Teruya Nakamura

Myocardial protection from ischemia/reperfusion injury by endogenous and exogenous HGF

Using a rat model of ischemia/reperfusion injury, we demonstrate here that HGF is cardioprotective due to its antiapoptotic effect on cardiomyocytes. Following transient myocardial ischemia and reperfusion, c-Met/HGF receptor expression rapidly increased in the ischemic myocardium, an event accompanied by a dramatic increase in plasma HGF levels in the infarcted rats. When endogenous HGF was neutralized with a specific antibody, the number of myocyte cell deaths increased markedly, the infarct area expanded, and the mortality increased to 50%, as compared with a control group in which there was no mortality. Plasma from the myocardial infarcted rats had cardioprotective effects on primary cultured cardiomyocytes, but these effects were significantly diminished by neutralizing HGF. In contrast, recombinant HGF administration reduced the size of infarct area and improved cardiac function by suppressing apoptosis in cardiomyocytes. HGF rapidly augmented Bcl-xL expression in injured cardiomyocytes both in vitro and in vivo. As apoptosis of cardiomyocytes is one of the major contributors to the pathogenesis in subjects with ischemia/reperfusion injury, prevention of apoptosis may prove to be a reasonable therapeutic strategy. Supplements of HGF, an endogenous cardioprotective factor, may be found clinically suitable in treating subjects with myocardial infarction.

A potential cardioprotective role of hepatocyte growth factor in myocardial infarction in rats

OBJECTIVE Cardiotrophic growth factors with anti-cell death actions on cardiac myocytes have gained attention for treatment of patients with myocardial infarction. Hepatocyte growth factor (HGF) plays a role in tissue repair and protection from injuries, however, the physiological role of HGF in the myocardium has not been well defined. We asked if HGF would afford to the infarcted myocardium. METHODS AND RESULTS Mature cardiac myocytes prepared from adult rats expressed barely detectable levels of the c-Met/HGF receptor, however, c-Met receptor expression increased during cultivation, which meant that cardiac myocytes are potential targets of HGF. Addition of hydrogen peroxide remarkably decreased the number of viable mature cardiac myocytes in primary culture, whereas treatment with HGF enhanced survival of the cells subjected to the oxidant stress. Although very low levels of c-Met/HGF receptor and HGF mRNA expression were seen in normal rat hearts, both c-Met/HGF receptor and HGF mRNA levels rapidly increased to much higher levels than normal, when the rats were subjected to myocardial infarction. Immunohistochemical analysis of the c-Met receptor indicated that this receptor was expressed in cardiomyocytes localized in the border regions of the viable myocardium and in non-infarcted regions following myocardial infarction. CONCLUSION The c-Met/HGF receptor is induced in cardiomyocytes following myocardial infarction and HGF exhibits protective effect on cardiomyocytes against oxidative stress. Our working hypothesis is that HGF may afford myocardial protection from myocardial infarction.

Watching DNA polymerase η make a phosphodiester bond

DNA synthesis has been extensively studied, but the chemical reaction itself has not been visualized. Here we follow the course of phosphodiester bond formation using time-resolved X-ray crystallography. Native human DNA polymerase η, DNA and dATP were co-crystallized at pH 6.0 without Mg2+. The polymerization reaction was initiated by exposing crystals to 1 mM Mg2+ at pH 7.0, and stopped by freezing at desired time points for structural analysis. The substrates and two Mg2+ ions are aligned within 40 s, but the bond formation is not evident until 80 s. From 80 to 300 s structures show a mixture of decreasing substrate and increasing product of the nucleotidyl-transfer reaction. Transient electron densities indicate that deprotonation and an accompanying C2′-endo to C3′-endo conversion of the nucleophile 3′-OH are rate limiting. A third Mg2+ ion, which arrives with the new bond and stabilizes the intermediate state, may be an unappreciated feature of the two-metal-ion mechanism.

Solution of the Structure of the TNF-TNFR2 Complex

Structural differences in the binding of tumor necrosis factor to its two receptors may aid in the development of receptor-specific therapeutics. Structural Differences The proinflammatory cytokine tumor necrosis factor (TNF) functions in the immune response; however, TNF also plays a pathophysiological role in diseases such as rheumatoid arthritis and Crohn’s disease. The effects of TNF are mediated by TNF receptor 1 (TNFR1) and TNFR2; whereas TNFR1 is ubiquitously expressed, TNFR2 is mostly restricted to cells of the immune system. Currently available therapies that block TNF include monoclonal antibodies against TNF and a soluble form of TNFR2; however, these therapies can result in serious side effects, some of which may be due to their nonselective effects. Here, Mukai et al. solved the structure of TNF in complex with TNFR2 and found differences between the ligand-binding interface of TNFR2 and that of TNFR1, whose structure is known. The authors also observed the formation of TNF-TNFR2 aggregates on the surface of transfected cells, which may be required for signal initiation. Solution of the TNFR2 structure may aid in the development of receptor-specific therapies. Tumor necrosis factor (TNF) is an inflammatory cytokine that has important roles in various immune responses, which are mediated through its two receptors, TNF receptor 1 (TNFR1) and TNFR2. Antibody-based therapy against TNF is used clinically to treat several chronic autoimmune diseases; however, such treatment sometimes results in serious side effects, which are thought to be caused by the blocking of signals from both TNFRs. Therefore, knowledge of the structural basis for the recognition of TNF by each receptor would be invaluable in designing TNFR-selective drugs. Here, we solved the 3.0 angstrom resolution structure of the TNF-TNFR2 complex, which provided insight into the molecular recognition of TNF by TNFR2. Comparison to the known TNFR1 structure highlighted several differences between the ligand-binding interfaces of the two receptors. Additionally, we also demonstrated that TNF-TNFR2 formed aggregates on the surface of cells, which may be required for signal initiation. These results may contribute to the design of therapeutics for autoimmune diseases.

Creation and X-ray structure analysis of the tumor necrosis factor receptor-1-selective mutant of a tumor necrosis factor-α antagonist

Tumor necrosis factor-α (TNF) induces inflammatory response predominantly through the TNF receptor-1 (TNFR1). Thus, blocking the binding of TNF to TNFR1 is an important strategy for the treatment of many inflammatory diseases, such as hepatitis and rheumatoid arthritis. In this study, we identified a TNFR1-selective antagonistic mutant TNF from a phage library displaying structural human TNF variants in which each one of the six amino acid residues at the receptor-binding site (amino acids at positions 84-89) was replaced with other amino acids. Consequently, a TNFR1-selective antagonistic mutant TNF (R1antTNF), containing mutations A84S, V85T, S86T, Y87H, Q88N, and T89Q, was isolated from the library. The R1antTNF did not activate TNFR1-mediated responses, although its affinity for the TNFR1 was almost similar to that of the human wild-type TNF (wtTNF). Additionally, the R1antTNF neutralized the TNFR1-mediated bioactivity of wtTNF without influencing its TNFR2-mediated bioactivity and inhibited hepatic injury in an experimental hepatitis model. To understand the mechanism underlying the antagonistic activity of R1antTNF, we analyzed this mutant using the surface plasmon resonance spectroscopy and x-ray crystallography. Kinetic association/dissociation parameters of the R1antTNF were higher than those of the wtTNF, indicating very fast bond dissociation. Furthermore, x-ray crystallographic analysis of R1antTNF suggested that the mutation Y87H changed the binding mode from the hydrophobic to the electrostatic interaction, which may be one of the reasons why R1antTNF behaved as an antagonist. Our studies demonstrate the feasibility of generating TNF receptor subtype-specific antagonist by extensive substitution of amino acids of the wild-type ligand protein.

Crystal structure of the IL-15-IL-15Ralpha complex, a cytokine-receptor unit presented in trans

Interleukin 15 (IL-15) and IL-2, which promote the survival of memory CD8+ T cells and regulatory T cells, respectively, bind receptor complexes that share β- and γ-signaling subunits. Receptor specificity is provided by unique, nonsignaling α-subunits. Whereas IL-2 receptor-α (IL-2Rα) is expressed together in cis with the β- and γ-subunits on T cells and B cells, IL-15Rα is expressed in trans on antigen-presenting cells. Here we present a 1.85-Å crystal structure of the human IL-15–IL-15Rα complex. The structure provides insight into the molecular basis of the specificity of cytokine recognition and emphasizes the importance of water in generating this very high-affinity complex. Despite very low IL-15–IL-2 sequence homology and distinct receptor architecture, the topologies of the IL-15–IL-15Rα and IL-2–IL-2Rα complexes are very similar. Our data raise the possibility that IL-2, like IL-15, might be capable of being presented in trans in the context of its unique receptor α-chain.

The Crystal Structure of the Green Tea Polyphenol (―)-Epigallocatechin Gallate―Transthyretin Complex Reveals a Novel Binding Site Distinct from the Thyroxine Binding Site

Amyloid fibril formation is associated with protein misfolding disorders, including neurodegenerative diseases such as Alzheimers, Parkinsons, and Huntingtons diseases. Familial amyloid polyneuropathy (FAP) is a hereditary disease caused by a point mutation of the human plasma protein, transthyretin (TTR), which binds and transports thyroxine (T(4)). TTR variants contribute to the pathogenesis of amyloidosis by forming amyloid fibrils in the extracellular environment. A recent report showed that epigallocatechin 3-gallate (EGCG), the major polyphenol component of green tea, binds to TTR and suppresses TTR amyloid fibril formation. However, structural analysis of EGCG binding to TTR has not yet been conducted. Here we first investigated the crystal structure of the EGCG-V30M TTR complex and found novel binding sites distinct from the thyroxine binding site, suggesting that EGCG has a mode of action different from those of previous chemical compounds that were shown to bind and stabilize the TTR tetramer structure. Furthermore, EGCG induced the oligomerization and monomer suppression in the cellular system of clinically reported TTR variants. Taken together, these findings suggest the possibility that EGCG may be a candidate compound for FAP therapy.

Structure–Function Relationship of Tumor Necrosis Factor (TNF) and Its Receptor Interaction Based on 3D Structural Analysis of a Fully Active TNFR1-Selective TNF Mutant

Tumor necrosis factor (TNF) is an important cytokine that suppresses carcinogenesis and excludes infectious pathogens to maintain homeostasis. TNF activates its two receptors [TNF receptor (TNFR) 1 and TNFR2], but the contribution of each receptor to various host defense functions and immunologic surveillance is not yet clear. Here, we used phage display techniques to generate receptor-selective TNF mutants that activate only one TNFR. These TNF mutants will be useful in the functional analysis of TNFR. Six amino acids in the receptor binding interface (near TNF residues 30, 80, and 140) were randomly mutated by polymerase chain reaction. Two phage libraries comprising over 5 million TNF mutants were constructed. By selecting the mutants without affinity for TNFR1 or TNFR2, we successfully isolated 4 TNFR2-selective candidates and 16 TNFR1-selective candidates, respectively. The TNFR1-selective candidates were highly mutated near residue 30, whereas TNFR2-selective candidates were highly mutated near residue 140, although both had conserved sequences near residues 140 and 30, respectively. This finding suggested that the phage display technique was suitable for identifying important regions for the TNF interaction with TNFR1 and TNFR2. Purified clone R1-6, a TNFR1-selective candidate, remained fully bioactive and had full affinity for TNFR1 without activating TNFR2, indicating the usefulness of the R1-6 TNF mutant in analyzing TNFR1 receptor function. To further elucidate the receptor selectivity of R1-6, we examined the structure of R1-6 by X-ray crystallography. The results suggested that R31A and R32G mutations strongly influenced electrostatic interaction with TNFR2, and that L29K mutation contributed to the binding of R1-6 to TNFR1. This phage display technique can be used to efficiently construct functional mutants for analysis of the TNF structure-function relationship, which might facilitate in silico drug design based on receptor selectivity.

Mycotic aneurysm of the infrarenal abdominal aorta infected by Clostridium septicum: A case report of surgical management and review of the literature

We report a surgical case of mycotic aneurysm of the infrarenal abdominal aorta infected by Clostridium septicum. The patient was first treated with an in situ prosthetic graft replacement. When the infection recurred 5 weeks after the aortic surgery, the patient was successfully treated by transposition of rectus abdominis muscle flap around the graft. Only 19 cases of mycotic aneurysm or aortic dissection caused by Clostridium septicum have been reported. Ten of 12 patients who underwent vascular surgery survived, whereas all 7 patients who did not undergo surgery died. Surgical treatment should be undertaken since the surgical results seem satisfactory.

Structural Insights into Differences in Drug-binding Selectivity between Two Forms of Human α1-Acid Glycoprotein Genetic Variants, the A and F1*S Forms

Human α1-acid glycoprotein (hAGP) in serum functions as a carrier of basic drugs. In most individuals, hAGP exists as a mixture of two genetic variants, the F1*S and A variants, which bind drugs with different selectivities. We prepared a mutant of the A variant, C149R, and showed that its drug-binding properties were indistinguishable from those of the wild type. In this study, we determined the crystal structures of this mutant hAGP alone and complexed with disopyramide (DSP), amitriptyline (AMT), and the nonspecific drug chlorpromazine (CPZ). The crystal structures revealed that the drug-binding pocket on the A variant is located within an eight-stranded β-barrel, similar to that found in the F1*S variant and other lipocalin family proteins. However, the binding region of the A variant is narrower than that of the F1*S variant. In the crystal structures of complexes with DSP and AMT, the two aromatic rings of each drug interact with Phe-49 and Phe-112 at the bottom of the binding pocket. Although the structure of CPZ is similar to those of DSP and AMT, its fused aromatic ring system, which is extended in length by the addition of a chlorine atom, appears to dictate an alternative mode of binding, which explains its nonselective binding to the F1*S and A variant hAGPs. Modeling experiments based on the co-crystal structures suggest that, in complexes of DSP, AMT, or CPZ with the F1*S variant, Phe-114 sterically hinders interactions with DSP and AMT, but not CPZ.