Analysis of the productivity of a continuous algal culture system

We describe a first-principles analysis of a system for the continuous culture of the green alga Scenedesmus obliquus under light-limiting conditions. According to this analysis, the productivity of the algal culture is given by the relation Y = E(m)I(0)AK(1 - e(-alphacl)) - GRcV, where Y = yield (g cells/h), E(m) = 0.20 (the maximum attainable photosynthetic conversion on an energy basis), A = illuminated area (m(2)), K = 0.156[(g cells/h/W), the energy equivalent of the algae], I(0) = light intensity (W/m(2)), alpha = extinction coefficient (L/cm/g),c = cell concentration (g/L), I = light path (cm), R = respiration rate (g carbon/g cells/h), V = culture volume (L), and G = ratio of g cells to g carbon (2.04). This formula is completely determined and has no free adjustable parameters. Using parameter values determined independently, the model accurately predicted the relationship of productivity to cell density in the culture system.     

Extracellular ATP Released by Osteoblasts Is A Key Local Inhibitor of Bone Mineralisation

Previous studies have shown that exogenous ATP (>1µM) prevents bone formation in vitro by blocking mineralisation of the collagenous matrix. This effect is thought to be mediated via both P2 receptor-dependent pathways and a receptor-independent mechanism (hydrolysis of ATP to produce the mineralisation inhibitor pyrophosphate, PP_i). Osteoblasts are also known to release ATP constitutively. To determine whether this endogenous ATP might exert significant biological effects, bone-forming primary rat osteoblasts were cultured with 0.5-2.5U/ml apyrase (which sequentially hydrolyses ATP to ADP to AMP + 2P_i). Addition of 0.5U/ml apyrase to osteoblast culture medium degraded extracellular ATP to <1% of control levels within 2 minutes; continuous exposure to apyrase maintained this inhibition for up to 14 days. Apyrase treatment for the first 72 hours of culture caused small decreases (≤25%) in osteoblast number, suggesting a role for endogenous ATP in stimulating cell proliferation. Continuous apyrase treatment for 14 days (≥0.5U/ml) increased mineralisation of bone nodules by up to 3-fold. Increases in bone mineralisation were also seen when osteoblasts were cultured with the ATP release inhibitors, NEM and brefeldin A, as well as with P2X1 and P2X7 receptor antagonists. Apyrase decreased alkaline phosphatase (TNAP) activity by up to 60%, whilst increasing the activity of the PP_i-generating ecto-nucleotide pyrophosphatase/phosphodiesterases (NPPs) up to 2.7-fold. Both collagen production and adipocyte formation were unaffected. These data suggest that nucleotides released by osteoblasts in bone could act locally, via multiple mechanisms, to limit mineralisation.     

BTNL2, a butyrophilin/B7-like molecule, is a negative costimulatory molecule modulated in intestinal inflammation

Butyrophilin-like 2 (BTNL2) is a butyrophilin family member with homology to the B7 costimulatory molecules, polymorphisms of which have been recently associated through genetic analyses to sporadic inclusion body myositis and sarcoidosis. We have characterized the full structure, expression, and function of BTNL2. Structural analysis of BTNL2 shows a molecule with an extracellular region containing two sets of two Ig domains, a transmembrane region, and a previously unreported cytoplasmic tail. Unlike most other butyrophilin members, BTNL2 lacks the prototypical B30.2 ring domain. TaqMan and Northern blot analysis indicate BTNL2 is predominantly expressed in digestive tract tissues, in particular small intestine and Peyer's patches. Immunohistochemistry with BTNL2-specific Abs further localizes BTNL2 to epithelial and dendritic cells within these tissues. Despite its homology to the B7 family, BTNL2 does not bind any of the known B7 family receptors such as CD28, CTLA-4, PD-1, ICOS, or B and T lymphocyte attenuator. Because of its localization in the gut and potential role in the immune system, BTNL2 expression was analyzed in a mouse model of inflammatory bowel disease. BTNL2 is overexpressed during both the asymptomatic and symptomatic phase of the Mdr1a knockout model of spontaneous colitis. In functional assays, soluble BTNL2-Fc protein inhibits the proliferation of murine CD4(+) T cells from the spleen, mesenteric lymph node, and Peyer's patch. In addition, BTNL2-Fc reduces proliferation and cytokine production from T cells activated by anti-CD3 and B7-related protein 1. These data suggest a role for BTNL2 as a negative costimulatory molecule with implications for inflammatory disease.     

Genome-wide interaction of genotype by erythrocyte n-3 fatty acids contributes to phenotypic variance of diabetes-related traits

Background

Little is known about the interplay between n-3 fatty acids and genetic variants for diabetes-related traits at the genome-wide level. The present study aimed to examine variance contributions of genotype by environment (GxE) interactions for different erythrocyte n-3 fatty acids and genetic variants for diabetes-related traits at the genome-wide level in a non-Hispanic white population living in the U.S.A. (n = 820). A tool for Genome-wide Complex Trait Analysis (GCTA) was used to estimate the genome-wide GxE variance contribution of four diabetes-related traits: HOMA-Insulin Resistance (HOMA-IR), fasting plasma insulin, glucose and adiponectin. A GxE genome-wide association study (GWAS) was conducted to further elucidate the GCTA results. Replication was conducted in the participants of the Boston Puerto Rican Health Study (BPRHS) without diabetes (n = 716).

Results

In GOLDN, docosapentaenoic acid (DPA) contributed the most significant GxE variance to the total phenotypic variance of both HOMA-IR (26.5%, P-nominal = 0.034) and fasting insulin (24.3%, P-nominal = 0.042). The ratio of arachidonic acid to eicosapentaenoic acid + docosahexaenoic acid contributed the most significant GxE variance to the total variance of fasting glucose (27.0%, P-nominal = 0.023). GxE variance of the arachidonic acid/eicosapentaenoic acid ratio showed a marginally significant contribution to the adiponectin variance (16.0%, P-nominal = 0.058). None of the GCTA results were significant after Bonferroni correction (P < 0.001). For each trait, the GxE GWAS identified a far larger number of significant single-nucleotide polymorphisms (P-interaction ≤ 10E-5) for the significant E factor (significant GxE variance contributor) than a control E factor (non-significant GxE variance contributor). In the BPRHS, DPA contributed a marginally significant GxE variance to the phenotypic variance of HOMA-IR (12.9%, P-nominal = 0.068) and fasting insulin (18.0%, P-nominal = 0.033).

Conclusion

Erythrocyte n-3 fatty acids contributed a significant GxE variance to diabetes-related traits at the genome-wide level.

Electronic supplementary material

The online version of this article (doi:10.1186/1471-2164-15-781) contains supplementary material, which is available to authorized users.     

Pharmacogenetic association of NOS3 variants with cardiovascular disease in patients with hypertension: the GenHAT study

Nitric oxide synthase 3 (NOS3) catalyzes production of NO in the endothelium and may play a role in cardiovascular disease (CVD). We assessed the pharmacogenetic associations of three NOS3 polymorphisms and three antihypertensive drugs with CVD outcomes. Hypertensive subjects (n = 30,280) from a multi-center, double-blind clinical trial were randomized to chlorthalidone, amlodipine, or lisinopril treatment (mean follow up, 4.9 years). Outcomes included coronary heart disease (CHD: fatal CHD and nonfatal myocardial infarction); stroke; heart failure (fatal, requiring hospitalization, or outpatient treatment); all-cause mortality; and end-stage renal disease (ESRD). Main effects of NOS3 variants on outcome and genotype-treatment interactions were tested. For NOS3 −690 C>T (rs3918226), a higher hazard ratio (HR) was found in minor allele carriers for CHD (CC = 1.00, CT+TT = 1.12 (95% confidence interval (CI) = 1.00–1.26), P = 0.048). For NOS3 −922 A>G (rs1800779), a higher HR was found in minor allele carriers for heart failure (AA = 1.00, AG+GG = 1.10 (CI = 1.00–1.21), P = 0.046). Significant pharmacogenetic findings were observed for stroke and all-cause mortality. For −690 C>T, a lower HR was observed for stroke in minor allele carriers when treated with amlodipine versus lisinopril (CC = 0.85 (CI = 0.73–0.99), CT+TT = 0.49 (CI = 0.31–0.80), P = 0.04). For glu298asp G>T (rs1799983), a lower HR was observed for all-cause mortality in minor allele carriers when treated with amlodipine versus lisinopril (GG = 1.01 (CI = 0.91–1.13), GT+TT = 0.85 (CI = 0.75–0.97), P = 0.04). We observed significant associations with NOS3 variants and CHD and heart failure and significant pharmacogenetic effects for stroke and all cause mortality. This suggests that NOS3 variants may potentially provide useful clinical information with respect to treatment decisions in the future.     

Hypoxia is a major stimulator of osteoclast formation and bone resorption

Hypoxia is known to act as a general stimulator of cells derived from marrow precursors. We investigated the effect of oxygen tension on the formation and function of osteoclasts, the cells responsible for bore resorption, which are of promonocytic origin. Using 7- and 13-day cultures of mouse marrow cells on ivory discs, we found that reducing oxygen tension from the ambient atmospheric level of 20% by increasing the proportion of nitrogen caused progressive increases in the formation of multinucleated osteoclasts and resorption pits. Peak effects occurred in 2% oxygen, where stimulations of resorption up to 21-fold were measured. Significant stimulations of osteoclast formation and resorption were observed even in severely hypoxic cultures gassed with 0.2% oxygen. Short-term cultures of cells disaggregated from rat bones indicated that hypoxia did not alter the resorptive activity of mature osteoclasts, but reduced their survival or adherence. In 3-day organ cultures of mouse calvarial bones, exposure to 2% oxygen resulted in maximal, fivefold stimulation of osteoclast-mediated calcium release, an effect equivalent to that of prostaglandin E(2) (PGE(2)), a reference osteolytic agent. Hypoxia also caused a moderate acidosis in calvarial cultures, presumably as a result of increased anaerobic metabolism; this observation is significant because osteoclast activation is dependent on extracellular acidification. Our experiments reveal a previously-overlooked mechanism of considerable potential importance for the regulation of bone destruction. These findings may help explain the bone loss associated with a wide range of pathological states involving local or systemic hypoxia, and emphasize the importance of the vasculature in bone.     

Genetic variants associated with VLDL, LDL and HDL particle size differ with race/ethnicity

Specific constellations of lipoprotein particle features, reflected as differences in mean lipoprotein particle diameters, are associated with risk of insulin resistance (IR) and cardiovascular disease (CVD). The associations of lipid profiles with disease risk differ by race/ethnicity, the reason for this is not clear. We aimed to examine whether there were additional genetic differences between racial/ethnic groups on lipoprotein profile. Genotypes were assessed using the Affymetrix 6.0 array in 817 related Caucasian participants of the Genetics of Lipid Lowering Drugs and Diet Network (GOLDN). Association analysis was conducted on fasting mean particle diameters using linear models, adjusted for age, sex and study center as fixed effects, and pedigree as a random effect. Replication of associations reaching P < 1.97 × 10^?05 (the level at which we achieved at least 80 % power to replicate SNP-phenotype associations) was conducted in the Caucasian population of the Multi-Ethnic Study of Atherosclerosis (MESA; N = 2,430). Variants which replicated across both Caucasian populations were subsequently tested for association in the African-American (N = 1,594), Chinese (N = 758), and Hispanic (N = 1,422) populations of MESA. Variants in the APOB gene region were significantly associated with mean VLDL diameter in GOLDN, and in the Caucasian and Hispanic populations of MESA, while variation in the hepatic lipase (LIPC) gene was associated with mean HDL diameter in both Caucasians populations only. Our findings suggest that the genetic underpinnings of mean lipoprotein diameter differ by race/ethnicity. As lipoprotein diameters are modifiable, this may lead new strategies to modify lipoprotein profiles during the reduction of IR that are sensitive to race/ethnicity.     

Vasoactive intestinal peptide binding autoantibodies in autoimmune humans and mice

Autoantibodies capable of binding the immunoregulatory neuropeptide vasoactive intestinal peptide (VIP) were detected in the sera of a mouse strain prone to autoimmune disease due to the lpr mutation (MRL/lpr). The autoantibodies were not present in control wildtype MRL/lpr mice, but they were readily detected in humans without autoimmune disease. The binding was due to low affinity VIP recognition. Increased VIP binding activity was evident in patients with systemic lupus erythematosus but not systemic sclerosis, Sjögren’s syndrome (SS), rheumatoid arthritis or autoimmune thyroiditis. Recombinant VIP binding Fv clones (fragment variable; the variable domains of the light and heavy chains antibody subunits joined with a peptide linker) were isolated from a phage display library prepared from lupus patients. One Fv clone displaying VIP-selective binding and several clones displaying cross-reactivity with unrelated peptides were identified. Replacement mutations in the VIP-selective clone were preferentially localized in the regions known to make contacts with the antigen, i.e. the complementarity determining regions, suggesting that the selective binding activity is due to immunological maturation of the antibodies. Frequent occurrences of autoantibody responses to VIP indicate that immunological tolerance to this neuropeptide can be readily broken. The depletion of VIP by specific antibodies in autoimmune disease may interfere with VIP regulation of T cells and inflammatory cells and result in further amplification of autoreactive immunological responses.     

Anaerobic Biodegradation of Hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX) by <Emphasis Type="Italic">Acetobacterium malicum</Emphasis> Strain HAAP-1 Isolated from a Methanogenic Mixed Culture

In previous work, we studied the anaerobic biodegradation of hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX) by a methanogenic mixed culture that biodegrades RDX by using H₂ as the sole electron donor. Strain HAAP-1 was isolated after enriching for the homoacetogens in a mineral medium containing RDX and an H₂-CO₂ (80:20) headspace. Strain HAAP-1 degraded 29.0 M RDX in <14 days and formed 13.0 mM acetate when grown in a mineral medium with an H₂-CO₂ headspace. Methylenedinitramine was observed as a transient intermediate, indicating ring cleavage had occurred. In live cultures containing an N₂-CO₂ headspace, RDX was not degraded, and no acetate was formed. The 16S rRNA gene sequence for strain HAAP-1, consisting of 1485 base pairs, had a 99.2% and 99.1% sequence similarity to Acetobacterium malicum and A. wieringae, respectively. This is the first report of RDX degradation by a homoacetogen growing autotrophically and extends the number of genera known to carry out this transformation.