Sonic hedgehog connects podocyte injury to mesangial activation and glomerulosclerosis
Dong Zhou, Haiyan Fu, Yang Han, Lu Zhang, Shijia Liu, Lin Lin, Donna B. Stolz, Youhua Liu
Dong Zhou, Haiyan Fu, Yang Han, Lu Zhang, Shijia Liu, Lin Lin, Donna B. Stolz, Youhua Liu
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Research Article Nephrology

Sonic hedgehog connects podocyte injury to mesangial activation and glomerulosclerosis

Abstract

Glomerular disease is characterized by proteinuria and glomerulosclerosis, two pathologic features caused by podocyte injury and mesangial cell activation, respectively. However, whether these two events are linked remains elusive. Here, we report that sonic hedgehog (Shh) is the mediator that connects podocyte damage to mesangial activation and glomerulosclerosis. Shh was induced in glomerular podocytes in various models of proteinuric chronic kidney diseases (CKD). However, mesangial cells in the glomeruli, but not podocytes, responded to hedgehog ligand. In vitro, Shh was induced in podocytes after injury and selectively promoted mesangial cell activation and proliferation. In a miniorgan culture of isolated glomeruli, Shh promoted mesangial activation but did not affect the integrity of podocytes. Podocyte-specific ablation of Shh in vivo exhibited no effect on proteinuria after adriamycin injection but hampered mesangial activation and glomerulosclerosis. Consistently, pharmacologic blockade of Shh signaling decoupled proteinuria from glomerulosclerosis. In humans, Shh was upregulated in glomerular podocytes in patients with CKD and its circulating level was associated with glomerulosclerosis but not proteinuria. These studies demonstrate that Shh mechanistically links podocyte injury to mesangial activation in the pathogenesis of glomerular diseases. Our findings also illustrate a crucial role for podocyte-mesangial communication in connecting proteinuria to glomerulosclerosis.

Authors

Dong Zhou, Haiyan Fu, Yang Han, Lu Zhang, Shijia Liu, Lin Lin, Donna B. Stolz, Youhua Liu

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Figure 1

Shh is induced in glomerular podocytes and selectively targets mesangial cells after injury.

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Shh is induced in glomerular podocytes and selectively targets mesangial...
(A) Representative micrographs show that Shh was induced in glomerular podocytes in various models of proteinuric kidney diseases, including adriamycin nephropathy (ADR), anti–glomerular basement membrane glomerulonephritis (anti-GBM), and diabetic kidney disease (DKD). Boxed areas are enlarged and presented below. Arrows indicate positive staining. Scale bar: 25 μm. (B) Quantitative determination of Shh+ podocytes in the glomeruli of different models. Shh+ podocytes were counted on 20 glomerular cross sections per mice; 5 mice per group. **P < 0.01 versus controls (n = 5, Student-Newman-Keuls test). (C) Quantitative, real-time PCR (qPCR) analyses reveal that Gli1 and Gli2 mRNA were induced at 5 weeks after ADR administration. *P < 0.05 versus shams (n = 6, t test). (D and E) Western blot analyses show that Shh was induced at 48 hours after incubation with various Wnt ligands in cultured podocytes. Cell lysates were immunoblotted with antibodies against Shh and α-tubulin. Wnt mix, a combination of Wnt1, Wnt3, and Wnt4 proteins; Wnt-CM, conditioned media of HKC-8 cells transfected with expression vector pHA-Wnt1 and pHA-Wnt4. Representative Western blot (D) and quantitative data (E) are shown. *P < 0.05 versus controls (n = 3, Student-Newman-Keuls test). (F and G) Identification of the hedgehog-responding cells in the glomeruli after kidney injury using Gli1-LacZ reporter mice. Gli1-LacZ reporter mice were injected with a single dose of ADR or chronic infusion of angiotensin II (Ang II). At 7 days after ADR or 14 days after Ang II, kidney sections were subjected to X-Gal staining. Arrows indicate β-Gal+ cells located at the mesangium. Images with X-Gal staining combined with PAS staining (G) are also presented. Dotted lines denote the border of glomerulus. Scale bar: 25 μm.