Impact of Diabetes and an SGLT2 Inhibitor on Glomerular Number and Volume in db/db Mice as Estimated by Synchrotron Radiation Micro-CT at SPring-8

To investigate the impact of diabetes and luseogliflozin, a sodium-glucose cotransporter 2 (SGLT2) inhibitor on the numbers and volumes of glomeruli in the whole kidneys, we performed CT imaging of diabetic db/db mice using synchrotron radiation at SPring-8. We found that there was no significant difference in the total glomerular number among mice. Diabetic mice had significantly larger glomerular volume in the mid-cortex compared to lean control db/m mice. Luseogliflozin reduced whole kidney volume, but not the glomerular hypertrophy in db/db mice. Luseogliflozin also decreased mesangial expansion and tubular damage in db/db mice. Luseogliflozin augmented hypoxia of S3 segment of proximal tubules in the juxtamedullary region and macula densa, as well as the number of intracellular vesicles in juxtaglomerular cells, and sustained upregulated renal renin expression in db/db mice. Luseogliflozin ameliorated hyperglycemia, glomerular and tubular injury, but not albuminuria. Db/db mice decreased the expression of renal megalin protein compared with that in db/m mice. Luseogliflozin-treated db/db mice also reduced the expression of megalin, accompanied with decreased reabsorbing urinary albumin as endocytotic ligand of megalin. In conclusion, our results suggest that oxygen metabolism and/or humoral factors more than blood glucose levels might determine the glomerular number and volume in diabetic kidney. Funding: This work was partially supported by a grant from the Japan Society for the Promotion of Science (JSPS KAKENHI grant no. 15K09372 to Y.T.), and by a Research Grant from the Japan Diabetes Foundation and Asahikawa Medical University (Research grant for Innovative Research in Life Science). Conflicts of Interests: Y.T. was also supported by several foundational grants, including grants from MSD, K.K., Eli Lilly and Company, Sanofi K.K., Takeda Pharmaceutical Co. and Taisho Pharmaceutical Co. No other potential conflicts of interest relevant to this article were reported. Ethical Approval Statement: These experiments were performed with the approval of the SPring-8 Proposal Review Committee (2012B1772, 2013A1655, 2013B1739).