Exploring the underlying biology of intrinsic cardiorespiratory fitness through integrative analysis of genomic variants and muscle gene expression profiling

Cardiopulmonary Exercise Testing in a Prospective Multicenter Cohort of Older Adults

PURPOSE

Cardiorespiratory fitness (CRF) measured by peak oxygen consumption (V̇O 2peak ) declines with aging and correlates with mortality and morbidity. Cardiopulmonary exercise testing (CPET) is the criterion method to assess CRF, but its feasibility, validity, and reliability in older adults are unclear. Our objective was to design and implement a dependable, safe, and reliable CPET protocol in older adults.

METHODS

V̇O 2peak was measured by CPET, performed using treadmill exercise in 875 adults ≥70 yr in the Study of Muscle, Mobility and Aging (SOMMA). The protocol included a symptom-limited peak (maximal) exercise and two submaximal walking speeds. An adjudication process was in place to review tests for validity if they met any prespecified criteria (V̇O 2peak <12.0 mL·kg -1 ·min -1 ; maximum heart rate <100 bpm; respiratory exchange ratio <1.05 and a rating of perceived exertion <15). A subset ( N = 30) performed a repeat test to assess reproducibility.

RESULTS

CPET was safe and well tolerated, with 95.8% of participants able to complete the V̇O 2peak phase of the protocol. Only 56 (6.4%) participants had a risk alert and only two adverse events occurred: a fall and atrial fibrillation. Mean ± SD V̇O 2peak was 20.2 ± 4.8 mL·kg -1 ·min -1 , peak heart rate 142 ± 18 bpm, and peak respiratory exchange ratio 1.14 ± 0.09. Adjudication was indicated in 47 tests; 20 were evaluated as valid and 27 as invalid (18 data collection errors, 9 did not reach V̇O 2peak ). Reproducibility of V̇O 2peak was high (intraclass correlation coefficient = 0.97).

CONCLUSIONS

CPET was feasible, effective, and safe for older adults, including many with multimorbidity or frailty. These data support a broader implementation of CPET to provide insight into the role of CRF and its underlying determinants of aging and age-related conditions.

Omics-driven investigation of the biology underlying intrinsic submaximal working capacity and its trainability

Submaximal exercise capacity is an indicator of cardiorespiratory fitness with clinical and public health implications. Submaximal exercise capacity and its response to exercise programs are characterized by heritability levels of about 40%. Using physical working capacity (power output) at a heart rate of 150 beats/min (PWC150) as an indicator of submaximal exercise capacity in subjects of the HERITAGE Family Study, we have undertaken multi-omics and in silico explorations of the underlying biology of PWC150 and its response to 20 wk of endurance training. Our goal was to illuminate the biological processes and identify panels of genes associated with human variability in intrinsic PWC150 (iPWC150) and its trainability (dPWC150). Our bioinformatics approach was based on a combination of genome-wide association, skeletal muscle gene expression, and plasma proteomics and metabolomics experiments. Genes, proteins, and metabolites showing significant associations with iPWC150 or dPWC150 were further queried for the enrichment of biological pathways. We compared genotype-phenotype associations of emerging candidate genes with reported functional consequences of gene knockouts in mouse models. We investigated the associations between DNA variants and multiple muscle and cardiovascular phenotypes measured in HERITAGE subjects. Two panels of prioritized genes of biological relevance to iPWC150 (13 genes) and dPWC150 (6 genes) were identified, supporting the hypothesis that genes and pathways associated with iPWC150 are different from those underlying dPWC150. Finally, the functions of these genes and pathways suggested that human variation in submaximal exercise capacity is mainly driven by skeletal muscle morphology and metabolism and red blood cell oxygen-carrying capacity.NEW & NOTEWORTHY Multi-omics and in silico explorations of the genes and underlying biology of submaximal exercise capacity and its response to 20 wk of endurance training were undertaken. Prioritized genes were identified: 13 genes for variation in submaximal exercise capacity in the sedentary state and 5 genes for the response level to endurance training, with no overlap between them. Genes and pathways associated with submaximal exercise capacity in the sedentary state are different from those underlying trainability.

Identification of optimal feature genes in patients with thyroid associated ophthalmopathy and their relationship with immune infiltration: a bioinformatics analysis

Background

Thyroid associated ophthalmopathy (TAO) is an organ-specific autoimmune disease that has a significant impact on individuals and society. The etiology of TAO is complicated and poorly understood. Thus, the goal of this study was to use bioinformatics to look into the pathogenesis of TAO and to identify the optimum feature genes (OFGs) and immune infiltration patterns of TAO.

Methods

Firstly, the GSE58331 microarray data set was utilized to find 366 differentially expressed genes (DEGs). To find important modular genes, the dataset was evaluated using weighted gene coexpression network analysis (WGCNA). Then, the overlap genes of major module genes and DEGs were further assessed by applying three machine learning techniques to find the OFGs. The CIBERSORT approach was utilized to examine immune cell infiltration in normal and TAO samples, as well as the link between optimum characteristic genes and immune cells. Finally, the related pathways of the OFGs were predicted using single gene set enrichment analysis (ssGSEA).

Results

KLB, TBC1D2B, LINC01140, SGCG, TMEM37, and LINC01697 were the six best feature genes that were employed to create a nomogram with high predictive performance. The immune cell infiltration investigation revealed that the development of TAO may include memory B cells, T cell follicular helper cells, resting NK cells, macrophages of type M0, macrophages of type M1, resting dendritic cells, active mast cells, and neutrophils. In addition, ssGSEA results found that these characteristic genes were closely associated with lipid metabolism pathways.

Conclusion

In this research, we found that KLB, TBC1D2B, LINC01140, SGCG, TMEM37, and LINC01697 are intimately associated with the development and progression of TAO, as well as with lipid metabolism pathways.

Cardiopulmonary Exercise Testing in a Prospective Multicenter Cohort of Older Adults: The Study of Muscle, Mobility and Aging (SOMMA)

BACKGROUND

Cardiorespiratory fitness (CRF) measured by peak oxygen consumption (VO2peak) declines with aging and correlates with mortality and morbidity. Cardiopulmonary Exercise Testing (CPET) has long been the criterion method to assess CRF, but its feasibility, efficacy and reliability in older adults is unclear. The large, multicenter Study of Muscle, Mobility and Aging (SOMMA) employed CPET to evaluate the mechanisms underlying declines in mobility with aging among community-dwelling older adults. Our primary objective was to design and implement a CPET protocol in older adults that was dependable, safe, scientifically valuable, and methodologically reliable.

METHODS

CPET was performed using treadmill exercise in 875 adults ≥70 years. A composite protocol included a symptom-limited peak exercise phase and two submaximal phases to assess cardiopulmonary ventilatory indices during 1) participants' preferred walking speed and 2) at slow walking speed of 1.5 mph (0.67 m/s). An adjudication process was in place to review tests for validity if they met any prespecified criteria (VO2peak <12.0 ml/kg/min; maximum heart rate (HR) <100 bpm; respiratory exchange ratio (RER) <1.05 and a rating of perceived exertion <15). A repeat test was performed in a subset (N=30) to assess reproducibility.

RESULTS

CPET was safe and well tolerated, with 95.8% of participants able to complete the VO2peak phase of the protocol. Only 56 (6.4%) participants had a risk alert during any phase of testing and only two adverse events occurred during the peak phase: a fall and atrial fibrillation. The average ± standard deviation for VO2peak was 20.2 ± 4.8 mL/kg/min, peak HR 142 ± 18 bpm, and peak RER 1.14 ± 0.09. VO2peak and RER were slightly higher in men than women. Adjudication was indicated in 47 participants; 20 were evaluated as valid, 27 as invalid (18 had a data collection error, 9 did not reach VO2peak). Reproducibility of VO2peak was high (intraclass correlation coefficient=0.97).

CONCLUSIONS

CPET was feasible, effective and safe for community-dwelling older adults, many of whom had multimorbidity and frailty. These data support a broader implementation of CPET to provide important insight into the role of CRF and its underlying determinants in aging and age-related conditions and diseases.

Clinical Perspective

What Is New?: Performing cardiopulmonary exercise testing in a community dwelling older adult with multimorbidities or frailty is feasible and exceptionally safe under highly trained exercise physiologists and physician supervision.Reproducibility of VO2peak among community-dwelling older adults with significant clinical complexity was high (intraclass correlation coefficient=0.97).The VO2peak observed was comparable to established normative data for older adults, and adds merit to the limited data collected on VO2peak norms in older adults.What Are the Clinical Implications?: Ventilatory gas collection during clinical cardiac stress testing may be valuable to plan of care in routine management of older adults due to the important role of aerobic fitness on morbidity and mortality.Cardiopulmonary exercise testing can provide insight into the role of cardiorespiratory fitness and its underlying determinants in aging and age-related conditions and diseases.

Causal associations between cardiorespiratory fitness and type 2 diabetes

Higher cardiorespiratory fitness is associated with lower risk of type 2 diabetes. However, the causality of this relationship and the biological mechanisms that underlie it are unclear. Here, we examine genetic determinants of cardiorespiratory fitness in 450k European-ancestry individuals in UK Biobank, by leveraging the genetic overlap between fitness measured by an exercise test and resting heart rate. We identified 160 fitness-associated loci which we validated in an independent cohort, the Fenland study. Gene-based analyses prioritised candidate genes, such as CACNA1C, SCN10A, MYH11 and MYH6, that are enriched in biological processes related to cardiac muscle development and muscle contractility. In a Mendelian Randomisation framework, we demonstrate that higher genetically predicted fitness is causally associated with lower risk of type 2 diabetes independent of adiposity. Integration with proteomic data identified N-terminal pro B-type natriuretic peptide, hepatocyte growth factor-like protein and sex hormone-binding globulin as potential mediators of this relationship. Collectively, our findings provide insights into the biological mechanisms underpinning cardiorespiratory fitness and highlight the importance of improving fitness for diabetes prevention.

The HERITAGE Family Study: A Review of the Effects of Exercise Training on Cardiometabolic Health, with Insights into Molecular Transducers

The aim of the HERITAGE Family Study was to investigate individual differences in response to a standardized endurance exercise program, the role of familial aggregation, and the genetics of response levels of cardiorespiratory fitness and cardiovascular disease and diabetes risk factors. Here we summarize the findings and their potential implications for cardiometabolic health and cardiorespiratory fitness. It begins with overviews of background and planning, recruitment, testing and exercise program protocol, quality control measures, and other relevant organizational issues. A summary of findings is then provided on cardiorespiratory fitness, exercise hemodynamics, insulin and glucose metabolism, lipid and lipoprotein profiles, adiposity and abdominal visceral fat, blood levels of steroids and other hormones, markers of oxidative stress, skeletal muscle morphology and metabolic indicators, and resting metabolic rate. These summaries document the extent of the individual differences in response to a standardized and fully monitored endurance exercise program and document the importance of familial aggregation and heritability level for exercise response traits. Findings from genomic markers, muscle gene expression studies, and proteomic and metabolomics explorations are reviewed, along with lessons learned from a bioinformatics-driven analysis pipeline. The new opportunities being pursued in integrative -omics and physiology have extended considerably the expected life of HERITAGE and are being discussed in relation to the original conceptual model of the study.

DMRT2 Interacts With FXR and Improves Insulin Resistance in Adipocytes and a Mouse Model

Insulin resistance (IR) plays a critical role in cardiovascular diseases and metabolic diseases. In this study, we identified the downregulation of DMRT2 in adipose tissues from insulin-resistant subjects through bioinformatics analysis and in an insulin-resistant mouse model through experimental analysis. DMRT2 overexpression significantly attenuated HDF-induced insulin resistance and inflammation in mice. Moreover, in control and insulin-resistant differentiated mouse 3T3-L1 adipocytes, DMRT2 overexpression attenuated but DMRT2 knockdown enhanced the insulin resistance of 3T3-L1 adipocytes. DMRT2 interacted with FXR and positively regulated FXR level and transcription activity. In both control and insulin-resistant differentiated mouse 3T3-L1 adipocytes, FXR knockdown enhanced the insulin resistance and attenuated the effects of DMRT2 overexpression upon 3T3-L1 adipocyte insulin resistance. In conclusion, we identify the downregulation of DMRT2 in the insulin-resistant mouse model and cell model. DMRT2 interacts with FXR and improves insulin resistance in adipocytes.

Multiomics Approach to Precision Sports Nutrition: Limits, Challenges, and Possibilities

Most sports nutrition guidelines are based on group average responses and professional opinion. Precision nutrition for athletes aims to improve the individualization of nutrition practices to optimize long-term performance and health. This is a 2-step process that first involves the acquisition of individual-specific, science-based information using a variety of sources including lifestyle and medical histories, dietary assessment, physiological assessments from the performance lab and wearable sensors, and multiomics data from blood, urine, saliva, and stool samples. The second step consists of the delivery of science-based nutrition advice, behavior change support, and the monitoring of health and performance efficacy and benefits relative to cost. Individuals vary widely in the way they respond to exercise and nutritional interventions, and understanding why this metabolic heterogeneity exists is critical for further advances in precision nutrition. Another major challenge is the development of evidence-based individualized nutrition recommendations that are embraced and efficacious for athletes seeking the most effective enhancement of performance, metabolic recovery, and health. At this time precision sports nutrition is an emerging discipline that will require continued technological and scientific advances before this approach becomes accurate and practical for athletes and fitness enthusiasts at the small group or individual level. The costs and scientific challenges appear formidable, but what is already being achieved today in precision nutrition through multiomics and sensor technology seemed impossible just two decades ago.

Learning From Human Responses to Deconditioning Environments: Improved Understanding of the "Use It or Lose It" Principle

Physical activity, mobility or patterned mobility (i.e., exercise) is intrinsic to the functioning of Homo sapiens, and required for maintenance of health. Thus, systems such as the musculoskeletal and cardiovascular systems appear to require constant reinforcement or conditioning to maintain integrity. Loss of conditioning or development of chronic deconditioning can have multiple consequences. The study of different types of deconditioning and their prevention or reversal can offer a number of clues to the regulation of these systems and point to how deconditioning poses risk for disease development and progression. From the study of deconditioning associated with spaceflight, a condition not predicted by evolution, prolonged bedrest, protracted sedentary behavior, as well as menopause and obesity and their consequences, provide a background to better understand human heterogeneity and how physical fitness may impact the risks for chronic conditions subsequent to the deconditioning. The effectiveness of optimized physical activity and exercise protocols likely depend on the nature of the deconditioning, the sex and genetics of the individual, whether one is addressing prevention of deconditioning-associated disease or disease-associated progression, and whether it is focused on acute or chronic deconditioning associated with different forms of deconditioning. While considerable research effort has gone into preventing deconditioning, the study of the process of deconditioning and its endpoints can provide clues to the regulation of the affected systems and their contributions to human heterogeneity that have been framed by the boundary conditions of Earth during evolution and the "use it or lose it" principle of regulation. Such information regarding heterogeneity that is elaborated by the study of deconditioning environments could enhance the effectiveness of individualized interventions to prevent deconditions or rescue those who have become deconditioned.

Background Inactivity Blunts Metabolic Adaptations to Intense Short-Term Training

PURPOSE

This study determined if the level of background physical inactivity (steps per day) influences the acute and short-term adaptations to intense aerobic training.

METHODS

Sixteen untrained participants (23.6 ± 1.7 yr) completed intense (80%-90% V˙O2peak) short-term training (5 bouts of exercise over 9 d) while taking either 4767 ± 377 steps per day (n = 8; low step) or 16,048 ± 725 steps per day (n = 8; high step). At baseline and after 1 d of acute exercise and then after the short-term training (posttraining), resting metabolic responses to a high-fat meal (i.e., plasma triglyceride concentration and fat oxidation) were assessed during a 6-h high-fat tolerance test. In addition, responses during submaximal exercise were recorded both before and after training during 15 min of cycling (~79% of pretraining V˙O2peak).

RESULTS

High step displayed a reduced incremental area under the curve for postprandial plasma triglyceride concentrations by 31% after acute exercise and by 27% after short-term training compared with baseline (P < 0.05). This was accompanied by increased whole-body fat oxidation (24% and 19%; P < 0.05). Furthermore, stress during submaximal exercise as reflected by heart rate, blood lactate, and deoxygenated hemoglobin were all reduced in high step (P < 0.05), indicating classic training responses. Despite completing the same training regimen, low step showed no significant improvements in postprandial fat metabolism or any markers of stress during submaximal exercise after training (P > 0.05). However, the two groups showed a similar 7% increase in V˙O2peak (P < 0.05).

CONCLUSION

When completing an intense short-term exercise training program, decreasing daily background steps from 16,000 to approximately 5000 steps per day blunts some of the classic cardiometabolic adaptations to training. The blunting might be more pronounced regarding metabolic factors (i.e., fat oxidation and blood lactate concentration) compared with cardiovascular factors (i.e., V˙O2peak).

Human plasma proteomic profiles indicative of cardiorespiratory fitness

Maximal oxygen uptake (VO₂max) is a direct measure of human cardiorespiratory fitness and is associated with health. However, the molecular determinants of interindividual differences in baseline (intrinsic) VO₂max, and of increases of VO₂max in response to exercise training (ΔVO₂max), are largely unknown. Here, we measure ~5,000 plasma proteins using an affinity-based platform in over 650 sedentary adults before and after a 20-week endurance-exercise intervention and identify 147 proteins and 102 proteins whose plasma levels are associated with baseline VO₂max and ΔVO₂max, respectively. Addition of a protein biomarker score derived from these proteins to a score based on clinical traits improves the prediction of an individual's ΔVO₂max. We validate findings in a separate exercise cohort, further link 21 proteins to incident all-cause mortality in a community-based cohort and reproduce the specificity of ~75% of our key findings using antibody-based assays. Taken together, our data shed light on biological pathways relevant to cardiorespiratory fitness and highlight the potential additive value of protein biomarkers in identifying exercise responsiveness in humans.

Understanding the Relationship between Intrinsic Cardiorespiratory Fitness and Serum and Skeletal Muscle Metabolomics Profile

Intrinsic cardiorespiratory fitness (iCRF) indicates the CRF level in the sedentary state. However, even among sedentary individuals, a wide interindividual variability is observed in the iCRF levels, whose associated molecular characteristics are little understood. This study aimed to investigate whether serum and skeletal muscle metabolomics profiles are associated with iCRF, measured by maximal power output (MPO). Seventy sedentary young adults were submitted to venous blood sampling, a biopsy of the vastus lateralis muscle and iCRF assessment. Blood serum and muscle tissue samples were analyzed by proton nuclear magnetic resonance (¹H NMR) spectroscopy. Metabolites related to iCRF were those supported by three levels of evidence: (1) correlation with iCRF, (2) significant difference between individuals with low and high iCRF, and (3) metabolite contribution to significant pathways associated with iCRF. From 43 serum and 70 skeletal muscle analyzed metabolites, iCRF was positively associated with levels of betaine, threonine, proline, ornithine, and glutamine in serum and lactate, fumarate, NADP+, and formate in skeletal muscle. Serum betaine and ornithine and skeletal muscle lactate metabolites explained 31.2 and 16.8%, respectively, of the iCRF variability in addition to body mass. The results suggest that iCRF in young adults is positively associated with serum and skeletal muscle metabolic levels, indicative of the amino acid and carbohydrate metabolism.

Circular RNA Involvement in the Protective Effect of Human Umbilical Cord Mesenchymal Stromal Cell-Derived Extracellular Vesicles Against Hypoxia/Reoxygenation Injury in Cardiac Cells

Human umbilical cord mesenchymal stromal cell-derived extracellular vesicles (HuMSC-EVs) can repair damaged tissues. The expression profile of circular RNAs (circRNAs) provides valuable insights into the regulation of the repair process and the exploration of the repair mechanism. AC16 cardiomyocytes were exposed to hypoxia/reoxygenation (H/R) injury and subsequently cultured with or without HuMSC-EVs (Group T and Group C, respectively). High-throughput RNA sequencing was implemented for the two groups. On the basis of the transcriptome data, gene ontology (GO), Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway, and network analyses were carried out to determine the differential gene expression profiles between the two groups. After screening the circRNA database, the results were proved by quantitative real-time polymerase chain reaction. The survival rate of cardiomyocytes exposed to H/R was increased by treatment with HuMSC-EVs. RNA-seq analysis showed that 66 circRNAs were differentially expressed in cardiomyocytes in the co-cultured group. The cellular responses to hypoxia and to decreased oxygen levels were at the top of the GO upregulated list for the two groups, while the vascular endothelial growth factor signaling pathway, long-term potentiation, and the glucagon signaling pathway were at the top of the KEGG pathway upregulated list for the two groups. In the same samples, the 10 most aberrantly upregulated circRNAs were chosen for further verification of their RNA sequences. Seven of the 10 most aberrant circRNAs were significantly upregulated in the co-cultured group and in the HuMSC-EVs. Our results revealed that upregulated circRNAs were abundant during the repair of damaged cardiomyocytes by HuMSC-EVs, which provides a new perspective for the repair of H/R by HuMSC-EVs.