mRNA expression of glomerular basement membrane proteins and TGF-beta1 in human membranous nephropathy

Podocyte Pathogenic Bone Morphogenetic Protein-2 Pathway and Immune Cell Behaviors in Primary Membranous Nephropathy

Primary membranous nephropathy (PMN) is one of the leading causes of end-stage renal disease, and the most frequent cause of massive proteinuria in nondiabetic adults, resulting in fatal complications. However, the underlying pathomechanisms of PMN remain largely unclear. Here, single-cell RNA sequencing is employed to analyze kidney biopsies from eleven PMN patients and seven healthy subjects. Profiling 44 060 cells from patients allowed us to characterize the cellular composition and cell-type-specific gene expression in the PMN kidney. The complement-induced BMP2/pSMAD1/COL4 pathway is identified as the pathogenic pathway in podocytes, bridging two key events, i.e., complement system activation and glomerular basement membrane thickening in PMN. Augmented infiltration and activation of myeloid leukocytes and B lymphocytes are found, profiling delicate crosstalk of immune cells in PMN kidneys. Overall, these results provide valuable insights into the roles of podocytes and immune cells in PMN, and comprehensive resources toward the complete understanding of PMN pathophysiology.

Protease-activated receptors in kidney diseases: A comprehensive review of pathological roles, therapeutic outcomes and challenges

Studies have demonstrated that protease-activated receptors (PARs) with four subtypes (PAR1-4) are mainly expressed in the renal epithelial, endothelial, and podocyte cells. Some endogenous and urinary proteases, namely thrombin, trypsin, urokinase, and kallikrein released during diseased conditions, are responsible for activating different subtypes of PARs. Each PAR receptor subtype is involved in kidney disease of distinct aetiology. PAR1 and PAR2 have shown differential therapeutic outcomes in rodent models of type-1 and type-2 diabetic kidney diseases due to the distinct etiological basis of each disease type, however such findings need to be confirmed in other diabetic renal injury models. PAR1 and PAR2 blockers have been observed to abolish drug-induced nephrotoxicity in rodents by suppressing tubular inflammation and fibrosis and preventing mitochondrial dysfunction. Notably, PAR2 inhibition improved autophagy and prevented fibrosis, inflammation, and remodeling in the urethral obstruction model. Only the PAR1/4 subtypes have emerged as a therapeutic target for treating experimentally induced nephrotic syndrome, where their respective antibodies attenuated the podocyte apoptosis induced upon thrombin activation. Strikingly PAR2 and PAR4 subtypes involvement has been tested in sepsis-induced acute kidney injury (AKI) and renal ischemia-reperfusion injury models. Thus, more studies are required to delineate the role of other subtypes in the sepsis-AKI model. Evidence suggests that PARs regulate oxidative, inflammatory stress, immune cell activation, fibrosis, autophagic flux, and apoptosis during kidney diseases.

Markers of renal fibrosis: How do they correlate with podocyte damage in glomerular diseases?

BACKGROUND

Renal fibrosis is the result of the interaction of cellular and molecular pathways, which is induced by sustained glomerular injury and involves the podocytes and multiple profibrotic factors. In this study, we investigated the correlation of the mRNA expression of podocyte proteins and profibrotic factors with renal fibrosis measured in renal biopsies of patients with primary and secondary glomerulopathies.

METHODS

Eighty-four adult patients with primary or secondary glomerular diseases and 12 controls were included. Demographic and clinical data were collected. Seventy-two percent of the renal biopsies were done less than one year from clinical disease manifestation. The quantification of the podocyte-associated mRNAs of alpha-actinin-4, podocin, and podocalyxin, as well as of the profibrotic factors TGF-β1, CTGF, and VEGF-A were quantified by real-time polymerase chain reaction. The percent positive area of renal fibrosis was measured by immunohistochemistry staining, using anti-CTGF and anti-HHF35 antibodies and unpolarized Sirius Red. Correlations between the expression of tissue mRNAs and the positive area of fibrosis for the measured markers were made by Spearman's rank correlation coefficient.

RESULTS

In relation to control biopsies, podocyte-specific proteins were downregulated in podocytopathies, in proliferative nephritis, in diabetic kidney disease (DRD), and in IgA nephropathy (IgAN). Messenger RNA of TGF-β1, CTGF, and VEGF-A was upregulated in patients with podocytopathies and in DRD but not in proliferative nephritis and IgAN. Tissue mRNA expression of TGF-β1, CTGF, and VEGF-A were strongly correlated with renal fibrosis, as measured by HHF35; however, the correlation, albeit significant, was moderate for Sirius Red and weak for CTGF. The percent positive area of renal fibrosis measured by Sirius Red was similar between podocytopathies and DRD and significantly higher in podocytopathies compared to IgAN or proliferative nephritis.

CONCLUSIONS

In patients with glomerular diseases, the mRNA of TGF-β1, CTGF, and VEGF-A correlated positively with the extent of renal fibrosis, and the positive area of fibrosis was larger in the podocytopathies and in DRD as measured by Sirius Red. The pathways connecting podocyte damage and activation of profibrotic factors to kidney tissue fibrosis need to be better investigated.

Impact of long-term high-fat diet intake gestational protein-restricted offspring on kidney morphology and function

Emerging evidence highlights the far-reaching consequences of high-fat diet (HFD) and obesity on kidney morphological and functional disorders. In the present study, we aim to evaluate the effects of early HFD intake on renal function and morphology in maternal protein-restricted offspring (LP). LP and normal protein-intake offspring (NP) were fed HFD (LPH and NPH, respectively) or standard rodent (LPN and NPN) diet from the 8th to 13th week of age. Blood pressure, kidney function, immunohistochemistry and scanning electron microscopy were analyzed. Increased total cholesterol and low-density lipoprotein serum levels were observed in LPH offspring. The adiposity index was reduced in the (LPN) group and, conversely, increased in the NPH and LPH groups. Blood pressure was higher beyond the 10th week of age in the LPH group compared with the other groups. Decreased urinary sodium excretion was observed in LP offspring, whereas the HFD-treated groups presented a decreased urine pH in a time-dependent fashion. The LPN, NPH and LPH groups showed increased expression of type 1 angiotensin II (AngII) receptor (AT1R), TGF-β1, collagen and fibronectin in the kidneys. Moreover, the adult fetal-programmed offspring showed pronounced effacement of the podocyte foot process associated with the rupture of cell membranes and striking urinary protein excretion, exacerbated by HFD treatment. To the best of our knowledge, this is the first study demonstrating that young fetal-programmed offspring submitted to long-term HFD intake have increased susceptibility to renal structural and functional disorders associated with an accentuated stage of fibrosis and tubular dysfunction.

Podocytes regulate the glomerular basement membrane protein nephronectin by means of miR-378a-3p in glomerular diseases

The pathophysiology of many proteinuric kidney diseases is poorly understood, and microRNAs (miRs) regulation of these diseases has been largely unexplored. Here, we tested whether miR-378a-3p is a novel regulator of glomerular diseases. MiR-378a-3p has two predicted targets relevant to glomerular function, the glomerular basement membrane matrix component, nephronectin (NPNT), and vascular endothelial growth factor VEGF-A. In zebrafish (Danio rerio), miR-378a-3p mimic injection or npnt knockdown by a morpholino oligomer caused an identical phenotype consisting of edema, proteinuria, podocyte effacement, and widening of the glomerular basement membrane in the lamina rara interna. Zebrafish vegf-A protein could not rescue this phenotype. However, mouse Npnt constructs containing a mutated 3'UTR region prevented the phenotype caused by miR-378a-3p mimic injection. Overexpression of miR-378a-3p in mice confirmed glomerular dysfunction in a mammalian model. Biopsies from patients with focal segmental glomerulosclerosis and membranous nephropathy had increased miR-378a-3p expression and reduced glomerular levels of NPNT. Thus, miR-378a-3p-mediated suppression of the glomerular matrix protein NPNT is a novel mechanism for proteinuria development in active glomerular diseases.

TGF-β: the connecting link between nephropathy and fibrosis

Renal fibrosis is the usual outcome of an excessive accumulation of extracellular matrix (ECM) that frequently occurs in membranous and diabetic nephropathy. The result of renal fibrosis would be end-stage renal failure, which requires costly dialysis or kidney transplantation. Renal fibrosis typically results from chronic inflammation via production of several molecules, such as growth factors, angiogenic factors, fibrogenic cytokines, and proteinase. All of these factors can stimulate excessive accumulation of ECM components through epithelial to mesenchymal transition (EMT), which results in renal fibrosis. Among these, transforming growth factor-beta (TGF-β) is proposed to be the major regulator in inducing EMT. Besides ECM protein synthesis, TGF-β is involved in hypertrophy, proliferation, and apoptosis in renal cells. In particular, TGF-β is likely to be most potent and ubiquitous profibrotic factor acting through several intracellular signaling pathways including protein kinases and transcription factors. Factors that regulate TGF-β expression in renal cell include hyperglycemia, angiotensin II, advance glycation end products, complement activation (C5b-9), and oxidative stress. Over the past several years, the common understanding of the pathogenic factors that lead to renal fibrosis in nephropathy has improved considerably. This review will discuss the recent findings on the mechanisms and role of TGF-β in membranous and diabetic nephropathy.

Involvement of renal corpuscle microRNA expression on epithelial-to-mesenchymal transition in maternal low protein diet in adult programmed rats

Prior study shows that maternal protein-restricted (LP) 16-wk-old offspring have pronounced reduction of nephron number and arterial hypertension associated with unchanged glomerular filtration rate, besides enhanced glomerular area, which may be related to glomerular hyperfiltration/overflow and which accounts for the glomerular filtration barrier breakdown and early glomerulosclerosis. In the current study, LP rats showed heavy proteinuria associated with podocyte simplification and foot process effacement. TGF-β1 glomerular expression was significantly enhanced in LP. Isolated LP glomeruli show a reduced level of miR-200a, miR-141, miR-429 and ZEB2 mRNA and upregulated collagen 1α1/2 mRNA expression. By western blot analyzes of whole kidney tissue, we found significant reduction of both podocin and nephrin and enhanced expression of mesenchymal protein markers such as desmin, collagen type I and fibronectin. From our present knowledge, these are the first data showing renal miRNA modulation in the protein restriction model of fetal programming. The fetal-programmed adult offspring showed pronounced structural glomerular disorders with an accentuated and advanced stage of fibrosis, which led us to state that the glomerular miR-200 family would be downregulated by TGF-β1 action inducing ZEB 2 expression that may subsequently cause glomeruli epithelial-to-mesenchymal transition.

Gα12 activation in podocytes leads to cumulative changes in glomerular collagen expression, proteinuria and glomerulosclerosis

Glomerulosclerosis is a common pathological finding that often progresses to renal failure. The mechanisms of chronic kidney disease progression are not well defined, but may include activation of numerous vasoactive and inflammatory pathways. We hypothesized that podocytes are susceptible to filtered plasma components, including hormones and growth factors that stimulate signaling pathways leading to glomerulosclerosis. Gα12 couples to numerous G-protein-coupled receptors (GPCRs) and regulates multiple epithelial responses, including proliferation, apoptosis, permeability and the actin cytoskeleton. Herein, we report that genetic activation of Gα12 in podocytes leads to time-dependent increases in proteinuria and glomerulosclerosis. To mimic activation of Gα12 pathways, constitutively active Gα12 (QL) was conditionally expressed in podocytes using Nphs2-Cre and LacZ/floxed QLα12 transgenic mice. Some QLα12(LacZ+/Cre+) mice developed proteinuria at 4-6 months, and most were proteinuric by 12 months. Proteinuria increased with age, and by 12-14 months, many demonstrated glomerulosclerosis with ultrastructural changes, including foot process fusion and both mesangial and subendothelial deposits. QLα12(LacZ+/Cre+) mice showed no changes in podocyte number, apoptosis, proliferation or Rho/Src activation. Real-time PCR revealed no significant changes in Nphs1, Nphs2, Cd2ap or Trpc6 expression, but Col4a2 message was increased in younger and older mice, while Col4a5 was decreased in older mice. Confocal microscopy revealed disordered collagen IVα1/2 staining in older mice and loss of α5 without changes in other collagen IV subunits. Taken together, these studies suggest that Gα12 activation promotes glomerular injury without podocyte depletion through a novel mechanism regulating collagen (α)IV expression, and supports the notion that glomerular damage may accrue through persistent GPCR activation in podocytes.

Mechanisms and consequences of TGF-ß overexpression by podocytes in progressive podocyte disease

In patients with progressive podocyte disease, such as focal segmental glomerulosclerosis (FSGS) and membranous nephropathy, upregulation of transforming growth factor-ß (TGF-ß) is observed in podocytes. Mechanical pressure or biomechanical strain in podocytopathies may cause overexpression of TGF-ß and angiotensin II (Ang II). Oxidative stress induced by Ang II may activate the latent TGF-ß, which then activates Smads and Ras/extracellular signal-regulated kinase (ERK) signaling pathways in podocytes. Enhanced TGF-ß activity in podocytes may lead to thickening of the glomerular basement membrane (GBM) by overproduction of GBM proteins and impaired GBM degradation in podocyte disease. It may also lead to podocyte apoptosis and detachment from the GBM, and epithelial-mesenchymal transition (EMT) of podocytes, initiating the development of glomerulosclerosis. Furthermore, activated TGF-ß/Smad signaling by podocytes may induce connective tissue growth factor and vascular endothelial growth factor overexpression, which could act as a paracrine effector mechanism on mesangial cells to stimulate mesangial matrix synthesis. In proliferative podocytopathies, such as cellular or collapsing FSGS, TGF-ß-induced ERK activation may play a role in podocyte proliferation, possibly via TGF-ß-induced EMT of podocytes. Collectively, these data bring new mechanistic insights into our understanding of the TGF-ß overexpression by podocytes in progressive podocyte disease.

TGF-β1 induces podocyte injury through Smad3-ERK-NF-κB pathway and Fyn-dependent TRPC6 phosphorylation

TGF-β1 plays an important role on podocyte injury and glomerular diseases, while the underlying molecular mechanisms are still elusive. Here, the potential role of the ion channel TRPC6 and the proximal signaling was explored in TGF-β1-treated mouse podocyte. Our results showed that TGF-β1 significantly increased podocyte apoptosis and induced obvious disorganization of actin filaments in a time-dependent pattern. In TGF-β1-treated podocyte, TRPC6 protein, especially the phosphorylated TRPC6, and the cytosolic free Ca(2+) level upregulated, which was evidently inhibited by the specific knockdown of TRPC6. TRPC6 knockdown also alleviated TGF-β1-induced podocyte apoptosis. Moreover, the Src kinase Fyn increased obviously in TGF-β1-treated podocyte, displaying increment of the active form pY418 and reduction of the inactive form pY530. Immunoprecipitation assay revealed that Fyn interacts with TRPC6 in podocyte. Notably, Fyn knockdown blocked TRPC6 phosphorylation and intracellular Ca(2+) increment following TGF-β1 stimulation, but not affect the expression of TRPC6 protein. In addition, Western blot showed that TGF-β1 induced significant activation of p-Smad3, p-ERK and RelA/p65. Importantly, obvious translocation of ERK and RelA/p65 to nuclei was observed in TGF-β1-treated podocyte, which was reduced by ERK inhibitor U0126. Both U0126 and NF-κB inhibitor PDTC obviously inhibited the increment of TRPC6 protein and the flux of cytosolic free Ca(2+) induced by TGF-β1. Together, we provide evidences that TGF-β1 induces podocyte damage by upregulating TRPC6 protein most possibly through Smad3-ERK-NF-κB pathway, in which Fyn-dependent tyrosine phosphorylation of TRPC6 might exert a crucial role on the activation of its channel function.

Limitation of podocyte proliferation improves renal function in experimental crescentic glomerulonephritis

BACKGROUND

Many forms of glomerular diseases are characterized by injury to the glomerular visceral epithelial cell, or podocyte, which usually results in depletion of podocyte number. However, in diseases where podocyte proliferation occurs there is a rapid decline in renal function. The consequences of inhibiting podocyte proliferation on renal function have not been fully established. At the level of the cell cycle, cyclin-dependent kinase 2 (CDK2) is required for proliferation.

METHODS

To determine if decreasing podocyte proliferation improves renal function, CDK2 activity was reduced with the purine analogue roscovitine in mice with antibody-induced experimental glomerulonephritis. Nephritic animals given vehicle, dimethyl sulfoxide (DMSO), served as control. Blood urea nitrogen (BUN), proteinuria, and renal histology were assessed at days 5 and 14 of disease.

RESULTS

Inhibiting CDK2 activity resulted in a marked decrease in glomerular DNA synthesis [5-bromo-2'-deoxyridine (BrdU) staining] in Roscovitine-treated animals at day 5 of nephritis (P < 0.05 versus control). This was associated with a significant decrease in BUN and glomerulosclerosis at day 14 (P < 0.01 versus control) and a decrease in the accumulation of the extracellular matrix protein laminin (P < 0.01 versus control).

CONCLUSION

Inhibiting podocyte proliferation in experimental glomerulonephritis is associated with improvement in renal function and histology, suggesting that inhibiting CDK2 activity is a potential therapeutic target for glomerular diseases characterized by podocyte proliferation.

Activation of the TGF-beta/Smad signaling pathway in focal segmental glomerulosclerosis

BACKGROUND

Although the pathogenetic relevance of transforming growth factor-beta (TGF-beta) to glomerulosclerosis is well established, it is not known whether a signal transduction cascade of TGF-beta is involved in the development of focal segmental glomerulosclerosis (FSGS), nor is it clear how TGF-beta 1 is activated during the course of FSGS formation.

METHODS

We examined the expression patterns of TGF-beta 1, thrombospondin-1 (TSP-1), TGF-beta type II receptor (TGF-beta IIR), phosphorylated Smad2/Smad3, and podocyte-specific epitopes [Wilms' tumor protein-1 (WT-1) and glomerular epithelial protein-1 (GLEPP-1)] in 15 renal biopsy specimens with idiopathic FSGS and six renal biopsies with no detectable abnormalities by means of immunohistochemistry. The mRNA expression patterns of TGF-beta 1, TGF-beta IIR, and TSP-1 were further evaluated by in situ hybridization in seven biopsies.

RESULTS

In the controls, immunostaining for TGF-beta 1, TSP-1, TGF-beta IIR, and phosphorylated Smad2/Smad3 was almost negligible, but an apparent signal for TGF-beta 1, TSP-1, and TGF-beta IIR mRNAs was observed in the visceral glomerular epithelial cells (GEC). In the cases of FSGS, the expression levels of TGF-beta 1, TSP-1, and TGF-betaIIR proteins and mRNAs and phosphorylated Smad2/Smad3 were significantly increased, particularly in the GEC of the sclerotic segments, wherein WT-1 and GLEPP-1 were not detected.

CONCLUSION

These results suggest that damage to podocyes may stimulate TGF-beta 1, TSP-1, and TGF-beta IIR expression in GEC, thereby activating the Smad signaling pathway and, in so doing, leading to overproduction of the extracellular matrix (ECM). Thus, a signal transduction cascade of the TGF-beta/Smad signaling pathway, which is activated in the GEC, appears to be involved in the development of FSGS.

Differential expression of nephrin in acquired human proteinuric diseases

BACKGROUND

The slit-diaphragm protein nephrin is an essential component of the glomerular filtration barrier. It is not clear whether renal injury in patients with acquired proteinuric diseases is associated with altered regulation of the nephrin gene or protein.

METHODS

We examined expression patterns of nephrin protein and messenger RNA (mRNA) in renal biopsy specimens from patients with minimal lesion (n = 7), focal segmental glomerulosclerosis (FSGS; n = 14), or membranous nephropathy (MN; n = 7) and controls (n = 8) by immunohistochemistry, immunoelectron microscopy, in situ hybridization, and polymerase chain reaction (PCR) amplification of nephrin complementary DNA.

RESULTS

In normal kidney, nephrin staining showed a diffuse interrupted linear pattern along the glomerular basement membrane (GBM). Nephrin staining in minimal lesion specimens showed a finely granular pattern along the GBM and was positive in cell bodies of visceral glomerular epithelial cells. Nephrin staining was most disrupted in FSGS specimens. Immunoelectron microscopy showed that nephrin-specific gold particles were almost absent in effaced foot processes in proteinuric patients. An in situ hybridization study showed significantly decreased nephrin mRNA-expressing cells in cases of FSGS and MN compared with controls. Reverse-transcription PCR showed significantly lower levels of nephrin mRNA in cases of FSGS and MN than controls, but no significant difference between minimal lesion cases and controls. Relative levels of glomerular nephrin mRNA correlated inversely with percentage of glomeruli with sclerosis in proteinuric diseases.

CONCLUSION

These results suggest that nephrin-expression patterns in proteinuric diseases are different according to the specific glomerular disease or severity of glomerular damage.

Expression of intercellular adhesion molecule-1 and vascular cell adhesion molecule-1 in human crescentic glomerulonephritis

AIMS

In glomerulonephritis, intercellular adhesion molecule-1 (ICAM-1) and vascular cell adhesion molecule-1 (VCAM-1) may play important roles in the formation of crescents. These studies are designed to evaluate the expression patterns of ICAM-1 and VCAM-1 in human crescentic glomerulonephritis and to determine the cellular origin of adhesion molecules in the crescentic lesions.

METHODS AND RESULTS

We examined the expression of ICAM-1 and VCAM-1 proteins in renal biopsies with cellular (n=7), fibrocellular (n=9) or fibrous (n=4) crescentic glomerulonephritis, and six controls by immunohistochemistry. mRNA expression of ICAM-1 and VCAM-1 was further evaluated by RNA in-situ hybridization. Cytokeratin or CD68 immunohistochemistry was performed on the same sections, where in-situ hybridization had been carried out. In cellular crescents, ICAM-1 and VCAM-1 proteins were over-expressed to a similar extent. Of the three types of crescents, the extent of ICAM-1 immunopositivity was the greatest in the cellular crescents and decreased towards the fibrous crescents (P < 0.05). Yet the extent of VCAM-1 immunoreactivity was not different between the types. Fibrous crescents still contained some epithelial cells and showed only VCAM-1 expression. In the glomeruli with cellular or fibrocellular crescents, the extent of ICAM-1 immunopositivity in the glomerular tufts was significantly larger than that of VCAM-1 (P < 0.05). In an in-situ hybridization study, the mRNA expression patterns of ICAM-1 and VCAM-1 paralleled their protein expressions. A double-labelling study showed that the signal for ICAM-1 and VCAM-1 mRNAs was mainly present in cytokeratin-positive and CD68-negative cells in the crescentic lesions.

CONCLUSIONS

These results suggest that glomerular parietal epithelial cells in cellular crescents up-regulate both ICAM-1 and VCAM-1, and that some epithelial cells retained in fibrous crescents persistently over-express VCAM-1, but not ICAM-1. They also suggest that ICAM-1 is involved in early leucocyte recruitment into glomeruli in crescentic glomerulonephritis.

mRNA expression of intercellular adhesion molecule-1 and vascular cell adhesion molecule-1 in acute renal allograft rejection

BACKGROUND

The intercellular adhesion molecule-1 (ICAM-1) and the vascular cell adhesion molecule-1 (VCAM-1) show a form of complementary distribution in normal and grafted kidneys. The molecular mechanism by which ICAM-1 and VCAM-1 are increased or induced on vascular cells during acute renal allograft rejection has not been clearly defined.

METHODS

We examined ICAM-1 and VCAM-1 mRNA expression in 17 renal allograft biopsies with (n=12) and without (n=5) features of acute rejection, and four control renal biopsies with no detectable abnormalities by RNA in situ hybridization. The expression of ICAM-1 and VCAM-1 protein was also assessed by immunohistochemical staining of frozen sections.

RESULTS

In controls and nonrejecting graft biopsies, the signals of the ICAM-1 and VCAM-1 transcripts in vascular cells were almost negligible. Specific signals of ICAM-1 and VCAM-1 mRNAs were detected on the endothelial cells of small muscular arteries in most cases with acute renal allograft rejection. The messages for ICAM-1 and VCAM-1 were also detected on arterial smooth muscle cells in all the five cases with severe type III rejection.

CONCLUSIONS

These results suggest that the induced appearance of ICAM-1 and VCAM-1 on the vascular cells of acutely rejecting renal transplants was related to actual cellular synthesis and that both adhesion molecules could act together in the rejection process. They also suggest that the expression of ICAM-1 and VCAM-1 genes by arterial smooth muscle cells may be an important cause of transmural arteritis in severe acute renal allograft rejection.