Kynurenine increases matrix metalloproteinase-1 and -3 expression in cultured dermal fibroblasts and improves scarring in vivo

Determination of Bioactive Compound Kynurenic Acid in Linum usitatissimum L

Kynurenic acid (KYNA) is a bioactive compound exhibiting multiple actions and positive effects on human health due to its antioxidant, anti-inflammatory and neuroprotective properties. KYNA has been found to have a beneficial effect on wound healing and the prevention of scarring. Despite notable progress in the research focused on KYNA observed during the last 10 years, KYNA's presence in flax (Linum usitatissimum L.) has not been proven to date. In the present study, parts of flax plants were analysed for KYNA synthesis. Moreover, eight different cultivars of flax seeds were tested for the presence of KYNA, resulting in a maximum of 0.432 µg/g FW in the seeds of the cultivar Jan. The level of KYNA was also tested in the stems and roots of two selected flax cultivars: an oily cultivar (Linola) and a fibrous cultivar (Nike). The exposure of plants to the KYNA precursors tryptophan and kynurenine resulted in higher levels of KYNA accumulation in flax shoots and roots. Thus, the obtained results indicate that KYNA might be synthesized in flax. The highest amount of KYNA (295.9 µg/g dry weight [DW]) was detected in flax roots derived from plants grown in tissue cultures supplemented with tryptophan. A spectroscopic analysis of KYNA was performed using the FTIR/ATR method. It was found that, in tested samples, the characteristic KYNA vibration bands overlap with the bands corresponding to the vibrations of biopolymers (especially pectin and cellulose) present in flax plants and fibres.

Different Kynurenine Pathway Dysregulation in Systemic Sclerosis in Men and Women

Systemic sclerosis (SSc), a predominantly female-affected systemic autoimmune disease, requires tailored treatment strategies contingent on organ involvement and symptom severity. Given SSc's inflammatory nature, the involvement of the kynurenine pathway (KP) in its pathophysiology is underexplored. Our study aimed to investigate sex-related differences in KP activation among SSc patients and assess the impact of angiotensin-converting enzyme (ACE) inhibitors and estimated glomerular filtration rate (eGFR) on KP metabolite concentrations. We enrolled 48 SSc patients and 53 healthy controls, quantifying KP metabolites (tryptophan (TRP), kynurenine (KYN), and kynurenic acid (KYNA)) in serum via high-performance liquid chromatography. Separate multivariate analyses of covariance (MANCOVAs) for women and men were performed to ascertain mean differences between patients and healthy controls while correcting for age. For our secondary objective, we conducted a MANCOVA to explore disparities in ACE inhibitor users and non-users among patients, with BMI correction. Our findings revealed decreased TRP concentrations but increased KYNA/TRP ratio and KYN/TRP ratio in both male and female SSc patients compared to their respective controls. Unlike women, SSc males exhibited higher KYN concentrations and decreased KYNA/KYN ratio relative to their controls. Additionally, SSc patients using ACE inhibitors had higher serum KYNA levels than non-users. Notably, we established a significant correlation between eGFR and KYNA in SSc patients. These results indicate differential KP activation in male and female SSc patients, with males demonstrating heightened KP activation. While ACE inhibitors may influence the KP in SSc patients, further research is necessary to comprehensively understand their impact on symptoms and prognosis in the context of these KP alterations.

The adipose-derived stem cell peptide ADSCP2 alleviates hypertrophic scar fibrosis via binding with pyruvate carboxylase and remodeling the metabolic landscape

AIM

The purpose of this study was to investigate the function and mechanism of a novel peptide derived from adipose-derived stem cell-conditioned medium (ADSC-CM).

METHODS

Mass spectrometry was applied to identify expressed peptides in ADSC-CM obtained at different time points. The cell counting kit-8 assay and quantitative reverse transcription polymerase chain reactions were performed to screen the functional peptides contained within ADSC-CM. RNA-seq, western blot, a back skin excisional model of BALB/c mice, the peptide pull-down assay, rescue experiments, untargeted metabolomics, and mixOmics analysis were performed to thoroughly understand the functional mechanism of selected peptide.

RESULTS

A total of 93, 827, 1108, and 631 peptides were identified in ADSC-CM at 0, 24, 48, and 72 h of conditioning, respectively. A peptide named ADSCP2 (DENREKVNDQAKL) derived from ADSC-CM inhibited collagen and ACTA2 mRNAs in hypertrophic scar fibroblasts. Moreover, ADSCP2 facilitated wound healing and attenuated collagen deposition in a mouse model. ADSCP2 bound with the pyruvate carboxylase (PC) protein and inhibited PC protein expression. Overexpressing PC rescued the reduction in collagen and ACTA2 mRNAs caused by ADSCP2. Untargeted metabolomics identified 258 and 447 differential metabolites in the negative and positive mode, respectively, in the ADSCP2-treated group. The mixOmics analysis, which integrated RNA-seq and untargeted metabolomics data, provided a more holistic view of the functions of ADSCP2.

CONCLUSION

Overall, a novel peptide derived from ADSC-CM, named ADSCP2, attenuated hypertrophic scar fibrosis in vitro and in vivo, and the novel peptide ADSCP2 might be a promising drug candidate for clinical scar therapy.

Dendritic cell-expressed IDO alleviates atherosclerosis by expanding CD4+CD25+Foxp3+Tregs through IDO-Kyn-AHR axis

Atherosclerosis is a chronic inflammatory disease, in which immune disorders constitute an essential part of vascular pathogenesis. Accumulating evidence indicates that dendritic cells (DCs) and their tryptophan metabolisms regulate host immune responses. However, the mechanistic involvement of metabolic products from DCs in dysregulating vascular immunity during the development of atherosclerosis is far from clear. Flow cytometry examination showed immune cells were accumulated and gradually increased in the atherosclerotic lesions during the atherosclerosis progression, in which IDO⁺DCs were enriched. To study the role of DC-expressed IDO in the development of atherosclerosis, we made a stable IDO-overexpressing DC line (IDO^oeDCs) by lentiviral infection for adoptive transfer into pro-atherosclerotic mice. Compared with DCs containing empty vector (Vector^CtrlDC)-treated group, treatment of IDO^oeDCs led to a significant reduction of atherosclerotic lesions in the aorta, with decreased aortic infiltration of Th1 immune cells and reduced vascular inflammation. Importantly, IDO^oeDCs increased aortic kynurenine (Kyn) concentration and aryl hydrocarbon receptor (AHR) expression, concomitant with CD4⁺CD25⁺Foxp3⁺Treg expansion in the aortic tissues, which were abrogated by AHR antagonist treatment. These results indicate that DC-expressed IDO reduces atherosclerotic lesions by inducing aortic CD4⁺CD25⁺Foxp3⁺Treg expansion through IDO-Kyn-AHR axis, which may represent a novel possibility for treatment or prevention of atherosclerosis.

Peptide deregulated in hypertrophic scar-1 alleviates hypertrophic scar fibrosis by targeting focal adhesion kinase and pyruvate kinase M2 and remodeling the metabolic landscape

Hypertrophic scarring is a fibrotic skin disease characterized by excessive deposition of collagens. Emerging evidence has suggested important roles for peptides in fibrosis-related diseases. Here, we demonstrate that a skin-derived endogenous peptide, peptide deregulated in hypertrophic scar-1 (PDHS1), with the sequence IATTTASAATAAAIGATPRAK, inhibits cell proliferation, promotes apoptosis, decreases the proportion of cells in S phase, and decreases collagen synthesis in hypertrophic scar fibroblasts. Additionally, treatment with PDHPS1 alleviates hypertrophic scarring in a rabbit ear model. PDHPS1 was found to bind to focal adhesion kinase (FAK) and to decrease its activity. PDHPS1 was also shown to bind to pyruvate kinase M2 (PKM2) and to decreased its expression. Smad2 phosphorylation is also inhibited by treatment with PDHPS1. Overexpression of FAK rescues the decreased expression of COL3A1 induced by PDHPS1 treatment. Targeted metabolomics revealed that PDHPS1 reprogramed metabolism that related to amino acid synthesis, leading to decreases of the key glycolysis intermediates glucose-6-phosphate and fructose-6-phosphate. These results demonstrated that the endogenous peptide PDHPS1 alleviates hypertrophic scar fibrosis in vitro and in vivo by targeting FAK and PKM2 and remodeling the metabolic landscape. Overall, treatment with PDHPS1 is a potential therapeutic strategy for hypertrophic scarring.

Ongoing Clinical Trials in Aging-Related Tissue Fibrosis and New Findings Related to AhR Pathways

Fibrosis is a pathological manifestation of wound healing that replaces dead/damaged tissue with collagen-rich scar tissue to maintain homeostasis, and complications from fibrosis contribute to nearly half of all deaths in the industrialized world. Ageing is closely associated with a progressive decline in organ function, and the prevalence of tissue fibrosis dramatically increases with age. Despite the heavy clinical and economic burden of organ fibrosis as the population ages, to date, there is a paucity of therapeutic strategies that are specifically designed to slow fibrosis. Aryl hydrocarbon receptor (AhR) is an environment-sensing transcription factor that exacerbates aging phenotypes in different tissues that has been brought back into the spotlight again with economic development since AhR could interact with persistent organic pollutants derived from incomplete waste combustion. In addition, gut microbiota dysbiosis plays a pivotal role in the pathogenesis of numerous diseases, and microbiota-associated tryptophan metabolites are dedicated contributors to fibrogenesis by acting as AhR ligands. Therefore, a better understanding of the effects of tryptophan metabolites on fibrosis modulation through AhR may facilitate the exploitation of new therapeutic avenues for patients with organ fibrosis. In this review, we primarily focus on how tryptophan-derived metabolites are involved in renal fibrosis, idiopathic pulmonary fibrosis, hepatic fibrosis and cardiac fibrosis. Moreover, a series of ongoing clinical trials are highlighted.

Aryl Hydrocarbon Receptor Mechanisms Affecting Chronic Kidney Disease

The aryl hydrocarbon receptor (AHR) is a basic helix-loop-helix transcription factor that binds diverse endogenous and xenobiotic ligands, which regulate AHR stability, transcriptional activity, and cell signaling. AHR activity is strongly implicated throughout the course of chronic kidney disease (CKD). Many diverse organic molecules bind and activate AHR and these ligands are reported to either promote glomerular and tubular damage or protect against kidney injury. AHR crosstalk with estrogen, peroxisome proliferator-activated receptor-γ, and NF-κB pathways may contribute to the diversity of AHR responses during the various forms and stages of CKD. The roles of AHR in kidney fibrosis, metabolism and the renin angiotensin system are described to offer insight into CKD pathogenesis and therapies.

Tryptophan Catabolism and Inflammation: A Novel Therapeutic Target For Aortic Diseases

Aortic diseases are the primary public health concern. As asymptomatic diseases, abdominal aortic aneurysm (AAA) and atherosclerosis are associated with high morbidity and mortality. The inflammatory process constitutes an essential part of a pathogenic cascade of aortic diseases, including atherosclerosis and aortic aneurysms. Inflammation on various vascular beds, including endothelium, smooth muscle cell proliferation and migration, and inflammatory cell infiltration (monocytes, macrophages, neutrophils, etc.), play critical roles in the initiation and progression of aortic diseases. The tryptophan (Trp) metabolism or kynurenine pathway (KP) is the primary way of degrading Trp in most mammalian cells, disturbed by cytokines under various stress. KP generates several bioactive catabolites, such as kynurenine (Kyn), kynurenic acid (KA), 3-hydroxykynurenine (3-HK), etc. Depends on the cell types, these metabolites can elicit both hyper- and anti-inflammatory effects. Accumulating evidence obtained from various animal disease models indicates that KP contributes to the inflammatory process during the development of vascular disease, notably atherosclerosis and aneurysm development. This review outlines current insights into how perturbed Trp metabolism instigates aortic inflammation and aortic disease phenotypes. We also briefly highlight how targeting Trp metabolic pathways should be considered for treating aortic diseases.

Tryptophan-Kynurenine Pathway in COVID-19-Dependent Musculoskeletal Pathology: A Minireview

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) causes coronavirus disease 2019 (COVID-19), affecting multiple organ systems, including the respiratory tract and lungs. Several studies have reported that the tryptophan-kynurenine pathway is altered in COVID-19 patients. The tryptophan-kynurenine pathway plays a vital role in regulating inflammation, metabolism, immune responses, and musculoskeletal system biology. In this minireview, we surmise the effects of the kynurenine pathway in COVID-19 patients and how this pathway might impact muscle and bone biology.

Local Inhibition of Indoleamine 2,3-Dioxygenase Mitigates Renal Fibrosis

Chronic kidney disease (CKD) is a major global health concern and renal fibrosis is an integral part of the pathophysiological mechanism underlying disease progression. In CKD patients, the majority of metabolic pathways are in disarray and perturbations in enzyme activity most likely contribute to the wide variety of comorbidities observed in these patients. To illustrate, catabolism of tryptophan by indoleamine 2,3-dioxygenase (IDO) gives rise to numerous biologically active metabolites implicated in CKD progression. Here, we evaluated the effect of antagonizing IDO on renal fibrogenesis. To this end, we antagonized IDO using 1-methyl-D-tryptophan (1-MT) and BMS-98620 in TGF-β-treated murine precision-cut kidney slices (mPCKS) and in mice subjected to unilateral ureteral obstruction (UUO). The fibrotic response was evaluated on both the gene and protein level using qPCR and western blotting. Our results demonstrated that treatment with 1-MT or BMS-985205 markedly reduced TGF-β-mediated fibrosis in mPCKS, as seen by a decreased expression of collagen type 1, fibronectin, and α-smooth muscle actin. Moreover, IDO protein expression clearly increased following UUO, however, treatment of UUO mice with either 1-MT or BMS-986205 did not significantly affect the gene and protein expression of the tested fibrosis markers. However, both inhibitors significantly reduced the renal deposition of collagen in UUO mice as shown by Sirius red and trichrome staining. In conclusion, this study demonstrates that IDO antagonism effectively mitigates fibrogenesis in mPCKS and reduces renal collagen accumulation in UUO mice. These findings warrant further research into the clinical application of IDO inhibitors for the treatment of renal fibrosis.

Validation strategies for identifying drug targets in dermal fibrotic disorders

Fibrotic skin disorders, such as keloid disease (KD), are common clinically challenging disorders with unknown etiopathogenesis and ill-defined treatment strategies that affect millions of people worldwide. Thus, there is an urgent need to discover novel therapeutics. The validation of potential drug targets is an obligatory step in discovering and developing new therapeutic agents for the successful treatment of dermal fibrotic conditions, such as KD. The integration of multi-omics data with traditional and modern technological approaches, such as RNA interference (RNAi) and genome-editing tools, would provide unique opportunities to identify and validate novel targets in KD during early drug development. Thus, in this review, we summarize the current and emerging drug discovery process with a focus on validation strategies of potential drug targets identified in dermal fibrosis.

Bioinformatic Analysis Reveals Central Role for Tumor-Infiltrating Immune Cells in Uveal Melanoma Progression

Tumor-infiltrating immune cells are capable of effective cancer surveillance, and their abundance is linked to better prognosis in numerous tumor types. However, in uveal melanoma (UM), extensive immune infiltrate is associated with poor survival. This study aims to decipher the role of different tumor-infiltrating cell subsets in UM in order to identify potential targets for future immunotherapeutic treatment. We have chosen the TCGA-UVM cohort as a training dataset and GSE22138 as a testing dataset by mining publicly available databases. The abundance of 22 immune cell types was estimated using CIBERSORTx. Then, to determine the significance of tumor-infiltrating cell subsets in UM, we built a multicell type prognostic signature, which was validated in the testing cohort. The created signature was built upon the negative prognostic role of CD8+ T cells and M0 macrophages and the positive role of neutrophils. Based on the created signature score, we divided the patients into low- and high-risk groups. Kaplan-Meier, Cox, and ROC analyses demonstrated superior performance of our risk score compared to either clinical or pathologic characteristics of both cohorts. Further, we found the molecular pathways associated with cancer immunoevasion and metastasis to be enriched in the high-risk group, explaining both the lack of adequate immune surveillance despite increased infiltration of CD8+ T cells as well as the higher metastatic potential. Genes associated with tryptophan metabolism (IDO1 and KYNU) and metalloproteinases were among the most differentially expressed between the high- and low-risk groups. Our correlation analyses interpreted in context of published in vitro data strongly suggest the central role of CD8+ T cells in shifting the UM tumor microenvironment towards suppressive and metastasis-promoting. Therefore, we propose further investigations of IDO1 and metalloproteinases as novel targets for immunotherapy in lymphocyte-rich metastatic UM patients.

Tryptophan catabolism is dysregulated in leiomyomas

OBJECTIVE

To determine the expression and functional roles of indoleamine 2,3-dioxygenase 1 (IDO1) and tryptophan 2,3-dioxygenase (TDO2) in leiomyoma.

DESIGN

Experimental study.

SETTING

Academic research laboratory.

PATIENT(S)

Women undergoing hysterectomy for leiomyoma.

INTERVENTION(S)

Blockade of IDO1 and TDO2.

MAIN OUTCOME MEASURE(S)

Expression of IDO1 and TDO2 in leiomyoma and the effects of their inhibitors on the extracellular matrix.

RESULT(S)

Leiomyoma expressed significantly higher levels of IDO1 and TDO2 messenger ribonucleic acid (mRNA; 60.3%, 35/58 pairs and 98.3%, 57/58 pairs, respectively) and protein (54%, 27/50 pairs and 92%, 46/50 pairs, respectively) as well as the enzyme activity marker kynurenine (78.3%, 36/46 pairs for IDO1/TDO2) compared with levels in matched myometrium. The expression of TDO2 but not IDO1 mRNA was significantly higher in fibroids from African American compared with that in Caucasian and Hispanic patients. The TDO2 but not the IDO1 protein and mRNA levels were more abundant in fibroids bearing the MED12 mutation compared with results in wild-type leiomyomas. Treatment of leiomyoma smooth muscle cell and myometrial smooth muscle cell spheroids with the TDO2 inhibitor 680C91 but not the IDO1 inhibitor epacadostat significantly repressed cell proliferation and the expression of collagen type I (COL1A1) and type III (COL3A1) in a dose-dependent manner; these effects were more pronounced in leiomyoma smooth muscle cells compared with myometrial smooth muscle cell spheroids.

CONCLUSION(S)

These results underscore the physiological significance of the tryptophan degradation pathway in the pathogenesis of leiomyomas and the potential utility of anti-TDO2 drugs for treatment of leiomyomas.

Current Approaches Targeting the Wound Healing Phases to Attenuate Fibrosis and Scarring

Cutaneous fibrosis results from suboptimal wound healing following significant tissue injury such as severe burns, trauma, and major surgeries. Pathologic skin fibrosis results in scars that are disfiguring, limit normal movement, and prevent patient recovery and reintegration into society. While various therapeutic strategies have been used to accelerate wound healing and decrease the incidence of scarring, recent studies have targeted the molecular regulators of each phase of wound healing, including the inflammatory, proliferative, and remodeling phases. Here, we reviewed the most recent literature elucidating molecular pathways that can be targeted to reduce fibrosis with a particular focus on post-burn scarring. Current research targeting inflammatory mediators, the epithelial to mesenchymal transition, and regulators of myofibroblast differentiation shows promising results. However, a multimodal approach addressing all three phases of wound healing may provide the best therapeutic outcome.

Immunometabolic Network Interactions of the Kynurenine Pathway in Cutaneous Malignant Melanoma

Dysregulation of the kynurenine pathway has been regarded as a mechanism of tumor immune escape by the enzymatic activity of indoleamine 2, 3 dioxygenase and kynurenine production. However, the immune-modulatory properties of other kynurenine metabolites such as kynurenic acid, 3-hydroxykynurenine, and anthranilic acid are poorly understood. In this study, plasma from patients diagnosed with metastatic cutaneous malignant melanoma (CMM) was obtained before (PRE) and during treatment (TRM) with inhibitors of mitogen-activated protein kinase pathway (MAPKIs). Immuno-oncology related protein profile and kynurenine metabolites were analyzed by proximity extension assay (PEA) and LC/MS-MS, respectively. Correlation network analyses of the data derived from PEA and LC/MS-MS identified a set of proteins that modulate the differentiation of Th1 cells, which is linked to 3-hydroxykynurenine levels. Moreover, MAPKIs treatments are associated with alteration of 3-hydroxykynurenine and 3hydroxyanthranilic acid (3HAA) concentrations and led to higher "CXCL11," and "KLRD1" expression that are involved in T and NK cells activation. These findings imply that the kynurenine pathway is pathologically relevant in patients with CMM.

ERK1/ATF-2 signaling axis contributes to interleukin-1β-induced MMP-3 expression in dermal fibroblasts

Matrix metalloproteinases (MMPs) play a pivotal role in tissue remodeling by degrading the extracellular matrix (ECM) components. This mechanism is implicated in a variety of physiological and pathological cellular processes including wound healing. One of the key proteins involved in this process is the proinflammatory cytokine interleukin-1β (IL-1β, which induces the expression of MMP-3 mRNA and the secretion of MMP-3 protein by dermal fibroblasts. In this study, we first investigated the contribution of activating transcription factor 2 (ATF-2) to IL-1β-induced MMP-3 expression in dermal fibroblasts. Our results showed that in cells transfected with ATF-2 siRNA or treated with the ATF-2 inhibitor SBI-0087702, IL-1β-induced MMP-3 mRNA expression was reduced. We also demonstrated that IL-1β stimulates the phosphorylation of ATF-2. These observations suggest that ATF-2 plays an important role in IL-1β-induced MMP-3 expression. Next, we investigated the role of MAPK signaling in ATF-2 activation. In cells treated with the extracellular signal-regulated kinase (ERK) inhibitor FR180240, as well as in cells transfected with ERK1 and ERK2 siRNAs, IL-1β-induced MMP-3 mRNA expression was reduced. In addition, we showed that IL-1β induced the phosphorylation of ERK1/2. These observations suggest that ERK1 and ERK2 are involved in IL-1β-induced MMP-3 expression. However, ERK1 and ERK2 do seem to play different roles. While the ERK inhibitor FR180204 inhibited IL-1β-induced ATF-2 phosphorylation, only in cells transfected with ERK1 siRNA, but not ERK2 siRNA, IL-1β-induced ATF-2 phosphorylation was reduced. These findings suggest that the ERK1/ATF-2 signaling axis contributes to IL-1β-induced MMP-3 expression in dermal fibroblasts.

Innate immune cell-epithelial crosstalk during wound repair

Skin and intestinal epithelial barriers play a pivotal role in protecting underlying tissues from harsh external environments. The protective role of these epithelia is, in part, dependent on a remarkable capacity to restore barrier function and tissue homeostasis after injury. In response to damage, epithelial wounds repair by a series of events that integrate epithelial responses with those of resident and infiltrating immune cells including neutrophils and monocytes/macrophages. Compromise of this complex interplay predisposes to development of chronic nonhealing wounds, contributing to morbidity and mortality of many diseases. Improved understanding of crosstalk between epithelial and immune cells during wound repair is necessary for development of better pro-resolving strategies to treat debilitating complications of disorders ranging from inflammatory bowel disease to diabetes. In this Review we focus on epithelial and innate immune cell interactions that mediate wound healing and restoration of tissue homeostasis in the skin and intestine.

A positive feedback between IDO1 metabolite and COL12A1 via MAPK pathway to promote gastric cancer metastasis

Background

IDO1 (Indoleamine 2,3-dioxygenase 1) inhibits host anti-tumor immune response by exhausting tryptophan in tumor microenvironment, but the pathogenic mechanisms of IDO1 in gastric cancer (GC) cells need to be further explored.

Methods

The aim of this study was to use CCLE (Cancer Cell Line Encyclopedia) transcriptomic data of GC cell lines for WGCNA (Weighted Gene Co-expression Network Analysis) analysis, and explore the potential functions and mechanisms of IDO1 in GC progression in vitro and in vivo.

Results

The higher expression level of IDO1 was identified in 4 out of 7 GC cell lines. Increased IDO1 expression strongly promoted cell migration via its metabolite kynurenine and was associated with pathways of immune activation according to GSEA (Gene Set Enrichment Analysis). The functions of IDO1 were closely associated with extracellular matrix, collagen metabolic and catabolic process by WGCNA analysis. Among five hub genes (AXL, SGCE, COL12A1, ANTXR1, LOXL2), COL12A1 and LOXL2 were upregulated in GC tissues. IDO1 disclosed positive correlation with six collagen genes by coefficient matrix diagram. Knockdown of IDO1 decreased the expression of LOXL2, COL6A1, COL6A2 and COL12A1 in GC cells in both mRNA and protein levels. Of them, knockdown of COL12A1 inhibited cell migration more apparently than knockdown of others. IDO1 and COL12A1 revealed synergistic efficacy on promoting cell migration via a positive feedback sustained by MAPK pathway. This bioprocess was mediated by IDO1 metabolite kynurenine and integrin β1. A popliteal lymph nodemetastasis model was established for verifying metastatic promotion of IDO1 and COL12A1 in GC.

Conclusions

IDO1 and COL12A1 synergistically promoted GC metastasis. The novel findings suggested that both IDO1 and COL12A1 may be promising targets on anti-cancer treatment in GC.

Electronic supplementary material

The online version of this article (10.1186/s13046-019-1318-5) contains supplementary material, which is available to authorized users.

Elevated kynurenine levels in diffuse cutaneous and anti-RNA polymerase III positive systemic sclerosis

Systemic sclerosis (SSc) is a systemic disease characterized by vasculopathy, progressive fibrosis and autoimmune activation. Tryptophan (Trp) metabolism has been linked to altered immune cell function and to malignancy. We have investigated the role of Trp metabolic pathway in SSc measuring serum Trp, Kynurenine (Kyn) and Trp/Kyn ratio in a cohort of 97 SSc patients and 10 healthy controls. Association with disease characteristics was evaluated. We found that Trp levels in SSc patients were significantly lower compared to HCs. We also found that patients with diffuse cutaneous (dcSSc) had lower levels of Trp compared to limited cutaneous (lcSSc). These results were paralleled by higher levels of Kyn found in SSc patients compared to HCs and significantly lower levels in dcSSc compared to lcSSc. The autoantibody profile was also found to be significantly associated with Kyn and Trp levels as anti-RNA-polymerase III (ARA) positive patients were shown to have lower Trp levels and higher Kyn levels compared with anti-centromere and anti-topoisomerase I positive patients. Moreover, the highest Trp/Kyn was found in ARA+ patients with dcSSc, suggesting that an activation of the Kyn pathway, is more specifically associated with this subset of SSc patients. Stability over time makes these markers of Trp metabolism feasible for SSc stratification.

miR-181b-5p promotes proliferation and inhibits apoptosis of hypertrophic scar fibroblasts through regulating the MEK/ERK/p21 pathway

Hypertrophic scar (HS) is a common skin disorder occurring during the wound healing process, and the pathogenesis of HS remains unclear. Previous studies indicated that miRNAs may be involved in the onset and progression of HS. In the present study, reverse transcription-quantitative polymerase chain reaction (RT-qPCR) and western blotting were used to investigate the expression of miR-181b-5p and decorin in HS tissues. Direct interaction between miR-181b-5p and decorin was confirmed using a dual-luciferase assay. Human HS fibroblasts (HSFbs) were cultured and transfected with miR-181b-5p mimics, and MTT assay and Annexin V fluorescein isothiocyanate/propidium iodide staining were performed to investigate the role of miR-181b-5p in the proliferation and apoptosis of HSFbs. Subsequently, the expression levels of mitogen-activated protein kinase kinase (MEK), phospho (p)-extracellular signal-regulated kinase (ERK) and p21 were determined in HSFbs transfected with miR-181b-5p mimics and untransfected cells using RT-qPCR and western blotting. The results indicated upregulation of miR-181b-5p and downregulation of decorin expression in HS tissues compared with normal skin samples. miR-181b-5p may regulate the expression of decorin through direct binding to the 3′-untranslated region, as demonstrated by the results of the dual-luciferase assay. Transfection with miR-181b-5p mimics in HSFbs enhanced cell proliferation, reduced apoptosis and increased the expression of MEK, p-ERK and p21. Furthermore, treatment with MEK inhibitor in HSFbs transfected with miR-181b-5p mimics partially inhibited miR-181b-5p-induced antiapoptotic effects. Taken together, increased expression of miR-181b-5p may serve important roles in the pathogenesis of HS through regulating the MEK/ERK/p21 pathway, suggesting that miR-181b-5p may be a therapeutic target for the treatment of HS.

Tryptophan metabolites kynurenine and serotonin regulate fibroblast activation and fibrosis

Fibrosis is a pathological form of aberrant tissue repair, the complications of which account for nearly half of all deaths in the industrialized world. All tissues are susceptible to fibrosis under particular pathological sets of conditions. Though each type of fibrosis has characteristics and hallmarks specific to that particular condition, there appear to be common factors underlying fibrotic diseases. One of these ubiquitous factors is the paradigm of the activated myofibroblast in the promotion of fibrotic phenotypes. Recent research has implicated metabolic byproducts of the amino acid tryptophan, namely serotonin and kynurenines, in the pathology or potential pharmacologic therapy of fibrosis, in part through their effects on development of myofibroblast phenotypes. Here, we review literature underlying what is known mechanistically about the effects of these compounds and their respective pathways on fibrosis. Pharmacologic administration of kynurenine improves scarring outcomes in vivo likely not only through its well-characterized immunosuppressive properties but also via its demonstrated antagonism of fibroblast activation and of collagen deposition. In contrast, serotonin directly promotes activation of fibroblasts via activation of canonical TGF-β signaling, and overstimulation with serotonin leads to fibrotic outcomes in vivo. Recently discovered feedback inhibition between serotonin and kynurenine pathways also reveals more information about the cellular physiology of tryptophan metabolism and may also underlie possible paradigms for anti-fibrotic therapy. Together, understanding of the effects of tryptophan metabolism on modulation of fibrosis may lead to the development of new therapeutic avenues for treatment through exploitation of these effects.

Amino Acid Profile of Synovial Fluid Following Intra-articular Ankle Fracture

BACKGROUND

Post-traumatic osteoarthritis (PTOA) is a frequent complication in patients with a previous traumatic joint injury, and the pathophysiology is not well understood. The goal of this study was to characterize the biochemical signature of amino acids, peptides, and amino acid metabolites in ankle synovial fluid following intra-articular fracture.

METHODS

Synovial fluid from both the injured and contralateral ankles of 19 patients with an intra-articular ankle fracture was obtained and analyzed via metabolic profiling. Follow-up analysis was performed after 6 months in 7 of these patients.

RESULTS

Statistical comparisons between injured and contralateral ankles revealed that 19 of the 66 measured amino acids, peptides, and amino acid metabolites were significantly elevated at time of fracture. Metabolites associated with glutathione metabolism exhibited the most elevated mean-fold changes, indicating a possible role for oxidative stress in fractured ankles. None of the metabolites elevated at baseline were significantly elevated after 6 months, but 6 metabolites had mean-fold changes greater than 2.1 at this time point. Multiple metabolites also exhibited significant correlations ( r > 0.575) with matrix metalloproteinase-1 and -9.

CONCLUSION

These results indicate the presence of amino acid metabolic products in the setting of ankle fracture and suggest that these changes in amino acid metabolism may be chronic and indicate a role for inflammation and collagen degradation in disease progression.

CLINICAL RELEVANCE

Changes in amino acid metabolism following intra-articular fracture may contribute to the progression to PTOA. This knowledge may allow for the identification and early treatment of patients at risk of developing PTOA.

LEVEL OF EVIDENCE

Level III, comparative series.

Characterization of In Vitro Reconstructed Human Normotrophic, Hypertrophic, and Keloid Scar Models

To understand scar pathology, develop new drugs, and provide a platform for personalized medicine, physiologically relevant human scar models are required, which are characteristic of different scar pathologies. Hypertrophic scars and keloids are two types of abnormal scar resulting from unknown abnormalities in the wound healing process. While they display different clinical behavior, differentiation between the two can be difficult-which in turn means that it is difficult to develop optimal therapeutic strategies. The aim of this study was to develop in vitro reconstructed human hypertrophic and keloid scar models and compare these to normotrophic scar and normal skin models to identify distinguishing biomarkers. Keratinocytes and fibroblasts from normal skin and scar types (normotrophic, hypertrophic, keloid) were used to reconstruct skin models. All skin models showed a reconstructed differentiated epidermis on a fibroblast populated collagen-elastin matrix. Both abnormal scar types showed increased contraction, dermal thickness, and myofibroblast staining compared to normal skin and normotrophic scar. Notably, the expression of extracellular matrix associated genes showed distinguishing profiles between all scar types and normal skin (hyaluronan synthase-1, matrix-metalloprotease-3), between keloid and normal skin (collagen type IV), between normal scar and keloid (laminin α1), and between keloid and hypertrophic scar (matrix-metalloprotease-1, integrin α5). Also, inflammatory cytokine and growth factor secretion (CCL5, CXCL1, CXCL8, CCL27, IL-6, HGF) showed differential secretion between scar types. Our results strongly suggest that abnormal scars arise from different pathologies rather than simply being on different ends of the scarring spectrum. Furthermore, such normal skin and scar models together with biomarkers, which distinguish the different scar types, would provide an animal free, physiologically relevant scar diagnostic and drug testing platform for the future.

Insights into the key roles of epigenetics in matrix macromolecules-associated wound healing

Extracellular matrix (ECM) is a dynamic network of macromolecules, playing a regulatory role in cell functions, tissue regeneration and remodeling. Wound healing is a tissue repair process necessary for the maintenance of the functionality of tissues and organs. This highly orchestrated process is divided into four temporally overlapping phases, including hemostasis, inflammation, proliferation and tissue remodeling. The dynamic interplay between ECM and resident cells exerts its critical role in many aspects of wound healing, including cell proliferation, migration, differentiation, survival, matrix degradation and biosynthesis. Several epigenetic regulatory factors, such as the endogenous non-coding microRNAs (miRNAs), are the drivers of the wound healing response. microRNAs have pivotal roles in regulating ECM composition during wound healing and dermal regeneration. Their expression is associated with the distinct phases of wound healing and they serve as target biomarkers and targets for systematic regulation of wound repair. In this article we critically present the importance of epigenetics with particular emphasis on miRNAs regulating ECM components (i.e. glycoproteins, proteoglycans and matrix proteases) that are key players in wound healing. The clinical relevance of miRNA targeting as well as the delivery strategies designed for clinical applications are also presented and discussed.

Obesity and Cancer: Existing and New Hypotheses for a Causal Connection

Existing explanations of obesity-associated cancer emphasise direct mutagenic effects of dietary components or hormonal imbalance. Some of these hypotheses are reviewed briefly, but recent evidence suggests a major role for chronic inflammation in cancer risk, possibly involving dietary content. These ideas include the inflammation-induced activation of the kynurenine pathway and its role in feeding and metabolism by activation of the aryl hydrocarbon receptor (AHR) and by modulating synaptic transmission in the brain. Evidence for a role of the kynurenine pathway in carcinogenesis then provides a potentially major link between obesity and cancer. A second new hypothesis is based on evidence that serine proteases can deplete cells of the tumour suppressors Deleted in Colorectal Cancer (DCC) and neogenin. These enzymes include mammalian chymotryptic proteases released by pro-inflammatory neutrophils and macrophages. Blood levels of chymotrypsin itself increase in parallel with food intake. The mechanistically similar bacterial enzyme subtilisin is widespread in the environment, animal probiotics, meat processing and cleaning products. Simple public health schemes in these areas, with selective serine protease inhibitors and AHR antagonists and could prevent a range of intestinal and other cancers.

Regulation of fibrotic changes by the synergistic effects of cytokines, dimensionality and matrix: Towards the development of an in vitro human dermal hypertrophic scar model

Current therapeutic strategies to reduce scarring in full thickness skin defect offer limited success due to poor understanding of scar tissue formation and the underlying signaling pathways. There is an urgent need to develop human cell based in vitro scar tissue models as animal testing is associated with ethical and logistic complications and inter-species variations. Pro-inflammatory cytokines play critical role in regulating scar development through complex interplay and interaction with the ECM and corresponding signaling pathways. In this context, we assessed the responses of cultured fibroblasts with respect to their differentiation into myofibroblasts using optimised cytokines (TGF-β1, IL-6 and IL-8) for scar formation in 2D (tissue culture plate, collagen type I coated plate) vs 3D collagen type I gel based constructs. We attempted to deduce the role of dimensionality of cell culture matrix in modulating differentiation, function and phenotype of cultured fibroblasts. Validation of the developed model showed similarity to etiology and pathophysiology of in vivo hypertrophic scar with respect to several features: 1) transition of fibroblasts to myofibroblasts with convincing expression of α-SMA stress fibers; 2) contraction; 3) excessive collagen and fibronectin secretion; 4) expression of fibrotic ECM proteins (SPARC and Tenascin); 5) low MMP secretion. Most importantly, we elucidated the involvement of TGF-β/SMAD and Wnt/β-catenin pathways in developing in vitro dermal scar. Hence, this relatively simple in vitro human scar tissue equivalent may serve as an alternative for testing and designing of novel therapeutics and help in extending our understanding of the complex interplay of cytokines and related dermal scar specific signaling.

STATEMENT OF SIGNIFICANCE

Scarring of the skin affects almost millions of people per year in the developed world alone, nevertheless the complex pathophysiology and the precise signaling mechanisms responsible for this phenomenon of skin scarring are still unknown. A number of anti-scar drugs are being developed and being tested on animals and monolayer models. However, testing the efficacy of these drugs on lab based 3D in vitro models may prove extremely useful in recapitulating the 3D microenvironment of the native scar tissue. In that context in this study we have demonstrated the development of 3D in vitro dermal scar model, by optimizing a constellation of factors, such as combination of cytokines (TGF-β1,IL-6,IL-8) and cellular dimensionality in inducing the differentiation of dermal fibroblasts to myofibroblasts. This in vitro scar model was successful in replicating hallmark features of hypertrophic scar such as excessive synthesis of fibrotic extracellular matrix, perturbed matrix homeostasis, contraction, diminished MMP synthesis. The study also highlighted significant involvement of TGF-β/SMAD and Wnt/β-catenin signaling pathways in in vitro scar formation.

Scarless wound healing: Transitioning from fetal research to regenerative healing

Since the discovery of scarless fetal skin wound healing, research in the field has expanded significantly with the hopes of advancing the finding to adult human patients. There are several differences between fetal and adult skin that have been exploited to facilitate scarless healing in adults including growth factors, cytokines, and extracellular matrix substitutes. However, no one therapy, pathway, or cell subtype is sufficient to support scarless wound healing in adult skin. More recently, products that contain or mimic fetal and adult uninjured dermis were introduced to the wound healing market with promising clinical outcomes. Through our review of the major experimental targets of fetal wound healing, we hope to encourage research in areas that may have a significant clinical impact. Additionally, we will investigate therapies currently in clinical use and evaluate whether they represent a legitimate advance in regenerative medicine or a vulnerary agent. WIREs Dev Biol 2018, 7:e309. doi: 10.1002/wdev.309 This article is categorized under: Adult Stem Cells, Tissue Renewal, and Regeneration > Regeneration Plant Development > Cell Growth and Differentiation Adult Stem Cells, Tissue Renewal, and Regeneration > Environmental Control of Stem Cells.

MicroRNA-222 regulates the viability of fibroblasts in hypertrophic scars via matrix metalloproteinase 1

The present study aimed to determine the expression of microRNA (miR)-222 in hypertrophic scar (HS) tissues, and investigate the regulatory mechanism of miR-222 in HS. A total of 36 patients diagnosed with HS between August 2013 and May 2016 were included in the present study. HS tissues and HS-adjacent tissues were collected from patients. Primary fibroblasts were obtained from HS tissue. Reverse transcription-quantitative polymerase chain reaction was used to measure mRNA levels of matrix metalloproteinase 1 (MMP1) and miR-222. Western blotting was conducted to determine MMP1 expression and an MTT assay was performed to measure the viability of fibroblasts. A dual luciferase reporter assay was used to identify the binding of miR-222 to MMP1 mRNA. It was demonstrated that MMP1 serves a role in HS at the transcription level and that increased MMP1 expression inhibited the viability of fibroblasts. miR-222 serves a regulatory role in HS by targeting its target gene MMP1 and regulates the expression of MMP1 by binding to its 3′-untranslated region. The decreased expression of miR-222 suppresses the viability of fibroblasts by regulating MMP1 expression. The present study demonstrated that the downregulation of MMP1 in HS tissues is associated with the upregulation of miR-222 expression. miR-222 may therefore regulate the viability of fibroblasts in HS and the expression of related proteins via MMP1.

Research Techniques Made Simple: Methodology and Applications of Förster Resonance Energy Transfer (FRET) Microscopy

Classical biochemical techniques have contributed a great deal to our understanding of the mechanisms regulating fundamental biological processes. However, these approaches are typically end-point, population-based assays and are often insufficient in examining transient molecular events. Förster resonance energy transfer (FRET) microscopy is a powerful technique capable of investigating dynamic interactions between proteins and a plethora of biochemical signaling events based on the development of specific biosensors. This technique exploits the principle that when FRET occurs, energy from a donor fluorophore is transferred to an acceptor fluorophore only when certain conditions are met. These include dependence on both distance and fluorophore orientation. In this article, applications of FRET microscopy to protein interactions and modifications are discussed, and examples are given of the types of biosensors that can be developed. There are a number of methods to measure FRET. The most common modalities and specific advantages and shortcomings for each are reviewed. Finally, general considerations and guidelines for choosing a method are discussed.

Tryptophan-Derived 3-Hydroxyanthranilic Acid Contributes to Angiotensin II-Induced Abdominal Aortic Aneurysm Formation in Mice In Vivo

BACKGROUND

Abnormal amino acid metabolism is associated with vascular disease. However, the causative link between dysregulated tryptophan metabolism and abdominal aortic aneurysm (AAA) is unknown.

METHODS

Indoleamine 2,3-dioxygenase (IDO) is the first and rate-limiting enzyme in the kynurenine pathway of tryptophan metabolism. Mice with deficiencies in both apolipoprotein e (Apoe) and IDO (Apoe^-/-/IDO^-/-) were generated by cross-breeding IDO^-/- mice with Apoe^-/- mice.

RESULTS

The acute infusion of angiotensin II markedly increased the incidence of AAA in Apoe^-/- mice, but not in Apoe^-/-/IDO^-/- mice, which presented decreased elastic lamina degradation and aortic expansion. These features were not altered by the reconstitution of bone marrow cells from IDO^+/+ mice. Moreover, angiotensin II infusion instigated interferon-γ, which induced the expression of IDO and kynureninase and increased 3-hydroxyanthranilic acid (3-HAA) levels in the plasma and aortas of Apoe^-/- mice, but not in IDO^-/- mice. Both IDO and kynureninase controlled the production of 3-HAA in vascular smooth muscle cells. 3-HAA upregulated matrix metallopeptidase 2 via transcription factor nuclear factor-κB. Furthermore, kynureninase knockdown in mice restrained 3-HAA, matrix metallopeptidase 2, and resultant AAA formation by angiotensin II infusion. Intraperitoneal injections of 3-HAA into Apoe^-/- and Apoe^-/-/IDO^-/- mice for 6 weeks increased the expression and activity of matrix metallopeptidase 2 in aortas without affecting metabolic parameters. Finally, human AAA samples had stronger staining with the antibodies against 3-HAA, IDO, and kynureninase than those in adjacent nonaneurysmal aortic sections of human AAA samples.

CONCLUSIONS

These data define a previously undescribed causative role for 3-HAA, which is a product of tryptophan metabolism, in AAA formation. Furthermore, these findings suggest that 3-HAA reduction may be a new target for treating cardiovascular diseases.

MicroRNA-22 may promote apoptosis and inhibit the proliferation of hypertrophic scar fibroblasts by regulating the mitogen-activated protein kinase kinase/extracellular signal-regulated kinase/p21 pathway

Hypertrophic scarring (HS) is a common skin disorder that occurs during the wound healing process, and the pathogenesis of HS remains unclear. Increasing evidence indicated that specific microRNAs (miRs) may be involved in the onset and progression of HS. In the present study, the association between miR-22 and HS was investigated. Reverse transcription-quantitative polymerase chain reaction (RT-qPCR) was performed to examine the expression of miR-22 in 30 HS and matched normal skin tissues. In addition, human hypertrophic scar fibroblasts (HSFBs) were cultured and transfected with miR-22 mimics, and MTT and Annexin V apoptosis assays were performed to investigate the role of miR-22 in the proliferation and apoptosis of the human HSFBs. Next, RT-qPCR and western blot assays were performed to compare the expression levels of mitogen-activated protein kinase kinase (MEK), extracellular signal-regulated kinase (ERK) and p21 in untransfected and miR-22 mimic-transfected skin fibroblasts. The results identified that miR-22 was significantly downregulated in HS tissues as compared with the normal skin. Furthermore, transfection with miR-22 mimics in human HSFBs led to inhibited cell proliferation, increased apoptosis, as well as to decreased MEK expression and ERK1/2 phosphorylation, and increased expression of p21. In conclusion, the present study was the first to prove that aberrant expression of miR-22 may serve an important role in the pathogenesis of HS by regulating the MEK/ERK/p21 pathway, thus suggesting that miR-22 has the potential to become a therapeutic target for the treatment of HS.

Cryopreserved cultured epithelial allografts for pediatric deep partial dermal burns: Early wound closure and suppression of scarring

BACKGROUND

In deep partial thickness dermal burns (DDB) where greater than 50% of the dermis is lost, severe pain, scarring and contractures occur. Therefore, skin grafting may be required. In children, scar contracture occurs because scarred skin does not stretch with growth creating the need for additional scar-releasing or skin-grafting surgeries. In order to resolve this problem, we used cryopreserved cultured epithelial allograft (cryopreserved allo-CEG), which can be grafted shortly after sustaining a wound. We reevaluated the promotion of early wound closure of burns and suppression of scarring by this treatment.

METHODS

Cryopreserved allo-CEGs were used to treat 50 cases of pediatric DDB from 1992 to 2000. These cases were reviewed with regard to the time until epithelialization, take percentage, and pain level. Also, in order to examine why cryopreserved allo-CEG promotes healing of burns and suppresses scarring, growth factors and cytokines in the cryopreserved allo-CEG were measured. Cryopreserved allo-CEG sheets were solubilized and concentrations of TGF-α, TGF-β1, IL-1α, IL-1β, PDGF-AA, VEGF, KGF, IL-6, b-FGF, as well as metalloprotease-1 (MMP-1) and HGF, which are noted to have scarring suppression effects, were measured before grafting.

RESULTS

Grafting of cryopreserved allo-CEGs in 50 cases of childhood DDB resulted in early epithelialization (9.32 ± 3.63 days on the average) and an almost 100% take rate. Also, pain relief (pain reduction or elimination, reduced need for anesthetics) was seen in all cases. Although 15-23 years have now elapsed, adverse events have not been observed. Cryopreserved allo-CEG contains IL-1α, IL-1β, PDGF-AA, TGF-α, TGF-β1, VEGF, and IL-6 have wound healing effects. The concentration of IL-1α was higher than the concentrations of other components, and this was followed by TGF-α, TGF-β1, b-FGF and VEGF. Although the concentration of MMP-1, which has a scarring suppression effect, was high, HGF was not detected.

CONCLUSION

Cryopreserved allo-CEG contains growth factors that promote wound healing and factors that suppress scarring. Three effects, namely (1) early wound closure, (2) scarring suppression, and (3) pain relief were seen with grafts of cryopreserved allo-CEG in cases of childhood DDB. These observations show that cryopreserved allo-CEG is clinically useful and effective for the treatment of childhood DDB.

Biochemical and Biological Attributes of Matrix Metalloproteinases

Matrix metalloproteinases (MMPs) are a family of zinc-dependent endopeptidases that are involved in the degradation of various proteins in the extracellular matrix (ECM). Typically, MMPs have a propeptide sequence, a catalytic metalloproteinase domain with catalytic zinc, a hinge region or linker peptide, and a hemopexin domain. MMPs are commonly classified on the basis of their substrates and the organization of their structural domains into collagenases, gelatinases, stromelysins, matrilysins, membrane-type (MT)-MMPs, and other MMPs. MMPs are secreted by many cells including fibroblasts, vascular smooth muscle (VSM), and leukocytes. MMPs are regulated at the level of mRNA expression and by activation of their latent zymogen form. MMPs are often secreted as inactive pro-MMP form which is cleaved to the active form by various proteinases including other MMPs. MMPs cause degradation of ECM proteins such as collagen and elastin, but could influence endothelial cell function as well as VSM cell migration, proliferation, Ca²⁺ signaling, and contraction. MMPs play a role in tissue remodeling during various physiological processes such as angiogenesis, embryogenesis, morphogenesis, and wound repair, as well as in pathological conditions such as myocardial infarction, fibrotic disorders, osteoarthritis, and cancer. Increases in specific MMPs could play a role in arterial remodeling, aneurysm formation, venous dilation, and lower extremity venous disorders. MMPs also play a major role in leukocyte infiltration and tissue inflammation. MMPs have been detected in cancer, and elevated MMP levels have been associated with tumor progression and invasiveness. MMPs can be regulated by endogenous tissue inhibitors of metalloproteinases (TIMPs), and the MMP/TIMP ratio often determines the extent of ECM protein degradation and tissue remodeling. MMPs have been proposed as biomarkers for numerous pathological conditions and are being examined as potential therapeutic targets in various cardiovascular and musculoskeletal disorders as well as cancer.

Abnormal kynurenine pathway of tryptophan catabolism in cardiovascular diseases

Kynurenine pathway (KP) is the primary path of tryptophan (Trp) catabolism in most mammalian cells. The KP generates several bioactive catabolites, such as kynurenine (Kyn), kynurenic acid (KA), 3-hydroxykynurenine (3-HK), xanthurenic acid (XA), and 3-hydroxyanthranilic acid (3-HAA). Increased catabolite concentrations in serum are associated with several cardiovascular diseases (CVD), including heart disease, atherosclerosis, and endothelial dysfunction, as well as their risk factors, including hypertension, diabetes, obesity, and aging. The first catabolic step in KP is primarily controlled by indoleamine 2,3-dioxygenase (IDO) and tryptophan 2,3-dioxygenase (TDO). Following this first step, the KP has two major branches, one branch is mediated by kynurenine 3-monooxygenase (KMO) and kynureninase (KYNU) and is responsible for the formation of 3-HK, 3-HAA, and quinolinic acid (QA); and another branch is controlled by kynurenine amino-transferase (KAT), which generates KA. Uncontrolled Trp catabolism has been demonstrated in distinct CVD, thus, understanding the underlying mechanisms by which regulates KP enzyme expression and activity is paramount. This review highlights the recent advances on the effect of KP enzyme expression and activity in different tissues on the pathological mechanisms of specific CVD, KP is an inflammatory sensor and modulator in the cardiovascular system, and KP catabolites act as the potential biomarkers for CVD initiation and progression. Moreover, the biochemical features of critical KP enzymes and principles of enzyme inhibitor development are briefly summarized, as well as the therapeutic potential of KP enzyme inhibitors against CVD is briefly discussed.

Hypertrophic Scarring in the Rabbit Ear: A Practical Model for Studying Dermal Fibrosis

Excessive fibrous tissue deposition after injury in the form of hypertrophic scar remains a major clinical challenge. The development of an animal model for such scarring has been extremely difficult because of a major difference between the healing process in laboratory animals and humans. Here, we describe the rabbit ear model for excessive dermal scarring which has some clinical and histological resemblance to human hypertrophic scar. Since its development, this model has been widely used to study the cellular and molecular biology of hypertrophic scarring and evaluate the efficacy of new therapeutic agents.

Transplanting Human Skin Grafts onto Nude Mice to Model Skin Scars

Hypertrophic scar (HTS) is a common outcome of deep dermal wound healing mainly followed mechanical, chemical, and thermal injuries in the skin. Because of the lack of the most effective prevention and treatment, it is particularly important to establish an ideal dermal animal model for improving the understanding of the pathogenesis and exploring therapeutic approaches of HTS. Compared to other dermal fibrotic animal models in rabbits, red Duroc pigs, guinea pigs, rats, and mice, the approach that uses normal human split-thickness skin grafted onto nude or other immunodeficient mice which develop scars that resemble human HTS offers the advantages of lower cost, easier manipulation, and shorter research period. In this chapter, we will introduce the detailed procedures to create the ideal dermal fibrotic mouse model.

The Aryl Hydrocarbon Receptor and Its Ligands Inhibit Myofibroblast Formation and Activation: Implications for Thyroid Eye Disease

Thyroid eye disease (TED) is a degenerative disease that manifests with detrimental tissue remodeling, myofibroblast accumulation, and scarring in the orbit of affected individuals. Currently, there are no effective therapies for TED that target or prevent the excessive tissue remodeling caused by myofibroblast formation and activation. The canonical cytokine that induces myofibroblast formation is transforming growth factor (TGF)-β. The TGF-β signaling pathway is influenced by aryl hydrocarbon receptor (AHR) signaling pathways. We hypothesized that AHR agonists can prevent myofibroblast formation in fibroblasts from patients with TED, and thus AHR ligands are potential therapeutics for the disease. Orbital fibroblasts explanted from patients with TED were treated with TGF-β to induce myofibroblast formation, contraction, and proliferation. We found that AHR ligands prevent TGF-β-dependent myofibroblast formation, and this ability is dependent on AHR expression. The AHR and AHR ligands block profibrotic Wnt signaling by inhibiting the phosphorylation of GSK3β to prevent myofibroblast formation. These results provide new insight into the molecular pathways underlying orbital scarring in TED. These novel studies highlight the potential of the AHR and AHR ligands as future therapeutic options for eye diseases and possibly also for other scarring conditions.

Growth factor pathways in hypertrophic scars: Molecular pathogenesis and therapeutic implications

Hypertrophic scars represent the most common complication of skin injury and are caused by excessive cutaneous wound healing characterized by hypervascularity and pathological deposition of extracellular matrix (ECM) components. To date, the optimal and specific treatment methods for hypertrophic scars have not been available in the clinic. Current paradigm has established fibroblasts and myofibroblasts as pivotal effector cells in the pathophysiology of wound healing. Their biological properties including origin, proliferation, migration, contraction and ECM regulation have profound impacts on the progression and regression of hypertrophic scars. These complex processes are executed and modulated by a signaling network involving a number of growth factors and cytokines. Of particular importance is transforming growth factor-β, platelet-derived growth factor, connective tissue growth factor, epidermal growth factor, and vascular endothelial growth factor. This review article briefly describes the biological functions of fibroblasts and myofibroblasts during hypertrophic scars, and thereafter examines the up-to-date molecular knowledge on the roles of key growth factor pathways in the pathophysiology of hypertrophic scars. Importantly, the therapeutic implications and future challenges of these molecular discoveries are critically discussed in the hope of advancing therapeutic approaches to limit pathological scar formation.

Targeted metabolic profiling of wounds in diabetic and nondiabetic mice

While cellular metabolism is known to regulate a number of key biological processes such as cell growth and proliferation, its role in wound healing is unknown. We hypothesized that cutaneous injury would induce significant metabolic changes and that the impaired wound healing seen in diabetes would be associated with a dysfunctional metabolic response to injury. We used a targeted metabolomics approach to characterize the metabolic profile of uninjured skin and full-thickness wounds at day 7 postinjury in nondiabetic (db/-) and diabetic (db/db) mice. By liquid chromatography mass spectrometry, we identified 129 metabolites among all tissue samples. Principal component analysis demonstrated that uninjured skin and wounds have distinct metabolic profiles and that diabetes alters the metabolic profile of both uninjured skin and wounds. Examining individual metabolites, we identified 62 with a significantly altered response to injury in the diabetic mice, with many of these, including glycine, kynurenate, and OH-phenylpyruvate, implicated in wound healing for the first time. Thus, we report the first comprehensive analysis of wound metabolic profiles, and our results highlight the potential for metabolomics to identify novel biomarkers and therapeutic targets for improved wound healing outcomes.

Kynurenine Modulates MMP-1 and Type-I Collagen Expression Via Aryl Hydrocarbon Receptor Activation in Dermal Fibroblasts

Dermal fibrosis is characterized by a high deposition of extracellular matrix (ECM) and tissue cellularity. Unfortunately all means of treating this condition are unsatisfactory. We have previously reported the anti-fibrotic effects of Kynurenine (Kyn), a tryptophan metabolite, in fibrotic rabbit ear model. Here, we report the mechanism by which Kyn modulates the expression of key ECM components in dermal fibroblasts. The results showed that Kyn activates aryl hydrocarbon receptor (AHR) nuclear translocation and up-regulates cytochrome-P450 (CYP1A-1) expression, the AHR target gene. A specific AHR antagonist, 6,2',4'-trimethoxyflavone, inhibited the Kyn-dependent modulation of CYP1A-1, MMP-1, and type-I collagen expression. Establishing the anti-fibrogenic effect of Kyn and its mechanism of action, we then developed nano-fibrous Kyn slow-releasing dressings and examined their anti-fibrotic efficacy in vitro and in a rat model. Our results showed the feasibility of incorporating Kyn into PVA/PLGA nanofibers, prolonging the Kyn release up to 4 days tested. Application of medicated-dressings significantly improved the dermal fibrosis indicated by MMP-1 induction, alpha-smooth muscle actin and type-I collagen suppression, and reduced tissue cellularity, T-cells and myofibroblasts. This study clarifies the mechanism by which Kyn modulates ECM expression and reports the development of a new slow-releasing anti-fibrogenic dressing. J. Cell. Physiol. 231: 2749-2760, 2016. © 2016 Wiley Periodicals, Inc.

Characterisation of the kynurenine pathway in skin-derived fibroblasts and keratinocytes

Acute UVB exposure triggers inflammation leading to the induction of indoleamine 2,3 dioxygenase (IDO1), one of the first enzymes in the kynurenine pathway (KP) for tryptophan degradation. However, limited studies have been undertaken to determine the catabolism of tryptophan within the skin. The aim of this study was two fold: (1) to establish if the administration of the proinflammatory cytokine interferon-gamma (IFN-γ) and/or UVB radiation elicits differential KP expression patterns in human fibroblast and keratinocytes; and (2) to evaluate the effect of KP metabolites on intracellular nicotinamide adenine dinucleotide (NAD(+) ) levels, and cell viability. Primary cultures of human fibroblasts and keratinocytes were used to examine expression of the KP at the mRNA level using qPCR, and at the protein level using immunocytochemistry. Cellular responses to KP metabolites were assessed by examining extracellular lactate dehydrogenase (LDH) activity and intracellular NAD(+) levels. Major downstream KP metabolites were analyzed using GC/MS and HPLC. Our data shows that the KP is fully expressed both in human fibroblasts and keratinocytes. Exposure to UVB radiation and/or IFN-γ causes significant changes in the expression pattern of downstream KP metabolites and enzymes. Exposure to various concentrations of KP metabolites showed marked differences in cell viability and intracellular NAD(+) production, providing support for involvement of the KP in the de novo synthesis of NAD(+) in the skin. This new information will have a significant impact on our understanding of the pathogenesis of UV related skin damage and the diagnosis of KP related disease states.

High-mobility Group Box Protein-1, Matrix Metalloproteinases, and Vitamin D in Keloids and Hypertrophic Scars

Keloids and hypertrophic scars represent excessive wound healing involving high production of collagen by skin fibroblasts. This review focuses on the role of high-mobility group box protein-1 (HMGB-1), matrix metalloproteinases (MMPs), and vitamin D in these conditions. Although the role of HMGB-1 in keloids and hypertrophic scars is unclear, the effect of HMGB-1 on fibroblasts suggests a profibrotic role and a potential contribution to excessive scarring. MMPs contribute extensively to wound healing and characteristically degrade the extracellular matrix. MMP-1 is decreased in keloids and hypertrophic scars. However, other MMPs, including MMP-2, have been found to be increased and are thought to possibly contribute to keloid expansion through peripheral extracellular matrix catabolism. Many novel therapeutic approaches to keloids and hypertrophic scars target MMPs and aim to increase their levels and catabolic activity. The higher prevalence of keloids in darker skin types may partially be due to a tendency for lower vitamin D levels. The physiologically active form of vitamin D, 1,25(OH)2D3, inhibits the proliferation of keloid fibroblasts, and correlations between vitamin D receptor polymorphisms, such as the TaqI CC genotype, and keloid formation have been reported. Additionally, vitamin D may exert an antifibrotic effect partially mediated by MMPs. Here, we critically discuss whether keloid and hypertrophic scar formation could be predicted based on vitamin D status and vitamin D receptor polymorphisms. Specifically, the findings identified HMGB-1, MMPs, and vitamin D as potential avenues for further clinical investigation and potentially novel therapeutic approaches to prevent the development of keloids and hypertrophic scars.

Matrix remodeling by MMPs during wound repair

Repair following injury involves a range of processes - such as re-epithelialization, scar formation, angiogenesis, inflammation, and more - that function, often together, to restore tissue architecture. MMPs carry out diverse roles in all of these activities. In this article, we discuss how specific MMPs act on ECM during two critical repair processes: re-epithelialization and resolution of scar tissue. For wound closure, we discuss how two MMPs - MMP1 in human epidermis and MMP7 in mucosal epithelia - facilitate re-epithelialization by cleaving different ECM or ECM-associated proteins to affect similar integrin:matrix adhesion. In scars and fibrotic tissues, we discuss that a variety of MMPs carry out a diverse range of activities that can either promote or limit ECM deposition. However, few of these MMP-driven activities have been demonstrated to be due a direct action on ECM.

An in-situ forming skin substitute improves healing outcome in a hypertrophic scar model

Wound repair requires a sequential series of biological events that begins with the deposition of a temporary scaffold within which cells can repair the skin. Without a scaffold, repair is essentially impossible. Aberrant wound healing, such as hypertrophic scarring or nonhealing, has a tremendous burden on healthcare and quality of life. Timely wound closure dramatically reduces the risk of infection and scarring. Cellular skin substitutes are opportune to meet this need. Our goal was to create an in-situ forming scaffold that can be easily combined with cells to rapidly form a dermal substitute within the wound bed. In this study, we evaluated the application of a polyvinyl alcohol-collagen-glycosaminoglycan-based biohybrid scaffold system in full-thickness wounds on a rabbit fibrotic ear model. Punch wounds (6 mm) were either untreated or filled with an acellular scaffold, a scaffold containing xenofibroblasts, or a scaffold containing xenofibroblasts expressing indoleamine 2,3-dioxygenase (IDO). Results demonstrated that (1) both acellular and IDO-expressing fibroblast in-situ forming scaffolds significantly reduced scar elevation index (1.24±0.05 and 1.25±0.03; p<0.05) and improved overall healing quality compared with xenofibroblast scaffolds and untreated wounds; (2) IDO-expressing fibroblast scaffolds significantly reduced T-cell infiltration into the scaffold-engrafted area (p<0.05); and (3) both IDO-expressing and acellular in-situ forming scaffolds demonstrated increased vessel-like and nerve-like structures (p<0.05). The results demonstrated that the use of the in-situ forming scaffold, and even more so when delivering IDO-expressing cells, improved healing outcome in full-thickness hypertrophic rabbit ear wounds.

Effects of kynurenine on CD3+ and macrophages in wound healing

As prolongation of the inflammation phase in a healing process frequently leads to wound impairment, here we queried whether kynurenine (Kyn) could modulate this phase of wound healing. To address this, a protein microarray, quantitative polymerase chain reaction (qPCR), flow cytometry for immune cells and immune cell proliferation in the presence and absence of Kyn were conducted and compared. The result of a protein microarray revealed that the expression of 12 pro-inflammatory cytokines and chemokines was modulated in Kyn-treated mouse splenocytes as compared with those of control. These findings were then evaluated by conducting a qPCR for the gene expression of these factors and showed a significant reduction in the gene expression of majority of these cytokines and chemokines (interleukin [IL]-2, IL-17, C-X-C motif chemokine ligand [CXCL] 10, CXCL1, C-C motif ligand [CCL] 12, CXCL9, CCL4, CXCL2, and CCL5) in response to Kyn treatment. To test the anti-inflammatory effect of Kyn in an animal model, dorsal surface wounds were generated in a mouse model and wounds received daily topical application of either nothing (control), dermal cream (second control), or Kyn cream using uninjured skin tissue as another control. The wounded tissues were harvested on days 3, 6, and 10 postwounding. As anticipated, the results of fluorescence-activated cell sorting analysis revealed that upon wounding, the number of total infiltrated CD3+ cells and macrophages (CD11b+) significantly increased on day 3, peaked on day 6, and reduced on day 10 post-wounding. Interestingly, as compared with those of uninjured and dermal cream alone-treated wounds, Kyn treatment significantly reduced the number of infiltrated CD3+ cells, but not CD11b+ cells, at different time intervals examined. These findings collectively suggest that Kyn, as a small molecule, can potentially be used to overcome the difficulties associated with persistency of inflammation in healing wounds.