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| Ureteral Obstruction-Induced Renal Fibrosis: An In Vivo Platform for
Mechanistic Discovery and Therapeutic Intervention |
| Amy D. Dobberfuhl1, Rohan Samarakoon2, Craig E. Higgins2, Badar M. Mian2, Jessica M. Overstreet2, Stephen P. Higgins2, Barry A. Kogan2 and Paul J. Higgins2* |
| 1The Urological Institute of Northeastern New York, Albany NY 12208, USA |
| 2Center for Cell Biology and Cancer Research, Albany Medical College, 47 New Scotland Avenue, Albany NY 12208, USA |
| *Corresponding author: |
Dr. Paul J. Higgins
Center for Cell Biology & Cancer
Research
Albany Medical College
47 New Scotland Avenue
Albany, New York
12208, USA
Tel: 518-262-5168
E-mail: higginp@mail.amc.edu |
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| Received June 30, 2012; Accepted July 02, 2012; Published July 03, 2012 |
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| Citation: Dobberfuhl AD, Samarakoon R, Higgins CE, Mian BM, Overstreet JM,
et al. (2012) Ureteral Obstruction-Induced Renal Fibrosis: An In Vivo Platform
for Mechanistic Discovery and Therapeutic Intervention. Cell Dev Biol 1:e107.
doi:10.4172/2168-9296.1000e107 |
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| Copyright: © 2012 Dobberfuhl AD, et al. This is an open-access article distributed
under the terms of the Creative Commons Attribution License, which permits
unrestricted use, distribution, and reproduction in any medium, provided the
original author and source are credited. |
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| Molecular Events Associated with Renal Fibrosis:
TGF-β/SMAD Signaling as Transducer of the Fibrotic
Phenotype |
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| Interstitial fibrosis, resulting in renal tissue destruction and
progressive impairment of organ function, is a hallmark of end-stage
kidney disease [1]. The primary sources of matrix synthesis during
renal fibrogenesis are activated fibroblasts or myofibroblasts. While
their origin remains uncertain, this cell type-predictor of disease
progression likely derives largely from resident fibroblasts and
epithelial-to-mesenchymal transdifferentiated (EMT) tubular epithelial
cells [2]. The transforming growth factor-β (TGF-β)/SMAD system is a
potent, perhaps the most well-characterized, inducer of myofibroblast
differentiation and EMT. TGF-β drives EMT in renal epithelial cells
and promotes fibrosis in animal models by engaging effector pathways
and their downstream target genes that impact both the inflammatory
and scarring stages of the injury response [3]. SMAD-mediated
signaling initiated by TGF-β is pivotal for induction of EMT, fibroblast
activation and renal fibrosis [2,3]. SMAD3, in particular, appears critical
in several in vivo models of renal fibrosis. This was, indeed, confirmed
by the finding that SMAD3-deficient mice are significantly protected
from disease progression. TGF-β also activates non-SMAD-dependent
pathways [4] that impact the expression of pro-fibrotic genes. The
continued characterization of such highly-interactive transduction
events initiated by TGF-β/TGF-β receptor interactions will likely lead
to identification of novel opportunities for anti-fibrotic therapy. |
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| Animal Models for Investigating Obstructive
Nephropathies and the Signaling Mechanisms
Associated with Renal Fibrosis |
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| Ureteral Unilateral Obstruction (UUO) is an established, relatively
short-term, animal model of injury-stimulated renal fibrosis that lends
itself to the dissection of critical mechanistic events and evaluation of
potential therapeutic targets [5]. Aside from its relative surgical ease,
UUO in rodents is pathophysiologically-relevant and recapitulates the
biology of human nephropathy associated with congenital urinary tract
anomalies (common in pediatric patients), obstructive urolithiasis
and age-related lower urinary tract obstruction. The basic pathology
of UUO in murine systems is highly reproducible. Within hours after
ureteral occlusion, the affected kidney is subject to sudden changes
in mechanical forces, increased oxidative stress upon generation of
free radicals and tissue ischemia resulting in a complex phenotypic
response including cellular apoptosis, inflammation (due to infiltrating
macrophages and expression of inflammatory cytokines), alterations
in gene expression, extracellular matrix (ECM) remodeling and EMT.
“Activated” fibroblasts derived from resident interstitial fibroblasts,
recruited from extra-renal sources (i.e., the circulation) or arising de
novo from EMT of the injured epithelium differentiate into matrixsecreting
myofibroblasts and initiate the process of ECM deposition.
With persistence of obstruction, overt fibrosis and massive epithelial
apoptosis develops with eventual tubular atrophy and loss of renal function. Tubulointerstitial fibrosis in this model appears dependent
on upregulation of TGF-β1 expression in the interstitial compartment.
Indeed, introduction of 15-mer TGF-β1 antisense phosphorothioate
oligodeoxynucleotides by retrograde ureteral injection or
administration of TGF-β1 siRNA suppresses tubulointerstitial fibrosis
in UUO with reduced expression of the TGF-β1 response genes. |
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| Consistent with the activation of TGF-β1 signaling in UUO, there
is a dramatic increase of SMAD2/3 phosphorylation and elevated
expression of plasminogen activator inhibitor-1 (SERPINE1, PAI-1)
in the obstructed kidney compared to the contralateral controls [2].
PAI-1 is particularly important in the overall context of tissue fibrosis
regardless of site and a prominent downstream target of the TGF-β1/
SMAD3 [4,5]. A major inhibitor of plasmin generation, PAI-1 inhibits
ECM degradation, thereby, contributing to interstitial fibrosis. PAI-1
null mice are, in fact, significantly protected from renal fibrosis and
excessive ECM accumulation. Increased PAI-1 expression has been
implicated in various animal models of renal diseases and is highly
induced by pro-fibrogenic and pro-inflammatory mediators including
angiotensin, CTGF, interleukins and TNF-α . PAI-1 null mice subjected
UUO, moreover, exhibit a significantly reduced inflammatory response
compared to wild-type controls suggesting that this SERPIN may
promote infiltration of macrophages and T-cells. PAI-1 also modulates
TGF-β1 signaling as PAI-1-null animals (compared to wild-type
controls subjected to obstructive nephropathy) have lower TGF-β1
levels. Recombinant PAI-1, in fact, activates the TGF-β1 promoter
suggesting that PAI-1 may initiate, and perhaps maintain, a potential
pro-fibrogenic “loop” in the context of renal disease. Hence, targeted
down-modulation of PAI-1 may provide significant, multiple-level,
therapeutic value in inhibiting fibrosis onset and progression as well as
in the more difficult clinical challenge of disease reversal. |
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| It is anticipated that cell & developmental biology will be an effective
vehicle to communicate these translationally-important findings to the
biomedical research community. |
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| Acknowledgements |
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| This work was supported by NIH grant GM057242. The authors regret that
space did not allow for citation of many of our colleagues important contributions.
Detailed descriptions of work discussed in this editorial, complete with appropriate
literature citations, can be found in the following recent publications: |
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| References |
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- Liu Y (2011) Cellular and molecular mechanisms of renal fibrosis. Nat Rev Nephrol 7: 684-696.
- Samarakoon R, Overstreet JM, Higgins SP, Higgins PJ (2012) TGF-β1→SMAD/p53/USF2→PAI-1 transcriptional axis in ureteral obstruction-induced renal fibrosis. Cell Tissue Res 347: 117-128.
- Lan HY (2011) Diverse roles of TGF-β/Smads in renal fibrosis and inflammation. Int J Biol Sci 7: 1056-1067.
- Samarakoon R, Higgins PJ (2008) Integration of non-SMAD and SMAD signaling in TGF-beta1-induced plasminogen activator inhibitor type-1 gene expression in vascular smooth muscle cells. Thromb Haemost 100: 976-983.
- Chevalier RL, Forbes MS, Thornhill BA (2009) Ureteral obstruction as a model of renal interstitial fibrosis and obstructive nephropathy. Kidney Int 75: 1145-1152.
- Eddy AA (2009) Serine proteases, inhibitors and receptors in renal fibrosis. Thromb Haemost 101: 656-664.
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