Decorin, biglycan and their endocytosis receptor in rat renal cortex

Molecular cues for immune cells from small leucine-rich repeat proteoglycans in their extracellular matrix-associated and free forms

In this review we highlight emerging immune regulatory functions of lumican, keratocan, fibromodulin, biglycan and decorin, which are members of the small leucine-rich proteoglycans (SLRP) of the extracellular matrix (ECM). These SLRPs have been studied extensively as collagen-fibril regulatory structural components of the skin, cornea, bone and cartilage in homeostasis. However, SLRPs released from a remodeling ECM, or synthesized by activated fibroblasts and immune cells contribute to an ECM-free pool in tissues and circulation, that may have a significant, but poorly understood foot print in inflammation and disease. Their molecular interactions and the signaling networks they influence also require investigations. Here we present studies on the leucine-rich repeat (LRR) motifs of SLRP core proteins, their evolutionary and functional relationships with other LRR pathogen recognition receptors, such as the toll-like receptors (TLRs) to bring some molecular clarity in the immune regulatory functions of SLRPs. We discuss molecular interactions of fragments and intact SLRPs, and how some of these interactions are likely modulated by glycosaminoglycan side chains. We integrate findings on molecular interactions of these SLRPs together with what is known about their presence in circulation and lymph nodes (LN), which are important sites of immune cell regulation. Recent bulk and single cell RNA sequencing studies have identified subsets of stromal reticular cells that express these SLRPs within LNs. An understanding of the cellular source, molecular interactions and signaling consequences will lead to a fundamental understanding of how SLRPs modulate immune responses, and to therapeutic tools based on these SLRPs in the future.

Osteoglycin: An ECM Factor Regulating Fibrosis and Tumorigenesis

The extracellular matrix (ECM) is made up of noncellular components that have special properties for influencing cell behavior and tissue structure. Small leucine-rich proteoglycans (SLRPs) are nonfibrillar ECM components that serve as structural scaffolds and signaling molecules. osteoglycin (OGN), a class III SLRP, is a ubiquitous ECM component that not only helps to organize the extracellular matrix but also regulates a number of important biological processes. As a glycosylated protein in the ECM, OGN was originally considered to be involved in fiber assembly and was reported to have a connection with fibrosis. In addition to these functions, OGN is found in a variety of cancer tissues and is implicated in cellular processes linked to tumorigenesis, including cell proliferation, invasion, metastasis, and epithelial-mesenchymal transition (EMT). In this review, we summarize the structure and functions of OGN as well as its biological and clinical importance in the context of fibrotic illness and tumorigenesis. This review aims to improve our understanding of OGN and provide some new strategies for the treatment of fibrosis and cancer.

Biglycan expression and its function in human ligamentum flavum

Hypertrophy of the ligamentum flavum (LF) is a major cause of lumbar spinal stenosis (LSS), and the pathology involves disruption of elastic fibers, fibrosis with increased cellularity and collagens, and/or calcification. Previous studies have implicated the increased expression of the proteoglycan family in hypertrophied LF. Furthermore, the gene expression profile in a rabbit experimental model of LF hypertrophy revealed that biglycan (BGN) is upregulated in hypertrophied LF by mechanical stress. However, the expression and function of BGN in human LF has not been well elucidated. To investigate the involvement of BGN in the pathomechanism of human ligamentum hypertrophy, first we confirmed increased expression of BGN by immunohistochemistry in the extracellular matrix of hypertrophied LF of LSS patients compared to LF without hypertrophy. Experiments using primary cell cultures revealed that BGN promoted cell proliferation. Furthermore, BGN induces changes in cell morphology and promotes myofibroblastic differentiation and cell migration. These effects are observed for both cells from hypertrophied and non-hypertrophied LF. The present study revealed hyper-expression of BGN in hypertrophied LF and function of increased proteoglycan in LF cells. BGN may play a crucial role in the pathophysiology of LF hypertrophy through cell proliferation, myofibroblastic differentiation, and cell migration.

Mechanism of Chronic Kidney Disease Progression and Novel Biomarkers: A Metabolomic Analysis of Experimental Glomerulonephritis

While a complex network of cellular and molecular events is known to be involved in the pathophysiological mechanism of chronic kidney disease (CKD), the divergence point between reversal and progression and the event that triggers CKD progression are still unknown. To understand the different mechanisms between reversible and irreversible kidney disease and to search for urinary biomarkers that can predict prognosis, a metabolomic analysis was applied to compare acute and chronic experimental glomerulonephritis (GN) models. Four metabolites, namely, epoxyoctadecenoic acid (EpOME), epoxyeicosatetraenoic acid (EpETE), α-linolenic acid (ALA), and hydroxyretinoic acid, were identified as predictive markers after comparing the chronic nephritis model with acute nephritis and control groups (false discovery rate adjusted p-value (q-value) < 0.05). Renal mRNA expression of cytochrome P450 and epoxide hydrolase was also identified as being involved in the production of epoxide metabolites from these polyunsaturated fatty acids (p < 0.05). These results suggested that the progression of chronic kidney disease is associated with abnormally activated epoxide hydrolase, leading to an increase in EpOME and EpETE as pro-inflammatory eicosanoids.

Catabolism of Newly Synthesized Decorin in vitro by Human Peritoneal Mesothelial Cells

Objective

Previous studies have shown that decorin and biglycan account for over 70% of the proteoglycans (PGs) synthesized by human peritoneal mesothelial cells (HPMCs). Since these PGs are involved in the control of cell growth, cell differentiation, and matrix assembly, we investigated their turnover in cultured HPMCs.

Methods

Confluent HPMCs were metabolically labeled with [35S]-sulfate and the labeled products isolated from the cell medium and the cell layer characterized by sensitivity to bacterial eliminases. Experiments were undertaken with exogenous labeled decorin, and its metabolic state was studied.

Results

In a 24-hour labeling period, 75% of the newly synthesized chondroitin sulfate/dermatan sulfate (CS/DS) PGs appeared in the culture medium, the majority of which (90%) was decorin. In the cell layer, protein-free glycosaminoglycan (GAG) chains accounted for 21% of the total CS/DS at 24 hours and exhibited constant specific activity at 12 – 16 hours. The latter material was turned over with a half-life of approximately 2.5 hours. Exogenous decorin underwent receptor-mediated endocytosis and subsequent intracellular degradation. Uptake but not degradation could be inhibited by heparin.

Conclusions

HPMCs are distinguished by a rapid turnover of decorin. A characteristic metabolic feature is the existence of a large intracellular pool of protein-free DS-GAGs. Understanding the control of decorin turnover in HPMCs might lead to delineation of its potential role in both the physiology and pathophysiology of the membrane in PD patients.

TGF-β1 inhibits the autophagy of podocytes by activating mTORC1 in IgA nephropathy

IgA nephropathy (IgAN) is a mesangial proliferative glomerulonephritis which often shows proteinuria, an indicator for podocyte damage. TGF-β1 has been known to contribute to podocyte injury by inducing apoptosis, cytoskeleton relocation or cytoskeleton loss. And Decorin, a small proteoglycan known to neutralize TGF-β1, was reported to induce autophagy in vascular endothelial cells. However, it remains unknown how TGF-β1 and Decorin can affect podocyte autophagy in mesangial proliferative glomerulonephritis. In this study, we used in vivo and in vitro models to find out the effect of TGF-β1 and Decorin on podocyte autophagy. P-rpS6 and p-ULK1 were detected by Western blot to show the activation of mTORC1 pathway following TGF-β1 treatment. Also, we collected serum from IgAN patients and anti-Thy1.1 nephritis, and quantified TGF-β1 and Decorin using ELISA. Together, we showed that TGF-β1 could activate mTORC1 and inhibit autophagy, while Decorin has precisely the opposite effect. As the mesangial cells (MCs) proliferate, TGF-β1 increases and Decorin decreases in the serum of IgAN and anti-Thy1.1 nephritis. This finding deepened our understanding regarding how MC proliferation could finally result in podocyte dysfunction.

Tumor-specific inhibitory action of decorin on different hepatoma cell lines

BACKGROUND

In spite of therapeutic approaches, liver cancer is still one of the deadliest type of tumor in which tumor microenvironment may play an active role in the outcome of the disease. Decorin, a small leucine-rich proteoglycan is not only responsible for assembly and maintenance of the integrity of the extracellular matrix, but a natural inhibitor of cell surface receptors, thus it exerts antitumorigenic effects. Here we addressed the question whether this effect of decorin is independent of the tumor phenotypes including differentiation, proliferation and invasion.

METHOD

Four hepatoma cell lines HepG2, Hep3B, HuH7 and HLE, possessing different molecular backgrounds, were selected to investigate. After proliferation tests, pRTK arrays, WB analyses, and immunofluorescent examinations were performed on decorin treated and control cells for comparison.

RESULTS

Significant growth inhibitory potential of decorin on three out of four hepatoma cell lines was proven, however the mode of its action was different. Induction of p21^WAF1/CIP1, increased inactivation of c-myc and β-catenin, and decrease of EGFR, GSK3β and ERK1/2 phosphorylation levels were observed in HepG2 cells, pathways already well-described in literature. However, in the p53 deficient Hep3B and HuH7, InsR and IGF-1R were the main receptors transmitting signals. In harmony with its receptor status, Hep3B cells displayed high level of activated AKT. As the cell line is retinoblastoma mutant, ATR/Chk1/Wee1 system might hinder the cell cycle in G2/M phase via phosphorylation of CDK1. In Huh7 cells, all RTKs were inhibited by decorin followed by downregulation of AKT. Furthermore, HuH7 cell line responded with concentration-dependent ERK activation and increased phospho-c-myc level. Decorin had only a non-significant effect on the proliferation rate of HLE cell line. However, it responded with a significant decrease of pAKT, c-myc and β-catenin activity. In this special cell line, the inhibition of TGFβ may be the first step of the protective effect of decorin.

CONCLUSIONS

Based on our results decorin may be a candidate therapeutic agent in the battle against liver cancer, but several questions need to be answered. It is certain that decorin is capable to exert its suppressor effect in hepatoma cells without respect to their phenotype and molecular background.

Small leucine rich proteoglycans in host immunity and renal diseases

The small leucine rich proteoglycans (SLRPs), structurally consisting of protein cores and various glycosaminoglycan side chains, are grouped into five classes based on common structural and functional properties. Besides being an important structural component of extracellular matrix (ECM), SLRPs have been implicated in the complex network of signal transduction and host immune responses. The focus of this review is on SLRPs in host immunity. Because host immunity plays an important part in the pathogenesis of renal diseases, the role of SLRPs in this set of diseases will also be discussed.

WW and C2 domain-containing proteins regulate hepatic cell differentiation and tumorigenesis through the hippo signaling pathway

The Hippo pathway regulates cell differentiation, proliferation, and apoptosis. Upon activation, it inhibits the import of the transcriptional coactivator yes-associated protein (YAP) into the nucleus, thus suppressing transcription of pro-proliferative genes. Hence, dynamic and precise control of the Hippo pathway is crucial for organ size control and the prevention of tumor formation. Hippo signaling is controlled by a growing number of upstream regulators, including WW and C2 domain-containing (WWC) proteins, which trigger a serine/threonine kinase pathway. One component of this is the large tumor suppressor (LATS) kinase, which phosphorylates YAP, trapping it in the cytoplasm. WWC proteins have been shown to interact with LATS in vitro and stimulate its kinase activity, thus directly promoting cytoplasmic accumulation of phosphorylated YAP. However, the function of the WWC proteins in the regulation of cell proliferation, organ size control, and tumor prevention in vivo has not yet been determined. Here, we show that loss of hepatic WWC expression in mice leads to tissue overgrowth, inflammation, fibrosis, and formation of liver carcinoma. WWC-deficient mouse livers display reduced LATS activity, increased YAP-mediated gene transcription, and enhanced proliferation of hepatic progenitor cells. In addition, loss of WWC expression in the liver accelerates the turnover of angiomotin proteins, which act as negative regulators of YAP activity.

CONCLUSION

Our data define an essential in vivo function for WWC proteins as regulators of canonical and noncanonical Hippo signaling in hepatic cell growth and liver tumorigenesis. Thus, expression of WWC proteins may serve as novel prognostic factors in human liver carcinoma. (Hepatology 2018;67:1546-1559).

Usp2-69 overexpression slows down the progression of rat anti-Thy1.1 nephritis

Mesangial proliferative glomerulonephritis is characterized by proliferation of mesangial cells (MCs) and transforming growth factor-β (TGF-β)-dependent stimulation of abnormal extracellular matrix (ECM) accumulation. We previously showed that Decorin--a leucine-rich proteoglycan inhibiting the progression of glomerulonephritis and glomerular sclerosis--can be degraded by the ubiquitin-proteasome pathway and deubiquitinated and stabilized by ubiquitin-specific processing protease 2-69(Usp2-69). Usp2-69 is highly expressed in the kidney and has been implicated in the regulation of cell proliferation and apoptosis. However, its role in mesangial proliferative glomerulonephritis remains unclear. Here, we explored the effect of Usp2-69 on MC proliferation and ECM deposition by transfecting Usp2-69 plasmid into rat anti-Thy1.1 nephritis model and into cultured MCs, as well as detected Usp2-69 and Decorin in rat anti-Thy1.1 nephritis model by western blot. Overexpressing Usp2-69 at the early stage, but not advanced stage, of anti-Thy1.1 nephritis alleviated cell proliferation and ECM deposition, which was shown by decreased Ki-67, Collagen IV and Fibronectin detected by immunohistochemistry. Overexpression also increased Decorin and decreased TGF-β1 and Collagen IV both in vitro and in vivo. In conclusion, our findings suggest that Usp2-69 overexpression alleviates the progression of rat anti-Thy1.1 nephritis and, therefore, that exogenous plasmid injection via the renal artery enhanced by electrotransfer technology could be a promising avenue for glomerular disease research.

Soluble biglycan as a biomarker of inflammatory renal diseases

Chronic renal inflammation is often associated with a progressive accumulation of various extracellular matrix constituents, including several members of the small leucine-rich proteoglycan (SLRP) gene family. It is becoming increasingly evident that the matrix-unbound SLRPs strongly regulate the progression of inflammation and fibrosis. Soluble SLRPs are generated either via partial proteolytic processing of collagenous matrices or by de novo synthesis evoked by stress or injury. Liberated SLRPs can then bind to and activate Toll-like receptors, thus modulating downstream inflammatory signaling. Preclinical animal models and human studies have recently identified soluble biglycan as a key initiator and regulator of various inflammatory renal diseases. Biglycan, generated by activated macrophages, can enter the circulation and its elevated levels in plasma and renal parenchyma correlate with unfavorable renal function and outcome. In this review, we will focus on the critical role of soluble biglycan in inflammatory signaling in various renal disorders. Moreover, we will provide new data implicating proinflammatory effects of soluble decorin in unilateral ureteral obstruction. Finally, we will critically evaluate the potential application of soluble biglycan vis-à-vis other SLRPs (decorin, lumican and fibromodulin) as a promising target and novel biomarker of inflammatory renal diseases.

Beyond tissue injury-damage-associated molecular patterns, toll-like receptors, and inflammasomes also drive regeneration and fibrosis

Tissue injury initiates an inflammatory response through the actions of immunostimulatory molecules referred to as damage-associated molecular patterns (DAMPs). DAMPs encompass a group of heterogenous molecules, including intracellular molecules released during cell necrosis and molecules involved in extracellular matrix remodeling such as hyaluronan, biglycan, and fibronectin. Kidney-specific DAMPs include crystals and uromodulin released by renal tubular damage. DAMPs trigger innate immunity by activating Toll-like receptors, purinergic receptors, or the NLRP3 inflammasome. However, recent evidence revealed that DAMPs also trigger re-epithelialization upon kidney injury and contribute to epithelial-mesenchymal transition and, potentially, to myofibroblast differentiation and proliferation. Thus, these discoveries suggest that DAMPs drive not only immune injury but also kidney regeneration and renal scarring. Here, we review the data from these studies and discuss the increasingly complex connection between DAMPs and kidney diseases.

Key roles for the small leucine-rich proteoglycans in renal and pulmonary pathophysiology

BACKGROUND

Small leucine-rich proteoglycans (SLRPs) are molecules that have signaling roles in a multitude of biological processes. In this respect, SLRPs play key roles in the evolution of a variety of diseases throughout the human body.

SCOPE OF REVIEW

We will critically review current developments in the roles of SLRPs in several types of disease of the kidney and lungs. Particular emphasis will be given to the roles of decorin and biglycan, the best characterized members of the SLRP gene family.

MAJOR CONCLUSIONS

In both renal and pulmonary disorders, SLRPs are essential elements that regulate several pathophysiological processes including fibrosis, inflammation and tumor progression. Decorin has remarkable antifibrotic and antitumorigenic properties and is considered a valuable potential treatment of these diseases. Biglycan can modulate inflammatory processes in lung and renal inflammation and is a potential target in the treatment of inflammatory conditions.

GENERAL SIGNIFICANCE

SLRPs can serve as either treatment targets or as potential treatment in renal or lung disease. This article is part of a Special Issue entitled Matrix-mediated cell behaviour and properties.

Proteoglycan synthesis and Golgi organization in polarized epithelial cells

A large number of complex glycosylation mechanisms take place in the Golgi apparatus. In epithelial cells, glycosylated protein molecules are transported to both the apical and the basolateral surface domains. Although the prevailing view is that the Golgi apparatus provides the same lumenal environment for glycosylation of apical and basolateral cargo proteins, there are indications that proteoglycans destined for the two opposite epithelial surfaces are exposed to different conditions in transit through the Golgi apparatus. We will here review data relating proteoglycan and glycoprotein synthesis to characteristics of the apical and basolateral secretory pathways in epithelial cells.

Biglycan: a multivalent proteoglycan providing structure and signals

Research over the past few years has provided fascinating results indicating that biglycan, besides being a ubiquitous structural component of the extracellular matrix (ECM), may act as a signaling molecule. Proteolytically released from the ECM, biglycan acts as a danger signal signifying tissue stress or injury. As a ligand of innate immunity receptors and activator of the inflammasome, biglycan stimulates multifunctional proinflammatory signaling linking the innate to the adaptive immune response. By clustering several types of receptors on the cell surface and orchestrating their downstream signaling events, biglycan is capable to autonomously trigger sterile inflammation and to potentiate the inflammatory response to microbial invasion. Besides operating in a broad biological context, biglycan also displays tissue-specific affinities to certain receptors and structural components, thereby playing a crucial role in bone formation, muscle integrity, and synapse stability at the neuromuscular junction. This review attempts to provide a concise summary of recent data regarding the involvement of biglycan in the regulation of inflammation and the musculoskeletal system, pointing out both a signaling and a structural role for this proteoglycan. The potential of biglycan as a novel therapeutic target or agent for the treatment of inflammatory diseases and skeletal muscular dystrophies is also addressed.

The proteoglycan biglycan enhances antigen-specific T cell activation potentially via MyD88 and TRIF pathways and triggers autoimmune perimyocarditis

Biglycan is a proteoglycan ubiquitously present in extracellular matrix of a variety of organs, including heart, and it was reported to be overexpressed in myocardial infarction. Myocardial infarction may be complicated by perimyocarditis through unknown mechanisms. Our aim was to investigate the capacity of TLR2/TLR4 ligand biglycan to enhance the presentation of specific Ags released upon cardiomyocyte necrosis. In vitro, OVA-pulsed bone marrow-derived dendritic cells from wild-type (WT; C57BL/6) and TLR2-, TLR4-, MyD88-, or TRIF-deficient mice were cotreated with LPS, biglycan, or vehicle and incubated with OVA-recognizing MHC I- or MHC II-restricted T cells. Biglycan enhanced OVA-specific cross-priming by >80% to MHC I-restricted T cells in both TLR2- and TLR4-pathway-dependent manners. Accordingly, biglycan-induced cross-priming by both MyD88- and TRIF-deficient dendritic cells (DCs) was strongly diminished. OVA-specific activation of MHC II-restricted T cells was predominantly TLR4 dependent. Our first in vivo correlate was a model of experimental autoimmune perimyocarditis triggered by injection of cardiac Ag-pulsed DCs (BALB/c). Biglycan-treated DCs triggered perimyocarditis to a comparable extent and intensity as LPS-treated DCs (mean scores 1.3 ± 0.3 and 1.5 ± 0.4, respectively). Substitution with TLR4-deficient DCs abolished this effect. In a second in vivo approach, WT and biglycan-deficient mice were followed 2 wk after induction of myocardial infarction. WT mice demonstrated significantly greater myocardial T lymphocyte infiltration in comparison with biglycan-deficient animals. We concluded that the TLR2/4 ligand biglycan, a component of the myocardial matrix, may enhance Ag-specific T cell priming, potentially via MyD88 and TRIF, and stimulate autoimmune perimyocarditis.

Small leucine-rich proteoglycans in kidney disease

Research over the past 2 decades provides ample evidence that small leucine-rich proteoglycans (SLRPs; such as decorin, biglycan, fibromodulin, and lumican) of the extracellular matrix are deeply involved in the regulation of inflammatory and fibrotic renal disorders. Initial efforts in SLRP research focused on the interaction between decorin and TGF-β because it had been unequivocally demonstrated that decorin treatment exerts beneficial effects in fibrotic disorders involving TGF-β overproduction in the kidney. This was followed by a paradigm shift in our understanding of SLRP biology, with new evidence showing that in addition to their role as structural matrix components, soluble SLRPs also act as signaling molecules regulating various complex biologic processes in a molecule- and cell-specific manner. With the identification of SLRP-derived endogenous ligands of Toll-like receptors, the general question regarding the mechanisms of SLRP-derived signaling in pathogen-dependent and independent renal inflammation arose. This led to the fascinating concept of SLRPs as autonomous triggers of sterile renal inflammation in response to renal stress or injury. This review focuses on the key biologic roles of SLRPs in the normal and diseased kidney with special emphasis on newly described signaling events triggered by these proteoglycans.

The progressive ankylosis protein regulates cementum apposition and extracellular matrix composition

BACKGROUND/AIMS

Tooth root cementum is sensitive to modulation of inorganic pyrophosphate (PP(i)), an inhibitor of hydroxyapatite precipitation. Factors increasing PP(i) include progressive ankylosis protein (ANK) and ectonucleotide pyrophosphatase/phosphodiesterase 1 (NPP1) while tissue nonspecific alkaline phosphatase hydrolyzes PP(i). Studies here aimed to define the role of ANK in root and cementum by analyzing tooth development in Ank knock-out (KO) mice versus wild type.

MATERIALS AND METHODS

Periodontal development in KO versus control mice was analyzed by histology, histomorphometry, immunohistochemistry, in situ hybridization, electron microscopy, and nanoindentation. Cementoblast cultures were used in vitro to provide mechanistic underpinnings for PP(i) modulation of cell function.

RESULTS

Over the course of root development, Ank KO cervical cementum became 8- to 12-fold thicker than control cervical cementum. Periodontal ligament width was maintained and other dentoalveolar tissues, including apical cementum, were unaltered. Cervical cementum uncharacteristically included numerous cells, from rapid cementogenesis. Ank KO increased osteopontin and dentin matrix protein 1 gene and protein expression, and markedly increased NPP1 protein expression in cementoblasts but not in other cell types. Conditional ablation of Ank in joints and periodontia confirmed a local role for ANK in cementogenesis. In vitro studies employing cementoblasts indicated that Ank and Enpp1 mRNA levels increased in step with mineral nodule formation, supporting a role for these factors in regulation of cementum matrix mineralization.

CONCLUSION

ANK, by modulating local PP(i), controls cervical cementum apposition and extracellular matrix. Loss of ANK created a local environment conducive to rapid cementogenesis; therefore, approaches modulating PP(i) in periodontal tissues have potential to promote cementum regeneration.

Etiopathology of chronic tubular, glomerular and renovascular nephropathies: clinical implications

Chronic kidney disease (CKD) comprises a group of pathologies in which the renal excretory function is chronically compromised. Most, but not all, forms of CKD are progressive and irreversible, pathological syndromes that start silently (i.e. no functional alterations are evident), continue through renal dysfunction and ends up in renal failure. At this point, kidney transplant or dialysis (renal replacement therapy, RRT) becomes necessary to prevent death derived from the inability of the kidneys to cleanse the blood and achieve hydroelectrolytic balance. Worldwide, nearly 1.5 million people need RRT, and the incidence of CKD has increased significantly over the last decades. Diabetes and hypertension are among the leading causes of end stage renal disease, although autoimmunity, renal atherosclerosis, certain infections, drugs and toxins, obstruction of the urinary tract, genetic alterations, and other insults may initiate the disease by damaging the glomerular, tubular, vascular or interstitial compartments of the kidneys. In all cases, CKD eventually compromises all these structures and gives rise to a similar phenotype regardless of etiology. This review describes with an integrative approach the pathophysiological process of tubulointerstitial, glomerular and renovascular diseases, and makes emphasis on the key cellular and molecular events involved. It further analyses the key mechanisms leading to a merging phenotype and pathophysiological scenario as etiologically distinct diseases progress. Finally clinical implications and future experimental and therapeutic perspectives are discussed.

Peroxisome proliferator-activated receptor (PPAR)gamma can inhibit chronic renal allograft damage

Chronic inflammation and fibrosis are the leading causes of chronic allograft failure. The nuclear receptor peroxisome proliferator-activated receptor (PPAR)gamma is a transcription factor known to have antidiabetogenic and immune effects, and PPARgamma forms obligate heterodimers with the retinoid X receptor (RXR). We have reported that a retinoic acid (RAR)/RXR-agonist can potently influence the course of renal chronic allograft dysfunction. In this study, in a Fischer to Lewis rat renal transplantation model, administration of the PPARgamma-agonist, rosiglitazone, independent of dose (3 or 30 mg/kgBW/day), lowered serum creatinine, albuminuria, and chronic allograft damage with a chronic vascular damage score as follows: 35.0 +/- 5.8 (controls) vs. 8.1 +/- 2.4 (low dose-Rosi; P < 0.05); chronic tubulointerstitial damage score: 13.6 +/- 1.8 (controls) vs. 2.6 +/- 0.4 (low dose-Rosi; P < 0.01). The deposition of extracellular matrix proteins (collagen, fibronectin, decorin) was strikingly lower. The expression of transforming growth factor-beta1 was inhibited, whereas that of bone morphogenic protein-7 (BMP-7) was increased. Intragraft mononuclear cells and activated fibroblast numbers were reduced by 50%. In addition, the migratory and proliferative activity of these cells was significantly inhibited in vitro. PPARgamma activation diminished the number of cells expressing the proinflammatory and fibrogenic proteoglycan biglycan. In macrophages its secretion was blocked by rosiglitazone in a predominantly PPARgamma-dependent manner. The combination of PPARgamma- and RAR/RXR-agonists resulted in additive effects in the inhibition of fibrosis. In summary, PPARgamma activation was potently immunosuppressive and antifibrotic in kidney allografts, and these effects were enhanced by a RAR/RXR-agonist.

Extracellular matrix molecules: potential targets in pharmacotherapy

The extracellular matrix (ECM) consists of numerous macromolecules classified traditionally into collagens, elastin, and microfibrillar proteins, proteoglycans including hyaluronan, and noncollagenous glycoproteins. In addition to being necessary structural components, ECM molecules exhibit important functional roles in the control of key cellular events such as adhesion, migration, proliferation, differentiation, and survival. Any structural inherited or acquired defect and/or metabolic disturbance in the ECM may cause cellular and tissue alterations that can lead to the development or progression of disease. Consequently, ECM molecules are important targets for pharmacotherapy. Specific agents that prevent the excess accumulation of ECM molecules in the vascular system, liver, kidney, skin, and lung; alternatively, agents that inhibit the degradation of the ECM in degenerative diseases such as osteoarthritis would be clinically beneficial. Unfortunately, until recently, the ECM in drug discovery has been largely ignored. However, several of today's drugs that act on various primary targets affect the ECM as a byproduct of the drugs' actions, and this activity may in part be beneficial to the drugs' disease-modifying properties. In the future, agents and compounds targeting directly the ECM will significantly advance the treatment of various human diseases, even those for which efficient therapies are not yet available.

Recipient Toll-like receptors contribute to chronic graft dysfunction by both MyD88- and TRIF-dependent signaling

Toll-like receptors (TLRs) recognize specific molecular patterns derived from microbial components (exogenous ligands) or stressed cells (endogenous ligands). Stimulation of these receptors leads to a pronounced inflammatory response in a variety of acute animal models. Chronic allograft dysfunction (CAD) was regarded as a candidate disease to test whether TLRs influence chronic fibrosing inflammation. Potential endogenous renal TLR ligands, specifically for TLR2 and TLR4, have now been detected by a significant upregulation of glucose regulated protein (GRP)-94, fibrinogen, heat shock protein (HSP)-60, HSP-70, biglycan (Bgn) and high-mobility group box chromosomal protein 1 (HMGB1) in the acute and chronic transplant setting. In a genetic approach to define the contribution of TLR2 and TLR4, and their adaptor proteins MyD88 and TRIF [Toll/interleukin (IL)-1 receptor domain-containing adaptor-protein inducing interferon beta], to CAD, kidney transplantation of TLR wild-type grafts to recipients who were deficient in TLR2, TLR4, TLR2/4, MyD88 and TRIF was performed. TLR and adaptor protein deficiencies significantly improved the excretory function of chronic kidney grafts by between 65% and 290%, and histopathologic signs of chronic allograft damage were significantly ameliorated. T cells, dendritic cells (DCs) and foremost macrophages were reduced in grafts by up to 4.5-fold. The intragraft concentrations of IL-6, IL-10, monocyte chemotactic protein-1 (MCP-1) and IL-12p70 were significantly lower. TLR-, MyD88- and TRIF-deficient recipients showed a significant reduction in fibrosis. alpha-smooth muscle actin (alpha-SMA)-positive cells were decreased by up to ninefold, and collagen I and III were reduced by up to twofold. These findings highlight the functional relevance of TLRs and their two major signaling pathways in graft-infiltrating mononuclear cells in the pathophysiology of CAD. A TLR signaling blockade may be a therapeutic option for the prevention of CAD.

SPARC is associated with gastric cancer progression and poor survival of patients

PURPOSE

The present study investigated the clinical significance of secreted protein, acidic and rich in cysteine (SPARC), in the development and progression of gastric cancer.

EXPERIMENTAL DESIGN

Immunohistochemistry was used to analyze SPARC, integrin beta1, and matrix metalloproteinase (MMP)-2 expression in 436 clinicopathologically characterized gastric cancer cases.

RESULTS

SPARC, integrin beta1, and MMP-2 protein levels were upregulated in gastric cancer lesions compared with adjacent noncancerous tissues. SPARC protein was detected in 334 of 436 human gastric cancer cases and was highly expressed in 239 tumors. We also found a positive correlation between expression of SPARC and MMP2, and SPARC and integrin beta1. In stages I, II, and III, the 5-year survival rate of patients with a high expression of SPARC was significantly lower than those in patients with low expression. In stage IV, SPARC expression did not correlate with the 5-year survival rate. Further multivariate analysis suggested that the depth of invasion; lymph node and distant metastasis; tumor-node-metastasis stage; and upregulation of SPARC, MMP-2, and integrin beta1, were independent prognostic indicators for the disease.

CONCLUSIONS

Our study provided a basis for the development of a novel biomarker for diagnosis and prognosis of gastric cancer. Expression of SPARC in gastric cancer is significantly associated with lymph node and distant metastasis, high MMP2 expression, high intergrin beta1 expression, and poor prognosis. SPARC, intergrin beta1, and MMP-2 protein could be useful markers to predict tumor progression.

Lysyl oxidase binds transforming growth factor-beta and regulates its signaling via amine oxidase activity

Lysyl oxidase (LOX), an amine oxidase critical for the initiation of collagen and elastin cross-linking, has recently been shown to regulate cellular activities possibly by modulating the functions of growth factors. In this study, we investigated the interaction between LOX and transforming growth factor-beta1 (TGF-beta1), a potent growth factor abundant in bone, the effect of LOX on TGF-beta1 signaling, and its potential mechanism. The specific binding between mature LOX and mature TGF-beta1 was demonstrated by immunoprecipitation and glutathione S-transferase pulldown assay in vitro. Both proteins were colocalized in the extracellular matrix in an osteoblastic cell culture system, and the binding complex was identified in the mineral-associated fraction of bone matrix. Furthermore, LOX suppressed TGF-beta1-induced Smad3 phosphorylation likely through its amine oxidase activity. The data indicate that LOX binds to mature TGF-beta1 and enzymatically regulates its signaling in bone and thus may play an important role in bone maintenance and remodeling.

Unilateral nephrectomy leads to up-regulation of syndecan-2- and TGF-beta-mediated glomerulosclerosis in syndecan-4 deficient male mice

Syndecan-4 is an ubiquitous, plasma membrane-spanning heparan sulfate proteoglycan involved in proliferation, differentiation, adhesion and migration of cells in vitro. Syndecan-4 knockout (KO) mice show no obvious defects but respond abnormally to experimental stress conditions. In the adult, syndecan-4 is the most abundant syndecan of renal tissue. We therefore investigated the consequences of syndecan-4 deficiency during progression of kidney disease using unilaterally nephrectomized mice, a model of glomerular hyperfiltration and renal hypertrophy. 60 days after unilateral nephrectomy (UNX), mesangial expansion, enhanced matrix production (collagens I and IV, fibronectin) and focal segmental glomerulosclerosis, resembling early stages of diabetic nephropathy, was apparent in male but not female syndecan-4 KO mice. No defect was detected in wild type UNX males. Syndecan-2 mRNA and protein were not detectable in renal glomeruli of wild type mice, but were induced specifically in the glomeruli of the syndecan-4 deficient kidneys after unilateral nephrectomy. Due to the structural similarities of syndecans-2 and -4 we hypothesize that de novo-production of syndecan-2 in kidneys after unilateral nephrectomy reflects a compensatory response. However, this response is counterproductive since syndecan-2 supports the pro-sclerotic activity of TGF-beta1 which is increased in parallel with syndecan-2 synthesis. By contrast, signaling through syndecan-4 negatively controls the production of pro-sclerotic TGF-beta1.

Advances in Targeting Drug Delivery to Glomerular Mesangial Cells by Long Circulating Cationic Liposomes for the Treatment of Glomerulonephritis

PURPOSE

Newly designed polyethylene glycol (PEG)-modified cationic liposomes, containing a novel cationic lipid TRX-20 (3,5-dipentadecyloxybenzamidine hydrochloride), bind specifically to cultured human mesangial cells, and not to endothelial cells. In this study, we investigated targeting the delivery of PEG-modified liposomes containing TRX-20 (TRX-liposomes) to mesangial cells and evaluated their pharmacokinetic behavior in a rat experimental glomerulonephritis model, using prednisolone phosphate (PSLP) as a model drug.

MATERIAL AND METHODS

TRX-liposomes were injected intravenously into experimental glomerulonephritic rats and normal rats to compare its pharmacokinetic behavior with that of non-cationic liposomes (PEG-liposomes). Rhodamine-labeled liposomes were used to evaluate the accumulation in inflamed kidneys. Pharmacological effects of three formulations of PSLP (i.e., a single injection of two liposomal formulations and daily injections of PSLP in saline solution) were estimated in terms of suppressing glomerular cell proliferation in the rat nephritis model.

RESULTS

TRX-liposomes markedly accumulated in the glomeruli of inflamed kidneys, but did not accumulate in the glomeruli of normal kidneys. Although the PEG-liposomes also accumulated in the glomeruli of the inflamed kidneys, their pharmacological behavior was quite different from that of the TRX-liposomes, which were internalized by the target cells. In a comparison among the three formulations of PSLP, the dose of TRX-liposomes required for significant suppression of glomerular cell proliferation was much less (dose of 0.032 mg/kg and above) than that required for the same effect by the PSLP saline solution (3.2 mg/kg daily; 12.8 mg/kg total) and PEG-liposomes (0.32 mg/kg). Interestingly, significant suppression of mesangial cell activation, as assessed by the expression of alpha-smooth muscle actin, was observed in nephritic rats treated with TRX-liposomes, but not in the other two treatment groups.

CONCLUSIONS

The pharmaceutical properties of TRX-liposomes due to their preferential binding to mesangial cells and long circulation time make this a likely candidate system for targeted drug delivery to the inflamed glomeruli of glomerulonephritis.

Beneficial effects of CCR1 blockade on the progression of chronic renal allograft damage

The biology of chemokines and their receptors have been linked to the development of chronic allograft damage. Effects of CCR1 antagonist BX 471 were studied in a Fischer to Lewis renal transplantation model at days 10, 21 and 42 after transplantation. BX 471 treatment did not effectively reduce signs of acute rejection at day 10 but significantly improved allograft function and morphology at day 21 posttransplantation. When therapy was initiated on day 21 after transplantation, glomerulosclerosis and tubulointerstitial fibrosis were significantly inhibited by day 42 posttransplantation. Parallel decrease in infiltrating and proliferating mononuclear cells (ED1, CD8 and Ki67) was observed in treated allografts. Expression of acute phase reactive and proinflammatory genes (HO-1, osteopontin) and molecules associated with fibrosis (PAI-1, TGF-beta1, biglycan) was downregulated at day 21; reduced collagen deposition was observed, parallel to a significant lower number of alpha-SMA+ interstitial myofibroblasts. In situ hybridization demonstrated that biglycan expression was reduced following CCR1 blockade in interstitium of treated allografts. CCR1 antagonism was found to inhibit CCL5-induced secretion of biglycan by macrophages in vitro. CCR1 blockade significantly inhibited development and progression of chronic allograft damage. CCR1 antagonists may represent a therapeutic option for chronic inflammation and fibrosis in renal grafts.

Role of fibrillin-1 in hypertensive and diabetic glomerular disease

The microfibrillar protein fibrillin-1 is a component of the mesangial matrix. Defects in fibrillin-1 predisposes individuals to vascular damage in Marfan syndrome, but the role of fibrillin-1 in kidney disease is unknown. We hypothesized that fibrillin-1 is involved in hypertensive or diabetic glomerular disease. DOCA-salt hypertension or streptozotocin (STZ) diabetes led to a significant increase in glomerular fibrillin-1 deposition. To test the functional role of fibrillin-1, DOCA hypertension and STZ diabetes were induced in mice homozygous for a mutation leading to a fivefold lower expression of fibrillin-1 (mgR/mgR). Untreated male mgR/mgR mice usually die from aortic dissection during the first 4 mo of life. All DOCA-treated mgR/mgR mice died within 2 wk after onset of DOCA treatment. DOCA-treated heterozygous (mgR/+) and their wild-type littermates displayed similar blood pressure levels, but albuminuria was significantly lower in mgR/+ than in wild-type mice after DOCA treatment. Similarly, STZ diabetic mgR/mgR and mgR/+ developed lower albuminuria than wild-type mice despite higher blood glucose levels in mgR/mgR and mgR/+ compared with wild-type mice. Blood pressure, blood glucose, and albuminuria did not differ among untreated mgR/mgR, mgR/+, and wild-type mice, respectively. In diabetic mgR/+ and mgR/mgR, but not in wild-type mice, an induction of glomerular decorin expression was observed. Thus underexpression of fibrillin-1 predisposes individuals to lethal aortic dissection in the presence of hypertension. On the other hand, albuminuria as a parameter of microvascular damage in hypertension and diabetes was ameliorated in fibrillin-1-underexpressing mice, possibly due to a compensatory upregulation of decorin. We conclude that fibrillin-1 may contribute to glomerular damage in hypertensive and diabetic kidney disease.

Glomerular expression of thrombospondin-1, transforming growth factor beta and connective tissue growth factor at different stages of diabetic nephropathy and their interdependent roles in mesangial response to diabetic stimuli

AIMS/HYPOTHESIS

We quantified the glomerular expression of thrombospondin-1 (THBS1, also known as TSP-1), transforming growth factor beta 1 (TGFB1, also known as TGF-beta1) and connective tissue growth factor (CTGF) at each stage of diabetic nephropathy. We also examined the roles of THBS1 and CTGF in mediating high-glucose- and glycated-albumin-induced synthesis of the matrix protein, fibronectin, by mesangial cells.

METHODS

THBS1, latent and active TGFB1, and CTGF, were detected by immunohistochemistry and in situ hybridisation in biopsies from 19 insulin-dependent diabetic patients with incipient, manifest and advanced diabetic nephropathy, and in 11 control kidneys. Findings were quantified by image analysis. Human mesangial cells were cultured with normal or high glucose, albumin or glycated albumin (Amadori product), +/-THBS1 or CTGF antisense oligonucleotides, or with peptide W, an inhibitor of TGFB1 bioactivation by THBS1. Proteins were measured by western blot analysis or ELISA.

RESULTS

In glomeruli of normal kidneys, mRNA and protein levels for THBS1, latent-TGFB1 and CTGF were low. They were increased in the incipient stage of diabetic nephropathy, predominantly in mesangial areas, with further increases at later stages of the disease. Little or no active TGFB1 immunostaining was detected prior to manifest diabetic nephropathy. In contrast to high-glucose conditions, increases in fibronectin synthesis that were stimulated by glycated albumin were not dependent on THBS1 activation of latent TGFB1. However, increased fibronectin synthesis in both conditions required CTGF.

CONCLUSIONS/INTERPRETATION

Increased glomerular expression of all three factors occurs from the earliest stage of diabetic nephropathy. In contrast to THBS1, CTGF is required for mesangial synthesis of fibronectin stimulated by high glucose or glycated albumin, and is thus a potential therapeutic target.

The matrix component biglycan is proinflammatory and signals through Toll-like receptors 4 and 2 in macrophages

Biglycan, a small leucine-rich proteoglycan, is a ubiquitous ECM component; however, its biological role has not been elucidated in detail. Here we show that biglycan acts in macrophages as an endogenous ligand of TLR4 and TLR2, which mediate innate immunity, leading to rapid activation of p38, ERK, and NF-kappaB and thereby stimulating the expression of TNF-alpha and macrophage inflammatory protein-2 (MIP-2). In agreement, the stimulatory effects of biglycan are significantly reduced in TLR4-mutant (TLR4-M), TLR2-/-, and myeloid differentiation factor 88-/- (MyD88-/-) macrophages and completely abolished in TLR2-/-/TLR4-M macrophages. Biglycan-null mice have a considerable survival benefit in LPS- or zymosan-induced sepsis due to lower levels of circulating TNF-alpha and reduced infiltration of mononuclear cells in the lung, which cause less end-organ damage. Importantly, when stimulated by LPS-induced proinflammatory factors, macrophages themselves are able to synthesize biglycan. Thus, biglycan, upon release from the ECM or from macrophages, can boost inflammation by signaling through TLR4 and TLR2, thereby enhancing the synthesis of TNF-alpha and MIP-2. Our results provide evidence for what is, to our knowledge, a novel role of the matrix component biglycan as a signaling molecule and a crucial proinflammatory factor. These findings are potentially relevant for the development of new strategies in the treatment of sepsis.

Quantification of collagen and proteoglycan deposition in a murine model of airway remodelling

BACKGROUND

Sub-epithelial extracellular matrix deposition is a feature of asthmatic airway remodelling associated with severity of disease, decline in lung function and airway hyperresponsiveness. The composition of, and mechanisms leading to, this increase in subepithelial matrix, and its importance in the pathogenesis of asthma are unclear. This is partly due to limitations of the current models and techniques to assess airway remodelling.

METHODS

In this study we used a modified murine model of ovalbumin sensitisation and challenge to reproduce features of airway remodelling, including a sustained increase in sub-epithelial matrix deposition. In addition, we have established techniques to accurately and specifically measure changes in sub-epithelial matrix deposition, using histochemical and immunohistochemical staining in conjunction with digital image analysis, and applied these to the measurement of collagen and proteoglycans.

RESULTS

24 hours after final ovalbumin challenge, changes similar to those associated with acute asthma were observed, including inflammatory cell infiltration, epithelial cell shedding and goblet cell hyperplasia. Effects were restricted to the bronchial and peribronchial regions with parenchymal lung of ovalbumin sensitised and challenged mice appearing histologically normal. By 12 days, the acute inflammatory changes had largely resolved and increased sub-epithelial staining for collagen and proteoglycans was observed. Quantitative digital image analysis confirmed the increased deposition of sub-epithelial collagen (33%, p < 0.01) and proteoglycans (32%, p < 0.05), including decorin (66%, p < 0.01). In addition, the increase in sub-epithelial collagen deposition was maintained for at least 28 days (48%, p < 0.001).

CONCLUSION

This animal model reproduces many of the features of airway remodelling found in asthma and allows accurate and reproducible measurement of sub-epithelial extra-cellular matrix deposition. As far as we are aware, this is the first demonstration of increased sub-epithelial proteoglycan deposition in an animal model of airway remodelling. This model will be useful for measurement of other matrix components, as well as for assessment of the molecular mechanisms contributing to, and agents to modulate airway remodelling.

Spatial organization of types I and II collagen in the canine meniscus

The meniscus of the knee joint is a fibrocartilage mainly composed of type I collagen and smaller amounts of type II collagen. The distribution of type II collagen in the canine meniscus and its spatial relationship to type I collagen was examined by immunohistochemistry and confocal microscopy. Dorsal and coronal slices of the mid-section of medial and lateral menisci from the knee joints of skeletally mature dogs were predigested with Streptomyces hyaluronate lyase and bacterial Protease enzyme XXIV. Monoclonal antibodies against type I collagen (CP17L) and type II collagen (II-II6B3) and an anti-type II collagen polyclonal antibody (AB759) were employed. The staining for type II collagen in the extracellular matrix of hyaline articular cartilage was diffuse without any identifiable spatial organization. In striking contrast, type II collagen in the fibrocartilage of the meniscus stained as an organized network. Type II collagen was distributed throughout the meniscus with the exception of the outer zone containing the blood vessels. Coronal and dorsal staining of the meniscus showed bundles of circumferential fibrils of type I that colocalized with type II collagen in specific sites. These bundles were enwrapped in a second organizational fibrillar system of types I and II collagen that also colocalized. Bundles of circumferential fibrils appeared in cross-section in coronal sections as dots within the interstitial spaces framed by the network of types I and II collagen of the second system. Confocal overlays showed that types I and II collagens were superimposed, suggesting a close spatial proximity between the two collagens. The cells were confined to the types I and II collagen fibrils that enwrapped the bundles. A striking feature of the radial tie fibers was patches of type II collagen without colocalized type I collagen. Our study reveals a unique network of type II collagen in fibrocartilage of the meniscus that serves as a morphological distinction between fibro- and hyaline cartilage.

Decorin deficiency leads to impaired angiogenesis in injured mouse cornea

Small leucine-rich proteoglycans play important roles in the organization of the extracellular matrix as well as for the regulation of cell behavior; two biological processes that are essential for angiogenesis. We investigated consequences of the targeted ablation of decorin (DCN), biglycan (BGN) and fibromodulin (FMOD) genes on inflammation-induced angiogenesis in the cornea. In wild-type mice, DCN was localized exclusively to the corneal stroma, while FMOD and BGN were more prominently expressed in epithelial cells. Endothelial cells from limbus blood vessels expressed BGN and FMOD, but no DCN. However, after induction of angiogenesis by chemical cauterization, DCN was expressed in the newly formed capillaries, together with BGN and FMOD. Notably, in DCN-deficient mice, the growth of vessels was significantly diminished, whereas it did not significantly change in FMOD- or BGN-deficient animals. Moreover, blood vessels of DCN-deficient mice exhibited a similar expression level of BGN as control mice, while FMOD was increased on day 3 after injury. These results indicate that DCN, in addition to its effects on fibrillogenesis, plays a regulatory role in angiogenesis and that FMOD in endothelial cells may be able to partially substitute for DCN.

Regulation of fibrillin-1 by biglycan and decorin is important for tissue preservation in the kidney during pressure-induced injury

There is growing evidence that the two small leucine-rich proteoglycans biglycan and decorin regulate the assembly of connective tissues and alter cell behavior during development and pathological processes. In this study, we have used an experimental animal model of unilateral ureteral ligation and mice deficient in either biglycan or decorin. We discovered that pressure-induced injury to the wild-type kidneys led to overexpression of decorin, biglycan, fibrillin-1, and fibrillin-2. In contrast, in biglycan-deficient kidneys the overexpression of fibrillin-1 was markedly attenuated and this was associated with cystic dilatation of Bowman's capsule and proximal tubules. Notably, we found that in ligated kidneys from decorin-null mice, fibrillin-1 expression was initially enhanced to the same extent as in wild-type animals. However, long-term obstruction resulted in down-regulation of fibrillin-1 and concurrent cystic dilatation of Bowman's capsule in 33% of kidneys at 5 months after obstruction. In all of the genotypes, no differences in fibrillin-2 expression were observed. These in vivo data correlated with a significant induction of fibrillin-1 expression in renal fibroblasts and mesangial cells by recombinant biglycan and decorin. Our results indicate a novel role for decorin and biglycan during pressure-induced renal injury by stimulating fibrillin-1 expression.

Potentiation of tumor necrosis factor alpha-induced secreted phospholipase A2 (sPLA2)-IIA expression in mesangial cells by an autocrine loop involving sPLA2 and peroxisome proliferator-activated receptor alpha activation

In rat mesangial cells, exogenously added secreted phospholipases A2 (sPLA2s) potentiate the expression of pro-inflammatory sPLA2-IIA first induced by cytokines like tumor necrosis factor-alpha (TNFalpha) and interleukin-1 beta. The transcriptional pathway mediating this effect is, however, unknown. Because products of PLA2 activity are endogenous activators of peroxisome proliferator-activated receptor alpha (PPAR alpha, we postulated that sPLA2s mediate their effects on sPLA2-IIA expression via sPLA2 activity and subsequent PPAR alpha activation. This study shows that various sPLA2s, including venom enzymes, human sPLA2-IIA, and wild-type and catalytically inactive H48Q mutant of porcine pancreatic sPLA2-IB, enhance the TNF alpha-induced sPLA2-IIA expression at the mRNA and protein levels. In cells transfected with luciferase sPLA2-IIA promoter constructs, sPLA2s are active only when the promoter contains a functional PPRE-1 site. The effect of exogenous sPLA2s is also blocked by the PPAR alpha inhibitor MK886. Interestingly, the expression of sPLA2-IIA induced by TNF alpha alone is also attenuated by MK886, by the sPLA2-IIA inhibitor LY311727, by heparinase, which prevents the binding of sPLA2-IIA to heparan sulfate proteoglycans, and by the specific cPLA2-alpha inhibitor pyrrolidine-1. Together, these data indicate that sPLA2-IIA released from mesangial cells by TNF alpha stimulates its own expression via an autocrine loop involving cPLA2 and PPAR alpha. This signaling pathway is also used by exogenously added sPLA2s including pancreatic sPLA2-IB and is distinct from that used by TNF alpha.

Biglycan, a nitric oxide-regulated gene, affects adhesion, growth, and survival of mesangial cells

During glomerular inflammation mesangial cells are the major source and target of nitric oxide that pro-foundly influences proliferation, adhesion, and death of mesangial cells. The effect of nitric oxide on the mRNA expression pattern of cultured rat mesangial cells was therefore investigated by RNA-arbitrarily-primed polymerase chain reaction. Employing this approach, biglycan expression turned out to be down-regulated time- and dose-dependently either by interleukin-1beta-stimulated endogenous nitric oxide production or by direct application of the exogenous nitric oxide donor, diethylenetriamine nitric oxide. There was a corresponding decline in the rate of biglycan biosynthesis and in the steady state level of this proteoglycan. In vivo, in a model of mesangioproliferative glomerulonephritis up-regulation of inducible nitric-oxide synthase mRNA was associated with reduced expression of biglycan in isolated glomeruli. Biglycan expression could be normalized, both in vitro and in vivo, by using a specific inhibitor of the inducible nitric-oxide synthase, l-N6-(l-iminoethyl)-l-lysine dihydrochloride. Further studies showed that biglycan inhibited cell adhesion on type I collagen and fibronectin because of its binding to these substrates. More importantly, biglycan protected mesangial cells from apoptosis by decreasing caspase-3 activity, and it counteracted the proliferative effects of platelet-derived growth factor-BB. These findings indicate a signaling role of biglycan and describe a novel pathomechanism by which nitric oxide modulates the course of renal glomerular disease through regulation of biglycan expression.

Proteoglycans and WT1 as markers for distinguishing adenocarcinoma, epithelioid mesothelioma, and benign mesothelium

Malignant mesothelioma is a tumour frequently accompanied by an effusion with elevated hyaluronan levels. To distinguish malignant mesothelioma, adenocarcinoma, and reactive benign mesothelium with cytological and histological methods including immunocytochemistry is a major diagnostic challenge. The Wilms' tumour susceptibility gene 1 (WT1), expressed during transition of mesenchyme to epithelial tissues, is regarded as a marker for the mesothelial lineage. Its effect on the cell phenotype may be regulated via the syndecans, i.e. proteoglycans on the cell surface. To determine how WT1, proteoglycans, and hyaluronan synthase are expressed in mesothelioma, adenocarcinoma, and reactive benign mesothelium, we studied these molecules at the mRNA and protein levels, with the additional purpose of finding diagnostic parameters. Adenocarcinoma cells produced more mRNA for syndecan-1, but cells derived from mesothelium expressed WT1, biglycan, and larger amounts of syndecan-2. The difference in gene expression of these two syndecans was best monitored by the ratio between them. Syndecan-4 was highly expressed in all malignant cell lines, this expression being 1.7-5 times greater than in benign mesothelial cells. Although hyaluronan synthase-1 and versican could not distinguish between the three conditions, versican expression was associated with a high rate of proliferation. These findings suggest that syndecan-1 and syndecan-2 together may be useful diagnostic markers, with stronger staining for the latter epitope in mesothelial tissues. The alternating appearance of these two syndecans can be shown not only by RT-PCR and FACS in vitro, but also by immunohistochemistry on clinical material.

Decorin transfection in human mesangial cells downregulates genes playing a role in the progression of fibrosis

The proteoglycan decorin inhibits TGF-beta; therefore, it could antagonize progression of fibrotic diseases associated with activation of TGF-beta(1). The effect of decorin transfection in human mesangial cells (HMCs) on the expression of genes related to kidney fibrosis was investigated. HMCs, isolated from glomeruli of healthy portions of human kidneys removed due to carcinoma, were histochemically typed. Decorin cDNA cloned in a eukaryotic expression vector was transfected into HMCs. Gene expression of fibrogenetic cytokines and fibrotic proteins TGF-beta(1), PDGF-beta, alpha(1) collagen type IV, alpha(1) collagen type I, fibronectin, and tenascin was analyzed, by reverse transcription polymerase chain reaction (RT-PCR), 24 hr after transfection. Immunoblotting analysis of protein extracts using anti-decorin IgG, revealed a positive signal of about 52 MDa, corresponding to the molecular weight of decorin, in cultures transfected with the decorin gene. Decorin mRNA increased about 12 times in cultures transfected with the construct pCR3.1-Deco. Cells with increased decorin synthesis showed a 61% decrease of TGF-beta(1) mRNA, a 71% reduction of alpha1 collagen type IV mRNA, and a 29% reduction of fibronectin mRNA. This study is the first to investigate decorin transfection into human mesangial cells, and supports the use of the decorin gene to control the progression of glomerular and interstitial fibrosis in kidney diseases.

Absence of decorin adversely influences tubulointerstitial fibrosis of the obstructed kidney by enhanced apoptosis and increased inflammatory reaction

Decorin, a small dermatan-sulfate proteoglycan, participates in extracellular matrix assembly and influences directly and indirectly cell behavior via interactions with signaling membrane receptors and transforming growth factor (TGF)-beta. We have therefore compared the development of tubulointerstitial kidney fibrosis in wild-type (WT) and decorin-/- mice in the model of unilateral ureteral obstruction. Without obstruction, kidneys from decorin-/- mice did not differ in any aspect from their WT counterparts. However, already 12 hours after obstruction decorin-/- animals showed lower levels of p27(KIP1) and soon thereafter a more pronounced up-regulation and activation of initiator and effector caspases followed by enhanced apoptosis of tubular epithelial cells. Later, a higher increase of TGF-beta1 became apparent. After 7 days, there was an up to 15-fold transient up-regulation of the related proteoglycan biglycan, which was mainly caused by the appearance of biglycan-expressing mononuclear cells. Other small proteoglycans showed no similar response. Because of enhanced degradation of type I collagen, end-stage kidneys from decorin-/- animals were more atrophic than WT kidneys. These data suggest that decorin exerts beneficial effects on tubulointerstitial fibrosis, primarily by influencing the expression of a key cyclin-dependent kinase inhibitor and by limiting the degree of apoptosis, mononuclear cell infiltration, tubular atrophy, and expression of TGF-beta1.

Nitric oxide induces MIP-2 transcription in rat renal mesangial cells and in a rat model of glomerulonephritis

Nitric oxide is a crucial mediator of several forms of glomerulonephritis. We examined the effects of NO on the mRNA expression pattern in glomerular mesangial cells by using a low-stringency reverse transcriptase-polymerase chain reaction method and detected a cDNA fragment that was induced by interleukin 1b (IL-1b) and further up-regulated by the NO donor diethylenetriamine-nitric oxide (DETA-NO). Each respective cDNA fragment was found to match with the cDNAs of rat macrophage inflammatory protein 2 (MIP-2) and GRO/cytokine-induced neutrophil chemoattractant 2b (CINC-2b). Further characterization of MIP-2 regulation by Northern blot analysis confirmed an NO- and IL-1b-dependent increase in MIP-2 mRNA levels. Moreover, inhibition of IL-1b-induced endogenous NO formation by the NO-synthase (NOS) inhibitor L-NMMA markedly attenuated MIP-2 protein expression. We cloned 770 bp of the 5'-flanking region of rat MIP-2 and fused this fragment to a luciferase reporter gene. Transfection of the construct into mesangial cells resulted in a 3.5-fold increase in luciferase activity in cells treated with DETA-NO when compared to controls, suggesting a transcriptional mechanism for NO-induced MIP-2 expression. Deletion and mutational analysis identified critical nuclear factor (NF)-kB and NF-IL-6 binding sites required for NO regulation of MIP-2. In vivo, inhibition of NO synthesis in the Thy-1.1 model of mesangioproliferative glomerulonephritis by the specific inducible-NOS inhibitor L-NIL resulted in a marked reduction of MIP-2 mRNA expression. Furthermore, infiltration of neutrophils into the glomerulus was dramatically attenuated in L-NIL-treated rats.

Small proteoglycans in human diabetic nephropathy: discrepancy between glomerular expression and protein accumulation of decorin, biglycan, lumican, and fibromodulin

Small leucine-rich proteoglycans (SLRPs), for example, decorin, biglycan, fibromodulin, and lumican, are extracellular matrix organizers and binding partners of TGF-b. Decorin is also involved in growth control and angiogenesis. Hence, these proteoglycans are likely of importance in the pathogenesis of diabetic glomerulosclerosis. In normal kidney, SLRPs were preferentially expressed in the tubulointerstitium. Weak expression occurred in the mesangial matrix. Biglycan was expressed by glomerular endothelial cells and, together with fibromodulin, by distal tubular cells and in collecting ducts. In all stages of diabetic nephropathy, there was a marked up-regulation of the proteoglycans in tubulointerstitium and glomeruli. Decorin and lumican became expressed in tubuli. However, in glomeruli, overexpression was not mirrored by local proteoglycan accumulation except in advanced nephropathy. In severe glomerulosclerosis, increased decorin concentrations were found in plasma and urine, and urinary TGF-b/decorin complexes could be demonstrated indirectly. The failure to detect an increased glomerular proteoglycan quantity during the development of nephropathy could be explained by assuming that they are secreted into the mesangial matrix, but cleared via the vasculature or the urinary tract, in part as complexes with TGF-b. They could thereby counteract the vicious circle being characterized by increased TGF-b production and increased matrix deposition in diabetic nephropathy.

Renal and urinary glycosaminoglycans in an experimental model of chronic renal failure in rats

The present paper reports the glomerular and renal individual glycosaminoglycan levels in an experimental model of chronic renal failure (CRF) that was induced in Wistar rats by five-sixths mass ablation. Glycemia, body weight, blood systolic pressure and urinary excretions of creatinine, albumin and glycosaminoglycans were measured for 12 weeks. At the end of the experiment, the weight and the glycosaminoglycan composition of the kidneys were determined. In control rats, heparan sulfate was the main glycosaminoglycan found both in whole kidney and isolated glomeruli, with trace amounts of dermatan sulfate. Isolated glomeruli presented higher heparan sulfate concentrations than whole kidney (expressed as mg/g dry weight). In CRF rats, albuminuria appeared from the 2 week on, and dermatan sulfate and chondroitin sulfate contents of the kidney increased, whereas heparan sulfate levels remained unaltered. Changes in urine glycosaminoglycans (heparan sulfate, chondroitin sulfate and dermatan sulfate) were not statistically significant. The increase in glomerular dermatan sulfate and chondroitin sulfate observed in this experimental model could be related to the mechanisms involved in the glomerulosclerosis and proteinuria that occur in CRF.

Antisense inhibition of decorin expression in myoblasts decreases cell responsiveness to transforming growth factor beta and accelerates skeletal muscle differentiation

Decorin is a member of the family of the small leucine-rich proteoglycans. In addition to its function as an extracellular matrix organizer, it has the ability to activate the epidermal growth factor receptor, and it forms complexes with various isoforms of transforming growth factor beta (TGF-beta). Decorin is expressed during skeletal muscle differentiation and is up-regulated in dystrophic muscle. In this study we investigated the role of decorin in TGF-beta-dependent inhibition of myogenesis. To probe the function of decorin during myogenesis, C(2)C(12) myoblasts were stably transfected with a plasmid expressing antisense decorin mRNA. The resulting inhibition of decorin expression led to the expression of myogenin, a master transcription factor for muscle differentiation, under growth conditions and accelerated skeletal muscle differentiation as determined by the expression of creatine kinase. In contrast myogenin expression was inhibited by adenovirally induced decorin expression or by adding exogenous decorin. Reduced synthesis of decorin resulted in a 7-fold decreased sensitivity to TGF-beta-mediated inhibition of myogenin expression. In contrast, adenovirally induced decorin expression in wild type cells resulted in a 5-fold increased sensitivity to TGF-beta-mediated inhibition of myogenin expression. Transfection studies with the TGF-beta-dependent promoter of the plasminogen activator inhibitor-1 coupled with luciferase revealed that the transducing receptors for TGF-beta1 and TGF-beta2 were involved in the different responses of wild type and antisense decorin myoblasts. These results demonstrate that a reduction of decorin expression or of decorin availability results in a decreased responsiveness to TGF-beta. These findings strongly suggest a new role for decorin during skeletal muscle terminal differentiation by activating TGF-beta-dependent signaling pathways.

Lectin and proteoglycan histochemistry of feline pacinian corpuscles

We studied carbohydrate residues of glycoproteins and proteoglycans (PGs) in peritoneal Pacinian corpuscles of five adult cats. Terminal monosaccharides of glycoproteins and related polysaccharides were identified by lectin histochemistry and the PGs and glycosaminoglycans (GAGs) by specific antibodies. The most intensive lectin staining reactions indicated an abundance of glycoconjugates with terminal mannose (Man) or sialic acid residues, but no complex-type oligosaccharides were detected within the corpuscles. Terminal fucose (Fuc) and galactose (Gal) residues typical for O-linked mucin-type glycoproteins generally associated with high water binding capacity were also absent. Antibodies against unsulfated chondroitin (C-0-S), chondroitin-4-sulfate (C-4-S), and decorin showed positive reactions in the interfibrillar spaces between the lamellae, around collagen fibers, and around the lamellae of the perineural capsule, especially in the outer parts known to contain Type II collagen. Biglycan showed a preference for the innermost part of the perineural capsule (intermediate layer), known to contain Type V collagen. Collagen V and biglycan are both linked to growth processes. Hyaluronic acid (HA), chondroitin-6-sulfate (C-6-S) chains, and a chondroitin sulfate proteoglycan (CSPG) were co-localized in the terminal glia. The study of carbohydrates with high water binding capacity may contribute to our understanding of the high viscoelasticity of Pacinian corpuscles.

Basement membrane and interstitial proteoglycans produced by MDCK cells correspond to those expressed in the kidney cortex

Multiple proteoglycans (PGs) are present in all basement membranes (BM) and may contribute to their structure and function, but their effects on cell behavior are not well understood. Their postulated functions include: a structural role in maintaining tissue histoarchitecture, or aid in selective filtration processes; sequestration of growth factors; and regulation of cellular differentiation. Furthermore, expression PGs has been found to vary in several disease states. In order to elucidate the role of PGs in the BM, a well-characterized model of polarized epithelium, Madin-Darby canine kidney (MDCK) cells has been utilized. Proteoglycans were prepared from conditioned medium by DEAE anion exchange chromatography. The eluted PGs were treated with heparitinase or chondroitinase ABC (cABC), separately or combined, followed by SDS-PAGE. Western blot analysis, using antibodies specific for various PG core proteins or CS stubs generated by cABC treatment, revealed that both basement membrane and interstitial PGs are secreted by MDCK cells. HSPGs expressed by MDCK cells are perlecan, agrin, and collagen XVIII. Various CSPG core proteins are made by MDCK cells and have been identified as biglycan, bamacan, and versican (PG-M). These PGs are also associated with mammalian kidney tubules in vivo.

Influence of decorin expression on transforming growth factor-beta-mediated collagen gel retraction and biglycan induction

Complex formation of transforming growth factor-beta (TGF-beta) with the small proteoglycan decorin has been considered to inactivate the cytokine. However, neither the TGF-beta-mediated stimulation of the retraction of collagen lattices in culture nor the enhanced transcription of biglycan were influenced by an excess of native decorin in the culture medium. In contrast, when MG-63 osteosarcoma cells were transfected with sense- or antisense-decorin-cDNA, which led to an over- or under-expression of the proteoglycan, they responded to TGF-beta differently. An inverse correlation between decorin expression and the TGF-beta-mediated stimulation of collagen gel retraction and biglycan induction, respectively, was found. These results are best explained by assuming that decorin is not inactivating but sequestering TGF-beta in the extracellular matrix.