N-acetyltyrosine-induced redox signaling in hormesis

A suite of adaptations allows insects to survive in hostile terrestrial environments for long periods of time. Temperature represents a key environmental factor for most ectothermic insects, and they rapidly acclimate to high and low temperatures. Vast amounts of data in this research field support the idea that an insect's ability to tolerate fluctuating temperatures can be regarded as a biphasic hormetic dose response. Observation indicates that their thermal hormetic response represents a conservative estimate of their intrinsic capacity for rapid adaptation to environmental changes in nature because they naturally experience diel or seasonal temperature fluctuations. It is therefore reasonable to suppose that the hormetic response in insects reflects a surplus physiological capacity to deal with temperature changes that they would experience naturally. Although it has been unknown how thermal acclimation is induced, a stress-dependent increase in N-acetyltyrosine (NAT) was recently found to occur in insect larvae who had endured high temperatures. NAT treatment was demonstrated to induce thermotolerance in several tested insect species. NAT was also identified in the serum of humans as well as mice, and its concentration in mice was shown to be increased by heat and restraint stress, with NAT pretreatment lowering the concentrations of corticosterone and peroxidized lipids in stressed mice. These recent findings may give us some hints about how long a hormetic response lasts. Here, I will discuss recent findings underlying hormetic responses induced by an intrinsic factor, NAT, and how the hormetic response may begin and end.     

Structural Confirmation of a Unique Carotenoid Lactoside,P457, in Symbiodinium sp. Strain nbrc 104787 Isolated from a Sea Anemone and its Distribution in Dinoflagellates and Various Marine Organisms

The molecular structure of the carotenoid lactoside P457, (3S,5R,6R,3′S,5′R,6′S)‐13′‐cis‐5,6‐epoxy‐3′,5′‐dihydroxy‐3‐(β‐d ‐galactosyl‐(1→4)‐β‐d ‐glucosyl)oxy‐6′,7′‐didehydro‐5,6,7,8,5′,6′‐hexahydro‐β,β‐caroten‐20‐al, was confirmed by spectroscopic methods using Symbiodinium sp. strain NBRC 104787 cells isolated from a sea anemone. Among various algae, cyanobacteria, land plants, and marine invertebrates, the distribution of this unique diglycosyl carotenoid was restricted to free‐living peridinin‐containing dinoflagellates and marine invertebrates that harbor peridinin‐containing zooxanthellae. Neoxanthin appeared to be a common precursor for biosynthesis of peridinin and P457, although neoxanthin was not found in peridinin‐containing dinoflagellates. Fucoxanthin‐containing dinoflagellates did not possess peridinin or P457; green dinoflagellates, which contain chlorophyll a and b, did not contain peridinin, fucoxanthin, or P457; and no unicellular algae containing both peridinin and P457, other than peridinin‐containing dinoflagellates, have been observed. Therefore, the biosynthetic pathways for peridinin and P457 may have been coestablished during the evolution of dinoflagellates after the host heterotrophic eukaryotic microorganism formed a symbiotic association with red alga that does not contain peridinin or P457.     

Hydrogen Cyanide Production due to Mid-Size Impacts in a Redox-Neutral N2-Rich Atmosphere

Cyanide compounds are amongst the most important molecules of the origin of life. Here, we demonstrate the importance of mid-size (0.1–1 km in diameter) hence frequent meteoritic impacts to the cyanide inventory on the early Earth. Subsequent aerodynamic ablation and chemical reactions with the ambient atmosphere after oblique impacts were investigated by both impact and laser experiments. A polycarbonate projectile and graphite were used as laboratory analogs of meteoritic organic matter. Spectroscopic observations of impact-generated ablation vapors show that laser irradiation to graphite within an N₂-rich gas can produce a thermodynamic environment similar to that produced by oblique impacts. Thus, laser ablation was used to investigate the final chemical products after this aerodynamic process. We found that a significant fraction (>0.1 mol%) of the vaporized carbon is converted to HCN and cyanide condensates, even when the ambient gas contains as much as a few hundred mbar of CO₂. As such, the column density of cyanides after carbon-rich meteoritic impacts with diameters of 600 m would reach ~10 mol/m² over ~10² km² under early Earth conditions. Such a temporally and spatially concentrated supply of cyanides may have played an important role in the origin of life.     

Kakeromamide A,a new cyclic pentapeptide inducing astrocyte differentiation isolated from the marine cyanobacterium Moorea bouillonii

Kakeromamide A (1), a new cyclic pentapeptide encompassing a thiazole ring moiety and a β-amino acid, was isolated from the marine cyanobacterium Moorea bouillonii. Its structure was elucidated by the spectral analysis and the modified Marfey’s method. Compound 1 induced differentiation of neural stem cells into astrocytes at the concentration of 10?µM.     

Comparison of cellular response in bovine intervertebral disc cells and articular chondrocytes: effects .of lipopolysaccharide on proteoglycan metabolism

Lipopolysaccharide (LPS) induces matrix degradation and markedly stimulates the production of several cytokines, i.e., interleukin-1β, −6, and −10, by disc cells and chondrocytes. We performed a series of experiments to compare cellular responses of cells from the bovine intervertebral disc (nucleus pulposus and annulus fibrosus) and from bovine articular cartilage to LPS. Alginate beads containing cells isolated from bovine intervertebral discs and articular cartilage were cultured with or without LPS in the presence of 10% fetal bovine serum. The DNA content and the rate of proteoglycan synthesis and degradation were determined. In articular chondrocytes, LPS strongly suppressed cell proliferation and proteoglycan synthesis in a dose-dependent manner and stimulated proteoglycan degradation. Compared with articular chondrocytes, nucleus pulposus cells responded in a similar, although less pronounced manner. However, treatment of annulus fibrosus cells with LPS showed no significant effects on proteoglycan synthesis or degradation. A slight, but statistically significant, inhibition of cell proliferation was observed at high concentrations of LPS in annulus fibrosus cells. Thus, LPS suppressed proteoglycan synthesis and stimulated proteoglycan degradation by articular chondrocytes and nucleus pulposus cells. The effects of LPS on annulus fibrosus cells were minor compared with those on the other two cell types. The dissimilar effects of LPS on the various cell types suggest metabolic differences between these cells and may further indicate a divergence in pathways of LPS signaling and a differential sensitivity to exogenous stimuli such as LPS.This work was supported in part by NIH grants 2-P50-AR39239 and 1-P01-AR48152.     

pH-dependent equilibrium between long lived near-UV intermediates of photoactive yellow protein

The long lived intermediate (signaling state) of photoactive yellow protein (PYP(M)), which is formed in the photocycle, was characterized at various pHs. PYP(M) at neutral pH was in equilibrium between two spectroscopically distinct states. Absorption maxima of the acidic form (PYP(M)(acid)) and alkaline form (PYP(M)(alkali)) were located at 367 and 356 nm, respectively. Equilibrium was represented by the Henderson-Hasselbalch equation, in which apparent pK(a) was 6.4. Content of alpha- and/or beta-structure of PYP(M)(acid) was significantly greater than PYP(M)(alkali) as demonstrated by the molar ellipticity at 222 nm. In addition, changes in amide I and II modes of beta-structure in the difference Fourier transform infrared spectra for formation of PYP(M)(acid) was smaller than that of PYP(M)(alkali). The vibrational mode at 1747 cm(-1) of protonated Glu-46 was found as a small band for PYP(M)(acid) but not for PYP(M)(alkali), suggesting that Glu-46 remains partially protonated in PYP(M)(acid), whereas it is fully deprotonated in PYP(M)(alkali). Small angle x-ray scattering measurements demonstrated that the radius of gyration of PYP(M)(acid) was 15.7 Angstroms, whereas for PYP(M)(alkali) it was 16.2 Angstroms. These results indicate that PYP(M)(acid) assumes a more ordered and compact structure than PYP(M)(alkali). Binding of citrate shifts this equilibrium toward PYP(M)(alkali). UV-visible absorption spectra and difference infrared spectra of the long lived intermediate formed from E46Q mutant was consistent with those of PYP(M)(acid), indicating that the mutation shifts this equilibrium toward PYP(M)(acid). Alterations in the nature of PYP(M) by pH, citrate, and mutation of Glu-46 are consistently explained by the shift of the equilibrium between PYP(M)(acid) and PYP(M)(alkali).     

Evidence for chloroplast control of external Ca2+-induced cytosolic Ca2+ transients and stomatal closure

The role of guard cell chloroplasts in stomatal function is controversial. It is usually assumed that stomatal closure is preceded by a transient increase in cytosolic free Ca(2+) concentration ([Ca(2+)](cyt)) in the guard cells. Here, we provide the evidence that chloroplasts play a critical role in the generation of extracellular Ca(2+) ([Ca(2+)](ext))-induced [Ca(2+)](cyt) transients and stomatal closure in Arabidopsis. CAS (Ca(2+) sensing receptor) is a plant-specific putative Ca(2+)-binding protein that was originally proposed to be a plasma membrane-localized external Ca(2+) sensor. In the present study, we characterized the intracellular localization of CAS in Arabidopsis with a combination of techniques, including (i) in vivo localization of green fluorescent protein (GFP) fused gene expression, (ii) subcellular fractionation and fractional analysis of CAS with Western blots, and (iii) database analysis of thylakoid membrane proteomes. Each technique produced consistent results. CAS was localized mainly to chloroplasts. It is an integral thylakoid membrane protein, and the N-terminus acidic Ca(2+)-binding region is likely exposed to the stromal side of the membrane. The phenotype of T-DNA insertion CAS knockout mutants and cDNA mutant-complemented plants revealed that CAS is essential for stomatal closure induced by external Ca(2+). In contrast, overexpression of CAS promoted stomatal closure in the absence of externally applied Ca(2+). Furthermore, using the transgenic aequorin system, we showed that [Ca(2+)](ext)-induced [Ca(2+)](cyt) transients were significantly reduced in CAS knockout mutants. Our results suggest that thylakoid membrane-localized CAS is essential for [Ca(2+)](ext)-induced [Ca(2+)](cyt) transients and stomatal closure.