Obliterative bronchiolitis (OB) is a major cause of allograft dysfunction after lung transplantation and is thought to result from immunologically mediated airway epithelial destruction and luminal fibrosis. Matrix metalloproteinases (MMPs) and tissue inhibitors of metalloproteinases (TIMPs) have been implicated in the regulation of lung inflammation, airway epithelial repair, and extracellular matrix remodeling and therefore may participate in the pathogenesis of OB. The goals of this study were to determine the expression profiles of MMPs and TIMPs and the role of TIMP-1 in the development of airway obliteration using the murine heterotopic tracheal transplant model of OB. We demonstrate the selective induction of MMP-3, MMP-9, MMP-12, and TIMP-1 in a temporally restricted manner in tracheal allografts compared with isografts. In contrast, the expression of MMP-7, TIMP-2, and TIMP-3 was decreased in allografts relative to isografts during the period of graft rejection. TIMP-1 protein localized to epithelial, mesenchymal, and inflammatory cells in the tracheal grafts in a temporally and spatially restricted manner. Using TIMP-1–deficient mice, we demonstrate that the absence of TIMP-1 in the donor trachea or the allograft recipient reduced luminal obliteration and increased re-epithelialization in the allograft compared with wild-type control at 28 d after transplantation. Our findings provide direct evidence that TIMP-1 contributes to the development of airway fibrosis in the heterotopic tracheal transplant model, and suggest a potential role for this proteinase inhibitor in the pathogenesis of OB in patients with lung transplant.
heterotopic tracheal transplant; matrix metalloproteinase; obliterative bronchiolitis; tissue inhibitor of metalloproteinase
Background. Dimethylarginines are inhibitors of NO synthesis and are involved in the pathogenesis of vascular diseases. In this study, we ask the question if asymmetric dimethylarginine (ADMA) and symmetric dimethylarginine (SDMA) levels change during fatal and reversible acute rejection, and contribute to the pathogenesis of chronic vasculopathy.
Methods. The Dark Agouti to Lewis rat strain combination was used to investigate fatal acute rejection. Fischer 344 kidneys were transplanted to Lewis rats to study reversible acute rejection episode and the process of chronic rejection. Isograft recipients and untreated Lewis rats were used as controls. l-arginine derivatives were determined by HPLC, and ADMA-metabolizing enzymes were studied by quantitative RT–PCR and western blotting.
Results. Renal transplantation transiently increased dimethylarginine levels independent of acute rejection. ADMA plasma levels did not importantly differ between recipients undergoing fatal or reversible acute rejection, whereas SDMA was even lower in recipients of Fisher 344 grafts. In comparison to isograft recipients, ADMA and SDMA levels were slightly elevated during reversible, but not during the process of chronic rejection. Increased dimethylarginine levels, however, did not block NO synthesis. Interestingly, protein methylation, but not ADMA degradation, was increased in allografts.
Conclusions. Our data do not support the concept that renal allografts are protected from fatal rejection by dimethylarginines. Dimethylarginines may play a role in triggering chronic rejection, but a contribution to vascular remodelling itself is improbable. In contrast, differential arginine methylation of yet unknown proteins by PRMT1 may be involved in the pathogenesis of acute and chronic rejection.
ADMA; kidney transplantation; l-arginine; rat; SDMA
A rat hepatoma cell line was shown to synthesize heparan sulfate and chondroitin sulfate proteoglycans. Unlike cultured hepatocytes, the hepatoma cells did not deposit these proteoglycans into an extracellular matrix, and most of the newly synthesized heparan sulfate proteoglycans were secreted into the culture medium. Heparan sulfate proteoglycans were also found associated with the cell surface. These proteoglycans could be solubilized by mild trypsin or detergent treatment of the cells but could not be displaced from the cells by incubation with heparin. The detergent-solubilized heparan sulfate proteoglycan had a hydrophobic segment that enabled it to bind to octyl- Sepharose. This segment could conceivably anchor the molecule in the lipid interior of the plasma membrane. The size of the hepatoma heparan sulfate proteoglycans was similar to that of proteoglycans isolated from rat liver microsomes or from primary cultures of rat hepatocytes. Ion-exchange chromatography on DEAE-Sephacel indicated that the hepatoma heparan sulfate proteoglycans had a lower average charge density than the rat liver heparan sulfate proteoglycans. The lower charge density of the hepatoma heparan sulfate can be largely attributed to a reduced number of N-sulfated glucosamine units in the polysaccharide chain compared with that of rat liver heparan sulfate. Hepatoma heparan sulfate proteoglycans purified from the culture medium had a considerably lower affinity for fibronectin-Sepharose compared with that of rat liver heparan sulfate proteoglycans. Furthermore, the hepatoma proteoglycan did not bind to the neoplastic cells, whereas heparan sulfate from normal rat liver bound to the hepatoma cells in a time-dependent reaction. The possible consequences of the reduced sulfation of the heparan sulfate proteoglycan produced by the hepatoma cells are discussed in terms of the postulated roles of heparan sulfate in the regulation of cell growth and extracellular matrix formation.
Basement membranes contain several proteoglycans, and those bearing heparan sulfate glycosaminoglycans such as perlecan and agrin usually predominate. Most mammalian basement membranes also contain chondroitin sulfate, and a core protein, bamacan, has been partially characterized. We have now obtained cDNA clones encoding the entire bamacan core protein of Mr = 138 kD, which reveal a five domain, head-rod-tail configuration. The head and tail are potentially globular, while the central large rod probably forms coiled-coil structures, with one large central and several very short interruptions. This molecular architecture is novel for an extracellular matrix molecule, but it resembles that of a group of intracellular proteins, including some proposed to stabilize the mitotic chromosome scaffold. We have previously proposed a similar stabilizing role for bamacan in the basement membrane matrix. The protein sequence has low overall homology, apart from very small NH2- and COOH-terminal motifs.
At the junctions between the distal globular domains and the coiled-coil regions lie glycosylation sites, with up to three N-linked oligosaccharides and probably three chondroitin chains. Three other Ser-Gly dipeptides are unfavorable for substitution. Fusion protein antibodies stained basement membranes in a pattern commensurate with bamacan, and they also Western blotted bamacan core protein from rat L2 cell cultures. The antibodies could also specifically immunoprecipitate an in vitro transcription/translation product from a full-length bamacan cDNA. The unusual structure of this proteoglycan is indicative of specific functional roles in basement membrane physiology, commensurate with its distinct expression in development and changes in disease models.
Osteocytes project long, slender processes throughout the mineralized matrix of bone, where they connect and communicate with effector cells. The interconnected cellular projections form the functional lacunocanalicular system, allowing fluid to pass for cell-to-cell communication and nutrient and waste exchange. Prevention of mineralization in the pericellular space of the lacunocanalicular pericellular space is crucial for uninhibited interstitial fluid movement. Factors contributing to the ability of the pericellular space of the lacunocanalicular system to remain open and unmineralized are unclear. Immunofluorescence and immunogold localization by transmission electron microscopy demonstrated perlecan/Hspg2 signal localized to the osteocyte lacunocanalicular system of cortical bone, and this proteoglycan was found in the pericellular space of the lacunocanalicular system. In this study we examined osteocyte lacunocanalicular morphology in mice deficient in the large heparan sulfate proteoglycan perlecan/Hspg2 in this tissue. Ultrastructural measurements with electron microscopy of perlecan/Hspg2-deficient mice demonstrated diminished osteocyte canalicular pericellular area, resulting from a reduction in the total canalicular area. Additionally, perlecan/Hspg2-deficient mice showed decreased canalicular density and a reduced number of transverse tethering elements per canaliculus. These data indicated that perlecan/Hspg2 contributed to the integrity of the osteocyte lacunocanalicular system by maintaining the size of the pericellular space, an essential task to promote uninhibited interstitial fluid movement in this mechanosensitive environment. This work thus identified a new barrier function for perlecan/Hspg2 in murine cortical bone. © 2011 American Society for Bone and Mineral Research.
OSTEOCYTE; PERLECAN/HSPG2; MECHANOSENSING; HEPARAN SULFATE; LACUNOCANALICULAR SYSTEM; CORTICAL BONE
In cardiac transplantation, chronic rejection takes the form of an occlusive vasculopathy. The mechanism underlying this disorder remains unclear. The purpose of this study was to investigate the role nitric oxide (NO) may play in the development of allograft arteriosclerosis. Rat aortic allografts from ACI donors to Wistar Furth recipients with a strong genetic disparity in both major and minor histocompatibility antigens were used for transplantation. Allografts collected at 28 d were found to have significant increases in both inducible NO synthase (iNOS) mRNA and protein as well as in intimal thickness when compared with isografts. Inhibiting NO production with an iNOS inhibitor increased the intimal thickening by 57.2%, indicating that NO suppresses the development of allograft arteriosclerosis. Next, we evaluated the effect of cyclosporine (CsA) on iNOS expression and allograft arteriosclerosis. CsA (10 mg/kg/d) suppressed the expression of iNOS in response to balloon-induced aortic injury. Similarly, CsA inhibited iNOS expression in the aortic allografts, associated with a 65% increase in intimal thickening. Finally, we investigated the effect of adenoviral-mediated iNOS gene transfer on allograft arteriosclerosis. Transduction with iNOS using an adenoviral vector suppressed completely the development of allograft arteriosclerosis in both untreated recipients and recipients treated with CsA. These results suggest that the early immune-mediated upregulation in iNOS expression partially protects aortic allografts from the development of allograft arteriosclerosis, and that iNOS gene transfer strategies may prove useful in preventing the development of this otherwise untreatable disease process.
Lipoprotein lipase (Lpl) acts on triglyceride-rich lipoproteins in the peripheral circulation, liberating free fatty acids for energy metabolism or storage. This essential enzyme is synthesized in parenchymal cells of adipose tissue, heart, and skeletal muscle and migrates to the luminal side of the vascular endothelium where it acts upon circulating lipoproteins. Prior studies suggested that Lpl is immobilized by way of heparan sulfate proteoglycans on the endothelium, but genetically altering endothelial cell heparan sulfate had no effect on Lpl localization or lipolysis. The objective of this study was to determine if extracellular matrix proteoglycans affect Lpl distribution and triglyceride metabolism.
Methods and Findings
We examined mutant mice defective in collagen XVIII (Col18), a heparan sulfate proteoglycan present in vascular basement membranes. Loss of Col18 reduces plasma levels of Lpl enzyme and activity, which results in mild fasting hypertriglyceridemia and diet-induced hyperchylomicronemia. Humans with Knobloch Syndrome caused by a null mutation in the vascular form of Col18 also present lower than normal plasma Lpl mass and activity and exhibit fasting hypertriglyceridemia.
This is the first report demonstrating that Lpl presentation on the lumenal side of the endothelium depends on a basement membrane proteoglycan and demonstrates a previously unrecognized phenotype in patients lacking Col18.
Chronic allograft nephropathy (CAN) is the leading cause of renal allograft loss in paediatric renal transplant recipients. CAN is the result of immunological and nonimmunological injury, including acute rejection episodes, hypoperfusion, ischaemia reperfusion, calcineurin toxicity, infection and recurrent disease. The development of CAN is often insidious and may be preceded by subclinical rejection in a well-functioning allograft. Classification of CAN is histological using the Banff classification of renal allograft pathology with classic findings of interstitial fibrosis, tubular atrophy, glomerulosclerosis, fibrointimal hyperplasia and arteriolar hyalinosis. Although improvement in immunosuppression has led to greater 1-year graft survival rates, chronic graft loss remains relatively unchanged and opportunistic infectious complications remain a problem. Protocol biopsy monitoring is not current practice in paediatric transplantation for CAN monitoring but may have a place if new treatment options become available. Newer immunosuppression regimens, closer monitoring of the renal allograft and management of subclinical rejection may lead to reduced immune injury leading to CAN in the paediatric population but must be weighed against the risk of increased immunosuppression and calcineurin inhibitor nephrotoxicity.
Chronic allograft nephropathy; CNI; Rejection; Kidney transplantation
We used antibodies raised against both a heparan sulfate proteoglycan purified from a mouse sarcoma and a chondroitin sulfate proteoglycan purified from a rat yolk sac carcinoma to study the appearance and distribution of proteoglycans in cultured cells. Normal rat kidney cells displayed a fibrillar network of immunoreactive material at the cell surface when stained with antibodies to heparan sulfate proteoglycan, while virally transformed rat kidney cells lacked such a surface network. Antibodies to chondroitin sulfate proteoglycan revealed a punctate pattern on the surface of both cell types. The distribution of these two proteoglycans was compared to that of fibronectin by double-labeling immunofluorescent staining. The heparan sulfate proteoglycan was found to codistribute with fibronectin, and fibronectin and laminin gave coincidental stainings. The distribution of chondroitin sulfate proteoglycan was not coincidental with that of fibronectin. Distinct fibers containing fibronectin but lacking chondroitin sulfate proteoglycan were observed. When the transformed cells were cultured in the presence of sodium butyrate, their morphology changed, and fibronectin, laminin, and heparan sulfate proteoglycan appeared at the cell surface in a pattern resembling that of normal cells. These results suggest that fibronectin, laminin, and heparan sulfate proteoglycan may be complexed at the cell surface. The proteoglycan may play a central role in assembly of such complexes since heparan sulfate has been shown to interact with both fibronectin and laminin.
Background: Extracellular transglutaminase-2 binds heparan sulfate and has adhesive/signaling pro-fibrotic functions.
Results: Two clusters of basic residues, distal in the linear sequence of transglutaminase-2, are required for heparin binding and cell adhesion.
Conclusion: Folding of the transglutaminase-2 protein brings basic residues in close proximity to form a functional heparin binding domain.
Significance: Mapping the heparan sulfate binding domain will enhance design of transglutaminase-2 inhibitors.
Heparan sulfate proteoglycans are critical binding partners for extracellular tranglutaminase-2 (TG2), a multifunctional protein involved in tissue remodeling events related to organ fibrosis and cancer progression. We previously showed that TG2 has a strong affinity for heparan sulfate (HS)/heparin and reported that the heparan sulfate proteoglycan syndecan-4 acts as a receptor for TG2 via its HS chains in two ways: by increasing TG2-cell surface trafficking/externalization and by mediating RGD-independent cell adhesion to fibronectin-TG2 matrix during wound healing. Here we have investigated the molecular basis of this interaction. Site-directed mutagenesis revealed that either mutation of basic RRWK (262–265) or KQKRK (598–602) clusters, forming accessible heparin binding sequences on the TG2 three-dimensional structure, led to an almost complete reduction of heparin binding, indicating that both clusters contribute to form a single binding surface. Mutation of residues Arg19 and Arg28 also led to a significant reduction in heparin binding, suggesting their involvement. Our findings indicate that the heparin binding sites on TG2 mainly comprise two clusters of basic amino acids, which are distant in the linear sequence but brought into spatial proximity in the folded “closed” protein, forming a high affinity heparin binding site. Molecular modeling showed that the identified site can make contact with a single heparin-derived pentasaccharide. The TG2-heparin binding mutants supported only weak RGD-independent cell adhesion compared with wild type TG2 or mutants with retained heparin binding, and both heparin binding clusters were critical for TG2-mediated cell adhesion. These findings significantly advance our knowledge of how HS/heparin influences the adhesive function of TG2.
Cell Adhesion; Extracellular Matrix; Fibronectin; Heparan Sulfate; Heparin; Heparan Sulfate Proteoglycans; Open Transglutaminase-2; Syndecan-4; Transglutaminase-2
Transplantation of growth-permissive cells or tissues was used to bridge a lesion cavity and induce axonal growth in experimental spinal cord injury (SCI). Axonal interactions between host and transplant may be affected by upregulation of inhibitory chondroitin sulfate proteoglycans (CSPGs) following various transplantation strategies. The extent of axonal growth and functional recovery after transplantation of embryonic spinal cord tissue decreases in adult compared to neonatal host. We hypothesized that CSPGs contribute to the decrease in the extent to which transplant supports axonal remodeling and functional recovery. Expression of CSPGs increased after overhemisection SCI in adult rats but not in neonates. Embryonic spinal cord transplant was surrounded by CSPGs deposited in host cord, and the interface between host and transplant seemed to contain a large amount of CSPGs. Intrathecally delivered chondroitinase ABC (C'ase) improved recovery of distal forelimb usage and skilled motor behavior after C4 overhemisection injury and transplantation in adults. This behavioral recovery was accompanied by an increased amount of raphespinal axons growing into the transplant, and raphespinal innervation to the cervical motor region was promoted by C'ase plus transplant. Moreover, C'ase increased the number of transplanted neurons that grew axons to the host cervical enlargement, suggesting that degradation of CSPGs supports remodeling not only of host axons but also axons from transplanted neurons. Our results suggest that CSPGs constitute an inhibitory barrier to prevent axonal interactions between host and transplant in adults, and degradation of the inhibitory barrier can potentiate transplant-mediated axonal remodeling and functional recovery after SCI.
chondroitin sulfate proteoglycans; transplantation; spinal cord injury; axonal remodeling; functional recovery; regeneration
Perlecan is a large multi-domain proteoglycan which is essential for normal cartilage development. In this study perlecan was localized in the pericellular matrix of hypertrophic chondrocytes in developing human cartilage rudiments. Perlecan immunopurified from medium conditioned by cultured human fetal chondrocytes was found to be substituted with heparan sulfate (HS), chondroitin sulfate (CS) and keratan sulfate (KS). Ligand and carbohydrate engagement (LACE) assays demonstrated that immunopurified chondrocyte-derived perlecan formed HS dependent ternary complexes with fibroblast growth factors (FGF) 2 and either FGFR receptors (FGFRs) 1 or 3, however these complexes were not biologically active in the BaF32 cell system. Chondrocyte-derived perlecan also formed HS dependent ternary complexes with FGF18 and FGFR3. The proliferation of BaF32 cells expressing FGFR3 was promoted by chondrocyte-derived perlecan in the presence of FGF18 and this activity was reduced by digesting the HS with either heparinase III or mammalian heparanase. These data suggest that FGF2 and 18 bind to discrete structures on the HS chains attached to chondrocyte-derived perlecan which modulate the growth factor activities. The presence and activity of mammalian heparanase may be important in the turnover of HS and subsequent signaling required for the establishment and maintenance of functional osteo-chondral junctions in long bone growth.
perlecan; heparan sulfate; fibroblast growth factor; fibroblast growth factor receptor; heparanase
Thrombospondin is a 420-kD platelet alpha-granule glycoprotein that binds specifically to heparin. We examined adhesion to thrombospondin of CHO K1 cells and three mutant CHO lines with varying deficiencies in glycosaminoglycan (GAG) synthesis. In an experiment in which the parent line (K1) had 78% adherence to thrombospondin adsorbed to tissue culture plastic, CHO S745 cells, with less than 6% normal GAG synthesis had 11% adherence. CHO S677 cells, with decreased heparan sulfate proteoglycan but increased chondroitin sulfate proteoglycan, had 42% adherence. CHO S803 cells, with decreased heparan sulfate proteoglycan and normal chondroitin sulfate proteoglycan, had 31% adherence. Heparin inhibited K1 cell adhesion to thrombospondin, but not fibronectin, in a concentration-dependent manner. Dermatan sulfate but not chondroitin sulfate was also inhibitory. There was markedly decreased K1 cell adhesion to a thrombospondin core fragment that lacked the heparin binding NH2-terminal domain. Purified heparin binding domain, although poorly adhesive when adsorbed to substratum, inhibited cell adhesion to intact thrombospondin. Adhesion was better for all cell lines tested, including three human tumor cell lines, when thrombospondin was adsorbed at pH 4.0 compared with pH 7.4. When adsorption of thrombospondin was done at pH 7.4, cell adhesion was better when thrombospondin was adsorbed in the presence of greater than or equal to 0.6 mM calcium, compared to 0.1 mM calcium or EDTA. These findings suggest that thrombospondin can adsorb to plastic with varying degrees of exposure of a cell adhesion domain. We conclude that the thrombospondin cell adhesion receptor on CHO cells is a heparan sulfate proteoglycan, and that cell adhesion to thrombospondin depends on conformation of adsorbed thrombospondin.
To investigate the expression of matrix metalloproteinase-2 (MMP-2) and tissue inhibitor of metallopropteinase-1 (TIMP-1) in the renal allografts of patients with chronic active antibody-mediated rejection (AMR), and to explore their role in the pathogenesis of AMR.
Immunohistochemistry assay and computer-assisted image analysis were used to detect the expression of MMP-2 and TIMP-1 in the renal allografts with interstitial fibrosis and tubular atrophy (IF/TA) in 46 transplant recipients and 15 normal renal tissue specimens as the controls. The association of the expression level of either MMP-2 or TIMP-1 with the pathological grade of IF/TA in AMR was analyzed.
The expression of either MMP-2 or TIMP-1 was significantly increased in the renal allografts of the recipients as compared with the normal renal tissue (P < 0.05). MMP-2 expression tended to decrease, while TIMP-1 and serum creatinine increased along with the increase of pathological grade of IF/TA (P < 0.05). In IF/TA groups, the expression of TIMP-1 was positively correlated to serum creatinine level (r = 0.718, P < 0.05).
It is suggested by the results that abnormal expressions of MMP-2 and TIMP-1 might play roles in the development of renal fibrosis in chronic AMR.
The virtual slide(s) for this article can be found here:
Matrix metalloproteinase-2; Tissue inhibitor of metalloproteinase-1; Chronic active antibody-mediate rejection; Interstitial fibrosis and tubular atrophy
Heparanase is an endo-β-glucuronidase that cleaves heparan sulfate side chains, leading to structural modifications that loosen the extracellular matrix barrier and associated with tumor metastasis, inflammation and angiogenesis. In addition, the highly sulfated heparan sulfate proteoglycans are important constituents of the glomerular basement membrane and its permselective properties. Recent studies suggest a role for heparanase in several experimental and human glomerular diseases associated with proteinuria such as diabetes, minimal change disease, and membranous nephropathy. Here, we quantified blood and urine heparanase levels in renal transplant recipients and patients with chronic kidney disease (CKD), and assessed whether alterations in heparanase levels correlate with proteinuria and renal function. We report that in transplanted patients, urinary heparanase was markedly elevated, inversely associated with estimated glomerular filtration rate (eGFR), suggesting a relationship between heparanase and graft function. In CKD patients, urinary heparanase was markedly elevated and associated with proteinuria, but not with eGFR. In addition, urinary heparanase correlated significantly with plasma heparanase in transplanted patients. Such a systemic spread of heparanase may lead to damage of cells and tissues alongside the kidney.The newly described association between heparanase, proteinuria and decreased renal function is expected to pave the way for new therapeutic options aimed at attenuating chronic renal allograft nephropathy, leading to improved graft survival and patient outcome.
Agrin is the key inducer of postsynaptic differentiations at the neuromuscular junction. The multidomain heparan sulfate proteoglycan is mediating via its N-terminal segment the interaction with laminin, whereas the C-terminal portion is responsible for Dystroglycan binding and clustering of the Acetylcholine receptor. Matrix metalloproteinases (MMP) are known to play essential roles in matrix remodeling, degradation and regulation of extracellular signaling networks.
Site-specific processing of Agrin provides key insight into regulatory effects of Matrix metalloproteinases (MMPs). Here, we present a detailed study of agrin processing by different MMPs together with a molecular understanding of binding and cleavage at both terminal fragments. The data suggest for a regulatory effect of MMP cleavage at particularly important functional sites of agrin. Cleave of agrin abolishes the agrin-laminin complex formation and the Acetylcholine receptor clustering at the neuromuscular junction.
Agrin is a target of specific MMP processing resulting in agrin subfragments with different regulatory activities. MMP processing is a powerful tool to regulate extracellular signaling networks.
Chronic allograft nephropathy (CAN) is a major indication for initiation of sirolimus (SRL) in renal transplantation (TX) to prevent deterioration of renal function. We evaluated whether the CAN score at time of sirolimus rescue (SRL-R) predicts renal allograft function. CAN score is the sum of the following 4 categories: glomerulopathy (cg, 0–3), interstitial fibrosis (ci, 0–3), tubular atrophy (ct, 0–3), and vasculopathy (cv, 0–3). This is a retrospective cohort study of renal transplant recipients from July 2001 to March 2004. Immunosuppression consisted of preconditioning with rabbit anti-thymocyte globulin or alemtuzumab and maintenance with tacrolimus (TAC) monotherapy with spaced weaning, if applicable, SRL-R was achieved by conversion from TAC, or by addition to reduced doses of TAC. Ninety patients received SRL. Thirty-three of these patients met the inclusion criteria of the following: (1) receipt of SRL for >6 months, and (2) follow-up of ≥6 months. There were 16 patients in the low-CAN (0–4) group and 17 patients in the high-CAN (>4) group. Cockcroft-Gault (C-G) glomerular filtration rate (GFR) was calculated at SRL-R and at 1, 3, 6, and 12 months. The ΔGFR was significantly better in the low-CAN group at 1, 3, and 6 months. A trend toward an improved ΔGFR was present at 12 months in the low-CAN group (P = .16). CAN scoring at the time of SRL-R predicts recovery of renal allograft function (as measured using ΔGFR), and should be used in preference to biochemical markers (Cr and C-G GFR), which may not be reliable predictors.
Fibroblast growth factor-18 (FGF-18) has been shown to regulate the growth plate chondrocyte proliferation, hypertrophy and cartilage vascularization necessary for endochondral ossification. The heparan sulfate proteoglycan perlecan is also critical for growth platechondrocyte proliferation. FGF-18 null mice exhibit a skeletal dwarfism similar to that of perlecan null mice. Growth plate perlecan contains chondroitin sulfate (CS) and heparan sulfate (HS) chains and FGF-18 is known to bind to heparin and to heparan sulfate from some sources. We used cationic filtration and immunoprecipitation assays to investigate the binding of FGF-18 to perlecan purified from the growth plate and to recombinant perlecan domains expressed in COS-7 cells. FGF-18 bound to perlecan with a kd of 145 nM. Near saturation, ~103 molecules of FGF-18 bound per molecule of perlecan. At the lower concentrations used, FGF-18 bound with a kd of 27.8 nM. This binding was not significantly altered by chondroitinase nor heparitinase digestion of perlecan, but was substantially and significantly reduced by reduction and alkylation of the perlecan core protein. This indicates that the perlecan core protein (and not the CS nor HS chains) is involved in FGF-18 binding. FGF-18 bound equally to full length perlecan purified from the growth plate and to recombinant domains I-III and III of perlecan. These data indicate that low affinity binding sites for FGF-18 are present in cysteine-rich regions of domain III of perlecan. FGF-18 stimulated 3H-thymidine incorporation in growth plate chondrocyte cultures derived from the lower and upper proliferating zones by 9- and 14-fold, respectively. The addition of perlecan reversed this increased incorporation in the lower proliferating chondrocytes by 74% and in the upper proliferating cells by 37%. These results suggest that perlecan can bind FGF-18 and alter the mitogenic effect of FGF-18 on growth plate chondrocytes.
Perlecan, a ubiquitous heparan sulfate proteoglycan, possesses angiogenic and growth-promoting attributes primarily by acting as a coreceptor for basic fibroblast growth factor (FGF-2). In this report we blocked perlecan expression by using either constitutive CMV-driven or doxycycline- inducible antisense constructs. Growth of colon carcinoma cells was markedly attenuated upon obliteration of perlecan gene expression and these effects correlated with reduced responsiveness to and affinity for mitogenic keratinocyte growth factor (FGF-7). Exogenous perlecan effectively reconstituted the activity of FGF-7 in the perlecan-deficient cells. Moreover, soluble FGF-7 specifically bound immobilized perlecan in a heparan sulfate-independent manner. In both tumor xenografts induced by human colon carcinoma cells and tumor allografts induced by highly invasive mouse melanoma cells, perlecan suppression caused substantial inhibition of tumor growth and neovascularization. Thus, perlecan is a potent inducer of tumor growth and angiogenesis in vivo and therapeutic interventions targeting this key modulator of tumor progression may improve cancer treatment.
The unc-52 gene encodes the nematode homologue of mammalian perlecan, the major heparan sulfate proteoglycan of the extracellular matrix. This is a large complex protein with regions similar to low-density lipoprotein receptors, laminin, and neural cell adhesion molecules (NCAMs). In this study, we extend our earlier work and demonstrate that a number of complex isoforms of this protein are expressed through alternative splicing. We identified three major classes of perlecan isoforms: a short form lacking the NCAM region and the C-terminal agrin-like region; a medium form containing the NCAM region, but still lacking the agrin-like region; and a newly identified long form that contains all five domains present in mammalian perlecan. Using region-specific antibodies and unc-52 mutants, we reveal a complex spatial and temporal expression pattern for these UNC-52 isoforms. As well, using a series of mutations affecting different regions and thus different isoforms of UNC-52, we demonstrate that the medium NCAM-containing isoforms are sufficient for myofilament lattice assembly in developing nematode body-wall muscle. Neither short isoforms nor isoforms containing the C-terminal agrin-like region are essential for sarcomere assembly or muscle cell attachment, and their role in development remains unclear.
Proteoglycans and hyaluronan play critical roles in heart development. In this study, human embryonic stem cells (hESC) were used as a model to quantify the synthesis of proteoglycans and hyaluronan in hESC in the early stages of differentiation, and after directed differentiation into cardiomyocytes. We demonstrated that both hESC and cardiomyocyte cultures synthesize an extracellular matrix (ECM) enriched in proteoglycans and hyaluronan. During cardiomyocyte differentiation, total proteoglycan and hyaluronan decreased and the proportion of proteoglycans bearing heparan sulfate chains was reduced. Versican, a chondroitin sulfate proteoglycan, accumulated in hESC and cardiomyocyte cultures. Furthermore, versican synthesized by hESC contained more N- and O-linked oligosaccharide than versican from cardiomyocytes. Transcripts for the versican variants, V0, V1, V2 and V3, increased in cardiomyocytes compared to hESC, with V1 most abundant. Hyaluronan in hESC had lower molecular weight than hyaluronan from cardiomyocyte cultures. These changes were accompanied by an increase in HAS-1 and HAS-2 mRNA in cardiomyocyte cultures, with HAS-2 most abundant. Interestingly, HAS-3 was absent from the cardiomyocyte cultures, but expressed by hESC. These results indicate that human cardiomyocyte differentiation is accompanied by specific changes in the expression and accumulation of ECM components and suggest a role for versican and hyaluronan in this process.
versican; hyaluronan; cardiomyocyte; differentiation; stem cells; glycosylation
The use of methylprednisolone (MP) and other corticosteroids for the treatment of acute liver allograft rejection is associated with severe toxicities in non-target tissues. Therefore, selective delivery of MP to the liver may improve its efficacy and alleviate its side effects. We investigated the effects of a novel liver-targeted dextran prodrug of MP (DMP) in an orthotopic rat liver transplantation (OLT) model.
The model consisted of a high responder rejection strain combination (Dark Agouti donors and Lewis recipients). Liver recipients were intravenously administered saline or a single subtherapeutic dose of MP (5 mg/kg) as the parent drug (MP) or its prodrug (DMP). Different groups were then monitored for graft survival or euthanized 5 or 9 days post-transplantation. Plasma chemistry, including alkaline phosphatase and bilirubin, allograft histology, and survival duration were determined.
Untreated recipients exhibited elevated plasma levels of liver injury markers, progressive portal and venous inflammation and cellular infiltration in liver allografts, and a mean graft survival time (MST) of 10.5 days. MP treatment did not alter any of these parameters. In contrast, a single dose of DMP resulted in a decrease in plasma levels of liver injury markers, a decrease in histological grade of rejection on day 5, and a substantial increase in MST (27.5 days).
These results demonstrate attenuation of acute rejection following local (allograft) immunosuppression with a single subtherapeutic dose of MP delivered as a liver-targeted prodrug. Dextran prodrugs may be useful for selective delivery of immunosuppressants to the liver following liver transplantation.
Dextran prodrugs; Methylprednisolone; Local immunosuppression; Targeted delivery; ALP, alkaline phosphatase; ALT, alanine aminotransferase; AST, aspartate aminotransferase; DMP, dextran methylprednisolone succinate; IL-2, interleukin-2; MP, methylprednisolone; OLT, orthotopic rat liver transplantation; RAI, rejection activity index; TNF-α, tumor necrosis factor-α
Heparan sulfate has been shown to be an important mediator of Plasmodium sporozoite homing and invasion of the liver, but the role of this glycosaminoglycan in mosquito vector host-sporozoite interactions is unknown. We have biochemically characterized the function of Anopheles gambiae peptide-O-xylosyltransferase (AgOXT1) and confirmed that AgOXT1 can modify peptides representing model heparan and chondroitin sulfate proteoglycans in vitro. Moreover, we also demonstrated that the mosquito salivary gland basal lamina proteoglycans are modified by heparan sulfate. We used RNAi-mediated knockdown of heparan sulfate biosynthesis in An. gambiae salivary glands to determine if Plasmodium falciparum sporozoites that are released from mosquito midgut oocysts use salivary gland heparan sulfate as a receptor for tissue invasion. Our data suggests that salivary gland basal lamina heparan sulfate glycosaminoglycans only partially mediate midgut sporozoite invasion of this tissue, and that in the absence of heparan sulfate, the presence of other surface co-receptors is sufficient to facilitate parasite entry.
Anopheles; malaria; glycobiology; glycosaminoglycan; cell invasion
Cultured human lung fibroblasts produce a large, nonhydrophobic heparan sulfate proteoglycan that accumulates in the extracellular matrix of the monolayer (Heremans, A., J. J. Cassiman, H. Van den Berghe, and G. David. 1988. J. Biol. Chem. 263: 4731-4739). A panel of four monoclonal antibodies, specific for four distinct epitopes on the 400-kD core protein of this extracellular matrix heparan sulfate proteoglycan, detects similar proteoglycans in human epithelial cell cultures. Immunohistochemistry of human tissues with the monoclonal antibodies reveals that these proteoglycans are concentrated at cell-matrix interfaces. Immunogold labeling of ultracryosections of human skin indicates that the proteoglycan epitopes are nonhomogeneously distributed over the width of the basement membrane. Immunochemical investigations and amino acid sequence analysis indicate that the proteoglycan from the fibroblast matrix shares several structural features with the large, low density heparan sulfate proteoglycan isolated from the Engelbreth-Holm-Swarm sarcoma. Thus, both epithelial cell sheets and individual mesenchymal cells accumulate a large heparan sulfate proteoglycan(s) at the interface with the interstitial matrix, where the proteoglycan may adopt a specific topological orientation with respect to this matrix.
The cell surface proteoglycan on normal murine mammary gland (NMuMG) epithelial cells consists of a lipophilic domain, presumably intercalated into the plasma membrane, and an ectodomain that binds via its glycosaminoglycan chains to matrix components, is released intact by proteases and is detected by monoclonal antibody 281-2. The antibody 281-2 also detects a proteoglycan in the culture medium conditioned by NMuMG cells. This immunoactive proteoglycan was purified to homogeneity using DEAE-cellulose chromatography, isopycnic centrifugation, and 281- 2 affinity chromatography. Comparison of the immunoreactive medium proteoglycan with the trypsin-released ectodomain revealed that these proteoglycans are indistinguishable by several criteria as both: (a) contain heparan sulfate and chondroitin sulfate chains; and (b) are similar in hydrodynamic size and buoyant density; (c) have the same size core protein (Mr approximately 53 kD); (d) are nonlipophilic as studied by liposomal intercalation and transfer to silicone-treated paper. Kinetic studies of the release of proteoglycan from the surface of suspended NMuMG cells are interpreted to indicate that the immunoreactive medium proteoglycan is derived directly from the cell surface proteoglycan. Suspension of the cells both augments the release and inhibits the replacement of cell surface proteoglycan. These results indicate that the cell surface proteoglycan of NMuMG cells can be shed by cleavage of its matrix-binding ectodomain from its membrane- associated domain, providing a mechanism by which the epithelial cells can loosen their proteoglycan-mediated attachment to the matrix.