Association between Cardiorespiratory Fitness and Circulating Proteins in 50-Year-Old Swedish Men and Women: a Cross-Sectional Study

Acute Exercise Increases GDF15 and Unfolded Protein Response/Integrated Stress Response in Muscle in Type 2 Diabetes

CONTEXT

Regular exercise is a key prevention strategy for obesity and type 2 diabetes (T2D). Exerkines secreted in response to exercise or recovery may contribute to improved systemic metabolism. Conversely, an impaired exerkine response to exercise and recovery may contribute to cardiometabolic diseases.

OBJECTIVE

We investigated if the exercise-induced regulation of the exerkine, growth differentiation factor 15 (GDF15) and its putative upstream regulators of the unfolded protein response (UPR)/integrated stress response (ISR) is impaired in skeletal muscle in patients with T2D compared with weight-matched glucose-tolerant men.

METHODS

Thirteen male patients with T2D and 14 age- and weight-matched overweight/obese glucose-tolerant men exercised at 70% of VO2max for 1 hour. Blood and skeletal muscle biopsies were sampled before, immediately after, and 3 hours into recovery. Serum and muscle transcript levels of GDF15 and key markers of UPR/ISR were determined. Additionally, protein/phosphorylation levels of key regulators in UPR/ISR were investigated.

RESULTS

Acute exercise increased muscle gene expression and serum GDF15 levels in both groups. In recovery, muscle expression of GDF15 decreased toward baseline, whereas serum GDF15 remained elevated. In both groups, acute exercise increased the expression of UPR/ISR markers, including ATF4, CHOP, EIF2K3 (encoding PERK), and PPP1R15A (encoding GADD34), of which only CHOP remained elevated 3 hours into recovery. Downstream molecules of the UPR/ISR including XBP1-U, XBP1-S, and EDEM1 were increased with exercise and 3 hours into recovery in both groups. The phosphorylation levels of eIF2α-Ser51, a common marker of unfolded protein response (UPR) and ISR, increased immediately after exercise in controls, but decreased 3 hours into recovery in both groups.

CONCLUSION

In conclusion, exercise-induced regulation of GDF15 and key markers of UPR/ISR are not compromised in patients with T2D compared with weight-matched controls.

Association between physical activity, growth differentiation factor 15 and bodyweight in older adults: A longitudinal mediation analysis

BACKGROUND

Late-life aging is often associated with appetite reduction and weight loss. Physical activity (PA) may prevent these processes, but the molecular mechanisms involved remain elusive. The present study investigated the putative mediating aspect of growth differentiation factor 15 (GDF-15), a stress signalling protein involved in aging, exercise and appetite control, on the association between PA and late-life-associated weight loss.

METHODS

One thousand eighty-three healthy adults (63.8% women) aged 70 years and over who participated in the Multidomain Alzheimer Preventive Trial were included. Bodyweight (kg) and PA levels (square root of metabolic equivalent of task-min/week) were assessed repeatedly from baseline to the 3-year visit, whereas plasma GDF-15 (pg/mL) was measured at the 1-year visit. Multiple linear regressions were performed to test the association between first-year mean PA level, 1-year visit GDF-15 concentration and subsequent bodyweight changes. Mediation analyses were used to investigate whether GDF-15 mediated the association between first-year mean PA levels and consecutive bodyweight changes.

RESULTS

Multiple regression analyses demonstrated that higher first-year mean PA levels significantly predicted lower GDF-15 and bodyweight at 1 year (B = -2.22; SE = 0.79; P = 0.005). In addition, higher 1-year visit GDF-15 levels were associated with faster subsequent bodyweight loss (Time × GDF-15 interaction B = -0.0004; SE = 0.0001; P = 0.003). Mediation analyses confirmed that GDF-15 mediated the association between first-year mean PA levels and subsequent bodyweight changes (mediated effect ab = 0.0018; bootstrap SE = 0.001; P < 0.05) and revealed that mean PA had no direct effect on subsequent bodyweight changes (c' = 0.006; SE = 0.008; P > 0.05).

CONCLUSIONS

This study suggests that GDF-15 may be one of the molecules mediating the link between PA and late-life weight loss, but mechanistic studies are necessary to further support the present findings.

Physical Inactivity Is Associated With Post-discharge Mortality and Re-hospitalization Risk Among Swedish Heart Failure Patients—The HARVEST-Malmö Study

Background

Several studies have examined the role of physical activity as a predictor of heart failure (HF) mortality and morbidity. Here, we aimed to evaluate the role of self-reported physical activity as an independent risk factor of post-discharge mortality and re-hospitalization in patients hospitalized for HF, as well as study the association between physical activity and 92 plasma proteins associated with cardiovascular disease (CVD).

Methods

Four-hundred-and-thirty-four patients hospitalized for HF (mean age 75 years; 32% women) were screened for physical activity derived from questionnaires in the Swedish national public health survey. The median follow-up time to death and re-hospitalization was 835 (interquartile range, 390–1,432) and 157 (43–583) days, respectively. Associations between baseline reported physical activity, mortality and re-hospitalization risk were analyzed using multivariable Cox regression analysis. Plasma samples from 295 study participants were analyzed with a proximity extension assay consisting of 92 proteins. Associations between proteins and physical activity were explored using a false discovery rate of <5%, and significant associations were taken forward to multivariate analyses.

Results

In the multivariate Cox regression model, physical inactivity, defined as physical activity time <1 h throughout the week was associated with increased risk of all-cause mortality (HR 1.71; CI95% 1.26–2.31; p = 5.9 × 10⁻⁴) as well as all-cause re-hospitalization (HR 1.27; CI95% 1.01–1.60; p = 0.038). Further, physical inactivity was associated with elevated plasma levels of Metalloproteinase inhibitor 4, Soluble interleukin 1 receptor-like 1, Elafin and Transferrin receptor protein 1, which are implicated in myocardial fibrosis, migration and apoptosis.

Conclusions

Self-reported low weekly physical activity is associated with increased risk of mortality and re-hospitalization in patients hospitalized for HF independent of traditional risk factors. Furthermore, physical inactivity was associated with elevated levels of 4 proteins linked to cardiovascular disease.

GDF15 in Appetite and Exercise: Essential Player or Coincidental Bystander?

Growth differentiation factor 15 (GDF15) has recently moved to the forefront of metabolism research. When administered pharmacologically, GDF15 reduces food intake and lowers body weight via the hindbrain-situated receptor GFRAL (glial cell-derived neurotrophic factor family receptor alpha-like). Endogenous GDF15 is a ubiquitous cellular stress signal that can be produced and secreted by a variety of cell types. Circulating levels are elevated in a series of disease states, but also in response to exogenous agents such as metformin, colchicine, AICAR, and cisplatin. Recently, exercise has emerged as a relevant intervention to interrogate GDF15 physiology. Prolonged endurance exercise increases circulating GDF15 to levels otherwise associated with certain pathological states and in response to metformin treatment. The jury is still out on whether GDF15 is a functional "exerkine" mediating organ-to-brain crosstalk or whether it is a coincidental bystander. In this review, we discuss the putative physiological implication of exercise-induced GDF15, focusing on the potential impact on appetite and metabolism.