An improvement in skeletal muscle mitochondrial capacity with short-term aerobic training is associated with changes in Tribbles 1 expression

Pulmonary rehabilitation improves exercise capacity, health-related quality of life, and cardiopulmonary function in patients with non-small cell lung cancer

BACKGROUND

Lung cancer significantly impairs exercise capacity and health-related quality of life (HRQL). Pulmonary rehabilitation (PR) has demonstrated positive effects on exercise capacity and HRQL in lung cancer patients. However, its impact on cardiopulmonary function needs further exploration. The aim of this study was to explore the effects of PR on cardiopulmonary function, exercise capacity and HRQL in patients with lung cancer.

METHODS

Patients with lung cancer were enrolled in a 12-week PR program. Each participant underwent a thorough evaluation, which included spirometry, cardiopulmonary exercise testing, respiratory muscle strength test, and evaluation of HRQL using the Chronic Obstructive Pulmonary Disease Assessment Test (CAT).

RESULTS

Fifty-six patients completed the PR program. Following PR, exercise capacity significantly improved, as evidenced by increased peak oxygen uptake and work rate (both p < 0.05). Exertional symptoms were notably reduced, including leg soreness and dyspnea at peak exercise, accompanied by a decrease in the CAT score (all p < 0.05). Furthermore, improvements in cardiopulmonary function were observed, encompassing respiratory muscle strength, ventilatory equivalent, tidal volume, stroke volume index, and cardiac index at peak exercise (all p < 0.05).

CONCLUSIONS

PR demonstrated notable enhancements in cardiopulmonary function, exertional symptoms, exercise capacity, and HRQL in patients with lung cancer.

TRIB1 regulates liver regeneration by antagonizing the NRF2-mediated antioxidant response

Robust regenerative response post liver injuries facilitates the architectural and functional recovery of the liver. Intrahepatic redox homeostasis plays a key role in liver regeneration. In the present study, we investigated the contributory role of Tribbles homolog 1 (Trib1), a pseudokinase, in liver regeneration and the underlying mechanism. We report that Trib1 expression was transiently down-regulated in animal and cell models of liver regeneration. Further analysis revealed that hepatocyte growth factor (HGF) repressed Trib1 transcription by evicting liver X receptor (LXRα) from the Trib1 promoter. Knockdown of Trib1 enhanced whereas over-expression of Trib1 suppressed liver regeneration after partial hepatectomy in mice. Of interest, regulation of liver regenerative response by Trib1 coincided with alterations of intracellular ROS levels, GSH levels, and antioxidant genes. Transcriptional assays suggested that Trib1 influenced cellular redox status by attenuating nuclear factor erythroid 2-related factor 2 (Nrf2) activity. Mechanistically, Trib1 interacted with the C-terminus of Nrf2 thus masking a potential nuclear localization signal (NLS) and blocking nuclear accumulation of Nrf2. Finally, correlation between Trib1 expression, Nrf2 nuclear localization, and cell proliferation was identified in liver specimens taken from patients with acute liver failure. In conclusion, our data unveil a novel pathway that depicts Trib1 as a critical link between intracellular redox homeostasis and cell proliferation in liver regeneration.

Aerobic training increases mitochondrial respiratory capacity in human skeletal muscle stem cells from sedentary individuals

The impact of aerobic training on human skeletal muscle cell (HSkMC) mitochondrial metabolism is a significant research gap, critical to understanding the mechanisms by which exercise augments skeletal muscle metabolism. We therefore assessed mitochondrial content and capacity in fully differentiated CD56+ HSkMCs from lean active (LA) and sedentary individuals with obesity (OS) at baseline, as well as lean/overweight sedentary individuals (LOS) at baseline and following an 18-day aerobic training intervention. Participants had in vivo skeletal muscle PCr recovery rate by 31P-MRS (mitochondrial oxidative kinetics) and cardiorespiratory fitness (VO2max) assessed at baseline. Biopsies of the vastus lateralis were performed for the isolation of skeletal muscle stem cells. LOS individuals repeated all assessments post-training. HSkMCs were evaluated for mitochondrial respiratory capacity by high resolution respirometry. Data were normalized to two indices of mitochondrial content (CS activity and OXPHOS protein expression) and a marker of total cell count (quantity of DNA).LA individuals had significantly higher VO2max than OS and LOS-Pre training; however, no differences were observed in skeletal muscle mitochondrial capacity, nor in carbohydrate- or fatty acid-supported HSkMC respiratory capacity. Aerobic training robustly increased in vivo skeletal muscle mitochondrial capacity of LOS individuals, as well as carbohydrate-supported HSkMC respiratory capacity. Indices of mitochondrial content and total cell count were similar among the groups and did not change with aerobic training.Our findings demonstrate that bioenergetic changes induced with aerobic training in skeletal muscle in vivo are retained in HSkMCs in vitro without impacting mitochondrial content, suggesting that training improves intrinsic skeletal muscle mitochondrial capacity.

Assessing mitochondrial respiration in permeabilized fibres and biomarkers for mitochondrial content in human skeletal muscle

AIM

Assessments of mitochondrial respiration and mitochondrial content are common in skeletal muscle research and exercise science. However, many sources of technical and biological variation render these analyses susceptible to error. This study aimed to better quantify the reliability of different experimental designs and/or techniques so as to assist researchers to obtain more reliable data.

METHODS

We examined the repeatability of maximal mitochondrial oxidative phosphorylation in permeabilized muscle fibres via high-resolution respirometry, and citrate synthase activity (a biomarker for mitochondrial content) in a microplate with spectrophotometery.

RESULTS

For mitochondrial respiration using permeabilized skeletal muscle fibres, the variability was reduced using three chambers and removing outliers compared to two chambers (CV reduced from 12.7% to 11.0%), and the minimal change that can be detected with 10 participants reduced from 17% to 13% according to modelling. For citrate synthase activity, the within-plate CV (3.5%) increased when the assay was repeated after 4 hours (CV = 10.2%) and 4 weeks (CV = 30.5%). The readings were correlated, but significantly different after 4 hours and 4 weeks.

CONCLUSION

This research provides evidence for important technical considerations when measuring mitochondrial respiration and content using citrate synthase activity as a biomarker. When assessing mitochondrial respiration in human skeletal muscle, the technical variability of high-resolution respirometry can be reduced by increasing technical repeats and excluding outliers, practices which are not currently common. When analysing citrate synthase activity, our results highlight the importance of analysing all samples from the same study at the same time.

An improvement in skeletal muscle mitochondrial capacity with short-term aerobic training is associated with changes in Tribbles 1 expression

Exercise training and physical activity are known to be associated with high mitochondrial content and oxidative capacity in skeletal muscle. Metabolic diseases including obesity and insulin resistance are associated with low mitochondrial capacity in skeletal muscle. Certain transcriptional factors such as PGC-1α are known to mediate the exercise response; however, the precise molecular mechanisms involved in the adaptation to exercise are not completely understood. We performed multiple measurements of mitochondrial capacity both in vivo and ex vivo in lean or overweight individuals before and after an 18-day aerobic exercise training regimen. These results were compared to lean, active individuals. Aerobic training in these individuals resulted in a marked increase in mitochondrial oxidative respiratory capacity without an appreciable increase in mitochondrial content. These adaptations were associated with robust transcriptome changes. This work also identifies the Tribbles pseudokinase 1, TRIB1, as a potential mediator of the exercise response in human skeletal muscle.

Competing tissue-specific functions for the Tribbles-1 plasma lipid associated locus

PURPOSE OF REVIEW

The pseudokinase Tribbles-1 (TRIB1) remains the focus of intense research since genome-wide association studies (GWAS) associated it with multiple cardiometabolic traits in humans, including plasma lipids and atherosclerosis. This review highlights recent advances in understanding the function of TRIB1 and what outstanding questions remain.

RECENT FINDINGS

Studies performed in a myeloid-specific Trib1 mouse model show that Trib1 contributes to foam cell formation, underscoring the importance of continued research into tissue-specific functions of TRIB1. Investigations of TRIB1 function in a 3D hepatic organoid model demonstrate that hepatic TRIB1 functions elucidated in mouse models are recapitulated in these organoid systems. Lastly, a recent study showed berberine, an existing lipid-lowering drug, to be acting via a TRIB1-dependent mechanism, highlighting both a novel regulator of TRIB1 expression and the potential of studying TRIB1 through existing therapeutics.

SUMMARY

TRIB1 remains one of the more fascinating loci to arise from cardiometabolic GWAS, given the constellation of traits it associates with. As genetic studies continue to link TRIB1 to metabolic phenotypes, more functional research on tissue-specific TRIB1, regulation of TRIB1 and its function in current therapies, as well as the reproduction of results from mice in human contexts are all necessary to increase our understanding of TRIB1 and its relevance.