Differential regulation of free-floating collagen gel contraction by human fetal and adult dermal fibroblasts in response to prostaglandin E2 mediated by an EP2/cAMP-dependent mechanism

Diversity of Mechanisms Underlying Latent TGF-β Activation in Recessive Dystrophic Epidermolysis Bullosa

Injury- and inflammation-driven progressive dermal fibrosis is a severe manifestation of recessive dystrophic epidermolysis bullosa-a genetic skin blistering disease caused by mutations in COL7A1. TGF-β activation plays a prominent part in progressing dermal fibrosis. However, the underlying mechanisms are not fully elucidated. TGF-β is secreted in a latent form, which has to be activated for its biological functions. In this study, we determined that recessive dystrophic epidermolysis bullosa fibroblasts have an enhanced capacity to activate the latent form. Mechanistic and functional assessment demonstrated that this process depends on multiple latent TGF-β activators, including TSP-1, RGD-binding integrins, matrix metalloproteinases, and ROS, which act in concert, in a self-perpetuating feedback loop to progress fibrosis. Importantly, our study also disclosed keratinocytes as prominent facilitators of fibrosis in recessive dystrophic epidermolysis bullosa. They stimulate microenvironmental latent TGF-β activation through enhanced production of the above mediators. Collectively, our study provides data on the molecular mechanism behind dysregulated TGF-β signaling in recessive dystrophic epidermolysis bullosa, which are much needed for the development of evidence-based fibrosis-delaying treatments.

Scarless wound healing: From development to senescence

An essential element of tissue homeostasis is the response to injuries, cutaneous wound healing being the most studied example. In the adults, wound healing aims at quickly restoring the barrier function of the skin, leading however to scar, a dysfunctional fibrotic tissue. On the other hand, in fetuses a scarless tissue regeneration takes place. During ageing, the wound healing capacity declines; however, in the absence of comorbidities a higher quality in tissue repair is observed. Senescent cells have been found to accumulate in chronic unhealed wounds, but more recent reports indicate that their transient presence may be beneficial for tissue repair. In this review data on skin wound healing and scarring are presented, covering the whole spectrum from early embryonic development to adulthood, and furthermore until ageing of the organism.

The altered mechanical phenotype of fetal fibroblasts hinders myofibroblast differentiation

During the dermal wound healing process, the mechanical rigidity of the newly deposited extracellular matrix and transforming growth factor‐β1 promote the transition of fibroblasts into myofibroblasts. Myofibroblasts generate large cellular forces that contract and remodel the extracellular matrix leading to scar formation. In contrast, myofibroblasts are not detected in fetal dermal wounds which are more compliant and contain less transforming growth factor‐β1 than adult wounds. Instead, fetal fibroblasts orchestrate scarless healing of dermal wounds resulting in healed tissues that resemble uninjured dermis. While these biomechanical differences suggest that the fetal wound environment promotes smaller cellular forces which enable regeneration, previous studies indicate that fetal fibroblasts have unique contractile properties that may facilitate scarless dermal repair. Therefore, we tested whether physiologic wound rigidities and transforming growth factor‐β1 induce contractile forces and myofibroblast differentiation of fetal dermal fibroblasts. In comparison to their adult dermal counterparts, we found that fetal fibroblasts exhibit a deficient contractile response to rigid extracellular matrix and transforming growth factor‐β1. Our data suggest that the contractile phenotype of fetal dermal fibroblasts limits their cellular force production and prevents their ability to differentiate into myofibroblasts.

The effects of cytosporone-B, a novel antifibrotic agent, on vocal fold fibroblasts

OBJECTIVES/HYPOTHESIS

Our laboratory recently described NR4A1 as an endogenous inhibitor of TGF-β-induced vocal fold (VF) fibrosis. Our prior report described the temporal expression of NR4A1 during VF healing in vivo and the effects of NR4A1 knockdown on fibroplastic cell activities in vitro. Based on these findings, we hypothesized that cytosporone-B (Csn-B), an NR4A1 agonist, may hold significant therapeutic potential.

STUDY DESIGN

In vitro.

METHODS

Human VF fibroblasts were exposed to TGF-β1+/-Csn-B. Expression of genes related to fibrosis were quantified. In addition, contraction was assayed as a surrogate for the fibrotic phenotype in our cell line.

RESULTS

TGF-B1 stimulated COL1A1 and ACTA2, as expected. Csn-B significantly downregulated TGF-β1-mediated upregulation of these genes (P = .009, P = .03, respectively). Csn-B had no effect on genes related to TGF-β/Smad signaling. Csn-B also decreased the TGF-β1-mediated contractile phenotype in our cells (P = .004).

CONCLUSIONS

NR4A1 is an endogenous inhibitor of fibrosis in the vocal folds and Csn-B, as an NR4A1 agonist, may evolve as an ideal, therapeutic candidate for this challenging condition.

LEVEL OF EVIDENCE

NA Laryngoscope, 128:E425-E428, 2018.

The Contractile Phenotype of Dermal Fetal Fibroblasts in Scarless Wound Healing

PURPOSE OF REVIEW

Injured skin in the mammalian fetus can heal regeneratively due to the ability of fetal fibroblasts to effectively reorganize the extracellular matrix (ECM). This process occurs without fetal fibroblasts differentiating into highly contractile myofibroblasts which cause scarring and fibrosis in adult wounds. Here, we provide a brief review of fetal wound healing and the evidence supporting a unique contractile phenotype in fetal fibroblasts. Furthermore, we discuss the biomechanical role of the ECM in driving myofibroblast differentiation in wound healing and the implications for new clinical modalities based on the biophysical properties of fetal fibroblasts.

RECENT FINDINGS

We and others have found that fetal fibroblasts are refractory to the environmental stimuli necessary for myofibroblast differentiation in adult wound healing including mechanical stress.

SUMMARY

Understanding the biomechanical mechanisms that regulate the contractile phenotype of fetal fibroblasts may unlock new avenues for anti-scarring therapies that target myofibroblast differentiation of adult fibroblasts.

Stem Cell-Mediated Paracrine Signaling Alters Fibroplasia in Human Vocal Fold Fibroblasts in Vitro

OBJECTIVES

Interactions between mesenchymal stem cells (MSCs) and native vocal fold fibroblasts (VFFs) have not been described in spite of promising preliminary data regarding the effects of MSCs on vocal fold repair in vivo. The current study employed a conditioned media (CM) model to investigate the paracrine effects of bone marrow-derived mesenchymal stem cells (BMSCs) on VFFs.

METHODS

Human VFFs were treated with transforming growth factor-β1 (TGF-β1; 10 ng/mL), CM from human BMSCs following 48 hours of TGF-β1 stimulation, or CM+TGF-β1. Proliferation, immunocytochemistry for alpha smooth muscle actin (αSMA), migration, and collagen gel contraction were quantified as well as transcription of components of the TGF-β signaling pathway.

RESULTS

Transforming growth factor-β1 accelerated proliferation and induced αSMA in VFFs; these effects were suppressed with CM ( P = .009, P < .001, respectively). The CM+TGF-β1 condition increased cell migration ( P = .02) and decreased gel contraction; CM+TGF-β1 also inhibited TGF-β signaling via significant upregulation of NR4A1 as well as downregulation of S MAD3 and TGF-β1 relative to TGF-β1 stimulation in the absence of CM ( P = .002, P < .001, and P = .005, respectively).

CONCLUSIONS

Conditioned media affected many profibrotic cell activities in TGF-β1-stimulated VFFs, likely related to altered TGF-β signaling. These data provide preliminary insight regarding the antifibrotic effects of MSCs and further support their progression to clinical utility.

NR4A1 is an endogenous inhibitor of vocal fold fibrosis

OBJECTIVES/HYPOTHESIS

NR4A1 was recently identified as an endogenous inhibitor of transforming growth factor (TGF)-β-induced fibrosis, and the role of this nuclear receptor has not been elucidated in tissue health or the response to injury in the vocal folds. Given the clinical implications of vocal fold fibrosis, we investigated NR4A1 expression during vocal fold wound healing in vivo and the regulatory roles of NR4A1 on vocal fold fibroblasts (VFFs) in vitro with the ultimate goal of developing targeted therapies for this challenging patient population.

STUDY DESIGN

In vivo and in vitro.

METHODS

In vivo, the temporal pattern of NR4A1 mRNA expression was quantified following rat vocal fold injury. In vitro, the role of NR4A1 on TGF-β1-mediated transcription of genes underlying fibrosis as well as myofibroblast differentiation and collagen gel contraction was quantified in our human VFF line. Small interfering RNA was employed to alter NR4A1 expression to further elucidate this complex system.

RESULTS

Nr4a1 mRNA increased 1 day after injury and peaked at 7 days. Knockdown of NR4A1 resulted in upregulation of COL1A1 and TGF-β1, with TGF-β1 stimulation (both P < .001) in VFFs. NR4A1 knockdown also resulted in increased α-smooth muscle actin-positive cells (P = .013) and contraction (P = .002) in response to TGF-β1.

CONCLUSIONS

NR4A1 has not been described in vocal fold health or disease. Upregulation of TGF-β following vocal fold injury was concurrent with increased NR4A1 expression. These data provide a foundation for the development of therapeutic strategies given persistent TGF-β signaling in vocal fold fibrosis.

LEVEL OF EVIDENCE

N/A Laryngoscope, 127:E317-E323, 2017.

The role of Smad3 in the fibrotic phenotype in human vocal fold fibroblasts

OBJECTIVES/HYPOTHESIS

To investigate the role of Smad3 as a regulator of transforming growth factor (TGF)-β1-mediated cell activities associated with fibrosis in normal human vocal fold fibroblasts. We also sought to confirm the temporal stability of Smad3 knockdown via small inhibitor ribonucleic acid (siRNA). Vocal fold fibroblasts were employed to determine the effects of Smad3 knockdown on TGF-β1-mediated migration and contraction, as well as regulation of connective tissue growth factor (CTGF). We hypothesized that Smad3 is an ideal candidate for therapeutic manipulation in vivo based on its role in fibrosis.

STUDY DESIGN

In vitro.

METHODS

Knockdown of Smad3 via siRNA was performed in our normal human vocal fold cell line. Three-dimensional collagen gel contraction and scratch assays were employed to determine the role of Smad3 on TGF-β1-mediated contraction and migration, respectively. The role Smad3 in the induction of CTGF was characterized via sodium dodecyl sulfate polyacrylamide gel electrophoresis. The effects of Smad3 signaling on Smad7 messenger (m)RNA and protein were also quantified.

RESULTS

Smad3 knockdown was temporally-stable up to 72 hours (P < 0.001), diminished TGF-β1-mediated collagen gel contraction and migration, and blunted induction of CTGF, but it had no effect on TGF-β1-mediated Smad7 mRNA or protein induction.

CONCLUSION

Transforming growth factor-β1 stimulated profibrotic cell activities in our cell line and these actions were largely reduced with Smad3 knockdown. These data provide continued support for therapeutic targeting of Smad3 for vocal fold fibrosis because it appears to regulate the fibrotic phenotype.

LEVEL OF EVIDENCE

N/A. Laryngoscope, 126:1151-1156, 2016.

Cigarette smoke condensate inhibits collagen gel contraction and prostaglandin E2 production in human gingival fibroblasts

BACKGROUND

Granulation tissue remodeling and myofibroblastic differentiation are critically important events during wound healing. Tobacco smoking has a detrimental effect in gingival tissue repair. However, studies evaluating the effects of cigarette smoke on these events are lacking.

MATERIAL AND METHODS

We used gingival fibroblasts cultured within free-floating and restrained collagen gels to simulate the initial and final steps of the granulation tissue phase during tissue repair. Collagen gel contraction was stimulated with serum or transforming growth factor-β1. Cigarette smoke condensate (CSC) was used to evaluate the effects of tobacco smoke on gel contraction. Protein levels of alpha-smooth muscle actin, β1 integrin, matrix metalloproteinase-3 and connective tissue growth factor were evaluated through Western blot. Prostaglandin E(2) (PGE(2)) levels were determined through ELISA. Actin organization was evaluated through confocal microscopy.

RESULTS

CSC reduced collagen gel contraction induced by serum and transforming growth factor-β1 in restrained collagen gels. CSC also altered the development of actin stress fibers in fibroblasts cultured within restrained collagen gels. PGE(2) levels were strongly diminished by CSC in three-dimensional cell cultures. However, other proteins involved in granulation tissue remodeling and myofibroblastic differentiation such as alpha-smooth muscle actin, β1 integrin, matrix metalloproteinase-3 and connective tissue growth factor, were unmodified by CSC.

CONCLUSIONS

CSC may alter the capacity of gingival fibroblasts to remodel and contract a collagen matrix. Inhibition of PGE(2) production and alterations of actin stress fibers in these cells may impair proper tissue maturation during wound healing in smokers.

Fetal wound healing biomarkers

Fetal skin has the intrinsic capacity for wound healing, which is not correlated with the intrauterine environment. This intrinsic ability requires biochemical signals, which start at the cellular level and lead to secretion of transforming factors and expression of receptors, and specific markers that promote wound healing without scar formation. The mechanisms and molecular pathways of wound healing still need to be elucidated to achieve a complete understanding of this remodeling system. The aim of this paper is to discuss the main biomarkers involved in fetal skin wound healing as well as their respective mechanisms of action.

Skin wound healing and scarring: fetal wounds and regenerative restitution

The adverse physiological and psychological effects of scars formation after healing of wounds are broad and a major medical problem for patients. In utero, fetal wounds heal in a regenerative manner, though the mechanisms are unknown. Differences in fetal scarless regeneration and adult repair can provide key insight into reduction of scarring therapy. Understanding the cellular and extracellular matrix alterations in excessive adult scarring in comparison to fetal scarless healing may have important implications. Herein, we propose that matrix can be controlled via cellular therapy to resemble a fetal-like matrix that will result in reduced scarring.

Increase in cellular cyclic AMP concentrations reverses the profibrogenic phenotype of cardiac myofibroblasts: a novel therapeutic approach for cardiac fibrosis

Tissue fibrosis is characterized by excessive production, deposition, and contraction of the extracellular matrix (ECM). The second messenger cAMP has antifibrotic effects in fibroblasts from several tissues, including cardiac fibroblasts (CFs). Increased cellular cAMP levels can prevent the transformation of CFs into profibrogenic myofibroblasts, a critical step that precedes increased ECM deposition and tissue fibrosis. Here we tested two hypotheses: 1) myofibroblasts have a decreased ability to accumulate cAMP in response to G protein-coupled receptor (GPCR) agonists, and 2) increasing cAMP will not only prevent, but also reverse, the myofibroblast phenotype. We found that myofibroblasts produce less cAMP in response to GPCR agonists or forskolin and have decreased expression of several adenylyl cyclase (AC) isoforms and increased expression of multiple cyclic nucleotide phosphodiesterases (PDEs). Furthermore, we found that forskolin-promoted increases in cAMP or N(6)-phenyladenosine-cAMP, a protein kinase A-selective analog, reverse the myofibroblast phenotype, as assessed by the expression of collagen Iα1, α-smooth muscle actin, plasminogen activator inhibitor-1, and cellular contractile abilities, all hallmarks of a fibrogenic state. These results indicate that: 1) altered expression of AC and PDE isoforms yield a decrease in cAMP concentrations of cardiac myofibroblasts (relative to CFs) that likely contributes to their profibrotic state, and 2) approaches to increase cAMP concentrations not only prevent fibroblast-to-myofibroblast transformation but also can reverse the profibrotic myofibroblastic phenotype. We conclude that therapeutic strategies designed to enhance cellular cAMP concentrations in CFs may provide a means to reverse excessive scar formation following injury and to treat cardiac fibrosis.

cAMP and Epac in the regulation of tissue fibrosis

Fibrosis, the result of excess deposition of extracellular matrix (ECM), in particular collagen, leads to scarring and loss of function in tissues that include the heart, lung, kidney and liver. The second messenger cAMP can inhibit the formation and extent of ECM during this late phase of inflammation, but the mechanisms for these actions of cAMP and of agents that elevate tissue cAMP levels are not well understood. In this article, we review the fibrotic process and focus on two recently recognized aspects of actions of cAMP and its effector Epac (Exchange protein activated by cAMP): (a) blunting of epithelial-mesenchymal transformation (EMT) and (b) down-regulation of Epac expression by profibrotic agents (e.g. TGF-β, angiotensin II), which may promote tissue fibrosis by decreasing Epac-mediated antifibrotic actions. Pharmacological approaches that raise cAMP or blunt the decrease in Epac expression by profibrotic agents may thus be strategies to block or perhaps reverse tissue fibrosis. LINKED ARTICLES This article is part of a themed section on Novel cAMP Signalling Paradigms. To view the other articles in this section visit http://dx.doi.org/10.1111/bph.2012.166.issue-2.

A review of fetal scarless healing

Wound healing is a complex process involving a number of processes. Fetal regeneration has been shown to have a number of differences compared to scar-forming healing. This review discusses the number of differences identified in fetal regeneration. Understanding these differences may result in new therapeutic targets which may reduce or even prevent scarring in adult healing.

International Union of Basic and Clinical Pharmacology. LXXXIII: classification of prostanoid receptors, updating 15 years of progress

It is now more than 15 years since the molecular structures of the major prostanoid receptors were elucidated. Since then, substantial progress has been achieved with respect to distribution and function, signal transduction mechanisms, and the design of agonists and antagonists (http://www.iuphar-db.org/DATABASE/FamilyIntroductionForward?familyId=58). This review systematically details these advances. More recent developments in prostanoid receptor research are included. The DP(2) receptor, also termed CRTH2, has little structural resemblance to DP(1) and other receptors described in the original prostanoid receptor classification. DP(2) receptors are more closely related to chemoattractant receptors. Prostanoid receptors have also been found to heterodimerize with other prostanoid receptor subtypes and nonprostanoids. This may extend signal transduction pathways and create new ligand recognition sites: prostacyclin/thromboxane A(2) heterodimeric receptors for 8-epi-prostaglandin E(2), wild-type/alternative (alt4) heterodimers for the prostaglandin FP receptor for bimatoprost and the prostamides. It is anticipated that the 15 years of research progress described herein will lead to novel therapeutic entities.

Differential effects of prostaglandin E(2) and enamel matrix derivative on the proliferation of human gingival and dermal fibroblasts and gingival keratinocytes

BACKGROUND AND OBJECTIVE

Elevated levels of prostaglandins contribute to periodontal destruction but can impair gingival healing by affecting local fibroblasts. Enamel matrix derivative (EMD) has beneficial effects on supporting and gingival tissues. We showed that prostaglandin E(2) (PGE(2) ) inhibits the proliferation of human gingival fibroblasts (hGFs) and that EMD stimulates it. Prostaglandins and EMD may also affect skin healing by targeting dermal fibroblasts (DFs). Thus, we compared the effects of these two agents on the proliferation of hGFs, human gingival keratinocytes (hGKs) and hDFs.

MATERIAL AND METHODS

Cells from healthy human gingiva or skin were treated with PGE(2) and/or EMD, and proliferation was assessed by measuring cell number and DNA synthesis.

RESULTS

In hGFs, PGE(2) (1 μm) inhibited proliferation while EMD stimulated it. When present together, EMD abolished the PGE(2) -induced inhibition. Serum increased (by a factor of 10) the amount of phosphorylated extracellular signal-regulated kinase (p-ERK), PGE(2) reduced it (by 70-80%) and EMD restored it when present with PGE(2). Prostaglandin E(2) stimulated cAMP production in hGFs while serum or EMD did not. Enamel matrix derivative stimulated hDF proliferation, but the inhibitory effect of PGE(2) was milder than with hGFs. When present together, EMD abolished the PGE(2) -induced inhibition. Enamel matrix derivative inhibited the proliferation of primary hGKs, but PGE(2) had no effect. Finally, we found that hDFs contained about five times less prostaglandin EP(2) receptor mRNA than hGFs, while hGKs contained none.

CONCLUSION

Prostaglandin E(2) inhibits and EMD stimulates hGF proliferation via distinct pathways. The different sensitivities of hDFs and hGKs to PGE(2) can be explained by the levels of EP(2) expression.

Prostaglandin E2 differentially regulates contraction and structural reorganization of anchored collagen gels by human adult and fetal dermal fibroblasts

Contraction and remodeling of granulation tissue by fibroblasts is a crucial component of dermal wound healing. Postnatal wounds heal with imperfect repair and scar formation, whereas tissue repair in fetal wounds is regenerative. Prostaglandin E2 (PGE2) modulates the behavior of fibroblasts in the wound bed. This study was designed to investigate the mechanism by which PGE2 regulates an in vitro model of granulation tissue, anchored collagen gels, by human adult and fetal dermal fibroblasts. We hypothesized that PGE2 differentially regulates contraction and remodeling of anchored collagen gels by these fibroblast phenotypes. These results indicate that once tension was generated, fetal fibroblasts exerted lower contractile forces resulting in less collagen contraction. This coincided with less prominent stress fibers, yet fetal fibroblasts were able to substantially remodel the collagen architecture. This mechanism was differentially modulated by PGE2 and was mimicked with a PGE2 receptor agonist, indicating a cyclic adenosine monophosphate (cAMP)-dependent mechanism through the EP2 receptor. However, direct up-regulation of cAMP led to decreases in contraction and remodeling by both fibroblast phenotypes indicating an altered signaling pathway. Therefore, targeting cAMP via the EP2 receptor could potentially decrease adult fibroblast contractile forces to the levels of the fetal fibroblast phenotype in order to decrease dermal scarring.