Abstract: TH-OR116

SIRT6-Knockout Mice Exhibit Marked Type IV Collagen Deposition, Causing Phenotypes Similar to Those of Diabetic Tubulopathy

Session Information

  • Scarred for Life?
    November 02, 2017 | Location: Room 394, Morial Convention Center
    Abstract Time: 06:06 PM - 06:18 PM

Category: Chronic Kidney Disease (Non-Dialysis)

  • 308 CKD: Mechanisms of Tubulointerstitial Fibrosis

Authors

  • Muraoka, Hirokazu, Keio University , Tokyo, Japan
  • Hasegawa, Kazuhiro, Keio University , Tokyo, Japan
  • Wakino, Shu, Keio University , Tokyo, Japan
  • Itoh, Hiroshi, Keio University , Tokyo, Japan
Background

The class of NAD-dependent deacetylase and longevity genes called sirtuins comprises seven isoforms (SIRT1 to SIRT7). Here we investigated the role of SIRT6 in the kidneys.

Results

We investigated the intrarenal distribution of SIRT6 expression in different physiological conditions using wild-type mice and human renal biopsy specimens. High Sirt6 levels were detected in the nucleus of proximal tubules (PTs), whereas low levels were observed in glomeruli and other tubules. To assess the temporal changes in SIRT6 expression in different physiological conditions, we modeled several kidney injuries. Among these, diabetic nephropathy models demonstrated marked alterations. We next evaluated the temporal changes in SIRT6 expression every 8 weeks (8W, 16W, 24W, and 32W) in STZ and db/db models. At 8W and 16W, SIRT6 expression exhibited no difference. However, SIRT6 expression was conspicuously downregulated at 24W and was further augmented at 32W in both STZ and db/db models. To delineate the endogenous role of SIRT6 in the kidneys, we newly created PT-specific SIRT6-conditional knockout (CKO) mice by crossbreeding SIRT6 flox/flox[Editor1] mice with g-GT Cre mice. PT-SIRT6-CKO mice exhibited marked proximal tubular basement membrane (TBM) thickening and widespread peri-proximal tubular fibrosis. We next tested the molecular mechanisms underlying tubulopathy augmentation caused by SIRT6 knockdown. By performing DNA microarray and confirmatory real-time PCR analyses after microdissecting PT-injured regions together with immunostaining and immunogold electron microscopy, we could demonstrate that tissue inhibitor metalloproteinase 1 (TIMP-1) mRNA levels were elevated, leading to decreased MMP-9 activity and upregulated type IV collagen protein levels. These changes were consistent with the phenotypes of PT-SIRT6-CKO mice. Lastly, we analyzed in detail the mechanisms whereby SIRT6 knockdown directly elevated TIMP-1 mRNA levels and revealed that SIRT6 deficiency in PTs directly hyperacetylated histone H3 lysine K9 and RELA at these target regions within the TIMP-1 promoter.

Conclusion

PT Sirt6 is suggested to be involved in type IV collagen-related TBM thickening and peritubular fibrosis, which directly regulates TIMP-1 expression and plays a crucial role in tissue fibrosis, especially in diabetic nephropathy.