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

LIC12254 Is a Leptospiral Protein That Interacts with Integrins via the RGD Motif

Pathogenic leptospires can bind to receptors on mammalian cells such as cadherins and integrins. Leptospira effectively adheres to cells, overcomes host barriers and spreads into the bloodstream, reaching internal target organs such as the lungs, liver and kidneys. Several microorganisms produce proteins that act as ligands of integrins through the RGD motif. Here, we characterized a leptospiral RGD-containing protein encoded by the gene lic12254. In silico analysis of pathogenic, intermediate and saprophytic species showed that LIC12254 is highly conserved among pathogenic species, and is unique in presenting the RGD motif. The LIC12254-coding sequence is greatly expressed in the virulent Leptospira interrogans L1-130 strain compared with the culture-attenuated L. interrogans M20 strain. We also showed that the recombinant protein rLIC12254 binds to αVβ8 and α8 human integrins most likely via the RGD motif. These interactions are dose-dependent and saturable, a typical property of receptor-ligand interactions. The binding of the recombinant protein lacking this motif-rLIC12254 ΔRAA-to αVβ8 was almost totally abolished, while that with the α8 human integrin was decreased by 65%. Taken together, these results suggest that this putative outer membrane protein interacts with integrins via the RGD domain and may play a key role in leptospirosis pathogenesis.

Mesangial cell: A hub in lupus nephritis

Lupus nephritis (LN) is a severe renal disease caused by the massive deposition of the immune complexes (ICs) in renal tissue, acting as one of the significant organ manifestations of systemic lupus erythematosus (SLE) and a substantial cause of death in clinical patients. As mesangium is one of the primary sites for IC deposition, mesangial cells (MCs) constantly undergo severe damage, resulting in excessive proliferation and increased extracellular matrix (ECM) production. In addition to playing a role in organizational structure, MCs are closely related to in situ immunomodulation by phagocytosis, antigen-presenting function, and inflammatory effects, aberrantly participating in the tissue-resident immune responses and leading to immune-mediated renal lesions. Notably, such renal-resident immune responses drive a second wave of MC damage, accelerating the development of LN. This review summarized the damage mechanisms and the in situ immune regulation of MCs in LN, facilitating the current drug research for exploring clinical treatment strategies.

Nephronectin-Integrin α8 signaling is required for proper migration of periocular neural crest cells during chick corneal development

During development, cells aggregate at tissue boundaries to form normal tissue architecture of organs. However, how cells are segregated into tissue precursors remains largely unknown. Cornea development is a perfect example of this process whereby neural crest cells aggregate in the periocular region prior to their migration and differentiation into corneal cells. Our recent RNA-seq analysis identified upregulation of nephronectin (Npnt) transcripts during early stages of corneal development where its function has not been investigated. We found that Npnt mRNA and protein are expressed by various ocular tissues, including the migratory periocular neural crest (pNC), which also express the integrin alpha 8 (Itgα8) receptor. Knockdown of either Npnt or Itgα8 attenuated cornea development, whereas overexpression of Npnt resulted in cornea thickening. Moreover, overexpression of Npnt variants lacking RGD-binding sites did not affect corneal thickness. Neither the knockdown nor augmentation of Npnt caused significant changes in cell proliferation, suggesting that Npnt directs pNC migration into the cornea. In vitro analyses showed that Npnt promotes pNC migration from explanted periocular mesenchyme, which requires Itgα8, focal adhesion kinase, and Rho kinase. Combined, these data suggest that Npnt augments cell migration into the presumptive cornea extracellular matrix by functioning as a substrate for Itgα8-positive pNC cells.

Co-Delivery of Dexamethasone and Captopril by α8 Integrin Antibodies Modified Liposome-PLGA Nanoparticle Hybrids for Targeted Anti-Inflammatory/Anti-Fibrosis Therapy of Glomerulonephritis

Purpose

Mesangial cells-mediated glomerulonephritis refers to a category of immunologically mediated glomerular injuries characterized by infiltration of circulating inflammatory cells, proliferation of mesangial cells, and the common pathological manifestation to the later stage is renal fibrosis, accompanied by excessive accumulation of extracellular matrix (ECM). Treatment regimens include glucocorticoids and immunosuppressive agents, but their off-target distribution causes severe systemic toxicity. Hence, specific co-delivery of “anti-inflammatory/anti-fibrosis” drugs to the glomerular mesangial cell (MC) region is expected to produce better therapeutic effects.

Methods

A novel kidney-targeted nanocarrier drug delivery system targeting MCs was constructed using passive targeting resulting from the difference in pore size between the glomerular endothelial layer and the basement membrane, and active targeting based on the specific binding of antibodies and antigens. Specifically, a liposome-nanoparticle hybrid (PLGA-LNHy) was formed by coating the surface of PLGA nanoparticles (NPs) with a phospholipid bilayer, and then PLGA-LNHy was co-modified with PEG and α8 integrin antibodies to obtain PLGA immunoliposomes (PLGA-ILs).

Results

The results showed that the obtained NPs had a core-shell structure, uniform and suitable particle size (119.1 ± 2.31 nm), low cytotoxicity, and good mesangial cell-entry ability, which can successfully accumulate in the glomerular MC region. Both dexamethasone (DXMS) and captopril (CAP) were loaded onto PLGA-ILs with a drug loading of 10.22 ± 1.00% for DXMS and 6.37 ± 0.25% for CAP (DXMS/CAP@PLGA-ILs). In vivo pharmacodynamics showed that DXMS/CAP@PLGA-ILs can effectively improve the pathological changes in the mesangial area and positive expression of proliferating cell nuclear antigen (PCNA) in glomeruli as well as reduce the expression of inflammatory factors, fibrotic factors and reactive oxygen species (ROS). Thus, renal inflammation and fibrosis were relieved.

Conclusion

We have provided a strategy to increase nanoparticle accumulation in MCs with the potential to implement regulatory effects of anti-inflammatory and anti-fibrosis in glomerulonephritis (GN).

Glomerular Endothelial Cells Are the Coordinator in the Development of Diabetic Nephropathy

The prevalence of diabetes is consistently rising worldwide. Diabetic nephropathy is a leading cause of chronic renal failure. The present study aimed to explore the crosstalk among the different cell types inside diabetic glomeruli, including glomerular endothelial cells, mesangial cells, podocytes, and immune cells, by analyzing an online single-cell RNA profile (GSE131882) of patients with diabetic nephropathy. Differentially expressed genes in the glomeruli were processed by gene enrichment and protein-protein interactions analysis. Glomerular endothelial cells, as well as podocytes, play a critical role in diabetic nephropathy. A subgroup of glomerular endothelial cells possesses characteristic angiogenesis genes, indicating that angiogenesis takes place in the progress of diabetic nephropathy. Immune cells such as macrophages, T lymphocytes, B lymphocytes, and plasma cells also contribute to the disease progression. By using iTALK, the present study reports complicated cellular crosstalk inside glomeruli. Dysfunction of glomerular endothelial cells and immature angiogenesis result from the activation of both paracrine and autocrine signals. The present study reinforces the importance of glomerular endothelial cells in the development of diabetic nephropathy. The exploration of the signaling pathways involved in aberrant angiogenesis reported in the present study shed light on potential therapeutic target(s) for diabetic nephropathy.

ITGA8 positive cells in the conventional outflow tissue exhibit Schlemm's canal endothelial cell properties

AIMS

Elevated intraocular pressure is primarily induced by the increased resistance of conventional outflow of aqueous humor. Dysfunction of the juxtacanalicular region of trabecular meshwork (TM) and Schlemm's canal (SC) endothelium, as the main conventional outflow tissue, have been implicated as the major reasons for the increased resistance. Integrins are widespread in these tissues, especially alpha8 integrin (ITGA8). We aim to investigate the properties of cells expressing ITGA8 in the conventional outflow tissue.

MAIN METHODS

Fluorescence in situ hybridization (FISH) and immunofluorescence (IF) were performed to detect the mRNA and protein levels of ITGA8 in human conventional outflow tissue. ITGA8-positive cells were isolated from the cultured human TM cells through a magnetic bead-based approach. Flow Cytometry was used to determine the purification efficiency. The expressions of TM and SC biomarkers and dexamethasone-induced myocilin secretion capacity of ITGA8-positive cells was assessed by Real-time PCR, IF and Western blot. A gel contraction assay was performed to evaluate contractility of ITGA8-positive cells after endothelin 1 treatment.

KEY FINDINGS

ITGA8 was found with robust expression near the inner wall of SC endothelium. After purification, the proportion of ITGA8-positive cells were increased by about 10%. ITGA8-positive cells were identified with the properties as SC endothelial cells, such as more robust expressions of SC biomarkers, less dexamethasone-inducible myocilin expression, and stronger contractility.

SIGNIFICANCE

This study demonstrated that cells expressing ITGA8 in SC region possess more properties as SC endothelial cells. Our data implicate a crucial role of ITGA8 in aqueous humor (AH) outflow resistance regulation.

A role for the alpha-8 integrin chain (itga8) in glomerular homeostasis of the kidney

Glomerulonephritis results in a dysregulation of glomerular cells and may end up in chronic alterations and subsequent loss of renal function. Therefore, understanding mechanisms, which contribute to maintain glomerular integrity, is a pivotal prerequisite for therapeutic interventions. The alpha-8 integrin chain seems to be an important player to maintain glomerular homeostasis by conferring mechanical stability and functional support for the renal capillary tuft.

Semaphorin-5A downregulation is associated with enhanced migration and invasion of BRAF-positive melanoma cells under vemurafenib treatment in melanomas with heterogeneous BRAF status

Tumor heterogeneity affects the efficacy of anticancer treatment as tumor subclones with distinct molecular patterns may be present within one tumor, leading to differing sensitivities to chemotherapeutic agents. In the present study, six melanoma tissue fragments were obtained from different parts of tumor of four patients and then the effect of vemurafenib treatment on biological characteristics and molecular processes of cell cultures was estimated by using MTT-test, apoptosis, migration and invasion assays, PCR real time. There was different BRAF status determined between cells derived from the central and peripheral regions of primary melanoma tumors. BRAF-positive melanoma cells showed an increased apoptotic rate under vemurafenib treatment, as well as increased migration and invasion rates, whereas BRAF-negative melanoma cells did not exhibit such tendency. Furthermore, semaphorin-5A levels were diminished in BRAF-positive cells, but not in BRAF-negative ones, which could be related to increased migration and invasion. Melanoma cells derived from different regions of the same tumor may differ by mutations status, molecular processes and biological response to target therapy. The downregulation of semaphorin-5A may be involved in divergent effects of anticancer agents on tumor cell biology.

Effects of Acute and Chronic Exposure to Residual Level Erythromycin on Human Intestinal Epithelium Cell Permeability and Cytotoxicity

Residual concentrations of erythromycin in food could result in gastrointestinal tract exposure that potentially poses a health-hazard to the consumer, affecting intestinal epithelial permeability, barrier function, microbiota composition, and antimicrobial resistance. We investigated the effects of erythromycin after acute (48 h single treatment with 0.03 μg/mL to 300 μg/mL) or chronic (repeated treatment with 0.3 µg/mL and 300 µg/mL erythromycin for five days) exposures on the permeability of human colonic epithelial cells, a model that mimics a susceptible intestinal surface devoid of commensal microbiota. Transepithelial electrical resistance (TER) measurements indicated that erythromycin above 0.3 µg/mL may compromise the epithelial barrier. Acute exposure increased cytotoxicity, while chronic exposure decreased the cytotoxicity. Quantitative PCR analysis revealed that only ICAM1 (intercellular adhesion molecule 1) was up-regulated during 0.3 μg/mL acute-exposure, while ICAM1, JAM3 (junctional adhesion molecule 3), and ITGA8 (integrin alpha 8), were over-expressed in the 300 μg/mL acute treatment group. However, during chronic exposure, no change in the mRNA expression was observed at 0.3 μg/mL, and only ICAM2 was significantly up-regulated after 300 μg/mL. ICAM1 and ICAM2 are known to be involved in the formation of extracellular matrices. These gene expression changes may be related to the immunoregulatory activity of erythromycin, or a compensatory mechanism of the epithelial cells to overcome the distress caused by erythromycin due to increased permeability.

Transformation of the Transcriptomic Profile of Mouse Periocular Mesenchyme During Formation of the Embryonic Cornea

Purpose

Defects in neural crest development are a major contributing factor in corneal dysgenesis, but little is known about the genetic landscape during corneal development. The purpose of this study was to provide a detailed transcriptome profile and evaluate changes in gene expression during mouse corneal development.

Methods

RNA sequencing was used to uncover the transcriptomic profile of periocular mesenchyme (pNC) isolated at embryonic day (E) 10.5 and corneas isolated at E14.5 and E16.5. The spatiotemporal expression of several differentially expressed genes was validated by in situ hybridization.

Results

Analysis of the whole-transcriptome profile between pNC and embryonic corneas identified 3815 unique differentially expressed genes. Pathway analysis revealed an enrichment of differentially expressed genes involved in signal transduction (retinoic acid, transforming growth factor-β, and Wnt pathways) and transcriptional regulation.

Conclusions

Our analyses, for the first time, identify a large number of differentially expressed genes during progressive stages of mouse corneal development. Our data provide a comprehensive transcriptomic profile of the developing cornea. Combined, these data serve as a valuable resource for the identification of novel regulatory networks crucial for the advancement of studies in congenital defects, stem cell therapy, bioengineering, and adult corneal diseases.

The Role of Focal Adhesion Kinase in Keratinocyte Fibrogenic Gene Expression

Abnormal skin scarring causes functional impairment, psychological stress, and high socioeconomic cost. Evidence shows that altered mechanotransduction pathways have been linked to both inflammation and fibrosis, and that focal adhesion kinase (FAK) is a key mediator of these processes. We investigated the importance of keratinocyte FAK at the single cell level in key fibrogenic pathways critical for scar formation. Keratinocytes were isolated from wildtype and keratinocyte-specific FAK-deleted mice, cultured, and sorted into single cells. Keratinocytes were evaluated using a microfluidic-based platform for high-resolution transcriptional analysis. Partitive clustering, gene enrichment analysis, and network modeling were applied to characterize the significance of FAK on regulating keratinocyte subpopulations and fibrogenic pathways important for scar formation. Considerable transcriptional heterogeneity was observed within the keratinocyte populations. FAK-deleted keratinocytes demonstrated increased expression of genes integral to mechanotransduction and extracellular matrix production, including Igtbl, Mmpla, and Col4a1. Transcriptional activities upon FAK deletion were not identical across all single keratinocytes, resulting in higher frequency of a minor subpopulation characterized by a matrix-remodeling profile compared to wildtype keratinocyte population. The importance of keratinocyte FAK signaling gene expression was revealed. A minor subpopulation of keratinocytes characterized by a matrix-modulating profile may be a keratinocyte subset important for mechanotransduction and scar formation.

Glomerular mesangial cell recruitment and function require the co-receptor neuropilin-1

Proteinuria has been reported in cancer patients receiving agents that target the transmembrane receptor neuropilin-1 (Nrp1) suggesting potential adverse effects on glomerular function. Here we show that Nrp1 is highly expressed by mesangial cells and that genetic deletion of the Nrp1 gene from PDGF receptor-β⁺ mesangial cells results in proteinuric disease and glomerulosclerosis, leading to renal failure and death within 6 wk of age in mice. The major defect is a failure of mesangial cell migration that is required to establish the mature glomerular tuft. In vitro data show that the potent chemotactic effect of PDGFB is lost in Nrp1-deficient mesangial cells. Biochemical analyses reveal that Nrp1 is required for PDGFB-dependent phosphorylation of p130 Crk-associated substrate (p130Cas), a large-scaffold molecule that is involved in motility of other cell types. In stark contrast, matrix adhesion and activation of ERK and Akt, which mediate proliferation of mesangial cells in response to PDGFB, are unaffected by the absence of Nrp1. Taken together, these results identify a critical cell-autonomous role for Nrp1 in the migratory behavior of mesangial cells and may help explain the renal effects that occur in patients receiving Nrp1-inhibitory drugs.

Physiological and Pathological Roles in Human Adrenal of the Glomeruli-Defining Matrix Protein NPNT (Nephronectin)

Primary aldosteronism is a common cause of hypertension, which becomes refractory if undiagnosed, but potentially curable when caused by an aldosterone-producing adenoma (APA). The discovery of somatic mutations and differences in clinical presentations led to recognition of small but common zona glomerulosa (ZG)-like adenomas, distinct from classical large zona fasciculata-like adenomas. The inverse correlation between APA size and aldosterone synthase expression prompted us to undertake a systematic study of genotype-phenotype relationships. After a microarray comparing tumor subtypes, in which NPNT (nephronectin) was the most highly (>12-fold) upregulated gene in ZG-like APAs, we aimed to determine its role in physiological and pathological aldosterone production. NPNT was identified by immunohistochemistry as a secreted matrix protein expressed exclusively around aldosterone-producing glomeruli in normal adrenal ZG and in aldosterone-dense ZG-like APAs; the highest expression was in ZG-like APAs with gain-of-function CTNNB1 mutations, whose removal cured hypertension in our patients. NPNT was absent from normal zona fasciculata, zona fasciculata-like APAs, and ZG adjacent to an APA. NPNT production was regulated by canonical Wnt pathway, and NPNT overexpression or silencing increased or reduced aldosterone, respectively. NPNT was proadhesive in primary adrenal and APA cells but antiadhesive and antiapoptotic in immortalized adrenocortical cells. The discovery of NPNT in the adrenal helped recognition of a common subtype of APAs and a pathway by which Wnt regulates aldosterone production. We propose that this arises through NPNT's binding to cell-surface integrins, stimulating cell-cell contact within glomeruli, which define ZG. Therefore, NPNT or its cognate integrin could present a novel therapeutic target.

Integrin α8 Is Abundant in Human, Rat, and Mouse Trophoblasts

OBJECTIVE

Integrins exert regulatory functions in placentogenesis. Null mutation of certain integrin α subunits leads to placental defects with subsequent fetal growth restriction or embryonic lethality in mice. So far, the placental role of α8 integrin remains to be determined.

METHODS

Localization of α8 integrin and its ligands, fibronectin (FN) and osteopontin (OPN), was studied by immunohistochemistry in human, rat, and mouse placenta. The vascularization of the placental labyrinth layer of α8 integrin-deficient mice was determined by CD31 staining. In humans, α8 integrin expression was assessed via real-time polymerase chain reaction in healthy placentas, in the placental pathologies such as intrauterine growth restriction (IUGR), preeclampsia, and HELLP-syndrome (hemolysis, elevated liver enzymes, low platelet count), as well as in primary extravillous trophoblasts (EVT) and villous trophoblasts.

RESULTS

In humans, α8 integrin was detected in first and third trimester syncytiotrophoblast and EVT. Although OPN showed the same localization, FN was observed in EVT only. No expressional changes in α8 integrin were detected in the placental pathologies studied. Rodent placenta showed α8 integrin expression in giant cells and in the labyrinth layer. The localization of OPN and FN, however, showed species-specific differences. Knockout of α8 integrin in mice did not cause IUGR, despite some reduction in labyrinth layer vascularization.

CONCLUSION

α8 Integrin is expressed in functional placental compartments among its ligands, OPN and/or FN, across species. Although this may point to a regulatory role in trophoblast function, our data from α8 integrin-deficient mice indicated only mild placental pathology. Thus, the lack of placental α8 integrin seems to be largely compensated for.

Pharyngeal morphogenesis requires fras1-itga8-dependent epithelial-mesenchymal interaction

Both Fras1 and Itga8 connect mesenchymal cells to epithelia by way of an extracellular 'Fraser protein complex' that functions in signaling and adhesion; these proteins are vital to the development of several vertebrate organs. We previously found that zebrafish fras1 mutants have craniofacial defects, specifically, shortened symplectic cartilages and cartilage fusions that spare joint elements. During a forward mutagenesis screen, we identified a new zebrafish mutation, b1161, that we show here disrupts itga8, as confirmed using CRISPR-generated itga8 alleles. fras1 and itga8 single mutants and double mutants have similar craniofacial phenotypes, a result expected if loss of either gene disrupts function of the Fraser protein complex. Unlike fras1 mutants or other Fraser-related mutants, itga8 mutants do not show blistered tail fins. Thus, the function of the Fraser complex differs in the craniofacial skeleton and the tail fin. Focusing on the face, we find that itga8 mutants consistently show defective outpocketing of a late-forming portion of the first pharyngeal pouch, and variably express skeletal defects, matching previously characterized fras1 mutant phenotypes. In itga8 and fras1 mutants, skeletal severity varies markedly between sides, indicating that both mutants have increased developmental instability. Whereas fras1 is expressed in epithelia, we show that itga8 is expressed complementarily in facial mesenchyme. Paired with the observed phenotypic similarity, this expression indicates that the genes function in epithelial-mesenchymal interactions. Similar interactions between Fras1 and Itga8 have previously been found in mouse kidney, where these genes both regulate Nephronectin (Npnt) protein abundance. We find that zebrafish facial tissues express both npnt and the Fraser gene fibrillin2b (fbn2b), but their transcript levels do not depend on fras1 or itga8 function. Using a revertible fras1 allele, we find that the critical window for fras1 function in the craniofacial skeleton is between 1.5 and 3 days post fertilization, which coincides with the onset of fras1-dependent and itga8-dependent morphogenesis. We propose a model wherein Fras1 and Itga8 interact during late pharyngeal pouch morphogenesis to sculpt pharyngeal arches through epithelial-mesenchymal interactions, thereby stabilizing the developing craniofacial skeleton.

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.

Alpha8 Integrin (Itga8) Signalling Attenuates Chronic Renal Interstitial Fibrosis by Reducing Fibroblast Activation, Not by Interfering with Regulation of Cell Turnover

The α8 integrin (Itga8) chain contributes to the regulation of cell proliferation and apoptosis in renal glomerular cells. In unilateral ureteral obstruction Itga8 is de novo expressed in the tubulointerstitium and a deficiency of Itga8 results in more severe renal fibrosis after unilateral ureteral obstruction. We hypothesized that the increased tubulointerstitial damage after unilateral ureteral obstruction observed in mice deficient for Itga8 is associated with altered tubulointerstitial cell turnover and apoptotic mechanisms resulting from the lack of Itga8 in cells of the tubulointerstitium. Induction of unilateral ureteral obstruction was achieved by ligation of the right ureter in mice lacking Itga8. Unilateral ureteral obstruction increased proliferation and apoptosis rates of tubuloepithelial and interstitial cells, however, no differences were observed in the tubulointerstitium of mice lacking Itga8 and wild type controls regarding fibroblast or proliferating cell numbers as well as markers of endoplasmic reticulum stress and apoptosis after unilateral ureteral obstruction. In contrast, unilateral ureteral obstruction in mice lacking Itga8 led to more pronounced tubulointerstitial cell activation i.e. to the appearance of more phospho-SMAD2/3-positive cells and more α-smooth muscle actin-positive cells in the tubulointerstitium. Furthermore, a more severe macrophage and T-cell infiltration was observed in these animals compared to controls. Thus, Itga8 seems to attenuate tubulointerstitial fibrosis in unilateral ureteral obstruction not via regulation of cell turnover, but via regulation of TGF-β signalling, fibroblast activation and/or immune cell infiltration.

Fibrillin-1 and alpha8 integrin are co-expressed in the glomerulus and interact to convey adhesion of mesangial cells

Fibrillin-1 is a microfibrillar extracellular matrix protein that was described to be a ligand for α8 integrin. α8 integrin is a matrix receptor specifically expressed in mesangial and smooth muscle cells of the kidney. In previous studies we detected glomerular expression of fibrillin-1. Moreover, fibrillin-1 promoted adhesion, migration, and proliferation of mesangial cells. We hypothesized that fibrillin-1 and α8 integrin might interact in the glomerulus, and thus, regulate mesangial cell properties. Our studies showed that fibrillin-1 and α8 integrin colocalize in the glomerular mesangium. Induction of experimental glomerulonephritis led to an increase of both fibrillin-1 and α8 integrin expression. In vitro studies revealed that mesangial cells deficient for α8 integrin adhere weaker to fibrillin-1 and migrate more easily on fibrillin-1 than wild-type mesangial cells. Baseline proliferation on fibrillin-1 is higher in α8 integrin-deficient mesangial cells, but the induction of proliferation is not different in α8 integrin-deficient and wild-type mesangial cells. We conclude that fibrillin-1 and α8 integrin interact, and thus, regulate mesangial cell adhesion and migration. The concomitant induction of both fibrillin-1 and α8 integrin in a self-limited model of glomerular injury points to a protective role of the interaction of fibrillin-1 with α8 integrin in the glomerulus resulting in reduced damage of the glomerular tuft as a consequence of firm adhesion of mesangial cells.

Under-expression of α8 integrin aggravates experimental atherosclerosis

Integrins play an important role in vascular biology. The α8 integrin chain attenuates smooth muscle cell migration but its functional role in the development of atherosclerosis is unclear. Therefore, we studied the contribution of α8 integrin to atherosclerosis and vascular remodelling. We hypothesized that α8 integrin expression is reduced in atherosclerotic lesions, and that its under-expression leads to a more severe course of atherosclerosis. α8 Integrin was detected by immunohistochemistry and qPCR and α8 integrin-deficient mice were used to induce two models of atherosclerotic lesions. First, ligation of the carotid artery led to medial thickening and neointima formation, which was quantified in carotid cross-sections. Second, after crossing into ApoE-deficient mice, the formation of advanced vascular lesions with atherosclerotic plaques was quantified in aortic en face preparations stained with Sudan IV. Parameters of renal physiology and histopathology were assessed: α8 integrin was detected in the media of human and murine vascular tissue and was down-regulated in arteries with advanced atherosclerotic lesions. In α8 integrin-deficient mice (α8(-/-) ) as well as α8(+/-) and α8(+/+) littermates, carotid artery ligation increased media:lumen ratios in all genotypes, with higher values in ligated α8(-/-) and α8(+/-) compared to ligated α8(+/+) animals. Carotid artery ligation increased smooth muscle cell number in the media of α8(+/+) mice and, more prominently, of α8(-/-) or α8(+/-) mice. On an ApoE(-/-) background, α8(+/-) and α8(-/-) mice developed more atherosclerotic plaques than α8(+/+) mice. α8 Integrin expression was reduced in α8(+/-) animals. Renal damage with increased serum creatinine and glomerulosclerosis was detected in α8(-/-) mice only. Thus, under-expression of α8 integrin aggravates vascular lesions, while a complete loss of α8 integrin results in reduced renal mass and additional renal disease in the presence of generalized atherosclerosis. Our data support the hypothesis that integrin α8β1 has a protective role in arterial remodelling and atherosclerosis.

Nephronectin expression in glomeruli of renal biopsy specimens from various kidney diseases: nephronectin is expressed in the mesangial matrix expansion of diabetic nephropathy

BACKGROUND

In a previous proteomic study, we detected increased expression of nephronectin in the glomeruli from patients with diabetic nephropathy (DN). The aim of the present study was to clarify the usefulness of determining glomerular expression of nephronectin in kidney disease.

METHODS

We performed immunohistochemical staining for nephronectin in renal biopsy specimens from patients with a variety of kidney diseases (n = 190). The percentage of nephronectin-positive areas in the glomeruli was analyzed using an image analyzer.

RESULTS

Nephronectin immunoreactivity was clearly, strongly positive in the mesangial expansion and nodular lesions of DN (n = 18), whereas nephronectin immunoreactivity was negative in IgA glomerulonephritis, membranoproliferative glomerulonephritis, lupus nephritis, membranous glomerulonephritis, minor glomerular abnormalities, crescentic glomerulonephritis, and other kidney diseases, such as amyloidosis and light chain deposition disease. Nephronectin was stained weakly in sclerotic lesions, such as focal segmental glomerulosclerosis and hypertensive nephropathy. The percentage of nephronectin-positive areas in the glomeruli from DN patients [15.1 ± 4.7% (n = 18)] was significantly higher than that for other kidney diseases [5.5 ± 3.6% (n = 172)] (p < 0.001). In multiple regression analyses, fasting plasma glucose and hemoglobin A1c were significantly associated with the increase in the percentage of nephronectin-positive areas in the glomeruli (β = 0.23, p < 0.001 and β = 0.16, p = 0.045, respectively).

CONCLUSIONS

The expression of nephronectin was sufficient to discriminate DN from other kidney diseases with mesangial matrix expansion and nodular lesions. We consider that nephronectin staining could be helpful in the diagnosis of DN.

Integrins in kidney disease

A major hallmark of chronic kidney injury is fibrosis, which is characterized by increased accumulation of extracellular matrix components that replace the damaged tissue. Normally, the synthesis and degradation of extracellular matrix components are finely regulated; however, when matrix replacement goes unchecked, there is unwanted and irreversible tissue scarring with consequent organ damage, organ failure, and, in certain cases, death. Many factors, including cell-matrix interactions, play a role in the development of renal fibrosis. Cell-matrix interactions are made possible by integrins, a family of transmembrane receptors that, upon binding to the extracellular matrix, activate intracellular signaling. Thus, they control various cell functions, including survival, proliferation, migration, and matrix homeostasis. Genetic mutations in humans and the development of animal models lacking integrins in selective parts of the kidney have improved our understanding of molecular mechanisms and pathways controlling matrix remodeling in kidney disease. Here we outline the major integrins involved in kidney disease and some of the major molecular mechanisms whereby integrins contribute to kidney fibrosis.

RGD-Dependent Epithelial Cell-Matrix Interactions in the Human Intestinal Crypt

Interactions between the extracellular matrix (ECM) and integrin receptors trigger structural and functional bonds between the cell microenvironment and the cytoskeleton. Such connections are essential for adhesion structure integrity and are key players in regulating transduction of specific intracellular signals, which in turn regulate the organization of the cell microenvironment and, consequently, cell function. The RGD peptide-dependent integrins represent a key subgroup of ECM receptors involved in the maintenance of epithelial homeostasis. Here we review recent findings on RGD-dependent ECM-integrin interactions and their roles in human intestinal epithelial crypt cells.

Integrins in renal development

The kidney develops from direct interactions between the ureteric bud and the metanephric mesenchyme. The ureteric bud gives rise to the collecting system and the metanephric mesenchyme to the nephrons. The complex process of renal development which occurs between these embryologically distinct structures is mediated by numerous factors, including the communication of cells with their surrounding extracellular matrix. Integrins are the principal cellular receptors for extracellular matrix proteins, and they play a role in organ and tissue development. In this review we focus on how integrins regulate renal development.

The role of cell-extracellular matrix interactions in glomerular injury

Glomerulosclerosis is characterized by excessive deposition of extracellular matrix within the glomeruli of the kidney, glomerular cell death, and subsequent loss of functional glomeruli. While in physiological situations the levels of extracellular matrix components are kept constant by a tight balance between formation and degradation, in the case of injury that results in fibrosis there is increased matrix deposition relative to its breakdown. Multiple factors control matrix synthesis and degradation, thus contributing to the development of glomerulosclerosis. This review focuses primarily on the role of cell-matrix interactions, which play a critical role in governing glomerular cell cues in both healthy and diseased kidneys. Cell-extracellular matrix interactions are made possible by various cellular receptors including integrins, discoidin domain receptors, and dystroglycan. Upon binding to a selective extracellular matrix protein, these receptors activate intracellular signaling pathways that can either downregulate or upregulate matrix synthesis and deposition. This, together with the observation that changes in the expression levels of matrix receptors have been documented in glomerular disease, clearly emphasizes the contribution of cell-matrix interactions in glomerular injury. Understanding the molecular mechanisms whereby extracellular matrix receptors regulate matrix homeostasis in the course of glomerular injury is therefore critical for devising more effective therapies to treat and ideally prevent glomerulosclerosis.

Gene expression in the efferent ducts, epididymis, and vas deferens during embryonic development of the mouse

The tissues of the male reproductive tract are characterized by distinct morphologies, from highly coiled to un-coiled. Global gene expression profiles of efferent ducts, epididymis, and vas deferens were generated from embryonic day 14.5 to postnatal day 1 as tissue-specific morphologies emerge. Expression of homeobox genes, potential mediators of tissue-specific morphological development, was assessed. Twenty homeobox genes were identified as either tissue-enriched, developmentally regulated, or both. Additionally, ontology analysis demonstrated cell adhesion to be highly regulated along the length of the reproductive tract. Regulators of cell adhesion with variable expression between the three tissues were identified including Alcam, various cadherins, and multiple integrins. Immunofluorescence localization of the cell adhesion regulators POSTN and CDH2 demonstrated cell adhesion in the epithelium and mesenchyme of the epididymis may change throughout development. These results suggest cell adhesion may be modulated in a tissue-specific manner, playing an important role in establishing each tissue's final morphology.

Lack of α8 integrin leads to morphological changes in renal mesangial cells, but not in vascular smooth muscle cells

Background

Extracellular matrix receptors of the integrin family are known to regulate cell adhesion, shape and functions. The α8 integrin chain is expressed in glomerular mesangial cells and in vascular smooth muscle cells. Mice deficient for α8 integrin have structural alterations in glomeruli but not in renal arteries. For this reason we hypothesized that mesangial cells and vascular smooth muscle cells differ in their respective capacity to compensate for the lack of α8 integrin.

Results

Wild type and α8 integrin-deficient mesangial cells varied markedly in cell morphology and expression or localization of cytoskeletal molecules. In α8 integrin-deficient mesangial cells α-smooth muscle actin and CTGF were downregulated. In contrast, there were no comparable differences between α8 integrin-deficient and wild type vascular smooth muscle cells. Expression patterns of integrins were altered in α8 integrin-deficient mesangial cells compared to wild type mesangial cells, displaying a prominent overexpression of α2 and α6 integrins, while expression patterns of the these integrins were not different between wild type and α8 integrin-deficient vascular smooth muscle cells, respectively. Cell proliferation was augmented in α8 integrin-deficient mesangial cells, but not in vascular smooth muscle cells, compared to wild type cells.

Conclusions

Our findings suggest that α8 integrin deficiency has differential effects in mesangial cells and vascular smooth muscle cells. While the phenotype of vascular smooth muscle cells lacking α8 integrin is not altered, mesangial cells lacking α8 integrin differ considerably from wild type mesangial cells which might be a consequence of compensatory changes in the expression patterns of other integrins. This could result in glomerular changes in α8 integrin-deficient mice, while the vasculature is not affected in these mice.

Lack of {alpha}8-integrin aggravates podocyte injury in experimental diabetic nephropathy

Development of diabetic nephropathy is accompanied by changes in integrin-mediated cell-matrix interactions. The α8-integrin chain is specifically expressed in mesangial cells of the glomerulus. During experimental hypertension, α8-integrin plays a protective role in the glomerulus. We hypothesized that α8-integrin is involved in maintaining the integrity of the glomerulus in diabetic nephropathy. Experimental streptozotocin (STZ) diabetes led to an increased expression and glomerular deposition of α8-integrin. To test the functional role of α8-integrin, STZ diabetes was induced in mice with a homozygous (α8-/-) or heterozygous (α8+/-) deletion of the α8-integrin gene and in wild-type litters (α8+/+). Blood glucose and mean arterial blood pressure were not different in α8-/- and α8+/+ mice after 6 wk of diabetes. However, diabetic α8-/- mice developed significantly higher albuminuria and more glomerulosclerosis than diabetic α8+/+ mice. Moreover, in diabetic α8-/- mice, the number of glomerular cells staining positive for the podocyte markers WT-1 and vimentin were reduced more prominently than in diabetic α8+/+. The filtration barrier protein nephrin was downregulated in diabetic glomeruli with the strongest reduction observed in α8-/- mice. Taken together, α8-/- mice developed more severe glomerular lesions and podocyte damage after onset of STZ diabetes than α8+/+ mice, indicating that α8-integrin is protective for the structure and function of the glomerulus and maintains podocyte integrity during the development of diabetic nephropathy.

Integrin alpha8beta1 regulates adhesion, migration and proliferation of human intestinal crypt cells via a predominant RhoA/ROCK-dependent mechanism

Background. Integrins are transmembrane αβ heterodimer receptors that function as structural and functional bridges between the cytoskeleton and ECM (extracellular matrix) molecules. The RGD (arginine-glycine-aspartate tripeptide motif)-dependent integrin α8β1 has been shown to be involved in various cell functions in neuronal and mesenchymal-derived cell types. Its role in epithelial cells remains unknown.

Results. Integrin α8β1 was found to be expressed in the crypt cell population of the human intestine but was absent from differentiating and mature epithelial cells of the villus. The function of α8β1 in epithelial crypt cells was investigated at the cellular level using normal HIECs (human intestinal epithelial cells). Specific knockdown of α8 subunit expression using an shRNA (small-hairpin RNA) approach showed that α8β1 plays important roles in RGD-dependent cell adhesion, migration and proliferation via a RhoA/ROCK (Rho-associated kinase)-dependent mechanism as demonstrated by active RhoA quantification and pharmacological inhibition of ROCK. Moreover, loss of α8β1, through RhoA/ROCK, impairs FA (focal adhesion) complex integrity as demonstrated by faulty vinculin recruitment.

Conclusions. Integrin α8β1 is expressed in epithelial cells. In intestinal crypt cells, α8β1 is closely involved in the regulation of adhesion, migration and cell proliferation via a predominant RhoA/ROCK-dependent mechanism. These results suggest an important role for this integrin in intestinal crypt cell homoeostasis.

Systems biology evaluation of immune responses induced by human host defence peptide LL-37 in mononuclear cells

The immune system is very complex, it involves the integrated regulation and expression of hundreds of proteins. To understand in greater detail how the human host defence immunomodulatory peptide LL-37 interacts with innate immunity, a systems approach was pursued. Polychromatic flow cytometry was employed to demonstrate that within human peripheral blood mononuclear cells, CD14+ monocytes, myeloid and plasmocytoid dendritic cells and T- and B-lymphocytes, all responded to LL-37, with the differential production of intracellular cytokines. Microarray analyses with CD14+ monocytes indicated the differential expression of 475 genes in response to stimulation with LL-37. To understand this complex response, bioinformatic interrogation, using InnateDB, of the gene ontology, signalling pathways and transcription factor binding sites was undertaken. Activation of the IkappaBalpha/NFkappaB, mitogen-activated protein kinases p38, ERK1/2 and JNK, and PI3K signalling pathways in response to LL-37 was demonstrated by pathway and ontology over-representation analyses, and confirmed experimentally by inhibitor studies. Computational analysis of the predicted transcription factor binding sites upstream of the genes that were regulated by LL-37 predicted the involvement of several transcription factors including NFkappaB and five novel factors, AP-1, AP-2, SP-1, E2F1, and EGR, which were experimentally confirmed to respond to LL-37 by performing transcription factor array studies on nuclear extracts from LL-37 treated mononuclear cells. These data are discussed as reflecting the integration of several responsive signalling pathways through the involvement of transcription factor complexes in gene expression activated by LL-37 in human mononuclear cells.

Deletion of the alpha8 integrin gene does not protect mice from myocardial fibrosis in DOCA hypertension

BACKGROUND

In the heart, the alpha8 integrin chain is expressed in fibroblasts and vascular smooth-muscle cells but its functional role in the myocardium is unknown. Integrins can contribute to tissue fibrosis in several organs. We tested the hypothesis that alpha8 integrin-mediated cell-matrix interactions add to cardiac fibrotic alterations during hypertension.

METHODS

Desoxycorticosterone-acetate (DOCA)-salt hypertension was induced in mice homozygous for a deletion of the alpha8 integrin chain and wild-type mice. Histological and immunohistochemical evaluations were performed in heart tissue.

RESULTS

Blood pressure was slightly higher in DOCA-treated alpha8 integrin-deficient mice compared to DOCA-treated wild types. Expression of alpha8 integrin and its ligands fibronectin and osteopontin was increased in the hearts of DOCA-treated wild types compared to salt-loaded controls. However, relative left ventricular weights did not differ between DOCA-treated wild types and alpha8 integrin-deficient mice. Moreover, expansion of collagen I immunoreactivity and cell proliferation was similar in both groups. The number of osteopontin-positive cells was not different in DOCA-treated alpha8 integrin-deficient and DOCA-treated wild-type mice. Despite of a comparable degree of fibrosis in both groups, alpha-smooth-muscle actin and discoidin domain receptor 2 (DDR2)-positive myofibroblasts were only detected in wild-type DOCA-treated mice, not in DOCA-treated alpha8 integrin-deficient mice.

CONCLUSIONS

The results show that lack of alpha8 integrin does not reduce fibrotic changes in the hearts of DOCA-salt hypertensive mice. Our findings do not argue for a profibrotic effect of an increased alpha8 integrin expression in the myocardium in hypertension.

A promoter polymorphism of the alpha 8 integrin gene and the progression of autosomal-dominant polycystic kidney disease

BACKGROUND/AIMS

Dysregulation of integrins is a feature of tissue remodeling in autosomal-dominant polycystic kidney disease (ADPKD). The alpha 8 beta 1 integrin (alpha8beta1) affects kidney development and the susceptibility to renal injury in mice. We investigated whether the -414 T/C polymorphism in the promoter region of the alpha 8 integrin chain gene (ITGA8) is associated with the progression of renal disease in ADPKD.

METHODS

Genotyping for the -414 T/C polymorphism was performed by allelic separation using RT-PCR in 294 patients with ADPKD. Alpha 8 integrin expression was detected by RT-PCR and immunohistochemistry.

RESULTS

41% of the study population reached end stage renal disease at a mean age of 51 +/- 12 years. The frequency of the -414 C allele was 0.194 in ADPKD. C allele carriers (CC and TC genotypes) were compared with patients homozygous for the T allele (TT genotype). Kaplan-Meier analysis revealed that end-stage renal failure occurred at a significantly younger age in TT homozygotes (median age, 47 years; 95% CI, 46-49 years) than in C allele carriers (median age, 51 years; 95% CI, 49-53 years; p = 0.046 by the log-rank test). When parameters of ADPKD patients were compared between genotype by analysis of variance, only age at onset of end-stage renal failure was significantly different (p = 0.026) whereas age at onset of hypertension, body surface area, 24-hour systolic and diastolic blood pressure did not differ. In kidneys of ADPKD, expression of alpha 8 integrin is increased and found de novo in cystic epithelia.

CONCLUSION

A polymorphism of the ITGA8 promoter modifies the progression of renal failure in ADPKD.

α8 Integrin overexpression in de-differentiated vascular smooth muscle cells attenuates migratory activity and restores the characteristics of the differentiated phenotype

Loss of the differentiated (contractile) phenotype of vascular smooth muscle cells (VSMCs) heightens their migratory activity. Integrins, as the main integrators of cell-extracellular matrix, regulate different aspects of cell behavior including migration and differentiation. alpha 8 beta 1 Integrin being expressed in cell types with contractile abilities is downregulated during VSMC phenotype modulation. In this report the ability of alpha 8 beta 1 integrin to induce the characteristics of the contractile phenotype as well as suppression of VSMC migratory activity was investigated. Forced expression of alpha 8 integrin in passage-5 rat VSMCs resulted in lower migratory activity. Western blot and immunoconfocal studies revealed that alpha 8 integrin overexpression was associated with the reappearance of VSMC contractile hallmarks including upregulation of contractile markers, assembly of stress fibres, and increased number of focal adhesions. alpha 8 Integrin overexpression in fibroblast-like Rat1 cells also induced SMC-like characteristics. alpha 8 Integrin-induced reappearance of the contractile hallmarks in de-differentiated VSMCs was impaired by RhoA inhibitors. These results provide evidences that alpha 8 integrin overexpression may assist phenotype-modulated VSMCs to revert to the contractile phenotype possibly via RhoA signaling pathway. Our findings suggest a dynamic role for alpha 8 beta 1 integrin to induce contractile phenotype as well as suppression of VSMC migration, a key player during arterial stenosis.

Glomerular regeneration is delayed in nephritic alpha 8-integrin-deficient mice: contribution of alpha 8-integrin to the regulation of mesangial cell apoptosis

BACKGROUND/AIMS

alpha(8)beta(1)-Integrin is expressed in mesangial cells. In vitro studies suggest a role for alpha(8)-integrin in the regulation of cell proliferation and apoptosis. We tested the hypothesis that alpha(8)-integrin is essential for the healing process after mesangioproliferative glomerulonephritis.

METHODS

Mice homozygous for a deletion of the alpha(8)-integrin chain were compared with wild-type mice. To study glomerular healing, we used the habu toxin model of reversible mesangioproliferative glomerulonephritis. Animals received 6 mg/kg habu toxin intravenously; controls received saline only.

RESULTS

Early mesangiolysis occurred in wild-type and alpha(8)-integrin-deficient mice. However, mesangiolysis was no longer detectable after 7 days in wild types but persisted after 14 days in alpha(8)-integrin-deficient animals. Mesangial activation marker alpha-smooth muscle actin was detectable only at day 7 in wild-type mice but persisted until day 14 in alpha(8)-integrin-deficient mice. In wild types, glomerular cell proliferation and apoptosis peaked at day 7 and decreased thereafter but remained elevated in alpha(8)-integrin-deficient mice until day 28. In cultivated mesangial cells, alpha(8)-integrin expression was associated with increased cell survival.

CONCLUSION

Interactions between alpha(8)-integrin and the mesangial matrix may contribute to healing of glomerular injury by influencing cell proliferation and apoptosis.

Fibrillin-1 regulates mesangial cell attachment, spreading, migration and proliferation

The microfibrillar protein fibrillin-1 is present in many organs, including the vasculature, eye, and dermis, and is thought to convey structural anchorage and elastic strength. Fibrillin-1 is also a component of the mesangial matrix. To assess the functional relevance of fibrillin-1 for cell-matrix interactions in the glomerulus, we studied the attachment, spreading, migration and proliferation of mesangial cells on fibrillin-1 and the regulation of fibrillin-1 in experimental anti-Thy1.1 nephritis displaying mesangial cell migration and proliferation in vivo. During the acute phase of experimental Thy1.1 nephritis, glomerular fibrillin-1 messenger ribonucleic acid expression and protein immunoreactivity were significantly induced as compared to controls. In a hexosaminidase-based adhesion assay, mesangial cells showed concentration-dependent attachment to fibrillin-1, similar to what was observed for fibronectin. The cell attachment was Arg-Gly-Asp dependent. Further, fibrillin-1 significantly promoted spreading and focal contact formation detected by immunostaining for vinculin. Mesangial cell migration, assessed by a transmigration assay, and proliferation, measured by a 5-bromo-2'-deoxy-uridine incorporation assay, were augmented by fibrillin-1. In diabetic mice underexpressing fibrillin-1, glomerular cell proliferation, determined by counting proliferating cell nuclear antigen-positive cells in renal sections, was significantly lower than in diabetic control mice. We conclude that fibrillin-1 promotes mesangial cell attachment, spreading, migration, and proliferation. We speculate that fibrillin-1 may thus contribute to mesangial hypercellularity during glomerular disease.

Rapid isolation of glomeruli coupled with gene expression profiling identifies downstream targets in Pod1 knockout mice

Mouse mutations have provided tremendous insights into the molecular basis of renal and glomerular development. However, genes often play important roles during multiple stages of nephrogenesis, making it difficult to determine the role of a gene in a specific cell lineage such as the podocyte. Conditional gene targeting and chimeric analysis are two possible approaches to dissect the function of genes in specific cell populations. However, these are labor-intensive and costly and require the generation, validation, and analysis of additional transgenic lines. For overcoming these shortcomings and, specifically, for studying the role of gene function in developing glomeruli, a technique to isolate and purify glomeruli from murine embryos was developed. Combined with gene expression profiling, this method was used to identify differentially expressed genes in glomeruli from Pod1 knockout (KO) mice that die in the perinatal period with multiple renal defects. Glomeruli from early developing stages (late S-shape/early capillary loop) onward can be isolated successfully from wild-type and KO kidneys at 18.5 d postcoitus, and RNA can readily be obtained and used for genome-wide microarray analysis. With this approach, 3986 genes that are differently expressed between glomeruli from Pod1 KO and wild-type mice were identified, including a four-fold reduction of alpha 8 integrin mRNA in glomeruli from Pod1 KO mice that was confirmed by immunostaining. This procedure may be adapted to any transgenic strain, providing a rapid and efficient method to dissect the function of specific genes in glomerular development.

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.

Integrin α8β1–fibronectin interactions promote cell survival via PI3 kinase pathway

Integrin signaling plays a critical role in many aspects of normal growth, differentiation, and injury response. In the adult, alpha8beta1 is expressed in alveolar myofibroblasts and is upregulated in pulmonary fibrosis and other models of organ injury. Following injury, survival of fibronectin-producing myofibroblasts cells is an important determinant of development of fibrosis. Using stable alpha8-transfected cell lines, we show that interactions of alpha8beta1 with its ligand, fibronectin, promote cell survival during serum deprivation. Multiple cell signaling pathways were activated following fibronectin adhesion, including PI3 kinase and MAP kinase. However, the alpha8-mediated cell survival was blocked by LY294002, a PI3 kinase inhibitor, but not by staurosporine, a PKC inhibitor, or PD98059, a MAPK kinase inhibitor. A dominant negative construct of PI3 kinase also inhibited alpha8-mediated cell survival. Therefore, alpha8-mediated survival appears to be mediated by the PI3 kinase pathway. Survival of alpha8-expressing myofibroblasts may contribute to persistent fibrosis following injury.

The mesenchymal alpha11beta1 integrin attenuates PDGF-BB-stimulated chemotaxis of embryonic fibroblasts on collagens

alpha11beta1 constitutes the most recent addition to the integrin family and has been shown to display a binding preference for interstitial collagens found in mesenchymal tissues. We have previously observed that when alpha11beta1 integrin is expressed in cells lacking endogenous collagen receptors, it can mediate PDGF-BB-dependent chemotaxis on collagen I in vitro. To determine in which cells PDGF and alpha11beta1 might cooperate in regulating cell migration in vivo, we studied in detail the expression and distribution of alpha11 integrin chain in mouse embryos and tested the ability of PDGF isoforms to stimulate the alpha11beta1-mediated cell migration of embryonic fibroblasts. Full-length mouse alpha11 cDNA was sequenced and antibodies were raised to deduced alpha11 integrin amino acid sequence. In the embryonic mouse head, alpha11 protein and RNA were localized to ectomesenchymally derived cells. In the periodontal ligament, alpha11beta1 was expressed as the only detectable collagen-binding integrin, and alpha11beta1 is thus a major receptor for cell migration and matrix organization in this cell population. In the remainder of the embryo, the alpha11 chain was expressed in a subset of mesenchymal cells including tendon/ligament fibroblasts, perichondrial cells, and intestinal villi fibroblasts. Most of the alpha11-expressing cells also expressed the alpha2 integrin chain, but no detectable overlap was found with the alpha1 integrin chain. In cells expressing multiple collagen receptors, these might function to promote a more stable cell adhesion and render the cells more resistant to chemotactic stimuli. Wild-type embryonic fibroblasts activated mainly the PDGF beta receptor in response to PDGF-BB and migrated on collagens I, II, III, IV, V, and XI in response to PDGF-BB in vitro, whereas mutant fibroblasts that lacked alpha11beta1 in their collagen receptor repertoire showed a stronger chemotactic response on collagens when stimulated with PDGF-BB. In the cellular context of embryonic fibroblasts, alpha11beta1 is thus anti-migratory. We speculate that the PDGF BB-dependent cell migration of mesenchymal cells is tightly regulated by the collagen receptor repertoire, and disturbances of this repertoire might lead to unregulated cell migration that could affect normal embryonic development and tissue structure.

β1-integrins and glomerular injury

The renal glomerulus is composed of three types of glomerular cells (mesangial cell (MC), endothelial cell and podocyte) and extracellular matrix (ECM) consisting of the glomerular basement membrane (GBM) and mesangial matrix. It constitutes a highly specialized microcirculation in which the permeability characteristics of the capillary wall allow its unique filtration function. The proliferation of MCs, an increase of mesangial ECM and detachment podocyte from GBM are key biological features of progressive glomerulonephritis (GN), leading to glomerular scarring and dysfunction. Thus, the study of the molecular and cellular mechanisms responsible for pathological glomerular alterations may help to elucidate the pathogenesis of progressive glomerular diseases. A growing body of evidence indicates that beta1 integrin family (beta1 integrins), that mainly mediates cell adhesion to ECM, controls cell behaviors such as cell migration, proliferation, apoptosis and ECM assembly. In addition, a correlation between glomerular expression of beta1 integrins and their ligand ECM components is observed in various human and experimental GN, suggesting that altered beta1 integrins-mediated cell behaviors may contribute to the progression of GN. It is now becoming apparent that the expression of glomerular beta1 integrins is not only critical for maintaining the glomerular capillary permeability but it modulates cell signaling pathways regulating the cell phenotypes involved in the progression of glomerular diseases.

Glomerular and renal vascular structural changes in alpha8 integrin-deficient mice

Integrins are matrix receptors that regulate cell-matrix interactions during development and in adult tissue. In the adult kidney, the alpha8 chain is specifically expressed in glomerular mesangial cells and vascular smooth muscle cells. alpha8-deficient (alpha8-/-) mice demonstrate reductions in renal mass, which can range from complete renal agenesis to the development of kidneys that are only slightly smaller than wild-type kidneys. No histologic abnormalities of these kidneys have been described. However, considering the prominent expression of alpha8 in glomeruli and renal vessels, it seemed unlikely that the kidneys of alpha8-/- mice would be completely normal. Therefore, the renal phenotype of adult alpha8-/- mice was investigated, for assessment of more subtle morphologic alterations in kidney tissue. alpha8-/- mice displayed a significant reduction in nephron number and an increase in glomerular volume, compared with wild-type control animals. Albuminuria was not different in wild-type and alpha8-/- mice. Quantitative morphologic analyses revealed that the glomeruli of alpha8-/- mice were hypercellular, with an increased number of mesangial cells, compared with wild-type mice. Mesangial matrix deposition (as demonstrated for collagen IV and the alpha8 ligand fibronectin) was expanded in alpha8-/- mice, compared with wild-type mice. Collagens I and III, which are not normally present in glomeruli, were detected in the glomeruli of alpha8-/- mice. Staining for other glomerular integrins demonstrated an increased abundance of the collagen receptor alpha2 integrin in alpha8-/- mice. The glomerular capillary length density was significantly greater in alpha8-/- mice than in wild-type mice. Cortical arterial vessel walls were not altered in alpha8-/- mice, but the capillaries of the peritubular network were widened. Despite the strong mesangial and vascular expression of alpha8, glomerular and renal vascular alterations in alpha8-/- mice were relatively mild. Only aged alpha8-/- mice demonstrated increased glomerular capillary widening, compared with control animals. The results suggest that the lack of alpha8 can be largely compensated for, at least in younger alpha8-/- mice. It is not yet clear whether the occurrence of collagens that are not normally present in glomeruli and the increased abundance of the collagen receptor alpha2 contribute to maintaining the glomerular structure in alpha8-/- mice. The compensatory mechanisms involved will be the subject of future research.