Adipose and skeletal muscle thermogenesis: studies from large animals

Mild Cold Stress at Ambient Temperature Elevates Muscle Calcium Cycling and Exercise Adaptations in Obese Female Mice

CONTEXT

Housing temperature is a critical regulator of mouse metabolism and thermoneutral housing can improve model translation to humans. However, the impact of housing temperature on the ability of wheel running exercise training to rescue the detrimental effect of diet-induced obese mice is currently not fully understood.

OBJECTIVE

To investigate how housing temperature affects muscle metabolism in obese mice with regard to calcium handling and exercise training (ET) adaptations in skeletal muscle, and benefits of ET on adiposity and glucometabolic parameters.

METHODS

Lean or obese female mice were housed at standard ambient temperature (22 °C) or thermoneutrality (30 °C) with/without access to running wheels. The metabolic phenotype was investigated using glucose tolerance tests, indirect calorimetry, and body composition. Molecular muscle adaptations were measured using immunoblotting, qPCR, and spectrophotometric/fluorescent assays.

RESULTS

Obese female mice housed at 22 °C showed lower adiposity, lower circulating insulin levels, improved glucose tolerance, and elevated basal metabolic rate compared to 30 °C housing. Mice exposed to voluntary wheel running exhibited a larger fat loss and higher metabolic rate at 22 °C housing compared to thermoneutrality. In obese female mice, glucose tolerance improved after ET independent of housing temperature. Independent of diet and training, 22 °C housing increased skeletal muscle sarco(endo)plasmic reticulum Ca2+ ATPase (SERCA) activity. Additionally, housing at 22 °C elevated the induction of training-responsive muscle proteins in obese mice.

CONCLUSION

Our findings highlight that housing temperature significantly influences adiposity, insulin sensitivity, muscle physiology, and exercise adaptations in diet-induced obese female mice.

Differential expression of ADRB1 causes different responses to norepinephrine in adipocytes of Duroc-Landrace-Yorkshire pigs and min pigs

Research has shown that pigs from different regions exhibit varying responses to cold stimuli. Typically, cold stimuli induce browning of white adipose tissue mediated by adrenaline, promoting non-shivering thermogenesis. However, the molecular mechanisms underlying differential response of pig breeds to norepinephrine are unclear. The aim of this study was to investigate the differences and molecular mechanisms of the effects of norepinephrine (NE) treatment on adipocytes of Min pigs (a cold-resistant pig breed) and Duroc-Landrace-Yorkshire (DLY) pigs. Real time-qPCR, western blot, and immunofluorescence were performed following NE treatment on cell cultures of adipocytes originating from Min pigs (n = 3) and DLY pigs (n = 3) to assess the expressions of adipogenesis markers, beige fat markers, and mitochondrial biogenesis markers. The results showed that NE did not affect browning of adipocytes in DLY pigs, whereas promoted browning of adipocytes in Min pigs. Further, the expression of ADRB1 (Adrenoceptor Beta 1, ADRB1) was higher in subcutaneous adipose tissue and adipocytes of Min pigs than those of DLY pigs. Overexpression of ADRB1 in DLY pig adipocytes enhanced sensitivity to NE, exhibiting decreased adipogenesis markers, upregulated beige fat markers, and increased mitochondrial biogenesis. Conversely, adipocytes treated with ADRB1 antagonist in Min pigs resulted in decreased cellular sensitivity to NE. Further studies revealed differential CpG island methylation in ADRB1 promoter region, with lower methylation levels in Min pigs compared to DLY pigs. In conclusion, differential methylation of the ADRB1 promoter region leads to different ADRB1 expression, resulting in varying responsiveness to NE in adipocytes of two pig breeds. Our results provide new insights for further analysis of the differential cold responsiveness in pig breeds from different regions.

(-)-epicatechin treatment did not modify the thermogenic pathway in the gastrocnemius muscle of male rat offspring obeses by programming

The aim of this study was to analyse the expression of genes related to the regulation of energy metabolism in skeletal muscle tissue by comparing male offspring in two age groups [at 110 and 245 postnatal days (pnd)] from a mother with obesity induced by a high-fat diet and (-)-epicatechin (Epi) administration. Four groups of six male offspring from different litters were randomly selected for the control groups [C and offspring of mothers with maternal obesity (MO)] or Epi intervention groups. We evaluated the effect of Epi on gastrocnemius tissue by analysing the mRNA and protein expression levels of Fndc5/irisin, Pgc-1α, Ucp3, and Sln. Epi significantly increased the Pgc-1α protein in the MO group of offspring at 110 pnd (p < 0.036, MO vs. MO+Epi), while at 245 pnd, Epi increased Fndc5/irisin mRNA expression in the MO+Epi group versus the MO group (p = 0.006).No differences were detected in Fndc5/irisin, Ucp3 or Sln mRNA or protein levels (including Pgc-1α mRNA) in the offspring at 110 pnd or in Pgc-1α, Ucp3, or Sln mRNA or protein levels (including Fndc5/irisin protein) at 245 pnd among the experimental groups. In conclusion, (-)-epicatechin treatment increased Fndc5/irisin mRNA expression and Pgc-α protein levels in the gastrocnemius muscle of offspring at postnatal days 110 and 245. Furthermore, it is suggested that the flavonoid effect in a model of obesity and its impact on thermogenesis in skeletal muscle are regulated by a different pathway than Fndc5/irisin.

Chronic melatonin treatment improves obesity by inducing uncoupling of skeletal muscle SERCA-SLN mediated by CaMKII/AMPK/PGC1α pathway and mitochondrial biogenesis in female and male Zücker diabetic fatty rats

Melatonin acute treatment limits obesity of young Zücker diabetic fatty (ZDF) rats by non-shivering thermogenesis (NST). We recently showed melatonin chronically increases the oxidative status of vastus lateralis (VL) in both obese and lean adult male animals. The identification of VL skeletal muscle-based NST by uncoupling of sarcoendoplasmic reticulum Ca2+-ATPase (SERCA)- sarcolipin (SLN) prompted us to investigate whether melatonin is a SERCA-SLN calcium futile cycle uncoupling and mitochondrial biogenesis enhancer. Obese ZDF rats and lean littermates (ZL) of both sexes were subdivided into two subgroups: control (C) and 12 weeks orally melatonin treated (M) (10 mg/kg/day). Compared to the control groups, melatonin decreased the body weight gain and visceral fat in ZDF rats of both sexes. Melatonin treatment in both sex obese rats restored the VL muscle skin temperature and sensitized the thermogenic effect of acute cold exposure. Moreover, melatonin not only raised SLN protein levels in the VL of obese and lean rats of both sexes; also, the SERCA activity. Melatonin treatment increased the SERCA2 expression in obese and lean rats (both sexes), with no effects on SERCA1 expression. Melatonin increased the expression of thermogenic genes and proteins (PGC1-α, PPARγ, and NRF1). Furthermore, melatonin treatment enhanced the expression ratio of P-CaMKII/CaMKII and P-AMPK/AMPK. In addition, it rose mitochondrial biogenesis. These results provided the initial evidence that chronic oral melatonin treatment triggers the CaMKII/AMPK/PGC1α axis by upregulating SERCA2-SLN-mediated NST in ZDF diabetic rats of both sexes. This may further contribute to the body weight control and metabolic benefits of melatonin.

Hypothalamic Neuromodulation of Hypothermia in Domestic Animals

When an organism detects decreases in their core body temperature, the hypothalamus, the main thermoregulatory center, triggers compensatory responses. These responses include vasomotor changes to prevent heat loss and physiological mechanisms (e.g., shivering and non-shivering thermogenesis) for heat production. Both types of changes require the participation of peripheral thermoreceptors, afferent signaling to the spinal cord and hypothalamus, and efferent pathways to motor and/or sympathetic neurons. The present review aims to analyze the scientific evidence of the hypothalamic control of hypothermia and the central and peripheral changes that are triggered in domestic animals.

Echinacoside stimulates myogenesis and ATP-dependent thermogenesis in the skeletal muscle via the activation of D1-like dopaminergic receptors

Recent studies have shown that some natural compounds from plants prevent obesity and related disorders, including the loss of skeletal muscle mass and strength. In this study, we investigated the effect of echinacoside (ECH), a caffeic acid glycoside from the phenylpropanoid class, on myogenesis and ATP-dependent thermogenesis in the skeletal muscle and its interaction with the dopaminergic receptors 1 and 5 (DRD1 and DRD5). We applied RT-PCR, immunoblot analysis, a staining method, and an assay kit to determine the effects of ECH on diverse target genes and proteins involved in skeletal muscle myogenesis and ATP-consuming futile processes. Our study demonstrated that ECH enhanced myogenic differentiation, glucose, and fatty acid uptake, as well as lipid catabolism, and induced ATP-dependent thermogenesis in vitro and in vivo. Moreover, ECH upregulated mitochondrial biogenesis proteins, mitochondrial oxidative phosphorylation (OXPHOS) complexes, and intracellular Ca2+ signaling as well as thermogenic proteins. These findings were further elucidated by mechanistic studies which showed that ECH mediates myogenesis via the DRD1/5 in C2C12 muscle cells. In addition, ECH stimulates α1-AR-mediated ATP-dependent thermogenesis via the DRD1/5/cAMP/SLN/SERCA1a pathway in C2C12 muscle cells. To the best of our knowledge, this is the first report that demonstrates the myogenic and thermogenic potential of ECH activity through the dopaminergic receptors. Understanding the novel functions of ECH in terms of its ability to prevent skeletal muscle loss and energy expenditure via ATP-consuming futile processes could help to develop potential alternative strategies to address muscle-related diseases, including combating obesity.

Diosmin Promotes Myogenesis via Activating the Akt/FOXO1 Pathway to Facilitate the Proliferation of C2C12 Myoblasts

Our previous study with artificial intelligence (AI)-assisted screening found that diosmin, a natural flavonoid extracted from citrus, may affect myoblast proliferation and differentiation. At present, few studies have been conducted regarding the biological function of diosmin in muscle cells. Here, using molecular biological techniques, we found that diosmin elevated the proliferation ability of C2C12 myoblasts via activating the Akt/FOXO1 pathway to promote FOXO1 nuclear export, thus repressing p27 protein expression, increasing CDK2, CDK4, and cyclin D1 and cyclin E1 protein expression and accelerating cell cycle transformation, which contributed to myogenesis. Moreover, diosmin suppressed differentiation of C2C12 myoblasts by delaying the terminal exit of the cell cycle in early differentiated myoblasts and inhibiting autophagic flux in mature myotubes. Furthermore, diosmin promoted myogenesis by activating the Akt/FOXO1 pathway to facilitate myoblast proliferation, which had a positive biological effect on the repair of muscle injury. This study revealed the effect and mechanism of diosmin on skeletal muscle cells and simultaneously provided a new candidate drug for the treatment of myopathy.

Effects of lysolecithins on performance, egg quality, blood profiles and liver histopathology in late-phase laying hens

1. This study investigated the effects of lysolecithins (LL) on performance, egg quality, blood profiles, relative organ weight and liver histopathology in laying hens.2. A total of 480 healthy 65-week-old Lohmann laying hens were randomly allocated into four treatments in a 2 × 2 factorial arrangement design with two levels of energy (AMEn, 11.08 MJ/kg and 12.94 MJ/kg) and two levels of LL (0 and 0.05%).3. Birds fed high energy diets had lower (P < 0.05) average daily intake and feed conversion rate during weeks 0-4, 5-8 and 0-8, but higher (P < 0.05) average egg weight (AEW) during trial weeks 0-4. There was an interaction in (P < 0.05) AEW during trial weeks 0-14 and 0-8 for energy and LL. The high energy diets increased yolk colour at the end of weeks 2 and 4, while addition of LL increased albumen height at the end of week 2. There was an interaction (P < 0.05) in yolk colour between energy and LL at the end of week 2. There was an interaction (P < 0.05) in serum superoxide dismutase and LDL-C throughout the experiment.4. The high energy diets increased (P < 0.05) the relative weight of abdominal fat compared with low energy diets. The high energy diets increased (P < 0.05) liver ether extract content and liver pathological injury score compared with low energy diets at the end of week 8, while the addition of LL decreased (P < 0.05) liver pathological injury score.5. The supplementation of LL in high energy diets could alleviate some negative effects on liver injury in late laying hens.

Echinacoside Induces UCP1- and ATP-Dependent Thermogenesis in Beige Adipocytes via the Activation of Dopaminergic Receptors

Echinacoside (ECH) is a naturally occurring phenylethanoid glycoside, isolated from Echinacea angustifolia, and this study aimed to analyze its effect on thermogenesis and its interaction with dopaminergic receptors 1 and 5 (DRD1 and DRD5) in 3T3-L1 white adipocytes and mice models. We employed RT-PCR, immunoblot, immunofluorescence, a staining method, and an assay kit to determine its impact. ECH showed a substantial increase in browning signals in vitro and a decrease in adipogenic signals in vivo. Additionally, analysis of the iWAT showed that the key genes involved in beiging, mitochondrial biogenesis, and ATP-dependent thermogenesis were upregulated while adipogenesis and lipogenesis genes were downregulated. OXPHOS complexes, Ca2+ signaling proteins as well as intracellular Ca2+ levels were also upregulated in 3T3-L1 adipocytes following ECH treatment. This was collectively explained by mechanistic studies which showed that ECH mediated the beiging process via the DRD1/5-cAMP-PKA and subsequent downstream molecules, whereas it co-mediated the α1-AR-signaling thermogenesis via the DRD1/5/SERCA2b/RyR2/CKmt pathway in 3T3-L1 adipocytes. Animal experiments revealed that there was a 12.28% reduction in body weight gain after the ECH treatment for six weeks. The effects of ECH treatment on adipose tissue can offer more insights into the treatment of obesity and metabolic syndrome.

Transcriptome Analysis Revealed Potential Genes of Skeletal Muscle Thermogenesis in Mashen Pigs and Large White Pigs under Cold Stress

Pigs are susceptible to cold stress due to the absence of brown fat caused by the partial deletion of uncoupling protein 1 during their evolution. Some local pig breeds in China exhibit potential cold adaptability, but research has primarily focused on fat and intestinal tissues. Skeletal muscle plays a key role in adaptive thermogenesis in mammals, yet the molecular mechanism of cold adaptation in porcine skeletal muscle remains poorly understood. This study investigated the cold adaptability of two pig breeds, Mashen pigs (MS) and Large White pigs (LW), in a four-day cold (4 °C) or normal temperature (25 °C) environment. We recorded phenotypic changes and collected blood and longissimus dorsi muscle for transcriptome sequencing. Finally, the PRSS8 gene was randomly selected for functional exploration in porcine skeletal muscle satellite cells. A decrease in body temperature and body weight in both LW and MS pigs under cold stress, accompanied by increased shivering frequency and respiratory frequency, were observed. However, the MS pigs demonstrated stable physiological homeostasis, indicating a certain level of cold adaptability. The LW pigs primarily responded to cold stress by regulating their heat production and glycolipid energy metabolism. The MS pigs exhibited a distinct response to cold stress, involving the regulation of heat production, energy metabolism pathways, and robust mitochondrial activity, as well as a stronger immune response. Furthermore, the functional exploration of PRSS8 in porcine skeletal muscle satellite cells revealed that it affected cellular energy metabolism and thermogenesis by regulating ERK phosphorylation. These findings shed light on the diverse transcriptional responses of skeletal muscle in LW and MS pigs under cold stress, offering valuable insights into the molecular mechanisms underlying cold adaptation in pigs.

Seasonal cold induces divergent structural/biochemical adaptations in different skeletal muscles of Columba livia: evidence for nonshivering thermogenesis in adult birds

Birds are endothermic homeotherms even though they lack the well-studied heat producing brown adipose tissue (BAT), found in several clades of eutherian mammals. Earlier studies in ducklings have demonstrated that skeletal muscle is the primary organ of nonshivering thermogenesis (NST) plausibly via futile calcium (Ca2+)-handling through ryanodine receptor (RyR) and sarco-endoplasmic reticulum Ca2+-ATPase (SERCA). However, recruitment of futile Ca2+-cycling in adult avian skeletal muscle has not been documented. Studies in mammals show remarkable mitochondrial remodeling concurrently with muscle NST during cold. Here, we wanted to define the mitochondrial and biochemical changes in the muscles in free-ranging adult birds and whether different skeletal muscle groups undergo similar seasonal changes. We analyzed four different muscles (pectoralis, biceps, triceps and iliotibialis) from local pigeon (Columba livia) collected during summer and winter seasons in two consecutive years. Remarkable increase in mitochondrial capacity was observed as evidenced from succinate dehydrogenase (SDH) and cytochrome c oxidase (COX) activity staining in all the muscles. Interestingly, fibers with low SDH activity exhibited greater cross-sectional area during winter in all muscles except iliotibialis and became peripherally arranged in individual fascicles of pectoralis, which might indicate increased shivering. Furthermore, gene expression analysis showed that SERCA, sarcolipin and RyR are up-regulated to different levels in the muscles analyzed indicating muscle NST via futile Ca2+-cycling is recruited to varying degrees in winter. Moreover, proteins of mitochondrial-SR-tethering and biogenesis also showed differential alterations across the muscles. These data suggest that tropical winter (∼15°C) is sufficient to induce distinct remodeling across muscles in adult bird.

A general overview of the multifactorial adaptation to cold: biochemical mechanisms and strategies

Cold environments are more frequent than people think. They include deep oceans, cold lakes, snow, permafrost, sea ice, glaciers, cold soils, cold deserts, caves, areas at elevations greater than 3000 m, and also artificial refrigeration systems. These environments are inhabited by a diversity of eukaryotic and prokaryotic organisms that must adapt to the hard conditions imposed by cold. This adaptation is multifactorial and includes (i) sensing the cold, mainly through the modification of the liquid-crystalline membrane state, leading to the activation of a two-component system that transduce the signal; (ii) adapting the composition of membranes for proper functions mainly due to the production of double bonds in lipids, changes in hopanoid composition, and the inclusion of pigments; (iii) producing cold-adapted proteins, some of which show modifications in the composition of amino acids involved in stabilizing interactions and structural adaptations, e.g., enzymes with high catalytic efficiency; and (iv) producing ice-binding proteins and anti-freeze proteins, extracellular polysaccharides and compatible solutes that protect cells from intracellular and extracellular ice. However, organisms also respond by reprogramming their metabolism and specifically inducing cold-shock and cold-adaptation genes through strategies such as DNA supercoiling, distinctive signatures in promoter regions and/or the action of CSPs on mRNAs, among others. In this review, we describe the main findings about how organisms adapt to cold, with a focus in prokaryotes and linking the information with findings in eukaryotes.

Constitutive Serotonin Tone as a Modulator of Brown Adipose Tissue Thermogenesis: A Rat Study

Brown adipose tissue (BAT), an important regulator of thermogenic and metabolic processes, is considered a promising target to combat metabolic disorders. The neurotransmitter and hormone serotonin (5HT) is a major modulator of energy homeostasis, with its central and peripheral pools acting in opposing ways. To better understand how individual variations in 5HT homeostasis influence the thermogenic functionality of BAT, we used a rat model consisting of two sublines with constitutively increased (high-5HT) or decreased (low-5HT) whole-body 5HT tone, developed by selective breeding for platelet 5HT parameters. We have shown that animals with constitutively low 5HT activity maintained at a standard housing temperature (22 °C) have greater interscapular BAT (iBAT) mass and higher iBAT metabolic activity (as evidenced by measurements of iBAT temperature and glucose uptake), accompanied by increased iBAT mRNA expression of key thermogenic genes, compared to animals with high 5HT tone. In response to further thermogenic challenges-intermittent cold exposure or treatment with a β₃-adrenergic agonist-5HT sublines show several functional and molecular differences linking constitutively low endogenous 5HT tone to higher BAT activity/capacity. Overall, the results support a role of 5-HT in the control of BAT thermogenesis They also suggest that individuals with lower 5HT activity may be more sensitive to β3-adrenergic drugs.

Multifaceted mitochondrial quality control in brown adipose tissue

Brown adipose tissue (BAT) controls mammalian core body temperature by non-shivering thermogenesis. BAT is extraordinarily rich in mitochondria, which have the peculiarity of generating heat by uncoupled respiration. Since the mitochondrial activity of BAT is subject to cycles of activation and deactivation in response to environmental temperature changes, an integrated mitochondrial quality control (MQC) system is of fundamental importance to ensure BAT physiology. Here, we provide an overview of the conventional and alternative mechanisms through which thermogenic adipocytes selectively remove damaged parts of mitochondria and how macrophages participate in the MQC system by removing extracellular mitochondrial waste to maintain the thermogenic function of BAT.

Recapitulating Antioxidant and Antibacterial Compounds into a Package for Tissue Regeneration: Dual Function Materials with Synergistic Effect

Oxidative damage and infection can prevent or delay tissue repair. Moreover, infection reinforces reactive oxygen species (ROS) formation, which makes the wound's condition even worse. Therefore, the need for antioxidant and antibacterial agents is felt for tissue regeneration. There are emerging up-and-coming biomaterials that recapitulate both properties into a package, offering an effective solution to turn the wound back into a healing state. In this article, the principles of antioxidant and antibacterial activity are summarized. The review starts with biological aspects, getting the readers to familiarize themselves with tissue barriers against infection. This is followed by the chemistry and mechanism of action of antioxidant and antibacterial materials (dual function). Eventually, the outlook and challenges are underlined to provide where the dual-function biomaterials are and where they are going in the future. It is expected that the present article inspires the designing of dual-function biomaterials to more advanced levels by providing the fundamentals and comparative points of view and paving the clinical way for these materials.

Rats lacking Ucp1 present a novel translational tool for the investigation of thermogenic adaptation during cold challenge

AIM

Valuable studies have tested the role of UCP1 on body temperature maintenance in mice, and we sought to knockout Ucp1 in rats (Ucp1-/- ) to provide insight into thermogenic mechanisms in larger mammals.

METHODS

We used CRISPR/Cas9 technology to create Ucp1-/- rats. Body weight and adiposity were measured, and rats were subjected to indirect calorimetry. Rats were maintained at room temperature or exposed to 4°C for either 24 h or 14 days. Analyses of brown and white adipose tissue and skeletal muscle were conducted via histology, western blot comparison of oxidative phosphorylation proteins, and qPCR to compare mitochondrial DNA levels and mRNA expression profiles. RNA-seq was performed in skeletal muscle.

RESULTS

Ucp1-/- rats withstood 4°C for 14 days, but core temperature steadily declined. All rats lost body weight after 14 days at 4°C, but controls increased food intake more robustly than Ucp1-/- rats. Brown adipose tissue showed signs of decreased activity in Ucp1-/- rats, while mitochondrial lipid metabolism markers in white adipose tissue and skeletal muscle were increased. Ucp1-/- rats displayed more visible shivering and energy expenditure than controls at 4°C. Skeletal muscle transcriptomics showed more differences between genotypes at 23°C than at 4°C.

CONCLUSION

Room temperature presented sufficient cold stress to rats lacking UCP1 to activate compensatory thermogenic mechanisms in skeletal muscle, which were only activated in control rats following exposure to 4°C. These results provide novel insight into thermogenic responses to UCP1 deficiency; and highlight Ucp1-/- rats as an attractive translational model for the study of thermogenesis.

Dopamine receptor D4 (DRD4) negatively regulates UCP1- and ATP-dependent thermogenesis in 3T3-L1 adipocytes and C2C12 muscle cells

The activation of beige fat and muscle tissues is an interesting and encouraging target for therapeutic intervention in obesity owing to their remarkable lipolytic activity and energy-consuming futile cycles. This study examined the effect of dopamine receptor D4 (DRD4) on lipid metabolisms as well as UCP1- and ATP-dependent thermogenesis in Drd4-silenced 3T3-L1 adipocytes and C2C12 muscle cells. Silencing of Drd4, followed by quantitative real-time PCR, immunoblot analysis, immunofluorescence, and staining methods, were applied to evaluate the effects of DRD4 on diverse target genes and proteins of both cells. The findings showed that DRD4 was expressed in the adipose and muscle tissues of normal and obese mice. Furthermore, the knockdown of Drd4 upregulated the expression of brown adipocyte-specific genes and proteins while downregulating lipogenesis and the adipogenesis marker proteins. Drd4 silencing also upregulated the expression of key signaling molecules involved in ATP-dependent thermogenesis in both cells. This was further elucidated by mechanistic studies showing that a Drd4 knockdown mediates UCP1-dependent thermogenesis via the cAMP/PKA/p38MAPK pathway in 3T3-L1 adipocytes and UCP1-independent thermogenesis via the cAMP/SLN/SERCA2a pathway in C2C12 muscle cells. In addition, siDrd4 also mediates myogenesis via the cAMP/PKA/ERK1/2/Cyclin D3 pathway in C2C12 muscle cells. Silencing of Drd4 promotes β3-AR-dependent browning in 3T3-L1 adipocytes and α1-AR/SERCA-based thermogenesis through an ATP-consuming futile process in C2C12 muscle cells. Understanding the novel functions of DRD4 on adipose and muscle tissues in terms of its ability to enhance energy expenditure and regulate whole-body energy metabolism will aid in developing novel obesity intervention techniques.

Distinct Transcriptional Responses of Skeletal Muscle to Short-Term Cold Exposure in Tibetan Pigs and Bama Pigs

Piglets are susceptible to cold, and piglet death caused by cold stress leads to economic losses in the pig industry in cold areas. Skeletal muscle plays a key role in adaptive thermogenesis in mammals, but the related mechanism in pigs is unclear. In this study, cold-tolerant Tibetan pigs and cold-sensitive Bama pigs were subjected to either a cold environment (4 °C) or a room temperature environment (25 °C) for 3 days. The biceps femoris (BF) and longissimus dorsi muscle (LDM) were collected for phenotypic analysis, and the BF was used for genome-wide transcriptional profiling. Our results showed that Tibetan pigs had a higher body temperature than Bama pigs upon cold stimulation. RNA-seq data indicated a stronger transcriptional response in the skeletal muscle of Tibetan pigs upon cold stimulation, as more differentially expressed genes (DEGs) were identified with the same criteria (p < 0.05 and fold change > 2). In addition, distinct pathway signaling patterns in skeletal muscle upon cold exposure were found between the breeds of pigs. Mitochondrial beta-oxidation-related genes and pathways were significantly upregulated in Tibetan pigs, indicating that Tibetan pigs may use fatty acids as the primary fuel source to protect against cold. However, the significant upregulation of inflammatory response- and glycolysis-related genes and pathways in the skeletal muscle of Bama pigs suggested that these pigs may use glucose as the primary fuel source in cold environments. Together, our study revealed the distinct transcriptional responses of skeletal muscle to cold stimulation in Tibetan pigs and Bama pigs and provided novel insights for future investigation of the cold adaptation mechanism in pigs.

Beyond its Psychiatric Use: The Benefits of Low-dose Lithium Supplementation

Lithium is most well-known for its mood-stabilizing effects in the treatment of bipolar disorder. Due to its narrow therapeutic window (0.5-1.2 mM serum concentration), there is a stigma associated with lithium treatment and the adverse effects that can occur at therapeutic doses. However, several studies have indicated that doses of lithium under the predetermined therapeutic dose used in bipolar disorder treatment may have beneficial effects not only in the brain but across the body. Currently, literature shows that low-dose lithium (≤0.5 mM) may be beneficial for cardiovascular, musculoskeletal, metabolic, and cognitive function, as well as inflammatory and antioxidant processes of the aging body. There is also some evidence of low-dose lithium exerting a similar and sometimes synergistic effect on these systems. This review summarizes these findings with a focus on low-dose lithium's potential benefits on the aging process and age-related diseases of these systems, such as cardiovascular disease, osteoporosis, sarcopenia, obesity and type 2 diabetes, Alzheimer's disease, and the chronic low-grade inflammatory state known as inflammaging. Although lithium's actions have been widely studied in the brain, the study of the potential benefits of lithium, particularly at a low dose, is still relatively novel. Therefore, this review aims to provide possible mechanistic insights for future research in this field.

Altered skeletal muscle sarco-endoplasmic reticulum Ca2+-ATPase calcium transport efficiency after a thermogenic stimulus

Exposure to predator threat induces a rapid and robust increase in skeletal muscle thermogenesis in rats. The central nervous system relays threat information to skeletal muscle through activation of the sympathetic nervous system, but muscle mechanisms mediating this thermogenesis remain unidentified. Given the relevance of sarcolipin-mediated futile calcium cycling through the sarco-endoplasmic reticulum Ca2+-ATPase (SERCA) pump to mammalian muscle nonshivering thermogenesis, we hypothesized that this plays a role in contextually induced muscle thermogenesis as well. This was assessed by measuring enzymatic activity of SERCA and sarcoplasmic reticulum Ca2+ transport, where the apparent coupling ratio (Ca2+ uptake rate divided by ATPase activity rate at a standard Ca2+ concentration) was predicted to decrease in association with muscle thermogenesis. Sprague-Dawley rats exposed to predator (ferret) odor (PO) showed a rapid decrease in the apparent coupling ratio in the soleus muscle, indicating SERCA uncoupling compared with control-odor-exposed rats. A rat model of high aerobic fitness and elevated muscle thermogenesis also demonstrated soleus muscle SERCA uncoupling relative to their obesity-prone, low-fitness counterparts. Both the high- and low-aerobic fitness rats showed soleus SERCA uncoupling with exposure to PO. Finally, no increase in sarcolipin expression in soleus muscle was detected with PO exposure. This dataset implicates muscle uncoupling of SERCA Ca2+ transport and ATP hydrolysis, likely through altered SERCA or sarcolipin function outside of translational regulation, as one contributor to the muscle thermogenesis provoked by exposure to predator threat. These data support the involvement of SERCA uncoupling in both muscle thermogenic induction and enhanced aerobic capacity.

Transcriptome analysis revealed potential genes involved in thermogenesis in muscle tissue in cold-exposed lambs

Cold tolerance is an important trait for sheep raised at high altitudes. Muscle tissue, comprising 30–40% of the total body mass, produces heat during cold exposure. However, little is known about the genetic mechanisms of this tissue and its role in thermogenesis in lambs. We examined genes in skeletal muscle tissue in a cold-adapted sheep breed, Altay, and a cold-intolerant sheep breed, Hu, when exposed to low air temperature. Three ewe-lambs of each breed were maintained at −5°C and three ewe-lambs of each breed were maintained at 20°C. After cold exposure for 25 days, the longissimus dorsi of each lamb was collected, and transcriptome profiles were sequenced and analyzed. The results of RNA-seq showed that the average reads among the four groups were 11.0 Gbase. The genome mapping rate averaged 88.1% and the gene mapping rate averaged 82.5%. The analysis of differentially expressed genes (DEGs) indicated that the peroxisome proliferator-activated receptors (PPAR), cAMP, and calcium signaling pathways and muscle contraction in muscle tissue were linked to thermogenesis in cold-exposed lambs. Furthermore, PCK1 (phosphoenolpyruvate carboxykinase1) increased glyceroneogenesis in cold-exposed Altay lambs, and APOC3 (apolipoprotein C3), LPL (lipoprotein lipase), and FABP4 (fatty acid binding protein 4, adipocyte) were involved in the intake and transport of free fatty acids. In Hu sheep, cAMP biosynthesis from ATP hydrolysis was regulated by ADCY10 (adenylate cyclase) and ADORA2a (adenosine A2a receptor). Skeletal muscle contraction was regulated by MYL2 (myosin light chain 2). In conclusion, cold exposure altered the expression level of genes involved in heat production in muscle tissue. Some potential mechanisms were revealed, including calcium ion transport in the calcium signaling pathway, fatty acid metabolism in the PPAR signaling pathway, and cAMP biosynthesis in the cAMP signaling pathway. This study implied that skeletal muscle plays an important role in thermoregulation in lambs.

Developmental programming: Impact of prenatal bisphenol-A exposure on liver and muscle transcriptome of female sheep

Gestational Bisphenol A (BPA) exposure leads to peripheral insulin resistance, and hepatic and skeletal muscle oxidative stress and lipotoxicity during adulthood in the female sheep offspring. To investigate transcriptional changes underlying the metabolic outcomes, coding and non-coding (nc) RNA in liver and muscle from 21-month-old control and prenatal BPA-treated (0.5 mg/kg/day from days 30 to 90 of gestation; Term: 147 days) female sheep were sequenced. Prenatal BPA-treatment dysregulated: expression of 194 genes (138 down, 56 up) in liver and 112 genes (32 down, 80 up) in muscle (FDR < 0.05 and abs log2FC > 0.5); 155 common gene pathways including mitochondrial-related genes in both tissues; 1415 gene pathways including oxidative stress and lipid biosynthetic process specifically in the liver (FDR < 0.01); 192 gene pathways including RNA biosynthetic processes in muscle (FDR < 0.01); 77 lncRNA (49 down, 28 up), 14 microRNAs (6 down, 8 up), 127 snoRNAs (63 down, 64 up) and 55 snRNAs (15 down, 40 up) in the liver while upregulating 6 lncRNA and dysregulating 65 snoRNAs (47 down, 18 up) in muscle (FDR < 0.1, abs log2FC > 0.5). Multiple ncRNA correlated with LCORL, MED17 and ZNF41 mRNA in liver but none of them in the muscle. Discriminant analysis identified (p < 0.05) PECAM, RDH11, ABCA6, MIR200B, and MIR30B in liver and CAST, NOS1, FASN, MIR26B, and MIR29A in muscle as gene signatures of gestational BPA exposure. These findings provide mechanistic clues into the development and/or maintenance of the oxidative stress and lipid accumulation and potential for development of mitochondrial and fibrotic defects contributing to the prenatal BPA-induced metabolic dysfunctions.

Maternal L-carnitine supplementation promotes brown adipose tissue thermogenesis of newborn goats after cold exposure

Brown adipose tissue (BAT) is an important component of energy expenditure and necessary to maintain body temperature for newborn mammals. In the previous study, we found that L-carnitine was enriched in BAT and promoted BAT adipogenesis and thermogenesis in goat brown adipocytes. However, whether dietary L-carnitine regulates BAT heat production and energy expenditure in lambs remains unclear. In this study, maternal L-carnitine supplementation elevated the rectal temperature, as well as the expression of UCP1 and mitochondrial DNA content to promote BAT thermogenesis in newborn goats. Moreover, maternal L-carnitine supplementation increased the levels of triglycerides (TG), non-esterified fatty acids (NEFA), and lactate in plasma, as well as the content of lipid droplet and glycogen in BAT of newborn goats. Lipidomic analysis showed that maternal L-carnitine supplementation remodeled the lipid composition of BAT in newborn goats. L-carnitine significantly increased the levels of TG and diglyceride (DG) and decreased the levels of glycerophospholipids and sphingolipids in BAT. Further studies showed that L-carnitine promoted TG and glycogen deposition in brown adipocytes through AMPKα. Our results indicate that maternal L-carnitine supplementation promotes BAT development and thermogenesis in newborn goats and provides new evidence for newborn goats to maintain body temperature in response to cold exposure.

Maternal high-fat diet alters thermogenic markers but not muscle or brown adipose cannabinoid receptors in adult rats

AIMS

The endocannabinoid system (ECS) increases food intake, appetite for fat and lipogenesis, while decreases energy expenditure (thermogenesis), contributing to metabolic dysfunctions. We demonstrated that maternal high-fat diet (HFD) alters cannabinoid signaling in brown adipose tissue (BAT) of neonate and weanling male rat offspring, which have increased adiposity but also higher energy expenditure in adulthood. In this study, the main objective was to investigate the ECS expression in thermogenic tissues as BAT and skeletal muscle of adult rats programmed by maternal HFD. We hypothesized that maternal HFD would modulate ECS and energy metabolism markers in BAT and skeletal muscle of adult male offspring.

MATERIALS AND METHODS

Female rats received standard diet (9.4 % of calories as fat) or isocaloric HFD (28.9 % of calories as fat) for 8 weeks premating and throughout gestation and lactation. Male offspring were weaned on standard diet and euthanatized in adulthood.

KEY FINDINGS

Maternal HFD increased body weight, adiposity, glycemia, leptinemia while decreased testosterone levels in adult offspring. Maternal HFD did not change cannabinoid receptors in BAT or skeletal muscle as hypothesized but increased the content of uncoupling protein and tyrosine hydroxylase (thermogenic markers) in parallel to changes in mitochondrial morphology in skeletal muscle of adult offspring.

SIGNIFICANCE

In metabolic programming models, the ECS modulation in the BAT and skeletal muscle may be more important early in life to adapt energy metabolism during maternal dietary insult, and other mechanisms are possibly involved in muscle metabolism long-term regulation.

Dietary adenosine 5’-monophosphate supplementation increases food intake and remodels energy expenditure in mice

Background

Methods

Results

Conclusions

Calcium cycling as a mediator of thermogenic metabolism in adipose tissue

Canonical non-shivering thermogenesis (NST) in brown and beige fat relies on uncoupling protein 1 (UCP1)-mediated heat generation, although alternative mechanisms of NST have been identified, including sarcoplasmic reticulum (SR)-calcium cycling. Intracellular calcium is a crucial cell signaling molecule for which compartmentalization is tightly regulated, and the sarco-endoplasmic calcium ATPase (SERCA) actively pumps calcium from the cytosol into the SR. In this review, we discuss the capacity of SERCA-mediated calcium cycling as a significant mediator of thermogenesis in both brown and beige adipocytes. Here, we suggest two primary mechanisms of SR calcium mediated thermogenesis. The first mechanism is through direct uncoupling of the ATPase and calcium pump activity of SERCA, resulting in the energy of ATP catalysis being expended as heat in the absence of calcium transport. Regulins, a class of SR membrane proteins, act to decrease the calcium affinity of SERCA and uncouple the calcium transport function from ATPase activity, but remain largely unexplored in adipose tissue thermogenesis. A second mechanism is through futile cycling of SR calcium whereby SERCA-mediated SR calcium influx is equally offset by SR calcium efflux, resulting in ATP consumption without a net change in calcium compartmentalization. A fuller understanding of the functional and mechanistic role of calcium cycling as a mediator of adipose tissue thermogenesis and how manipulation of these pathways can be harnessed for therapeutic gain remains unexplored. Significance Statement Enhancing thermogenic metabolism in brown or beige adipose tissue may be of broad therapeutic utility to reduce obesity and metabolic syndrome. Canonical BAT-mediated thermogenesis occurs via uncoupling protein 1 (UCP1). However, UCP1-independent pathways of thermogenesis, such as sarcoplasmic (SR) calcium cycling, have also been identified, but the regulatory mechanisms and functional significance of these pathways remain largely unexplored. Thus, this mini-review discusses the state of the field with regard to calcium cycling as a thermogenic mediator in adipose tissue.

UCP1 Knockin Induces Lipid Dynamics and Transcriptional Programs in the Skeletal Muscles of Pigs

Uncoupling protein 1 (UCP1), the hallmark protein responsible for nonshivering thermogenesis in adipose tissue (especially brown adipose tissue) has regained researchers' attention in the context of metabolic disorders following the realization that UCP1 can be activated in adult humans and reconstituted in pigs. Both skeletal muscle and adipose tissue are highly dynamic tissues that interact at the metabolic and hormonal level in response to internal and external stress, and they coordinate in maintaining whole-body metabolic homeostasis. Here, we utilized lipidomics and transcriptomics to identify the altered lipid profiles and regulatory pathways in skeletal muscles from adipocyte-specific UCP1 knock-in (KI) pigs. UCP1 KI changed the contents of glycerophospholipids and acyl carnitines of skeletal muscles. Several metabolic regulatory pathways were more enriched in the UCP1 KI skeletal muscle. Comparison of the transcriptomes of adipose and skeletal muscle suggested that nervous system or chemokine signaling might account for the crosstalk between these two tissues in UCP1 KI pigs. Comparison of the lipid biomarkers from UCP1 KI pigs and other mammals suggested associations between UCP1 KI-induced metabolic alternations and metabolic and muscle dysfunction. Our study reveals the lipid dynamics and transcriptional programs in the skeletal muscle of UCP1 KI pigs and suggests that a network regulates metabolic homeostasis between skeletal muscle and adipose tissue.

Lack of TRPV1 aggravates obesity-associated hypertension through the disturbance of mitochondrial Ca2+ homeostasis in brown adipose tissue

The combination of obesity and hypertension is associated with high morbidity and mortality; however, the mechanism underlying obesity-induced hypertension remains unclear. In this study, we detected the possible effects of TRPV1, a previously identified antihypertensive calcium (Ca²⁺) channel in adipose tissue, on the occurrence of obesity and hypertension in mice lacking UCP1, a spontaneously genetically manipulated obesity model, by generating TRPV1 and UCP1 double knockout mice. In these mice, obesity and hypertension appeared earlier and were more severe than in mice with the knockout of UCP1 or TRPV1 alone. The knockout of TRPV1 in UCP1 knockout mice further reduced functional brown adipose tissue (BAT) generation; decreased resting oxygen consumption, heat production, and locomotor activities; and was accompanied by severe mitochondrial respiratory dysfunction in BAT. Mechanistically, TRPV1, UCP1, and LETM1 acted as a complex to maintain an appropriate mitochondrial Ca²⁺ level, and TRPV1 knockout caused a compensatory increase in mitochondrial Ca²⁺ uptake via LETM1 activation. However, the compensatory response was blocked in UCP1^−/− mice, resulting in dramatically reduced mitochondrial Ca²⁺ uptake and higher production of ATP and oxidative stress. This study provides in vivo evidence for the critical role of BAT mitochondrial Ca²⁺ homeostasis in obesity-associated hypertension and indicates that the TRPV1/UCP1/LETM1 complex may be an alternative intervention target.

Developmental Programming: Prenatal Testosterone Excess on Liver and Muscle Coding and Noncoding RNA in Female Sheep

Prenatal testosterone (T)-treated female sheep manifest peripheral insulin resistance, ectopic lipid accumulation, and insulin signaling disruption in liver and muscle. This study investigated transcriptional changes and transcriptome signature of prenatal T excess-induced hepatic and muscle-specific metabolic disruptions. Genome-wide coding and noncoding (nc) RNA expression in liver and muscle from 21-month-old prenatal T-treated (T propionate 100 mg intramuscular twice weekly from days 30-90 of gestation; term: 147 days) and control females were compared. Prenatal T (1) induced differential expression of messenger RNAs (mRNAs) in liver (15 down, 17 up) and muscle (66 down, 176 up) (false discovery rate < 0.05, absolute log2 fold change > 0.5); (2) downregulated mitochondrial pathway genes in liver and muscle; (3) downregulated hepatic lipid catabolism and peroxisome proliferator-activated receptor (PPAR) signaling gene pathways; (4) modulated noncoding RNA (ncRNA) metabolic processes gene pathway in muscle; and (5) downregulated 5 uncharacterized long noncoding RNA (lncRNA) in the muscle but no ncRNA changes in the liver. Correlation analysis showed downregulation of lncRNAs LOC114112974 and LOC105607806 was associated with decreased TPK1, and LOC114113790 with increased ZNF470 expression. Orthogonal projections to latent structures discriminant analysis identified mRNAs HADHA and SLC25A45, and microRNAs MIR154A, MIR25, and MIR487B in the liver and ARIH1 and ITCH and miRNAs MIR369, MIR10A, and MIR10B in muscle as potential biomarkers of prenatal T excess. These findings suggest downregulation of mitochondria, lipid catabolism, and PPAR signaling genes in the liver and dysregulation of mitochondrial and ncRNA gene pathways in muscle are contributors of lipotoxic and insulin-resistant hepatic and muscle phenotype. Gestational T excess programming of metabolic dysfunctions involve tissue-specific ncRNA-modulated transcriptional changes.

Neuronatin promotes SERCA uncoupling and its expression is altered in skeletal muscles of high-fat diet-fed mice

Neuronatin (NNAT) is a transmembrane protein in the endoplasmic reticulum involved in metabolic regulation. It shares sequence homology with sarcolipin (SLN), which negatively regulates the sarco(endo)plasmic reticulum Ca²⁺ -ATPase (SERCA) that maintains energy homeostasis in muscles. Here, we examined whether NNAT could uncouple the Ca²⁺ transport activity of SERCA from ATP hydrolysis, similarly to SLN. NNAT significantly reduced Ca²⁺ uptake without altering SERCA activity, ultimately lowering the apparent coupling ratio of SERCA. This effect of NNAT was reversed by the adenylyl cyclase activator forskolin. Furthermore, soleus muscles from high fat diet (HFD)-fed mice showed a significant downregulation in NNAT content compared with chow-fed mice, whereas an upregulation in NNAT content was observed in fast-twitch muscles from HFD- versus chow- fed mice. Therefore, NNAT is a SERCA uncoupler in cells and may function in adaptive thermogenesis.

Sex differences in nonshivering thermogenesis in the wild

Nonshivering thermogenesis (NST) is a key mechanism that allows mammals to control their body temperature. Sex can frequently affect thermoregulatory requirements; therefore, males and females can be expected to differ significantly in their NST capacity. Several sex-related differences in NST have been described in laboratory animals and humans; however, these parameters are relatively rarely studied in animals living under natural conditions. Here, I briefly review factors that may be responsible for this disparity and point out two situations that should be particularly promising in searching for sex differences in NST under natural conditions: the lactation period and potential mitonuclear conflicts over NST control in species with genetic polymorphism.

Integrated application of metabolomics and RNA-seq reveals thermogenic regulation in goat brown adipose tissues

Brown adipose tissue (BAT) plays an important role on no shivering thermogenesis during cold exposure to maintain animal body temperature and energy homeostasis. However, knowledge of the cellular transition from white adipose tissue (WAT) to BAT is still limited. In this study, we provided a comprehensive metabolomics and transcriptional signatures of goat BAT and WAT. A total of 157 metabolites were significantly changed, including 81 upregulated and 76 downregulated metabolites. In addition, we identified the citric acid cycle, fatty acid elongation, and degradation pathways as coordinately activated in BAT. Interestingly, five unsaturated fatty acids (Eicosadienoic Acid, C20:2; γ-Linolenic acid, C20:3; Arachidonic Acid, C20:4; Adrenic acid, C22:4; Docosahexaenoic acid, C22:6), Succinate, L-carnitine, and L-palmitoyl-carnitine were found to be abundant in BAT. Furthermore, L-carnitine, an intermediate of fatty acid degradation, is required for goat brown adipocyte differentiation and thermogenesis through activating AMPK pathway. However, L-carnitine decreased lipid accumulation through inducing lipolysis and thermogenesis in white adipocytes. These results revealed that there are the significant alterations in transcriptomic and metabolomic profiles between goat WAT and BAT, which may contribute to better understanding the roles of metabolites in BAT thermogenesis process.

Lipophorin receptor 1 (LpR1) in Drosophila muscle influences life span by regulating mitochondrial aging

Sarcopenia is a syndrome characterized by progressive loss of muscle mass and function during aging. Although mitochondrial dysfunction and related metabolic defects precede age-related changes in muscle, their contributions to muscle aging are still not well known. In this study, we used a Drosophila model to investigate the role of lipophorin receptors (LpRs), a Drosophila homologue of the mammalian very low-density lipoprotein receptor (VLDLR), in mitochondrial dynamics and muscle aging. Muscle-specific knockdown of LpR1 or LpR2 resulted in mitochondrial dysfunction and reduced proteostasis, which contributed to muscle aging. Activation of AMP-activated protein kinase (AMPK) ameliorated muscle dysfunction induced by LpR1 knockdown. These results suggest that LpR1/VLDLR is a novel key target that modulates age-dependent lipid remodeling and muscle homeostasis.

Effects of temperature on proliferation of myoblasts from donor piglets with different thermoregulatory maturities

Background

Climate change and the associated risk for the occurrence of extreme temperature events or permanent changes in ambient temperature are important in the husbandry of farm animals. The aim of our study was to investigate the effects of permanent cultivation temperatures below (35 °C) and above (39 °C, 41 °C) the standard cultivation temperature (37 °C) on porcine muscle development. Therefore, we used our porcine primary muscle cell culture derived from satellite cells as an in vitro model. Neonatal piglets have limited thermoregulatory stability, and several days after birth are required to maintain their body temperature. To consider this developmental step, we used myoblasts originating from thermolabile (five days of age) and thermostable piglets (twenty days of age).

Results

The efficiency of myoblast proliferation using real-time monitoring via electrical impedance was comparable at all temperatures with no difference in the cell index, slope or doubling time. Both temperatures of 37 °C and 39 °C led to similar biochemical growth properties and cell viability. Only differences in the mRNA expression of myogenesis-associated genes were found at 39 °C compared to 37 °C with less MYF5, MYOD and MSTN and more MYH3 mRNA. Myoblasts grown at 35 °C are smaller, exhibit higher DNA synthesis and express higher amounts of the satellite cell marker PAX7, muscle growth inhibitor MSTN and metabolic coactivator PPARGC1A. Only permanent cultivation at 41 °C resulted in higher HSP expression at the mRNA and protein levels. Interactions between the temperature and donor age showed that MYOD, MYOG, MYH3 and SMPX mRNAs were temperature-dependently expressed in myoblasts of thermolabile but not thermostable piglets.

Conclusions

We conclude that 37 °C to 39 °C is the best physiological temperature range for adequate porcine myoblast development. Corresponding to the body temperatures of piglets, it is therefore possible to culture primary muscle cells at 39 °C. Only the highest temperature of 41 °C acts as a thermal stressor for myoblasts with increased HSP expression, but it also accelerates myogenic development. Cultivation at 35 °C, however, leads to less differentiated myoblasts with distinct thermogenetic activity. The adaptive behavior of derived primary muscle cells to different cultivation temperatures seems to be determined by the thermoregulatory stability of the donor piglets.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12860-021-00376-4.

Exosome-Derived MicroRNAs of Human Milk and Their Effects on Infant Health and Development

Multiple biologically active components of human milk support infant growth, health and development. Milk provides a wide spectrum of mammary epithelial cell-derived extracellular vesicles (MEVs) for the infant. Although the whole spectrum of MEVs appears to be of functional importance for the growing infant, the majority of recent studies report on the MEV subfraction of milk exosomes (MEX) and their miRNA cargo, which are in the focus of this review. MEX and the dominant miRNA-148a play a key role in intestinal maturation, barrier function and suppression of nuclear factor-κB (NF-κB) signaling and may thus be helpful for the prevention and treatment of necrotizing enterocolitis. MEX and their miRNAs reach the systemic circulation and may impact epigenetic programming of various organs including the liver, thymus, brain, pancreatic islets, beige, brown and white adipose tissue as well as bones. Translational evidence indicates that MEX and their miRNAs control the expression of global cellular regulators such as DNA methyltransferase 1-which is important for the up-regulation of developmental genes including insulin, insulin-like growth factor-1, α-synuclein and forkhead box P3-and receptor-interacting protein 140, which is important for the regulation of multiple nuclear receptors. MEX-derived miRNA-148a and miRNA-30b may stimulate the expression of uncoupling protein 1, the key inducer of thermogenesis converting white into beige/brown adipose tissue. MEX have to be considered as signalosomes derived from the maternal lactation genome emitted to promote growth, maturation, immunological and metabolic programming of the offspring. Deeper insights into milk's molecular biology allow the conclusion that infants are both "breast-fed" and "breast-programmed". In this regard, MEX miRNA-deficient artificial formula is not an adequate substitute for breastfeeding, the birthright of all mammals.

Dynamic Expression Profiles of Circular RNAs during Brown to White Adipose Tissue Transformation in Goats (Capra hircus)

Simple Summary

In our study, we launched RNA-seq in order to investigate the potential functions of circRNA during brown adipose tissue (BAT) to white adipose tissue (WAT) transformation. As a result, 6610 circRNAs and 61 differentially expressed circRNAs (DEcircRNAs) were identified. Moreover, 65 miRNAs were detected that could potentially interact with DEcircRNAs. The present study provides a detailed circRNA expression landscape and evidence for circRNA functions in the transformation from BAT to WAT.

Abstract

Adipose tissues are mainly divided into brown adipose tissue (BAT) and white adipose tissue (WAT). WAT mainly functions to buffer excess calories, whereas BAT plays a role in the non-shivering thermogenesis to maintain body temperature and energy balance. Moreover, circRNAs play important roles in various biological processes. However, knowledge of the expression profile and function of circRNAs from BAT to WAT remains largely unknown. In this study, a total of 6610 unique circRNAs were identified in the perirenal adipose tissues of 1-day, 30-days, and 1-year goats. Functional annotation revealed that host genes of circRNAs were involved in some BAT-related pathways, such as the thyroid hormone signaling pathway, MAPK signaling pathway, and VEGF signaling pathway. Furthermore, a total of 61 DEcircRNAs were detected across three stages. Additionally, five selected circRNAs were validated by RNase R assay, qPCR, and Sanger sequencing. Finally, the circRNA–miRNA network was constructed between the DEcircRNAs and their miRNA binding sites.

Developmental programming: Adipose depot-specific transcriptional regulation by prenatal testosterone excess in a sheep model of PCOS

Prenatal testosterone (T)-treated female sheep manifest adipose depot-specific disruptions in inflammatory/oxidative state, adipocyte differentiation and thermogenic adipocyte distribution. The objective of this study was to identify common and divergent gene pathways underlying prenatal T excess-induced adipose depot-specific disruptions. RNA sequencing and network analyses were undertaken with visceral (VAT), subcutaneous (SAT), epicardiac (ECAT) and perirenal (PRAT) adipose tissues from control and prenatal T-treated (100 mg T propionate twice a week from days 30-90 of gestation) female sheep at 21 months of age. Increased expression of adiposity and inflammation-related genes in VAT and genes that promote differentiation of white adipocytes in SAT were congruous with their metabolic roles with SAT favoring uptake/storage of free fatty acids and triglycerides and VAT favoring higher rate of fatty acid turnover and lipolysis. Selective upregulation of cardiac muscle and renoprotection genes in ECAT and PRAT respectively are suggestive of protective paracrine actions. Expression profile in prenatal T-treated sheep paralleled depot-specific dysfunctions with increased proinflammatory genes in VAT, reduced adipocyte differentiation genes in VAT and SAT and increased vascular related gene expression in PRAT. The high expression of genes involved in cardiomyocyte function in ECAT is suggestive of cardioprotective function being maintained to overcome the prenatal T-induced cardiac dysfunction and hypertension. These findings coupled with changes in gene pathways and networks involved in chromatin modification, extracellular matrix, immune and mitochondrial function, and endoplasmic reticulum to Golgi transport suggest that dysregulation in gene expression underlie prenatal T-treatment induced functional differences among adipose depots and manifestation of metabolic dysfunction.

Body Protein Sparing in Hibernators: A Source for Biomedical Innovation

Proteins are not only the major structural components of living cells but also ensure essential physiological functions within the organism. Any change in protein abundance and/or structure is at risk for the proper body functioning and/or survival of organisms. Death following starvation is attributed to a loss of about half of total body proteins, and body protein loss induced by muscle disuse is responsible for major metabolic disorders in immobilized patients, and sedentary or elderly people. Basic knowledge of the molecular and cellular mechanisms that control proteostasis is continuously growing. Yet, finding and developing efficient treatments to limit body/muscle protein loss in humans remain a medical challenge, physical exercise and nutritional programs managing to only partially compensate for it. This is notably a major challenge for the treatment of obesity, where therapies should promote fat loss while preserving body proteins. In this context, hibernating species preserve their lean body mass, including muscles, despite total physical inactivity and low energy consumption during torpor, a state of drastic reduction in metabolic rate associated with a more or less pronounced hypothermia. The present review introduces metabolic, physiological, and behavioral adaptations, e.g., energetics, body temperature, and nutrition, of the torpor or hibernation phenotype from small to large mammals. Hibernating strategies could be linked to allometry aspects, the need for periodic rewarming from torpor, and/or the ability of animals to fast for more or less time, thus determining the capacity of individuals to save proteins. Both fat- and food-storing hibernators rely mostly on their body fat reserves during the torpid state, while minimizing body protein utilization. A number of them may also replenish lost proteins during arousals by consuming food. The review takes stock of the physiological, molecular, and cellular mechanisms that promote body protein and muscle sparing during the inactive state of hibernation. Finally, the review outlines how the detailed understanding of these mechanisms at play in various hibernators is expected to provide innovative solutions to fight human muscle atrophy, to better help the management of obese patients, or to improve the ex vivo preservation of organs.

Skeletal muscle non-shivering thermogenesis as an attractive strategy to combat obesity

Obesity is a chronic disease derived from disequilibrium between energy intake and energy expenditure and evolving as a challenging epidemiological disease in the 21st century. It is urgently necessary to solve this issue by searching for effective strategies and safe drugs. Skeletal muscle could be a potential therapeutic target for the prevention and treatment of obesity and its associated complications due to non-shivering thermogenesis (NST) function. Skeletal muscle NST is based dominantly on futile sarcoplasmic reticulum Ca²⁺ ATPase (SERCA) pump cycling that leads to a rise in cytosolic Ca²⁺, increased adenosine triphosphate (ATP) hydrolysis and heat production. This review will highlight the mechanisms of skeletal muscle NST, including SLN mediated SERCA pump futile cycling, SR-mitochondrial crosstalk and increased mitochondrial biogenesis, and thermogenesis induced by uncoupling proteins 3 (UCP3). We then summarize natural products targeting the pathogenesis of obesity via skeletal muscle NST, offering new insights into pharmacotherapy and potential drug candidates to combat obesity.

Nutmeg extract potentially alters characteristics of white adipose tissue in rats

Background

Browning of white adipose tissue (WAT) is a promising approach to obesity treatment. During browning, WAT transforms into beige adipose tissue through stimulation of the peroxisome proliferator activated receptor γ (PPARγ). Nutmeg, one of the Indonesian herbs, reportedly has dual roles as a PPARα/γ partial agonist. Even though nutmeg has been traditionally used in body weight reduction, there is limited information regarding the potential role of nutmeg in browning of WAT.

Objectives

In this study, we explored the effect of nutmeg seed extract (NuSE) as a potential inductor of WAT browning.

Methods

Twelve male Wistar rats, 5–6 weeks old, were divided into control and nutmeg groups. The rats in nutmeg group were given NuSE for 12 weeks by oral gavage. After 12 weeks, the rat's inguinal WAT and brown adipose tissue (BAT) were collected, weighed and stored at − 80°C until use.

Results

We observed that even though NuSE did not reduce the final body weight, it significantly reduced body weight gain. NuSE also increased protein levels of peroxisome proliferator activated receptor γ coactivator 1α (PGC‐1α) and uncoupling protein 3 (UCP3) significantly and tended to increase UCP2 and UCP1 levels. Furthermore, NuSE induced macroscopic and microscopic morphological changes of inguinal WAT, marked by significantly increased adipocyte numbers and decreased adipocyte size.

Conclusions

Even though NuSE did not increase UCP1 significantly, it potentially alters inguinal WAT characteristics and leads to browning through PGC‐1α and UCP3 induction. However, UCP3’s specific mechanism in WAT browning remains unclear. Our findings could contribute to obesity treatment in the future.

Chronic cold exposure induces mitochondrial plasticity in deer mice native to high altitudes

KEY POINTS

Small mammals native to high altitude must sustain high rates of thermogenesis to cope with cold. Skeletal muscle is a key site of shivering and non-shivering thermogenesis, but the importance of mitochondrial plasticity in cold hypoxic environments remains unresolved. We examined high-altitude deer mice, which have evolved a high capacity for aerobic thermogenesis, to determine the mechanisms of mitochondrial plasticity during chronic exposure to cold and hypoxia, alone and in combination. Cold exposure in normoxia or hypoxia increased mitochondrial leak respiration and decreased phosphorylation efficiency and OXPHOS coupling efficiency, which may serve to augment non-shivering thermogenesis. Cold also increased muscle oxidative capacity, but reduced the capacity for mitochondrial respiration via complex II relative to complexes I and II combined. High-altitude mice had a more oxidative muscle phenotype than low-altitude mice. Therefore, both plasticity and evolved changes in muscle mitochondria contribute to thermogenesis at high altitude.

ABSTRACT

Small mammals native to high altitude must sustain high rates of thermogenesis to cope with cold and hypoxic environments. Skeletal muscle is a key site of shivering and non-shivering thermogenesis, but the importance of mitochondrial plasticity in small mammals at high altitude remains unresolved. High-altitude deer mice (Peromyscus maniculatus) and low-altitude white-footed mice (P. leucopus) were born and raised in captivity, and chronically exposed as adults to warm (25°C) normoxia, warm hypoxia (12 kPa O2 ), cold (5°C) normoxia, or cold hypoxia. We then measured oxidative enzyme activities, oxidative fibre density and capillarity in the gastrocnemius, and used a comprehensive substrate titration protocol to examine the function of muscle mitochondria by high-resolution respirometry. Exposure to cold in both normoxia or hypoxia increased the activities of citrate synthase and cytochrome oxidase. In lowlanders, this was associated with increases in capillary density and the proportional abundance of oxidative muscle fibres, but in highlanders, these traits were unchanged at high levels across environments. Environment had some distinct effects on mitochondrial OXPHOS capacity between species, but the capacity of complex II relative to the combined capacity of complexes I and II was consistently reduced in both cold environments. Both cold environments also increased leak respiration and decreased phosphorylation efficiency and OXPHOS coupling efficiency in both species, which may serve to augment non-shivering thermogenesis. These cold-induced changes in mitochondrial function were overlaid upon the generally more oxidative phenotype of highlanders. Therefore, both plasticity and evolved changes in muscle mitochondria contribute to thermogenesis at high altitudes.

The role of the super-relaxed state of myosin in human metabolism

Background

The super-relaxed state of myosin (SRX) plays a fundamental role in maintaining the low resting metabolic rate of skeletal muscle. Our previous work on this state has been in animal models. Piperine is a small molecule that has been shown to destabilize the SRX in rabbit fast twitch fibers.

Methods

Here we extend this work to human muscle obtained from biopsies of the vastus lateralis of both lean and obese subjects. The slow release of nucleotides by myosin in the SRX was measured by incubating permeable fibers in a fluorescent analog of ATP and chasing with ATP.

Results

The fraction of myosin heads in the SRX was 0.48 ± 0.04 with a lifetime of 148 ± 5 s in lean subjects and a fraction of 0.41 ± 0.05 and a lifetime of 176 ± 7 s in obese subjects. Addition of 100 μM piperine decreased the SRX population by 43 ± 7% in lean subjects and 36 ± 7% in obese subjects, with little change in lifetimes. Addition of piperine to human cardiac cells had no effect on the SRX, a requirement for a drug to treat metabolic diseases.

Conclusions

In human muscle the SRX and its responses to piperine are similar to those seen previously, with no significant differences between muscles from lean and obese subjects. Thus analogs of piperine that have greater specificity could provide effective treatment for metabolic diseases. The SRX provides a potential mechanism contributing to the large dynamic range of metabolic rate.

Neuronatin regulates whole-body metabolism: is thermogenesis involved?

Neuronatin (NNAT) was originally discovered in 1995 and labeled as a brain developmental gene due to its abundant expression in developing brains. Over the past 25 years, researchers have uncovered NNAT in other tissues; notably, the hypothalamus, pancreatic β‐cells, and adipocytes. Recent evidence in these tissues indicates that NNAT plays a significant role in metabolism whereby it regulates food intake, insulin secretion, and adipocyte differentiation. Furthermore, genetic deletion of Nnat in mice lowers whole‐body energy expenditure and increases susceptibility to diet‐induced obesity and glucose intolerance; however, the underlying cellular mechanisms remain unknown. Based on its sequence homology with phospholamban, NNAT has a purported role in regulating the sarco(endo)plasmic reticulum Ca²⁺ ATPase (SERCA) pump. However, NNAT also shares sequence homology with sarcolipin, which has the unique property of uncoupling the SERCA pump, increasing whole‐body energy expenditure and thus promoting adaptive thermogenesis in states of caloric excess or cold exposure. Thus, in this article, we discuss the accumulating evidence suggestive of NNAT’s role in whole‐body metabolic regulation, while highlighting its potential to mediate adaptive thermogenesis via SERCA uncoupling.

Emergent Coordination of the CHKB and CPT1B Genes in Eutherian Mammals: Implications for the Origin of Brown Adipose Tissue

Mitochondrial fatty acid oxidation (FAO) contributes to the proton motive force that drives ATP synthesis in many mammalian tissues. In eutherian (placental) mammals, brown adipose tissue (BAT) can also dissipate this proton gradient through uncoupling protein 1 (UCP1) to generate heat, but the evolutionary events underlying the emergence of BAT are unknown. An essential step in FAO is the transport of cytoplasmic long chain acyl-coenzyme A (acyl-CoA) into the mitochondrial matrix, which requires the action of carnitine palmitoyltransferase 1B (CPT1B) in striated muscle and BAT. In eutherians, the CPT1B gene is closely linked to the choline kinase beta (CHKB) gene, which is transcribed from the same DNA strand and terminates just upstream of CPT1B. CHKB is a rate-limiting enzyme in the synthesis of phosphatidylcholine (PC), a predominant mitochondrial membrane phospholipid, suggesting that the coordinated expression of CHKB and CPT1B may cooperatively enhance mitochondrial FAO. The present findings show that transcription of the eutherian CHKB and CPT1B genes is linked within a unitary epigenetic domain targeted to the CHKB gene, and that that this regulatory linkage appears to have resulted from an intergenic deletion in eutherians that significantly altered the distribution of CHKB and CPT1B expression. Informed by the timing of this event relative to the emergence of BAT, the phylogeny of CHKB-CPT1B synteny, and the insufficiency of UCP1 to account for eutherian BAT, these data support a mechanism for the emergence of BAT based on the acquisition of a novel capacity for adipocyte FAO in a background of extant UCP1.

Adaptive thermogenesis enhances the life-threatening response to heat in mice with an Ryr1 mutation

Mutations in the skeletal muscle Ca2+ release channel, the type 1 ryanodine receptor (RYR1), cause malignant hyperthermia susceptibility (MHS) and a life-threatening sensitivity to heat, which is most severe in children. Mice with an MHS-associated mutation in Ryr1 (Y524S, YS) display lethal muscle contractures in response to heat. Here we show that the heat response in the YS mice is exacerbated by brown fat adaptive thermogenesis. In addition, the YS mice have more brown adipose tissue thermogenic capacity than their littermate controls. Blood lactate levels are elevated in both heat-sensitive MHS patients with RYR1 mutations and YS mice due to Ca2+ driven increases in muscle metabolism. Lactate increases brown adipogenesis in both mouse and human brown preadipocytes. This study suggests that simple lifestyle modifications such as avoiding extreme temperatures and maintaining thermoneutrality could decrease the risk of life-threatening responses to heat and exercise in individuals with RYR1 pathogenic variants.

Using RNA-Seq to Identify Reference Genes of the Transition from Brown to White Adipose Tissue in Goats

Simple Summary

Brown adipose tissue (BAT) plays important roles in unique non-shivering thermogenesis. It is necessary to select reference genes during the transition process from brown (BAT) to white adipose tissue (WAT) for Quantitative PCR (qPCR) analysis. In this study, CTNNB, PFDN5 and EIF3M, selected from RNA sequencing data, were the most suitable reference genes. The present study provides a detailed analysis of the expression stability of reference genes for the study of gene expression profiling during the transition process from BAT to WAT.

Abstract

Brown adipose tissues have unique non-shivering thermogenesis functions, can be found in newborn ruminate animals, and then are gradually replaced by white adipose tissues in adulthood. For the purpose of exploring the intrinsic mechanism underlying the conversion process from brown (BAT) to white adipose tissue (WAT), it is necessary to utilize Quantitative PCR (qPCR) to study gene expression profiling. In this study, we identified reference genes that were consistently expressed during the transformation from goat BAT to WAT using RNA-seq data. Then, twelve genes were evaluated as candidate reference genes for qPCR in goat perirenal adipose tissue using three tools (geNorm, Normfinder, and BestKeeper). In addition, the selected reference genes were used to normalize the gene expression of PGC-1α and GPAT4. It was found that traditional reference genes, such as GAPDH, RPLP0, HPRT1, and PPIA were not suitable for target gene normalization. In contrast, CTNNB, PFDN5, and EIF3M, selected from RNA sequencing data, showed the least variation and were recommended as the best reference genes during the transformation from BAT to WAT.