Linagliptin inhibits high glucose-induced transdifferentiation of hypertrophic scar-derived fibroblasts to myofibroblasts via IGF/Akt/mTOR signalling pathway

Targeting cluster of differentiation 26 / dipeptidyl peptidase 4 (CD26/DPP4) in organ fibrosis

Cluster of differentiation 26 (CD26)/dipeptidyl peptidase 4 (DPP4) is an exopeptidase that is expressed as a transmembrane protein in many organs but also present in a circulating soluble form. Beyond its enzymatic and costimulatory activity, CD26/DPP4 is involved in the pathogenesis of chronic fibrotic diseases across many organ types, such as liver cirrhosis, kidney fibrosis and lung fibrosis. Organ fibrosis is associated with a high morbidity and mortality, and there are no causative therapies that can effectively attenuate the progress of the disease. Growing evidence suggests that inhibiting CD26/DPP4 can modulate the profibrotic tissue microenvironment and thus reduce fibrotic changes within affected organs. This review summarizes the role of CD26/DPP4 in fibroproliferative disorders and highlights new opportunities for an antifibrotic treatment by CD26/DPP4 inhibition. As a major advantage, CD26/DPP4 inhibitors have been in safe and routine clinical use in type 2 diabetes for many years and thus qualify for repurposing to repurpose as a promising therapeutic against fibrosis. LINKED ARTICLES: This article is part of a themed issue on Translational Advances in Fibrosis as a Therapeutic Target. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v180.22/issuetoc.

Noncoding RNAs: Master Regulator of Fibroblast to Myofibroblast Transition in Fibrosis

Myofibroblasts escape apoptosis and proliferate abnormally under pathological conditions, especially fibrosis; they synthesize and secrete a large amount of extracellular matrix (ECM), such as α-SMA and collagen, which leads to the distortion of organ parenchyma structure, an imbalance in collagen deposition and degradation, and the replacement of parenchymal cells by fibrous connective tissues. Fibroblast to myofibroblast transition (FMT) is considered to be the main source of myofibroblasts. Therefore, it is crucial to explore the influencing factors regulating the process of FMT for the prevention, treatment, and diagnosis of FMT-related diseases. In recent years, non-coding RNAs, including microRNA, long non-coding RNAs, and circular RNAs, have attracted extensive attention from scientists due to their powerful regulatory functions, and they have been found to play a vital role in regulating FMT. In this review, we summarized ncRNAs which regulate FMT during fibrosis and found that they mainly regulated signaling pathways, including TGF-β/Smad, MAPK/P38/ERK/JNK, PI3K/AKT, and WNT/β-catenin. Furthermore, the expression of downstream transcription factors can be promoted or inhibited, indicating that ncRNAs have the potential to be a new therapeutic target for FMT-related diseases.

Linagliptin ameliorates pulmonary fibrosis in systemic sclerosis mouse model via inhibition of endothelial-to-mesenchymal transition

Systemic sclerosis (SSc) is a connective tissue disease that often causes pulmonary fibrosis. Dipeptidyl peptidase 4 (DPP4) inhibitor has shown anti-fibrotic properties in various fibrotic diseases. However, only two studies have reported its anti-fibrosis effects in pulmonary fibrosis, and the mechanism is not completely clear. In the present study, we further investigated the protective effects of linagliptin, a highly specific DPP4 inhibitor, on pulmonary fibrosis in SSc mouse model and the potential mechanisms. The results showed that linagliptin ameliorated pulmonary fibrosis in SSc mouse model, as evidenced by improved pathological changes of lung and body weight loss induced by BLM. Linagliptin also reduced BLM-induced oxidative stress, inflammation in lung in vivo. We revealed that linagliptin attenuated BLM-induced endothelial-to-mesenchymal transition (EndMT) in vitro and in vivo. BLM-induced enhanced migration ability of endothelial cells was also alleviated by linagliptin. Moreover, we confirmed that the Akt/mammalian target of rapamycin pathway was involved in BLM-induced EndMT in vivo, which was suppressed by linagliptin. In summary, we further confirmed the therapeutic effects of linagliptin on pulmonary fibrosis in SSc mouse model, which is based on its inhibitory effects on EndMT, oxidative stress, and inflammation.

The serine proteases dipeptidyl-peptidase 4 and urokinase are key molecules in human and mouse scar formation

Despite recent advances in understanding skin scarring, mechanisms triggering hypertrophic scar formation are still poorly understood. In the present study, we investigate mature human hypertrophic scars and developing scars in mice at single cell resolution. Compared to normal skin, we find significant differences in gene expression in most cell types present in scar tissue. Fibroblasts show the most prominent alterations in gene expression, displaying a distinct fibrotic signature. By comparing genes upregulated in murine fibroblasts during scar development with genes highly expressed in mature human hypertrophic scars, we identify a group of serine proteases, tentatively involved in scar formation. Two of them, dipeptidyl-peptidase 4 (DPP4) and urokinase (PLAU), are further analyzed in functional assays, revealing a role in TGFβ1-mediated myofibroblast differentiation and over-production of components of the extracellular matrix in vitro. Topical treatment with inhibitors of DPP4 and PLAU during scar formation in vivo shows anti-fibrotic activity and improvement of scar quality, most prominently after application of the PLAU inhibitor BC-11. In this study, we delineate the genetic landscape of hypertrophic scars and present insights into mechanisms involved in hypertrophic scar formation. Our data suggest the use of serine protease inhibitors for the treatment of skin fibrosis.

Targeting Dermal Fibroblast Subtypes in Antifibrotic Therapy: Surface Marker as a Cellular Identity or a Functional Entity?

Fibroblasts are the chief effector cells in fibrotic diseases and have been discovered to be highly heterogeneous. Recently, fibroblast heterogeneity in human skin has been studied extensively and several surface markers for dermal fibroblast subtypes have been identified, holding promise for future antifibrotic therapies. However, it has yet to be confirmed whether surface markers should be looked upon as merely lineage landmarks or as functional entities of fibroblast subtypes, which may further complicate the interpretation of cellular function of these fibroblast subtypes. This review aims to provide an update on current evidence on fibroblast surface markers in fibrotic disorders of skin as well as of other organ systems. Specifically, studies where surface markers were treated as lineage markers and manipulated as functional membrane proteins are both evaluated in parallel, hoping to reveal the underlying mechanism behind the pathogenesis of tissue fibrosis contributed by various fibroblast subtypes from multiple angles, shedding lights on future translational researches.

Gene expression profile of epithelial-mesenchymal transition mediators in papillary thyroid cancer

PURPOSE

Platelet derived growth receptor alpha (PDGFRA) promotes the epithelial-mesenchymal transition (EMT) in thyroid follicular cells and is linked to lymphatic metastases in papillary thyroid cancer (PTC). We probed the regulatory network of genes linked to PDGFRA and EMT, comparing matched patient primary tumor and metastatic specimens, as well as engineered cell lines and ex vivo primary cultures with and without PDGFRA.

METHODS

Freshly isolated thyroid tumors with or without metastases, with matching neighboring benign or normal tissue, was isolated for comparative transcriptional analysis using a TaqMan Low Density array (TLDA) assay with genes representing important markers of EMT, cellular adhesion, apoptosis, differentiation, senescence, and signal transduction pathways in thyroid cancer. Transfected primary cultures and immortalized cell lines were also analyzed with respect to PDGFRA expression and cell phenotype.

RESULTS

We reveal the consistent upregulation of serine protease DPP4 and structural protein SPP1 with the progression of PTC to metastatic disease, as well as with PDGFRA expression. Conversely, epithelial integrity gene TFF3 and transcription factor SOX10 were strongly down-regulated. This gene network also includes important mediators of EMT including DSG1, MMP3, MMP9, and BECN. We observed similar genomic changes in ex vivo normal thyroid cells transfected with PDGFRA that also exhibited a partially dedifferentiated phenotype. In particular, we observed lamellopodia with induction of PDGFRA and illustrate that DPP4 and SPP1 were upregulated in this process, with decreased TFF3 and SOX10 as seen in tissue specimens. PDGFRA did decrease nuclear protein levels of differentiation factor TTF1, but not the transcription of TTF1 and PAX8.

CONCLUSIONS

We demonstrate that PDGFRA activates EMT pathways and decreases expression of genes favoring epithelial integrity, pushing follicular cells toward a dedifferentiated phenotype. SPP1 and DPP4, previously linked with adverse outcomes in thyroid cancer, appear to be regulated by PDGFRA. PDGFRA expression promotes metastatic disease through multiple EMT levers that favor formation of an invasive phenotype and increased metalloproteinase expression.

The mechanism of sitagliptin inhibition of colorectal cancer cell lines' metastatic functionalities

The cell membrane glycoprotein CD26 with peptidase activity (DPP4) and/or its soluble CD26/DPP4 counterpart expression and/or activity are altered in several cancers. Its role in metastasis development was recently highlighted by the discovery of CD26⁺ cancer stem cell subsets and the fact that clinical DPP4 inhibitors showed antimetastatic effects in animal models. Also, diabetic patients treated with the DPP4 inhibitor sitagliptin showed greater overall survival after colorectal or lung cancer surgery than patients under other diabetic therapies. However, the mechanism of action of these inhibitors in this context is unclear. We studied the role of CD26 and its DPP4 enzymatic activity in malignant cell features such as cell-to-cell homotypic aggregation, cancer cell motility, and invasion in a panel of human colorectal cancer (CRC) cell lines, avoiding models that include the physiological role of DPP4 in chemotaxis. Present results indicate that CD26 participates in the induction of cell invasion, motility, and aggregation of CD26-positive CRC cell lines. Moreover, only invasion and motility assays, which are collagen matrix-dependent, showed a decrease upon treatment with the DPP4 inhibitor sitagliptin. Sitagliptin showed opposite effects to those of transforming growth factor-β1 on epithelial-to-mesenchymal transition and cell cycle, but this result does not explain its CD26/DPP4-dependent effect. These results contribute to the elucidation of the molecular mechanisms behind sitagliptin inhibition of metastatic traits. At the same time, this role of sitagliptin may help to define areas of medicine where DPP4 inhibitors might be introduced. However, they also suggest that additional tools against CD26 as a target might be used or developed for metastasis prevention in addition to gliptins.

The role of Dipeptidyl Peptidase-4 in cutaneous disease

Dipeptidyl peptidase-4 (DPP4) is a multifunctional, transmembrane glycoprotein present on the cell surface of various tissues. It is present in multiple molecular forms including cell surface and soluble. The role of DPP4 and its inhibition in cutaneous dermatoses have been a recent point of investigation. DPP4 exerts a notable influence on T-cell biology, the induction of skin-specific lymphocytes, and the homeostasis between regulatory and effector T cells. Moreover, DPP4 interacts with a broad range of molecules, including adenosine deaminase, caveolin-1, CXCR4 receptor, M6P/insulin-like growth factor II-receptor and fibroblast activation protein-α, triggering downstream effects that modulate the immune response, cell adhesion and chemokine activity. DPP4 expression on melanocytes, keratinocytes and fibroblasts further alters cell function and, thus, has crucial implications in cutaneous pathology. As a result, DPP4 plays a significant role in bullous pemphigoid, T helper type 1-like reactions, cutaneous lymphoma, melanoma, wound healing and fibrotic disorders. This review illustrates the multifactorial role of DPP4 expression, regulation, and inhibition in cutaneous diseases.

Hepatoprotective effect of linagliptin against liver fibrosis induced by carbon tetrachloride in mice

The current study aimed to investigate linagliptin for its potential role in the prevention of liver fibrosis progression. Balb-C mice were randomly allocated into five groups (10 each): (i) control; (ii) mice were injected intraperitoneally with 50 μL carbon tetrachloride (CCl₄) in corn oil in a dose of 0.6 μL/g three times per week for four weeks; (iii) linagliptin was administered orally in a daily dose of 10 mg/kg simultaneously with CCl₄; (iv) silymarin was administered orally in a daily dose of 200 mg/kg concomitantly with CCl₄; and (v) only linagliptin was administered. Hepatic injury was manifested in the CCl₄ group by elevation of biochemical parameters (alanine aminotransferase (ALT), aspartate aminotransferase (AST), alkaline phosphatase (ALP)), and hepatic fibrosis was evident histopathologically by increased METAVIR score and immunostaining expression of alpha-smooth muscle actin (α-SMA), as well as increased liver tissue oxidative stress parameters, transforming growth factor-β1 (TGF-β1), and mammalian target of rapamycin (mTOR). Linagliptin was able to stop the progression of liver fibrosis, evident histopathologically with reduced METAVIR score and α-SMA expression. The possible mechanism may be via suppression of oxidative stress, TGF-β1, and mTOR, which was associated with improvement of serum biochemical parameters ALT and AST. In conclusion, linagliptin might help to protect the liver against persistent injury-related consequences.

Targeting Tunable Physical Properties of Materials for Chronic Wound Care

Chronic wounds caused by infections, diabetes, and radiation exposures are becoming a worldwide growing medical burden. Recent progress highlighted the physical signals determining stem cell fates and bacterial resistance, which holds potential to achieve a better wound regeneration in situ. Nanoparticles (NPs) would benefit chronic wound healing. However, the cytotoxicity of the silver NPs (AgNPs) has aroused many concerns. This review targets the tunable physical properties (i.e., mechanical-, structural-, and size-related properties) of either dermal matrixes or wound dressings for chronic wound care. Firstly, we discuss the recent discoveries about the mechanical- and structural-related regulation of stem cells. Specially, we point out the currently undocumented influence of tunable mechanical and structural properties on either the fate of each cell type or the whole wound healing process. Secondly, we highlight novel dermal matrixes based on either natural tropoelastin or synthetic elastin-like recombinamers (ELRs) for providing elastic recoil and resilience to the wounded dermis. Thirdly, we discuss the application of wound dressings in terms of size-related properties (i.e., metal NPs, lipid NPs, polymeric NPs). Moreover, we highlight the cytotoxicity of AgNPs and propose the size-, dose-, and time-dependent solutions for reducing their cytotoxicity in wound care. This review will hopefully inspire the advanced design strategies of either dermal matrixes or wound dressings and their potential therapeutic benefits for chronic wounds.

Botulinum toxin type A prevents the phenotypic transformation of fibroblasts induced by TGF‑β1 via the PTEN/PI3K/Akt signaling pathway

Hypertrophic scar (HS) is a common type of dermatosis. Botulinum toxin type A (BTXA) can exert an anti-HS effect; however, the regulatory mechanisms underlying this effect remain unclear. Thus, the aim of this study was to examine the effects of BTXA on phosphatase and tensin homolog deleted on chromosome ten (PTEN) expression and the fibroblast phenotypic transformation induced by transforming growth factor (TGF)-β1, which is an important regulatory factor involved in the process of HS. For this purpose, fibroblasts were treated with various concentrations of BTXA and then treated with 10 ng/ml of TGF-β1 with gradient concentrations of BTXA. The proliferation and apoptosis of fibroblasts were measured by cell counting kit-8 assay (CCK-8) and flow cytometry, respectively. PTEN methylation was analyzed by methylation-specific PCR (MSP) and DNA methyltransferase (DNMT) activity was determined using a corresponding kit. RT-qPCR and western blot analysis were performed to detect the transcription and translation levels. The results revealed that BTXA suppressed the proliferation and increased the apoptosis of fibroblasts treated with TGF-β1 in a dose-dependent manner. BTXA in combination with TGF-β1 suppressed the expression of molecules related to the extracellular matrix (ECM), epithelial-mesenchymal transition (EMT) and apoptosis. BTXA reduced the PTEN methylation level and downregulated the expression levels of methylation-associated genes. BTXA also inhibited the phosphorylation of phosphoinositide 3-kinase (PI3K) and Akt. On the whole, the findings of this study indicate that BTXA may inhibit fibroblast phenotypic transformation by regulating PTEN methylation and the phosphorylation of related pathways. The findings of this study can provide a theoretical basis for HS treatment.