Cloning of rodent megsin revealed its up-regulation in mesangioproliferative nephritis

SERPINB7 Expression Predicts Poor Pancreatic Cancer Survival Upon Gemcitabine Treatment

Stratification of patients with pancreatic ductal adenocarcinoma (PDAC) remains a key challenge in the field of clinical oncology. No predictive biomarkers have yet been found for any available treatment options. Previously, we identified SERPINB7 as a putative biomarker for PDAC and thus, herein, we aimed to validate our previous findings and assessed the predictive value of SERPINB7. Patients who underwent surgery and received gemcitabine (gem) or gemcitabine plus nab-paclitaxel (gem/nab) as adjuvant therapy, between 2011 and 2017, were included in this study (n = 57). Expression level of SERPINB7 was assessed in tumor tissue by immunohistochemistry (IHC) and RNA in situ hybridization (RNA ISH). Its association with disease-free survival (DFS) and overall survival (OS) was investigated. While IHC did not show any correlation between survival and the protein level of SERPINB7, RNA ISH revealed that expression of SERPINB7 was associated with a poor DFS (P = .01) and OS (P = .002) in the gem group but not in the gem/nab. Adjusted Cox-regression analysis confirmed the independent predictive value of SERPINB7 on OS (P = .006, HR: 3.47; 95% CI: 1.49–8.09) in the gem group. In conclusion, SERPINB7 was identified as the first predictive RNA biomarker for PDAC. This study suggests that patients who expressed SERPINB7 might receive another treatment than gem alone.

Association of Megsin Gene Variants With IgA Nephropathy in Northwest Chinese Population: A STROBE-Compliant Observational Study

Megsin is a mesangial cell-predominant gene that encodes a serpin family protein which is expressed in the renal mesangium. Overexpression of megsin has been observed in the glomeruli of patients with IgA nephropathy (IgAN). The aim of this study was to evaluate the association of megsin polymorphisms (rs1055901 and rs1055902) with IgAN in a Chinese population.We examined 351 patients with histologically proven IgAN and compared them with 310 age, sex, and ethnicity-matched healthy subjects. Two single nucleotide polymorphisms (SNPs) in megsin were genotyped by Sequenom MassARRAY. SPSS 18.0 was used for statistical analyses, and SNP Stats to test for associations between these polymorphisms and IgAN risk. Odds ratios with 95% confidence intervals were used to assess the relationships.We found that rs1055901 and rs1055902 SNPs were not correlated with susceptibility to IgAN in Northwest Chinese population. Analyses of the relationship between genotypes and clinical variables indicated that in patients with IgAN, rs1055901 was associated with 24-hour proteinuria, an increase in blood pressure, and Lee's grade (P = 0.04, 0.02, and 0.04, respectively), and rs1055902 was associated with 24-hour proteinuria and Lee's grade (P = 0.03 and 0.01, respectively). However, the results showed no association between these gene variants and sex of the patients.These results indicate that megsin gene variants may play a role in the severity, development, and/or progression of IgAN in Northwest Chinese population.

Association of megsin 2093C/T, 2180C/T and C25663G gene polymorphism with the risk of IgA nephropathy

The association between megsin 2093C/T, 2180C/T and C25663G gene polymorphisms and IgA nephropathy (IgAN) risk remains unclear. We aimed to evaluate the association between megsin 2093C/T, 2180C/T and C25663G gene polymorphisms and IgAN risk by performing a meta-analysis. Eligible studies were searched according to predefined criteria by using electronic databases. Six articles were identified for the analysis of the association between megsin 2093C/T, 2180C/T and C25663G gene polymorphisms and IgAN risk. 2093C/T C allele was associated with IgAN risk in overall populations and Asians (overall populations: p = 0.014, Asians: p = 0.037). 2093C/T CC/TT genotype was not associated with IgAN risk in overall populations, Caucasians and Asians. 2180C/T C allele was correlated with IgAN risk in Caucasians (p = 0.024). 2180C/T CC/TT genotype was not associated with IgAN risk in overall populations, Caucasians and Asians. C25663G gene polymorphism was not associated with IgAN onset in Asians. In conclusion, megsin 2093C/T C allele may be genetic marker for IgAN susceptibility in overall populations and Asians. 2180C/T C allele may be risk factor for IgAN onset in Caucasians. However, more studies should be performed in the future.

Megsin gene: its genomic analysis, pathobiological functions, and therapeutic perspectives

It is critical to uncover genes specifically expressed in individual cell types for further understanding of cell biology and pathology. In order to elucidate pathogenesis of renal disease, we performed functional quantitative analysis of the genome in human kidney cells and compared the expression levels of a variety of kidney transcripts with those in other non-kidney cells. As a result, we identified a novel human gene, megsin, which is a new serine protease inhibitor (serpin) predominantly expressed in the kidney. Megsin is up-regulated in kidney disease. Genomic analysis revealed an association of the polymorphisms of megsin gene with susceptibility and/or progression of kidney disease. Its overexpression in rodents has led to the recognition of two different kidney abnormalities. The first disorder is linked to megsin biological effect itself and the other to its conformational abnormality recently called the serpinopathy. In the latter model, the cellular and tissue damage is induced by the endoplasmic reticulum (ER) stress due to conformational disorder resulting from megsin tertiary structure. In both types, the inhibition of megsin's activity or abnormal conformational change should open new therapeutic perspectives. The desire to prevent these abnormalities with the hope to offer new therapeutic strategies has stimulated the development of megsin inhibitors by a structure based drug design approach relying on a precisely known three dimensional megsin structure.

Estrogen-induced uterine abnormalities in TIMP-1 deficient mice are associated with elevated plasmin activity and reduced expression of the novel uterine plasmin protease inhibitor serpinb7

Tissue inhibitor of metalloproteinase-1 (TIMP-1) is a multifunctional protein capable of regulating a variety of biological processes in a wide array of tissue and cell types. We have previously demonstrated that TIMP-1 deficient mice exhibit alterations in normal uterine morphology and physiology. Most notably, absence of TIMP-1 is associated with an altered uterine phenotype characterized by profound branching of the uterine lumen and altered adenogenesis. To begin to assess the mechanism by which TIMP-1 may control these uterine events, we utilized steroid-treated ovariectomized wild-type and TIMP-1 null mice exposed to estrogen for 72 hr. Administration of estrogen to TIMP-1 deficient mice resulted in development of an abnormal uterine histo-architecture characterized by increased endometrial gland density, luminal epithelial cell height, and abnormal lumen structure. To determine the mediators which may contribute to the abnormal uterine morphology in the TIMP-1 deficient mice, cDNA microarray analysis was performed. Analysis revealed that expression of two plasmin inhibitors (serpbinb2 and serbinb7) was significantly reduced in the TIMP-1 null mice. Associated with the reduction in expression of these inhibitors was a significant increase in plasmin activity. Localization of the novel uterine serpinb7 revealed that expression was confined to the luminal and glandular epithelial cells. Further, expression of uterine serpinb7 was decreased by estrogen and showed an inverse relationship with plasmin activity. We conclude from these studies that in addition to controlling MMP activity, TIMP-1 may also control activity of serine proteases through modulation of serine protease inhibitors such as serpinb7.

The role of megsin, a serine protease inhibitor, in diabetic mesangial matrix accumulation

In diabetic nephropathy decreased activities of matrix metalloproteinase (MMP)-2, MMP-9 and plasmin contribute to mesangial matrix accumulation. Megsin, a novel member of the serine protease inhibitor superfamily, is predominantly expressed in mesangial cells and is up-regulated in diabetic nephropathy and its overexpression spontaneously induces progressive mesangial expansion in mice. High-glucose stimulated megsin mRNA expression in an in vivo model of type II diabetic nephropathy as well as in vitro in cultured mesangial cells. Megsin potentially inhibits total enzymatic activities of MMP-2 and -9 and plasmin, indicating decreased degradation of mesangial matrix. A specific monoclonal anti-megsin neutralizing antibody restored MMP activity in a transforming growth factor-beta independent manner. Our study suggests that the mesangial matrix accumulation caused by hyperglycemia in diabetes might be due at least in part to up-regulation of megsin which can inhibit plasmin and MMP activities.

A severe diabetic nephropathy model with early development of nodule-like lesions induced by megsin overexpression in RAGE/iNOS transgenic mice

Many factors are involved in the pathogenesis of diabetic nephropathy. A single gene abnormality may be prerequisite but insufficient to the disease to manifest. It is therefore only when a second or sometimes a third damage is associated that the consequences of pathogenic phenotypes become evident. We generated the triple transgenic mice overexpressing megsin (a novel glomerular-specific serpin), a receptor for advanced glycation end products (RAGE), and inducible nitric oxide synthase (iNOS). Compared with the single- or two-gene transgenic mice, the triple transgenic mice developed, at an early age (16 weeks), severe albuminuria and renal damage with all of the characteristics of human diabetic nephropathy (i.e., glomerular hypertrophy, diffuse mesangial expansion, inflammatory cell infiltration, and interstitial fibrosis). Interestingly, 30-40% of glomeruli exhibit nodule-like lesions. Oxidative and carbonyl stress makers (pentosidine, N(epsilon)-carboxymethyllysine, and 8-hydroxy-deoxyguanosine) were significantly higher in the triple transgenic mice. The iNOS transgenic mice have a diabetes phenotype, the renal consequences of which are moot, and the superimposition of RAGE leads to more conspicuous manifestations. By additional overexpression of megsin, a gene known to be involved in mesangial proliferation and expansion, these local consequences become dramatically manifest and approximate those observed in human pathology. This multiple hit approach is of interest in consideration of the sequential events during development of diabetic nephropathy.

Synergistic Contributions of Carbonyl Stress and Megsin in Diabetic Nephropathy

Diabetic nephropathy is the most common cause of end-stage renal failure. The primary glomerular changes in diabetic nephropathy are diffuse and nodular glomerulosclerosis, manifested by an increase in mesangial matrix. Research has demonstrated that advanced glycation end products (AGEs), oxidative stress, and carbonyl stress might play a crucial role in the pathogenesis of diabetic nephropathy via multiple mechanisms. AGEs augment extracellular matrix synthesis, contribute to the release of proinflammatory cytokines and expression of growth factors and adhesion molecules, and interact with the renin-angiotensin system. Megsin is a novel serine protease inhibitor predominantly expressed in mesanguim. Megsin is upregulated in kidney samples of patients with diabetic nephropathy. Transgenic mice overexpressing megsin spontaneously develop kidney disease characterized by mesangial injury. Megsin is likely to contribute to mesangial injury in the process of diabetic nephropathy. Lack of appropriate animal models has hampered understanding the pathogenesis of diabetic nephropathy and development of effective therapies. Megsin and AGEs are suitable targets for new drugs of diabetic nephropathy and for the development of appropriate animal models of diabetic nephropathy.

Involvement of endoplasmic reticulum (ER) stress in podocyte injury induced by excessive protein accumulation

BACKGROUND

An imbalance between protein load and folding capacity is referred to as endoplasmic reticulum (ER) stress. As a defense mechanism, cells express ER stress inducible chaperons, such as oxygen-regulated proteins 150 (ORP150) and glucose-regulated proteins (GRPs). While ER stress is important in various diseases, a pathophysiologic role for ER stress in kidney disease remains elusive. Here we investigate expression of ER stress proteins in cultured rat podocytes as well as in our recently developed animal model of abnormal protein retention within the ER of podocytes (i.e., megsin transgenic rat).

METHODS

The expression of ER stress inducible proteins (ORP150, GRP78, or GRP94) in cultured podocytes treated with tunicamycin, A23187, SNAP, hypoxia, or hyperglycemia, and the renal tissues or isolated glomeruli from megsin transgenic rats was analyzed by Western blotting analysis, immunohistochemistry, or confocal microscopy.

RESULTS

Cultured podocytes demonstrated that treatment with tunicamycin, A23187, and SNAP, but not hypoxia or hyperglycemia, up-regulate expression of ER stress proteins. Extracts of isolated glomeruli from megsin transgenic rats reveal marked up-regulation of ER stress chaperones in podocytes, which was supported by immunohistochemical analysis. Confocal microscopy revealed that ER stress in podocytes was associated with cellular injury. Podocytes of transgenic rats overexpressing a mutant megsin, without the capacity for polymerization within the ER, do not exhibit ER stress or podocyte damage, suggesting a pathogenic role of ER retention of polymerized megsin.

CONCLUSION

This paper implicates a crucial role for the accumulation of excessive proteins in the podocyte ER in the induction of ER stress and associated podocyte injury.

Accelerated Glomerular Injury in Hemi-Nephrectomized Transgenic Mice of Mesangial Cell-Predominant Serpin, Megsin

Mesangial cells play a critical role in the maintenance of normal glomerular functions such as matrix remodeling and immune complex disposal. We recently identified a novel human mesangium-predominant gene, megsin, which is a new member of the serine protease inhibitor (serpin) superfamily. While our previous studies demonstrated progressive mesangial matrix expansion and an increase in the number of mesangial cells in megsin transgenic mice, it took 40 weeks to develop these manifestations. Here we performed hemi-nephrectomy to accelerate glomerular injury in megsin transgenic mice. Hemi-nephrectomized transgenic mice developed focal segmental mesangial expansion, which was associated with proteinuria. Megsin has thus a biologically relevant influence on the development of glomerular damage. The hemi-nephrectomized model of this transgenic mouse might serve as a tool to investigate the mechanisms of glomerular disease.

Novel insights into renal fibrosis

PURPOSE OF REVIEW

Renal fibrosis characterizes a common endpoint of diverse renal diseases which leads to functional impairment ultimately resulting in terminal renal failure.

RECENT FINDINGS

Recent advances in this field led to the discovery of several novel mediators as well as novel aspects of known mediators. Studies on the origin and role of specific renal cell types involved in renal fibrosis identified bone marrow derived mesangial progenitors and offered substantial evidence for the concept of epithelial to mesenchymal transition. Much progress has also been made in better understanding of the interactions between different mediators and between mediators and renal target cells. Compounds designed on the basis of this current knowledge have proven to be potent inhibitors of the development of renal fibrosis or might even induce resolution of renal fibrosis.

SUMMARY

The number and diversity of recent studies in this field offer hope for new treatment regimes in our clinical efforts towards prevention and regression of progressive fibrosing renal diseases.

Transcriptional regulation of a mesangium-predominant gene, megsin

The cDNA of a new human mesangium-predominant gene, megsin, a novel member of the serpin superfamily, has recently been cloned. This study investigates the regulatory mechanisms of megsin gene expression. A genomic clone of the human megsin gene was obtained by screening bacterial artificial chromosome (BAC) library with the megsin cDNA. The analysis for exon-intron junctions of megsin genomic DNA demonstrated that the gene contained 8 exons and 7 introns, spanned 20 kbp, and that the genomic structure of the serpin superfamily was highly conserved. Fluorescence in situ hybridization (FISH) revealed that the megsin gene is localized in chromosome 18q21.3, close to the other serpin genes. The transcriptional start site, located by primer extension analysis, was 391 bp upstream from the start codon. The sequence and reporter analyses on 4021-bp-long 5'-flanking region of megsin gene demonstrated a consensus promoter segment within this region and a relatively strong promoter activity in human mesangial cells and A431, a human tumor cell line recently reported to express a novel serpin identical with megsin. Moreover, this study utilized site-directed and deletion mutagenesis analyses, and electrophoretic mobility shift assay identified one positive regulatory motif, an incomplete activator protein-1 (AP-1) binding motif (CTGATTCAC) within the -120 to -112 region. This cis-acting element in the 5'-flanking region of megsin is involved in the activation of the megsin gene in mesangial cells.

Overexpression of the serpin megsin induces progressive mesangial cell proliferation and expansion

Mesangial cells maintain normal glomerular function by mediating ECM remodeling and immune complex disposal. We have recently identified megsin, a novel member of the serine protease inhibitor (serpin) superfamily predominantly expressed in the mesangium. While our previous studies suggested a role for megsin in the pathogenesis of human glomerular diseases, its exact biological significance remained unknown. Here we produced two lines of megsin transgenic mice. Overexpression of megsin led to progressive mesangial matrix expansion and an increase in the number of mesangial cells. These glomerular lesions were accompanied by an augmented immune complex deposition, together with Ig's and complement. Binding and functional assays in vitro identified plasmin as one biological substrate of megsin and confirmed its activity as a proteinase inhibitor. Transgenic animals exhibiting nephritis as a result of treatment with anti--glomerular basement membrane antiserum showed significantly more persistent expansion of the mesangial ECM than was seen in parental mice. Megsin therefore exerts a biologically relevant influence on mesangial function, and on the mesangial microenvironment, such that simple overexpression of this endogenous serpin engenders elementary mesangial lesions.

Cloning and characterization of a novel subunit of protein serine/threonine phosphatase 4 from mesangial cells

Mesangial cells play an important role in maintaining glomeruli structure and function and in the pathogenesis of glomerular diseases. With a novel approach using a rapid large-scale DNA sequencing strategy and computerized data processing, a new human gene, PP4(Rmeg) was cloned. The full-length cDNA clone of human PP4(Rmeg) coded for a novel 950-amino acid protein, which was similar to a subunit of protein serine/threonine phosphatase 4 (PP4). Recombinant PP4(Rmeg) produced in COS-7 cells bound to the catalytic subunit of PP4. PP4(Rmeg) is therefore structurally and functionally related to the recently reported regulatory subunit of PP4, PP4(R1). Amino acid sequence analysis of rat PP4(Rmeg) homologue revealed that the sequences were well conserved between human and rat (86.3% identity). Northern blot analyses of human tissues and cultured cells demonstrated that the regulatory subunits were expressed abundantly in human cultured mesangial cells, although their expression was relatively ubiquitous. In situ hybridization studies in normal human renal tissues confirmed their expression in glomeruli in vivo. The expression was upregulated in glomeruli of anti-Thy1 glomerulonephritis rats before mesangial proliferation. These data demonstrate that PP4(Rmeg) is a novel regulatory subunit of PP4, which is expressed ubiquitously but abundantly in mesangial cells. Its pathophysiologic role in mesangial cells and glomerulus remains unknown. As PP4 is an essential protein for nucleation, growth, and stabilization of microtubules at centrosomes/spindle pole bodies during cell division, PP4(Rmeg) may play a role in regulation of mitosis in mesangial cells.