Abstract: SA-PO111
Elevation of NMN in the TG Mice Overexpressing Nampt in the Proximal Tubules Suppresses Albuminuria and Diabetic Tubulopathy by Maintaining Megalin Expression
Session Information
- Diabetic Kidney Disease: Basic - III
October 27, 2018 | Location: Exhibit Hall, San Diego Convention Center
Abstract Time: 10:00 AM - 12:00 PM
Category: Diabetic Kidney Disease
- 601 Diabetic Kidney Disease: Basic
Authors
- Hasegawa, Kazuhiro, Keio University, Tokyo, Japan
- Wakino, Shu, Keio University, Tokyo, Japan
- Itoh, Hiroshi, Keio University, Tokyo, Japan
Background
Nicotinamide phosphoribosyltransferase (Nampt) synthesizes nicotinamide mononculeotide (NMN), which is the precursor of nicotinamide adenosine diphosphate (NAD). Nampt is expressed more abundantly in proximal tubules (PTs) than in other tissues. NMN injections have been shown to suppress acute kidney injury; however, the effects of renal NMN or Nampt in diabetic nephropathy remain unclear. We created kidney-specific Nampt-overexpressing transgenic (TG) mice using the promoter sodium-phosphate cotransporter IIa (Npt2) driven specifically in PTs for investigating them.
Methods
Wild-type littermate (WT) or TG 8-week old male mice were subjected to intraperitoneal injections of 50 mg/kg/day streptozotocin (STZ) or saline (Sal) for 5 days (WT+Sal, WT+STZ, TG+Sal, TG+STZ).
Results
After 16 weeks, Nampt, NMN, and NAD levels in WT+STZ were decreased, but were rescued in TG+STZ. Tubular Basement membrane (TBM) thickening, type IV collagen deposition, and PT apoptosis were significantly higher in WT+STZ, and were attenuated in TG+STZ. Our DNA microarray analyses showed the profibrotic and proapoptotic gene, tissue inhibitor of metalloproteinases 1 (TIMP-1), was highly increased in WT+STZ, but suppressed in TG+STZ. Glomerular changes such as glomerular basement membrane (GBM) thickening and podocyte foot-process effacement occurred in both WT+STZ and TG+STZ. However, the albuinuria present in WT+STZ was significantly suppressed in TG+STZ. Thus, we hypothesized that TG elevates albumin reabsorption despite not affecting podocytes. Consistent with this, albumin endocytosis and megalin expression were reduced in WT+STZ, but retained in TG+STZ, whereas cubilin was not altered. In promoter assays, the decrease in Nampt/NMN/NAD repressed Sirt6 activity, which acetylated and activated RelA binding to TIMP-1 promoter regions. The transfection of TIMP-1 vector in cultured PTs causes excessive collagen IV production and Erk phosphorylation, which reportedly reduces megalin expression and elevates PT apoptosis. These changes were totally blocked in TG mice.
Conclusion
Nampt TG/NMN/NAD potentiates Sirt6 activity, deacetylating RelA and silencing TIMP-1 transcription. This protects against TBM thickening, type IV collagen deposition, and Erk activation. Thus, Nampt appears to maintain megalin and albumin reabsorption.