Induction of connective tissue growth factor expression by sphingosylphosphorylcholine in cultured human skin fibroblasts

CTIP2 and lipid metabolism: regulation in skin development and associated diseases

INTRODUCTION

COUP-TF INTERACTING PROTEIN 2 (CTIP2) is a crucial transcription factor exhibiting its control through coupled modulation of epigenetic modification and transcriptional regulation of key genes related to skin, immune, and nervous system development. Previous studies have validated the essential role of CTIP2 in skin development and maintenance, propagating its effects in epidermal permeability barrier (EPB) homeostasis, wound healing, inflammatory diseases, and epithelial cancers. Lipid metabolism dysregulation, on the other hand, has also established its independent emerging role over the years in normal skin development and various skin-associated ailments. This review focuses on the relatively unexplored connections between CTIP2-mediated control of lipid metabolism and alteration of EPB homeostasis, delayed wound healing, inflammatory diseases exacerbation, and cancer promotion and progression.

AREAS COVERED

Here we have discussed the intricate interplay of various endogenous lipids and lipoproteins accompanying skin development and associated disease processes and the possible link to CTIP2-mediated regulation of lipid metabolism.

EXPERT OPINION

Establishing the link between CTIP2 and lipid metabolism alterations in the context of skin morphogenesis and diverse types of skin diseases including cancer can help us identify novel targets for effective therapeutic intervention.

A novel sphingosylphosphorylcholine and sphingosine-1-phosphate receptor 1 antagonist, KRO-105714, for alleviating atopic dermatitis

Background

Atopic dermatitis (eczema) is a type of inflammation of the skin, which presents with itchy, red, swollen, and cracked skin. The high global incidence of atopic dermatitis makes it one of the major skin diseases threatening public health. Sphingosylphosphorylcholine (SPC) and sphingosine-1-phosphate (S1P) act as pro-inflammatory mediators, as an angiogenesis factor and a mitogen in skin fibroblasts, respectively, both of which are important biological responses to atopic dermatitis. The SPC level is known to be elevated in atopic dermatitis, resulting from abnormal expression of sphingomyelin (SM) deacylase, accompanied by a deficiency in ceramide. Also, S1P and its receptor, sphingosine-1-phosphate receptor 1 (S1P1) are important targets in treating atopic dermatitis.

Results

In this study, we found a novel antagonist of SPC and S1P1, KRO-105714, by screening 10,000 compounds. To screen the compounds, we used an SPC-induced cell proliferation assay based on a high-throughput screening (HTS) system and a human S1P1 protein-based [³⁵S]-GTPγS binding assay. In addition, we confirmed the inhibitory effects of KRO-105714 on atopic dermatitis through related cell-based assays, including a tube formation assay, a cell migration assay, and an ELISA assay on inflammatory cytokines. Finally, we confirmed that KRO-105714 alleviates atopic dermatitis symptoms in a series of mouse models.

Conclusions

Taken together, our data suggest that SPC and S1P1 antagonist KRO-105714 has the potential to alleviate atopic dermatitis.

Transition from inflammation to proliferation: a critical step during wound healing

The ability to rapidly restore the integrity of a broken skin barrier is critical and is the ultimate goal of therapies for hard-to-heal-ulcers. Unfortunately effective treatments to enhance healing and reduce scarring are still lacking. A deeper understanding of the physiology of normal repair and of the pathology of delayed healing is a prerequisite for the development of more effective therapeutic interventions. Transition from the inflammatory to the proliferative phase is a key step during healing and accumulating evidence associates a compromised transition with wound healing disorders. Thus, targeting factors that impact this phase transition may offer a rationale for therapeutic development. This review summarizes mechanisms regulating the inflammation-proliferation transition at cellular and molecular levels. We propose that identification of such mechanisms will reveal promising targets for development of more effective therapies.

Bioactive lipid mediators in skin inflammation and immunity

The skin is the primary barrier from the outside environment, protecting the host from injury, infectious pathogens, water loss and solar ultraviolet radiation. In this role, it is supported by a highly organized system comprising elements of innate and adaptive immunity, responsive to inflammatory stimuli. The cutaneous immune system is regulated by mediators such as cytokines and bioactive lipids that can initiate rapid immune responses with controlled inflammation, followed by efficient resolution. However, when immune responses are inadequate or mounted against non-infectious agents, these mediators contribute to skin pathologies involving unresolved or chronic inflammation. Skin is characterized by active lipid metabolism and fatty acids play crucial roles both in terms of structural integrity and functionality, in particular when transformed to bioactive mediators. Eicosanoids, endocannabinoids and sphingolipids are such key bioactive lipids, intimately involved in skin biology, inflammation and immunity. We discuss their origins, role and influence over various cells of the epidermis, dermis and cutaneous immune system and examine their function in examples of inflammatory skin conditions. We focus on psoriasis, atopic and contact dermatitis, acne vulgaris, wound healing and photodermatology that demonstrate dysregulation of bioactive lipid metabolism and examine ways of using this insight to inform novel therapeutics.

Sphingosylphosphorylcholine induces stress fiber formation via activation of Fyn-RhoA-ROCK signaling pathway in fibroblasts

Sphingosylphosphorylcholine (SPC), a bioactive sphingolipid, has recently been reported to modulate actin cytoskeleton rearrangement. We have previously demonstrated Fyn tyrosine kinase is involved in SPC-induced actin stress fiber formation in fibroblasts. However, Fyn-dependent signaling pathway remains to be elucidated. The present study demonstrates that RhoA-ROCK signaling downstream of Fyn controls stress fiber formation in SPC-treated fibroblasts. Here, we found that SPC-induced stress fiber formation was inhibited by C3 transferase, dominant negative RhoA or ROCK. SPC activated RhoA, which was blocked by pharmacological inhibition of Fyn activity or dominant negative Fyn. Constitutively active Fyn (ca-Fyn) stimulated stress fiber formation and localized with F-actin at the both ends of stress fibers, both of which were prevented by Fyn translocation inhibitor eicosapentaenoic acid (EPA). In contrast, inhibition of ROCK abolished only the formation of stress fibers, without affecting the localization of ca-Fyn. These results allow the identification of the molecular events downstream SPC in stress fiber formation for a better understanding of stress fiber formation involving Fyn.

Adverse effects of high glucose and free fatty acid on cardiomyocytes are mediated by connective tissue growth factor

Diabetic cardiomyopathy is characterized by interstitial fibrosis and cardiomyocyte hypertrophy and apoptosis. Also known as CCN2, connective tissue growth factor (CTGF) is implicated in the fibrosis; however, whether it contributes to cardiomyocytes changes and adverse effects of high glucose and lipids on these cells remains unknown. Hearts from streptozotocin-induced diabetic rats had elevated CTGF and changes of pathological myocardial hypertrophy, fibrosis, and cardiomyocyte apoptosis. Rat H9c2 cardiomyocytes were then treated with recombinant human (rh)CTGF, high glucose, or the saturated free fatty acid palmitate. Each reagent induced cell hypertrophy, as indicated by the ratio of total protein to cell number, cell size, and gene expression of cardiac hypertrophy marker genes atrial natriuretic peptide (ANP), and α-skeletal actin. Each treatment also caused apoptosis measured by increased caspase3/7 activity, apoptotic cells by transferase-mediated dUTP nick end labeling (TUNEL) assay, and lower viable cell number. Further studies showed CTGF mRNA was rapidly induced by high glucose and palmitate in H9c2 cells and in mouse neonatal cardiomyocyte primary cultures. small interfering RNA against CTGF blocked the high glucose and palmitate induction of hypertrophy and apoptosis. In addition, these CTGF effects were through the tyrosine kinase A (TrkA) receptor with tyrosine kinase activity, which has previously been implicated in CTGF signaling: TrkA was phosphorylated by CTGF, and a specific TrkA blocker abrogated CTGF-induced effects on hypertrophy and apoptosis. For the first time in any system, fatty acid is newly identified as a regulator of CTGF, and this work implicates autocrine CTGF as a mediator of adverse effects of high glucose and fatty acids in cardiomyocytes.

Imbalance between activin A and follistatin drives postburn hypertrophic scar formation in human skin

Hypertrophic scarring is a skin disorder characterized by persistent inflammation and fibrosis that may occur after wounding or thermal injury. Altered production of cytokines and growth factors, such as TGF-beta, play an important role in this process. Activin A, a member of the TGF-beta family, shares the same intra-cellular Smad signalling pathway with TGF-beta, but binds to its own specific transmembrane receptors and to follistatin, a secreted protein that inhibits activin by sequestration. Recent studies provide evidences of a novel role of activin A in inflammatory and repair processes. The aim of this study was to evaluate the importance of activin A and follistatin expression in the different phases of scar evolution. Immunostaining of sections obtained from active phase hypertrophic scars (AHS) revealed the presence of a high number of alpha-SMA(+) myofibroblasts and DC-SIGN(+) dendritic cells coexpressing activin A. Ex-vivo AHS fibroblasts produced more activin and less follistatin than normal skin or remission phase hypertrophic scar (HS) fibroblasts, both in basal conditions and upon TGF-betas stimulation. We demonstrate that fibroblasts do express activin receptors, and that this expression is not affected by TGF-betas. Treatment of HS fibroblasts with activin A induced Akt phosphorylation, promoted cell proliferation, and enhanced alpha-SMA and type I collagen expression. Follistatin reduced proliferation and suppressed activin-induced collagen expression. These results indicate that the activin/follistatin interplay has a role in HS formation and evolution. The impact of these observations on the understanding of wound healing and on the identification of new therapeutic targets is discussed.

The role of lysosphingolipids in the regulation of biological processes

This review summarizes data on the role of lysosphingolipids (glucosyl- and galactosylsphingosines, sphingosine-1-phosphate, sphingosine-1-phosphocholine) in the regulation of various biological processes in normal and pathological states.

Sphingosylphosphorylcholine stimulates expression of fibronectin through TGF-beta1-Smad-dependent mechanism in human mesenchymal stem cells

Sphingosylphosphorylcholine (SPC) has been reported to stimulate the expression of fibronectin (FN), which plays a key role in cell recruitment and adhesion during wound healing. In a previous study, we reported that SPC induces differentiation of human adipose tissue-derived mesenchymal stem cells (hATSCs) to smooth muscle-like cell types through ERK-dependent autocrine secretion of TGF-beta1 and delayed activation of the TGF-beta1-Smad pathway. In the present study, we demonstrated that SPC dose- and time-dependently increased the expression of FN in hATSCs. Pretreatment of the cells with U0126, an MEK inhibitor, markedly attenuated the SPC-induced expression of FN and delayed phosphorylation of Smad2, suggesting that ERK is involved in the SPC induction of FN expression through activation of Smad2. In addition, the SPC-induced expression of FN and delayed activation of Smad2 were abrogated by SB-431542, a TGF-beta type I receptor kinase inhibitor, or anti-TGF-beta1 neutralizing antibody. Furthermore, the SPC-induced expression of FN was abrogated by adenoviral expression of Smad7, an inhibitory Smad, or short interference RNA (siRNA)-mediated depletion of endogenous Smad2 expression, suggesting that SPC induces the expression of FN through ERK-dependent activation of the TGF-beta1-Smad2 crosstalk pathway. Adhesion of U937 monocytic cells to hATSCs was enhanced by pretreatment of hATSCs with SPC or TGF-beta1 for 4 days, and the peptide GRGDSP (an antagonist of fibronectin receptors) blocked the adhesion of U937 cells to the hATSCs. These results led us to suggest that SPC-induced FN expression plays a pivotal role in the wound healing by stimulating adhesion and recruitment of leukocytes.

Paradoxical changes in muscle gene expression in insulin-resistant subjects after sustained reduction in plasma free fatty acid concentration

Lipid oversupply plays a role in developing insulin resistance in skeletal muscle, decreasing expression of nuclear-encoded mitochondrial genes, and increasing extracellular matrix remodeling. To determine if a decrease in plasma lipid content reverses these abnormalities, insulin-resistant subjects with a family history of type 2 diabetes had euglycemic clamps and muscle biopsies before and after acipimox treatment to suppress free fatty acids. Free fatty acids fell from 0.584 +/- 0.041 to 0.252 +/- 0.053 mmol/l (P < 0.001) and glucose disposal increased from 5.28 +/- 0.46 to 6.31 +/- 0.55 mg . kg(-1) . min(-1) (P < 0.05) after acipimox; intramuscular fatty acyl CoA decreased from 10.3 +/- 1.9 to 4.54 +/- 0.82 pmol/mg muscle (P < 0.01). Paradoxically, expression of PGC-1-and nuclear-encoded mitochondrial genes decreased after acipimox, and expression of collagens I and III alpha-subunits (82- and 21-fold increase, respectively, P < 0.05), connective tissue growth factor (2.5-fold increase, P < 0.001), and transforming growth factor-beta1 increased (2.95-fold increase, P < 0.05). Therefore, a reduction in lipid supply does not completely reverse the molecular changes associated with lipid oversupply in muscle. Changes in expression of nuclear-encoded mitochondrial genes do not always correlate with changes in insulin sensitivity.

Sphingosylphosphorylcholine-induced interleukin-6 production is mediated by protein kinase C and p42/44 extracellular signal-regulated kinase in human dermal fibroblasts

BACKGROUND

Sphingosylphosphorylcholine (SPC) has been reported as a novel lipid mediator that exerts various actions on wound healing process.

OBJECTIVE

The aim of this study is to evaluate the involvement of interleukin-6 (IL-6) in SPC-induced wound healing acceleration.

METHODS

We performed immunohistochemical analysis to demonstrate the IL-6 induction by SPC. To analyze the signaling events, skin fibroblasts were treated with SPC, and then RT-PCR, ELISA and Western blot analyses were carried out.

RESULTS

SPC markedly induced interleukin-6 (IL-6) expression in rabbit ear wound. SPC also induced IL-6 expression at both the mRNA and protein levels in human dermal fibroblasts cultured in vitro. SPC rapidly phosphorylated p42/44 extracellular signal-regulated kinase (ERK). Pretreatment with PD 98059, a specific MAPK kinase 1/2 inhibitor, markedly suppressed SPC-induced IL-6 expression in a dose-dependent manner. Protein kinase C (PKC) activation by phorbol myristate acetate (PMA) potentiated IL-6 mRNA expression, whereas PKC inhibition by bisindolylmaleimide blocked SPC-induced p42/44 ERK phosphorylation and IL-6 expression. Over-expression of PKCalpha markedly induced the IL-6 expression and p42/44 ERK activation.

CONCLUSION

These results suggest that SPC-induced IL-6 production is mediated by PKC-dependent p42/44 ERK activation in human dermal fibroblasts cultured in vitro.

Modulation by bradykinin of angiotensin type 1 receptor-evoked RhoA activation of connective tissue growth factor expression in human lung fibroblasts

The mechanisms regulating the opposing physiological actions of bradykinin (BK) and angiotensin II (AngII) are not well understood. Here we investigate signaling interactions between these two effectors. Connective tissue growth factor (CTGF) expression in IMR-90, human lung fibroblasts, is used as the endpoint target. In these cells the BK B2 receptor (BKB2R) is expressed constitutively, while no binding of AngII is detected. An inducible expression system is used to insert AngII receptor 1 (AT1R) and to obtain a signal level in response to AngII at the magnitude of BK. AngII and BK activate G protein-coupled targets, arachidonate release from cellular phospholipid stores, and intracellular phosphatidylinositol turnover equally. Both activate ERK, JNK, and p38 equally. However, AngII activates, whereas BK inactivates, RhoA. AngII induces a rapid (1 h) CTGF mRNA expression. RhoA siRNA and RhoA activation inhibitor, Y-27632, markedly reduce the AngII effect. Simultaneous treatment with BK and AngII attenuates the AT1R action. Additionally, BK in the absence of AngII lowers CTGF mRNA expression below basal levels over a span of 4 h. An AT1R/BKB2R chimera lacking heterotrimeric G protein coupling continues to activate MAP kinases to the same extent as wild-type (WT) AT1R and BKB2R. However, the increase of CTGF mRNA expression by this mutant is low, almost identical with that obtained by the simultaneous treatment of the WT AT1R-expressing cells with BK and AngII. In this context the chimeric receptor displays the characteristics of both receptors. These data demonstrate that, in human lung fibroblasts, BK modulates the action of AngII through the small G protein RhoA, but in a Galphai/Galphaq-independent manner.