Dipeptidyl peptidases in atherosclerosis: expression and role in macrophage differentiation, activation and apoptosis

Unravelling the role of dipeptidyl peptidases-8/9 (DPP-8/9) in inflammatory osteoporosis: a comprehensive study investigating chrysin as a potential anti-osteoporotic agent

OBJECTIVES

This study aimed to investigate the role of dipeptidyl peptidase-8 and 9 (DPP-8/9) enzymes in inflammatory bone loss using a 4-vinylcyclohexene diepoxide (VCD)-induced model in Wistar rats. Additionally, we evaluated the therapeutic potential of inhibiting these enzymes with the flavonoid chrysin.

METHODS

Inflammatory osteoporosis was induced by administering VCD that elevated interleukin-6 (IL-6) and tumour necrosis factor-alpha (TNF-α) levels. DPP-8/9 enzyme expression and various bone markers were assayed using serum. Further analysis included bone microarchitecture, histology, and immunohistochemistry. Additionally, chrysin's potential to inhibit DPP-8/9 and mitigate VCD-induced inflammatory bone loss was also evaluated.

KEY FINDINGS

VCD administration in rats caused ovotoxicity that increased IL-6 and TNF-α levels, resulting in significant bone loss. Serum analysis revealed elevated bone resorption markers and DPP-8/9 enzyme levels. Inhibiting DPP-8/9 with 1G244 reversed these effects, confirmed by histology, immunohistochemistry, and micro-CT scans. Moreover, chrysin significantly reduced DPP-8/9 levels compared with the untreated group, improved bone markers, and lower inflammatory cytokines, indicating reduced osteoclastogenesis.

CONCLUSION

This study highlights the role of DPP-8/9 in inflammation-induced osteoporosis. Following inhibition of DPP-8/9, we observed improved bone markers with preservation of trabecular bone mineral density in rats. Additionally, chrysin demonstrated potential as an anti-DPP-8/9 agent, suggesting its viability for future therapeutic interventions in DPP-8/9-related inflammatory diseases.

Programmed death of macrophages in atherosclerosis: mechanisms and therapeutic targets

Atherosclerosis is a progressive inflammatory disorder of the arterial vessel wall characterized by substantial infiltration of macrophages, which exert both favourable and detrimental functions. Early in atherogenesis, macrophages can clear cytotoxic lipoproteins and dead cells, preventing cytotoxicity. Efferocytosis - the efficient clearance of dead cells by macrophages - is crucial for preventing secondary necrosis and stimulating the release of anti-inflammatory cytokines. In addition, macrophages can promote tissue repair and proliferation of vascular smooth muscle cells, thereby increasing plaque stability. However, advanced atherosclerotic plaques contain large numbers of pro-inflammatory macrophages that secrete matrix-degrading enzymes, induce death in surrounding cells and contribute to plaque destabilization and rupture. Importantly, macrophages in the plaque can undergo apoptosis and several forms of regulated necrosis, including necroptosis, pyroptosis and ferroptosis. Regulated necrosis has an important role in the formation and expansion of the necrotic core during plaque progression, and several triggers for necrosis are present within atherosclerotic plaques. This Review focuses on the various forms of programmed macrophage death in atherosclerosis and the pharmacological interventions that target them as a potential means of stabilizing vulnerable plaques and improving the efficacy of currently available anti-atherosclerotic therapies.

Active site-directed probes targeting dipeptidyl peptidases 8 and 9

Dipeptidyl peptidases (DPP) 8 and 9 are intracellular serine proteases that play key roles in various biological processes and recent findings highlight DPP8 and DPP9 as potential therapeutic targets for hematological and inflammasome-related diseases. Despite the substantial progress, the precise biological functions of these proteases remain elusive, and the lack of selective chemical tools hampers ongoing research. In this paper, we describe the synthesis and biochemical evaluation of the first active site-directed DPP8/9 probes which are derived from DPP8/9 inhibitors developed in-house. Specifically, we synthesized fluorescent inhibitors containing nitrobenzoxadiazole (NBD), dansyl (DNS) and cyanine-3 (Cy3) reporters to visualize intracellular DPP8/9. We demonstrate that the fluorescent inhibitors have high affinity and selectivity towards DPP8/9 over related S9 family members. The NBD-labeled DPP8/9 inhibitors were nominated as the best in class compounds to visualize DPP8/9 in human cells. Furthermore, a method has been developed for selective labeling and visualization of active DPP8/9 in vitro by fluorescence microscopy. A collection of potent and selective biotinylated DPP8/9-targeting probes was also prepared by replacing the fluorescent reporter with a biotin group. The present work provides the first DPP8/9-targeting fluorescent compounds as useful chemical tools for the study of DPP8 and DPP9's biological functions.

Characterization of the proteome of stable and unstable carotid atherosclerotic plaques using data-independent acquisition mass spectrometry

BACKGROUND

Currently, noninvasive imaging techniques and circulating biomarkers are still insufficient to accurately assess carotid plaque stability, and an in-depth understanding of the molecular mechanisms that contribute to plaque instability is still lacking.

METHODS

We established a clinical study cohort containing 182 patients with carotid artery stenosis. After screening, 39 stable and 49 unstable plaques were included in the discovery group, and quantitative proteomics analysis based on data independent acquisition was performed for these plaque samples. Additionally, 35 plaques were included in the validation group to validate the proteomics results by immunohistochemistry analysis.

RESULTS

A total of 397 differentially expressed proteins were identified in stable and unstable plaques. These proteins are primarily involved in ferroptosis and lipid metabolism-related functions and pathways. Plaque validation results showed that ferroptosis- and lipid metabolism-related proteins had different expression trends in stable plaques versus unstable fibrous cap regions and lipid core regions. Ferroptosis- and lipid metabolism-related mechanisms in plaque stability were discussed.

CONCLUSIONS

Our results may provide a valuable strategy for revealing the mechanisms affecting plaque stability and will facilitate the discovery of specific biomarkers to broaden the therapeutic scope.

Dipeptidyl-Aminopeptidases 8 and 9 Regulate Autophagy and Tamoxifen Response in Breast Cancer Cells

The cytosolic dipeptidyl-aminopeptidases 8 (DPP8) and 9 (DPP9) belong to the DPPIV serine proteases with the unique characteristic of cleaving off a dipeptide post-proline from the N-termini of substrates. To study the role of DPP8 and DPP9 in breast cancer, MCF-7 cells (luminal A-type breast cancer) and MDA.MB-231 cells (basal-like breast cancer) were used. The inhibition of DPP8/9 by 1G244 increased the number of lysosomes in both cell lines. This phenotype was more pronounced in MCF-7 cells, in which we observed a separation of autophagosomes and lysosomes in the cytosol upon DPP8/9 inhibition. Likewise, the shRNA-mediated knockdown of either DPP8 or DPP9 induced autophagy and increased lysosomes. DPP8/9 inhibition as well as the knockdown of the DPPs reduced the cell survival and proliferation of MCF-7 cells. Additional treatment of MCF-7 cells with tamoxifen, a selective estrogen receptor modulator (SERM) used to treat patients with luminal breast tumors, further decreased survival and proliferation, as well as increased cell death. In summary, both DPP8 and DPP9 activities confine macroautophagy in breast cancer cells. Thus, their inhibition or knockdown reduces cell viability and sensitizes luminal breast cancer cells to tamoxifen treatment.

Non-Specific Inhibition of Dipeptidyl Peptidases 8/9 by Dipeptidyl Peptidase 4 Inhibitors Negatively Affects Mesenchymal Stem Cell Differentiation

DPP4 may play a relevant role in MSC differentiation into osteoblasts or adipocytes. Dipeptidyl peptidase 4 (DPP4) inhibitors (DPP4i), such as sitagliptin and vildagliptin, are used as antidiabetic drugs. However, vildagliptin is not a specific DPP4i and also inhibits DPP8/9, which is involved in energy metabolism and immune regulation. The aim of this study is to evaluate how sitagliptin, vildagliptin or 1G244 (a DPP8/9 specific inhibitor) may influence cell viability, as well as osteogenic and adipogenic differentiation in human mesenchymal stem cells (MSC). Viability, apoptosis, osteoblastogenesis and adipogenesis markers, as well as protein synthesis of β-catenin, were studied in MSC cultures induced to differentiate into osteoblasts or adipocytes in the presence or absence of sitagliptin, vildagliptin or 1G244. The two tested DPP4i did not affect MSC viability, but 1G244 significantly decreased it in MSC and osteoblast-induced cells. Additionally, 1G244 and vildagliptin inhibited osteogenesis and adipogenesis, unlike sitagliptin. Therefore, inhibition of DPP4 did not affect MSC viability and differentiation, whereas inhibition of DPP8/9 negatively affected MSC. To the best of our knowledge, these results show for the first time that DPP8/9 have an important role in the viability and differentiation of human MSC. This data can be considered for human clinical use of drugs affecting DPP8/9 activity.

The antiatherosclerotic action of 1G244 - An inhibitor of dipeptidyl peptidases 8/9 - is mediated by the induction of macrophage death

BACKGROUND

Targeting cell death to induce favorable functional and morphological changes within atherosclerotic plaques has long been postulated as a promising anti-atherosclerotic strategy. In this regard, inhibition of dipeptidyl peptidases 8/9 has received special attention in the context of chronic inflammatory diseases due to its regulatory role in macrophage death in vivo.

METHODS

The present study investigates the influence of prolonged treatment with 1G244 - an inhibitor of dipeptidyl peptidases 8/9 - on the development of the advanced atherosclerosis plaque in apoE-knockout mice, using morphometric and molecular methods.

RESULTS

1G244 administration has led to a reduction in atherosclerotic plaque size in an apoE-knockout mice model. Moreover, it reduced the content of in-plaque macrophages, attributed by immunohistochemical phenotyping to the pro-inflammatory M1-like activation state of these cells. Inhibition of dipeptidyl peptidases 8/9 augmented the lytic form of death response of activated macrophages in-vitro.

CONCLUSIONS

In summary, inhibition of DPP 8/9 elicited an anti-atherosclerotic effect in apoE^-/- mice, which can be attributed to the lytic form of death induction in activated macrophages, as assessed by the in vitro BMDM model. This, in turn, results in a reduction of the plaque area without its transformation towards a rupture-prone morphology.

ProCPU Is Expressed by (Primary) Human Monocytes and Macrophages and Expression Differs between States of Differentiation and Activation

Carboxypeptidase U (CPU, TAFIa, CPB2) is a potent attenuator of fibrinolysis that is mainly synthesized by the liver as its inactive precursor proCPU. Aside from its antifibrinolytic properties, evidence exists that CPU can modulate inflammation, thereby regulating communication between coagulation and inflammation. Monocytes and macrophages play a central role in inflammation and interact with coagulation mechanisms resulting in thrombus formation. The involvement of CPU and monocytes/macrophages in inflammation and thrombus formation, and a recent hypothesis that proCPU is expressed in monocytes/macrophages, prompted us to investigate human monocytes and macrophages as a potential source of proCPU. CPB2 mRNA expression and the presence of proCPU/CPU protein were studied in THP-1, PMA-stimulated THP-1 cells and primary human monocytes, M-CSF-, IFN-γ/LPS-, and IL-4-stimulated-macrophages by RT-qPCR, Western blotting, enzyme activity measurements, and immunocytochemistry. CPB2 mRNA and proCPU protein were detected in THP-1 and PMA-stimulated THP-1 cells as well as in primary monocytes and macrophages. Moreover, CPU was detected in the cell medium of all investigated cell types and it was demonstrated that proCPU can be activated into functionally active CPU in the in vitro cell culture environment. Comparison of CPB2 mRNA expression and proCPU concentrations in the cell medium between the different cell types provided evidence that CPB2 mRNA expression and proCPU secretion in monocytes and macrophages is related to the degree to which these cells are differentiated. Our results indicate that primary monocytes and macrophages express proCPU. This sheds new light on monocytes and macrophages as local proCPU sources.

Nonenzymatic function of DPP4 promotes diabetes-associated cognitive dysfunction through IGF-2R/PKA/SP1/ERp29/IP3R2 pathway-mediated impairment of Treg function and M1 microglia polarization

BACKGROUND

Impairment of regulatory T (Treg) cells function is implicated in the pathogenesis of immune imbalance-mediated cognitive impairment. A complete understanding of whether and how this imbalance affect cognitive function in type 2 diabetes is lacking, and the driver affecting this imbalance remains unknown.

METHODS

We examined the impact of enzymatic and non-enzymatic function of DPP4 on Treg cell impairment, microglia polarization and diabetes-associated cognitive defects and identified its underlying mechanism in type 2 diabetic patients with cognitive impairment and in db/db mice.

RESULTS

We report that DPP4 binds to IGF2-R on Treg cell surface and activates PKA/SP1 signaling, which upregulate ERp29 expression and promote its binding to IP3R2, thereby inhibiting IP3R2 degradation and promoting mitochondria-associated ER membrane formation and mitochondria calcium overload in Tregs. This, in turn, impairs Tregs function and polarizes microglia toward a pro-inflammatory phenotype in the hippocampus and finally leads to neuroinflammation and cognitive impairment in type 2 diabetes. Importantly, inhibiting DPP4 enzymatic activity in type 2 diabetic patients or mutating DPP4 enzymatic active site in db/db mice did not reverse these changes. However, IGF-2R knockdown or blockade ameliorated these effects both in vivo and in vitro.

CONCLUSION

These findings highlight the nonenzymatic role of DPP4 in impairing Tregs function, which may facilitate the design of novel immunotherapies for diabetes-associated cognitive impairment.

New insights into the role of dipeptidyl peptidase 8 and dipeptidyl peptidase 9 and their inhibitors

Dipeptidyl peptidase 8 (DPP8) and 9 (DPP9) are widely expressed in mammals including humans, mainly locate in the cytoplasm. The DPP8 and DPP9 (DPP8/9) belong to serine proteolytic enzymes, they can recognize and cleave N-terminal dipeptides of specific substrates if proline is at the penultimate position. Because the localization of DPP8/9 is different from that of DPP4 and the substrates for DPP8/9 are not yet completely clear, their physiological and pathological roles are still being further explored. In this article, we will review the recent research advances focusing on the expression, regulation, and functions of DPP8/9 in physiology and pathology status. Emerging research results have shown that DPP8/9 is involved in various biological processes such as cell behavior, energy metabolism, and immune regulation, which plays an essential role in maintaining normal development and physiological functions of the body. DPP8/9 is also involved in pathological processes such as tumorigenesis, inflammation, and organ fibrosis. In recent years, related research on immune cell pyroptosis has made DPP8/9 a new potential target for the treatment of hematological diseases. In addition, DPP8/9 inhibitors also have great potential in the treatment of tumors and chronic kidney disease.

Association of the rs17574 DPP4 Polymorphism with Premature Coronary Artery Disease in Diabetic Patients: Results from the Cohort of the GEA Mexican Study

Previously, it has been reported that hypoalphalipoproteinemia (HA) is associated with rs17574 DDP4 polymorphism. Considering that in diabetic patients, HA is often present and is a risk factor for premature coronary artery disease (pCAD), the study aimed to evaluate the association of this polymorphism with pCAD in diabetic individuals. We genotyped the rs17574 polymorphism in 405 pCAD patients with T2DM, 736 without T2DM, and 852 normoglycemic individuals without pCAD and T2DM as controls. Serum DPP4 concentration was available in 818 controls, 669 pCAD without T2DM, and 339 pCAD with T2DM. The rs17574 polymorphism was associated with lower risk of pCAD (padditive = 0.007; pdominant = 0.003, pheterozygote = 0.003, pcodominant1 = 0.003). In pCAD with T2DM patients, DPP4 levels were lower when compared with controls (p < 0.001). In the whole sample, individuals with the rs17574 GG genotype have the lowest protein levels compared with AG and AA (p = 0.039) carriers. However, when the same analysis was repeated separately in all groups, a significant difference was observed in the pCAD with T2DM patients; carriers of the GG genotype had the lowest protein levels compared with AG and AA (p = 0.037) genotypes. Our results suggest that in diabetic patients, the rs17574G DPP4 allele could be considered as a protective genetic marker for pCAD. DPP4 concentrations were lower in the diabetic pCAD patients, and the rs17574GG carriers had the lowest protein levels.

CD26 Deficiency Controls Macrophage Polarization Markers and Signal Transducers during Colitis Development and Resolution

Ulcerative colitis (UC) is a multifactorial condition characterized by a destructive immune response that failed to be attenuated by common regulatory mechanisms which reduce inflammation and promote mucosa healing. The inhibition of CD26, a multifunctional glycoprotein that controls the immune response via its dipeptidyl peptidase (DP) 4 enzyme activity, was proven to have beneficial effects in various autoimmune inflammatory diseases. The polarization of macrophages into either pro-inflammatory M1 or anti-inflammatory M2 subclass is a key intersection that mediates the immune-inflammatory process in UC. Hence, we hypothesized that the deficiency of CD26 affects that process in the dextran sulfate sodium (DSS)-induced model of UC. We found that mRNA expression of M2 markers arginase 1 and Fizz were increased, while the expression of M1 marker inducible NO synthase was downregulated in CD26−/− mice. Decreased STAT1 mRNA, as well as upregulated pSTAT6 and pSTAT3, additionally support the demonstrated activation of M2 macrophages under CD26 deficiency. Finally, we investigated DP8 and DP9, proteins with DP4-like activity, and found that CD26 deficiency is not a key factor for the noted upregulation of their expression in UC. In conclusion, we demonstrate that CD26 deficiency regulates macrophage polarization toward the anti-inflammatory M2 phenotype, which is driven by STAT6/STAT3 signaling pathways. This process is additionally enhanced by the reduction of M1 differentiation via the suppression of proinflammatory STAT1. Therefore, further studies should investigate the clinical potential of CD26 inhibitors in the treatment of UC.

Recent advance in treatment of atherosclerosis: Key targets and plaque-positioned delivery strategies

Atherosclerosis, a chronic inflammatory disease of vascular wall, is a progressive pathophysiological process with lipids oxidation/depositing initiation and innate/adaptive immune responses. The coordination of multi systems covering oxidative stress, dysfunctional endothelium, diseased lipid uptake, cell apoptosis, thrombotic and pro-inflammatory responding as well as switched SMCs contributes to plaque growth. In this circumstance, inevitably, targeting these processes is considered to be effective for treating atherosclerosis. Arriving, retention and working of payload candidates mediated by targets in lesion direct ultimate therapeutic outcomes. Accumulating a series of scientific studies and clinical practice in the past decades, lesion homing delivery strategies including stent/balloon/nanoparticle-based transportation worked as the potent promotor to ensure a therapeutic effect. The objective of this review is to achieve a very brief summary about the effective therapeutic methods cooperating specifical targets and positioning-delivery strategies in atherosclerosis for better outcomes.

Molecular pathways and role of epigenetics in the idiopathic pulmonary fibrosis

Idiopathic pulmonary fibrosis (IPF) is a fatal lung disease with unknown etiological factors that can progress to other dangerous diseases like lung cancer. Environmental and genetic predisposition are the two major etiological or risk factors involved in the pathology of the IPF. Among the environmental risk factors, smoking is one of the major causes for the development of IPF. Epigenetic pathways like nucleosomes remodeling, DNA methylation, histone modifications and miRNA mediated genes play a crucial role in development of IPF. Mutations in the genes make the epigenetic factors as important drug targets in IPF. Transcriptional changes due to environmental factors are also involved in the progression of IPF. The mutations in human telomerase reverse transcriptase (hTERT) have shown decreased life expectancy in IPF patients. The TERT-gene is highly expressed in chronic smokers and makes the role of epigenetics evident. Drug like nintedanib acts through vascular endothelial growth factor receptors (VEGFR), while drug pirfenidone acts through transforming growth factor (TGF), which is useful in IPF. Gefitinib, a tyrosine kinase inhibitor of EGFR, is useful as an anti-fibrosis agent in preclinical models. Newer drugs such as Celgene-CC90001 and FibroGen-FG-3019 are currently under investigations acts through the modulating epigenetic mechanisms. Thus, the study on epigenetics opens a wide window for the discovery of newer drugs. This study provides an elementary analysis of multiple regulators of epigenetics and their roles associated with the pathology of IPF. Further, this review also includes epigenetic drugs under development in preclinical and clinical stages.

Perforin, COVID-19 and a possible pathogenic auto-inflammatory feedback loop

During COVID‐19 infection, reduced function of natural killer (NK) cells can lead to both compromised viral clearance and dysregulation of the immune response. Such dysregulation leads to overproduction of cytokines, a raised neutrophil/lymphocyte ratio and monocytosis. This in turn increases IL‐6 expression, which promotes scar and thrombus formation. Excess IL‐6 also leads to a further reduction in NK function through downregulation of perforin expression, therefore forming a pathogenic auto‐inflammatory feedback loop. The perforin/granzyme system of cytotoxicity is the main mechanism through which NK cells and cytotoxic T lymphocytes eliminate virally infected host cells, as well as being central to their role in regulating immune responses to microbial infection. Here, we present epidemiological evidence suggesting an association between perforin expression and resistance to COVID‐19. In addition, we outline the manner in which a pathogenic auto‐inflammatory feedback loop could operate and the relationship of this loop to genes associated with severe COVID‐19. Such an auto‐inflammatory loop may be amenable to synergistic multimodal therapy.

Pleiotropic Benefits of DPP-4 Inhibitors Beyond Glycemic Control

Dipeptidyl peptidase (DPP)-4 inhibitors are oral anti-diabetic medications that block the activity of the ubiquitous enzyme DPP-4. Inhibition of this enzyme increases the level of circulating active glucagon-like peptide (GLP)-1 secreted from L-cells in the small intestine. GLP-1 increases the glucose level, dependent on insulin secretion from pancreatic β-cells; it also decreases the abnormally increased level of glucagon, eventually decreasing the blood glucose level in patients with type 2 diabetes. DPP-4 is involved in many physiological processes other than the degradation of GLP-1. Therefore, the inhibition of DPP-4 may have numerous effects beyond glucose control. In this article, we review the pleiotropic effects of DPP-4 inhibitors beyond glucose control, including their strong beneficial effects on the stress induced accelerated senescence of vascular cells, and the possible clinical implications of these effects.

Dipeptidyl peptidase 4 inhibitors: Applications in innate immunity?

Dipeptidyl peptidase (DPP)-4 inhibitors are a class of orally available, small molecule inhibitors that prolong the insulinotropic activity of the incretin hormone glucagon-like peptide-1 (GLP-1) and are highly effective for the treatment of Type-2 diabetes. DPP4 can also cleave several immunoregulatory peptides including chemokines. Emerging evidence continues to implicate DPP4 inhibitors as immunomodulators, with recent findings suggesting DPP4 inhibitors modify specific aspects of innate immunity. This review summarises recent insights into how DPP4 inhibitors could be implicated in endothelial, neutrophil and monocyte/macrophage mediated immunity. Additionally, this review highlights additional avenues of research with DPP4 inhibitors in the context of the COVID-19 pandemic.

DPP4 Activity, Hyperinsulinemia, and Atherosclerosis

CONTEXT

Obesity and type 2 diabetes are associated with chronic hyperinsulinemia, elevated plasma levels of dipeptidyl peptidase-4 (DPP4), and a pro-atherosclerotic milieu.

EVIDENCE ACQUISITION

PubMed search of the term "insulin and atherosclerosis," "hyperinsulinemia," "atherosclerosis," or "cardiovascular outcomes" cross-referenced with "DPP4." Relevant research and review articles were reviewed.

EVIDENCE SYNTHESIS

Hyperinsulinemia in the setting of insulin resistance promotes vascular inflammation, vascular smooth muscle cell growth, pathological cholesterol profile, hypertension, and recruitment of immune cells to the endothelium, all contributing to atherosclerosis. DPP4 has pleiotropic functions and its activity is elevated in obese humans. DPP4 mirrors hyperinsulinemia's atherogenic actions in the insulin resistant state, and genetic deletion of DPP4 protects rodents from developing insulin resistance and improves cardiovascular outcomes. DPP4 inhibition in pro-atherosclerotic preclinical models results in reduced inflammation and oxidative stress, improved endothelial function, and decreased atherosclerosis. Increased incretin levels may have contributed to but do not completely account for these benefits. Small clinical studies with DPP4 inhibitors demonstrate reduced carotid intimal thickening, improved endothelial function, and reduced arterial stiffness. To date, this has not been translated to cardiovascular risk reduction for individuals with type 2 diabetes with prior or exaggerated risk of cardiovascular disease.

CONCLUSION

DPP4 may represent a key link between central obesity, insulin resistance, and atherosclerosis. The gaps in knowledge in DPP4 function and discrepancy in cardiovascular outcomes observed in preclinical and large-scale randomized controlled studies with DPP4 inhibitors warrant additional research.

Fluorescence Determination of Peptidase Activity Based on the Quenching of a Fluorophore-Labelled Peptide by Graphene Oxide

In this study, a fluorescence detection strategy is reported for the peptidase activity assay, which is based on fluorescence resonance energy transfer (FRET) from a fluorophore-labelled peptide to graphene oxide (GO). By the hydrolysis of the peptide, the fluorophore-labelled peptide releases the fluorophore 5-carboxyfluorescein, which can avoid quenching from GO. Thus, the increased intensity of the obtained fluorescence signal in the assay is directly dependent on the peptidase activity. As a model case of the developed strategy, the activity determination of pancreatic elastase (PE) is performed. Under the optimal experimental conditions at an excitation wavelength of 494 nm, the activity of PE can be determined in the range from 0.003 to 0.10 U/mL, with a detection limit of 0.001 U/mL at the emission wavelength of 518 nm. This is ultra-sensitive for the determination of PE. The specificity of the method is demonstrated by the analysis of PE under complex conditions using fetal bovine serum as the substrate. Hence, the developed method might provide an intrinsically convenient, sensitive platform for the PE activity assay and related biochemical studies due to its homogeneous, and fluorescence-based detection strategy.

Decrease of the pro-inflammatory M1-like response by inhibition of dipeptidyl peptidases 8/9 in THP-1 macrophages - quantitative proteomics of the proteome and secretome

BACKGROUND

Cellular peptidases are an emerging target of novel pharmacological strategies in inflammatory diseases and cancer. In this context, the dipeptidyl peptidases 8 and 9 (DPP8/9) have gained special attention due to their activities in the immune cells. However, in spite of more than hundred protein substrates identified to date by mass spectrometry-based analysis, the cellular DPP8/9 functions are still elusive.

METHODS

We applied the proteomic approach (iTRAQ-2DLC-MS/MS) to comprehensively analyze the role of DPP8/9 in the regulation of macrophage activation by in-depth protein quantitation of THP-1 proteome and secretome.

RESULTS

Cells pre-incubated with DPP8/9 inhibitor (1G244) prior activation (LPS or IL-4/IL-13) diminished the expression levels of M1-like response markers, but not M2-like phenotype features. This was accompanied by multiple intra- and extra-cellular protein abundance changes in THP-1 cells, related to cellular metabolism, mitochondria and endoplasmic reticulum function, as well as those engaged with inflammatory and apoptotic processes, including previously reported and novel DPP8/9 targets.

CONCLUSIONS

Inhibition of DPP 8/9 had a profound effect on the THP-1 macrophage proteome and secretome, evidencing the decrease of the pro-inflammatory M1-like response. Presented results are to our best knowledge the first which, among others, highlight the metabolic effects of DPP8/9 inhibition in macrophages.

Native, Intact Glucagon-Like Peptide 1 Is a Natural Suppressor of Thrombus Growth Under Physiological Flow Conditions

OBJECTIVE

In patients with diabetes mellitus, increased platelet reactivity predicts cardiac events. Limited evidence suggests that DPP-4 (dipeptidyl peptidase 4) influences platelets via GLP-1 (glucagon-like peptide 1)-dependent effects. Because DPP-4 inhibitors are frequently used in diabetes mellitus to improve the GLP-1-regulated glucose metabolism, we characterized the role of DPP-4 inhibition and of native intact versus DPP-4-cleaved GLP-1 on flow-dependent thrombus formation in mouse and human blood. Approach and Results: An ex vivo whole blood microfluidics model was applied to approach in vivo thrombosis and study collagen-dependent platelet adhesion, activation, and thrombus formation under shear-flow conditions by multiparameter analyses. In mice, in vivo inhibition or genetic deficiency of DPP-4 (Dpp4^-/-), but not of GLP-1-receptors (Glp1r^-/-), suppressed flow-dependent platelet aggregation. In human blood, GLP-1(7-36), but not DPP-4-cleaved GLP-1(9-36), reduced thrombus volume by 32% and impaired whole blood thrombus formation at both low/venous and high/arterial wall-shear rates. These effects were enforced upon ADP costimulation and occurred independently of plasma factors and leukocytes. Human platelets did not contain detectable levels of GLP-1-receptor transcripts. Also, GLP-1(7-36) did not inhibit collagen-induced aggregation under conditions of stirring or stasis of platelets, pointing to a marked flow-dependent role.

CONCLUSIONS

Native, intact GLP-1 is a natural suppressor of thrombus growth under physiological flow conditions, with DPP-4 inhibition and increased intact GLP-1 suppressing platelet aggregation under flow without a main relevance of GLP-1-receptor on platelets.

Vildagliptin, a DPP-4 Inhibitor, Attenuates Endothelial Dysfunction and Atherogenesis in Nondiabetic Apolipoprotein E-Deficient Mice

Dipeptidyl peptidase-4 (DPP-4) inhibitors are novel antidiabetic agents with possible vascular protection effects. Endothelial dysfunction is an initiation step in atherogenesis. The purpose of this study was to investigate whether vildagliptin (Vilda) attenuates the development of endothelial dysfunction and atherosclerotic lesions in nondiabetic apolipoprotein E-deficient (ApoE^-/-) mice. Eight-week-old nondiabetic ApoE^-/- mice fed a Western-type diet received Vilda (50 mg/kg/day) for 20 weeks or 8 weeks. After 20 weeks of treatment, Vilda administration reduced atherogenesis in the aortic arch as determined by en face Sudan IV staining compared with the vehicle group (P < 0.05). Vilda also reduced lipid accumulation (P < 0.05) and vascular cell adhesion molecule-1 (VCAM-1) expression (P < 0.05) and tended to decrease macrophage infiltration (P = 0.05) into atherosclerotic plaques compared with vehicle. After 8 weeks of treatment, endothelium-dependent vascular reactivity was examined. Vilda administration significantly attenuated the impairment of endothelial function in nondiabetic ApoE^-/- mice compared with the vehicle group (P < 0.05). Vilda treatment did not alter metabolic parameters, including blood glucose level, in both study protocols. To investigate the mechanism, aortic segments obtained from wild-type mice were incubated with exendin-4 (Ex-4), a glucagon-like peptide-1 (GLP-1) analog, in the presence or absence of lipopolysaccharide (LPS). Ex-4 attenuated the impairment of endothelium-dependent vasodilation induced by LPS (P < 0.01). Furthermore, Ex-4 promoted phosphorylation of eNOS at Ser1177 which was decreased by LPS in human umbilical endothelial cells (P < 0.05). Vilda inhibited the development of endothelial dysfunction and prevented atherogenesis in nondiabetic ApoE^-/- mice. Our results suggested that GLP-1-dependent amelioration of endothelial dysfunction is associated with the atheroprotective effects of Vilda.

Development of a 13C Stable Isotope Assay for Dipeptidyl Peptidase-4 Enzyme Activity A New Breath Test for Dipeptidyl Peptidase Activity

Dipeptidyl peptidase-4 inhibitors (DPP4i) are a class of orally available, small molecule inhibitors for the management of Type-II diabetes. A rapid, real-time, functional breath test for DPP4 enzyme activity could help to define DPP4i efficacy in patients that are refractory to treatment. We aimed to develop a selective, non-invasive, stable-isotope ¹³C-breath test for DPP4. In vitro experiments were performed using high (Caco-2) and low (HeLa) DPP4 expressing cells. DPP gene expression was determined in cell lines by qRT-PCR. A DPP4 selective ¹³C-tripeptide was added to cells in the presence and absence of the DPP4 inhibitor Sitagliptin. Gas samples were collected from the cell headspace and ¹³CO₂ content quantified by isotope ratio mass spectrometry (IRMS). DPP4 was highly expressed in Caco-2 cells compared to HeLa cells and using the ¹³C-tripeptide, we detected a high ¹³CO₂ signal from Caco2 cells. Addition of Sitaglitpin to Caco2 cells significantly inhibited this ¹³CO₂ signal. ¹³C-assay DPP4 activity correlated positively with the enzyme activity detected using a colorimetric substrate. We have developed a selective, non-invasive, ¹³C-assay for DPP4 that could have broad translational applications in diabetes and gastrointestinal disease.

CD26/DPP4 - a potential biomarker and target for cancer therapy

CD26/dipeptidyl peptidase (DPP)4 is a membrane-bound protein found in many cell types of the body, and a soluble form is present in body fluids. There is longstanding evidence that various primary tumors and also metastases express CD26/DPP4 to a variable extent. By cleaving dipeptides from peptides with a proline or alanine in the penultimate position at the N-terminus, it regulates the activity of incretin hormones, chemokines and many other peptides. Due to these effects and interactions with other molecules, a tumor promoting or suppressing role can be attributed to CD26/DPP4. In this review, we discuss the existing evidence on the expression of soluble or membrane-bound CD26/DPP4 in malignant diseases, along with the most recent findings on CD26/DPP4 as a therapeutic target in specific malignancies. The expression and possible involvement of the related DPP8 and DPP9 in cancer are also reviewed. A higher expression of CD26/DPP4 is found in a wide variety of tumor entities, however more research on CD26/DPP4 in the tumor microenvironment is needed to fully explore its use as a tumor biomarker. Circulating soluble CD26/DPP4 has also been studied as a cancer biomarker, however, the observed decrease in most cancer patients does not seem to be cancer specific. Encouraging results from experimental work and a recently reported first phase clinical trial targeting CD26/DPP4 in mesothelioma, renal and urological tumors pave the way for follow-up clinical studies, also in other tumor entities, possibly leading to the development of more effective complementary therapies against cancer.

M2 Macrophages as a Potential Target for Antiatherosclerosis Treatment

Atherosclerosis is a chronic progressive inflammation course, which could induce life-threatening diseases such as stroke and myocardial infarction. Optimal medical treatments for atherosclerotic risk factors with current antihypertensive and lipid-lowering drugs (for example, statins) are widely used in clinical practice. However, many patients with established disease still continue to have recurrent cardiovascular events in spite of treatment with a state-of-the-art therapy. Atherosclerotic cardiovascular disease (ASCVD) remains the leading cause of mortality worldwide. Hence, current treatment of atherosclerosis is still far from being satisfactory. Recently, M2 macrophages have been found associated with atherosclerosis regression. The M2 phenotype can secrete anti-inflammatory factors such as IL-10 and TGF-β, promote tissue remodeling and repairing through collagen formation, and clear dying cells and debris by efferocytosis. Therefore, modulators targeting macrophages' polarization to the M2 phenotype could be another promising treatment strategy for atherosclerosis. Two main signaling pathways, the Akt/mTORC/LXR pathway and the JAK/STAT6 pathway, are found playing important roles in M2 polarization. In addition, researchers have reported several potential approaches to modulate M2 polarization. Inhibiting or activating some kinds of enzymes, affecting transcription factors, or acting on several membrane receptors could regulate the polarization of the M2 phenotype. Besides, biomolecules, for example vitamin D, were found to affect the process of M2 polarization. Pomegranate juice could promote M2 polarization via unclear mechanism. In this review, we will discuss how M2 macrophages affect atherosclerosis regression, signal transduction in M2 polarization, and outline potential targets and compounds that affect M2 polarization, thus controlling the progress of atherosclerosis.

DPP8/DPP9 inhibition elicits canonical Nlrp1b inflammasome hallmarks in murine macrophages

Activating germline mutations in the human inflammasome sensor NLRP1 causes palmoplantar dyskeratosis and susceptibility to Mendelian autoinflammatory diseases. Recent studies have shown that the cytosolic serine dipeptidyl peptidases DPP8 and DPP9 suppress inflammasome activation upstream of NLRP1 and CARD8 in human keratinocytes and peripheral blood mononuclear cells. Moreover, pharmacological inhibition of DPP8/DPP9 protease activity was shown to induce pyroptosis in murine C57BL/6 macrophages without eliciting other inflammasome hallmark responses. Here, we show that DPP8/DPP9 inhibition in macrophages that express a Bacillus anthracis lethal toxin (LeTx)-sensitive Nlrp1b allele triggered significantly accelerated pyroptosis concomitant with caspase-1 maturation, ASC speck assembly, and secretion of mature IL-1β and IL-18. Genetic ablation of ASC prevented DPP8/DPP9 inhibition-induced caspase-1 maturation and partially hampered pyroptosis and inflammasome-dependent cytokine release, whereas deletion of caspase-1 or gasdermin D triggered apoptosis in the absence of IL-1β and IL-18 secretion. In conclusion, blockade of DPP8/DPP9 protease activity triggers rapid pyroptosis and canonical inflammasome hallmarks in primary macrophages that express a LeTx-responsive Nlrp1b allele.

Targeting dipeptidyl peptidase 8 genes inhibits proliferation, migration and invasion by inhibition of cyclin D1 and MMP2MMP9 signal pathway in cervical cancer

BACKGROUND

DPP8 is a member of the dipeptidyl peptidase IV family, which belongs to the S9b protease subfamily. It regulates cell proliferation, apoptosis, migration and invasion during cancer progression.

METHODS

To investigate the role of DPP8 in cervical cancer, we examined DPP8 levels in cervical cancer tissues and cells. The localization of DPP8 was determined by immunofluorescence staining. Subsequently, SiHa and HeLa cells were treated with small interfering RNA (siRNA)-DPP8. We used cell cycle analysis, an 5-ethyl-2'-deoxyuridine assay proliferation assay and a cellular apoptosis assay to determine the effect of DPP8 on the proliferation and apoptosis of cervical cancer cells. We used a Transwell assay to assess the number of transfection cancer cells migrating through the matrix. A real-time polymerase chain reaction and western blot analysis were used to analyze the expression of related proteins and to determine the phenotype caused by the depletion or overexpression of DPP8 in cervical cancer cells.

RESULTS

We observed that DPP8 was highly expressed in cervical cancer tissues and cells. DPP8 expression was observed in the cytosol and in the perinuclear area, as well as in the nuclei of cervical cancer cells. Notably, when cells were treated with siRNA-DPP8, the expression of BAX increased, and the expression of cyclin D1, Bcl-2, MMP2 and MMP9 was downregulated. In cervical cancer cell lines, silencing the expression of DPP8 not only suppressed the proliferation, migration and invasion of the cervical cancer cells, but also promoted cervical cancer cell apoptosis.

CONCLUSIONS

The data obtained in the present study reveal that DPP8 promotes the progression of cervical cancer.

Prolyl carboxypeptidase activity in the circulation and its correlation with body weight and adipose tissue in lean and obese subjects

Background

Prolyl carboxypeptidase (PRCP) is involved in the regulation of body weight, likely by hydrolysing alpha-melanocyte-stimulating hormone and apelin in the hypothalamus and in the periphery. A link between PRCP protein concentrations in plasma and metabolic disorders has been reported. In this study, we investigated the distribution of circulating PRCP activity and assessed its relation with body weight and adipose tissue in obese patients and patients who significantly lost weight.

Methods

PRCP activity was measured using reversed-phase high-performance liquid chromatography in different isolated blood fractions and primary human cells to investigate the distribution of circulating PRCP. PRCP activity was measured in serum of individuals (n = 75) categorized based on their body mass index (BMI < 25.0; 25.0–29.9; 30.0–39.9; ≥ 40.0 kg/m²) and the diagnosis of metabolic syndrome. Differences in serum PRCP activity were determined before and six months after weight loss, either by diet (n = 45) or by bariatric surgery (n = 24). Potential correlations between serum PRCP activity and several metabolic and biochemical parameters were assessed. Additionally, plasma PRCP concentrations were quantified using a sensitive ELISA in the bariatric surgery group.

Results

White blood cells and plasma contributed the most to circulating PRCP activity. Serum PRCP activity in lean subjects was 0.83 ± 0.04 U/L and increased significantly with a rising BMI (p<0.001) and decreased upon weight loss (diet, p<0.05; bariatric surgery, p<0.001). The serum PRCP activity alteration reflected body weight changes and was found to be positively correlated with several metabolic parameters, including: total, abdominal and visceral adipose tissue. Plasma PRCP concentration was found to be significantly correlated to serum PRCP activity (0.865; p<0.001). Additionally, a significant decrease (p<0.001) in plasma PRCP protein concentration (mean ± SD) before (18.2 ± 3.7 ng/mL) and 6 months after bariatric surgery (15.7 ± 2.7 ng/mL) was found.

Conclusion

Our novel findings demonstrate that white blood cells and plasma contributed the most to circulating PRCP activity. Additionally, we have shown that there were significant correlations between serum PRCP activity and various metabolic parameters, and that plasma PRCP concentration was significantly correlated to serum PRCP activity. These novel findings on PRCP activity in serum support further investigation of its in vivo role and involvement in several metabolic diseases.

DPP9 enzymatic activity in hematopoietic cells is dispensable for mouse hematopoiesis

Dipeptidyl peptidase 9 (DPP9) is a ubiquitously expressed intracellular prolyl peptidase implicated in immunoregulation. However, its physiological relevance in the immune system remains largely unknown. We investigated the role of DPP9 enzyme in immune system by characterizing DPP9 knock-in mice expressing a catalytically inactive S729A mutant of DPP9 enzyme (DPP9^ki/ki mice). DPP9^ki/ki mice show reduced number of lymphoid and myeloid cells in fetal liver and postnatal blood but their hematopoietic cells are fully functional and able to reconstitute lymphoid and myeloid lineages even in competitive mixed chimeras. These studies demonstrate that inactivation of DPP9 enzymatic activity does not lead to any perturbations in mouse hematopoiesis.

The effect of CD26-deficiency on dipeptidyl peptidase 8 and 9 expression profiles in a mouse model of Crohn's disease

The involvement of dipeptidyl peptidase (DP) IV/CD26 (DPP IV/CD26) family members in the pathogenesis of Crohn's disease (CD), an autoimmune inflammatory condition of the gut, is effected mainly through proteolytic cleavage of immunomodulatory substrates and DPP IV/CD26's costimulatory function. DP8 and DP9 are proteases with diverse functions including cell interactions, apoptosis, and immune response but their localization remains to be clarified. We assessed the impact of DPP IV/CD26 deficiency (CD26^-/- ) on the expression profiles of DP8 and DP9 by qPCR and immunodetection as well as quantified DP8/9 enzyme activity in distinctive phases of a chemically-induced CD model in mice. CD26^-/- did not affect colon DP8 mRNA expression, while the physiological concentration of DP8 protein is decreased in CD26^-/- mice but rises in inflammation (P < 0.05). On the other hand, DP9 mRNA level is significantly increased in CD26^-/- mice in inflammation as well as healing with the DP9 concentration being almost twofold increased (P < 0.05) in all experimental points in CD26^-/- mice compared to wild-type indicating the expected up-regulation in CD26^-/- conditions. Surprisingly, dominantly intracellular DP8 and DP9 were found in abundance in serum. DP8/9 activity is decreased in the inflamed colon, whereas its contribution to the overall serum DPP IV/CD26-like activity is negligible, suggesting the importance of their extra-enzymatic functions. To summarize, CD induction generated gene, protein and enzymatic changes of DP8 and DP9 so their involvement in inflammation development and/or healing process is implicated, especially in CD26^-/- , and the question of their subcellular localization should be revised.

DPP9 enzyme activity controls survival of mouse migratory tongue muscle progenitors and its absence leads to neonatal lethality due to suckling defect

Dipeptidyl peptidase 9 (DPP9) is an intracellular N-terminal post-proline-cleaving enzyme whose physiological function remains largely unknown. We investigated the role of DPP9 enzyme in vivo by characterizing knock-in mice expressing a catalytically inactive mutant form of DPP9 (S729A; DPP9^ki/ki mice). We show that DPP9^ki/ki mice die within 12-18h after birth. The neonatal lethality can be rescued by manual feeding, indicating that a suckling defect is the primary cause of neonatal lethality. The suckling defect results from microglossia, and is characterized by abnormal formation of intrinsic muscles at the distal tongue. In DPP9^ki/ki mice, the number of occipital somite-derived migratory muscle progenitors, forming distal tongue intrinsic muscles, is reduced due to increased apoptosis. In contrast, intrinsic muscles of the proximal tongue and extrinsic tongue muscles, which derive from head mesoderm, develop normally in DPP9^ki/ki mice. Thus, lack of DPP9 activity in mice leads to impaired tongue development, suckling defect and subsequent neonatal lethality due to impaired survival of a specific subset of migratory tongue muscle progenitors.

Sitagliptin attenuates high glucose-induced alterations in migration, proliferation, calcification and apoptosis of vascular smooth muscle cells through ERK1/2 signal pathway

Background/Aims

This study investigated the effects of sitagliptin on migration, proliferation, calcification and apoptosis of vascular smooth muscle cells (VSMCs) under high glucose (HG) conditions.

Methods

VSMCs were isolated from the thoracic aorta of Sprague Dawley rats. The cultured VSMCs were subjected to control medium, mannitol medium, HG medium (25 mM), pretreatment with 200 nM sitagliptin in control or HG medium, or the ERK1/2 inhibitor PD98059 in HG medium. Cell proliferation, migration, apoptosis and calcification were determined.

Results

HG conditions promoted the proliferation, migration, calcification and impairment of apoptosis in VSMCs compared with controls (P<0.05). Pretreatment with sitagliptin effectively attenuated proliferation, migration, calcification of cells and increased apoptosis of HG-cultured VSMCs as compared with the HG group (P<0.05). Culture with HG resulted in the up-regulation of p-ERK1/2 in VSMCs, whereas sitagliptin pretreatment could inhibit HG-induced p-ERK1/2 expression. In addition, the ERK1/2 inhibitor PD98059, inhibited proliferation, migration, calcification and promoted the apoptosis of HG-cultured VSMCs compared with the HG group (P<0.05).

Conclusion

The effects of sitagliptin on VSMC under high glucose condition were achieved through ERK1/2 signaling pathways.

Crystal structure of Porphyromonas gingivalis dipeptidyl peptidase 4 and structure-activity relationships based on inhibitor profiling

The Gram-negative anaerobe Porphyromonas gingivalis is associated with chronic periodontitis. Clinical isolates of P. gingivalis strains with high dipeptidyl peptidase 4 (DPP4) expression also had a high capacity for biofilm formation and were more infective. The X-ray crystal structure of P. gingivalis DPP4 was solved at 2.2 Å resolution. Despite a sequence identity of 32%, the overall structure of the dimer was conserved between P. gingivalis DPP4 and mammalian orthologues. The structures of the substrate binding sites were also conserved, except for the region called S2-extensive, which is exploited by specific human DPP4 inhibitors currently used as antidiabetic drugs. Screening of a collection of 450 compounds as inhibitors revealed a structure-activity relationship that mimics in part that of mammalian DPP9. The functional similarity between human and bacterial DPP4 was confirmed using 124 potential peptide substrates.

Additive effects of atorvastatin combined with sitagliptin on rats with myocardial infarction: a pilot study

INTRODUCTION

Atorvastatin and sitagliptin are able to exert cardio-protective effects. However, whether atorvastatin plus sitagliptin could confer additive benefits for rats with myocardial infarction (MI) is unknown.

MATERIAL AND METHODS

Forty rats with MI were produced and 37 surviving rats were randomly divided into atorvastatin (10 mg/kg daily, n = 9), sitagliptin (10 mg/kg daily, n = 9), combined (10 mg/kg daily atorvastatin plus 10 mg/kg daily sitagliptin, n = 9), and control groups (3 ml normal saline daily, n = 10). Fourteen days later, cardiac function was detected and fasting venous blood was sampled for lipid profiles and glucose evaluation. Cardiac tissues were used for hematoxylin-eosin staining, for interleukin-6 (IL-6) and tumor necrotic factor-α (TNF-α) evaluation, and for rho-associated kinase 2 (ROCK2) assessment.

RESULTS

Fourteen days after MI, the inflammatory reaction regarding the degree of leukocyte infiltration and IL-6 and TNF-α expression in cardiac tissues was ameliorated in atorvastatin and sitagliptin groups compared to the control group (p < 0.05). In addition, ROCK2 was attenuated by either atorvastatin or sitagliptin (p < 0.05). Echocardiography showed that cardiac function was significantly improved with atorvastatin and sitagliptin therapy (p < 0.05). Overall, all these benefits were further enhanced by combined therapy, suggesting that atorvastatin combined with sitagliptin therapy has additive effects on reducing cardiac inflammation and improving cardiac function. No significant changes in lipid profiles or glucose were observed, suggesting that the benefits derived from atorvastatin and sitagliptin therapy might not depend on cholesterol and glucose modulation.

CONCLUSIONS

In rats with MI, atorvastatin plus sitagliptin therapy provides additive effects for cardio-protection, and mechanisms operating in these processes may be due to ROCK2 diminishment.

Histamine promotes the differentiation of macrophages from CD11b+ myeloid cells and formation of foam cells through a Stat6-dependent pathway

BACKGROUND AND AIMS

The enzyme histidine decarboxylase (Hdc), which generates histamine, is highly expressed in CD11b⁺Gr-1⁺ myeloid cells that play a critical role in infection, inflammation and tumorigenesis. The aim of this study was to explore the role of Hdc-expressing CD11b⁺ myeloid cells or histamine in atherogenesis.

METHODS

Hdc-EGFP bacterial artificial chromosome (BAC) transgenic reporter mice (Hdc-EGFP) were used to track Hdc expression during the development of atherosclerosis. The expression of EGFP fluorescence was examined by immunofluorescence staining in a variety of adult tissues. Wild-type (WT), Apoe knockout (Apoe^-/-), Hdc knockout (Hdc^-/-), and Stat6 knockout (Stat6^-/-) mice were used. Serum concentration of histamine was determined with ELISA. Changes in subsets of immune cells were evaluated by flow cytometry (FACS). Non-invasive tracking of the expression of CD11b⁺ myeloid cells was tested using ¹²⁵I-anti-CD11b SPECT/CT imaging in the early stages of atherogenesis. Microarray analysis and RT-PCR were applied to detect gene expressions while Western blot was used to assess protein levels.

RESULTS

Using Hdc-EGFP transgenic mice, we demonstrated that Hdc⁺CD11b⁺ myeloid cells increase in the circulation in response to hypercholesterolemia and contribute to foam cell formation in atherosclerosis. Histamine deficiency in Hdc knockout (Hdc^-/-) mice repressed the differentiation of CD11b⁺Ly6C^high classically activated M1-type macrophages and CD11b⁺CD11c⁺ dendritic cells (DCs), which was associated with downregulation of signal transducer and activator of transcription 6 (Stat6) expression. Furthermore, the results of in vivo and in vitro studies demonstrated that histamine could promote macrophage differentiation and foam cell formation via the Stat6 signal.

CONCLUSIONS

Modulation of histamine and Stat6-signaling may represent an attractive therapeutic strategy for the prevention or treatment of atherosclerosis.

The expression of proline-specific enzymes in the human lung

The pathophysiology of lung diseases is very complex and proteolytic enzymes may play a role or could be used as biomarkers. In this review, the literature was searched to make an overview of what is known on the expression of the proline-specific peptidases dipeptidyl peptidase (DPP) 4, 8, 9, prolyl oligopeptidase (PREP) and fibroblast activation protein α (FAP) in the healthy and diseased lung. Search terms included asthma, chronic obstructive pulmonary disease (COPD), lung cancer, fibrosis, ischemia reperfusion injury and pneumonia. Knowledge on the loss or gain of protein expression and activity during disease might tie these enzymes to certain cell types, substrates or interaction partners that are involved in the pathophysiology of the disease, ultimately leading to the elucidation of their functional roles and a potential therapeutic target. Most data could be found on DPP4, while the other enzymes are less explored. Published data however often appear to be conflicting, the applied methods divers and the specificity of the assays used questionable. In conclusion, information on the expression of the proline-specific peptidases in the healthy and diseased lung is lacking, begging for further well-designed research.

Contribution of upregulated dipeptidyl peptidase 9 (DPP9) in promoting tumoregenicity, metastasis and the prediction of poor prognosis in non-small cell lung cancer (NSCLC)

Dipeptidyl peptidase 9 (DPP9) is encoded by DPP9, which belongs to the DPP4 gene family. Proteins encoded by these genes have unique peptidase and extra‐enzymatic functions that have been linked to various diseases including cancers. Here, we describe the expression pattern and biological function of DPP9 in non‐small‐cell lung cancer (NSCLC). The repression of DPP9 expression by small interfering RNA inhibited cell proliferation, migration, and invasion. Moreover, we explored the role of DPP9 in regulating epithelial‐mesenchymal transition (EMT). The epithelial markers E‐cadherin and MUC1 were significantly increased, while mesenchymal markers vimentin and S100A4 were markedly decreased in DPP9 knockdown cells. The downregulation of DPP9 in the NSCLC cells induced the expression of apoptosis‐associated proteins both in vitro and in vivo. We investigated the protein expression levels of DPP9 by tissue microarray immunohistochemical assay (TMA‐IHC) (n = 217). Further we found mRNA expression levels of DPP9 in 30 pairs of clinical NSCLC tissues were significantly lower than in the adjacent non‐cancerous tissues. Survival analysis showed that the overexpression of DPP9 was a significant independent factor for poor 5‐year overall survival in patients with NSCLC (p = 0.003). Taken together, DPP9 expression correlates with poor overall survival in NSCLC.

What's new?

Non‐small‐cell lung cancer (NSCLC) is associated with multiple genetic and epigenetic changes. Nonetheless, mechanisms underlying its initiation and progression are not well understood. The present study identifies a role for dipeptidyl peptidase 9 (DPP9), a DPP4 family member with suspected influence on tumor initiation and metastasis. In lung cancer cells in vitro, DPP9 repression inhibited cell proliferation, migration, and invasion, while its repression in vivo dramatically slowed tumor growth, greatly reducing tumor volume in DPP9 knockdown mice. In clinical NSCLC specimens, DPP9 upregulation was significantly associated with advanced TNM stage and was negatively prognostic for overall survival.

The Dipeptidyl Peptidases 4, 8, and 9 in Mouse Monocytes and Macrophages: DPP8/9 Inhibition Attenuates M1 Macrophage Activation in Mice

Atherosclerosis remains the leading cause of death in Western countries. Dipeptidyl peptidase (DPP) 4 has emerged as a novel target for the prevention and treatment of atherosclerosis. Family members DPP8 and 9 are abundantly present in macrophage-rich regions of atherosclerotic plaques, and DPP9 inhibition attenuates activation of human M1 macrophages in vitro. Studying this family in a mouse model for atherosclerosis would greatly advance our knowledge regarding their potential as therapeutic targets. We found that DPP4 is downregulated during mouse monocyte-to-macrophage differentiation. DPP8 and 9 expression seems relatively low in mouse monocytes and macrophages. Viability of primary mouse macrophages is unaffected by DPP4 or DPP8/9 inhibition. Importantly, DPP8/9 inhibition attenuates macrophage activation as IL-6 secretion is significantly decreased. Mouse macrophages respond similarly to DPP inhibition, compared to human macrophages. This shows that the mouse could become a valid model species for the study of DPPs as therapeutic targets in atherosclerosis.

DPP8 and DPP9 inhibition induces pro-caspase-1-dependent monocyte and macrophage pyroptosis

Val-boroPro (Talabostat, PT-100), a nonselective inhibitor of post-proline cleaving serine proteases, stimulates mammalian immune systems through an unknown mechanism of action. Despite this lack of mechanistic understanding, Val-boroPro has attracted substantial interest as a potential anticancer agent, reaching phase 3 trials in humans. Here we show that Val-boroPro stimulates the immune system by triggering a proinflammatory form of cell death in monocytes and macrophages known as pyroptosis. We demonstrate that the inhibition of two serine proteases, DPP8 and DPP9, activates the pro-protein form of caspase-1 independent of the inflammasome adaptor ASC. Activated pro-caspase-1 does not efficiently process itself or IL-1β but does cleave and activate gasdermin D to induce pyroptosis. Mice lacking caspase-1 do not show immune stimulation after treatment with Val-boroPro. Our data identify what is to our knowledge the first small molecule that induces pyroptosis and reveals a new checkpoint that controls the activation of the innate immune system.

DPP9 is a novel component of the N-end rule pathway targeting the tyrosine kinase Syk

The aminopeptidase DPP9 removes dipeptides from N-termini of substrates having a proline or alanine in second position. Although linked to several pathways including cell survival and metabolism, the molecular mechanisms underlying these outcomes are poorly understood. We identified a novel interaction of DPP9 with Filamin A, which recruits DPP9 to Syk, a central kinase in B-cell signalling. Syk signalling can be terminated by degradation, requiring the ubiquitin E3 ligase Cbl. We show that DPP9 cleaves Syk to produce a neo N-terminus with serine in position 1. Pulse-chases combined with mutagenesis studies reveal that Ser1 strongly influences Syk stability. Furthermore, DPP9 silencing reduces Cbl interaction with Syk, suggesting that DPP9 processing is a prerequisite for Syk ubiquitination. Consistently, DPP9 inhibition stabilizes Syk, thereby modulating Syk signalling. Taken together, we demonstrate DPP9 as a negative regulator of Syk and conclude that DPP9 is a novel integral aminopeptidase of the N-end rule pathway.

Dipeptidyl peptidase 9 substrates and their discovery: current progress and the application of mass spectrometry-based approaches

The enzyme members of the dipeptidyl peptidase 4 (DPP4) gene family have the very unusual capacity to cleave the post-proline bond to release dipeptides from the N-terminus of peptide/protein substrates. DPP4 and related enzymes are current and potential therapeutic targets in the treatment of type II diabetes, inflammatory conditions and cancer. Despite this, the precise biological function of individual dipeptidyl peptidases (DPPs), other than DPP4, and knowledge of their in vivo substrates remains largely unknown. For many years, identification of physiological DPP substrates has been difficult due to limitations in the available tools. Now, with advances in mass spectrometry based approaches, we can discover DPP substrates on a system wide-scale. Application of these approaches has helped reveal some of the in vivo natural substrates of DPP8 and DPP9 and their unique biological roles. In this review, we provide a general overview of some tools and approaches available for protease substrate discovery and their applicability to the DPPs with a specific focus on DPP9 substrates. This review provides comment upon potential approaches for future substrate elucidation.

[Effects of Porphyromonas gingivalis on interleukin-33 expression in rabbit vascular endothelium tissues]

OBJECTIVE

To investigate interleukin-33 (IL-33) in the arterial vascular endothelium of rabbits infected with Porphyromonas gingivalis (P. gingivalis), and to explore the relationship between P. gingivalis and atherosclerosis.

METHODS

A total of 24 rabbits were randomly divided into control and experimental groups. The experimental group received intravenous injection of P. gingivalis once a week for 12 weeks to establish a coronary atherosclerosis model. The rabbits in the control group were injected with equal volume of physiological saline. All the rabbits were killed after 13 weeks. The IL-33 expression levels in the arterial vascular endothelium of the rabbits were detected through immunohistochemistry, reverse transcription polymerase chain reaction, and Western blot analysis. The effects of P. gingivalis on the IL-33 expression in the arterial vascular endothelium of the rabbits were analyzed.

RESULTS

The relative expression levels of IL-33 mRNA in the vascular endothelium cells were 58.244±2.407, and the relative expression levels of IL-33 protein were 1.863±0.171 in the experimental group. The relative expression levels of IL-33 mRNA were 3.143±0.805, and the relative expression levels of IL-33 protein were 0.537±
0.028 in the control group. The expression levels of IL-33 mRNA and protein of vascular endothelium cells in the experimental group were significantly higher than those of the control group (P<0.01).

CONCLUSIONS

P. gingivalis infection promotes IL-33 expression levels in vascular endothelial cells and may regulate the occurrence and development of atherosclerosis.
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Identifying neuropeptide Y (NPY) as the main stress-related substrate of dipeptidyl peptidase 4 (DPP4) in blood circulation

BACKGROUND

Dipeptidyl peptidase 4 (DPP4; EC 3.4.14.5; CD26) is a membrane-bound or shedded serine protease that hydrolyzes dipeptides from the N-terminus of peptides with either proline or alanine at the penultimate position. Substrates of DPP4 include several stress-related neuropeptides implicated in anxiety, depression and schizophrenia. A decline of DPP4-like activity has been reported in sera from depressed patient, but not fully characterized regarding DPP4-like enzymes, therapeutic interventions and protein.

METHODS

Sera from 16 melancholic- and 16 non-melancholic-depressed patients were evaluated for DPP4-like activities and the concentration of soluble DPP4 protein before and after treatment by anti-depressive therapies. Post-translational modification of DPP4-isoforms and degradation of NPY, Peptide YY (PYY), Galanin-like peptide (GALP), Orexin B (OrxB), OrxA, pituitary adenylate cyclase-activating polypeptide (PACAP) and substance P (SP) were studied in serum and in ex vivo human blood. N-terminal truncation of biotinylated NPY by endothelial membrane-bound DPP4 versus soluble DPP4 was determined in rat brain perfusates and spiked sera.

RESULTS

Lower DPP4 activities in depressed patients were reversed by anti-depressive treatment. In sera, DPP4 contributed to more than 90% of the overall DPP4-like activity and correlated with its protein concentration. NPY displayed equal degradation in serum and blood, and was equally truncated by serum and endothelial DPP4. In addition, GALP and rat OrxB were identified as novel substrates of DPP4.

CONCLUSION

NPY is the best DPP4-substrate in blood, being truncated by soluble and membrane DPP4, respectively. The decline of soluble DPP4 in acute depression could be reversed upon anti-depressive treatment. Peptidases from three functional compartments regulate the bioactivity of NPY in blood.

Sitagliptin inhibits endothelin-1 expression in the aortic endothelium of rats with streptozotocin-induced diabetes by suppressing the nuclear factor-κB/IκBα system through the activation of AMP-activated protein kinase

Emerging evidence suggests that dipeptidyl peptidase-4 (DPP-4) inhibitors, including sitagliptin, exert favourable effects on the vascular endothelium. DPP-4 inhibitors suppress the degradation of glucagon-like peptide-1 (GLP‑1), which has been reported to enhance nitric oxide (NO) production. However, the effects of DPP-4 inhibitors on endothelin-1 (ET-1) expression in the aorta, as well as the underlying mechanisms responsible for these effects, have yet to be investigated in animal models of diabetes mellitus (DM). In the present study, the rats were randomly divided into the following four groups: i) control; ii) DM; iii) DM + low‑dose sitagliptin (10 mg/kg); and iv) DM + high‑dose sitagliptin (30 mg/kg). Apart from the control group, all the rats received a high-fat diet for 8 weeks prior to the induction of diabetes with an intraperitoneal injection of streptozotocin. The treatments were then administered for 12 weeks. The serum levels of ET-1, NO, GLP-1 and insulin were measured as well as endothelial function. The expression of ET-1, AMP-activated protein kinase (AMPK) and nuclear factor (NF)-κB/IκBα were determined. After 12 weeks of treatment, the diabetic rats receiving sitagliptin showed significantly elevated serum levels of GLP-1 and NO, and reduced levels of ET-1. Moreover, sitagliptin significantly attenuated endothelial dysfunction as well as the remodeling of the aortic wall. Notably, sitagliptin inhibited ET-1 expression at the transcriptional and translational level in the aorta, which may have been mediated by the suppression of the NF-κB/IκBα system induced by AMPK activation. The majority of the above-mentioned effects were dose dependent. Taken together, the findings of the present study indicate that sitagliptin inhibits ET-1 expression in the aortic endothelium by suppressing the NF-κB/IκBα system through the activation of the AMPK pathway in diabetic rats. These findings further demonstrate some of the vasoprotective properties of DPP-4 inhibitors in vivo.

Hepatocellular carcinoma: Mouse models and the potential roles of proteases

Primary liver cancer is the second most common cause of mortality from cancer. The most common models of hepatocellular carcinoma, which use a chemical and/or metabolic insult, xenograft, or genetic manipulation, are discussed in this review. In the tumour microenvironment lymphocytes, fibroblasts, endothelial cells and antigen presenting cells are important determinants of cell fate. These cells make a range of proteases that modify the biological activity of other proteins, particularly extracellular matrix proteins that alter cell migration of tumour cells, fibroblasts and leucocytes, and chemokines that alter leucocyte migration. The DPP4 family of post-proline peptidase enzymes modifies cell movement and the activities of many bioactive molecules including growth factors and chemokines.

Dipeptidyl peptidase 9 enzymatic activity influences the expression of neonatal metabolic genes

The success of dipeptidyl peptidase 4 (DPP4) inhibition as a type 2 diabetes therapy has encouraged deeper examination of the post-proline DPP enzymes. DPP9 has been implicated in immunoregulation, disease pathogenesis and metabolism. The DPP9 enzyme-inactive (Dpp9 gene knock-in; Dpp9 gki) mouse displays neonatal lethality, suggesting that DPP9 enzyme activity is essential in neonatal development. Here we present gene expression patterns in these Dpp9 gki neonatal mice. Taqman PCR arrays and sequential qPCR assays on neonatal liver and gut revealed differential expression of genes involved in cell growth, innate immunity and metabolic pathways including long-chain-fatty-acid uptake and esterification, long-chain fatty acyl-CoA binding, trafficking and transport into mitochondria, lipoprotein metabolism, adipokine transport and gluconeogenesis in the Dpp9 gki mice compared to wild type. In a liver cell line, Dpp9 knockdown increased AMP-activated protein kinase phosphorylation, which suggests a potential mechanism. DPP9 protein levels in liver cells were altered by treatment with EGF, HGF, insulin or palmitate, suggesting potential natural DPP9 regulators. These gene expression analyses of a mouse strain deficient in DPP9 enzyme activity show, for the first time, that DPP9 enzyme activity regulates metabolic pathways in neonatal liver and gut.

Probing for improved selectivity with dipeptide-derived inhibitors of dipeptidyl peptidases 8 and 9: the impact of P1-variation

The influence of P1-variation on DPP8/9 inhibitor selectivity is investigated.

Effects and mechanism of moderate aerobic exercise on impaired fasting glucose improvement

BACKGROUND

Exercise is beneficial for blood glucose metabolism. However, whether moderate aerobic exercise could improve impaired fasting glucose is unknown. And the mechanism is also needed to investigate.

METHODS

A cross-sectional research was performed and 120 participants with impaired fasting glucose (IFG) were randomly assigned into active and controlled groups. Briefly, participants in active group were required to take moderate aerobic exercise at least 30 min for five times per week, whereas in controlled group, participants were also advised to take exercise but not mandatorily required the same degree as that of active group. At baseline and 3 month's follow-up, laboratory and demographic variables were compared.

RESULTS

At baseline, no significant between-group differences were observed. Generally, leukocyte ROCK2 activity in the active and controlled groups were 58.7 ± 6.0 mg/mL and 60.2 ± 7.3 mg/mL, and daily average exercise time at baseline in both groups was extremely little, with 5.2 ± 3.8 min and 5.9 ± 3.5 min, respectively. After 3 months' follow-up, 52 and 56 participants in the active and controlled groups completed the whole program. Compared to baseline, leukocyte ROCK2 activity and daily average exercise time were improved in both groups. Nonetheless, compared to the controlled group, leukocyte ROCK2 activity was reduced more profoundly and the daily average exercise time was longer in the active group (37.5 ± 6.3 min versus 18.3 ± 7.2 min, p < 0.05). Moreover, the percentage of IFG in the active group was decreased more prominently than the controlled group (76.9% versus 82.1%, p < 0.05). Multivariate regression analyses revealed that exercise time and leukocyte ROCK2 activity was significantly associated with IFG, with OR of 0.836 (active group versus controlled group, 95% CI 0.825-0.852, p < 0.05) in exercise time, and 1.043 (controlled group versus active group, 95% CI 1.021-1.069, p < 0.05) in leukocyte ROCK2 activity. In addition, exercise time was significantly associated with leukocyte ROCK2 activity, with OR of 0.822 (active group versus controlled group, 95% CI 0.818-0.843, p < 0.05).

CONCLUSION

In subjects with IFG, increased daily average exercise time is beneficial for improving fasting blood glucose metabolism, and the mechanism may be associated with its effects on attenuating leukocyte ROCK2 activity.