Analysis of Thermogenesis Experiments with CalR

Betaine delays age-related muscle loss by mitigating Mss51-induced impairment in mitochondrial respiration via Yin Yang1

BACKGROUND

Mitochondrial dysfunction is one of the hallmarks of aging and a leading contributor to sarcopenia. Nutrients are essential for improving mitochondrial function and skeletal muscle health during the aging process. Betaine is a nutrient with potential muscle-preserving properties. However, whether and how betaine could regulate the mitochondria function in aging muscle are poorly understood. We aimed to explore the molecular target and underlying mechanism of betaine in attenuating the age-related mitochondrial dysfunction in skeletal muscle.

METHODS

Young mice (YOU, 2 months), old mice (OLD, 15 months), and old mice with betaine treatment (BET, 15 months) were fed for 12 weeks. The effects of betaine on muscle mass, strength, function, and subcellular structure of muscle fibres were assessed. RNA sequencing (RNA-seq) was conducted to identify the molecular target of betaine. The impacts of betaine on mitochondrial-related molecules, superoxide accumulation, and oxidative respiration were examined using western blotting (WB), immunofluorescence (IF) and seahorse assay. The underlying mechanism of betaine regulation on the molecular target to maintain mitochondrial function was investigated by luciferase reporter assay, chromatin immunoprecipitation and electrophoretic mobility shift assay. Adenoassociated virus transfection, succinate dehydrogenase staining (SDH), and energy expenditure assessment were performed on 20-month-old mice for validating the mechanism in vivo.

RESULTS

Betaine intervention demonstrated anti-aging effects on the muscle mass (P = 0.017), strength (P = 0.010), and running distance (P = 0.013). Mitochondrial-related markers (ATP5a, Sdha, and Uqcrc2) were 1.1- to 1.5-fold higher in BET than OLD (all P ≤ 0.036) with less wasted mitochondrial vacuoles accumulating in sarcomere. Bioinformatic analysis from RNA-seq displayed pathways related to mitochondrial respiration activity was higher enriched in BET group (NES = -0.87, FDR = 0.10). The quantitative real time PCR (qRT-PCR) revealed betaine significantly reduced the expression of a novel mitochondrial regulator, Mss51 (-24.9%, P = 0.002). In C2C12 cells, betaine restored the Mss51-mediated suppression in mitochondrial respiration proteins (all P ≤ 0.041), attenuated oxygen consumption impairment, and superoxide accumulation (by 20.7%, P = 0.001). Mechanically, betaine attenuated aging-induced repression in Yy1 mRNA expression (BET vs. OLD: 2.06 vs. 1.02, P = 0.009). Yy1 transcriptionally suppressed Mss51 mRNA expression both in vitro and in vivo. This contributed to the preservation of mitochondrial respiration, improvement for energy expenditure (P = 0.008), and delay of muscle loss during aging process.

CONCLUSIONS

Altogether, betaine transcriptionally represses Mss51 via Yy1, improving age-related mitochondrial respiration in skeletal muscle. These findings suggest betaine holds promise as a dietary supplement to delay skeletal muscle degeneration and improve age-related mitochondrial diseases.

Crosstalk between corepressor NRIP1 and cAMP signaling on adipocyte thermogenic programming

OBJECTIVES

Nuclear receptor interacting protein 1 (NRIP1) suppresses energy expenditure via repression of nuclear receptors, and its depletion markedly elevates uncoupled respiration in mouse and human adipocytes. We tested whether NRIP1 deficient adipocytes implanted into obese mice would enhance whole body metabolism. Since β-adrenergic signaling through cAMP strongly promotes adipocyte thermogenesis, we tested whether the effects of NRIP1 knock-out (NRIP1KO) require the cAMP pathway.

METHODS

NRIP1KO adipocytes were implanted in recipient high-fat diet (HFD) fed mice and metabolic cage studies conducted. The Nrip1 gene was disrupted by CRISPR in primary preadipocytes isolated from control vs adipose selective GsαKO (cAdGsαKO) mice prior to differentiation to adipocytes. Protein kinase A inhibitor was also used.

RESULTS

Implanting NRIP1KO adipocytes into HFD fed mice enhanced whole-body glucose tolerance by increasing insulin sensitivity, reducing adiposity, and enhancing energy expenditure in the recipients. NRIP1 depletion in both control and GsαKO adipocytes was equally effective in upregulating uncoupling protein 1 (UCP1) and adipocyte beiging, while β-adrenergic signaling by CL 316,243 was abolished in GsαKO adipocytes. Combining NRIP1KO with CL 316,243 treatment synergistically increased Ucp1 gene expression and increased the adipocyte subpopulation responsive to beiging. Estrogen-related receptor α (ERRα) was dispensable for UCP1 upregulation by NRIPKO.

CONCLUSIONS

The thermogenic effect of NRIP1 depletion in adipocytes causes systemic enhancement of energy expenditure when such adipocytes are implanted into obese mice. Furthermore, NRIP1KO acts independently but cooperatively with the cAMP pathway in mediating its effect on adipocyte beiging.

Liver mitochondrial cristae organizing protein MIC19 promotes energy expenditure and pedestrian locomotion by altering nucleotide metabolism

Liver mitochondria undergo architectural remodeling that maintains energy homeostasis in response to feeding and fasting. However, the specific components and molecular mechanisms driving these changes and their impact on energy metabolism remain unclear. Through comparative mouse proteomics, we found that fasting induces strain-specific mitochondrial cristae formation in the liver by upregulating MIC19, a subunit of the MICOS complex. Enforced MIC19 expression in the liver promotes cristae formation, mitochondrial respiration, and fatty acid oxidation while suppressing gluconeogenesis. Mice overexpressing hepatic MIC19 show resistance to diet-induced obesity and improved glucose homeostasis. Interestingly, MIC19 overexpressing mice exhibit elevated energy expenditure and increased pedestrian locomotion. Metabolite profiling revealed that uracil accumulates in the livers of these mice due to increased uridine phosphorylase UPP2 activity. Furthermore, uracil-supplemented diet increases locomotion in wild-type mice. Thus, MIC19-induced mitochondrial cristae formation in the liver increases uracil as a signal to promote locomotion, with protective effects against diet-induced obesity.

Indirect Calorimetry to Assess Energy Balance in Mice: Measurement and Data Analysis

Understanding the factors affecting body weight regulation requires careful measurement of food intake and metabolic rates. Modern indirect calorimetry systems are designed to record these features. Here, we describe our approach for reproducible analysis of energy balance experiments performed using indirect calorimetry. CalR, a free online web tool, calculates both instantaneous and cumulative totals for metabolic variables including food intake, energy expenditure, and energy balance making it an excellent start for analyzing energy balance experiments. Energy balance may be one of the most important metrics that CalR calculates as it provides a clear picture of metabolic trends resulting from experimental interventions. Because of the complexity of indirect calorimetry devices and the frequency of mechanical breakdowns, we place a heavy emphasis on the importance of data refinement and visualization. Plots representing energy intake or energy expenditure versus body mass or physical activity can help to identify a malfunctioning apparatus. We also introduce a critical visualization of experimental quality control: a plot of the change in energy balance versus the change in body mass, which simultaneously represents many of the essential components of indirect calorimetry. These analyses and data visualizations allow the investigator to make inferences about experimental quality control and the validity of experimental results.