Running performance at high running velocities is impaired but V'O(₂max) and peripheral endothelial function are preserved in IL-6⁻/⁻ mice

Acute exercise modulates Trim63 and Bmal1 in the skeletal muscle of IL-10 knockout mice

The anti-inflammatory role of physical exercise is mediated by interleukin 10 (IL-10), and their release is possibly upregulated in response to IL-6. Previous studies demonstrated that mice lacking IL-6 (IL-6 KO mice) exhibited diminished exercise tolerance, and reduced strength. Rev-erbα, a transcriptional suppressor involved in circadian rhythm, has been discovered to inhibit the expression of genes linked to bodily functions, encompassing inflammation and metabolism. It also plays a significant role in skeletal muscle and exercise performance capacity. Given the potential association between Rev-erbα and the immune system and the fact that both pathways are modulated following acute aerobic exercise, we examined the physical performance of IL-10 KO mice and analyzed the modulation of the atrophy and Rev-erbα pathways in the muscle of wild type (WT) and IL-10 KO mice following one session of acute exercise. For each phenotype, WT and IL-10 KO were divided into two subgroups (Control and Exercise). The acute exercise session started at 6 m/min, followed by 3 m/min increments every 3 min until animal exhaustion. Two hours after the end of the exercise protocol, the gastrocnemius muscle was removed and prepared for the reverse transcription-quantitative polymerase chain reaction (RT-q-PCR) and immunoblotting technique. In summary, compared to WT, the IL-10 KO animals showed lower body weight and grip strength in the baseline. The IL-10 control group presented a lower protein content of BMAL1. After the exercise protocol, the IL-10 KO group had higher mRNA levels of Trim63 (atrophy signaling pathway) and lower mRNA levels of Clock and Bmal1 (Rev-erbα signaling pathway). This is the first study showing the relationship between Rev-erbα and atrophy in IL-10 KO mice. Also, we accessed a public database that analyzed the gastrocnemius of MuRF KO mice submitted to two processes of muscle atrophy, a denervation surgery and dexamethasone (Dexa) injections. Independently of knockout, the denervation demonstrated lower Nr1d1 levels. In conclusion, IL-10 seems to be a determinant in the Rev-erbα pathway and atrophy after acute exercise, with no modulation in the baseline state.

Myoglobin deficiency impairs maximal oxygen uptake and exercise performance: a lesson from Mb-/- mice

Myoglobin (Mb) plays an important role at rest and during exercise as a reservoir of oxygen and has been suggested to regulate NO• bioavailability under hypoxic/acidic conditions. However, its ultimate role during exercise is still a subject of debate. We aimed to study the effect of Mb deficiency on maximal oxygen uptake (V ̇ O 2 max ${\dot V_{{{\mathrm{O}}_2}\max }}$ ) and exercise performance in myoglobin knockout mice (Mb-/- ) when compared to control mice (Mb+/+ ). Furthermore, we also studied NO• bioavailability, assessed as nitrite (NO2 - ) and nitrate (NO3 - ) in the heart, locomotory muscle and in plasma, at rest and during exercise at exhaustion both in Mb-/- and in Mb+/+ mice. The mice performed maximal running incremental exercise on a treadmill with whole-body gas exchange measurements. The Mb-/- mice had lower body mass, heart and hind limb muscle mass (P < 0.001). Mb-/- mice had significantly reduced maximal running performance (P < 0.001).V ̇ O 2 max ${\dot V_{{{\mathrm{O}}_2}\max }}$ expressed in ml min-1 in Mb-/ - mice was 37% lower than in Mb+/+ mice (P < 0.001) and 13% lower when expressed in ml min-1  kg body mass-1 (P = 0.001). Additionally, Mb-/- mice had significantly lower plasma, heart and locomotory muscle NO2 - levels at rest. During exercise NO2 - increased significantly in the heart and locomotory muscles of Mb-/- and Mb+/+ mice, whereas no significant changes in NO2 - were found in plasma. Our study showed that, contrary to recent suggestions, Mb deficiency significantly impairsV ̇ O 2 max ${\dot V_{{{\mathrm{O}}_2}\max }}$ and maximal running performance in mice. KEY POINTS: Myoglobin knockout mice (Mb-/- ) possess lower maximal oxygen uptake (V ̇ O 2 max ${\dot V_{{{\mathrm{O}}_2}\max }}$ ) and poorer maximal running performance than control mice (Mb+/+ ). Respiratory exchange ratio values at high running velocities in Mb-/- mice are higher than in control mice suggesting a shift in substrate utilization towards glucose metabolism in Mb-/- mice at the same running velocities. Lack of myoglobin lowers basal systemic and muscle NO• bioavailability, but does not affect exercise-induced NO2 - changes in plasma, heart and locomotory muscles. The present study demonstrates that myoglobin is of vital importance forV ̇ O 2 max ${\dot V_{{{\mathrm{O}}_2}\max }}$ and maximal running performance as well as explains why previous studies have failed to prove such a role of myoglobin when using the Mb-/- mouse model.

The Molecular Mechanisms of Fuel Utilization during Exercise

Exercise is widely recognized for its positive impact on human health and well-being. The process of utilizing substrates in skeletal muscle during exercise is intricate and governed by complex mechanisms. Carbohydrates and lipids serve as the primary fuel sources for skeletal muscle during exercise. It is now understood that fuel selection during exercise is not solely determined by physical activity itself but is also influenced by the overall metabolic state of the body. The balance between lipid and carbohydrate utilization significantly affects exercise capacity, including endurance, fatigue, and overall performance. Therefore, comprehensively understanding the regulation of substrate utilization during exercise is of utmost importance. The aim of this review is to provide an extensive overview of the current knowledge regarding the pathways involved in the regulation of substrate utilization during exercise. By synthesizing existing research, we can gain a holistic perspective on the intricate relationship between exercise, metabolism, and fuel selection. This advanced understanding has the potential to drive advancements in the field of exercise science and contribute to the development of personalized exercise strategies for individuals looking to optimize their performance and overall health.

IL-6 deletion decreased REV-ERBα protein and influenced autophagy and mitochondrial markers in the skeletal muscle after acute exercise

Interleukin 6 (IL-6) acts as a pro and anti-inflammatory cytokine, has an intense correlation with exercise intensity, and activates various pathways such as autophagy and mitochondrial unfolded protein response. Also, IL-6 is interconnected to circadian clock-related inflammation and can be suppressed by the nuclear receptor subfamily 1, group D, member 1 (Nr1d1, protein product REV-ERBα). Since IL-6 is linked to physical exercise-modulated metabolic pathways such as autophagy and mitochondrial metabolism, we investigated the relationship of IL-6 with REV-ERBα in the adaptations of these molecular pathways in response to acute intense physical exercise in skeletal muscle. The present study was divided into three experiments. In the first one, wild-type (WT) and IL-6 knockout (IL-6 KO) mice were divided into three groups: Basal time (Basal; sacrificed before the acute exercise), 1 hour (1hr post-Ex; sacrificed 1 hour after the acute exercise), and 3 hours (3hr post-Ex; sacrificed 3 hours after the acute exercise). In the second experiment, C2C12 cells received IL-6 physiological concentrations or REV-ERBα agonist, SR9009. In the last experiment, WT mice received SR9009 injections. After the protocols, the gastrocnemius muscle or the cells were collected for reverse transcription-quantitative polymerase chain reaction (RTq-PCR) and immunoblotting techniques. In summary, the downregulation of REV-ERBα, autophagic flux, and most mitochondrial genes was verified in the IL-6 KO mice independent of exercise. The WT and IL-6 KO treated with SR9009 showed an upregulation of autophagic genes. C2C12 cells receiving IL-6 did not modulate the Nr1d1 mRNA levels but upregulated the expression of some mitochondrial genes. However, when treated with SR9009, IL-6 and mitochondrial gene expression were upregulated in C2C12 cells. The autophagic flux in C2C12 suggest the participation of REV-ERBα protein in the IL-6-induced autophagy. In conclusion, the present study verified that the adaptations required through physical exercise (increases in mitochondrial content and improvement of autophagy machinery) might be intermediated by an interaction between IL-6 and REVERBα.

Role of interleukin-6 in inhibiting hepatic autophagy markers in exercised mice

BACKGROUND

Based on the crosstalk of inflammation with apoptosis, autophagy, and endoplasmic reticulum (ER) stress, the main objective of this study was to explore the role of interleukin-6 (IL-6) on genes and proteins related to these phenomena in the livers of mice submitted to acute exhaustive exercise.

METHODS

Reverse transcription-quantitative polymerase chain reaction and immunoblotting technique were used to evaluate the livers of wild-type (WT) and IL-6 knockout (KO) mice at baseline (BL) and 3 h after the acute exhaustive physical exercise (EE).

RESULTS

Compared to the WT at baseline, the IL-6 KO had lower exhaustion velocity, mRNA levels of Mtor, Ulk1, Map1lc3b, and Mapk14, and protein contents of ATG5 and p-p70S6K/p70S6K. For the WT group, the EE decreased glycemia, mRNA levels of Casp3, Mtor, Ulk1, Foxo1a, Mapk14, and Ppargc1a, and protein contents of ATG5 and p-p70S6K/p70S6K, but increased mRNA levels of Sqstm1. For the IL-6 KO group, the EE decreased glycemia, mRNA levels of Casp3 and Foxo1a, and protein contents of pAkt/Akt and Mature/Pro IL-1beta, but increased mRNA levels of Sqstm1, and protein contents of p-AMPK/AMPK.

CONCLUSION

The inhibition of the hepatic autophagy markers induced by the acute EE was attenuated in IL-6 KO mice, highlighting a new function of this cytokine.

Exhaustive acute exercise-induced ER stress is attenuated in IL-6-knockout mice

The endoplasmic reticulum (ER) stress and inflammation relationship occurs at different levels and is essential for the adequate homeostatic function of cellular systems, becoming harmful when chronically engaged. Intense physical exercise enhances serum levels of interleukin 6 (IL-6). In response to a chronic exhaustive physical exercise protocol, our research group verified an increase of the IL-6 concentration and ER stress proteins in extensor digitorium longus (EDL) and soleus. Based on these results, we hypothesized that IL-6-knockout mice would demonstrate a lower modulation in the ER stress proteins compared to the wild-type mice. To clarify the relationship between exercise-induced IL-6 increased and ER stress, we studied the effects of an acute exhaustive physical exercise protocol on the levels of ER stress proteins in the skeletal muscles of IL-6-knockout (KO) mice. The WT group displayed a higher exhaustion time compared to the IL-6 KO group. After 1 h of the acute exercise protocol, the serum levels of IL-6 and IL-10 were enhanced in the WT group. Independent of the experimental group, the CHOP and cleaved caspase 12/total caspase 12 ratio in EDL as well as ATF6 and CHOP in soleus were sensitive to the acute exercise protocol. Compared to the WT group, the oscillation patterns over time of BiP in EDL and soleus as well as of peIF2-alpha/eIF2-alpha ratio in soleus were attenuated for the IL-6 KO group. In conclusion, IL-6 seems to be related with the ER stress homeostasis, once knockout mice presented attenuation of BiP in EDL and soleus as well as of pEiF2-alpha/EiF2-alpha ratio in soleus after the acute exhaustive physical exercise protocol.

The Impact of Exercise in Rodent Models of Chronic Pain

PURPOSE OF REVIEW

Physical activity is increasingly recommended for chronic pain. In this review, we briefly survey recent, high-quality meta-analyses on the effects of exercise in human chronic pain populations, followed by a critical discussion of the rodent literature.

RECENT FINDINGS

Most meta-analytical studies on the effects of exercise in human chronic pain populations describe moderate improvements in various types of chronic pain, despite substantial variability in the outcomes reported in the primary literature. The most consistent findings suggest that while greater adherence to exercise programs produces better outcomes, there is minimal support for the superiority of one type of exercise over another. The rodent literature similarly suggests that while regular exercise reduces hypersensitivity in rodent models of chronic pain, exercise benefits do not appear to relate to either the type of injury or any particular facet of the exercise paradigm. Potential factors underlying these results are discussed, including the putative involvement of stress-induced analgesic effects associated with certain types of exercise paradigms. Exercise research using rodent models of chronic pain would benefit from increased attention to the role of stress in exercise-induced analgesia, as well as the incorporation of more clinically relevant exercise paradigms.

Role of gp130 in basal and exercise-trained skeletal muscle mitochondrial quality control

The IL-6 cytokine family activates intracellular signaling pathways through glycoprotein-130 (gp130), and this signaling has established regulatory roles in muscle glucose metabolism and proteostasis. Although the IL-6 family has been implicated as myokines regulating the muscles' metabolic response to exercise, gp130's role in mitochondrial quality control involving fission, fusion, mitophagy, and biogenesis is not well understood. Therefore, we examined gp130's role in basal and exercise-trained muscle mitochondrial quality control. Muscles from C57BL/6, skeletal muscle-specific gp130 knockout (KO) mice, and C₂C₁₂ myotubes, were examined. KO did not alter treadmill run-to-fatigue or indices of mitochondrial content [cytochrome- c oxidase (COX) activity] or biogenesis (AMPK, peroxisome proliferator-activated receptor-γ coactivator-1α, mitochondrial transcription factor A, and COX IV). KO increased mitochondrial fission 1 protein (FIS-1) while suppressing mitofusin-1 (MFN-1), which was recapitulated in myotubes after gp130 knockdown. KO induced ubiquitin-binding protein p62, Parkin, and ubiquitin in isolated mitochondria from gastrocnemius muscles. Knockdown of gp130 in myotubes suppressed STAT3 and induced accumulation of microtubule-associated protein-1 light chain 3B (LC3)-II relative to LC3-I. Suppression of myotube STAT3 did not alter FIS-1 or MFN-1. Exercise training increased muscle gp130 and suppressed STAT3. KO did not alter the exercise-training induction of COX activity, biogenesis, FIS-1, or Beclin-1. KO increased MFN-1 and suppressed 4-hydroxynonenal after exercise training. These findings suggest a role for gp130 in the modulation of mitochondrial dynamics and autophagic processes. NEW & NOTEWORTHY Although the IL-6 family of cytokines has been implicated in the regulation of skeletal muscle protein turnover and metabolism, less is understood about its role in mitochondrial quality control. We examined the glycoprotein-130 receptor in the regulation of skeletal muscle mitochondria quality control in the basal and exercise-trained states. We report that the muscle glycoprotein-130 receptor modulates basal mitochondrial dynamics and autophagic processes and is not necessary for exercise-training mitochondrial adaptations to quality control.

Endurance training-induced changes in the GH-IGF-I axis influence maximal muscle strength in previously untrained men

OBJECTIVE

In this study we have determined the effects of 20weeks of endurance running training on the GH-IGF-I axis changes in the context of the skeletal muscle performance and physical capacity level.

DESIGN

Before and after the endurance training program a maximal incremental exercise tests, a 1500m race and a muscle strength measurements were performed and the blood samples were taken to determine both resting as well as end-exercise serum growth hormone (GH), insulin-like growth hormone-I (IGF-I), insulin-like growth hormone binding protein-3 (IGFBP-3) and plasma interleukin-6 (IL-6) concentrations.

RESULTS

20weeks of endurance running training improved power output generated at the end of the maximal incremental test by 24% (P<0.012), 1500m running time by 13% (P<0.012) and maximal muscle strength by 9% (P<0.02). End-exercise IGF-I/IGFBP-3 ratio was decreased by 22% after the training (P<0.04) and the magnitude of IGF-I/IGFBP-3 ratio decrease (ΔIGF-I/IGFBP-3_ex) was 2.3 times higher after the training (P<0.04). The magnitude of the exercise-induced changes in IGFBP-3 concentration was also significantly higher (P<0.04) and there was a trend toward lower end-exercise IGF-I concentration (P=0.08) after the training. These changes were accompanied by a significantly higher (30%) end-exercise IL-6 concentration (P<0.01) as well as by a 3.4 times higher magnitude of IL-6 increase (P<0.02) after the training. Moreover, there were strong positive correlations between changes in resting serum IGF-I concentration (ΔIGF-I_res) and IGF-I/IGFBP-3 ratio (ΔIGF-I/IGFBP-3_res) and changes in muscle strength (ΔMVC) (r=0.95, P=0.0003 and r=0.90, P=0.002, respectively).

CONCLUSIONS

The training-induced changes in the components of the GH-IGF-I axis may have additive effects on skeletal muscle performance and physical capacity improvement.

Fast-to-slow shift of muscle fiber-type composition by dietary apple polyphenols in rats: Impact of the low-dose supplementation

Our previous studies demonstrated that an 8-week intake of 5% (w/w) apple polyphenol (APP) in the diet improves muscle endurance of young-adult rats. In order to identify a lower limit of the dietary contribution of APP to the effect, the experiments were designed for lower-dose supplementation (8-week feeding of 0.5% APP in AIN-93G diet) to 12-week-old male Sprague-Dawley rats. Results clearly showed that the 0.5% APP diet significantly up-regulates slower myosin-heavy-chain (MyHC) isoform ratios (IIx and IIa relative to total MyHC) and myoglobin expression in lower hind-limb muscles examined (P < 0.05). There was a trend to increased fatigue resistance detected from measurements of relative isometric plantar-flexion force torque generated by a stimulus train delivered to the tibial nerve (F(98, 1372) = 1.246, P = 0.0574). Importantly, there was no significant difference in the animal body-phenotypes or locomotor activity shown as total moving distance in light and dark periods. Therefore, the present study encourages the notion that even low APP-intake may increase the proportions of fatigue-resistant myofibers, and has promise as a strategy for modifying performance in human sports and improving function in age-related muscle atrophy.

Exercise capacity and cardiac hemodynamic response in female ApoE/LDLR(-/-) mice: a paradox of preserved V'O2max and exercise capacity despite coronary atherosclerosis

We assessed exercise performance, coronary blood flow and cardiac reserve of female ApoE/LDLR^−/− mice with advanced atherosclerosis compared with age-matched, wild-type C57BL6/J mice. Exercise capacity was assessed as whole body maximal oxygen consumption (V’O_2max), maximum running velocity (v_max) and maximum distance (DIST_max) during treadmill exercise. Cardiac systolic and diastolic function in basal conditions and in response to dobutamine (mimicking exercise-induced cardiac stress) were assessed by Magnetic Resonance Imaging (MRI) in vivo. Function of coronary circulation was assessed in isolated perfused hearts. In female ApoE/LDLR^−/− mice V’O_2max, v_max and DIST_max were not impaired as compared with C57BL6/J mice. Cardiac function at rest and systolic and diastolic cardiac reserve were also preserved in female ApoE/LDLR^−/− mice as evidenced by preserved fractional area change and similar fall in systolic and end diastolic area after dobutamine. Moreover, endothelium-dependent responses of coronary circulation induced by bradykinin (Bk) and acetylcholine (ACh) were preserved, while endothelium-independent responses induced by NO-donors were augmented in female ApoE/LDLR^−/− mice. Basal COX-2-dependent production of 6-keto-PGF_1α was increased. Concluding, we suggest that robust compensatory mechanisms in coronary circulation involving PGI₂- and NO-pathways may efficiently counterbalance coronary atherosclerosis-induced impairment in V’O_2max and exercise capacity.