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

Three-dimensional morphometry of kidney in New Zealand rabbit using unbiased design-based stereology

The rabbit is widely used as a laboratory animal in experimental models of kidney diseases. This species is also important from a veterinary perspective as a companion animal. Stereology has been accepted as an accurate approach to kidney morphometry. The objective of the present project was to provide normal quantitative stereological parameters for adult rabbit kidneys. The left kidneys of five adult male New Zealand rabbits were used. Isotropic sections were obtained using the orientation method. Total kidney volume was calculated by the Cavalieri principle. The volume fraction of the renal structures was estimated using the point counting system. The lengths of the proximal convoluted tubule (PCT) and distal convoluted tubule (DCT) were calculated using counting frames. The total glomerular number was accounted for using the physical/fractionator technique. The mean glomerular volume was obtained by dividing the total volume of glomeruli by their total number. The total volume of rabbit kidneys calculated was 10.39 ± 1.98 cm3. The fractional volume of the kidney cortex and medulla accounted for 57.79 ± 0.65% and 42.2 ± 0.65%, respectively. The total glomerular volume was 2.18 ± 0.32% of the whole kidney. The total number of glomeruli in the rabbit kidney was estimated as 204.68 ± 12 × 103. The mean glomerular volume measured 1.07 ± 0.12 × 106 μm3. The total length of PCT and DCT was 2.96 ± 0.29 km and 1.38 ± 0.24 km, respectively. These findings can be used as a reference in experimental nephrology research and may help to expand the knowledge of nephrology in mammals by comparing with available data on humans and other species. RESEARCH HIGHLIGHTS: Three-dimensional morphometry of adult rabbit kidney structures was analyzed using quantitative stereology. Total volume of kidney, fractional volume of cortex and medulla, length of renal tubules and number of nephrons were estimated. These three-dimensional morphometrical data can be used as a reference in experimental nephrology research and may help to expand the knowledge of nephrology in mammals.

Podocyte protease activated receptor 1 stimulation in mice produces focal segmental glomerulosclerosis mirroring human disease signaling events

About 30% of patients who have a kidney transplant with underlying nephrotic syndrome (NS) experience rapid relapse of disease in their new graft. This is speculated to be due to a host-derived circulating factor acting on podocytes, the target cells in the kidney, leading to focal segmental glomerulosclerosis (FSGS). Our previous work suggests that podocyte membrane protease receptor 1 (PAR-1) is activated by a circulating factor in relapsing FSGS. Here, the role of PAR-1 was studied in human podocytes in vitro, and using a mouse model with developmental or inducible expression of podocyte-specific constitutively active PAR-1, and using biopsies from patients with nephrotic syndrome. In vitro podocyte PAR-1 activation caused a pro-migratory phenotype with phosphorylation of the kinase JNK, VASP protein and docking protein Paxillin. This signaling was mirrored in podocytes exposed to patient relapse-derived NS plasma and in patient disease biopsies. Both developmental and inducible activation of transgenic PAR-1 (NPHS2 Cre PAR-1Active+/-) caused early severe nephrotic syndrome, FSGS, kidney failure and, in the developmental model, premature death. We found that the non-selective cation channel protein TRPC6 could be a key modulator of PAR-1 signaling and TRPC6 knockout in our mouse model significantly improved proteinuria and extended lifespan. Thus, our work implicates podocyte PAR-1 activation as a key initiator of human NS circulating factor and that the PAR-1 signaling effects were partly modulated through TRPC6.

miR-486-5p Restrains Extracellular Matrix Production and Oxidative Damage in Human Trabecular Meshwork Cells by Targeting TGF-β/SMAD2 Pathway

Background

Glaucoma is characterized by elevated intraocular pressure caused by aqueous outflow dysfunction. Trabecular meshwork plays a key role in controlling intraocular pressure by modulating aqueous outflow. This study investigated the protective effects of miR-486-5p in H₂O₂-stimulated human trabecular meshwork cells (TMCs).

Methods

TMCs were disposed with 300 μM H₂O₂ to establish oxidative damage models in vitro. miR-486-5p mimics and its controls were transfected into TMCs, and cell apoptosis and extracellular matrix production (ECM) genes were measured by flow cytometry, western blotting, and immunofluorescence staining. Activities of superoxide dismutase (SOD) and malondialdehyde (MDA) were also assayed. Online tools and luciferase reporter assays were used to uncover the relationship between miR-486-5p and the TGF-β/SMAD2 pathway.

Results

We found that H₂O₂-induced oxidative damage in TMCs and miR-486-5p was downregulated in H₂O₂-stimulated TMCs. Overexpression of miR-486-5p mitigated H₂O₂-induced oxidative damage by inhibiting apoptosis, reducing cleaved caspase-3/9 expression, reducing MDA levels, and increasing SOD levels as well as downregulating ECM genes. SMAD2 was demonstrated to be targeted by miR-486-5p, and miR-486-5p inhibited TGF-β/SMAD2 signaling in H₂O₂-stimulated TMCs. Additionally, SMAD2 was upregulated by H₂O₂, and SMAD2 upregulation abrogated the protective effects of miR-486-5p against H₂O₂-induced injury.

Conclusion

miR-486-5p restrains H₂O₂-induced oxidative damage in TMCs by targeting the TGF-β/SMAD2 pathway.

JNK and p38 Inhibitors Prevent Transforming Growth Factor-β1-Induced Myofibroblast Transdifferentiation in Human Graves' Orbital Fibroblasts

Transforming growth factor-β1 (TGF-β1)-induced myofibroblast transdifferentiation from orbital fibroblasts is known to dominate tissue remodeling and fibrosis in Graves’ ophthalmopathy (GO). However, the signaling pathways through which TGF-β1 activates Graves’ orbital fibroblasts remain unclear. This study investigated the role of the mitogen-activated protein kinase (MAPK) pathway in TGF-β1-induced myofibroblast transdifferentiation in human Graves’ orbital fibroblasts. The MAPK pathway was assessed by measuring the phosphorylation of p38, c-Jun N-terminal kinase (JNK), and extracellular-signal-regulated kinase (ERK) by Western blots. The expression of connective tissue growth factor (CTGF), α-smooth muscle actin (α-SMA), and fibronectin representing fibrogenesis was estimated. The activities of matrix metalloproteinases (MMPs) and tissue inhibitors of metalloproteinases (TIMPs) responsible for extracellular matrix (ECM) metabolism were analyzed. Specific pharmacologic kinase inhibitors were used to confirm the involvement of the MAPK pathway. After treatment with TGF-β1, the phosphorylation levels of p38 and JNK, but not ERK, were increased. CTGF, α-SMA, and fibronectin, as well as TIMP-1 and TIMP-3, were upregulated, whereas the activities of MMP-2/-9 were inhibited. The effects of TGF-β1 on the expression of these factors were eliminated by p38 and JNK inhibitors. The results suggested that TGF-β1 could induce myofibroblast transdifferentiation in human Graves’ orbital fibroblasts through the p38 and JNK pathways.

Cat Kidney Glomeruli and Tubules Evaluated by Design-Based Stereology

Renal function is related to its structure and three-dimensional structural parameters correlate better with the kidney function than two-dimensional structural parameters. Stereology is the current gold-standard technique for the morphometrical evaluation of kidney structures. This study describes morphometric features of the kidney of the cat using design-based stereological techniques aimed to introduce the cat as a translational model in nephrology and provide basic findings for diagnosis and treatment of kidney diseases in this species. Left kidneys of four cats were included in the present study. The kidney volume, volume fraction of cortex and medulla, glomerular volume, glomerular mean volume, glomerular number, and proximal convoluted tubule (PCT) and distal convoluted tubule (DCT) length were estimated. The kidney volume was estimated to 11.4 ± 1.3 cm³ . The volume fraction of cortex and medulla was 65.6 ± 2% and 34.2 ± 2%, respectively. The total number of glomeruli was estimated to be 186 ± 11 × 10³ using the physical disector/fractionator method. The mean glomerular volume was estimated to be 1.54 ± 0.06 × 10⁶ μm³ and the glomerular volume was covering 2.13 ± 0.34% of the whole kidney. The total length of PCT and DCT was estimated to be 2.26 ± 0.48 km and 505 ± 43 m, respectively. Our data might contribute to the knowledge of kidneys in mammals and provide a comparison with available data on human and other mammals. Anat Rec, 302:1846-1854, 2019. © 2019 American Association for Anatomy.

Fast diffusion kurtosis imaging of fibrotic mouse kidneys

Diffusion kurtosis imaging (DKI) is sensitive to tissue microstructure and may therefore be useful in the diagnosis and monitoring of disease in brain and body organs. Generally, diffusion magnetic resonance imaging (dMRI) in the body is challenging because of the heterogeneous body composition, which can cause image artefacts as a result of chemical shifts and susceptibility differences. In addition, the abdomen possesses physiological factors (e.g. breathing, heartbeat, blood flow) which may severely reduce image quality, especially when echo planar imaging is employed, as is typical in dMRI. Collectively, these challenging measurement conditions impede the use and exploration of DKI in the body. This impediment is further exacerbated by the traditionally large amount of data required for DKI and the low signal-to-noise ratio at the b-values needed to effectively probe the kurtosis regime. Recently introduced fast DKI techniques reduce the challenge of DKI in the body by decreasing the data requirement substantially, so that, for example, triggering and breath-hold techniques may be applied for the entire DKI acquisition without causing unfeasible scan times. One common pathological condition for which body DKI may be of immediate clinical value is kidney fibrosis, which causes progressive changes in organ microstructure. With its sensitivity to microstructure, DKI is an obvious candidate for a non-invasive evaluation method. We present preclinical evidence indicating that the rapidly obtainable tensor-derived mean kurtosis ( W̅) distinguishes moderately fibrotic kidneys from healthy controls. The presence and degree of fibrosis are confirmed by histology, which also indicates fibrosis as the main driver behind the DKI differences observed between groups. We therefore conclude that fast kurtosis is a likely candidate for an MRI-based method for the detection and monitoring of renal fibrosis. We provide protocol recommendations for fast renal DKI in humans based on a b-value optimisation performed using data acquired at 3 T in normal human kidney.

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.

TGF-β1/Smads and miR-21 in Renal Fibrosis and Inflammation

Renal fibrosis, irrespective of its etiology, is a final common stage of almost all chronic kidney diseases. Increased apoptosis, epithelial-to-mesenchymal transition, and inflammatory cell infiltration characterize the injured kidney. On the molecular level, transforming growth factor-β1 (TGF-β1)-Smad3 signaling pathway plays a central role in fibrotic kidney disease. Recent findings indicate the prominent role of microRNAs, small noncoding RNA molecules that inhibit gene expression through the posttranscriptional repression of their target mRNAs, in different pathologic conditions, including renal pathophysiology. miR-21 was also shown to play a dynamic role in inflammatory responses and in accelerating injury responses to promote organ failure and fibrosis. Understanding the cellular and molecular bases of miR-21 involvement in the pathogenesis of kidney diseases, including inflammatory reaction, could be crucial for their early diagnosis. Moreover, the possibility of influencing miR-21 level by specific antagomirs may be considered as an approach for treatment of renal diseases.

Renal PET-imaging with (11)C-metformin in a transgenic mouse model for chronic kidney disease

Background

Organic cation transporters (OCTs) in the renal proximal tubule are important for the excretion of both exo- and endogenous compounds, and chronic kidney disease (CKD) alter the expression of OCT. Metformin is a well-known substrate for OCT, and recently, we demonstrated that positron emission tomography (PET) with 11C-labelled metformin (¹¹C-metformin) is a promising approach to evaluate the function of OCT. The aim of this study is therefore to examine renal pharmacokinetics of ¹¹C-metformin and expression of OCTs in a transgenic (RenTGF-β1) mouse model of CKD.

Methods

Age- and sex-matched RenTGF-β1 (Tg) and wildtype (WT) mice were used (5–8/group). Animals received an iv bolus of ¹¹C-metformin followed by 90-min dynamic PET and MRI scan. PET data were analysed using a one-tissue compartment model. Renal protein abundance of OCT2 (by Western blot) as well as OCT1, OCT2, and MATE1 messenger RNA (mRNA) (by RT-PCR) was examined.

Results

Protein expression of the basolateral uptake transporter OCT2 was 1.5-fold lower in Tg mice compared to WT mice while OCT1 and MATE1 mRNA expression did not differ between the two groups. The influx rate constant of ¹¹C-metformin in renal cortex (K₁) was 2.2-fold lower in transgenic mice whereas the backflux rate constant (k₂) was similar in the two groups, consistent with protein expression. Total body clearance (TBC) correlated within each group linearly with K₁.

Conclusions

In conclusion, this study demonstrates that both renal OCT2 expression and ¹¹C-metformin uptake are reduced in CKD mice. This potentially makes ¹¹C-metformin valuable as a PET probe to evaluate kidney function.

Restoration of Haemoglobin Level Using Hydrodynamic Gene Therapy with Erythropoietin Does Not Alleviate the Disease Progression in an Anaemic Mouse Model for TGFβ1-Induced Chronic Kidney Disease

Erythropoietin, Epo, is a 30.4 kDa glycoprotein hormone produced primarily by the fetal liver and the adult kidney. Epo exerts its haematopoietic effects by stimulating the proliferation and differentiation of erythrocytes with subsequent improved tissue oxygenation. Epo receptors are furthermore expressed in non-haematopoietic tissue and today, Epo is recognised as a cytokine with many pleiotropic effects. We hypothesize that hydrodynamic gene therapy with Epo can restore haemoglobin levels in anaemic transgenic mice and that this will attenuate the extracellular matrix accumulation in the kidneys. The experiment is conducted by hydrodynamic gene transfer of a plasmid encoding murine Epo in a transgenic mouse model that overexpresses TGF-β1 locally in the kidneys. This model develops anaemia due to chronic kidney disease characterised by thickening of the glomerular basement membrane, deposition of mesangial matrix and mild interstitial fibrosis. A group of age matched wildtype littermates are treated accordingly. After a single hydrodynamic administration of plasmid DNA containing murine EPO gene, sustained high haemoglobin levels are observed in both transgenic and wildtype mice from 7.5 ± 0.6 mmol/L to 9.4 ± 1.2 mmol/L and 10.7 ± 0.3 mmol/L to 15.5 ± 0.5 mmol/L, respectively. We did not observe any effects in the thickness of glomerular or tubular basement membrane, on the expression of different collagen types in the kidneys or in kidney function after prolonged treatment with Epo. Thus, Epo treatment in this model of chronic kidney disease normalises haemoglobin levels but has no effect on kidney fibrosis or function.

ShenKang injection suppresses kidney fibrosis and oxidative stress via transforming growth factor-β/Smad3 signalling pathway in vivo and in vitro

Objectives

The purpose of this study is to investigate the antifibrosis and antioxidation of ShenKang injection (SKI) in vivo and in vitro and to evaluate potential mechanisms involved in the treatment of chronic kidney disease (CKD).

Methods

In experimental animal studies, CKD was established by 5/6 nephrectomy (5/6Nx). Serum creatinine (Scr) and blood urea nitrogen (BUN) were determined. Histopathological tests were performed by H&E and Masson trichrome stained. The protein expressions of fibronectin (FN), collagen Ι, α-smooth muscle actin (α-SMA) and transforming growth factor-β (TGF-β) and phosphorylation of Smad3 were measured in 5/6Nx rats. In Human kidney proximal tubular cell line (HK-2) cells, the effects of TGF-β/Smad3 signalling pathway on renal fibrosis and oxidative injury were examined.

Key findings

5/6Nx induced severe renal damages. Treatment of rats with SKI markedly reduced levels of Scr and BUN, alleviated expression of fibrosis-associated signalling molecules and reduced expression of TGF-β and phosphorylated Smad3. Meanwhile, in HK-2 cells, after exposure to TGF-β and H2O2, the protein expression of renal fibrosis was significantly increased. The generation of oxidative stress was also elevated. The severity of fibrosis and oxidative damage appears to be reduced after treatment with SKI.

Conclusion

SKI inhibits renal fibrosis and oxidative stress through downregulation of TGF-β/Smad3 signalling pathway.

Ozone oxidative preconditioning inhibits renal fibrosis induced by ischemia and reperfusion injury in rats

Ischemia and reperfusion injury (IRI) is a crucial contributor to the development of renal fibrosis. Ozone has been proposed as a novel medical therapy for various conditions, including organ IRI. The aim of this study was to investigate whether ozone oxidative preconditioning (OzoneOP) has a beneficial effect in preventing the development of renal fibrosis following IRI. Sprague Dawley rats were subjected to 45 min of ischemia followed by 8 weeks of reperfusion. Prior to surgery, rats in the OzoneOP group were treated with ozone and those in the IRI and Sham groups were untreated. Blood samples were collected for the detection of blood urea nitrogen (BUN) and creatinine (Cr) levels. To assess tissue fibrosis, Masson’s trichrome staining was performed. Immunohistochemistry was also performed to determine the localization of α-smooth muscle actin (α-SMA). Reverse transcription quantitative polymerase chain reaction (RT-qPCR) and western blotting were conducted to analyze the expression of transforming growth factor (TGF)-β1, α-SMA and Smad7. The levels of BUN and Cr did not significantly differ between groups. Rats pretreated with ozone showed markedly less interstitial fibrosis than untreated rats following IRI. In addition, immunohistochemistry revealed that α-SMA expression was attenuated in the OzoneOP group compared with the IRI group. RT-qPCR and western blot analysis showed that OzoneOP inhibited the IRI-induced increases in α-SMA and TGF-β1 expression levels, and that the IRI-induced reduction in the expression of Smad7 was inhibited in the OzoneOP group. The results indicate that OzoneOP has beneficial effects on ischemic renal fibrosis. OzoneOP may exert its protective effects by a mechanism involving modulation of the TGF-β1/Smad7 pathway.