DPP4 Knockdown Research Articles

SOX9 promotes hypoxic pulmonary hypertension through stabilization of DPP4 in pulmonary artery smooth muscle cells

Pulmonary hypertension (PH) is a progressive cardiopulmonary disorder characterized by pulmonary vascular remodeling (PVR), primarily due to the excessive proliferation of pulmonary artery smooth muscle cells (PASMCs). This study aimed to investigate the role and molecular mechanism of SOX9 in hypoxic PH in rats. The findings revealed that SOX9 was upregulated in the pulmonary arteries and PASMCs of hypoxia-exposed rats. SOX9 knockdown inhibited hypoxia-induced proliferation and migration of PASMCs, reduced PVR, and subsequently alleviated hypoxia-induced PH in rats, suggesting that SOX9 plays a critical role in PH. Further investigation demonstrated that SOX9 interacted with DPP4, preventing its ubiquitin degradation in hypoxia-exposed PASMCs. DPP4 knockdown inhibited hypoxia-induced PASMC proliferation and migration, and administration of the DPP4 inhibitor sitagliptin (5 mg/kg) significantly reduced PVR and alleviated hypoxia-induced PH in rats, indicating that SOX9 contributes to PH by stabilizing DPP4. The results also showed that hypoxia induced YAP1 expression and dephosphorylation, leading to YAP1 nuclear localization. YAP1 knockdown promoted the degradation of HIF-1α in hypoxia-exposed PASMCs and inhibited hypoxia-induced proliferation and migration of PASMCs. Additionally, HIF-1α, as a transcription factor, promoted SOX9 expression by binding to the SOX9 promoter in hypoxia-exposed PASMCs. In conclusion, hypoxia promotes the proliferation and migration of PASMCs through the regulation of the YAP1/HIF-1α/SOX9/DPP4 signaling pathway, leading to PH in rats. These findings suggest that SOX9 may serve as a potential prognostic marker and therapeutic target for PH.

Functional Roles of CD26/DPP4 in Bleomycin-Induced Pulmonary Hypertension Associated with Interstitial Lung Disease.

Pulmonary hypertension (PH) with interstitial lung diseases (ILDs) often causes intractable conditions. CD26/Dipeptidyl peptidase-4 (DPP4) is expressed in lung constituent cells and may be related to the pathogenesis of various respiratory diseases. We aimed to clarify the functional roles of CD26/DPP4 in PH-ILD, paying particular attention to vascular smooth muscle cells (SMCs). Dpp4 knockout (Dpp4KO) and wild type (WT) mice were administered bleomycin (BLM) intraperitoneally to establish a PH-ILD model. The BLM-induced increase in the right ventricular systolic pressure and the right ventricular hypertrophy observed in WT mice were attenuated in Dpp4KO mice. The BLM-induced vascular muscularization in small pulmonary vessels in Dpp4KO mice was milder than that in WT mice. The viability of TGFβ-stimulated human pulmonary artery SMCs (hPASMCs) was lowered due to the DPP4 knockdown with small interfering RNA. According to the results of the transcriptome analysis, upregulated genes in hPASMCs with TGFβ treatment were related to pulmonary vascular SMC proliferation via the Notch, PI3K-Akt, and NFκB signaling pathways. Additionally, DPP4 knockdown in hPASMCs inhibited the pathways upregulated by TGFβ treatment. These results suggest that genetic deficiency of Dpp4 protects against BLM-induced PH-ILD by alleviating vascular remodeling, potentially through the exertion of an antiproliferative effect via inhibition of the TGFβ-related pathways in PASMCs.

DPP-4 exacerbates LPS-induced endothelial cells inflammation via integrin-α5β1/FAK/AKT signaling

Endothelial dysfunction plays a pivotal role in the pathogenesis of acute lung injury (ALI)/acute respiratory distress syndrome (ARDS). Dipeptidyl peptidase IV (DPP-4), a cell surface glycoprotein, has been implicated in endothelial inflammation and barrier dysfunction. In this study, the role of DPP-4 on lipopolysaccharide (LPS)-induced pulmonary microvascular endothelial cells (HPMECs) dysfunction and the underlying mechanism were investigated by siRNA-mediated knockdown of DPP-4. Our results indicated that LPS (1 μg/ml) challenge resulted in either the production and releasing of DPP-4, as well as the secretion of IL-6 and IL-8 in HPMECs. DPP-4 knockdown inhibited chemokine releasing and monolayer hyper-permeability in LPS challenged HPMECs. When cocultured with human polymorphonuclear neutrophils (PMNs), DPP4 knockdown suppressed LPS-induced neutrophil-endothelial adhesion, PMN chemotaxis and trans-endothelial migration. Western blotting showed that DPP-4 knockdown attenuated LPS-induced activation of TLR4/NF-κB pathway. Immunoprecipitation and liquid chromatography-tandem mass spectrometry revealed that DPP-4 mediated LPS-induced endothelial inflammation by interacting with integrin-α5β1. Moreover, exogenous soluble DPP-4 treatment sufficiently activated integrin-α5β1 downstream FAK/AKT/NF-κB signaling, thereafter inducing ICAM-1 upregulation in HPMECs. Collectively, our results suggest that endothelia synthesis and release DPP-4 under the stress of endotoxin, which interact with integrin-α5β1 complex in an autocrine or paracrine manner to exacerbate endothelial inflammation and enhance endothelial cell permeability. Therefore, blocking DDP-4 could be a potential therapeutic strategy to prevent endothelial dysfunction in ALI/ARDS.

Down-regulation of DPP4 by TGFβ1/miR29a-3p inhibited proliferation and promoted migration of ovarian cancer cells

ObjectiveTo explore the DPP4 expression changes and functions in ovarian cancer (OV), as well as the regulation mechanism for DDP4.MethodsGEPIA2, GSE18520, GSE26712 and UALCAN were used to analyze differences in DPP4 expression between OV tumors and control tissues. Serum DPP4 levels were measured by ELISA. The prognostic values of DPP4 were evaluated using a Kaplan–Meier (KM) plotter. Small interfering RNA was used for DPP4 knockdown in OVCAR-3 and SKOV-3 cells. CCK-8 and scratch healing assays were used to determine the cells’ proliferation and migration abilities. Flow cytometry (FCM) was used to detect the cell cycle and apoptosis. A dual-luciferase assay was designed to confirm the regulatory effect of miR-29a-3p on DPP4.ResultsThe expressions of DPP4 mRNA and protein were decreased in OV tumor tissues. Serum DPP4 levels decreased in OV patients. KM plotter analysis showed correlation between high DPP4 expression and a poor prognosis in OV patients. By targeting knockdown of DPP4, we found that OVCAR-3 and SKOV-3 cells’ proliferation was inhibited, while cell’s migration ability was significantly promoted. FCM analysis showed that DPP4 knockdown induced a decrease in the S phase. Furthermore, DPP4 was shown to be downregulated by miR-29a-3p and TGFβ1 in OVCAR-3 cells, and miR-29a-3p expression was upregulated by TGFβ1. The effects of miR-29a-3p and TGFβ1 on OVCAR-3 cells’ biological behaviors were consistent with DPP4 knockdown.ConclusionDPP4 was downregulated in OV patients. DPP4 knockdown significantly inhibited OVCAR-3 and SKOV-3 cell proliferation and promoted cell migration. DDP4 can be downregulated by TGFβ1 through the upregulation of miR-29a-3p in OV cells.

Inhibition of Dipeptidyl Peptidase-4 Activates Autophagy to Promote Survival of Breast Cancer Cells via the mTOR/HIF-1α Pathway.

Autophagy plays a complex role in breast cancer cell survival, metastasis, and chemotherapeutic resistance. Dipeptidyl peptidase (DPP)-4, a therapeutic target for type 2 diabetes mellitus, is also involved in autophagic flux. The potential influence of DPP-4 suppression on cancer biology remains unknown. Here, we report that DPP-4 deficiency promotes breast cancer cell survival via the induction of autophagy by the C-X-C motif chemokine 12 (CXCL12)/C-X-C receptor 4 (CXCR4)/mammalian target of rapamycin (mTOR)/hypoxia inducible factor (HIF)-1α axis. DPP-4 knockdown and DPP-4 inhibitor KR62436 (KR) treatment both increased the levels of LC3II and HIF-1α in cultured human breast and mouse mammary cancer cells. The KR-induced autophagic phenotype in cancer cells was inhibited by treatment with the CXCR4 inhibitor AMD3100 and rapamycin. HIF-1α knockdown also suppressed breast cancer autophagy induced by KR. The autophagy inhibitor 3-methyladenine significantly blocked the KR-mediated suppression of cleaved caspase-3 levels and apoptosis in breast cancer cell lines. Finally, we found that the metformin-induced apoptosis of DPP-4-deficient 4T1 mammary cancer cells was associated with the suppression of autophagy. Our findings identify a novel role for DPP-4 inhibition in the promotion of breast cancer survival by inducing CXCL12/CXCR4/mTOR/HIF-1α axis-dependent autophagy. Metformin is a potential drug that counteracts the breast cancer cell survival system.

Metformin Mitigates DPP-4 Inhibitor-Induced Breast Cancer Metastasis via Suppression of mTOR Signaling.

The biological influence of antidiabetic drugs on cancer cells and diabetic cancer patients has not yet been completely elucidated. We reported that a dipeptidyl peptidase (DPP)-4 inhibitor accelerates mammary cancer metastasis by inducing epithelial-mesenchymal transition (EMT) through the CXCL12/CXCR4/mTOR axis. Metformin has been shown to inhibit the mTOR signaling pathway. In this study, we investigated whether metformin mitigates breast cancer metastasis induced by a DPP-4 inhibitor via suppression of mTOR signaling. In cultured mouse mammary and human breast cancer cells, metformin suppressed DPP-4 inhibitor KR62436 (KR)-induced EMT and cell migration via suppression of the mTOR pathway associated with AMPK activation. For the in vivo study, metformin intervention was performed in an allograft 4T1 breast cancer model mouse with or without KR. We also analyzed mice transplanted with shRNA-mediated DPP-4 knockdown 4T1 cells. Treatment with metformin inhibited the lung metastasis of DPP-4-deficient 4T1 mammary tumor cells generated by either KR administration or DPP-4 knockdown. Immunostaining of primary tumors indicated that DPP-4 suppression promoted the expression of EMT-inducing transcription factor Snail through activation of the CXCR4-mediated mTOR/p70S6K pathway in an allograft breast cancer model; metformin abolished this alteration. Metformin treatment did not alter DPP-4-deficiency-induced expression of CXCL12 in either plasma or primary tumors. Our findings suggest that metformin may serve as an antimetastatic agent by mitigating the undesirable effects of DPP-4 inhibitors in patients with certain cancers. IMPLICATIONS: Metformin could combat the detrimental effects of DPP-4 inhibitor on breast cancer metastasis via mTOR suppression, suggesting the potential clinical relevance. VISUAL OVERVIEW: http://mcr.aacrjournals.org/content/molcanres/19/1/61/F1.large.jpg.

FosB recruits KAT5 to potentiate the growth and metastasis of papillary thyroid cancer in a DPP4-dependent manner

ObjectiveDipeptidyl peptidase IV (DPP4) has been indicated as a possible prognostic biomarker in papillary thyroid cancer (PTC). However, the mechanism of DPP4 during metastasis of PTC remains unclear. In this study, we investigated whether lysine acetyltransferase 5 (KAT5) and FBJ murine osteosarcoma viral oncogene homolog B (FosB) synergistically regulate high DPP4 expression in PTC. MethodsPTC tissues and matched paracancerous tissues were harvested, followed by the establishment of IHH-4 and TPC-1 cells with downregulation of DPP4. The relevance of DPP4 on the metastasis of PTC cells was assessed. Subsequently, the effect of KAT5 on the transcription of DPP4 was verified. The binding relationship between FosB and DPP4 was predicted by a bioinformatics website. Functional rescue experiments were performed to evaluate cell activities after overexpression of KAT5 or FosB in cells with DPP4 knockdown. ResultsDPP4 was overexpressed in PTC tissues and cell lines, which was correlated with higher risks for metastases and poorer survival. DPP4 downregulation curtailed cell growth and metastasis. Moreover, KAT5 acetylated DPP4 promoter histone, which promoted transcription activation of DPP4. Subsequently, FosB recruited KAT5 at the DPP4 promoter, thereby enhancing DPP4 transcriptional activation. Further overexpression of KAT5 or FosB in cells with low expression of DPP4 promoted cell activity. Finally, DPP4 expedited p62 nuclear translocation to elevate Keap1/Nrf2 expression, thus facilitating the growth and metastasis of PTC cells. ConclusionFosB enhanced the growth and metastasis of PTC cells by recruiting histone acetyltransferases KAT5 to increase DPP4 transcription and activate the p62/Keap1/Nrf2 signaling.

Pro-Angiogenic and Pro-Inflammatory Regulation by lncRNA MCM3AP-AS1-Mediated Upregulation of DPP4 in Clear Cell Renal Cell Carcinoma.

Clear cell renal cell carcinoma (ccRCC) represents the most common type of renal cell carcinoma (RCC) in adults, in addition to the worst prognosis among the common epithelial kidney tumors. Inflammation and angiogenesis seem to potentiate tumor growth and metastasis of the malignancy. The current study explored the contributions of the lncRNA MCM3AP-AS1 in tumor-associated inflammation and angiogenesis in ccRCC with a specific focus on its transcriptional regulation and its interactions with transcription factor E2F1 and DPP4. Tumor tissues and matched adjacent non-tumor tissues were collected from 78 ccRCC patients. Methylation-specific PCR and ChIP assays were applied to detect the methylation at the promoter region of MCM3AP-AS1. Dual-luciferase reporter assay, RIP, RNA pull-down, and ChIP assays were employed to confirm the interactions between MCM3AP-AS1, E2F1, and DPP4. Nude mice were subcutaneously xenografted with human ccRCC cells. Cell proliferation was evaluated by CCK-8 assays and EDU staining in ccRCC cells in vitro and by immunohistochemical staining of Ki67 in vivo. Inflammation was examined by detecting the secretion of pro-inflammatory cytokines (TNF-α, IL-1β, and IL-6). Pro-angiogenic ability of ccRCC cells was assessed by the co-culture with human umbilical vein endothelial cells (HUVEC) in vitro and by microvessel density (MVD) measurements and angiogenesis in the chicken chorioallantoic membrane. MCM3AP-AS1 was highly-expressed in ccRCC and associated with poor patient survival. Demethylation of MCM3AP-AS1 was noted in ccRCC tissues and cells. Over-expression of MCM3AP-AS1 enhanced cell proliferation, the release of pro-inflammatory cytokines, and the tube formation of HUVECs in cultured human Caki-1 and 786-O cells. MCM3AP-AS1 was shown to enhance the E2F1 enrichment at the DPP4 promoter, to further increase the expression of DPP4. Knockdown of DPP4 could abate pro-angiogenic and pro-inflammatory abilities of MCM3AP-AS1 in ccRCC cells. Pro-angiogenic and pro-inflammatory abilities of MCM3AP-AS1 in vivo were confirmed in mice subcutaneously xenografted with human ccRCC cells. Our findings demonstrate a novel mechanism by which lncRNA MCM3AP-AS1 exerts pro-angiogenic and pro-inflammatory effects, highlighting the potential of MCM3AP-AS1 as a promising target for treating ccRCC.

Quantitative proteomic analysis identifies novel regulators of methotrexate resistance in choriocarcinoma

ObjectiveAlthough methotrexate (MTX) is commonly used for the treatment of choriocarcinoma, chemoresistance to MTX may occur in a considerable fraction of patients. Further understanding on the mechanisms of MTX resistance would help to develop more effective therapy for choriocarcinoma. MethodsQuantitative proteomic approach involving TMT labeling and LC-MS/MS was used to identify MTX resistance-related proteomic profiles in choriocarcinoma cell models. Pathway and process enrichment analysis were conducted to identify MTX resistance-related biological processes/molecular pathways. CCK-8 viability assay, clonogenic survival assay, and BrdU incorporation analysis were used to examine the chemosensitivity to MTX in choriocarcinoma cells. ResultsIn total, 5704 protein groups were identified, among which 4997 proteins were quantified. Bioinformatic analysis revealed that multiple biological processes/molecular pathways might be associated with MTX resistance in JEG3/JEG3/MTX cell systems. DPP4 and METTL7A were selected for further investigation. Increased expression of DPP4 or METTL7A was observed in MTX-resistant cancer cell lines and choriocarcinoma tissues. Knockdown of DPP4 or METTL7A significantly decreased cell viability, impaired clonogenesis, and increased apoptosis after MTX treatment in JEG3/MTX and JAR/MTX cells; while over-expression of DPP4 or METTL7A promoted cell viability and reduced apoptosis following exposure to MTX in JEG3, JAR and BEWO cells. Further, DPP4 and METTL7A differentially activated prosurvival signaling pathways including PI3K/AKT, ERK1/2 and STAT3, and attenuated the accumulation of reactive oxygen species (ROS) in choriocarcinoma cell lines. ConclusionsDPP4 and METTL7A might promote MTX resistance through activating pro-survival signaling pathways and attenuating the accumulation of ROS in choriocarcinoma cells. Targeting DPP4 and METTL7A might be useful to sensitize choriocarcinoma cells to MTX-based chemotherapy.

Dipeptidylpeptidase 4 as a Marker of Activated Fibroblasts and a Potential Target for the Treatment of Fibrosis in Systemic Sclerosis.

Expression of dipeptidylpeptidase 4 (DPP-4) identifies a dermal fibroblast lineage involved in scarring during wound healing. The role of DDP-4 in tissue fibrosis is, however, unknown. The aim of the present study was to evaluate DPP-4 as a potential target for the treatment of fibrosis in patients with systemic sclerosis (SSc). Expression of DPP-4 in skin biopsy samples and dermal fibroblasts was analyzed by real-time polymerase chain reaction, immunofluorescence, and Western blot analyses. The activity of DPP-4 was modulated by overexpression, knockdown, and pharmacologic inhibition of DPP4 using sitagliptin and vildagliptin. The effects of DPP4 inhibition were analyzed in human dermal fibroblasts and in different mouse models of SSc (each n = 6). The expression of DPP-4 and the number of DPP-4-positive fibroblasts were increased in the fibrotic skin of SSc patients, in a transforming growth factor β (TGFβ)-dependent manner. DPP-4-positive fibroblasts expressed higher levels of myofibroblast markers and collagen (each P < 0.001 versus healthy controls). Overexpression of DPP4 promoted fibroblast activation, whereas pharmacologic inhibition or genetic inactivation of DPP4 reduced the proliferation, migration, and expression of contractile proteins and release of collagen (each P < 0.001 versus control mice) by interfering with TGFβ-induced ERK signaling. DPP4-knockout mice were less sensitive to bleomycin-induced dermal and pulmonary fibrosis (P < 0.0001 versus wild-type controls). Treatment with DPP4 inhibitors promoted regression of fibrosis in mice that had received bleomycin challenge and mice with chronic graft-versus-host disease, and ameliorated fibrosis in TSK1 mice (each P < 0.001 versus untreated controls). These antifibrotic effects were associated with a reduction in inflammation. DPP-4 characterizes a population of activated fibroblasts and shows that DPP-4 regulates TGFβ-induced fibroblast activation in the fibrotic skin of SSc patients. Inhibition of DPP4 exerts potent antifibrotic effects when administered in well-tolerated doses. As DPP4 inhibitors are already in clinical use for diabetes, these results may have direct translational implications for the treatment of fibrosis in patients with SSc.

A siRNA mediated hepatic dpp4 knockdown affects lipid, but not glucose metabolism in diabetic mice.

Systemic inhibition of dipeptidyl peptidase 4 (dpp4) represents an effective and established treatment option for type 2 diabetes (T2D). The current study investigated in mice if a liver selective knock-down of dpp4 by therapeutic siRNAs could be a novel, similarly effective treatment option for T2D. Furthermore, the potential effects on hepatic steatosis, inflammation and lipid metabolism were investigated after hepato-selective knock-down of dpp4. The knock-down efficiency and IC50 values of siRNAs targeting dpp4 were analyzed in PC3 cells. In two independent studies, either db/db mice or C57BL/6J mice were injected intravenously with a liposomal formulation of siRNAs targeting either dpp4 or a non-targeting control, followed by metabolically characterization. In comparator groups, additional cohorts of mice were treated with an oral dpp4 inhibitor. In both animal studies, we observed a robust knock-down (~75%) of hepatic dpp4 with a potent siRNA. Hepatic dpp4 knockdown did not significantly affect glucose metabolism or circulating incretin concentrations in both animal studies. However, in obese and diabetic db/db mice hepatic steatosis was reduced and hepatic mRNA expression of acaca, scd1, fasn and pparg was significantly lower after siRNA treatment. Systemic inhibition of the enzymatic dpp4 activity by an oral dpp4 inhibitor significantly improved glucose handling in db/db mice but did not affect hepatic endpoints. These data demonstrate that a targeted reduction of dpp4 expression in the liver may not be sufficient to improve whole-body glucose metabolism in obese and diabetic mice but may improve hepatic lipid metabolism.

A liver selective knockdown of Dpp4 by therapeutic siRNA affects lipid metabolism but fails to improve glucose control in diabetic mice

Searchable abstracts of presentations at key conferences in endocrinology ISSN 1470-3947 (print) | ISSN 1479-6848 (online)

Inhibition of Dipeptidyl Peptidase-4 Accelerates Epithelial-Mesenchymal Transition and Breast Cancer Metastasis via the CXCL12/CXCR4/mTOR Axis.

Dipeptidyl peptidase (DPP)-4 is a multifunctional glycoprotein involved in various biological and pathologic processes. DPP-4 has been widely recognized as a therapeutic target for type 2 diabetes mellitus but is also implicated in the development of human malignancies. Here, we show that inhibition of DPP-4 accelerates breast cancer metastasis via induction of CXCL12/CXCR4, which activates mTOR to promote epithelial-mesenchymal transition (EMT). In cultured cells, DPP-4 knockdown induced EMT and cell migration. Treatment with the DPP-4 inhibitor KR62436 (KR) promoted primary tumor growth and lung metastasis in a 4T1 tumor allograft mouse model; DPP-4 knockdown in 4T1 cells displayed similar phenotypes in vivo and in vitro. KR treatment enhanced the levels of CXCL12/CXCR4 and phosphorylated mTOR, which were associated with the induction of EMT in metastatic cancer cells. KR-induced EMT in cancer cells was inhibited by treatment with the CXCR4 inhibitor AMD3100 or the mTOR inhibitor rapamycin, and AMD3100 suppressed KR-induced metastasis in vivo. Our findings suggest that DPP-4 plays a significant role in cancer biology and that inhibition of DPP-4 promotes cancer metastasis via induction of the CXCL12/CXCR4/mTOR/EMT axis. SIGNIFICANCE: These findings reveal that inhibition of DPP-4 increases the metastatic potential of breast cancer. This is especially important given the potential use of DPP-4 inhibition as a therapeutic strategy for type 2 diabetes.

Circulating Levels of Soluble Dipeptidyl Peptidase-4 Are Dissociated from Inflammation and Induced by Enzymatic DPP4 Inhibition

Dipeptidyl peptidase-4 (DPP-4) controls glucose homeostasis through enzymatic termination of incretin action. We report that plasma DPP-4 activity correlates with body weight and fat mass, but not glucose control, in mice. Genetic disruption of adipocyte Dpp4 expression reduced plasma DPP-4 activity in older mice but did not perturb incretin levels or glucose homeostasis. Knockdown of hepatocyte Dpp4 completely abrogated the obesity-associated increase in plasma DPP-4 activity, reduced liver cytokine expression, and partially attenuated inflammation in adipose tissue without changes in incretin levels or glucose homeostasis. In contrast, circulating levels of soluble DPP4 (sDPP4) were dissociated from inflammation in mice with endothelial-selective or global genetic inactivation of Dpp4. Remarkably, inhibition of DPP-4 enzymatic activity upregulated circulating levels of sDPP4 originating from endothelial or hematopoietic cells without inducing systemic or localized inflammation.Collectively, these findings reveal unexpected complexity in regulation of soluble versus enzymatic DPP-4 and control of inflammation and glucose homeostasis.

Inhibition of DPP4 enhances inhibitory synaptic transmission through activating the GLP-1/GLP-1R signaling pathway in a rat model of febrile seizures

Dipeptidyl peptidase-IV (DPP4) is a cell surface serine peptidase widely expressed in the brain. Recent studies suggest that DPP4 contributes to the development of febrile seizures (FS); however, the underlying mechanism is still unclear. Thus, we investigated the role of DPP4 in the progression of FS at the molecular and electrophysiological levels using FS models in vivo and in vitro. Herein, we found that both the mRNA and protein levels of DPP4 were upregulated in the FS model. Administration of the pharmacological DPP4 inhibitor sitagliptin suppressed the hyperthermia-induced neuronal excitability as determined via whole-cell patch-clamp recordings in vitro. Interestingly, sitagliptin administration activated the glucagon-like peptide-1 (GLP-1)/GLP-1 receptor (GLP-1R) pathway by increasing the expression of GLP-1 and GLP-1R in a rat model of FS. Moreover, administration of the GLP-1R inhibitor exendin9-39 increased seizure severity, and sitagliptin reversed the effect, as shown in the electroencephalogram (EEG) and patch-clamp results in a rat model of FS. Furthermore, the GLP-1R-mediated reduction in GABAergic transmission was enhanced by sitagliptin and DPP4 knockdown through increasing miniature inhibitory post-synaptic currents (mIPSCs) in vitro accompanied by increased synaptic release of GABA in vivo. Taken together, our results demonstrate a role of DPP4 in regulating GABAergic transmission via the GLP-1/GLP-1R pathway. These findings indicated that DPP4 may represent a novel therapeutic strategy and target for FS.

Dipeptidyl Peptidase IV as a Prognostic Marker and Therapeutic Target in Papillary Thyroid Carcinoma

Dipeptidyl peptidase IV (DPP4) is overexpressed in thyroid cancer and certain malignancies. Furthermore, DPP4 has been identified as a discriminatory marker for thyroid cancer. However, it remains unclear whether DPP4 expression plays a prognostic role. The aim of this study was to investigate the expression and function of DPP4 in thyroid cancer and the mechanisms involved. We determined the expression of DPP4 by immunohistochemistry in tissue microarrays of thyroid tumors. In vitro functional studies were performed after genetic and pharmacological inhibition of DPP4. Gene expression and pathway analyses were used to identify downstream targets. The therapeutic potential of DPP4 inhibition was evaluated in a mouse xenograft model. High DPP4 expression was associated with extrathyroidal extension (P < 0.001), BRAF mutation (P < 0.001), and advanced tumor stage (P = 0.007) in papillary thyroid cancer. Patients in the high-DPP4 expression group were less likely to be classified as having no evidence of disease at final follow-up (P = 0.042). DPP4 silencing or treatment with DPP4 inhibitors significantly suppressed colony formation, cell migration, and invasion. Analysis of differentially expressed genes after DPP4 knockdown suggested that the transforming growth factor-β signaling pathway is involved. In vivo experiments revealed that sitagliptin treatment reduced tumor growth and xenograft transforming growth factor-β receptor I expression. Increased DPP4 expression is associated with cellular invasion and more aggressive disease in papillary thyroid cancer. Targeting DPP4 may be a therapeutic strategy for DPP4-expressing thyroid cancer.

Dipeptidyl peptidase-4 impairs insulin signaling and promotes lipid accumulation in hepatocytes

Dipeptidyl-peptidase 4 [DPP-4) has evolved into an important target in diabetes therapy due to its role in incretin hormone metabolism. In contrast to its systemic effects, cellular functions of membranous DPP-4 are less clear. Here we studied the role of DPP-4 in hepatic energy metabolism.In order to distinguish systemic from cellular effects we established a cell culture model of DPP-4 knockdown in human hepatoma cell line HepG2.DPP-4 suppression was associated with increased basal glycogen content due to enhanced insulin signaling as shown by increased phosphorylation of insulin-receptor substrate 1 (IRS-1), protein kinase B/Akt and mitogen-activated protein kinases (MAPK)/ERK, respectively. Additionally, glucose-6-phosphatase cDNA expression was significantly decreased in DPP-4 deficiency. Reduced triglyceride content in DPP-4 knockdown cells was paralleled by enhanced expressions of peroxisome proliferator-activated receptor alpha (PPARα) and carnitine palmitoyltransferase −1 (CPT-1) while sterol regulatory element-binding protein 1c (SREBP-1c) expression was significantly decreased.Our data suggest that hepatic DPP-4 induces a selective pathway of insulin resistance with reduced glycogen storage, enhanced glucose output and increased lipid accumulation in the liver. Hepatic DPP-4 might be a novel target in fatty liver disease in patients with glucose intolerance.

Interactions of DPP-4 and integrin β1 influences endothelial-to-mesenchymal transition

Integrin β1 and dipeptidyl peptidase (DPP)-4 play roles in endothelial cell biology. Vascular endothelial growth factor (VEGF)-A inhibits endothelial-to-mesenchymal transition (EndMT) through VEGF-R2, but through VEGF-R1 promotes EndMT by reducing the bioavailability of VEGF-A. Here we tested whether DPP-4-integrin β1 interactions have a role in EndMT in the renal fibrosis of diabetic nephropathy. In streptozotocin-induced fibrotic kidneys in diabetic CD-1 mice, levels of endothelial DPP-4, integrin β1, and phospho-integrin β1 were all higher and associated with plasma cystatin C elevation. The DPP-4 inhibitor linagliptin ameliorated kidney fibrosis, reduced plasma cystatin C levels, and suppressed endothelial levels of DPP-4, integrin β1, and phospho-integrin β1. In cultured endothelial cells, DPP-4 and integrin β1 physically interacted. Suppression of DPP-4 by siRNA was associated with suppression of integrin β1 and vice versa. Knockdown of either integrin β1 or DPP-4 resulted in the silencing of TGF-β2-induced TGF-β receptor heterodimer formation, smad3 phosphorylation, and EndMT. DPP-4 negatively regulated endothelial viability signaling by VEGF-R2 suppression and VEGF-R1 induction in endothelial cells. Thus, DPP-4 and integrin β1 interactions regulate key endothelial cell signal transduction in both physiological and pathological conditions including EndMT. Hence, inhibiting DPP-4 may be a therapeutic target for treating kidney fibrosis in diabetes.

A Potential Role for Dendritic Cell/Macrophage-Expressing DPP4 in Obesity-Induced Visceral Inflammation

Dipeptidyl peptidase-4 (DDP4) inhibitors target the enzymatic degradation of incretin peptides and represent a major advance in the treatment of type 2 diabetes. DPP4 has a number of nonenzymatic functions that involve its interaction with adenosine deaminase (ADA) and other extracellular matrix proteins. Here, we assessed the nonenzymatic role of DPP4 in regulating dendritic cell (DC)/macrophage–mediated adipose inflammation in obesity. Both obese humans and rodents demonstrated increased levels of DPP4 expression in DC/macrophage cell populations from visceral adipose tissue (VAT). The DPP4 expression increased during monocyte differentiation to DC/macrophages and with lipopolysaccharide (LPS)-induced activation of DC/macrophages. The DPP4 colocalized with membrane-bound ADA on human DCs and enhanced the ability of the latter to stimulate T-cell proliferation. The DPP4 interaction with ADA in human DC/macrophages was competitively inhibited by the addition of exogenous soluble DPP4. Knockdown of DPP4 in human DCs, but not pharmacologic inhibition of their enzymatic function, significantly attenuated the ability to activate T cells without influencing its capacity to secrete proinflammatory cytokines. The nonenzymatic function of DPP4 on DC may play a role in potentiation of inflammation in obesity by interacting with ADA. These findings suggest a novel role for the paracrine regulation of inflammation in adipose tissue by DPP4.

Abstract 92: A Novel Role for Dipeptidyl Peptidase-4 and Adenosine Deaminase in Regulating Macrophage and Dendritic Cell Function: Implications for Treatment of Type 2 Diabetes

Introduction: In addition to its powerful effects on glycemic control via enzymatic degradation of incretins, Dipeptidyl peptidase-4 (DDP4) also exerts non-metabolic functions. Despite the ubiquitous use of DPP4 inhibitors in the treatment of Type 2 diabetes (T2D), their effects on immune cell function are poorly understood. Hypothesis: In this study, we investigated the hypothesis that DPP4 may play a critical role in modulating T cell proliferation through its expression on dendritic cells (DCs) and further characterized its role in adipose inflammation in patients with morbid obesity. Methods: Monocytes were isolated from peripheral blood of healthy donors. DCs were induced from monocytes by rhGM-CSF and rhIL-4. DPP4 expression and T-cell proliferation were detected by flow cytometry. DPP4 knockdown was accomplished by transient transfection with DPP4-specific siRNA. Human visceral adipose tissues were used for stromal vascular fraction isolation. Results: 7.5±3.1% (n=10) of peripheral monocytes expressed DPP4. DPP4 dramatically increased when monocyte was differentiated to DC/Macrophage or activated by LPS. Interestingly, DPP4 expression was much higher on the DC/Macrophage in adipose tissue than that of peripheral blood. Furthermore, an increase of DPP4 on adipose tissue macrophages in obese patients was observed (13.2±2.4 vs. 7.9±1.6 for obese vs. lean, n=5). And there was a correlation between DPP4 expression and insulin level (y = 0.9094x-3.6088, R 2 =0.6943). Cell surface DPP4 was able to bind adenosine deaminase (ADA). The binding enhanced the capability of DCs to stimulate T-cell proliferation by relieving the suppressive effect of adenosine on T-cell proliferation. Knockdown of DPP4 on DCs by siRNA attenuated their ability to stimulate T-cell proliferation without influence on the secretion of pro-inflammatory cytokines by DCs. Conclusions: DPP4 on DCs mediates binding of ADA and may re-create a microenvironment suitable for T-cell proliferation. This interaction in DCs between ADA and DPP4 may promote adipose T-cell inflammation and play facilatatory role in T2D. Pro-inflammatory effects of DPP4 and the elucidation of its enzymatic v.s. non-enzymatic contributions may be of fundamental importance in the understanding of T2D.