Glomerular expression of hydrogen peroxide-inducible clone-5 in human and rat progressive mesangial proliferative glomerulonephritis

Hic-5 deficiency attenuates the activation of hepatic stellate cells and liver fibrosis through upregulation of Smad7 in mice

BACKGROUND & AIM

Hydrogen peroxide-inducible clone-5 (Hic-5), also named as transforming growth factor beta-1-induced transcript 1 protein (Tgfb1i1), was found to be induced by TGF-β. Previous studies have shown that TGF-β is a principal mediator of hepatic stellate cell (HSC) activation in liver fibrosis. However, this process remains elusive. In this study, we aimed to define the role of Hic-5 in HSC activation and liver fibrosis.

METHODS

We examined the expression levels of Hic-5 during HSCs activation and in fibrotic liver tissues by quantitative real-time reverse transcriptase polymerase chain reaction, Western blot and immunohistochemistry. Hic-5 knockout (KO) and wild-type (WT) mice were subjected to bile duct ligation (BDL) or carbon tetrachloride (CCl4) injection to induce liver fibrosis.

RESULTS

Hic-5 expression was strongly upregulated in activated HSCs of the human fibrotic liver tissue and BDL or CCl4-induced mouse liver fibrosis. Hic-5 deficiency significantly attenuated mouse liver fibrosis and HSC activation. Furthermore, Hic-5 knockdown by siRNA in vivo repressed CCl4-induced liver fibrosis in mice. Mechanistically, the absence of Hic-5 significantly inhibited the TGF-β/Smad2 signaling pathway, proved by increasing Smad7 expression, resulting in reduced collagen production and α-smooth muscle actin expression in the activated HSCs.

CONCLUSION

Hic-5 deficiency attenuates the activation of HSCs and liver fibrosis though reducing the TGF-β/Smad2 signaling by upregulation of Smad7. Thus, Hic-5 can be regarded as a potential therapeutic target for liver fibrosis.

Extracellular matrix-induced Hic-5 expression in glomerular mesangial cells leads to a prosclerotic phenotype independent of TGF-β

Chronic fibroproliferative diseases account for approximately 45% of all deaths in the developed world. In the kidney, glomerulosclerosis is the underlying pathology in approximately half of patients with renal failure receiving dialysis. Mesangial cell expression of the LIM protein hydrogen peroxide-induced clone-5 (Hic-5) is important in its pathogenesis. Hic-5 expression increases following mesangial cell attachment to collagen I, associated with increased collagen I expression and increased susceptibility to apoptosis both in vitro and in experimental glomerulosclerosis. TGF-β has an established role in many fibrotic diseases, including glomerulosclerosis, where it increases collagen I deposition in vivo and promotes mesangial cell apoptosis in vitro. In other cell types, TGF-β induces Hic-5 expression. We investigated whether Hic-5-induced changes in mesangial cell phenotype were TGF-β-dependent. Adding exogenous TGF-β to mesangial cell cultures failed to increase Hic-5 expression; blocking TGF-β signaling did not reduce Hic-5 expression. However, inducing Hic-5 expression in mesangial cells by adhesion to collagen I led to TGF-β expression, which was abolished by small interfering RNA (siRNA) Hic-5 knockdown. Mesangial cells expressing Hic-5 showed altered latent TGF-β-binding protein expression and Smad signaling, with enhanced susceptibility to TGF-β-induced apoptosis. Mesangial cell attachment to collagen I led to increased Hic-5 expression within 2-4 h and increased procollagen I transcription within 12 h, whereas adding TGF-β to siRNA Hic-5 knockdown mesangial cells increased procollagen I transcription to a lesser degree after 48 h. Mesangial cell Hic-5 expression was associated with increased α-smooth muscle actin and plasminogen activator inhibitor-1 expression. Taken together, these data indicate that there is a prosclerotic feedback loop in mesangial cells dependent on matrix-derived signals in which Hic-5 is a pivotal signaling protein. This feedback loop is TGF-β-independent. The role of TGF-β-dependent and -independent sclerotic pathways merit further investigation.

Hydrogen peroxide-inducible clone-5 regulates mesangial cell proliferation in proliferative glomerulonephritis in mice

Hydrogen peroxide-inducible clone-5 (Hic-5) is a transforming growth factor (TGF)-β1-inducible focal adhesion protein. We previously demonstrated that Hic-5 was localized in mesangial cells and its expression was associated with glomerular cell proliferation and matrix expansion in human and rat glomerulonephritis (GN). In the present study, we first assessed the role of Hic-5 in mesangioproliferative GN by injecting Habu venom into heminephrectomized wild type (Hic-5+/+) and Hic-5-deficient (Hic-5-/-) mice. Hic-5+/+ GN mice exhibited glomerular cell proliferation on day 7. Surprisingly, glomerular cell number and Ki-67-positive cells in Hic-5-/- GN mice were significantly greater than those in Hic-5+/+ GN mice on day 7, although the number of glomerular apoptotic cells and the expression of growth factors (platelet-derived growth factor-BB and TGF-β1) and their receptors were similarly increased in both Hic-5+/+ and Hic-5-/- GN mice. In culture experiments, proliferation assays showed that platelet-derived growth factor-BB and TGF-β1 enhanced the proliferation of Hic-5-/- mesangial cells compared with Hic-5+/+ mesangial cells. In addition, mitogenic regulation by Hic-5 was associated with altered and coordinated expression of cell cycle-related proteins including cyclin D1 and p21. The present results suggest that Hic-5 might regulate mesangial cell proliferation in proliferative GN in mice. In conclusion, modulation of Hic-5 expression might have a potential to prevent mesangial cell proliferation in the acute mitogenic phase of glomerulonephritis.

Inhibition of collagen I accumulation reduces glomerulosclerosis by a Hic-5-dependent mechanism in experimental diabetic nephropathy

Glomerulosclerosis of any cause is characterized by loss of functional glomerular cells and deposition of excessive amounts of interstitial collagens including collagen I. We have previously reported that mesangial cell attachment to collagen I leads to upregulation of Hic-5 in vitro, which mediates mesangial cell apoptosis. Furthermore, glomerular Hic-5 expression was increased during the progression of experimental glomerulosclerosis. We hypothesized that reducing collagen I accumulation in glomerulosclerosis would in turn lower Hic-5 expression, reducing mesangial cell apoptosis, and thus maintaining glomerular integrity. We examined archive renal tissue from rats undergoing experimental diabetic glomerulosclerosis, treated with the transglutaminase-2 inhibitor NTU281. Untreated animals exhibited increased glomerular collagen I accumulation, associated with increased glomerular Hic-5 expression, apoptosis, and mesangial myofibroblast transdifferentiation characterized by α-smooth muscle actin (α-SMA) expression. NTU281 treatment reduced glomerular collagen I accumulation, Hic-5 and α-SMA expression, and apoptosis. Proteinurea and serum creatinine levels were significantly reduced in animals with reduced Hic-5 expression. In vitro studies of Hic-5 knockdown or overexpression show that mesangial cell apoptosis and expression of both α-SMA and collagen I are Hic-5 dependent. Together, these data suggest that there exists, in vitro and in vivo, a positive feedback loop whereby increased levels of collagen I lead to increased mesangial Hic-5 expression favoring not only increased apoptosis, but also mesangial myofibroblast transdifferentiation and increased collagen I expression. Prevention of collagen I accumulation interrupts this Hic-5-dependent positive feedback loop, preserving glomerular architecture, cellular phenotype, and function.

Involvement of the intrarenal renin-angiotensin system in experimental models of glomerulonephritis

The intrarenal renin-angiotensin system (RAS) has several pathophysiologic functions not only in blood pressure regulation but also in the development of glomerulonephritis (GN). Angiotensin II (Ang II) is the biologically active product of the RAS. Locally produced Ang II induces inflammation, renal cell growth, mitogenesis, apoptosis, migration, and differentiation, regulates the gene expression of bioactive substances, and activates multiple intracellular signaling pathways, leading to tissue damage. Activation of the Ang II type 1 (AT1) receptor pathway results in the production of proinflammatory mediators, cell proliferation, and extracellular matrix synthesis, which facilitates glomerular injury. Previous studies have shown that angiotensin-converting enzyme inhibitors and/or AT1 receptor blockers have beneficial effects in experimental GN models and humans with various types of GN, and that these effects are more significant than their suppressive effects on blood pressure. In this paper, we focus on intrarenal RAS activation in the pathophysiology of experimental models of GN.