Dynamic Turnover of PI4P and PI(4,5)P2 under Hypoxia Controls Electrostatic Plasma Membrane Targeting

Phosphatidylinositol (PtdIns) 4-phosphate (PI4P) and phosphatidylinositol 4,5-biphosphate (PI(4,5)P2 or PIP2) are key phosphoinositides that determine the identity of the plasma membrane (PM) and regulate numerous key biological events there. To date, the complex mechanisms regulating the homeostasis and dynamic turnover of PM PI4P and PIP2 in response to various physiological conditions and stresses remain to be fully elucidated. Here we report that hypoxia in Drosophila induces acute and reversible depletion of PM PI4P and PIP2 that severely disrupts the electrostatic PM targeting of multiple polybasic polarity proteins. Genetically encoded ATP sensors confirmed that hypoxia induces acute and reversible reduction of cellular ATP levels which showed a strong real-time correlation with the levels of PM PI4P and PIP2 in cultured cells. By combining genetic manipulations with quantitative imaging assays we showed that PI4KIIIa, as well as Rbo/EFR3 and TTC7 that are essential for targeting PI4KIIIa to PM, are required for maintaining the homeostasis and dynamic turnover of PM PI4P and PIP2 under normoxia and hypoxia. Our results revealed that in cells challenged by energetic stresses triggered by hypoxia, ATP inhibition and possibly ischemia, dramatic turnover of PM PI4P and PIP2 could have profound impact on many cellular processes including electrostatic PM targeting of numerous polybasic proteins.

Human-relevant near-organ neuromodulation of the immune system via the splenic nerve

Neuromodulation of immune function by stimulating the autonomic connections to the spleen has been demonstrated in rodent models. Consequently, neuroimmune modulation has been proposed as a new therapeutic strategy for the treatment of inflammatory conditions. However, demonstration of the translation of these immunomodulatory mechanisms in anatomically and physiologically relevant models is still lacking. Additionally, translational models are required to identify stimulation parameters that can be transferred to clinical applications of bioelectronic medicines. Here, we performed neuroanatomical and functional comparison of the mouse, rat, pig, and human splenic nerve using in vivo and ex vivo preparations. The pig was identified as a more suitable model of the human splenic innervation. Using functional electrophysiology, we developed a clinically relevant marker of splenic nerve engagement through stimulation-dependent reversible reduction in local blood flow. Translation of immunomodulatory mechanisms were then assessed using pig splenocytes and two models of acute inflammation in anesthetized pigs. The pig splenic nerve was shown to locally release noradrenaline upon stimulation, which was able to modulate cytokine production by pig splenocytes. Splenic nerve stimulation was found to promote cardiovascular protection as well as cytokine modulation in a high- and a low-dose lipopolysaccharide model, respectively. Importantly, splenic nerve–induced cytokine modulation was reproduced by stimulating the efferent trunk of the cervical vagus nerve. This work demonstrates that immune responses can be modulated by stimulation of spleen-targeted autonomic nerves in translational species and identifies splenic nerve stimulation parameters and biomarkers that are directly applicable to humans due to anatomical and electrophysiological similarities.

Structural analysis and reaction mechanism oaf malate dehydrogenase from Geobacillus stearothermophilus

Malate dehydrogenase (MDH) catalyzes the reversible reduction of oxaloacetate (OAA) to L-malate using nicotinamide adenine dinucleotide hydrogen. MDH has two characteristic loops, the mobile loop and the catalytic loop, in the active site. On binding to the substrate, the enzyme undergoes a structural change from the open-form, with an open conformation of the mobile loop, to the closed-form, with the loop in a closed conformation. In this study, three crystals of MDH from a moderate thermophile, Geobacillus stearothermophilus (gs-MDH) were used to determine four different enzyme structures (resolutions, 1.95–2.20 Å), each of which was correspondingly assigned to its four catalytic states. Two OAA-unbound structures exhibited the open-form, while the other two OAA-bound structures exhibited both the open- and closed-form. The structural analysis suggested that the binding of OAA to the open-form gs-MDH promotes conformational change in the mobile loop and simultaneously activates the catalytic loop. The mutations on the key amino acid residues involving the proposed catalytic mechanism significantly affected the gs-MDH activity, supporting our hypothesis. These findings contribute to the elucidation of the detailed molecular mechanism underlying the substrate recognition and structural switching during the MDH catalytic cycle.

The Mammalian Cytosolic Type 2 (R)-β-hydroxybutyrate Dehydrogenase (BDH2) is 4-oxo-L-proline Reductase (EC 1.1.1.104)

The early studies on chicken embryos revealed that exposition to 4-oxo-L-proline resulted in the explicit increase in 4-hydroxy-L-proline content in their tissues. In 1962, 4-oxo-L-proline reductase, an enzyme responsible for the reduction of 4-oxo-L-proline, was partially purified from rabbit kidneys and characterized biochemically, but only recently the molecular identity of the enzyme has been unveiled in our laboratory. The present investigation reports the purification, identification as well as biochemical characterization of 4-oxo-L-proline reductase. The enzyme was purified from rat kidneys about 280-fold. Following mass spectrometry analysis of the purified protein preparation, the mammalian cytosolic type 2 (R)-β-hydroxybutyrate dehydrogenase (BDH2) emerged as the only meaningful candidate for the reductase. Rat and human BDH2 were expressed in E. coli, purified, and shown to catalyze the reversible reduction of 4-oxo-L-proline to cis-4-hydroxy-L-proline, as confirmed by chromatographic and mass spectrometry analysis. Specificity studies carried out on both enzymes showed that 4-oxo-L-proline was the best substrate, particularly the human enzyme acted with 9400-fold higher catalytic efficiencies on 4-oxo-L-proline than on (R)-β-hydroxybutyrate. Finally, HEK293T cells efficiently metabolized 4-oxo-L-proline to cis-4-hydroxy-L-proline and simultaneously accumulated trans-4-hydroxy-L-proline in the culture medium, suggesting that 4-oxo-L-proline is most likely an inhibitor of trans-4-hydroxy-L-proline metabolism in human cells. We conclude that BDH2 is mammalian 4-oxo-L-proline reductase that converts 4-oxo-L-proline to cis-4-hydroxy-L-proline, and not to trans-4-hydroxy-L-proline as currently thought, and hypothesize that the enzyme may be considered as a potential source of cis-4-hydroxy-L-proline in mammalian tissues.

Síntesis regioespecífica y estudio electroquímico de dos derivados carboxílicos C60 solubles en agua

We report a new methodology for the synthesis of two highly symmetric equatorial malonate hexaadducts of C60 fullerene. The synthetic methodology is based on a series of protection and deprotection steps that allow the preparation of a fullerene [60] functionalized with six symmetrical positioned malonate addends without using complicated and expensive separation techniques (highperformance liquid chromatography, HPLC) or long reaction times. This methodology allowed us to prepare the carboxylic adducts 6 (equatorial octacarboxylic tetraadduct of C60) and 8 (equatorial dodecacarboxylic hexakisadduct of C60). As far as we now, compound 6 has not yet been reported. We also studied the electronic properties of the main compounds by UV-Vis spectroscopy and cyclic voltammetry (CV). The reported fullerene adducts exhibited several reversible reduction processes whose electron transfers are controlled by diffusion.

Changes of Pd Oxidation State in Pd/Al2O3 Catalysts Using Modulated Excitation DRIFTS

Infrared spectroscopy is typically not used to establish the oxidation state of metal-based catalysts. In this work, we show that the baseline of spectra collected in diffuse reflectance mode of a series of Pd/Al2O3 samples of increasing Pd content varies significantly and reversibly under alternate pulses of CO or H2 and O2. Moreover, these baseline changes are proportional to the Pd content in Pd/Al2O3 samples exhibiting comparable Pd particle size. Similar measurements by X-ray absorption spectroscopy on a different 2 wt.% Pd/Al2O3 confirm that the baseline changes reflect the reversible reduction-oxidation of Pd. Hence, we demonstrate that changes in oxidation state of metal-based catalysts can be determined using diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) and that this behavior is part of the spectral changes that are returned by experiments under operando conditions.

Synthesis, Structure and Bonding Nature of Heavy Dipnictene Radical Anions

Cyclic voltammetry studies of two L(X)Ga-substituted dipnictenes [L(R2N)GaE]2 (E = Sb, R = Me 1; E =Bi; R = Et 2; L = HC[C(Me)NDipp]2; Dipp= 2,6-i-Pr2C6H3) showed reversible reduction events....