Light conditions affect rhythmic expression of aquaporin 5 and anoctamin 1 in rat submandibular glands

Ryouichi Satou,Yoshiyuki Shibukawa,Maki Kimura,Naoki Sugihara

doi:10.1016/j.heliyon.2019.e02792

Abstract

Circadian rhythms regulate various physiological functions and are, therefore, essential for health. Light helps regulate the master and peripheral clocks. The secretion rates of saliva and electrolytes follow a circadian rhythm as well. However, the relationship between the molecular mechanism of saliva water secretion and the peripheral circadian rhythm in salivary glands is not yet clear. The transmembrane proteins aquaporin5 (Aqp5) and anoctamin1 (Ano1) are essential for water transport in the submandibular glands (SGs). The purpose of this study was to reveal the effect of light conditioning on the peripheral clock in SGs. We examined temporal expression patterns among clock genes, Aqp5 and Ano1, in rat SGs under light/dark (LD) and dark/dark (DD) conditions. We observed circadian rhythmic expression of Bmal1, Per2, Cry1, Aqp5, and Ano1 mRNAs under both LD and DD conditions. The expression levels of Aqp5 and Ano1 peaked 6 h earlier under the DD condition than under the LD condition. Maintenance of the circadian rhythm of Aqp5 and Ano1 expression even under the DD condition indicates that Aqp5 and Ano1 may be controlled by clock genes; such genes are called clock-controlled genes (CCGs). Western blot analysis revealed the circadian oscillation and peak shift of AQP5 and ANO1expression under DD conditions. Clock genes may regulate the rhythmic expression of Ano1 and Aqp5 and may control osmic gradients in SGs.

Highlights

Circadian rhythms, which measure time on a scale of 24 h, regulate various physiological functions such as sleep cycle, blood pressure, hormone secretion, metabolism and salivary secretion in mammals [1, 2]
We examined temporal relative expression of the clock genes mRNA in the submandibular glands (SGs) every 6 h from ZT0 to ZT48
We demonstrated that Bmal1, Per2, circadian locomotor output cycles kaput (Clock), and Cry1 show rhythmic circadian expression in SGs under LD and dark/dark cycle (DD) conditions (Fig. 1)

Summary

Introduction

Circadian rhythms, which measure time on a scale of 24 h, regulate various physiological functions such as sleep cycle, blood pressure, hormone secretion, metabolism and salivary secretion in mammals [1, 2]. The rhythm is orchestrated by a master clock and several peripheral biological clocks. Peripheral clocks in organs are regulated by a master clock [1]. Peripheral biological clocks are regulated independently by clock genes. The intracellular clock mechanism of the clock genes is based on transcriptional and translational feedback loops, which are called transcription translation oscillating loops (TTLs) [1, 3]. Multiple studies have suggested that the clock genes of peripheral clocks regulate physiological function in organs [4, 6, 8]. Little is known about their roles in salivary glands

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