Hypomorphic expression of parathyroid Bmal1 disrupts the internal parathyroid circadian clock and increases parathyroid cell proliferation in response to uremia.

The molecular circadian clock is an evolutionary adaptation to anticipate recurring changes in the environment and to coordinate variations in activity, metabolism and hormone secretion. Parathyroid hyperplasia in uremia is a significant clinical challenge. Here, we examined changes in the transcriptome of the murine parathyroid gland over 24 hours and found a rhythmic expression of parathyroid signature genes, such as Casr, Vdr, Fgfr1 and Gcm2. Overall, 1455 genes corresponding to 6.9% of all expressed genes had significant circadian rhythmicity. Biological pathway analysis indicated that the circadian clock system is essential for the regulation of parathyroid cell function. To study this, a novel mouse strain with parathyroid gland-specific knockdown of the core clock gene Bmal1 (PTHcre;Bmal1flox/flox) was created. Dampening of the parathyroid circadian clock rhythmicity was found in these knockdown mice, resulting in abrogated rhythmicity of regulators of parathyroid cell proliferation such as Sp1, Mafb, Gcm2 and Gata3, indicating circadian clock regulation of these genes. Furthermore, the knockdown resulted in downregulation of genes involved in mitochondrial function and synthesis of ATP. When superimposed by uremia, these PTHcre;Bmal1flox/flox mice had an increased parathyroid cell proliferative response, compared to wild type mice. Thus, our findings indicate a role of the internal parathyroid circadian clock in the development of parathyroid gland hyperplasia in uremia.

Roles of NAD+ in Acute and Chronic Kidney Diseases.

Nicotinamide adenine dinucleotide (oxidized form, NAD+) is a critical coenzyme, with functions ranging from redox reactions and energy metabolism in mitochondrial respiration and oxidative phosphorylation to being a central player in multiple cellular signaling pathways, organ resilience, health, and longevity. Many of its cellular functions are executed via serving as a co-substrate for sirtuins (SIRTs), poly (ADP-ribose) polymerases (PARPs), and CD38. Kidney damage and diseases are common in the general population, especially in elderly persons and diabetic patients. While NAD+ is reduced in acute kidney injury (AKI) and chronic kidney disease (CKD), mounting evidence indicates that NAD+ augmentation is beneficial to AKI, although conflicting results exist for cases of CKD. Here, we review recent progress in the field of NAD+, mainly focusing on compromised NAD+ levels in AKI and its effect on essential cellular pathways, such as mitochondrial dysfunction, compromised autophagy, and low expression of the aging biomarker αKlotho (Klotho) in the kidney. We also review the compromised NAD+ levels in renal fibrosis and senescence cells in the case of CKD. As there is an urgent need for more effective treatments for patients with injured kidneys, further studies on NAD+ in relation to AKI/CKD may shed light on novel therapeutics.

A molecular circadian clock operates in the parathyroid gland and is disturbed in chronic kidney disease associated bone and mineral disorder.

Circadian rhythms in metabolism, hormone secretion, cell cycle and locomotor activity are regulated by a molecular circadian clock with the master clock in the suprachiasmatic nucleus of the central nervous system. However, an internal clock is also expressed in several peripheral tissues. Although about 10% of all genes are regulated by clock machinery an internal molecular circadian clock in the parathyroid glands has not previously been investigated. Parathyroid hormone secretion exhibits a diurnal variation and parathyroid hormone gene promoter contains an E-box like element, a known target of circadian clock proteins. Therefore, we examined whether an internal molecular circadian clock is operating in parathyroid glands, whether it is entrained by feeding and how it responds to chronic kidney disease. As uremia is associated with extreme parathyroid growth and since disturbed circadian rhythm is related to abnormal growth, we examined the expression of parathyroid clock and clock-regulated cell cycle genes in parathyroid glands of normal and uremic rats. Circadian clock genes were found to be rhythmically expressed in normal parathyroid glands and this clock was minimally entrained by feeding. Diurnal regulation of parathyroid glands was next examined. Significant rhythmicity of fibroblast-growth-factor-receptor-1, MafB and Gata3 was found. In uremic rats, deregulation of circadian clock genes and the cell cycle regulators, Cyclin D1, c-Myc, Wee1 and p27, which are influenced by the circadian clock, was found in parathyroid glands as well as the aorta. Thus, a circadian clock operates in parathyroid glands and this clock and downstream cell cycle regulators are disturbed in uremia and may contribute to dysregulated parathyroid proliferation in secondary hyperparathyroidism.

Circadian rhythms of mineral metabolism in chronic kidney disease-mineral bone disorder.

PURPOSE OF REVIEW: The circadian rhythms have a systemic impact on all aspects of physiology. Kidney diseases are associated with extremely high-cardiovascular mortality, related to chronic kidney disease-mineral bone disorder (CKD-MBD), involving bone, parathyroids and vascular calcification. Disruption of circadian rhythms may cause serious health problems, contributing to development of cardiovascular diseases, metabolic syndrome, cancer, organ fibrosis, osteopenia and aging. Evidence of disturbed circadian rhythms in CKD-MBD parameters and organs involved is emerging and will be discussed in this review. RECENT FINDINGS: Kidney injury induces unstable behavioral circadian rhythm. Potentially, uremic toxins may affect the master-pacemaker of circadian rhythm in hypothalamus. In CKD disturbances in the circadian rhythms of CKD-MBD plasma-parameters, activin A, fibroblast growth factor 23, parathyroid hormone, phosphate have been demonstrated. A molecular circadian clock is also expressed in peripheral tissues, involved in CKD-MBD; vasculature, parathyroids and bone. Expression of the core circadian clock genes in the different tissues is disrupted in CKD-MBD. SUMMARY: Disturbed circadian rhythms is a novel feature of CKD-MBD. There is a need to establish which specific input determines the phase of the local molecular clock and to characterize its regulation and deregulation in tissues involved in CKD-MBD. Finally, it is important to establish what are the implications for treatment including the potential applications for chronotherapy.

Circadian rhythm of activin A and related parameters of mineral metabolism in normal and uremic rats.

Activin A is a new fascinating player in chronic kidney disease-mineral and bone disorder (CKD-MBD), which is implicated in progressive renal disease, vascular calcification, and osteodystrophy. Plasma activin A rises early in the progression of renal disease. Disruption of circadian rhythms is related to increased risk of several diseases and circadian rhythms are observed in mineral homeostasis, bone parameters, and plasma levels of phosphate and PTH. Therefore, we examined the circadian rhythm of activin A and CKD-MBD-related parameters (phosphate, PTH, FGF23, and klotho) in healthy controls and CKD rats (5/6 nephrectomy) on high-, standard- and low-dietary phosphate contents as well as during fasting conditions. Plasma activin A exhibited circadian rhythmicity in healthy control rats with fourfold higher values at acrophase compared with nadir. The rhythm was obliterated in CKD. Activin A was higher in CKD rats compared with controls when measured at daytime but not significantly when measured at evening/nighttime, stressing the importance of time-specific reference intervals when interpreting plasma values. Plasma phosphate, PTH, and FGF23 all showed circadian rhythms in control rats, which were abolished or disrupted in CKD. Plasma klotho did not show circadian rhythm. Thus, the present investigation shows, for the first time, circadian rhythm of plasma activin A. The rhythmicity is severely disturbed by CKD and is associated with disturbed rhythms of phosphate and phosphate-regulating hormones PTH and FGF23, indicating that disturbed circadian rhythmicity is an important feature of CKD-MBD.

New Insights to the Crosstalk between Vascular and Bone Tissue in Chronic Kidney Disease-Mineral and Bone Disorder.

Vasculature plays a key role in bone development and the maintenance of bone tissue throughout life. The two organ systems are not only linked in normal physiology, but also in pathophysiological conditions. The chronic kidney disease-mineral and bone disorder (CKD-MBD) is still the most serious complication to CKD, resulting in increased morbidity and mortality. Current treatment therapies aimed at the phosphate retention and parathyroid hormone disturbances fail to reduce the high cardiovascular mortality in CKD patients, underlining the importance of other factors in the complex syndrome. This review will focus on vascular disease and its interplay with bone disorders in CKD. It will present the very late data showing a direct effect of vascular calcification on bone metabolism, indicating a vascular-bone tissue crosstalk in CKD. The calcified vasculature not only suffers from the systemic effects of CKD but seems to be an active player in the CKD-MBD syndrome impairing bone metabolism and might be a novel target for treatment and prevention.

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.

Effect of NAD+ boosting on kidney ischemia-reperfusion injury.

Acute kidney injury (AKI) is associated with a very high mortality and an increased risk for progression to chronic kidney disease (CKD). Ischemia-reperfusion injury (IRI) is a model for AKI, which results in tubular damage, dysfunction of the mitochondria and autophagy, and in decreased cellular nicotinamide adenine dinucleotide (NAD+) with progressing fibrosis resulting in CKD. NAD+ is a co-enzyme for several proteins, including the NAD+ dependent sirtuins. NAD+ augmentation, e.g. by use of its precursor nicotinamide riboside (NR), improves mitochondrial homeostasis and organismal metabolism in many species. In the present investigation the effects of prophylactic administration of NR on IRI-induced AKI were studied in the rat. Bilateral IRI reduced kidney tissue NAD+, caused tubular damage, reduced α-Klotho (klotho), and altered autophagy flux. AKI initiated progression to CKD, as shown by induced profibrotic Periostin (postn) and Inhibin subunit beta-A, (activin A / Inhba), both 24 hours and 14 days after surgery. NR restored tissue NAD+ to that of the sham group, increased autophagy (reduced p62) and sirtuin1 (Sirt1) but did not ameliorate renal tubular damage and profibrotic genes in the 24 hours and 14 days IRI models. AKI induced NAD+ depletion and impaired autophagy, while augmentation of NAD+ by NR restored tissue NAD+ and increased autophagy, possibly serving as a protective response. However, prophylactic administration of NR did not ameliorate tubular damage of the IRI rats nor rescued the initiation of fibrosis in the long-term AKI to CKD model, which is a pivotal event in CKD pathogenesis.

Diurnal variation of magnesium and the mineral metabolism in patients with chronic kidney disease.

Increasing levels of magnesium in blood are associated with reduced risk of cardiovascular disease in chronic kidney disease (CKD). Magnesium supplementation may reduce the progression of vascular calcification in CKD. The diurnal pattern and effect of fasting on magnesium in blood and urine in CKD is unknown, and knowledge of this may influence management of magnesium supplementation. We included ten patients with CKD stage four without diabetes mellitus and ten healthy controls. Participants were admitted to our hospital ward for a 24-h study period. Blood and urine samples were collected in a non-fasting state at 8 o'clock in the morning and every third hour hereafter until the final samples in a fasting state at 8 o'clock the following morning. We found no diurnal variation in plasma magnesium (p = 0.097) in either group, but a significant diurnal variation in urinary excretion of magnesium (p = 0.044) in both CKD and healthy controls with no significant interaction between the two groups, and thus no suggestion that CKD affects diurnal variation of plasma magnesium or urinary magnesium excretion. The levels of plasma magnesium were not significantly different in fasting and non-fasting conditions. Magnesium in plasma does not display a significant diurnal variation and can be measured at any time of day and in both fasting and non-fasting conditions. Urinary magnesium excretion displays diurnal variation, which is likely related to increased uptake of magnesium during meals and helps maintain a stable concentration of magnesium in blood.