Division of Nephrology and Center for Lung Biology, Department of Medicine and Pathology, Howard Hughes Medical Institute, and Institute for Stem Cell and Regenerative Medicine, University of Washington, Seattle, WA 98109.
Fibrosis of vital organs is a major public health problem with limited therapeutic options. Mesenchymal cells including microvascular mural cells (pericytes) are major progenitors of scar-forming myofibroblasts in kidney and other organs. Here we show pericytes in healthy kidneys have active WNT/β-catenin signaling responses that are markedly up-regulated following kidney injury. Dickkopf-related protein 1 (DKK-1), a ligand for the WNT coreceptors low-density lipoprotein receptor-related proteins 5 and 6 (LRP-5 and LRP-6) and an inhibitor of WNT/β-catenin signaling, effectively inhibits pericyte activation, detachment, and transition to myofibroblasts in vivo in response to kidney injury, resulting in attenuated fibrogenesis, capillary rarefaction, and inflammation. DKK-1 blocks activation and proliferation of established myofibroblasts in vitro and blocks pericyte proliferation to PDGF, pericyte migration, gene activation, and cytoskeletal reorganization to TGF-β or connective tissue growth factor. These effects are largely independent of inhibition of downstream β-catenin signaling. DKK-1 acts predominantly by inhibiting PDGF-, TGF-β-, and connective tissue growth factor-activated MAPK and JNK signaling cascades, acting via LRP-6 with associated WNT ligand. Biochemically, LRP-6 interacts closely with PDGF receptor β and TGF-β receptor 1 at the cell membrane, suggesting that it may have roles in pathways other than WNT/β-catenin. In summary, DKK-1 blocks many of the changes in pericytes required for myofibroblast transition and attenuates established myofibroblast proliferation/activation by mechanisms dependent on LRP-6 and WNT ligands but not the downstream β-catenin pathway.
"Renal β-catenin is increased in experimental models of renal fibrosis (He et al., 2009; Ren et al., 2013; Surendran et al., 2005) and its systemic inhibition can reduce fibrosis (Hao et al., 2011). However, although DKK-1, a Wnt antagonist significantly reduced renal β-catenin abundance (He et al., 2009), the anti-fibrotic effects of DKK-1 were found to be independent of β-catenin in UUO and I/R models of fibrosis (Ren et al., 2013). Moreover, gene deletion of β-catenin in tubular epithelium did not reduce renal fibrosis (Zhou et al., 2013). "
"In addition to this well known effect, this molecule may induce perivascular cells to produce connective tissue growth factor (CTGF), which stimulates extracellular matrix production and fibrosis
. In fact, in presence of CTGF, pericytes differentiate toward a migratory and myofibroblast phenotype
. VEGF has been suggested to be involved in the pathogenesis of SSc and its expression is markedly increased in different cell types, both in the epidermis and dermis of patients with SSc and in the bloodstream, correlating with organ manifestations
[Show abstract][Hide abstract] ABSTRACT: Systemic sclerosis (SSc) is characterized by vascular alteration and fibrosis, the former probably leading to fibrosis via the ability of both endothelial cells and pericytes to differentiate toward myofibroblast. It is well known that vascular endothelial growth factor A (VEGF-A, hereafter referred to as VEGF) may induce a profibrotic phenotype on perivascular cells. Caveolin-1 (Cav-1) is involved in the regulation of VEGF signaling, playing a role in the transport of internalized VEGF receptor 2 (VEGFR2) toward degradation, thus decreasing VEGF signaling. In this work, we assessed the levels of Cav-1 in SSc bone marrow mesenchymal stem cells (SSc-MSCs), a pericyte surrogate, and correlate these results with VEGF signaling, focusing onpotential pathogenic pathways leading to fibrosis.
We explored the VEGF signaling assessing: (1) Cav-1 expression; (2) its co-localization with VEGFR2; (3) the activity of VEGFR2, by IF, immunoprecipitation, and western blot. In SSc-MSCs, Cav-1 levels were lower when compared to healthy controls (HC)-MSCs. Furthermore, the Cav-1/VEGFR2 co-localization and the ubiquitination of VEGFR2 were impaired in SSc-MSCs, suggesting a decreased degradation of the receptor and, as a consequence, the tyrosine phosphorylation of VEGFR2 and the PI3-kinase-Akt pathways were significantly increased when compared to HC. Furthermore, an increased connective tissue growth factor (CTGF) expression was observed in SSc-MSCs. Taken together, these data suggested the upregulation of VEGF signaling in SSc-MSCs. Furthermore, after silencing Cav-1 expression in HC-MSCs, an increased CTGF expression in HC-MSCs was observed, mirroring the results obtained in SSc-MSCs, and confirming the potential role that the lack of Cav-1 may play in the persistent VEGF signaling .
During SSc, the lower levels of Cav-1 may contribute to the pathogenesis of fibrosis via an upregulation of the VEGF signaling in perivascular cells which are shifted to a profibrotic phenotype.
"Wnt/β-catenin signaling modulates the recruitment and resolution of inflammatory cells Since Wnt/β-catenin signaling is required for blastema formation and regenerative outgrowth in zebrafish caudal fins (Ito et al., 2007; Kawakami et al., 2006; Poss et al., 2000; Stoick-Cooper et al., 2007a,b), but also modulates inflammatory processes including scar formation, fibrosis, wound healing and tissue remodeling in mammals (French et al., 2004; Ren et al., 2013; Koch et al., 2011), we investigated whether there might be a role for Wnt/β-catenin signaling in regulating inflammation during fin regeneration. "
[Show abstract][Hide abstract] ABSTRACT: Neutrophils and macrophages, as key mediators of inflammation, have defined functionally important roles in mammalian tissue repair. Although recent evidence suggests that similar cells exist in zebrafish and also migrate to sites of injury in larvae, whether these cells are functionally important for wound healing or regeneration in adult zebrafish is unknown. To begin to address these questions, we first tracked neutrophils (lyzC(+), mpo(+)) and macrophages (mpeg1(+)) in adult zebrafish following amputation of the tail fin, and detailed a migratory timecourse that revealed conserved elements of the inflammatory cell response with mammals. Next, we used transgenic zebrafish in which we could selectively ablate macrophages, which allowed us to investigate whether macrophages were required for tail fin regeneration. We identified stage-dependent functional roles of macrophages in mediating fin tissue outgrowth and bony ray patterning, in part through modulating levels of blastema proliferation. Moreover, we also sought to detail molecular regulators of inflammation in adult zebrafish and identified Wnt/β-catenin as a signaling pathway that regulates the injury microenvironment, inflammatory cell migration and macrophage phenotype. These results provide a cellular and molecular link between components of the inflammation response and regeneration in adult zebrafish.
Development 07/2014; 141(13):2581-91. DOI:10.1242/dev.098459 · 6.46 Impact Factor
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