Deletion of the secretory vesicle proteins IA-2 and IA-2beta disrupts circadian rhythms of cardiovascular and physical activity

Extracellular vesicles are dynamic regulators of maternal glucose homeostasis during pregnancy

Homeostatic regulation of the maternal milieu during pregnancy is critical for maternal and fetal health. The placenta facilitates critical communication between maternal and fetal compartments, in part, through the production of extracellular vesicles (EVs). EVs enable tissue synchrony via cell-cell and long-distance communication and are at their highest circulating concentration during pregnancy. While much work has been done investigating how physiological challenges in pregnancy affect the fetus, the role of placental communication in maternal health has not been well examined. We previously identified placental O-glycosyl transferase (OGT), a glucose-sensing enzyme, as a target of maternal stress where OGT levels and activity affected the O-glycosylation of proteins critical for EV cargo loading and secretion. Here, we hypothesized that placental OGT plays an essential role in maternal homeostatic regulation during pregnancy via its regulation of maternal circulating EV concentrations. Our studies found that changes to key metabolic factors over the circadian cycle, including glucocorticoids, insulin, and glucose, were significantly associated with changes in circulating EV concentration. Targeting placental OGT in mice, we found a novel significant positive relationship between placental OGT and maternal circulating EV concentration that was associated with improving maternal glucose tolerance during pregnancy. Finally, an intravenous elevation in EVs, matching the concentration of EVs during pregnancy, shifted non-pregnant female glucose sensitivity, blunted glucose variance, and improved synchrony of glucose uptake. These data suggest an important and novel role for circulating EVs as homeostatic regulators important in maternal health during pregnancy.

Knockdown of Ptprn-2 delays the onset of puberty in female rats

In the present study, we evaluated how Ptprn-2 (encoding tyrosine phosphatase, receptor type, N2 polypeptide protein) affects the onset of puberty in female rats. We evaluated the expression of Ptprn-2 mRNA and protein in the hypothalamus-pituitary-ovary axis of female rats using real-time quantitative reverse transcription polymerase chain reaction (RT-qPCR) and immunofluorescence at infancy, prepuberty, puberty, peripuberty, and adulthood. We evaluated the effects of Ptprn-2 gene knockdown on different aspects of reproduction-related biology in female rats, including the expression levels of puberty-related genes in vivo and in vitro, the time to onset of puberty, the concentration of serum reproductive hormones, the morphology of ovaries, and the ultrastructure of pituitary gonadotropin cells. Our results demonstrated that PTPRN-2 was primarily distributed in the arcuate nucleus (ARC), periventricular nucleus (PeN), adenohypophysis, and the ovarian follicular theca, stroma, and granulosa cells of female rats at various stages. Ptprn-2 mRNA levels significantly varied between peripuberty and puberty (P < 0.05) in the hypothalamus and pituitary gland. In hypothalamic cells, Ptprn-2 knockdown decreased the expression of Ptprn-2 and Rfrp-3 mRNA (P < 0.05) and increased the levels of Gnrh and Kiss-1 mRNA (P < 0.05). Ptprn-2 knockdown in the hypothalamus resulted in delayed vaginal opening compared to the control group (n = 12, P < 0.01), and Ptprn-2, Gnrh, and Kiss-1 mRNA levels (P < 0.05) all decreased, while the expression of Igf-1 (P < 0.05) and Rfrp-3 mRNA (P < 0.01) increased. The concentrations of FSH and P₄ in the serum of Ptprn-2 knockdown rats were lower than in control animals (P < 0.05). Large transverse perimeters and longitudinal perimeters (P < 0.05) were found in the ovaries of Ptprn-2 knockdown rats. There were fewer large secretory particles from gonadotropin cells in adenohypophysis tissue of the Ptprn-2 knockdown group compared to the control group. This indicates that Ptprn-2 knockdown can regulate levels of Gnrh, Kiss-1, and Rfrp-3 mRNA in the hypothalamus, regulate the concentration of serum FSH and P₄, and alter the morphology of ovarian and gonadotropin cells, delaying the onset of puberty in female rats.

Extracellular Vesicles: Potential Participants in Circadian Rhythm Synchronization

The circadian rhythm (CR) is a set of autonomous endogenous oscillators. Exposure to the 24-hour day-night cycle synchronizes our CR system, maintaining homeostasis and human health. Several mechanisms for the CR system have been proposed, including those underlying the function (transcriptional-translational negative-feedback loops, or TTFLs), mechanisms regulating the TTFLs, and the mechanism by which the "server clock" is synchronized to environmental time. Several pathways downstream of the "server clock" perform well-characterized biological functions. However, the synchronization between the "server clock" (the endogenous master clock seated in the suprachiasmatic nucleus within the hypothalamus) and the "client clock" (imbedded in nearly every cell in the form of interlocking TTFLs) is difficult to explain with current theories. Extracellular vesicles (EVs), which are involved in intercellular communication and have recently been found to participate in regulation of the "client clock", might be the answer to this question. In this review, we summarize the current knowledge of CRs, TTFLs, and EVs, examine research findings about the functions of EVs in the CR system, and discuss the issues requiring attention in future research.

Combining Human Epigenetics and Sleep Studies in Caenorhabditis elegans: A Cross-Species Approach for Finding Conserved Genes Regulating Sleep

Study Objectives

We aimed to test a combined approach to identify conserved genes regulating sleep and to explore the association between DNA methylation and sleep length.

Methods

We identified candidate genes associated with shorter versus longer sleep duration in college students based on DNA methylation using Illumina Infinium HumanMethylation450 BeadChip arrays. Orthologous genes in Caenorhabditis elegans were identified, and we examined whether their loss of function affected C. elegans sleep. For genes whose perturbation affected C. elegans sleep, we subsequently undertook a small pilot study to re-examine DNA methylation in an independent set of human participants with shorter versus longer sleep durations.

Results

Eighty-seven out of 485,577 CpG sites had significant differential methylation in young adults with shorter versus longer sleep duration, corresponding to 52 candidate genes. We identified 34 C. elegans orthologs, including NPY/flp-18 and flp-21, which are known to affect sleep. Loss of five additional genes alters developmentally timed C. elegans sleep (B4GALT6/bre-4, DOCK180/ced-5, GNB2L1/rack-1, PTPRN2/ida-1, ZFYVE28/lst-2). For one of these genes, ZFYVE28 (also known as hLst2), the pilot replication study again found decreased DNA methylation associated with shorter sleep duration at the same two CpG sites in the first intron of ZFYVE28.

Conclusions

Using an approach that combines human epigenetics and C. elegans sleep studies, we identified five genes that play previously unidentified roles in C. elegans sleep. We suggest sleep duration in humans may be associated with differential DNA methylation at specific sites and that the conserved genes identified here likely play roles in C. elegans sleep and in other species.

Meta-analysis of transcriptomic datasets identifies genes enriched in the mammalian circadian pacemaker

The master circadian pacemaker in mammals is located in the suprachiasmatic nuclei (SCN) which regulate physiology and behaviour, as well as coordinating peripheral clocks throughout the body. Investigating the function of the SCN has often focused on the identification of rhythmically expressed genes. However, not all genes critical for SCN function are rhythmically expressed. An alternative strategy is to characterize those genes that are selectively enriched in the SCN. Here, we examined the transcriptome of the SCN and whole brain (WB) of mice using meta-analysis of publicly deposited data across a range of microarray platforms and RNA-Seq data. A total of 79 microarrays were used (24 SCN and 55 WB samples, 4 different microarray platforms), alongside 17 RNA-Seq data files (7 SCN and 10 WB). 31 684 MGI gene symbols had data for at least one platform. Meta-analysis using a random effects model for weighting individual effect sizes (derived from differential expression between relevant SCN and WB samples) reliably detected known SCN markers. SCN-enriched transcripts identified in this study provide novel insights into SCN function, including identifying genes which may play key roles in SCN physiology or provide SCN-specific drivers.

Pathophysiologic changes in IA-2/IA-2β null mice are secondary to alterations in the secretion of hormones and neurotransmitters

IA-2 and IA-2β are transmembrane proteins of dense-core vesicles (DCV). The deletion of these proteins results in a reduction in the number of DCV and the secretion of hormones and neurotransmitters. As a result, this leads to a variety of pathophysiologic changes. The purpose of this review is to describe these changes, which are characterized by glucose intolerance, female infertility, behavior and learning abnormalities and alterations in the diurnal circadian rhythms of blood pressure, heart rate, spontaneous physical activity and body temperature. These findings show that the deletion of IA-2 and IA-2β results in multiple pathophysiologic changes and represents a unique in vivo model for studying the effect of hormone and neurotransmitter reduction on known and still unrecognized targets.

The Ia-2β intronic miRNA, miR-153, is a negative regulator of insulin and dopamine secretion through its effect on the Cacna1c gene in mice

AIMS/HYPOTHESIS

miR-153 is an intronic miRNA embedded in the genes that encode IA-2 (also known as PTPRN) and IA-2β (also known as PTPRN2). Islet antigen (IA)-2 and IA-2β are major autoantigens in type 1 diabetes and are important transmembrane proteins in dense core and synaptic vesicles. miR-153 and its host genes are co-regulated in pancreas and brain. The present experiments were initiated to decipher the regulatory network between miR-153 and its host gene Ia-2β (also known as Ptprn2).

METHODS

Insulin secretion was determined by ELISA. Identification of miRNA targets was assessed using luciferase assays and by quantitative real-time PCR and western blots in vitro and in vivo. Target protector was also employed to evaluate miRNA target function.

RESULTS

Functional studies revealed that miR-153 mimic suppresses both glucose- and potassium-induced insulin secretion (GSIS and PSIS, respectively), whereas miR-153 inhibitor enhances both GSIS and PSIS. A similar effect on dopamine secretion also was observed. Using miRNA target prediction software, we found that miR-153 is predicted to target the 3'UTR region of the calcium channel gene, Cacna1c. Further studies confirmed that Cacna1c mRNA and protein are downregulated by miR-153 mimics and upregulated by miR-153 inhibitors in insulin-secreting freshly isolated mouse islets, in the insulin-secreting mouse cell line MIN6 and in the dopamine-secreting cell line PC12.

CONCLUSIONS/INTERPRETATION

miR-153 is a negative regulator of both insulin and dopamine secretion through its effect on Cacna1c expression, which suggests that IA-2β and miR-153 have opposite functional effects on the secretory pathway.

The minimal promoter region of the dense-core vesicle protein IA-2: transcriptional regulation by CREB

AIMS

IA-2 is a transmembrane protein found in the dense-core vesicles (DCV) of neuroendocrine cells and one of the major autoantigens in type 1 diabetes. DCV are involved in the secretion of hormones (e.g., insulin) and neurotransmitters. Stimulation of pancreatic β cells with glucose upregulates the expression of IA-2 and an increase in IA-2 results in an increase in the number of DCV. Little is known, however, about the promoter region of IA-2 or the transcriptional factors that regulate the expression of this gene.

METHODS

In the present study, we constructed eight deletion fragments from the upstream region of the IA-2 transcription start site and linked them to a luciferase reporter.

RESULTS

By this approach, we have identified a short bp region (-216 to +115) that has strong promoter activity. We also identified a transcription factor, cAMP responsive element-binding protein (CREB), which binds to two CREB-related binding sites located in this region. The binding of CREB to these sites enhanced IA-2 transcription by more than fivefold. We confirmed these findings by site-directed mutagenesis, chromatin immunoprecipitation assays and RNAi inhibition.

CONCLUSION

Based on these findings, we conclude that the PKA pathway is a critical, but not the exclusive signaling pathway involved in IA-2 gene expression.

Genetic deletion of MT1 melatonin receptors alters spontaneous behavioral rhythms in male and female C57BL/6 mice

Behaviors vary over the 24h light/dark cycle and these temporal patterns reflect in part modulation by circadian neural circuits and hormones, such as melatonin. The goal of this study was to investigate the involvement of MT1 melatonin receptors in behavioral regulation by comparing male and female C57 wild type (WT) mice with C57 mice with genetic deletion of the MT1 receptor (MT1KO). A comprehensive array of fifteen distinct spontaneous behaviors was recorded continuously in the homecage over multiple days using the HomeCageScan system. Behaviors assessed were activity-like (i.e. come down, hang, jump, walk), exploration-like (i.e. dig, groom, rear up, sniff, stretch), resting-like (i.e. awake, remain low, rest, twitch) and ingestion-like (i.e. drink, eat). Phenotypic array and temporal distribution analysis revealed distinct behavioral rhythms that differed between WT and MT1KO mice. The rhythms were consistent from day to day in males and varied with the estrous cycle in females. We also studied the role of MT1 receptors on depressive and anxiety-like behaviors. Genetic deletion of MT1 receptors increased immobility time in the forced swim test and decreased the number of marbles buried in the marble burying test in both male and female C57 mice. We conclude that MT1 melatonin receptors are involved in neural pathways modulating diurnal rhythms of spontaneous behavior in the homecage as well as pathways regulating depressive and anxiolytic-like behaviors.

Sorting nexin 19 regulates the number of dense core vesicles in pancreatic β-cells

Aims/Introduction:  Insulinoma‐associated protein 2 (IA‐2) regulates insulin secretion and the number of dense core vesicles (DCV). However, the mechanism of regulation of DCV number by IA‐2 is unknown. We examined the effect of sorting nexin 19 (SNX19), an IA‐2 interacting protein, on insulin secretion and the number of dense core vesicles (DCV).

Materials and Methods:  Stable SNX19 knockdown (SNX19KD) MIN6, a mouse pancreatic β‐cell line, and stable SNX19‐reintroduced SNX19KD MIN6 were established. Quantification of DCV, and lysosomes was carried out using electron micrographs. The half‐life of DCV was detected by pulse‐chase experiment.

Results:  Insulin secretion and content were decreased in stable SNX19KD MIN6 cells compared with those in control MIN6 cells. Electron micrographs showed that DCV number in SNX19KD cells was decreased by approximately 75% and that DCV size was decreased by approximately 40% compared with those in control cells, respectively. Furthermore, when SNX19 was reintroduced in SNX19KD cells, insulin content, insulin secretion and DCV number were increased. The half‐life of DCV was decreased in SNX19KD cells, but was increased in SNX19KD cells in which SNX19 was reintroduced. The number of lysosomes and the activity of lysosome enzyme cathepsin D were increased by approximately threefold in SNX19KD cells compared with those in control cells. In contrast, they were decreased to approximately half to one‐third in SNX19‐reintroduced SNX19KD cells.

Conclusions:  SNX19 regulates the number of DCV and insulin content by stabilizing DCV in β‐cells. (J Diabetes Invest, doi: 10.1111/j.2040‐1124.2011.00138.x, 2012)

The dense core vesicle protein IA-2, but not IA-2β, is required for active avoidance learning

The islet-antigens IA-2 and IA-2β are major autoantigens in type-1 diabetes and transmembrane proteins in dense core vesicles (DCV). Recently we showed that deletion of both IA-2 and IA-2β alters the secretion of hormones and neurotransmitters and impairs behavior and learning. The present study was designed to evaluate the contribution to learning of each of these genes by using single knockout (SKO) and double knockout (DKO) mice in an active avoidance test. After 5 days of training, wild-type (WT) mice showed 60-70% active avoidance responses, whereas the DKO mice showed only 10-15% active avoidance responses. The degree of active avoidance responses in the IA-2 SKO mice was similar to that of the DKO mice, but in contrast, the IA-2β SKO mice behaved like WT mice showing 60-70% active avoidance responses. Molecular studies revealed a marked decrease in the phosphorylation of the cAMP response element-binding protein (CREB) and Ca(2+)/calmodulin-dependent protein kinase II (CAMKII) in the striatum and hippocampus of the IA-2 SKO and DKO mice, but not in the IA-2β SKO mice. To evaluate the role of CREB and CAMKII in the SKO and DKO mice, GBR-12909, which selectively blocks the dopamine uptake transporter and increases CREB and CAMKII phosphorylation, was administered. GBR-12909 restored the phosphorylation of CREB and CAMKII and increased active avoidance learning in the DKO and IA-2 SKO to near the normal levels found in the WT and IA-2β SKO mice. We conclude that in the absence of the DCV protein IA-2, active avoidance learning is impaired.

Pseudophosphatases: methods of analysis and physiological functions

Protein tyrosine phosphatases (PTPs) are key enzymes in the regulation of cellular homeostasis and signaling pathways. Strikingly, not all PTPs bear enzymatic activity. A considerable fraction of PTPs are enzymatically inactive and are known as pseudophosphatases. Despite the lack of activity they execute pivotal roles in development, cell biology and human disease. The present review is focused on the methods used to identify pseudophosphatases, their targets, and physiological roles. We present a strategy for detailed enzymatic analysis of inactive PTPs, regulation of inactive PTP domains and identification of binding partners. Furthermore, we provide a detailed overview of human pseudophosphatases and discuss their regulation of cellular processes and functions in human pathologies.

Diurnal rhythmicity in biological processes involved in bioavailability of functional food factors

In the past few decades, many types of functional factors have been identified in dietary foods; for example, flavonoids are major groups widely distributed in the plant kingdom. However, the absorption rates of the functional food factors are usually low, and many of these are difficult to be absorbed in the intact forms because of metabolization by biological processes during absorption. To gain adequate beneficial effects, it is therefore mandatory to know whether functional food factors are absorbed in sufficient quantity, and then reach target organs while maintaining beneficial effects. These are the reasons why the bioavailability of functional food factors has been well investigated using rodent models. Recently, many of the biological processes have been reported to follow diurnal rhythms recurring every 24 h. Therefore, absorption and metabolism of functional food factors influenced by the biological processes may vary with time of day. Consequently, the evaluation of the bioavailability of functional food factors using rodent models should take into consideration the timing of consumption. In this review, we provide a perspective overview of the diurnal rhythm of biological processes involved in the bioavailability of functional food factors, particularly flavonoids.

Immunohistochemical analysis of IA-2 family of protein tyrosine phosphatases in rat gastrointestinal endocrine cells

Islet-associated protein-2 (IA-2) and IA-2β (also known as phogrin) are unique neuroendocrine-specific protein tyrosine phosphatases (PTPs). The IA-2 family of PTPs was originally identified from insulinoma cells and discovered to be major autoantigens in type 1 diabetes. Despite its expression in the neural and canonical endocrine tissues, data on expression of the IA-2 family of PTPs in gastrointestinal endocrine cells (GECs) are limited. Therefore, we immunohistochemically investigated the expression of the IA-2 family of PTPs in the rat gastrointestinal tract. In the stomach, IA-2 and IA-2β were expressed in GECs that secrete serotonin, somatostatin, and cholecystokinin/gastrin-1. In addition to these hormones, secretin, gastric inhibitory polypeptide (also known as the glucose-dependent insulinotropic peptide), glucagon-like peptide-1, and glucagon, but not ghrelin were coexpressed with IA-2 or IA-2β in duodenal GECs. Pancreatic islet cells that secrete gut hormones expressed the IA-2 family of PTPs. The expression patterns of IA-2 and IA-2β were comparable. These results reveal that the IA-2 family of PTPs is expressed in a cell type-specific manner in rat GECs. The extensive expression of the IA-2 family of PTPs in pancreo-gastrointestinal endocrine cells and in the enteric plexus suggests their systemic contribution to nutritional control through a neuroendocrine signaling network.

Disruption of gene expression rhythms in mice lacking secretory vesicle proteins IA-2 and IA-2β

Insulinoma-associated protein (IA)-2 and IA-2β are transmembrane proteins involved in neurotransmitter secretion. Mice with targeted disruption of both IA-2 and IA-2β (double-knockout, or DKO mice) have numerous endocrine and physiological disruptions, including disruption of circadian and diurnal rhythms. In the present study, we have assessed the impact of disruption of IA-2 and IA-2β on molecular rhythms in the brain and peripheral oscillators. We used in situ hybridization to assess molecular rhythms in the hypothalamic suprachiasmatic nuclei (SCN) of wild-type (WT) and DKO mice. The results indicate significant disruption of molecular rhythmicity in the SCN, which serves as the central pacemaker regulating circadian behavior. We also used quantitative PCR to assess gene expression rhythms in peripheral tissues of DKO, single-knockout, and WT mice. The results indicate significant attenuation of gene expression rhythms in several peripheral tissues of DKO mice but not in either single knockout. To distinguish whether this reduction in rhythmicity reflects defective oscillatory function in peripheral tissues or lack of entrainment of peripheral tissues, animals were injected with dexamethasone daily for 15 days, and then molecular rhythms were assessed throughout the day after discontinuation of injections. Dexamethasone injections improved gene expression rhythms in liver and heart of DKO mice. These results are consistent with the hypothesis that peripheral tissues of DKO mice have a functioning circadian clockwork, but rhythmicity is greatly reduced in the absence of robust, rhythmic physiological signals originating from the SCN. Thus, IA-2 and IA-2β play an important role in the regulation of circadian rhythms, likely through their participation in neurochemical communication among SCN neurons.

Adipokines and central control in adenosine A1 receptor dependent glucose metabolism

Adenosine A1 receptor-deficient mice develop a phenotype of insulin resistance and grow fat. Participating pathophysiological pathways are not understood in detail yet, as discussed in our recent manuscript. This commentary further explores possible pathophysiological mechanisms with emphasis on the roles of the adipokines resistin, retinol-binding protein 4, adiponectin and the function of the gastric hormone ghrelin in adenosine mediated central regulation of energy balance. The postulate of an important function of ghrelin/A1AR axis provides a good hypothetical basis for further investigations to clarify the mechanism of A1AR-dependent metabolic homeostasis.

Dynamic neuronal network organization of the circadian clock and possible deterioration in disease

In mammals, the suprachiasmatic nuclei (SCNs) function as a circadian pacemaker that drives 24-h rhythms in physiology and behavior. The SCN is a multicellular clock in which the constituent oscillators show dynamics in their functional organization and phase coherence. Evidence has emerged that plasticity in phase synchrony among SCN neurons determines (i) the amplitude of the rhythm, (ii) the response to continuous light, (iii) the capacity to respond to seasonal changes, and (iv) the phase-resetting capacity. A decrease in circadian amplitude and phase-resetting capacity is characteristic during aging and can be a result of disease processes. Whether the decrease in amplitude is caused by a loss of synchronization or by a loss of single-cell rhythmicity remains to be determined and is important for the development of strategies to ameliorate circadian disorders.

Linking neural activity and molecular oscillations in the SCN

Neurons in the suprachiasmatic nucleus (SCN) function as part of a central timing circuit that drives daily changes in our behaviour and underlying physiology. A hallmark feature of SCN neuronal populations is that they are mostly electrically silent during the night, start to fire action potentials near dawn and then continue to generate action potentials with a slow and steady pace all day long. Sets of currents are responsible for this daily rhythm, with the strongest evidence for persistent Na(+) currents, L-type Ca(2+) currents, hyperpolarization-activated currents (I(H)), large-conductance Ca(2+) activated K(+) (BK) currents and fast delayed rectifier (FDR) K(+) currents. These rhythms in electrical activity are crucial for the function of the circadian timing system, including the expression of clock genes, and decline with ageing and disease. This article reviews our current understanding of the ionic and molecular mechanisms that drive the rhythmic firing patterns in the SCN.

Deletion of Ia-2 and/or Ia-2β in mice decreases insulin secretion by reducing the number of dense core vesicles

AIMS/HYPOTHESIS

Islet antigen 2 (IA-2) and IA-2β are dense core vesicle (DCV) transmembrane proteins and major autoantigens in type 1 diabetes. The present experiments were initiated to test the hypothesis that the knockout of the genes encoding these proteins impairs the secretion of insulin by reducing the number of DCV.

METHODS

Insulin secretion, content and DCV number were evaluated in islets from single knockout (Ia-2 [also known as Ptprn] KO, Ia-2β [also known as Ptprn2] KO) and double knockout (DKO) mice by a variety of techniques including electron and two-photon microscopy, membrane capacitance, Ca(2+) currents, DCV half-life, lysosome number and size and autophagy.

RESULTS

Islets from single and DKO mice all showed a significant decrease in insulin content, insulin secretion and the number and half-life of DCV (p < 0.05 to 0.001). Exocytosis as evaluated by two-photon microscopy, membrane capacitance and Ca(2+) currents supports these findings. Electron microscopy of islets from KO mice revealed a marked increase (p < 0.05 to 0.001) in the number and size of lysosomes and enzymatic studies showed an increase in cathepsin D activity (p < 0.01). LC3 protein, an indicator of autophagy, also was increased in islets of KO compared with wild-type mice (p < 0.05 to 0.01) suggesting that autophagy might be involved in the deletion of DCV.

CONCLUSIONS/INTERPRETATION

We conclude that the decrease in insulin content and secretion, resulting from the deletion of Ia-2 and/or Ia-2β, is due to a decrease in the number of DCV.

Expression and rhythmic modulation of circulating microRNAs targeting the clock gene Bmal1 in mice

MicroRNAs (miRNAs) interact with 3' untranslated region (UTR) elements of target genes to regulate mRNA stability or translation and thus play a role in regulating many different biological processes, including circadian rhythms. However, specific miRNAs mediating the regulation of essential clock genes remain largely unknown. Because vesicles containing membrane-bound miRNAs are present in the circulatory system, we examined miRNAs predicted to target the clock gene, Bmal1, for evidence of rhythmic fluctuations in circulating levels and modulatory effects on the 3' UTR activity of Bmal1. A number of miRNAs with Bmal1 as a predicted target were expressed in the serum of mice exposed to LD 12:12 and of these miRNAs, miR-152 and miR-494 but not miR-142-3p were marked by diurnal oscillations with bimodal peaks in expression occurring near the middle of the day and 8 or 12 hr later during the night. Co-transfection of pre-miR over-expression constructs for miR-494 and miR-142-3p in HEK293 cells had significant effects in repressing luciferase-reported Bmal1 3' UTR activity by as much as 60%, suggesting that these miRNAs may function as post-transcriptional modulators of Bmal1. In conjunction with previous studies implicating miRNAs as extracellular regulatory signals, our results suggest that circulating miRNAs may play a role in the regulation of the molecular clockworks in peripheral circadian oscillators.

Fast delayed rectifier potassium current: critical for input and output of the circadian system

The ability to generate intrinsic circadian rhythms in electrical activity appears to be a key property of central pacemaker neurons and one essential to the function of the circadian timing system. Previous work has demonstrated that suprachiasmatic nucleus (SCN) neurons express the fast delayed rectifier (FDR) potassium current and raise questions about the function of this current. Here, we report that mice lacking both Kcnc1 and Kcnc2 genes [double knock-out (dKO)] fail to express the Kv3.1 and 3.2 channels in the SCN as well as exhibit a greatly reduced FDR current. SCN neurons from these dKO mice exhibit reduced spontaneous activity during the day as well as reduced NMDA-evoked excitatory responses during the night. Interestingly, the daily rhythm in PER2 expression in the SCN was not altered in the dKO mice, although the photic induction of c-Fos was attenuated. Behaviorally, the dKO mice exhibited extremely disrupted daily rhythms in wheel-running behavior. In a light/dark cycle, some of the dKO mice were arrhythmic, whereas others expressed a diurnal rhythm with low amplitude and significant activity during the day. When placed in constant darkness, the dKO mice exhibited low-amplitude, fragmented rhythms and attenuated light responses. Together, these data are consistent with the hypothesis that the FDR current is critical for the generation of robust circadian rhythms in behavior as well as the synchronization of the circadian system to the photic environment.