Abstract: FR-PO382
TGF-β1 Increases LTBP-2 via RelA, and Elevated LTBP-2 Stimulates TGF-β1 Secretion via ERK, Forming a Positive Feedback Vicious Loop and Resulting in the De-Differentiation of Proximal Tubules
Session Information
- Diabetic Kidney Disease: Basic - II
October 26, 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
Latent transforming growth factor-β-1 binding protein-2 (LTBP-2) does not bind to transforming growth factor-β1 (TGF-β1) unlike other LTBPs. Reportedly, serum LTBP-2 levels were elevated statistically; thus, it is considered as a potential prognostic marker in the progressive stages of diabetic kidney disease. Although LTBP-2 seems to regulate the TGF-β1 bioactivity, except direct bindings, the effect of LTBP-2 in the kidneys is unclear.
Methods
We evaluated the regulatory mechanism of the LTBP-2 expression and primary function of LTBP-2.
Results
In wild-type mice, LTBP-2 is expressed only in proximal tubules (PTs). Diabetic nephropathy, such as
STZ and db/db mice, demonstrated remarkably upregulated LTBP-2 in PTs. UUO models also marginally increased LTBP-2 immunostaining in collecting tubules but not in PTs. By treating humoral factors that are considered crucial mediators in the pathogenesis of diabetic renal injury or renal fibrosis, such as high glucose, AGE, angiotensin II, TGF-β1, TNF-α, and interleukin 6, only the TGF-β1 administration markedly elevated the LTBP-2 mRNA and protein expression in time- and dose-dependent way in cultured PTs. TRANSFAC analysis, luciferase assays, and EMSA revealed that the promoter region spanning −1666 to −1436, especially the RelA binding site, was essential for the basal LTBP-2 gene promoter activity and TGF-β1–induced LTBP-2 gene upregulation. Erk phosphorylation was markedly elevated by the transfection of LTBP-2 cDNA vector into HK-2 cells, resulting in the de-differentiation of PTs such as reducing E-cadherin expression, increasing fibronectin expression, and TGF-β1 secretion. Conversely, LTBP-2 siRNA administration under TGF-β1 treatment silenced Erk phosphorylation, resulting in blocking the de-differentiation of PTs. When cells were treated with Erk inhibitor, these phenotypic changes were prevented.
Conclusion
Renal fibrogenetic changes in diabetic nephropathy were attributed to the upregulation of LTBP-2 via the RelA activation by TGF-β1. Elevated LTBP-2 triggers the stimulation of TGF-β1 secretion via Erk signaling, forming a positive feedback vicious loop and resulting in the de-differentiation of PTs. Overall, silencing LTBP-2 is a novel therapeutic target for blocking diabetic tubulopathy or fibrotic changes.