Bacterial lipopolysaccharide down-regulates expression of GTP cyclohydrolase I feedback regulatory protein.

GTP cyclohydrolase I feedback regulatory protein (GFRP) is a 9.7-kDa protein regulating GTP cyclohydrolase I activity in dependence of tetrahydrobiopterin and phenylalanine concentrations, thus enabling stimulation of tetrahydrobiopterin biosynthesis by phenylalanine to ensure its efficient metabolism by phenylalanine hydroxylase. Here, we were interested in regulation of GFRP expression by proinflammatory cytokines and stimuli, which are known to induce GTP cyclohydrolase I expression. Recombinant human GFRP stimulated recombinant human GTP cyclohydrolase I in the presence of phenylalanine and mediated feedback inhibition by tetrahydrobiopterin. Levels of GFRP mRNA in human myelomonocytoma (THP-1) cells remained unaltered by treatment of cells with interferon-gamma or interleukin-1beta, but were significantly down-regulated by bacterial lipopolysaccharide (LPS, 1 microg/ml), without or with cotreatment by interferon-gamma, which strongly up-regulated GTP cyclohydrolase I expression and activity. GFRP expression was also suppressed in human umbilical vein endothelial cells treated with 1 microg/ml LPS, as well as in rat tissues 7 h post intraperitoneal injection of 10 mg/kg LPS. THP-1 cells stimulated with interferon-gamma alone showed increased pteridine synthesis by addition of phenylalanine to the culture medium. Cells stimulated with interferon-gamma plus LPS, in contrast, showed phenylalanine-independent pteridine synthesis. These results demonstrate that LPS down-regulates expression of GFRP, thus rendering pteridine synthesis independent of metabolic control by phenylalanine.     

The creatine kinase system is essential for optimal refill of the sarcoplasmic reticulum Ca2+ store in skeletal muscle.

Muscle function depends on an adequate ATP supply to sustain the energy consumption associated with Ca(2+) cycling and actomyosin sliding during contraction. In this regulation of energy homeostasis, the creatine kinase (CK) circuit for high energy phosphoryl transfer between ATP and phosphocreatine plays an important role. We earlier established a functional connection between the activity of the CK system and Ca(2+) homeostasis during depolarization and contractile activity of muscle. Here, we show how CK activity is coupled to the kinetics of spontaneous and electrically induced Ca(2+) transients in the sarcoplasm of myotubes. Using the UV ratiometric Ca(2+) probe Indo-1 and video-rate confocal microscopy in CK-proficient and -deficient cultured cells, we found that spontaneous and electrically induced transients were dependent on ryanodine-sensitive Ca(2+) release channels, sarcoplasmic/endoplasmic reticulum Ca(2+)-ATPase pumps, extracellular calcium, and functional mitochondria in both cell types. However, at increasing sarcoplasmic Ca(2+) load (induced by electrical stimulation at 0.1, 1, and 10 Hz), the Ca(2+) removal rate and the amount of Ca(2+) released per transient were gradually reduced in CK-deficient (but not wild-type) myotubes. We conclude that the CK/phosphocreatine circuit is essential for efficient delivery of ATP to the sarcoplasmic/endoplasmic reticulum Ca(2+)-ATPase pumps and thereby directly influences sarcoplasmic reticulum refilling and the kinetics of the sarcoplasmic Ca(2+) signals.     

Requirement for Tyrosine Kinase-ERK1/2 Signaling in α1β1 Integrin-Mediated Collagen Matrix Remodeling by Rat Mesangial Cells

Abnormal mesangial extracellular matrix remodeling by mesangial cells (MCs) is the hallmark of progressive glomerulonephritis (GN). We recently showed, using a type I collagen gel contraction assay, that α1β1 integrin-dependent MC adhesion and migration are necessary cell behaviors for collagen matrix remodeling. To further determine the mechanism of α1β1 integrin-mediated collagen remodeling, we studied the signaling pathways of MCs that participate in the regulation of collagen gel contraction. Immunoprecipitation and phosphotyrosine detection revealed that gel contraction is associated with the enhanced activity and phosphorylation of ERK1/2 by MCs. The tyrosine kinase inhibitors herbimycin and genistein inhibited collagen gel contraction dose dependently. Furthermore, targeting ERK1/2 activity with a MEK inhibitor, PD98059, and antisense ERK1/2 hindered gel contraction in a dose-dependent manner. Similar inhibitory effects on gel contraction and ERK1/2 phosphorylation were observed when MC-mediated gel contraction was performed in the presence of function-blocking anti-α1 or anti-β1 integrin antibodies. However, cell adhesion and migration assays indicated that PD98059 and antisense ERK1/2 blocked α1β1 integrin-dependent MC migration, but did not interfere with collagen adhesion, although there was a marked decrease in ERK1/2 phosphorylation and ERK1/2 protein expression in cell adhesion on type I collagen. None of the above could affect membrane expression of α1β1 integrin. These results suggested that ERK1/2 activation is critical for the α1β1 integrin-dependent MC migration necessary for collagen matrix reorganization. We therefore conclude that ERK1/2 may serve as a possible target for pharmacological inhibition of pathological collagen matrix formation in GN.     

Recent and historical discharge of a large European river system - oxygen isotopic composition of river water and skeletal aragonite of Unionidae in the Rhine

Seasonal variations in the oxygen isotopic composition of Rhine River water were analyzed in detail and compared with the oxygen isotopic record from recent and historical specimens of freshwater bivalves (Unionidae). The purpose of this study was to investigate the potential use of these aragonitic bivalves as proxy recorders for varying amounts and sources of discharge, and thereby infer climate change. Seasonal variations in the river water δ¹⁸O are on the order of 1-2‰. During summer, Alpine melt-water contributes significantly to the total discharge, resulting in average values of −10 to −10.5‰, whereas the non-Alpine contribution is higher during winter, as indicated by mean δ¹⁸O values of −8.5 to −9‰. The basic pattern of the modern seasonal variation of δ¹⁸O of river water can be described by a numerical mass balance approximation of the various contributions from the Alpine and non-Alpine catchments with their average δ¹⁸O composition. The δ¹⁸O of growth increments in the prismatic shell layer of Anodonta corresponds perfectly to what is predicted by known fractionation of ¹⁸O between water and aragonite. Shell growth is restricted to water temperatures above 8-10°C, so variations in δ¹⁸O and the river water temperature are faithfully recorded by relatively large growth increments during summer. The distinctive isotopic signatures of individual flood events during summer and autumn are also recorded in the shells.     

Interaction of nitrogen and phosphorus nutrition in determining growth

In this paper we discuss the differences and similarities in the growth response of tomato plants to N and P limitation, and to their interaction. Two detailed growth experiments, with varied N or P supply, were conducted in order to unravel the effects of N and P limitation on growth of young tomato plants (Lycopersicon esculentum Mill.). Relative growth rate (RGR) initially increased sharply with increasing plant P concentration but leveled off at higher plant P concentrations. In contrast, RGR increased gradually with increasing plant N concentration before it leveled off at higher plant N concentrations. The relationship of RGR with organic leaf N and P showed the same shape as with total N and P concentrations, respectively. The difference in response is most likely due to the different roles of N and P in the machinery of the plant's energy metabolism (e.g., photosynthesis, respiration). Plant N concentration decreased with increasing P limitation. We show that this decrease cannot be explained by a shift in dry-mass partitioning. Our results suggest that the decrease in N concentration with increasing P limitation may be mediated by a decrease in leaf cytokinin levels and is less likely due to decreased energy availability at low P conditions. Dry-mass partitioning to the roots was closely linearly related to the leaf reduced-N concentration. However, treatments that were severely P limited deviated from this relationship.     

Maximum Number of Habitable Planets at the Time of Earth's Origin: New Hints for Panspermia?

New discoveries have fuelled the ongoing discussion of panspermia, i.e. the transport of life from one planet to another within the solar system (interplanetary panspermia) or even between different planetary systems (interstellar panspermia). The main factor for the probability of interstellar panspermia is the average density of stellar systems containing habitable planets. The combination of recent results for the formation rate of Earth-like planets with our estimations of extrasolar habitable zones allows us to determine the number of habitable planets in the Milky Way over cosmological time scales. We find that there was a maximum number of habitable planets around the time of Earth's origin. If at all, interstellar panspermia was most probable at that time and may have kick-started life on our planet.