Development of the circadian clockwork in the kidney

Targeting NR1D1 in organ injury: challenges and prospects

Nuclear receptor subfamily 1, group D, member 1 (NR1D1, also known as REV-ERBα) belongs to the nuclear receptor (NR) family, and is a heme-binding component of the circadian clock that consolidates circadian oscillators. In addition to repressing the transcription of multiple clock genes associated with circadian rhythms, NR1D1 has a wide range of downstream target genes that are intimately involved in many physiopathological processes, including autophagy, immunity, inflammation, metabolism and aging in multiple organs. This review focuses on the pivotal role of NR1D1 as a key transcription factor in the gene regulatory network, with particular emphasis on the milestones of the latest discoveries of NR1D1 ligands. NR1D1 is considered as a promising drug target for treating diverse diseases and may contribute to research on innovative biomarkers and therapeutic targets for organ injury-related diseases. Further research on NR1D1 ligands in prospective human trials may pave the way for their clinical application in many organ injury-related disorders.

Renal tubular SGK1 is required to achieve blood pressure surge and circadian rhythm

Blood pressure (BP) follows a circadian pattern that rises during the active phase of the day (morning surge) and decreases during the inactive (night dipping) phase of the day. The morning surge coincides with increased circulating glucocorticoids and aldosterone, ligands for glucocorticoid receptors and mineralocorticoid receptors, respectively. Serum- and glucocorticoid-induced kinase 1 (SGK1), a clock-controlled and glucocorticoid receptor- and mineralocorticoid receptor-induced gene, plays a role in BP regulation in human and animal models. However, the role of SGK1 in BP circadian regulation has not yet been demonstrated. Using telemetry, we analyzed BP in the inducible renal tubule-specific Sgk1Pax8/LC1 model under basal K+ diet (1% K+) and high-K+ diet (HKD; 5% K+). Our data revealed that, under basal conditions, renal SGK1 plays a minor role in BP regulation; however, after 1 wk of HKD, Sgk1Pax8/LC1 mice exhibited significant defects in diastolic BP (DBP), including a blunted surge, a decreased amplitude, and reduced day/night differences. After prolonged HKD (7 wk), Sgk1Pax8/LC1 mice had lower BP than control mice and exhibited reduced DBP amplitude, together with decreased DBP day/night differences and midline estimating statistic of rhythm (MESOR). Interestingly, renal SGK1 deletion increased pulse pressure, likely secondary to an increase in circulating aldosterone. Taken together, our data suggest that 1) the kidney plays a significant role in setting the BP circadian rhythm; 2) renal tubule SGK1 mediates the BP surge and, thus, the day/night BP difference; 3) long-term renal SGK1 deletion results in lower BP in mutant compared with control mice; and 4) renal SGK1 indirectly regulates pulse pressure due to compensatory alterations in aldosterone levels.NEW & NOTEWORTHY Dysregulation of blood pressure (BP) circadian rhythm is associated with metabolic, cardiovascular, and kidney diseases. Our study provides experimental evidence demonstrating, for the first time, that renal tubule serum- and glucocorticoid-induced kinase 1 (SGK1) plays an essential role in inducing the BP surge. Inhibitors and activators of SGK1 signaling are parts of several therapeutic strategies. Our findings highlight the importance of the drug intake timing to be in phase with SGK1 function to avoid dysregulation of BP circadian rhythm.

Dissociation of sodium-chloride cotransporter expression and blood pressure during chronic high dietary potassium supplementation

Dietary potassium (K+) supplementation is associated with a lowering effect in blood pressure (BP), but not all studies agree. Here, we examined the effects of short- and long-term K+ supplementation on BP in mice, whether differences depend on the accompanying anion or the sodium (Na+) intake and molecular alterations in the kidney that may underlie BP changes. Relative to the control diet, BP was higher in mice fed a high NaCl (1.57% Na+) diet for 7 weeks or fed a K+-free diet for 2 weeks. BP was highest on a K+-free/high NaCl diet. Commensurate with increased abundance and phosphorylation of the thiazide sensitive sodium-chloride-cotransporter (NCC) on the K+-free/high NaCl diet, BP returned to normal with thiazides. Three weeks of a high K+ diet (5% K+) increased BP (predominantly during the night) independently of dietary Na+ or anion intake. Conversely, 4 days of KCl feeding reduced BP. Both feeding periods resulted in lower NCC levels but in increased levels of cleaved (active) α and γ subunits of the epithelial Na+ channel ENaC. The elevated BP after chronic K+ feeding was reduced by amiloride but not thiazide. Our results suggest that dietary K+ has an optimal threshold where it may be most effective for cardiovascular health.

Multi-Omics Reveal Interplay between Circadian Dysfunction and Type2 Diabetes

Type 2 diabetes is one of the leading threats to human health in the 21st century. It is a metabolic disorder characterized by a dysregulated glucose metabolism resulting from impaired insulin secretion or insulin resistance. More recently, accumulated epidemiological and animal model studies have confirmed that circadian dysfunction caused by shift work, late meal timing, and sleep loss leads to type 2 diabetes. Circadian rhythms, 24-h endogenous biological oscillations, are a fundamental feature of nearly all organisms and control many physiological and cellular functions. In mammals, light synchronizes brain clocks and feeding is a main stimulus that synchronizes the peripheral clocks in metabolic tissues, such as liver, pancreas, muscles, and adipose tissues. Circadian arrhythmia causes the loss of synchrony of the clocks of these metabolic tissues and leads to an impaired pancreas β-cell metabolism coupled with altered insulin secretion. In addition to these, gut microbes and circadian rhythms are intertwined via metabolic regulation. Omics approaches play a significant role in unraveling how a disrupted circadian metabolism causes type 2 diabetes. In the present review, we emphasize the discoveries of several genes, proteins, and metabolites that contribute to the emergence of type 2 diabetes mellitus (T2D). The implications of these discoveries for comprehending the circadian clock network in T2D may lead to new therapeutic solutions.

Circadian clocks of the kidney: function, mechanism, and regulation

An intrinsic cellular circadian clock is located in nearly every cell of the body. The peripheral circadian clocks within the cells of the kidney contribute to the regulation of a variety of renal processes. In this review, we summarize what is currently known regarding the function, mechanism, and regulation of kidney clocks. Additionally, the effect of extrarenal physiological processes, such as endocrine and neuronal signals, on kidney function is also reviewed. Circadian rhythms in renal function are an integral part of kidney physiology, underscoring the importance of considering time of day as a key biological variable. The field of circadian renal physiology is of tremendous relevance, but with limited physiological and mechanistic information on the kidney clocks this is an area in need of extensive investigation.

Circadian Clock Regulation of Developmental Time in the Kidney

We report the emergence of an endogenous circadian clock that regulates organogenesis in mouse fetal kidney. We detect circadian rhythms both in vivo with transcriptional profiling and ex vivo by bioluminescence. High-resolution structural analysis of embryonic explants reveals that global or local clock disruption results in defects that resemble human congenital abnormalities of the kidney. The onset of fetal rhythms strongly correlates with the timing of a distinct transition in branching and growth rates during a gestational window of high fetal growth demands. Defects in clock mutants typically have been attributed to accelerated aging; however, our study establishes a role for the fetal circadian clock as a developmental timer that regulates the pathways that control organogenesis, branching rate, and nephron number and thus plays a fundamental role in kidney development.

The trophoblast clock controls transport across placenta in mice

In mammals, 24-h rhythms of physiology and behavior are organized by a body-wide network of clock genes and proteins. Despite the well-known function of the adult circadian system, the roles of maternal, fetal and placental clocks during pregnancy are poorly defined. In the mature mouse placenta, the labyrinth zone (LZ) is of fetal origin and key for selective nutrient and waste exchange. Recently, clock gene expression has been detected in LZ and other fetal tissues; however, there is no evidence of a placental function controlled by the LZ clock. Here, we demonstrate that specifically the trophoblast layer of the LZ harbors an already functional clock by late gestation, able to regulate in a circadian manner the expression and activity of the xenobiotic efflux pump, ATP-binding cassette sub-family B member 1 (ABCB1), likely gating the fetal exposure to drugs from the maternal circulation to certain times of the day. As more than 300 endogenous and exogenous compounds are substrates of ABCB1, our results might have implications in choosing the maternal treatment time when aiming either maximal/minimal drug availability to the fetus/mother.

The MTNR1A mRNA is stabilized by the cytoplasmic hnRNPL in renal tubular cells

The downregulation of melatonin receptor 1A (MTNR1A) is associated with a range of pathological conditions, including membranous nephropathy. Knowledge of the mechanism underlying MTNR1A expression has been limited to the transcriptional regulation level. Here, RNA interference screening in human kidney cells revealed that heterogeneous nuclear ribonucleoprotein L (hnRNPL) upregulated MTNR1A RNA post-transcriptionally. hnRNPL knockdown or overexpression led to increased or decreased levels of cyclic adenosine monophosphate-responsive element-binding protein phosphorylation, respectively. Molecular studies showed that cytoplasmic hnRNPL exerts a stabilizing effect on the MTNR1A transcript through CA-repeat elements in its coding region. Further studies revealed that the interaction between hnRNPL and MTNR1A serves to protect MNTR1A RNA degradation by the exosome component 10 protein. MTNR1A, but not hnRNPL, displays a diurnal rhythm in mouse kidneys. Enhanced levels of MTNR1A recorded at midnight correlated with robust binding activity between cytoplasmic hnRNPL and the MTNR1A transcript. Both hnRNPL and MTNR1A were decreased in the cytoplasm of tubular epithelial cells from experimental membranous nephropathy kidneys, supporting their clinical relevance. Collectively, our data identified cytoplasmic hnRNPL as a novel player in the upregulation of MTNR1A expression in renal tubular epithelial cells, and as a potential therapeutic target.

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.

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 Clock Genes in Diabetic Kidney Disease (DKD)

PURPOSE OF REVIEW

The purpose of this review is to provide a brief summary about the current state of knowledge regarding the circadian rhythm in the regulation of normal renal function.

RECENT FINDINGS

There is a lack of information regarding how the circadian clock mechanisms may contribute to the development of diabetic kidney disease. We discuss recent findings regarding mechanisms that are established in diabetic kidney disease and are known to be linked to the circadian clock as possible connections between these two areas. Here, we hypothesize various mechanisms that may provide a link between the clock mechanism and kidney disease in diabetes based on available data from humans and rodent models.

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.

Circadian calcium feeding regime in laying hens related to zinc concentration, gene expression of circadian clock, calcium transporters and oxidative status

The study was conducted to investigate the effects of different circadian calcium feeding regimes on parameters of Zn status and gene expression of circadian clock, calcium transporters and oxidative status in laying hens. In total, 180 of 41-weeks Brown Hy-line laying hens were assigned randomly into three groups, 1-CON group (Control Ca, diets contained 3.4% Ca at both 0730 and 1530 h), 2-HL group (High-low Ca, diets contained 3.6%-3.2% Ca respectively) and 3-LH group (Low-high Ca, diets contained 3.2%-3.6% Ca respectively), which were fed a certain amount of control diet at 0730 h and 1530 h. Blood, tibia, jejunum and kidney samples were collected at 4 h intervals with initial starting at 0800 h after 10 weeks of experiment. Compared with the CON group: 1) the serum zinc in HL group increased at 2000 h, but lower at 1600 h in LH group (P < 0.05). 2) in jejunum, circadian clock genes including CLOCK and BMAL1 expression of HL group were down-regulated at 0000 h and 1600 h, as well as CLOCK, BMAL1, Cry2, Per3 and calcium transporter gene NCX1 in LH group at 2000 h (P < 0.05). 3) in kidney, CLOCK, Cry1, Cry2 and Per3 of LH group were up-regulated at 0400 h, CLOCK at 0000 h as well, while CLOCK at 2000 h were down-regulated (P < 0.05). 4) in kidney, the calcium transporters including PMCA, CaBP and CA of LH group were up-regulated at 0000 h, but PMCA and CaBP of LH group were down-regulated at 0800 h, 1200 h and 1600 h, as well as CA at 1600 h and PMCA at 2000 h of LH group (P < 0.05), and the oxidative gene SOD of the LH group was up-regulated at 0400 h, as well as CAT at 0400 h, SOD and GPX1 at 1200 h in HL group, but SOD at 1600 h and 2000 h, and GPX1 at 1600 h were down-regulated in LH group (P < 0.05). These results demonstrated that the dynamic circadian calcium feeding regime affected circadian rhythms of serum zinc concentration as well as the expression of certain genes related to the circadian clock, calcium transport and antioxidative capacity, and circadian calcium feeding regimes may therefore be considered with regard to improving the calcium usability.

Maternal eating behavior is a major synchronizer of fetal and postnatal peripheral clocks in mice

Most living organisms show circadian rhythms in physiology and behavior. These oscillations are generated by endogenous circadian clocks, present in virtually all cells where they control key biological processes. To study peripheral clocks in vivo, we developed an original model, the Rev-Luc mouse to follow noninvasively and longitudinally Rev-Luc oscillations in peripheral clocks using in vivo bioluminescence imaging. We found in vitro and in vivo a robust diurnal rhythm of Rev-Luc, mainly in liver, intestine, kidney and adipose tissues. We further confirmed in vivo that Rev-Luc peripheral tissues are food-entrainable oscillators, not affected by age or sex. These data strongly support the relevance of the Rev-Luc model for circadian studies, especially to investigate in vivo the establishment and the entrainment of the rhythm throughout ontogenesis. We then showed that Rev-Luc expression develops dynamically and gradually, both in amplitude and in phase, during fetal and postnatal development. We also demonstrate for the first time that the immature peripheral circadian system of offspring in utero is mainly entrained by maternal cues from feeding regimen. The prenatal entrainment will also differentially determine the Rev-Luc expression in pups before weaning underlining the importance of the maternal chrononutrition on the circadian system entrainment of the offspring.

Circadian alignment in a foster mother improves the offspring's pathological phenotype

KEY POINTS

In mammals, the mother-offspring interaction is essential for health later in adulthood. The impact of altered timing and quality of maternal care on the offspring's circadian system was assessed using a cross-strain fostering approach. Better maternal care facilitated the development of amplitudes of Bmal1 clock gene expression in the central clock, as well as the clock-driven activity/rest rhythm, and also its entrainment to the external light/dark cycle. Worse maternal care impaired entrainment of the central clock parameters in the Wistar rat during the early developmental stages. Better maternal care remedied the dampened amplitudes of the colonic clock, as well as cardiovascular functions. The results provide compelling evidence that the circadian phenotype of a foster mother may affect the pathological symptoms of the offspring, even if they are genetically programmed.

ABSTRACT

In mammals, the mother-offspring interaction is essential for health later in adulthood. Maternal care is determined by the circadian phenotype of the mother. The impact of altered timing and quality of maternal care on the circadian system was assessed using a cross-strain fostering approach, with 'abnormal' (i.e. circadian misaligned) care being represented by spontaneously hypertensive rats (SHR) and 'normal' care by Wistar rats. The SHR mothers worsened synchrony of the central clock in the suprachiasmatic nuclei with the light/dark cycle in Wistar rat pups, although this effect disappeared after weaning. The maternal care provided by Wistar rat mothers to SHR pups facilitated the development of amplitudes of the Bmal1 expression rhythm in the suprachiasmatic nuclei of the hypothalamus, as well as the clock-driven activity/rest rhythm and its entrainment to the external light/dark cycle. The peripheral clocks in the liver and colon responded robustly to cross-strain fostering; the circadian phenotype of the Wistar rat foster mother remedied the dampened amplitudes of the colonic clock in SHR pups and improved their cardiovascular functions. In general, the more intensive maternal care of the Wistar rat mothers improved most of the parameters of the abnormal SHR circadian phenotype in adulthood; conversely, the less frequent maternal care of the SHR mothers worsened these parameters in the Wistar rat during the early developmental stages. Altogether, our data provide compelling evidence that the circadian phenotype of a foster mother may positively and negatively affect the regulatory mechanisms of various physiological parameters, even if the pathological symptoms are genetically programmed.

The sodium phosphate cotransporter family and nicotinamide phosphoribosyltransferase contribute to the daily oscillation of plasma inorganic phosphate concentration

Circulating inorganic phosphate exhibits a remarkable daily oscillation based on food intake. In humans and rodents, the daily oscillation in response to food intake may be coordinated to control the intestinal absorption, renal excretion, cellular shifts, and extracellular concentration of inorganic phosphate. However, mechanisms regulating the resulting oscillation are unknown. Here we investigated the roles of the sodium phosphate cotransporter SLC34 (Npt2) family and nicotinamide phosphoribosyltransferase (Nampt) in the daily oscillation of plasma inorganic phosphate levels. First, it is roughly linked to urinary inorganic phosphate excretion. Second, expression of renal Npt2a and Npt2c, and intestinal Npt2b proteins also exhibit a dynamic daily oscillation. Analyses of Npt2a, Npt2b, and Npt2c knockout mice revealed the importance of renal inorganic phosphate reabsorption and cellular inorganic phosphate shifts in the daily oscillation. Third, experiments in which nicotinamide and a specific Nampt inhibitor (FK866) were administered in the active and rest phases revealed that the Nampt/NAD⁺ system is involved in renal inorganic phosphate excretion. Additionally, for cellular shifts, liver-specific Nampt deletion disturbed the daily oscillation of plasma phosphate during the rest but not the active phase. In systemic Nampt^+/- mice, NAD levels were significantly reduced in the liver, kidney, and intestine, and the daily oscillation (active and rest phases) of the plasma phosphate concentration was attenuated. Thus, the Nampt/NAD⁺ system for Npt2 regulation and cellular shifts to tissues such as the liver play an important role in generating daily oscillation of plasma inorganic phosphate levels.

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.

Molecular origin of the kidney clock

Increasing evidence suggests that a functional circadian clock in the kidney contributes to the regulation of renal function including blood pressure and sodium balance. When does this kidney clock begin ticking? Meszaros et al. provide the first evidence that the endogenous molecular machinery of the circadian clock begins oscillating in the late fetal kidney. These findings have important implications for our understanding of how homeostasis is maintained in early life.