Tubule-Derived Wnts Are Required for Fibroblast Activation and Kidney Fibrosis

Abstract

Cell-cell communication Wnt ligands is necessary in regulating embryonic development and has been implicated in CKD. Because Wnt ligands are ubiquitously expressed, the exact cellular source of the Wnts involved in CKD remains undefined. To address this issue, we generated two conditional knockout mouse lines in which Wntless (Wls), a dedicated cargo receptor that is obligatory for Wnt secretion, was selectively ablated in tubular epithelial cells or interstitial fibroblasts. Blockade of Wnt secretion by genetic deletion of Wls in renal tubules markedly inhibited myofibroblast activation and reduced renal fibrosis after unilateral ureteral obstruction. This effect associated with decreased activation of-catenin and downstream gene expression and preserved tubular epithelial integrity. In contrast, fibroblast-specific deletion of Wls exhibited little effect on the severity of renal fibrosis after obstructive or ischemia-reperfusion injury. , incubation of normal rat kidney fibroblasts with tubule-derived Wnts promoted fibroblast proliferation and activation. Furthermore, compared with kidney specimens from patients without CKD, biopsy specimens from patients with CKD also displayed increased expression of multiple Wnt proteins, predominantly in renal tubular epithelium. These results illustrate that tubule-derived Wnts have an essential role in promoting fibroblast activation and kidney fibrosis epithelial-mesenchymal communication.

New insights into the role and mechanism of Wnt/β‐catenin signalling in kidney fibrosis

“…Selective blockade of Wnt secretion from tubular epithelium in mice effectively preserves tubular epithelial cell integrity, inhibits myofibroblast activation and inflammation, and ultimately ameliorates kidney fibrosis after obstructive injury. In contrast, conditional knockout of Wls gene in interstitial fibroblasts does not affect the severity of kidney injury and fibrosis after obstructive and unilateral ischemia/reperfusion injury . Consistent with these results, another independent study demonstrated that proximal tubular induction of Wnt1 expression alone is efficient to cause interstitial myofibroblast activation and increase matrix protein production .…”

“…As Wnt ligands are widely expressed in virtually all types of cells in the kidney, one unsolved question was the cellular source(s) of the Wnt ligands that play a predominant role in mediating fibrotic responses. Immunostaining for Wnt proteins in human kidney biopsies from CKD patients reveal that multiple Wnt ligands are induced predominantly in renal tubular epithelium, as well as in the cells of renal interstitium, which presumably include fibroblasts, pericytes, infiltrating inflammatory cells and vascular and lymphatic endothelial cells . Because Wntless (Wls) protein, also known as Evenness interrupted and Sprinter, is a conserved multi‐span transmembrane cargo receptor dedicated to the trafficking and secretion of all Wnt ligands, genetic ablation of its gene in a cell type‐specific fashion will block Wnt secretion from that particular type of cells.…”

“…In the past several years, numerous hypotheses have been postulated, such as partial epithelial‐to‐mesenchymal transition (EMT), cell cycle arrest, metabolic alterations and accelerated tubular cell senescence . Despite these distinct possibilities, one common and unifying sequel is the conversion of normal tubular cells to a secretory phenotype, characterized by active production and secretion of a range of profibrotic factors, such as transforming growth factor‐β (TGF‐β), Wnt and hedgehog ligands …”

Failed Tubule Recovery, AKI-CKD Transition, and Kidney Disease Progression

“…125 Two weeks after maleic acid, patchy fibrosis with mononuclear cell infiltrates developed around atrophic tubules 39 together with capillary rarefaction and myofibroblast increase in the interstitium (unpublished observations). Furthermore, selective proximal tubule injury produced by diphtheria toxin treatment and Kidney Injury Molecule-1 or Notch1 overexpression leads to interstitial inflammation, fibrosis, and CKD [126][127][128] ; recent studies suggest that tubule-derived wnt and sonic hedgehog ligands, tubule-specific activity of ADAM17 protease, and other pathologies strictly localized to tubules are sufficient to drive interstitial fibrosis 41,58,62,[129][130][131][132][133] We note here that such cross-talk between injured tubules, peritubular capillaries, and interstitial cells through locally activated mechanisms has the advantage of circumscribing the fibrotic response and minimizing dissociation of nephron function and vascular perfusion.…”

Wnt Signaling in Kidney Development and Disease

“…10 Notably, the cellular source of Wnt ligands in the fibrotic kidneys is largely from the tubular epithelium. 103,104 The activation of Wnt signaling leads to dramatic accumulation of β-catenin and upregulation of its target genes, such as c-Myc, Twist, TCF1 , and fibronectin in renal epithelial cells. 10 Both in vitro and in vivo studies illustrate that Wnt/β-catenin controls several key fibrosis-related downstream genes, such as Snail1, fibronectin, plasminogen activator inhibitor-1 ( PAI-1 ), matrix metalloproteinase 7 ( MMP-7 ), and multiple components of the renin–angiotensin system (RAS), including angiotensinogen, renin, angiotensin converting enzyme ( ACE ), and angiotensin receptor type 1 ( AT1 ).…”