Mice lacking Smad3 are protected against streptozotocin-induced diabetic glomerulopathy

Store-operated calcium entry suppressed the TGF-β1/Smad3 signaling pathway in glomerular mesangial cells

Our previous study demonstrated that the abundance of extracellular matrix proteins was suppressed by store-operated Ca²⁺ entry (SOCE) in mesangial cells (MCs). The present study was conducted to investigate the underlying mechanism focused on the transforming growth factor-β1 (TGF-β1)/Smad3 pathway, a critical pathway for ECM expansion in diabetic kidneys. We hypothesized that SOCE suppressed ECM protein expression by inhibiting this pathway in MCs. In cultured human MCs, we observed that TGF-β1 (5 ng/ml for 15 h) significantly increased Smad3 phosphorylation, as evaluated by immunoblot. However, this response was markedly inhibited by thapsigargin (1 µM), a classical activator of store-operated Ca²⁺ channels. Consistently, both immunocytochemistry and immunoblot showed that TGF-β1 significantly increased nuclear translocation of Smad3, which was prevented by pretreatment with thapsigargin. Importantly, the thapsigargin effect was reversed by lanthanum (La³⁺; 5 µM) and GSK-7975A (10 µM), both of which are selective blockers of store-operated Ca²⁺ channels. Furthermore, knockdown of Orai1, the pore-forming subunit of the store-operated Ca²⁺ channels, significantly augmented TGF-β1-induced Smad3 phosphorylation. Overexpression of Orai1 augmented the inhibitory effect of thapsigargin on TGF-β1-induced phosphorylation of Smad3. In agreement with the data from cultured MCs, in vivo knockdown of Orai1 specific to MCs using a targeted nanoparticle small interfering RNA delivery system resulted in a marked increase in abundance of phosphorylated Smad3 and in nuclear translocation of Smad3 in the glomerulus of mice. Taken together, our results indicate that SOCE in MCs negatively regulates the TGF-β1/Smad3 signaling pathway.

Nano-sized carriers in gene therapy for renal fibrosis in vivo

Renal fibrosis is the final common pathway leading to end-stage renal failure regardless of underlying initial nephropathies. No specific therapy has been established for renal fibrosis. Gene therapy is a promising strategy for the treatment of renal fibrosis. Nano-sized carriers including viral vectors and non-viral vectors have been shown to enhance the delivery and treatment effects of gene therapy for renal fibrosis in vivo. This review focuses on the mechanisms of renal fibrosis and the in vivo technologies and methodologies of nano-sized carriers in gene therapy for renal fibrosis. RESPONSIBLE EDITOR Alexander Seifalian Director of Nanotechnology & Regenerative Medicine Ltd., The London BioScience Innovation Centre, London, UNITED KINGDOM.

Magnolol Attenuates Concanavalin A-induced Hepatic Fibrosis, Inhibits CD4+ T Helper 17 (Th17) Cell Differentiation and Suppresses Hepatic Stellate Cell Activation: Blockade of Smad3/Smad4 Signalling

Magnolol is a pharmacological biphenolic compound extracted from Chinese herb Magnolia officinalis, which displays anti-inflammatory and antioxidant effects. This study was aimed at exploring the potential effect of magnolol on immune-related liver fibrosis. Herein, BALB/c mice were injected with concanavalin A (ConA, 8 mg/kg/week) up to 6 weeks to establish hepatic fibrosis, and magnolol (10, 20, 30 mg/kg/day) was given to these mice orally throughout the whole experiment. We found that magnolol preserved liver function and attenuated liver fibrotic injury in vivo. In response to ConA stimulation, the CD4⁺ T cells preferred to polarizing towards CD4⁺ T helper 17 (Th17) cells in liver. Magnolol was observed to inhibit Th17 cell differentiation in ConA-treated liver in addition to suppressing interleukin (IL)-17A generation. Hepatic stellate cells were activated in fibrotic liver as demonstrated by increased alpha smooth muscle actin (α-SMA) and desmin. More transforming growth factor (TGF)-β1 and activin A were secreted into the serum. Magnolol suppressed this abnormal HSC activation. Furthermore, the phosphorylation of Smad3 in its linker area (Thr179, Ser 204/208/213) was inhibited by magnolol. In vitro, the recombinant IL-17A plus TGF-β1 or activin A induced activation of human LX2 HSCs and promoted their collagen production. Smad3/Smad4 signalling pathway was activated in LX2 cells exposed to the fibrotic stimuli, as illustrated by the up-regulated phospho-Smad3 and the enhanced interaction between Smad3 and Smad4. These alterations were suppressed by magnolol. Collectively, our study reveals a novel antifibrotic effect of magnolol on Th17 cell-mediated fibrosis.

The methyltransferase SET9 regulates TGF B-1 activation of renal fibroblasts via interaction with SMAD3

Chronic kidney disease (CKD) is a global socioeconomic problem. It is characterised by the presence of differentiated myofibroblasts that, in response to TGF B-1, produce tissue fibrosis, leading to renal failure. Here we define a novel interaction between the SET9 lysine methyltransferase and SMAD3, the principle mediator of TGF B-1 signalling in myofibroblasts. We show that SET9 deficient fibroblasts exhibit globally altered gene expression profiles in response to TGF B-1, whilst overexpression of SET9 enhances SMAD3 transcriptional activity. We also show that SET9 facilitates SMAD3 nuclear import and controls SMAD3 protein degradation, in a manner involving ubiquitination. On a cellular level, we demonstrate that SET9 is broadly required for TGF B-1 effects in diseased primary renal fibroblasts; SET9 promotes fibroblast migration into wounds, expression of extracellular matrix proteins, collagen contractility and myofibroblast differentiation. Finally, we demonstrate that SET9 is recruited to the α-smooth muscle actin gene in response to TGF B-1, providing a mechanism by which SET9 regulates myofibroblast contractility and differentiation. Together with previous studies, we make the case for SET9 inhibition in the treatment of progressive CKD.

Activation of FXR protects against renal fibrosis via suppressing Smad3 expression

Renal fibrosis is the common pathway of most chronic kidney disease progression to end-stage renal failure. The nuclear receptor FXR (farnesoid X receptor), a multiple functional transcription factor, plays an important role in protecting against fibrosis. The TGFβ-Smad signaling has a central role in kidney fibrosis. However, it remains unclear whether FXR plays direct anti-fibrotic effect in renal fibrosis via regulating TGFβ-Smad pathway. In this study, we found that the level of FXR was negatively correlated with that of Smad3 and fibronectin (a marker of fibrosis) in human fibrotic kidneys. Activation of FXR suppressed kidney fibrosis and downregulated Smad3 expression, which was markedly attenuated by FXR antagonist. Moreover, the FXR-mediated repression of fibrosis was significantly alleviated by ectopic expression of Smad3. Luciferase reporter assay revealed that FXR activation inhibited the transcriptional activity of Smad3 gene promoter. The in vivo experiments showed that FXR agonist protected against renal fibrosis and downregulated Smad3 expression in UUO mice. These results suggested that FXR may serve as an important negative regulator for manipulating Smad3 expression, and the FXR/Smad3 pathway may be a novel target for the treatment of renal fibrosis.

C-Reactive Protein Promotes Diabetic Kidney Disease in db/db Mice via the CD32b-Smad3-mTOR signaling Pathway

C-reactive protein (CRP) is associated with progressive diabetic nephropathy in patients with type-2 diabetes (T2DN). However, role of CRP in T2DN remains unclear. We report here that CRP is pathogenic in T2DN in db/db mice that express human CRP (CRPtg-db/db). Compared to the littermate db/db mice, CRPtg-db/db developed more severe T2DN, showing higher levels of fasting blood glucose and microalbuminuria and more progressive renal inflammation and fibrosis. Enhanced T2DN in CRPtg-db/db mice were associated with over-activation of CRP-CD32b, NF-κB, TGF-β/Smad3, and mTOR signaling. Further studies in vitro defined that CRP activated Smad3 directly at 15 mins via the CD32b- ERK/p38 MAP kinase crosstalk pathway and indirectly at 24 hours through a TGF-β1-dependent mechanism. Importantly, CRP also activated mTOR signaling at 30 mins via a Smad3-dependent mechanism as Smad3 bound mTOR physically and CRP-induced mTOR signaling was abolished by a neutralizing CD32b antibody and a specific Smad3 inhibitor. Finally, we also found that CRP induced renal fibrosis through a CD32b-Smad3-mTOR pathway because blocking mTOR signaling with rapamycin inhibited CRP-induced CTGF and collagen I expression. Thus, CRP is pathogenic in T2DN. CRP may promote CD32b- NF-κB signaling to mediate renal inflammation; whereas, CRP may enhance renal fibrosis in T2DN via CD32b-Smad3-mTOR signaling.

Podocytes: the Weakest Link in Diabetic Kidney Disease?

Diabetes is increasing in prevalence and is the leading cause of end-stage renal disease in the United States. Diabetic kidney disease is considered a proteinuric glomerular disease. Although the glomerulus is composed of various cell types, research suggests that podocytes are critical to overall glomerular health. Podocyte injury has been identified as a pivotal event resulting in proteinuric kidney disease, glomerulosclerosis, and loss of renal function. Thus, understanding the signaling mechanisms that trigger podocyte injury in diabetic kidney disease might allow for the development of targeted therapeutics to prevent or ameliorate progression to end-stage renal failure. This review focuses on the role of podocytes in diabetic kidney disease.

TGF-β: the master regulator of fibrosis

Transforming growth factor-β (TGF-β) is the primary factor that drives fibrosis in most, if not all, forms of chronic kidney disease (CKD). Inhibition of the TGF-β isoform, TGF-β1, or its downstream signalling pathways substantially limits renal fibrosis in a wide range of disease models whereas overexpression of TGF-β1 induces renal fibrosis. TGF-β1 can induce renal fibrosis via activation of both canonical (Smad-based) and non-canonical (non-Smad-based) signalling pathways, which result in activation of myofibroblasts, excessive production of extracellular matrix (ECM) and inhibition of ECM degradation. The role of Smad proteins in the regulation of fibrosis is complex, with competing profibrotic and antifibrotic actions (including in the regulation of mesenchymal transitioning), and with complex interplay between TGF-β/Smads and other signalling pathways. Studies over the past 5 years have identified additional mechanisms that regulate the action of TGF-β1/Smad signalling in fibrosis, including short and long noncoding RNA molecules and epigenetic modifications of DNA and histone proteins. Although direct targeting of TGF-β1 is unlikely to yield a viable antifibrotic therapy due to the involvement of TGF-β1 in other processes, greater understanding of the various pathways by which TGF-β1 controls fibrosis has identified alternative targets for the development of novel therapeutics to halt this most damaging process in CKD.

MicroRNA-196a/b Mitigate Renal Fibrosis by Targeting TGF-β Receptor 2

Organ-specific microRNAs have essential roles in maintaining normal organ function. However, the microRNA profile of the kidney and the role of microRNAs in modulating renal function remain undefined. We performed an unbiased assessment of the genome-wide microRNA expression profile in 14 mouse organs using Solexa deep sequencing and found that microRNA-196a (miR-196a) and miR-196b are selectively expressed in kidney, with 74.37% of mouse total miR-196a and 73.19% of mouse total miR-196b distributed in the kidneys. We confirmed the predominant expression of miR-196a/b in mouse and human kidney, particularly in the glomeruli and tubular epithelium, by quantitative RT-PCR and in situ hybridization assays. During unilateral ureteral obstruction (UUO)-induced mouse renal fibrosis, renal miR-196a/b levels rapidly decreased. Elevation of renal miR-196a/b expression by hydrodynamic-based delivery of a miR-196a/b-expressing plasmid before or shortly after UUO significantly downregulated profibrotic proteins, including collagen 1 and α-smooth muscle actin, and mitigated UUO-induced renal fibrosis. In contrast, depletion of renal miR-196a/b by miR-196a/b antagomirs substantially aggravated UUO-induced renal fibrosis. Mechanistic studies further identified transforming growth factor beta receptor II (TGFβR2) as a common target of miR-196a and miR-196b. Decreasing miR-196a/b expression in human HK2 cells strongly activated TGF-β-Smad signaling and cell fibrosis; whereas increasing miR-196a/b levels in mouse primary cultured tubular epithelial cells inhibited TGF-β-Smad signaling. In the UUO model, miR-196a/b silenced TGF-β-Smad signaling, decreased the expression of collagen 1 and α-smooth muscle actin, and attenuated renal fibrosis. Our findings suggest that elevating renal miR-196a/b levels may be a novel therapeutic strategy for treating renal fibrosis.

Regulatory roles of microRNA-21 in fibrosis through interaction with diverse pathways (Review)

MicroRNA-21 (miR-21) is a small, non-coding RNA which can regulate gene expression at the post‑transcriptional level. While the fibrogenic process is vital in tissue repair, proliferation and transition of fibrogenic cells combined with an imbalance of secretion and degradation of the extracellular matrix results in excessive tissue remodeling and fibrosis. Recent studies have indicated that miR‑21 is overexpressed during fibrosis and can regulate the fibrogenic process in a variety of organs and tissues via diverse pathways. The present review summarized the significant roles of miR-21 in fibrosis and discussed the underlying key pathways.

Transforming growth factor-β1 and diabetic nephropathy

Transforming growth factor-β1 (TGF-β1) is established to be involved in the pathogenesis of diabetic nephropathy. The diabetic milieu enhances oxidative stress and induces the expression of TGF-β1. TGF-β1 promotes cell hypertrophy and extracellular matrix accumulation in the mesangium, which decreases glomerular filtration rate and leads to chronic renal failure. Recently, TGF-β1 has been demonstrated to regulate urinary albumin excretion by both increasing glomerular permeability and decreasing reabsorption in the proximal tubules. TGF-β1 also increases urinary excretion of water, electrolytes and glucose by suppressing tubular reabsorption in both normal and diabetic conditions. Although TGF-β1 exerts hypertrophic and fibrogenic effects in diabetic nephropathy, whether suppression of the function of TGF-β1 can be an option to prevent or treat the complication is still controversial. This is partly because adrenal production of mineralocorticoids could be augmented by the suppression of TGF-β1. However, differentiating the molecular mechanisms for glomerulosclerosis from those for the suppression of the effects of mineralocorticoids by TGF-β1 may assist in developing novel therapeutic strategies for diabetic nephropathy. In this review, we discuss recent findings on the role of TGF-β1 in diabetic nephropathy.

Kidney glycosphingolipids are elevated early in diabetic nephropathy and mediate hypertrophy of mesangial cells

Glycosphingolipids (GSLs) play a role in insulin resistance and diabetes, but their role in diabetic nephropathy (DN) has received limited attention. We used 9- and 17-wk-old nondiabetic db/m and diabetic db/db mice to examine the role of GSLs in DN. Cerebrosides or monoglycosylated GSLs [hexosylceramides (HexCers); glucosyl- and galactosylceramides] and lactosylceramide (LacCers) were elevated in db/db mouse kidney cortices, specifically in glomeruli, and also in urine. In our recent paper (25), we observed that the kidneys exhibited glomerular hypertrophy and proximal tubular vacuolization and increased fibrosis markers at these time points. Mesangial cells contribute to hyperglycemia-induced glomerular hypertrophy in DN. Hyperglycemic culture conditions, similar to that present in diabetes, were sufficient to elevate mesangial cell HexCers and increase markers of fibrosis, extracellular matrix proteins, and cellular hypertrophy. Inhibition of glucosylceramide synthase or lowering glucose levels decreased markers of fibrosis and extracellular matrix proteins and reversed mesangial cell hypertrophy. Hyperglycemia increased phosphorylated (p)SMAD3 and pAkt levels and reduced phosphatase and tensin homolog levels, which were reversed with glucosylceramide synthase inhibition. These data suggest that inhibition of glucosylceramide synthase reversed mesangial cell hypertrophy through decreased pAkt and pSmad3 and increased pathways responsible for protein degradation. Importantly, urinary GSL levels were higher in patients with DN compared with healthy control subjects, implicating a role for these lipids in human DN. Thus, hyperglycemia in type II diabetes leads to renal dysfunction at least in part by inducing accumulation of HexCers and LacCers in mesangial cells, resulting in fibrosis, extracellular matrix production, and hypertrophy.

Development of antisense oligonucleotide (ASO) technology against Tgf-β signaling to prevent scarring during flexor tendon repair

Flexor tendons (FT) in the hand provide near frictionless gliding to facilitate hand function. Upon injury and surgical repair, satisfactory healing is hampered by fibrous adhesions between the tendon and synovial sheath. In the present study we used antisense oligonucleotides (ASOs), specifically targeted to components of Tgf-β signaling, including Tgf-β1, Smad3 and Ctgf, to test the hypothesis that local delivery of ASOs and suppression of Tgf-β1 signaling would enhance murine FT healing by suppressing adhesion formation while maintaining strength. ASOs were injected in to the FT repair site at 2, 6 and 12 days post-surgery. ASO treatment suppressed target gene expression through 21 days. Treatment with Tgf-β1, Smad3 or Ctgf ASOs resulted in significant improvement in tendon gliding function at 14 and 21 days, relative to control. Consistent with a decrease in adhesions, Col3a1 expression was significantly decreased in Tgf-β1, Smad3 and Ctgf ASO treated tendons relative to control. Smad3 ASO treatment enhanced the maximum load at failure of healing tendons at 14 days, relative to control. Taken together, these data support the use of ASO treatment to improve FT repair, and suggest that modulation of the Tgf-β1 signaling pathway can reduce adhesions while maintaining the strength of the repair.

The role of CTGF in diabetic retinopathy

Connective tissue growth factor (CTGF, CCN2) contributes to fibrotic responses in diabetic retinopathy, both before clinical manifestations occur in the pre-clinical stage of diabetic retinopathy (PCDR) and in proliferative diabetic retinopathy (PDR), the late clinical stage of the disease. CTGF is a secreted protein that modulates the actions of many growth factors and extracellular matrix (ECM) proteins, leading to tissue reorganization, such as ECM formation and remodeling, basal lamina (BL) thickening, pericyte apoptosis, angiogenesis, wound healing and fibrosis. In PCDR, CTGF contributes to thickening of the retinal capillary BL and is involved in loss of pericytes. In this stage, CTGF expression is induced by advanced glycation end products, and by growth factors such as vascular endothelial growth factor (VEGF) and transforming growth factor (TGF)-β. In PDR, the switch from neovascularization to a fibrotic phase - the angio-fibrotic switch - in PDR is driven by CTGF, in a critical balance with vascular endothelial growth factor (VEGF). We discuss here the roles of CTGF in the pathogenesis of DR in relation to ECM remodeling and wound healing mechanisms, and explore whether CTGF may be a potential novel therapeutic target in the clinical management of early as well as late stages of DR.

Pentoxifylline Attenuates Proteinuria in Anti-Thy1 Glomerulonephritis via Downregulation of Nuclear Factor-κB and Smad2/3 Signaling

Anti-Thy1 glomerulonephritis is a rat nephritis model closely simulating human mesangial proliferative glomerulonephritis. It affects primarily the mesangium, yet displays substantial proteinuria during the course. This study investigated the molecular signals underlying proteinuria in this disease and the modulation of which by the known antiproteinuric agent, pentoxifylline. Male Wistar rats were randomly divided into a control group and nephritic groups with or without treatment with IMD-0354 (an IκB kinase inhibitor), SB431542 (an activin receptor-like kinase inhibitor) or pentoxifylline. Kidney sections were prepared for histological examinations. Glomeruli were isolated for mRNA and protein analysis. Urine samples were collected for protein and nephrin quantitation. One day after nephritis induction, proteinuria developed together with ultrastructural changes of the podocyte and downregulation of podocyte mRNA and protein expression. These were associated with upregulation of tumor necrosis factor (TNF)-α and transforming growth factor (TGF)-β/activins mRNAs and activation of nuclear factor (NF)-κB p65 and Smad2/3. IMD-0354 attenuated proteinuria on d 1, whereas SB431542 decreased proteinuria on d 3 and 5, in association with partial restoration of downregulated podocyte mRNA and protein expression. Pentoxifylline attenuated proteinuria and nephrinuria through the course, plus inhibition of p-NF-κB p65 (d 1) and p-Smad2/3 (d 5) and partial reversal of downregulated podocyte mRNA and protein. Our data show that the pathogenesis of proteinuria in anti-Thy1 glomerulonephritis involves TNF-α and TGF-β/activin pathways, and the evolution of this process can be attenuated by pentoxifylline via downregulation of NF-κB and Smad signals and restoration of the podocyte component of the glomerular filtration barrier.

Interactions of DPP-4 and integrin β1 influences endothelial-to-mesenchymal transition

Integrin β1 and dipeptidyl peptidase (DPP)-4 play roles in endothelial cell biology. Vascular endothelial growth factor (VEGF)-A inhibits endothelial-to-mesenchymal transition (EndMT) through VEGF-R2, but through VEGF-R1 promotes EndMT by reducing the bioavailability of VEGF-A. Here we tested whether DPP-4-integrin β1 interactions have a role in EndMT in the renal fibrosis of diabetic nephropathy. In streptozotocin-induced fibrotic kidneys in diabetic CD-1 mice, levels of endothelial DPP-4, integrin β1, and phospho-integrin β1 were all higher and associated with plasma cystatin C elevation. The DPP-4 inhibitor linagliptin ameliorated kidney fibrosis, reduced plasma cystatin C levels, and suppressed endothelial levels of DPP-4, integrin β1, and phospho-integrin β1. In cultured endothelial cells, DPP-4 and integrin β1 physically interacted. Suppression of DPP-4 by siRNA was associated with suppression of integrin β1 and vice versa. Knockdown of either integrin β1 or DPP-4 resulted in the silencing of TGF-β2-induced TGF-β receptor heterodimer formation, smad3 phosphorylation, and EndMT. DPP-4 negatively regulated endothelial viability signaling by VEGF-R2 suppression and VEGF-R1 induction in endothelial cells. Thus, DPP-4 and integrin β1 interactions regulate key endothelial cell signal transduction in both physiological and pathological conditions including EndMT. Hence, inhibiting DPP-4 may be a therapeutic target for treating kidney fibrosis in diabetes.

TGF-β/Smad signaling in renal fibrosis

TGF-β (transforming growth factor-β) is well identified as a central mediator in renal fibrosis. TGF-β initiates canonical and non-canonical pathways to exert multiple biological effects. Among them, Smad signaling is recognized as a major pathway of TGF-β signaling in progressive renal fibrosis. During fibrogenesis, Smad3 is highly activated, which is associated with the down-regulation of an inhibitory Smad7 via an ubiquitin E3-ligases-dependent degradation mechanism. The equilibrium shift between Smad3 and Smad7 leads to accumulation and activation of myofibroblasts, overproduction of ECM (extracellular matrix), and reduction in ECM degradation in the diseased kidney. Therefore, overexpression of Smad7 has been shown to be a therapeutic agent for renal fibrosis in various models of kidney diseases. In contrast, another downstream effecter of TGF-β/Smad signaling pathway, Smad2, exerts its renal protective role by counter-regulating the Smad3. Furthermore, recent studies demonstrated that Smad3 mediates renal fibrosis by down-regulating miR-29 and miR-200 but up-regulating miR-21 and miR-192. Thus, overexpression of miR-29 and miR-200 or down-regulation of miR-21 and miR-192 is capable of attenuating Smad3-mediated renal fibrosis in various mouse models of chronic kidney diseases (CKD). Taken together, TGF-β/Smad signaling plays an important role in renal fibrosis. Targeting TGF-β/Smad3 signaling may represent a specific and effective therapy for CKD associated with renal fibrosis.

Tanshinone IIA attenuates renal fibrosis and inflammation via altering expression of TGF-β/Smad and NF-κB signaling pathway in 5/6 nephrectomized rats

PURPOSE

In traditional Chinese medicine, Tanshinone IIA is used to treat chronic kidney disease (CKD). However, its biological activity and mechanism of action in renal fibrosis and inflammation are not fully identified. The current study was conducted to determine the effects of Tanshinone IIA treatment on CKD by assessing potential modulation of the TGF-β/Smad and NF-κB signaling pathway.

METHODS

CKD was produced in rats by 5/6 nephrectomy. They were then divided into the following groups: control (sham operation); CKD (5/6 nephrectomy); 5/6 nephrectomy+Tanshinone IIA (10mg/kg in average, once a day for 16 weeks). Serum and urine samples were obtained from animals in each group, and serum creatinine (Scr), blood urea nitrogen (BUN) levels and 24h urinary protein excretion were measured. Tissue samples from the kidney were used for morphometric studies (Masson's trichrome). The expression of fibronectin protein and collagen types I, III, IV, and TGF-β, TNF-α, CXCL-1, MCP-1, RANTES mRNA were evaluated using immunohistochemistry and RT-PCR analysis; the TGF-β/Smad and NF-κB signaling pathway was detected by immunohistochemistry and Western blot analysis.

RESULTS

The following effects were observed in CKD rats treated with Tanshinone IIA: (1) marked improvements in Scr, and 24h urine protein excretion; (2) significant reductions in protein and mRNA levels of fibronectin, collagen III, and collagen IV and TNF-α, MCP-1, and CXCL-1; (3) significantly inhibited the TGF-β/Smad and NF-κB signaling activation.

CONCLUSIONS

These results suggest that Tanshinone IIA suppresses renal fibrosis and inflammation via altering expression of TGF-β/Smad and NF-κB pathway in the remnant kidney, thus supporting the potential of Tanshinone IIA as a new therapeutic agent for slowing the progression of CKD.

The role of endoglin in kidney fibrosis

Tubulointerstitial fibrosis and glomerulosclerosis, are a major feature of end stage chronic kidney disease (CKD), characterised by an excessive accumulation of extracellular matrix (ECM) proteins. Transforming growth factor beta-1 (TGF-β1) is a cytokine with an important role in many steps of renal fibrosis such as myofibroblast activation and proliferation, ECM protein synthesis and inflammatory cell infiltration. Endoglin is a TGF-β co-receptor that modulates TGF-β responses in different cell types. In numerous cells types, such as mesangial cells or myoblasts, endoglin regulates negatively TGF-β-induced ECM protein expression. However, recently it has been demonstrated that 'in vivo' endoglin promotes fibrotic responses. Furthermore, several studies have demonstrated an increase of endoglin expression in experimental models of renal fibrosis in the kidney and other tissues. Nevertheless, the role of endoglin in renal fibrosis development is unclear and a question arises: Does endoglin protect against renal fibrosis or promotes its development? The purpose of this review is to critically analyse the recent knowledge relating to endoglin and renal fibrosis. Knowledge of endoglin role in this pathology is necessary to consider endoglin as a possible therapeutic target against renal fibrosis.

Cell biology of diabetic nephropathy: Roles of endothelial cells, tubulointerstitial cells and podocytes

Diabetic nephropathy is the major cause of end-stage renal failure throughout the world in both developed and developing countries. Diabetes affects all cell types of the kidney, including endothelial cells, tubulointerstitial cells, podocytes and mesangial cells. During the past decade, the importance of podocyte injury in the formation and progression of diabetic nephropathy has been established and emphasized. However, recent findings provide additional perspectives on pathogenesis of diabetic nephropathy. Glomerular endothelial damage is already present in the normoalbuminuric stage of the disease when podocyte injury starts. Genetic targeting of mice that cause endothelial injury leads to accelerated diabetic nephropathy. Tubulointerstitial damage, previously considered to be a secondary effect of glomerular protein leakage, was shown to have a primary significance in the progression of diabetic nephropathy. Emerging evidence suggests that the glomerular filtration barrier and tubulointerstitial compartment is a composite, dynamic entity where any injury of one cell type spreads to other cell types, and leads to the dysfunction of the whole apparatus. Accumulation of novel knowledge would provide a better understanding of the pathogenesis of diabetic nephropathy, and might lead to a development of a new therapeutic strategy for the disease.

Effects of astragalus injection on the TGFβ/Smad pathway in the kidney in type 2 diabetic mice

Background

In traditional Chinese medicine, astragalus injection is used to treat diabetic nephropathy (DN). The current study was conducted to determine the effects of astragalus injection on DN by assessing potential modulation of the transforming growth factor beta TGFβ/Smad signaling pathway.

Methods

Diabetic, male KKAy mice, aged 14 weeks were randomly divided into a model group and an astragalus treatment group, while age-matched male C57BL/6J mice were selected as controls. The treatment group received daily intraperitoneal injections of astragalus (0.03 ml/10 g.d), while the model group received injections of an equivalent volume of saline. Mice were euthanized after 24 weeks. Serum samples were obtained from animals in each group, and blood glucose, creatinine, and urea nitrogen levels were measured. Tissue samples from the kidney were used for morphometric studies. The expression of TGFβ1, TGFβR-Ι, Smad3, and Smad7 were evaluated using reverse transcription-polymerase chain reaction (RT-PCR), and western blot analysis.

Results

Mice in the model group became obese, and suffered complications, including hyperglycemia, polyuria, and proteinuria. Astragalus treatment significantly reduced albuminuria, improved renal function, and ameliorated changes in renal histopathology. Moreover, administration of astragalus injection increased Smad7 expression, and inhibited the expression of TGFβR-Ι, Smad3 and its phosphorylation, and decreased the mRNA level of TGFβ1.

Conclusions

The TGFβ/Smad signaling pathway plays an important role in the development of DN. Administration of astragalus injection could prevent or mitigate DN by rebalancing TGFβ/Smad signaling, and could play a protective role in DN-induced renal damage in KKAy mice.

Chaihuang-Yishen granule inhibits diabetic kidney disease in rats through blocking TGF-β/Smad3 signaling

OBJECTIVE

Increasing evidence shows that TGF-β1 is a key mediator in diabetic nephropathy (DN) and induces renal fibrosis positively by Smad3 but negatively by Smad7. However, treatment of DN by blocking the TGF-β/Smad pathway remains limited. The present study investigated the anti-fibrotic effect of a traditional Chinese medicine, Chaihuang-Yishen granule (CHYS), on DN.

RESEARCH DESIGN AND METHODS

Protective role of CHYS in DN was examined in an accelerated type 1 DN induced by streptozotocin in uninephrectomized Wistar rats. CHYS, at a dose of 0.56 g/kg body weight, was administered by a daily gastric gavage for 20 weeks and the therapeutic effect and potential mechanisms of CHYS on diabetic kidney injury were examined.

RESULTS

Treatment with CHYS attenuated diabetic kidney injury by significantly inhibiting 24-h proteinuria and progressive renal fibrosis including glomerulosclerotic index, tubulointerstitial fibrosis index, and upregulation of extracellular matrix (collagen I, IV, and fibronectin), despite the same levels of blood glucose. Further studies revealed that inhibition of renal fibrosis in CHYS-treated diabetic rats was associated with inhibition of TGF-β1/Smad3 signaling as demonstrated by upregulation of Smad7 but downregulation of TGF-β1, TGF-β receptors, activation of Smad3, and expression of miRNA-21.

CONCLUSIONS

CHYS may be a therapeutic agent for DN. CHYS attenuates DN by blocking TGF-β/Smad3-mediated renal fibrosis.

New insights into molecular mechanisms of diabetic kidney disease

Diabetic kidney disease remains a major microvascular complication of diabetes and the most common cause of chronic kidney failure requiring dialysis in the United States. Medical advances over the past century have substantially improved the management of diabetes mellitus and thereby have increased patient survival. However, current standards of care reduce but do not eliminate the risk of diabetic kidney disease, and further studies are warranted to define new strategies for reducing the risk of diabetic kidney disease. In this review, we highlight some of the novel and established molecular mechanisms that contribute to the development of the disease and its outcomes. In particular, we discuss recent advances in our understanding of the molecular mechanisms implicated in the pathogenesis and progression of diabetic kidney disease, with special emphasis on the mitochondrial oxidative stress and microRNA targets. Additionally, candidate genes associated with susceptibility to diabetic kidney disease and alterations in various cytokines, chemokines, and growth factors are addressed briefly.

Endothelial dysfunction exacerbates renal interstitial fibrosis through enhancing fibroblast Smad3 linker phosphorylation in the mouse obstructed kidney

Endothelial dysfunction and enhanced transforming growth factor-β (TGF-β)/Smad3 signalling are common features of progressive renal fibrosis. This study investigated a potential link between these mechanisms. In unilateral ureteric obstruction (UUO) we observed an acute (6 hr) down-regulation of nitric oxide synthase 3 (NOS3/eNOS) levels and increased phosphorylation of the linker region of Smad3 at T179 and S208 in Smad3/JNK complexes. These events preceded Smad3 C-terminal domain phosphorylation and the induction of myofibroblast proliferation at 48 hrs. Mice deficient in NOS3 showed enhanced myofibroblast proliferation and collagen accumulation compared to wild type mice in a 7 day UUO model. This was associated with enhanced phosphorylation of Smad3 T179 and S208 by 92% and 88%, respectively, whereas Smad3-C-terminal phosphorylation was not affected. Resolvin D1 (RvD1) can suppress renal fibrosis in the UUO model, and further analysis herein showed that RvD1 protected against endothelial dysfunction and suppressed Smad3/JNK complex formation with a consequent reduction in phosphorylation of Smad3 T179 and S208 by 78% and 65%, respectively, while Smad3 C-terminal phosphorylation was unaltered. In vitro, conditioned media from mouse microvascular endothelial cells (MMEC) treated with a general inhibitor of nitric oxide synthase (L-NAME) augmented the proliferation and collagen production of renal fibroblasts (NRK49F cells) compared to control MMEC media and this was associated with increased phosphorylation of JNK and Smad3 T179 and S208, whereas Smad3-C-terminal domain phosphorylation was unaffected. The addition of RvD1 to L-NAME treated MMEC abrogated these effects of the conditioned media on renal fibroblasts. Finally, Smad3 T179/V and S208/A mutations significantly inhibit TGF-β1 induced up-regulation collagen I promoter. In conclusion, these data suggest that endothelial dysfunction can exacerbate renal interstitial fibrosis through increased fibroblast proliferation and collagen production via enhanced Smad3 linker phosphorylation.

Differential effects of Smad3 targeting in a murine model of chronic kidney disease

Transforming growth factor (TGF)‐β1 has a pivotal role in the pathogenesis of progressive kidney diseases that are characterized by fibrosis. The main intracellular signaling pathway of TGF‐β1 is the Smad system, where Smad2 and Smad3 play a central role in transcriptional regulation of target genes involved in extracellular matrix (ECM) metabolism. This study analyzes the hypothesis that blockade of Smad3 attenuates the development of TGF‐β1‐driven renal fibrosis. This was examined in vivo in a transgenic model of TGF‐β1‐induced chronic kidney disease with Smad3 or without Smad3 expression and in vitro in mesangial cells and glomerular endothelial cells with Smad2/3 inhibitors or Smad3‐knockdown. Electron microscopy was used for evaluation of morphological changes, real‐time polymerase chain reaction for detection of RNA expression, and immunohistochemistry for localization of ECM components. Matrix metalloproteinase (MMP) level was assessed by gelatin zymography electrophoresis and located by in situ zymography. The results show TGF‐β1‐induced mesangial matrix expansion, tubulointerstitial fibrosis, and tubular basement membrane thickening that are attenuated by Smad3 deletion, whereas TGF‐β1‐induced glomerular basement membrane thickening is not shown. The amount and distribution profile of MMP‐2 may suggest a role of the enzyme herein. We conclude that Smad3 targeting is not exclusively beneficial as Smad3 has diverse transcriptional regulatory effects in different cell types in the kidney.

Deletion of Smad3 protects the kidney from developing transforming growth factor (TGF)‐β1‐induced tubulointerstitial fibrosis, mesangial matrix expansion, and tubular basement membrane thickening, but not glomerular basement membrane thickening. The favorable effects of Smad3 deficiency can be explained by reduced deposition of collagen subtypes. The cell‐specific changes of matrix metalloproteinase expression can be a result of altered TGF‐β1 signaling.

Inhibition of KCa3.1 suppresses TGF-β1 induced MCP-1 expression in human proximal tubular cells through Smad3, p38 and ERK1/2 signaling pathways

It is well known that TGF-β1 plays a central role in renal fibrosis due in large part to stimulation of inflammatory responses. KCa3.1, a potassium channel protein, has been suggested as a potential therapeutic target for diseases such as sickle cell anemia, autoimmunity, atherosclerosis and more recently, kidney fibrosis. Blockade of KCa3.1 has been shown to ameliorate renal fibrosis in diabetic mice in association with reduced TGF-β1 signaling. However, the centrality of KCa3.1 activation to TGF-β1 induced inflammation remains unknown. In this study, human proximal tubular cells (HK2 cells) were incubated with TGF-β1 (2 ng/ml) for 48 h in the presence or absence of KCa3.1 siRNA or the KCa3.1 inhibitor TRAM34. HK2 cells overexpressing KCa3.1 were studied in parallel. The mRNA and protein expression of monocyte chemoattractant protein-1 (MCP-1) were measured by qRT-PCR and ELISA. Downstream TGF-β1 signaling molecules Smad3, p38 and ERK1/2 were measured by Western blot analysis. Using whole-cell patch clamp techniques we found that TGFβ-1 induced a large KCa3.1 K-current that was inhibited by TRAM34. TGF-β1 also increased MCP-1 mRNA and protein expression in HK2 cells compared to control, an effect that was reversed by in the presence of KCa3.1 siRNA. Similarly, TRAM34 significantly reduced the TGF-β1-mediated increase in MCP-1 at both the mRNA and protein levels. Inhibition of KCa3.1 with KCa3.1 siRNA or TRAM34 also reduced TGF-β1-induced phosphorylation of Smad3, p38 and ERK1/2 MAPK pathways. Conversely overexpression of KCa3.1 induced TGF-β1 signaling cascades and expression of MCP-1. The present study is consistent with a key role for KCa3.1 renal proximal tubular cells in mediating the TGF-β1 induction of MCP-1 expression in HK2 cells via Smad3, p38 and ERK1/2 MAPK signaling pathways.

microRNA in the development of diabetic complications

Today's world population is currently faced with a new type of non-transmissible pandemic: obesity. This lifestyle-related condition is driving the emergence of the diabetes pandemic through the development of low-level chronic inflammation. In recent years, a novel class of non-coding RNA, microRNA (miRNA), have emerged as being important regulators of numerous biological functions. Among these functions are basic maintenance of cell signalling and tissue architecture. Disruption of miRNA levels can contribute not only to the development of the chronic inflammation observed in obese diabetics, but also the development of both pancreatic β-cell dysfunction and loss, along with insulin resistance in metabolic tissues. These primary events set the scene for dysfunction of other tissues, including the retina, kidney, peripheral nerves, heart and the vasculature as a whole. Here, miRNAs again play a deterministic role in the development of a range of diseases collectively termed diabetic complications. Disturbances in miRNA levels appear to be reflected in the serum of patients and this may prove to be diagnostic in patients prior to clinical manifestation of disease, thus improving management of diabetes and its associated complications. Not only are miRNAs displaying promise as an early biomarker for disease, but a number of these miRNAs are displaying therapeutic potential with several in pre-clinical development. The present review aims to highlight our current understanding of miRNAs and their interaction with inflammatory signalling in the development and progression of diabetes and its complications. Utilization of miRNAs as biomarkers and therapeutic targets will also be considered.

A nonclassical vitamin D receptor pathway suppresses renal fibrosis

The TGF-β superfamily comprises pleiotropic cytokines that regulate SMAD and non-SMAD signaling. TGF-β-SMAD signal transduction is known to be involved in tissue fibrosis, including renal fibrosis. Here, we found that 1,25-dihydroxyvitamin D3-bound [1,25(OH)2D3-bound] vitamin D receptor (VDR) specifically inhibits TGF-β-SMAD signal transduction through direct interaction with SMAD3. In mouse models of tissue fibrosis, 1,25(OH)2D3 treatment prevented renal fibrosis through the suppression of TGF-β-SMAD signal transduction. Based on the structure of the VDR-ligand complex, we generated 2 synthetic ligands. These ligands selectively inhibited TGF-β-SMAD signal transduction without activating VDR-mediated transcription and significantly attenuated renal fibrosis in mice. These results indicate that 1,25(OH)2D3-dependent suppression of TGF-β-SMAD signal transduction is independent of VDR-mediated transcriptional activity. In addition, these ligands did not cause hypercalcemia resulting from stimulation of the transcriptional activity of the VDR. Thus, our study provides a new strategy for generating chemical compounds that specifically inhibit TGF-β-SMAD signal transduction. Since TGF-β-SMAD signal transduction is reportedly involved in several disorders, our results will aid in the development of new drugs that do not cause detectable adverse effects, such as hypercalcemia.

Serine-204 in the linker region of Smad3 mediates the collagen-I response to TGF-β in a cell phenotype-specific manner

Regulation of TGF-β1/Smad3 signaling in fibrogenesis is complex. Previous work by our lab suggests that ERK MAP kinase phosphorylates the linker region (LR) of Smad3 to enhance TGF-β-induced collagen-I accumulation. However the roles of the individual Smad3LR phosphorylation sites (T179, S204, S208 and S213) in the collagen-I response to TGF-β are not clear. To address this issue, we tested the ability of Smad3 constructs expressing wild-type Smad3 or Smad3 with mutated LR phosphorylation sites to reconstitute TGF-β-stimulated COL1A2 promoter activity in Smad3-null or -knockdown cells. Blocking ERK in fibroblasts and renal mesangial cells inhibited both S204 phosphorylation and Smad3-mediated COL1A2 promoter activity. Mutations replacing serine at S204 or S208 in the linker region decreased Smad3-mediated COL1A2 promoter activity, whereas mutating T179 enhanced basal COL1A2 promoter activity and did not prevent TGF-β stimulation. Interestingly, mutation of all four Smad3LR sites (T179, S204, S208 and S213) was not inhibitory, suggesting primacy of the two inhibitory sites. These results suggest that in these mesenchymal cells, phosphorylation of the T179 and possibly S213 sites may act as a brake on the signal, whereas S204 phosphorylation by ERK in some manner releases that brake. Renal epithelial cells (HKC) respond differently from MEF or mesangial cells; blocking ERK neither changed TGF-β-stimulated S204 phosphorylation nor prevented Smad3-mediated COL1A2 promoter activity in HKC. Furthermore, re-expression of wild type-Smad3 or the S204A-Smad3 mutant in Smad3-knockdown HKC reconstituted Smad3-mediated COL1A2 promoter activity. Collectively, these data suggest that Serine-204 phosphorylation in the Smad3LR is a critical event by which ERK enhances Smad3-mediated COL1A2 promoter activity in mesenchymal cells.

Notch Signaling Molecules Activate TGF- β in Rat Mesangial Cells under High Glucose Conditions

The involvement of the Notch signaling pathway in the cellular differentiation of the mammalian kidney is established. Recently, the dysregulation of Notch signaling molecules has been identified in acute and chronic renal injuries, fibrosis models, and diabetic kidney biopsies. The canonical Notch ligand , Jagged1, is upregulated in a transforming growth factor-beta- (TGF- β -) dependent manner during chronic kidney disease. TGF- β , a central mediator of renal fibrosis, also is a major contributor to the development of diabetic nephropathy. To explore the roles and possible mechanisms of Notch signaling molecules in the pathogenesis of diabetic nephropathy, we exposed cultured rat mesangial cells to a γ -secretase inhibitor (DAPT) or high glucose and measured the expression of Notch signaling molecules and the fibrosis index. Notch pathway-related molecules, TGF- β , and fibronectin increased with exposure to high glucose and decreased with DAPT treatment. Our results suggest that the Notch signaling pathway may precipitate diabetic nephropathy via TGF- β activation.

Molecular mechanisms in the pathogenesis of diabetic nephropathy: an update

Diabetes mellitus is known to trigger retinopathy, neuropathy and nephropathy. Diabetic nephropathy, a long-term major microvascular complication of uncontrolled hyperglycemia, affects a large population worldwide. Recent findings suggest that numerous pathways are activated during the course of diabetes mellitus and that these pathways individually or collectively play a role in the induction and progression of diabetic nephropathy. However, clinical strategies targeting these pathways to manage diabetic nephropathy remain unsatisfactory, as the number of diabetic patients with nephropathy is increasing yearly. To develop ground-breaking therapeutic options to prevent the development and progression of diabetic nephropathy, a comprehensive understanding of the molecular mechanisms involved in the pathogenesis of the disease is mandatory. Therefore, the purpose of this paper is to discuss the underlying mechanisms and downstream pathways involved in the pathogenesis of diabetic nephropathy.

Role of the TGF-β/BMP-7/Smad pathways in renal diseases

TGF-β (transforming growth factor-β) and BMP-7 (bone morphogenetic protein-7), two key members in the TGF-β superfamily, play important but diverse roles in CKDs (chronic kidney diseases). Both TGF-β and BMP-7 share similar downstream Smad signalling pathways, but counter-regulate each other to maintain the balance of their biological activities. During renal injury in CKDs, this balance is significantly altered because TGF-β signalling is up-regulated by inducing TGF-β1 and activating Smad3, whereas BMP-7 and its downstream Smad1/5/8 are down-regulated. In the context of renal fibrosis, Smad3 is pathogenic, whereas Smad2 and Smad7 are renoprotective. However, this counter-balancing mechanism is also altered because TGF-β1 induces Smurf2, a ubiquitin E3-ligase, to target Smad7 as well as Smad2 for degradation. Thus overexpression of renal Smad7 restores the balance of TGF-β/Smad signalling and has therapeutic effect on CKDs. Recent studies also found that Smad3 mediated renal fibrosis by up-regulating miR-21 (where miR represents microRNA) and miR-192, but down-regulating miR-29 and miR-200 families. Therefore restoring miR-29/miR-200 or suppressing miR-21/miR-192 is able to treat progressive renal fibrosis. Furthermore, activation of TGF-β/Smad signalling inhibits renal BMP-7 expression and BMP/Smad signalling. On the other hand, overexpression of renal BMP-7 is capable of inhibiting TGF-β/Smad3 signalling and protects the kidney from TGF-β-mediated renal injury. This counter-regulation not only expands our understanding of the causes of renal injury, but also suggests the therapeutic potential by targeting TGF-β/Smad signalling or restoring BMP-7 in CKDs. Taken together, the current understanding of the distinct roles and mechanisms of TGF-β and BMP-7 in CKDs implies that targeting the TGF-β/Smad pathway or restoring BMP-7 signalling may represent novel and effective therapies for CKDs.

Transforming growth factor-β, bioenergetics, and mitochondria in renal disease

The transforming growth factor-β (TGF-β) family comprises more than 30 family members that are structurally related secreted dimeric cytokines, including TGF-β, activins, and bone morphogenetic proteins/growth and differentiation factors. TGF-β are pluripotent regulators of cell proliferation, differentiation, apoptosis, migration, and adhesion of many different cell types. TGF-β pathways are highly evolutionarily conserved and control embryogenesis, tissue repair, and tissue homeostasis in invertebrates and vertebrates. Aberrations in TGF-β activity and signaling underlie a broad spectrum of developmental disorders and major pathologies in human beings, including cancer, fibrosis, and autoimmune diseases. Recent observations have indicated an emerging role for TGF-β in the regulation of mitochondrial bioenergetics and oxidative stress responses characteristic of chronic degenerative diseases and aging. Conversely, energy and metabolic sensory pathways cross-regulate mediators of TGF-β signaling. Here, we review TGF-β and regulation of bioenergetic and mitochondrial functions, including energy and oxidant metabolism and apoptotic cell death, as well as their emerging relevance in renal biology and disease.

TGF-β/Smad signaling in kidney disease

Chronic progressive kidney diseases typically are characterized by active renal fibrosis and inflammation. Transforming growth factor-β1 (TGF-β1) is a key mediator in the development of renal fibrosis and inflammation. TGF-β1 exerts its biological effects by activating Smad2 and Smad3, which is regulated negatively by an inhibitory Smad7. In the context of fibrosis, although Smad3 is pathogenic, Smad2 and Smad7 are protective. Under disease conditions, Smads also interact with other signaling pathways, such as the mitogen-activated protein kinase and nuclear factor-κB pathways. In contrast to the pathogenic role of active TGF-β1, latent TGF-β1 plays a protective role in renal fibrosis and inflammation. Furthermore, recent studies have shown that TGF-β/Smad signaling plays a regulating role in microRNA-mediated renal injury. Thus, targeting TGF-β signaling by gene transfer of either Smad7 or microRNAs into diseased kidneys has been shown to retard progressive renal injury in a number of experimental models. In conclusion, TGF-β/Smad signaling plays a critical role in renal fibrosis and inflammation. Advances in understanding of the mechanisms of TGF-β/Smad signaling in renal fibrosis and inflammation during chronic kidney diseases should provide a better therapeutic strategy to combat kidney diseases.

Smad3 linker phosphorylation attenuates Smad3 transcriptional activity and TGF-β1/Smad3-induced epithelial-mesenchymal transition in renal epithelial cells

Transforming growth factor-β1 (TGF-β1) has a distinct role in renal fibrosis associated with epithelial-mesenchymal transition (EMT) of the renal tubules and synthesis of extracellular matrix. Smad3 plays an essential role in fibrosis initiated by EMT. Phosphorylation of Smad3 in the C-terminal SSXS motif by type I TGF-β receptor kinase is essential for mediating TGF-β response. Smad3 activity is also regulated by phosphorylation in the linker region. However, the functional role of Smad3 linker phosphorylation is not well characterized. We now show that Smad3 EPSM mutant, which mutated the four phosphorylation sites in the linker region, markedly enhanced TGF-β1-induced EMT of Smad3-deficient primary renal tubular epithelial cells, whereas Smad3 3S-A mutant, which mutated the C-terminal phosphorylation sites, was unable to induce EMT in response to TGF-β1. Furthermore, immunoblotting and RT-PCR analysis showed a marked induction of fibrogenic gene expression with a significant reduction in E-cadherin in HK2 human renal epithelial cells expressing Smad3 EPSM. TGF-β1 could not induce the expression of α-SMA, vimentin, fibronectin and PAI-1 or reduce the expression of E-cadherin in HK2 cells expressing Smad3 3S-A in response to TGF-β1. Our results suggest that Smad3 linker phosphorylation has a negative regulatory role on Smad3 transcriptional activity and TGF-β1/Smad3-induced renal EMT. Elucidation of mechanism regulating the Smad3 linker phosphorylation can provide a new strategy to control renal fibrosis.

TGFβ-stimulated microRNA-21 utilizes PTEN to orchestrate AKT/mTORC1 signaling for mesangial cell hypertrophy and matrix expansion

Transforming growth factor-β (TGFβ) promotes glomerular hypertrophy and matrix expansion, leading to glomerulosclerosis. MicroRNAs are well suited to promote fibrosis because they can repress gene expression, which negatively regulate the fibrotic process. Recent cellular and animal studies have revealed enhanced expression of microRNA, miR-21, in renal cells in response to TGFβ. Specific miR-21 targets downstream of TGFβ receptor activation that control cell hypertrophy and matrix protein expression have not been studied. Using 3′UTR-driven luciferase reporter, we identified the tumor suppressor protein PTEN as a target of TGFβ-stimulated miR-21 in glomerular mesangial cells. Expression of miR-21 Sponge, which quenches endogenous miR-21 levels, reversed TGFβ-induced suppression of PTEN. Additionally, miR-21 Sponge inhibited TGFβ-stimulated phosphorylation of Akt kinase, resulting in attenuation of phosphorylation of its substrate GSK3β. Tuberin and PRAS40, two other Akt substrates, and endogenous inhibitors of mTORC1, regulate mesangial cell hypertrophy. Neutralization of endogenous miR-21 abrogated TGFβ-stimulated phosphorylation of tuberin and PRAS40, leading to inhibition of phosphorylation of S6 kinase, mTOR and 4EBP-1. Moreover, downregulation of miR-21 significantly suppressed TGFβ-induced protein synthesis and hypertrophy, which were reversed by siRNA-targeted inhibition of PTEN expression. Similarly, expression of constitutively active Akt kinase reversed the miR-21 Sponge-mediated inhibition of TGFβ-induced protein synthesis and hypertrophy. Furthermore, expression of constitutively active mTORC1 prevented the miR-21 Sponge-induced suppression of mesangial cell protein synthesis and hypertrophy by TGFβ. Finally, we show that miR-21 Sponge inhibited TGFβ-stimulated fibronectin and collagen expression. Suppression of PTEN expression and expression of both constitutively active Akt kinase and mTORC1 independently reversed this miR-21-mediated inhibition of TGFβ-induced fibronectin and collagen expression. Our results uncover an essential role of TGFβ-induced expression of miR-21, which targets PTEN to initiate a non-canonical signaling circuit involving Akt/mTORC1 axis for mesangial cell hypertrophy and matrix protein synthesis.

Chromatin modifications associated with diabetes

Accelerated rates of vascular complications are associated with diabetes mellitus. Environmental factors including hyperglycaemia contribute to the progression of diabetic complications. Epidemiological and experimental animal studies identified poor glycaemic control as a major contributor to the development of complications. These studies suggest that early exposure to hyperglycaemia can instigate the development of complications that present later in the progression of the disease, despite improved glycaemic control. Recent experiments reveal a striking commonality associated with gene-activating hyperglycaemic events and chromatin modification. The best characterised to date are associated with the chemical changes of amino-terminal tails of histone H3. Enzymes that write specified histone tail modifications are not well understood in models of hyperglycaemia and metabolic memory as well as human diabetes. The best-characterised enzyme is the lysine specific Set7 methyltransferase. The contribution of Set7 to the aetiology of diabetic complications may extend to other transcriptional events through methylation of non-histone substrates.

Genetic deficiency of Smad3 protects the kidneys from atrophy and interstitial fibrosis in 2K1C hypertension

Although the two-kidney, one-clip (2K1C) model is widely used as a model of human renovascular hypertension, mechanisms leading to the development of fibrosis and atrophy in the cuffed kidney and compensatory hyperplasia in the contralateral kidney have not been defined. Based on the well-established role of the transforming growth factor (TGF)-β signaling pathway in renal fibrosis, we tested the hypothesis that abrogation of TGF-β/Smad3 signaling would prevent fibrosis in the cuffed kidney. Renal artery stenosis (RAS) was established in mice with a targeted disruption of exon 2 of the Smad3 gene (Smad3 KO) and wild-type (WT) controls by placement of a polytetrafluoroethylene cuff on the right renal artery. Serial pulse-wave Doppler ultrasound assessments verified that blood flow through the cuffed renal artery was decreased to a similar extent in Smad3 KO and WT mice. Two weeks after surgery, systolic blood pressure and plasma renin activity were significantly elevated in both the Smad3 KO and WT mice. The cuffed kidney of WT mice developed renal atrophy (50% reduction in weight after 6 wk, P < 0.0001), which was associated with the development of interstitial fibrosis, tubular atrophy, and interstitial inflammation. Remarkably, despite a similar reduction of renal blood flow, the cuffed kidney of the Smad3 KO mice showed minimal atrophy (9% reduction in weight, P = not significant), with no significant histopathological alterations (interstitial fibrosis, tubular atrophy, and interstitial inflammation). We conclude that abrogation of TGF-β/Smad3 signaling confers protection against the development of fibrosis and atrophy in RAS.

Activin Receptor-Like Kinase 5 Inhibitor Attenuates Fibrosis in Fibroblasts Derived from Peyronie's Plaque

Purpose

Transforming growth factor-β1 (TGF-β1) is the key fibrogenic cytokine associated with Peyronie's disease (PD). The aim of this study was to determine the antifibrotic effect of 3-((5-(6-Methylpyridin-2-yl)-4-(quinoxalin-6-yl)-1H-imidazol-2-yl) methyl)benzamide (IN-1130), a small-molecule inhibitor of the TGF-β type I receptor activin receptor-like kinase 5 (ALK5), in fibroblasts isolated from human PD plaque.

Materials and Methods

Plaque tissue from a patient with PD was used for primary fibroblast culture, and we then characterized primary cultured cells. Fibroblasts were pretreated with IN-1130 (10 µM) and then stimulated with TGF-β1 protein (10 ng/ml). We determined the inhibitory effect of IN-1130 on TGF-β1-induced phosphorylation of Smad2 and Smad3 or the nuclear translocation of Smad proteins in fibroblasts. Western blot analyses for plasminogen activator inhibitor-1, fibronectin, collagen I, and collagen IV were performed to evaluate effect of IN-1130 on the production of extracellular matrix proteins.

Results

The treatment of fibroblasts with TGF-β1 significantly increased phosphorylation of Smad2 and Smad3 and induced translocation of Smad proteins from the cytoplasm to the nucleus. Pretreatment with IN-1130 substantially inhibited TGF-β1-induced phosphorylation of Smad2 and Smad3 and nuclear accumulation of Smad proteins. The TGF-β1-induced production of extracellular matrix proteins was also significantly inhibited by treatment with IN-1130 and returned to basal levels.

Conclusions

Overexpression of TGF-β and activation of Smad transcriptional factors are known to play a crucial role in the pathogenesis of PD. Thus, inhibition of the TGF-β signaling pathway by ALK5 inhibitor may represent a promising therapeutic strategy for treating PD.

Role of parathyroid hormone-related protein in the pro-inflammatory and pro-fibrogenic response associated with acute pancreatitis

Pancreatitis is a common and potentially lethal necro-inflammatory disease with both acute and chronic manifestations. Current evidence suggests that the accumulated damage incurred during repeated bouts of acute pancreatitis (AP) can lead to chronic disease, which is associated with an increased risk of pancreatic cancer. While parathyroid hormone-related protein (PTHrP) exerts multiple effects in normal physiology and disease states, its function in pancreatitis has not been previously addressed. Here we show that PTHrP levels are transiently elevated in a mouse model of cerulein-induced AP. Treatment with alcohol, a risk factor for both AP and chronic pancreatitis (CP), also increases PTHrP levels. These effects of cerulein and ethanol are evident in isolated primary acinar and stellate cells, as well as in the immortalized acinar and stellate cell lines AR42J and irPSCc3, respectively. Ethanol sensitizes acinar and stellate cells to the PTHrP-modulating effects of cerulein. Treatment of acinar cells with PTHrP (1-36) increases expression of the inflammatory mediators interleukin-6 (IL-6) and intracellular adhesion protein (ICAM-1), suggesting a potential autocrine loop. PTHrP also increases apoptosis in AR42J cells. Stellate cells mediate the fibrogenic response associated with pancreatitis; PTHrP (1-36) increases procollagen I and fibronectin mRNA levels in both primary and immortalized stellate cells. The effects of cerulein and ethanol on levels of IL-6 and procollagen I are suppressed by the PTH1R antagonist, PTHrP (7-34). Together these studies identify PTHrP as a potential mediator of the inflammatory and fibrogenic responses associated with alcoholic pancreatitis.

Smads as therapeutic targets for chronic kidney disease

Renal fibrosis is a hallmark of chronic kidney disease (CKD). It is generally thought that transforming growth factor-β1 (TGF-β1) is a key mediator of fibrosis and mediates renal scarring positively by Smad2 and Smad3, but negatively by Smad7. Our recent studies found that in CKD, TGF-β1 is not a sole molecule to activate Smads. Many mediators such as angiotensin II and advanced glycation end products can also activate Smads via both TGF-β-dependent and independent mechanisms. In addition, Smads can interact with other signaling pathways, such as the mitogen-activated protein kinase and nuclear factor-kappaB (NF-κB) pathways, to regulate renal inflammation and fibrosis. In CKD, Smad2 and Smad3 are highly activated, while Smad7 is reduced or lost. In the context of fibrosis, Smad3 is pathogenic and mediates renal fibrosis by upregulating miR-21 and miR-192, but down-regulating miR-29 and miR-200 families. By contrast, Smad2 and Smad7 are protective. Overexpression of Smad7 inhibits both Smad3-mediated renal fibrosis and NF-κB-driven renal inflammation. Interestingly, Smad4 has diverse roles in renal fibrosis and inflammation. The complexity and distinct roles of individual Smads in CKD suggest that treatment of CKD should aim to correct the imbalance of Smad signaling or target the Smad3-dependent genes related to fibrosis, rather than to block the general effect of TGF-β1. Thus, treatment of CKD by overexpression of Smad7 or targeting Smad3-dependent miRNAs such as downregulation of miR-21 or overexpression of miR-29 may represent novel therapeutic strategies for CKD.