Search

Nicotinamide adenine dinucleotide (oxidized form, NAD

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.

BACKGROUND AND AIMS Proper rhythms in metabolism, hormone secretion and activity are maintained by a molecular circadian clock. The central clock in central nervous system (CNS) receives light input via retina to regulate timing of activity. Peripheral clocks are found in a number of tissues regulating an estimated 8–10% of all expressed genes[1]. We have previously shown that an internal circadian clock operates in the parathyroid gland (PTG) which is disturbed in a rat model of chronic kidney disease (CKD)[2]. Here, we examined the PTG transcriptome of wildtype mice over 24-h and compared with our novel mouse strain with PTG-specific circadian clock knockdown (by PTG-specific knockdown of core circadian clock gene Bmal1) to investigate the role of the PTG clock. METHOD PTG-specific knockdown of Bmal1 was generated by crossing PTHcre-mice with Bmal1flox/flox mice (WT) creating PTHcre; Bmal1flox/flox mice (KD). PTGs of WT and KD were harvested at 4-h interval and 24-h gene expression was examined by RNAseq. Circadian rhythmicity was assessed by cosinor-analysis and JTK_CYCLE algorithm. Cluster analysis was performed using the Mfuzz package in R. The clusterProfiler R package was used for gene ontology enrichment and gene set enrichment analysis (GSEA) with FDR-adjusted P-value at RESULTS A total of 6.85% of all expressed genes were significantly rhythmic in the wildtype PTG, including parathyroid signature genes Casr, Vdr, Klotho, Fgfr1 and Gcm2. Rhythmic genes were divided into nine clusters based on similar expression profile, indicating common regulation. Gene ontology analysis revealed that five clusters showed significant enrichment of genes involved in regulating transcription (cluster 1), mitochondrial ATP synthesis by oxidative phosphorylation (cluster 2), secretion (cluster 3), peptide biosynthesis (cluster 4) and cell cycle (cluster 5) (Figure 1). KD mice had global dampening of rhythmicity of PTG circadian clock genes as well as parathyroid signature genes compared to WT and significant downregulation of genes involved in mitochondrial ATP synthesis at four consecutive timepoints compared to WT by GSEA analysis (Figure 2A + B). Gene ontology analysis of all downregulated genes across timepoints in KD mice revealed multiple interconnected enriched terms related to mitochondrial ATP synthesis (Figure 2C). CONCLUSION Dampened rhythm of PTG circadian clock genes also reduced rhythmicity of parathyroid signature genes and downregulated genes involved in mitochondrial function and ATP synthesis in four separate comparisons. This indicates importance of the internal PTG molecular clock for parathyroid function.

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.