Collagen phagocytosis and apoptosis are induced by high level alkaline phosphatase expression in rat fibroblasts

Macrophages and Fibroblasts Differentially Contribute to Tattoo Stability

BACKGROUND

Little information is available about the complexity and function of skin cells contributing to the high stability of tattoos. It has been shown that dermal macrophages play an important role in the storage and maintenance of pigment particles. By contrast, the impact of dermal fibroblasts, forming the connective tissue of the skin, on the stability of the tattoo is not known.

METHOD

In this study, we compared the cell number and the particle load in dermal macrophages versus dermal fibroblasts, isolated from tail skin of tattooed mice.

RESULTS

Microscopic analysis revealed that both cell populations contained the tattoo particles, although in largely different amounts. A small number of macrophages with high side scatter intensity contained a large quantity of pigment particles, whereas a high number of dermal fibroblasts harbored only a few pigment particles. Using the CD64dtr mouse model that allows for selective, diphtheria toxin-mediated depletion of macrophages, we have previously shown that macrophages hold the tattoo in place by capture-release and recapture cycles. In the tattooed skin of macrophage-depleted mice, the content of pigment particles in fibroblasts did not change; however, the total number of fibroblasts carrying particles increased.

CONCLUSION

The present study demonstrates that dermal macrophages and fibroblasts contribute in different ways to the tattoo stability and further improves our knowledge on tattoo persistence.

Tissue-nonspecific alkaline phosphatase is activated in enterocytes by oxidative stress via changes in glycosylation

BACKGROUND

Intestinal inflammation produces an induction of alkaline phosphatase (AP) activity that is attributable in part to augmented expression, accompanied by a change in isoform, in epithelial cells.

METHODS

This study focuses on induction of AP in intestinal epithelial cells in vitro.

RESULTS

Treatment with the oxidants H2O2, monochloramine, or tButOOH increases AP activity in vitro in Caco-2, HT29, and IEC18 cells. We selected IEC18 cells for further testing. Basal AP activity in IEC18 cells is of the tissue-nonspecific (bone-liver-kidney) type, as indicated by Northern and Western blot analysis. Oxidative stress augments AP activity and the sensitivity of the enzyme to levamisole, homoarginine, and heat in IEC18 cells. Increased immunoreactivity to tissue-nonspecific AP antibodies suggests an isoform shift from liver to either kidney or bone type. This effect occurs without changes at the mRNA level and is sensitive to tunicamycin, an inhibitor of N-glycosylation, and neuraminidase digestion. Saponin and deoxycholate produce similar effects to oxidants. Butyrate but not proinflammatory cytokines or LPS can induce a similar effect but without toxicity. The AP increase is not prevented by modulators of the MAPK, NF-κB, calcium, and cyclic adenosine monophosphate (cAMP) pathways, and is actually enhanced by actinomycin D via higher cell stress.

CONCLUSIONS

Oxidative stress causes a distinct increase in enterocyte AP activity together with cell toxicity via changes in the glycosylation of the enzyme that correspond to a shift in isotype within the tissue-nonspecific paradigm. We speculate that this may have physiological implication for gut defense.

Encapsulation of Myxobolus pendula (Myxosporidia) by epithelioid cells of its cyprinid host Semotilus atromaculatus

Spores of Myxobolus pendula develop within the cores of complex cysts on the gill arch of creek chub Semotilus atromaculatus. Adjacent to, and surrounding, the spores are concentric layers of stratified interdigitating cells, whose nature was examined by transmission electron microscopy and by immunohistochemical and molecular biological techniques. In situ hybridization data using parasite-derived ribosomal DNA as a probe indicate that infection leads to the encapsulation of developing plasmodia by host immune cells that form an epithelioid granuloma. Epithelioid cell-cell adhesion is effected by desmosomes anchored intracellularly to cytokeratin intermediate filaments. High levels of alkaline phosphatase activity are associated with regions of cellular interdigitation. The granuloma may serve to limit the spread of the parasite to surrounding tissues but does not appear to inhibit diffusion of oxygen and nutrients to the developing spores.

The Serum Glycoprotein Fetuin-A Promotes Lewis Lung Carcinoma Tumorigenesis via Adhesive-Dependent and Adhesive-Independent Mechanisms

Fetuin-A is a serum glycoprotein in the cystatin family associated with the regulation of soft tissue calcification. We tested the role of systemic fetuin in tumor cell growth and metastasis by injecting Lewis lung carcinoma (LLC) cells into fetuin-A null and their wild-type (WT) littermate control C57BL/6 mice via the tail vein, s.c., and intrasplenic routes. In the experimental metastasis assay, the lungs of the WT mice were filled with metastatic nodules, whereas the lungs of the fetuin-A null mutant mice were virtually free of colonies at the end of 2 weeks. Lung colonization responded to the levels of serum fetuin-A in a dose-dependent manner, as observed by the formation of half as many colonies in mice heterozygous for the fetuin-A locus compared with homozygous WT mice and restoration of lung colonization by the administration of purified fetuin-A to fetuin-A-null mice. Serum fetuin-A also influenced the growth of LLC cells injected s.c.: fetuin-A-null mice developed small s.c. tumors only after a substantial delay. Similarly, intrasplenic injection of LLC cells resulted in rapid colonization of the liver with metastasis to the lungs within 2 weeks in the WT but not fetuin-A null mice. To examine the mechanism by which fetuin-A influences LLC colonization and growth, we showed that LLC tumor cells adhere to fetuin-A in a Ca2+-dependent fashion, resulting in growth of the tumor cells. These studies support the role of fetuin-A as a major growth promoter in serum that can influence tumor establishment and growth.

Regulation of Tension-induced Mechanotranscriptional Signals by the Microtubule Network in Fibroblasts

Mechanical loading of connective tissues induces the expression of extracellular matrix and cytoskeletal genes that are involved in matrix remodeling. These processes depend in part on force transmission through beta1 integrins and actin filaments, but the role of microtubules in regulating mechanotranscriptional responses is not well defined. We assessed the involvement of microtubules in the mechanotranscriptional regulation of filamin A, an actin-cross-linking protein that protects cells against force-induced apoptosis by stabilizing cell membranes. Collagen-coated magnetite beads and magnetic fields were used to apply tensile forces to cultured fibroblasts at focal adhesions. Force enhanced recruitment of alpha-tubulin and the plus end microtubule-binding protein cytoplasmic linker protein-170 (CLIP-170) at focal adhesions. Immunoprecipitation studies demonstrated no direct binding of tubulin to actin or filamin A, but CLIP-170 interacted with tubulin, filamin A, and beta-actin. The association of CLIP-170 with beta-actin was enhanced by force. Force activated the p38 mitogen-activated protein kinase, increased filamin A expression, and induced the relocation of p38 and filamin A to focal adhesions. Disruption of microtubules with nocodazole, independent of force application, enhanced filamin A expression and Sp1-mediated filamin A promoter activity, while stabilization of microtubules with Taxol inhibited force induction of both filamin A mRNA and protein. We conclude that in response to tensile forces applied through beta1 integrins and actin the microtubule network modulates mechanotranscriptional coupling of filamin A.

Interaction of p38 and Sp1 in a mechanical force-induced, beta 1 integrin-mediated transcriptional circuit that regulates the actin-binding protein filamin-A

Connective tissue cells in mechanically active environments survive applied physical forces by modifying actin cytoskeletal structures that stabilize cell membranes. In fibroblasts, tensile forces induce the expression of filamin-A, a mechanoprotective actin-binding protein, but the mechanisms and protein interactions by which force activates filamin-A transcription are not defined. We found that in fibroblasts, application of tensile forces through collagen-coated magnetite beads to cell surface beta(1) integrins induced filamin-A expression. This induction required actin filaments and selective activation of the p38 mitogen-activated protein kinase. Force promoted the redistribution of p38 to the integrin/bead locus and the nucleus as well as enhanced binding of the transcription factor Sp1 to proximal, regulatory domains of the filamin-A promoter. Force application increased association of Sp1 with p38 and phosphorylation of Sp1. Transcriptional activation of filamin-A in force-treated fibroblasts was subsequently mediated by Sp1-binding sites on the filamin-A promoter. These results provide evidence for a mechanically coupled transcriptional circuit that originates at the magnetite bead/integrin locus, activates p38, tethers p38 to actin filaments, promotes binding of p38 to Sp1 in the nucleus, and induces filamin-A expression.

Cell death and mechanoprotection by filamin a in connective tissues after challenge by applied tensile forces

Cells in mechanically challenged environments must cope with high amplitude forces to maintain cell viability and tissue homeostasis. Currently, force-induced cell death and the identity of mechanoprotective factors are not defined. We examined death in cultured periodontal fibroblasts, connective tissue cells that are exposed to heavy applied forces in vivo. Static tensile forces (0.48 piconewtons/microm2 cell area) were applied through magnetite beads coated with collagen or bovine serum albumin. There was a time-dependent increase of the percentage of propidium iodide-permeable cells in force-loaded cultures incubated with collagen but not bovine serum albumin beads, indicating a role for integrins. Cells exhibited reduced mitochondrial membrane potential, increased caspase-3 activation, nuclear condensation, terminal deoxynucleotidyl transferase nick end labeling staining, and detachment from the culture dish. The caspase-3 inhibitor acetyl-Asp-Glu-Val-Asp-aldehyde reduced detachment 3-fold. There was a rapid (<10-s) decrease in plasma membrane potential after force application, which, in filamin A-deficient melanoma cells, contributed to irreversible cell depolarization. In fibroblast cultures, cells with increased permeability to propidium iodide exhibited approximately 2-fold less filamin A content than impermeable cells. Fibroblasts transfected with antisense filamin A constructs or with filamin A constructs without an actin-binding domain exhibited 2-3-fold increased proportions of dead cells relative to controls. We conclude that high amplitude forces delivered through integrins can promote apoptosis in a proportion of cells and that filamin A confers mechanoprotection by preventing membrane depolarization.

Phagocytosis of fibronectin and collagens type I, III, and V by human gingival and periodontal ligament fibroblasts in vitro

BACKGROUND

Electron microscopic studies have suggested that the volume density of collagen-containing vacuoles in fibroblasts is higher in the periodontal ligament (PDL) than in the gingiva. Whether this difference reflects intrinsic differences in phagocytic capacity among the cells in these tissues is not known.

METHODS

PDL and gingival fibroblasts were isolated from subjects and cultured under identical conditions in the presence of fluorescent beads coated with collagen type I, III, or V or fibronectin. Control beads were coated with bovine serum albumin or an enamel matrix protein mixture that does not constitute part of the extracellular matrix of PDL and gingiva. After various time intervals (1 to 24 hours), the percentage of cells that had internalized beads was assessed by flow cytometry. Since alkaline phosphatase activity has been suggested to play a role in collagen phagocytosis, the activity of this enzyme was determined for all cell populations.

RESULTS

The results demonstrated the following order in the percentage of cells internalizing protein-coated beads: fibronectin > collagen type I > III > V. Internalization of collagen type I-coated beads exceeded that of beads coated with bovine serum albumin or enamel matrix proteins by 6 and 3 times, respectively. No differences were observed in collagen phagocytic activity between PDL and gingival fibroblasts, and no relationship could be demonstrated between collagen phagocytosis and alkaline phosphatase activity.

CONCLUSIONS

We conclude that differences in collagen phagocytosis between PDL and gingiva, as observed in vivo, are not likely to be explained in terms of intrinsic phagocytic capacities of these cells.

Cytoprotection against mechanical forces delivered through beta 1 integrins requires induction of filamin A

Cells in mechanically active environments can activate cytoprotective mechanisms to maintain membrane integrity in the face of potentially lethal applied forces. Cytoprotection may be mediated by expression of membrane-associated cytoskeletal proteins including filamin A, an actin-binding protein that increases the rigidity of the subcortical actin cytoskeleton. In this study, we tested the hypotheses that applied forces induce the expression of filamin A specifically and that this putative protective response inhibits cell death. Magnetically generated forces were applied to protein-coated magnetite beads bound to human gingival fibroblasts, cells with constitutively low basal levels of filamin A mRNA and protein. Forces applied through collagen or fibronectin, but not bovine serum albumin or poly-l-lysine-coated beads, increased mRNA and protein content of filamin A by 3-7-fold. Forces had no effect on the expression of other filamin isotypes or other cytoskeletal proteins. This effect was dependent on the duration of force and was blocked by anti-beta(1) integrin antibodies. Force also stimulated a 60% increase in expression of luciferase under the control of a filamin A promoter in transiently transfected Rat2 fibroblasts and was dependent on Sp1 transcription factor binding sites located immediately upstream of the transcription start site. Experiments with actinomycin D-treated cells showed that the increased filamin A expression after force application was due in part to prolongation of mRNA half-life. Antisense filamin oligonucleotides blocked force-induced filamin A expression and increased cell death by >2-fold above controls. The force-induced regulation of filamin A was dependent on intact actin filaments. We conclude that cells from mechanically active environments can couple diverse signals from forces applied through beta-integrins to up-regulate the production of cytoprotective cytoskeletal proteins, typified by filamin A.

Differential regulation of placental and germ cell alkaline phosphatases by glucocorticoid and sodium butyrate in human gastric carcinoma cell line TMK-1

The expression and regulation of alkaline phosphatase (AP) was studied in the human gastric cancer cell line TMK-1. Biochemical analysis, reverse transcription-polymerase chain reaction, and Northern blot analysis demonstrated that the cells express placental, germ cell, and intestinal AP isozymes constitutively. Dexamethasone (Dex), a synthetic glucocorticoid, was shown to specifically induce the placental AP activity to about 10-fold and sodium butyrate (NaBu) induced germ cell AP activity to about 4-fold, respectively. In contrast, these two agents showed little effect on the level of intestinal isozymes. Dex and NaBu also differentially induced the mRNA levels of the placental and germ cell APs. Northern blot analysis of the placental AP transcript in the presence of the transcription inhibitor, 5, 6-dichloro-1-beta-D-ribofuranosyl benzimidazole, revealed that the half-life of placental AP mRNA is about 27 h for both the Dex-treated and untreated cells. Nuclear run-on transcription analysis indicated an apparent increase in the rate of placental AP gene transcription in Dex-treated cells. These results indicated that the effect of Dex occurred primarily by activation of the placental AP gene transcription in the cells. In order to study the direct Dex and NaBu effect on AP gene expression, the proximal promoter regions of AP genes were fused to luciferase reporter vectors. Despite the high similarity in nucleotide sequences of these two genes, transient transfection analysis demonstrated that Dex and NaBu exerted a specific stimulation only through the respective placental and germ cell AP gene promoter. Taken together, this study indicates that the expression of PAP and GCAP isozymes have specific regulatory mechanisms that can be differentially controlled by signals including glucocorticoid and NaBu.

Fetal fetuin selectively induces apoptosis in cancer cell lines and shows anti-cancer activity in tumor animal models

An apoptosis-inducing protein with molecular weight of 60 kDa has been purified from fetal bovine serum. The N-terminal amino acid sequence of this protein (e.g. I-P-L-D-P-V-A-G-Y-K) reveals that it is bovine fetuin, a fetal protein functioning to control embryogenesis. The apoptosis-inducing activity of fetuin is totally dependent on zinc. Depletion of zinc ion from fetuin or substitution of zinc ion by barium ion completely abolished the apoptosis-inducing activity of fetuin. Interestingly, while the fetuin isolated from fetal serum selectively induces apoptosis in cancer without affecting normal cells, the fetuin isolated from mature serum is completely inactive. This suggests that the biological activity of fetuin is under developmental regulation. In vivo, tumor animal model studies showed that fetuin enhanced survival by up to 141% in P388 leukemia animal model in mice. Fetuin was also found to inhibit prostate cancer formation in a PC-3 prostate cancer model in mice.

Cell-cell adhesion in human fibroblasts requires calcium signaling

In connective tissues, intercellular adhesion is essential for tissue morphogenesis, development and wound healing. However, the signaling mechanisms initiated by cell-cell adhesion in fibroblasts and that regulate it are not known. In this study we tested the hypothesis that intracellular calcium signaling is required to mediate intercellular adhesion between fibroblasts. Fura-2 or fluo-3 labeled human fibroblasts were used to investigate calcium homeostasis during intercellular adhesion. After contact with suspended fibroblasts there was a rise in cytosolic free calcium ([Ca2+]i) and multiple calcium oscillations in substrate-attached cells. Antibodies against the extracellular but not the cytoplasmic domain of cadherin induced a similar calcium response, indicating that these responses were initiated by cadherin binding. As shown by the near-plasma membrane Ca2+ indicator (Fura-C18) and by confocal microscopy of fluo-3-loaded cells, [Ca2+]i transients probably originated at sites of cell-cell contact. Cell-cell adhesion was dependent on both calcium influx through membrane channels and release of Ca2+ from internal calcium stores, because the calcium channel inhibitor LaCl3 or pretreatment of cells with thapsigargin significantly inhibited (&gt;35%) cell-cell attachment. The [Ca2+]i changes induced by cell-cell adhesion were temporally correlated with increased recruitment of intercellular junctional proteins into the cytoskeleton and movement of GFP-actin to sites of cell-cell contact. [Ca2+]i responses induced by intercellular adhesion were essential for both junctional protein recruitment and the establishment of strong cell-cell contacts, as loading cells with BAPTA/AM significantly inhibited cell-cell adhesion and recruitment of cadherins and beta-catenin to the actin cytoskeleton. Actin depolymerization by cytochalasin D dramatically reduced cell-cell adhesion and recruitment of cadherins and catenin to the actin cytoskeleton. These results demonstrate that cadherin-cadherin interaction induces [Ca2+]i transients during cell-cell adhesion in fibroblasts, and these calcium signals regulate cell-cell adhesion through remodeling of cortical actin and recruitment of cadherins and beta-catenin into intercellular junctions.

Effect of tissue non-specific alkaline phosphatase in maintenance of structure of murine colon and stomach

The gastrointestinal tract of mammals secretes a phospholipid-rich membrane that is enriched in alkaline phosphatase (AP) and surfactant proteins (surfactant-like particle, SLP). The production of this particle is stimulated in the small intestine by fat feeding and in cultured cells in vitro by transfection with intestinal alkaline phosphatase (IAP). To test whether tissue non-specific alkaline phosphatase (TNAP) was a factor in stimulating surfactant-like particle production in stomach and colon (tissues expressing TNAP), mice lacking this enzyme were studied. Mice were harvested at 8 days of life, when body weight of homozygous animals (TNAP -/-) was about half that of congenic controls (TNAP +/+) or heterozygotes (TNAP +/-), but before seizures had begun. No difference in content of the major SLP protein (65 kDa) by Western blotting or immunocytochemistry was seen in stomach or colon of TNAP -/- vs. TNAP +/+ animals, but the content was only about half in the IAP-expressing small bowel. Transmission electron microscopy of the TNAP -/- small bowel showed large dilated lysosomes and residual bodies. Colonocytes and gastric surface epithelial cells from the same animals showed mitochondria containing homogeneous dense inclusions, consistent with neutral lipid. In the underweight homozygous animals, there was a decrease in the neuronal content of submucosal ganglia in the jejunum and ileum and of myenteric ganglia in the jejunum of TNAP -/- animals. These findings suggest that (1) TNAP is not important in maintaining surfactant-like particle content of tissues that express TNAP, (2) normal fat absorption is important in maintaining SLP content in the small intestine, and (3) TNAP is important in the maintenance of some intestinal structures, and perhaps their function.

Expression and regulation of alkaline phosphatases in human breast cancer MCF-7 cells

The effect of retinoic acid and dexamethasone on alkaline phosphatase (AP) expression was investigated in human breast cancer MCF-7 cells. Cellular AP activity was induced significantly by retinoic acid or dexamethasone in a time-dependent and dose-dependent fashion. A marked synergistic induction of AP activity was observed when the cells were incubated with both agents simultaneously. Two AP isozymes, tissue-nonspecific (TNAP) and intestinal (IAP), were shown to be expressed in MCF-7 cells as confirmed by the differential rate of thermal inactivation of these isozymes and RT-PCR. Based on the two-isozyme thermal-inactivation model, the specific activities for TNAP and IAP in each sample were analyzed. TNAP activity was induced only by retinoic acid and IAP activity was induced only by dexamethasone. Whereas dexamethasone conferred no significant effect on TNAP activity, retinoic acid was shown to inhibit IAP activity by approximately 50%. Interestingly, TNAP was found to be the only isozyme activity superinduced when the cells were costimulated with retinoic acid and dexamethasone. Northern blot and RT-PCR analysis were then used to demonstrate that the steady-state TNAP mRNA level was also superinduced, which indicates that the superinduction is regulated at the transcriptional or post-transcriptional levels. In the presence of the glucocorticoid receptor antagonist RU486, the dexamethasone-mediated induction of IAP activity was blocked completely as expected. However, the ability of RU486 to antagonize the action of glucocorticoid was greatly compromised in dexamethasone-mediated superinduction of TNAP activity. Furthermore, in the presence of retinoic acid, RU486 behaved as an agonist, and conferred superinduction of TNAP gene expression in the same way as dexamethasone. Taken together, these observations suggest that the induction of IAP activity by dexamethasone and the superinduction of TNAP by dexamethasone were mediated through distinct regulatory pathways. In addition, retinoic acid plays an essential role in the superinduction of TNAP gene expression by enabling dexamethasone to exert its agonist activity, which otherwise has no effect.

New face of an old enzyme: alkaline phosphatase may contribute to human tissue aging by inducing tissue hardening and calcification

Tissue nonspecific alkaline phosphatase (AP) plays a well-known role in bone mineralization. This role was first suggested by a human AP deficiency disease, hypophosphatasia. Further studies with AP gene knockout mice have also suggested a role for AP in mineralization. However, AP is also expressed in other human tissues besides bone and cartilage, and this raises a question as to whether AP may also play a role in pathological mineralization such as dystrophic and vascular calcification. In vitro studies carried out in our laboratory indicate that a variety of cell types stably expressing membrane-bound AP can affect extracellular mineralization regardless of the tissue from which the cell lines originated (e.g. fibroblasts, vascular endothelial cells, or renal epithelial cells). This AP-mediated extracellular mineralization is both substrate/dependent and culture environment/dependent and may be consistent with a putative role for AP in pathological mineralization in tissues other than bone and cartilage. In this regard, it is interesting to note that high levels of AP are observed in vascular endothelia of small arterioles in brain and heart. It is probable that expression of AP in small arterioles of brain and heart may also contribute to the vascular hardening and calcification observed in humans. This in turn could be related to vascular aging, vascular disease, and the resultant weakening of and/or rupture of vessel walls.