Microcurrent stimulation activates the circadian machinery in mice

Inhibition of G protein-coupled receptor 68 using homoharringtonine attenuates chronic kidney disease-associated cardiac impairment

Chronic kidney disease (CKD) induces cardiac inflammation and fibrosis and reduces survival. We previously demonstrated that G protein-coupled receptor 68 (GPR68) promotes cardiac inflammation and fibrosis in mice with 5/6 nephrectomy (5/6Nx) and patients with CKD. However, no method of GPR68 inhibition has been found that has potential for therapeutic application. Here, we report that Cephalotaxus harringtonia var. nana extract and homoharringtonine ameliorate cardiac inflammation and fibrosis under CKD by suppressing GPR68 function. Reagents that inhibit the function of GPR68 were explored by high-throughput screening using a medicinal plant extract library (8,008 species), and we identified an extract from Cephalotaxus harringtonia var. nana as a GPR68 inhibitor that suppresses inflammatory cytokine production in a GPR68 expression-dependent manner. Consumption of the extract inhibited inflammatory cytokine expression and cardiac fibrosis and improved the decreased survival attributable to 5/6Nx. Additionally, homoharringtonine, a cephalotaxane compound characteristic of C. harringtonia, inhibited inflammatory cytokine production. Homoharringtonine administration in drinking water alleviated cardiac fibrosis and improved heart failure and survival in 5/6Nx mice. A previously unknown effect of C. harringtonia extract and homoharringtonine was revealed in which GPR68-dependent inflammation and cardiac dysfunction were suppressed. Utilizing these compounds could represent a new strategy for treating GPR68-associated diseases, including CKD.

Circadian expression of Glycoprotein 2 (Gp2) gene is controlled by a molecular clock in mouse Peyer's patches

The expression levels of many cell-surface proteins vary with the time of day. Glycoprotein 2 (Gp2), specifically expressed on the apical surface of M cells in Peyer's patches, functions as a transcytotic receptor for mucosal antigens. We report that cAMP response element-binding protein (CREB) regulates the transcription of the Gp2 gene, thereby generating the circadian change in its expression in mouse Peyer's patches. The transcytotic receptor activity of Gp2 was increased during the dark phase when the Gp2 protein abundance increased. Rhythmic expression of clock gene mRNA was observed in mouse Peyer's patches, and expression levels of Gp2 mRNA also exhibited circadian oscillation, with peak levels during the early dark phase. The promoter region of the mouse Gp2 gene contains several cAMP response elements (CREs). Chromatin immunoprecipitation assays revealed that CREB bound to the CREs in the Gp2 gene in Peyer's patches. Forskolin, which promotes CREB phosphorylation, increased the transcription of the Gp2 gene in Peyer's patches. As phosphorylation of CREB protein was increased when Gp2 gene transcription was activated, CREB may regulate the rhythmic expression of Gp2 mRNA in Peyer's patches. These findings suggest that intestinal immunity is controlled by the circadian clock system.