Sonic Hedgehog Signaling Mediates Epithelial–Mesenchymal Communication and Promotes Renal Fibrosis

Abstract

Sonic hedgehog (Shh) signaling is a developmental signal cascade that plays an essential role in regulating embryogenesis and tissue homeostasis. Here, we investigated the potential role of Shh signaling in renal interstitial fibrogenesis. Ureteral obstruction induced Shh, predominantly in the renal tubular epithelium of the fibrotic kidneys. Using Gli1 lacZ knock-in mice, we identified renal interstitial fibroblasts as Shhresponding cells. In cultured renal fibroblasts, recombinant Shh protein activated Gli1 and induced a-smooth muscle actin (a-SMA), desmin, fibronectin, and collagen I expression, suggesting that Shh signaling promotes myofibroblast activation and matrix production. Blockade of Shh signaling with cyclopamine abolished the Shh-mediated induction of Gli1, Snail1, a-SMA, fibronectin, and collagen I. In vivo, the kidneys of Gli1-deficient mice were protected against the development of interstitial fibrosis after obstructive injury. In wild-type mice, cyclopamine did not affect renal Shh expression but did inhibit induction of Gli1, Snail1, and a-SMA. In addition, cyclopamine reduced matrix expression and mitigated fibrotic lesions. These results suggest that tubule-derived Shh mediates epithelial-mesenchymal communication by targeting interstitial fibroblasts after kidney injury. We conclude that Shh/Gli1 signaling plays a critical role in promoting fibroblast activation, production of extracellular matrix, and development of renal interstitial fibrosis.

Sonic hedgehog signaling in kidney fibrosis: a master communicator

“…Although the damaged tubular cells may undergo a variety of maladaptive changes such as partial epithelial-mesenchymal transition (EMT), cell cycle arrest, defects in cell metabolism (Grande et al, 2015; Kang et al, 2015; Liu, 2010; Lovisa et al, 2015), one common consequence of these diverse responses is converting to a secretory phenotype (Zhou and Liu, 2016). Indeed, marked induction of Shh protein is observed in the fibrotic kidneys in all commonly used CKD models, including folic acid (FA), unilateral ureteral obstruction (UUO), ischemia reperfusion injury (IRI), adriamycin (ADR) and 5/6 nephrectomy, although it is barely detectable in normal kidneys (Ding et al, 2012; Fabian et al, 2012; Rauhauser et al, 2015; Zhou et al, 2014). In human biopsy specimens, Shh is also specifically induced in renal tubular epithelium of the diseased kidney, regardless of the initial etiologies (Zhou et al, 2014).…”

“…In vitro , a variety of pathologic cues such as TGF-β1 and Wnt induces Shh mRNA expression and protein secretion by tubular epithelial cells. Based on these observations, we recently propose that Shh is a novel, inducible, tubule-derived growth factor that mediates epithelial-mesenchymal communication (EMC) after kidney injury (Ding et al, 2012; Zhou et al, 2014). …”

“…The population of Shh-responsive Gli1-positive cells is markedly expanded in renal interstitium after Shh transgene expression. In vitro , human recombinant Shh protein activated Ptch1 and Gli1 and induced α-smooth muscle actin (α-SMA), desmin, Snail1, fibronectin, and collagen I expression (Ding et al, 2012; Zhou et al, 2014), suggesting a critical role for Shh signaling in regulating myofibroblast activation and matrix production. Shh also promotes cultured rat kidney fibroblast proliferation and stimulates the induction of numerous proliferation-related genes (Zhou et al, 2014).…”

“…This conclusion is also supported by genetic and pharmacologic manipulations of the Shh downstream mediators Smo or Gli proteins. It is shown that the kidneys in Gli1-deficient mice are protected against the development of tubulointerstitial fibrosis after UUO (Ding et al, 2012; Rauhauser et al, 2015). Smo inhibitors such as cyclopamine also repress the induction of Gli1, Snail1 and α-SMA, and reduce matrix expression and mitigate fibrotic lesions in obstructive nephropathy (Ding et al, 2012; Rauhauser et al, 2015), although it does not affect renal Shh expression.…”

“…There are three hedgehog ligands in mammals: Sonic hedgehog (Shh), Indian hedgehog (Ihh) and Desert hedgehog (Dhh), of which Shh is the best characterized (Lum and Beachy, 2004). Accumulating studies have demonstrated an activated Shh signaling in fibrotic CKD, suggesting a potential connection between aberrant regulation of this signaling and kidney fibrosis (Ding et al, 2012; Fabian et al, 2012; Kramann et al, 2015; Rauhauser et al, 2015; Zhou et al, 2014). …”