Metabolic Cycles Are Linked to the Cardiovascular Diurnal Rhythm in Rats with Essential Hypertension

Background: The loss of diurnal rhythm in blood pressure (BP) is an important predictor of end-organ damage in hypertensive and diabetic patients. Recent evidence has suggested that two major physiological circadian rhythms, the metabolic and cardiovascular rhythms, are subject to regulation by overlapping molecular pathways, indicating that dysregulation of metabolic cycles could desynchronize the normal diurnal rhythm of BP with the daily light/dark cycle. However, little is known about the impact of changes in metabolic cycles on BP diurnal rhythm. Methodology/Principal Findings: To test the hypothesis that feeding-fasting cycles could affect the diurnal pattern of BP, we used spontaneously hypertensive rats (SHR) which develop essential hypertension with disrupted diurnal BP rhythms and examined whether abnormal BP rhythms in SHR were caused by alteration in the daily feeding rhythm. We found that SHR exhibit attenuated feeding rhythm which accompanies disrupted rhythms in metabolic gene expression not only in metabolic tissues but also in cardiovascular tissues. More importantly, the correction of abnormal feeding rhythms in SHR restored the daily BP rhythm and was accompanied by changes in the timing of expression of key circadian and metabolic genes in cardiovascular tissues. Conclusions/Significance: These results indicate that the metabolic cycle is an important determinant of the cardiovascula

Selective up-regulation of JunD transcript and protein expression in vasopressinergic supraoptic nucleus (SON) neurones in water deprived rats.

The magnocellular neurones (MCN) of the supraoptic nucleus (SON) undergo reversible changes during dehydration. We hypothesise that alterations in steady-state transcript levels might be partially responsible for this plasticity. In turn, regulation of transcript abundance might be mediated by transcription factors. We have previously used microarrays to identify changes in the expression of mRNAs encoding transcription factors in response to water deprivation. We observed down-regulation of 11 and up-regulation of 31 transcription factor transcripts, including members of the AP-1 gene family, namely c-fos, c-jun, fosl1 and junD. As JunD expression and regulation within the SON has not been previously described, we have used in situ hybridisation and quantitative RT-PCR to confirm the array results, demonstrating a significant increase in JunD mRNA levels following 24-hours and 72-hours of water deprivation. Western blot and immunohistochemistry revealed a significant increase in JunD protein expression following dehydration. Double staining fluorescence immunohistochemistry with a neurone specific marker (NeuN) demonstrated that JunD staining is predominantly neuronal. Additionally, JunD immunoreactivity is observed primarily in vasopressin containing neurones with markedly less staining seen in oxytocin containing MCNs. Furthermore, JunD is highly co-expressed with c-Fos in MCNs of the SON following dehydration. These results suggest that JunD plays a role in the regulation of gene expression within MCNs of the SON in association with other Fos and Jun family members

The Circadian Clock Maintains Cardiac Function by Regulating Mitochondrial Metabolism in Mice

<div><p>Cardiac function is highly dependent on oxidative energy, which is produced by mitochondrial respiration. Defects in mitochondrial function are associated with both structural and functional abnormalities in the heart. Here, we show that heart-specific ablation of the circadian clock gene <i>Bmal1</i> results in cardiac mitochondrial defects that include morphological changes and functional abnormalities, such as reduced enzymatic activities within the respiratory complex. Mice without cardiac <i>Bmal1</i> function show a significant decrease in the expression of genes associated with the fatty acid oxidative pathway, the tricarboxylic acid cycle, and the mitochondrial respiratory chain in the heart and develop severe progressive heart failure with age. Importantly, similar changes in gene expression related to mitochondrial oxidative metabolism are also observed in C57BL/6J mice subjected to chronic reversal of the light-dark cycle; thus, they show disrupted circadian rhythmicity. These findings indicate that the circadian clock system plays an important role in regulating mitochondrial metabolism and thereby maintains cardiac function.</p></div

Circadian desynchronization not only disrupts rhythms but also reduces the expression levels of clock and metabolic genes in the heart of C57BL/6J mice with PE-induced cardiomyopathy.

<p>(A-C) Relative expression levels of genes regulating (A) clock machinery as well as (B) glucose and (C) lipid metabolism in heart. All heart tissues used were from PE-infused animals subjected to either a fixed or a disrupted LD cycle as described in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0112811#pone-0112811-g005" target="_blank">Figure 5A</a> (n = 4 per group per time point). To provide a 24-h overall mean expression level, the data over a 24-h time period in each group were also averaged and are expressed using a bar graph format. Data are the mean ± SEM. *<i>P</i><0.05, **<i>P</i><0.01, unpaired two-tailed Student's <i>t</i>-test.</p

Circadian desynchronization impairs mitochondrial function in the hearts of C57BL/6J mice with PE-induced cardiomyopathy.

<p>(A-B) Relative expression levels of genes regulating (A) mitochondrial structure or (B) mitochondrial oxidative metabolism in heart. All heart tissues used are from PE-infused animals subjected to either a fixed or a disrupted LD cycle as described in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0112811#pone-0112811-g005" target="_blank">Figure 5A</a> (n = 4 per group per time point). To provide a 24-h overall mean expression level, the data over a 24-h time period in each group were also averaged and are expressed in bar graph format. (C) Enzymatic activity of complex I in PE-infused animals exposed to a fixed or disrupted LD cycle (n = 4–5 per group). The complex I activity is expressed per milligram of tissue used for mitochondrial isolation. (D) The relative number of mitochondria in the left ventricular muscle was counted using electron microscope images. Representative images are shown. Data are the mean ± SEM. *<i>P</i><0.05, **<i>P</i><0.01, unpaired two-tailed Student's <i>t</i>-test.</p

<i>H-Bmal1</i>^−/− mice develop progressive congestive heart failure with age.

<p>(A) Representative gross morphology of hearts from 12-week-old control and <i>H-Bmal1</i>^−/− mice. (B) Ratios of heart weight to body weight (HW/BW) at 12 weeks of age (n = 6 per group). (C) Low-power views after H&E staining of transverse sections from control and <i>Bmal1</i>^−/− hearts at 12 weeks of age. (D) LV lateral wall thickness determined in histological images used in (C) (n = 5 per group). (E) Echocardiographic analysis in 12-week-old control and <i>H-Bmal1</i>^−/− animals (n = 8–9 per group). LV internal diameter at diastole (LVIDd) and at systole (LVIDs) and fractional shortening (FS) are shown in bar graph format. (F) Transcript expression levels of <i>ANP</i> and <i>BNP</i> in control and <i>H-Bmal1</i>^−/− mice at 12 weeks of age (n = 6 per group). (G) Kaplan-Meier survival curves of control and <i>H-Bmal1</i>^−/− animals (n = 31 per group). (H) Low-power views (top panels, scale bar: 1 mm) and high-magnification views (bottom panels, scale bar: 25 µm) of Masson's trichrome staining of heart sections from 33-week-old control and <i>H-Bmal1</i>^−/− mice. (I) High-magnification views of H&E staining of lung (top panels) and liver (bottom panels) sections from the same animals used in (H). Scale bar: 50 µm. Data are the mean ± SEM. *<i>P</i><0.05, **<i>P</i><0.01, unpaired two-tailed Student's <i>t</i>-test.</p