Circadian regulation of renal function and potential role in hypertension

New insights into the mechanisms of diabetic kidney disease: Role of circadian rhythm and Bmal1

It is common for diabetic kidney disease (DKD) to be complicated by abnormal blood glucose, blood lipids, and blood pressure rhythms. Thus, it is essential to examine diagnostic and treatment plans from the perspective of circadian disruption. This brief review discusses the clinical relevance of circadian rhythms in DKD and how the core clock gene encoding brain and muscle arnt-like protein 1 (BMAL1) functions owing to the importance of circadian rhythm disruption processes, including the excretion of urinary protein and irregular blood pressure, which occur in DKD. Exploring Bmal1 and its potential mechanisms and signaling pathways in DKD following contact with Sirt1 and NF-κB is novel and important. Finally, potential pharmacological and behavioral intervention strategies for DKD circadian rhythm disturbance are outlined. This review aids in unveiling novel, potential molecular targets for DKD based on circadian rhythms.

Circadian Urinary Excretion of Water, and Not Salt, Is Affected by the White Coat Effect

Hypertension is an important morbidity factor. The prognostic consequences of the white-coat effect have been studied extensively. The repercussion on the circadian rhythm of urinary water and salt excretion in the same subgroup remain, conversely, among the open topics. Postulating an impaired diurnal sodium and volume excretion we decided to investigate both, in subjects with or without a white-coat effect, in the general population. A sample of 1023 subjects, has been considered. We collected 24-h urine samples, divided in day and night, and we measured the blood pressure with an Ambulatory Blood Pressure Monitoring (ABPM). ABPM values were then compared with physician collected in-office values to assign subjects to the group with or without the white-coat effect. Concerning the circadian pattern of urinary sodium excretion, we found no significant differences between the groups. There was instead in the white-coat effect group a higher night/day ratio of urinary water excretion. The white-coat effect, has been considered a potential hypertension precursor, and its consequent handling could be prospectively relevant in hypertension prevention. The absence of repercussions on the urinary circadian sodium excretion pattern and on the potentially related risk factors in subjects with a white coat effect is reassuring. The clinical significance of the impact on the night/day ratio of water excretion needs to be further investigated.

Circadian gene expression in mouse renal proximal tubule

Circadian variability in kidney function is well recognized but is often ignored as a potential confounding variable in physiological experiments. Here, we have created a data resource consisting of expression levels for mRNA transcripts in microdissected proximal tubule segments from mice as a function of the time of day. Small-sample RNA sequencing was applied to microdissected S1 proximal convoluted tubules and S2 proximal straight tubules. After stringent filtering, the data were analyzed using JTK-Cycle to detect periodicity. The data set is provided as a user-friendly webpage at https://esbl.nhlbi.nih.gov/Databases/Circadian-Prox2/. In proximal convoluted tubules, 234 transcripts varied in a circadian manner (4.0% of the total). In proximal straight tubules, 334 transcripts varied in a circadian manner (5.3%). Transcripts previously known to be associated with corticosteroid action and with increased flow were found to be overrepresented among circadian transcripts peaking during the "dark" portion of the day [zeitgeber time (ZT)14-22], corresponding to peak levels of corticosterone and glomerular filtration rate in mice. To ask whether there is a time-of-day dependence of protein abundances in the kidney, we carried out LC-MS/MS-based proteomics in whole mouse kidneys at ZT12 and ZT0. The full data set (n = 6,546 proteins) is available at https://esbl.nhlbi.nih.gov/Databases/Circadian-Proteome/. Overall, 293 proteins were differentially expressed between ZT12 and ZT0 (197 proteins greater at ZT12 and 96 proteins greater at ZT0). Among the regulated proteins, only nine proteins were found to be periodic in the RNA-sequencing analysis, suggesting a high level of posttranscriptional regulation of protein abundances.NEW & NOTEWORTHY Circadian variation in gene expression can be an important determinant in the regulation of kidney function. The authors used RNA-sequencing transcriptomics and LC-MS/MS-based proteomics to identify gene products expressed in a periodic manner. The data were used to construct user-friendly web resources.

The Vascular Circadian Clock in Chronic Kidney Disease

Chronic kidney disease is associated with extremely high cardiovascular mortality. The circadian rhythms (CR) have an impact on vascular function. The disruption of CR causes serious health problems and contributes to the development of cardiovascular diseases. Uremia may affect the master pacemaker of CR in the hypothalamus. A molecular circadian clock is also expressed in peripheral tissues, including the vasculature, where it regulates the different aspects of both vascular physiology and pathophysiology. Here, we address the impact of CKD on the intrinsic circadian clock in the vasculature. The expression of the core circadian clock genes in the aorta is disrupted in CKD. We propose a novel concept of the disruption of the circadian clock system in the vasculature of importance for the pathology of the uremic vasculopathy.

Bidirectional and Temporal Association Between Hypertension and Microalbuminuria: A Longitudinal Study in Chinese Adults

Background Although hypertension and microalbuminuria are closely interrelated, the magnitude and temporal sequence of the bidirectional association between hypertension and microalbuminuria are largely unknown. We aimed to delineate the bidirectional and temporal relationship between hypertension and microalbuminuria. Methods and Results Leveraging a longitudinal cohort of Chinese adults who had blood pressure and urinary albumin measured twice 4 years apart, we examined the temporal association between hypertension and microalbuminuria by bidirectional and cross-lagged panel analysis. All participants were free of cardiovascular disease and chronic kidney disease at baseline. Bidirectional association analysis found that baseline microalbuminuria predicted the risk of incident hypertension (odds ratio=1.75, P=0.028), and baseline blood pressure also significantly predicted the risk of microalbuminuria (odds ratios=1.27 and 1.21 for a per-SD increase in systolic and diastolic blood pressure, respectively; all P<0.05). Cross-lagged panel analysis demonstrated a bottom-line significant relationship of baseline systolic blood pressure to follow-up urinary albumin ( P=0.079), which is significantly weaker than the other direction of the relationship of baseline urinary albumin to follow-up blood pressures (all P<0.001). Conclusions These findings indicate a significant bidirectional association between microalbuminuria and hypertension in Chinese adults. Elevated urinary albumin excretion is more likely to precede hypertension. The causality between microalbuminuria and hypertension needs further investigation.

Circadian rhythms and the kidney

Numerous physiological functions exhibit substantial circadian oscillations. In the kidneys, renal plasma flow, the glomerular filtration rate and tubular reabsorption and/or secretion processes have been shown to peak during the active phase and decline during the inactive phase. These functional rhythms are driven, at least in part, by a self-sustaining cellular mechanism termed the circadian clock. The circadian clock controls different cellular functions, including transcription, translation and protein post-translational modifications (such as phosphorylation, acetylation and ubiquitylation) and degradation. Disruption of the circadian clock in animal models results in the loss of blood pressure control and substantial changes in the circadian pattern of water and electrolyte excretion in the urine. Kidney-specific suppression of the circadian clock in animals implicates both the intrinsic renal and the extrarenal circadian clocks in these pathologies. Alterations in the circadian rhythm of renal functions are associated with the development of hypertension, chronic kidney disease, renal fibrosis and kidney stones. Furthermore, renal circadian clocks might interfere with the pharmacokinetics and/or pharmacodynamics of various drugs and are therefore an important consideration in the treatment of some renal diseases or disorders.

Circadian variation in the release of small extracellular vesicles can be normalized by vesicle number or TSG101

Numerous candidate biomarkers in urine extracellular vesicles (EVs) have been described for kidney diseases, but none are yet in clinical use, possibly due to a lack of proper normalization. Proper normalization corrects for normal biological variation in urine flow rate or concentration, which can vary by over one order of magnitude. Here, we observed inter- and intra-animal variation in urine excretion rates of small EVs (<200 nm in diameter) in healthy rats as a series of six 4-h fractions. To visualize intra-animal variation, we normalized a small EV excretion rate to a peak excretion rate, revealing a circadian pattern for each rat. This circadian pattern was distinct from urine volume, urine albumin, urine creatinine, and urine albumin-to-creatinine ratio. Furthermore, urine small EV excretion was not significantly altered by sex, food/water deprivation, or ischemic acute kidney injury. Urine excretion of the exosomal/small EV marker protein tumor susceptibility gene 101 (TSG101) displayed a similar circadian pattern to urine small EV excretion; both measurements were highly correlated (R² = 0.85), with an average stoichiometry of 10.0 molecules of TSG101/vesicle in healthy rats. The observed stoichiometry of TSG101/vesicle in rat urine translated to human spot urine samples (10.2 molecules/vesicle) and cultured kidney-derived cell lines (human embryonic kidney-293 and normal rat kidney 52E cells). Small EV number and its surrogate, TSG101 protein, can normalize for circadian variation when testing candidate biomarkers in small EVs. Just as creatinine has emerged as the customary normalization factor for liquid-phase urine biomarkers, vesicle number and its surrogate, molecules of exosome/small EV-associated TSG101, should be considered as viable, normalizing factors for small EV biomarkers.

Melatonin therapy protects against renal injury before and after release of bilateral ureteral obstruction in rats

AIM

Blockage of the urinary tract is often connected with renal function impediment, including reductions in glomerular filtration rate (GFR) and the power to control sodium as well as water elimination through urination. Melatonin, known to be the primary product of the pineal gland, prevents renal damage caused by ischemic reperfusion. However, the effects of melatonin on urinary obstruction, as well as release of obstruction induced kidney injury are still largely unknown. The aim of present study was to investigate the effect of melatonin on mediating protection against renal injury triggered from either bilateral ureteral obstruction (BUO) or BUO release (BUO-R).

MAIN METHODS

Adult male Sprague-Dawley rats (n = 60) were clustered into six treatment groups: sham treated-1; BUO-non-treated (24 h BUO only); BUO + melatonin; sham treated-2; BUO-48hR (24 h of BUO and then release for 2 days); and BUO-48hR + melatonin. Kidney tissues, blood and urine samples were obtained for further assessment.

KEY FINDINGS

It was found that melatonin treatment remarkably promoted the recovery of the handling capacity of urinary excretion of water as well as sodium in BUO and BUO-48hR models. Melatonin treatment partially inhibited inflammatory cytokine expression and the downregulation of aquaporin (AQPs, AQP-1, -2 and -3) expression in these two models. Moreover, the cytoarchitecture of BUO rats exposed to melatonin was well preserved.

SIGNIFICANCE

Melatonin treatment potently prevents BUO or BUO-R induced renal injury, which may be partially attributed to restoring the expression of AQPs and inhibition of inflammatory response, as well as preserving renal ultrastructural integrity.

Systemic Succinate Homeostasis and Local Succinate Signaling Affect Blood Pressure and Modify Risks for Calcium Oxalate Lithogenesis

BACKGROUND

In the kidney, low urinary citrate increases the risk for developing kidney stones, and elevation of luminal succinate in the juxtaglomerular apparatus increases renin secretion, causing hypertension. Although the association between stone formation and hypertension is well established, the molecular mechanism linking these pathophysiologies has been elusive.

METHODS

To investigate the relationship between succinate and citrate/oxalate levels, we assessed blood and urine levels of metabolites, renal protein expression, and BP (using 24-hour telemetric monitoring) in male mice lacking slc26a6 (a transporter that inhibits the succinate transporter NaDC-1 to control citrate absorption from the urinary lumen). We also explored the mechanism underlying this metabolic association, using coimmunoprecipitation, electrophysiologic measurements, and flux assays to study protein interaction and transport activity.

RESULTS

Compared with control mice, slc26a6^-/- mice (previously shown to have low urinary citrate and to develop calcium oxalate stones) had a 40% decrease in urinary excretion of succinate, a 35% increase in serum succinate, and elevated plasma renin. Slc26a6^-/- mice also showed activity-dependent hypertension that was unaffected by dietary salt intake. Structural modeling, confirmed by mutational analysis, identified slc26a6 and NaDC-1 residues that interact and mediate slc26a6's inhibition of NaDC-1. This interaction is regulated by the scaffolding protein IRBIT, which is released by stimulation of the succinate receptor SUCNR1 and interacts with the NaDC-1/slc26a6 complex to inhibit succinate transport by NaDC-1.

CONCLUSIONS

These findings reveal a succinate/citrate homeostatic pathway regulated by IRBIT that affects BP and biochemical risk of calcium oxalate stone formation, thus providing a potential molecular link between hypertension and lithogenesis.

Fetal Programming of Renal Dysfunction and High Blood Pressure by Chronodisruption

Adverse prenatal conditions are known to impose significant trade-offs impinging on health and disease balance during adult life. Among several deleterious factors associated with complicated pregnancy, alteration of the gestational photoperiod remains largely unknown. Previously, we reported that prenatal manipulation of the photoperiod has adverse effects on the mother, fetus, and adult offspring; including cardiac hypertrophy. Here, we investigated whether chronic photoperiod shifting (CPS) during gestation may program adult renal function and blood pressure regulation. To this end, pregnant rats were subjected to CPS throughout pregnancy to evaluate the renal effects on the fetus and adult offspring. In the kidney at 18 days of gestation, both clock and clock-controlled gene expression did not display a daily pattern, although there were recurrent weaves of transcriptional activity along the 24 h in the control group. Using DNA microarray, significant differential expression was found for 1,703 transcripts in CPS relative to control fetal kidney (835 up-regulated and 868 down-regulated). Functional genomics assessment revealed alteration of diverse gene networks in the CPS fetal kidney, including regulation of transcription, aldosterone-regulated Na+ reabsorption and connective tissue differentiation. In adult offspring at 90 days of age, circulating proinflammatory cytokines IL-1β and IL-6 were increased under CPS conditions. In these individuals, CPS did not modify kidney clock gene expression but had effects on different genes with specific functions in the nephron. Next, we evaluated several renal markers and the response of blood pressure to 4%NaCl in the diet for 4 weeks (i.e., at 150 days of age). CPS animals displayed elevated systolic blood pressure in basal conditions that remained elevated in response to 4%NaCl, relative to control conditions. At this age, CPS modified the expression of Nhe3, Ncc, Atp1a1, Nr3c1 (glucocorticoid receptor), and Nr3c2 (mineralocorticoid receptor); while Nkcc, Col3A1, and Opn were modified in the CPS 4%+NaCl group. Furthermore, CPS decreased protein expression of Kallikrein and COX-2, both involved in sodium handling. In conclusion, gestational chronodisruption programs kidney dysfunction at different levels, conceivably underlying the prehypertensive phenotype observed in the adult CPS offspring.

Role of melatonin receptor 1A and pituitary homeobox-1 coexpression in protecting tubular epithelial cells in membranous nephropathy

Membranous nephropathy (MN), a type of glomerular nephritis, is one of the most common causes of nephrotic syndrome in adults. Although it is known that melatonin plays a protective role in MN, the role of melatonin receptors in the pathophysiology of MN is unclear. Using an experimental MN model and clinical MN specimens, we studied melatonin receptor expression and found that melatonin receptor 1A (MTNR1A) expression was significantly downregulated in renal tubular epithelial cells. Molecular studies showed that the transcription factor pituitary homeobox-1 (PITX1) promoted MTNR1A expression via direct binding to its promoter. Treatment of a human tubular cell line with albumin to induce injury resulted in the stable reduction in MTNR1A and PITX1 expression. PITX1 levels were significantly downregulated in tubular epithelial cells from mice MN kidneys and MN renal specimens. Knockdown of MTNR1A, PITX1, or cyclic adenosine monophosphate-responsive element-binding protein (CREB) decreased E-cadherin (CDH1) expression, but upregulated Per2 and α-smooth muscle actin (αSMA) expression. Blockade of the MTNR1A receptor with luzindole in MN mice further impaired renal function; this was accompanied by CDH1 downregulation and Per2 and αSMA upregulation. Together, our results suggest that in injured tissue, decreased PITX1 expression at the MTNR1A promoter regions leads to decreased levels of MTNR1A in renal tubular epithelial cells, which increases the future risk of MN.

ASK family kinases mediate cellular stress and redox signaling to circadian clock

The cellular stress response and circadian clock system are fundamental functions in homeostatic regulation in almost all organisms. However, whether these two mechanisms are interlocked with each other, and the key molecule that links cellular stress and the circadian clock, remain unclear. Here we identify ASK family kinases that are essential for the circadian clock to respond to cellular stress, and report that Ask1 transcription is rhythmically controlled by the circadian clock. Moreover, LC-MS/MS–based proteomic analysis provides insight into a molecular mechanism in which dephosphorylation-triggered changes to the ASK complex mediate cellular stress to the circadian clock. From the perspective of cell signaling, our present findings expand previously reported roles of stress signaling toward regulation of the circadian clock.

Daily rhythms of behaviors and physiologies are generated by the circadian clock, which is composed of clock genes and the encoded proteins forming transcriptional/translational feedback loops (TTFLs). The circadian clock is a self-sustained oscillator and flexibly responds to various time cues to synchronize with environmental 24-h cycles. However, the key molecule that transmits cellular stress to the circadian clockwork is unknown. Here we identified apoptosis signal-regulating kinase (ASK), a member of the MAPKKK family, as an essential mediator determining the circadian period and phase of cultured cells in response to osmotic changes of the medium. The physiological impact of ASK signaling was demonstrated by a response of the clock to changes in intracellular redox states. Intriguingly, the TTFLs drive rhythmic expression of Ask genes, indicating ASK-mediated association of the TTFLs with intracellular redox. In behavioral analysis, Ask1, Ask2, and Ask3 triple-KO mice exhibited compromised light responses of the circadian period and phase in their activity rhythms. LC-MS/MS–based proteomic analysis identified a series of ASK-dependent and osmotic stress-responsive phosphorylations of proteins, among which CLOCK, a key component of the molecular clockwork, was phosphorylated at Thr843 or Ser845 in the carboxyl-terminal region. These findings reveal the ASK-dependent stress response as an underlying mechanism of circadian clock flexibility.

The significance of circadian rhythms and dysrhythmias in critical illness

Many physiological and cellular processes cycle with time, with the period between one peak and the next being roughly equal to 24 h. These circadian rhythms underlie 'permissive homeostasis', whereby anticipation of periods of increased energy demand or stress may enhance the function of individual cells, organ systems or whole organisms. Many physiological variables related to survival during critical illness have a circadian rhythm, including the sleep/wake cycle, haemodynamic and respiratory indices, immunity and coagulation, but their clinical significance remains underappreciated. Critically ill patients suffer from circadian dysrhythmia, manifesting overtly as sleep disturbance and delirium, but with widespread covert effects on cellular and organ function. Environmental and pharmacological strategies that ameliorate or prevent circadian dysrhythmia have demonstrated clinical benefit. Harnessing these important biological phenomena to match metabolic supply to demand and bolster cell defenses at the apposite time may be a future therapeutic strategy in the intensive care unit.

Neuroendocrine abnormalities in Parkinson's disease

Neuroendocrine abnormalities are common in Parkinson's disease (PD) and include disruption of melatonin secretion, disturbances of glucose, insulin resistance and bone metabolism, and body weight changes. They have been associated with multiple non-motor symptoms in PD and have important clinical consequences, including therapeutics. Some of the underlying mechanisms have been implicated in the pathogenesis of PD and represent promising targets for the development of disease biomarkers and neuroprotective therapies. In this systems-based review, we describe clinically relevant neuroendocrine abnormalities in Parkinson's disease to highlight their role in overall phenotype. We discuss pathophysiological mechanisms, clinical implications, and pharmacological and non-pharmacological interventions based on the current evidence. We also review recent advances in the field, focusing on the potential targets for development of neuroprotective drugs in Parkinson's disease and suggest future areas for research.

Potassium Homeostasis, Oxidative Stress, and Human Disease

Potassium is the most abundant cation in the intracellular fluid and it plays a vital role in the maintenance of normal cell functions. Thus, potassium homeostasis across the cell membrane, is very critical because a tilt in this balance can result in different diseases that could be life threatening. Both Oxidative stress (OS) and potassium imbalance can cause life threatening health conditions. OS and abnormalities in potassium channel have been reported in neurodegenerative diseases. This review highlights the major factors involved in potassium homeostasis (dietary, hormonal, genetic, and physiologic influences), and discusses the major diseases and abnormalities associated with potassium imbalance including hypokalemia, hyperkalemia, hypertension, chronic kidney disease, and Gordon's syndrome, Bartter syndrome, and Gitelman syndrome.

Nephron-Specific Deletion of Circadian Clock Gene Bmal1 Alters the Plasma and Renal Metabolome and Impairs Drug Disposition

The circadian clock controls a wide variety of metabolic and homeostatic processes in a number of tissues, including the kidney. However, the role of the renal circadian clocks remains largely unknown. To address this question, we performed a combined functional, transcriptomic, and metabolomic analysis in mice with inducible conditional knockout (cKO) of BMAL1, which is critically involved in the circadian clock system, in renal tubular cells (Bmal1lox/lox/Pax8-rtTA/LC1 mice). Induction of cKO in adult mice did not produce obvious abnormalities in renal sodium, potassium, or water handling. Deep sequencing of the renal transcriptome revealed significant changes in the expression of genes related to metabolic pathways and organic anion transport in cKO mice compared with control littermates. Furthermore, kidneys from cKO mice exhibited a significant decrease in the NAD+-to-NADH ratio, which reflects the oxidative phosphorylation-to-glycolysis ratio and/or the status of mitochondrial function. Metabolome profiling showed significant changes in plasma levels of amino acids, biogenic amines, acylcarnitines, and lipids. In-depth analysis of two selected pathways revealed a significant increase in plasma urea level correlating with increased renal Arginase II activity, hyperargininemia, and increased kidney arginine content as well as a significant increase in plasma creatinine concentration and a reduced capacity of the kidney to secrete anionic drugs (furosemide) paralleled by an approximate 80% decrease in the expression level of organic anion transporter 3 (SLC22a8). Collectively, these results indicate that the renal circadian clocks control a variety of metabolic/homeostatic processes at the intrarenal and systemic levels and are involved in drug disposition.

Circadian disruption: New clinical perspective of disease pathology and basis for chronotherapeutic intervention

Biological processes are organized in time as innate rhythms defined by the period (τ), phase (peak [Φ] and trough time), amplitude (A, peak-trough difference) and mean level. The human time structure in its entirety is comprised of ultradian (τ < 20 h), circadian (20 h > τ < 28 h) and infradian (τ > 28 h) bioperiodicities. The circadian time structure (CTS) of human beings, which is more complicated than in lower animals, is orchestrated and staged by a brain central multioscillator system that includes a prominent pacemaker - the suprachiasmatic nuclei of the hypothalamus. Additional pacemaker activities are provided by the pineal hormone melatonin, which circulates during the nighttime, and the left and right cerebral cortices. Under ordinary circumstances this system coordinates the τ and Φ of rhythms driven by subservient peripheral cell, tissue and organ clock networks. Cyclic environmental, feeding and social time cues synchronize the endogenous 24 h clocks and rhythms. Accordingly, processes and functions of the internal environment are integrated in time for maximum biological efficiency, and they are also organized and synchronized in time to the external environment to ensure optimal performance and response to challenge. Artificial light at night (ALAN) exposure can alter the CTS as can night work, which, like rapid transmeridian displacement by air travel, necessitates realignment of the Φ of the multitude of 24 h rhythms. In 2001, Stevens and Rea coined the phrase "circadian disruption" (CD) to label the CTS misalignment induced by ALAN and shift work (SW) as a potential pathologic mechanism of the increased risk for cancer and other medical conditions. Current concerns relating to the effects of ALAN exposure on the CTS motivated us to renew our long-standing interest in the possible role of CD in the etiopathology of common human diseases and patient care. A surprisingly large number of medical conditions involve CD: adrenal insufficiency; nocturia; sleep-time non-dipping and rising blood pressure 24 h patterns (nocturnal hypertension); delayed sleep phase syndrome, non-24 h sleep/wake disorder; recurrent hypersomnia; SW intolerance; delirium; peptic ulcer disease; kidney failure; depression; mania; bipolar disorder; Parkinson's disease; Smith-Magenis syndrome; fatal familial insomnia syndrome; autism spectrum disorder; asthma; byssinosis; cancers; hand, foot and mouth disease; post-operative state; and ICU outcome. Poorly conceived medical interventions, for example nighttime dosing of synthetic corticosteroids and certain β-antagonists and cyclic nocturnal enteral or parenteral nutrition, plus lifestyle habits, including atypical eating times and chronic alcohol consumption, also can be causal of CD. Just as surprisingly are the many proven chronotherapeutic strategies available today to manage the CD of several of these medical conditions. In clinical medicine, CD seems to be a common, yet mostly unrecognized, pathologic mechanism of human disease as are the many effective chronotherapeutic interventions to remedy it.

A Protective Role for Androgen Receptor in Clear Cell Renal Cell Carcinoma Based on Mining TCGA Data

Androgen receptor (AR) is expressed in normal murine and human kidneys of both genders, but its physiologic role is uncertain. Several studies showed loss of AR in renal cell carcinoma (RCC) in conjunction with increasing clinical stage and pathological grade, but others found that higher AR expression correlated with worse outcomes. Limited functional studies with renal cell lines suggested tumor-promoting activity of AR. In this study, we queried transcriptomic, proteomic, epigenetic and survival data from The Cancer Genome Atlas (TCGA) to evaluate AR expression and its association with overall survival in three subtypes of RCC (clear cell [ccRCC], papillary [pRCC], and chromophobe [chRCC]). We found that although there was no significant difference in AR mRNA expression in ccRCC of males vs. females, AR protein expression in ccRCC was significantly higher in male compared to female patients. More importantly, higher expression of AR at both transcript and protein levels was associated with improved overall survival in both genders with ccRCC, but did not predict survival of either gender with pRCC or chRCC. Genes whose transcript levels were associated with AR mRNA levels significantly overlapped between ccRCC and pRCC, but not with chRCC, suggesting a similar transcriptional program mediated by AR in ccRCC and pRCC. Ingenuity pathway analysis also identified overlapping pathways and upstream regulators enriched in AR-associated genes in ccRCC and pRCC. Hypermethylation of CpG sites located in the promoter and first exon of AR was associated with loss of AR expression and poor overall survival. Our findings support a tumor suppressor role for AR in both genders that might be exploited to decrease the incidence or progression of ccRCC.

Association of daylight saving time transitions with incidence and in-hospital mortality of myocardial infarction in Finland

INTRODUCTION

Circadian rhythm disturbance increases cardiovascular risk but the effects of daylight saving time (DST) transitions on the risk of myocardial infarction (MI) are unclear.

METHODS

We studied association of DST transitions in 2001-2009 with incidence and in-hospital mortality of MI admissions nationwide in Finland. Incidence rations (IR) of observed incidences on seven days following DST transition were compared to expected incidences.

RESULTS

Incidence of MI increased on Wednesday (IR 1.16; CI 1.01-1.34) after spring transition (6298 patients' cohort). After autumn transition (8161 patients' cohort), MI incidence decreased on Monday (IR 0.85; CI 0.74-0.97) but increased on Thursday (IR 1.15; CI 1.02-1.30). The overall incidence of MI during the week after each DST transition did not differ from control weeks. Patient age or gender, type of MI or in-hospital mortality were not associated with transitions. Renal insufficiency was more common among MI patients after spring transition (OR 1.81; CI 1.06-3.09; p < 0.05). Diabetes was less common after spring transition (OR 0.71; CI 0.55-0.91; p = 0.007), but more common after autumn transition (OR 1.21; 1.00-1.46; p < 0.05).

CONCLUSIONS

DST transitions are followed by changes in the temporal pattern but not the overall rate of MI incidence. Comorbidities may modulate the effects DST transitions.

Taking into account circadian rhythm when conducting experiments on animals

Do your kidneys know what time it is? Mounting evidence from human studies and animal models strongly suggests that the answer to this question is yes. The time has come to start reporting the time of day at which renal physiology studies are performed.

Transcriptional regulation of NHE3 and SGLT1 by the circadian clock protein Per1 in proximal tubule cells

We have previously demonstrated that the circadian clock protein period (Per)1 coordinately regulates multiple genes involved in Na(+) reabsorption in renal collecting duct cells. Consistent with these results, Per1 knockout mice exhibit dramatically lower blood pressure than wild-type mice. The proximal tubule is responsible for a majority of Na(+) reabsorption. Previous work has demonstrated that expression of Na(+)/H(+) exchanger 3 (NHE3) oscillates with a circadian pattern and Na(+)-glucose cotransporter (SGLT)1 has been demonstrated to be a circadian target in the colon, but whether these target genes are regulated by Per1 has not been investigated in the kidney. The goal of the present study was to determine if Per1 regulates the expression of NHE3, SGLT1, and SGLT2 in the kidney. Pharmacological blockade of nuclear Per1 entry resulted in decreased mRNA expression of SGLT1 and NHE3 but not SGLT2 in the renal cortex of mice. Per1 small interfering RNA and pharmacological blockade of Per1 nuclear entry in human proximal tubule HK-2 cells yielded the same results. Examination of heterogeneous nuclear RNA suggested that the effects of Per1 on NHE3 and SGLT1 expression occurred at the level of transcription. Per1 and the circadian protein CLOCK were detected at promoters of NHE3 and SGLT1. Importantly, both membrane and intracellular protein levels of NHE3 and SGLT1 were decreased after blockade of nuclear Per1 entry. This effect was associated with reduced activity of Na(+)-K(+)-ATPase. These data demonstrate a role for Per1 in the transcriptional regulation of NHE3 and SGLT1 in the kidney.

Sleep disorders and inflammatory disease activity: chicken or the egg?

Sleep dysfunction is a highly prevalent condition that has long been implicated in accelerating disease states characterized by having an inflammatory component such as systemic lupus erythematosus, HIV, and multiple sclerosis. Inflammatory bowel disease (IBD) is a chronic, debilitating disease that is characterized by waxing and waning symptoms, which are a direct result of increased circulating inflammatory cytokines. Recent studies have demonstrated sleep dysfunction and the disruption of the circadian rhythm to result in an upregulation of inflammatory cytokines. Not only does this pose a potential trigger for disease flares but also an increased risk of malignancy in this subset of patients. This begs to question whether or not there is a therapeutic role of sleep cycle and circadian rhythm optimization in the prevention of IBD flares. Further research is needed to clarify the role of sleep dysfunction and alterations of the circadian rhythm in modifying disease activity and also in reducing the risk of malignancy in patients suffering from IBD.

Rhythmic control of activity and sleep by class B1 GPCRs

Members of the class B1 family of G-protein coupled receptors (GPCRs) whose ligands are neuropeptides have been implicated in regulation of circadian rhythms and sleep in diverse metazoan clades. This review discusses the cellular and molecular mechanisms by which class B1 GPCRs, especially the mammalian VPAC2 receptor and its functional homologue PDFR in Drosophila and C. elegans, regulate arousal and daily rhythms of sleep and wake. There are remarkable parallels in the cellular and molecular roles played by class B1 intercellular signaling pathways in coordinating arousal and circadian timekeeping across multiple cells and tissues in these very different genetic model organisms.

Evening -versus morning- dosing drug therapy for chronic kidney disease patients with hypertension: a systematic review

BACKGROUND/AIMS

There is a strong correlation between non-dipping status and cardiovascular events in chronic kidney disease (CKD) patients. Our study is designed to identify the effect of evening administration of antihypertensive drugs to hypertensive CKD patients.

METHODS

A comprehensive search of Medline, Embase, the Chinese Biomedical Literature Database, Wanfang Data, Chinese National Knowledge Infrastructure, and the Cochrane Central Register of Controlled Trials was performed in July 2014. Concurrent controlled or crossover trials (including randomized and non-randomized experimental trials) designed to evaluate the effects of evening- versus morning-dosing hypertensive drug regimens on clinical outcomes in CKD patients with hypertension were included. All statistical analyses were performed using the RevMan software, which is available free from the Cochrane Collaboration.

RESULTS

Seven trials involving 1277 patients were identified, and the randomized controlled trials (RCTs) and non-randomized controlled trials (non-RCTs) were classified into two groups. Taking at least one blood pressure-lowering medication at bedtime was not shown to reduce total death (P=0.056) or cardiovascular death (P=0.059) but was shown to reduce total events (P<0.001) and major cardiovascular events (P<0.001) in both RCTs and non-RCTs. Compared with a morning dosing regimen, taking antihypertensive drug in the evening significantly lowered nighttime systolic blood pressure (SBP) (P<0.0001) and diastolic blood pressure (P<0.05) in patients in the RCTs but did not affect blood pressure in patients in the non-RCTs (P<0.05). There is limited evidence from one non-RCT that taking an antihypertensive drug (benazepril 10 mg) in the evening did not increase adverse events (P=0.72) or withdrawals due to adverse events (P=0.64).

CONCLUSIONS

A regimen of antihypertensive drugs in the evening should be considered for CKD patients with hypertension to lower nighttime blood pressure and help prevent total events and cardiovascular mortality. More studies are needed to verify the results of this study.

Regulation of Potassium Homeostasis

Potassium is the most abundant cation in the intracellular fluid, and maintaining the proper distribution of potassium across the cell membrane is critical for normal cell function. Long-term maintenance of potassium homeostasis is achieved by alterations in renal excretion of potassium in response to variations in intake. Understanding the mechanism and regulatory influences governing the internal distribution and renal clearance of potassium under normal circumstances can provide a framework for approaching disorders of potassium commonly encountered in clinical practice. This paper reviews key aspects of the normal regulation of potassium metabolism and is designed to serve as a readily accessible review for the well informed clinician as well as a resource for teaching trainees and medical students.

A role for the circadian clock protein Per1 in the regulation of the NaCl co-transporter (NCC) and the with-no-lysine kinase (WNK) cascade in mouse distal convoluted tubule cells

It has been well established that blood pressure and renal function undergo circadian fluctuations. We have demonstrated that the circadian protein Per1 regulates multiple genes involved in sodium transport in the collecting duct of the kidney. However, the role of Per1 in other parts of the nephron has not been investigated. The distal convoluted tubule (DCT) plays a critical role in renal sodium reabsorption. Sodium is reabsorbed in this segment through the actions of the NaCl co-transporter (NCC), which is regulated by the with-no-lysine kinases (WNKs). The goal of this study was to test if Per1 regulates sodium transport in the DCT through modulation of NCC and the WNK kinases, WNK1 and WNK4. Pharmacological blockade of nuclear Per1 entry resulted in decreased mRNA expression of NCC and WNK1 but increased expression of WNK4 in the renal cortex of mice. These findings were confirmed by using Per1 siRNA and pharmacological blockade of Per1 nuclear entry in mDCT15 cells, a model of the mouse distal convoluted tubule. Transcriptional regulation was demonstrated by changes in short lived heterogeneous nuclear RNA. Chromatin immunoprecipitation experiments demonstrated interaction of Per1 and CLOCK with the promoters of NCC, WNK1, and WNK4. This interaction was modulated by blockade of Per1 nuclear entry. Importantly, NCC protein expression and NCC activity, as measured by thiazide-sensitive, chloride-dependent (22)Na uptake, were decreased upon pharmacological inhibition of Per1 nuclear entry. Taken together, these data demonstrate a role for Per1 in the transcriptional regulation of NCC, WNK1, and WNK4.

DEC1/STRA13/SHARP2 and DEC2/SHARP1 coordinate physiological processes, including circadian rhythms in response to environmental stimuli

Daily physiological and behavioral rhythms are regulated by endogenous circadian molecular clocks. Clock proteins DEC1 (BHLHe40) and DEC2 (BHLHe41) belong to the basic helix-loop-helix protein superfamily, which contains other clock proteins CLOCK and BMAL1. DEC1 and DEC2 are induced by CLOCK:BMAL1 heterodimer via the CACGTG E-box in the promoter and, thereafter, suppress their own expression by competing with CLOCK:BMAL1 for the DNA binding. This negative feedback DEC loop together with the PER loop involving PER and CRY, the other negative clock regulators, maintains the circadian rhythm of Dec1 and Dec2 expression. DEC1 is induced by light pulse and adjusts the circadian phase of the central clock in the suprachiasmatic nucleus, whereas DEC1 upregulation by TGF-β resets the circadian phase of the peripheral clocks in tissues. Furthermore, DEC1 and DEC2 modulate the clock output signals to control circadian rhythms in behavior and metabolism. In addition to the functions in the clocks, DEC1 and DEC2 are involved in hypoxia responses, immunological reactions, and carcinogenesis. These DEC actions are mediated by the direct binding to the E-box elements in target genes or by protein-protein interactions with transcription factors such as HIF-1α, RXRα, MyoD, and STAT. Notably, numerous growth factors, hormones, and cytokines, along with ionizing radiation and DNA-damaging agents, induce Dec1 and/or Dec2 in a tissue-specific manner. These findings suggest that DEC1 and DEC2 play a critical role in animal adaptation to various environmental stimuli.

Molecular bases of circadian rhythmicity in renal physiology and pathology

The physiological processes that maintain body homeostasis oscillate during the day. Diurnal changes characterize kidney functions, comprising regulation of hydro-electrolytic and acid-base balance, reabsorption of small solutes and hormone production. Renal physiology is characterized by 24-h periodicity and contributes to circadian variability of blood pressure levels, related as well to nychthemeral changes of sodium sensitivity, physical activity, vascular tone, autonomic function and neurotransmitter release from sympathetic innervations. The circadian rhythmicity of body physiology is driven by central and peripheral biological clockworks and entrained by the geophysical light/dark cycle. Chronodisruption, defined as the mismatch between environmental-social cues and physiological-behavioral patterns, causes internal desynchronization of periodic functions, leading to pathophysiological mechanisms underlying degenerative, immune related, metabolic and neoplastic diseases. In this review we will address the genetic, molecular and anatomical elements that hardwire circadian rhythmicity in renal physiology and subtend disarray of time-dependent changes in renal pathology.