Acute exercise increases syndecan-1 and -4 serum concentrations

Lower levels of plasma syndecan-4 are associated with loss of body weight and fat-free mass after bariatric surgery

OBJECTIVE

Bariatric surgery induces a significant loss of both fat mass (FM) and fat-free mass (FFM). The proteoglycan receptor syndecan-4 (SDC4) plays a crucial role in adipose tissue and skeletal muscle functions. Thus, this study was performed (i) to assess plasma SDC4 levels after both Sleeve Gastrectomy (SG) and Roux-en-Y Gastric Bypass (RYGB) surgeries, and (ii) to explore potential associations with changes in body composition variables.

RESULTS

Twenty-six patients (17 females) with severe obesity underwent SG (n = 13) or RYGB (n = 13) and were followed up to 1 year (1Y). Body weight, FM, FFM, and SCD4 were measured at baseline (BL), and at week 11 (W11) and 1Y after surgery. Independently of procedure, there was a significant body weight loss at W11, with an average FM and FFM reduction of 13.7 ± 0.6 kg and 5.3 ± 0.5 kg, respectively. Participants continued to lose weight afterwards, with a total weigth loss of 38.2 ± 1.5 kg at 1Y. No associations were found at BL between SDC4 levels and any anthropometric variable; however, SDC4 levels were lower than BL at both W11 and 1Y, independently of type of surgery. Additionally, changes in SDC4 between BL and 1Y were positively correlated with weight and FFM loss during the same period.

TRIAL REGISTRATION

ClinicalTrials.gov NCT04051190 on 09/08/2019.

Exploring Syndecan-4 and MLP and Their Interaction in Primary Cardiomyocytes and H9c2 Cells

The transmembrane proteoglycan syndecan-4 is known to be involved in the hypertrophic response to pressure overload. Although multiple downstream signaling pathways have been found to be involved in this response in a syndecan-4-dependent manner, there are likely more signaling components involved. As part of a larger syndecan-4 interactome screening, we have previously identified MLP as a binding partner to the cytoplasmic tail of syndecan-4. Interestingly, many human MLP mutations have been found in patients with hypertrophic (HCM) and dilated cardiomyopathy (DCM). To gain deeper insight into the role of the syndecan-4-MLP interaction and its potential involvement in MLP-associated cardiomyopathy, we have here investigated the syndecan-4-MLP interaction in primary adult rat cardiomyocytes and the H9c2 cell line. The binding of syndecan-4 and MLP was analyzed in total lysates and subcellular fractions of primary adult rat cardiomyocytes, and baseline and differentiated H9c2 cells by immunoprecipitation. MLP and syndecan-4 localization were determined by confocal microscopy, and MLP oligomerization was determined by immunoblotting under native conditions. Syndecan-4-MLP binding, as well as MLP self-association, were also analyzed by ELISA and peptide arrays. Our results showed that MLP-WT and syndecan-4 co-localized in many subcellular compartments; however, their binding was only detected in nuclear-enriched fractions of isolated adult cardiomyocytes. In vitro, syndecan-4 bound to MLP at three sites, and this binding was reduced in some HCM-associated MLP mutations. While MLP and syndecan-4 also co-localized in many subcellular fractions of H9c2 cells, these proteins did not bind at baseline or after differentiation into cardiomyocyte-resembling cells. Independently of syndecan-4, mutated MLP proteins had an altered subcellular localization in H9c2 cells, compared to MLP-WT. The DCM- and HCM-associated MLP mutations, W4R, L44P, C58G, R64C, Y66C, K69R, G72R, and Q91L, affected the oligomerization of MLP with an increase in monomeric at the expense of trimeric and tetrameric recombinant MLP protein. Lastly, two crucial sites for MLP self-association were identified, which were reduced in most MLP mutations. Our data indicate that the syndecan-4-MLP interaction was present in nuclear-enriched fractions of isolated adult cardiomyocytes and that this interaction was disrupted by some HCM-associated MLP mutations. MLP mutations were also linked to changes in MLP oligomerization and self-association, which may be essential for its interaction with syndecan-4 and a critical molecular mechanism of MLP-associated cardiomyopathy.

Molecular insights of exercise therapy in disease prevention and treatment

Despite substantial evidence emphasizing the pleiotropic benefits of exercise for the prevention and treatment of various diseases, the underlying biological mechanisms have not been fully elucidated. Several exercise benefits have been attributed to signaling molecules that are released in response to exercise by different tissues such as skeletal muscle, cardiac muscle, adipose, and liver tissue. These signaling molecules, which are collectively termed exerkines, form a heterogenous group of bioactive substances, mediating inter-organ crosstalk as well as structural and functional tissue adaption. Numerous scientific endeavors have focused on identifying and characterizing new biological mediators with such properties. Additionally, some investigations have focused on the molecular targets of exerkines and the cellular signaling cascades that trigger adaption processes. A detailed understanding of the tissue-specific downstream effects of exerkines is crucial to harness the health-related benefits mediated by exercise and improve targeted exercise programs in health and disease. Herein, we review the current in vivo evidence on exerkine-induced signal transduction across multiple target tissues and highlight the preventive and therapeutic value of exerkine signaling in various diseases. By emphasizing different aspects of exerkine research, we provide a comprehensive overview of (i) the molecular underpinnings of exerkine secretion, (ii) the receptor-dependent and receptor-independent signaling cascades mediating tissue adaption, and (iii) the clinical implications of these mechanisms in disease prevention and treatment.

Multi-omics reveals changed energy metabolism of liver and muscle by caffeine after mice swimming

In recent years, numerous studies have investigated the effects of caffeine on exercise, and provide convincing evidence for its ergogenic effects on exercise performance. However, the precise mechanisms underlying these ergogenic effects remain unclear. In this study, an exercise swimming model was conducted to investigate the effects of orally administered with caffeine before swimming on the alterations of proteome and energy metabolome of liver and muscle after swimming. We found proteins in liver, such as S100a8, S100a9, Gabpa, Igfbp1 and Sdc4, were significantly up-regulated, while Rbp4 and Tf decreased after swimming were further down-regulated in caffeine group. The glycolysis and pentose phosphate pathways in liver and muscle were both significantly down-regulated in caffeine group. The pyruvate carboxylase and amino acid levels in liver, including cysteine, serine and tyrosine, were markedly up-regulated in caffeine group, exhibiting a strong correlation with the increased pyruvic acid and oxaloacetate levels in muscle. Moreover, caffeine significantly decreased the lactate levels in both liver and muscle after swimming, potentially benefiting exercise performance.

Neuraminidase inhibition improves endothelial function in diabetic mice

Neuraminidases cleave sialic acids from glycocalyx structures and plasma neuraminidase activity is elevated in type 2 diabetes (T2D). Therefore, we hypothesize circulating neuraminidase degrades the endothelial glycocalyx and diminishes flow-mediated dilation (FMD), whereas its inhibition restores shear mechanosensation and endothelial function in T2D settings. We found that compared with controls, subjects with T2D have higher plasma neuraminidase activity, reduced plasma nitrite concentrations, and diminished FMD. Ex vivo and in vivo neuraminidase exposure diminished FMD and reduced endothelial glycocalyx presence in mouse arteries. In cultured endothelial cells, neuraminidase reduced glycocalyx coverage. Inhalation of the neuraminidase inhibitor, zanamivir, reduced plasma neuraminidase activity, enhanced endothelial glycocalyx length, and improved FMD in diabetic mice. In humans, a single-arm trial (NCT04867707) of zanamivir inhalation did not reduce plasma neuraminidase activity, improved glycocalyx length, or enhanced FMD. Although zanamivir plasma concentrations in mice reached 225.8 ± 22.0 ng/mL, in humans were only 40.0 ± 7.2 ng/mL. These results highlight the potential of neuraminidase inhibition for ameliorating endothelial dysfunction in T2D and suggest the current Food and Drug Administration-approved inhaled dosage of zanamivir is insufficient to achieve desired outcomes in humans.NEW & NOTEWORTHY This work identifies neuraminidase as a key mediator of endothelial dysfunction in type 2 diabetes that may serve as a biomarker for impaired endothelial function and predictive of development and progression of cardiovascular pathologies associated with type 2 diabetes (T2D). Data show that intervention with the neuraminidase inhibitor zanamivir at effective plasma concentrations may represent a novel pharmacological strategy for restoring the glycocalyx and ameliorating endothelial dysfunction.

Training-induced impairment of endothelial function in track and field female athletes

Professional athletes are often exposed to high training loads that may lead to overfatigue, overreaching and overtraining that might have a detrimental effects on vascular health. We determined the effects of high training stress on endothelial function assessed by the flow-mediated dilation (FMD) and markers of glycocalyx shedding. Vascular examination as well as broad biochemical, hormonal and cardiometabolic evaluation of sprint and middle-distance female runners were performed after 2 months of preparatory training period and compared to age-matched control group of women. Female athletes presented with significantly reduced FMD (p < 0.01) and higher basal serum concentrations of hyaluronan (HA) and syndecan-1 (SDC-1) (p < 0.05 and p < 0.001, respectively), that was accompanied by significantly lower basal serum testosterone (T) and free testosterone (fT) concentrations (p < 0.05) and higher cortisol (C) concentration (p < 0.05). It resulted in significantly lower T/C and fT/C ratios in athletes when compared to controls (p < 0.01). Moreover, fT/C ratio were significantly positively correlated to FMD and negatively to HA concentrations in all studied women. Accordingly, the training load was significantly negatively correlated with T/C, fT/C and FMD and positively with the concentrations of HA and SDC-1. We concluded that young female track and field athletes subjected to physical training developed impairment of endothelial function that was associated with anabolic-catabolic hormone balance disturbances. Given that training-induced impairment of endothelial function may have a detrimental effects on vascular health, endothelial status should be regularly monitored in the time-course of training process to minimalize vascular health-risk in athletes.

The female syndecan-4−/− heart has smaller cardiomyocytes, augmented insulin/pSer473-Akt/pSer9-GSK-3β signaling, and lowered SCOP, pThr308-Akt/Akt and GLUT4 levels

Background: In cardiac muscle, the ubiquitously expressed proteoglycan syndecan-4 is involved in the hypertrophic response to pressure overload. Protein kinase Akt signaling, which is known to regulate hypertrophy, has been found to be reduced in the cardiac muscle of exercised male syndecan-4−/− mice. In contrast, we have recently found that pSer473-Akt signaling is elevated in the skeletal muscle (tibialis anterior, TA) of female syndecan-4−/− mice. To determine if the differences seen in Akt signaling are sex specific, we have presently investigated Akt signaling in the cardiac muscle of sedentary and exercised female syndecan-4−/− mice. To get deeper insight into the female syndecan-4−/− heart, alterations in cardiomyocyte size, a wide variety of different extracellular matrix components, well-known syndecan-4 binding partners and associated signaling pathways have also been investigated.

Methods: Left ventricles (LVs) from sedentary and exercise trained female syndecan-4−/− and WT mice were analyzed by immunoblotting and real-time PCR. Cardiomyocyte size and phosphorylated Ser473-Akt were analyzed in isolated adult cardiomyocytes from female syndecan-4−/− and WT mice by confocal imaging. LV and skeletal muscle (TA) from sedentary male syndecan-4−/− and WT mice were immunoblotted with Akt antibodies for comparison. Glucose levels were measured by a glucometer, and fasting blood serum insulin and C-peptide levels were measured by ELISA.

Results: Compared to female WT hearts, sedentary female syndecan-4−/− LV cardiomyocytes were smaller and hearts had higher levels of pSer473-Akt and its downstream target pSer9-GSK-3β. The pSer473-Akt inhibitory phosphatase PHLPP1/SCOP was lowered, which may be in response to the elevated serum insulin levels found in the female syndecan-4−/− mice. We also observed lowered levels of pThr308-Akt/Akt and GLUT4 in the female syndecan-4−/− heart and an increased LRP6 level after exercise. Otherwise, few alterations were found. The pThr308-Akt and pSer473-Akt levels were unaltered in the cardiac and skeletal muscles of sedentary male syndecan-4−/− mice.

Conclusion: Our data indicate smaller cardiomyocytes, an elevated insulin/pSer473-Akt/pSer9-GSK-3β signaling pathway, and lowered SCOP, pThr308-Akt/Akt and GLUT4 levels in the female syndecan-4−/− heart. In contrast, cardiomyocyte size, and Akt signaling were unaltered in both cardiac and skeletal muscles from male syndecan-4−/− mice, suggesting important sex differences.

Exerkines in health, resilience and disease

The health benefits of exercise are well-recognized and are observed across multiple organ systems. These beneficial effects enhance overall resilience, healthspan and longevity. The molecular mechanisms that underlie the beneficial effects of exercise, however, remain poorly understood. Since the discovery in 2000 that muscle contraction releases IL-6, the number of exercise-associated signalling molecules that have been identified has multiplied. Exerkines are defined as signalling moieties released in response to acute and/or chronic exercise, which exert their effects through endocrine, paracrine and/or autocrine pathways. A multitude of organs, cells and tissues release these factors, including skeletal muscle (myokines), the heart (cardiokines), liver (hepatokines), white adipose tissue (adipokines), brown adipose tissue (baptokines) and neurons (neurokines). Exerkines have potential roles in improving cardiovascular, metabolic, immune and neurological health. As such, exerkines have potential for the treatment of cardiovascular disease, type 2 diabetes mellitus and obesity, and possibly in the facilitation of healthy ageing. This Review summarizes the importance and current state of exerkine research, prevailing challenges and future directions.

Proteomic analysis reveals exercise training induced remodelling of hepatokine secretion and uncovers syndecan-4 as a regulator of hepatic lipid metabolism

Objective

Non-alcoholic fatty liver disease (NAFLD) is linked to impaired lipid metabolism and systemic insulin resistance, which is partly mediated by altered secretion of liver proteins known as hepatokines. Regular physical activity can resolve NAFLD and improve its metabolic comorbidities, however, the effects of exercise training on hepatokine secretion and the metabolic impact of exercise-regulated hepatokines in NAFLD remain unresolved. Herein, we examined the effect of endurance exercise training on hepatocyte secreted proteins with the aim of identifying proteins that regulate metabolism and reduce NAFLD severity.

Methods

C57BL/6 mice were fed a high-fat diet for six weeks to induce NAFLD. Mice were exercise trained for a further six weeks, while the control group remained sedentary. Hepatocytes were isolated two days after the last exercise bout, and intracellular and secreted proteins were detected using label-free mass spectrometry. Hepatocyte secreted factors were applied to skeletal muscle and liver ex vivo and insulin action and fatty acid metabolism were assessed. Syndecan-4 (SDC4), identified as an exercise-responsive hepatokine, was overexpressed in the livers of mice using adeno-associated virus. Whole-body energy homeostasis was assessed by indirect calorimetry and skeletal muscle and liver metabolism was assessed using radiometric techniques.

Results

Proteomics analysis detected 2657 intracellular and 1593 secreted proteins from mouse hepatocytes. Exercise training remodelled the hepatocyte proteome, with differences in 137 intracellular and 35 secreted proteins. Bioinformatic analysis of hepatocyte secreted proteins revealed enrichment of tumour suppressive proteins and proteins involved in lipid metabolism and mitochondrial function, and suppression of oncogenes and regulators of oxidative stress. Hepatocyte secreted factors from exercise trained mice improved insulin action in skeletal muscle and increased hepatic fatty acid oxidation. Hepatocyte-specific overexpression of SDC4 reduced hepatic steatosis, which was associated with reduced hepatic fatty acid uptake, and blunted pro-inflammatory and pro-fibrotic gene expression. Treating hepatocytes with recombinant ectodomain of SDC4 (secreted form) recapitulated these effects with reduced fatty acid uptake, lipid storage and lipid droplet accumulation.

Conclusions

Remodelling of hepatokine secretion is an adaptation to regular exercise training that induces changes in metabolism in the liver and skeletal muscle. SDC4 is a novel exercise-responsive hepatokine that decreases fatty acid uptake and reduces steatosis in the liver. By understanding the proteomic changes in hepatocytes with exercise, these findings have potential for the discovery of new therapeutic targets for NAFLD.

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Exercise training remodels hepatokine secretion.

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Exercise regulated secreted factors improve insulin action in skeletal muscle.

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Syndecan-4 (SDC4) is a novel exercise-induced hepatokine.

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SDC4 reduces hepatic fatty acid uptake and hepatic steatosis.

Potential Mechanisms for How Long-Term Physical Activity May Reduce Insulin Resistance

Insulin became available for the treatment of patients with diabetes 100 years ago, and soon thereafter it became evident that the biological response to its actions differed markedly between individuals. This prompted extensive research into insulin action and resistance (IR), resulting in the universally agreed fact that IR is a core finding in patients with type 2 diabetes mellitus (T2DM). T2DM is the most prevalent form of diabetes, reaching epidemic proportions worldwide. Physical activity (PA) has the potential of improving IR and is, therefore, a cornerstone in the prevention and treatment of T2DM. Whereas most research has focused on the acute effects of PA, less is known about the effects of long-term PA on IR. Here, we describe a model of potential mechanisms behind reduced IR after long-term PA to guide further mechanistic investigations and to tailor PA interventions in the therapy of T2DM. The development of such interventions requires knowledge of normal glucose metabolism, and we briefly summarize an integrated physiological perspective on IR. We then describe the effects of long-term PA on signaling molecules involved in cellular responses to insulin, tissue-specific functions, and whole-body IR.

Human glycocalyx shedding: Systematic review and critical appraisal

BACKGROUND

The number of studies measuring breakdown products of the glycocalyx in plasma has increased rapidly during the past decade. The purpose of the present systematic review was to assess the current knowledge concerning the association between plasma concentrations of glycocalyx components and structural assessment of the endothelium.

METHODS

We performed a literature review of Pubmed to determine which glycocalyx components change in a wide variety of human diseases and conditions. We also searched for evidence of a relationship between plasma concentrations and the thickness of the endothelial glycocalyx layer as obtained by imaging methods.

RESULTS

Out of 3,454 publications, we identified 228 that met our inclusion criteria. The vast majority demonstrate an increase in plasma glycocalyx products. Sepsis and trauma are most frequently studied, and comprise approximately 40 publications. They usually report 3-4-foldt increased levels of glycocalyx degradation products, most commonly of syndecan-1. Surgery shows a variable picture. Cardiac surgery and transplantations are most likely to involve elevations of glycocalyx degradation products. Structural assessment using imaging methods show thinning of the endothelial glycocalyx layer in cardiovascular conditions and during major surgery, but thinning does not always correlate with the plasma concentrations of glycocalyx products. The few structural assessments performed do not currently support that capillary permeability is increased when the plasma levels of glycocalyx fragments in plasma are increased.

CONCLUSIONS

Shedding of glycocalyx components is a ubiquitous process that occurs during both acute and chronic inflammation with no sensitivity or specificity for a specific disease or condition.

Circulating Levels of the Heparan Sulfate Proteoglycan Syndecan-4 Positively Associate with Blood Pressure in Healthy Premenopausal Women

Syndecans (SDCs) are transmembrane proteins that are present on most cell types where they play a role in multiple physiological processes, including cell-matrix adhesion and inflammation. Growing evidence suggests that elevated levels of both shed SDC1 and SDC4 are associated with hypertension and cardiovascular diseases, but their relationships with cardiovascular risk factors in healthy individuals are unknown. The primary objective of this study was to investigate whether serum levels of SDC4 and SDC1 were associated with body composition, hemodynamic parameters, pro-inflammatory cytokine concentrations, and urinary noradrenaline and dopamine levels in healthy women (17 African American and 20 European American) between the ages of 20 and 40 years old. Univariate analyses revealed only a significant (p < 0.05) inverse correlation between serum SDC1 and body fat percentage. On the other hand, serum SDC4 was positively correlated with systolic blood pressure, diastolic blood pressure, and urinary levels of noradrenaline and dopamine. Serum SDC4 was also a significant predictor of systolic blood pressure in a multivariate regression model that included fat-free mass and urinary dopamine levels as significant independent variables. The result did not change even adjusting for race. Our findings indicate that SDC4 has an important role in the physiological regulation of blood pressure.

Acute exercise-induced glycocalyx shedding does not differ between exercise modalities, but is associated with total antioxidative capacity

OBJECTIVES

Regular physical exercise is known to protect endothelial integrity. It has been proposed that acute exercise-induced changes of the (anti-)oxidative system influence early (glycocalyx shedding) and sustained endothelial activation (shedding of endothelial cells, ECs) as well as endothelial-cell repair by circulating hematopoietic stem and progenitor cells (HPCs). However, results are not conclusive and data in trained participants performing different exercise modalities is lacking.

DESIGN

Eighteen healthy, well-trained participants (9 runners, 9 cyclists; age: 29.7 ± 4.2 yrs) performed a strenuous acute exercise session consisting of 4 bouts of 4-min high-intensity with decreasing power profile and 3-min low-intensity in-between.

METHODS

Average power/speed of intense phases was 85% of the peak achieved in a previous incremental test. Before and shortly after exercise, total oxidative and antioxidative capacities (TAC), shedding of syndecan-1, heparan sulfate, hyaluronan, ECs, and circulating HPCs were investigated.

RESULTS

TAC decreased from 1.81 ± 0.42 nmol/L to 1.47 ± 0.23 nmol/L post-exercise (p = 0.010) only in runners. Exercise-induced early and sustained endothelial activation were enhanced post-exercise- syndecan-1: 103.2 ± 63.3 ng/mL to 111.3 ± 71.3 ng/mL, heparan sulfate: from 2637.9 ± 800.1 ng/mL to 3197.1 ± 1416.3 ng/mL, both p < 0.05; hyaluronan: 84.3 ± 21.8 ng/mL to 121.4 ± 29.4 ng/mL, ECs: from 6.6 ± 4.5 cells/μL to 9.5 ± 6.2 cells/μL, both p < 0.01; results were not different between exercise modalities and negatively related to TAC concentrations post-exercise. HPC proportions and self-renewal ability were negatively, while EC concentrations were positively associated with circulating hyaluronan concentrations.

CONCLUSIONS

These results highlight the importance of the antioxidative system to prevent the endothelium from acute exercise-induced vascular injury - independent of exercise modality - in well-trained participants. Endothelial-cell repair is associated with hyluronan signaling, possibly a similar mechanism as in wound repair.

Effects of a single aerobic exercise on perfused boundary region and microvascular perfusion: a field study

The endothelium and the glycocalyx play a pivotal role in regulating microvascular function and perfusion in health and critical illness. It is unknown today, whether aerobic exercise immediately affects dimensions of the endothelial surface layer (ESL) in relation to microvascular perfusion as a physiologic adaption to increased nutritional demands. This monocentric observational study was designed to determine real-time ESL and perfusion measurements of the sublingual microcirculation using sidestream dark field imaging performed in 14 healthy subjects before and after completing a 10 km trial running distance. A novel image acquisition and analysis software automatically analysed the perfused boundary region (PBR), an inverse parameter for red blood cell (RBC) penetration of the ESL, in vessels between 5 and 25 µm diameter. Microvascular perfusion was assessed by calculating RBC filling percentage. There was no significant immediate effect of exercise on PBR and RBC filling percentage. Linear regression analysis revealed a distinct association between change of PBR and change of RBC filling percentage (regression coefficient β: − 0.026; 95% confidence interval − 0.043 to − 0.009; p = 0.006). A single aerobic exercise did not induce a change of PBR or RBC filling percentage. The endothelium of the microvasculature facilitates efficient perfusion in vessels reacting with an increased endothelial surface layer.