Lysophosphatidic Acid Interacts with Transforming Growth Factor-β Signaling to Mediate Keratinocyte Growth Arrest and Chemotaxis

Smad transcription factors as mediators of 7 transmembrane G protein-coupled receptor signalling

The Smad transcription factors are well known for their role at the core of transforming growth factor-β (TGF-β) signalling. However, recent evidence shows that the Smad transcription factors play a vital role downstream of other classes of receptors including G protein-coupled receptors (GPCR). The versatility of Smad transcription factors originated from the two regions that can be differently activated by the TGF-β receptor superfamily or through the recruitment of intracellular kinases stimulated by other receptors classes such as GPCRs. The classic GPCR signalling cascade is further expanded to conditional adoption of the Smad transcription factor under the stimulation of Akt, demonstrating the unique involvement of the Smad transcription factor in GPCR signalling pathways in disease environments. In this review, we provide a summary of the signalling pathways of the Smad transcription factors as an important downstream mediator of GPCRs, presenting exciting opportunities for discovering new therapeutic targets for diseases.

Lysophosphatidic Acid Receptors LPAR5 and LPAR2 Inversely Control Hydroxychloroquine-Evoked Itch and Scratching in Mice

Lysophosphatidic acids (LPAs) evoke nociception and itch in mice and humans. In this study, we assessed the signaling paths. Hydroxychloroquine was injected intradermally to evoke itch in mice, which evoked an increase of LPAs in the skin and in the thalamus, suggesting that peripheral and central LPA receptors (LPARs) were involved in HCQ-evoked pruriception. To unravel the signaling paths, we assessed the localization of candidate genes and itching behavior in knockout models addressing LPAR5, LPAR2, autotaxin/ENPP2 and the lysophospholipid phosphatases, as well as the plasticity-related genes Prg1/LPPR4 and Prg2/LPPR3. LacZ reporter studies and RNAscope revealed LPAR5 in neurons of the dorsal root ganglia (DRGs) and in skin keratinocytes, LPAR2 in cortical and thalamic neurons, and Prg1 in neuronal structures of the dorsal horn, thalamus and SSC. HCQ-evoked scratching behavior was reduced in sensory neuron-specific Advillin-LPAR5-/- mice (peripheral) but increased in LPAR2-/- and Prg1-/- mice (central), and it was not affected by deficiency of glial autotaxin (GFAP-ENPP2-/-) or Prg2 (PRG2-/-). Heat and mechanical nociception were not affected by any of the genotypes. The behavior suggested that HCQ-mediated itch involves the activation of peripheral LPAR5, which was supported by reduced itch upon treatment with an LPAR5 antagonist and autotaxin inhibitor. Further, HCQ-evoked calcium fluxes were reduced in primary sensory neurons of Advillin-LPAR5-/- mice. The results suggest that LPA-mediated itch is primarily mediated via peripheral LPAR5, suggesting that a topical LPAR5 blocker might suppress "non-histaminergic" itch.

Emerging roles of lysophosphatidic acid receptor subtype 5 (LPAR5) in inflammatory diseases and cancer

Lysophosphatidic acid (LPA) is a bioactive lipid mediator that regulates a variety of cellular functions such as cell proliferation, migration, survival, calcium mobilization, cytoskeletal rearrangements, and neurite retraction. The biological actions of LPA are mediated by at least six G protein-coupled receptors known as LPAR1-6. Given that LPAR1-3 were among the first LPARs identified, the majority of research efforts have focused on understanding their biology. This review provides an in-depth discussion of LPAR5, which has recently emerged as a key player in regulating normal intestinal homeostasis and modulating pathological conditions such as pain, itch, inflammatory diseases, and cancer. We also present a chronological overview of the efforts made to develop compounds that target LPAR5 for use as tool compounds to probe or validate LPAR5 biology and therapeutic agents for the treatment of inflammatory diseases and cancer.

Lysophosphatidic Acid Is an Inflammatory Lipid Exploited by Cancers for Immune Evasion via Mechanisms Similar and Distinct From CTLA-4 and PD-1

Immunological tolerance has evolved to curtail immune responses against self-antigens and prevent autoimmunity. One mechanism that contributes to immunological tolerance is the expression of inhibitory receptors by lymphocytes that signal to dampen immune responses during the course of an infection and to prevent immune-mediated collateral damage to the host. The understanding that tumors exploit these physiological mechanisms to avoid elimination has led to remarkable, but limited, success in the treatment of cancer through the use of biologics that interfere with the ability of cancers to suppress immune function. This therapy, based on the understanding of how T lymphocytes are normally activated and suppressed, has led to the development of therapeutic blocking antibodies, referred to as immune checkpoint blockade, which either directly or indirectly promote the activation of CD8 T cells to eradicate cancer. Here, we highlight the distinct signaling mechanisms, timing and location of inhibition used by the CTLA-4 and PD-1 inhibitory receptors compared to a novel inhibitory signaling axis comprised of the bioactive lipid, lysophosphatidic acid (LPA), signaling via the LPA5 receptor expressed by CD8 T cells. Importantly, abundant evidence indicates that an LPA-LPA5 signaling axis is also exploited by diverse cancers to suppress T cell activation and function. Clearly, a thorough molecular and biochemical understanding of how diverse T cell inhibitory receptors signal to suppress T cell antigen receptor signaling and function will be important to inform the choice of which complimentary checkpoint blockade modalities might be used for a given cancer.

Epicardial TGFβ and BMP Signaling in Cardiac Regeneration: What Lesson Can We Learn from the Developing Heart?

The epicardium, the outer layer of the heart, has been of interest in cardiac research due to its vital role in the developing and diseased heart. During development, epicardial cells are active and supply cells and paracrine cues to the myocardium. In the injured adult heart, the epicardium is re-activated and recapitulates embryonic behavior that is essential for a proper repair response. Two indispensable processes for epicardial contribution to heart tissue formation are epithelial to mesenchymal transition (EMT), and tissue invasion. One of the key groups of cytokines regulating both EMT and invasion is the transforming growth factor β (TGFβ) family, including TGFβ and Bone Morphogenetic Protein (BMP). Abundant research has been performed to understand the role of TGFβ family signaling in the developing epicardium. However, less is known about signaling in the adult epicardium. This review provides an overview of the current knowledge on the role of TGFβ in epicardial behavior both in the development and in the repair of the heart. We aim to describe the presence of involved ligands and receptors to establish if and when signaling can occur. Finally, we discuss potential targets to improve the epicardial contribution to cardiac repair as a starting point for future investigation.

In Vitro Wound Healing Assays to Investigate Epidermal Migration

Re-epithelialization after cutaneous injury is a complex and multifaceted process that incorporates numerous cellular components interacting in a myriad of pathways. One of the most crucial aspects of this process is the initiation of keratinocyte migration to fill the wound bed. Re-epithelialization involves both the individual and collective movement of epidermal cells under the control of integrated signaling paradigms. It is therefore essential to develop a simple methodology to dissect the basic movement of epidermal cells in vitro. Scratch assays are relatively simple experiments in which a single layer of cells are plated onto a prepared dish with multiple furrows created in the cell bed. The resulting cellular migration to fill the wound bed can then be imaged and processed quantitatively to investigate migration rates and other factors of interest. Here, we provide important adaptations to the classic scratch assay to make it a robust, reproducible, and quantitative tool for the evaluation of epidermal cell migration.

Lysophosphatidic acid regulates the motility of MCF10CA1a breast cancer cell sheets via two opposing signaling pathways

Aberrant cell migration leads to the dispersal of malignant cells. The ubiquitous lipid mediator lysophosphatidic acid (LPA) modulates cell migration and is implicated in tumor progression. Yet, the signaling cascades that regulate LPA's effect on cell motility remain unclear. Using time-lapse imaging and quantitative analyses, we studied the role of signaling cascades that act downstream of LPA on the motility of MCF10CA1a breast cancer cells. We found that LPA alters cell motility via two major signaling pathways. The Rho/ROCK signaling cascade is the predominant pathway that increases E-Cadherin containing cell-cell adhesions and cortical arrangement of actomyosin to promote slow, directional, spatially coherent and temporally consistent movement. In contrast, Gαi/o- and Gαq/11-dependent signaling cascades lessen directionality and support the independent movement of cells. The net effect of LPA on breast cancer cell migration therefore results from the integrated signaling activity of the Rho/ROCK and Gαi/o- and Gαq/11-dependent pathways, thus allowing for a dynamic migratory response to changes in the cellular or microenvironmental context.

Lysophosphatidic acid (LPA) as a pro-fibrotic and pro-oncogenic factor: a pivotal target to improve the radiotherapy therapeutic index

Radiation-induced fibrosis is widely considered as a common but forsaken phenomenon that can lead to clinical sequela and possibly vital impairments. Lysophosphatidic acid is a bioactive lipid involved in fibrosis and probably in radiation-induced fibrosis as suggested in recent studies. Lysophosphatidic acid is also a well-described pro-oncogenic factor, involved in carcinogenesis processes (proliferation, survival, angiogenesis, invasion, migration). The present review highlights and summarizes the links between lysophosphatidic acid and radiation-induced fibrosis, lysophosphatidic acid and radioresistance, and proposes lysophosphatidic acid as a potential central actor of the radiotherapy therapeutic index. Besides, we hypothesize that following radiotherapy, the newly formed tumour micro-environment, with increased extracellular matrix and increased lysophosphatidic acid levels, is a favourable ground to metastasis development. Lysophosphatidic acid could therefore be an exciting therapeutic target, minimizing radio-toxicities and radio-resistance effects.

Epidermal loss of Gαq confers a migratory and differentiation defect in keratinocytes

G-protein coupled receptors (GPCRs), which activate heterotrimeric G proteins, are an essential class of transmembrane receptors that are responsible for a myriad of signaling events in normal and pathologic conditions. Two members of the G protein family, Gα_q and Gα₁₁, activate one of the main GPCR pathways and function as oncogenes by integrating mitogen-stimulated signaling cascades that are active under malignant conditions. Recently, it has been shown that targeted deletion of Gα₁₁ and Gα_q from endothelial cells impairs the Rho-mediated formation of focal adherens junctions, suggesting that Gα_11/q signaling may also play a significant role in cytoskeletal-mediated cellular responses in epithelial cells. Indeed, combined deletion of Gα₁₁ and Gα_q confers a significant migratory defect in keratinocytes that delays cutaneous wound healing in an in vivo setting. This delay can be attributed to a defect during the reepithelialization phase due to significantly attenuated migratory capacity of Gα_q-null keratinocytes under combined Gα₁₁ deficiency. In fact, cells lacking Gα_11/q demonstrate a severely reduced ability to respond to mitogenic and migratory signals in the microenvironment, leading to inappropriate and premature terminal differentiation. These results suggest that Gα_11/q signaling pathways may be critical for integrating mitogenic signals and cytoskeletal function to achieve normal physiological responses. Emergence of a malignant phenotype may therefore arise from both under- and overexpression of Gα_11/q signaling, implicating its upstream regulation as a potential therapeutic target in a host of pathologic conditions.

Lysophosphatidic acid regulates adhesion molecules and enhances migration of human oral keratinocytes

Oral keratinocytes are connected via cell-to-cell adhesions to protect underlying tissues from physical and bacterial damage. Lysophosphatidic acids (LPAs) are a family of phospholipid mediators that have the ability to regulate gene expression, cytoskeletal rearrangement, and cytokine/chemokine secretion, which mediate proliferation, migration, and differentiation. Several forms of LPA are found in saliva and gingival crevicular fluid, but it is unknown how they affect human oral keratinocytes (HOK). The aim of the present study was therefore to examine how different LPA forms affect the expression of adhesion molecules and the migration and proliferation of HOK. Keratinocytes were isolated from gingival biopsies obtained from healthy donors and challenged with different forms of LPA. Quantitative real-time RT-PCR, immunocytochemistry, and flow cytometry were used to analyze the expression of adhesion molecules. Migration and proliferation assays were performed. Lysophosphatidic acids strongly promoted expression of E-cadherin and occludin mRNAs and translocation of E-cadherin protein from the cytoplasm to the membrane. Occludin and claudin-1 proteins were up-regulated by LPA. Migration of HOK in culture was increased, but proliferation was reduced, by the addition of LPA. This indicates that LPA can have a role in the regulation of the oral epithelial barrier by increasing the expression of adhesion molecules of HOK, by promotion of migration and by inhibition of proliferation.

Cross-talk between lysophosphatidic acid receptor 1 and tropomyosin receptor kinase A promotes lung epithelial cell migration

Lysophosphatidic acid (LPA) is a bioactive lysophospholipid, which plays a crucial role in the regulation of cell proliferation, migration, and differentiation. LPA exerts its biological effects mainly through binding to cell-surface LPA receptors (LPA1-6), which belong to the G protein-coupled receptor (GPCR) family. Recent studies suggest that cross-talk between receptor tyrosine kinases (RTKs) and GPCRs modulates GPCRs-mediated signaling. Tropomyosin receptor kinase A (TrkA) is a RTK, which mediates nerve growth factor (NGF)-induced biological functions including cell migration in neuronal and non-neuronal cells. Here, we show LPA1 transactivation of TrkA in murine lung epithelial cells (MLE12). LPA induced tyrosine phosphorylation of TrkA in both time- and dose-dependent manners. Down-regulation of LPA1 by siRNA transfection attenuated LPA-induced phosphorylation of TrkA, suggesting a cross-talk between LPA1 and TrkA. To investigate the molecular regulation of the cross-talk, we focused on the interaction between LPA1 and TrkA. We found that LPA induced interaction between LPA1 and TrkA. The LPA1/TrkA complex was localized on the plasma membrane and in the cytoplasm. The C-terminus of LPA1 was identified as the binding site for TrkA. Inhibition of TrkA attenuated LPA-induced phosphorylation of TrkA and LPA1 internalization, as well as lung epithelial cell migration. These studies provide a molecular mechanism for the transactivation of TrkA by LPA, and suggest that the cross-talk between LPA1 and TrkA regulates LPA-induced receptor internalization and lung epithelial cell migration.

Lysophosphatidic acid promotes cell migration through STIM1- and Orai1-mediated Ca2+(i) mobilization and NFAT2 activation

Lysophosphatidic acid (LPA) enhances cell migration and promotes wound healing in vivo, but the intracellular signaling pathways regulating these processes remain incompletely understood. Here we investigated the involvement of agonist-induced Ca²⁺ entry and STIM1 and Orai1 proteins in regulating nuclear factor of activated T cell (NFAT) signaling and LPA-induced keratinocyte cell motility. As monitored by Fluo-4 imaging, stimulation with 10 μℳ LPA in 60 μℳ Ca²⁺_o evoked Ca²⁺_i transients owing to store release, whereas addition of LPA in physiological 1.2 mℳ Ca²⁺_o triggered store release coupled to extracellular Ca²⁺ entry. Store-operated Ca²⁺ entry (SOCE) was blocked by the SOCE inhibitor diethylstilbestrol (DES), STIM1 silencing using RNA interference (RNAi), and expression of dominant/negative Orai1^R91W. LPA induced significant NFAT activation as monitored by nuclear translocation of green fluorescent protein-tagged NFAT2 and a luciferase reporter assay, which was impaired by DES, expression of Orai1^R91W, and inhibition of calcineurin using cyclosporin A (CsA). By using chemotactic migration assays, LPA-induced cell motility was significantly impaired by STIM1, CsA, and NFAT2 knockdown using RNAi. These data indicate that in conditions relevant to epidermal wound healing, LPA induces SOCE and NFAT activation through Orai1 channels and promotes cell migration through a calcineurin/NFAT2-dependent pathway.

Gene expression of the lysophosphatidic acid receptor 1 is a target of transforming growth factor beta

The lysophosphatidic acid (LPA) receptor LPA₁/Edg2 is the first identified LPA receptor. Although its wide tissue distribution and biological functions have been well studied, little is known about how LPA₁ is transcriptionally regulated. In the current study, we showed that LPA₁ is a physiological target of transforming growth factor beta (TGFβ)-mediated repression. In both normal and neoplastic cells, TGFβ inhibits LPA₁ promoter activity, LPA₁ mRNA expression, and LPA₁-dependent chemotaxis and tumor cell invasion. Knockdown of the TGFβ intracellular effector Smad3 or Smad4 with lentivirally transduced shRNA relieved these inhibitory effects of TGFβ. Interestingly, the LPA₁ promoter contains two potential TGFβ inhibitory elements (TIEs), each consisting of a Smad binding site and an adjacent E2F4/5 element, structurally similar to the TIE found on the promoter of the well-defined TGFβ target gene c-myc. Deletion and point mutation analyses indicate that the distal TIE located at 401 bp from the transcription initiation site, is required for TGFβ repression of the LPA₁ promoter. A DNA pull-down assay showed that the -401 TIE was capable of binding Samd3 and E2F4 in TGFβ-treated cells. TGFβ-induced binding of the Smad complex to the native -401 TIE sequence of the LPA₁ gene promoter was further verified by chromatin immunoprecipitation assays. We therefore identified a novel role of TGFβ in the control of LPA₁ expression and LPA₁-coupled biological functions, adding LPA₁ to the list of TGFβ-repressed target genes.

Somatostatin inhibits cell migration and reduces cell counts of human keratinocytes and delays epidermal wound healing in an ex vivo wound model

The peptide hormone somatostatin (SST) and its five G protein-coupled receptors (SSTR1-5) were described to be present in the skin, but their cutaneous function(s) and skin-specific signalling mechanisms are widely unknown. By using receptor specific agonists we show here that the SSTRs expressed in keratinocytes are functionally coupled to the inhibition of adenylate cyclase. In addition, treatment with SSTR4 and SSTR5/1 specific agonists significantly influences the MAP kinase signalling pathway. As epidermal hormone receptors in general are known to regulate re-epithelialization following skin injury, we investigated the effect of SST on cell counts and migration of human keratinocytes. Our results demonstrate a significant inhibition of cell migration and reduction of cell counts by SST. We do not observe an effect on apoptosis and necrosis. Analysis of signalling pathways showed that somatostatin inhibits cell migration independent of its effect on cAMP. Migrating keratinocytes treated with SST show altered cytoskeleton dynamics with delayed lamellipodia formation. Furthermore, the activity of the small GTPase Rac1 is diminished, providing evidence for the control of the actin cytoskeleton by somatostatin receptors in keratinocytes. While activation of all receptors leads to redundant effects on cell migration, only treatment with a SSTR5/1 specific agonist resulted in decreased cell counts. In accordance with reduced cell counts and impaired migration we observe delayed re-epithelialization in an ex vivo wound healing model. Consequently, our experiments suggest SST as a negative regulator of epidermal wound healing.

Lysophosphatidic acid-activated Cl- current activity in human systemic sclerosis skin fibroblasts

OBJECTIVES

SSc (scleroderma) is an often fatal disease characterized by widespread tissue fibrosis. Fibroblasts play a key role in SSc-associated fibrosis. This study was designed to determine: (i) whether fibroblasts isolated from skin of patients with SSc have increased lysophosphatidic acid-activated Cl- current (IClLPA) activity vs healthy controls; (ii) whether myofibroblast differentiation is involved in SSc skin fibrosis; and (iii) whether SSc fibroblasts have different proliferation rates vs controls.

METHODS

Skin biopsies were taken from involved and uninvolved skin of SSc patients and controls. Whole-cell perforated patch-clamping was used to measure IClLPA activity in fibroblasts isolated and cultured from these biopsies. Western blotting was used to measure α-smooth muscle actin (α-SMA). Proliferation was measured using a colorimetric assay.

RESULTS

Fibroblasts cultured from SSc skin show significantly increased IClLPA activity following LPA exposure compared with control skin fibroblasts. α-SMA protein was significantly increased in cultured SSc skin fibroblasts vs controls. No significant differences in proliferation rates were found.

CONCLUSIONS

Elevated IClLPA activity is a hallmark of SSc skin fibroblasts. Blocking IClLPA activation may be a new therapeutic approach for treating SSc-associated fibrosis.

Lysophosphatidic Acid Upregulates Laminin-332 Expression during A431 Cell Colony Dispersal

Lysophosphatidic acid (LPA) is a bioactive phospholipid that affects various biological functions, such as cell proliferation, migration, survival, wound healing, and tumor invasion through LPA receptors. Previously, we reported that LPA induces A431 colony dispersal, accompanied by disruption of cell-cell contacts and cell migration. However, it remains unclear how LPA affects cell migration and gene expression during A431 colony dispersal. In this paper, we performed cDNA microarray analysis to investigate this question by comparing gene expression between untreated and LPA-treated A431 cells. Interestingly, these results revealed that LPA treatment upregulates several TGF-β1 target genes, including laminin-332 (Ln-332) components (α3, β3, and γ2 chains). Western blot analysis also showed that LPA increased phosphorylation of Smad2, an event that is carried out by TGF-β1 interactions. Among the genes upregulated, we further addressed the role of Ln-332. Real-time PCR analysis confirmed the transcriptional upregulation of all α3, β3, and γ2 chains of Ln-332 by LPA, corresponding to the protein level increases revealed by western blot. Further, the addition of anti-Ln-332 antibody prevented LPA-treated A431 colonies from dispersing. Taken together, our results suggest that LPA-induced Ln-332 plays a significant role in migration of individual cells from A431 colonies.

New insights into the mechanism of fibroblast to myofibroblast transformation and associated pathologies

Myofibroblasts are a differentiated cell type essential for wound healing, participating in tissue remodeling following insult. Myofibroblasts are typically activated fibroblasts, although they can also be derived from other cell types, including epithelial cells, endothelial cells, and mononuclear cells. In most organ systems, cell signals initiated following tissue-specific insult or during the metastatic process lead to differentiation of fibroblasts or other precursor cells to the myofibroblast phenotype. In addition to their beneficial and necessary role in wound healing, myofibroblasts also contribute to a number of pathologies, primarily fibrotic processes and tumor invasiveness. This review explores both traditional and nontraditional concepts of myofibroblast differentiation in the cornea, skin, heart, and other tissues, as well as some of the pathologies associated with myofibroblast activities.

Agonist-induced calcium entry correlates with STIM1 translocation

The mechanisms of agonist-induced calcium entry (ACE) following depletion of intracellular calcium stores have not been fully established. We report here that calcium-independent phospholipase A (iPLA₂) is required for robust Ca²⁺ entry in HaCaT keratinocytes following ATP or UTP stimulation. Lysophosphatidic acid (LPA), an unrelated agonist, evoked Ca²⁺ release without inducing robust Ca²⁺ entry. Both LPA and UTP induced the redistribution of STIM1 into puncta which localized to regions near or at the plasma membrane, as well as within the cytoplasm. Plasma membrane-associated STIM1 remained high for up to 10 min after UTP stimulation, whereas it had returned almost to baseline by that time point in LPA-stimulated cells. This correlated with faster reloading of the endoplasmic reticulum Ca²⁺ stores in LPA treated cells. Thus by differentially regulating store-refilling after agonist-mediated depletion, LPA and UTP may exert distinct effects on the duration of STIM1 localization at the plasma membrane, and thus, on the magnitude and duration of ACE.

Regulation and biological activities of the autotaxin-LPA axis

Autotaxin (ATX), or nucleotide pyrophosphatase/phosphodiesterase 2 (NPP2), is an exo-enzyme originally identified as a tumor cell autocrine motility factor. ATX is unique among the NPPs in that it primarily functions as a lysophospholipase D, converting lysophosphatidylcholine into the lipid mediator lysophosphatidic acid (LPA). LPA acts on specific G protein-coupled receptors to elicit a wide range of cellular responses, ranging from cell proliferation and migration to neurite remodeling and cytokine production. While LPA signaling has been studied extensively over the last decade, we are only now beginning to explore the properties and biological importance of ATX as the major LPA-producing phospholipase. In this review, we highlight recent advances in our understanding of the ATX-LPA axis, giving first an update on LPA action and then focusing on ATX, in particular its regulation, its link to cancer and its vital role in vascular development.

Reactive Oxygen Species Mediated Sustained Activation of Protein Kinase C α and Extracellular Signal-Regulated Kinase for Migration of Human Hepatoma Cell Hepg2

The tumor promoter 12-O-tetradecanoylphorbol-13-acetate (TPA) can trigger growth inhibition, epithelial-mesenchymal transition (EMT)-like cell scattering, and migration of hepatoma cells HepG2 in a protein kinase C-alpha (PKC-alpha)-dependent manner. Saikosaponin a, an ingredient of antitumorigenic Chinese herb Sho-Saiko-to, inhibited cell growth but did not induce EMT-like cell scattering and cell migration of HepG2. Saikosaponin a and TPA induced transient (for 30 minutes) and sustained (until 6 hours) phosphorylation of extracellular signal-regulated kinase (ERK), respectively. Generation of the reactive oxygen species (ROS) was induced by TPA, but not saikosaponin a, for 3 hours. As expected, scavengers of ROS, such as superoxide dismutase, catalase, and mannitol, and the thiol-containing antioxidant N-acetylcystein dramatically suppressed the TPA-triggered cell migration but not growth inhibition of HepG2. The generation of ROS induced by TPA was PKC, but not ERK, dependent. On the other hand, scavengers of ROS and N-acetylcystein also prevented PKC activation and ERK phosphorylation induced by TPA. On the transcriptional level, TPA can induce gene expression of integrins alpha5, alpha6, and beta1 and reduce gene expression of E-cahedrin in a PKC- and ROS-dependent manner. In conclusion, ROS play a central role in mediating TPA-triggered sustained PKC and ERK signaling for regulation of gene expression of integrins and E-cahedrin that are responsible for EMT and migration of HepG2.

Tissue regeneration and in loco administration of platelet derivatives: clinical outcome, heterogeneous products, and heterogeneity of the effector mechanisms

BACKGROUND

In loco administration of platelet (PLT) derivatives is a relatively new auxiliary treatment for tissue regeneration to be hastened. Enthusiastic reports are faced by more critical ones. The more obvious rationale for the in vivo administration of PLT derivatives resides in their growth factor content.

STUDY DESIGN AND METHODS

The relevant literature was systematically reviewed. Close scrutiny of the technical details was carried out to find out the procedural differences accounting for conflicting results.

RESULTS

An impressively vast heterogeneity of conduct was found in both in vitro and in vivo studies. Major outcome-affecting variables were recognized such as those associated with PLT preparation; growth factor measurement; proliferation test; dose, timing, and administration of the PLT derivatives; study design; and primary endpoints.

CONCLUSIONS

So many variables were found making standardization or confrontation of the in vitro and the in vivo studies barely conceivable or manageable. The mechanisms of action are very complex. The attribution of tissue regeneration capacity of PLT derivatives solely to the PLT-derived growth factors is simplistic. The results obtained through in vitro experiments are indicative for general mechanisms. Their simplistic hold to the complex in vivo environment may be misleading.

Production of lysophosphatidic acid in blister fluid: involvement of a lysophospholipase D activity

Lysophosphatidic acid (LPA) is present in abundance in serum resulting from platelet activation and is also found in other biological fluids. LPA controls numerous cellular responses and plays a role in specific functions such as wound healing, especially in the skin. Nevertheless, its presence in the skin has never been investigated. Since re-epithelialization occurs after blister rupture, we tested the presence of endogenous LPA in blister fluid and investigated a possible mechanism for its biosynthesis and biological functions. Using a radioenzymatic assay, LPA was detected in 33 blister fluids originating from 24 bullous dermatoses, and at higher concentrations than in plasma. In parallel, blister fluids contained a lysophospholipase D (LPLD) activity but no detectable phospholipase A2 activity. The expressions of the LPLD autotaxin (ATX) and of LPA1-receptor (LPA1-R) were greatly increased in blister skin when compared with normal skin. Finally, LPA was found to have a positive effect on the migration of cultured keratinocytes. These results show that LPA is present in blister fluid synthesized by the LPLD ATX. Due to its ability to enhance keratinocyte migration, LPA in blister fluid could, via the LPA1-R, play an important role in re-epithelialization occurring after blister rupture.