Gelsolin mediates collagen phagocytosis through a rac-dependent step

Regulation of Mitochondrial Function by the Actin Cytoskeleton

The regulatory role of actin cytoskeleton on mitochondrial function is a growing research field, but the underlying molecular mechanisms remain poorly understood. Specific actin-binding proteins (ABPs), such as Gelsolin, have also been shown to participate in the pathophysiology of mitochondrial OXPHOS disorders through yet to be defined mechanisms. In this mini-review, we will summarize the experimental evidence supporting the fundamental roles of actin cytoskeleton and ABPs on mitochondrial trafficking, dynamics, biogenesis, metabolism and apoptosis, with a particular focus on Gelsolin involvement in mitochondrial disorders. The functional interplay between the actin cytoskeleton, ABPs and mitochondrial membranes for the regulation of cellular homeostasis thus emerges as a new exciting field for future research and therapeutic approaches.

Recombinant Human Plasma Gelsolin Stimulates Phagocytosis while Diminishing Excessive Inflammatory Responses in Mice with Pseudomonas aeruginosa Sepsis

Plasma gelsolin (pGSN) is a highly conserved abundant circulating protein, characterized by diverse immunomodulatory activities including macrophage activation and the ability to neutralize pro-inflammatory molecules produced by the host and pathogen. Using a murine model of Gram-negative sepsis initiated by the peritoneal instillation of Pseudomonas aeruginosa Xen 5, we observed a decrease in the tissue uptake of IRDye^®800CW 2-deoxyglucose, an indicator of inflammation, and a decrease in bacterial growth from ascitic fluid in mice treated with intravenous recombinant human plasma gelsolin (pGSN) compared to the control vehicle. Pretreatment of the murine macrophage line RAW264.7 with pGSN, followed by addition of Pseudomonas aeruginosa Xen 5, resulted in a dose-dependent increase in the proportion of macrophages with internalized bacteria. This increased uptake was less pronounced when cells were pretreated with pGSN and then centrifuged to remove unbound pGSN before addition of bacteria to macrophages. These observations suggest that recombinant plasma gelsolin can modulate the inflammatory response while at the same time augmenting host antibacterial activity.

Mechanisms of Mixed Th1/Th2 Responses in Mice Induced by Albizia julibrissin Saponin Active Fraction by in Silico Analysis

The purified active fraction of Albizia julibrissin saponin (AJSAF) is an ideal adjuvant candidate that improves antigen-specific both cellular and humoral immune responses and elicits mixed Th1/Th2 responses, but its mechanisms remain unclear. The key features of action of AJSAF were investigated in mice immunized with Newcastle disease virus-based recombinant influenza vaccine (rL-H5) and AJSAF at the same leg (AJSAF+rL-H5) or different legs (AJSAF/rL-H5). The adjuvant activity of AJSAF on rL-H5 is strictly dependent on their spatial colocalization. Serum H5 antigen (H5Ag)-specific IgG, IgG1, IgG2a, and IgG2b antibody titers in AJSAF+rL-H5 group were significantly higher than those in AJSAF/rL-H5 group. The mechanisms of selectivity of Th1 or Th2 in mice induced by AJSAF was explored by the transcriptomic and proteomic profiles of H5Ag-stimulated splenocytes from the immunized mice using gene microarray and two-dimensional difference gel electrophoresis coupled with matrix-assisted laser desorption/ionization time-of-flight mass spectrometry. Compared to rL-H5 alone, AJSAF/rL-H5 induced more differentially expressed genes (DEGs) than AJSAF+rL-H5, whereas AJSAF+rL-H5 upregulated higher mRNA expression of Th1 (T-bet, IFN-γ, TNF-α, IL-12β, and IL-12Rβ1) and Th2 (IL-10 and AICDA) immune response genes. The neutrophil response and its derived S100A8 and S100A9 might be involved in the AJSAF-mediated Th1 response. Meanwhile, AJSAF might induce the adaptive immune responses by improving a local innate immune microenvironment. These findings expanded the current knowledge on the mechanisms of action of saponin-based adjuvants, and provided new insights into how adjuvants shape adaptive immune responses.

Structure, regulation and related diseases of the actin-binding protein gelsolin

Gelsolin (GSN), one of the most abundant actin-binding proteins, is involved in cell motility, shape and metabolism. As a member of the GSN superfamily, GSN is a highly structured protein in eukaryotic cells that can be regulated by calcium concentration, intracellular pH, temperature and phosphatidylinositol-4,5-bisphosphate. GSN plays an important role in cellular mechanisms as well as in different cellular interactions. Because of its participation in immunologic processes and its interaction with different cells of the immune system, GSN is a potential candidate for various therapeutic applications. In this review, we summarise the structure of GSN as well as its regulating and functional roles, focusing on distinct diseases such as Alzheimer's disease, rheumatoid arthritis and cancer. A short overview of GSN as a therapeutic target in today's medicine is also provided.

Plasma Gelsolin: Indicator of Inflammation and Its Potential as a Diagnostic Tool and Therapeutic Target

Gelsolin, an actin-depolymerizing protein expressed both in extracellular fluids and in the cytoplasm of a majority of human cells, has been recently implicated in a variety of both physiological and pathological processes. Its extracellular isoform, called plasma gelsolin (pGSN), is present in blood, cerebrospinal fluid, milk, urine, and other extracellular fluids. This isoform has been recognized as a potential biomarker of inflammatory-associated medical conditions, allowing for the prediction of illness severity, recovery, efficacy of treatment, and clinical outcome. A compelling number of animal studies also demonstrate a broad spectrum of beneficial effects mediated by gelsolin, suggesting therapeutic utility for extracellular recombinant gelsolin. In the review, we summarize the current data related to the potential of pGSN as an inflammatory predictor and therapeutic target, discuss gelsolin-mediated mechanisms of action, and highlight recent progress in the clinical use of pGSN.

Extracellular matrix endocytosis in controlling matrix turnover and beyond: emerging roles in cancer

The extracellular matrix (ECM) is a network of secreted proteins that, beyond providing support for tissues and organs, is involved in the regulation of a variety of cell functions, including cell proliferation, polarity, migration and oncogenic transformation. ECM homeostasis is maintained through a tightly controlled balance between synthesis, deposition and degradation. While the role of metalloproteases in ECM degradation is widely recognised, the contribution of ECM internalisation and intracellular degradation to ECM maintenance has been mostly overlooked. In this review, I will summarise what is known about the molecular mechanisms mediating ECM endocytosis and how this process impacts on diseases, such as fibrosis and cancer.

[Research progression of the relationship between integrin α2β1 and drug-induced gingival overgrowth]

Drug-induced gingival overgrowth (DIGO) is characterized by fibrous gingival hyperplasia and increased gingival volume. DIGO is histologically associated with proliferation of cells and deposition of extracellular matrices, particularly collagen. Integrin α2β1 is related to collagen phagocytosis and involved in the occurrence and progression of DIGO. This paper reviews the progress of research on the relationship between integrin α2β1 and DIGO.

The Role of Calcium and Magnesium Ions in Uptake of β-Amyloid Peptides by Microglial Cells

Amyloid peptides 1-40 and 1-42 (Aβ 1-40 and Aβ 1-42) are major components of diffuse and neuritic senile plaques present in the brain of patients with Alzheimer's disease. Their interaction with microglial cells was studied using a system partly mimicking these plaques, which consisted in heat-killed yeast particles coated with either Aβ 1-40 or Aβ 1-42. Using these particles, it has been shown in our laboratory that LRP is involved mainly in the elimination of Aβ 1-42-coated heat-killed yeast particles and partly in that of Aβ 1-40-coated heat-killed yeast particles by microglial cells in culture. We show here that in the presence of calcium and magnesium ions extracellular chelators, namely EDTA (for both ions) and EGTA (for calcium ions), the internalization of coated heat-killed particles was impaired. In the presence of BAPTA-AM, an intracellular chelator of calcium ions and thapsigargin, an inhibitor of the endoplasmic reticulum calcium pump, no effect was observed on the phagocytosis of Aβ 1-40-coated heat-killed yeast particles, whereas that of Aβ 1-42-coated heat-killed yeast particles was affected. These results suggest that different signaling mechanisms are involved after the internalization of Aβ 1-40 and Aβ 1-42.

Hypoxia Augments Increased HIF-1α and Reduced Survival Protein p-Akt in Gelsolin (GSN)-Dependent Cardiomyoblast Cell Apoptosis

Cytoskeleton filaments play an important role in cellular functions such as maintaining cell shape, cell motility, intracellular transport, and cell division. Actin-binding proteins (ABPs) have numerous functions including regulation of actin filament nucleation, elongation, severing, capping, cross linking, and actin monomer sequestration. Gelsolin (GSN) is one of the actin-binding proteins. Gelsolin (GSN) is one of the actin-binding proteins that regulate cell morphology, differentiation, movement, and apoptosis. GSN also regulates cell morphology, differentiation, movement, and apoptosis. In this study, we have used H9c2 cardiomyoblast cell and H9c2-GSN stable clones to understand the roles and mechanisms of GSN overexpression in hypoxia-induced cardiomyoblast cell death. The data show that hypoxia or GSN overexpression induces HIF-1α expression and reduces the expression of survival markers p-Akt and Bcl-2 in H9c2 cardiomyoblast cells. Under hypoxic conditions, GSN overexpression further reduces p-Akt expression and elevates total as well as cleaved GSN levels and HIF-1α levels. In addition, GSN overexpression enhances apoptosis in cardiomyoblasts under hypoxia. Hypoxic challenge further induced activated caspase-3 and cell death that was attenuated after GSN knock down, which implies that GSN is a critical therapeutic target against hypoxia-induced cardiomyoblast cell death.

Gelsolin Promotes Radioresistance in Non-Small Cell Lung Cancer Cells Through Activation of Phosphoinositide 3-Kinase/Akt Signaling

Gelsolin is an actin-binding protein and acts as an important regulator of cell survival. This study aimed to determine the function of gelsolin in the radioresistance of non-small cell lung cancer cells. We examined the expression of gelsolin in radioresistant A549 and H460 cells and their parental cells. The effects of gelsolin overexpression and knockdown on the clonogenic survival and apoptosis of non-small cell lung cancer cells after irradiation were studied. The involvement of phosphoinositide 3-kinase/Akt signaling in the action of gelsolin was checked. We found that gelsolin was significantly upregulated in radioresistant A549 and H460 cells. Overexpression of gelsolin significantly ( P < .05) increased the number of colonies from irradiated A549 and H460 cells compared to transfection of empty vector. In contrast, knockdown of gelsolin significantly ( P < .05) suppressed colony formation after irradiation. Gelsolin-overexpressing cells displayed reduced apoptosis in response to irradiation, which was coupled with decreased levels of cleaved caspase-3 and poly adenosine diphosphate-ribose polymerase. Ectopic expression of gelsolin significantly ( P < .05) enhanced the phosphorylation of Akt compared to nontransfected cells. Pretreatment with the phosphoinositide 3-kinase inhibitor LY294002 (20 μmol/L) significantly decreased clonogenic survival and enhanced apoptosis in gelsolin-overexpressing A549 and H460 cells after irradiation. Taken together, gelsolin upregulation promotes radioresistance in non-small cell lung cancer cells, at least partially, through activation of phosphoinositide 3-kinase/Akt signaling.

Adseverin mediates RANKL-induced osteoclastogenesis by regulating NFATc1

Adseverin is a Ca2+-dependent actin filament-severing protein that has been reported to regulate exocytosis via rearrangements of the actin cytoskeleton in secretory cells. However, the role of adseverin in bone cells has not yet been well characterized. Here, we investigated the role of adseverin in osteoclastogenesis using primary osteoclast precursor cells. Adseverin expression was upregulated during RANKL (receptor activator of nuclear factor-κB ligand)-induced osteoclast differentiation. Moreover, genetic silencing of adseverin decreased the number of osteoclasts generated by RANKL. Adseverin knockdown also suppressed the RANKL-mediated induction of nuclear factor of activated T-cell c1 (NFATc1), which is a key transcription factor in osteoclastogenesis. In addition, adseverin knockdown impaired bone resorption and the secretion of bone-degrading enzymes from osteoclasts. These effects were accompanied by decreased NFATc1 expression and the activation of nuclear factor-κB. Collectively, our results indicate that adseverin has a crucial role in osteoclastogenesis by regulating NFATc1.

Plasma Proteome Biomarkers of Inflammation in School Aged Children in Nepal

Inflammation is a condition stemming from complex host defense and tissue repair mechanisms, often simply characterized by plasma levels of a single acute reactant. We attempted to identify candidate biomarkers of systemic inflammation within the plasma proteome. We applied quantitative proteomics using isobaric mass tags (iTRAQ) tandem mass spectrometry to quantify proteins in plasma of 500 Nepalese children 6–8 years of age. We evaluated those that co-vary with inflammation, indexed by α-1-acid glycoprotein (AGP), a conventional biomarker of inflammation in population studies. Among 982 proteins quantified in >10% of samples, 99 were strongly associated with AGP at a family-wise error rate of 0.1%. Magnitude and significance of association varied more among proteins positively (n = 41) than negatively associated (n = 58) with AGP. The former included known positive acute phase proteins including C-reactive protein, serum amyloid A, complement components, protease inhibitors, transport proteins with anti-oxidative activity, and numerous unexpected intracellular signaling molecules. Negatively associated proteins exhibited distinct differences in abundance between secretory hepatic proteins involved in transporting or binding lipids, micronutrients (vitamin A and calcium), growth factors and sex hormones, and proteins of largely extra-hepatic origin involved in the formation and metabolic regulation of extracellular matrix. With the same analytical approach and the significance threshold, seventy-two out of the 99 proteins were commonly associated with CRP, an established biomarker of inflammation, suggesting the validity of the identified proteins. Our findings have revealed a vast plasma proteome within a free-living population of children that comprise functional biomarkers of homeostatic and induced host defense, nutrient metabolism and tissue repair, representing a set of plasma proteins that may be used to assess dynamics and extent of inflammation for future clinical and public health application.

Always cleave up your mess: targeting collagen degradation to treat tissue fibrosis

Pulmonary fibrosis is a vexing clinical problem with no proven therapeutic options. In the normal lung there is continuous collagen synthesis and collagen degradation, and these two processes are precisely balanced to maintain normal tissue architecture. With lung injury there is an increase in the rate of both collagen production and collagen degradation. The increase in collagen degradation is critical in preventing the formation of permanent scar tissue each time the lung is exposed to injury. In pulmonary fibrosis, collagen degradation does not keep pace with collagen production, resulting in extracellular accumulation of fibrillar collagen. Collagen degradation occurs through both extracellular and intracellular pathways. The extracellular pathway involves cleavage of collagen fibrils by proteolytic enzyme including the metalloproteinases. The less-well-described intracellular pathway involves binding and uptake of collagen fragments by fibroblasts and macrophages for lysosomal degradation. The relationship between these two pathways and their relevance to the development of fibrosis is complex. Fibrosis in the lung, liver, and skin has been associated with an impaired degradative environment. Much of the current scientific effort in fibrosis is focused on understanding the pathways that regulate increased collagen production. However, recent reports suggest an important role for collagen turnover and degradation in regulating the severity of tissue fibrosis. The objective of this review is to evaluate the roles of the extracellular and intracellular collagen degradation pathways in the development of fibrosis and to examine whether pulmonary fibrosis can be viewed as a disease of impaired matrix degradation rather than a disease of increased matrix production.

Gelsolin expression increases β1 -integrin affinity and L1210 cell adhesion

Integrins are functionally regulated by "inside-out" signaling, in that stimulus-induced signaling pathways act on the intracellular integrin tail to regulate the activity of the receptor on the outside. Both a change in conformation (affinity) and clustering (avidity/valency) of the receptors occurs, but the mechanisms that regulate inside out signaling are not completely understood. Previously, we identified gelsolin in a proteomics screen to identify proteins involved in inside-out control of integrins using the lymphocytic leukemia cell line L1210. Furthermore, we showed that gelsolin was involved in affinity regulation of β1 -integrins in the leukemic cell line U937. Here, we examined how gelsolin regulates β1 -integrin affinity in the leukemia cell line L1210. We show that gelsolin is mainly expressed at the cell membrane and is present near β1 -integrins. The role for actin polymerization in integrin affinity regulation was examined using the actin modulating agent jasplakinolide, which decreased β1 -integrin affinity. Similarly, knock-down of gelsolin in L1210 cells also decreased β1 -integrin affinity and cell adhesion to collagen. These data suggest that increased actin polymerization through gelsolin regulates β1 -integrin affinity and cell adhesion.

Collagen remodeling by phagocytosis is determined by collagen substrate topology and calcium-dependent interactions of gelsolin with nonmuscle myosin IIA in cell adhesions

Cell adhesion to collagen presented on beads activates Ca²⁺ entry and promotes the formation of phagosomes enriched with NMMIIA and gelsolin. The Ca²⁺-dependent interaction of gelsolin and NMMIIA in turn enables actin remodeling and enhances collagen degradation by phagocytosis.

We examine how collagen substrate topography, free intracellular calcium ion concentration ([Ca²⁺]_i, and the association of gelsolin with nonmuscle myosin IIA (NMMIIA) at collagen adhesions are regulated to enable collagen phagocytosis. Fibroblasts plated on planar, collagen-coated substrates show minimal increase of [Ca²⁺]_i, minimal colocalization of gelsolin and NMMIIA in focal adhesions, and minimal intracellular collagen degradation. In fibroblasts plated on collagen-coated latex beads there are large increases of [Ca²⁺]_i, time- and Ca²⁺-dependent enrichment of NMMIIA and gelsolin at collagen adhesions, and abundant intracellular collagen degradation. NMMIIA knockdown retards gelsolin recruitment to adhesions and blocks collagen phagocytosis. Gelsolin exhibits tight, Ca²⁺-dependent binding to full-length NMMIIA. Gelsolin domains G4–G6 selectively require Ca²⁺ to interact with NMMIIA, which is restricted to residues 1339–1899 of NMMIIA. We conclude that cell adhesion to collagen presented on beads activates Ca²⁺ entry and promotes the formation of phagosomes enriched with NMMIIA and gelsolin. The Ca²⁺ -dependent interaction of gelsolin and NMMIIA in turn enables actin remodeling and enhances collagen degradation by phagocytosis.

Flightless I is a focal adhesion-associated actin-capping protein that regulates cell migration

The role of adhesion-associated actin-binding proteins in cell migration is not well defined. In mouse fibroblasts we screened for focal adhesion-associated proteins that were isolated with collagen-coated beads and detected by tandem mass spectrometry. We identified flightless I (FliI) as an actin-binding protein in focal adhesion fractions, which was verified by immunoblotting. By confocal microscopy most FliI was distributed throughout the cytosol and in focal adhesions. By sedimentation assays and in vitro binding assays, we found that FliI associates with actin filaments and actin monomers. Assays using purified proteins showed that FliI inhibits actin polymerization and caps but does not sever actin filaments. Cells with FliI knockdown or cells overexpressing FliI migrated more or less rapidly, respectively, than wild-type controls. Compared with controls, cells with FliI knockdown were less adherent than wild-type cells, exhibited reduced numbers of focal adhesions containing activated β1 integrins and vinculin, and exhibited increased incorporation of actin monomers into nascent filaments at focal adhesions. These data indicate that FliI regulates cell migration through its localization to focal adhesions and its ability to cap actin filaments, which collectively affect focal adhesion maturation.

Mannose receptor 2 attenuates renal fibrosis

Mannose receptor 2 (Mrc2) expresses an extracellular fibronectin type II domain that binds to and internalizes collagen, suggesting that it may play a role in modulating renal fibrosis. Here, we found that Mrc2 levels were very low in normal kidneys but subsets of interstitial myofibroblasts and macrophages upregulated Mrc2 after unilateral ureteral obstruction (UUO). Renal fibrosis and renal parenchymal damage were significantly worse in Mrc2-deficient mice. Similarly, Mrc2-deficient Col4α3(-/-) mice with hereditary nephritis had significantly higher levels of total kidney collagen, serum BUN, and urinary protein than Mrc2-sufficient Col4α3(-/-) mice. The more severe phenotype seemed to be the result of reduced collagen turnover, because procollagen III (α1) mRNA levels and fractional collagen synthesis in the wild-type and Mrc2-deficient kidneys were similar after UUO. Although Mrc2 associates with the urokinase receptor, differences in renal urokinase activity did not account for the increased fibrosis in the Mrc2-deficient mice. Treating wild-type mice with a cathepsin inhibitor, which blocks proteases implicated in Mrc2-mediated collagen degradation, worsened UUO-induced renal fibrosis. Cathepsin mRNA profiles were similar in Mrc2-positive fibroblasts and macrophages, and Mrc2 genotype did not alter relative cathepsin mRNA levels. Taken together, these data establish an important fibrosis-attenuating role for Mrc2-expressing renal interstitial cells and suggest the involvement of a lysosomal collagen turnover pathway.

Gelsolin and non-muscle myosin IIA interact to mediate calcium-regulated collagen phagocytosis

The formation of adhesion complexes is the rate-limiting step for collagen phagocytosis by fibroblasts, but the role of Ca(2+) and the potential interactions of actin-binding proteins in regulating collagen phagocytosis are not well defined. We found that the binding of collagen beads to fibroblasts was temporally and spatially associated with actin assembly at nascent phagosomes, which was absent in gelsolin null cells. Analysis of tryptic digests isolated from gelsolin immunoprecipitates indicated that non-muscle (NM) myosin IIA may bind to gelsolin. Immunostaining and immunoprecipitation showed that gelsolin and NM myosin IIA associated at collagen adhesion sites. Gelsolin and NM myosin IIA were both required for collagen binding and internalization. Collagen binding to cells initiated a prolonged increase of [Ca(2+)](i), which was absent in cells null for gelsolin or NM myosin IIA. Collagen bead-induced increases of [Ca(2+)](i) were associated with phosphorylation of the myosin light chain, which was dependent on gelsolin. NM myosin IIA filament assembly, which was dependent on myosin light chain phosphorylation and increased [Ca(2+)](i), also required gelsolin. Ionomycin-induced increases of [Ca(2+)](i) overcame the block of myosin filament assembly in gelsolin null cells. We conclude that gelsolin and NM myosin IIA interact at collagen adhesion sites to enable NM myosin IIA filament assembly and localized, Ca(2+)-dependent remodeling of actin at the nascent phagosome and that these steps are required for collagen phagocytosis.

Proteomic analysis of serum proteins in acute ischemic stroke patients treated with acupuncture

In the present study, we have investigated the effects of acupuncture on (1) serum protein expression that might have a beneficial effect on stroke patients and (2) the strength of limb muscles in stroke patients. A total of 35 acute ischemic stroke (IS) patients were divided into two groups, one receiving drug treatment alone and the other receiving electroacupuncture (EA) and drug treatment. EA treatment was performed on eight acupuncture points once a day for 10 consecutive days. Serum proteins were detected using a proteomics method based on two-dimensional gel electrophoresis, and the specificity of proteins was confirmed by Western blotting. Changes of limb muscle strength were measured using a modified Medical Research Council grading scale. After EA, SerpinG1 protein expression in serum was down-regulated while the expressions of gelsolin, complement component I, C3, C4B and beta-2-glycoprotein I proteins were up-regulated in patients. The changes of serum protein expression were further confirmed by Western blotting in a majority of the cases. The muscle strength of limbs was increased after EA in 18 patients. EA appears to be effective in regulating differential expression of multiple serum proteins involved in stroke, and also in enhancement of muscle strength recovery in acute IS patients despite an individual variation.

Multifunctional roles of gelsolin in health and diseases

Gelsolin, a Ca(2+) -regulated actin filament severing, capping, and nucleating protein, is an ubiquitous, multifunctional regulator of cell structure and metabolism. More recent data show that gelsolin can act as a transcriptional cofactor in signal transduction and its own expression and function can be influenced by epigenetic changes. Here, we review the functions of the plasma and cytoplasmic forms of gelsolin, and their manifold impacts on cancer, apoptosis, infection and inflammation, cardiac injury, pulmonary diseases, and aging. An improved understanding of the functions and regulatory mechanisms of gelsolin may lead to new considerations of this protein as a potential biomarker and/or therapeutic target.

Regulation of myofibroblast activities: calcium pulls some strings behind the scene

Myofibroblast-induced remodeling of collagenous extracellular matrix is a key component of our body's strategy to rapidly and efficiently repair damaged tissues; thus myofibroblast activity is considered crucial in assuring the mechanical integrity of vital organs and tissues after injury. Typical examples of beneficial myofibroblast activities are scarring after myocardial infarct and repair of damaged connective tissues including dermis, tendon, bone, and cartilage. However, deregulation of myofibroblast contraction causes the tissue deformities that characterize hypertrophic scars as well as organ fibrosis that ultimately leads to heart, lung, liver and kidney failure. The phenotypic features of the myofibroblast, within a spectrum going from the fibroblast to the smooth muscle cell, raise the question as to whether it regulates contraction in a fibroblast- or muscle-like fashion. In this review, we attempt to elucidate this point with a particular focus on the role of calcium signaling. We suggest that calcium plays a central role in myofibroblast biological activity not only in regulating contraction but also in mediating intracellular and extracellular mechanical signals, structurally organizing the contractile actin-myosin cytoskeleton, and establishing lines of intercellular communication.

Force-induced myofibroblast differentiation through collagen receptors is dependent on mammalian diaphanous (mDia)

The development of fibrosis promotes the differentiation of myofibroblasts, pro-fibrotic cells, which contribute to tissue dysfunction. Myofibroblast differentiation is dependent on actin assembly, which in response to force, is mediated by various actin-binding proteins including the mammalian Diaphanous-related formins (mDia). We examined the role of mDia in the mechano-sensing pathway that leads to force-induced expression of alpha-smooth muscle actin (SMA), a marker and critical determinant of myofibroblast differentiation. In cells treated with siRNA to knockdown mDia and then subjected to tensile force using collagen-coated magnetite beads attached to beta1 integrins, actin assembly was inhibited at bead contact sites. Force-induced nuclear translocation of MRTF-A, a transcriptional co-activator of SMA, was reduced 50% by mDia knockdown. The expression of the transcriptional co-activator of SMA, serum response factor, was reduced by 50% after siRNA knockdown of mDia or by 100% in cells transfected with catalytically inactive mDia. Force-induced activation of the SMA promoter and SMA expression were blocked by knockdown of siRNA of mDia. In anchored collagen gel assays to measure myofibroblast-mediated contraction, knockdown of mDia reduced contraction by 50%. We conclude that mDia plays an important role in the development of force-induced transcriptional activation of SMA and myofibroblast differentiation.

A 2D-DIGE approach to identify proteins involved in inside-out control of integrins

Leukocyte integrins are functionally regulated by "inside-out" signaling, meaning that stimulus-induced signaling pathways act on the intracellular integrin tail and induce activation of the receptor at the outside. Both a change in conformation (affinity) and in clustering (avidity/valency) of the receptors has been described to occur. This inside-out signaling is essential for adequate migration of leukocytes to inflammatory sites; however, the exact underlying mechanism is not known. We used two variants of a mouse acute lymphocytic leukemia cell line (L1210), a suspension (L1210-S) and an adherent (L1210-A) variant that were characterized by nonactivated and activated integrins (beta(1), beta(2) and beta(3)), respectively. L1210-S and L1210-A cells were compared on protein expression profiles by two-dimensional fluorescence difference in-gel electrophoresis (2D-DIGE). We found 86 protein spots that were more than 1.25-fold different between L1210-A and L1210-S. Only 4 protein spots were more than 2.5-fold different. We identified 29 proteins by mass spectrometry among which were gelsolin, L-plastin, and Rho GTPase dissociation inhibitor 2. These proteins were upregulated in the L1210-A cells versus L1210-S, which was verified by Western blot analysis. Overexpression of gelsolin in U937 resulted in increased high affinity integrin expression and cell adhesion. Comparison of functionally different cell lines from similar origin by 2D-DIGE might be a successful approach to identify regulatory proteins involved in integrin inside-out control.

FAK, PIP5KIγ and gelsolin cooperatively mediate force-induced expression of α-smooth muscle actin

During the development of pressure-induced cardiac hypertrophy, fibroblasts are activated to become myofibroblasts, which exhibit actin-cytoskeletal remodeling and express α-smooth muscle actin (SMA; encoded by ACTA2). Currently, the mechanosensing signaling pathways that regulate SMA expression are not defined. Because focal-adhesion complexes are putative mechanosensing organelles, we examined the role of focal adhesion kinase (FAK) and its interaction with gelsolin in the regulation of SMA expression. We subjected NIH3T3 cells to tensile forces (0.65 pN/μm2) by using collagen-coated magnetite beads attached to integrins. After stimulation by mechanical force, FAK and gelsolin were recruited to magnetite beads and there was increased phosphorylation of Tyr397FAK. Mechanical force enhanced SMA promoter activity by twofold; this increased activity was blocked by FAK knockdown using siRNA and by deletion of gelsolin. Force-induced nuclear translocation of MRTF-A, a transcriptional co-activator of SMA that is regulated by actin filaments, was also reduced by FAK knockdown. Phosphatidylinositol (4,5)-bisphosphate [PtdIns(4,5)P2], which uncaps gelsolin from actin filaments, was enriched at sites of force application. Type-I phosphatidylinositol 4-phosphate 5 kinase-γ (PIP5KIγ), which generates PtdIns(4,5)P2, associated with FAK and was required for force-mediated SMA-promoter activity and actin assembly. Catalytically inactive PIP5KIγ inhibited force-induced phosphorylation of FAK at Tyr397. These data suggest a novel pathway in which mechanosensing by FAK regulates actin assembly via gelsolin and the activity of PIP5KIγ; actin assembly in turn controls SMA expression via MRTF-A.

Integrin-dependent phagocytosis: spreading from microadhesion to new concepts

By linking actin dynamics to extracellular components, integrins are involved in a wide range of cellular processes that are associated with or require cytoskeletal remodelling and cell-shape changes. One such function is integrin-dependent phagocytosis, a process that several integrins are capable of mediating and that allows the binding and clearance of particles. Integrin-dependent phagocytosis is involved in a wide range of physiological processes, from the clearance of microorganisms and apoptotic-cell removal to extracellular-matrix remodelling. Integrin signalling is also exploited by microbial pathogens for entry into host cells. Far from being a particular property of specific integrins and specialised cells, integrin-dependent uptake is emerging as a general, intrinsic ability of most integrins that is associated with their capacity to signal to the actin cytoskeleton. Integrin-mediated phagocytosis can therefore be used as a robust model in which to study integrin regulation and signalling.

Collagen phagocytosis is regulated by the guanine nucleotide exchange factor Vav2

Collagen phagocytosis is a crucial alpha2beta1-integrin-dependent process that mediates extracellular matrix remodeling by fibroblasts. We showed previously that after initial contact with collagen, activated Rac1 accelerates collagen phagocytosis but the Rac guanine nucleotide exchange factors (GEFs) that regulate Rac are not defined. We examined here the GEFs that regulate collagen phagocytosis in mouse fibroblasts. Collagen binding enhanced Rac1 activity (5-20 min) but not Cdc42 or RhoA activity. Analysis of collagen bead-associated proteins showed enrichment with Vav2, which correlated temporally with increased Rac1 activity. Knockdown of Vav2 prevented Rac activation, recruitment of Rac1 to collagen bead binding sites, and collagen bead binding, but knockdown of Sos-1 or beta-Pix had no effect on Rac activation or collagen binding. Vav2 was associated with the nucleotide-free Rac1 mutant (G15ARac1) after collagen binding. Collagen bead binding promoted phosphorylation of Vav2, which temporally correlated with Rac1 activation and which required Src kinase activity. Blockage of Src activity prevented collagen bead-induced Rac activation and collagen bead binding. Collectively these data indicate that Vav2 regulates the Rac1 activity associated with the binding step of collagen phagocytosis.

Duplicated gelsolin family genes in zebrafish: a novel scinderin-like gene (scinla) encodes the major corneal crystallin

We have previously identified a gelsolin-like protein (C/L-gelsolin) as a corneal crystallin in zebrafish. Here we show by phylogenetic analysis that there are at least six genes encoding gelsolin-like proteins based on their gelsolin domains in zebrafish: gsna and gsnb group with the vertebrate gelsolin gene, scina and scinb group with the scinderin (adseverin) gene, and scinla (C/L-gelsolin) and scinlb are novel scinderin-like genes. RT-PCR showed that scinla, scinlb, and gsnb are preferentially expressed in the adult cornea whereas gsna is expressed to a similar extent in cornea, lens, brain, and heart; scina and scinb expression were detectable only in whole zebrafish and not in these adult tissues. Quantitative RT-PCR and 2-dimensional polyacrylamide gel electrophoresis followed by MALDI/TOF mass spectroscopy confirmed high expression of beta-actin and scinla, moderate expression of scinlb, and very low expression of gsna and gsnb in the cornea. Finally, transgenic zebrafish carrying a green fluorescent protein reporter transgene driven by a 4 kb scinla promoter fragment showed expression in the cornea, snout, dorsal fin, and tail fin of 3-day-old zebrafish larvae. Our data suggest that scinla and scinlb are diverged paralogs of the vertebrate scinderin gene and show that scinla encodes the zebrafish corneal crystallin previously called C/L-gelsolin.

The intriguing normal acute inflammatory response in mice lacking vimentin

Neutrophils express only two intermediate filament proteins, vimentin and, to a lesser extent, lamin B. Lamin B mutant mice die shortly after birth; however, mice lacking vimentin (vim(-/-)) develop and reproduce normally. Herein, we investigate for the first time the role of vimentin in general inflammation in vivo and in neutrophil functions ex vivo. Using the murine air pouch model, we show that the inflammatory response induced by lipopolysaccharide, interleukin-21 or carageenan is, intriguingly, uncompromised in vim(-/-) mice and that neutrophil functions are not altered ex vivo. Our results suggest that vimentin is dispensable for the establishment of an acute inflammatory response in vivo. In addition, based on several criteria presented in this study, one has to accept the existence of a very complex compensatory mechanism to explain the intriguing normal inflammatory response in absence of vimentin.

Cyclosporin inhibition of collagen remodeling is mediated by gelsolin

Cyclosporin A (CsA) inhibits collagen remodeling by interfering with the collagen-binding step of phagocytosis. In rapidly remodeling connective tissues such as human periodontium this interference manifests as marked tissue overgrowth and loss of function. Previous data have shown that CsA inhibits integrin-induced release of Ca(2+) from internal stores, which is required for the binding step of collagen phagocytosis. Because gelsolin is a Ca(2+)-dependent actin-severing protein that mediates collagen phagocytosis, we determined whether gelsolin is a CsA target. Compared with vehicle controls, CsA treatment of wild-type mice increased collagen accumulation by 60% in periodontal tissues; equivalent increases were seen in vehicle-treated gelsolin-null mice. Collagen degradation by phagocytosis in cultured gelsolin wild-type fibroblasts was blocked by CsA, comparable to levels of vehicle-treated gelsolin-null fibroblasts. In wild-type cells treated with CsA, collagen binding was similar to that of gelsolin-null fibroblasts transfected with a gelsolin-severing mutant and treated with vehicle. CsA blocked collagen-induced Ca(2+) fluxes subjacent to bound collagen beads, gelsolin recruitment, and actin assembly at bead sites. CsA reduced gelsolin-dependent severing of actin in wild-type cells to levels similar to those in gelsolin-null fibroblasts. We conclude that CsA-induced accumulation of collagen in the extracellular matrix involves disruption of the actin-severing properties of gelsolin, thereby inhibiting the binding step of collagen phagocytosis.

Methylglyoxal inhibits the binding step of collagen phagocytosis

Bacterial infection-induced fibrosis affects a wide variety of tissues, including the periodontium, but the mechanisms that dysregulate matrix turnover and mediate fibrosis are not defined. Since collagen turnover by phagocytosis is an important pathway for matrix remodeling, we studied the effect of the bacterial and eukaryotic cell metabolite, methylglyoxal (MGO), on the binding step of phagocytosis by periodontal fibroblasts. Type 1 collagen was treated with various concentrations of methylglyoxal, an important glucose metabolite that modifies Arg and Lys residues. The extent of MGO-induced modifications was authenticated by amino acid analysis, solubility, and cross-linking. Cells were incubated with fluorescent beads coated with collagen, and the percentage of phagocytic cells was estimated by flow cytometry. MGO inhibited collagen binding (20% of control for 10 mm MGO) in a time- and concentration-dependent manner. MGO-induced inhibition of binding was prevented by aminoguanidine, which blocks the formation of collagen cross-links. MGO reduced collagen binding strength and blocked intracellular calcium signaling. MGO modified the Arg residue in the critical alpha2beta1 integrin-binding recognition sequence of triple helical collagen peptides, whereas MGO-induced cross-linking of Lys residues played only a small role in binding inhibition. Thus, MGO modifications of Arg residues in collagen could be a key factor in the impaired degradation of collagen that promotes fibrosis in chronic infections, such as periodontitis.

Beyond the epithelium: Cadherin function in fibrous connective tissues

In fibrous connective tissues, fibroblasts are organized into syncytia, cellular networks that enable matrix remodeling and that are interconnected by intercellular adherens junctions (AJs). The AJs of fibroblasts are mediated by N-cadherin, a broadly expressed classical cadherin that is critically involved in developmental processes, wound healing and several diseases of mesenchymal tissues. In contrast to E-cadherin-dependent junctions of epithelia, the formation of AJs in fibrous connective tissues is relatively uncharacterized. Work over the last several years has documented an expanding list of molecules which function to regulate N-cadherin mediated junctions such as: Fer, PTP1B, cortactin, calcium, gelsolin, PIP5KIgamma, PIP2, and the Rho family of GTPases. We present an overview on the regulation of N-cadherin-mediated junction formation that highlights recent molecular advances in the field and rationalizes the roles of N-cadherin in connective tissue function.

Gelsolin and diseases

Gelsolin is a calcium-activated actin filament severing and capping protein found in many cell types and as a secreted form in the plasma of vertebrates. Mutant mice for gelsolin as well as clinical studies have shown that gelsolin is linked to a number of pathological conditions such as inflammation, cancer and amyloidosis. The tight regulation of gelsolin by calcium is crucial for its physiological role and constitutive activation leads to apoptosis. In the following we will give an overview on how gelsolin is regulated by calcium, and which clinical conditions have been linked to lack or misregulation of gelsolin.

Mechanism of depolymerization and severing of actin filaments and its significance in cytoskeletal dynamics

The actin cytoskeleton is one of the major structural components of the cell. It often undergoes rapid reorganization and plays crucial roles in a number of dynamic cellular processes, including cell migration, cytokinesis, membrane trafficking, and morphogenesis. Actin monomers are polymerized into filaments under physiological conditions, but spontaneous depolymerization is too slow to maintain the fast actin filament dynamics observed in vivo. Gelsolin, actin-depolymerizing factor (ADF)/cofilin, and several other actin-severing/depolymerizing proteins can enhance disassembly of actin filaments and promote reorganization of the actin cytoskeleton. This review presents advances as well as a historical overview of studies on the biochemical activities and cellular functions of actin-severing/depolymerizing proteins.

The small GTPase R-Ras regulates organization of actin and drives membrane protrusions through the activity of PLCepsilon

R-Ras, an atypical member of the Ras subfamily of small GTPases, enhances integrin-mediated adhesion and signaling through a poorly understood mechanism. Dynamic analysis of cell spreading by total internal reflection fluorescence (TIRF) microscopy demonstrated that active R-Ras lengthened the duration of initial membrane protrusion, and promoted the formation of a ruffling lamellipod, rich in branched actin structures and devoid of filopodia. By contrast, dominant-negative R-Ras enhanced filopodia formation. Moreover, RNA interference (RNAi) approaches demonstrated that endogenous R-Ras contributed to cell spreading. These observations suggest that R-Ras regulates membrane protrusions through organization of the actin cytoskeleton. Our results suggest that phospholipase Cepsilon (PLCepsilon) is a novel R-Ras effector mediating the effects of R-Ras on the actin cytoskeleton and membrane protrusion, because R-Ras was co-precipitated with PLCepsilon and increased its activity. Knockdown of PLCepsilon with siRNA reduced the formation of the ruffling lamellipod in R-Ras cells. Consistent with this pathway, inhibitors of PLC activity, or chelating intracellular Ca2+ abolished the ability of R-Ras to promote membrane protrusions and spreading. Overall, these data suggest that R-Ras signaling regulates the organization of the actin cytoskeleton to sustain membrane protrusion through the activity of PLCepsilon.

Lesion-induced gelsolin upregulation in the hippocampus following entorhinal deafferentation

Gelsolin is an actin-binding protein that regulates actin filament-severing and capping activity in the various processes of cell motilities. Here, we report the expression of gelsolin mRNA and protein in the hippocampus following transections of the entorhinal afferents. Northern blot analysis showed that transcript of gelsolin was upregulated in a transient manner in the deafferented hippocampus by 1.3-, 2.1-, 1.7-, and 1.1- folds of controls, respectively, at 1, 3, 7, and 15 days postlesion (dpl). In situ hybridization and immunohistochemistry confirmed the temporal expression of gelsolin specifically in the entorhinally denervated zones: the stratum lacunosum-molecular (SLM) of the hippocampus and the outer molecular layer (OML) of the dentate gyrus (DG), which initiated as early as at 1 dpl, reached the maximum at 3 dpl, remained prominently elevated by 7 dpl, and discernibly higher at 15 dpl than that of controls. Double labeling of either gelsolin mRNA or protein with markers of glial cells (Griffonia simplicifolia IB4 and CD11b for microglial cells, GFAP for astroglial cells) revealed that gelsolin was highly expressed by both activated microglia and astrocytes. The results suggest that the spatiotemporal upregulation of gelsolin in the hippocampus is induced by entorhinal deafferentation, and that gelsolin would participate in the activation processes of both microglial and astroglial cells and thereby, indirectly play important roles in the subsequent lesion-induced neural reorganization in the hippocampus following entorhinal deafferentation.

Drug-induced gingival overgrowth--a review

Drug-induced gingival overgrowth is a side effect associated with 3 types of drugs: anticonvulsants (phenytoin), immunosuppressive agents (cyclosporine A), and various calcium channel blockers for cardiovascular diseases. Gingival overgrowth is characterized by the accumulation of extracellular matrix in gingival connective tissues, particularly collagenous components with various degrees of inflammation. Although the mechanisms of these disorders have not been elucidated, recent studies suggest that these disorders seem to be induced by the disruption of homeostasis of collagen synthesis and degradation in gingival connective tissue, predominantly through the inhibition of collagen phagocytosis of gingival fibroblasts. The integrins are a large family of heterodimeric transmembrane receptors for extracellular matrix molecules. alpha2beta1 integrin serves as a specific receptor for type I collagen on fibroblasts, and alpha2 integrin has been shown to play a crucial role in collagen phagocytosis. Actin filaments, which are assembled from monomers and oligomers, are involved in collagen internalization after binding to integrins. Furthermore, the implication of intracellular calcium in the regulation of integrin-mediated binding activity and gelsolin activity, known as a calcium-dependent actin-severing protein, is also described. In this review, we focus on collagen metabolism in drug-induced gingival overgrowth, focusing on the regulation of collagen phagocytosis in fibroblasts.

Phosphorylation of N-cadherin-associated cortactin by Fer kinase regulates N-cadherin mobility and intercellular adhesion strength

Cortactin regulates the strength of nascent N-cadherin-mediated intercellular adhesions through a tyrosine phosphorylation-dependent mechanism. Currently, the functional significance of cortactin phosphorylation and the kinases responsible for the regulation of adhesion strength are not defined. We show that the nonreceptor tyrosine kinase Fer phosphorylates cadherin-associated cortactin and that this process is involved in mediating intercellular adhesion strength. In wild-type fibroblasts N-cadherin ligation-induced transient phosphorylation of Fer, indicating that junction formation activates Fer kinase. Tyrosine phosphorylation of cortactin after N-cadherin ligation was strongly reduced in fibroblasts expressing only catalytically inactive Fer (D743R), compared with wild-type cells. In wild-type cells, N-cadherin-coated bead pull-off assays induced fourfold greater endogenous N-cadherin association than in D743R cells. Fluorescence recovery after photobleaching showed that GFP-N-cadherin mobility at nascent contacts was 50% faster in wild-type than D743R cells. In shear wash-off assays, nascent intercellular adhesion strength was twofold higher in wild-type than D743R cells. Cortactin recruitment to adhesions was independent of Fer kinase activity, but was impacted by N-cadherin ligation-provoked Rac activation. We conclude that N-cadherin ligation induces Rac-dependent cortactin recruitment and Fer-dependent cortactin phosphorylation, which in turn promotes enhanced mobilization and interaction of surface expressed N-cadherin in contacting cells.

Separate functions of gelsolin mediate sequential steps of collagen phagocytosis

Collagen phagocytosis is a critical mediator of extracellular matrix remodeling. Whereas the binding step of collagen phagocytosis is facilitated by Ca2+-dependent, gelsolin-mediated severing of actin filaments, the regulation of the collagen internalization step is not defined. We determined here whether phosphatidylinositol-4,5-bisphosphate [PI(4,5)P2] regulation of gelsolin is required for collagen internalization. In gelsolin null fibroblasts transfected with gelsolin severing mutants, actin severing and collagen binding were strongly impaired but internalization and actin monomer addition at collagen bead sites were much less affected. PI(4,5)P2 accumulated around collagen during internalization and was associated with gelsolin. Cell-permeable peptides mimicking the PI(4,5)P2 binding site of gelsolin blocked actin monomer addition, the association of gelsolin with actin at phagosomes, and collagen internalization but did not affect collagen binding. Collagen beads induced recruitment of type 1 gamma phosphatidylinositol phosphate kinase (PIPK1gamma661) to internalization sites. Dominant negative constructs and RNA interference demonstrated a requirement for catalytically active PIPK1gamma661 for collagen internalization. We conclude that separate functions of gelsolin mediate sequential stages of collagen phagocytosis: Ca2+-dependent actin severing facilitates collagen binding, whereas PI(4,5)P2-dependent regulation of gelsolin promotes the actin assembly required for internalization of collagen fibrils.

Integrin clustering drives phagocytosis coupled to collagenase 1 induction through RhoA GTPase and superoxide production

Integrin-mediated phagocytosis in fibroblasts is associated to collagenase 1 induction when the particles are coated with high-affinity binding ligands. This study shows that the high density of ligand coating on the particle elicits RhoA-dependent particle uptake coupled to signal transduction. Integrin clustering induced by anti-integrin antibodies or cell surface-binding lectins is sufficient to trigger the pathway. The GTPase RhoA is recruited in response to integrin aggregation at the plasma membrane when uptake is inhibited at 4 degrees C and is necessary for particle engulfment, as function interference with the dominant negative mutant RhoAN19, but not with RacN17, abrogates particle ingestion. Phagocytosis driven by clustering is associated with signal transduction through a transient rise in cellular hydrogen peroxide production to induce a proinflammatory cascade leading to collagenase 1 induction.

Evolution of the gelsolin family of actin-binding proteins as novel transcriptional coactivators

The gelsolin gene family encodes a number of higher eukaryotic actin-binding proteins that are thought to function in the cytoplasm by severing, capping, nucleating or bundling actin filaments. Recent evidence, however, suggests that several members of the gelsolin family may have adopted unexpected nuclear functions including a role in regulating transcription. In particular, flightless I, supervillin and gelsolin itself have roles as coactivators for nuclear receptors, despite the fact that their divergence appears to predate the evolutionary appearance of nuclear receptors. Flightless I has been shown to bind both actin and the actin-related BAF53a protein, which are subunits of SWI/SNF-like chromatin remodelling complexes. The primary sequences of some actin-related proteins such as BAF53a exhibit conservation of residues that, in actin itself, are known to interact with gelsolin-related proteins. In summary, there is a growing body of evidence supporting a biological role in the nucleus for actin, Arps and actin-binding proteins and, in particular, the gelsolin family of actin-binding proteins.

Degradation of extracellular matrix by extrahepatic stellate cells in the intestine of the lamprey,Lampetra japonica

To investigate the mechanisms involved in the atrophy of the intestines in lampreys (Lampetra japonica) during the spawning migration stage, we examined by morphological methods their intestines with special reference to degradation of extracellular matrix (ECM) components. Stellate cells are known to be distributed not only in the liver (hepatic stellate cells) but also in other organs, such as the pancreas, intestine, lung, and kidney (extrahepatic stellate cells). Hepatic stellate cells are well known to be able to biosynthesize, secrete, and degrade ECM. Therefore, we investigated the cellular and molecular mechanisms involved in the atrophy of the intestines by focusing on these intestinal extrahepatic stellate cells. The cells were found to contain phagocytosed and degraded collagen fibrils, which are one of the ECM components. A positive reaction for trimetaphosphatase (TMPase, a cytochemical marker of lysosomes) was preferentially detected in round or elongated vesicles in the intestinal extrahepatic stellate cells and the deposits of the reaction products coexisted with the degraded collagen fibrils. However, the basement membrane of the intestine, which membrane is also an ECM component, was preserved throughout the spawning migration stage of the lamprey and accumulated as a mass of thick membrane, suggesting the existence of a special mechanism for selective digestion of ECM components. These results indicate that the intestinal extrahepatic stellate cells in Lampetra japonica during its spawning migration stage might play an important mechanistic role in the atrophy of lamprey intestines by phagocytizing collagen fibrils and digesting the phagocytized collagen fibrils in their lysosomes.