Skeletal muscle: Energy metabolism, fiber types, fatigue and adaptability

Skeletal muscles cope with a large range of activities, from being able to support the body weight during long periods of upright standing to perform explosive movements in response to an unexpected threat. This requires systems for energy metabolism that can provide energy during long periods of moderately increased energy consumption as well as being able to rapidly increasing the rate of energy production more than 100-fold in response to explosive contractions. In this short review we discuss how muscles can deal with these divergent demands. We first outline the major energy metabolism pathways in skeletal muscle. Next we describe metabolic differences between different muscle fiber types. Contractile performance declines during intense activation, i.e. fatigue develops, and we discuss likely underlying mechanisms. Finally, we discuss the ability of muscle fibers to adapt to altered demands, and mechanisms behind these adaptations. The accumulated experimental evidence forces us to conclude that most aspects of energy metabolism involve multiple and overlapping signaling pathways, which indicates that the control of energy metabolism is too important to depend on one single molecule or mechanism.     

Role of quorum sensing and antimicrobial component production by Serratia plymuthica in formation of biofilms, including mixed biofilms with Escherichia coli

We have previously characterized the N-acyl-l-homoserine lactone-based quorum-sensing system of the biofilm isolate Serratia plymuthica RVH1. Here we investigated the role of quorum sensing and of quorum-sensing-dependent production of an antimicrobial compound (AC) on biofilm formation by RVH1 and on the cocultivation of RVH1 and Escherichia coli in planktonic cultures or in biofilms. Biofilm formation of S. plymuthica was not affected by the knockout of splI or splR, the S. plymuthica homologs of the luxI or luxR quorum-sensing gene, respectively, or by the knockout of AC production. E. coli grew well in mixed broth culture with RVH1 until the latter reached 8.5 to 9.5 log CFU/ml, after which the E. coli colony counts steeply declined. In comparison, only a very small decline occurred in cocultures with the S. plymuthica AC-deficient and splI mutants. Complementation with exogenous N-hexanoyl-l-homoserine lactone rescued the wild-type phenotype of the splI mutant. The splR knockout mutant also induced a steep decline of E. coli, consistent with its proposed function as a repressor of quorum-sensing-regulated genes. The numbers of E. coli in 3-day-old mixed biofilms followed a similar pattern, being higher with S. plymuthica deficient in SplI or AC production than with wild-type S. plymuthica, the splR mutant, or the splI mutant in the presence of N-hexanoyl-l-homoserine lactone. Confocal laser scanning microscopic analysis of mixed biofilms established with strains producing different fluorescent proteins showed that E. coli microcolonies were less developed in the presence of RVH1 than in the presence of the AC-deficient mutant.     

Management implications of the biodiversity and socio-economic impacts of shrimp trawler by-catch in Bahía de Kino, Sonora, México

The shrimp fishery is the most economically important fishery in Mexico. The trawler-based portion of this fishery results in high rates of by-catch. This study quantifies and describes the biodiversity of by-catch associated with trawling in the Bahía de Kino region of Sonora, Mexico. Data were collected from 55 trawls, on six boats, over 14 nights, during November of 2003, 2004, 2006-2009. By-catch rates within trawl samples averaged 85.9% measured by weight. A total of 183 by-catch species were identified during the course of this study, including 97 species of bony fish from 43 families, 19 species of elasmobranchs from 12 families, 66 species of invertebrates from eight phyla, and one species of marine turtle; seven of the documented by-catch species are listed on the IUCN Red List, CITES, or the Mexican NOM-059-ECOL-2010; 35 species documented in the by-catch are also targeted by local artisanal fishers. Some of the species frequently captured as juveniles in the by-catch are economically important to small-scale fishers in the region, and are particularly sensitive to overexploitation due to their life histories. This study highlights the need for further research quantifying the impacts of high levels of by-catch upon small-scale fishing economies in the region and presents strong ecological and economic rationale for by-catch management within the shrimp fishery of the Gulf of California. Site-specific by-catch management plans should be piloted in the Bahía de Kino region to address the growing momentum in national and international fisheries policy regimes toward the reduction of by-catch in shrimp fisheries.     

Microbiome dynamics of human epidermis following skin barrier disruption

Background

Recent advances in sequencing technologies have enabled metagenomic analyses of many human body sites. Several studies have catalogued the composition of bacterial communities of the surface of human skin, mostly under static conditions in healthy volunteers. Skin injury will disturb the cutaneous homeostasis of the host tissue and its commensal microbiota, but the dynamics of this process have not been studied before. Here we analyzed the microbiota of the surface layer and the deeper layers of the stratum corneum of normal skin, and we investigated the dynamics of recolonization of skin microbiota following skin barrier disruption by tape stripping as a model of superficial injury.

Results

We observed gender differences in microbiota composition and showed that bacteria are not uniformly distributed in the stratum corneum. Phylogenetic distance analysis was employed to follow microbiota development during recolonization of injured skin. Surprisingly, the developing neo-microbiome at day 14 was more similar to that of the deeper stratum corneum layers than to the initial surface microbiome. In addition, we also observed variation in the host response towards superficial injury as assessed by the induction of antimicrobial protein expression in epidermal keratinocytes.

Conclusions

We suggest that the microbiome of the deeper layers, rather than that of the superficial skin layer, may be regarded as the host indigenous microbiome. Characterization of the skin microbiome under dynamic conditions, and the ensuing response of the microbial community and host tissue, will shed further light on the complex interaction between resident bacteria and epidermis.     

Insulin resistance and impaired functional vasodilation in obese Zucker rats

Individuals with metabolic syndrome exhibit insulin resistance and an attenuated functional vasodilatory response to exercise. We have shown that impaired functional vasodilation in obese Zucker rats (OZRs) is associated with enhanced thromboxane receptor (TP)-mediated vasoconstriction. We hypothesized that insulin resistance, hyperglycemia/hyperlipidemia, and the resultant ROS are responsible for the increased TP-mediated vasoconstriction in OZRs, resulting in impaired functional vasodilation. Eleven-week-old male lean Zucker rats (LZRs) and OZRs were fed normal rat chow or chow containing rosiglitazone (5 mg.kg(-1).day(-1)) for 2 wk. In another set of experiment, LZRs and OZRs were treated with 2 mM tempol (drinking water) for 7-10 days. After the treatments, spinotrapezius muscles were prepared, and arcade arteriolar diameters were measured following muscle stimulation and arachidonic acid (AA) application (10 muM) in the absence and presence of the TP antagonist SQ-29548 (1 muM). OZRs exhibited higher insulin, glucose, triglyceride, and superoxide levels and increased NADPH oxidase activity compared with LZRs. Functional and AA-induced vasodilations were impaired in OZRs. Rosiglitazone treatment improved insulin, glucose, triglyceride, and superoxide levels as well as NADHP oxidase activity in OZRs. Both rosiglitazone and tempol treatment improved vasodilatory responses in OZRs with no effect in LZRs. SQ-29548 treatment improved vasodilatory responses in nontreated OZRs with no effect in LZRs or treated OZRs. These results suggest that insulin resistance and the resultant increased ROS impair functional dilation in OZRs by increasing TP-mediated vasoconstriction.     

Heat Shock Protein-Mediated Resistance to High Hydrostatic Pressure in Escherichia coli

A random library of Escherichia coli MG1655 genomic fragments fused to a promoterless green fluorescent protein (GFP) gene was constructed and screened by differential fluorescence induction for promoters that are induced after exposure to a sublethal high hydrostatic pressure stress. This screening yielded three promoters of genes belonging to the heat shock regulon (dnaK, lon, clpPX), suggesting a role for heat shock proteins in protection against, and/or repair of, damage caused by high pressure. Several further observations provide additional support for this hypothesis: (i) the expression of rpoH, encoding the heat shock-specific sigma factor σ³², was also induced by high pressure; (ii) heat shock rendered E. coli significantly more resistant to subsequent high-pressure inactivation, and this heat shock-induced pressure resistance followed the same time course as the induction of heat shock genes; (iii) basal expression levels of GFP from heat shock promoters, and expression of several heat shock proteins as determined by two-dimensional sodium dodecyl sulfate-polyacrylamide gel electrophoresis of proteins extracted from pulse-labeled cells, was increased in three previously isolated pressure-resistant mutants of E. coli compared to wild-type levels.     

Fasting Decreases the Content of D-Chiroinositol in Human Skeletal Muscle

Two classes of inositol phosphoglycans have been implicated as second messengers of insulin, one that activates pyruvate dehydrogenase and contains D-chiroinositol, and one that inhibits cyclic AMP–dependent protein kinase and contains myoinositol. We examined the effects of a 3-day fast on muscle contents of inositols in healthy humans. An oral glucose tolerance test was performed and a biopsy was obtained from the quadriceps femoris muscle after an overnight fast and after a 72-hour fast. The 72-hour fast significantly increased plasma glucose (1.5- to 2-fold) and insulin (2- to 4-fold) after glucose ingestion versus the values after the overnight fast, indicating the manifestation of peripheral insulin resistance. The 72-hour fast resulted in an ∼20% decrease in the muscle content of D-chiroinositol (P < 0.02), but no change in the myoinositol content. These data demonstrate that fasting specifically decreases the muscle content of D-chiroinositol in human muscle and this may contribute to the finding that insulin-mediated activation of pyruvate dehydrogenase is attenuated after short-term starvation.     

Through the Eyes of Children: Perceptions of Environmental Change in Tropical Forests

This study seeks to understand children''s perceptions of their present and future environments in the highly biodiverse and rapidly changing landscapes of Kalimantan, Indonesian Borneo. We analyzed drawings by children (target age 10–15 years) from 22 villages, which show how children perceive the present conditions of forests and wildlife surrounding their villages and how they expect conditions to change over the next 15 years. Analyses of picture elements and their relationships to current landscape variables indicate that children have a sophisticated understanding of their environment and how different environmental factors interact, either positively or negatively. Children appear to have landscape-dependent environmental perceptions, showing awareness of past environmental conditions and many aspects of recent trends, and translating these into predictions for future environmental conditions. The further removed their present landscape is from the originally forested one, the more environmental change they expect in the future, particularly declines in forest cover, rivers, animal diversity and increases in temperature and natural disasters. This suggests that loss of past perceptions and associated “shifting environmental baselines” do not feature strongly among children on Borneo, at least not for the perceptions we investigated here. Our findings that children have negative expectations of their future environmental conditions have important political implications. More than other generations, children have a stake in ensuring that future environmental conditions support their long-term well-being. Understanding what drives environmental views among children, and how they consider trade-offs between economic development and social and environmental change, should inform optimal policies on land use. Our study illuminates part of the complex interplay between perceptions of land cover and land use change. Capturing the views of children through artistic expressions provides a potentially powerful tool to influence public and political opinions, as well as a valuable approach for developing localized education and nature conservation programs.