Augmented cytoplasmic Smad4 induces acceleration of TGF-?1 signaling in renal tubulointerstitial cells of hereditary nephrotic ICGN mice with chronic renal fibrosis; possible role for myofibroblastic differentiation

Abstract

The Institute of Cancer Research (ICR)-derived glomerulonephritis (ICGN) mouse is a hereditary model animal for nephrotic syndrome with chronic renal tubulointerstitial fibrosis. In most fibrotic diseases, myofibroblastic differentiation is considered to play crucial roles in pathogenesis of fibrosis and is dominantly regulated by the transforming growth factor (TGF)-beta1 signaling system. To reveal the pathogenic mechanism of chronic renal fibrosis in ICGN mice, we examined the expression and localization of TGF-beta1 signal transducer proteins (TGF-beta receptor-I and -II, Smad2/3 and Smad4) in kidney sections and in primarily cultured tubulointerstitial fibroblasts (TIFs). In kidneys of ICGN mice, many tubulointerstitial cells were differentiated to myofibroblastic cells and were alpha-smooth muscle actin (alphaSMA)-positive. The numbers of alphaSMA-positive TIFs prepared from kidneys of ICGN mice (ICGN-TIFs), but not those of ICR control mice (ICR-TIFs), increased during cell culture. No significant differences in production or activation of TGF-beta1 between ICGN-TIFs and ICR-TIFs were seen by enzyme-linked immunosorbent assay. In vitro transcriptional reporter assay for TGF-beta1 and Western immunoblotting for TGF-beta1 signal transducers showed no notable differences in the expression levels of TGF-beta receptor-I or -II or Smad2/3 between these TIFs. However, augmented cytoplasmic Smad4 protein in ICGN-TIFs, but not ICR-TIFs, seemed to cause hypersensitivity against TGF-beta1, and the eventual nuclear localization of Smad2/3-Smad4 complex was increased in ICGN-TIFs. Thus, the abnormal cytoplasmic augmentation of Smad4 induces acceleration of TGF-beta1 signaling in the renal tubulointerstitial cells of ICGN mice.

Dysfunction of Erythropoietin-Producing Interstitial Cells in the Kidneys of ICR-derived Glomerulonephritis (ICGN) Mice

“…As previously reported [9,29,[31][32][33][34][35][36], sclerotic glomeruli, highly expanded or occluded renal tubules, and appearance of cysts were observed in the kidneys of the progressing stage of ICGN mice compared to ICR control mice. The brush border of the expanded proximal tubules showed weakened intensity of PAS staining, whereas the glomeruli showed stronger intensity ( Fig.…”

“…Homozygous ICGN mice exhibit proteinuria at a young age, later develop hypoproteinemia, hyperlipidemia, severe anemia and systemic edema, and eventually die as a result of CRD [20,21]. In the kidneys, most of the renal tubules expand and many kinds of extracellular matrix (ECM) components accumulate abnormally in glomeruli and the tubulointerstitium because of the overproduction and stabilization of ECM components, and the inhibition of ECM breakdown [9,29,[31][32][33]. Irregular cellular kinetics are also noted in ICGN mice, and age-dependent increases in apoptotic cell and proliferating cell densities have been reported [34].…”

Regulation of Renal Fibrosis by Macrophage Polarization

“…TGFβ1 is a potential inducer of EMT, while the effect of TGFβ1 is efficiently inhibited by BMP7 [1,2,3,4,8,9,10,11]. The crosstalk between TGFβ1 and BMP7 coordinates the repair and recovery of the injured kidney [12,13,14].…”

“…During EMT, tubular epithelial cells acquire a mesenchymal phenotype with enhanced migratory capacity, and then these transformed cells migrate from the renal tubular microenvironment into the interstitial space, as a major contributor to the pathogenesis of renal fibrosis. Meanwhile, fibroblasts also transform into myofibroblasts that generate excess deposition of extracellular matrix in response to cytokines, chemokines and other signaling molecules [1,2,3,4]. …”

Smad4 suppresses the progression of renal cell carcinoma via the activation of forkhead box protein H1

“…A higher frequency of Smad4 inactivation was observed in liver metastases than in extrahepatic metastases (10) and colorectal cancer patients expressing high Smad4 levels have been shown to have a longer survival time than the patients with low levels (11). Smad4 increases the levels of signaling in renal tubulointerstitial cells in a mouse model of renal disease (12). However, the potential role and molecular events of Smad4 signaling in RCC have remained elusive.…”