxymelatonin (6-OH-MLT) and 6-chloromelatonin quenched 1O2 phosphorescence with similar kq values. We also compared the photosensitized photobleaching rate of MLT with that of other indoles, which revealed that MLT is the most sensitive to 1O2 bleaching. Hydroxylation of the indole moiety in 5-OH-T and 6-OH-MLT makes them more sensitive to photodegradation. In the absence of exogenous photosensitizers MLT itself can generate 1O2 with low quantum yield (0.1 in CH3CN) upon UV excitation. Thus, the processes we investigated may occur in the skin and eyes during physiological circadian rhythm (photo)signaling involving MLT and other indoles. Our results indicate that all the indoles studied, including MLT, are quite efficient yet very similar 1O2 quenchers. This directly shows that the exceptional antioxidant ability proposed for MLT is unsubstantiated when merely chemical mechanism(s) are considered in vivo, and it must predominantly involve humoral regulation that mobilizes other antioxidant defenses in living organisms.