Protracted Exposure to a Sub-background Radiation Environment Negatively Impacts the Anhydrobiotic Recovery of Desiccated Yeast Sentinels

ABSTRACT

Experiments that examine the impacts of subnatural background radiation exposure provide a unique approach to studying the biological effects of low-dose radiation. These experiments often need to be conducted in deep underground laboratories in order to filter surface-level cosmic radiation. This presents some logistical challenges in experimental design and necessitates a model organism with minimal maintenance. As such, desiccated yeast ( Saccharomyces cerevisiae ) is an ideal model system for these investigations. This study aimed to determine the impact of prolonged sub-background radiation exposure in anhydrobiotic (desiccated) yeast at SNOLAB in Sudbury, Ontario, Canada. Two yeast strains were used: a normal wild type and an isogenic recombinational repair-deficient rad51 knockout strain ( rad51 Δ). Desiccated yeast samples were stored in the normal background surface control laboratory (68.0 nGy h -1 ) and in the sub-background environment within SNOLAB (10.1 nGy h -1 ) for up to 48 wk. Post-rehydration survival, growth rate, and metabolic activity were assessed at multiple time points. Survival in the sub-background environment was significantly reduced by a factor of 1.39 and 2.67 in the wild type and rad51 ∆ strains, respectively. Post-rehydration metabolic activity measured via alamarBlue reduction remained unchanged in the wild type strain but was 26% lower in the sub-background rad51 ∆ strain. These results demonstrate that removing natural background radiation negatively impacts the survival and metabolism of desiccated yeast, highlighting the potential importance of natural radiation exposure in maintaining homeostasis of living organisms.

Lysophosphatidic acid receptor 1 (LPA1) antagonists as potential migrastatics for triple negative breast cancer

Metastasis is responsible for about 90% of cancer deaths. Anti-metastatic drugs, termed as migrastatics, offer a distinctive therapeutic approach to address cancer migration and invasion. However, therapeutic exploitation of metastasis-specific targets remains limited, and the effective prevention and suppression of metastatic cancer continue to be elusive. Lysophosphatidic acid receptor 1 (LPA1) is activated by an endogenous lipid molecule LPA, leading to a diverse array of cellular activities. Previous studies have shown that the LPA/LPA1 axis supports the progression of metastasis for many types of cancer. In this study, we report the synthesis and biological evaluation of fluorine-containing triazole derivatives as potent LPA1 antagonists, offering potential as migrastatic drugs for triple negative breast cancer (TNBC). In particular, compound 12f, the most potent and highly selective in this series with an IC50 value of 16.0 nM in the cAMP assay and 18.4 nM in the calcium mobilization assay, inhibited cell survival, migration, and invasion in the TNBC cell line. Interestingly, the compound did not induce apoptosis in TNBC cells and demonstrated no cytotoxic effects. These results highlight the potential of LPA1 as a migrastatic target. Consequently, the LPA1 antagonists developed in this study hold promise as potential migrastatic candidates for TNBC.

Effects of prenatal dexamethasone exposure on adult C57BL/6J mouse metabolism and oxidative stress

Prenatal glucocorticoid exposure has been shown to alter hypothalamic-pituitary-adrenal axis function resulting in altered fetal development that can persist through adulthood. Fetal exposure to excess dexamethasone, a synthetic glucocorticoid, has been shown to alter adult behaviour and metabolism. This study investigated the effects prenatal dexamethasone exposure had on adult offspring cardiac and liver metabolism and oxidative stress. Pregnant C57BL/6 mice received a dose of 0.4 mg/kg dexamethasone on gestational days 15-17. Once pups were approximately 7 months old, glucose uptake was determined using positron emission tomography and insulin resistance (IR) was determined by homeostatic model assessment (HOMA) IR calculation. Oxidative stress was assessed by measuring 4-hydroxynonenal protein adduct formation and total reactive oxygen species. Female dexamethasone group had significantly increased glucose uptake when insulin stimulated compared to vehicle-treated mice. HOMA IR revealed no evidence of IR in either male or female offspring. There was also no change in oxidative stress markers in either cardiac or liver tissues of male or female offspring. These data suggest that prenatal dexamethasone exposure in male mice does not alter oxidative stress or metabolism. However, prenatal dexamethasone exposure increased glucocorticoids, cardiac glucose uptake, and pAkt signaling in female heart tissues in adult mice, suggesting there are sex differences in prenatal dexamethasone exposure.

Shockwave therapy and fibromyalgia and its effect on pain, blood markers, imaging, and participant experience - a multidisciplinary randomized controlled trial

BACKGROUND

Patients with fibromyalgia experience chronic, widespread pain. It remains a misunderstood disorder with multimodal treatments providing mixed results.

OBJECTIVES

To examine the effects of radial shockwave therapy (RSWT) compared to placebo on pain, pain catastrophizing, psychological indices, blood markers, and neuroimaging. Study-related experiences were also explored qualitatively.

METHODS

Quantitative sensory testing (QST), Visual Analog Scale (VAS), Beighton Scoring Screen (BSS), Pain Catastrophizing Scale (PCS), blood biomarker (Interleukin (IL)-6 and IL-10), and brain fMRI were measured pre- and post-treatment along with a post-treatment survey. The RSWT group received five treatments (one week apart over five-week period) to the three most painful areas (500 shocks at 1.5 bar and 15 Hz, then 1000 shocks at 2 bar and 8 Hz, and finally 500 shocks at 1.5 bar and 15 Hz) versus sham treatment for the placebo group.

RESULTS

There were no statistically significant differences in the BSS for hypermobility (p = .21; d = .74), PCS (p = .70; d = .22), VAS (p = .17-.61; d = .20-.83) scores, QST for skin temperature and stimuli (p = .14-.65; d = .25-.88), and for the pressure pain threshold (p = .71-.93; d = .05-.21). The VAS scores had clinically significant changes (MCID greater than 13.90) with improved pain scores in the RSWT group. Neuroimaging scans revealed no cortical thickness changes. Post-treatment surveys revealed pain and symptom improvements and offered hope to individuals.

CONCLUSION

RSWT was implemented safely, without any negative treatment effects reported, and acted as a pain modulator to reduce sensitivity.

CLINICAL TRIALS REGISTRATION

ClinicalTrials.gov identification number NCT02760212.

Long-term aspartame and saccharin intakes are related to greater volumes of visceral, intermuscular, and subcutaneous adipose tissue: the CARDIA study

BACKGROUND

Artificial sweetener (ArtSw) intakes have been previously associated with higher BMI in observational studies and may promote visceral and skeletal muscle adipose tissue (AT) accumulation. This study aimed to determine whether habitual, long-term ArtSw or diet beverage intakes are related to greater AT depot volumes and anthropometry-related outcomes.

METHODS

A validated diet history questionnaire was administered at baseline, year 7, and year 20 examinations in 3088 men and women enrolled in the Coronary Artery Risk Development in Young Adults cohort (CARDIA), mean age of 25.2 years and mean BMI of 24.5 kg/m2 at baseline. Volumes of visceral (VAT), intermuscular (IMAT), and subcutaneous adipose tissue (SAT) were assessed by computed tomography at year 25. Linear regression evaluated associations of aspartame, saccharin, sucralose, total ArtSw, and diet beverage intakes with AT volumes, anthropometric measures, and 25-year change in anthropometry. Cox regression estimated associations of ArtSw with obesity incidence. Adjustments were made for demographic and lifestyle factors, total energy intake, and the 2015 healthy eating index.

RESULTS

Total ArtSw, aspartame, saccharin, and diet beverage intakes were positively associated with VAT, SAT, and IMAT volumes (all ptrend ≤ 0.001), but no associations were observed for sucralose intake (all ptrend > 0.05). In addition, total ArtSw, saccharin, aspartame, and diet beverage intakes were associated with greater body mass index, body weight, waist circumference, and their increases over a 25-year period. Except for saccharin (ptrend = 0.13), ArtSw, including diet soda, was associated with greater risks of incident obesity over a median 17.5-year follow-up (all ptrend < 0.05).

CONCLUSIONS

Results suggest that long-term intakes of aspartame, saccharin, or diet soda may increase AT deposition and risk of incident obesity independent of diet quality or caloric intake. Coupled with previous evidence, alternatives to national recommendations to replace added sugar with ArtSw should be considered since both may have health consequences.

Overexpression of FRA1 (FOSL1) Leads to Global Transcriptional Perturbations, Reduced Cellular Adhesion and Altered Cell Cycle Progression

FRA1 (FOSL1) is a transcription factor and a member of the activator protein-1 superfamily. FRA1 is expressed in most tissues at low levels, and its expression is robustly induced in response to extracellular signals, leading to downstream cellular processes. However, abnormal FRA1 overexpression has been reported in various pathological states, including tumor progression and inflammation. To date, the molecular effects of FRA1 overexpression are still not understood. Therefore, the aim of this study was to investigate the transcriptional and functional effects of FRA1 overexpression using the CGL1 human hybrid cell line. FRA1-overexpressing CGL1 cells were generated using stably integrated CRISPR-mediated transcriptional activation, resulting in a 2-3 fold increase in FRA1 mRNA and protein levels. RNA-sequencing identified 298 differentially expressed genes with FRA1 overexpression. Gene ontology analysis showed numerous molecular networks enriched with FRA1 overexpression, including transcription-factor binding, regulation of the extracellular matrix and adhesion, and a variety of signaling processes, including protein kinase activity and chemokine signaling. In addition, cell functional assays demonstrated reduced cell adherence to fibronectin and collagen with FRA1 overexpression and altered cell cycle progression. Taken together, this study unravels the transcriptional response mediated by FRA1 overexpression and establishes the role of FRA1 in adhesion and cell cycle progression.

Absence of Depressive and Anxious Behavior with Genetic Dysregulation in Adult C57Bl/6J Mice after Prenatal Exposure to Ionizing Radiation

The exposure of ionizing radiation during early gestation often leads to deleterious and even lethal effects; however, few extensive studies have been conducted on late gestational exposures. This research examined the behavior al effects of C57Bl/6J mouse offspring exposed to low dose ionizing gamma irradiation during the equivalent third trimester. Pregnant dams were randomly assigned to sham or exposed groups to either low dose or sublethal dose radiation (50, 300, or 1000 mGy) at gestational day 15. Adult offspring underwent a behavioral and genetic analysis after being raised under normal murine housing conditions. Our results indicate very little change in the behavioral tasks measuring general anxiety, social anxiety, and stress-management in animals exposed prenatally across the low dose radiation conditions. Quantitative real-time polymerase chain reactions were conducted on the cerebral cortex, hippocampus, and cerebellum of each animal; results indicate some dysregulation in markers of DNA damage, synaptic activity, reactive oxygen species (ROS) regulation, and methylation pathways in the offspring. Together, our results provide evidence in the C57Bl/6J strain, that exposure to sublethal dose radiation (<1000 mGy) during the last period of gestation leads to no observable changes in behaviour when assessed as adults, although some changes in gene expression were observed for specific brain regions. These results indicate that the level of oxidative stress occurring during late gestation for this mouse strain is not sufficient for a change in the assessed behavioral phenotype, but results in some modest dysregulation of the genetic profile of the brain.

Chronic glucocorticoid exposure causes brown adipose tissue whitening, alters whole-body glucose metabolism and increases tissue uncoupling protein-1

Adipose tissue (AT) has been found to exist in two predominant forms, white and brown. White adipose tissue (WAT) is the body's conventional storage organ, and brown adipose tissue (BAT) is responsible for non-shivering thermogenesis which allows mammals to produce heat and regulate body temperature. Studies examining BAT and its role in whole-body metabolism have found that active BAT utilizes glucose and circulating fatty acids and is associated with improved metabolic outcomes. While the beiging of WAT is a growing area of interest, the possibility of the BAT depot to "whiten" and store more triglycerides also has metabolic and health implications. Currently, there are limited studies that examine the effects of chronic stress and its ability to induce a white-like phenotype in the BAT depot. This research examined how chronic exposure to the murine stress hormone, corticosterone, for 4 weeks can affect the whitening process of BAT in C57BL/6 male mice. Separate treatments with mirabegron, a known β3-adrenergic receptor agonist, were used to directly compare the effects of corticosterone with a beiging phenotype. Corticosterone-treated mice had significantly higher body weight (p ≤ 0.05) and BAT mass (p ≤ 0.05), increased adipocyte area (p ≤ 0.05), were insulin resistant (p ≤ 0.05), and significantly elevated expressions of uncoupling protein 1 (UCP-1) in BAT (p ≤ 0.05) while mitochondrial content remained unchanged. This whitened phenotype has not been previously associated with increased uncoupling proteins under chronic stress and may represent a compensatory mechanism being initiated under these conditions. These findings have implications for the study of BAT in response to chronic glucocorticoid exposure potentially leading to BAT dysfunction and negative impacts on whole-body glucose metabolism.

Ovariectomized Rat Model and Shape Variation in the Bony Labyrinth

Postmenopausal osteoporosis is a serious concern in aging individuals, but has not been explored for its potential to alter the shape of the inner ear by way of increased remodelling in the otic capsule. The otic capsule, or bony labyrinth, is thought to experience uniquely limited remodelling after development due to high levels of osteoprotegerin. On this basis, despite the widespread remodelling that accompanies osteoporosis, we hypothesize that both the shape and volume of the semicircular canals will resist such changes. To test this hypothesis, we conducted three-dimensional geometric morphometric shape analysis on microcomputed tomographic data collected on the semicircular canals of an ovariectomized (OVX) rat model. A Procrustes ANOVA found no statistically significant differences in shape between surgery and sham groups, and morphological disparity testing likewise found no differences in shape variation. Univariate testing found no differences in semicircular volume between OVX and control groups. The range of variation in the OVX group, however, is greater than in the sham group but this difference does not reach statistical significance, perhaps because of a combination of small effect size and low sample size. This finding suggests that labyrinthine shape remains a tool for assessing phylogeny and function in the fossil record, but that it is possible that osteoporosis may be contributing to intraspecific shape variation in the bony labyrinth. This effect warrants further exploration at a microstructural level with continued focus on variables related to remodelling. This article is protected by copyright. All rights reserved.

Cystathionine gamma-lyase/H2 S signaling facilitates myogenesis under aging and injury condition

Hydrogen sulfide (H₂ S) can be endogenously produced and belongs to the class of signaling molecules known as gasotransmitters. Cystathionine gamma-lyase (CSE)-derived H₂ S is implicated in the regulation of cell differentiation and the aging process, but the involvements of the CSE/H₂ S system in myogenesis upon aging and injury have not been explored. In this study, we demonstrated that CSE acts as a major H₂ S-generating enzyme in skeletal muscles and is significantly down-regulated in aged skeletal muscles in mice. CSE deficiency exacerbated the age-dependent sarcopenia and cardiotoxin-induced injury/regeneration in mouse skeletal muscle, possibly attributed to inefficient myogenesis. In contrast, supplement of NaHS (an H₂ S donor) induced the expressions of myogenic genes and promoted muscle regeneration in mice. In vitro, incubation of myoblast cells (C2C12) with H₂ S promoted myogenesis, as evidenced by the inhibition of cell cycle progression and migration, altered expressions of myogenic markers, elongation of myoblasts, and formation of multinucleated myotubes. Myogenesis was also found to upregulate CSE expression, while blockage of CSE/H₂ S signaling resulted in a suppression of myogenesis. Mechanically, H₂ S significantly induced the heterodimer formation between MEF2c and MRF4 and promoted the binding of MEF2c/MRF4 to myogenin promoter. MEF2c was S-sulfhydrated at both cysteine 361 and 420 in the C-terminal transactivation domain, and blockage of MEF2c S-sulfhydration abolished the stimulatory role of H₂ S on MEF2c/MRF4 heterodimer formation. These findings support an essential role for H₂ S in maintaining myogenesis, presenting it as a potential candidate for the prevention of age-related sarcopenia and treatment of muscle injury.

The effects of exercise and active assisted cycle ergometry in post-operative total knee arthroplasty patients - a randomized controlled trial

Purpose

The purpose of this study was to examine the effect of the use of an active assisted cycle ergometer as an adjunct to post-operative treatment following total knee arthroplasty.

Method

A total of 55 participants aged 50–80 years who had undergone unilateral total knee arthroplasty were randomly assigned to either the control group (standard of care) or the active assisted cycle ergometer (AACE) group. The effect on patient motivation, blood biomarkers, and knee pain, function, range of motion (ROM), strength, and swelling was examined. Qualitative feedback was also obtained post-operatively.

Results

Although there was no statistically significant difference in the standard of care compared to the AACE group, there was a trend for a greater reduction in knee pain on the visual analog scale, improved Lower Extremity Functional Scale scores, and knee extension ROM and strength. A greater percentage of the experimental group demonstrated higher motivation. There was no significant difference in swelling or blood biomarker measures. Qualitative feedback from the AACE group post-operatively was also positive.

Conclusions

The use of an AACE protocol as an adjunct to total knee arthroplasty rehabilitation may improve post-operative clinical outcomes. This study has been registered at clinicaltrials.gov (identifier NCT02265523, Oct 16 2014). Level of evidence: Level 1 – randomized controlled trial. Further research with a larger sample size is needed to confirm the benefits of the ergometer use.

Supplementary Information

The online version contains supplementary material available at 10.1186/s40634-021-00363-w.

Lasting Effects of Low to Non-Lethal Radiation Exposure during Late Gestation on Offspring's Cardiac Metabolism and Oxidative Stress

Ionizing radiation (IR) is known to cause fetal programming, but the physiological effects of low-dose IR are not fully understood. This study examined the effect of low (50 mGy) to non-lethal (300 and 1000 mGy) radiation exposure during late gestation on cardiac metabolism and oxidative stress in adult offspring. Pregnant C57BL/6J mice were exposed to 50, 300, or 1000 mGy of gamma radiation or Sham irradiation on gestational day 15. Sixteen weeks after birth, ¹⁸F-Fluorodeoxyglucose (FDG) uptake was examined in the offspring using Positron Emission Tomography imaging. Western blot was used to determine changes in oxidative stress, antioxidants, and insulin signaling related proteins. Male and female offspring from irradiated dams had lower body weights when compared to the Sham. 1000 mGy female offspring demonstrated a significant increase in ¹⁸F-FDG uptake, glycogen content, and oxidative stress. 300 and 1000 mGy female mice exhibited increased superoxide dismutase activity, decreased glutathione peroxidase activity, and decreased reduced/oxidized glutathione ratio. We conclude that non-lethal radiation during late gestation can alter glucose uptake and increase oxidative stress in female offspring. These data provide evidence that low doses of IR during the third trimester are not harmful but higher, non-lethal doses can alter cardiac metabolism later in life and sex may have a role in fetal programming.

Oxidative Stress Mediates the Fetal Programming of Hypertension by Glucocorticoids

The field of cardiovascular fetal programming has emphasized the importance of the uterine environment on postnatal cardiovascular health. Studies have linked increased fetal glucocorticoid exposure, either from exogenous sources (such as dexamethasone (Dex) injections), or from maternal stress, to the development of adult cardiovascular pathologies. Although the mechanisms are not fully understood, alterations in gene expression driven by altered oxidative stress and epigenetic pathways are implicated in glucocorticoid-mediated cardiovascular programming. Antioxidants, such as the naturally occurring polyphenol epigallocatechin gallate (EGCG), or the superoxide dismutase (SOD) 4-hydroxy-TEMPO (TEMPOL), have shown promise in the prevention of cardiovascular dysfunction and programming. This study investigated maternal antioxidant administration with EGCG or TEMPOL and their ability to attenuate the fetal programming of hypertension via Dex injections in WKY rats. Results from this study indicate that, while Dex-programming increased blood pressure in male and female adult offspring, administration of EGCG or TEMPOL via maternal drinking water attenuated Dex-programmed increases in blood pressure, as well as changes in adrenal mRNA and protein levels of catecholamine biosynthetic enzymes phenylalanine hydroxylase (PAH), tyrosine hydroxylase (TH), dopamine beta hydroxylase (DBH), and phenylethanolamine N-methyltransferase (PNMT), in a sex-specific manner. Furthermore, programmed male offspring displayed reduced antioxidant glutathione peroxidase 1 (Gpx1) expression, increased superoxide dismutase 1 (SOD1) and catalase (CAT) expression, and increased pro-oxidant NADPH oxidase activator 1 (Noxa1) expression in the adrenal glands. In addition, prenatal Dex exposure alters expression of epigenetic regulators histone deacetylase (HDAC) 1, 5, 6, 7, 11, in male and HDAC7 in female offspring. These results suggest that glucocorticoids may mediate the fetal programming of hypertension via alteration of epigenetic machinery and oxidative stress pathways.

Mirabegron: The most promising adipose tissue beiging agent

Accumulation of white adipose tissue (WAT) underlies the obesity epidemic, leading to current therapeutic techniques that are being investigated for their ability to activate/“beige” this tissue. Adipose tissue (AT) beiging has been reported through intermittent cold exposure (CE), exercise, and β3‐Adrenergic Receptor (β3AR) agonists. But how AT beiging can help in the treatment of metabolic disorders like obesity and type 2 diabetes (T2D) remains largely unexplored. This review summarizes recent research on the use of β3AR agonist, mirabegron (Myrbetriq®), in stimulating beiging in AT. Researchers have only recently been able to determine the optimal therapeutic dose of mirabegron for inducing beiging in subcutaneous/ inguinal WAT, where the benefits of AT activation are evident without the undesired cardiovascular side effects. To determine whether the effects that mirabegron elicits are metabolically beneficial, a comparison of the undisputed findings resulting from intermittent CE‐induced beiging and the disputed findings from exercise‐induced beiging was conducted. Given the recent in vivo animal and clinical studies, the understanding of how mirabegron can be metabolically beneficial for both lean and obese individuals is more clearly understood. These studies have demonstrated that circulating adipokines, glucose metabolism, and lipid droplet (LD) size are all positively affected by mirabegron administration. Recent studies have also demonstrated that mirabegron has similar outcomes to intermittent CE and displays more direct evidence for beiging than those produced with exercise. With these current findings, mirabegron is considered the most promising and safest β3AR agonist currently available that has the potential to be used in the therapeutic treatment of metabolic disorders, and future studies into its interaction with different conditions may prove to be useful as part of a treatment plan in combination with a healthy diet and exercise.

A novel specialized tissue culture incubator designed and engineered for radiobiology experiments in a sub-natural background radiation research environment

Extensive research has been conducted investigating the effects of ionizing radiation on biological systems, including specific focus at low doses. However, at the surface of the planet, there is the ubiquitous presence of ionizing natural background radiation (NBR) from sources both terrestrial and cosmic. We are currently conducting radiobiological experiments examining the impacts of sub-NBR exposure within SNOLAB. SNOLAB is a deep underground research laboratory in Sudbury, Ontario, Canada located 2 km beneath the surface of the planet. At this depth, significant shielding of NBR components is provided by the rock overburden. Here, we describe a Specialized Tissue Culture Incubator (STCI) that was engineered to significantly reduce background ionizing radiation levels. The STCI was installed 2 km deep underground within SNOLAB. It was designed to allow precise control of experimental variables such as temperature, atmospheric gas composition and humidity. More importantly, the STCI was designed to reduce radiological contaminants present within the underground laboratory. Quantitative measurements validated the STCI is capable of maintaining an appropriate experimental environment for sub-NBR experiments. This included reduction of sub-surface radiological contaminants, most notably radon gas. The STCI presents a truly novel piece of infrastructure enabling future research into the effects of sub-NBR exposure in a highly unique laboratory setting.

Leucine Potentiates Glucose-mediated 18F-FDG Uptake in Brown Adipose Tissue via β-Adrenergic Activation

Significant depots of brown adipose tissue (BAT) have been identified in many adult humans through positron emission tomography (PET), with the amount of BAT being inversely correlated with obesity. As dietary activation of BAT has implications for whole body glucose metabolism, leucine was used in the present study to determine its ability to promote BAT activation resulting in increased glucose uptake. In order to assess this, 2-deoxy-2-(fluorine-18)fluoro-d-glucose (¹⁸F-FDG) uptake was measured in C57BL/6 mice using microPET after treatment with leucine, glucose, or both in interscapular BAT (IBAT). Pretreatment with propranolol (PRP) was used to determine the role of β-adrenergic activation in glucose and leucine-mediated ¹⁸F-FDG uptake. Analysis of maximum standardized uptake values (SUV_MAX) determined that glucose administration increased ¹⁸F-FDG uptake in IBAT by 25.3%. While leucine did not promote ¹⁸F-FDG uptake alone, it did potentiate glucose-mediated ¹⁸F-FDG uptake, increasing ¹⁸F-FDG uptake in IBAT by 22.5%, compared to glucose alone. Pretreatment with PRP prevented the increase in IBAT ¹⁸F-FDG uptake following the combination of glucose and leucine administration. These data suggest that leucine is effective in promoting BAT ¹⁸F-FDG uptake through β-adrenergic activation in combination with glucose.

Dose threshold for radiation induced fetal programming in a mouse model at 4 months of age: Hepatic expression of genes and proteins involved in glucose metabolism and glucose uptake in brown adipose tissue

Exposure to ionizing radiation contributing to negative health outcomes is a widespread concern. However, the impact of low dose and sub-lethal dose radiation (SLDR) exposures remain contentious, particularly in pregnant women who represent a vulnerable group. The fetal programming hypothesis states that an adverse in utero environment or stress during development of an embryo or fetus can result in permanent physiologic changes often resulting in progressive metabolic dysfunction with age. To assess changes in gene expression profiles of glucose/insulin signaling and lipid metabolism caused by radiation exposure in utero, pregnant C57Bl/6J mice were irradiated using a dose response ranging from low dose to SLDR and compared to a Sham-irradiated group. mRNA expression analysis in 16 week old offspring (n = 84) revealed that genes involved in metabolic function including glucose metabolism, insulin signaling and lipid metabolism were unaffected by prenatal radiation exposures up to 300 mGy. However, female offspring of dams exposed to 1000 mGy had upregulated expression of genes contributing to insulin resistance and gluconeogenesis. In a second cohort of mice, the effects of SLDR on fetal programming of hepatic SOCS3 and PEPCK protein expression were assessed. 4 month old female offspring of dams irradiated at 1000 mGy had: 1) increased liver weights, 2) increased hepatic expression of proteins involved in glucose metabolism and 3) increased ¹⁸F-fluorodeoxyglucose (FDG) uptake in interscapular brown adipose tissue (IBAT) measured by positron emission tomography (PET) (n = 25). The results of this study indicate that prenatal radiation exposure does not affect metabolic function up to 300 mGy and 1000 mGy may be a threshold dose for sex-specific alterations in glucose uptake and hepatic gene and protein expression of SOCS3, PEPCK, PPARGC1A and PPARGC1B. These findings suggest that SLDR doses alter glucose uptake in IBAT and hepatic gene and protein expression of offspring and these changes may progress with age.

Ascorbic acid diminishes bone morphogenetic protein 2-induced osteogenic differentiation of muscle precursor cells

INTRODUCTION

Muscle precursor cells (MPC) are integral to the maintenance of skeletal muscle and have recently been implicated in playing a role in bone repair. The primary objective of this study was to understand better the role of oxidative stress during the osteogenic differentiation of MPCs.

METHODS

Muscle precursor cells were treated with various combinations of ascorbic acid (AA), bone morphogenetic protein (BMP)-2, and either a superoxide dismutase analog (4-hydroxy-TEMPO [TEMPOL]) or polyethyleneglycol-conjugated catalase. Muscle precursor cell proliferation and differentiation were determined, and alkaline phosphatase activity was measured as an index of osteogenic differentiation.

RESULTS

After treatment with 200 μM AA, superoxide was increased 1.5-fold, whereas AA in combination with 100 ng/ml BMP-2 did not increase alkaline phosphatase (ALP) activity. When cells were treated with TEMPOL in combination with 100 ng/ml BMP-2 and 200 μM AA, ALP activity significantly increased.

DISCUSSION

These data suggest that increasing oxidative stress with AA induces sublethal oxidative stress that prevents BMP-2-induced osteogenic differentiation of MPCs. Muscle Nerve 59:501-508, 2019.

Whey Protein Supplementation Improves Rehabilitation Outcomes in Hospitalized Geriatric Patients: A Double Blinded, Randomized Controlled Trial

Whey protein supplementation (WPS) has been shown to improve functional outcomes in populations that are able to participate in high-intensity resistance training. The purpose of the study was to evaluate the efficacy of WPS on rehabilitation outcomes in a frail, hospitalized elderly population. Men and women (n = 47) were randomly assigned to either a control group or WPS group for the length of their hospital stay. Several functional and serum measures were determined pre- and post-intervention. WPS significantly increased average daily protein intake and was well tolerated. The WPS group exhibited significant improvements in grip strength and knee extensor force over the control group, and a significant positive correlation was found between change in prealbumin and percent-increase knee extensor force. These findings support the use of WPS to improve protein nutritional status and rehabilitation outcomes in a clinical setting involving a frail, elderly population.

Searching for novel PET radiotracers: imaging cardiac perfusion, metabolism and inflammation

Advances in medical imaging technology have led to an increased demand for radiopharmaceuticals for early and accurate diagnosis of cardiac function and diseased states. Myocardial perfusion, metabolism, and hypoxia positron emission tomography (PET) imaging radiotracers for detection of cardiac disease lack specificity for targeting inflammation that can be an early indicator of cardiac disease. Inflammation can occur at all stages of cardiac disease and currently, 18F-fluorodeoxyglucose (FDG), a glucose analog, is the standard for detecting myocardial inflammation. 18F-FDG has many ideal characteristics of a radiotracer but lacks the ability to differentiate between glucose uptake in normal cardiomyocytes and inflammatory cells. Developing a PET radiotracer that differentiates not only between inflammatory cells and normal cardiomyocytes, but between types of immune cells involved in inflammation would be ideal. This article reviews current PET radiotracers used in cardiac imaging, their limitations, and potential radiotracer candidates for imaging cardiac inflammation in early stages of development of acute and chronic cardiac diseases. The select radiotracers reviewed have been tested in animals and/or show potential to be developed as a radiotracer for the detection of cardiac inflammation by targeting the enzymatic activities or subpopulations of macrophages that are recruited to an injured or infected site.

Non-radioactive 2-deoxy-2-fluoro-D-glucose inhibits glucose uptake in xenograft tumours and sensitizes HeLa cells to doxorubicin in vitro

A glucose analog called 2-deoxy-D-glucose (2DG) has been successfully used to sensitize cancer cells to ROS-inducing cancer treatments such as ionizing radiation, through the inhibition of glycolysis. However, the use of 2DG can be limited by several factors such as availability, non-specific cytotoxicity, and chemoresistance under hypoxic conditions. The purpose of this study was to investigate the use of non-radioactive 2-deoxy-2-fluoro-D-glucose (¹⁹FDG), a drug that potentially addresses current limitations of 2DG. The effectiveness of using either 2DG or ¹⁹FDG in combination with doxorubicin (Dox) in HeLa cells was determined in both normoxia and hypoxia. We have also shown that under both oxygen conditions, ¹⁹FDG-treated cells produce less lactate than 2DG-treated cells, an important finding that suggests improved inhibition of glycolysis, the preferential pathway for cancerous cells. When used in combination with Dox, we have demonstrated a significant decrease in the number of viable cells, with the effect of ¹⁹FDG remaining stable across both normoxic and hypoxic conditions. Moreover, the assessment of apoptosis and necrosis revealed that ¹⁹FDG maintained its ability to sensitize HeLa cells to Dox in hypoxia, but 2DG was only effective under normoxic conditions. The retained effectiveness of ¹⁹FDG in combination with Dox under hypoxic conditions, suggests that ¹⁹FDG may be efficacious for sensitizing hypoxic regions of solid tumour masses. Importantly, the ability of ¹⁹FDG to inhibit glucose uptake in vivo was also confirmed using positron emission tomography (PET) of xenograft tumours. The results displayed here suggest ¹⁹FDG is a promising combination therapy, which may lead to decreased ROS scavenging via glycolysis, and enhanced treatment success.

Impact of Ionizing Radiation on the Cardiovascular System: A Review

Radiation therapy has become one of the main forms of treatment for various types of cancers. Cancer patients previously treated with high doses of radiation are at a greater risk to develop cardiovascular complications later in life. The heart can receive varying doses of radiation depending on the type of therapy and can even reach doses in the range of 17 Gy. Multiple studies have highlighted the role of oxidative stress and inflammation in radiation-induced cardiovascular damage. Doses of ionizing radiation below 200 mGy, however, have been shown to have beneficial effects in some experimental models of radiation-induced damage, but low-dose effects in the heart is still debated. Low-dose radiation may promote heart health and reduce damage from oxidative stress and inflammation, however there are few studies focusing on the impact of low-dose radiation on the heart. In this review, we summarize recent studies from animal models and human data focusing on the effects and mechanism(s) of action of radiation-induced damage to the heart, as well as the effects of high and low doses of radiation and dose rates.

Two common variants of human papillomavirus type 16 E6 differentially deregulate sugar metabolism and hypoxia signalling in permissive human keratinocytes

Human papillomavirus type 16 (HPV16) is responsible for most cancers attributable to HPV infection and naturally occurring variants of the HPV16 E6 oncoprotein predispose individuals to varying risk for developing cancer. Population studies by us and others have demonstrated that the common Asian-American E6 (AAE6) variant is a higher risk factor for cervical cancer than the E6 of another common variant, the European prototype (EPE6). However, a complete understanding of the molecular processes fundamental to these epidemiological findings is still lacking. Our previously published functional studies of these two E6 variants showed that AAE6 had a higher immortalization and transformation potential than EPE6. Proteomic analysis revealed markedly different protein patterns between these variants, especially with respect to key cellular metabolic enzymes. Here, we tested the Warburg effect and hypoxia signalling (hallmarks of cancer development) as plausible mechanisms underlying these observations. Lactate and glucose production were enhanced in AAE6-transduced keratinocytes, likely due to raised levels of metabolic enzymes, but independent of hypoxia-inducible factor 1 alpha (HIF-1α) activity. The HIF-1α protein level and activity were elevated by AAE6 in hypoxic conditions, leading to a hypoxia-tolerant phenotype with enhanced migratory potential. The deregulation of HIF-1α was caused by the AAE6 variant's ability to augment mitogen-activated protein kinase/extracellular related kinase signalling. The present study reveals prominent underlying mechanisms of the AAE6's enhanced oncogenic potential.

Voluntary physical activity prevents insulin resistance in a tissue specific manner

Physical inactivity and a sedentary lifestyle are risk factors for the development of type 2 diabetes. Here, we identified the effects 8 weeks of voluntary physical activity had on the prevention of insulin resistance in mouse skeletal muscles and liver (a hallmark of T2D). To do this, 8 week old C57BL/6J mice with (RUN) and without (SED) voluntary access to running wheels were fed a standard rodent chow ad libitum for 8 weeks. In the liver, there was a 2.5-fold increase in insulin stimulated Akt^SER473 phosphorylation, and a threefold increase in insulin-stimulated (0.5 U/kg) GSK3β^SER9 phosphorylation in RUN compared to SED mice. Although not induced in skeletal muscles, there was a twofold increase in SOCS3 expression in SED compared to RUN mice in the liver. There was no difference in the glucose tolerance test between groups. This study was the first to show differences in liver insulin sensitivity after 8 weeks of voluntary physical activity, and increased SOCS3 expression in the liver of sedentary mice compared to active mice. These findings demonstrate that even in young mice that would normally be considered healthy, the lack of physical activity leads to insulin resistance representing the initial pathogenesis of impaired glucose metabolism leading to type 2 diabetes.

Interleukin-6 deficiency causes tissue-specific changes in signaling pathways in response to high-fat diet and physical activity

This study was designed to investigate the role of interleukin‐6 (IL‐6) on high‐fat diet (HFD)‐induced glucose intolerance, and the response to voluntary physical activity in the prevention of insulin resistance. Six‐week‐old wild‐type (WT) and IL‐6 knockout (KO) mice with (RUN) or without (SED) access to running wheels were fed a HFD (60% from kcal) for 4 weeks. A glucose tolerance test revealed that blood glucose levels were 25–30% higher in KO RUN compared to all other groups. In WT RUN, weight gain was positively correlated with total caloric intake; however, this correlation was absent in KO RUN. In soleus muscle, there was a 2‐fold increase in SOCS3 expression in KO RUN compared to all other groups. In gastrocnemius and plantaris muscles, Akt phosphorylation was 31% higher in WT RUN compared to WT SED, but this effect of running was absent in KO mice. Additionally, there was a 2.4‐fold increase in leptin expression in KO RUN compared to KO SED in the gastrocnemius and plantaris muscles. In the liver, there was a 2‐ to 3.8‐fold increase in SOCS3 expression in KO SED compared to all other groups, and AMPKα phosphorylation was 27% higher in WT mice (both RUN and SED) compared to KO mice (both RUN and SED). This study provides new insights into the role of the IL‐6 in metabolism and energy storage, and highlights tissue‐specific changes in early signaling pathways in response to HFD for 4 weeks. The collective findings suggest that endogenous IL‐6 is important for the prevention of insulin resistance leading to type 2 diabetes.

This study was designed to investigate the role of interleukin‐6 (IL‐6) on high‐fat diet (HFD)‐induced glucose intolerance, and the response to voluntary physical activity in the prevention of insulin resistance. This study provides new insight into the role of the IL‐6 in metabolism and energy storage, and highlights tissue‐specific changes in early signaling pathways in response to HFD for 4 weeks. The collective findings suggest that endogenous IL‐6 is important for the prevention of insulin resistance leading to type 2 diabetes.

Metformin induces apoptosis and cell cycle arrest mediated by oxidative stress, AMPK and FOXO3a in MCF-7 breast cancer cells

Recent studies have demonstrated that the anti-diabetic drug, metformin, can exhibit direct antitumoral effects, or can indirectly decrease tumor proliferation by improving insulin sensitivity. Despite these recent advances, the underlying molecular mechanisms involved in decreasing tumor formation are not well understood. In this study, we examined the antiproliferative role and mechanism of action of metformin in MCF-7 cancer cells treated with 10 mM of metformin for 24, 48, and 72 hours. Using BrdU and the MTT assay, it was found that metformin demonstrated an antiproliferative effect in MCF-7 cells that occurred in a time- and concentration- dependent manner. Flow cytometry was used to analyze markers of cell cycle, apoptosis, necrosis and oxidative stress. Exposure to metformin induced cell cycle arrest in G₀-G₁ phase and increased cell apoptosis and necrosis, which were associated with increased oxidative stress. Gene and protein expression were determined in MCF-7 cells by real time RT-PCR and western blotting, respectively. In MCF-7 cells metformin decreased the activation of IRβ, Akt and ERK1/2, increased p-AMPK, FOXO3a, p27, Bax and cleaved caspase-3, and decreased phosphorylation of p70S6K and Bcl-2 protein expression. Co-treatment with metformin and H₂O₂ increased oxidative stress which was associated with reduced cell number. In the presence of metformin, treating with SOD and catalase improved cell viability. Treatment with metformin resulted in an increase in p-p38 MAPK, catalase, MnSOD and Cu/Zn SOD protein expression. These results show that metformin has an antiproliferative effect associated with cell cycle arrest and apoptosis, which is mediated by oxidative stress, as well as AMPK and FOXO3a activation. Our study further reinforces the potential benefit of metformin in cancer treatment and provides novel mechanistic insight into its antiproliferative role.

Pro-inflammatory mediation of myoblast proliferation

Skeletal muscle satellite cell function is largely dictated by the surrounding environment following injury. Immune cell infiltration dominates the extracellular space in the injured area, resulting in increased cytokine concentrations. While increased pro-inflammatory cytokine expression has been previously established in the first 3 days following injury, less is known about the time course of cytokine expression and the specific mechanisms of cytokine induced myoblast function. Therefore, the expression of IL-1β and IL-6 at several time points following injury, and their effects on myoblast proliferation, were examined. In order to do this, skeletal muscle was injured using barium chloride in mice and tissue was collected 1, 5, 10, and 28 days following injury. Mechanisms of cytokine induced proliferation were determined in cell culture using both primary and C2C12 myoblasts. It was found that there is a ∼20-fold increase in IL-1β (p≤0.05) and IL-6 (p = 0.06) expression 5 days following injury. IL-1β increased proliferation of both primary and C2C12 cells ∼25%. IL-1β stimulation also resulted in increased NF-κB activity, likely contributing to the increased proliferation. These data demonstrate for the first time that IL-1β alone can increase the mitogenic activity of primary skeletal muscle satellite cells and offer insight into the mechanisms dictating satellite cell function following injury.

The antioxidant resveratrol down-regulates inflammation in an in-vitro model of Pseudomonas aeruginosa infection of lung epithelial cells

Pseudomonas aeruginosa is a Gram-negative opportunistic pathogen that can cause severe pulmonary infection in immunocompromized individuals. During the infectious process, P. aeruginosa provokes a potent inflammatory response and induces the release of reactive oxygen species (ROS). Cells undergo oxidative stress when cellular antioxidants are unable to effectively scavenge and detoxify ROS, resulting in lung damage. Resveratrol (3,5,4'-trihydroxystilbene) is a natural polyphenolic compound with recognized antioxidant effects. We hypothesized that owing to its antioxidant activities, resveratrol can attenuate an inflammatory response in P. aeruginosa-infected cells. Lung epithelial A549 cells were pre-treated with 100 μmol/L of resveratrol for 5 h, followed by infection with P. aeruginosa. Intracellular ROS generation was used as an indicator of P. aeruginosa-induced oxidative stress, and cell surface expression of Fas receptor and activation of caspases-3 and -7 as indicators of apoptosis. We also measured the surface expression of intercellular adhesion molecule (ICAM)-1 and enzymes related to inflammation and redox signaling. Resveratrol significantly reduced ROS generation, ICAM-1, and human beta-defensin-2 expression, as well as the markers of apoptosis in A549 cells infected with P. aeruginosa, and up-regulated glutathione peroxidase, suggesting its potential therapeutic role in protecting the lungs against the deleterious effects of P. aeruginosa infection.

The IL-6 Paradox: Context Dependent Interplay of SOCS3 and AMPK

Insulin resistance is the principle step towards the progression of type 2 diabetes, and has been linked to increased circulating levels of cytokines, leading to chronic low-grade inflammation. Specifically, in chronic disease states increased IL-6 is thought to play a critical role in the regulation of insulin resistance in the peripheral tissues, and has been used as a marker of insulin resistance. There is also an endogenous up-regulation of IL-6 in response to exercise, which has been linked to improved insulin sensitivity. This leads to the question "how can elevated IL-6 lead to the development of insulin resistance, and yet also lead to increased insulin sensitivity?" Resolving the dual role of IL-6 in regulating insulin resistance/sensitivity is critical to the development of potential therapeutic interventions. This review summarizes the literature on the seemingly paradoxical role of elevated IL-6 on insulin signalling, including the activation of AMPK and the involvement of leptin and SOCS3.

Exercise training prevents development of cardiac contractile dysfunction in hypertensive TG (mREN-2)27 rats

BACKGROUND

Angiotensin-II (Ang-II) contributes to cardiac remodeling and left ventricular dysfunction. In contrast, exercise may have beneficial effects on left ventricular structure and function.

METHODS AND RESULTS

We investigated the effects of low-intensity exercise training (ET) on in vivo cardiac function in hypertensive TG (mREN-2)27 rats (Ren-2) which develop left ventricular hypertrophy and dysfunction. Ren-2 rats and Sprague Dawley (SD) controls (4-5 weeks) began treadmill exercise every day for 5-6 weeks. Cardiac function was evaluated by echocardiography. Cardiac output and stroke volume were increased by ET in both 8-wk-old SD and Ren-2. Slope of mitral deceleration time, a non-invasive measure of diastolic function, was lower in the Ren-2 rats, but not changed by ET. LV collagen deposition, as assessed by hydroxyproline assay, was not affected by rat strain or ET at 10-11 weeks of age. Left ventricular B-type natriuretic peptide mRNA levels were higher in the Ren-2 rats (100%), but not affected by ET. Both alpha (~14.5 fold) and beta (~2.5 fold) myosin heavy chain mRNA were higher in the LV of Ren-2 rats (p < 0.05), but were not changed by ET.

CONCLUSION

Low-intensity exercise training in Ren-2 rats, a model of Ang-II-mediated hypertension, maintains cardiac index and stroke volume in the presence of impaired diastolic function at 8 wks of age.

Age-related impairment of T cell-induced skeletal muscle precursor cell function

Sarcopenia is the age-associated loss of skeletal muscle mass and strength. Recent evidence suggests that an age-associated loss of muscle precursor cell (MPC) functionality contributes to sarcopenia. The objectives of the present study were to examine the influence of activated T cells on MPCs and determine whether an age-related defect in this signaling occurs. MPCs were collected from the gastrocnemius and plantaris of 3-mo-old (young) and 32-mo-old (old) animals. Splenic T cells were harvested using anti-CD3 Dynabead isolation. T cells were activated for 48 h with costimulation of 100 IU/ml interleukin-2 (IL-2) and 5 μg/ml of anti-CD28. Costimulation increased 5-bromo-2'-deoxyuridine incorporation of T cells from 13.4 ± 4.6% in control to 64.8 ± 6.0% in costimulated cells. Additionally, T cell cytokines increased proliferation on MPCs isolated from young muscle by 24.0 ± 5.7%, whereas there was no effect on MPCs isolated from aged muscle. T cell cytokines were also found to be a chemoattractant. T cells were able to promote migration of MPCs isolated from young muscle; however, MPCs isolated from aged muscle did not respond to the T cell-released chemokines. Conversely, whereas T cell-released cytokines did not affect myogenesis of MPCs isolated from young animals, there was a decrease in MPCs isolated from old animals. These data suggest that T cells may play a critical role in mediating MPC function. Furthermore, aging may alter T cell-induced MPC function. These findings have implications for developing strategies aimed at increasing MPC migration and proliferation leading to an improved regenerative capacity of aged skeletal muscle.

IGF-I activates the mouse type IIb myosin heavy chain gene

IGF-I increases skeletal muscle mass, but whether IGF-I increases type IIb myosin heavy chain (MyHC) transcriptional activity is not known. C2C12 myotubes were cultured with or without IGF-I to determine whether IGF-I increases type IIb MyHC promoter activity, and if so, what region of the promoter might IGF-I signaling regulate. At differentiation days 3 and 4, IGF-I increased type IIb MyHC mRNA and mouse 3.0-kb type IIb MyHC promoter activity. Deletion construct studies identified a potential IGF-I-responsive region between 1.25 and 1.2 kb of the type IIb MyHC promoter, which contained an exact 6-bp T-cell factor/lymphoid enhancer factor (Tcf/Lef) binding site at position -1206 to -1201. Site-specific mutation of the putative Tcf/Lef binding site reduced IGF-I-induced 1.3-kb type IIb MyHC promoter activity. To identify potential IGF-I signaling molecules, the phosphatidylinositol 3-kinase (PI3K) inhibitors wortmannin and LY-294002 were both found to markedly attenuate IGF-I activation of the 1.3-kb type IIb MyHC promoter. Downstream signaling of IGF-I can phosphorylate and inactivate GSK-3beta, thereby enhancing beta-catenin protein. The GSK-3beta inhibitor, LiCl, dramatically enhanced IGF-I induction of the 1.3-kb type IIb MyHC promoter, and constitutively active GSK-3beta attenuated IGF-I-induced 1.3-kb type IIb MyHC promoter activity. Finally, IGF-I increased nuclear beta-catenin protein, and small interfering RNA knockdown of beta-catenin attenuated IGF-I-induced 1.3-kb type IIb MyHC promoter activity and type IIb MyHC mRNA. In summary, IGF-I stimulation of C2C12 myotubes increases mouse type IIb MyHC promoter activity, likely through signaling of PI3K, GSK-3beta, beta-catenin, and a Tcf/Lef binding site at -1,206 to -1,201 bp in the promoter.

Fibroblast growth factor 2-stimulated proliferation is lower in muscle precursor cells from old rats

In aged skeletal muscle, impairments in regrowth and regeneration may be explained by a decreased responsiveness of muscle precursor cells (MPCs) to environmental cues such as growth factors. We hypothesized that impaired responsiveness to fibroblast growth factor 2 (FGF2) in MPCs from old animals would be explained by impaired FGF2 signalling. We determined that 5-bromo-2'-deoxyuridine (BrdU) incorporation and cell number increase less in MPCs from 32- compared with 3-month-old rats. In the presence of FGF2, we demonstrated that there were age-associated differential expression patterns for FGF receptor 1 and 2 mRNAs. Measurement of downstream signalling revealed that that mitogen-activated protein kinase/ERK kinase 1/2 (MEK1/2)-extracellular signal-regulated kinase 1/2, protein kinase C and p38 were FGF2-driven pathways in MPCs. Uniquely, protein kinase C signalling was shown to play the largest role in FGF2-stimulated proliferation in MPCs. c-Jun N-terminal kinase (JNK) signalling was ruled out as an FGF2-stimulated proliferation pathway in MPCs. Inhibition of JNK had no effect on FGF2 signalling to BrdU incorporation, and FGF2 treatment was associated with increased phosphorylation of p38, which inhibits, rather than stimulates, BrdU incorporation in MPCs. Surprisingly, the commonly used vehicle, dimethyl sulphoxide, rescued proliferation in MPCs from old animals. These findings provide insight for the development of effective treatment strategies that target the age-related impairments of MPC proliferation in old skeletal muscle.

Muscle precursor cells isolated from aged rats exhibit an increased tumor necrosis factor- alpha response

Improving muscle precursor cell (MPC, muscle-specific stem cells) function during aging has been implicated as a key therapeutic target for improving age-related skeletal muscle loss. MPC dysfunction during aging can be attributed to both the aging MPC population and the changing environment in skeletal muscle. Previous reports have identified elevated levels of tumor necrosis factor- alpha (TNF- alpha ) in aging, both circulating and locally in skeletal muscle. The purpose of the present study was to determine if age-related differences exist between TNF- alpha -induced nuclear factor-kappa B (NF- kappaB) activation and expression of apoptotic gene targets. MPCs isolated from 32-month-old animals exhibited an increased NF- kappaB activation in response to 1, 5, and 20 ng mL(-1) TNF- alpha, compared to MPCs isolated from 3-month-old animals. No age differences were observed in the rapid canonical signaling events leading to NF- kappaB activation or in the increase in mRNA levels for TNF receptor 1, TNF receptor 2, TNF receptorassociated factor 2 (TRAF2), or Fas (CD95) observed after 2 h of TNF- alpha stimulation. Interestingly, mRNA levels for TRAF2 and the cell death-inducing receptor, Fas (CD95), were persistently upregulated in response to 24 h TNF- alpha treatment in MPCs isolated from 32-month-old animals, compared to 3-month-old animals. Our data indicate that age-related differences may exist in the regulatory mechanisms responsible for NF- kappaB inactivation, which may have an effect on TNF- alpha-induced apoptotic signaling. These findings improve our understanding of the interaction between aged MPCs and the changing environment associated with age, which is critical for the development of potential clinical interventions aimed at improving MPC function with age.

Anti-TNF treatment reduces rat skeletal muscle wasting in monocrotaline-induced cardiac cachexia

The aim was to explore efficacy of tumor necrosis factor (TNF) inhibitors in attenuating increases in anorexia and ubiquitin proteasome pathway transcripts in cardiac cachexia, a potentially lethal condition that responds poorly to current treatments. Cardiac cachexia was rapidly induced with monocrotaline in Sprague-Dawley rats. Either soluble TNF receptor-1 or the general inhibitor of TNF production, pentoxifylline, was given to diminish TNF action on the first indication of cachexia. Animals were anesthetized with a ketamine-xylazine-acepromazine cocktail, and then skeletal muscles were removed for subsequent measurements including ubiquitin proteasome pathway transcripts and Western blots. Both soluble TNF receptor-1 and pentoxifylline attenuated losses in both body and skeletal muscle masses and also reduced increases in selected ubiquitin proteasome pathway transcripts. The action of soluble TNF receptor-1 was partly through reversal of reduced food consumption, while the effects of pentoxifylline were independent of food intake. Here we demonstrate, for the first time, that attenuation of anorexia by soluble TNF receptor-1 treatment in monocrotaline-induced cardiac cachexia is responsible for attenuating increases in some ubiquitin proteasome pathway transcripts as well as preserving body mass and attenuating loss of skeletal muscle mass.

Sirt1 increases skeletal muscle precursor cell proliferation

It is important to understand the mechanisms that control muscle precursor cell (MPC) proliferation for the development of countermeasures to offset the deleterious effects of the aging-related loss of skeletal muscle mass (and myonuclei) and the impaired ability of old muscle to regrow and regenerate. Over-expression of the NAD+-dependent histone deacetylase Sirt1 increased MPC proliferation and cell cycle progression as evidenced by increased 5-bromo-2'-deoxyuridine (BrdU) incorporation, an increase in cell number, proliferating cell nuclear antigen expression, and the phosphorylation of retinoblastoma protein. Associated with the Sirt1-mediated increase in MPC cycle progression were the bidirectional decreases and increases in the expression of the cyclin-dependent kinase inhibitors p21(Waf/Cip1) and p27(Kip1), respectively. Based upon our recent observation that lowering oxygen (O2) in culture from ambient (20%) to estimated physiological levels (5%) increased MPC proliferation, we next measured Sirt1 protein at 5% and 20% O2. Interestingly, in addition to increased proliferation in MPCs cultured at 5% O2, Sirt1 expression increased, compared to 20% O2. Using O2 levels as a platform to modulate basal Sirt1 protein, activation of Sirt1 activity with resveratrol in 20% O2 increased MPC proliferation while inhibition of Sirt1 with nicotinamide in 5% O2 lowered proliferation. For the first time, Sirt1 has been shown to increase MPC proliferation. These findings could have clinical significance since MPC proliferation has important implications in regulating skeletal muscle growth, maintenance, and repair, and the aging-related loss of skeletal muscle mass.

Age-dependent FOXO regulation of p27Kip1 expression via a conserved binding motif in rat muscle precursor cells

Previously, we have demonstrated that forkhead box O3a (FOXO3a) overexpression increased p27(Kip1) promoter activity and protein expression, whereas it decreased proliferation in muscle precursor cells (MPCs). The objectives of the present study were to 1) locate and identify FOXO regulatory elements in the rat p27(Kip1) promoter using deletion analysis of a promoter/reporter construct and 2) determine if age-related differences exist in FOXO-induced p27(Kip1) expression. The full-length (-4.0/+0.4 kb) rat p27(Kip1) promoter construct revealed that both FOXO1 and FOXO3a induced an increase in transcriptional activity. Interestingly, MPCs isolated from old animals exhibited an increased FOXO3a-induced p27(Kip1) promoter activity compared with MPCs isolated from young animals. Deletion of a 253-bp portion of the 5'-untranslated region (UTR) resulted in a significant decrease in FOXO-induced p27(Kip1) promoter expression. Site-specific mutation of a daf-16 family protein-binding element (DBE) within this 253-bp portion of the 5'-UTR also demonstrated a decrease in FOXO-induced p27(Kip1) promoter expression. These data suggest that a putative FOXO regulatory element located in the 5'-UTR of the rat p27(Kip1) gene plays a role in the age-dependent differences in FOXO3a-dependent p27(Kip1) promoter expression. These findings have implications for developing treatment strategies aimed at increasing the proliferation of MPCs and regenerative capacity of aged skeletal muscle.

p21(Cip1) expression is increased in ambient oxygen, compared to estimated physiological (5%) levels in rat muscle precursor cell culture

OBJECTIVE

While it is common practice to culture cells in the presence of ambient oxygen (approximately 21% O2), O2 level observed in the physiological environment is often much lower. Previous efforts to culture a variety of different stem cells, including muscle precursor cells (MPC), under O2 conditions that better mimic in vivo conditions have resulted in enhanced proliferation. In the present study, we hypothesized that 20% O2 in culture represents a sufficient stimulus to cause increased expression of two key negative regulators of the cell-cycle Cip/Kip family of cyclin-dependent kinase inhibitors, p21(Cip1) and p27(Kip1), in MPCs.

MATERIALS AND METHODS

MPCs were isolated from Fischer 344 x Brown Norway F(1) hybrid male rats and O2 was adjusted in culture using a tri-gas incubator.

RESULTS

5-Bromo-2'-deoxyuridine incorporation, cell number and nuclear proliferating cell nuclear antigen expression were all decreased after 48 h culture in 20% O2, compared to 5% O2. Twenty per cent O2 had no effect on either p27(Kip1) promoter activity or protein expression. Although p21(Cip1) promoter activity remained unchanged between 5% and 20% O2, there were significant increases in both p21(Cip1) mRNA and protein expression. Furthermore, 20% O2 caused an increase in p21(Cip1) mRNA stability and p53 transcription factor activity.

CONCLUSION

These findings are considered important because they reveal p21(Cip1) as a critical regulatory protein that needs to be considered when interpreting proliferation data from MPCs studied in culture. In addition, O2-dependent regulation of MPC proliferation is relevant to conditions, including sarcopenia, heart failure, cancer and muscular dystrophy, where increased oxidative stress exists.

FoxO3a preferentially induces p27Kip1 expression while impairing muscle precursor cell-cycle progression

Previous work has demonstrated that forkhead transcription factors, which include the FoxO subfamily, play a critical role in muscle atrophy by inducing expression of the atrophy-related ubiquitin ligases. The proliferation of muscle precursor cells (MPC) is also essential for skeletal muscle mass. The hypothesis was tested that the FoxO forkhead transcription factor FoxO3a hinders MPC proliferation. The present studies were designed to determine the effects of overexpression of FoxO3a on in vitro proliferation of MPCs. MPCs infected with an adenovirus for wild-type FoxO3a had decreased DNA synthesis as detected by the incorporation of 5-bromo-2' deoxyuridine. In general, cyclin-dependent kinase inhibitors, including p27(Kip1)and p21(Waf/Cip1), inhibit cell proliferation. Associated with the impaired MPC proliferation, we found an increase in the promoter activity and protein levels of the cyclin-dependent kinase inhibitor p27(Kip1), whereas there was no effect and a decrease in the promoter activity and protein levels of p21(Waf/Cip1). FoxO3a overexpression had no effect on either the phosphorylation of retinoblastoma protein (ser780) or cyclin D1 protein levels, suggesting that FoxO3a does not effect the early phase of the G(1)-S transition. In addition to its ability to induce muscle atrophy, these studies identify FoxO3a as a negative regulator of MPC proliferation. Our findings suggest that attenuating increased FoxO3a may restore MPC proliferation to prevent atrophy and improve the regenerative capacity of skeletal muscle.

Exercise-induced attenuation of obesity, hyperinsulinemia, and skeletal muscle lipid peroxidation in the OLETF rat

The Otsuka Long-Evans Tokushima fatty (OLETF) rat is a model of hyperphagic obesity in which the animals retain the desire to run voluntarily. Running wheels were provided for 4-wk-old OLETF rats for 16 wk before they were killed 5 h (WL5), 53 h (WL53), or 173 h (WL173) after the wheels were locked. Sedentary (SED) OLETF rats that were not given access to running wheels served as age-matched cohorts. Epididymal fat pad mass, adipocyte volume, and adipocyte number were 58%, 39%, and 47% less, respectively, in WL5 than SED rats. Contrary to cessation of daily running in Fischer 344 x Brown Norway rats, epididymal fat did not increase during the first 173 h of running cessation in the OLETF runners. Serum insulin and glucose levels were 77% and 29% less, respectively, in WL5 than SED rats. Oil red O staining for intramyocellular lipid accumulation was not statistically different among groups. However, lipid peroxidation levels, as determined by total trans-4-hydroxy-2-nonenal (4-HNE) and 4-HNE normalized to oil red O, was higher in epitrochlearis muscles of SED than WL5, WL53, and WL173 rats. mRNA levels of glutathione S-transferase-alpha type 4, an enzyme involved in cellular defense against electrophilic compounds such as 4-HNE, were higher in epitrochlearis muscle of WL53 than WL173 and SED rats. In contrast, 4-HNE levels in omental fat were unaltered. Epitrochlearis muscle palmitate oxidation and relative transcript levels for peroxisome proliferator-activated receptor-delta and peroxisome proliferator-activated receptor-gamma coactivator type 1 were surprisingly not different between runners and SED rats. In summary, voluntary running was associated with lower levels of lipid peroxidation in skeletal muscle without significant changes in intramyocellular lipids or mitochondrial markers in OLETF rats at 20 wk of age. Therefore, even in a genetic animal model of extreme overeating, daily physical activity promotes improved health of skeletal muscle.

Functional overload attenuates plantaris atrophy in tumor-bearing rats

BACKGROUND

Late stage cancer malignancies may result in severe skeletal muscle wasting, fatigue and reduced quality of life. Resistance training may attenuate these derangements in cancer patients, but how this hypertrophic response relates to normal muscle adaptations in healthy subjects is unknown. Here, we determined the effect of resistance training on muscle mass and myosin heavy chain (MHC) isoform composition in plantaris muscles from tumor-bearing (TB) rats.

METHODS

Age- and gender-matched Buffalo rats were used for all studies (n = 6/group). Suspensions of Morris Hepatoma MH7777 cells or normal saline were injected subcutaneously into the dorsum. Six weeks after cell implantation, muscles from TB rats were harvested, weighed and processed for ATP-independent proteasome activity assays. Once tumor-induced atrophy had been established, subgroups of TB rats underwent unilateral, functional overload (FO). Healthy, sham-operated rats served as controls. After six weeks, the extent of plantaris hypertrophy was calculated and MHC isoform compositions were determined by gel electrophoresis.

RESULTS

Six weeks of tumor growth reduced body mass and the relative masses of gastrocnemius, plantaris, tibialis anterior, extensor digitorum longus, and diaphragm muscles (p < or = 0.05). Percent reductions in body mass had a strong, negative correlation to final tumor size (r = -0.78). ATP-independent proteasome activity was increased in plantaris muscles from TB rats (p < or = 0.05). In healthy rats, functional overload (FO) increased plantaris mass ~44% compared to the contralateral control muscle, and increased the relative percentage of MHC type I and decreased the relative percentage of MHC type IIb compared to the sham-operated controls (p < or = 0.05). Importantly, plantaris mass was increased ~24% in TB-FO rats and adaptations to MHC isoform composition were consistent with normal, resistance-trained muscles.

CONCLUSION

Despite significant skeletal muscle derangements due to cancer, muscle retains the capacity to respond normally to hypertrophic stimuli. Specifically, when challenged with functional overload, plantaris muscles from TB rats displayed greater relative mass, increased percentages of MHC type I and decreased percentages of MHC type IIb. Therefore, resistance training paradigms should provide relative morphological and functional benefits to cancer patients suffering from muscle wasting.

Fundamental questions about genes, inactivity, and chronic diseases

Currently our society is faced with the challenge of understanding the biological basis for the epidemics of obesity and many chronic diseases, including Type 2 diabetes. Physical inactivity increases the relative risk of coronary artery disease by 45%, stroke by 60%, hypertension by 30%, and osteoporosis by 59%. Moreover, physical inactivity is cited as an actual cause of chronic disease by the US Centers of Disease Control. Physical activity was obligatory for survival for the Homo genus for hundreds of thousands of years. This review will present evidence that suggests that metabolic pathways selected during the evolution of the human genome are inevitably linked to physical activity. Furthermore, as with many other environmental interactions, cycles of physical activity and inactivity interact with genes resulting in a functional outcome appropriate for the environment. However, as humans are less physically active, there is a maladaptive response that leads to metabolic dysfunction and many chronic diseases. How and why these interactions occur are fundamental questions in biology. Finally, a perspective to future research in physical inactivity-gene interaction is presented. This information is necessary to provide the molecular evidence required to further promote the primary prevention of chronic diseases through physical activity, identify those molecules that will allow early disease detection, and provide society with the molecular information needed to counter the current strategy of adding physical inactivity into our lives.