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

Assessment of the effects of transforming growth factor beta1 (TGF-β1)-Smad2/3 on fibrosis in rat myofascial trigger points using point shear wave elastography

Background & Aims

Myofascial trigger points (MTrPs) are highly sensitive irritated points within a tense belt of skeletal muscle, and are the main cause of muscle pain and dysfunction. MTrPs can also cause paraesthesia and autonomic nervous dysfunction. Furthermore, long-term and chronic MTrPs can cause muscle atrophy and even disability, seriously affecting the quality of life and mental health of patients, and increasing the social and economic burden. However, to date, there have been few studies on fibrogenesis and changes in MTrPs. Therefore, this study investigated whether transforming growth factor beta1 (TGF-β1)-Smad2/3 participates in the formation of MTrPs and how it affects fibrosis using point shear wave elastography.

Methods

Forty Sprague‒Dawley rats were randomly divided into the MTrPs group and the control group. Blunt injury combined with eccentric exercise was used to establish an MTrPs model. Electromyography (EMG), haematoxylin and eosin (H&E) staining and transmission electron microscopy (TEM) were used to verify the model. The collagen volume fraction was measured by Masson staining, the protein expression of TGF-β1 and p-Smad2/3 was measured by Western blotting (WB) and immunohistochemistry (IHC), and the shear wave velocity (SWV) was measured by point shear wave elastography.

Results

EMG, H&E and TEM examination indicated that the modelling was successful. The collagen volume fraction and the protein expression of TGF-β1 and p-Smad2/3 were higher in the MTrPs group than in the control group. The SWV of the MTrPs group was also higher than that of the control group. These differences suggest that MTrPs may exhibit fibrosis. The correlations between the collagen volume fraction and SWV and between the collagen volume fraction and TGF-β1 were positive.

Conclusion

Fibrotic conditions may be involved in the formation of MTrPs. Ultrasound point shear wave elastography and assessment of TGF-β1 and p-Smad2/3 expression can reflect the degree of MTrPs fibrosis to some extent. Further exploration of the important role of TGF-β1 and Smad2/3 in the pathogenesis of MTrPs will be of great significance for clinical treatment.

Tensin 2-deficient nephropathy - mechanosensitive nephropathy, genetic susceptibility

Tensin 2 (TNS2), a focal adhesion protein, is considered to anchor focal adhesion proteins to β integrin as an integrin adaptor protein and/or serve as a scaffold to facilitate the interactions of these proteins. In the kidney, TNS2 localizes to the basolateral surface of glomerular epithelial cells, i.e., podocytes. Loss of TNS2 leads to the development of glomerular basement membrane lesions and abnormal accumulation of extracellular matrix in maturing glomeruli during the early postnatal stages. It subsequently results in podocyte foot process effacement, eventually leading to glomerulosclerosis. Histopathological features of the affected glomeruli in the middle stage of the disease include expansion of the mesangial matrix without mesangial cell proliferation. In this review, we provide an overview of TNS2-deficient nephropathy and discuss the potential mechanism underlying this mechanosensitive nephropathy, which may be applicable to other glomerulonephropathies, such as CD151-deficient nephropathy and Alport syndrome. The onset of TNS2-deficient nephropathy strictly depends on the genetic background, indicating the presence of critical modifier genes. A better understanding of molecular mechanisms of mechanosensitive nephropathy may open new avenues for the management of patients with glomerulonephropathies.

Study of the mechanism underlying hsa-miR338-3p downregulation to promote fibrosis of the synovial tissue in osteoarthritis patients

Osteoarthritis (OA) is a degenerative joint disease characterized by the degradation of joint cartilage, the formation of osteophyma at joint margins, and synovial changes. Whereas lesions of the joint cartilage were the key point of the research and treatment of osteoarthritis before, a recent study showed that the synovium plays a crucial role in the pathological progress of OA. The inflammatory environment in the joints of OA patients always results in the overactivation of fibroblast-like synoviocytes (FLSs), which produce a multitude of inflammatory factors and media, not only leading to the degradation and injury of the cartilage tissue and promoting the development of osteoarthritis but also resulting in synovial fibrosis and joint stiffness. Therefore, the synovium has attracted increasing attention in the research of OA, and the study of the mechanism of activation of FLSs and the fibrosis of joint synovium may shed new light on OA treatment. By using high-throughput screening, we have identified that hsa-miR338-3p is significantly downregulated in the synovial tissue and joint effusion from OA patients. A functional study showed that overexpression of hsa-miR338-3p in the FLSs inhibited the TGF-β1-induced overactivation of the TGF-β/Smad fibrosis regulation pathway by suppressing TRAP-1 expression and thus reducing the TGF-β1-induced activation of the FLSs and the expression of vimentin and collagen I, two fibrosis markers. Meanwhile, a mechanism study also showed that the upregulation of hsa-miR338-3p reduced Smad2/3 phosphorylation by suppressing TRAP-1 and thus inhibited the TGF-β/Smad pathway and TIMP1, a downstream protein. The present study, for the first time, illustrates the role of hsa-miR338-3p in synovial fibrosis in OA patients and the related mechanism, which is of importance to the treatment of OA and its complications by targeting the FLSs and synovial tissue. Hsa-miR338-3p not only has the potential to be a target for the gene therapy of OA but also has the potential to be a new marker for the diagnosis of clinical progression in OA patients.

The Treatment of Fibrosis of Joint Synovium and Frozen Shoulder by Smad4 Gene Silencing in Rats

Soft tissue fibrosis at the joint induced by inflammation is the pathological basis of frozen shoulder. In the present study, we utilized a lentiviral approach to silence the Smad4 gene in an in vitro fibrosis model of fibroblasts and an in vivo frozen shoulder model. We observed the change in the fibrosis process and the biological indicators of frozen shoulder. The in vitro fibrosis models (Rat myoblasts L6, Rat synovial cell RSC-364 and Rat chondrocytes RCs) were established using TGF-β1 induction, and the effect of Smad4 gene silencing on fibrosis was analyzed. The method of Kanno A was employed to establish a rat model of frozen shoulder, and Smad4 in the relevant part was knocked down with the lentiviral approach. We then examined the abduction and rotation angles and the length of synovial intima and measured the inflammatory factors in effusion and the fibrotic markers of tissues. We found that Smad4 knockdown suppressed the proliferation and expression of fibrotic markers in L6, RSC-364 and RCs cells induced by TGF-β1. MMP activity measurements showed that Smad4 knockdown significantly reversed the decrease in MMP activity in these three cell lines that were induced by TGF-β1. Furthermore, using lentivirus in the rat frozen shoulder model, we found that Smad4 silencing attenuated the inflammatory response and fibrosis. It significantly inhibited the increase of the Vimentin, α-SMA, collagen I and III, Lama1 and Timp1 proteins in synovial tissue as well as the inflammatory factors of TNF-a, IL-1α/β, IL-6 and IL-10 in effusion. MMP acidity assays revealed that Smad4 silencing inhibited MMP activity in the synovial, cartilage and ligament tissues in the model animals. The assessment of the phosphorylated Smad2/3 in the nuclei isolated from the synovial tissues showed that Smad4 silencing significantly inhibited the phosphorylation and subsequent nuclear translocation of Smad2/3 proteins. Moreover, Smad4-shRNA lentivirus inhibited the decrease in both the abduction and rotation angles caused by immobilization as well as the decrease in the length of the synovial intima. Based on shoulder movement data, Smad4 knockdown can increase the rotation limitation caused by immobilization. In summary, Smad4 silencing can suppress chronic inflammation and fibrosis in joint tissues by inhibiting the TGF-β/Smad pathway and can play a positive role in the prevention and treatment of joint stiffness.

IGF-1 protects tubular epithelial cells during injury via activation of ERK/MAPK signaling pathway

Injury of renal tubular epithelial cells can induce acute renal failure and obstructive nephropathy. Previous studies have shown that administration of insulin-like growth factor-1 (IGF-1) ameliorates the renal injury in a mouse unilateral ureteral obstruction (UUO) model, whereas the underlying mechanisms are not completely understood. Here, we addressed this question. We found that the administration of IGF-1 significantly reduced the severity of the renal fibrosis in UUO. By analyzing purified renal epithelial cells, we found that IGF-1 significantly reduced the apoptotic cell death of renal epithelial cells, seemingly through upregulation of anti-apoptotic protein Bcl-2, at protein but not mRNA level. Bioinformatics analyses and luciferase-reporter assay showed that miR-429 targeted the 3'-UTR of Bcl-2 mRNA to inhibit its protein translation in renal epithelial cells. Moreover, IGF-1 suppressed miR-429 to increase Bcl-2 in renal epithelial cells to improve survival after UUO. Furthermore, inhibition of ERK/MAPK signaling pathway in renal epithelial cells abolished the suppressive effects of IGF-1 on miR-429 activation, and then the enhanced effects on Bcl-2 in UUO. Thus, our data suggest that IGF-1 may protect renal tubular epithelial cells via activation of ERK/MAPK signaling pathway during renal injury.

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

Smad4 has recently been identified as a tumor suppressor gene in a variety of cancers, yet the role of Smad4 in renal cell carcinoma (RCC) remained to be elusive. Therefore, the aim of the present study was to explore the function of Smad4 in RCC. The expression of Smad4 reduced the growth rate of RCC. The levels of Smad4 and forkhead box protein H1 (FOXH1) mRNA were reduced, while the levels of estrogen receptor were increased in RCC cells compared with those in human renal epithelial cells (P<0.01). Western blot analysis showed an identical trend among the three molecules. Glutathione S‑transferase pull‑down and immunoprecipitation assays proved the interaction between Smad4 and FOXH1. An immunofluorescence assay revealed that Smad4 and FOXH1 were colocalized in the nuclei of RCC cells. Smad4 interacts with Smad2 and migrates into the nucleus, where it interacts with FOXH1 to repress the protein expression of estrogen receptor. These results indicate that Smad4 acts as a tumor suppressor by activating FOXH1, and then suppressing the expression of estrogen receptor, in addition to tumor migration and invasion. Hence, Smad4 should be investigated as a potential target for the treatment for RCC.

[Effects of Chinese herbal medicine Yiqi Huoxue Formula on TGF-β/smad signal transduction pathway and connective tissue growth factor in rats with renal interstitial fibrosis]

OBJECTIVE

To observe the effects of Yiqi Huoxue Formula (YQHXF), a compound Chinese herbal medicine, on transforming growth factor-β (TGF-β)/smad signal transduction pathway and connective tissue growth factor (CTGF) in rats with renal interstitial fibrosis

METHODS

Unilateral ureteral obstruction (UUO) rat model was established and the rats were randomly divided into 5 groups: untreated group, high-, medium-, and low-dose YQHXF groups and fosinopril sodium group. Another group with sham operation was set as control. All rats were administered with corresponding drugs for 3 weeks. After the last administration, each rat was sacrificed and weighed and the serum was separated for creatinine (Cr) and blood urea nitrogen (BUN) detection. Kidneys of the rats were taken out, and mRNA and protein expressions of TGF-β, smad2, smad7 and CTGF were measured with real-time fluorescent quantitative reverse transcription-polymerase chain reaction and Western blotting respectively; fibrosis of the kidney tissue was observed with hematoxylin-eosin (HE) staining and Masson trichrome staining.

RESULTS

Compared with sham-operation group, Cr and BUN in serum of UUO groups were increased, while high-dose YQHXF treatment decreased the UUO-induced increase of Cr and BUN levels. HE staining and Masson staining results showed that the renal tubular epithelial cells in untreated group got atrophied; lumens of renal tubules expanded; fibroplastic proliferation and inflammatory cell infiltration were observed in renal interstitium; the number of glomerulus decreased and collagen increased significantly compared with sham-operation group. In the high- and medium-dose YQHXF groups and fosinopril sodium group, the histopathological changes of inflammatory cell infiltration, fibroplastic proliferation, expansion of lumens of renal tubules was improved as compared with the untreated group. The mRNA and protein expressions of TGF-β, smad2 and CTGF in untreated group were higher than those in sham-operation group (P<0.05), and the mRNA and protein expressions of smad7 in untreated group were lower than those in the sham-operation group (P<0.05). Compared with untreated group, high- and medium-dose of YQHXF significantly down-regulated the mRNA and protein expressions of TGF-β, smad2 and CTGF (P<0.01, P<0.05), and up-regulated the mRNA and protein expressions of smad7 (P<0.01, P<0.05).

CONCLUSIONS

The mRNA expression of CTGF in UUO rats may be regulated by TGF-β/smad signaling transduction pathway. YQHXF might inhibit the expression of CTGF through down-regulation of TGF-β and smad2 and up-regulation of smad7, thus inhibiting the progression of renal interstitial fibrosis.

The molecular mediators of type 2 epithelial to mesenchymal transition (EMT) and their role in renal pathophysiology

Common to all forms of chronic kidney disease is the progressive scarring of the tubulo-interstitial space, associated with the acquisition and accumulation of activated myofibroblasts. Many of these myofibroblasts are generated when tubular epithelial cells progressively lose their epithelial characteristics (cell-cell contact, microvilli, tight-junction proteins, apical-basal polarity) and acquire features of a mesenchymal lineage, including stress fibres, filopodia and augmented matrix synthesis. This process, known as epithelial to mesenchymal transition (EMT), plays an important role in progressive kidney disease. For EMT to occur in tubular cells, the transcriptional activation (and derepression) of genes required to sustain mesenchymal-type structures and functions (e.g. vimentin, alpha-smooth muscle actin) must occur alongside repression (or deactivation) of genes that act to maintain the epithelial phenotype (e.g. E-cadherin, bone morphogenic protein 7). Several factors have been suggested as potential initiators of EMT. With a few key exceptions, these triggers require the induction of transforming growth factor beta (TGF-beta) and downstream mediators, including SMADs, CTGF, ILK and SNAI1. Activation of TGF-beta receptors is also able to stimulate a range of additional pathways (so-called non-SMAD activation), including RhoA, mitogen-activated protein kinase and phosphoinositide 3-kinase signalling cascades, that also contribute to EMT and renal fibrogenesis. This review examines in detail the molecular mediators of EMT in tubular cells and its potential role as a long-lasting mediator of metabolic stress.

Transforming growth factor-beta and angiotensin in fibrosis and burn injuries

This review considers the roles of transforming growth factor-beta (TGF-beta), the signaling Smad proteins, and angiotensin II (AT II) in conditions leading to human fibrosis. The goal is to update the burn practitioner and researcher about this important pathway and to introduce AT II as a possible synergistic signal to TGF-beta in burn scarring. Literature searches of the MEDLINE database were performed for English manuscripts combinations of TGF-beta, Smad, angiotensin, fibrosis, burn, and scar. AT II and TGF-beta both activate the Smad protein system, which leads to the expression of genes related to fibrosis. In fibrotic conditions, such as tubulointerstitial nephritis, systemic sclerosis, and myocardial infarctions, AT II acts both independently and synergistically with TGF-beta. Both AT II and TGF-beta act through a messenger system, the Smad proteins that lead to excessive extracellular matrix formation. Treatment and research implications are reviewed. The interaction between AT II and TGF-beta leading to fibrosis is well described in some human diseases. This pathway may be of importance in human burn scarring as well.

Expression of macrophage metalloelastase (MMP-12) in podocytes of hereditary nephrotic mice (ICGN strain)

The Institute for Cancer Research (ICR)-derived glomerulonephritis (ICGN) mouse is a good model for renal fibrosis. In the glomeruli and tubulointerstitium of ICGN mouse kidneys, the components of the extracellular matrix (ECM) accumulated, and matrix metalloproteinases (MMPs) participated in this process. To clarify the mechanism of renal fibrosis, we investigated the expression and localization of macrophage metalloelastase (MMP-12), whose functions in kidney diseases are not fully understood, and its regulatory molecules, monocyte chemoattractive protein-1 (MCP-1) and CC chemokine receptor 2 (CCR2), in the kidneys of ICGN mice by RT-PCR, Western blotting and immunohistochemical staining, respectively. Extensive expression of MMP-12 mRNA and its protein was noted in ICGN mice with progressed nephrotic syndrome. The increase in MMP-12 expression occurred predominantly in podocytes. Furthermore, MCP-1 and CCR2 were also increased in podocytes of the ICGN strain. These results suggest that the expression of MMP-12 is involved in the progression of nephrotic syndrome in ICGN mice.

TGF-beta1/Smad7 signaling stimulates renal tubulointerstitial fibrosis induced by AAI

A progressive tubulointerstitial nephropathy is mainly induced by aristolochic acid I (AAI), but a comprehensive understanding of this process is still missing. By using mouse primary renal tubular epithelial cells (RTECs) cultured in vitro and combining with two AAI treatment types (dose-response studies and time-response studies), we sought to investigate the nephrotoxicity of AAI further. Following our molecular and pharmacological studies, we found that high doses of AAI could lead to the death of RTECs within a short time, but low doses in a long duration only induce the epithelial cells to transform into myofibroblasts (MFs). This was also immediately identified by the increased expression of vimentin and de novo expression of alpha-smooth muscle actin (alpha-SMA) with the loss of cytokeratin 18 (CK18) by semiquantitative reverse transcriptase-PCR (RT-PCR) and immunofluorescence staining. The transcriptional level of transforming growth factor-beta1 (TGF-beta1) in the group treated with AAI significantly increased twice as much as the control. Smad2 mRNA level in the group with 50 ng/mL AAI declined by 23.4% at 24 hr, then increased by 180.0% at 36 hr; it was also evidently increased (217.4%) after being treated with 30 ng/mL AAI for 24 hr. Meanwhile, Smad7 mRNA level was down-regulated by AAI in dose- and time-dependence. Furthermore, by cotransfecting in mouse primary RTECs, the transcriptional level of Smad7 promoter-luciferase reporter gene was significantly down-regulated by AAI (300 ng/mL), and the expression of myofibroblast-specific markers induced by AAI was also suppressed by the specific antagonist of TGF-beta1 receptors (SB-431542). Collectively, the present results suggest that AAI may induce cytotoxicity through its conductive epithelial to mesenchymal transition, and TGF-beta1/Smad7 signaling can stimulate renal tubulointerstitial fibrosis induced by AAI.

Transforming growth factor-β1 mediated up-regulation of lysyl oxidase in the kidneys of hereditary nephrotic mouse with chronic renal fibrosis

Lysyl oxidase (LOX), an extracellular enzyme, plays a key role in the post-translational modification of collagens and elastin, catalyzing inter- and intra-crosslinking reactions. Because the crosslinked extracellular matrices (ECMs) are highly resistant to degradative enzymes, it is considered that the over-expression of LOX may cause severe fibrotic degeneration. In the present study, we addressed the role of LOX-mediated crosslinking in chronic renal tubulointerstitial fibrosis using an animal model of hereditary nephrotic syndrome, the Institute of Cancer Research (ICR)-derived glomerulonephritis (ICGN) mouse. Ribonuclease protection assay (RPA) revealed that LOX mRNA expression was up-regulated in the kidneys of ICGN mice as compared with control ICR mice. High-level expression of LOX and transforming growth factor (TGF)-beta1 (an up-regulator of LOX) mRNA was detected in tubular epithelial cells of ICGN mouse kidneys by in situ hybridization. Type-I and -III collagens, major substrates for LOX, were accumulated in tubulointerstitium of ICGN mouse kidneys. The present findings imply that TGF-beta1 up-regulates the production of LOX in tubular epithelial cells of ICGN mouse kidneys, and the excessive LOX acts on interstitial collagens and catalyzes crosslinking reactions. As a result, the highly crosslinked collagens induce an irreversible progression of chronic renal tubulointerstitial fibrosis in the kidneys of ICGN mice.

Prostacyclin signaling in the kidney: implications for health and disease

The balance between vasodilator and vasoconstrictor pathways is key to the maintenance of homeostasis and the outcome of disease. In the kidney, prostaglandins (PGs) uphold this balance and regulate renal function: hemodynamics, renin secretion, growth responses, tubular transport processes, and cell fate. With the advent of cyclooxygenase (COX)-2-selective inhibitors, targeted deletions in mice (COX knockouts, PG receptor knockouts), and the discovery of intracrine signaling options for PGs (peroxisome proliferator-activated receptors and perinuclear PGE2receptors: EP1,3,4), many advances have been made in the study of arachidonic acid metabolites. Although prostacyclin (PGI2) is a major product of the COX pathway, there is very little emphasis on its importance to the kidney. This review will discuss PGI2biology and its relevance to different aspects of renal disease (growth, fibrosis, apoptosis), highlighting the most significant research from the past decade of PGI2literature, what we have learned from other organ systems, while stressing the significance of cross talk between various PGI2signaling pathways and its implications for renal health and disease.

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

Anemia is a major secondary symptom in chronic renal disorder (CRD), but the precise cause of insufficient production of erythropoietin (EPO) remains unclear owing to the controversial localization of EPO-producing cells in the kidneys. The ICR-derived glomerulonephritis (ICGN) mouse, a new hereditary nephrotic mouse, is an appropriate model of anemia associated with CRD. By using an amplified in situ hybridization technique, we detected and counted the renal EPO-producing cells under both normoxic and hypoxic conditions. The expression levels of renal EPO mRNA were quantified and oxygen gradients were also assessed immunohistochemically. Amplified in situ hybridization clarified that EPO-producing cells were peritubular interstitial cells in the middle region of renal cortex in both ICR and ICGN mice. Hypoxia (7% O2) induced low oxygen tension in proximal tubular epithelial cells of renal cortex, and increased the expression of EPO mRNA and the number of EPO-producing cells in both ICR and ICGN mice. However, hypoxia did not increase the serum EPO levels in ICGN mice. The ICGN mouse is a good model for anemia associated with CRD, and the suppression of EPO protein production in the renal EPO-producing cells is considered to be a potential cause of anemia associated with CRD.

Changes in Smad expression and subcellular localization in bleomycin-induced pulmonary fibrosis

Administration of bleomycin (BM) produces inflammation and fibrosis of the lung in humans and experimental animals. The molecular defects by which BM induces these pathological effects have not been studied in detail. We studied the expression of Smad family proteins, key molecules involved in mediating transforming growth factor (TGF)-β signaling from the cell membrane to the nucleus, during the early and late phases of BM-induced fibrogenesis. Pulmonary fibrosis was induced in male Sprague-Dawley rats by a single intratracheal injection (1.5 units) of BM. Control rats received saline. Rats were killed at 3, 5, 7, 14, and 28 days after BM, cytosolic and nuclear proteins were extracted and isolated from lung tissues, and Smad proteins were probed with specific antibodies. In BM-exposed lung tissue, compared with control, Smad3 decreased persistently in the cytosol and increased transiently in the nucleus. There was a persistent increase in phosphorylation and nuclear accumulation of Smad2/3. Smad4 was increased transiently in both the cytosol and nucleus. A significant and progressive decrease in the expression of Smad7, the endogenous inhibitor of TGF-β/Smad signaling, was observed after BM instillation. Collectively, our results indicate that an imbalance between agonistic Smads2–4 and antagonistic Smad7 may result in the unchecked activation of an autocrine TGF-β loop, which contributes to the pathogenesis of BM-induced pulmonary fibrosis.