Apoptosis of cultured rat glomerular mesangial cells induced by IgG2a monoclonal anti-Thy-1 antibodies

Characterization of CD90/Thy-1 as a crucial molecular signature for myogenic differentiation in human urine-derived cells through single-cell RNA sequencing

Human urine-derived cells (UDCs) are primary cultured cells originating from the upper urinary tract and are known to be multipotent. We previously developed MYOD1-transduced UDCs (MYOD1-UDCs) as a model recapitulating the pathogenesis of Duchenne muscular dystrophy (DMD) caused by a lack of dystrophin. MYOD1-UDCs also allow evaluation of the efficacy of exon skipping with antisense oligonucleotides. However, despite the introduction of MYOD1, some MYOD1-UDCs failed to form myotubes, possibly because of heterogeneity among UDCs. Here, we carried out single-cell RNA-sequencing analyses and revealed that CD90/Thy-1 was highly expressed in a limited subpopulation of UDCs with high myogenic potency. Furthermore, CD90-positive MYOD1-UDCs, but not CD90-negative cells, could form myotubes expressing high levels of myosin heavy chain and dystrophin. Notably, overexpression of CD90 in CD90-negative MYOD1-UDCs did not enhance myogenic differentiation, whereas CD90 suppression in CD90-positive UDCs led to decreased myotube formation and decreased myosin heavy chain expression. CD90 may thus contribute to the fusion of single-nucleated MYOD1-UDCs into myotubes but is not crucial for promoting the expression of late muscle regulatory factors. Finally, we confirmed that CD90-positive MYOD1-UDCs derived from patients with DMD were a valuable tool for obtaining a highly reproducible and stable evaluation of exon skipping using antisense oligonucleotide.

A Profibrotic Phenotype in Naïve and in Fibrotic Lung Myofibroblasts Is Governed by Modulations in Thy-1 Expression and Activation

Lung fibrosis is characterized by abnormal accumulation of Thy-deficient fibroblasts in the interstitium of the alveolar space. We have previously shown in bleomycin-treated chimeric Thy1-deficient mice with wild-type lymphocytes that Thy1-deficient fibroblasts accumulate and promote fibrosis and an “inflammation-free” environment. Here, we aimed to identify the critical effects of Thy1, or the absence of Thy1, in lung myofibroblast profibrotic functions, particularly proliferation and collagen deposition. Using specific Thy1 siRNA in Thy1-positive cells, Thy1 knockout cells, Thy1 cDNA expression vector in Thy1-deficient cells, and Thy1 cross-linking, we evaluated cell proliferation (assessed by cell mass and BrdU uptake), differentiation (using immunofluorescence), and collagen deposition (using Sircol assay). We found that myofibroblast Thy1 cross-linking and genetic manipulation modulate cell proliferation and expression of Fgf (fibroblast growth factor) and Angtl (angiotensin) receptors (using qPCR) that are involved in myofibroblast proliferation, differentiation, and collagen deposition. In conclusion, lung myofibroblast downregulation of Thy1 expression is critical to increase proliferation, differentiation, and collagen deposition.

Suramin inhibits antibody binding to cell surface antigens and disrupts complement-mediated mesangial cell lysis

Suramin inhibits immune responses and protects cells against inflammatory cell injury. However, little is known about its mechanisms. Using an in vitro model of glomerular mesangial cell (MC) lysis induced by antibodies plus complement, we investigated the potential protective effects and mechanisms of suramin on immunologic cell injury. Exposure of rat MCs to anti-Thy-1 antibody plus complement or anti-MC rabbit serum caused complement-dependent cell lysis, which was blocked by suramin and its structural analogue NF023 and NF049, but not by PPADS, an antagonist of purinergic receptors. Addition of exogenous ATP also failed to affect MC lysis. Further analysis revealed that suramin interfered with antibody binding to cell membrane antigens and suppressed antibody-induced phosphorylation of several proteins, including p38. Inhibition of p38 with chemical inhibitor significantly attenuated cell injury. Collectively, our results indicate that suramin protects cells against antibody-initiated and complement-dependent cell injury through inhibition of antibody binding to cell surface antigens and suppression of p38 activation. Our study thus provides novel mechanistic insights into the actions of suramin and suggests that suramin might be used to treat certain immune diseases.

The roles of THY1 and integrin beta3 in cell adhesion during theca cell layer formation and the effect of follicle-stimulating hormone on THY1 and integrin beta3 localization in mouse ovarian follicles

The mechanism of theca cell layer formation in mammalian ovaries has not been elucidated. In the present study, we examined the roles of THY1 and integrin beta3 in theca cell layer formation during mouse folliculogenesis. The localization pattern of THY1 and integrin beta3 in adult mouse ovary was investigated immunohistochemically. The strongest THY1 signal was observed in theca cell layers from secondary to preantral follicles, at which time theca cells have begun to participate in follicle formation. Integrin beta3 also localized to the theca cell layer of secondary to preantral follicles and showed a localization pattern similar to that of THY1. Moreover, the role of THY1 in theca cell layer formation was examined using a follicle culture system. When anti-THY1 antibody was added to this culture, no theca cell layers were formed, and the granulosa cells were distanced from each other. Because a THY1 signal was not observed in ovaries at stages earlier than prepuberty, THY1 localization also appeared to be affected by mouse development. This possibility was examined by determining the effect of administering follicle-stimulating hormone, luteinizing hormone, and 17beta-estradiol to 7-day-old mice on THY1 localization in the ovary 3 days later. Only follicle-stimulating hormone induced a THY1 signal in 10-day-old mouse ovaries. No THY1 signal was observed in untreated 10-day-old ovaries. In conclusion, THY1 might play a role in cell adhesion via binding to integrin beta3 in mouse ovaries. The present results suggest that THY1 localization may be affected by follicle-stimulating hormone in mouse ovaries.

Expression, purification and use of recombinant annexin V for the detection of apoptotic cells

Apoptosis is a mode of programmed cell death that is widely used to eliminate cells during development, tissue homeostasis, infection or in response to injury. Alterations to the plasma membranes of apoptotic cells trigger recognition and engulfment of such cells by phagocytes. Measurement of plasma membrane phosphatidylserine externalization, using fluorescently labeled annexin V, is widely used for the detection of apoptotic cells. Here we describe protocols for bacterial expression, purification and FITC labeling of recombinant annexin V. By following the method outlined in this protocol, it is possible to produce milligram amounts of recombinant annexin V within 3 d. We also describe a method for the assessment of annexin V binding to cell populations by flow cytometry or fluorescence microscopy.

Thy-1, a versatile modulator of signaling affecting cellular adhesion, proliferation, survival, and cytokine/growth factor responses

Thy-1 is a 25-37 kDa glycosylphosphatidylinositol (GPI)-anchored protein involved in T cell activation, neurite outgrowth, apoptosis, tumor suppression, wound healing, and fibrosis. To mediate these diverse effects, Thy-1 participates in multiple signaling cascades. In this review, we discuss Thy-1 signaling primarily in non-immunologic cell types, including neurons, mesangial cells, ovarian cancer cells, nasopharyngeal carcinoma cells, endothelial cells, and fibroblasts. We review the current literature regarding Thy-1 signaling via integrins, protein tyrosine kinases, and cytokines and growth factors; and the roles of these signaling pathways in cellular adhesion, apoptosis, cell proliferation, and cell adhesion and migration. We also discuss the role of Thy-1 localization to lipid rafts, and of the GPI anchor in Thy-1 signaling. Ongoing research on the mechanisms of Thy-1 signaling will add to our understanding of the diverse physiologic and pathologic processes in which Thy-1 plays a role.

Thy-1 as a regulator of cell-cell and cell-matrix interactions in axon regeneration, apoptosis, adhesion, migration, cancer, and fibrosis

Thy-1 (CD90) is a 25-37 kDa glycosylphosphatidylinositol (GPI) -anchored glycoprotein expressed on many cell types, including T cells, thymocytes, neurons, endothelial cells, and fibroblasts. Activation of Thy-1 can promote T cell activation, and this role of Thy-1 is reviewed elsewhere. Thy-1 also affects numerous nonimmunologic biological processes, including cellular adhesion, neurite outgrowth, tumor growth, migration, and cell death. In reviewing the nonimmunologic functions of Thy-1, we discuss the phenotype of the Thy-1 null mouse, signaling pathways modulated by Thy-1, the role of the GPI anchor in Thy-1 localization to lipid rafts and signaling, and regulation of Thy-1 expression. Thy-1 is an important regulator of cell-cell and cell-matrix interactions, with important roles in nerve regeneration, metastasis, inflammation, and fibrosis.

The leukotriene B4 receptor antagonist ONO-4057 inhibits mesangioproliferative changes in anti-Thy-1 nephritis

OBJECTIVE

ONO-4057 is a specific leukotriene B4 (LTB4) receptor antagonist which inhibits human neutrophil aggregation, chemotaxis and degranulation induced by LTB4. This study was conducted to evaluate the role of LTB4 in glomerulonephritis, and to examine whether ONO-4057 moderated anti-Thy-1 nephritis.

METHODS

Experiment 1: Sixty Wistar rats were divided into three groups. Rats of Group A (n = 20) underwent intraperitoneal administration of placebo as a control group, rats of Group B (n = 20) first underwent intraperitoneal administration of 100 mg/kg ONO-4057 and rats of Group C (n = 20) first underwent intraperitoneal administration of 300 mg/kg ONO-4057 daily from day 3 before anti-Thy-1 antibody (OX7) injection to day 14 after OX7 injection, respectively. Experiment 2: Forty rats were divided into two groups. ONO-group (n = 20) was treated with 300 mg/kg BW of ONO-4057 and placebo-group (n = 20) with placebo daily from days 1 to 13 after OX7 injection. Urine and blood samples were collected and the kidneys were extirpated from five rats of each group sacrificed at 3 h, 24 h, day 7 or day 14 after the injection of OX7 in both experiments. Urinary protein excretion, renal function and pathological findings were analysed in each group of both experiments.

RESULTS

(1) Glomerular infiltration by polymorphonuclear leucocytes (PMNs) and macrophages at 3 h was less in Groups B and C than in Group A, and matrix scores at day 7 were lower in Groups B and C than in Group A. Injury scores did not differ among the groups. (2) Urinary protein excretion at day 7 was less in Group C than in Group A. (3) Neither pathological findings nor urinary protein excretion differed between ONO-group and placebo-group.

CONCLUSION

These results suggest that LTB4 is associated not with the pathogenesis of complement-dependent mesangial cell lysis but with that of mesangial proliferative change in anti-Thy-1 nephritis.

Vascular endothelial growth factor-D is a survival factor for human breast carcinoma cells

Vascular endothelial growth factor-D (VEGF-D) stimulates growth of vascular and lymphatic endothelial cells by signaling through the tyrosine kinase receptors KDR (VEGFR-2) and Flt-4 (VEGFR-3). In the present study, we examined the effects of VEGF-D on apoptosis in human MCF-7 and MDA-MB-231 breast carcinoma cells. Because VEGF-D was not expressed constitutively in vitro, stable VEGF-D transfectants were produced. The VEGF-D-expressing MCF-7 and MDA-MB-231 lines displayed resistance to apoptosis induced by hypoxia, staurosporin and cycloheximide. Increased Bcl-2 expression, decreased homogenous caspase activities and inhibition of poly(ADP-ribose) polymerase cleavage were associated with inhibition of apoptosis in VEGF-D-expressing clones. Also, caspase-3 activation was suppressed in the VEGF-D expressing MDA-MB-231 clone. The antiapoptotic effect of VEGF-D in vitro was recapitulated in vivo using VEGF-D-expressing MDA-MB-231 xenografts. The lack of VEGFR-2 protein expression by Western blot and ineffectiveness of a neutralizing VEGFR-2 antibody in eliminating the antiapoptotic effects of VEGF-D suggest a different and yet unknown signaling mechanism. Our findings indicate that VEGF-D has a novel function as a survival factor of breast carcinoma cells in addition to its established functions as an angiogenic and lymphangiogenic factor.

Toluene and p-xylene induced LLC-PK1 apoptosis

Occupational exposure to organic solvents was found to be associated with development and progression of tubulo-interstitial fibrosis and chronic renal failure. However, the cellular mechanism by which this occurs remains elusive. This study was conducted to evaluate the mode of cell death in proximal tubular cells exposed to organic solvents. LLC-PK1 cell line cytotoxicity due to exposure to 1 mM of either p-xylene or toluene was compared to untreated control by cell viability, LDH release, and DNA fragmentation. Cells were exposed to solvents for 96 hrs. Toluene and p-xylene reduced cell viability and increased DNA fragmentation. LDH release was unchanged. These data indicates that long-term exposure to organic solvents is associated with proximal tubule cell apoptosis, which may be the mechanism of progressive renal fibrosis and renal failure in patients with high solvent exposure.

Organic Solvent‐Induced Proximal Tubular Cell Toxicity via Caspase‐3 Activation

BACKGROUND

Occupational exposure to solvents may be associated with development and progression of tubulo-interstitial fibrosis and chronic renal failure. However, the cellular mechanisms by which this occurs remain elusive.

MATERIALS AND METHODS

The cytotoxicity of proximal tubular cells (LLC-PK1) exposed to 106 mg/mL of p-xylene or 92 mg/mL of toluene was compared with untreated controls using cell viability (MTS assay) and caspase-3 activity, with or without caspase-3 selective inhibitor.

RESULTS

Both compounds reduced cell viability and increased caspase-3 activation (P < 0.005). Inhibition of caspase-3 by the selective inhibitor DEVD-CHO prevented injury (P < 0.001) and inhibited solvent-induced caspase-3 activation (P < 0.005).

CONCLUSION

Inhibition of caspase-3, the critical caspase in the apoptosis process, prevents cell injury in LLC-PK1. This suggests that caspase-3 may play a pivotal role in solvent-induced proximal tubular cell injury.

Clusterin is up-regulated in glomerular mesangial cells in complement-mediated injury

BACKGROUND

Clusterin is a soluble complement regulatory protein that binds to C5b-7 and inhibits generation of membrane attack complex, C5b-9. Glomerular deposition of clusterin has been observed in human and experimental membranous nephropathy in association with C5b-9 and immune deposits. However, it is controversial as to whether clusterin observed in glomeruli is synthesized by the resident glomerular cells or is derived from the circulation. We examined whether clusterin is expressed by resident glomerular cells exposed to complement-mediated injury.

METHODS

In vitro, cultured mesangial cells were exposed to antithymocyte serum immunoglobulin G and 5% normal rat serum as a complement source. In vivo, we induced anti-Thy1 nephritis in rats and examined the kidneys on days 8 and 29.

RESULTS

We observed increased expression of clusterin in cultured rat glomerular mesangial cells stimulated by sublytic complement attack. We also demonstrated that in comparison with control rats, both a marked increase in clusterin mRNA in the glomeruli and marked deposition of clusterin protein in the mesangial area occurred in the OX-7-treated rats on day 8 in association with C5b-9 deposition and on day 29.

CONCLUSION

Clusterin was induced in glomerular mesangial cells during the course of immune-mediated injuries. This up-regulation of clusterin may play a critical role in protecting mesangial cells from complement attack.

Contribution of apoptotic cell death to renal injury

Cell number abnormalities are frequent in renal diseases, and range from the hypercellularity of postinfectious glomerulonephritis to the cell depletion of chronic renal atrophy. Recent research has shown that apoptosis and its regulatory mechanisms contribute to cell number regulation in the kidney. The role of apoptosis ranges from induction to repair and progression of renal injury. Death ligands and receptors, such as TNF and FasL, proapoptotic and antiapoptotic Bcl-2 family members and caspases have all been shown to participate in apoptosis regulation in the course of renal injury. These proteins represent potential therapeutic targets, which should be further explored.

Regulation of mesangial cell apoptosis and proliferation by intracellular Ca(2+) signals

BACKGROUND

In inflammatory glomerular diseases, proliferation, as well as apoptosis of mesangial cells (MCs), has been shown histomorphologically. Both processes may regulate the cellular content of the mesangium by closely influencing each other. In the present study, we examined whether the cytoplasmic free Ca(2+) concentration [Ca(2+)](i) is involved as a key second messenger in the regulation of proliferative and apoptotic events.

METHODS

Thapsigargin, an inhibitor of the endoplasmic Ca(2+)-Mg(2+)-ATPase, was used as a test substance to investigate the role of [Ca(2+)](i) in signaling MC apoptosis and growth in vitro. Apoptosis was determined by nuclear chromatin staining with Hoechst 33258, by a [3H]-thymidine-based DNA fragmentation assay or by flow cytometry detecting binding of FITC-conjugated annexin V. Proliferation was measured by [3H]-thymidine incorporation into acid-precipitable material and corroborated by cell counting.

RESULTS

Thapsigargin significantly induced apoptosis and inhibited proliferation dose dependently in nanomolar concentrations without evoking necrotic damage when administered not longer than 12 hours. Significant apoptosis was measurable after a six-hour treatment of MCs with thapsigargin. Determination of [Ca(2+)](i) by fura-2-dependent spectrofluorometry showed that thapsigargin was able to induce prolonged [Ca(2+)](i) rises that could be prevented by preincubation with the intracellular Ca(2+) chelator 1, 2-bis(2-aminophenoxy)-ethane-N,N,N', N'-tetra-acetic acid (BAPTA) acetomethyl ester (AM). BAPTA had no influence on MC viability but reversed thapsigargin-induced apoptosis to control levels. After thapsigargin treatment (100 nmol/L, 12 hours), apoptotic MCs had a significantly higher [Ca(2+)](i) of 251 +/- 25 nmol/L (N = 41) as compared with MCs that were not or not yet apoptotic ([Ca(2+)](i) of 116 +/- 20 nmol/L, N = 26, P < 0,05). Platelet-derived growth factor (PDGF), a well-characterized growth factor for MCs, reversed the effects of thapsigargin on proliferation and apoptosis in a similar fashion as BAPTA. PDGF acutely stimulated increases of [Ca2+]i but abolished thapsigargin-dependent, but not angiotensin II- or ATP-induced Ca(2+) rises when administered during a 12-hour preincubation.

CONCLUSIONS

Our data suggest that a sustained increase of [Ca(2+)](i) may serve as a signal to trigger MC apoptosis. Growth factors such as PDGF can abolish apoptosis induced by elevations of [Ca(2+)](i) by altering intracellular Ca(2+) signaling.

Distinctive roles of neutrophils and monocytes in anti-thy-1 nephritis

Anti-Thy-1.1 glomerulonephritis as an experimental model for mesangial proliferative glomerulonephritis was induced in Wistar rats by a single injection of monoclonal IgG2a-anti-Thy-1.1 antibody (ER4G). This transient model is complement-mediated and leads to mesangial-cell (MC) lysis followed by MC proliferation, glomerular microaneurysm formation, glomerular influx of polymorphonuclear leukocytes (PMNs) and macrophages, proteinuria, and hematuria. In this study we investigated the distinctive roles of infiltrating PMNs or monocytes/macrophages by treating rats with an antibody against rat integrin CD11b/CD18 (ED7) or by depletion of monocytes with multilamellar clodronate liposomes, respectively. ED7 administration resulted in reduction of the influx of PMNs in glomeruli during the first 6 days after induction of Thy-1.1 nephritis, whereas treatment with an isotype-matched irrelevant antibody (PEN9) or with phosphate-buffered saline had no effect on macrophage influx. Increased glomerular C3 and C6 deposition on days 1 and 3 was seen in the ED7-treated rats but not seen in the control groups. In addition, the ED7-treated group showed an increased number of aneurysmatic glomeruli and more severe hematuria. Monocyte/macrophage depletion led to a significant reduction of mesangial matrix expansion, although mesangial proliferation, proteinuria, and hematuria remained unaltered. These results, together with the known effects of PMN-derived enzymes on C3 cleavage, suggest that a reduction in the influx of PMNs results in sparing of C3 and consequently of more complement activation in the glomerulus with increased complement-mediated damage. Our data indicate that infiltrating PMNs and monocytes/macrophages play distinctive roles during inflammation in this model of MC glomerulonephritis.

Regulation of glomerular cell number by apoptosis

While commonly viewed as leading to glomerular scarring and end-stage renal failure, glomerular cell proliferation may be a beneficial response that promotes the injured glomerulus to return to its proper function. This brief review looks at the potentially counterbalancing influences that cause glomerular cells to survive, undergo mitosis, differentiate or die.

The terminal sequence of complement plays an essential role in antibody-mediated renal cell apoptosis

Mesangial cell (MC) injury is a characteristic feature in the early phase of Thy.1 nephritis. The present study investigates the contribution of complement to MC apoptosis in this experimental model of kidney disease in rats. Thy.1 nephritis was induced by injection of mouse anti-Thy.1 monoclonal antibody (ER4G). To assess the contribution of the terminal sequence of complement on apoptosis, the studies were performed in complement-sufficient PVG/c (PVG/c+) rats and in rats deficient in complement C6 (PVG/c-). Apoptosis was monitored by assessment of the number of condensed nuclei in kidney sections stained with periodic acid-Schiff (PAS) and by the terminal deoxynucleotidyl transferase-mediated nick end labeling (TUNEL) method and expressed as number of apoptotic cells per 50 glomerular cross sections. In the PAS method, 1 h after intravenous injection of ER4G, PVG/c+ rats exhibited 160.9 +/- 49.5 apoptotic cells, whereas PVG/c- rats had only 3.2 +/- 1.4 apoptotic cells. Control rats exhibited 0.9 +/- 0.6 apoptotic cells. These findings were confirmed with the TUNEL method. In PVG/c- rats, a maximum number of 8.8 +/- 3.1 TUNEL-positive (TUNEL+) cells was found at 6 h followed by a decline thereafter. In PVG/c+ rats, apoptosis was associated with deposition of C6 and C5b-9. Restoration of the complement system of PVG/c- rats with purified human C6 resulted in an increase of apoptosis at 1 h after injection of ER4G from minimal numbers to 239.9 +/- 52.4 TUNEL+ cells. These studies appear to indicate for the first time that the terminal sequence of complement is involved in induction of apoptosis.

Neuronal death and survival in two models of hypoxic-ischemic brain damage

Two unilateral hypoxic-ischemia (HI) models (moderate and severe) in immature rat brain have been used to investigate the role of various transcription factors and related proteins in delayed neuronal death and survival. The moderate HI model results in an apoptotic-like neuronal death in selectively vulnerable regions of the brain while the more severe HI injury consistently produces widespread necrosis resulting in infarction, with some necrosis resistant cell populations showing evidence of an apoptotic type death. In susceptible regions undergoing an apoptotic-like death there was not only a prolonged induction of the immediate early genes, c-jun, c-fos and nur77, but also of possible target genes amyloid precursor protein (APP751) and CPP32. In contrast, increased levels of BDNF, phosphorylated CREB and PGHS-2 were found in cells resistant to the moderate HI insult suggesting that these proteins either alone or in combination may be of importance in the process of neuroprotection. An additional feature of both the moderate and severe brain insults was the rapid activation and/or proliferation of glial cells (microglia and astrocytes) in and around the site of damage. The glial response following HI was associated with an upregulation of both the CCAAT-enhancer binding protein alpha (microglia only) and NFkappaB transcription factors.

Platelet-derived growth factor and fibroblast growth factor differentially regulate interleukin 1beta- and cAMP-induced nitric oxide synthase expression in rat renal mesangial cells

Platelet-derived growth factor (PDGF) and basic fibroblast growth factor (bFGF) regulate mesangial cell proliferation and matrix production in vitro and in vivo and crucially participate in the pathogenesis of glomerulonephritis. We investigated whether PDGF-BB and bFGF influence nitric oxide (NO) production, another important effector molecule in inflammatory glomerular injury. Inducible NO synthase (iNOS) induction in rat glomerular mesangial cells has been described in response to two principal classes of activating signals comprising inflammatory cytokines such as interleukin 1beta (IL-1beta) or elevation of cyclic AMP (cAMP). Treatment of mesangial cells with IL-1beta induces iNOS activity measured as nitrite levels in cell culture supernatants. Coincubation of mesangial cells with PDGF-BB inhibits production of nitrite by approximately 95%. This effect can be reversed by the simultaneous incubation of PDGF-BB in the presence of calphostin C, a potent and selective inhibitor of protein kinase C. In contrast, incubation of cells in the presence of bFGF potentiates IL-1beta-induced production of NO and is functionally associated with an increased rate of apoptosis of mesangial cells. Western blot analyses reveal that PDGF-BB causes a decrease in the formation of iNOS protein which is preceded by decreases in iNOS mRNA steady state levels. bFGF drastically increases iNOS protein levels as well as the corresponding iNOS mRNA steady state levels. Nuclear run-on experiments reveal that PDGF-BB decreases the IL-1beta-induced transcription rate of the iNOS gene, whereas bFGF potentiates the transcriptional activity of the iNOS gene. Northern blot analyses demonstrate that bFGF strongly potentiates the formation of IL-1beta-induced IL-1 type I receptor mRNA levels, whereas PDGF-BB has no effect. Treatment of mesangial cells with the membrane-permeable cAMP analogue N6, O-2'-dibutyryladenosine 3',5'-phosphate (Bt2cAMP) markedly increases the production of nitrite. Whereas PDGF-BB does not affect cAMP-induced nitrite levels, bFGF strongly potentiates them. PDGF-BB alters neither cAMP-induced iNOS protein levels nor the corresponding iNOS mRNA steady state levels. By contrast, bFGF superinduces cAMP-stimulated iNOS protein and iNOS mRNA levels. These changes by bFGF are due to an increase in cAMP-induced transcriptional activity of the iNOS gene which is not affected by PDGF-BB. In summary, the results show that PDGF and bFGF differentially regulate iNOS expression in mesangial cells in a stimulus-specific way. The timely sequence of expression of PDGF and bFGF and of cytokines like IL-1 will crucially determine the amounts of NO produced and the functional consequences thereof in the course of progressive glomerular diseases.

Induction of mesangial interleukin-6 synthesis by apoptotic U937 cells and monocytes

Infiltration of the glomerular mesangium by monocytes and macrophages is a central pathologic feature in various forms of glomerulonephritis. Dependent on the presence and activity of local survival factors, monocytes may undergo apoptosis. Therefore, we looked for the interaction between cultured human mesangial cells (HMC) and intact, necrotic or apoptotic monocytic cells with different stages of programmed cell death (U937 cells and blood-derived human monocytes) and the possible evoked secretory responses of HMC. Interleukin-6 (IL-6) synthesis of HMC after a two hour co-culture with late apoptotic U937 cells was significantly increased (505 +/- 55 pg/ml) as compared to intact U937 cells (349 +/- 27 pg/ml; HMC alone, 319 +/- 62 pg/ml), and was further elevated after 20 hours (815 +/- 108 pg/ml). U937 cells alone, after incubation in HMC-conditioned medium or after coincubation with HMC, did not produce any detectable IL-6. A high mesangial IL-6 synthesis in response to apoptotic U937 cells was dependent on the cellular contact between HMC and U937 and could not be mimicked by apoptotic U937 culture supernatants. Radiolabeling studies indicated that HMC bound (16.6 +/- 2.4%) and ingested (12.5 +/- 1.9%) apoptotic U937 cells to a much higher amount as compared to intact U937 (5.3 +/- 2.0% binding; 5.0 +/- 1.1% phagocytosis). Binding and ingestion of monocytic cells undergoing apoptosis was confirmed by morphologic studies using electron microscopy. Incubation of HMC with a blocker of the CD36/ vitronectin receptor (VnR) dependent recognition mechanism of phagocytes for apoptotic leukocytes (RGDS peptide) did not alter binding, phagocytosis or IL-6 synthesis of HMC in response to apoptotic U937. Phospho-L-serine as an antagonist of the phosphatidylserine (PS) mediated recognition pathway for apoptotic cell disposal was able to reduce binding and IL-6 production by HMC but not phagocytosis. Thus, binding of apoptotic monocytic cells by HMC rather than ingestion may be the prerequisite for a stimulated secretory response. To elucidate whether binding and phagocytosis of particles in general might stimulate HMC to produce IL-6, we looked for mesangial IL-6 production after binding and ingestion of opsonized zymosan particles. In this case, IL-6 synthesis was markedly down-regulated. Furthermore, HMC proliferated after zymosan treatment, whereas after apoptotic cell uptake the mesangial cell number remained constant. In conclusion, apoptotic monocytic cells provoked an enhanced mesangial IL-6 synthesis by a PS-dependent recognition mechanism. This secretory response may have secondary implications for humoral or cellular processes within the mesangium.

RGD-containing peptides trigger apoptosis in glomerular mesangial cells of adult human kidneys

Substantial evidence was given that different Arg-Gly-Asp (RGD)-containing peptides, linear Arg-Gly-Asp-Ser (RGDS) and cyclic Arg-Gly-Asp-Phe (RGDF), which are sequences present in fibronectin and vitronectin and which can bind alpha5beta1 and alpha(v)beta3 integrins, respectively, both induced apoptosis and expression of interleukin-1beta-converting enzyme (ICE) in cultured glomerular mesangial cells from adult human kidneys, with consistent apoptosis features appearing as nuclei condensation and fragmentation, internucleosomal DNA fragmentation, and DNA content decrease. These results indicated that both fibronectin and vitronectin may be important in the survival of human glomerular mesangial cells and that stable cyclic RGD(D)FV peptide may be a candidate to be used for regulating apoptosis in vivo.

Efficient induction of apoptosis in cultured rat glomerular mesangial cells by dimeric monoclonal IgA anti-Thy-1 antibodies

Apoptosis of glomerular cells (GMC) has been observed in the early phase as well as the resolution phase of Thy-1 nephritis. Recently, we and others reported that IgG2a (ER4G) and IgG1 (OX7) monoclonal mouse anti-Thy-1 antibodies (anti-Thy-1 MoAb) are able to induce apoptosis of rat GMC in vivo. The purpose of this study was to investigate whether cross-linking of Thy-1 would influence the degree of apoptosis in cultured rat GMC using monomeric and dimeric IgA anti-Thy-1 MoAb. IgA anti-Thy-1 MoAb (ER4A) was generated by class switching of the IgG producing ER4 (ER4G) hybridoma. The ER4A clone spontaneously produces monomeric (m-ER4A) and dimeric IgA anti-Thy-1 MoAb *di-ER4A). Unaltered epitope specificity of ER4A was confirmed by blocking experiments of the binding of fluorescence labeled ER4G to cultured rat GMC with unlabeled ER4A on FACS. For the experiments of apoptosis, quiescent rat GMC were incubated for eight hours with medium alone or with medium in the presence of 10 micrograms/ml of m-ER4A, di-ER4A or control IgA MoAb of corresponding sizes. Apoptosis was assessed by morphological studies, agarose gel electrophoresis and quantitative FACS analyses using terminal deoxynucleotidyl transferase (TDT) method and the annexin V method. The TDT method detects specific-DNA nicking in apoptosis. The annexin V method detects early membrane changes during apoptosis. In morphological studies, cells incubated with m-ER4A and di-ER4A showed typical apoptotic features such as nuclear condensation and fragmentation. DNA isolated from the cells incubated with di-ER4A was cleaved into a distinctive ladder pattern compatible with apoptosis. In contrast, both medium alone and control IgA MoAb did not reveal detectable changes in morphological studies and agarose gel electrophoresis. In quantitative analyses by FACS using the TDT method and the annexin method, both m-ER4A and di-ER4A induced significantly higher percentages of apoptosis in rat GMC as compared to the controls. Furthermore, di-ER4A was considerably more efficient than m-ER4A in inducing apoptosis possibly through additional cross-linking of Thy-1 on the cell surface. This notion was confirmed by experiments, in which the addition of goat anti-mouse kappa antibodies enhanced apoptosis of rat GMC pre-sensitized with m-ER4A. Taken together, our results indicate that apoptosis of rat GMC by anti-Thy-1 antibodies is enhanced by cross-linking of Thy-1 on the cell surface. These studies are of importance for our understanding of mechanisms that may play a role in glomerular diseases.

Apoptosis during wound healing, fibrocontractive diseases and vascular wall injury

Following injury, tissue repair involves inflammation, granulation tissue formation and scar constitution. Granulation tissue develops from the connective tissue surrounding the damaged or missing area and contains mainly small vessels, inflammatory cells, fibroblasts and myofibroblasts. As the wound closes and evolves into a scar, there is a striking decrease in cellularity, including disappearance of typical myofibroblasts. The question arises as to what process is responsible for granulation tissue cell disappearance. Our results (in cutaneous wounds) and results of other laboratories (particularly in lungs and kidney) suggest that apoptosis is the mechanism responsible for the evolution of granulation tissue into a scar. During excessive scarring (hypertrophic scar or fibrosis), it is conceivable that the process of apoptosis cannot take place. After experimental endothelial injury in an artery, accumulation of smooth muscle cells participates in the formation of intimal thickening. Apoptotic features have been observed in cells of intimal thickening and also within human atherosclerotic plaques. In the case of atherosclerosis, apoptosis could be detrimental: since smooth muscle cells participate in plaque stability, apoptosis could lead to weakening and rupture of the plaque. These results underline the fact that both increased cell survival or excessive cell death can be associated with pathological disorders. Specific therapies devised to enhance or decrease the susceptibility of individual cell types to apoptosis development could modify the evolution of a variety of human diseases.

Nitric oxide donors induce apoptosis in glomerular mesangial cells, epithelial cells and endothelial cells

Renal mesangial cells exposed to inflammatory cytokines produce high concentrations of nitric oxide (NO) which may exert cytotoxic actions. We report here that glomerular mesangial cells, endothelial cells and epithelial cells in culture are themselves targets for NO and undergo apoptotic cell death upon exposure to high concentrations of NO. NO generated from different NO-releasing compounds as well as NO-saturated solution induce apoptosis in all three cell types as demonstrated by internucleosomal DNA fragmentation, an enrichment of cytosolic DNA/histone complexes, an increasing number of cellular 3'-OH-fragmented DNA ends and typical nuclear chromatin condensation. Induction of apoptosis was found to be dependent on protein synthesis and is preceded by expression of the tumour suppressor gene product p53 in mesangial cells. Induction of inducible NO synthase in mesangial cells by interleukin-1 beta leads to excessive formation of NO by the cells as measured by nitrite production. However, there was no evidence for apoptotic changes in mesangial cells triggered by endogenously produced NO. Co-cultures of glomerular endothelial or epithelial cells with interleukin-1 beta-activated mesangial cells expressing inducible NO synthase do not show apoptotic alterations in endothelial or epithelial cells. Moreover, preincubation of mesangial cells with interleukin-1 beta protects the cells from apoptosis induced by subsequent addition of exogenous NO thus suggesting that interleukin-1 beta not only triggers the expression of inducible NO synthase and massive NO formation but simultaneously stimulates a protecting principle in the cells. In summary, these results suggest that exogenous NO can induce apoptosis in all three types of intrinsic glomerular cells. However, whether endogenously produced NO can fulfil this function critically depends on a balance between a yet to be defined protective mechanism and inducible NO synthase expression in mesangial cells in response to interleukin-1 beta and eventually other inflammatory cytokines.

Induction of microhematuria by an IgA isotype switch variant of a monoclonal anti-Thy-1.1 antibody in the rat

IgA nephropathy (IgAN) is a chronic form of glomerulonephritis (GN) characterized by the deposition in the glomerular mesangium of mainly IgA. An experimental form of mesangial proliferative GN can be induced in rats by either polyclonal or monoclonal antibodies against Thy-1.1, a glycoprotein present on the surface of MC. The IgG-mediated renal inflammation is complement dependent and associated with influx of platelets and monocytes. In the present study we switched an IgG2a anti-Thy-1.1 (ER4G) producing hybridoma to an IgA anti-Thy-1.1 (ER4A) producing clone and analyzed the effects of IgA anti-Thy-1.1 in rats. FPLC analysis by gel filtration revealed that the IgA produced by the hybridoma cells was mainly dimeric and polymeric. Infusion of rats with purified ER4A (1 mg/kg) resulted in the deposition of IgA in a mesangial pattern in the glomeruli, similar to that found with ER4G. While administration of ER4G resulted in proteinuria, no significant urinary protein excretion was found in rats treated with ER4A. However, significant microhematuria was observed in rats receiving either ER4A or ER4G. Furthermore, the administration of ER4A was not accompanied by activation of complement, and no significant influx of monocytes or polymorphonuclear leukocytes was observed in contrast to the rats receiving ER4G. We conclude that microhematuria is selectively induced in Wistar rats by mouse IgA anti-Thy-1.1 without detectable complement-mediated injury to MC. These studies may be of importance in understanding the mechanisms leading to IgAN in patients.