Regulation of the mesangial cell myofibroblast phenotype by actin polymerization

Interplay between extracellular matrix components and cellular and molecular mechanisms in kidney fibrosis

Chronic kidney disease (CKD) is characterized by pathological accumulation of extracellular matrix (ECM) proteins in renal structures. Tubulointerstitial fibrosis is observed in glomerular diseases as well as in the regeneration failure of acute kidney injury (AKI). Therefore, finding antifibrotic therapies comprises an intensive research field in Nephrology. Nowadays, ECM is not only considered as a cellular scaffold, but also exerts important cellular functions. In this review, we describe the cellular and molecular mechanisms involved in kidney fibrosis, paying particular attention to ECM components, profibrotic factors and cell-matrix interactions. In response to kidney damage, activation of glomerular and/or tubular cells may induce aberrant phenotypes characterized by overproduction of proinflammatory and profibrotic factors, and thus contribute to CKD progression. Among ECM components, matricellular proteins can regulate cell-ECM interactions, as well as cellular phenotype changes. Regarding kidney fibrosis, one of the most studied matricellular proteins is cellular communication network-2 (CCN2), also called connective tissue growth factor (CTGF), currently considered as a fibrotic marker and a potential therapeutic target. Integrins connect the ECM proteins to the actin cytoskeleton and several downstream signaling pathways that enable cells to respond to external stimuli in a coordinated manner and maintain optimal tissue stiffness. In kidney fibrosis, there is an increase in ECM deposition, lower ECM degradation and ECM proteins cross-linking, leading to an alteration in the tissue mechanical properties and their responses to injurious stimuli. A better understanding of these complex cellular and molecular events could help us to improve the antifibrotic therapies for CKD.

Mesangial Cells and Renal Fibrosis

The main cellular constituents in glomerular mesangium are mesangial cells, which account for approximately 30-40% of the total cells in the glomerulus. Together with the mesangial matrix, mesangial cells form the glomerular basement membrane (GBM) in the glomerulus, whose main function is to perform the filtration. Under the pathologic conditions, mesangial cells are activated, leading to hyperproliferation and excess extracellular matrix (ECM). Moreover, mesangial cells also secrete several kinds of inflammatory cytokines, adhesion molecules, chemokines, and enzymes, all of which participate in the process of renal glomerular fibrosis. During the past years, researchers have revealed the roles of mesangial cells and the associated signal pathways involved in renal fibrosis. In this section, we will discuss how mesangial cells are activated and its contributions to renal fibrosis, as well as the molecular mechanisms and novel anti-fibrotic agents. Full understanding of the contributions of mesangial cells to renal fibrosis will benefit the clinical drug developing.

Protective effect of cadmium-induced autophagy in rat renal mesangial cells

Cadmium damages renal cells, and in particular may cause mesangial cell death by necrosis or apoptosis, depending on exposure conditions in cultured cells. However, there is an uncertainty as to whether Cd²⁺-induced autophagy can protect mesangial cells against these other mechanisms of cell death. We have used autophagy-incompetent mouse embryonic fibroblast (MEF) cells lacking the Atg16 gene, as well as cultured rat mesangial cells (RMC) in which Atg16 has been silenced, to examine this issue. Measuring the processing of LC3-I to LC3-II and expression of sequestosome-1 (p62), we define conditions under which RMC can be induced to undergo autophagy in response to 0-20 µM CdCl₂. Similarly, Cd²⁺ can initiate autophagy in MEF cells. However, when autophagy is compromised, either by gene knockout in MEF cells or by RNA silencing in RMC, cell viability is decreased, and concomitantly a Cd²⁺ dose-dependent increase in pro-caspase-3 cleavage indicates the initiation of apoptotic cell death. In contrast to some previous reports, Cd²⁺-induced autophagy is not correlated with increased levels of cellular reactive oxygen species but, among a panel of kinases investigated, is suppressed by inhibition of the Jun kinase. We conclude that concentrations of Cd²⁺ that initiate autophagy may afford renal mesangial cells some degree of protection against other modes (apoptosis, necrosis) of cell death.

ROCK/actin/MRTF signaling promotes the fibrogenic phenotype of fibroblast-like synoviocytes derived from the temporomandibular joint

Malocclusion caused by abnormal jaw development or muscle overuse during mastication results in abnormal mechanical stress to the tissues surrounding the temporomandibular joint (TMJ). Excessive mechanical stress against soft and hard tissues around the TMJ is involved in the pathogenesis of inflammatory diseases, including osteoarthritis (OA). OA-related fibrosis is a possible cause of joint stiffness in OA. However, cellular and molecular mechanisms underlying fibrosis around the TMJ remain to be clarified. Here, we established a cell line of fibroblast‑like synoviocytes (FLSs) derived from the mouse TMJ. Then, we examined whether the Rho‑associated coiled‑coil forming kinase (ROCK)/actin/myocardin-related transcription factor (MRTF) gene regulatory axis positively regulates the myofibroblast (MF) differentiation status of FLSs. We found that i) FLSs extensively expressed the MF markers α‑smooth muscle actin (α‑SMA) and type I collagen; and ii) an inhibitor against the actin‑polymerizing agent ROCK, Y‑27632; iii) an actin-depolymerizing agent cytochalasin B; iv) an inhibitor of the MRTF/serum response factor‑regulated transcription, CCG‑100602, clearly suppressed the mRNA levels of α‑SMA and type I collagen in FLSs; and v) an MF differentiation attenuator fibroblast growth factor‑1 suppressed filamentous actin formation and clearly suppressed the mRNA levels of α-SMA and type I collagen in FLSs. These results strongly suggest that the ROCK/actin/MRTF axis promotes the fibrogenic activity of synoviocytes around the TMJ. Our findings partially clarify the molecular mechanisms underlying the emergence of TMJ‑OA and may aid in identifying drug targets for treating this condition at the molecular level.

The role of IFI35 in lupus nephritis and related mechanisms

OBJECTIVES

It's reported that multiple genes in the IFN-γ/STAT1 pathway were hypomethylated and associated with the pathogenesis of lupus nephritis (LN). Our previous study using microarray analysis suggested that interferon induced 35-kDa protein (IFI35) was hypomethylated and increased in LN. However, the role of IFI35 in LN and related mechanism remains to be elucidate.

METHODS

The expressions of IFNγR, STAT1, IFI35 and MBD2 in the human kidneys tissues was detected by real-time PCR and Western blot. The protein levels of IFI35 in the human kidney tissues were detected by immunohistochemistry. The methylation status of IFNγR, STAT1 and IFI35 were detected by methylation specific PCR. Cell proliferation assay was evaluated using cell counting kit 8; pcDNA-IFI35 (pcDNA-MBD2) or IFI35 RNAi (MBD2 RNAi) was used to upregulated or downregulated the expression of the IFI35 and MBD2.

RESULTS

The expressions of IFNγR, STAT1 and IFI35 in the LN kidneys were significantly higher than controls. IFI35 was expressed in mesangial cells, and positively correlated with the proliferation of mesangial cells. IFNγR, STAT1and IFI35 was hypomethylated and MBD2 was increased in LN kidneys. In vitro data confirmed those findings: after stimulating with the serum from LN patients, the proliferation of human renal mesangial cells (HRMCs) was increased. The expressions of the three members of IFNγ signal pathway were hypomethylated and upregulated. However, this effect was reversed by MBD2 knockdown. IFI35 promoted the proliferation of HRMCs and was regulated by MBD2.

CONCLUSION

Our results demonstrated that IFI35 enhances the proliferation of mesangial cells and was regulated by MBD2 in LN.

Activation of endothelial NAD(P)H oxidase accelerates early glomerular injury in diabetic mice

Increased generation of reactive oxygen species (ROS) is a common denominative pathogenic mechanism underlying vascular and renal complications in diabetes mellitus. Endothelial NAD(P)H oxidase is a major source of vascular ROS, and it has an important role in endothelial dysfunction. We hypothesized that activation of endothelial NAD(P)H oxidase initiates and worsens the progression of diabetic nephropathy, particularly in the development of albuminuria. We used transgenic mice with endothelial-targeted overexpression of the catalytic subunit of NAD(P)H oxidase, Nox2 (NOX2TG). NOX2TG mice were crossed with Akita insulin-dependent diabetic (Akita) mice that develop progressive hyperglycemia. We compared the progression of diabetic nephropathy in Akita versus NOX2TG-Akita mice. NOX2TG-Akita mice and Akita mice developed significant albuminuria above the baseline at 6 and 10 weeks of age, respectively. Compared with Akita mice, NOX2TG-Akita mice exhibited higher levels of NAD(P)H oxidase activity in glomeruli, developed glomerular endothelial perturbations, and attenuated expression of glomerular glycocalyx. Moreover, in contrast to Akita mice, the NOX2TG-Akita mice had numerous endothelial microparticles (blebs), as detected by scanning electron microscopy, and increased glomerular permeability. Furthermore, NOX2TG-Akita mice exhibited distinct phenotypic changes in glomerular mesangial cells expressing α-smooth muscle actin, and in podocytes expressing increased levels of desmin, whereas the glomeruli generated increased levels of ROS. In conclusion, activation of endothelial NAD(P)H oxidase in the presence of hyperglycemia initiated and exacerbated diabetic nephropathy characterized by the development of albuminuria. Moreover, ROS generated in the endothelium compounded glomerular dysfunctions by altering the phenotypes of mesangial cells and compromising the integrity of the podocytes.

Endothelin receptor blockade ameliorates renal injury by inhibition of RhoA/Rho-kinase signalling in deoxycorticosterone acetate-salt hypertensive rats

PURPOSE OF REVIEW

Excessive production of fibrosis is a feature of hypertension-induced renal injury. Activation of RhoA/Rho-kinase (ROCK) axis has been shown in deoxycorticosterone acetate (DOCA)-salt hypertensive rats. We assessed whether selective endothelin receptor blockers can attenuate renal fibrosis by inhibiting RhoA/ROCK axis in DOCA-salt rats.

METHODS

At 4 weeks after the start of DOCA-salt treatment and uninephrectomization, male Wistar rats were randomized into three groups for 4 weeks: vehicle, ABT-627 (endothelin-A receptor inhibitor) and A192621 (endothelin-B receptor inhibitor).

RESULTS

DOCA-salt was characterized by increased blood pressure, decreased renal function, increased proteinuria, increased glomerulosclerosis and tubulointerstitial fibrosis with myofibroblast accumulation, increased renal endothelin-1 levels and RhoA activity along with increased expression of connective tissue growth factor at both mRNA and protein levels as compared with uninephrectomized control male Wistar rats. Treatment with a selective mineralocorticoid receptor antagonist, eplerenone, ameliorated proteinuria. Impaired renal function and histological changes were overcome by treatment with ABT-627, but not with A192621. The beneficial effects of bosentan, a nonspecific endothelin receptor blocker, on proteinuria, RhoA activity, and connective tissue growth factor levels were similar to ABT-627. Furthermore, in an isolated perfuse kidney, a RhoA inhibitor, C3 exoenzyme, and two ROCK inhibitors, fasudil and Y-27632, significantly attenuated connective tissue growth factor levels.

CONCLUSIONS

These results indicate that DOCA-salt elevates renal endothelin-1 levels and RhoA activity via activation of mineralocorticoid receptor, resulting in renal fibrosis and proteinuria. Endothelin-A receptor blockade can attenuate DOCA-salt-induced renal fibrosis probably through the inhibition of RhoA/ROCK activity and connective tissue growth factor expression.

Qufeng Tongluo Prescription () inhibits mesangial cell proliferation and promotes apoptosis through regulating cell cycle progression

OBJECTIVE

To study the effects and possible underlying mechanism of Qufeng Tongluo Prescription (, QFTL) on the regulation of mesangial cells (MCs) proliferation and apoptosis.

METHODS

The MCs used in this experiment have undergone five passages induced by lipopolysaccharide (LPS). Changes in the proliferation, apoptosis, cell cycle regulatory proteins and mRNA expression levels of the MCs after administration of Benazepril or QFTL were measured by methyl thiazolyl tetrazolium (MTT) reduction assay, flow cytometry, Western blot and quantitative real-time polymerase chain reaction (qRT-PCR), respectively.

RESULTS

The addition of Benazepril or QFTL serum inhibited LPS-induced MC proliferation after treatment for 24, 48 and 72 h, respectively (P<0.05 or P<0.01). Moreover, the inhibitory effect is more significant in the QFTL group at 48 h (P<0.05). Compared with the control group, LPS-induced cell proliferation decreased the number of cells in G1 phase versus cells in S and G2/M phases, while the addition of QFTL and Benazepril serum increased the ratio of cells at G1 phase (P<0.05 or P<0.01) to cells at S phase (P<0.01), implicating the cell cycle inhibition effect exerted by QFTL. LPS decreased the level of MC apoptosis, compared with the control group (P<0.05), while QFTL and Benazepril serum increased the level of MC apoptosis (P<0.01). Moreover, the difference between the QFTL group and the Benazepril group was statistically significant (P<0.01). Compared with the control group, the protein and mRNA expression levels of cylinD1, cyclin dependent kinase 2 (CDK2) and p21 were significantly increased (P<0.05 or P<0.01), p27 was decreased but with no statistical significance (P>0.05); After being treated with QFTL and Benazepril serum, the protein and mRNA expression levels of cylinD1, CDK2, p21 were decreased and p27 increased significantly (P<0.05 or P<0.01); Compared with the Benazepril group, QFTL show better effects on protein and mRNA expression levels of cylinD1, CDK2 (P<0.05 or P<0.01) and p21 protein expression (P<0.05).

CONCLUSION

QFTL inhibits MCs proliferation, promotes MCs apoptosis through an underlying mechanism of down-regulating the protein and mRNA expression levels of cylinD1, CDK2, p21 and up-regulation of the expression level of p27.

The antigen-binding fragment of anti-double-stranded DNA IgG enhances F-actin formation in mesangial cells by binding to alpha-actinin-4

Anti-double-stranded DNA (dsDNA) IgG causes renal damage in patients with lupus nephritis by cross-reacting with multiple autoantigens, including alpha-actinin-4, in mesangial cells (MCs). However, how the cross-reactions play a role in mesangial phenotypic abnormalities is not well understood. Here, we investigated the effects of the fragment antigen-binding (Fab) of anti-dsDNA IgG3 on the biochemical properties of alpha-actinin-4. Experiments revealed that anti-dsDNA Fab specifically binds to alpha-actinin-4, but not G-actin. The binding by anti-dsDNA Fab sequentially increases the positive charge of alpha-actinin-4 and inhibits the affinity of alpha-actinin-4 to calcium ions. By the low shear viscosity and a co-sedimentation assay, we found that the alpha-actinin-4-induced F-actin gelation improves when anti-dsDNA Fab is added. However, the Fab control has no such effect on F-actin gelation. Furthermore, the in vitro cultured MCs exhibit higher F-actin expression and transforming growth factor- β1 synthesis after the incubation with anti-dsDNA Fab. Therefore, our results indicated that anti-dsDNA Fab may enhance F-actin formation by the proprietary modification of alpha-actinin-4, which could partially explain the myofibroblast-like phenotype of MCs in anti-dsDNA-positive lupus nephritis.

Multi-layered hypertrophied MEE formation by microtubule disruption via GEF-H1/RhoA/ROCK signaling pathway

BACKGROUND

Formation of the secondary palate is complex and disturbance during palatal fusion may result in cleft palate. The processes of adhesion, intercalation, and disappearance of medial edge epithelia (MEE) are characterized by morphological changes requiring dynamic cytoskeletal rearrangement. Microtubules are one of the cytoskeletal elements involved in maintenance of cell morphology. Microtubule-disrupting drugs have been reported to cause craniofacial malformations including cleft palate. The mechanisms underlying the failure of palatal fusion remain poorly understood. We evaluated the effect of nocodazole (NDZ), a drug that disrupts microtubules, on palatal fusion in organ culture.

RESULTS

NDZ caused failure of palatal fusion due to the induction of a multi-layered hypertrophied MEE in the mid-region of the secondary palatal shelves. Microtubule disruption increased RhoA activity and stress fiber formation. Pharmacological inhibition of the RhoA/ROCK pathway blocked multi-layered MEE formation. Partial prevention of hypertrophied MEE was observed with Y27632 and cytochalasin, but not with blebbistatin. NDZ induced re-localization of GEF-H1 into cytoplasm from cell-cell junctions.

CONCLUSIONS

The present study provided evidence that the GEF-H1/RhoA/ROCK pathway plays a pivotal role in linking microtubule disassembly to the remodeling of the actin cytoskeleton, which resulted in a multi-layered hypertrophied MEE and failure of palatal fusion.

Peptide corresponding to the C terminus of tissue factor pathway inhibitor inhibits mesangial cell proliferation and activation in vivo

Mesangial cells (MsCs) are one of the resident cell types in the glomerulus and are important with respect to its function and structure. The activation and proliferation of MsCs occur in several types of glomerulonephritis, particularly proliferative glomerulonephritis, producing a series of protein factors and matrix components that impair the normal structure and function of the glomerulus. To inhibit proliferation or induction of apoptosis is considered to be one mechanism that can be used to treat these diseases. In previous studies, we found that the tissue factor pathway inhibitor (TFPI) induces the apoptosis of cultured rat MsCs. Here, we expressed a series of TFPI fragments as fusion proteins to maltose binding protein (MBP-TFPI(162-188), MBP-TFPI(187-241), MBP-TFPI(240-276), MBP-TFPI(162-241), MBP-TFPI(187-276) and MBP-TFPI(162-276)) and applied them to cultured rat mesangial cells. The C terminus of TFPI, a peptide corresponding to residues 240-276 of TFPI, was confirmed to induce apoptosis of MsCs in vitro. To observe the effect of this peptide on MsCs in vivo, we performed intramuscular gene transfer treatment on a rat model of proliferative glomerulonephritis with a plasmid containing the gene for the C terminus of TFPI. This revealed that the C terminus of TFPI exhibited suppressive effects on the activation and proliferation of MsCs and, thereby, improved renal function. Our data indicate that the C terminus of TFPI could be used in the treatment of proliferative glomerulonephritis.

YB-1 acts as a ligand for Notch-3 receptors and modulates receptor activation

Y-box (YB) protein-1 is secreted by mesangial and immune cells after cytokine challenge, but extracellular functions are unknown. Here, we demonstrate that extracellular YB-1 associates with outer cell membrane components and interacts with extracellular Notch-3 receptor domains. The interaction appears to be specific for Notch-3, as YB-1-green fluorescent protein binds to the extracellular domains and full-length forms of Notch-3 but not to Notch-1. YB-1-green fluorescent protein and Notch-3 proteins co-localize at cell membranes, and extracellular YB-1 activates Notch-3 signaling, resulting in nuclear translocation of the Notch-3 intracellular domain and up-regulation of Notch target genes. The YB-1/Notch-3 interaction may be of particular relevance for inflammatory mesangioproliferative disease, as both proteins co-localize in an experimental nephritis model and receptor activation temporally and spatially correlates with YB-1 expression.

Marine toxins and the cytoskeleton: a new view of palytoxin toxicity

Palytoxin is a marine toxin first isolated from zoanthids (genus Palythoa), even though dinoflagellates of the genus Ostreopsis are the most probable origin of the toxin. Ostreopsis has a wide distribution in tropical and subtropical areas, but recently these dinoflagellates have also started to appear in the Mediterranean Sea. Two of the most remarkable properties of palytoxin are the large and complex structure (with different analogs, such as ostreocin-D or ovatoxin-a) and the extreme acute animal toxicity. The Na(+)/K(+)-ATPase has been proposed as receptor for palytoxin. The marine toxin is known to act on the Na(+) pump and elicit an increase in Na(+) permeability, which leads to depolarization and a secondary Ca(2+) influx, interfering with some functions of cells. Studies on the cellular cytoskeleton have revealed that the signaling cascade triggered by palytoxin leads to actin filament system distortion. The activity of palytoxin on the actin cytoskeleton is only partially associated with the cytosolic Ca(2+) changes; therefore, this ion represents an important factor in altering this structure, but it is not the only cause. The goal of the present minireview is to compile the findings reported to date about: (a) how palytoxin and analogs are able to modify the actin cytoskeleton within different cellular models; and (b) what signaling mechanisms could be involved in the modulation of cytoskeletal dynamics by palytoxin.

Expression of alpha-actinin-1 in human glomerular mesangial cells in vivo and in vitro

Recent studies have demonstrated important roles of alpha-actinins in glomerular disease, while little information is known about the expression profile of alpha-actinins in human glomerular mesangial cells. Here, immunofluorescence and confocal microscopy showed that alpha-actinin-1 exclusively distributed along mesangial cells in human glomeruli of IgA nephropathy. RT-PCR and Western blot further confirmed the expression of alpha-actinin-1 in primary cultured human mesangial cells. We also found that transforming growth factor-beta 1 (TGF-beta 1) stimulated ACTN1 gene transcription and that transiently transfected alpha-actinin-1 significantly increased TGF-beta 1-induced plasminogen activator inhibitor-1 (PAI-1) promoter activity in human mesangial cells. These findings suggest that alpha-actinin-1 may play a role in human glomerular disease.

Abnormal cytoskeletal protein expression in cultured skin fibroblasts from type 1 diabetes mellitus patients with nephropathy: A proteomic approach

Diabetic nephropathy (DN) develops in about 40% of insulin-dependent type 1 diabetes mellitus (T1DM) patients, and is associated not only with diabetes duration and metabolic control, but also with a genetic predisposition. Constitutive alterations of cytoskeletal proteins may play a role in the development of DN. We investigated the expression of these proteins in cultured skin fibroblasts, obtained from long-term T1DM patients with and without DN but comparable metabolic control, and from matched healthy subjects, by means of 2-DE electrophoresis and MS-MALDI analyses. In T1DM with DN, compared to the other two groups, quantitative analyses revealed an altered expression of 17 spots (p<0.05-p<0.01), corresponding to 12 unique proteins. In T1DM with DN, beta-actin and three isoforms of tubulin beta-2 chain, tropomodulin-3, and LASP-1 were decreased, whereas two tubulin beta-4 chain isoforms, one alpha actinin-4 isoform, membrane-organizing extension spike protein (MOESIN), FLJ00279 (corresponding to a fragment of myosin heavy chain, non-muscle type A), vinculin, a tropomyosin isoform, and the macrophage capping protein were increased. A shift in caldesmon isoforms was also detected. These results demonstrate an association between DN and the constitutive expression of cytoskeleton proteins in cultured skin fibroblasts from T1DM with DN, which may retain pathophysiologycal implications.

Plasticity of mesangial cells: a basis for understanding pathological alterations

In the last two decades, the ability of mesangial cells to respond to various stimuli or injurious agents by altering their phenotype and function has become recognized. The plasticity of these mesangial cells has been linked to the morphological and functional alterations responsible for the pathologic findings. Many of the glomerular disorders target the mesangium as the primary and/or initial site of injury. Understanding how mesangial cells are altered in the various conditions provides a platform for conceptualizing pathologic mechanisms and defining key steps amenable to therapeutic intervention. The present paper reviews the normal and altered mesangium with an emphasis on mechanisms involved in alterations of mesangial homeostasis. Mesangial cells and matrix are very important in maintaining normal glomerular structure, and function and the plasticity of these cells is responsible for pathological manifestations, repair, and scarring. Our more sophisticated understanding of mesangial cell behavior and matrix biology provides very useful information to help design new therapeutic approaches to the treatment of renal diseases. The potential for bone marrow-derived cells to differentiate into mesangial cells and repopulate damaged mesangium, thus "healing" what is today considered to be irreversible damage represents an exciting new area of research.

Regulation of TGF-beta1/MAPK-mediated PAI-1 gene expression by the actin cytoskeleton in human mesangial cells

The importance of transforming growth factor-beta1 (TGF-beta1) in plasminogen activator inhibitor-1 (PAI-1) gene expression has been established, but the precise intracellular mechanisms are not fully understood. Our hypothesis is that the actin cytoskeleton is involved in TGF-beta1/MAPK-mediated PAI-1 expression in human mesangial cells. Examination of the distributions of actin filaments (F-actin), alpha-actinin, extracellular signal-regulated kinase (ERK) and c-Jun N-terminal kinase (JNK) by immunofluorescence and immunoprecipitation revealed that ERK and JNK associate with alpha-actinin along F-actin and that TGF-beta1 stimulation promote the dissociation of ERK and JNK with F-actin. Disassembly of the actin cytoskeleton inhibited phosphorylation of ERK and JNK and modulated PAI-1 expression and promoter activity under both basal and TGF-beta1-stimulated conditions. Stabilizing actin prevented dephosphorylation of ERK and JNK. ERK and JNK inhibitors and overexpressed dominant negative mutants antagonized the ability of TGF-beta1 to increase PAI-1 expression and promoter activity. Disassembly of F-actin also inhibited AP-1 DNA binding activity as determined by electrophoretic mobility shift assay using AP-1 consensus oligonucleotides derived from human PAI-1 promoter. F-actin stabilization prevented loss of AP-1 DNA binding activity. Therefore, changes in actin cytoskeleton modulate the ability of TGF-beta1 to stimulate PAI-1 expression through a mechanism dependent on the activation of MAPK/AP-1 pathways.

Alterations in cytoskeletal protein expression by mycophenolic acid in human mesangial cells requires Rac inactivation

In response to glomerular injury, mesangial cells are activated into myofibroblasts, which contribute to the physiopathology of glomerulosclerosis. We have previously shown that chronic treatment of cultured human mesangial cells with mycophenolic acid (MPA), a specific inhibitor of guanosine nucleotide synthesis, prevents their activation and alters cytoskeleton protein expression and associated functions, such as contractility and migratory capacity. The aim of the present study was to explore the mechanisms underlying MPA-induced mesangial cytoskeleton alterations. We therein show that coincubation with guanosine (100 microM) compensates for the effects of MPA on mesangial cell proliferation and migration, and prevents MPA-induced overexpression of alpha-smooth muscle actin (SMA) and basic calponin (b-calp), indicating that guanylates are involved in mesangial responses to MPA. MPA decreased the GTP-bound (active) form of both RhoA, Rac1 and Cdc42, and specifically altered the expression level of Rac1. Pharmacological inhibition of RhoA activity reduced expression of both SMA and calponin, whereas overexpression of a dominant-negative form of Rac1 increased SMA expression. Conversely, overexpression of constitutively active Rac1 resulted in SMA and b-calp down-regulation, and fully prevented their stimulation by MPA, indicating that Rac inactivation is responsible for MPA effects on mesangial cytoskeletal expression. These results show that in human mesangial cells, RhoA and Rac1 exert opposite effects on the expression of two major cytoskeletal proteins: SMA and basic calponin. Moreover, these data highlight for the first time an integrated mechanism whereby MPA regulates mesangial phenotype, which is mediated by loss of Rac activity.

Caspase-1-dependent pore formation during pyroptosis leads to osmotic lysis of infected host macrophages

Salmonella enterica serovar Typhimurium invades host macrophages and induces a unique caspase-1-dependent pathway of cell death termed pyroptosis, which is activated during bacterial infection in vivo. We demonstrate DNA cleavage during pyroptosis results from caspase-1-stimulated nuclease activity. Although poly(ADP-ribose) polymerase (PARP) activation by fragmented DNA depletes cellular ATP to cause lysis during oncosis, the rapid lysis characteristic of Salmonella-infected macrophages does not require PARP activity or DNA fragmentation. Membrane pores between 1.1 and 2.4 nm in diameter form during pyroptosis of host cells and cause swelling and osmotic lysis. Pore formation requires host cell actin cytoskeleton rearrangements and caspase-1 activity, as well as the bacterial type III secretion system (TTSS); however, insertion of functional TTSS translocons into the host membrane is not sufficient to directly evoke pore formation. Concurrent with pore formation, inflammatory cytokines are released from infected macrophages. This mechanism of caspase-1-mediated cell death provides additional experimental evidence supporting pyroptosis as a novel pathway of inflammatory programmed cell death.

Involvements of Rho-Kinase and TGF-β Pathways in Aldosterone-Induced Renal Injury

Recent studies have suggested a role for aldosterone in the pathogenesis of renal injury. This study investigated the potential contributions of Rho-kinase and TGF-beta pathways to aldosterone-induced renal injury. Rats were uninephrectomized and then treated for 5 wk with 1% NaCl in a drinking solution and one of the following: Vehicle (2% ethanol, subcutaneously; n = 9); aldosterone (0.75 microg/h, subcutaneously; n = 9); or aldosterone + fasudil, a specific Rho-kinase inhibitor (10 mg/kg per d, subcutaneously; n = 8). Phosphorylation of myosin phosphate target subunit-1 (MYPT1) and Smad2/3 in renal cortical tissue was measured by Western blotting with anti-phospho MYPT1 and Smad2/3 antibodies, respectively. Rats that received aldosterone infusion exhibited hypertension and severe renal injury characterized by proteinuria, glomerular sclerosis, and tubulointerstitial fibrosis with increases in alpha-smooth muscle actin staining and numbers of monocytes/macrophages in the interstitium. Renal cortical mRNA levels of types I and III collagen, TGF-beta, connective tissue growth factor, and monocyte chemoattractant protein-1 as well as Smad2/3 phosphorylation were significantly increased in rats that received aldosterone infusion. All of these changes were associated with an increase in renal tissue MYPT1 phosphorylation. Treatment with fasudil did not alter BP but significantly ameliorated proteinuria and renal injury in rats that received aldosterone infusion. Furthermore, fasudil prevented MYPT1 phosphorylation and markedly decreased alpha-smooth muscle actin staining, numbers of monocytes/macrophages, mRNA levels of types I and III collagen, TGF-beta, connective tissue growth factor and monocyte chemoattractant protein-1, and Smad2/3 activity in renal cortical tissues. These results provide evidence, for the first time, that Rho-kinase is substantially involved in aldosterone-induced renal injury through activation of a TGF-beta-dependent pathway.

Beta8 integrin binds Rho GDP dissociation inhibitor-1 and activates Rac1 to inhibit mesangial cell myofibroblast differentiation

Alpha(v)beta8 integrin expression is restricted primarily to kidney, brain, and placenta. Targeted alpha(v) or beta8 deletion is embryonic lethal due to defective placenta and brain angiogenesis, precluding investigation of kidney alpha(v)beta8 function. We find that kidney beta8 is localized to glomerular mesangial cells, and expression is decreased in mouse models of glomerulosclerosis, suggesting that beta8 regulates normal mesangial cell differentiation. To interrogate beta8 signaling pathways, yeast two-hybrid and co-precipitation studies demonstrated beta8 interaction with Rho guanine nucleotide dissociation inhibitor-1 (GDI). Selective beta8 stimulation enhanced beta8-GDI interaction as well as Rac1 (but not RhoA) activation and lamellipodia formation. Mesangial cells from itgb8-/- mice backcrossed to a genetic background that permitted survival, or gdi-/- mice, which develop glomerulosclerosis, demonstrated RhoA (but not Rac1) activity and alpha-smooth muscle actin assembly, which characterizes mesangial cell myofibroblast transformation in renal disease. To determine whether Rac1 directly modulates RhoA-associated myofibroblast differentiation, mesangial cells were transduced with inhibitory Rac peptide fused to human immunodeficiency virus-Tat, resulting in enhanced alpha-smooth muscle actin organization. We conclude that the beta8 cytosolic tail in mesangial cells organizes a signaling complex that culminates in Rac1 activation to mediate wild-type differentiation, whereas decreased beta8 activation shifts mesangial cells toward a RhoA-dependent myofibroblast phenotype.

Molecular Mechanisms and Therapeutic Strategies of Chronic Renal Injury: Role of Rho-Kinase in the Development of Renal Injury

Rho/Rho-kinase plays an important role not only in the vasoconstrictor mechanism but also in cellular morphology, motility, adhesion, and proliferation. This pathway also serves to modulate the structure and function of various kidney cells including tubular epithelial cells, mesangial cells, and podocytes. The inhibition of the Rho/Rho-kinase pathway elicits marked increases in renal blood flow in vivo and dilates both afferent and efferent arterioles preconstricted by angiotensin II in vitro. In renal injury, intrarenal angiotensin II is reported to be activated, which subsequently would upregulate the Rho-kinase pathway. A selective Rho-kinase inhibitor, fasudil, has recently been shown to improve renal damage resulting from hypertensive glomerulosclerosis, unilateral ureteral obstruction (for interstitial renal fibrosis) and subtotal nephrectomy. Of interest, fasudil upregulated the expression of p27(kip1), a cyclin-dependent kinase inhibitor, and increased the p27(kip1) immuno-positive cells in both glomeruli and tubulointerstitium with the use of immunohistochemistry. Collectively, the Rho-kinase pathway is involved in the pathogenesis of renal injury. Clinical application of this type of therapy however awaits further investigations.

Actin cytoskeleton of rabbit intestinal cells is a target for potent marine phycotoxins

Biotoxins produced by harmful marine microalgae (phycotoxins) can be accumulated into seafood, representing a great risk for public health. Some of these phycotoxins are responsible for a variety of gastrointestinal disturbances; however, the relationship between their mechanism of action and toxicity in intestinal cells is still unknown. The actin cytoskeleton is an important and highly complicated structure in intestinal cells, and on that basis our aim has been to investigate the effect of representative phycotoxins on the enterocyte cytoskeleton. We have quantified for the first time the loss of enterocyte microfilament network induced by each toxin and recorded fluorescence images using a laser-scanning cytometer and confocal microscopy. Our data show that pectenotoxin-6, maitotoxin, palytoxin and ostreocin-D cause a significant reduction in the actin cytoskeleton. In addition, we found that the potency of maitotoxin, palytoxin and ostreocin-D to damage filamentous actin is related to Ca2+ influx in enterocytes. Those results identify the cytoskeleton as an early target for the toxic effect of those toxins.

Expression of alphasmooth muscle actin in lens epithelia from human donors and cataract patients

In order to re-evaluate functional implications of alphasmooth muscle actin (alphaSMA) expression in lens epithelial cells (LECs), we assessed its presence in donor lenses without visible opacities (DON), lenses with mature cataract (CAT), and cataractous lenses with posterior subcapsular opacities (PSO) or anterior subcapsular fibrosis (ASF). The levels of alphaSMA and transforming growth factor-beta2 (TGFbeta2) mRNAs were measured by classical and real-time PCR. Expression and structural organisation of alphaSMA protein and beta-catenin were monitored by Western blotting and confocal microscopy. All DON analysed contained measurable amounts of alphaSMA mRNA. In CAT without and with PSO, mRNA expression was increased and, again more than doubled in ASF. TGFbeta2 mRNA expression varied widely between the individual samples but was slightly increased in ASF. No correlation existed between alphaSMA or TGFbeta2 expression and the age of the donors in any of the lens categories. Confocal microscopy revealed that, in DON and CAT, alphaSMA was preferentially expressed in a simple granular pattern in single or small clusters of LECs within a normally shaped cobblestone epithelium. Locally, the granules were merged into short stretches at the cell margin. In CAT, a few abnormally shaped cells contained polygonal alphaSMA structures and short stress fibres. In CAT with PSO and ASF, polygons and stress fibre bundles predominated in spindle-shaped cells. Expression patterns of different complexity were often present in the same epithelium. Apical polygons and basal stress fibres were detected within the same cell and may reflect instability of the interface between epithelium and cortical fibres and changes in adhesion to the capsule, respectively. High levels of betacatenin mRNA and protein were present in all lens types. However, with increasing complexity of alphaSMA organisation, betacatenin staining disappeared from the cell margin and basal infoldings and was shifted towards the cytoplasm and nucleus. The presence of alphaSMA in DON, the absence of any correlation between mRNA level and age, and the modest increase in complexity of alphaSMA-containing structures in CAT argue against an inevitable link between alphaSMA expression and the development of age-related cataract. Low levels of alphaSMA expression may reflect repair of normal wear and tear. In pathologic situations such as PSO and ASF, persisting stimulation and additional incentives may induce increased alphaSMA expression and more elaborate patterning, eventually leading to completion of EMT.

Tubular CD146 Expression in Nephropathies Is Related to Chronic Renal Failure

BACKGROUND

CD146, a member of the immunoglobulin superfamily, is mainly expressed at the endothelial junction. The soluble form of CD146 is increased in the serum of patients with chronic renal failure. The aim of the study was to investigate CD146 expression on biopsies of normal kidney and nephropathies.

METHODS

We did an immunohistochemical analysis of 10 normal renal tissues and 126 patients with nephropathies.

RESULTS

The mean age of the patients was 47.5 +/- 18 years with 65% of men. At the time of the biopsy, 73 patients (57.9%) had a renal failure and the mean proteinuria was 3.3 +/- 2.9 g/24 h. Inflammatory syndrome was present in 60 (47.6%) patients. Fibrous interstitial changes from minimal lesions to diffuse lesions were seen in 105 (83.3%) biopsies; the mean glomerulosclerosis index was 16.9 +/- 19.7%. Normal kidneys showed CD146 staining on endothelial cells, smooth muscle cells, and mesangium. Normal tubular cells were not stained. If endocapillary proliferation was present, the mesangial CD146 expression was higher. This mesangial expression correlated with proteinuria (p = 0.007) and not with renal failure (p = 0.07). A de novo expression on tubular cells was found in 53 patients (42%) and this expression correlated with age (p < 0.001), male sex (p = 0.04), glomerulosclerosis (p < 0.001), interstitial fibrosis (p < 0.001), and renal failure (p < 0.001).

CONCLUSION

Renal CD146 expression is of interest for determining the pathogenesis of mesangial alterations during glomerular injuries and of tubular phenotypic changes during chronic renal failure.

Smooth muscle actin determines mechanical force-induced p38 activation

The mitogen-activated protein kinase p38 is activated by mechanical force, but the cellular elements that mediate force-induced p38 phosphorylation are not defined. As alpha-smooth muscle actin (SMA) is an actin isoform associated with force generation in fibroblasts, we asked if SMA participates in the activation of p38 by force. Tensile forces (0.65 pn/mum(2)) generated by magnetic fields were applied to collagen-coated magnetite beads bound to Rat-2 cells. Immunoblotting showed that p38alpha was the predominant p38 isoform. Analysis of bead-associated proteins demonstrated that SMA enrichment of collagen receptor complexes required the alpha2beta1 integrin. SMA was present almost entirely as filaments. Swinholide depolymerized SMA filaments and blocked force-induced p38 phosphorylation and force-induced increases of SMA. Knockdown of SMA (70% reduction) using RNA interference did not affect beta-actin but inhibited force-induced p38 phosphorylation by 50%. Inhibition of Rho kinase blocked SMA filament assembly, force-induced increases of SMA, and force-induced p38 activation. Force application increased SMA content and enhanced the association of phosphorylated p38 with SMA filaments. Blockade of p38 phosphorylation by SB203586 abrogated force-induced increases of SMA. In cells transfected with SMA promoter-beta-galactosidase fusion constructs, co-transfection with constitutively active p38 or MKK6 increased SMA promoter activity by 2.5-3-fold. Dominant negative p38 blocked force-induced activation of the SMA promoter. In SMA negative cells, there was no force-induced p38 phosphorylation. We conclude that force-induced p38 phosphorylation is dependent on an SMA filament-dependent pathway that uses a feed-forward amplification loop to synergize force-induced SMA expression with p38 activation.

Mechanisms of force generation and transmission by myofibroblasts

The myofibroblast has been shown to have a key role in tissue reconstruction after injury and pathological changes characterized by fibrosis. Force generation by the myofibroblast depends on the isometric contraction of stress fibers containing alpha-smooth muscle actin, and is mediated through Rho/Rho-kinase. The force is transmitted by vinculin and tensin-containing "supermature" focal adhesions, which connect stress fibers with the extracellular matrix. Force production and transmission by the myofibroblast are modulated by the coordinated action of cytokines, extracellular matrix components and mechanical tension. Regulation of these phenomena will be important for therapeutic strategies aimed at influencing fibrocontractive diseases.

Phenotypic modulation of cultured bladder smooth muscle cells and the expression of inducible nitric oxide synthase

Phenotypic modulation of smooth muscle is associated with various pathological conditions, including bladder dysfunction. Cytoskeletal dynamics modulate the cell phenotype and were recently shown to be involved in regulation of inducible nitric oxide synthase (iNOS). We tested the hypothesis that the cell differentiation status affects iNOS expression, and that iNOS is preferentially expressed in immature dedifferentiated bladder smooth muscle cells (BSMC). Isolated at BSMC were put into different stages of differentiation by serum deprivation on laminin-coated plates in the presence of IGF-I and by interaction with Rho signaling and actin polymerization. iNOS and smooth muscle-myosin heavy chain (SM-MHC) protein expression were investigated with Western blot analysis. Our results showed iNOS protein in BSMC exposed to interleukin-1 beta (2 ng/ml) + TNF-alpha (50 ng/ml). Growth of BSMC in serum-free medium on laminin in the presence of IGF-I increased SM-MHC expression, whereas cytokine-induced iNOS was inhibited. Disruption of F-actin with latrunculin B (0.5 microM) potentiated iNOS expression and decreased SM-MHC expression. Rho inhibition with C3 (2.5 microg/ml) increased iNOS expression, whereas SM-MHC expression was slightly decreased. Rho-kinase inhibition with Y-27632 (10 microM) mediated a decrease in iNOS and a slight increase in SM-MHC expression. In conclusion, the capacity of BSMC to express iNOS was negatively correlated to differentiation status measured as SM-MHC expression. Actin cytoskeletal dynamics and Rho signaling are involved in regulation of cytokine-induced iNOS expression in BSMC. Phenotypic changes and impairment in actin cytoskeleton formation may potentiate cytokine activation and in turn increase nitric oxide production in the bladder during disease.

Rho kinase inhibitors block activation of pancreatic stellate cells

1. In response to pancreatic injury and in cell culture, pancreatic stellate cells (PSCs) are transformed ('activated') into highly proliferative myofibroblast-like cells, which express alpha-smooth muscle actin (alpha-SMA), and produce type I collagen and other extracellular matrix components. There is accumulating evidence that activated PSCs play important roles in pancreatic fibrosis and inflammation. 2. The small GTP-binding protein Rho has emerged as an important regulator of the actin cytoskeleton and cell morphology through the downstream effector Rho kinase (ROCK). But, the roles of Rho-ROCK pathway in PSCs are unknown. Here, we examined the effects of (+)-(R)-trans-4-(1-aminoethyl)-N-(4-pyridyl) cyclohexanecarboxamide (Y-27632) and HA-1077 (fasudil), specific inhibitors of ROCK, on the activation of PSCs. 3. PSCs were isolated from the pancreas of male Wistar rats after perfusion with collagenase P. The actin cytoskeleton was analyzed by phalloidin staining. Expression of RhoA and ROCK was examined by immunostaining and Western blotting. Effects of Y-27632 and HA-1077 on alpha-SMA expression, platelet-derived growth factor-induced proliferation and chemotaxis, and collagen production were assessed. 4. Culture-activated PSCs developed a well-spread cell shape, with extended stress fiber formation. PSCs expressed RhoA, ROCK-1, and ROCK-2. 5. Y-27632 caused disassembly of stress fibers. Y-27632 and HA-1077 inhibited alpha-SMA expression, proliferation, chemotaxis, and type I collagen production in culture-activated PSCs. 6. In addition, Y-27632 and HA-1077 inhibited spontaneous activation of freshly isolated PSCs in culture on plastic. 7. These findings suggest a role of Rho-ROCK pathway in the activation process of PSCs by regulating the actin cytoskeleton, and a potential application of Rho-ROCK pathway inhibitors for the treatment of pancreatic inflammation and fibrosis.