Homocysteine-induced endoplasmic reticulum stress causes dysregulation of the cholesterol and triglyceride biosynthetic pathways

Hepatic steatosis is common in patients having severe hyperhomocysteinemia due to deficiency for cystathionine beta-synthase. However, the mechanism by which homocysteine promotes the development and progression of hepatic steatosis is unknown. We report here that homocysteine-induced endoplasmic reticulum (ER) stress activates both the unfolded protein response and the sterol regulatory element-binding proteins (SREBPs) in cultured human hepatocytes as well as vascular endothelial and aortic smooth muscle cells. Activation of the SREBPs is associated with increased expression of genes responsible for cholesterol/triglyceride biosynthesis and uptake and with intracellular accumulation of cholesterol. Homocysteine-induced gene expression was inhibited by overexpression of the ER chaperone, GRP78/BiP, thus demonstrating a direct role of ER stress in the activation of cholesterol/triglyceride biosynthesis. Consistent with these in vitro findings, cholesterol and triglycerides were significantly elevated in the livers, but not plasmas, of mice having diet-induced hyperhomocysteinemia. This effect was not due to impaired hepatic export of lipids because secretion of VLDL-triglyceride was increased in hyperhomocysteinemic mice. These findings suggest a mechanism by which homocysteine-induced ER stress causes dysregulation of the endogenous sterol response pathway, leading to increased hepatic biosynthesis and uptake of cholesterol and triglycerides. Furthermore, this mechanism likely explains the development and progression of hepatic steatosis and possibly atherosclerotic lesions observed in hyperhomocysteinemia.

Cyclodextrins in the treatment of a mouse model of Niemann-Pick C disease

Niemann-Pick type C (NPC) is a neurodegenerative disorder characterized by greatly altered somatic cholesterol metabolism. The NPC1 gene has recently been cloned and shown to have sequence homology to other sterol-sensing proteins. We have used a mouse model with a disrupted npc1 gene to study the effects of the cholesterol-mobilizing compound, 2-hydroxypropyl-beta-cyclodextrins (HPBCD), on the clinical course of this disorder. Treatment with two HPBCDs, with varying levels of 2-hydroxypropyl substitution, had effects in delaying neurological symptoms and in decreasing liver cholesterol storage while a third HPBCD was without effect. The ameliorating effect was not improved by longer exposure times (commencement of exposure in utero), however, it is not known if there is transplacental transfer of HPBCDs. The combination of HPBCD with probucol or nifedipine (which have previously been shown to lower liver cholesterol in this animal model) markedly decreased liver storage of unesterified cholesterol without altering the depressed levels of esterified cholesterol. The slight effects of the HPBCDs on neurological symptoms may be partially due to their apparent non-permeation of the blood-brain barrier (BBB). This non-permeation was assayed with radioactive tracers and was also present in the mdr1a knockout mice which have greatly increased BBB permeability for many drugs. Intrathecal delivery of HPBCD by an Alzet osmotic minipump did not improve its efficacy in ameliorating neurological symptoms.

Pharmacological and genetic modifications of somatic cholesterol do not substantially alter the course of CNS disease in Niemann-Pick C mice

Niemann-Pick type C (NPC) is a neurodegenerative disorder with somatically altered cholesterol metabolism. The NPC1 gene has recently been cloned and shown to have sequences shared with known sterol-sensing proteins. We have used a mouse model with a disrupted Npc1 gene to study two cholesterol-lowering drugs (nifedipine and probucol) and the effects of introducing a null mutation in the low-density lipoprotein receptor (LDLR). Although these treatments significantly ameliorated liver cholesterol storage, little effect on the onset of neurological symptoms was found.

Repair of UV damage in plants by nucleotide excision repair: Arabidopsis UVH1 DNA repair gene is a homolog of Saccharomyces cerevisiae Rad1

To analyze plant mechanisms for resistance to UV radiation, mutants of Arabidopsis that are hypersensitive to UV radiation (designated uvh and uvr) have been isolated. UVR2 and UVR3 products were previously identified as photolyases that remove UV-induced pyrimidine dimers in the presence of visible light. Plants also remove dimers in the absence of light by an as yet unidentified dark repair mechanism and uvh1 mutants are defective in this mechanism. The UVH1 locus was mapped to chromosome 5 and the position of the UVH1 gene was further delineated by Agrobacterium-mediated transformation of the uvh1-1 mutant with cosmids from this location. Cosmid NC23 complemented the UV hypersensitive phenotype and restored dimer removal in the uvh1-1 mutant. The cosmid encodes a protein similar to the S. cerevisiae RAD1 and human XPF products, components of an endonuclease that excises dimers by nucleotide excision repair (NER). The uvh1-1 mutation creates a G to A transition in intron 5 of this gene, resulting in a new 3' splice site and introducing an in-frame termination codon. These results provide evidence that the Arabidopsis UVH1/AtRAD1 product is a subunit of a repair endonuclease. The previous discovery in Lilium longiflorum of a homolog of human ERCC1 protein that comprises the second subunit of the repair endonuclease provides additional evidence for the existence of the repair endonuclease in plants. The UVH1 gene is strongly expressed in flower tissue and also in other tissues, suggesting that the repair endonuclease is widely utilized for repair of DNA damage in plant tissues.

Isolation and functional characterization of Ca2+/H+ antiporters from cyanobacteria

Genome sequences of cyanobacteria, Synechocystis sp. PCC 6803, Anabaena sp. PCC 7120, and Thermosynechococcus elongatus BP-1 revealed the presence of a single Ca2+/H+ antiporter in these organisms. Here, we isolated the putative Ca2+/H+ antiporter gene from Synechocystis sp. PCC 6803 (synCAX) as well as a homologous gene from a halotolerant cyanobacterium Aphanothece halophytica (apCAX). In contrast to plant vacuolar CAXs, the full-length apCAX and synCAX genes complemented the Ca2+-sensitive phenotype of an Escherichia coli mutant. ApCAX and SynCAX proteins catalyzed specifically the Ca2+/H+ exchange reaction at alkaline pH. Immunological analysis suggested their localization in plasma membranes. The Synechocystis sp. PCC 6803 cells disrupted of synCAX exhibited lower Ca2+ efflux activity and a salt-sensitive phenotype. Overexpression of ApCAX and SynCAX enhanced the salt tolerance of Synechococcus sp. PCC 7942 cells. Mutagenesis analyses indicate the importance of two conserved acidic amino acid residues, Glu-74 and Glu-324, in the transmembrane segments for the exchange activity. These results clearly indicate that cyanobacteria contain a Ca2+/H+ antiporter in their plasma membranes, which plays an important role for salt tolerance.

Altered expression of caveolin-1 and increased cholesterol in detergent insoluble membrane fractions from liver in mice with Niemann-Pick disease type C

Niemann-Pick type C (NPC) is an autosomal recessive disease characterized by impaired cholesterol homeostasis due to a defect in the intracellular transport of unesterified cholesterol. While accumulation of lysosomal cholesterol is the most apparent microscopic finding, cholesterol has also been shown to accumulate in the trans-cisternae of the Golgi apparatus. Caveolin-1, a cholesterol-binding protein that cycles between the Golgi apparatus and the plasma membrane, has been hypothesized to participate in cholesterol transport. Using the BALB/c murine model for NPC disease, we found that the expression of caveolin-1 in total liver homogenates from heterozygous and homozygous affected animals was altered. Immunoblot analysis of liver homogenates from heterozygous mice revealed that caveolin-1 is significantly (p < 0.005) elevated, 4.9 fold, compared to normal mice. Total liver homogenates from homozygous affected mice also had a significant (p < 0.05) increase in caveolin-1 expression, 1.6 fold, compared to normal mice. Immunohistochemical staining of liver cross-sections revealed that the increased caveolin-1 was localized to sinusoidal endothelial cells in heterozygous mice. The Triton insoluble floating fraction (TIFF) was isolated using liver from each genotype and analyzed for caveolin-1 expression. Caveolin-1 in the TIFF from heterozygous mice was significantly (p < 0.01) elevated, 1.8 fold, compared to normal and homozygous affected animals; normal and homozygous affected animals, however, were not significantly different from each other. The TIFF isolated from homozygous affected mice revealed a 15 fold increase in unesterified cholesterol compared to the TIFF isolated from heterozygous and normal mice. In summary, these findings demonstrate an altered expression of caveolin-1 in liver from heterozygous and homozygous NPC mice and increased concentration of cholesterol from TIFF in homozygous affected NPC mice. The identification of these alterations in the TIFF suggests involvement of detergent insoluble membrane structures, possibly caveolae and/or detergent insoluble glycosphingolipid-enriched complexes (DIGs), in the cholesterol trafficking defect in this disorder.

The Npc1 mutation causes an altered expression of caveolin-1, annexin II and protein kinases and phosphorylation of caveolin-1 and annexin II in murine livers

We have previously demonstrated (1) an increased expression of caveolin-1 in murine heterozygous and homozygous Niemann-Pick type C (NPC) livers, and (2) an increased concentration of unesterified cholesterol in a detergent insoluble caveolae-enriched fraction from homozygous livers. To define further the relationship between caveolin-1 function and the cholesterol trafficking defect in NPC, we examined the expression and distribution of additional caveolar and signal transduction proteins. The expression of annexin II was significantly increased in homozygous liver homogenates and the Triton X-100 insoluble floating fraction (TIFF). Phosphoamino acid analysis of caveolin-1 and annexin II from the homozygous TIFF demonstrated an increase in serine and tyrosine phosphorylation, respectively. To determine the basis for increased phosphorylation of these proteins, the expression and distribution of several protein kinases was examined. The expression of PKCalpha, PKCzeta and pp60-src (protein kinases) were significantly increased in both heterozygous and homozygous liver homogenates, while PKCdelta was increased only in homozygous livers. Of the protein kinases analyzed, only CK IIalpha was significantly enriched in the heterozygous TIFF. Finally, the concentration of diacylglycerol in the homozygous TIFF was significantly increased and this elevation may modulate PKC distribution and function. These results provide additional evidence for involvement of a caveolin-1 containing cellular fraction in the pathophysiology of NPC and also suggest that the Npc1 gene product may directly or indirectly, regulate the expression and distribution of signaling molecules.

One-step biosynthesis of α-keto-γ-methylthiobutyric acid from L-methionine by an Escherichia coli whole-cell biocatalyst expressing an engineered L-amino acid deaminase from Proteus vulgaris

α-Keto-γ-methylthiobutyric acid (KMTB), a keto derivative of l-methionine, has great potential for use as an alternative to l-methionine in the poultry industry and as an anti-cancer drug. This study developed an environment friendly process for KMTB production from l-methionine by an Escherichia coli whole-cell biocatalyst expressing an engineered l-amino acid deaminase (l-AAD) from Proteus vulgaris. We first overexpressed the P. vulgarisl-AAD in E. coli BL21 (DE3) and further optimized the whole-cell transformation process. The maximal molar conversion ratio of l-methionine to KMTB was 71.2% (mol/mol) under the optimal conditions (70 g/L l-methionine, 20 g/L whole-cell biocatalyst, 5 mM CaCl₂, 40°C, 50 mM Tris-HCl [pH 8.0]). Then, error-prone polymerase chain reaction was used to construct P. vulgarisl-AAD mutant libraries. Among approximately 10⁴ mutants, two mutants bearing lysine 104 to arginine and alanine 337 to serine substitutions showed 82.2% and 80.8% molar conversion ratios, respectively. Furthermore, the combination of these mutations enhanced the catalytic activity and molar conversion ratio by 1.3-fold and up to 91.4% with a KMTB concentration of 63.6 g/L. Finally, the effect of immobilization on whole-cell transformation was examined, and the immobilized whole-cell biocatalyst with Ca²⁺ alginate increased reusability by 41.3% compared to that of free cell production. Compared with the traditional multi-step chemical synthesis, our one-step biocatalytic production of KMTB has an advantage in terms of environmental pollution and thus has great potential for industrial KMTB production.

A Biomechanical Comparison between Taylor's Spatial Frame and Ilizarov External Fixator

ABSTRACT

Taylor's spatial frame (TSF) and Ilizarov external fixators (IEF) are two circular external fixator commonly used to address complex deformity and fractures. There is currently no data available comparing the biomechanical properties of these two external fixators. This study looks into the mechanical characteristics of each system. TSF rings with 6 oblique struts, 4 tube connectors, 4 threaded rods, and 6 threaded rods were compared to a standard IEF rings with 4 threaded rods. Compression and torsional loading was performed to the frame as well as construct with Polyvinylchloride tubes. TSF rings with 4 tube connectors had the highest stiffness (3288 N/mm) while TSF rings with 6 struts was the least stiff. The situation was reversed for torsion where TSF rings with 6 oblique struts had the highest torsional stiffness (82.01 Nm/Degree) and frame Ilizarov rings with 4 threaded rods the least. Standard TSF construct of two ring with 6 oblique struts have better torsional stiffness and lower axial stiffness compared to the standard IEF.

KEY WORDS

Taylor's Spatial Frame, Ilizarov External Fixator, Biomechanical properties.

Antinuclear autoantibodies (ANA) in Gulf War-related illness and chronic fatigue syndrome (CFS) patients

It is established that veterans of the 1991 Gulf War have an increased frequency of experiencing multiple symptoms. The underlying mechanism of these ailments is unclear, although they do not correspond to any clearly defined syndrome. The most common symptoms overlap with those of chronic fatigue syndrome (CFS). CFS was recently associated with a novel subtype of antinuclear autoantibody (ANA) that reacts with nuclear envelope (NE) antigens. NE autoantibodies are not known to be linked with any distinct clinical condition, but have been observed in patients with unusual mixed chronic autoimmune disorders and connective tissue diseases. In this study we examined whether NE ANAs are a feature of patients with CFS and symptomatic Gulf War veterans (sGWV). We studied the prevalence of ANA in 130 sGWV, 90 well Gulf War veterans (wGWV), 128 symptomatic Bosnia and Era veterans (sBEV), 100 CFS patients, and 111 healthy control subjects matching for age and sex. We found no significant difference in the prevalence of ANAs between any of the groups. None of the patients/or veterans we studied had ANA of the NE type. Our results show that multisymptom illness due to CFS or related to Gulf War service is not associated with antinuclear autoimmunity.

Transporter engineering and enzyme evolution for pyruvate production from d/l-alanine with a whole-cell biocatalyst expressing l-amino acid deaminase from Proteus mirabilis

Pyruvate, which has been widely used in the food, pharmaceutical, and agrochemical industries, can be produced by “one-step pyruvate production” method from d/l-alanine with a whole-cell E. coli biocatalyst expressing l-amino acid deaminase (pm1) from Proteus mirabilis.

Growth performance of thai pangus (Pangasius hypophthalmus) in polyculture system using different supplementary feeds

Thai pangus polyculture with carps has been increasing for its high potential, however very few attempts were made to compare its growth using different types of feed. A research was undertaken to assess the effect of three types of feed on growth of Thai pangus (Pangasius hypophthalmus) and rohu (Labeo rohita) in polyculture system for 11 months from 15 May 2005 to 15 April 2006 in Khulna. Growth performance using Hand-made Feed (F1) was compared with two commercial fish feed, Sunney Feed (F2) and Saudi-Bangla Feed (F3) in three respective treatments of T1, T2 and T3. All treatments were carried out in triplicate at 24700/ha for Thai pangus and 4940/ha for rohu. Average initial weight of Thai pangus and rohu were 4.5 and 33.5g respectively. Growth performance was influenced by feed type. Average final weight of Thai pangus and rohu were 820 and 710; 846 and 770; and 872 and 717g with specific growth rate 1.58 and 0.93; 1.59 and 0.95 and 1.60 and 0.93 % day -1 in T1, T2 and T3 respectively. Feed conversion ratio was estimated 2.3 in T1, 2.1 in T2 and 1.96 in T3. The result showed a typical increasing trend of final weight and specific growth rate of Thai pangus along with the increasing of feed protein level. But rohu showed highest growth in T2 where protein level was 26-30% which was lower than that of T3 (Protein level 28-32%). The study suggests that suitable protein level and quality feed is required for adequate growth of fish. Key words: Feed, Thai pangus, Polyculture, Growth.     doi:10.3329/ujzru.v27i0.1956 Univ. j. zool. Rajshahi Univ. Vol. 27, 2008 pp. 59-62

Two-Step Production of Phenylpyruvic Acid from L-Phenylalanine by Growing and Resting Cells of Engineered Escherichia coli: Process Optimization and Kinetics Modeling

Phenylpyruvic acid (PPA) is widely used in the pharmaceutical, food, and chemical industries. Here, a two-step bioconversion process, involving growing and resting cells, was established to produce PPA from l-phenylalanine using the engineered Escherichia coli constructed previously. First, the biotransformation conditions for growing cells were optimized (l-phenylalanine concentration 20.0 g·L-1, temperature 35°C) and a two-stage temperature control strategy (keep 20°C for 12 h and increase the temperature to 35°C until the end of biotransformation) was performed. The biotransformation conditions for resting cells were then optimized in 3-L bioreactor and the optimized conditions were as follows: agitation speed 500 rpm, aeration rate 1.5 vvm, and l-phenylalanine concentration 30 g·L-1. The total maximal production (mass conversion rate) reached 29.8 ± 2.1 g·L-1 (99.3%) and 75.1 ± 2.5 g·L-1 (93.9%) in the flask and 3-L bioreactor, respectively. Finally, a kinetic model was established, and it was revealed that the substrate and product inhibition were the main limiting factors for resting cell biotransformation.

Integrating error-prone PCR and DNA shuffling as an effective molecular evolution strategy for the production of α-ketoglutaric acid byl-amino acid deaminase

l-Amino acid deaminases (LAADs; EC 1.4.3.2) belong to a family of amino acid dehydrogenases that catalyze the formation of α-keto acids froml-amino acids.

Rewriting the Metabolic Blueprint: Advances in Pathway Diversification in Microorganisms

Living organisms have evolved over millions of years to fine tune their metabolism to create efficient pathways for producing metabolites necessary for their survival. Advancement in the field of synthetic biology has enabled the exploitation of these metabolic pathways for the production of desired compounds by creating microbial cell factories through metabolic engineering, thus providing sustainable routes to obtain value-added chemicals. Following the past success in metabolic engineering, there is increasing interest in diversifying natural metabolic pathways to construct non-natural biosynthesis routes, thereby creating possibilities for producing novel valuable compounds that are non-natural or without elucidated biosynthesis pathways. Thus, the range of chemicals that can be produced by biological systems can be expanded to meet the demands of industries for compounds such as plastic precursors and new antibiotics, most of which can only be obtained through chemical synthesis currently. Herein, we review and discuss novel strategies that have been developed to rewrite natural metabolic blueprints in a bid to broaden the chemical repertoire achievable in microorganisms. This review aims to provide insights on recent approaches taken to open new avenues for achieving biochemical production that are beyond currently available inventions.

Air Quality Dispersion Modelling to Evaluate CIPP Installation Styrene Emissions

Cured-in-place pipe (CIPP) is one of the most popular in situ rehabilitation techniques to repair sewer and water pipes. While there are multiple approaches to curing CIPP, steam-curing of styrene-based resins has been found to be associated with air-borne chemical emissions. Health officials, utilities and industry representatives have recognized the need to know more about these emissions, especially styrene. Such concern has led to multiple studies investigating the concentrations of volatile organic compounds on CIPP installation sites. This study expands upon previous effort by modeling worst-case, steam-cured CIPP emissions over a 5-year weather record. The effort also includes calibration of the model to emissions averages over the work day rather than instantaneous field measurements. Dispersion modelling software, AERMOD, was utilized to model the styrene component of CIPP emissions on two CIPP installation sites in the US. Based on the analysis results, it was found that the styrene emitted from stacks dissipates rapidly with styrene concentrations only exceeding minimum health and safety threshold levels at distances close to the stack (2 m or less). The values predicted by the model analysis are comparable with the field measured styrene concentrations from other studies. Current safety guidelines in the US recommend a 4.6-m (15-ft) safety perimeter for stack emission points. The results of this study indicate that significant and lasting health impacts are unlikely outside recommended safety perimeter. The results also validate the importance of enforcing recommended safety guidance on steam-cured CIPP sites.

Engineered microbial consortia for next-generation feedstocks

Addressing urgent environmental challenges, this commentary emphasizes the need for green, bio-based solutions in chemical production from renewable feedstocks. It highlights advanced metabolic engineering of microbial strains and the use of microbial consortia as innovative approaches for efficient resource recovery. These strategies aim to enhance the conversion of diverse renewable feedstocks, including agricultural residues, industrial by-products, and greenhouse gases, into value-added chemicals. This article discusses cutting-edge techniques in renewable feedstock upcycling, utilizing both engineered unicellular and multicellular systems. It advocates a paradigm shift in sustainable biomanufacturing, focusing on transforming renewable resources into value-added products. This approach is crucial for developing a circular bioeconomy, aligning with global efforts to mitigate environmental impacts.

Identification and monitoring of cell heterogeneity from plasmid recombination during limonene production

Detecting alterations in plasmid structures is often performed using conventional molecular biology. However, these methods are laborious and time-consuming for studying the conditions inducing these mutations, which prevent real-time access to cell heterogeneity during bioproduction. In this work, we propose combining both flow cytometry and fluorescence-activated cell sorting, integrated with mechanistic modelling to study conditions that lead to plasmid recombination using a limonene-producing microbial system as a case study. A gene encoding GFP was introduced downstream of the key enzymes involved in limonene biosynthesis to enable real-time kinetics monitoring and the identification of cell heterogeneity according to microscopic and flow cytometric analyses. Three different plasmid configurations (one correct and two incorrect) were identified through cell sorting based on subpopulations expressing different levels of GFP at 10 and 50 µM IPTG. Higher limonene production (530 mg/L) and lower subpopulation proportion carrying the incorrect plasmid (12%) were observed for 10 µM IPTG compared to 50 µM IPTG (96 mg/L limonene and more than 70% of cell population carrying the incorrect plasmid, respectively) in 100 mL production culture. We also managed to derive exploratory hypotheses regarding the plasmid recombination region using the model and successfully validated them experimentally. Additionally, the results also showed that limonene production was proportional to GFP fluorescence intensity. This correlation could serve as an alternative to using biosensors for a high-throughput screening process. The developed method enables rapid identification of plasmid recombination at single-cell level and correlates the heterogeneity with bioproduction performance. KEY POINTS: • Strategy to study plasmid recombination during bioproduction. • Different plasmid structures can be identified and monitored by flow cytometry. • Mathematical modelling suggests specific alterations in plasmid structures.