22-Hydroxycholesterols regulate lipid metabolism differently than T0901317 in human myotubes

The nuclear liver X receptors (LXRalpha and beta) are regulators of lipid and cholesterol metabolism. Oxysterols are known LXR ligands, but the functional role of hydroxycholesterols is at present unknown. In human myotubes, chronic exposure to the LXR ligand T0901317 promoted formation of diacylglycerol (DAG) and triacylglycerol (TAG), 22-R-hydroxycholesterol (22-R-HC) had no effect, and 22-S-hydroxycholesterol (22-S-HC) reduced the formation. In accordance with this, 22-HC and T0901317 regulated the expression of fatty acid transporter CD36, stearoyl-CoA desaturase-1, acyl-CoA synthetase long chain family member 1 and fatty acid synthase (FAS) differently; all genes were increased by T0901317, 22-R-HC did not change their expression level, while 22-S-HC reduced it. Transfection studies confirmed that the FAS promoter was activated by T0901317 and repressed by 22-S-HC through an LXR response element in the promoter. Both 22-R-HC and T0901317 increased gene expression of LXRalpha, sterol regulatory element-binding protein 1c and ATP-binding cassette transporter A1, while 22-S-HC had little effect. In summary, 22-R-HC regulated lipid metabolism and mRNA expression of some LXR target genes in human myotubes differently than T0901317. Moreover, 22-S-HC did not behave like an inactive ligand; it reduced synthesis of complex lipids and repressed certain genes involved in lipogenesis and lipid handling.     

Causes and consequences of adaptive seasonal sex ratio variation in house sparrows

1. Here we examine how sex ratio variation in house sparrow broods interacts with other demographic traits and parental characteristics to improve the understanding of adaptive significance and demographic effects on variation in sex ratio. 2. The sex ratio in complete broods did not deviate significantly from parity (54.9% males). 3. There was sex-specific seasonal variation in the probability of recruitment. Male nestlings that hatched late in the breeding season had larger probability of surviving than early hatched males. 4. An adaptive adjustment of sex ratio should favour production of an excess of males late in the breeding season. Accordingly, the proportion of male offspring increased throughout the breeding season. 5. A significant nonlinear relationship was present between sex ratio and age of the female. However, there was no relationship between parental phenotype and standardized hatch day that could explain the observed seasonal change in sex ratio. 6. The sex-specific number of offspring recruited by a pair to subsequent generations was closely related to the brood sex ratio. 7. These results indicate an adaptive adjustment of sex ratio to seasonal variation in environmental conditions that affects the offspring fitness of the two sexes differently. Our results also suggest that such a sex ratio variation can strongly influence the demography and structural composition of small passerine populations.     

Low genetic variance in the duration of the incubation period in a collared flycatcher (Ficedula albicollis) population

The avian incubation period is associated with high energetic costs and mortality risks suggesting that there should be strong selection to reduce the duration to the minimum required for normal offspring development. Although there is much variation in the duration of the incubation period across species, there is also variation within species. It is necessary to estimate to what extent this variation is genetically determined if we want to predict the evolutionary potential of this trait. Here we use a long-term study of collared flycatchers to examine the genetic basis of variation in incubation duration. We demonstrate limited genetic variance as reflected in the low and nonsignificant additive genetic variance, with a corresponding heritability of 0.04 and coefficient of additive genetic variance of 2.16. Any selection acting on incubation duration will therefore be inefficient. To our knowledge, this is the first time heritability of incubation duration has been estimated in a natural bird population.     

Palmitic acid follows a different metabolic pathway than oleic acid in human skeletal muscle cells; lower lipolysis rate despite an increased level of adipose triglyceride lipase

Development of insulin resistance is positively associated with dietary saturated fatty acids and negatively associated with monounsaturated fatty acids. To clarify aspects of this difference we have compared the metabolism of oleic (OA, monounsaturated) and palmitic acids (PA, saturated) in human myotubes. Human myotubes were treated with 100μM OA or PA and the metabolism of [(14)C]-labeled fatty acid was studied. We observed that PA had a lower lipolysis rate than OA, despite a more than two-fold higher protein level of adipose triglyceride lipase after 24h incubation with PA. PA was less incorporated into triacylglycerol and more incorporated into phospholipids after 24h. Supporting this, incubation with compounds modifying lipolysis and reesterification pathways suggested a less influenced PA than OA metabolism. In addition, PA showed a lower accumulation than OA, though PA was oxidized to a relatively higher extent than OA. Gene set enrichment analysis revealed that 24h of PA treatment upregulated lipogenesis and fatty acid β-oxidation and downregulated oxidative phosphorylation compared to OA. The differences in lipid accumulation and lipolysis between OA and PA were eliminated in combination with eicosapentaenoic acid (polyunsaturated fatty acid). In conclusion, this study reveals that the two most abundant fatty acids in our diet are partitioned toward different metabolic pathways in muscle cells, and this may be relevant to understand the link between dietary fat and skeletal muscle insulin resistance.     

Population persistence in a landscape context: the case of endangered arctic fox populations in Fennoscandia

Anthropogenic fragmentation of habitat and populations is recognized as one of the most important factors influencing loss of biodiversity. Since it is difficult to quantify demographic parameters in small populations, we need alternative methods to elucidate important factors affecting the viability of local populations. The Fennoscandian arctic fox inhabits a naturally fragmented alpine tundra environment, but historic anthropogenic impacts have further fragmented its distribution. After almost 80 yr of protection, the population remains critically endangered. Both intrinsic factors (related to the isolation and size of sub‐populations) and extrinsic factors (related to environmental conditions influencing patch quality and interspecific competition) have been proposed as explanations for the lack of population growth. To distinguish between these hypotheses, we conducted a spatially explicit analysis that compares areas where the species has persisted with areas where it has become locally extinct. We used characteristics of the fragments of alpine tundra habitat and individual arctic fox breeding dens (including both currently active dens and historically active dens) within the fragments to evaluate the importance of habitat characteristics and connectivity in explaining variation in persistence within a fragment. The number of reproductive events in a fragment was related to the size of the fragment, but not more than expected following a 1:1 relationship, suggesting little effect of fragment size on the relative number of reproductions. The likelihood of a den being used for breeding was positively associated with factors minimising interspecific competition as well as increasing within‐fragment connectivity. These results support the idea that the failure of Fennoscandian arctic fox to recover is caused by demographic factors that can be related to fine‐scale Allee or Allee‐like effects, as well as environmental influences related to increased competition and exclusion by red foxes.     

Remodeling of Oxidative Energy Metabolism by Galactose Improves Glucose Handling and Metabolic Switching in Human Skeletal Muscle Cells

Cultured human myotubes have a low mitochondrial oxidative potential. This study aims to remodel energy metabolism in myotubes by replacing glucose with galactose during growth and differentiation to ultimately examine the consequences for fatty acid and glucose metabolism. Exposure to galactose showed an increased [¹⁴C]oleic acid oxidation, whereas cellular uptake of oleic acid uptake was unchanged. On the other hand, both cellular uptake and oxidation of [¹⁴C]glucose increased in myotubes exposed to galactose. In the presence of the mitochondrial uncoupler carbonylcyanide p-trifluormethoxy-phenylhydrazone (FCCP) the reserve capacity for glucose oxidation was increased in cells grown with galactose. Staining and live imaging of the cells showed that myotubes exposed to galactose had a significant increase in mitochondrial and neutral lipid content. Suppressibility of fatty acid oxidation by acute addition of glucose was increased compared to cells grown in presence of glucose. In summary, we show that cells grown in galactose were more oxidative, had increased oxidative capacity and higher mitochondrial content, and showed an increased glucose handling. Interestingly, cells exposed to galactose showed an increased suppressibility of fatty acid metabolism. Thus, galactose improved glucose metabolism and metabolic switching of myotubes, representing a cell model that may be valuable for metabolic studies related to insulin resistance and disorders involving mitochondrial impairments.     

Deep sympatric mtDNA divergence in the autumnal moth (Epirrita autumnata)

Deep sympatric intraspecific divergence in mtDNA may reflect cryptic species or formerly distinct lineages in the process of remerging. Preliminary results from DNA barcoding of Scandinavian butterflies and moths showed high intraspecific sequence variation in the autumnal moth, Epirrita autumnata. In this study, specimens from different localities in Norway and some samples from Finland and Scotland, with two congeneric species as outgroups, were sequenced with mitochondrial and nuclear markers to resolve the discrepancy found between mtDNA divergence and present species‐level taxonomy. We found five COI sub‐clades within the E. autumnata complex, most of which were sympatric and with little geographic structure. Nuclear markers (ITS2 and Wingless) showed little variation and gave no indications that E. autumnata comprises more than one species. The samples were screened with primers for Wolbachia outer surface gene (wsp) and 12% of the samples tested positive. Two Wolbachia strains were associated with different mtDNA sub‐clades within E. autumnata, which may indicate indirect selection/selective sweeps on haplotypes. Our results demonstrate that deep mtDNA divergences are not synonymous with cryptic speciation and this has important implications for the use of mtDNA in species delimitation, like in DNA barcoding.     

Experimental Parameterisation of Principal Physics in Buoyancy Variations of Marine Teleost Eggs

It is generally accepted that the high buoyancy of pelagic marine eggs is due to substantial influx of water across the cell membrane just before ovulation. Here we further develop the theoretical basis by applying laboratory observations of the various components of the fertilized egg in first-principle equations for egg specific gravity (ρ_egg) followed by statistical validation. We selected Atlantic cod as a model animal due to the affluent amount of literature on this species, but also undertook additional dedicated experimental works. We found that specific gravity of yolk plus embryo is central in influencing ρ_egg and thereby the buoyancy. However, our established framework documents the effect on ρ_egg of the initial deposition of the heavy chorion material in the gonad prior to spawning. Thereafter, we describe the temporal changes in ρ_egg during incubation: Generally, the eggs showed a slight rise in ρ_egg from fertilization to mid-gastrulation followed by a gradual decrease until full development of main embryonic organs just before hatching. Ontogenetic changes in ρ_egg were significantly associated with volume and mass changes of yolk plus embryo. The initial ρ_egg at fertilization appeared significantly influenced by the chorion volume fraction which is determined by the combination of the final chorion volume of the oocyte and of the degree of swelling (hydrolyzation) prior to spawning. The outlined principles and algorithms are universal in nature and should therefore be applicable to fish eggs in general.     

Electrical pulse stimulation of cultured human skeletal muscle cells as an in vitro model of exercise

Background and Aims

Physical exercise leads to substantial adaptive responses in skeletal muscles and plays a central role in a healthy life style. Since exercise induces major systemic responses, underlying cellular mechanisms are difficult to study in vivo. It was therefore desirable to develop an in vitro model that would resemble training in cultured human myotubes.

Methods

Electrical pulse stimulation (EPS) was applied to adherent human myotubes. Cellular contents of ATP, phosphocreatine (PCr) and lactate were determined. Glucose and oleic acid metabolism were studied using radio-labeled substrates, and gene expression was analyzed using real-time RT-PCR. Mitochondrial content and function were measured by live imaging and determination of citrate synthase activity, respectively. Protein expression was assessed by electrophoresis and immunoblotting.

Results

High-frequency, acute EPS increased deoxyglucose uptake and lactate production, while cell contents of both ATP and PCr decreased. Chronic, low-frequency EPS increased oxidative capacity of cultured myotubes by increasing glucose metabolism (uptake and oxidation) and complete fatty acid oxidation. mRNA expression level of pyruvate dehydrogenase complex 4 (PDK4) was significantly increased in EPS-treated cells, while mRNA expressions of interleukin 6 (IL-6), cytochrome C and carnitin palmitoyl transferase b (CPT1b) also tended to increase. Intensity of MitoTracker®Red FM was doubled after 48 h of chronic, low-frequency EPS. Protein expression of a slow fiber type marker (MHCI) was increased in EPS-treated cells.

Conclusions

Our results imply that in vitro EPS (acute, high-frequent as well as chronic, low-frequent) of human myotubes may be used to study effects of exercise.     

New environmental metabarcodes for analysing soil DNA: potential for studying past and present ecosystems

Metabarcoding approaches use total and typically degraded DNA from environmental samples to analyse biotic assemblages and can potentially be carried out for any kinds of organisms in an ecosystem. These analyses rely on specific markers, here called metabarcodes, which should be optimized for taxonomic resolution, minimal bias in amplification of the target organism group and short sequence length. Using bioinformatic tools, we developed metabarcodes for several groups of organisms: fungi, bryophytes, enchytraeids, beetles and birds. The ability of these metabarcodes to amplify the target groups was systematically evaluated by (i) in silico PCRs using all standard sequences in the EMBL public database as templates, (ii) in vitro PCRs of DNA extracts from surface soil samples from a site in Varanger, northern Norway and (iii) in vitro PCRs of DNA extracts from permanently frozen sediment samples of late-Pleistocene age (~16,000-50,000 years bp) from two Siberian sites, Duvanny Yar and Main River. Comparison of the results from the in silico PCR with those obtained in vitro showed that the in silico approach offered a reliable estimate of the suitability of a marker. All target groups were detected in the environmental DNA, but we found large variation in the level of detection among the groups and between modern and ancient samples. Success rates for the Pleistocene samples were highest for fungal DNA, whereas bryophyte, beetle and bird sequences could also be retrieved, but to a much lesser degree. The metabarcoding approach has considerable potential for biodiversity screening of modern samples and also as a palaeoecological tool.