Stat3 Controls Tubulointerstitial Communication during CKD

Frank Bienaimé

Mordi Muorah

Lucie Yammine

Martine Burtin

Mélanie Broueilh+8 authors

Supplementary Material

Supplemental Data:

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^{Institut National de la Santé et de la Recherche Médicale U1151, Université Paris Descartes, Institut Necker Enfants Malades, Department of Growth and Signaling,}

^{Service d’Explorations Fonctionnelles, and}

^{Service de Néphrologie—Transplantation, Hôpital Necker Enfants Malades, Paris, France;}

^{Institut National de la Santé et de la Recherche Médicale U1016, Centre National de la Recherche Scientifique, Unité Mixte de Recherche 8104, Université Paris Descartes, Institut Cochin, Paris, France;}

^{Department of Human Genetics, Leiden University Medical Center, Leiden, The Netherlands; and}

^{Department of Biotechnology and Health Sciences, Molecular Biotechnology Center, Torino University, Turin, Italy}

^{Corresponding author.}

Correspondence: Dr. Fabiola Terzi, Institut National de la Santé et de la Recherche Médicale U1151, Team: Mechanisms and Therapeutic Strategies of Chronic Kidney Disease, Hôpital Necker Enfants Malades, Tour Lavoisier, 6ème étage, 149 Rue de Sèvres, 75015 Paris, France. Email rf.mresni@izret.aloibaf

Received 2015 Sep 14; Accepted 2016 Mar 24.

Abstract

In CKD, tubular cells may be involved in the induction of interstitial fibrosis, which in turn, leads to loss of renal function. However, the molecular mechanisms that link tubular cells to the interstitial compartment are not clear. Activation of the Stat3 transcription factor has been reported in tubular cells after renal damage, and Stat3 has been implicated in CKD progression. Here, we combined an experimental model of nephron reduction in mice from different genetic backgrounds and genetically modified animals with in silico and in vitro experiments to determine whether the selective activation of Stat3 in tubular cells is involved in the development of interstitial fibrosis. Nephron reduction caused Stat3 phosphorylation in tubular cells of lesion-prone mice but not in resistant mice. Furthermore, specific deletion of Stat3 in tubular cells significantly reduced the extent of interstitial fibrosis, which correlated with reduced fibroblast proliferation and matrix synthesis, after nephron reduction. Mechanistically, in vitro tubular Stat3 activation triggered the expression of a specific subset of paracrine profibrotic factors, including Lcn2, Pdgfb, and Timp1. Together, our results provide a molecular link between tubular and interstitial cells during CKD progression and identify Stat3 as a central regulator of this link and a promising therapeutic target.

Keywords: chronic kidney disease, Cell Signaling, Pathophysiology of Renal Disease and Progression, renal tubular epithelial cells, renal fibrosis, transcriptional profiling

Abstract

Chronic reduction of renal function, the common denominator of CKD, represents a worldwide health concern. Grossly, 10% of the adult population is estimated to suffer from CKD.¹ These patients display an increased risk of death and cardiovascular morbidity that is proportional to the decline of renal function.²,³ Moreover, because of its progressive nature, CKD may lead to ESRD, which requires RRT, substantially altering life quality and expectancy.

Clinical studies have shown that the decline of renal function correlates more closely with the severity of interstitial fibrosis than with glomerular damage.⁴–⁶ Recent finding indicate that the activation of renal fibroblasts by paracrine factors plays a critical role in the development of renal fibrosis.⁷ It is known that the overwork imposed by adaptation leads to mechanical and metabolic stresses of tubular cells, which in turn, start to synthesize soluble mediators of CKD progression. Similarly, leakage of albumin from the damaged glomerular barrier also leads to the damage of tubular cells with the subsequent production of profibrotic mediators. Thus, it is tempting to speculate that, by delivering fibrogenic paracrine cues to interstitial fibroblasts, tubular cell activation is a crucial step of CKD progression.

Signal transducers and activators of transcription (Stats) are versatile transcription factors that mediate the intracellular signaling of various molecular pathways.⁸ Stat activation begins by their recruitment to membrane receptors, where they are phosphorylated. This phosphorylation allows both dimerization and nuclear accumulation of the activated Stat, which binds to cognate elements on promoters of responsive genes.⁹ Among the seven known Stat genes, Stat3 displays unique features. It has the largest spectrum of potential activators, including various cytokines, hormones, and growth factors.¹⁰ Contrary to the other members, Stat3 is the only one with inactivation that leads to embryonic lethality in mice.¹¹ Another peculiar characteristic of Stat3 is its ability to regulate gene networks that are highly variable from one cell type to another one.¹²–¹⁶ In addition, Stat3 has been described to have nontranscriptional roles in regulating cell migration¹⁷ and mitochondrial electron transport chain.¹⁸,¹⁹

Recent studies have implicated Stat3 in the progression of CKD. Indeed, in several human and experimental nephropathies, Stat3 activation has been shown in different compartments of the damaged kidney, including tubular cells.²⁰–²⁷ Interestingly, both Stat3 haploinsufficiency and Stat3 pharmacologic inhibition have been shown to decrease lesion progression in HIV-associated nephropathy,²⁵ diabetes,²³ or ureteral obstruction.²⁸ Although these studies were conducted in specific experimental models, they point to Stat3 as an important mediator of CKD progression. However, the molecular mechanisms involved in the deleterious effect of Stat3 remain to be elucidated. Remarkably, a few studies have shown that Stat3 is mechanistically involved in the communication between epithelial cells and fibroblasts.²⁹–³¹ Taking all of these data together, we hypothesized that Stat3 orchestrates the communication between tubular and interstitial cells, leading to the development of interstitial fibrosis.

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Acknowledgments

We thank Pauline Barre, Sophie Berissi, Noemi Gadessaud, Christine Bole, and the Laboratoire Expérimentation Transgenese Animal Histology and Genomics Platforms for technical assistance. We also thank Denise Laouari for discussion. We are grateful to Cecilia Bondjers (Gottenberg University, Gottenberg, Sweden) and Noel Lammande (College de France, Paris, France) for the antiplatelet–derived growth factor receptor–β probe.

This work was supported by Institut National de la Santé et de la Recherche Médicale, Université Paris Descartes, Assistance Publique - Hôpitaux de Paris, Agence Nationale Recherche, Fondation de la Recherche Médicale, pharma Research and Early Development Roche Laboratories (Basel, Switzerland), Whoami Laboratoire d'Excellence, and Institut Roche de Recherche et Médecine Translationnelle (Paris, France).

Acknowledgments

Footnotes

Published online ahead of print. Publication date available at www.jasn.org.

See related editorial, “Beyond EMT: Epithelial STAT3 as a Central Regulator of Fibrogenesis,” on pages 3502–3504.

This article contains supplemental material online at http://jasn.asnjournals.org/lookup/suppl/doi:10.1681/ASN.2015091014/-/DCSupplemental.

Footnotes

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