Palmitate and oleate induction of acylation stimulating protein resistance in 3T3-L1 adipocytes and preadipocytes

Acylation stimulating protein (ASP) stimulates triglyceride synthesis and glucose transport via its receptor C5L2. The aims were (i) to evaluate ASP response under insulin-resistant conditions and (ii) to identify mechanisms of ASP resistance using 3T3-L1 adipocytes and preadipocytes. Overnight incubation with palmitate (PAL) or oleate (OLE) induced dose-dependent inhibition of ASP-stimulated glucose transport in adipocytes (198 +/- 18% +ASP, 100 +/- 4% basal, 131 +/- 14% + ASP + 1 mmol/L PAL) and preadipocytes (287 +/- 21% + ASP, 100 +/- 4% basal, 109 +/- 13% + ASP + 1 mmol/L PAL). In adipocytes, dose-dependent maximal C5L2 mRNA decreases were -41 +/- 15% and -82 +/- 2%, with decreased cell-surface C5L2 of -55 +/- 12% and -39 +/- 9% (1 mmol/L PAL and OLE, respectively) with no change in preadipocytes. Adipocytes treated with PAL or OLE evidenced inhibition of ASP stimulation of G proteins: Gbeta (-50%), Galphaq/11 (-50%) and protein kinase C: PKCalpha-P (-52%), PKCzeta-P (-43%). Fatty acid-induced ASP resistance via C5L2 may contribute to altered adipose tissue function and obesity/insulin resistance phenotype in humans.     

Central Adiposity Determines Prevalence Differences of the Metabolic Syndrome

Objective: To compare the expression of the metabolic syndrome in Spain and San Antonio, TX, two populations with major differences regarding their cardiovascular risk profile. Research Methods and Procedures: Cross‐sectional analysis of population‐based, epidemiological surveys using the metabolic syndrome definition of the National Cholesterol Education Program. In San Antonio, we limited our analysis to non‐Hispanic whites because non‐Hispanic whites are largely of European ancestry (n = 1339 in San Antonio and 2947 in Spain) Results: In men, increased central adiposity was more prevalent in San Antonio than in Spain (29.7 vs. 23.0%, p < 0.0001); in women, it was less prevalent in San Antonio than in Spain (40.2 vs. 66.4%, p < 0.0001). The metabolic syndrome followed that same pattern: more prevalent in men (28.9 vs. 20.8%, p = 0.019) and less in women from San Antonio (27.1 vs. 30.9%, p < 0.0001). In subjects with the metabolic syndrome, most women had increased central adiposity (92.6% in San Antonio and 97.5% in Spain), and most men had either increased central adiposity or blood pressure (99.2% in San Antonio and 95.0% in Spain). Discussion: Contrary to men, the metabolic syndrome is more prevalent in Spanish women than in women from San Antonio with differences that mirror differences in central adiposity. Central adiposity and blood pressure may be used to exclude the metabolic syndrome. Considering recent secular trends in obesity, we predict there will be an increase in the prevalence of the metabolic syndrome in both populations in the coming years.     

The OSBP-related proteins: a novel protein family involved in vesicle transport,cellular lipid metabolism,and cell signalling

Proteins/genes showing high sequence homology to the mammalian oxysterol binding protein (OSBP) have been identified in a variety of eukaryotic organisms from yeast to man. The unifying feature of the gene products denoted as OSBP-related proteins (ORPs) is the presence of an OSBP-type ligand binding (LB) domain. The LB domains of OSBP and its closest homologue bind oxysterols, while data on certain other family members suggest interaction with phospholipids. Many ORPs also have a pleckstrin homology (PH) domain in the amino-terminal region. The PH domains of the family members studied in detail are known to interact with membrane phosphoinositides and play an important role in the intracellular targeting of the proteins. It is plausible that the ORPs constitute a regulatory apparatus that senses the status of specific lipid ligands in membranes, using the PH and/or LB domains, and mediates information to yet poorly known downstream machineries. Functional studies carried out on the ORP proteins in different organisms indicate roles of the gene family in diverse cellular processes including control of lipid metabolism, regulation of vesicle transport, and cell signalling events.     

Characterization of cyanobacterial β‐carotene ketolase and hydroxylase genes in Escherichia coli,and their application for astaxanthin biosynthesis

Carotenoid biosynthesis is highly conserved and well characterized up to the synthesis of β‐carotene. Conversely, the synthesis of astaxanthin from β‐carotene is less well characterized. Regardless, astaxanthin is a highly sought natural product, due to its various industrial applications and elevated antioxidant capacity. In this article, 12 β‐carotene ketolase and 4 β‐carotene hydroxylase genes, isolated from 5 cyanobacterial species, are investigated for their function, and potential for microbial astaxanthin synthesis. Further, this in vivo comparison identifies and applies the most promising genetic elements within a dual expression vector, which is maintained in Escherichia coli. Here, combined overexpression of individual β‐carotene ketolase and β‐carotene hydroxylase genes, within a β‐carotene accumulating host, enables a 23.5‐fold improvement in total carotenoid yield (1.99 mg g^?1), over the parental strain, with >90% astaxanthin. Biotechnol. Bioeng. 2009;103: 944–955. © 2009 Wiley Periodicals, Inc.     

A hidden square-root boundary between growth rate and biomass yield

Although the theoretical value of biomass yield can be calculated from metabolic network stoichiometry, the growth rate is difficult to predict. Since the rate and yield can vary independently, no simple relationship has been discovered between these two variables. In this work, we analyzed the well-accepted enzyme kinetics and uncovered a hidden boundary for growth rate, which is determined by the square-root of three physiological parameters: biomass yield, the substrate turnover number, and the maximum synthesis rate of the turnover enzyme. Cells cannot grow faster than the square-root of the product of these parameters. This analysis is supported by experimental data and involves essentially no assumptions except (i) the cell is not undergoing a downshift transition, (ii) substrate uptake enzyme activity is proportional to its copy number. This simple boundary (not correlation) has escaped notice for many decades and suggests that the yield calculation does not predict the growth rate, but gives an upper limit for the growth rate. The relationship also explains how growth rate is affected by the yield and sheds lights on strain design for product formation.     

Metabolic, hygric and ventilatory physiology of a hypermetabolic marsupial, the honey possum (Tarsipes rostratus)

The honey possum is the only non-volant mammal to feed exclusively on a diet of nectar and pollen. Like other mammalian and avian nectarivores, previous studies indicated that the honey possum’s basal metabolic rate was higher than predicted for a marsupial of equivalent body mass. However, these early measurements have been questioned. We re-examined the basal metabolic rate (2.52 ± 0.222 ml O₂ g⁻¹ h⁻¹) of the honey possum and confirm that it is indeed higher (162%) than predicted for other marsupials both before and after accounting for phylogenetic history. This, together with its small body mass (5.4 ± 0.14 g; 1.3% of that predicted by phylogeny) may be attributed to its nectarivorous diet and mesic distribution. Its high-basal metabolic rate is associated with a high-standard body temperature (36.6 ± 0.48°C) and oxygen extraction (19.4%), but interestingly the honey possum has a high point of relative water economy (17.0°C) and its standard evaporative water loss (4.33 ± 0.394 mg H₂O g⁻¹ h⁻¹) is not elevated above that of other marsupials, despite its mesic habitat and high dietary water intake.     

Calcium signals activated by ghrelin and D-Lys-GHRP-6 ghrelin antagonist in developing dorsal root ganglion glial cells

Ghrelin is a hormone regulating energy homeostasis via interaction with its receptor, GHSR-1a. Ghrelin activities in dorsal root ganglia (DRG) cells are unknown. Herein we show that ghrelin induces a change of cytosolic calcium concentration in both glia and neurons of embryonic chick DRG. Both RT-PCR and binding studies performed with fluorescent ghrelin in the presence of either unlabeled ghrelin or GHSR-1a antagonist D-Lys³-GHRP-6, indicate that DRG cells express GHSR-1a. In glial cells the response is characterized by a rapid transient rise in [Ca²⁺]_i followed by a long lasting rise. The calcium elevation is dependent on calcium release from thapsigargin-sensitive intracellular stores and on activation of two distinct Ca²⁺ entry pathways, a receptor activated calcium entry and a store operated calcium entry. Surprisingly, D-Lys³-GHRP-6 exerts several activities in the absence of exogenous ghrelin: (i) it activates calcium release from thapsigargin-sensitive intracellular stores and calcium entry via voltage-operated channels in non-neuronal cells; (ii) it inhibits calcium oscillations in non-neuronal cells exhibiting spontaneous Ca²⁺ activity and iii) it promotes apoptosis of DRG cells, both neurons and glia. In summary, we provide the first evidence for ghrelin activity in DRG, and we also demonstrate that the widely used D-Lys³-GHRP-6 ghrelin antagonist features ghrelin independent activities.     

Identification of cell-wall stress as a hexose-dependent and osmosensitive regulator of plant responses

Development, abiotic and biotic stress each affect the physical architecture and chemical composition of the plant cell wall, making maintenance of cell-wall integrity an important component of many plant processes. Cellulose biosynthesis inhibition (CBI) was employed to impair the functional integrity of the cell wall, and the plant's response to this specific stress was characterized in an Arabidopsis seedling model system. CBI caused changes in the expression of genes involved in mechanoperception, the response to microbial challenge, and lignin and cell-wall polysaccharide biosynthesis. Following CBI, activation of a UDP- d -xylose 4-epimerase gene correlated with increases in arabinose and uronic acid content in seedling cell walls. Activation of pathogen response genes, lignin deposition and lesion formation were dependent on externally supplied sugars and were suppressed by osmotic support. Lignin deposition in the root elongation zone caused by CBI was reduced in atrbohd (NADPH oxidase) mutant seedlings but increased in jasmonic acid resistant1 ( jar1-1 ) mutant seedlings. Phytohormone measurements showed that CBI-induced increases in jasmonic (JA) and salicylic acids were dependent on sugar availability and prevented by osmotic support. We show that CBI activates responses commonly attributed to both abiotic and microbial challenges. Glucose/sucrose and turgor pressure are critical components in maintenance of cell-wall integrity and the regulation of induced responses, including JA biosynthesis. Lignin deposition induced by CBI is regulated by JAR1-1 and NADPH oxidase-dependent signalling processes. Our results identify components of the mechanism that mediates the response to impairment of cell-wall integrity in Arabidopsis thaliana .