Background/Purpose:  Circadian rhythm is a universal phenomenon that allows organisms to anticipate and respond to changes in their environment by regulating sleep and feeding patterns, blood pressure, metabolism, detoxification and response to pathogens. In the kidney intrinsic circadian rhythm of a subset of genes is associated with circadian regulation of GFR, blood pressure, urine pH, Na and K excretion and detoxification of drugs. We found a disturbance of expression of key clock transcriptional regulators in the kidneys of mice with SLE nephritis. The purpose of these experiments was to determine how this abnormality affected transcriptional regulation of renally expressed genes and immune cell homeostasis.

Methods:  We studied NZB/W mice at the age of 12 weeks (without proteinuria) and 30 weeks (with 300mg/dl proteinuria). Kidneys and blood were harvested at 4 hour intervals. Kidneys were perfused with PBS and used to generate RNA, protein lysates and single cells for flow cytometry analysis. Whole blood counts were performed in a BD analyzer and white blood cell subtypes were analyzed using flow cytometry. RNA was analyzed using RNASeq and real-time PCR. Lysates were analyzed for expression of BMAL1 and Per2.

Results: Young NZB/W mice have normal circadian oscillation of peripheral WBCs. Circadian oscillation of peripheral blood RBCs, lymphocytes and neutrophils was likewise normal in the nephritic mice. There was a marked increase of circulating renal macrophages in the nephritic mice but circadian rhythm of Ly6C^hi vs Ly6C^lo cells followed a normal pattern. Kidneys of young NZB/W mice displayed a normal circadian pattern of expression of the master transcriptional regulators of circadian rhythm including Bmal1, Clock, Per and Cry genes. By contrast, kidneys from the nephritic mice had attenuated rhythm of these genes with inversion of the normal pattern. This abnormality was confirmed in two different sets of mice using qPCR. To determine how this affected general gene expression in the kidneys we performed mRNASeq of whole perfused kidneys. Of the 18952 genes detected by RNASeq, 2442 genes (12.9%) were regulated in a circadian fashion in young mice and 2074 (10.9%) in nephritic mice. There was little overlap in the two genesets, confirming a marked dysregulation of normal circadian patterns of renal gene expression. Although many of the genes that were upregulated in nephritic compared with young mice at any time of the day were associated with immune and inflammatory processes, analysis of the genes whose circadian rhythm was dysregulated in nephritic mice indicated that most are involved in metabolic rather than immune processes.

Conclusion:  Circadian dysfunction in the setting of lupus nephritis may have important implications for the delivery and metabolism of therapeutics. Because circadian transcriptional regulators can influence the severity of inflammation and fibrosis, dysfunction of the renal circadian clock might also contribute to the progression of renal injury and may therefore be a potentially druggable target for therapeutic intervention.

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/disturbance-of-renal-circadian-rhythm-in-lupus-nephritis/