Role of Energy Metabolism in the Thermogenic Gene Program

In murine and human brown adipose tissue (BAT), mitochondria are powerful generators of heat. Emerging evidence has suggested that the actions of mitochondria extend beyond this conventional biochemical role. In mouse BAT and cultured brown adipocytes, impaired mitochondrial respiratory capacity is accompanied by attenuated expression of Ucp1, a key thermogenic gene, implying a mitochondrial retrograde signaling. However, few have investigated this association in the context of mitochondria-nucleus communication. Using mice with adipose-specific ablation of LRPPRC, a regulator of respiratory capacity, we show that respiration-dependent retrograde signaling from mitochondria to nucleus contributes to transcriptional and metabolic reprogramming of BAT. Impaired respiratory capacity triggers down-regulation of thermogenic and oxidative genes, promoting a storage phenotype in BAT. This retrograde regulation functions by interfering with promoter-specific recruitment of PPARg. In addition, cytosolic calcium may mediate the retrograde signal from mitochondria to nucleus. These data are consistent with a model whereby BAT connects its respiratory capacity to thermogenic gene expression, which in turn contributes to determining its metabolic commitment. Additionally, we find that augmented respiratory capacity activates the thermogenic gene program in inguinal (subcutaneous) white adipose tissue (IWAT) from adipose-specific LRPPRC transgenic mice. When fed a high-fat diet at thermoneutrality, these mice exhibit metabolic improvements as shown by reduced fat mass and improved insulin sensitivity. Furthermore, there is increased recruitment of brown-like adipocytes in IWAT and thus energy expenditure is significantly increased, providing a potential explanation for protection from obesity. These data suggest that augmented respiratory capacity promotes ‘browning’ of IWAT, which has beneficial effects on obesity and diabetes

Role of Energy Metabolism in the Brown Fat Gene Program

In murine and human brown adipose tissue (BAT), mitochondria are powerful generators of heat that safely metabolize fat, a feature that has great promise in the fight against obesity and diabetes. Recent studies suggest that the actions of mitochondria extend beyond their conventional role as generators of heat. There is mounting evidence that impaired mitochondrial respiratory capacity is accompanied by attenuated expression of Ucp1 and other BAT-selective genes, implying that mitochondria exert transcriptional control over the brown fat gene program. In this review, we discuss the current understanding of brown fat mitochondria, their potential role in transcriptional control of the brown fat gene program, and potential strategies to treat obesity in humans by leveraging thermogenesis in brown adipocytes

OXPHOS-Mediated Induction of NAD+ Promotes Complete Oxidation of Fatty Acids and Interdicts Non-Alcoholic Fatty Liver Disease

OXPHOS is believed to play an important role in non-alcoholic fatty liver disease (NAFLD), however, precise mechanisms whereby OXPHOS influences lipid homeostasis are incompletely understood. We previously reported that ectopic expression of LRPPRC, a protein that increases cristae density and OXPHOS, promoted fatty acid oxidation in cultured primary hepatocytes. To determine the biological significance of that observation and define underlying mechanisms, we have ectopically expressed LRPPRC in mouse liver in the setting of NAFLD. Interestingly, ectopic expression of LRPPRC in mouse liver completely interdicted NAFLD, including inflammation. Consistent with mitigation of NAFLD, two markers of hepatic insulin resistance-ROS and PKCepsilon activity-were both modestly reduced. As reported by others, improvement of NAFLD was associated with improved whole-body insulin sensitivity. Regarding hepatic lipid homeostasis, the ratio of NAD+ to NADH was dramatically increased in mouse liver replete with LRPPRC. Pharmacological activators and inhibitors of the cellular respiration respectively increased and decreased the [NAD+]/[NADH] ratio, indicating respiration-mediated control of the [NAD+]/[NADH] ratio. Supporting a prominent role for NAD+, increasing the concentration of NAD+ stimulated complete oxidation of fatty acids. Importantly, NAD+ rescued impaired fatty acid oxidation in hepatocytes deficient for either OXPHOS or SIRT3. These data are consistent with a model whereby augmented hepatic OXPHOS increases NAD+, which in turn promotes complete oxidation of fatty acids and protects against NAFLD

Graphdiyne as a high-capacity lithium ion battery anode material

Using the first-principles calculations, we explored the feasibility of using graphdiyne, a 2D layer of sp and sp2 hybrid carbon networks, as lithium ion battery anodes. We found that the composite of the Li-intercalated multilayer ??-graphdiyne was C6Li7.31 and that the calculated voltage was suitable for the anode. The practical specific/volumetric capacities can reach up to 2719 mAh g-1/2032 mAh cm-3, much greater than the values of ???372 mAh g-1/???818 mAh cm -3, ???1117 mAh g-1/???1589 mAh cm-3, and ???744 mAh g-1 for graphite, graphynes, and ??-graphdiyne, respectively. Our calculations suggest that multilayer ??-graphdiyne can serve as a promising high-capacity lithium ion battery anode.open3

Mitochondrial retrograde signaling connects respiratory capacity to thermogenic gene expression

Mitochondrial respiration plays a crucial role in determining the metabolic state of brown adipose tissue (BAT), due to its direct roles in thermogenesis, as well as through additional mechanisms. Here, we show that respiration-dependent retrograde signaling from mitochondria to nucleus contributes to genetic and metabolic reprogramming of BAT. In mouse BAT, ablation of LRPPRC (LRP130), a potent regulator of mitochondrial transcription and respiratory capacity, triggers down-regulation of thermogenic genes, promoting a storage phenotype in BAT. This retrograde regulation functions by inhibiting the recruitment of PPARgamma to the regulatory elements of thermogenic genes. Reducing cytosolic Ca2+ reverses the attenuation of thermogenic genes in brown adipocytes with impaired respiratory capacity, while induction of cytosolic Ca2+ is sufficient to attenuate thermogenic gene expression, indicating that cytosolic Ca2+ mediates mitochondria-nucleus crosstalk. Our findings suggest respiratory capacity governs thermogenic gene expression and BAT function via mitochondria-nucleus communication, which in turn leads to either a thermogenic or storage mode

Nutrient sensing by the mitochondrial transcription machinery dictates oxidative phosphorylation

Sirtuin 3 (SIRT3), an important regulator of energy metabolism and lipid oxidation, is induced in fasted liver mitochondria and implicated in metabolic syndrome. In fasted liver, SIRT3-mediated increases in substrate flux depend on oxidative phosphorylation (OXPHOS), but precisely how OXPHOS meets the challenge of increased substrate oxidation in fasted liver remains unclear. Here, we show that liver mitochondria in fasting mice adapt to the demand of increased substrate oxidation by increasing their OXPHOS efficiency. In response to cAMP signaling, SIRT3 deacetylated and activated leucine-rich protein 130 (LRP130; official symbol, LRPPRC), promoting a mitochondrial transcriptional program that enhanced hepatic OXPHOS. Using mass spectrometry, we identified SIRT3-regulated lysine residues in LRP130 that generated a lysine-to-arginine (KR) mutant of LRP130 that mimics deacetylated protein. Compared with wild-type LRP130 protein, expression of the KR mutant increased mitochondrial transcription and OXPHOS in vitro. Indeed, even when SIRT3 activity was abolished, activation of mitochondrial transcription and OXPHOS by the KR mutant remained robust, further highlighting the contribution of LRP130 deacetylation to increased OXPHOS in fasted liver. These data establish a link between nutrient sensing and mitochondrial transcription that regulates OXPHOS in fasted liver and may explain how fasted liver adapts to increased substrate oxidation

KLF15 Is a Molecular Link between Endoplasmic Reticulum Stress and Insulin Resistance

Obesity places major demands on the protein folding capacity of the endoplasmic reticulum (ER), resulting in ER stress, a condition that promotes hepatic insulin resistance and steatosis. Here we identify the transcription factor, Kruppel-like factor 15 (KLF15), as an essential mediator of ER stress-induced insulin resistance in the liver. Mice with a targeted deletion of KLF15 exhibit increased hepatic ER stress, inflammation, and JNK activation compared to WT mice; however, KLF15-/- mice are protected against hepatic insulin resistance and fatty liver under high-fat feeding conditions and in response to pharmacological induction of ER stress. The mammalian target of rapamycin complex 1 (mTORC1), a key regulator of cellular energy homeostasis, has been shown to cooperate with ER stress signaling pathways to promote hepatic insulin resistance and lipid accumulation. We find that the uncoupling of ER stress and insulin resistance in KLF15-/- liver is associated with the maintenance of a low energy state characterized by decreased mTORC1 activity, increased AMPK phosphorylation and PGC-1α expression and activation of autophagy, an intracellular degradation process that enhances hepatic insulin sensitivity. Furthermore, in primary hepatocytes, KLF15 deficiency markedly inhibits activation of mTORC1 by amino acids and insulin, suggesting a mechanism by which KLF15 controls mTORC1-mediated insulin resistance. This study establishes KLF15 as an important molecular link between ER stress and insulin action

Regulation of BRCA1 stability through the tandem UBX domains of isoleucyl-tRNA synthetase 1

Aminoacyl-tRNA synthetases possess unique domains. In this study the structure of the vertebrate IARS1 and EARS1 complex reveals that vertebrate IARS1 protects the DNA repair factor BRCA1 from proteolytic degradation via its UBX-fold domain. Aminoacyl-tRNA synthetases (ARSs) have evolved to acquire various additional domains. These domains allow ARSs to communicate with other cellular proteins in order to promote non-translational functions. Vertebrate cytoplasmic isoleucyl-tRNA synthetases (IARS1s) have an uncharacterized unique domain, UNE-I. Here, we present the crystal structure of the chicken IARS1 UNE-I complexed with glutamyl-tRNA synthetase 1 (EARS1). UNE-I consists of tandem ubiquitin regulatory X (UBX) domains that interact with a distinct hairpin loop on EARS1 and protect its neighboring proteins in the multi-synthetase complex from degradation. Phosphomimetic mutation of the two serine residues in the hairpin loop releases IARS1 from the complex. IARS1 interacts with BRCA1 in the nucleus, regulates its stability by inhibiting ubiquitylation via the UBX domains, and controls DNA repair function

Efficacy and Safety of Sipjeondaebo-Tang (Shi-Quan-Da-Bu-Tang) for Chronic Fatigue Syndrome: Study Protocol for a Multicenter, Randomized, Double-Blind, Placebo-Controlled Trial

Background. Sipjeondaebo-tang (SDT), also known as Shi-Quan-Da-Bu-Tang, is a treatment for both qi and blood deficiency syndromes in traditional Korean medicine. It is also used to treat chronic fatigue syndrome (CFS) in Korea. Herein, we present the protocol for a study to assess the efficacy and safety of SDT for treating CFS. Methods. This will be a multicenter, randomized, double-blind, controlled trial with two parallel-treatment arms: an SDT group and a placebo group. Ninety-six patients with CFS aged between 19 and 65 years will be recruited from two hospitals in Korea. Participants will be randomly allocated at a ratio of 1 : 1 between the two groups. Participants will receive 3 g doses of SDT or placebo thrice daily for 8 weeks. Follow-up evaluations will be performed for 4–6 weeks after the drug administration period. The primary outcome will be the rating of participants’ fatigue symptoms using the Checklist Individual Strength questionnaire. Outcomes will be assessed at baseline, week 4, and week 8, as well as during follow-up. An efficacy evaluation and safety assessment will be performed. This study will be based on the Consolidated Standards of Reporting Trials (CONSORT) guidelines and the Standard Protocol Items: Recommendations for Interventional Trials (SPIRIT) 2013 statement. This protocol and informed consent guidelines were reviewed and approved by the institutional review board of Kyung Hee University Korean Medicine Hospital at Gangdong in the Republic of Korea (KHNMCOH 2017-06-004-001). The protocol was registered with the Clinical Research Information Service. Written informed consent will be obtained from all study participants prior to enrollment in the study. Results will be published in a peer-reviewed journal and presented at a scientific conference. Discussion. This study is expected to provide novel, accurate information regarding the 38 efficacy and safety of SDT for CFS in adults. Trial Registration. This trial is registered with https://cris.nih.go.kr; CRIS identifier (KCT0002684) registered on February 9, 2018