Adhesion molecules in the glomerular mesangium

Abnormal glomerular basement membrane maturation impairs mesangial cell differentiation during murine postnatal nephrogenesis

Although mesangial cell-glomerular basement membrane (GBM) connections play a key role in maintaining the glomerular capillary loop structure, information remains limited about how these connections are formed during glomerulogenesis. We have previously shown that weakened podocyte-GBM interactions owing to tensin 2 (Tns2) deficiency lead to abnormal GBM maturation during postnatal glomerulogenesis. Here, we investigated whether abnormal GBM maturation affected mesangial cell-GBM connections and mesangial cell differentiation. Histological analysis of the outer cortical glomeruli in Tns2-deficient mice revealed that GBM materials overproduced by stressed immature podocytes accumulated in the mesangium and interrupted the formation of mesangial cell-GBM connections, resulting in fewer capillary loops compared with that of normal glomeruli. In addition, expression of α-smooth muscle actin, an immature mesangial cell marker, persisted in mesangial cells of Tns2-deficient outer cortical glomeruli even after glomerulogenesis was completed, resulting in mesangial expansion. Furthermore, analysis of mouse primary mesangial cells revealed that mesangial cell differentiation depended on the type of extracellular matrix components to which the cells adhered, suggesting the participation of mesangial cell-GBM connections in mesangial cell differentiation. These findings suggest that abnormal GBM maturation affects mesangial cell differentiation by impairing mesangial cell-GBM connections.NEW & NOTEWORTHY Mesangial cell-glomerular basement membrane (GBM) connections play an important role in maintaining the structural integrity of the glomerular tuft. However, information remains scarce about how GBM maturation affects the formation of these connections during glomerular development. Here, we show that abnormal GBM maturation due to tensin 2 deficiency affects mesangial cell differentiation by impairing mesangial cell-GBM connections during postnatal glomerulogenesis.

Sourcing cells for in vitro models of human vascular barriers of inflammation

The vascular system plays a critical role in the progression and resolution of inflammation. The contributions of the vascular endothelium to these processes, however, vary with tissue and disease state. Recently, tissue chip models have emerged as promising tools to understand human disease and for the development of personalized medicine approaches. Inclusion of a vascular component within these platforms is critical for properly evaluating most diseases, but many models to date use "generic" endothelial cells, which can preclude the identification of biomedically meaningful pathways and mechanisms. As the knowledge of vascular heterogeneity and immune cell trafficking throughout the body advances, tissue chip models should also advance to incorporate tissue-specific cells where possible. Here, we discuss the known heterogeneity of leukocyte trafficking in vascular beds of some commonly modeled tissues. We comment on the availability of different tissue-specific cell sources for endothelial cells and pericytes, with a focus on stem cell sources for the full realization of personalized medicine. We discuss sources available for the immune cells needed to model inflammatory processes and the findings of tissue chip models that have used the cells to studying transmigration.

The Feasibility of Targeted Magnetic Iron Oxide Nanoagent for Noninvasive IgA Nephropathy Diagnosis

IgA nephropathy is the most common glomerular disease in the world and has become a serious threat to human health. Accurate and non-invasive molecular imaging to detect and recognize the IgA nephropathy is critical for the subsequent timely treatment; otherwise, it may progress to end-stage renal disease and lead to glomerular dysfunction. In this study, we have developed a sensitive, specific, and biocompatible integrin αvβ3-targeted superparamagnetic Fe₃O₄ nanoparticles (NPs) for the noninvasive magnetic resonance imaging (MRI) of integrin αvβ3, which is overexpressed in glomerular mesangial region of IgA nephropathy. The rat model of IgA nephropathy was successfully established and verified by biochemical tests and histological staining. Meanwhile, the clinical ¹⁸F-AlF-NOTA-PRGD2 probe molecule was utilized to visualize and further confirmed the IgA nephropathy in vivo via positron emission computed tomography. Subsequently, the Fe₃O₄ NPs were conjugated with arginine–glycine–aspartic acid (RGD) molecules (Fe₃O₄-RGD), and their integrin αvβ3-targeted T2-weighted imaging (T2WI) potential has been carefully evaluated. The Fe₃O₄-RGD demonstrated great relaxation in vivo. The T2WI signal of renal layers in the targeted group at 3 h after intravenous injection of Fe₃O₄-RGD was distinctly lower than baseline, indicating MRI signal decreased in the established IgA nephropathy rat model. Moreover, the TEM characterization and Prussian blue staining confirmed that the Fe₃O₄-RGD was located at the region of glomerulus and tubular interstitium. Moreover, no obvious signal decreased was detected in the untargeted Fe₃O₄ treated and normal groups. Collectively, our results establish the possibility of Fe₃O₄-RGD serving as a feasible MRI agent for the noninvasive diagnosis of IgA nephropathy.

Mesangial Cells Exhibit Features of Antigen-Presenting Cells and Activate CD4+ T Cell Responses

Background

Mesangial cells play a prominent role in the development of inflammatory diseases and autoimmune disorders of the kidney. Mesangial cells perform the essential functions of helping to ensure that the glomerular structure is stable and regulating capillary flow, and activated mesangial cells acquire proinflammatory activities. We investigated whether activated mesangial cells display immune properties and control the development of T cell immunity.

Methods

Flow cytometry analysis was used to study the expression of antigen-presenting cell surface markers and costimulatory molecules in mesangial cells. CD4+ T cell activation induced by mesangial cells was detected in terms of T cell proliferation and cytokine production.

Results

IFN-γ-treated mesangial cells express membrane proteins involved in antigen presentation and T cell activation, including MHC-II, ICAM-1, CD40, and CD80. This finding suggests that activated mesangial cells can take up and present antigenic peptides to initiate CD4+ T cell responses and thus act as nonprofessional antigen-presenting cells. Polarization of naïve CD4+ T cells (Th0 cells) towards the Th1 phenotype was induced by coculture with activated mesangial cells, and the resulting Th1 cells showed increased mRNA and protein expression of inflammation-associated genes.

Conclusion

Mesangial cells can present antigen and modulate CD4+ T lymphocyte proliferation and differentiation. Interactions between mesangial cells and T cells are essential for sustaining the inflammatory response in a variety of glomerulonephritides. Therefore, mesangial cells might participate in immune function in the kidney.

Tensin Is Expressed in Glomerular Mesangial Cells and Is Related to Their Attachment to Surrounding Extracellular Matrix

Glomerular expression of tensin was immunohistochemically studied in normal and diseased rat kidneys to determine whether tensin might be related to specific binding in individual glomerular cells. Normal rat kidneys displayed an intense immunofluorescence reaction for tensin along the basal aspects of proximal and distal tubule cells and parietal epithelial cells of Bowman's capsules. In glomeruli, a positive reaction for tensin was detected only in the mesangial areas. Immunoelectron microscopy revealed a positive reaction in the mesangial cell (MC) processes. RT-PCR and immunoprecipitation demonstrated mRNA and protein levels of tensin in cultured rat MCs. Mesangial tensin expression was decreased when the mesangium was injured by Habu snake venom. During the regenerative process after mesangiolysis, tensin expression was not detected in early-phase proliferating MCs that did not have extracellular matrix (ECM). The expression of tensin recovered in late-phase proliferating MCs, which became attached to regenerated ECM. It appears that tensin is related to MC attachment to surrounding ECM, which suggests that signal transduction regulated by tensin may be related to a specific mechanism of MC matrix regeneration. Furthermore, tensin can act as a marker for rat MCs because the expression of tensin was detected only in MCs in glomeruli.

Cell biology of mesangial cells: the third cell that maintains the glomerular capillary

The renal glomerulus consists of glomerular endothelial cells, podocytes, and mesangial cells, which cooperate with each other for glomerular filtration. We have produced monoclonal antibodies against glomerular cells in order to identify different types of glomerular cells. Among these antibodies, the E30 clone specifically recognizes the Thy1.1 molecule expressed on mesangial cells. An injection of this antibody into rats resulted in mesangial cell-specific injury within 15 min, and induced mesangial proliferative glomerulonephritis in a reproducible manner. We examined the role of mesangial cells in glomerular function using several experimental tools, including an E30-induced nephritis model, mesangial cell culture, and the deletion of specific genes. Herein, we describe the characterization of E30-induced nephritis, formation of the glomerular capillary network, mesangial matrix turnover, and intercellular signaling between glomerular cells. New molecules that are involved in a wide variety of mesangial cell functions are also introduced.

Mesangial cell αvβ8-integrin regulates glomerular capillary integrity and repair

αvβ8-Integrin is most abundantly expressed in the kidney, brain, and female reproductive organs, and its cognate ligand is latent transforming growth factor (LTGF)-β. Kidney αvβ8-integrin localizes to mesangial cells, and global β8-integrin gene (Itgb8) deletion results in embryonic lethality due to impaired placentation and cerebral hemorrhage. To circumvent the lethality and better define kidney αvβ8-integrin function, Cre-lox technology was used to generate mesangial-specific Itgb8-null mice. Platelet-derived growth factor-β receptor (PDGFBR)-Cre mice crossed with a reporter strain revealed functional Cre recombinase activity in a predicted mesangial pattern. However, mating between two different PDGFBR-Cre or Ren1(d)-Cre strains with Itgb8 (flox/-) mice consistently resulted in incomplete recombination, with no renal phenotype in mosaic offspring. Induction of a renal phenotype with Habu snake venom, a reversible mesangiolytic agent, caused exaggerated glomerular capillary microaneurysms and delayed recovery in Cre(+/-) PDGFRB (flox/-) mice compared with Cre(+/-) PDGFRB (flox/+) control mice. To establish the mechanism, in vitro experiments were conducted in Itgb8-null versus Itgb8-expressing mesangial cells and fibroblasts, which revealed β8-integrin-regulated adhesion to Arg-Gly-Asp (RGD) peptides within a mesangial-conditioned matrix as well as β8-integrin-dependent migration on RGD-containing LTGF-β or vitronectin matrices. We speculate that kidney αvβ8-integrin indirectly controls glomerular capillary integrity through mechanical tension generated by binding RGD peptides in the mesangial matrix, and healing after glomerular injury may be facilitated by mesangial cell migration, which is guided by transient β8-integrin interactions with RGD ligands.

Early diagnosis of acute kidney injury

There is a considerable lack of data concerning the diagnostic testing for kidney damage after surgical procedures. In this situation the most important variables should be examined with respect to their clinical informative value, the costs associated with their analysis, and their potential use in routine diagnostic testing. Forty patients in the surgical intensive care unit (ICU) with acute kidney injury (AKI) that developed during their stay of 13–18 (median, 16) days in the ICU were examined daily during their entire ICU admission. The bulk of the laboratory research consisted of the measurement of creatinine, urea, and sodium, as well as clearances rates and diuresis. Various tests for diagnosing regional renal damage (enzymes and proteins) were also carried out. The included photometry, nephelometric analysis, and ELISA (enzyme-linked immunosorbent assay). Five days before an AKI became evident, pathologic levels of urinary α1-microglobulin (tubular parameter) could already be confirmed. Serum creatinine values or creatinine clearance indicated the presence of disease only 1 day before the AKI was seen. Our results show that determination of α1-microglobulin and immunoglobulin G (glomerular parameter) levels, in addition to the level of urea in serum, be recommended for patients in surgical intensive care units who are at risk for AKI. Use of these procedures can achieve early recognition and sufficiently precise localization of renal damage.

Adapting mass spectrometry-based platforms for clinical proteomics applications: The capillary electrophoresis coupled mass spectrometry paradigm

Single biomarker detection is common in clinical laboratories due to the currently available method spectrum. For various diseases, however, no specific single biomarker could be identified. A strategy to overcome this diagnostic void is to shift from single analyte detection to multiplexed biomarker profiling. Mass spectrometric methods were employed for biomarker discovery in body fluids. The enormous complexity of biofluidic proteome compartments implies upstream fractionation. For this reason, mass spectrometry (MS) was coupled to two-dimensional gel electrophoresis, liquid chromatography, surface-enhanced laser desorption/ionization, or capillary electrophoresis (CE). Differences in performance and operating characteristics make them differentially suited for routine laboratory applications. Progress in the field of clinical proteomics relies not only on the use of an adequate technological platform, but also on a fast and efficient proteomic workflow including standardized sample preparation, proteomic data processing, statistical validation of biomarker selection, and sample classification. Based on CE-MS analysis, we describe how proteomic technology can be implemented in a clinical laboratory environment. In the last part of this review, we give an overview of CE-MS-based clinical studies and present information on identity and biological significance of the identified peptide biomarkers providing evidence of disease-induced changes in proteolytic processing and posttranslational modification.

Electrophoretic methods for analysis of urinary polypeptides in IgA-associated renal diseases

We evaluated the utility of SDS-PAGE/Western blot and CE coupled with MS (CE-MS) for detection of urinary polypeptide biomarkers of renal disease in patients with IgA-associated glomerulonephritides. In a reference cohort of 402 patients with various renal disorders and 207 healthy controls, we defined CE-MS patterns of renal damage and IgA nephropathy (IgAN). In a blinded analysis of a separate cohort of patients with IgAN (n = 10), Henoch-Schoenlein purpura (HSP) with nephritis (n = 10), and IgA-associated glomerulonephritis due to hepatitis C virus (HCV)-induced cirrhosis (n = 9), and healthy controls (n = 12), we compared SDS-PAGE/Western blot and CE-MS against clinical urinalysis for detection of urinary proteins/polypeptides. Urinalysis indicated proteinuria for 50, 90, and 33% of patients, respectively, and for none of the healthy controls. SDS-PAGE/Western blot showed urinary polypeptides abnormality for 90, 80, and 67% of patients, respectively, and for none of the healthy controls. CE-MS indicated a Renal Damage Pattern in 80, 80, and 100 of patients, respectively, and in 17% of healthy controls, with the more specific IgAN Pattern in 90, 90, and 1%, respectively, and in none of the healthy controls. Based on differences in CE-MS patterns, the disease mechanisms may differ among various IgA-associated glomerulonephritides. These exploratory findings should be evaluated in a prospective study with contemporaneous renal biopsy and urinary testing. If validated, it may be feasible to adapt the CE-MS methodology to develop novel tests to detect renal injury at earlier stages, assess clinical manifestations, and monitor responses to therapy in patients with IgA-associated renal diseases.

Urinary biomarkers of IgA nephropathy and other IgA-associated renal diseases

IgA nephropathy is the most common primary glomerulonephritis and is a frequent cause for chronic kidney disease in children and young adults. Glomerular deposition of IgA also characterizes other renal disorders, including Henoch-Schoenlein purpura nephritis and immune-complex glomerulonephritis afflicting patients with liver disease due to chronic infection with the hepatitis C virus. Several treatment options are often considered, with the goal to prevent end-stage renal failure. Unfortunately, the diagnosis currently requires an invasive procedure, a renal biopsy. Because of the inherent risks, repetitive renal biopsy is frequently foregone as a means to monitor the clinical course or response to treatment. Recent advances in the analysis of the urinary proteome suggest that the excreted polypeptides include disease-specific patterns. We review recent studies of the various techniques for the identification and validation of such urinary biomarkers of IgA-associated glomerulonephritides. Currently, capillary electrophoresis coupled with mass spectrometry (MS) offers the greatest promise. To date, it seems more likely that disease-specific urinary polypeptide biomarkers are comprised of a panel of several distinct and well-defined peptides rather than a single molecule. Even most patients in clinical remission with normal clinical testing (dipstick urinalysis and quantitative proteinuria) were correctly classified by the pattern of polypeptides identified by capillary electrophoresis coupled with MS. With confirmation and refinement, such urinary testing may provide a tool for the diagnosis and monitoring of patients with IgA-associated renal diseases that is more sensitive than current standard clinical testing and far less risky than renal biopsy.

Cell adhesion molecules in chemically-induced renal injury

Cell adhesion molecules are integral cell-membrane proteins that maintain cell-cell and cell-substrate adhesion and in some cases act as regulators of intracellular signaling cascades. In the kidney, cell adhesion molecules, such as the cadherins, the catenins, the zonula occludens protein-1 (ZO-1), occludin and the claudins are essential for maintaining the epithelial polarity and barrier integrity that are necessary for the normal absorption/excretion of fluid and solutes. A growing volume of evidence indicates that these cell adhesion molecules are important early targets for a variety of nephrotoxic substances including metals, drugs, and venom components. In addition, it is now widely appreciated that molecules, such as intracellular adhesion molecule-1 (ICAM-1), integrins, and selectins play important roles in the recruitment of leukocytes and inflammatory responses that are associated with nephrotoxic injury. This review summarizes the results of recent in vitro and in vivo studies indicating that these cell adhesion molecules may be primary molecular targets in many types of chemically-induced renal injury. Some of the specific agents that are discussed include cadmium (Cd), mercury (Hg), bismuth (Bi), cisplatin, aminoglycoside antibiotics, S-(1,2-dichlorovinyl)-l-cysteine (DCVC), and various venom toxins. This review also includes a discussion of the various mechanisms, by which these substances can affect cell adhesion molecules in the kidney.

Inhibitory effects of Cnidium officinale Makino and Tabanus fulvus Meigan on the high glucose-induced proliferation of glomerular mesangial cells

This study describes a potent activity of Cnidium officinale Makino (Cnidii rhizoma) and Tabanus fulvus Meigan (Tabanus) as an inhibitor of high glucose-induced proliferation of glomerular mesangial cells (GMCs). Raising the ambient glucose concentration from 5.6 to 25 mM for 24 h caused a dramatic increase in [3H]thymidine incorporation, and these increases were attenuated by treatment of GMCs with the extracts of Cnidii rhizoma and Tabanus (2.5-20 microg/ml) in a dose-dependent manner. In contrast, extracts of Cnidii rhizoma or Tabanus (20 microg/ml) did not change the growth of GMCs cultured under normal glucose condition. To clarify the mechanism involved in anti-proliferative activity of these medicines, this study examined the effects of Cnidii rhizoma and Tabanus on high glucose-stimulated extracellular matrix (ECM) protein accumulation and transforming growth factor-beta1 (TGF-beta1) production. Exposure of GMCs to high glucose significantly stimulated the ECM protein, collagen and fibronectin, accumulation and TGF-beta1 secretion, and these changes were dramatically diminished by treatment of GMCs with extracts of Cnidii rhizoma or Tabanus (10 microg/ml). Taken together, these results indicate that Cnidii rhizoma and Tabanus inhibit the high glucose-induced GMC proliferation partially through suppressing the ECM accumulation and TGF-beta1 production, suggesting that these medicines may be a promising agent for treating the development and progression of diabetic glomerulopathy.

Binding of the chemokine SLC/CCL21 to its receptor CCR7 increases adhesive properties of human mesangial cells

BACKGROUND

Adherence of human mesangial cells to the surrounding matrix contributes to glomerular homeostasis and is important for the maintenance of glomerular architecture and function in normal adult human kidney. The expression of chemokines and corresponding chemokine receptors on adjacent intrinsic renal cells indicates a novel chemokine/chemokine receptor function on nonimmune cells important for glomerular homeostasis. A constitutive expression of the chemokine SLC/CCL21 on human podocytes and of its corresponding receptor CCR7 on mesangial cells was shown before. SLC/CCL21 has a positive effect on proliferation and migration of mesangial cells and leads to increased cell survival in Fas-induced apoptosis. In leukocytes chemokines mediate integrin-dependent firm adhesion. Therefore, we examined the influence of chemokine receptor CCR7 activation by SLC/CCL21 on adhesive properties of human mesangial cells to matrix molecules.

METHODS

Adhesion assays, mechanical detachment assays, and evaluation of integrin activation by integrin-linked kinase activity were performed. Changes in the cytoskeletal F-actin were illustrated by phalloidin immunofluorescence staining.

RESULTS

SLC/CCL21 stimulation enhanced adhesiveness to fibronectin in a time- and concentration-dependent manner. SLC/CCL21 also increased the firmness of mesangial cells adhesion as judged by detachment assays. Furthermore activation of integrin-linked kinase occurred with SLC/CCL21 addition to mesangial cells, resulting in increased phosphorylation of glycogen synthase kinase-3 (GSK-3) and protein kinase B (PKB/Akt). Exposure of mesangial cells to SLC/CCL21 also resulted in F-actin rearrangements with membrane ruffling and extensions leading to bridging between mesangial cells.

CONCLUSION

Activation of CCR7 on mesangial cells by SLC/CCL21 enhances the degree and firmness of cell adhesion and increases cell spreading and the formation of cell-cell contacts. This includes integrin-linked kinase activation and F-actin rearrangements. Thus, local chemokine generation and chemokine receptor expression on mesangial cells may play an important role in the maintenance of glomerular homeostasis and in local remodeling processes.

Influence of beta3 integrin gene Leu/Pro33 polymorphism on primary glomerulonephritis

BACKGROUND

Beta3 integrin subunit is expressed as alpha(IIb)beta3 integrin on platelets and as alpha(v)beta3 integrin on a variety of cells including renal endothelial, mesangial and tubular cells. Leu33/Pro33 polymorphism of beta3 integrin has been associated with altered platelet functions, cardiovascular complications and the incidence of acute rejection episodes in renal transplantation. We investigated its influence on IgA nephropathy (IgAN), focal segmental glomerulosclerosis (FSGS) and membranous glomerulonephritis (MGN).

METHODS

We studied 251 patients with biopsy-proven primary glomerulonephritis (IgAN n = 127, FSGS n = 71, MGN n = 53) followed up for 6.3 +/- 5.3 years and 100 control subjects. Patients were classified according to the slope of reciprocal serum creatinine into slow (n = 162) and fast progressors (n = 89). Leu33/Pro33 polymorphism was determined by PCR amplification followed by restriction with the endonuclease Bcnl.

RESULTS

The genotype frequencies were similar in patients and controls (n.s.). Initial renal function, proteinuria and blood pressure did not differ significantly between patients with different genotypes (n.s.). The genotype frequencies were similar in slow and fast progressors (n.s.). Furthermore, Leu33/Pro33 polymorphism had no impact on renal survival in the Kaplan-Meier analysis (n.s.).

CONCLUSION

Our results indicate that beta3 integrin Leu33/Pro33 polymorphism is not a risk factor or a marker of progression in primary glomerulonephritis.

Phytolacca americana inhibits the high glucose-induced mesangial proliferation via suppressing extracellular matrix accumulation and TGF-beta production

This study describes a potential of Phytolaccaceae (Phytolacca americana var.) as an inhibitor of high glucose-stimulated production of extracellular matrix (ECM) proteins and TGF-beta in cultured glomerular mesangial cells (GMCs). Raising the ambient glucose concentration for 24 hrs caused a dose-dependent increase in [3H]thymidine incorporation of GMCs, and the maximal response was achieved at 20 mM. Phytolaccaceae extracts (2.5-20 microg/ml) inhibited the high glucose-induced [3H]thymidine incorporation in a dose-dependent manner, and the concentrations tested here did not affect to the cell viability. Exposure of the GMCs to 20 mM glucose caused both ECM (collagen and fibronectin) accumulation and TGF-beta secretion, and these changes were significantly diminished by treatment of GMCs with Phytolaccaceae (10 microg/ml). Taken together, these results indicate that Phytolaccaceae inhibits the high glucose-induced GMCs proliferation partially through suppressing accumulation of ECM components and TGF-beta production, suggesting that Phytolaccaceae may be a promising agent for treating the development and progression of diabetic glomerulopathy.

Role of alpha8 integrin in mesangial cell adhesion, migration, and proliferation

BACKGROUND

Extracellular matrix receptors of the integrin family are known to regulate cell adhesion, migration, and proliferation. The alpha8 integrin chain is expressed in the glomerulus exclusively by mesangial cells. The contribution of alpha8 to mesangial cell function, however, has not yet been studied.

METHODS

Mesangial cells from wild-type and alpha8-deficient mice were isolated and characterized. Integrin expression was assessed by real-time polymerase chain reaction (PCR), Western blot, or fluorescence-activated cell sorter (FACS) analysis. Cell adhesion was determined by conventional attachment assay and a centrifugal assay for cell adhesion. Cell migration was determined by a fluorescence-based transmigration assay and a chemotaxis assay. Proliferation rates were determined by BrdU and [3H]-thymidine assays.

RESULTS

On the alpha8 ligands fibronectin and vitronectin, but not on collagens, attachment of alpha8-deficient mesangial cells was reduced compared to wild-type cells. In contrast, alpha8-deficient mesangial cells migrated more easily and displayed an increased proliferative response on fibronectin or vitronectin, but not on collagens, compared to wild-type cells. These effects were not due to an up-regulation of the fibronectin or vitronectin receptors alpha5 or alphav in alpha8-deficient mesangial cells, as the cell surface expression of integrins alpha5 and alphav was comparable in wild-type and alpha8-deficient mesangial cells.

CONCLUSION

These findings confirm a role for alpha8 integrin in the regulation of the mesangial cell phenotype. alpha8 integrin seems to promote adhesion, but inhibit migration and proliferation of mesangial cells. Thus, the data support the hypothesis that alpha8 integrin could play an important role for maintaining tissue integrity in the glomerulus during glomerular injury.

Blocking of alpha 5 integrin stimulates production of TGF-beta and PAI-1 by human mesangial cells

Expression of integrin, which mediates cell-matrix interaction, is affected by several cytokines, in particular by transforming growth factor-beta (TGF-beta). However, it is unknown whether, in an opposite way, a specific integrin is involved in cytokine synthesis. We tested this hypothesis. Function-blocking anti-alpha 5 integrin (fibronectin receptor) antibody increased TGF-beta secretion in growth-arrested human mesangial cells (2.3-fold) compared with control IgG or anti-alpha v beta 3 integrin (receptor for several matrix proteins) antibody. It also increased the secretion of plasminogen activator inhibitor-1 (PAI-1), a protein associated with matrix increase, by 3.2-fold. The increase in PAI-1 secretion induced by anti-alpha 5 integrin antibody was not abrogated by anti-TGF-beta neutralizing antibody. These results indicate that function-blocking of anti-alpha 5 integrin stimulates TGF-beta as well as PAI-1 production, suggesting that alpha 5 integrin is involved in fibrotic process. Function-modulation of a specific integrin thus appears to play a role in glomerular remodeling.

Mesangial cells organize the glomerular capillaries by adhering to the G domain of laminin alpha5 in the glomerular basement membrane

In developing glomeruli, laminin alpha5 replaces laminin alpha1 in the glomerular basement membrane (GBM) at the capillary loop stage, a transition required for glomerulogenesis. To investigate domain-specific functions of laminin alpha5 during glomerulogenesis, we produced transgenic mice that express a chimeric laminin composed of laminin alpha5 domains VI through I fused to the human laminin alpha1 globular (G) domain, designated Mr51. Transgene-derived protein accumulated in many basement membranes, including the developing GBM. When bred onto the Lama5 -/- background, Mr51 supported GBM formation, preventing the breakdown that normally occurs in Lama5 -/- glomeruli. In addition, podocytes exhibited their typical arrangement in a single cell layer epithelium adjacent to the GBM, but convolution of glomerular capillaries did not occur. Instead, capillaries were distended and exhibited a ballooned appearance, a phenotype similar to that observed in the total absence of mesangial cells. However, here the phenotype could be attributed to the lack of mesangial cell adhesion to the GBM, suggesting that the G domain of laminin alpha5 is essential for this adhesion. Analysis of an additional chimeric transgene allowed us to narrow the region of the alpha5 G domain essential for mesangial cell adhesion to alpha5LG3-5. Finally, in vitro studies showed that integrin alpha3beta1 and the Lutheran glycoprotein mediate adhesion of mesangial cells to laminin alpha5. Our results elucidate a mechanism whereby mesangial cells organize the glomerular capillaries by adhering to the G domain of laminin alpha5 in the GBM.

CTGF mediates TGF-beta-induced fibronectin matrix deposition by upregulating active alpha5beta1 integrin in human mesangial cells

Excessive deposition of fibronectin in the glomerular mesangium in diabetic nephropathy (DN) is partly due to the induction of transforming growth factor-beta (TGF-beta) by high glucose. TGF-beta induces its downstream mediator connective tissue growth factor (CTGF), which stimulates fibronectin matrix synthesis, a process that requires the presence of alpha5beta1 integrin. Although TGF-beta has been shown to upregulate alpha5beta1 integrin expression in human mesangial cells (HMC), little is known about the effect of CTGF on levels of this receptor. This study tested whether CTGF modulates alpha5beta1 expression by HMC in culture and whether changes induced by TGF-beta are mediated through the induction of CTGF. FACS analysis showed that both TGF-beta and CTGF significantly increased cell-surface alpha5beta1 levels compared with basal conditions. RT-PCR indicated that the changes were at the level of transcription. Treatment of cells with TGF-beta and antisense CTGF oligonucleotides significantly reduced the TGF-beta-induced increases in alpha5beta1 levels. CTGF and TGF-beta also significantly increased levels of ligand-occupied cell-surface beta1 integrins and cell adhesion to fibronectin, the main alpha5beta1 substrate. Antisense CTGF significantly reduced the number of adherent cells from TGF-beta-stimulated cultures. Finally, alpha5beta1 blocking antibodies inhibited HMC fibronectin matrix deposition, confirming the importance of this receptor for this process. Taken together, these data provide evidence that CTGF controls alpha5beta1 expression by HMC in vitro. Alterations in alpha5beta1 levels induced by TGF-beta are mediated at least in part through the induction of CTGF, and specific targeting of either alpha5beta1 or CTGF could be useful in controlling excessive fibronectin matrix production in DN.

Discoidin domain receptor 1 controls growth and adhesion of mesangial cells

Various types of collagen are known as modulators of mesangial cell proliferation. Here the function of the collagen-binding tyrosine kinase receptor discoidin domain receptor 1 (DDR1) in mesangial cells is investigated. The expression of DDR1 in the mouse kidney is confirmed by Northern analysis. In primary mesangial cells isolated from wild-type and DDR1-null mice, tyrosine phosphorylation in response to collagen-stimulation, adhesion to collagen, and cellular proliferation were measured. DDR1 phosphorylation was induced after overnight incubation of cells with type I collagen. Compared with wild-type cells, the adhesion of DDR1-null cells was drastically reduced. In contrast, DDR1-knockout cells showed significantly enhanced proliferation compared with wild-type cells. Both effects were largely independent of the collagen-binding alpha1/beta1 integrin function. This study found that the increased proliferation rate of DDR1-null cells is caused by a constitutive upregulation of p42/p44 and p38 mitogen-activated protein kinases (MAPK) activity. This is the first evidence indicating that DDR1 could be involved in the proliferative stage of renal disorders.

Metal-catalyzed oxidation of extracellular matrix proteins promotes human mesangial cell apoptosis and is associated with enhanced expression of Bax and caspase activation

Oxidative injury in glomerular disease may oxidize extracellular matrix proteins which might modulate their interaction with mesangial cells and thereby account for the hypocellularity seen in advanced glomerulosclerosis. In this study we evaluated whether oxidation of extracellular matrix could modulate human mesangial cell apoptosis. Human mesangial cells were seeded onto plates coated with unmodified (control) or oxidized Matrigel, laminin, or type IV collagen. Mesangial cell apoptosis was increased on oxidized Matrigel as well as on oxidized laminin and type IV collagen. Mesangial cells behaved similarly on plates coated with control and oxidized forms of the integrin ligand-containing peptide GRGDSP. Cells on oxidized matrix demonstrated enhanced expression of Bax, increased fragmentation of PARP, and diminished apoptosis in the presence of the interleukin-1 beta converting enzyme inhibitor Ac-Tyr-Val-Ala-Asp-aldehyde. These data suggest that oxidation of extracellular matrix proteins may enhance human mesangial cell apoptosis via a mechanism that appears to involve enhanced expression of Bax and caspase activation. This may account for irreversible mesangial hypocellularity in glomerulosclerosis.

Platelet collagen receptor alpha2beta1 integrin and glycoprotein IIIa Pl(A1/A2) polymorphisms are not associated with nephropathy in type 2 diabetes

Platelet glycoprotein receptors play a role in the pathogenesis of chronic diabetic complications. Genetic polymorphisms of the alpha2beta1 integrin and glycoprotein IIIa (GPIIIa) have been associated with myocardial infarction, stroke, and diabetic retinopathy. To identify risk factors for their development in a cohort of patients with type 2 diabetes, we evaluated clinical variables and genetic polymorphisms in the alpha2beta1 integrin and GPIIIa genes. Two hundred thirty-four subjects with type 2 diabetes (126 patients with and 108 patients without diabetic nephropathy), as well as 217 nondiabetic healthy subjects, were recruited for this study. Clinical factors for investigation included sex, age at diagnosis, duration of diabetes, body mass index (BMI), and fasting plasma glucose, hemoglobin A(1c) (HbA(1c)), total cholesterol, and triglyceride levels. Genotypes were determined by polymerase chain reaction and restriction fragment length polymorphism analyses. No difference in the Bgl II polymorphism of the alpha2beta1 integrin gene was found between patients with type 2 diabetes with or without nephropathy (11 [8.7%], 47 [37.3%], and 68 patients [54.0%] versus 10 [9.3%], 32 [29.6%], and 66 patients [61.1%] for Bgl II+/+, Bgl II+/-, and Bgl II-/-, respectively; P = 0.271). Multiple logistic regression analyses showed that duration of diabetes, BMI, hypertension, and poor glycemic control were four independent predictors for the development of diabetic nephropathy. No contribution of the Bgl II+ allele of the alpha2beta1 integrin was found for the risk for nephropathy (odds ratio, 1.258; 95% confidence interval, 0.655 to 2.418; P = 0.490). The Pl(A2) allele genotype was not found among our studied subjects. In conclusion, age, duration of diabetes, BMI, and HbA(1c) level are strong predictors for nephropathy in patients with type 2 diabetes. However, the Bgl II polymorphism of the alpha2beta1 integrin gene and the Apa I polymorphism of the platelet GPIIIa gene do not have a major role in the development of diabetic nephropathy in our population.

Bacitracin inhibits fibronectin matrix assembly by mesangial cells in high glucose

BACKGROUND

Accumulation of mesangial extracellular matrix is a major characteristic of diabetic nephropathy (DN). Expression of several extracellular matrix proteins is up-regulated in human mesangial cells (HMC) cultured in high glucose. One protein, fibronectin (FN), associates to form an insoluble disulfide-linked matrix and possesses inherent protein-disulfide isomerase (PDI) activity. Bacitracin is a known PDI inhibitor. We tested the hypothesis that inhibiting FN-PDI activity with bacitracin would disrupt excessive FN-matrix assembly by cultured HMCs grown under high glucose conditions.

METHODS

The effect of bacitracin on FN-PDI activity was tested using an RNase-refolding assay. High glucose cultures of HMC were labeled with (3)H-leucine, with and without bacitracin, and (3)H-FN immunoprecipitated from the medium and sequential extracts of cell layers to distinguish insoluble FN. FN transcription was assessed by reverse transcription-polymerase chain reaction (RT-PCR). Pericellular FN-matrix was examined by immunohistology.

RESULTS

Bacitracin inhibited the PDI activity of FN, with maximal inhibition at 1.0 mmol/L. Treatment of HMC cultures grown in high glucose with bacitracin brought about changes in the distribution of newly synthesized FN. With increasing concentrations of bacitracin there was a significant reduction in the level of FN present as an insoluble matrix of HMC cultures maintained in high glucose, and a corresponding increase in FN in medium. Decreases in FN matrix laid down by HMCs treated with different concentrations of bacitracin were seen by immunohistology. FN mRNA levels were unchanged.

CONCLUSION

PDI inhibition of FN reduces its association into an insoluble matrix and potentially provides a new approach to reduce excessive matrix deposition in DN.

[Renal expression of intercellular adhesion molecule-1 (ICAM-1) in IgA deposit mesangial nephropathy. A tubulointerstitial lesion marker]

BACKGROUND

The aim of this study was to determine the significance of the renal expression of ICAM-1 in IgA nephropathy (IgAN).

PATIENTS AND METHOD

First, we identified ICAM-1 (CD54) expression in tubular epithelial cells and interstitial leucocytes in renal biopsies from 45 patients with IgAN and 29 patients with non-glomerulonephritis nephropathy (non-GN). We then analysed the relationship between this expression and both histological and clinical data at the time of renal biopsy and after 2.4 (2) (X [SD]) years in IgAN, and 1.8 (1.5) years in non-GN.

RESULTS

In IgAN, tubular ICAM-1 positive staining was seen in 25 (55%) biopsies; it was associated with extracapillary proliferation, glomerulosclerosis involving less than 50% of glomerular area, interstitial cell infiltration and tubular atrophy. ICAM-1 positive interstitial leucocytes were 234 (307)/mm2; this expression correlated with glomerulosclerosis, tubular atrophy, interstitial fibrosis and serum creatinine (Cr) level. In patients with 50% increase in Cr level, ICAM-1 positive interstitial leucocytes were 516 (360)/mm2 as compared with 66 (87.8)/mm2 (U = 16; p < 0.005) in patients with stable Cr. In non-GN, tubular ICAM-1 expression was observed in 7 (24%) biopsies.

CONCLUSIONS

Tubular and Interstitial expression of ICAM-1 can be a marker of tubulointerstitial damage in IgAN. Interstitial ICAM-1, rather than tubular ICAM-1, may predict the progression of this disease.

Integrin expression and IgA nephropathy: in vitro modulation by IgA with altered glycosylation and macromolecular IgA

BACKGROUND

Signal transduction by mesangial cell (MC) integrins regulates cell growth and survival, extracellular matrix production, and organization. The aim of the study was to investigate human MC integrin modulation by differently glycosylated IgA and macromolecular IgA, which are thought to play a pathogenetic role in IgA nephropathy (IgAN).

METHODS

MCs were incubated with purified human polymeric IgA, heat-aggregated IgA, IgA glycoforms generated by enzymatic hydrolysis of saccharide residues and serum fractions from IgAN patients, and controls isolated by lectin affinity and containing IgA with peculiar glycan patterns. Integrins were quantitated by flow cytometry.

RESULTS

Cultured MCs highly expressed alphavbeta3 and some alpha3beta1; alphavbeta3 was up-regulated by matrix components (P < 0.02). In vitro desialylated and degalactosylated polymeric human IgA enhanced alphavbeta3 expression on cultured MCs (P < 0.001). Serum IgA glycoforms isolated from IgAN patients with high exposure of internal sugars, GalNAc, Neu5Ac2,6GalNAc, and Man enhanced alphav expression on cultured MCs more than healthy controls. CONCLUSIONS.: These data support the hypothesis that IgA glycation plays a role in modulating the cell-matrix interaction, and that this mechanism can be operating in IgAN.

Stretch-induced mesangial cell ERK1/ERK2 activation is enhanced in high glucose by decreased dephosphorylation

Glomerular hypertension and hyperglycemia are major determinants of diabetic nephropathy. We sought to identify the mechanisms whereby stretch-induced activation of mesangial cell extracellular signal-regulated kinase 1 and 2 (ERK1/ERK2) is enhanced in high glucose (HG). Mesangial cells cultured on fibronectin Flex I plates in normal glucose (NG; 5.6 mM) or HG (30 mM), were stretched by 15% elongation at 60 cycles/min for up to 60 min. In HG, a 5-min stretch increased ERK1/ERK2 phosphorylation by 6.4 +/- 0.4/4.3 +/- 0.3-fold (P < 0.05 vs. NG stretch). In contrast, p38 phosphorylation was increased identically by stretch in NG and HG. Unlike many effects of HG, augmentation of ERK activity by HG was not dependent on protein kinase C (PKC) as indicated by downregulation of PKC with 24-h phorbol ester or inhibition with bisindolylmaleimide IV. In both NG and HG, pretreatment with arginine-glycine-aspartic acid peptide (0.5 mg/ml) to inhibit integrin binding or with cytochalasin D (100 ng/ml) to disassemble filamentous (F) actin, significantly reduced phosphorylation of ERK1/ERK2 and p38. To determine whether the rate of mitogen-activated protein kinase dephosphorylation is affected by HG, cellular kinase activity was inhibited by depleting ATP. Post-ATP depletion, phosphorylation of ERK1/ERK2 was reduced to 36 +/- 9/51 +/- 14% vs. 9 +/- 5/7 +/- 6% in NG (P < 0.05, n = 5). Thus stretch-induced ERK1/ERK2 and p38 activation in both NG and HG is beta(1)-integrin and F-actin dependent. Stretch-induced ERK1/ERK2 is enhanced in high glucose by diminished dephosphorylation, suggesting reduced phosphatase activity in the diabetic milieu. Enhanced mesangial cell ERK1/ERK2 signaling in response to the combined effects of mechanical stretch and HG may contribute to the pathogenesis of diabetic nephropathy.

Distinct structural forms of type I collagen modulate cell cycle regulatory proteins in mesangial cells

BACKGROUND

Extracellular matrix molecules profoundly regulate cell behavior, including proliferation. In glomerulonephritis, type I collagen accumulates in the mesangium and is constantly structurally modified and degraded during the course of the disease.

METHODS

We studied how two structurally distinct forms of type I collagen, monomer versus polymerized fibrils, affect cell proliferation, mitogen-activated protein kinase (MAPK) activation, and expression of G1-phase regulatory proteins in cultured rat mesangial cells (MCs). To analyze the possible involvement of collagen-binding integrins in type I collagen-derived growth signals further, distribution patterns of integrin chains were examined by immunocytochemistry.

RESULTS

Polymerized type I collagen completely prevented the increase of DNA synthesis and cell replication induced by 5% fetal calf serum (FCS) or 25 ng/mL platelet-derived growth factor (PDGF) in MCs on monomer type I collagen. Protein expression of cyclins D1 and E was markedly down-regulated in MCs plated on polymerized type I collagen for eight hours in 5% FCS, as compared with MCs on monomer type I collagen. Incubation with 5% FCS reduced expression of the cdk-inhibitor protein p27Kip1 on monomer but not on polymerized type I collagen. Moreover, polymerized type I collagen markedly reduced cyclin E-associated kinase activity in the presence of 5% FCS. Polymerized type I collagen diminished the PDGF-induced phosphorylation and nuclear translocation of p42/p44 MAPK, but did not affect phosphorylation of PDGF beta-receptors. In MCs plated on monomer type I collagen, alpha1, alpha2, and beta1 integrin chains were recruited into focal contacts. However, on polymerized type I collagen, alpha2 and beta1, but not alpha1, integrin chains were condensed into focal contacts.

CONCLUSIONS

The growth-inhibitory effect of polymerized type I collagen is characterized by rapid changes of expression and/or activation of MAPK and G1-phase regulators and could result from the lack of alpha1beta1 integrin signaling in MCs on polymerized type I collagen. Conceivably, deposition of polymerized type I collagen might reflect a reparative response to control MC replication in glomerular inflammation.

Microangiopathy in kidney and simultaneous pancreas/kidney recipients treated with tacrolimus: evidence of endothelin and cytokine involvement

BACKGROUND

In the past 3 years, three transplant recipients [one kidney, two simultaneous pancreas/kidney (SPK)] developed a thrombotic thrombocytopenic purpura-like clinical syndrome. This was characterized by an abrupt fall in the hematocrit and platelet count with evidence of hemolysis (fragmented red blood cells and schistocytes) and transplant kidney dysfunction during the first 2 weeks after transplantation. This was also associated with pancreatic dysfunction in the two SPK recipients. In all three patients, elevated tacrolimus levels (>24 ng/ml) occurred.

METHODS

Serum cytokine and endothelin levels were determined retrospectively from stored (-70 degrees C) sera.

RESULTS

In each case tacrolimus was discontinued, and treatment with plasmapheresis, fresh frozen plasma, steroids, and OKT3 was begun. The clinical courses varied from mild (one patient), to moderate (one patient), to severe (one patient), complicated with seizures and coma. Each patient responded clinically and ultimately was converted to cyclosporine A, and/or mycophenolate mofetil. These clinical events were associated with a rise in serum levels of endothelin and several cytokines. Levels of endothelin were elevated at 209+/-137 pg/ml, particularly in the severe episode where peak levels reached 480 pg/ml (normal 0-20 pg/ml). Peak levels of IL-8 (104+/-36 pg/ml), interleukin- (IL) 10 (238+/-105 pg/ml), and/or IL-12 (306+/-119 pg(ml) mean+/-SE, occurred during or before the clinical event. Serum levels of tumor necrosis factor-a and interferon-gamma were elevated in 2 patients while levels of IL-2, IL-4, and IL-6 were not elevated during the acute phase.

CONCLUSIONS

These data are consistent with a mechanism of microangiopathy involving endothelial cell injury (associated with tacrolimus treatment), and accompanied by cytokines (IL-10, IL-12, tumor necrosis factor-a, interferon-gamma) that affect expression of adhesion molecules, chemokines (IL-8) that direct the influx of white blood cells and endothelins that may exacerbate underlying hypertension and increase shear force-related red blood cell destruction.

Alpha8 integrin in glomerular mesangial cells and in experimental glomerulonephritis

BACKGROUND

Mesangial cell (MC) proliferation and extracellular matrix accumulation are typical responses of renal glomeruli to injury. Extracellular matrix components are known to affect MC behavior, which is mediated primarily via integrin receptors of the beta1 family. In addition to alpha1, alpha3, alpha5, and alpha6 chains of beta1 integrins, recent studies have shown the alpha8 chain to be expressed in glomeruli and renal vasculature. alpha8beta1 can serve as a receptor for fibronectin, which is abundant in the mesangium. We investigated the glomerular expression pattern of the alpha8 chain in renal tissues of mouse, rat, and humans as well as in cultured MCs. In addition, the regulation of alpha8 expression in MCs was studied in culture and in nephritic rats.

METHODS

The expression of alpha8 protein in kidney tissue and cultured MCs was investigated by immunohistochemistry, immunocytochemistry, and Western blotting. The effects of TGF-beta1 on alpha8 mRNA levels in MCs were studied by Northern blot analysis. In addition, time course studies of glomerular abundance and localization of alpha8 were performed in rats with mesangioproliferative anti-Thy1.1 nephritis.

RESULTS

In tissue sections of normal human, rat, and mouse kidney, we found strong immunohistochemical staining for alpha8 in the mesangium and in the media of renal arterioles. Double staining for alpha8 and Thy1.1, a surface antigen of rat MCs, showed alpha8 to be specifically expressed in MCs but not in glomerular endothelial and epithelial cells. In anti-Thy1.1 nephritis of rats, the glomerular abundance of alpha8 protein was reduced in the early mesangiolytic phase but was increased greatly with subsequent MC proliferation, peaking at day 6 of disease. At later stages of this reversible form of nephritis, the number of MCs and the extent mesangial alpha8 staining declined to control levels. Cell culture experiments revealed that freshly plated MCs organize alpha8 into focal contacts within one hour after attachment to fibronectin and vitronectin substrata, showing colocalization with focal contact proteins vinculin and talin. Stimulation of MCs with transforming growth factor-beta1 led to increases of alpha8 mRNA and protein levels.

CONCLUSIONS

These results show that in human, rat, and mouse glomeruli, alpha8 integrin is strongly and exclusively expressed in MCs. Gene expression of alpha8 is regulated in cultured MCs, and alpha8 protein abundance is regulated in vivo and in MC culture. It is currently unclear what functional properties this integrin receptor protein has with regard to MC anchorage to extracellular matrix and modulation of the MC phenotype in normal and diseased glomeruli. However, in view of its abundance in the mesangium, alpha8beta1 integrin could be an important MC receptor of matrix ligands and may play a role in the embryology, physiology, and pathophysiology of the glomerular capillary tuft.

Inactivation of kinase cascades in mesangial cells grown on collagen type I

Growth on collagen type I gels is known to suppress the mitogenic responsiveness of mesangial cells. Because these cells proliferate in some renal diseases and themselves synthesize collagen type I, we examined the influence of growth on collagen upon several kinase signaling cascades involved in mesangial cell proliferation. Quiescent mesangial cells grown on collagen type I and then stimulated with serum showed a markedly diminished induction of the protooncogene c-fos, compared with their counterparts on plastic or fibronectin. This effect was accompanied by decreased activation of mitogen-activated (Erk family) and Ca2+/calmodulin-dependent protein kinases. Cells on collagen showed lower basal protein kinase C (PKC) activity and diminished levels of PKC-alpha and -zeta isoforms. Global phosphorylation of tyrosine residues was diminished on collagen, and tyrosine phosphorylation of Erk and focal adhesion kinase in response to serum was not detected, in contrast to cells on plastic. We conclude that attachment of mesangial cells to collagen type I results in a broad suppression of protein phosphorylation that is reflected in diminished induction of the c-fos gene and probably underlies the conversion of cultured mesangial cells to a nonproliferative phenotype.

Regulation of survival and death of mesangial cells by extracellular matrix

BACKGROUND

Cell-matrix interactions exert major effects on such phenotypic features as cell growth and differentiation. Apoptosis is an active form of cell death that is crucial for maintaining the appropriate number of cells as well as the organization of tissue. Recently, it has been suggested that apoptosis of the mesangial cells (MC) is important in glomerular remodeling after injury. The MC are surrounded by an extracellular matrix (ECM) in vivo. Since in disease conditions the mesangial matrix is altered quantitatively and qualitatively, it is of interest to determine whether cell-matrix interactions may influence apoptosis of the MC.

METHODS

We first investigated the differences in the susceptibility to apoptotic stimuli of the MC cultured on various ECM components (type I collagen, fibronectin, basement membrane matrix). We then determined whether the inhibition of MC-matrix interactions would affect apoptosis. Finally, interactions between MC and matrix were disrupted by the inhibition of beta1-integrin expression with antisense oligonucleotides (ODN).

RESULTS

When MC were cultured on type I collagen or fibronectin and deprived of serum for eight hours, the extracted DNA from the MC demonstrated an internucleosomal ladder pattern on gel electrophoresis that constituted the biochemical characteristic of apoptosis. However, no ladder pattern was apparent when MC were cultured on basement membrane matrix. The attachment of cells was completely inhibited when the MC were cultured on agarose-coated dishes for 24 hours. Gel electrophoresis of DNA extracted from these cells showed a ladder pattern. However, the MC attached to the substratum did not show any apoptosis. MC showed an increase in apoptotic cell death after treatment with antisense ODN against beta1-integrin molecule.

CONCLUSIONS

These results indicate that normal ECM may prevent the MC from undergoing apoptosis and serve as a survival factor for MC. Signals from ECM that prevent apoptosis may be mediated by beta1-integrin molecules.