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Clinical trials suggested that the vascular system can remember episodes of poor glycemic control through a phenomenon known as hyperglycemic memory (HGM). HGM is associated with long-term diabetic vascular complications in type 1 and type 2 diabetes, although the molecular mechanism of that association is not clearly understood. We hypothesized that transglutaminase 2 (TGase2) and intracellular reactive oxygen species (ROS) play a key role in HGM-induced vascular dysfunction. We found that hyperglycemia induced persistent oxidative stress, expression of inflammatory adhesion molecules, and apoptosis in the aortic endothelium of HGM mice whose blood glucose levels had been normalized by insulin supplementation. TGase2 activation and ROS generation were in a vicious cycle in the aortic endothelium of HGM mice and also in human aortic endothelial cells after glucose normalization, which played a key role in the sustained expression of inflammatory adhesion molecules and apoptosis. Our findings suggest that the TGase2-ROS vicious cycle plays an important role in HGM-induced endothelial dysfunction.—Lee, J.-Y., Lee, Y.-J., Jeon, H.-Y., Han, E.-T., Park, W. S., Hong, S.-H., Kim, Y.-M., Ha, K.-S. The vicious cycle between transglutaminase 2 and reactive oxygen species in hyperglycemic memory–induced endothelial dysfunction.

Transglutaminase 2 (TGase2), a multifunctional enzyme exhibiting both transamidase and kinase activity, is involved in a variety of cellular processes and diseases. However, details of the regulation of TGase2 have not been reported due to the lack of a suitable assay to examine both activities on the same platform under near-physiologic conditions. Thus, we developed an on-chip dual enzyme activity assay for TGase2 to simultaneously monitor the transamidase and kinase activities. Reaction mixtures specific for each enzyme activity were applied onto osteopontin arrays, and enzyme activity was monitored by sequential probing with Cy5-strepavidin and Pro-Q Diamond stain. This approach was used to determine the optimal concentrations of ATP, Mg2+, and Ca2+ for dual-activity assays. The optimized assay was then used to investigate regulation of TGase2 transamidase and kinase activities by various cofactors that could potentially affect its conformation. Monothiol- and disulfide-containing compounds differentially regulated TGase2 transamidase and kinase activities. Acetylation of TGase2 activated the kinase activity but had no effect on the transamidase activity. Phosphorylation and dephosphorylation of TGase2 reciprocally regulated the transamidase and kinase activities. The new approach described here is thus useful for screening potential regulators of TGase2 transamidase and kinase and investigating the pathogenesis of TGase2-associated diseases.

C-peptide has a beneficial effect against diabetic complications, but its role in hyperglycemia-induced metastasis is unknown. We investigated hyperglycemia-mediated pulmonary vascular leakage and metastasis and C-peptide inhibition of these molecular events using human pulmonary microvascular endothelial cells (HPMVECs) and streptozotocin-induced diabetic mice. VEGF, which is elevated in the lungs of diabetic mice, activated transglutaminase 2 (TGase2) in HPMVECs by sequential elevation of intracellular Ca2+ and reactive oxygen species (ROS) levels. VEGF also induced vascular endothelial (VE)-cadherin disruption and increased the permeability of endothelial cells, both of which were prevented by the TGase inhibitors monodansylcadaverine and cystamine or TGM2-specific small interfering RNA. C-peptide prevented VEGF-induced VE-cadherin disruption and endothelial cell permeability through inhibiting ROS-mediated activation of TGase2. C-peptide supplementation inhibited hyperglycemia-induced ROS generation and TGase2 activation and prevented vascular leakage and metastasis in the lungs of diabetic mice. The role of TGase2 in hyperglycemia-induced pulmonary vascular leakage and metastasis was further demonstrated in diabetic Tgm2-/- mice. These findings demonstrate that hyperglycemia induces metastasis, and C-peptide prevents the hyperglycemia-induced metastasis in the lungs of diabetic mice by inhibiting VEGF-induced TGase2 activation and subsequent vascular leakage.-Jeon, H.-Y., Lee, Y.-J., Kim, Y.-S., Kim, S.-Y., Han, E.-T., Park, W. S., Hong, S.-H., Kim, Y.-M., Ha, K.-S. Proinsulin C-peptide prevents hyperglycemia-induced vascular leakage and metastasis of melanoma cells in the lungs of diabetic mice.

We investigated the beneficial effects of midazolam against vascular endothelial growth factor (VEGF)-induced vascular leakage and its molecular mechanism of action in human retinal endothelial cells (HRECs) and the retinas of diabetic mice. Midazolam inhibited VEGF-induced elevation of intracellular Ca2+, generation of reactive oxygen species (ROS), and transglutaminase activation in HRECs; these effects were reversed by the GABA, type A (GABAA) receptor antagonist flumazenil but not by the translocator protein antagonist PK11195. Midazolam also prevented VEGF-induced disassembly of adherens junctions and in vitro permeability. Intravitreal injection of midazolam prevented hyperglycemia-induced ROS generation, transglutaminase activation, and subsequent vascular leakage in the retinas of diabetic mice, and those effects were reversed by flumazenil. The roles of flumazenil were further supported by identifying GABAA receptors in mouse retinas. Thus, midazolam prevents hyperglycemia-induced vascular leakage by inhibiting VEGF-induced intracellular events in the retinas of diabetic mice.-Lee, Y.-J., Kim, M., Lee, J.-Y., Jung, S.-H., Jeon, H.-Y., Lee, S.-A., Kang, S., Han, E.-T., Park, W. S., Hong, S.-H., Kim, Y.-M., Ha, K.-S. The benzodiazepine anesthetic midazolam prevents hyperglycemia-induced microvascular leakage in the retinas of diabetic mice.

Midazolam is an anesthetic agent commonly used for anesthesia and sedation in surgery. However, there is no information on the role of midazolam in hyperglycemia-induced cancer metastasis to date. In this study, we investigated the effects of midazolam on inhibiting metastases in the lungs of diabetic mice and on human pulmonary microvascular endothelial cells (HPMVECs). Subcutaneous injection of midazolam inhibited hyperglycemia-induced cancer metastasis in the lungs of diabetic mice. Midazolam also prevented the generation of ROS, activation of TGase, and subsequent vascular leakage in the lungs of diabetic mice. Furthermore, in vitro studies with HPMVECs confirmed that midazolam inhibited VEGF-induced intracellular events including ROS generation, TGase activation, and disruption of vascular endothelial-cadherins, thus preventing the permeability of endothelial cells. Notably, midazolam had no direct effect on the migration or proliferation of melanoma cells, instead acting upon endothelial cells. The midazolam-mediated inhibition of VEGF-induced intracellular events was reversed by treatment with the GABAA receptor antagonist flumazenil. These findings suggest that midazolam prevents hyperglycemia-induced cancer metastasis by inhibiting VEGF-induced intracellular events and subsequent vascular leakage via the GABAA receptors in the lungs of diabetic mice.

Glucose-6-phosphate dehydrogenase (G6PD) plays a principal role in the regulation of oxidative stress by modulating the nicotinamide adenine dinucleotide phosphate pool and is expected to be associated with metabolic diseases such as diabetes mellitus (DM). However, it is unclear whether hyperglycemia increases G6PD activity levels in DM because suitable assays for quantifying the activity in a high-throughput manner are lacking. Using liquid droplet arrays tailored to analyze tissue lysates, we performed G6PD activity profiling in eight tissues of normal and diabetic mice: brain, heart, kidney, liver, lung, muscle, spleen, and thyroid. Diabetic mice exhibited significantly higher G6PD activities in the kidney, liver, spleen, and thyroid than normal mice; no significant difference was found in the brain, heart, lung, or muscle. We also performed G6PD expression profiling in the eight tissues using Western blot analysis. Diabetic mice showed significantly elevated G6PD expression levels in the kidney, lung, spleen, and thyroid compared with normal mice; no significant difference was found in the brain, heart, liver, or muscle. An analysis of G6PD activity-expression profiles demonstrated tissue-specific changes in response to hyperglycemia. Thus, our approach would be helpful for understanding the role of G6PD in tissue-based pathogenesis of diabetic complications.

The Plasmodium vivax merozoite surface protein 1 paralog (PvMSP1P), which has epidermal growth factor (EGF)-like domains, was identified as a novel erythrocyte adhesive molecule. This EGF-like domain (PvMSP1P-19) elicited high level of acquired immune response in patients. Antibodies against PvMSP1P significantly reduced erythrocyte adhesion activity to its unknown receptor. To determine PvMSP1P-19-specific antibody function and B-cell epitopes in vivax patients, five monoclonal antibodies (mAbs) and 18-mer peptides were generated. The mAb functions were determined by erythrocyte-binding inhibition assay and invasion inhibition assay with P. knowlesi. B-cell epitopes of PvMSP1P-19 domains were evaluated by peptide microarray. The pvmsp1p-19 sequences showed limited polymorphism in P. vivax worldwide isolates. The 1BH9-A10 showed erythrocyte binding inhibitory by interaction with the N-terminus of PvMSP1P-19, while this mAb failed to recognize PkMSP1P-19 suggesting the species-specific for P. vivax. Other mAbs showed cross-reactivity with PkMSP1P-19. Among them, the 2AF4-A2 and 2AF4-A6 mAb significantly reduced parasite invasion through C-terminal recognition. The linear B-cell epitope in naturally exposed P. vivax patient was identified at three linear epitopes. In this study, PvMSP1P-19 N-terminal-specific 1BH9-A10 and C-terminal-specific 2AF4 mAbs showed functional activity for epitope recognition suggesting that PvMSP1P may be useful for vaccine development strategy for specific single epitope to prevent P. vivax invasion.

Tryptophan-rich antigens (TRAgs) are an antigen family that has been identified in human and rodent malaria parasites. TRAgs have been proposed as candidate antigens for potential vaccines. The Plasmodium vivax TRAg (PvTRAg) family includes 36 members. Each PvTRAg contains a tryptophan-rich (TR) domain in the C-terminal region. In this study, we recombinantly expressed all 36 PvTRAgs using a cell-free expression system, and, for the first time, profiled the IgG antibody responses against all PvTRAgs in the sera from 96 vivax malaria patients and 40 healthy individuals using protein microarray technology. The mean seropositive rate for all PvTRAgs was 60.3%. Among them, nine PvTRAgs were newly identified in this study and showed a seropositive rate of >50%. Five of them, PvTRAg_13, PvTRAg_15, PvTRAg_16, PvTRAg_26, and PvTRAg_29, produced higher levels of IgG antibody, even in low-endemicity countries. In addition, the results of an immunofluorescence analysis suggest that PvTRAgs are, at least in part, associated with caveola-vesicle complexes, a unique structure of P. vivax-infected erythrocytes. The mechanism of formation and the function of these abundant membrane structures are not known. Further investigation aimed at determining the functions of these proteins would lead to a better understanding of the blood-stage biology of P. vivax.

Protein kinases play a critical role in a wide variety of cellular processes through post-translational protein phosphorylation and identification of their substrate proteins is important for understanding the enzymes’ mechanism of action and elucidating their functions in physiological and disease processes. However, there have been few systematic investigations of protein kinase substrates due to a lack of high-throughput kinetic assays. Thus, we designed an on-chip protein kinase assay for profiling kinase kinetic parameters by introducing the phosphorylation rate (Vp) under physiological conditions, instead of the maximal velocity (Vmax), in a high-throughput manner. We applied this method to the kinetic analysis of protein kinase A (PKA) for 28 nuclear, cytosolic, plasma membrane, and extracellular target proteins to determine the substrate affinity (Km), Vp (FIATP10/s), and substrate preference (Vp/Km). We then constructed a map of PKA's kinetic parameters with respect to the 28 proteins based on subcellular localization. Thus, the on-chip protein kinase kinetic profiling is an ideal approach for systematically investigating substrate proteins of protein kinases and fully characterizing the enzymes’ physiological functions.

Aims Insulin is a central peptide hormone required for carbohydrate metabolism; however, its role in diabetes-associated pulmonary disease is unknown. Here, we investigated the preventative effect of insulin against hyperglycemia-induced pulmonary vascular leakage and its molecular mechanism of action in the lungs of diabetic mice. Main methods Vascular endothelial growth factor (VEGF) activated transglutaminase 2 (TGase2) by sequentially elevating intracellular Ca2+ and reactive oxygen species (ROS) levels in primary human pulmonary microvascular endothelial cells (HPMVECs). Key findings Insulin inhibited VEGF-induced TGase2 activation, but did not affect intracellular Ca2+ elevation and ROS generation. Insulin prevented VEGF-induced vascular leakage by inhibiting TGase2-mediated c-Src phosphorylation, disassembly of VE-cadherin and β-catenin, and stress fiber formation. Insulin replacement therapy prevented hyperglycemia-induced TGase2 activation, but not ROS generation, in the lungs of diabetic mice. Insulin also prevented vascular leakage and cancer metastasis in the diabetic lung. Notably, vascular leakage was not detectable in the lungs of TGase2-null (Tgm2−/−) diabetic mice. Significance These findings demonstrate that insulin prevents hyperglycemia-induced pulmonary vascular leakage in diabetic mice by inhibiting VEGF-induced TGase2 activation rather than ROS generation.

Background Although a number of Plasmodium vivax proteins have been identified, few have been investigated as potential vaccine candidates. This study characterized the Plasmodium vivax merozoite surface antigen 180 (PvMSA180, PVX_094920), a novel P. vivax antigenic protein. Methods The target gene was amplified as four overlapping domains (D1, D2, D3 and D4) to enable expression of the recombinant protein using cell-free and bacterial expression systems. The recombinant PvMSA180 proteins were used in protein microarrays to evaluate the humoral immune response of 72 vivax-infected patients and 24 vivax-naïve individuals. Antibodies produced in mice against the PvMSA180-D1 and -D4 domains were used to assess the subcellular localization of schizont-stage parasites with immunofluorescence assays. A total of 51 pvmsa180 sequences from 12 countries (41 sequences from PlasmoDB and 6 generated in this study) were used to determine the genetic diversity and genealogical relationships with DNAsp and NETWORK software packages, respectively. Results PvMSA180 consists of 1603 amino acids with a predicted molecular mass of 182 kDa, and has a signal peptide at the amino-terminus. A total of 70.8% of patients (51/72) showed a specific antibody response to at least one of the PvMSA180 domains, and 20.8% (15/72) exhibited a robust antibody response to at least three of the domains. These findings suggest that PvMSA180 is targeted by the humoral immune response during natural infection with P. vivax. Immunofluorescence analysis demonstrated that PvMSA180 is localized on the merozoite surface of schizont-stage parasites, and pvmsa180 sequences originating from various geographic regions worldwide showed low genetic diversity. Twenty-two haplotypes were found, and haplotype 6 (Hap_6, 77%) of pvmsa180 was detected in isolates from six countries. Conclusions A novel P. vivax surface protein, PvMSA180, was characterized in this study. Most of P. vivax-infected patients had specific antibodies against particular antigenic domains, indicating that this protein is immunogenic in naturally exposed populations. Genetic analysis of worldwide isolates showed that pvmsa180 is less polymorphic than other well-known candidates and that some haplotypes are common to several countries. However, additional studies with a larger sample size are necessary to evaluate the antibody responses in geographically separated populations, and to identify the function of PvMSA180 during parasite invasion. Electronic supplementary material The online version of this article (doi:10.1186/s12936-017-1760-9) contains supplementary material, which is available to authorized users.

Transglutaminase 2 (TG2) is an enzyme that plays a critical role in a wide variety of cellular processes through its multifunctional activities. TG2 kinase has emerged as an important regulator of apoptosis, as well as of chromatin structure and function. However, systematic investigation of TG2 kinase substrates is limited due to a lack of a suitable TG2 kinase activity assays. Thus, we developed a novel on-chip TG2 kinase activity assay for quantitative determination of TG2 kinase activity and for screening TG2 kinase substrate proteins in a high-throughput manner. Quantitative TG2 kinase activity was determined by selective detection of substrate protein phosphorylation on the surface of well-type amine arrays. The limit of detection (LOD) of this assay was 4.34μg/ml. We successfully applied this new activity assay to the kinetic analysis of 27 TG2-related proteins for TG2 kinase activity in a high-throughput manner and determined Michaelis-Menten constants (Km) of these proteins. We used the Km values and cellular locations of the TG2-related proteins to construct a substrate affinity map for TG2 kinase. Therefore, this on-chip TG2 kinase activity assay has a strong potential for the systematic investigation of substrate proteins and will be helpful for studying new physiological functions.