Understanding preferences for receiving health communications and information about clinical trials: a cross-sectional study among US adults.

OBJECTIVE: Effective health communication is critical for understanding and acting on health information. This cross-sectional study explored participants' understanding of their health condition, their preferences for receiving health communications, and their interest in receiving clinical trial results across several therapeutic areas. METHODS: The study recruited participants via social media, email newsletters, and advocacy organizations. An online screener captured demographic information (health conditions, age, race/ethnicity, gender, and education). Eligible participants were emailed an online survey assessing preferred sources and formats for receiving health information, interest in learning about topics related to the results of clinical trials, and health literacy levels. RESULTS: In total, 449 participants (median age, 35 years [range, 18-76]; White, 53%; higher education, 65%; mean (range) health literacy score, 1.9 [0.4-3.0]) from 45 US states completed the survey representing 12 disease indications (bipolar, blood and solid tumor cancers, irritable bowel syndrome, inflammatory bowel disease, major depressive disorder, migraine, Parkinson's, psoriasis/atopic dermatitis, retinal vein occlusion/macular degeneration, rheumatoid arthritis, and spasticity). Healthcare providers were the preferred source of health information (59%), followed by Internet searches (11%). Least preferred sources were social media (5%), friends/family (3%), and email newsletters (2%). Participants preferred multiple formats and ranked reading materials online as most preferred (33%), along with videos (28%) and infographics (27%). Printed materials (14%) and audio podcasts (9%) were the least preferred formats. A majority of the participants reported that the health information they found was hard to understand (57%) and confusing (62%). Most participants (85%) were somewhat/very interested in learning about clinical trial results, with the highest interest in short summaries of safety (78%) and efficacy (74%) results. CONCLUSION: Effective health communication may be achieved via multiple formats shared directly by healthcare providers.

Researchers wanted to learn how people preferred to receive health-related communications, including information about the results of clinical trials. They surveyed 449 people from 45 US states with 12 different health conditions. The survey questions asked people about their preferred sources and ways of getting health information. It also asked about their interest in learning about clinical trials related to their health condition. The results showed that most people preferred to get health information from their healthcare providers (59%). The Internet was the second most popular choice (11%) for getting health information. People did not like getting health information from social media, friends or family, or email newsletters as much. When it came to how health information was shared, people liked reading materials online (33%), watching videos (28%), and looking at infographics (27%). They did not like printed materials and audio podcasts as much. Most people (85%) were interested in learning about the results of clinical trials in short summaries. They wanted to know about the safety (78%) and how well the treatments worked (74%) in the short summaries. In conclusion, people liked getting health information from healthcare providers like doctors, nurses, and others in different formats. Sharing information in different formats through healthcare providers may improve communication for patients with different health conditions.

Glucagon-like peptide-1/glucagon receptor agonism associates with reduced metabolic adaptation and higher fat oxidation: A randomized trial.

OBJECTIVE: This study tested the hypothesis that treatment with the glucagon-like peptide-1/glucagon receptor agonist SAR425899 would lead to a smaller decrease in sleeping metabolic rate (SMR; kilocalories/day) than expected from the loss of lean and fat mass (metabolic adaptation). METHODS: This Phase 1b, double-blind, randomized, placebo-controlled study was conducted at two centers in inpatient metabolic wards. Thirty-five healthy males and females with overweight and obesity (age = 36.5 ± 7.1 years) were randomized to a calorie-reduced diet (-1000 kcal/d) and escalating doses (0.06-0.2 mg/d) of SAR425899 (n = 17) or placebo (n = 18) for 19 days. SMR was measured by whole-room calorimetry. RESULTS: Both groups lost weight (-3.68 ± 1.37 kg placebo; -4.83 ± 1.44 kg SAR425899). Those treated with SAR425899 lost more weight, fat mass, and fat free mass (p < 0.05) owing to a greater achieved energy deficit than planned. The SAR425899 group had a smaller reduction in body composition-adjusted SMR (p = 0.002) as compared with placebo, but not 24-hour energy expenditure. Fat oxidation and ketogenesis increased in both groups, with significantly greater increases with SAR425899 (p < 0.05). CONCLUSIONS: SAR425899 led to reduced selective metabolic adaptation and increased lipid oxidation, which are believed to be beneficial for weight loss and weight-loss maintenance.

Energy intake as a short-term biomarker for weight loss in adults with obesity receiving liraglutide: A randomized trial.

BACKGROUND AND OBJECTIVE: Obesity is a chronic disease associated with many serious comorbidities. Pharmacologic therapies are approved for the treatment of obesity; however, short-term biomarkers to predict weight loss are not well understood. This study aimed to determine the ability of single-meal energy intake (EI) to predict weight loss in participants with obesity treated with liraglutide. METHODS: In this randomized, double-blind, placebo-controlled study, participants received subcutaneous liraglutide (titrated to 3.0 mg/day) or placebo once daily, with inpatient assessments at baseline and weeks 3 and 6. The primary endpoint was change from baseline (CFB) in EI during consecutive ad libitum lunch meals at weeks 3 and 6. Secondary endpoints included CFB in 24- and 48-h EI, weight, appetite scores, and gastric emptying measures. RESULTS: Sixty-one participants were randomized (n = 32, liraglutide; n = 29, placebo). The least squares mean (LSM) difference (95% CI; p-value) in CFB in EI during ad libitum lunch meals between the liraglutide and placebo groups was -236 (-322, -149; p < 0.0001) kcal at week 3 and -244 (-339, -148, p < 0.0001) kcal at week 6. The liraglutide group experienced significant weight loss at weeks 3 and 6, compared with placebo. Weight loss was significantly correlated with EI, but not with appetite score or gastric emptying. CONCLUSIONS: EI during a single meal is a robust clinical predictor of weight changes in participants with obesity. Future clinical trials can utilize EI at a single meal as a predictor of weight loss.

Metabolic adaptation characterizes short-term resistance to weight loss induced by a low-calorie diet in overweight/obese individuals.

BACKGROUND: Low-calorie diet (LCD)-induced weight loss demonstrates response heterogeneity. Physiologically, a decrease in energy expenditure lower than what is predicted based on body composition (metabolic adaptation) and/or an impaired capacity to increase fat oxidation may hinder weight loss. Understanding the metabolic components that characterize weight loss success is important for optimizing weight loss strategies. OBJECTIVES: We tested the hypothesis that overweight/obese individuals who had lower than expected weight loss in response to a 28-d LCD would be characterized by 1) impaired fat oxidation and 2) whole-body metabolic adaptation. We also characterized the molecular mechanisms associated with weight loss success/failure. METHODS: This was a retrospective comparison of participants who met their predicted weight loss targets [overweight/obese diet sensitive (ODS), n = 23, females = 21, males = 2] and those that did not [overweight/obese diet resistant (ODR), n = 14, females = 12, males = 2] after a 28-d LCD (900-1000 kcal/d). We used whole-body (energy expenditure and fat oxidation) and tissue-specific measurements (metabolic proteins in skeletal muscle, gene expression in adipose tissue, and metabolites in serum) to detect metabolic properties and biomarkers associated with weight loss success. RESULTS: The ODR group had greater mean ± SD metabolic adaptation (-175 ± 149 kcal/d; +119%) than the ODS group (-80 ± 108 kcal/d) after the LCD (P = 0.030). Mean ± SD fat oxidation increased similarly for both groups from baseline (0.0701 ± 0.0206 g/min) to day 28 (0.0869 ± 0.0269 g/min; P < 0.001). A principal component analysis factor comprised of serum 3-hydroxybutyric acid, citrate, leucine/isoleucine, acetyl-carnitine, and 3-hydroxylbutyrlcarnitine was associated with weight loss success at day 28 (std. ß = 0.674, R2 = 0.479, P < 0.001). CONCLUSIONS: Individuals who achieved predicted weight loss targets after a 28-d LCD were characterized by reduced metabolic adaptation. Accumulation of metabolites associated with acetyl-CoA excess and enhanced ketogenesis was identified in the ODS group.This trial was registered at clinicaltrials.gov as NCT01616082.

An improvement in skeletal muscle mitochondrial capacity with short-term aerobic training is associated with changes in Tribbles 1 expression.

Exercise training and physical activity are known to be associated with high mitochondrial content and oxidative capacity in skeletal muscle. Metabolic diseases including obesity and insulin resistance are associated with low mitochondrial capacity in skeletal muscle. Certain transcriptional factors such as PGC-1α are known to mediate the exercise response; however, the precise molecular mechanisms involved in the adaptation to exercise are not completely understood. We performed multiple measurements of mitochondrial capacity both in vivo and ex vivo in lean or overweight individuals before and after an 18-day aerobic exercise training regimen. These results were compared to lean, active individuals. Aerobic training in these individuals resulted in a marked increase in mitochondrial oxidative respiratory capacity without an appreciable increase in mitochondrial content. These adaptations were associated with robust transcriptome changes. This work also identifies the Tribbles pseudokinase 1, TRIB1, as a potential mediator of the exercise response in human skeletal muscle.

Plasma Myokine Concentrations After Acute Exercise in Non-obese and Obese Sedentary Women.

Exercise and physical activity levels influence myokine release from skeletal muscle and contribute to circulating concentrations. Indeed, many myokines, including interleukin (IL)-6, IL-15, secreted protein acidic rich in cysteine (SPARC), and fibroblast growth factor (FGF) 21 are higher in the circulation after an exercise bout. Since these peptides modulate muscle metabolism and can also be targeted toward other tissues to induce adaptations to energy demand, they are of great interest regarding metabolic diseases. Therefore, we set out to compare, in six women with obesity (BMI ≥30 kg/m2) and five healthy women (BMI 22-29.9 kg/m2), the effect of an acute bout of moderate-intensity, continuous cycling exercise (60 min, 60% VO2peak) on the release of myokines (IL-6, IL-8, IL-10, IL-13, IL-15, SPARC, and FGF21) in plasma for a 24-h time course. We found that plasma IL-8 and SPARC levels were reduced in the group of women with obesity, whereas plasma IL-13 concentrations were elevated in comparison to non-obese women both before and after the exercise bout. We also found that plasma FGF21 concentration during the 24 h following the bout of exercise was regulated differently in the non-obese in comparison to obese women. Plasma concentrations of FGF21, IL-6, IL-8, IL-15, and IL-18 were regulated by acute exercise. Our results confirm the results of others concerning exercise regulation of circulating myokines while providing insight into the time course of myokine release in circulation after an acute exercise bout and the differences in circulating myokines after exercise in women with or without obesity.

Unconscious or underpowered? Probabilistic cuing of visual attention.

Recent debate about the reliability of psychological research has raised concerns about the prevalence of false positives in our discipline. However, false negatives can be just as concerning in areas of research that depend on finding support for the absence of an effect. This risk is particularly high in unconscious learning experiments, where researchers commonly seek to demonstrate that people can learn to perform a task in the absence of any explicit knowledge of the information that drives performance. The fact that some unconscious learning effects are typically studied with small samples and unreliable awareness measures makes false negatives especially likely. In the present article we focus on a popular unconscious learning paradigm, probabilistic cuing of visual attention, as a case study. First, we show that, at the meta-analytic level, previous experiments reveal positive signs of participant awareness, although individual studies are severely underpowered to detect this. Second, we report the results of 2 empirical studies in which participants' awareness was tested with alternative and more sensitive dependent measures, both of which manifest positive evidence of awareness. We also show that, based on the predictions of a formal model of probabilistic cuing and given the reliabilities of the dependent measures collected in these experiments, any statistical test aimed at detecting a significant correlation between learning and awareness is doomed to return a nonsignificant result, even if at the latent level both constructs are actually related and participants' knowledge is completely explicit. (PsycINFO Database Record (c) 2019 APA, all rights reserved).

GDF15 Provides an Endocrine Signal of Nutritional Stress in Mice and Humans.

GDF15 is an established biomarker of cellular stress. The fact that it signals via a specific hindbrain receptor, GFRAL, and that mice lacking GDF15 manifest diet-induced obesity suggest that GDF15 may play a physiological role in energy balance. We performed experiments in humans, mice, and cells to determine if and how nutritional perturbations modify GDF15 expression. Circulating GDF15 levels manifest very modest changes in response to moderate caloric surpluses or deficits in mice or humans, differentiating it from classical intestinally derived satiety hormones and leptin. However, GDF15 levels do increase following sustained high-fat feeding or dietary amino acid imbalance in mice. We demonstrate that GDF15 expression is regulated by the integrated stress response and is induced in selected tissues in mice in these settings. Finally, we show that pharmacological GDF15 administration to mice can trigger conditioned taste aversion, suggesting that GDF15 may induce an aversive response to nutritional stress.

Effects of 13-Hour Hyperglucagonemia on Energy Expenditure and Hepatic Glucose Production in Humans.

Glucagon (GCG) acutely stimulates energy expenditure (EE) and hepatic glucose production (HGP) in humans, but whether these effects persist during hyperglucagonemia of longer duration is unclear. Using a prospective, randomized, single-blind, crossover study design, we therefore measured EE and rates of glucose appearance (glucose RA) during three separate infusion protocols in healthy lean males: A) 10-h overnight GCG infusion (6 ng/[kg × min]) followed by 3-h infusion of GCG, octreotide (OCT), and insulin (INS) for basal replacement; B) overnight saline (SAL) infusion followed by GCG/OCT/INS infusion; and C) overnight SAL infusion followed by SAL/OCT/INS infusion. Sleep EE, measured at 6 to 7 h of the overnight infusion, was increased 65-70 kcal/24 h in A compared with B and C. During the 3-h infusion, mean resting EE remained significantly increased in A versus C by ∼50 kcal/24 h; in B, resting EE increased with a statistical trend but was not significantly greater than in C. Glucose RA increased to comparable levels in A and B. We conclude that in healthy lean males, stimulation of EE and HGP is sustained during hyperglucagonemia of longer duration when insulin secretion is inhibited. The increase in EE at the present GCG dose was of marginal clinical significance.

Active individuals have high mitochondrial content and oxidative markers in their abdominal subcutaneous adipose tissue.

OBJECTIVE: Exercise training (training) effects on white adipose tissue (WAT) thermogenic and oxidative capacities in humans are inconclusive. This study aimed to investigate whether an active lifestyle is characterized by thermogenic and/or oxidative transcriptional markers in human WAT. METHODS: In vivo maximal muscle ATP synthetic rates (ATPmax) were measured by 31 P-MRS, body composition by DXA, and peak oxygen uptake (VO2 peak) by cycle ergometry in active (n = 7) and sedentary (SED) individuals before and after 3 weeks of training (n = 9, SED only). mRNA expressions of brown adipose and ß-oxidation markers, as well as mitochondrial DNA content (mtDNA), were measured by qRT-PCR and qPCR, respectively, in WAT. RESULTS: ATPmax and VO2 peak were higher in active versus SED individuals. Following training in SED individuals, ATPmax and VO2 peak increased. Proliferator-activated receptor gamma coactivator-1α and carnitine palmitoyltransferase-1ß gene expressions and mtDNA content were significantly higher in WAT of active versus SED individuals before training. mRNA contents of brown and beige-specific markers were not different between cohorts. Training effectively increased ATPmax and VO2 peak but had no effect on mtDNA content or expressions of genes that regulate thermogenic and oxidative capacities in WAT. CONCLUSIONS: Results indicate that an active lifestyle is characterized by elevated mitochondrial content and oxidative, not thermogenic, markers of WAT.

Enhancing fire department home visiting programs: results of a community intervention trial.

This study evaluates the impact of an enhanced fire department home visiting program on community participation and installation of smoke alarms, and describes the rate of fire and burn hazards observed in homes. Communities were randomly assigned to receive either a standard or enhanced home visiting program. Before implementing the program, 603 household surveys were completed to determine comparability between the communities. During a 1-year intervention period, 171 home visits took place with 8080 homes. At baseline, 60% of homes did not have working smoke alarms on every level, 44% had unsafe water temperatures, and 72% did not have carbon monoxide alarms. Residents in the enhanced community relative to those in the standard community were significantly more likely to let the fire fighters into their homes (75 vs 62%). Among entered homes, those in the enhanced community were significantly more likely to agree to have smoke alarms installed (95 vs 92%), to be left with a working smoke alarm on every level of the home (84 vs 78%), and to have more smoke alarms installed per home visited (1.89 vs 1.74). The high baseline rates of home hazards suggest that fire department home visiting programs should take an "all hazards" approach. Community health workers and community partnerships can be effective in promoting fire departments' fire and life safety goals. Public health academic centers should partner with the fire service to help generate evidence on program effectiveness that can inform decision making about resource allocation for prevention.

"I could cry, the amount of shoes I can't get into": A qualitative exploration of the factors that influence retail footwear selection in women with rheumatoid arthritis.

BACKGROUND: Studies have reported that women with rheumatoid arthritis (RA) are not wearing NHS supplied therapeutic footwear; therefore it is likely they are wearing footwear sourced through retailers. Previous research gives limited information (largely associated with cosmesis) on people's perceptions on the relationships that exist between retail footwear, well-being and quality of life. This study aimed to explore the perceptions of women with RA regarding their choice of retail footwear and identify the factors influencing retail footwear selection. METHODS: Eleven women with RA wearing normal retail footwear were recruited from an out-patient podiatry clinic in the south east of England. Semi-structured interviews were carried out and an interpretative phenomenological approach was adopted for data collection and transcript analysis. RESULTS: Six key themes were revealed from the analysis: (1) the nature of foot complaints and deformities, (2) aesthetic appearance and design of footwear, (3) body image, (4) psychosocial aspects, (5) Perceptions of footwear and (6) the therapeutic value of retail shoes. These contributed to an overarching concept of loss of choice associated with retail footwear. In particular, the areas discussed most frequently throughout were themes (2), (3) and (4), which were notably more 'emotional' in nature. CONCLUSIONS: Limitations in retail footwear for these women have impacted on their individuality, linking significantly with their body image. The loss of choice in footwear as a consequence of the disease impacts negatively on emotions, wellbeing and was identified in reduced self-perceived quality of life.

A phase I/IItrial of MYO-029 in adult subjects with muscular dystrophy.

OBJECTIVE: Myostatin is an endogenous negative regulator of muscle growth and a novel target for muscle diseases. We conducted a safety trial of a neutralizing antibody to myostatin, MYO-029, in adult muscular dystrophies (Becker muscular dystrophy, facioscapulohumeral dystrophy, and limb-girdle muscular dystrophy). METHODS: This double-blind, placebo-controlled, multinational, randomized study included 116 subjects divided into sequential dose-escalation cohorts, each receiving MYO-029 or placebo (Cohort 1 at 1 mg/kg; Cohort 2 at 3 mg/kg; Cohort 3 at 10 mg/kg; Cohort 4 at 30 mg/kg). Safety and adverse events were assessed by reported signs and symptoms, as well as by physical examinations, laboratory results, echocardiograms, electrocardiograms, and in subjects with facioscapulohumeral dystrophy, funduscopic and audiometry examinations. Biological activity of MYO-029 was assessed through manual muscle testing, quantitative muscle testing, timed function tests, subject-reported outcomes, magnetic resonance imaging studies, dual-energy radiographic absorptiometry studies, and muscle biopsy. RESULTS: MYO-029 had good safety and tolerability with the exception of cutaneous hypersensitivity at the 10 and 30 mg/kg doses. There were no improvements noted in exploratory end points of muscle strength or function, but the study was not powered to look for efficacy. Importantly, bioactivity of MYO-029 was supported by a trend in a limited number of subjects toward increased muscle size using dual-energy radiographic absorptiometry and muscle histology. INTERPRETATION: This trial supports the hypothesis that systemic administration of myostatin inhibitors provides an adequate safety margin for clinical studies. Further evaluation of more potent myostatin inhibitors for stimulating muscle growth in muscular dystrophy should be considered.

Biomarkers in the development of novel disease-modifying therapies for osteoarthritis.

Identification and utilization of biomarkers is vitally important for the successful development of disease-modifying osteoarthritis drugs. Biochemical and imaging platforms hold great promise to deliver such biomarkers. Studies indicate a marked increase in biochemical products arising from the breakdown and biosynthesis of collagen, extracellular matrix and bone in osteoarthritis. These molecules have been associated with disease severity and may also have prognostic value as indicators of disease progression. However, issues including biological variability and lack of tissue specificity currently hinder the utility of these molecular markers in drug development. Imaging technologies hold great potential for sensitive and accurate measurement of disease-related structural damage. Drawbacks, including expense, need for validation and limited accessibility also limit the utility of these technologies. In this article, the potential value and challenges in developing and utilizing biomarkers in disease-modifying osteoarthritis drug development will be discussed.

Genetic disruption of calcineurin improves skeletal muscle pathology and cardiac disease in a mouse model of limb-girdle muscular dystrophy.

Calcineurin (Cn) is a Ca(2+)/calmodulin-dependent serine/threonine phosphatase that regulates differentiation-specific gene expression in diverse tissues, including the control of fiber-type switching in skeletal muscle. Recent studies have implicated Cn signaling in diminishing skeletal muscle pathogenesis associated with muscle injury or disease-related muscle degeneration. For example, use of the Cn inhibitor cyclosporine A has been shown to delay muscle regeneration following toxin-induced injury and inhibit regeneration in the dystrophin-deficient mdx mouse model of Duchenne muscular dystrophy. In contrast, transgenic expression of an activated mutant of Cn in skeletal muscle was shown to increase utrophin expression and reduce overall disease pathology in mdx mice. Here we examine the effect of altered Cn activation in the context of the delta-sarcoglycan-null (scgd(-/-)) mouse model of limb-girdle muscular dystrophy. In contrast to results discussed in mdx mice, genetic deletion of a loxP-targeted calcineurin B1 (CnB1) gene using a skeletal muscle-specific cre allele in the scgd(-/-) background substantially reduced skeletal muscle degeneration and histopathology compared with the scgd(-/-) genotype alone. A similar regression in scgd-dependent disease manifestation was also observed in calcineurin Abeta (CnAbeta) gene-targeted mice in both skeletal muscle and heart. Conversely, increased Cn expression using a muscle-specific transgene increased cardiac fibrosis, decreased cardiac ventricular shortening, and increased muscle fiber loss in the quadriceps. Our results suggest that inhibition of Cn may benefit select types of muscular dystrophy.

Age-dependent effect of myostatin blockade on disease severity in a murine model of limb-girdle muscular dystrophy.

Myostatin (MSTN) is a muscle-specific secreted peptide that functions to limit muscle growth through an autocrine regulatory feedback loop. Loss of MSTN activity in cattle, mice, and humans leads to a profound phenotype of muscle overgrowth, associated with more and larger fibers and enhanced regenerative capacity. Deletion of MSTN in the mdx mouse model of Duchenne muscular dystrophy enhances muscle mass and reduces disease severity. In contrast, loss of MSTN activity in the dyW/dyW mouse model of laminin-deficient congenital muscular dystrophy, a much more severe and lethal disease model, does not improve all aspects of muscle pathology. Here we examined disease severity associated with myostatin (mstn-/-) deletion in mice nullizygous for delta-sarcoglycan (scgd-/-), a model of limb-girdle muscular dystrophy. Early loss of MSTN activity achieved either by monoclonal antibody administration or by gene deletion each improved muscle mass, regeneration, and reduced fibrosis in scgd-/- mice. However, antibody-mediated inhibition of MSTN in late-stage dystrophic scgd-/- mice did not improve disease. These findings suggest that MSTN inhibition may benefit muscular dystrophy when instituted early or if disease is relatively mild but that MSTN inhibition in severely affected or late-stage disease may be ineffective.

Genetic loss of calcineurin blocks mechanical overload-induced skeletal muscle fiber type switching but not hypertrophy.

The serine/threonine phosphatase calcineurin is an important regulator of calcium-activated intracellular responses in eukaryotic cells. In higher eukaryotes, calcium/calmodulin-mediated activation of calcineurin facilitates direct dephosphorylation and nuclear translocation of the transcription factor nuclear factor of activated T-cells (NFAT). Recently, controversy has surrounded the role of calcineurin in mediating skeletal muscle cell hypertrophy. Here we examined the ability of calcineurin-deficient mice to undergo skeletal muscle hypertrophic growth following mechanical overload (MOV) stimulation or insulin-like growth factor-1 (IGF-1) stimulation. Two distinct models of calcineurin deficiency were employed: calcineurin Abeta gene-targeted mice, which show a approximately 50% reduction in total calcineurin, and calcineurin B1-LoxP-targeted mice crossed with a myosin light chain 1f cre knock-in allele, which show a greater than 80% loss of total calcineurin only in skeletal muscle. Calcineurin Abeta-/- and calcineurin B1-LoxP(fl/fl)-MLC-cre mice show essentially no defects in muscle growth in response to IGF-1 treatment or MOV stimulation, although calcineurin Abeta-/- mice show a basal defect in total fiber number in the plantaris and a mild secondary reduction in growth, consistent with a developmental defect in myogenesis. Both groups of gene-targeted mice show normal increases in Akt activation following MOV or IGF-1 stimulation. However, overload-mediated fiber-type switching was dramatically impaired in calcineurin B1-LoxP(fl/fl)-MLC-cre mice. NFAT-luciferase reporter transgenic mice failed to show a correlation between IGF-1- or MOV-induced hypertrophy and calcineurin-NFAT-dependent signaling in vivo. We conclude that calcineurin expression is important during myogenesis and fiber-type switching, but not for muscle growth in response to hypertrophic stimuli.

Calcineurin/NFAT coupling participates in pathological, but not physiological, cardiac hypertrophy.

Calcineurin (PP2B) is a calcium/calmodulin-activated, serine-threonine phosphatase that transmits signals to the nucleus through the dephosphorylation and translocation of nuclear factor of activated T cell (NFAT) transcription factors. Whereas calcineurin-NFAT signaling has been implicated in regulating the hypertrophic growth of the myocardium, considerable controversy persists as to its role in maintaining versus initiating hypertrophy, its role in pathological versus physiological hypertrophy, and its role in heart failure. To address these issues, NFAT-luciferase reporter transgenic mice were generated and characterized. These mice showed robust and calcineurin-specific activation in the heart that was inhibited with cyclosporin A. In the adult heart, NFAT-luciferase activity was upregulated in a delayed, but sustained manner throughout eight weeks of pathological cardiac hypertrophy induced by pressure-overload, or more dramatically following myocardial infarction-induced heart failure. In contrast, physiological hypertrophy as produced in two separate models of exercise training failed to show significant calcineurin-NFAT coupling in the heart at multiple time points, despite measurable increases in heart to body weight ratios. Moreover, stimulation of hypertrophy with growth hormone-insulin-like growth factor-1 (GH-IGF-1) failed to activate calcineurin-NFAT signaling in the heart or in culture, despite hypertrophy, activation of Akt, and activation of p70 S6K. Calcineurin Abeta gene-targeted mice also showed a normal hypertrophic response after GH-IGF-1 infusion. Lastly, exercise- or GH-IGF-1-induced cardiac growth failed to show induction of hypertrophic marker gene expression compared with pressure-overloaded animals. Although a direct cause-and-effect relationship between NFAT-luciferase activity and pathological hypertrophy was not proven here, our results support the hypothesis that separable signaling pathways regulate pathological versus physiological hypertrophic growth of the myocardium, with calcineurin-NFAT potentially serving a regulatory role that is more specialized for maladaptive hypertrophy and heart failure.

Targeted inhibition of p38 MAPK promotes hypertrophic cardiomyopathy through upregulation of calcineurin-NFAT signaling.

The MAPKs are important transducers of growth and stress stimuli in virtually all eukaryotic cell types. In the mammalian heart, MAPK signaling pathways have been hypothesized to regulate myocyte growth in response to developmental signals or physiologic and pathologic stimuli. Here we generated cardiac-specific transgenic mice expressing dominant-negative mutants of p38alpha, MKK3, or MKK6. Remarkably, attenuation of cardiac p38 activity produced a progressive growth response and myopathy in the heart that correlated with the degree of enzymatic inhibition. Moreover, dominant-negative p38alpha, MKK3, and MKK6 transgenic mice each showed enhanced cardiac hypertrophy following aortic banding, Ang II infusion, isoproterenol infusion, or phenylephrine infusion for 14 days. A mechanism underlying this enhanced-growth profile was suggested by the observation that dominant-negative p38alpha directly augmented nuclear factor of activated T cells (NFAT) transcriptional activity and its nuclear translocation. In vivo, NFAT-dependent luciferase reporter transgenic mice showed enhanced activation in the presence of the dominant-negative p38alpha transgene before and after the onset of cardiac hypertrophy. More significantly, genetic disruption of the calcineurin Abeta gene rescued hypertrophic cardiomyopathy and depressed functional capacity observed in p38-inhibited mice. Collectively, these observations indicate that reduced p38 signaling in the heart promotes myocyte growth through a mechanism involving enhanced calcineurin-NFAT signaling.

Altered skeletal muscle phenotypes in calcineurin Aalpha and Abeta gene-targeted mice.

Calcineurin is a calcium-regulated serine-threonine protein phosphatase that controls developmental and inducible biological responses in diverse cell types, in part through activation of the transcription factor nuclear factor of activated T cells (NFAT). In skeletal muscle, calcineurin has been implicated in the regulation of myoblast differentiation, hypertrophy of mature myofibers, and fiber type switching in response to alterations in intracellular calcium concentration. However, considerable disagreement persists about the functional role of calcineurin signaling in each of these processes. Here we evaluated the molecular phenotypes of skeletal muscle from both calcineurin Aalpha and calcineurin Abeta gene-targeted mice. Calcineurin Aalpha was observed to be the predominant catalytic isoform expressed in nearly all skeletal muscles examined. Neither calcineurin Aalpha or Abeta null mice showed any gross growth-related alterations in skeletal muscle, nor was fiber size or number altered in glycolytic/fast muscle types. In contrast, both calcineurin Aalpha and Abeta gene-targeted mice demonstrated an alteration in myofiber number in the soleus, an oxidative/slow-type muscle. More significantly, calcineurin Aalpha and Abeta gene-targeted mice showed a dramatic down-regulation in the oxidative/slow fiber type program in multiple muscles (both slow and fast). Associated with this observation, NFAT-luciferase reporter transgenic mice showed significantly greater activity in slow fiber-containing muscles than in fast. However, only calcineurin Aalpha null mice showed a defect in NFAT nuclear occupancy or NFAT-luciferase transgene activity in vivo. Collectively, our results suggest that calcineurin signaling plays a critical role in regulating skeletal muscle fiber type switching but not hypertrophy. Our results also suggest that fiber type switching occurs through an NFAT-independent mechanism.