Molecular bases of circadian rhythmicity in renal physiology and pathology

Day-Time Declamping Is Associated with Better Outcomes in Kidney Transplantation: The Circarein Study

Despite improvements in organ preservation techniques and efforts to minimize the duration of cold ischemia, ischemia–reperfusion (IR) injury remains associated with poor graft function and long-term survival in kidney transplantation. We recently demonstrated a clinically significant day-time variation in myocardial tolerance to IR, transcriptionally orchestrated by the circadian clock. Patient and graft post-transplant survival were studied in a cohort of 10,291 patients first transplanted between 2006 and 2017 to test whether kidney graft tolerance to IR depends on the time-of-the-day of clamping/declamping, and thus impacts graft and patient survival. Post-transplant 1- and 3-year survival decreased with increasing ischemia duration. Time-of-the-day of clamping did not influence outcomes. However, night-time (vs. day-time) declamping was associated with a significantly worse post-transplant survival. After adjustment for other predictors, night-time (vs. day-time) declamping remained associated with a worse 1-year (HR = 1.26 (1.08–1.47), p = 0.0028 by Cox multivariable analysis) and 3-year (HR = 1.14 (1.02–1.27), p = 0.021) outcome. Interestingly, the deleterious impact of prolonged ischemia time (>15 h) was partially compensated by day-time (vs. night-time) declamping. Compared to night-time declamping, day-time declamping was associated with a better prognosis of kidney transplantation despite a longer duration of cold ischemia.

Antagonistic effects of finerenone and spironolactone on the aldosterone-regulated transcriptome of human kidney cells

Aldosterone, the main mineralocorticoid hormone in humans, plays a pivotal role in the control of water and salt reabsorption via activation of the mineralocorticoid receptor (MR). Alterations in MR signaling pathway lead to renal dysfunction, including chronic kidney disease and renal fibrosis, that can be prevented or treated with mineralocorticoid receptor antagonists (MRAs). Here, we used RNA-Sequencing to analyze effects of two MRAs, spironolactone and finerenone, on the aldosterone-induced transcriptome of a human renal cell line stably expressing the MR. Bioinformatics analysis of the data set reveals the identity of hundreds of genes induced or repressed by aldosterone. Their regulation is modulated in a time-dependent manner and, for the induced genes, depends on the aldosterone-driven direct binding of the MR onto its genomic targets that we have previously characterized. Although both MRAs block aldosterone-induced as well as aldosterone-repressed genes qualitatively similarly, finerenone has a quantitatively more efficient antagonism on some aldosterone-induced genes. Our data provide the first complete transcriptome for aldosterone on a human renal cell line and identifies pro-inflammatory markers (IL6, IL11, CCL7, and CXCL8) as aldosterone-repressed genes.

Light and Circadian Signaling Pathway in Pregnancy: Programming of Adult Health and Disease

Light is a crucial environmental signal that affects elements of human health, including the entrainment of circadian rhythms. A suboptimal environment during pregnancy can increase the risk of offspring developing a wide range of chronic diseases in later life. Circadian rhythm disruption in pregnant women may have deleterious consequences for their progeny. In the modern world, maternal chronodisruption can be caused by shift work, jet travel across time zones, mistimed eating, and excessive artificial light exposure at night. However, the impact of maternal chronodisruption on the developmental programming of various chronic diseases remains largely unknown. In this review, we outline the impact of light, the circadian clock, and circadian signaling pathways in pregnancy and fetal development. Additionally, we show how to induce maternal chronodisruption in animal models, examine emerging research demonstrating long-term negative implications for offspring health following maternal chronodisruption, and summarize current evidence related to light and circadian signaling pathway targeted therapies in pregnancy to prevent the development of chronic diseases in offspring.

Chronodisruption: A Poorly Recognized Feature of CKD

Multiple physiological variables change over time in a predictable and repetitive manner, guided by molecular clocks that respond to external and internal clues and are coordinated by a central clock. The kidney is the site of one of the most active peripheral clocks. Biological rhythms, of which the best known are circadian rhythms, are required for normal physiology of the kidneys and other organs. Chronodisruption refers to the chronic disruption of circadian rhythms leading to disease. While there is evidence that circadian rhythms may be altered in kidney disease and that altered circadian rhythms may accelerate chronic kidney disease (CKD) progression, there is no comprehensive review on chronodisruption and chronodisruptors in CKD and its manifestations. Indeed, the term chronodisruption has been rarely applied to CKD despite chronodisruptors being potential therapeutic targets in CKD patients. We now discuss evidence for chronodisruption in CKD and the impact of chronodisruption on CKD manifestations, identify potential chronodisruptors, some of them uremic toxins, and their therapeutic implications, and discuss current unanswered questions on this topic.

A systematic integrative approach reveals novel microRNAs in diabetic nephropathy

Background:

Despite huge efforts, the underlying molecular mechanisms of diabetic nephropathy (DN) are yet elusive, and holistic views have rarely been generated. Considering the complexity of DN pathogenesis, the integration of datasets from different molecular types to construct a multilayer map of DN can provide a comprehensive insight toward the disease mechanisms and also can generate new knowledge. Here, we have re-analyzed two mRNA microarray datasets related to glomerular and tubulointerstitial compartments of human diabetic kidneys.

Materials and Methods:

The quality of the datasets was confirmed by unsupervised hierarchical clustering and principal component analysis. For each dataset, differentially expressed (DE) genes were identified, and transcription factors (TFs) regulating these genes and kinases phosphorylating the TFs were enriched. Furthermore, microRNAs (miRNAs) targeting the DE genes, TFs, and kinases were detected. Based on the harvested genes for glomeruli and tubulointerstitium, key signaling pathways and biological processes involved in diseases pathogenesis were recognized. In addition, the interaction of different elements in each kidney compartment was depicted in multilayer networks, and topology analysis was performed to identify key nodes. Central miRNAs whose target genes were most likely to be related to DN were selected, and their expressions were quantitatively measured in a streptozotocin-induced DN mouse model.

Results:

Among the examined miRNAs, miR-208a-3p and miR-496a-3p are, for the first time, found to be significantly overexpressed in the cortex of diabetic kidneys compared to controls.

Conclusion:

We predict that miR-208 is involved in oxygen metabolism and regulation of cellular energy balance. Furthermore, miR-496 potentially regulates protein metabolism and ion transport. However, their exact functions remain to be investigated in future studies. Taken together, starting from transcriptomics data, we have generated multilayer interaction networks and introduced novel players in DN.

Circadian Variation in Vasoconstriction and Vasodilation Mediators and Baroreflex Sensitivity in Hypertensive Rats

The purpose of this study was to evaluate the relationship between the circadian profile of the vasorelaxing substances calcitonin gene-related peptide (CGRP) and epoxyeicosatrienoic acids (EETs) and the vasconstrictive agent endothelin-1 (ET1) and the daily rhythms of cardiac hemodynamic indices (CHI) and baroreflex (BRS) in Wistar rats with 1 kidney-1 clip model of arterial hypertension (1K-1C AH). The animals were divided into 3 groups: I- sham-operated (SO), II- 4-week and III- 8-week 1K-1C AH rats. Plasma concentration of ET1, CGRP and EET’s were investigated every 4 h. In conscious freely moving 1K-1C AH rats unlike SO animals blood pressure (BP), heart period (HP) and BRS underwent significant circadian fluctuations, with more marked increase in mean values of BP in 8-week hypertensive rats in comparison to 4-week hypertensive rats (179 ± 5 vs. 162 ± 4 mm Hg, p < 0.05). These alterations correlated with more significant reduction in HP (138 ± 5 vs. 150 ± 6 ms, p < 0,05) and BRS (0.44 ± 0.04 vs. 0.58 ± 0.04 ms mm Hg^–1, p < 0.05) in 8-week 1K-1C AH rats. The acrophases of BP in 8-week 1K-1C AH rats in comparison with 4-week were shifted to more late night hours (1:58 a.m. vs. 11:32 p.m.) and in both groups of animals corresponded to lowest circadian plasma levels of CGRP and EETs and to greatest level of ET1. SO rats were characterized by lower values of BP (121 ± 3 mm Hg, p < 0,05) and higher indices of HP (158 ± 2 ms, p < 0,05) and BRS (0.86 ± 0.02 ms mmHg^–1, p < 0,001) in comparison with 1K-1C AH rats 4-week duration. The acrophases of BP, HP and BRS in hypertensive animals were revealed at 14.8 ± 0.5 h, 13.6 ± 0.4 h and 13.1 ± 0.2 h, which correlated with maximal circadian contents of ET1 and CGRP at 24:00 h and EETs at 12:00 h and were shifted in comparison to sham-operated group. In rats with 1K-1C AH, plasma levels of ET1, CGRP and EETs undergo circadian fluctuation with corresponding alterations in CHI and BRS which are more markedly expressed on the late stage of diseases and could be used in future for predictive, preventive, and personalized treatment of arterial hypertension.

24-Hour Profile of Blood Pressure, Heart Rate, Excretion of Electrolytes, and Locomotor Activity in Wistar-Kyoto and SHR Rats Under Conditions of Free-Run Rhythm

We presented the results of our study of chronostructure of BP, HR, electrolyte excretion, and locomotor activity under conditions of "free-run rhythm" (light deprivation). In adult male Wistar-Kyoto (normotensive) and SHR (spontaneously hypertensive) rats, BP, biopotentials of the heart (ECG), and locomotor activity were recorded over 24 h by telemetric monitoring and the rate of excretion of electrolytes (Na⁺, K⁺, Ca²⁺, and Mg²⁺) during the nighttime and daytime hours was measured. It was found that under free-run rhythm, 24-h profiles of BP, HR, excretory function of the kidneys, and locomotor activity underwent more considerable changes in normotensive Wistar-Kyoto rats in comparison with hypertensive SHR rats. However, hypertensive rats demonstrated pronounced changes in rhythmic characteristics of HR, which can restrict adaptation reserves of the cardiovascular system.

Chronobiology in nephrology: the influence of circadian rhythms on renal handling of drugs and renal disease treatment

INTRODUCTION

Chronobiology studies the phenomenon of rhythmicity in living organisms. The circadian rhythms are genetically determined and regulated by external synchronizers (the daylight cycle). Several biological processes involved in the pharmacokinetics and pharmacodynamics of drugs are subjected to circadian variations. Chronopharmacology studies how biological rhythms influence pharmacokinetics, pharmacodynamics, and toxicity, and determines whether time-of-day administration modifies the pharmacological characteristics of the drug. Chronotherapy applies chronopharmacological studies to clinical treatments, determining the best biological time for dosing: when the beneficial effects are maximal and the incidence and/or intensity of related side effects and toxicity are minimal. Most water-soluble drugs or drug metabolites are eliminated by urine through the kidney. The rate of drug clearance in the urine depends on several intrinsic variables related to renal function including renal blood flow, glomerular filtration rate, the ability of the kidney to reabsorb or to secrete drugs, urine flow, and urine pH, which influences the degree of urine acidification. Curiously, all these variables present a circadian behavior in different mammalian models.

CONCLUSION

The circadian rhythms have influence in the renal physiology, pathophysiology, and pharmacology, and these data should be taken into account in clinical nephrology practice.

Maternal melatonin or agomelatine therapy prevents programmed hypertension in male offspring of mother exposed to continuous light

Hypertension can originate from early-life insults, whereas maternal melatonin therapy can be protective in a variety of models of programmed hypertension. We hypothesize that melatonin or melatonin receptor agonist agomelatine can prevent programmed hypertension in adult offspring induced by maternal exposure to continuous light. Female Sprague-Dawley pregnant rats randomly divided into four groups: controls, rats exposed to continuous light, exposed to continuous light plus treated with agomelatine (50 mg/day i.p.), and exposed to continuous light plus treated with 0.01% melatonin in drinking water throughout pregnancy and lactation period. Male offspring (n = 10/group) from three litters were examined at 12 weeks of age. Maternal continuous light exposure-induced hypertension in male offspring, which was prevented by melatonin or agomelatine therapy. Continuous light exposure did not affect melatonin pathway in adult offspring kidney. Genes that belong to the renin-angiotensin system (RAS), sodium transporters, AMP-activated protein kinase pathway, and circadian rhythm were potentially involved in the maternal exposure to continuous light-induced programmed hypertension. Maternal agomelatine therapy decreased Ace expression but increased Agtr2 and Mas1. Maternal melatonin therapy prevented the increases of Slc9a3, Slc12a3, and Atp1a1 expression induced by maternal continuous light exposure. In conclusion, maternal melatonin or agomelatine therapy prevents programmed hypertension induced by maternal exposure to continuous light. Agomelatine and melatonin reprogram the RAS and sodium transporters differentially, to prevent negative programming of continuous light. Our data highlight candidate genes and pathways in renal programming as targets for therapeutic approaches to prevent programmed hypertension caused by early-life disturbance of the circadian rhythm.

Does mean arterial blood pressure scale with body mass in mammals? Effects of measurement of blood pressure

For at least the last 30 years, it has been discussed whether mean arterial blood pressure (MAP) is independent of body mass or whether it increases in accordance with the vertical height between the heart and the brain. The debate has centred on the most appropriate mathematical models for analysing allometric scaling and phylogenetic relationships; there has been previously little focus on evaluating the validity of underlying physiological data. Currently, the 2 most comprehensive scaling analyses are based on data from 47 species of mammals, based on 114 references. We reviewed all available references to determine under which physiological conditions MAP had been recorded. In 44 (38.6%) of the cited references, MAP was measured in anaesthetized animals. Data from conscious animals were reported in 59 (51.8%) of references; of these, 3 (2.6%) were radiotelemetric studies. In 5 species, data were reported from both anaesthetized and conscious animals, and the mean difference in the MAP between these settings was 20 ± 29 mm Hg. From a literature search, we identified MAP measurements performed by radiotelemetry in 11 of the 47 species included in the meta-analyses. A Bland-Altman analysis showed a bias of 1 mm Hg with 95% confidence interval (from -35 to 36 mm Hg); that is, the limits of agreement between radiotelemetric studies and studies in restrained animals were double the supposed difference in the MAP between the mouse and elephant. In conclusion, the existing literature does not provide evidence for either a positive or neutral scaling of arterial pressure to body mass across taxa.

Clock Genes, Metabolism, and Cardiovascular Risk

The molecular clockwork drives rhythmic oscillations of signaling pathways managing intermediate metabolism; the circadian timing system synchronizes behavioral cycles and anabolic/catabolic processes with environmental cues, mainly represented by light/darkness alternation. Metabolic pathways, bile acid synthesis, and autophagic and immune/inflammatory processes are driven by the biological clock. Proper timing of hormone secretion, metabolism, bile acid turnover, autophagy, and inflammation with behavioral cycles is necessary to avoid dysmetabolism. Disruption of the biological clock and mistiming of body rhythmicity with respect to environmental cues provoke loss of internal synchronization and metabolic derangements, causing liver steatosis, obesity, metabolic syndrome, and diabetes mellitus.

Translational contributions to tissue specificity in rhythmic and constitutive gene expression

Background

The daily gene expression oscillations that underlie mammalian circadian rhythms show striking differences between tissues and involve post-transcriptional regulation. Both aspects remain poorly understood. We have used ribosome profiling to explore the contribution of translation efficiency to temporal gene expression in kidney and contrasted our findings with liver data available from the same mice.

Results

Rhythmic translation of constantly abundant messenger RNAs (mRNAs) affects largely non-overlapping transcript sets with distinct phase clustering in the two organs. Moreover, tissue differences in translation efficiency modulate the timing and amount of protein biosynthesis from rhythmic mRNAs, consistent with organ specificity in clock output gene repertoires and rhythmicity parameters. Our comprehensive datasets provided insights into translational control beyond temporal regulation. Between tissues, many transcripts show differences in translation efficiency, which are, however, of markedly smaller scale than mRNA abundance differences. Tissue-specific changes in translation efficiency are associated with specific transcript features and, intriguingly, globally counteracted and compensated transcript abundance variations, leading to higher similarity at the level of protein biosynthesis between both tissues.

Conclusions

We show that tissue specificity in rhythmic gene expression extends to the translatome and contributes to define the identities, the phases and the expression levels of rhythmic protein biosynthesis. Moreover, translational compensation of transcript abundance divergence leads to overall higher similarity at the level of protein production across organs. The unique resources provided through our study will serve to address fundamental questions of post-transcriptional control and differential gene expression in vivo.

Electronic supplementary material

The online version of this article (doi:10.1186/s13059-017-1222-2) contains supplementary material, which is available to authorized users.

High Fat Diets Sex-Specifically Affect the Renal Transcriptome and Program Obesity, Kidney Injury, and Hypertension in the Offspring

Obesity and related disorders have increased concurrently with an increased consumption of saturated fatty acids. We examined whether post-weaning high fat (HF) diet would exacerbate offspring vulnerability to maternal HF-induced programmed hypertension and kidney disease sex-specifically, with a focus on the kidney. Next, we aimed to elucidate the gene–diet interactions that contribute to maternal HF-induced renal programming using the next generation RNA sequencing (NGS) technology. Female Sprague-Dawley rats received either a normal diet (ND) or HF diet (D12331, Research Diets) for five weeks before the delivery. The offspring of both sexes were put on either the ND or HF diet from weaning to six months of age, resulting in four groups of each sex (maternal diet/post-weaning diet; n = 5–7/group): ND/ND, ND/HF, HF/ND, and HF/HF. Post-weaning HF diet increased bodyweights of both ND/HF and HF/HF animals from three to six months only in males. Post-weaning HF diet increased systolic blood pressure in male and female offspring, irrespective of whether they were exposed to maternal HF or not. Male HF/HF offspring showed greater degrees of glomerular and tubular injury compared to the ND/ND group. Our NGS data showed that maternal HF diet significantly altered renal transcriptome with female offspring being more HF-sensitive. HF diet induced hypertension and renal injury are associated with oxidative stress, activation of renin-angiotensin system, and dysregulated sodium transporters and circadian clock. Post-weaning HF diet sex-specifically exacerbates the development of obesity, kidney injury, but not hypertension programmed by maternal HF intake. Better understanding of the sex-dependent mechanisms that underlie HF-induced renal programming will help develop a novel personalized dietary intervention to prevent obesity and related disorders.

Circadian mRNA expression: insights from modeling and transcriptomics

Circadian clocks synchronize organisms to the 24 h rhythms of the environment. These clocks persist under constant conditions, have their origin at the cellular level, and produce an output of rhythmic mRNA expression affecting thousands of transcripts in many mammalian cell types. Here, we review the charting of circadian output rhythms in mRNA expression, focusing on mammals. We emphasize the challenges in statistics, interpretation, and quantitative descriptions that such investigations have faced and continue to face, and outline remaining outstanding questions.

The Circadian Clock in the Regulation of Renal Rhythms

Since the kidney is integral to maintenance of fluid and ion homeostasis, and therefore blood pressure regulation, its proper function is paramount. Circadian fluctuations in blood pressure, renal blood flow, glomerular filtration rate, and sodium and water excretion have been documented for decades, if not longer. Recent studies on the role of circadian clock proteins in the regulation of a variety of renal transport genes suggest that the molecular clock in the kidney controls circadian fluctuations in renal function. The circadian clock appears to be a critical regulator of renal function with important implications for the treatment of renal pathologies, which include chronic kidney disease and hypertension. The development, regulation, and mechanism of the kidney clock are reviewed here.

SIRT1 and circadian gene expression in pancreatic ductal adenocarcinoma: Effect of starvation

Pancreatic cancer (PC), the fourth leading cause of cancer-related deaths, is characterized by high aggressiveness and resistance to chemotherapy. Pancreatic carcinogenesis is kept going by derangement of essential cell processes, such as proliferation, apoptosis, metabolism and autophagy, characterized by rhythmic variations with 24-h periodicity driven by the biological clock. We assessed the expression of the circadian genes ARNLT, ARNLT2, CLOCK, PER1, PER2, PER3, CRY1, CRY2 and the starvation-activated histone/protein deacetylase SIRT1 in 34 matched tumor and non-tumor tissue specimens of PC patients, and evaluated in PC derived cell lines if the modulation of SIRT1 expression through starvation could influence the temporal pattern of expression of the circadian genes. We found a significant down-regulation of ARNLT (p = 0.015), CRY1 (p = 0.013), CRY2 (p = 0.001), PER1 (p < 0.0001), PER2 (p < 0.001), PER3 (p = 0.001) and SIRT1 (p = 0.017) in PC specimens. PER3 and CRY2 expression levels were lower in patients with jaundice at diagnosis ( < 0.05). Having adjusted for age, adjuvant therapy and tumor stage, we evidenced that patients with higher PER2 and lower SIRT1 expression levels showed lower mortality (p = 0.028). Levels and temporal patterns of expression of many circadian genes and SIRT1 significantly changed upon serum starvation in vitro, with differences among four different PC cell lines examined (BXPC3, CFPAC, MIA-PaCa-2 and PANC-1). Serum deprivation induced changes of the overall mean level of the wave and amplitude, lengthened or shortened the cycle time and phase-advanced or phase-delayed the rhythmic oscillation depending on the gene and the PC cell line examined. In conclusion, a severe deregulation of expression of SIRT1 and circadian genes was evidenced in the cancer specimens of PC patients, and starvation influenced gene expression in PC cell lines, suggesting that the altered interplay between SIRT1 and the core circadian proteins could represent a crucial player in the process of pancreatic carcinogenesis.

The biological clock and the molecular basis of lysosomal storage diseases

The lysosomal storage disorders encompass nearly fifty diseases provoked by lack or deficiency of enzymes essential for the breakdown of complex molecules and hallmarked by accumulation in the lysosomes of metabolic residues. Histochemistry and cytochemistry studies evidenced patterns of circadian variation of the lysosomal marker enzymes, suggesting that lysosomal function oscillates rhythmically during the 24-h day. The circadian rhythmicity of cellular processes is driven by the biological clock ticking through transcriptional/translational feedback loops hardwired by circadian genes and proteins. Malfunction of the molecular clockwork may provoke severe deregulation of downstream gene expression regulating a complex array of cellular functions leading to anatomical and functional changes. In this review we highlight that all the genes mutated in lysosomal storage disorders encode circadian transcripts suggesting a direct participation of the biological clock in the pathophysiological mechanisms underlying cellular and tissue derangements hallmarking these hereditary diseases. The 24-h periodicity of oscillation of gene transcription and translation could lead in physiological conditions to circadian rhythmicity of fluctuation of enzyme levels and activity, so that gene transfer could be envisaged to reproduce 24-h periodicity of variation of enzymatic dynamics and circadian rhythmicity could have an impact on the schedule of enzyme replacement therapy.

Long-term effects of maternal citrulline supplementation on renal transcriptome prevention of nitric oxide depletion-related programmed hypertension: the impact of gene-nutrient interactions

Maternal malnutrition can elicit gene expression leading to fetal programming. l-citrulline (CIT) can be converted to l-arginine to generate nitric oxide (NO). We examined whether maternal CIT supplementation can prevent N^G-nitro-l-arginine-methyl ester (l-NAME, NO synthase inhibitor)-induced programmed hypertension and examined their effects on the renal transcriptome in male offspring using next generation RNA sequencing (RNA-Seq) technology. Pregnant Sprague-Dawley rats received l-NAME administration at 60mg/kg/day subcutaneously via osmotic minipump during pregnancy alone or with additional 0.25% l-citrulline solution in drinking water during the whole period of pregnancy and lactation. Male offspring were assigned to three groups: control, l-NAME, and l-NAME + CIT. l-NAME exposure induced hypertension in the 12-week-old offspring, which CIT therapy prevented. Identified differentially expressed genes in l-NAME and CIT-treated offspring kidneys, including Guca2b, Hmox1, Hba2, Hba-a2, Dusp1, and Serpine1 are related to regulation of blood pressure (BP) and oxidative stress. In conclusion, our data suggests that the beneficial effects of CIT supplementation are attributed to alterations in expression levels of genes related to BP control and oxidative stress. Our results suggest that early nutritional intervention by CIT has long-term impact on the renal transcriptome to prevent NO depletion-related programmed hypertension. However, our RNA-Seq results might be a secondary phenomenon. The implications of epigenetic regulation at an early stage of programming deserve further clarification.

Non-alcoholic fatty liver disease: the role of nuclear receptors and circadian rhythmicity

Non-alcoholic fatty liver disease (NAFLD) is the accumulation of triglycerides in the hepatocytes in the absence of excess alcohol intake, and is caused by an imbalance between hepatic synthesis and breakdown of fats, as well as fatty acid storage and disposal. Liver metabolic pathways are driven by circadian biological clocks, and hepatic health is maintained by proper timing of circadian patterns of metabolic gene expression with the alternation of anabolic processes corresponding to feeding/activity during wake times, and catabolic processes characterizing fasting/resting during sleep. A number of nuclear receptors in the liver are expressed rhythmically, bind hormones and metabolites, sense energy flux and expenditure, and connect the metabolic pathways to the molecular clockwork throughout the 24-h day. In this review, we describe the role played by the nuclear receptors in the genesis of NAFLD in relationship with the circadian clock circuitry.

Circadian clock circuitry in colorectal cancer

Colorectal cancer is the most prevalent among digestive system cancers. Carcinogenesis relies on disrupted control of cellular processes, such as metabolism, proliferation, DNA damage recognition and repair, and apoptosis. Cell, tissue, organ and body physiology is characterized by periodic fluctuations driven by biological clocks operating through the clock gene machinery. Dysfunction of molecular clockworks and cellular oscillators is involved in tumorigenesis, and altered expression of clock genes has been found in cancer patients. Epidemiological studies have shown that circadian disruption, that is, alteration of bodily temporal organization, is a cancer risk factor, and an increased incidence of colorectal neoplastic disease is reported in shift workers. In this review we describe the involvement of the circadian clock circuitry in colorectal carcinogenesis and the therapeutic strategies addressing temporal deregulation in colorectal cancer.

Characterization of biological pathways associated with a 1.37 Mbp genomic region protective of hypertension in Dahl S rats

The goal of the present study was to narrow a region of chromosome 13 to only several genes and then apply unbiased statistical approaches to identify molecular networks and biological pathways relevant to blood-pressure salt sensitivity in Dahl salt-sensitive (SS) rats. The analysis of 13 overlapping subcongenic strains identified a 1.37 Mbp region on chromosome 13 that influenced the mean arterial blood pressure by at least 25 mmHg in SS rats fed a high-salt diet. DNA sequencing and analysis filled genomic gaps and provided identification of five genes in this region, Rfwd2, Fam5b, Astn1, Pappa2, and Tnr. A cross-platform normalization of transcriptome data sets obtained from our previously published Affymetrix GeneChip dataset and newly acquired RNA-seq data from renal outer medullary tissue provided 90 observations for each gene. Two Bayesian methods were used to analyze the data: 1) a linear model analysis to assess 243 biological pathways for their likelihood to discriminate blood pressure levels across experimental groups and 2) a Bayesian graphical modeling of pathways to discover genes with potential relationships to the candidate genes in this region. As none of these five genes are known to be involved in hypertension, this unbiased approach has provided useful clues to be experimentally explored. Of these five genes, Rfwd2, the gene most strongly expressed in the renal outer medulla, was notably associated with pathways that can affect blood pressure via renal transcellular Na(+) and K(+) electrochemical gradients and tubular Na(+) transport, mitochondrial TCA cycle and cell energetics, and circadian rhythms.

Rheumatoid arthritis and the biological clock

Rheumatoid arthritis (RA) is an autoimmune disease of unknown cause and a chronic and progressive inflammatory disorder ensuing in genetically predisposed subjects, characterized by synovitis causing joint destruction, as well as inflammation in body organ systems, leading to anatomical alteration and functional disability. Immune competent cells, deregulated synoviocytes and cytokines play a key role in the pathophysiological mechanisms. The immune system function shows time-related variations related to the influence of the neuroendocrine system and driven by the circadian clock circuitry. Immune processes and symptom intensity in RA are characterized by oscillations during the day following a pattern of circadian rhythmicity. A cross-talk between inflammatory and circadian pathways is involved in RA pathogenesis and underlies the mutual actions of disruption of the circadian clock circuitry on immune system function as well as of inflammation on the function of the biological clock. Modulation of molecular processes and humoral factors mediating in RA the interplay between the biological clock and the immune response and underlying the rhythmic fluctuations of pathogenic processes and symptomatology could represent a promising therapeutic strategy in the future.

Possible contribution of chronobiology to cardiovascular health

The daily variations found in many aspects of physiology are collectively known as circadian rhythm (from "circa" meaning "about" and "dien" meaning "day"). Circadian oscillation in clock gene expression can generate quantitative or functional variations of the molecules directly involved in many physiological functions. This paper reviews the molecular mechanisms of the circadian clock, the transmission of circadian effects to cardiovascular functions, and the effects of circadian dysfunction on cardiovascular diseases. An evaluation of the operation of the internal clock is needed in clinical settings and will be an effective tool in the diagnosis of circadian rhythm disorders. Toward this end, we introduce a novel non-invasive method for assessing circadian time-regulation in human beings through the utilization of hair follicle cells.