The clock gene Bmal1 inhibits kidney expression of SGLT2 and glucose reabsorption via the NR1d1/NRF1 pathway

Background & Aims: The nuclear receptor subfamily 1, group D, member 1 (Nr1d1, also called Rev-erbα) is highly expressed in the kidney, and its transcriptional activity is increased by the clock gene Bmal1 (ARNTL or MOP3). Here we studied the roles and functional interactions of Bmal1 and Nr1d1 in mouse kidney, particularly in regulating the expression of the glucose transporter SGLT2 (SLC5A2) and glucose reabsorption. Methods: We performed histologic and biochemical analyses of kidney tissues from male C57BL/6 and Bmal1-knockout mice and performed gene expression analyses to identify genes regulated by Bmal1. The effects of fasting and refeeding on renal expression of Sglt2 was examined in male C57BL/6, Bmal1-knockout, and Nr1d1-knockout mice. Some mice were given hemin to stimulate Nr1d1 gene expression (daily for 1 week) at 12:00 with 100 μg/kg/day; renal glucose reabsorption, and glucose and fatty acid levels were measured. Renal proximal tubule epithelial cells (RPTECs) were generated from C57BL/6 and Bmal1-knockout mice and glucose uptake determined. Luciferase reporter assays were performed using HK2 cell. Results: We found that kidney SGLT2 mRNA and protein expression and glucose absorption were increased in Bmal1-knockout mice compared with C57BL/6 mice. Expression of SGLT2 was affected by fasting and refeeding in C57BL/6 mice, but not in Bmal1-knockout or Nr1d1-knockout mice. Bmal1-knockout mice also presented with higher levels of renal fatty acids compared with C57BL/6 mice. Hemin injection reduced expression of SGLT2, decreased glucose re-absorption in RPTECs, and increased levels of fatty acid in kidney; these changes were not observed in Bmal1-knockout mice. Nuclear respiratory factor 1 (NRF1), which regulates glucose, activated transcription of Sglt2. Fasting caused MAPK signing pathway to phosphorylate Bmal1, which activated NR1d1 and inhibited NRF1 activity and thereby reduced Sglt2 expression. Conclusions: The data indicate that fasting activates Bmal1 and Nr1d1, which inhibits NRF1 and leads to repression of renal SGLT2 expression and glucose reabsorption. This is the first study that mechanistically links food intake to the regulation of kidney glucose transport through a circadian clock gene. NIH National Heart, Lung, and Blood Institute grant R56 HL137912-01, and American Heart Association grant-in-aid 16GRNT30960027 to PX; NIH R01DK112042 to VV This is the full abstract presented at the American Physiology Summit 2023 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.