Exercise-induced Growth Research Articles

Reduced exercise-induced growth hormone secretion among children with attention-deficit hyperactivity disorder

PurposeAttention-deficit/hyperactivity disorder (ADHD) is typically a chronic, often lifelong condition. Data suggest that ADHD itself and its treatment may be associated with dysregulated growth, including height and BMI. The reason for this association is yet unknown. The objective of this study was to examine differences in growth hormone (GH) response to exercise between children who had received a diagnosis of ADHD and age- and gender-matched controls. We reasoned that the normal increase in circulating GH seen in response to exercise would be blunted in children with ADHD. MethodsWe recruited 13 treatment-naïve children with newly diagnosed ADHD and 14 age-matched controls (all male) and measured GH response to an exercise test in which the work was scaled to each subject's physical capability. ResultsThere was no difference in the peak heart rate achieved during exercise between controls and ADHD participants (196.6 ± 1.5 vs. 196.5 ± 2.1 bpm, respectively) and lactate response to exercise (53.8 ± 5.0 vs. 47.9 ± 3.8 mg/dl, respectively). After exercise, GH increased significantly in the control subjects (p < 0.005), while GH responses were substantially blunted in the ADHD group (p = NS) even though the work performed did not differ from controls. ConclusionsOur data suggest that GH excretion after exercise challenge in children with ADHD is impaired. This can be detected using a minimally invasive, nonpharmacologic challenge and may link ADHD with growth impairment in some children.Trial registration number:NCT00945971

Abstract 278: Aerobic exercise suppresses melanoma tumor growth via upregulating ERK5 S496 phosphorylation

Abstract Hypoxia, immune cell infiltration, and drug delivery are key elements of therapeutic efficacy in solid tumors. Each are strongly influenced by the tumor microenvironment. Identification of novel methods to change the microenvironment is needed to improve the response of solid tumors, including melanoma, to therapies like immune checkpoint blockade. We and others have demonstrated that aerobic exercise remodels tumor microenvironment in multiple tumor types. Here, we present data to suggest that this exercise-induced remodeling of the tumor microenvironment is partially dependent on modulation of ERK5 in both tumor endothelium and infiltrating immune cells. The depletion of ERK5 in tumor-associated macrophages inhibits the growth of melanoma and lung carcinoma in mouse models, and the depletion of ERK5 in keratocytes prevents tumorigenesis promoted by inflammation. Multiple reports have shown the potential therapeutic approach of both ERK5 knockdown and pharmacological kinase inhibition in regulating inflammation and tumorigenesis. Here we identify the role of ERK5 S496 phosphorylation, known to promote inflammatory signaling, as a novel mediator of exercise induced tumor microenvironment alterations. Utilizing two melanoma models, we found that aerobic exercise suppresses the growth of YUMMER 1.7 tumors but not B16F10 in mice. Consistent with this, single cell RNA sequencing revealed reductions in myeloid derived suppressor cells and a shift in T cell populations favoring a non-exhausted phenotype in YUMMER 1.7. Flow cytometry evaluation demonstrated significantly more CD8+ T cells in YUMMER 1.7, but not in B16F10, tumors from exercised mice. Interestingly, we found increased phosphorylation of ERK5 at the S496 residue when ECs were treated with serum from exercised mice ex vivo. We also found the crucial role of ERK5 S496 phosphorylation in promoting both inflammation and proliferation in ERK5 TEY motif phosphorylation (kinase activity) and transactivation-independent manner in both ECs and macrophages. We generated ERK5 S496A knock-in mice, and found that the ability of exercise to suppress YUMMER 1.7 tumor growth was completely lost in ERK5 S496A knock-in mice, suggesting that ERK5 S496 phosphorylation is a key in exercise-induced tumor growth suppression. We are currently evaluating immune cell infiltration into tumors with or without exercise in the ERK5 S496A knock-in model relative to wild type mice. Our data suggest that ERK5 S496 phosphorylation is a critical mediator of the tumor microenvironment. The often neglected role of ERK5 S496 signaling should be carefully considered in the interpretation of prior reports of ERK5 knockdown and pharmacological kinase inhibition relative to tumorigenesis. Citation Format: Hannah Savage, Sumedha Pareek, Jonghae Lee, Riccardo Ballaro, Venkatasubrahman Samanthapudi, Kyung Ae Ko, Masaki Imanishi, Sivareddy Kotla, Jun-ichi Abe, Keri Schadler. Aerobic exercise suppresses melanoma tumor growth via upregulating ERK5 S496 phosphorylation [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 278.

The Embryonic Mouse Hindbrain and Postnatal Retina as In Vivo Models to Study Angiogenesis.

Angiogenesis, the growth of new blood vessels from pre-existing ones, is a fundamental process for organ development, exercise-induced muscle growth, and wound healing, but is also associated with different diseases such as cancer and neovascular eye disease. Accordingly, elucidating the molecular and cellular mechanisms of angiogenesis has the potential to identify new therapeutic targets to stimulate new vessel formation in ischemic tissues or inhibit pathological vessel growth in disease. This chapter describes the mouse embryo hindbrain and postnatal retina as models to study physiological angiogenesis and provides detailed protocols for tissue dissection, sample staining and analysis.

Abstract 13218: CITED4 is Required for Exercise-Induced Cardiac Growth and Cardiomyogenesis in Mice

Introduction: CITED4 (CBP/p300-interacting transactivators with E [glutamic acid]/D [aspartic acid]-rich-carboxylterminal domain 4) is a transcriptional regulator which limits pathologic remodeling after ischemic and pressure overload models of cardiac stress. It is also upregulated in the heart with exercise, an effective intervention which induces physiological hypertrophy and cardiomyogenesis in adult mice. We hypothesized that CITED4 is required for exercise-induced cardiac growth and cardiomyogenesis. Methods and Results: Eight- to ten-week-old mice with cardiomyocyte-specific CITED4 knockout (C4KO) and littermate controls underwent 8 weeks of voluntary wheel running in comparison to sedentary controls. 5-Ethynyl-2′-deoxyuridine (EdU) was injected subcutaneously every two days for the first two weeks. There were no significant differences in cardiac size and function at baseline between C4KO and control mice. In control mice, running increased heart weight to tibial length ratio (HW/TL, 6.26±0.25 vs 7.37±0.75, p=0.01, n=5-9 per group), heart weight to body weight ratio (HW/BW, 4.08±0.40 vs 4.93±0.48, p=0.01), and cardiomyocyte (CM) size without affecting fractional shortening (FS), consistent with physiologic remodeling. There was also a nonsignificant trend to increased EdU+ CMs in the control exercised mice (2.96±2.34% vs 5.23±6.28%, p=0.44), suggestive of previously documented exercise-induced cardiomyogenesis. In contrast, running did not change HW/TL and CM size in C4KO mice (HW/TL, 6.44±0.48 vs 6.66±0.29, p=0.22, n= 0-13 per group) but reduced %FS (58.78±3.27 vs 53.67±4.59, p=0.03) and increased chamber size (LVIDs, 1.32±0.13 vs 1.50±0.17, p=0.032), suggesting maladaptive cardiac remodeling with exercise, confirming prior findings observed in a more extreme swim-exercise model. Rather than the expected increase, hearts from exercised C4KO mice had fewer EdU+ CMs compared to sedentary C4KO mice (3.76±2.60% vs 2.11±0.76%, p=0.05) and reduced expression of cell cycle genes Cdkn1b, Cyclin B1, Cdkn2a, and Ki-67. Conclusions: CITED4 is required for exercise-induced cardiomyogenesis, CM hypertrophy, and adaptive remodeling. CITED4 deficiency leads to maladaptive cardiac remodeling with physiologic stress.

Characterization of Exercise-Induced Myocardium Growth Using Finite Element Modeling and Bayesian Optimization.

Cardiomyocyte growth can occur in both physiological (exercised-induced) and pathological (e.g., volume overload and pressure overload) conditions leading to left ventricular (LV) hypertrophy. Studies using animal models and histology have demonstrated the growth and remodeling process at the organ level and tissue–cellular level, respectively. However, the driving factors of growth and the mechanistic link between organ, tissue, and cellular growth remains poorly understood. Computational models have the potential to bridge this gap by using constitutive models that describe the growth and remodeling process of the myocardium coupled with finite element (FE) analysis to model the biomechanics of the heart at the organ level. Using subject-specific imaging data of the LV geometry at two different time points, an FE model can be created with the inverse method to characterize the growth parameters of each subject. In this study, we developed a framework that takes in vivo cardiac magnetic resonance (CMR) imaging data of exercised porcine model and uses FE and Bayesian optimization to characterize myocardium growth in the transverse and longitudinal directions. The efficacy of this framework was demonstrated by successfully predicting growth parameters of 18 synthetic LV targeted masks which were generated from three LV porcine geometries. The framework was further used to characterize growth parameters in 4 swine subjects that had been exercised. The study suggested that exercise-induced growth in swine is prone to longitudinal cardiomyocyte growth (58.0 ± 19.6% after 6 weeks and 79.3 ± 15.6% after 12 weeks) compared to transverse growth (4.0 ± 8.0% after 6 weeks and 7.8 ± 9.4% after 12 weeks). This framework can be used to characterize myocardial growth in different phenotypes of LV hypertrophy and can be incorporated with other growth constitutive models to study different hypothetical growth mechanisms.

The Influence Of Limb Blood Flow On Muscle Growth With Different Resistance Training Protocols

Exercise-induced muscle growth may be dependent upon the baseline vascular network or the ability to increase this network through training. Given the cost of protein synthesis, the delivery of nutrients to the muscle could serve as a physiologic limiter to exercise-induced growth. PURPOSE: To determine if baseline resting blood flow or the change in resting blood flow moderates the change in muscle thickness throughout different resistance training protocols. METHODS: Forty individuals were included for analysis. Four distinct training conditions were compared throughout the upper and lower body before and after eight weeks of training: 1) 15% 1RM with no blood flow restriction (Low Load); 2) 15% 1RM with 40% of resting arterial occlusion pressure (Low Load+40%); 3) 15% 1RM with 80% of resting arterial occlusion pressure (Low Load+80%); and 4) traditional resistance training at 70% 1RM (High Load). Each limb of the participant was randomly assigned to a training condition. Blood flow was quantified by strain gauge plethysmography and muscle size was measured via ultrasound at 11 separate sites (3 in the biceps and 8 in the thighs). To examine if limb blood flow moderated the changes in muscle thickness between groups, while accounting for our within/between subject design, two-factor (condition x limb blood flow) analysis of variance was used. RESULTS: Muscle thickness increased in all conditions. Resting blood flow changed the greatest for the Low Load +80% and High Load conditions in both the upper and lower body (~0.5 ml·min·100 ml-1). There was no evidence for moderation for baseline resting limb blood flow. However, there was for the change in blood flow at the 70% site for the biceps. Those with smaller changes in resting blood flow had greater changes in muscle size following high load resistance training compared to the Low Load (β = 0.26, p = 0.0024), Low Load+40% (β = 0.21, p = 0.0022), and the Low Load+80% (β = 0.17, p = 0.038) conditions. CONCLUSIONS: The baseline vascular network seems sufficient for young individuals to mount an anabolic response. Participants who had the smallest change in blood flow in the high load condition had the greatest changes in muscle thickness compared to the other exercise conditions. The lack of moderation at other sites indicates that this finding should be interpreted with caution.

Cellular and molecular pathways controlling muscle size in response to exercise.

From the discovery of ATP and motor proteins to synaptic neurotransmitters and growth factor control of cell differentiation, skeletal muscle has provided an extreme model system in which to understand aspects of tissue function. Muscle is one of the few tissues that can undergo both increase and decrease in size during everyday life. Muscle size depends on its contractile activity, but the precise cellular and molecular pathway(s) by which the activity stimulus influences muscle size and strength remain unclear. Four correlates of muscle contraction could, in theory, regulate muscle growth: nerve-derived signals, cytoplasmic calcium dynamics, the rate of ATP consumption and physical force. Here, we summarise the evidence for and against each stimulus and what is known or remains unclear concerning their molecular signal transduction pathways and cellular effects. Skeletal muscle can grow in three ways, by generation of new syncytial fibres, addition of nuclei from muscle stem cells to existing fibres or increase in cytoplasmic volume/nucleus. Evidence suggests the latter two processes contribute to exercise-induced growth. Fibre growth requires increase in sarcolemmal surface area and cytoplasmic volume at different rates. It has long been known that high-force exercise is a particularly effective growth stimulus, but how this stimulus is sensed and drives coordinated growth that is appropriately scaled across organelles remains a mystery.

Exercise duration and cohort affect variability and longevity of the response to exercise training in California Yellowtail (Seriola dorsalis)

Five cohorts of cultured California Yellowtail (Seriola dorsalis) were used in exercise training experiments to assess the duration of exercise necessary to induce a positive growth and fitness response, quantify the variability and replicability of this response between cohorts, and track the longevity (persistence) of exercise-induced benefits following removal from the exercise stimulus. Custom-designed raceways were used to continuously exercise juvenile yellowtail at their optimal swimming speed for two, three, or four weeks following which several fitness metrics including measures of somatic growth, white muscle fiber area, metabolic rate, and feed conversion were tracked for up to 20 weeks post exercise in comparison to non-exercised controls. Within a cohort, the longest duration of exercise (4 weeks) generally had the largest and longest-lasting impact on growth, followed by the 3-week, and then the 2-week exercise regimes. However, all exercise treatments showed substantial variability in the magnitude and longevity of the response between cohorts. For example, the positive growth response (increase in mass above that of controls) of the 4-week swimming group ranged from 9.8% to 37.8% between cohorts. This variability in the exercise response between cohorts is similar in magnitude to that associated with other experimentally manipulated variables in the exercise regimes of previous studies, and thus highlights the need for additional species-specific experiments to quantify replicability of positive exercise results. In addition, the longevity of exercise-induced benefits was highly variable between cohorts and generally not retained for prolonged periods post exercise. Most notably, the exercise-induced growth response which may result from muscle hypertrophy (increase in white muscle fiber size) during exercise, subsided within weeks. Taken together, these results indicate that exercise can play an important role in the growth and fitness of S. dorsalis and other species, however the duration of the exercise, as well as the timing of exercise in the rearing process likely have important implications for optimizing exercise training for aquaculture enhancement.

Heart Rate Recovery, Blood Pressure Recovery, and 24-hour Heart Rate among Firefighters

The purpose of the present study was to examine the effects of 3 days isoenergetic high-fat/low-carbohydrate diet (HF-LC) relative to low-fat/high-carbohydrate diet (LF-HC) on the exercise-induced growth hormone (GH) response in healthy male subjects.Ten healthy young males participated in this study. Each subject consumed the HF-LC (18 ± 1% protein, 61 ± 2% fat, 21 ± 1% carbohydrate, 2720 kcal per day) for 3 consecutive days after consuming the LF-HC (18 ± 1% protein, 20 ± 1% fat, 62 ± 1% carbohydrate, 2755 kcal per day) for 3 consecutive days. After each dietary intervention period, the hormonal and metabolic responses to an acute exercise (30 min of continuous pedaling at 60% of V˙O2max) were compared. The intramyocellular lipid (IMCL) contents in the vastus lateralis, soleus, and tibialis anterior were evaluated by proton magnetic resonance spectroscopy.Serum GH concentrations increased significantly during the exercise after both the HF-LC and LF-HC periods (P < 0.05). However, the exercise-induced GH response was not significantly different between the two periods. Fat utilization and lipolytic responses during the exercise were enhanced significantly after the HF-LC period compared with the LF-HC period. IMCL content did not differ significantly in any portion of muscle after the dietary interventions.We could not show that short-term HF-LC consumption changed significantly exercise-induced GH response or IMCL content in healthy young males.

P5399microRNA-486 mediates exercise-induced cardiac growth and prevents cardiac ischemia-reperfusion injury

Abstract Background Molecules mediating exercise-induced physiological cardiac growth may be beneficial to prevent cardiac injury and remodeling. MicroRNA-486 (miR-486) is a muscle-enriched microRNA which was found to be increased in exercised heart. However, the role of miR-486 in exercise-induced cardiac growth is largely unknown. Purpose We aimed to study the function of miR-486 in exercise-induced cardiac growth, and to investigate its potential role in protection against cardiac ischemia/reperfusion (I/R) injury. Methods Male C57BL/6 adult mice were subjected to 3-week swimming exercise to induce physiological cardiac growth. Knockdown of miR-486 was performed by intramyocardial injection of miR-486 sponge to evaluate the role of miR-486 in exercise-induced cardiac growth. Moreover, intramyocardial injection of miR-486 overexpression lentivirus was performed to investigate whether miR-486 could reduce infarct size in mice suffered from acute I/R injury (30 min ligation and 24 hr reperfusion of left anterior descending coronary artery). Meanwhile, the functional role of miR-486 was evaluated in neonatal rat cardiomyocytes (NRCMs) treated with oxygen glucose deprivation/reperfusion (OGDR) using Tunel staining. Finally, function-rescue assays were performed to identify target genes of miR-486. Results Exercise significantly upregulated miR-486 in the heart, which was reduced by intramyocardial injection of miR-486 sponge. Exercise induced-cardiac growth was abolished in mice with intramyocardial injection of miR-486 sponge, as evidenced by reduced heart weight/body weight ratio and heart weight/tibia length ratio compared to control exercised-mice, suggesting a potential role of miR-486 in mediating exercise-induced cardiac growth. Meanwhile, we found that intramyocardial injection of miR-486 overexpression lentivirus was able to reduce the infarct size as determined by TTC staining. Moreover, in OGDR-induced apoptosis of NRCMs, miR-486 mimics was able to reduce cardiomyocyte apoptosis, while miR-486 inhibitor performed the opposite. Finally, PTEN and FoxO1 were identified as target genes of miR-486 in the control of cardiomyocyte apoptosis. Conclusions miR-486 mediates exercise-induced cardiac growth and protects against cardiac I/R injury. Increasing miR-486 might serve as a potential target to reduce myocardial apoptosis upon I/R injury. Acknowledgement/Funding This work was supported by the grants from National Natural Science Foundation of China 81722008, 91639101 and 81570362 to JJ Xiao, 81770401 to Y Bei

292-LB: The Exercise-Like Impacts of Conditioned Media Harvested from Cultured Dental Pulp Stem Cells on Myokine Expressions in Skeletal Muscles

Exercise improves not only glycemic control, but also other metabolic disorders in diabetic patients. Furthermore, exercise also stimulate muscle-derived secreted factors, myokines, via muscle contraction. The receptors of myokines expressed in the whole body and myokines affect autocrine, paracrine, and systemic functions for all people and patients with diabetes. In this study, we have demonstrated that there are exercise-like impacts of conditioned media from cultured dental pulp stem cells (DPSCs) on myokine expressions in skeletal muscles. DPSCs were isolated and cultured from the mandibular incisors of 6-week-old male Sprague-Dawley (SD) rats. Conditioned media from DPSCs (DPSC-CM) was collected after 24-hour culture of DPSCs in the serum-free medium and concentrated by a factor of 10. We firstly investigated the effects of DPSC-CM on exercise-induced myokines, follistatin-like 1 (Fstl1), Fractalkine, and fibroblast growth factor 21 (FGF-21) in C2C12 myotubes. DPSC-CM significantly increased the gene expressions of Fstl1 (209±16%, P&amp;lt;0.01), Fractalkine(182±41%, P&amp;lt;0.05), and FGF-21 (1021±39%, P&amp;lt;0.01) in C2C12 myotubes. To confirm these effects in vivo, we administered DPSC-CM (1.0 ml/rat) into 10 sites of unilateral hindlimb skeletal muscles of male SD rats, and examined the effects on myokine gene and protein expression. DPSC-CM significantly increased Fstl1 gene expression in the gastrocnemius muscles (477±140%, P&amp;lt;0.05). Immunohistochemical staining revealed that the expression of Fstl1 was increased in the DPSC-CM-injected gastrocnemius muscles. These results suggest that there is a novel exercise-like impact of DPSC-CM on skeletal muscles. Disclosure S. Kanada: None. E. Makino: None. N. Nakamura: None. M. Miyabe: None. M. Ito: None. M. Hata: None. T. Saiki: None. T. Minato: None. K. Miyazawa: None. S. Goto: None. T. Matsubara: None. K. Naruse: None.

Growth Hormone Concentrations in Different Body Fluids Before and After Moderate Exercise.

BackgroundGrowth hormone (GH) has many direct and indirect actions and roles including substrate regulation and priming of some cells of the immune system, and the expected aspects of growth and repair. Different concentrations in human body fluids reflect the exercise-induced growth hormone response (EIGR) after exercise. In populations such as elite athletes, the invasive nature of venous sampling is poorly accepted. Thus, this study examines possible viable alternatives such as urine and saliva samples and the GH concentration.MethodsA heterogeneous group of 11 males (age 26.0 ± 5.0 years; body mass 76.5 ± 9.3 kg; VO2peak 57.0 ± 6.0 mL kg−1 min−1) ran for 40 min on a treadmill at 5 % below their individually indentified lactate threshold pace. Samples of urine, saliva and blood were collected immediately pre- and post-test and at 30 and 60 min post-test.ResultsSalivary GH was correlated with serum pre- and post-exercise (p < 0.001); urinary GH was correlated with serum (p < 0.05). However, despite being significantly correlated, it is clear from the large differences in absolute concentration in the three media that the appearance of serum GH due to exercise is different from that of the appearance of salivary and urinary GH. This aspect of compartmental exchanges is very difficult to define and to investigate. Differences in any analyte concentration in different compartments are to be expected between different media, and hence the same medium should be used where the same ‘pattern of response’ can be tracked.ConclusionsThe results suggest that urinary and saliva sampling cannot substitute for venous sampling with respect to exercise-induced changes in GH concentration. The use of the analyses in these three areas may be appropriate for further investigation.

A 3-day high-fat/low-carbohydrate diet does not alter exercise-induced growth hormone response in healthy males

ObjectiveThe purpose of the present study was to examine the effects of 3days isoenergetic high-fat/low-carbohydrate diet (HF-LC) relative to low-fat/high-carbohydrate diet (LF-HC) on the exercise-induced growth hormone (GH) response in healthy male subjects. DesignTen healthy young males participated in this study. Each subject consumed the HF-LC (18±1% protein, 61±2% fat, 21±1% carbohydrate, 2720kcal per day) for 3 consecutive days after consuming the LF-HC (18±1% protein, 20±1% fat, 62±1% carbohydrate, 2755kcal per day) for 3 consecutive days. After each dietary intervention period, the hormonal and metabolic responses to an acute exercise (30min of continuous pedaling at 60% of V˙O2max) were compared. The intramyocellular lipid (IMCL) contents in the vastus lateralis, soleus, and tibialis anterior were evaluated by proton magnetic resonance spectroscopy. ResultsSerum GH concentrations increased significantly during the exercise after both the HF-LC and LF-HC periods (P<0.05). However, the exercise-induced GH response was not significantly different between the two periods. Fat utilization and lipolytic responses during the exercise were enhanced significantly after the HF-LC period compared with the LF-HC period. IMCL content did not differ significantly in any portion of muscle after the dietary interventions. ConclusionsWe could not show that short-term HF-LC consumption changed significantly exercise-induced GH response or IMCL content in healthy young males.

Abstract 220: miR-486 Mediates the Benefits of Exercise in Attenuating Cardiac Fibrosis

MicroRNAs (miRNAs, miRs), a novel group of small non-coding RNAs, play important roles in cardiac fibrosis. Exercise-induced physiological cardiac growth is associated with hypertrophy and proliferation of cardiomyocytes. In addition, exercise has been shown to inhibit cardiac fibrosis. However, relative little is known about whether exercise could attenuating cardiac fibrosis via targeting miRNA. miR-486 is a muscle enriched miRNAs, however, its role in heart is relative unclear. The current study aimed to investigate the role of miR-486 in exercise-induced cardiac growth in a 3-week swimming training murine model as well as in the function of cardiac fibroblasts and production of extracellular matrix (ECM) using neonatal rat cardiac fibroblasts in primary culture. Our data showed that exercised mice displayed increased about three-fold expression of miR-486 in hearts as measured by microarray analysis and qRT-PCRs. EdU proliferation assays demonstrated that miR-486 mimics decreased (5.90%±0.57% vs 4.02%±0.27% in nc-mimics vs miR-486-mimics, respectively), while miR-486 inhibitor increased the proliferation of cardiac fibroblasts in vitro (5.87%±0.16% vs 9.60%±0.58% in nc-inhibitor vs miR-486-inhibitor, respectively). Although downregulation of miR-486 had no regulatory effect on α-sma and collagen-1 gene expression in cardiac fibroblasts, overexpression of miR-486 significantly reduced the mRNA level of α-sma (1.01±0.08 vs 0.28±0.04 in nc-mimics vs miR-486-mimics, respectively) and collagen-1(1.02±0.12 vs 0.58±0.09 in nc-mimics vs miR-486-mimics, respectively), indicative of attenuated activation of fibroblasts and reduced production of ECM. These data reveal that miR-486 is essentially involved in the proliferation and activation of cardiac fibroblasts, and might be a key regulator mediating the benefit of exercise in preventing cardiac fibrosis.

Abstract 112: An Exercise-induced MicroRNA Pathway That Protects Against Apoptosis and Pathological Cardiac Dysfunction

Background: Exercise induces physiological cardiac growth and protects against adverse cardiac remodeling. microRNAs (miRNA) are important regulators in cardiovascular pathology and disease. Less is known about miRNA roles in the cardiac effects of exercise, and we investigated their roles in exercise-induced cardiac growth. Methods and Results: Based on cardiac miRNA profiling in two exercise models (swimming, running) and functional screening in neonatal rat cardiomyocytes (NRCMs), miR-222 was selected for further study. miR-222 was upregulated ~2-fold in both exercise models, pathological hypertrophic and failing hearts (p&lt;0.05). We found that ERK, JNK and p38 signal pathways are involved in FBS increasing miR-222 in NRCMs. miR-222 increased NRCM proliferation and size (p&lt;0.01) and reduced NRCM apoptosis induced by serum starvation with or without doxorubicin. Four potential miR-222 targets ( p27 , Hipk1 , Hipk2 , and Hmbox-1 ) were identified and confirmed as direct targets. siRNA knockdown (KD) of p27 or Hipk2 inhibited NRCM apoptosis. To investigate miR-222’s cardiac role in vivo , we made transgenic mice with cardiac-specific, inducible (TgI-miR-222) or constitutive (TgC-miR-222) expression of miR-222. RT-PCR showed that miR-222 is increased ~6-fold in TgI-miR-222 hearts after induction and ~10-fold in TgC-miR-222 hearts. Surprisingly, both transgenic lines have normal heart size and function, and the 4 miR-222 targets are unaffected at baseline. After ischemia-reperfusion injury (IRI), TgI-miR-222 had no difference in initial infarct size or dysfunction but were protected against adverse remodeling over the next six weeks with better function (p&lt;0.01), less cardiac fibrosis (68%, p&lt;0.05), and reduced CM apoptosis (300%, p&lt;0.05). Two weeks after TAC, TgC-miR-222 had less increase in cardiac mass (HW/TL, p&lt;0.05), better cardiac function ([[Unable to Display Character: &amp;#8710;]]32%, p&lt;0.01), reduced expression of markers of fibrosis ( Col1a1 , Col3a1 , Mmp2, p&lt;0.05 ) and apoptosis ( Caspase 1, 3, 8, p&lt;0.05). Four months after TAC, TgC-miR-222 had improved survival (p&lt;0.05) compared to wide type controls. Conclusion: Cardiac miR-222 is upregulated by exercise and protects against adverse remodeling and cardiac dysfunction after IRI or TAC.

Thyroid hormone and estrogen regulate exercise-induced growth hormone release.

Growth hormone (GH) regulates whole body metabolism, and physical exercise is the most potent stimulus to induce its secretion in humans. The mechanisms underlying GH secretion after exercise remain to be defined. The aim of this study was to elucidate the role of estrogen and pituitary type 1 deiodinase (D1) activation on exercise-induced GH secretion. Ten days after bilateral ovariectomy, animals were submitted to 20 min of treadmill exercise at 75% of maximum aerobic capacity and tissues were harvested immediately or 30 min after exercise. Non-exercised animals were used as controls. A significant increase in D1 activity occurred immediately after exercise (~60%) in sham-operated animals and GH was higher (~6-fold) 30 min after exercise. Estrogen deficient rats exhibited basal levels of GH and D1 activity comparable to those found in control rats. However, after exercise both D1 activity and serum GH levels were blunted compared to sedentary rats. To understand the potential cause-effect of D1 activation in exercise-induced GH release, we pharmacologically blocked D1 activity by propylthiouracil (PTU) injection into intact rats and submitted them to the acute exercise session. D1 inhibition blocked exercise-induced GH secretion, although basal levels were unaltered. In conclusion, estrogen deficiency impairs the induction of thyroid hormone activating enzyme D1 in the pituitary, and GH release by acute exercise. Also, acute D1 activation is essential for exercise-induced GH response.

Accommodating the cost of growth and swimming in fish-the applicability of exercise-induced growth to juvenile hapuku (Polyprion oxygeneios).

Induced-swimming can improve the growth and feed conversion efficiency of finfish aquaculture species, such as salmonids and Seriola sp., but some species, such as Atlantic cod, show no or a negative productivity response to exercise. As a possible explanation for these species-specific differences, a recent hypothesis proposed that the applicability of exercise training, as well as the exercise regime for optimal growth gain (ERopt growth), was dependent upon the size of available aerobic metabolic scope (AMS). This study aimed to test this hypothesis by measuring the growth and swimming metabolism of hapuku, Polyprion oxygeneios, to different exercise regimes and then reconciling the metabolic costs of swimming and specific dynamic action (SDA) against AMS. Two 8-week growth trials were conducted with ERs of 0.0, 0.25, 0.5, 0.75, 1, and 1.5 body lengths per second (BL s−1). Fish in the first trial showed a modest 4.8% increase in SGR over static controls in the region 0.5–0.75 BL s−1 whereas the fish in trial 2 showed no significant effect of ER on growth performance. Reconciling the SDA of hapuku with the metabolic costs of swimming showed that hapuku AMS is sufficient to support growth and swimming at all ERs. The current study therefore suggests that exercise-induced growth is independent of AMS and is driven by other factors.

Exercise-Induced growth hormone during acute sleep deprivation.

The effect of acute (24‐h) sleep deprivation on exercise‐induced growth hormone (GH) and insulin‐like growth factor‐1 (IGF‐1) was examined. Ten men (20.6 ± 1.4 years) completed two randomized 24‐h sessions including a brief, high‐intensity exercise bout following either a night of sleep (SLEEP) or (24‐h) sleep deprivation (SLD). Anaerobic performance (mean power [MP], peak power [PP], minimum power [MinP], time to peak power [TTPP], fatigue index, [FI]) and total work per sprint [TWPS]) was determined from four maximal 30‐sec Wingate sprints on a cycle ergometer. Self‐reported sleep 7 days prior to each session was similar between SLEEP and SLD sessions (7.92 ± 0.33 vs. 7.98 ± 0.39 h, P =0.656, respectively) and during the actual SLEEP session in the lab, the total amount of sleep was similar to the 7 days leading up to the lab session (7.72 ± 0.14 h vs. 7.92 ± 0.33 h, respectively) (P =0.166). No differences existed in MP, PP, MinP, TTPP, FI, TWPS, resting GH concentrations, time to reach exercise‐induced peak GH concentration (TTP), or free IGF‐1 between sessions. GH area under the curve (AUC) (825.0 ± 199.8 vs. 2212.9 ± 441.9 μg/L*min, P <0.01), exercise‐induced peak GH concentration (17.8 ± 3.7 vs. 39.6 ± 7.1 μg/L, P <0.01) and ΔGH (peak GH – resting GH) (17.2 ± 3.7 vs. 38.2 ± 7.3 μg/L, P <0.01) were significantly lower during the SLEEP versus SLD session. Our results indicate that the exercise‐induced GH response was significantly augmented in sleep‐deprived individuals.

Abstract 238: miR-222 is Necessary for Exercise-induced Cardiac Growth and Protects Against Pathological Cardiac Remodeling

Exercise induces cardiac growth, protects against adverse remodeling, and may also induce a regenerative response. Since microRNAs (miRNA) play important roles in cardiovascular disease, we investigated their role in the cardiac exercise response. We used the TaqMan rodent miRNA array to profile cardiac miRNA expressed at three weeks in two exercise models (swimming, running) compared to sedentary controls. Sixteen concordantly regulated miRNAs were identified and validated in both models, and examined for functional effects in neonatal rat ventricular cardiomyocytes (CMs). miR-222 was upregulated ~two-fold in both models and increased CM size (22%, p&lt;0.01) and proliferation markers (EdU and Ki67, p&lt;0.01). Bioinformatic and expression analyses identified four potential miR-222 targets (p27, Hipk1, Hipk2, and Hmbox-1) in CMs. These were confirmed as direct targets by luciferase assays, site-directed mutagenesis, and immunoblotting. siRNA knockdown (KD) of p27 or Hipk1 induced neonatal CM proliferation, while siRNA KD of Hmbox-1 increased CM size. To examine miR-222’s role in vivo, LNA-antimiR-222 was injected via tail vein or subcutaneously and shown to reduce cardiac miR-222 levels to 1.5% (p&lt;0.01). Untreated animals subjected to three weeks of swimming had the expected increase in heart size (15% in HW/TL, p&lt;0.05), CM size (26%, p&lt;0.05), and markers of CM proliferation (Ki67 and pHH3, p&lt;0.05). Increases in heart and CM size were unaffected by control LNA-antimiR but completely blocked by LNA-antimiR-222, while CM proliferation markers decreased (60%, p&lt;0.05). To see if miR-222 is sufficient to mediate the benefits of exercise, we made transgenic mice with cardiac-specific, regulated expression of miR-222 (Tg-miR-222). Tg-miR-222 have normal heart size and function at baseline. After ischemia-reperfusion injury (IRI), Tg-miR-222 had similar initial dysfunction but were protected against adverse remodeling over the next six weeks with better function (p&lt;0.01), less cardiac fibrosis (68%, p&lt;0.05), and increased CM proliferation markers (63%, p&lt;0.05). Conclusion: Cardiac miR-222 is upregulated by exercise, necessary for exercise-induced cardiac growth, and protects against pathological cardiac remodeling after IRI.

4weeks of high-intensity interval training does not alter the exercise-induced growth hormone response in sedentary men.

SummaryThis study determined the effects of high-intensity interval training on the exercise-induced growth hormone (GH) responses, whole body and regional fat content. Twenty-four sedentary males were randomized to either a high-intensity interval training (HIT) group or a low-intensity continuous training (LT) group. The HIT group performed intermittent exercises at 85% of , whereas the LT group performed continuous exercise for 22 min at 45% of . Before and after 4 weeks of training, hormonal and metabolic responses to acute exercise were determined. Acute exercise significantly increased GH concentrations in both groups (p < 0.05). However, the responses did not change after training period in either group. Furthermore, the training did not significantly affect intramyocellular or intrahepatic lipid content in either group. The present study indicates that 4 weeks of high-intensity interval training does not alter the exercise-induced GH responses, whole body fat mass or intramyocellular and intrahepatic lipid content in sedentary males.