Cell Biology – Immunology – Pathology
Kidney International (2000) 58, 618–628; doi:10.1046/j.1523-1755.2000.00208.x
Interstitial fibrosis in mice with overload proteinuria: Deficiency of TIMP-1 is not protective
Allison A Eddy, Heungsoo Kim, Jesús López-Guisa, Takashi Oda, Paul D Soloway with the technical assistance of, Lori Mcculloch, Elaine Liu and Diane Wing
The Children's Hospital and Regional Medical Center, University of Washington, Seattle, Washington, and Department of Molecular and Cellular Biology, Roswell Park Cancer Institute, Buffalo, New York, USA; and the Hospital for Sick Children, Department of Pediatrics, University of Toronto, Toronto, Canada
Correspondence: Dr Allison Eddy, Division of Nephrology, Children's Hospital and Regional Medical Center, Mail Stop CH-46, 4800 Sand Point Way NE, Seattle, Washington 98105, USA. E-mail: aeddy@u.washington.edu
Received 29 October 1999; Revised 18 February 2000; Accepted 12 March 2000.
Abstract
Interstitial fibrosis in mice with overload proteinuria: Deficiency of TIMP-1 is not protective.
Background
Progressive renal interstitial fibrosis is characterized by up-regulated expression of the gene that encodes the tissue inhibitor of metalloproteinases-1 (TIMP-1), a regulator of extracellular matrix remodeling, suggesting that impaired matrix turnover contributes to the fibrogenic process. The present study was designed to develop a murine model of renal interstitial fibrosis, and to determine the functional significance of up-regulated Timp-1 expression by comparing the severity of this renal disease in wild-type mice and mice genetically deficient in Timp-1.
Methods
Initial pilot studies developed and characterized a murine model of bovine serum albumin (BSA)-induced protein-overload proteinuria with respect to the degree of proteinuria, severity of interstitial fibrosis, and renal mRNA levels for genes encoding matrix proteins, transforming growth factor-
1 (TGF-1), and TIMP-1, -2, -3, and -4. In the final study, the severity of interstitial fibrosis was compared in wild-type and Timp-1–deficient mice after six weeks of proteinuria.
Results
Mice injected with large daily intraperitoneal doses of BSA developed proteinuria, interstitial inflammation, and progressive interstitial fibrosis. A time course study based on measurements after one, two, and six weeks of BSA injections showed increased renal mRNA levels for the matrix genes procollagens 
1(I), 1(III), and 2(IV) and TGF-1 and Timp-1. Timp-2 and Timp-3 genes were constitutively expressed at high levels in the normal kidneys and showed little change in the proteinuric kidneys. Timp-4 transcripts were not detected in any of the kidneys. After six weeks of BSA overload-proteinuria, the groups (N = 8 per group) of wild-type and Timp-1–deficient mice developed significant interstitial fibrosis compared with the control saline-injected groups. The severity of the interstitial fibrosis was similar in both proteinuric groups based on an assessment of the final kidney weight, total kidney collagen content, and the number of interstitial fields with increased fibronectin staining.
Conclusions
Results of the present study indicate that TIMP-1 deficiency does not alter the degree of interstitial fibrosis in the murine overload proteinuria model. Potential explanations include Timp-1 genetic redundancy, as suggested by the observation that, despite significant intrarenal induction of the Timp-1 gene expression, net renal metalloproteinase-9 (MMP-9) activity was not significantly altered. TIMP-1 is a multifunctional protein that may play a metalloproteinase-independent role in response to renal injury.
Keywords:
tissue inhibitor of metalloproteinase, fibrosis, murine model, renoprotection, proteinuria
