Physiological circadian rhythm of cardiac myosin-binding protein C (cMyC) and cardiac troponin

Introduction Cardiac myosin-binding protein C (cMyC) is a novel protein biomarker of myocardial injury, with a promising role in the triage and risk stratification of patients with cardiac disease. Understanding the physiological diurnal oscillation of cMyC and cardiac troponin is important for the interpretation of single and serial measurements within the biomarker-assisted triage and risk stratification algorithms. Purpose In this study, we aim to assess and compare the physiological diurnal oscillation of cMyC and cardiac troponin cTnT and cTnI. Method Twenty-six consecutive hourly blood samples were drawn between 08.30 am and 09.30 am (+1 day) from normotensive 24 individuals without a recent history of acute myocardial infarction, for the measurement of cMyC, cardiac troponin T (Roche hs-cTnT) and I (Abbott hs-cTnI). Fitted cosinor sine regression model (with R, version 3.6.1) was used to assess the presence and significance of circadian oscillation of the biomarker, and to estimate the respective amplitude and acrophase (the time of peak activity). Amplitude and acrophase were compared across the biomarkers that exhibited significant circadian rhythm. Results Mean age was 72±7. 79% of participants (n=19) were men. All participants were free from renal disease. On population-mean cosinor analysis, hs-cTnI exhibited random diurnal oscillation, whereas significant circadian rhythm was detected for cMyC and hs-cTnT (p=0.015 and <0.001, respectively) (Figure 1). The circadian rhythm of cMyC is characterised by gradually increasing concentrations from early afternoon until early morning (acrophase 03:03 am, 95% CI 01:54–04:26 am) compared to hs-cTnT concentrations which exhibits delayed increase and a later peak (acrophase, 08:01, 95% CI 07:10–08:51 am), p=0.028 for acrophase difference (Figure 1). Diurnal rhythm remained significant after correction for possible posture-induced changes in plasma volume. To allow direct comparison between amplitudes, the measurements of cMyC and hs-TnT were normalised to the respective 08:30 am value, re-fitted cosinor model did not show significant difference between the amplitudes (amplitude ng/L, 0.12, 95% CI 0.07–0.15 vs 0.11, 95% CI 0.08–0.12, for normalised cMyC vs hs-cTnT, respectively; p=0.67). Conclusion Significant circadian rhythm exists for cMyC and hs-cTnT, with 5-hours phase difference between the two biomarkers (cMyC ahead of hs-cTnT). The cause of this rhythmic variation is unknown, but the phase difference is consistent with the previously described disparity in the release of cMyC and cTnT after iatrogenic myocardial injury, raising the possibility of an underlying diurnal variation in myocardial vulnerability. Studies are required to assess the impact of this physiological phenomenon on the performance of the biomarkers within unadjused diagnostic algorithms FUNDunding Acknowledgement Type of funding sources: Foundation. Main funding source(s): British Heart FoundationStichting de Weijerhorst

Dysbiosis of the Saliva Microbiome in Patients With Polycystic Ovary Syndrome

Significant differences in salivary microbiota communities between polycystic ovary syndrome (PCOS) patients and healthy controls have been reported, and interestingly, some salivary microbiota exhibit diurnal oscillation in healthy people. However, whether the diurnal oscillation of salivary microbiota is present in PCOS patients is unknown. In this study, we describe the differences in the saliva microbiome between the PCOS group and the control group at different time points over 24 h. 16S rRNA gene amplicon sequencing was performed on salivary and fecal samples from 10 PCOS patients and 10 healthy controls, and salivary samples were collected at 6-h intervals over 24 h (Zeitgeber (ZT)0, ZT6, ZT12, and ZT18). Among the salivary samples, those from the PCOS group showed significant differences from those of the control group at each time point. Differences were evident in taxa level and metabolic pathways. Interestingly, we found that PCOS disrupted the diurnal rhythm of the salivary microbiota abundance, as determined in the group of healthy women. In addition, no similar changes were found in PCOS patients and controls between the oral and fecal microbiota, including differential microbiota at the phylum level. In this study, significant differences in the composition of the salivary microbiota between PCOS and healthy women were detected at different time points. We also showed that the diurnal rhythm of relative abundance of the salivary microbiota was disrupted in patients with PCOS, which might be related to development of oral-related diseases and systematic metabolic disorders.

BMAL1 Disrupted Intrinsic Diurnal Oscillation in Rat Cerebrovascular Contractility of Simulated Microgravity Rats by Altering Circadian Regulation of miR-103/CaV1.2 Signal Pathway

The functional and structural adaptations in cerebral arteries could be one of the fundamental causes in the occurrence of orthostatic intolerance after space flight. In addition, emerging studies have found that many cardiovascular functions exhibit circadian rhythm. Several lines of evidence suggest that space flight might increase an astronaut’s cardiovascular risks by disrupting circadian rhythm. However, it remains unknown whether microgravity disrupts the diurnal variation in vascular contractility and whether microgravity impacts on circadian clock system. Sprague-Dawley rats were subjected to 28-day hindlimb-unweighting to simulate the effects of microgravity on vasculature. Cerebrovascular contractility was estimated by investigating vasoconstrictor responsiveness and myogenic tone. The circadian regulation of CaV1.2 channel was determined by recording whole-cell currents, evaluating protein and mRNA expressions. Then the candidate miRNA in relation with Ca2+ signal was screened. Lastly, the underlying pathway involved in circadian regulation of cerebrovascular contractility was determined. The major findings of this study are: (1) The clock gene BMAL1 could induce the expression of miR-103, and in turn modulate the circadian regulation of CaV1.2 channel in rat cerebral arteries at post-transcriptional level; and (2) simulated microgravity disrupted intrinsic diurnal oscillation in rat cerebrovascular contractility by altering circadian regulation of BMAL1/miR-103/CaV1.2 signal pathway.

Time-dependent sequestration of RVE8 by LNK proteins shapes the diurnal oscillation of anthocyanin biosynthesis

Circadian clocks sustain 24-h rhythms in physiology and metabolism that are synchronized with the day/night cycle. In plants, the regulatory network responsible for the generation of rhythms has been broadly investigated over the past years. However, little is known about the intersecting pathways that link the environmental signals with rhythms in cellular metabolism. Here, we examine the role of the circadian components REVEILLE8/LHY-CCA1-LIKE5 (RVE8/LCL5) and NIGHT LIGHT–INDUCIBLE AND CLOCK-REGULATED genes (LNK) shaping the diurnal oscillation of the anthocyanin metabolic pathway. Around dawn, RVE8 up-regulates anthocyanin gene expression by directly associating to the promoters of a subset of anthocyanin biosynthetic genes. The up-regulation is overcome at midday by the repressing activity of LNK proteins, as inferred by the increased anthocyanin gene expression in lnk1/lnk2 double mutant plants. Chromatin immunoprecipitation assays using LNK and RVE8 misexpressing plants show that RVE8 binding to target promoters is precluded in LNK overexpressing plants and conversely, binding is enhanced in the absence of functional LNKs, which provides a mechanism by which LNKs antagonize RVE8 function in the regulation of anthocyanin accumulation. Based on their previously described transcriptional coactivating function, our study defines a switch in the regulatory activity of RVE8–LNK interaction, from a synergic coactivating role of evening-expressed clock genes to a repressive antagonistic function modulating anthocyanin biosynthesis around midday.