Exercise-responsive phosphoproteins in the heart

Proteomic and phosphoproteomic profiling in heart failure with preserved ejection fraction (HFpEF)

Although the prevalence of heart failure with preserved ejection fraction (HFpEF) is increasing, evidence-based therapies for HFpEF remain limited, likely due to an incomplete understanding of this disease. This study sought to identify the cardiac-specific features of protein and phosphoprotein changes in a murine model of HFpEF using mass spectrometry. HFpEF mice demonstrated moderate hypertension, left ventricle (LV) hypertrophy, lung congestion and diastolic dysfunction. Proteomics analysis of the LV tissue showed that 897 proteins were differentially expressed between HFpEF and Sham mice. We observed abundant changes in sarcomeric proteins, mitochondrial-related proteins, and NAD-dependent protein deacetylase sirtuin-3 (SIRT3). Upregulated pathways by GSEA analysis were related to immune modulation and muscle contraction, while downregulated pathways were predominantly related to mitochondrial metabolism. Western blot analysis validated SIRT3 downregulated cardiac expression in HFpEF vs. Sham (0.8 ± 0.0 vs. 1.0 ± 0.0; P < 0.001). Phosphoproteomics analysis showed that 72 phosphosites were differentially regulated between HFpEF and Sham LV. Aberrant phosphorylation patterns mostly occurred in sarcomere proteins and nuclear-localized proteins associated with contractile dysfunction and cardiac hypertrophy. Seven aberrant phosphosites were observed at the z-disk binding region of titin. Additional agarose gel analysis showed that while total titin cardiac expression remained unaltered, its stiffer N2B isoform was significantly increased in HFpEF vs. Sham (0.144 ± 0.01 vs. 0.127 ± 0.01; P < 0.05). In summary, this study demonstrates marked changes in proteins related to mitochondrial metabolism and the cardiac contractile apparatus in HFpEF. We propose that SIRT3 may play a role in perpetuating these changes and may be a target for drug development in HFpEF.

Structural Alternation in Heat Shock Proteins of Activated Macrophages

The inflammatory response of macrophages is an orderly and complex process under strict regulation accompanied by drastic changes in morphology and functions. It is predicted that proteins will undergo structural changes during these finely regulated processes. However, changes in structural proteome in macrophages during the inflammatory response remain poorly characterized. In the present study, we applied limited proteolysis coupled mass spectrometry (LiP-MS) to identify proteome-wide structural changes in lipopolysaccharide (LPS)-activated macrophages. We identified 386 structure-specific proteolytic fingerprints from 230 proteins. Using the Gene Ontology (GO) biological process enrichment, we discovered that proteins with altered structures were enriched into protein folding-related terms, in which HSP60 was ranked as the most changed protein. We verified the structural changes in HSP60 by using cellular thermal shift assay (CETSA) and native CETSA. Our results showed that the thermal stability of HSP60 was enhanced in activated macrophages and formed an HSP10-less complex. In conclusion, we demonstrate that in situ structural systems biology is an effective method to characterize proteomic structural changes and reveal that the structures of chaperone proteins vary significantly during macrophage activation.

The application of proteomics in muscle exercise physiology

INTRODUCTION

Exercise offers protection from non-communicable diseases and extends healthspan by offsetting natural physiological declines that occur in older age. Striated muscle is the largest bodily organ; it underpins the capacity for physical work, and the responses of muscle to exercise convey the health benefits of a physically active lifestyle. Proteomic surveys of muscle provide a means to study the protective effects of exercise and this review summaries some key findings from literature listed in PubMed during the last 10 years that have led to new insight in muscle exercise physiology.

AREAS COVERED

'Bottom-up' analyses involving liquid-chromatography tandem mass spectrometry (LC-MS/MS) of peptide digests have become the mainstay of proteomic studies and have been applied to muscle mitochondrial fractions. Enrichment techniques for post-translational modifications, including phosphorylation, acetylation and ubiquitination, have evolved and the analysis of site-specific modifications has become a major area of interest in exercise proteomics. Finally, we consider emergent techniques for dynamic analysis of muscle proteomes that offer new insight to protein turnover and the contributions of synthesis and degradation to changes in protein abundance in response to exercise training.

EXPERT OPINION

Burgeoning methods for dynamic proteome profiling offer new opportunities to study the mechanisms of muscle adaptation.

SPEG: a key regulator of cardiac calcium homeostasis

Proper cardiac Ca2+ homeostasis is essential for normal excitation-contraction coupling. Perturbations in cardiac Ca2+ handling through altered kinase activity has been implicated in altered cardiac contractility and arrhythmogenesis. Thus, a better understanding of cardiac Ca2+ handling regulation is vital for a better understanding of various human disease processes. 'Striated muscle preferentially expressed protein kinase' (SPEG) is a member of the myosin light chain kinase family that is key for normal cardiac function. Work within the last 5 years has revealed that SPEG has a crucial role in maintaining normal cardiac Ca2+ handling through maintenance of transverse tubule formation and phosphorylation of junctional membrane complex proteins. Additionally, SPEG has been causally impacted in human genetic diseases such as centronuclear myopathy and dilated cardiomyopathy as well as in common acquired cardiovascular disease such as heart failure and atrial fibrillation. Given the rapidly emerging role of SPEG as a key cardiac Ca2+ regulator, we here present this review in order to summarize recent findings regarding the mechanisms of SPEG regulation of cardiac excitation-contraction coupling in both physiology and human disease. A better understanding of the roles of SPEG will be important for a more complete comprehension of cardiac Ca2+ regulation in physiology and disease.

Exercise and cardiac health: physiological and molecular insights

The cardiac benefits of exercise have been recognized for centuries. Studies have undisputedly shown that regular exercise is beneficial for the cardiovascular system in young, old, healthy and diseased populations. For these reasons, physical activity has been recommended worldwide for cardiovascular disease prevention and treatment. Although the benefits of exercise are clear, understanding of the molecular triggers that orchestrate these effects remains incomplete and has been a topic of intense research in recent years. Here, we provide a comprehensive review of the cardiac effects of physical activity, beginning with a brief history of exercise in cardiovascular medicine and then discussing seminal work on the physiological effects of exercise in healthy, diseased and aged hearts. Later, we revisit pioneering work on the molecular mechanisms underlying the cardiac benefits of exercise, and we conclude with our view on the translational potential of this knowledge as a powerful platform for cardiovascular disease drug discovery.

Diurnal Differences in Human Muscle Isometric Force In Vivo Are Associated with Differential Phosphorylation of Sarcomeric M-Band Proteins

We investigated whether diurnal differences in muscle force output are associated with the post-translational state of muscle proteins. Ten physically active men (mean ± SD; age 26.7 ± 3.7 y) performed experimental sessions in the morning (08:00 h) and evening (17:00 h), which were counterbalanced in order of administration and separated by at least 72 h. Knee extensor maximal voluntary isometric contraction (MVIC) force and peak rate of force development (RFD) were measured, and samples of vastus lateralis were collected immediately after exercise. MVIC force was greater in the evening (mean difference of 67 N, 10.2%; p < 0.05). Two-dimensional (2D) gel analysis encompassed 122 proteoforms and discovered 6 significant (p < 0.05; false discovery rate [FDR] = 10%) diurnal differences. Phosphopeptide analysis identified 1693 phosphopeptides and detected 140 phosphopeptides from 104 proteins that were more (p < 0.05, FDR = 22%) phosphorylated in the morning. Myomesin 2, muscle creatine kinase, and the C-terminus of titin exhibited the most robust (FDR < 10%) diurnal differences. Exercise in the morning, compared to the evening, coincided with a greater phosphorylation of M-band-associated proteins in human muscle. These protein modifications may alter the M-band structure and disrupt force transmission, thus potentially explaining the lower force output in the morning.

Effects of a titin mutation on force enhancement and force depression in mouse soleus muscles

The active isometric force produced by muscles varies with muscle length in accordance with the force-length relationship. Compared with isometric contractions at the same final length, force increases after active lengthening (force enhancement) and decreases after active shortening (force depression). In addition to cross-bridges, titin has been suggested to contribute to force enhancement and depression. Although titin is too compliant in passive muscles to contribute to active tension at short sarcomere lengths on the ascending limb and plateau of the force-length relationship, recent evidence suggests that activation increases titin stiffness. To test the hypothesis that titin plays a role in force enhancement and depression, we investigated isovelocity stretching and shortening in active and passive wild-type and mdm (muscular dystrophy with myositis) soleus muscles. Skeletal muscles from mdm mice have a small deletion in the N2A region of titin and show no increase in titin stiffness during active stretch. We found that: (1) force enhancement and depression were reduced in mdm soleus compared with wild-type muscles relative to passive force after stretch or shortening to the same final length; (2) force enhancement and force depression increased with amplitude of stretch across all activation levels in wild-type muscles; and (3) maximum shortening velocity of wild-type and mdm muscles estimated from isovelocity experiments was similar, although active stress was reduced in mdm compared with wild-type muscles. The results of this study suggest a role for titin in force enhancement and depression, which contribute importantly to muscle force during natural movements.

Striated muscle-specific serine/threonine-protein kinase beta segregates with high versus low responsiveness to endurance exercise training

Bidirectional selection for either high or low responsiveness to endurance running has created divergent rat phenotypes of high-response trainers (HRT) and low-response trainers (LRT). We conducted proteome profiling of HRT and LRT gastrocnemius of 10 female rats (body weight 279 ± 35 g; n = 5 LRT and n = 5 HRT) from generation 8 of selection. Differential analysis of soluble proteins from gastrocnemius was conducted by label-free quantitation. Genetic association studies were conducted in 384 Russian international-level athletes (age 23.8 ± 3.4 yr; 202 men and 182 women) stratified to endurance or power disciplines. Proteomic analysis encompassed 1,024 proteins, 76 of which exhibited statistically significant (P < 0.05, false discovery rate <1%) differences between HRT and LRT muscle. There was significant enrichment of enzymes involved in glycolysis/gluconeogenesis in LRT muscle but no enrichment of gene ontology phrases in HRT muscle. Striated muscle-specific serine/threonine-protein kinase-beta (SPEG-β) exhibited the greatest difference in abundance and was 2.64-fold greater (P = 0.0014) in HRT muscle. Coimmunoprecipitation identified 24 potential binding partners of SPEG-β in HRT muscle. The frequency of the G variant of the rs7564856 polymorphism that increases SPEG gene expression was significantly greater (32.9 vs. 23.8%; OR = 1.6, P = 0.009) in international-level endurance athletes (n = 258) compared with power athletes (n = 126) and was significantly associated (β = 8.345, P = 0.0048) with a greater proportion of slow-twitch fibers in vastus lateralis of female endurance athletes. Coimmunoprecipitation of SPEG-β in HRT muscle discovered putative interacting proteins that link with previously reported differences in transforming growth factor-β signaling in exercised muscle.

Mass Spectrometry-Based Analysis of Time-Resolved Proteome Quantification

The aspect of time is essential in biological processes and thus it is important to be able to monitor signaling molecules through time. Proteins are key players in cellular signaling and they respond to many stimuli and change their expression in many time-dependent processes. Mass spectrometry (MS) is an important tool for studying proteins, including their posttranslational modifications and their interaction partners-both in qualitative and quantitative ways. In order to distinguish the different trends over time, proteins, modification sites, and interacting proteins must be compared between different time points, and therefore relative quantification is preferred. In this review, the progress and challenges for MS-based analysis of time-resolved proteome dynamics are discussed. Further, aspects on model systems, technologies, sampling frequencies, and presentation of the dynamic data are discussed.

Low-intensity exercise in the prevention of cardiac insulin resistance-related inflammation and disturbances in NOS and MMP-9 regulation in fructose-fed ovariectomized rats

Exercise is important nonpharmacological treatment for improvement of insulin sensitivity in menopause. However, its effect on menopausal cardiac insulin resistance is needing further research. We investigated protective effects of low-intensity exercise on cardiac insulin signaling, inflammation, regulation of nitric oxide synthase (NOS) and matrix metalloproteinase 9 (MMP-9) in ovariectomized (OVX) Wistar rats, submitted to 10% fructose solution for 9 weeks. OVX rats were divided into control, sedentary fructose, and exercise fructose groups. Measurements of physical and biochemical characteristics were carried out to evaluate metabolic syndrome development. Messenger RNA and protein levels and phosphorylation of cardiac insulin signaling molecules, endothelial and inducible NOS (eNOS and iNOS), p65 subunit of nuclear factor κB (NFκB), tumor necrosis factor α (TNF-α), suppressor of cytokine signaling 3 (SOCS3), and MMP-9 were analyzed. Fructose increased insulin level, homeostasis model assessment (HOMA) index, and visceral adipose tissue weight, while low-intensity exercise prevented insulin level and HOMA index increase. Fructose also decreased cardiac pAkt (Ser473), peNOS (Ser1177) and increased insulin receptor substrate 1 (IRS1) phosphorylation at Ser307, pNFκB (Ser276) and NFκB and MMP-9 content, without any effect on iNOS, protein-tyrosine phosphatase 1B, TNF-α, and SOCS3. Exercise prevented changes in pIRS1 (Ser307), pAkt (Ser473), peNOS (Ser1177), pNFκB (Ser276), and NFκB expression. In addition, exercise increased pIRS1 (Tyr632), pAkt (Thr308), and eNOS expression. Low-intensity exercise prevented cardiac insulin signaling disarrangement in fructose-fed OVX rats and therefore eNOS dysfunction, as well as pro-inflammatory signaling activation, without effect on tissue remodeling, suggesting physical training as a way to reduce cardiovascular risk.

Unraveling obscurins in heart disease

Obscurins, expressed from the single OBSCN gene, are a family of giant, modular, cytoskeletal proteins that play key structural and regulatory roles in striated muscles. They were first implicated in the development of heart disease in 2007 when two missense mutations were found in a patient diagnosed with hypertrophic cardiomyopathy (HCM). Since then, the discovery of over a dozen missense, frameshift, and splicing mutations that are linked to various forms of cardiomyopathy, including HCM, dilated cardiomyopathy (DCM), and left ventricular non-compaction (LVNC), has highlighted OBSCN as a potential disease-causing gene. At this time, the functional consequences of the identified mutations remain largely elusive, and much work has yet to be done to characterize the disease mechanisms of pathological OBSCN variants. Herein, we describe the OBSCN mutations known to date, discuss their potential impact on disease development, and provide future directions in order to better understand the involvement of obscurins in heart disease.