Fibronectin accumulation in glomerulosclerotic lesions: self-assembly sites and the heparin II binding domain

Clinicopathological factors for tubulointerstitial injury in lupus nephritis

OBJECTIVE

To investigate the incidence of tubulointerstitial injury in lupus nephritis (LN) and to examine clinicopathological factors that could indicate the presence of tubulointerstitial injury.

METHODS

This study included 98 patients with LN. Clinical data and the pathological results of the initial renal biopsy were collected.

RESULTS

The frequency of each tubulointerstitial injury parameter was over 50%, except for the interstitial edema, in the 98 patients investigated in this study. The most frequently detected tubulointerstitial injury parameter was tubular atrophy in this study. Neutrophil infiltration/karyorrhexis, wire loop lesion, and arteriosclerosis were observed frequently in patients with tubulointerstitial injuries. High serum creatinine and blood urea nitrogen (BUN) were observed more frequently in patients with tubulointerstitial injuries except tubular degeneration. The multivariable regression analysis showed a relationship between neutrophil infiltration/karyorrhexis and interstitial fibrosis/tubular degeneration, a relationship between wire loop lesion and tubulointerstitial inflammation/edema, and a relationship between arteriosclerosis and tubulointerstitial injuries (except interstitial edema). Patients with tubular degeneration had lower D-Dimer levels compared with those without. Patients with interstitial fibrosis had higher blood leukocyte counts than those without. The rate of low response to therapy was 13% among those without tubulointerstitial inflammation, but 35% in those with interstitial inflammation (P = 0.03).

CONCLUSION

Acute and chronic renal tubulointerstitial lesions are often found along with glomerular and vascular lesions. Immune and vascular factors are probably involved in tubulointerstitial injuries. Tubulointerstitial inflammation may be the initiator of chronic renal injury and may predict response to therapy.Key Points•To provide a theoretical basis for tubulointerstitial injury in LN.

The Structure of the Periostin Gene, Its Transcriptional Control and Alternative Splicing, and Protein Expression

Although many studies have described the role of periostin in various diseases, the functions of periostin derived from alternative splicing and proteinase cleavage at its C-terminus remain unknown. Further experiments investigating the periostin structures that are relevant to diseases are essential for an in-depth understanding of their functions, which would accelerate their clinical applications by establishing new approaches for curing intractable diseases. Furthermore, this understanding would enhance our knowledge of novel functions of periostin related to stemness and response to mechanical stress .

Treatment with lecinoxoids attenuates focal and segmental glomerulosclerosis development in nephrectomized rats

Focal segmental glomerulosclerosis (FSGS) is a scarring process associated with chronic low‐grade inflammation ascribed to toll‐like receptor (TLR) activation and monocyte migration. We developed synthetic, small‐molecule lecinoxoids, VB‐201 and VB‐703, that differentially inhibit TLR‐2‐ and TLR‐4‐mediated activation and monocyte migration. The efficacy of anti‐inflammatory lecinoxoid treatment on FSGS development was explored using a 5/6 nephrectomy rat model. Five‐sixths of nephrectomized rats were treated with lecinoxoids VB‐201, VB‐703 or PBS, for 7 weeks. Upon sacrifice, albumin/creatinine ratio, glomerulosclerosis, fibrosis‐related gene expression and the number of glomerular and interstitial monocyte were evaluated. Treatment of nephrectomized rats with lecinoxoids ameliorated glomerulosclerosis. The percentage of damaged glomeruli, glomerular sclerosis and glomeruli fibrotic score was significantly reduced following VB‐201 and VB‐703 treatment. VB‐703 attenuated the expression of fibrosis hallmark genes collagen, fibronectin (FN) and transforming growth factor β (TGF‐β) in kidneys and improved albumin/creatinine ratio with higher efficacy than did VB‐201, but only VB‐201 significantly reduced the number of glomerular and interstitial monocytes. These results indicate that treatment with TLR‐2, and more prominently, TLR‐4 antagonizing lecinoxioids, is sufficient to significantly inhibit FSGS. Moreover, inhibiting monocyte migration can also contribute to treatment of FSGS. Our data demonstrate that targeting TLR‐2‐TLR‐4 and/or monocyte migration directly affects the priming phase of fibrosis and may consequently perturb disease parthogenesis.

Introductory review: periostin-gene and protein structure

Although many studies have described the role of periostin in various diseases, the function of the periostin protein structures derived from alternative splicing and proteinase cleavage at the C-terminal remain unknown. Further experiments revealing the protein structures that are highly related to diseases are essential to understand the function of periostin in depth, which would accelerate its clinical application by establishing new approaches for curing intractable diseases. Furthermore, this understanding would enhance our knowledge of novel functions of periostin related to stemness and response to mechanical stress.

Molecular and Immunological Basis of Tubulo-Interstitial Injury in Lupus Nephritis: a Comprehensive Review

Lupus nephritis is an important cause of kidney failure in patients of Asian, African, or Hispanic descent. Its etiology and pathogenesis are multifactorial and remain to be elucidated. Accumulating evidence suggests that anti-double-stranded DNA (dsDNA) antibodies play a critical role in the pathogenesis, through its direct binding to cross-reactive antigens on resident renal cells or indirect binding through chromatin material to extracellular matrix components, resulting in complement activation, cell activation and proliferation, and induction of inflammatory and fibrotic processes. While tubulo-interstitial damage portends poor long-term renal prognosis, the mechanisms leading to tubulo-interstitial injury in lupus nephritis has received relatively less attention to date. Immune deposition along the tubular basement membrane is often observed in lupus nephritis and correlates with tubulo-interstitial infiltration of immune cells and interstitial fibrosis. Anti-dsDNA antibodies bind to resident renal cells, including proximal renal tubular epithelial cells, and contribute to renal inflammation and fibrosis. There is emerging evidence that epigenetic influence such as DNA methylation, histone modification, and microRNAs (miRs) also contribute to kidney fibrosis. Overexpression of miR-150 is observed in renal biopsies from patients with lupus nephritis and correlates with kidney fibrosis and chronicity score. Mycophenolate mofetil (MMF) is an established and effective standard-of-care therapy for patients with lupus nephritis. Accumulating data suggest that in addition to its immunosuppressive actions on lymphocyte proliferation, mycophenolic acid (MPA), the active metabolite of MMF, can exert a direct effect on nonimmune cells. Mediators of inflammation and fibrosis induced by anti-dsDNA antibodies in cultured proximal renal tubular epithelial cells are ameliorated by the addition of MPA, suggesting that in addition to its immunosuppressive actions, MPA may also have a beneficial effect in improving tubulo-interstitial inflammation and fibrosis through its direct action on proximal renal tubular epithelial cells.

MRT letter: application of novel "in vivo cryotechnique" in living animal kidneys

AIM

To compare the influence of different fixation procedures on morphologic studies in living mice, and to identify the advantages of the "in vivo cryotechnique" (IVCT).

METHODS

We prepared mouse kidneys using four different fixation methods: conventional immersion-fixation, quick-freezing following resection of the kidney, quick-freezing following perfusion-fixation, and IVCT.

RESULTS

Kidney glomeruli were noticeably contracted after conventional immersion-fixation or quick-freezing following resection compared to glomeruli from tissues preserved by the IVCT. With the IVCT, both albumin and IgG were colocalized exclusively along or within the glomerular capillary loops; however, immunoreactivity of these proteins in the other three methods was clearly detected in the Bowman's space and apical cytoplasm of the proximal tubules. With the IVCT, immunoreactivity of collagen type IV was very weak at the glomerular basement membrane (GBM) until microwave treatment, which increased its immunoreactivity. In contrast, the immunoreactivity was clearly detected at the GBM with or without microwave treatment with quick-freezing following perfusion-fixation. With quick-freezing following perfusion-fixation, aquaporin-1 (AQP-1) was irregularly distributed in a disorganized manner on the brush border and apical cell membrane along the proximal tubules. But AQP-1 was labeled intensely and regularly along the brush border and apical cell membrane andonly weakly along the basolateral membrane of the proximal tubules with the IVCT.

CONCLUSION

The IVCT may reliably maintain soluble serum proteins and renal intrinsic proteins such as AQP-1 in situ and capture transient structures and functional changes in vivo.

Application of periodic acid-Schiff fluorescence emission for immunohistochemistry of living mouse renal glomeruli by an "in vivo cryotechnique"

To identify the distribution of endogenous serum proteins in living mouse renal glomeruli under various hemodynamic conditions, we used the periodic acid-Schiff (PAS) and its fluorescence emission as a marker for the glomerular basement membrane (GBM). The immunostaining for collagen type IV was hardly observed without microwave treatment in specimens prepared by an "in vivo cryotechnique". However, PAS staining and its fluorescence emission could be clearly visualized at the GBM with the "in vivo cryotechnique". Under normotensive conditions, immunoreaction products of albumin and immunoglobulin G heavy and light chains (IgG(H+L)) were localized within glomerular capillary loops (GCL) but not colocalized with the PAS fluorescence emission of the GBM. Under heart-arrest conditions and with quick-freezing of resected tissues, albumin, IgG (H+L), immunoglobulin kappa light chain, and IgG1 heavy chain (IgG1) were immunolocalized within the GCL and mesangial areas, but only albumin and the kappa light chain were additionally immunolocalized in Bowman's space, indicating their passage through the GBM. Under acute hypertensive conditions, both albumin and the kappa light chain, but not IgG1, were clearly immunolocalized along the GBM and in the Bowman's space, indicating their increased passage through the GBM. The overlapping areas of PAS fluorescence emission and the albumin or kappa light chain appeared to be larger with quick-freezing and under the heart arrest or acute hypertensive conditions than under normal circulation, whereas those of PAS emission and IgG1 did not differ among these conditions. The serum proteins passing through the GBM were clearly visualized with the "in vivo cryotechnique", immunofluorescence staining, and PAS fluorescence emission.

Transactivation of the Epidermal Growth Factor Receptor by Angiotensin II in Glomerular Podocytes

BACKGROUND/AIMS

Activation of angiotensin II (ANG2) receptors stimulates extracellular signal-regulated kinases (ERKs) that, in some cell systems, are mediated by transactivating the epidermal growth factor (EGF) receptor (EGFR) through mechanisms involving matrix metalloprotease (MMP)-stimulated processing of heparin-binding EGF (HB-EGF) from its precursor.

METHODS

The signaling pathways linked to ANG2-dependent ERK activation were determined in an immortalized mouse podocyte cell line by monitoring ANG2-stimulated phosphorylation of ERK1/2.

RESULTS

ANG2 induced transient ERK phosphorylation that was maximal at 5 min and then rapidly dissipated. ANG2-dependent ERK activation was inhibited by: (1) the type-1 ANG2-selective antagonist losartan; (2) the type-2 ANG2-selective antagonist PD123319; (3) an inhibitor of MMP2/9; (4) the EGFR kinase inhibitor AG1478, and (5) the HB-EGF antagonists CRM197 and heparin. ANG2-dependent ERK activation was mediated by both protein kinase C (PKC)- and calcium-dependent mechanisms and was associated with tyrosine phosphorylation of EGFR. To determine if ANG2-dependent HB-EGF release could act in a paracrine fashion on adjacent cells, HEK293 cells were stably transfected with green fluorescent protein-tagged ERK2 (GFP-ERK2). In stably transfected HEK293 cells, EGF stimulated phosphorylation of endogenous ERK1/2 as well as GFP-ERK2. In contrast, ANG2 had no effect on ERK phosphorylation in stably transfected HEK293 cells. When podocytes were co-cultured with stably transfected HEK293 cells, however, treatment with ANG2 rapidly stimulated GFP-ERK2 phosphorylation. Both the MMP2/9 inhibitor and AG1478 attenuated ANG2-dependent phosphorylation of GFP-ERK2 in the co-culture system.

CONCLUSIONS

These data indicate that ERK activation is induced by ANG2 in podocytes by mechanisms involving ANG2-dependent release of HB-EGF which, in turn, may act in an autocrine and paracrine fashion to stimulate ERK activity.

Low molecular weight heparin in the treatment of puromycin-induced nephrosis

Heparin may have a beneficial effect in proteinuric renal diseases, where negative charges of the glomerular capillary membrane are compromised. We evaluated the role of low molecular weight heparin (LMWH - 3000 Da) in puromycin aminonucleoside (PAN)-induced focal and segmental glomerulosclerosis in male Wistar rats: Controls (C) n=7, LMWH-treated group, n=9, subcutaneously (SC), 6 mg/kg every day. The PAN group (n=7) received 7 doses on weeks 0, 1, 2, 4, 6, 8, 10 (SC - 2mg/100g), and a group PAN+LMWH (n=6). After 12 weeks, cholesterol and triglycerides were higher in nephrotic groups, as well as proteinuria and urinary IgG. Kidney weight, glomerular volume, and glomerular sclerosis index were higher in the PAN-treated groups. Glomerular capillary length density (L(Vcap)) and glomerular capillary surface density (S(Vcap)) were lower in the PAN group, and mesangial fractional volume was higher. Fibronectin immunostaining was more intense in the PAN group, and collagens I and III were absent in the studied glomeruli. Thus, LMWH prevented mesangial expansion and capillaries changes, showing antiproliferative properties, despite worsening glomerular permeability changes in the PAN model. In conclusion, LMWH interferes in the complications of PAN model, but not through inhibition of the proteinuria.

Uniform overexpression and rapid accessibility of alpha5beta1 integrin on blood vessels in tumors

Integrin alpha5beta1 is among the proteins overexpressed on tumor vessels and is a potential target for diagnostics and therapeutics. Here, we mapped the distribution of alpha5beta1 integrin in three murine tumor models and identified sites of expression that are rapidly accessible to intravascular antibodies. When examined by conventional immunohistochemistry, alpha5beta1 integrin expression was strong on most blood vessels in RIP-Tag2 transgenic mouse tumors, adenomatous polyposis coli (apc) mouse adenomas, and implanted MCa-IV mammary carcinomas. Expression increased during malignant progression in RIP-Tag2 mice. However, immunoreactivity was also strong in normal pancreatic ducts, intestinal smooth muscle, and several other sites. To determine which sites of expression were rapidly accessible from the bloodstream, we intravenously injected anti-alpha5beta1 integrin antibody and 10 minutes to 24 hours later examined the amount and distribution of labeling. The injected antibody strongly labeled tumor vessels at all time points but did not label most normal blood vessels or gain access to pancreatic ducts or intestinal smooth muscle. Intense vascular labeling by anti-alpha5beta1 integrin antibody co-localized with the uniform CD31 immunoreactivity of tumor vessels and contrasted sharply with the patchy accumulation of nonspecific IgG at sites of leakage. This strategy of injecting antibodies revealed the uniform overexpression and rapid accessibility of alpha5beta1 integrin on tumor vessels and may prove useful in assessing other potential therapeutic targets in cancer.

Insights into the mechanisms of renal fibrosis: is it possible to achieve regression?

Recent evidence suggests that the progression of renal fibrosis is a reversible process, at least in experimental models. The present review summarizes the new insights concerning the mechanisms of progression and regression of renal disease and examines this novel evidence under the light of feasibility and transfer to human nephropathies. The involved mechanisms are discussed with particular emphasis on the fibrotic role of vasoactive peptides such as angiotensin II and endothelin and growth factors such as transforming growth factor (TGF)-beta. The possibility of regression is introduced by presenting the in vivo efficiency of antihypertensive treatments and of systems that antagonize the fibrogenic action of TGF-beta such as bone morphogenic protein-7 and HGF. Finally, we provide a brief description of the promising future directions and clinical considerations about the applications of the experimental data to humans.

Alternatively spliced isoforms of fibronectin in immune-mediated glomerulosclerosis: the role of TGF? and IL-4

Fibronectin (FN) is the main extracellular matrix component in glomerulosclerotic lesions. There are different FN isoforms that result from alternative splicing at the EDA and EDB regions of FN mRNA. Increased inclusion of EDA and EDB, which can be elicited by TGFbeta, may be conducive to the development of glomerulosclerosis (GS). TGFbeta and IL-4 have previously been shown to play a role in the development of GS. In this study, the mRNA splicing patterns for EDA+ and EDB+ fibronectin were investigated in vivo in various experimental sclerotic glomerulopathies, in vitro in rat mesangial cells (MC) that were stimulated by TGFbeta or transfected with IL-4, and in human kidney biopsies with GS from patients with various kidney diseases. Analysis of glomerular FN mRNA demonstrated inclusion of both ED regions in rats with anti-Thy1 nephritis or chronic serum sickness and in mice with anti-GBM glomerulonephritis. Inclusion of both the EDA and EDB regions was associated with glomerular TGFbeta expression. In contrast, in mice with Th2-mediated graft-versus-host disease, a model for lupus nephritis, the FN transcripts included neither the EDA nor the EDB region, and renal TGFbeta expression was absent. Compared to normal MCs in culture, MCs transfected with IL-4 produced lower amounts of FN and demonstrated less EDA inclusion, while MC that had been treated with TGFbeta showed increased production of FN and more EDA inclusion. Renal biopsies from patients with renal diseases, except those taken from patients with lupus nephritis, showed higher TGFbeta levels, higher FN levels, and more EDA inclusion than controls. TGFbeta may be a key player in the development of GS by inducing local FN production and alternative splicing of FN mRNA. In lupus glomerulonephritis, in which the involvement of TGFbeta in GS is less prominent, Th2 cytokines such as IL-4 probably account for increased intrarenal collagen synthesis and subsequent FN accumulation from the circulation. In conclusion, neither alternative FN splicing, nor a high transcription level of TGFbeta, appears to be a general prerequisite for the development of GS.