Brown adipose tissue: function and physiological significance

A key role for P2RX5 in brown adipocyte differentiation and energy homeostasis

Brown adipocytes are defined based on a distinct morphology and genetic signature that includes, amongst others, the expression of the Purinergic 2 Receptor X5 (P2RX5). However, the role of P2RX5 in brown adipocyte and brown adipose tissue function is poorly characterized. In the present study, we conducted a metabolic characterization of P2RX5 knockout male mice; next, we characterized this purinergic pathway in a cell-autonomous context in brown adipocytes. We then tested the role of the P2RX5 receptor agonism in metabolic responses in vivo in conditions of minimal adaptive thermogenesis requirements. Our data show that loss of P2RX5 causes reduced brown adipocyte differentiation in vitro, and browning in vivo. Lastly, we unravel a previously unappreciated role for P2RX5 agonism to exert an anti-obesity effect in the presence of enhanced brown adipose tissue recruitment in male mice housed at thermoneutrality. Altogether, our data support a role for P2RX5 in mediating brown adipocyte differentiation and function that could be further targeted for benefits in the context of adipose tissue pathology and metabolic diseases.

A comparative assessment of reference genes in mouse brown adipocyte differentiation and thermogenesis in vitro

Adipogenic differentiation and thermogenesis in brown adipose tissue (BAT) undergo dynamic processes, altering phenotypes and gene expressions. Proper reference genes in gene expression analysis are crucial to mitigate experimental variances and ensure PCR efficacy. Unreliable reference genes can lead to erroneous gene expression quantification, resulting in data misinterpretation. This study focused on identifying suitable reference genes for mouse brown adipocyte research, utilizing brown adipocytes from the Ucp1-luciferase ThermoMouse model. Comparative analysis of gene expression data under adipogenesis and thermogenesis conditions was conducted, validating 13 housekeeping genes through various algorithms, including DeltaCq, BestKeeper, geNorm, Normfinder, and RefFinder. Tbp and Rer1 emerged as optimal references for Ucp1 and Pparg expression in brown adipogenesis, while Tbp and Ubc were ideal for the expression analysis of these target genes in thermogenesis. Conversely, certain conventional references, including Actb, Tubb5, and Gapdh, proved unstable as reference genes under both conditions. These findings stress the critical consideration of reference gene selection in gene expression analysis within specific biological systems to ensure accurate conclusions.

Cross-talk between adipose tissue and microbiota-gut-brain-axis in brain development and neurological disorder

The gut microbiota is an important factor responsible for the physiological processes as well as pathogenesis of host. The communication between central nervous system (CNS) and microbiota occurs by different pathways i.e., chemical, neural, immune, and endocrine. Alteration in gut microbiota i.e., gut dysbiosis causes alteration in the bidirectional communication between CNS and gut microbiota and linked to the pathogenesis of neurological and neurodevelopmental disorder. Therefore, now-a-days microbiota-gut-brain-axis (MGBA) has emerged as therapeutic target for the treatment of metabolic disorder. But, experimental data available on MGBA from basic research has limited application in clinical study. In present study we first summarized molecular mechanism of microbiota interaction with brain physiology and pathogenesis via collecting data from different sources i.e., PubMed, Scopus, Web of Science. Furthermore, evidence shows that adipose tissue (AT) is active during metabolic activities and may also interact with MGBA. Hence, in present study we have focused on the relationship among MGBA, brown adipose tissue, and white adipose tissue. Along with this, we have also studied functional specificity of AT, and understanding heterogeneity among MGBA and different types of AT. Therefore, molecular interaction among them may provide therapeutic target for the treatment of neurological disorder.

Decoding temporal thermogenesis: coregulator selectivity and transcriptional control in brown and beige adipocytes

In mammals, brown adipose tissue (BAT) and beige adipocytes in white adipose tissue (WAT) play pivotal roles in maintaining body temperature and energy metabolism. In mice, BAT quickly stimulates thermogenesis by activating brown adipocytes upon cold exposure. In the presence of chronic cold stimuli, beige adipocytes are recruited in inguinal WAT to support heat generation. Accumulated evidence has shown that thermogenic execution of brown and beige adipocytes is regulated in a fat depot-specific manner. Recently, we have demonstrated that ubiquitin ligase ring finger protein 20 (RNF20) regulates brown and beige adipocyte thermogenesis through fat-depot-specific modulation. In BAT, RNF20 regulates transcription factor GA-binding protein alpha (GABPα), whereas in inguinal WAT, RNF20 potentiates transcriptional activity of peroxisome proliferator-activated receptor-gamma (PPARγ) through the degradation of nuclear corepressor 1 (NCoR1). This study proposes the molecular mechanisms by which co-regulator(s) selectively and temporally control transcription factors to coordinate adipose thermogenesis in a fat-depot-specific manner. In this Commentary, we provide molecular features of brown and beige adipocyte thermogenesis and discuss the underlying mechanisms of distinct thermogenic processes in two fat depots.

Oct-B: A derivative of L-BAIBA significantly alleviating high-fat diet-induced obesity in mice

The rising prevalence of obesity is a global health concern. Supplementation with (S)-β-aminoisobutyric acid (L-BAIBA) has shown potential in preventing obesity and related metabolic disorders induced by high-fat diets. However, developing effective and low-toxicity BAIBA derivatives remains a challenging yet promising field. In this study, we introduce Oct-B, a novel BAIBA ester compound, which exhibits 80-fold greater efficacy than L-BAIBA in alleviating obesity in high-fat diet-fed mice. Our results demonstrate that Oct-B significantly reduces serum TG, TC, LDL-C, and the activities of ALT and AST, and also reduces TG and TC in liver, surpassing the effects of L-BAIBA. Histological analysis shows that Oct-B significantly decreases lipid accumulation in liver tissues, normalizes mast cells in white adipose tissue, and upregulates the expression of UCP1 protein in white adipose tissue. The qRT-PCR results indicated Oct-B alleviates obesity by downregulating lipogenic genes (PPARγ, ACC1, FAS), upregulating lipolysis related genes (PPARα, HSL) and thermogenic gene UCP1. Additionally, quantitative mass spectrometry reveals a marked increase in L-BAIBA levels in white fat, brown fat, serum, and muscle following Oct-B administration. These findings suggest that Oct-B is an efficient L-BAIBA substitute, offering a promising therapeutic approach for preventing and treating high-fat diet-induced obesity.

Reversing Pdgfrβ signaling restores metabolically active beige adipocytes by alleviating ILC2 suppression in aged and obese mice

OBJECTIVE

Platelet Derived Growth Factor Receptor Beta (Pdgfrβ) suppresses the formation of cold temperature-induced beige adipocytes in aged mammals. We aimed to determine if deleting Pdgfrβ in aged mice could rejuvenate metabolically active beige adipocytes by activating group 2 innate lymphoid cells (ILC2), and whether this effect could counteract diet-induced obesity-associated beige fat decline.

METHODS

We employed Pdgfrβ gain-of-function and loss-of-function mouse models targeting beige adipocyte progenitor cells (APCs). Our approach included cold exposure, metabolic cage analysis, and age and diet-induced obesity models to examine beige fat development and metabolic function under varied Pdgfrβ activity.

RESULTS

Acute cold exposure alone enhanced metabolic benefits in aged mice, irrespective of beige fat generation. However, Pdgfrβ deletion in aged mice reestablished the formation of metabolically functional beige adipocytes, enhancing metabolism. Conversely, constitutive Pdgfrβ activation in young mice stymied beige fat development. Mechanistically, Pdgfrβ deletion upregulated IL-33, promoting ILC2 recruitment and activation, whereas Pdgfrβ activation reduced IL-33 levels and suppressed ILC2 activity. Notably, diet-induced obesity markedly increased Pdgfrβ expression and Stat1 signaling, which inhibited IL-33 induction and ILC2 activation. Genetic deletion of Pdgfrβ restored beige fat formation in obese mice, improving whole-body metabolism.

CONCLUSIONS

This study reveals that cold temperature exposure alone can trigger metabolic activation in aged mammals. However, reversing Pdgfrβ signaling in aged and obese mice not only restores beige fat formation but also renews metabolic function and enhances the immunological environment of white adipose tissue (WAT). These findings highlight Pdgfrβ as a crucial target for therapeutic strategies aimed at combating age- and obesity-related metabolic decline.

Brown adipose tissue: a potential target for aging interventions and healthy longevity

Brown Adipose Tissue (BAT) is a type of fat tissue that can generate heat and plays an important role in regulating body temperature and energy metabolism. Enhancing BAT activity through medication, exercise and other means has become a potential effective method for treating metabolic disorders. Recently, there has been increasing evidence suggesting a link between BAT and aging. As humans age, the volume and activity of BAT decrease, which may contribute to the development of age-related diseases. Multiple organelles signaling pathways have been reported to be involved in the aging process associated with BAT. Therefore, we aimed to review the evidence related to the association between aging process and BAT decreasing, analyze the potential of BAT as a predictive marker for age-related diseases, and explore potential therapeutic strategies targeting BAT for aging interventions and healthy longevity.

Dietary Lactate Intake and Physical Exercise Synergistically Reverse Brown Adipose Tissue Whitening to Ameliorate Diet-Induced Obesity

Physical exercise represents an effective strategy for combating obesity via brown adipose tissue (BAT) activation, but the mechanism remains unclear. In this study, we demonstrated that the cooperation between lactate and adrenoceptor signaling regulated BAT activity during exercise. The lactate receptor GPR81 was highly expressed in the BAT of lean mice, whereas its expression was markedly decreased in obese mice. Notably, the level of GPR81 in BAT could be upregulated by exercise. The blockade of lactate production or GPR81 significantly impaired exercise-induced BAT activation. In addition, dietary lactate intake enhanced the efficacy of physical exercise in alleviating BAT whitening in obese mice, as evidenced by the improved mitochondrial ultrastructure, reduced lipid droplets, increased UCP1 expression, and elevated mitochondrial DNA content. Further data indicated that norepinephrine triggered UCP1 activation through both the cAMP/PKA and Ca2+/CaMK pathways during exercise, while lactate mediated this process via the GPR81-Ca2+/CaMK cascade. Our findings unveil a novel mechanism in the regulation of BAT function by physical exercise, providing a promising lifestyle intervention to improve metabolic health.

Therapeutic effects of FGF21 mimetic bFKB1 on MASH and atherosclerosis in Ldlr-/-.Leiden mice

Fibroblast growth factor 21 (FGF21) is a promising target for treatment of obesity-associated diseases including metabolic dysfunction-associated steatohepatitis (MASH) and atherosclerosis. We evaluated the effects of the bispecific anti-FGF21-β klotho (KLB) agonist antibody bFKB1 in a preclinical model of MASH and atherosclerosis. Low-density lipoprotein receptor knockout (Ldlr-/-).Leiden mice received a high-fat diet for 20 weeks, followed by treatment with an isotype control antibody or bFKB1 for 12 weeks. Effects on plasma risk markers and (histo)pathology of liver, adipose tissue, and heart were evaluated alongside hepatic transcriptomics analysis. bFKB1 lowered body weight (-21%) and adipose tissue mass (-22%) without reducing food intake. The treatment also improved plasma insulin (-80%), cholesterol (-48%), triglycerides (-76%), alanine transaminase (ALT: -79%), and liver weight (-43%). Hepatic steatosis and inflammation were strongly reduced (macrovesicular steatosis -34%; microvesicular steatosis -100%; inflammation -74%) and while the total amount of fibrosis was not affected, bFKB1 did decrease new collagen formation (-49%). Correspondingly, hepatic transcriptomics and pathway analysis revealed the mechanistic background underlying these histological improvements, demonstrating broad inactivation of inflammatory and profibrotic transcriptional programs by bFKB1. In epididymal white adipose tissue, bFKB1 reduced adipocyte size (-16%) and inflammation (-52%) and induced browning, signified by increased uncoupling protein-1 (UCP1) protein expression (8.5-fold increase). In the vasculature, bFKB1 had anti-atherogenic effects, lowering total atherosclerotic lesion area (-38%). bFKB1 has strong beneficial metabolic effects associated with a reduction in hepatic steatosis, inflammation, and atherosclerosis. Analysis of new collagen formation and profibrotic transcriptional programs indicate that bFKB1 treatment may have antifibrotic potential in a longer treatment duration as well.

Influence of Mitochondrial NAD(P) + Transhydrogenase (NNT) on Hypothalamic Inflammation and Metabolic Dysfunction Induced by a High-Fat Diet in Mice

The mitochondrial protein NAD(P)+ transhydrogenase (NNT) has been implicated in the metabolic derangements observed in obesity. Mice with the C57BL/6J genetic background bear a spontaneous mutation in the Nnt gene and are known to exhibit increased susceptibility to diet-induced metabolic disorders. Most of the studies on NNT in the context of diet-induced obesity have compared C57BL/6J mice with other mouse strains, where differences in genetic background can serve as confounding factors. Moreover, these studies have predominantly employed a high-fat diet (HFD) consisting of approximately 60% of calories from fat, which may not accurately mimic real-world fat-rich diets. In this study, we sought to examine the role of NNT in diet-induced hypothalamic inflammation and metabolic syndrome by using a congenic mice model lacking NNT, along with a HFD providing approximately 45% of calories from fat. Our findings indicate that mice lacking NNT were more protected from HFD-induced weight gain but presented a worse performance on glucose tolerance test, albeit not in insulin tolerance test. Interestingly, the brown adipose tissue of HFD-fed Nnt +/+ mice presented a greater mass and a higher whole-tissue ex-vivo oxygen consumption rate. Also, HFD increased the expression of the inflammatory markers Il1β, Tlr4 and Iba1 in the hypothalamus of Nnt -/- mice. In conclusion, our study highlights the importance of NNT in the context of diet-induced obesity and metabolic syndrome, indicating its contribution to mitigate hypothalamic inflammation and suggesting its role in the brown adipose tissue increased mass.

Sympathetic innervation of interscapular brown adipose tissue is not a predominant mediator of OT-elicited reductions of body weight gain and adiposity in male diet-induced obese rats

Recent studies indicate that central administration of oxytocin (OT) reduces body weight (BW) in high fat diet-induced obese (DIO) rodents by reducing energy intake and increasing energy expenditure (EE). Previous studies in our lab have shown that administration of OT into the fourth ventricle (4V; hindbrain) elicits weight loss and stimulates interscapular brown adipose tissue temperature (TIBAT) in DIO rats. We hypothesized that OT-elicited stimulation of sympathetic nervous system (SNS) activation of IBAT contributes to its ability to activate BAT and reduce BW in DIO rats. To test this, we determined the effect of disrupting SNS activation of IBAT on OT-elicited stimulation of TIBAT and reduction of BW in DIO rats. We first confirmed that bilateral surgical SNS denervation to IBAT was successful based on having achieved ≥ 60% reduction in IBAT norepinephrine (NE) content from DIO rats. NE content was selectively reduced in IBAT by 94.7 ± 2.7, 96.8 ± 1.8 and 85.9 ± 6.1% (P<0.05) at 1, 6 and 7-weeks post-denervation, respectively, and was unchanged in liver or inguinal white adipose tissue. We then measured the impact of bilateral surgical SNS denervation to IBAT on the ability of acute 4V OT (1, 5 μg) to stimulate TIBAT in DIO rats. We found that the high dose of 4V OT (5 μg) stimulated TIBAT similarly between sham and denervated rats (P=NS) and that the effects of 4V OT to stimulate TIBAT did not require beta-3 adrenergic receptor signaling. We subsequently measured the effect of bilateral surgical denervation of IBAT on the effect of chronic 4V OT (16 nmol/day) or vehicle infusion to reduce BW, adiposity and energy intake in DIO rats. Chronic 4V OT reduced BW gain by -7.2 ± 9.6 g and -14.1 ± 8.8 g in sham and denervated rats (P<0.05 vs vehicle treatment), respectively, and this effect was similar between groups (P=NS). These effects were associated with reductions in adiposity and energy intake (P<0.05). Collectively, these findings support the hypothesis that sympathetic innervation of IBAT is not required for central OT to increase BAT thermogenesis and reduce BW gain and adiposity in male DIO rats.

Maresin2 negatively regulates DC's maturation via the MAPK/NF-κB pathway in DCs

OBJECTIVE

To observe the effects and mechanisms of Maresin2 on the function of DCs(Dendritic cells).

METHOD

The levels of IL-6, IL-12, TNF-α and IL-1β secreted by BMDCs (Bone marrow-derived Dendritic cells) after Maresin2 treatment were detected by ELISA. At the same time, the expressions of costimulatory molecules CD40 and CD86 on the surface, the ability of phagocytosis of ovalbumin(OVA) antigen, and antigen presentation function in BMDCs were analyzed by flow cytometry. Finally, MAPK and NF-κB pathway signaling phosphorylation in Maresin2-treated BMDCs were detected by western blot.

RESULTS

The secretion levels of IL-6, IL-12, TNF-α and IL-1β were significantly decreased in the Maresin2 treatment group after LPS treatment (P < 0.05). The expression levels of CD86 and CD40 were significantly decreased after Maresin2 treatment (P < 0.05). Maresin2 enhanced the phagocytosis ability of ovalbumin(OVA) (P < 0.05), but the ability of antigen presentation of BMDCs with the treatment of Maresin2 changed slightly (P > 0.05). Phosphorylation of p38, JNK, p65, ikka/β and ERK peaked at 15 min in the LPS group, while phosphorylation of p-p38 and p-ERK weakened 30 min and 60 min after treatment with Maresin2.

CONCLUSIONS

Maresin2 inhibits inflammatory cytokine secretion but enhances phagocytosis via the MAPK/NF-κB pathway in BMDCs, which may contribute to negatively regulating inflammation.

Pregnancy zone protein, a potential research target in multiple diseases

Pregnancy zone protein (PZP) is an antiprotease-resistant immunosuppressant belonging to the α-macroglobulin (αM) protein family. PZP is secreted by the liver and was found to be upregulated in plasma during pregnancy. α-2-macroglobulin (Α2M) shares 71 % serial homology with PZP, but low PZP levels do not lead to increased A2M levels in pregnancy. PZP can interact with several factors such as low-density lipoprotein receptor-associated protein (LRP), transforming growth factor-β (TGF-β), 78 kDa glucose-regulated protein (GRP78), and glycoside A (GdA). PZP is involved in the development of glycolipid metabolism disorders, bronchiectasis, Alzheimer's disease (AD), rheumatoid arthritis (RA), myocardial infarction (MI) and inflammatory bowel disease (IBD). PZP is also associated with the progression of tumorigenesis such as breast cancer (BC), homologyepatocellular carcinoma (HCC), lung adenocarcinoma (LAC), and colorectal cancer (CRC). Therefore, this review analyzes the role of PZP in pathophysiology of various diseases.

Phenotypic characteristics of adipocyte-like cells generated from C2C12 myoblasts cultured with chicken serum

The aim of this study was to clarify the transcriptional and metabolic characteristics of C2C12 myoblasts cultured in Dulbecco's Modified Eagle Medium (DMEM) containing 20 % chicken serum (CHS) (C2C12-CHS cells) compared with C2C12 myoblasts cultured in DMEM containing 20 % fetal bovine serum (FBS) (C2C12-FBS cells). After 3 days of culture, C2C12-CHS cells showed a marked accumulation of lipid droplets, accompanied by increased expression levels of brown adipocyte-related genes (i.e., Bmp7, Prdm16, Ucp1, Cidea, Pgc1α, Cox7a1, Cox8, and β3-adorenoceptor). Furthermore, stimulation of β3-adorenoceptor by its selective agonist, mirabegron, increased the mRNA expression of Ucp1 and Pgc1α in C2C12-CHS cells. Wide-targeted metabolomic analysis performed by gas chromatography-tandem mass spectrometry revealed that the metabolic profile of C2C12-CHS cells was obviously different to that of C2C12-FBS cells. Additionally, the metabolomic analysis indicated that β3-adrenoceptor stimulation by mirabegron upregulated energy metabolism in C2C12-CHS cells as seen in brown adipocytes. These results suggest that C2C12-CHS cells may differentiate into brown adipocyte-like cells, accompanied by increased functional β3-adrenoceptor.

Sympathetic Innervation of Interscapular Brown Adipose Tissue Is Not a Predominant Mediator of Oxytocin-Induced Brown Adipose Tissue Thermogenesis in Female High Fat Diet-Fed Rats

Recent studies have indicated that hindbrain [fourth ventricle (4V)] administration of the neurohypophyseal hormone, oxytocin (OT), reduces body weight, energy intake and stimulates interscapular brown adipose tissue temperature (TIBAT) in male diet-induced obese (DIO) rats. What remains unclear is whether chronic hindbrain (4V) OT can impact body weight in female high fat diet-fed (HFD) rodents and whether this involves activation of brown adipose tissue (BAT). We hypothesized that OT-elicited stimulation of sympathetic nervous system (SNS) activation of interscapular brown adipose tissue (IBAT) contributes to its ability to activate BAT and reduce body weight in female high HFD-fed rats. To test this hypothesis, we determined the effect of disrupting SNS activation of IBAT on OT-elicited stimulation of TIBAT and reduction of body weight in DIO rats. We first measured the impact of bilateral surgical SNS denervation to IBAT on the ability of acute 4V OT (0.5, 1, and 5 µg ≈ 0.5, 0.99, and 4.96 nmol) to stimulate TIBAT in female HFD-fed rats. We found that the high dose of 4V OT (5 µg ≈ 4.96 nmol) stimulated TIBAT similarly between sham rats and denervated rats (p = NS). We subsequently measured the effect of bilateral surgical denervation of IBAT on the effect of chronic 4V OT (16 nmol/day ≈ 16.1 μg/day) or vehicle infusion to reduce body weight, adiposity and energy intake in female HFD-fed rats (N = 7-8/group). Chronic 4V OT reduced body weight gain (sham: -18.0 ± 4.9 g; denervation: -15.9 ± 3.7 g) and adiposity (sham: -13.9 ± 3.7 g; denervation: -13.6 ± 2.4 g) relative to vehicle treatment (p < 0.05) and these effects were similar between groups (p = NS). These effects were attributed, in part, to reduced energy intake evident during weeks 2 (p < 0.05) and 3 (p < 0.05). To test whether these results translate to other female rodent species, we also examined the effect of chronic 4V infusion of OT on body weight and adiposity in two strains of female HFD-fed mice. Similar to what we found in the HFD-fed rat model, we also found that chronic 4V OT (16 nmol/day) infusion resulted in reduced body weight gain, adiposity and energy intake in female DIO C57BL/6J and DBA/2J mice (p < 0.05 vs. vehicle). Together, these findings suggest that (1) sympathetic innervation of IBAT is not necessary for OT-elicited increases in BAT thermogenesis and weight loss in female HFD-fed rats and (2) the effects of OT to reduce weight gain and adiposity translate to other female mouse models of diet-induced obesity (DIO).

Effects of the Fungicide Prothioconazole on Lipid Metabolism in Mice: Whitening Alterations of Brown Adipose Tissue

With considerable concerns about the associations between metabolic disorders and agricultural biocides, there are scattered data suggesting that the triazole fungicide prothioconazole (PTC) at lower doses than the no observed adverse effect level of 5000 μg/kg/d possibly has the potential to disrupt glycolipid metabolism in mammals. Here, we investigated the effects of 50, 500, and 5000 μg/kg/d of PTC on glycolipid metabolism in mice following 8 weeks of administration via drinking water, with specific attention on brown adipose tissue (BAT) and white adipose tissue (WAT) in addition to the liver. We found that along with the increased serum triglyceride level in the 5000 μg/kg/d group, small fatty vacuoles occurred in livers in all treatment groups, indicating lipid accumulation. No change in WAT was observed, but PTC caused BAT whitening, characterized by adipocyte hypertrophy, more unilocular adipocytes with enlarged lipid droplets, reduced UCP1 levels, and down-regulated Doi2 expression, and even the dose of 50 μg/kg/d was effective. Transcriptomic analysis revealed immune inhibition and circadian rhythm disturbance in BAT from the 5000 μg/kg/d group, which are in agreement with BAT whitening and inactivation. On employing the C3H10T1/2 cells in vitro, we found that PTC treatment concentration-dependently promoted lipid accumulation in brown adipocytes, along with altered expression of thermogenesis-related and circadian genes. Taken together, our study shows that low doses of PTC caused BAT whitening, calling for much attention to the new target by pollutants.

Structural basis of respiratory complex adaptation to cold temperatures

In response to cold, mammals activate brown fat for respiratory-dependent thermogenesis reliant on the electron transport chain. Yet, the structural basis of respiratory complex adaptation upon cold exposure remains elusive. Herein, we combined thermoregulatory physiology and cryoelectron microscopy (cryo-EM) to study endogenous respiratory supercomplexes from mice exposed to different temperatures. A cold-induced conformation of CI:III2 (termed type 2) supercomplex was identified with a ∼25° rotation of CIII2 around its inter-dimer axis, shortening inter-complex Q exchange space, and exhibiting catalytic states that favor electron transfer. Large-scale supercomplex simulations in mitochondrial membranes reveal how lipid-protein arrangements stabilize type 2 complexes to enhance catalytic activity. Together, our cryo-EM studies, multiscale simulations, and biochemical analyses unveil the thermoregulatory mechanisms and dynamics of increased respiratory capacity in brown fat at the structural and energetic level.

Effective Prevention and Treatment of Acute Leukemias in Mice by Activation of Thermogenic Adipose Tissues

Acute myeloid leukemia (AML) and acute lymphoblastic leukemia (ALL) are common hematological malignancies in adults. Despite considerable research advances, the development of standard therapies, supportive care, and prognosis for the majority of AML and ALL patients remains poor and the development of new effective therapy is urgently needed. Here, it is reported that activation of thermogenic adipose tissues (TATs) by cold exposure or β3-adrenergic receptor agonists markedly alleviated the development and progression of AML and ALL in mouse leukemia models. TAT activation (TATA) monotherapy substantially reduces leukemic cells in bone marrow and peripheral blood, and suppresses leukemic cell invasion, including hepatomegaly and splenomegaly. Notably, TATA therapy prolongs the survivals of AML- and ALL-bearing mice. Surgical removal of thermogenic brown adipose tissue (BAT) or genetic deletion of uncoupling protein 1 (UCP1) largely abolishes the TATA-mediated anti-leukemia effects. Metabolomic pathway analysis demonstrates that glycolytic metabolism, which is essential for anabolic leukemic cell growth, is severely impaired in TATA-treated leukemic cells. Moreover, a combination of TATA therapy with chemotherapy produces enhanced anti-leukemic effects and reduces chemotoxicity. These data provide a new TATA-based therapeutic paradigm for the effective treatment of AML, ALL, and likely other types of hematological malignancies.

Maintenance of thermogenic adipose tissues despite loss of the H3K27 acetyltransferases p300 or CBP

Brown and beige adipose tissues are specialized for thermogenesis and are important for energy balance in mice. Mounting evidence suggests that chromatin-modifying enzymes are integral for the development, maintenance, and functioning of thermogenic adipocytes. p300 and cAMP-response element binding protein (CREB)-binding protein (CBP) are histone acetyltransferases (HATs) responsible for writing the transcriptionally activating mark H3K27ac. Despite their homology, p300 and CBP do have unique tissue- and context-dependent roles, which have yet to be examined in brown and beige adipocytes specifically. We assessed the requirement of p300 or CBP in thermogenic fat using uncoupling protein 1 (Ucp1)-Cre-mediated knockdown in mice to determine whether their loss impacted tissue development, susceptibility to diet-induced obesity, and response to pharmacological induction via β3-agonism. Despite successful knockdown, brown adipose tissue mass and expression of thermogenic markers were unaffected by loss of either HAT. As such, knockout mice developed a comparable degree of diet-induced obesity and glucose intolerance to that of floxed controls. Furthermore, "browning" of white adipose tissue by the β3-adrenergic agonist CL-316,243 remained largely intact in knockout mice. Although p300 and CBP have nonoverlapping roles in other tissues, our results indicate that they are individually dispensable within thermogenic fats specifically, possibly due to functional compensation by one another.NEW & NOTEWORTHY The role of transcriptionally activating H3K27ac epigenetic mark has yet to be examined in mouse thermogenic fats specifically, which we achieved here via Ucp1-Cre-driven knockdown of the histone acetyltransferases (HAT) p300 or CBP under several metabolic contexts. Despite successful knockdown of either HAT, brown adipose tissue was maintained at room temperature. As such, knockout mice were indistinguishable to controls when fed an obesogenic diet or when given a β3-adrenergic receptor agonist to induce browning of white fat. Unlike other tissues, thermogenic fats are resilient to p300 or CBP ablation, likely due to sufficient functional overlap between them.

Sodium-glucose cotransporter 2 inhibitors and renin-angiotensin-aldosterone system, possible cellular interactions and benefits

Sodium glucose cotransporter 2 inhibitors (SGLT2is) are a newly developed class of anti-diabetics which exert potent hypoglycemic effects in the diabetic milieu. However, the evidence suggests that they also have extra-glycemic effects. The renin-angiotensin-aldosterone system (RAAS) is a hormonal system widely distributed in the body that is important for water and electrolyte homeostasis as well as renal and cardiovascular function. Therefore, modulating RAAS activity is a main goal in patients, notably diabetic patients, which are at higher risk of complications involving these organ systems. Some studies have suggested that SGLT2is have modulatory effects on RAAS activity in addition to their hypoglycemic effects and, thus, these drugs can be considered as promising therapeutic agents for renal and cardiovascular disorders. However, the exact molecular interactions between SGLT2 inhibition and RAAS activity are not clearly understood. Therefore, in the current study we surveyed the literature for possible molecular mechanisms by which SGLT2is modulate RAAS activity.

SGLT2 inhibitor canagliflozin reduces visceral adipose tissue in db/db mice by modulating AMPK/KLF4 signaling and regulating mitochondrial dynamics to induce browning

Obesity is characterized by excessive accumulation of adipose tissue (mainly visceral). The morphology and function of mitochondria are crucial for regulating adipose browning and weight loss. Research suggests that the SGLT2 inhibitor canagliflozin may induce weight loss through an unknown mechanism, particularly targeting visceral adipose tissue. While Krueppel-Like Factor 4 (KLF4) is known to be essential for energy metabolism and mitochondrial function, its specific impact on visceral adipose tissue remains unclear. We administered canagliflozin to db/db mice for 8 weeks, or exposed adipocytes to canagliflozin for 24 h. The expression levels of browning markers, mitochondrial dynamics, and KLF4 were assessed. Then we validated the function of KLF4 through overexpression in vivo and in vitro. Adenosine monophosphate-activated protein kinase (AMPK) agonists, inhibitors, and KLF4 si-RNA were employed to elucidate the relationship between AMPK and KLF4. The findings demonstrated that canagliflozin significantly decreased body weight in db/db mice and augmented cold-induced thermogenesis. Additionally, canagliflozin increased the expression of mitochondrial fusion-related factors while reducing the levels of fission markers in epididymal white adipose tissue. These consistent findings were mirrored in canagliflozin-treated adipocytes. Similarly, overexpression of KLF4 in both adipocytes and db/db mice yielded comparable results. In all, canagliflozin mitigates obesity in db/db mice by promoting the brown visceral adipocyte phenotype through enhanced mitochondrial fusion via AMPK/KLF4 signaling.

Adjustments in energy metabolism of brown adipose tissue in heat-acclimated Kunming mice

The thermogenic capacity of brown adipose tissue (BAT) in rodents decreases with prolonged heat exposure. However, the underlying mechanisms are not well understood. In this study, Kunming mice were acclimated at 23 ± 1 °C and 33 ± 1 °C for four weeks each to examine the body heat balance and BAT alterations. Results showed that heat-acclimated Kunming mice exhibited reduced body mass and elevated body temperature. Additionally, they displayed lower resting metabolic rates, diminished non-shivering thermogenesis, and reduced BAT thermogenic function. Metabolically, there was a significant reduction in several key metabolites involved in energy metabolism in BAT, including thiamine pyrophosphate, citric acid, cis-Aconitate, isocitric acid, oxoglutaric acid, succinate, fumarate, L-Malic acid, oxaloacetate, flavin mononucleotide, nicotinamide adenine dinucleotide, and adenosine 5'-triphosphate. These findings suggest that BAT adapts to heat acclimation by regulating pathways related to pyruvate oxidation, tricarboxylic acid cycle, and oxidative phosphorylation, which may help maintain thermal homeostasis in Kunming mice.

Adipose Tissue Plasticity: A Comprehensive Definition and Multidimensional Insight

Adipose tissue is composed of adipocytes, stromal vascular fraction, nerves, surrounding immune cells, and the extracellular matrix. Under various physiological or pathological conditions, adipose tissue shifts cellular composition, lipid storage, and organelle dynamics to respond to the stress; this remodeling is called "adipose tissue plasticity". Adipose tissue plasticity includes changes in the size, species, number, lipid storage capacity, and differentiation function of adipocytes, as well as alterations in the distribution and cellular composition of adipose tissue. This plasticity has a major role in growth, obesity, organismal protection, and internal environmental homeostasis. Moreover, certain thresholds exist for this plasticity with significant individualized differences. Here, we comprehensively elaborate on the specific connotation of adipose tissue plasticity and the relationship between this plasticity and the development of many diseases. Meanwhile, we summarize possible strategies for treating obesity in response to adipose tissue plasticity, intending to provide new insights into the dynamic changes in adipose tissue and contribute new ideas to relevant clinical problems.

Cigarette smoke extract decreases human bone marrow mesenchymal stromal cell adipogenic differentiation

BACKGROUND

Smoking and nicotine impose detrimental health effects including adipose tissue dysfunction. Despite extensive physiological evidence, the cellular mechanisms remain poorly understood, with few studies examining the effects of cigarette smoke extract (CSE) or nicotine on adipocyte differentiation.

METHODS

Primary human bone marrow-derived mesenchymal stromal cells (MSCs) were exposed to CSE or nicotine (50-500 ng/ml) during adipogenic differentiation. Cell viability and metabolic activity were assessed via MTT assay. Lipid droplet accumulation was evaluated using Sudan III staining and quantitative image analysis. Adiponectin, IL6, and IL8 concentrations were measured after 35 days using ELISA.

RESULTS

At these doses, CSE and nicotine do not immediately affect cell viability but inhibit undifferentiated cell proliferation. Notably, both agents at 50 ng/ml significantly increased lipid accumulation during adipogenesis, while higher CSE doses nearly completely inhibited this process. Additionally, CSE dose-dependently decreased adiponectin secretion and increased IL6 and IL8, indicating a shift towards an inflammatory state. Nicotine alone primarily increased IL6 secretion with less pronounced effects.

CONCLUSION

The study highlights the complex impact of CSE and nicotine on adipocyte function during early differentiation from MSCs. Dose-dependent changes in lipid accumulation, cytokine, and adiponectin secretion induced by CSE and nicotine can partly explain smoking-related adipose tissue dysfunction.

Slit3 Fragments Orchestrate Neurovascular Expansion and Thermogenesis in Brown Adipose Tissue

Brown adipose tissue (BAT) represents an evolutionary innovation enabling placental mammals to regulate body temperature through adaptive thermogenesis. Brown adipocytes are surrounded by a dense network of blood vessels and sympathetic nerves that support their development and thermogenic function. Cold exposure stimulates BAT thermogenesis through the coordinated induction of brown adipogenesis, angiogenesis, and sympathetic innervation. However, how these distinct processes are coordinated remains unclear. Here, we identify Slit guidance ligand 3 (Slit3) as a new niche factor that mediates the crosstalk among adipocyte progenitors, endothelial cells, and sympathetic nerves. We show that adipocyte progenitors secrete Slit3 which regulates both angiogenesis and sympathetic innervation in BAT and is essential for BAT thermogenesis in vivo. Proteolytic cleavage of Slit3 generates secreted Slit3-N and Slit3-C fragments, which activate distinct receptors to stimulate angiogenesis and sympathetic innervation, respectively. Moreover, we introduce bone morphogenetic protein-1 (Bmp1) as the first Slit protease identified in vertebrates. In summary, this study underscores the essential role of Slit3-mediated neurovascular network expansion in enabling cold-induced BAT adaptation. The co-regulation of neurovascular expansion by Slit3 fragments provides a bifurcated yet harmonized approach to ensure a synchronized response of BAT to environmental challenges. This study presents the first evidence that adipocyte progenitors regulate tissue innervation, revealing a previously unrecognized dimension of cellular interaction within adipose tissue.

Fatty acids promote uncoupled respiration via the ATP/ADP carrier in white adipocytes

Adipocytes store energy as triglycerides, while mobilizing energy when needed via lipolysis. Triglyceride lipolysis releases fatty acids and glycerol into the circulation to fuel other tissues. However, a significant fraction of fatty acids released by lipolysis are retained within the white adipose tissue and handled by adipocytes. While some of these retained fatty acids are re-esterified in white adipocytes1-6, the a substantial amount undergo oxidative metabolism via a pathway regulated by the nongenomic effects of STAT37-10. Here we report that fatty acids promote uncoupled oxidative metabolism in white adipocytes via the ATP/ADP carrier, contributing to thermogenesis and cold tolerance in obese thermoneutral-adapted mice, independent of brown adipose tissue and muscle activity. Our results suggest that uncoupled respiration in white adipocytes significantly contributes to whole-body energy expenditure and could be a promising target for obesity treatment.

The Herbal Blend of Sphaeranthus indicus and Garcinia mangostana Reduces Adiposity in High-Fat Diet Obese Mice

Obesity is swiftly becoming a global epidemic, leading to numerous metabolic disorders and substantial socio-economic burdens. Investigating natural bioactive compounds is crucial to support the use of traditional anti-obesity medications while mitigating the adverse effects. This study posited that a combination of Sphaeranthus indicus and Garcinia mangostana (Meratrim) could prevent fat accumulation in obese mice. We used 4-week-old C57BL/6NTac mice, dividing them into six groups: (1) normal diet (ND); (2) high-fat diet (HFD, 45% kcal from fat); (3-5) Meratrim150, Meratrim300, and Meratrim450 (HFD with 150, 300, and 450 mg/kg bw of Meratrim); and (6) Metformin (HFD with 150 mg/kg bw of metformin). Meratrim was administered orally each day for 20 weeks. The group receiving 450 mg/kg of Meratrim showed a significant reduction in body weight and fat mass without changes in food consumption. The Meratrim450 group had markedly lower triglyceride levels in both serum and liver. Importantly, Meratrim-supplemented mice improved lipid homeostasis by inhibiting hepatic de novo lipogenesis and activating energy catabolic pathways such as non-shivering thermogenesis in brown adipose tissue. Our results suggest that the herbal mixture of Sphaeranthus indicus and Garcinia mangostana (Meratrim) is a promising natural anti-obesity agent, owing to its efficacy in reducing body fat and enhancing lipid homeostasis.

Inter-organ cross-talk in human cancer cachexia revealed by spatial metabolomics

BACKGROUND

Cancer cachexia (CCx) presents a multifaceted challenge characterized by negative protein and energy balance and systemic inflammatory response activation. While previous CCx studies predominantly focused on mouse models or human body fluids, there's an unmet need to elucidate the molecular inter-organ cross-talk underlying the pathophysiology of human CCx.

METHODS

Spatial metabolomics were conducted on liver, skeletal muscle, subcutaneous and visceral adipose tissue, and serum from cachectic and control cancer patients. Organ-wise comparisons were performed using component, pathway enrichment and correlation network analyses. Inter-organ correlations in CCx altered pathways were assessed using Circos. Machine learning on tissues and serum established classifiers as potential diagnostic biomarkers for CCx.

RESULTS

Distinct metabolic pathway alteration was detected in CCx, with adipose tissues and liver displaying the most significant (P ≤ 0.05) metabolic disturbances. CCx patients exhibited increased metabolic activity in visceral and subcutaneous adipose tissues and liver, contrasting with decreased activity in muscle and serum compared to control patients. Carbohydrate, lipid, amino acid, and vitamin metabolism emerged as highly interacting pathways across different organ systems in CCx. Muscle tissue showed decreased (P ≤ 0.001) energy charge in CCx patients, while liver and adipose tissues displayed increased energy charge (P ≤ 0.001). We stratified CCx patients by severity and metabolic changes, finding that visceral adipose tissue is most affected, especially in cases of severe cachexia. Morphometric analysis showed smaller (P ≤ 0.05) adipocyte size in visceral adipose tissue, indicating catabolic processes. We developed tissue-based classifiers for cancer cachexia specific to individual organs, facilitating the transfer of patient serum as minimally invasive diagnostic markers of CCx in the constitution of the organs.

CONCLUSIONS

These findings support the concept of CCx as a multi-organ syndrome with diverse metabolic alterations, providing insights into the pathophysiology and organ cross-talk of human CCx. This study pioneers spatial metabolomics for CCx, demonstrating the feasibility of distinguishing cachexia status at the organ level using serum.

The Therapeutic Potential of Theobromine in Obesity: A Comprehensive Review

Obesity, characterized by chronic low-grade inflammation, is a significant health concern. Phytochemicals found in plants are being explored for therapeutic use, particularly in combating obesity. Among these, theobromine, commonly found in cocoa and chocolate, shows promise. Although not as extensively studied as caffeine, theobromine exhibits positive effects on human health. It improves lipid profiles, aids in asthma treatment, lowers blood pressure, regulates gut microbiota, reduces tumor formation, moderates blood glucose levels, and acts as a neuroprotective agent. Studies demonstrate its anti-obesity effects through mechanisms such as browning of white adipose tissue, activation of brown adipose tissue, anti-inflammatory properties, and reduction of oxidative stress. This study aims to suggest theobromine as a potential therapeutic agent against obesity-related complications.

Early Adipogenesis and Upregulation of UCP1 in Mesenchymal Stromal Cells Stimulated by Devitalized Microfragmented Fat (MiFAT)

Adipose tissue is mainly composed by adipocytes. Moreover, mesenchymal stromal/stem cells (MSCs), macrophages, endothelial cells, and extracellular matrix components are present. The variety of molecules as cytokines and growth factors of its structure very rich in blood vessel makes it also similar to a true endocrine organ that however needs still to be fully investigated. In our study, we used human lipoaspirate to obtain mechanically microfragmented fat (MiFAT) which was washed and then devitalized by freezing-thawing cycles. In our experiments, thawed MiFAT was used to stimulate cultures of MSCs from two different sources (adipose tissue and gingiva papilla) in comparison with a traditional stimulation in vitro obtained by culturing MSCs with adipogenic medium. MSCs stimulated with MiFAT showed a very early production of lipid droplets, after only 3 days, that correlated with an increased expression of adipokines. Furthermore, a significant upregulation of PPAR gamma 1 alpha coactivator (PPARGC1A) was observed with an overexpression of uncoupling protein 1 (UCP1) that suggest a pattern of differentiation compatible with the beige-brown fat.

Maid gene dysfunction promotes hyperobesity via the reduction of adipose tissue inflammation in Mc4r gene-deficient mice

The onset and progression mechanisms of metabolic dysfunction-associated steatotic liver disease (MASLD) and metabolic dysfunction-associated steatohepatitis (MASH) are being studied. We developed and analyzed a new mouse model of obesity by combining maternal Id-like molecule (Maid) and melanocortin-4 receptor (Mc4r) gene deletions. Four mice, each at 12 and 28 weeks of age, were analyzed for each genotype: Maid gene knockout, Mc4r gene knockout, combined Mc4r and Maid gene knockout, and Mc4r gene knockout with a high-fat diet. Mice with a combined deficiency of Mc4r and Maid gene showed significantly more severe obesity compared to all other genotypes, but no liver fibrosis or a decline in metabolic status were observed. In visceral white adipose tissue, Maid and Mc4r gene knockout mice had fewer CD11c-positive cells and lower mRNA expression of both inflammatory and anti-inflammatory cytokines. Furthermore, Maid and Mc4r gene knockout mice showed lower expression of adipocytokines in visceral white adipose tissue and uncoupling protein-1 in scapular brown adipose tissue. The expression of adipocytokines and uncoupling protein-1 is regulated by sympathetic nerve signaling that contribute severe obesity in Maid and Mc4r gene knockout mice. These mechanisms contribute hyperobesity in Maid and Mc4r gene knockout mice.

Brown Adipose Tissue Activity and Childhood Exposure to Cold Are Associated With Hot Flashes at Menopause

OBJECTIVE

Hot flashes (HFs) are experienced as sudden sensations of heat. We hypothesized that brown adipose tissue (BAT) activation could increase the likelihood of HFs in winter. The aim of this study was to test whether women with more BAT activity were more likely to experience self-reported or biometrically measured HFs.

METHODS

Women aged 45-55 years (n = 270) participated in face-to-face interviews and anthropometric and ambulatory measures. Level of BAT activity was estimated from the difference in supraclavicular skin temperature measured by infrared thermography before and after cooling. Logistic regressions were applied to examine whether bothersome HFs (yes/no) during the past 2 weeks were associated with BAT activity, adjusting for menopausal status, childhood exposure to cold, waist/hip ratio, and self-reported health. Linear regressions were used to examine the frequency of self-reported and biometrically measured HFs during the study period and BAT activity, adjusting for potential confounders.

RESULTS

Menopausal status, childhood exposure to cold, waist-to-hip ratio (WHR), and self-reported health were associated with both BAT activity and HFs. After adjusting for potential confounders, an increase in BAT activity almost tripled the likelihood of bothersome HFs (OR 2.84, 95% CI 1.26-6.43). In linear regressions, BAT activity was not associated with frequency of subjective or objective HFs during the study period, but childhood exposure to cold was associated with subjective HF report (β = 0.163, p = 0.010).

CONCLUSION

To our knowledge, this is the first study of BAT activation and HFs. Our results support a role for BAT activity in HF experience. Therefore, we encourage further examination of the role of BAT, as well as childhood exposure to cold, in HFs.

Multi-organ transcriptome atlas of a mouse model of relative energy deficiency in sport

Insufficient energy intake to meet energy expenditure demands of physical activity can result in systemic neuroendocrine and metabolic abnormalities in activity-dependent anorexia and relative energy deficiency in sport (REDs). REDs affects >40% of athletes, yet the lack of underlying molecular changes has been a hurdle to have a better understanding of REDs and its treatment. To assess the molecular changes in response to energy deficiency, we implemented the "exercise-for-food" paradigm, in which food reward size is determined by wheel-running activity. By using this paradigm, we replicated several aspects of REDs in female and male mice with high physical activity and gradually reduced food intake, which results in weight loss, compromised bone health, organ-specific mass changes, and altered rest-activity patterns. By integrating transcriptomics of 19 different organs, we provide a comprehensive dataset that will guide future understanding of REDs and may provide important implications for metabolic health and (athletic) performance.

Mitochondrial membrane lipids in the regulation of bioenergetic flux

Oxidative phosphorylation (OXPHOS) occurs through and across the inner mitochondrial membrane (IMM). Mitochondrial membranes contain a distinct lipid composition, aided by lipid biosynthetic machinery localized in the IMM and class-specific lipid transporters that limit lipid traffic in and out of mitochondria. This unique lipid composition appears to be essential for functions of mitochondria, particularly OXPHOS, by its effects on direct lipid-to-protein interactions, membrane properties, and cristae ultrastructure. This review highlights the biological significance of mitochondrial lipids, with a particular spotlight on the role of lipids in mitochondrial bioenergetics. We describe pathways for the biosynthesis of mitochondrial lipids and provide evidence for their roles in physiology, their implications in human disease, and the mechanisms by which they regulate mitochondrial bioenergetics.

Development of a functional beige fat cell line uncovers independent subclasses of cells expressing UCP1 and the futile creatine cycle

Although uncoupling protein 1 (UCP1) is established as a major contributor to adipose thermogenesis, recent data have illustrated an important role for alternative pathways, particularly the futile creatine cycle (FCC). How these pathways co-exist in cells and tissues has not been explored. Beige cell adipogenesis occurs in vivo but has been difficult to model in vitro; here, we describe the development of a murine beige cell line that executes a robust respiratory response, including uncoupled respiration and the FCC. The key FCC enzyme, tissue-nonspecific alkaline phosphatase (TNAP), is localized almost exclusively to mitochondria in these cells. Surprisingly, single-cell cloning from this cell line shows that cells with the highest levels of UCP1 express little TNAP, and cells with the highest expression of TNAP express little UCP1. Immunofluorescence analysis of subcutaneous fat from cold-exposed mice confirms that the highest levels of these critical thermogenic components are expressed in distinct fat cell populations.

The function of brown adipose tissue at different sites of the body in Brandt's voles during cold acclimation

Ambient temperatures have great impacts on thermoregulation of small mammals. Brown adipose tissue (BAT), an obligative thermogenic tissue for small mammals, is localized not only in the interscapular depot (iBAT), but also in supraclavicular, infra/subscapular, cervical, paravertebral, and periaortic depots. The iBAT is known for its cold-induced thermogenesis, however, less has been paid attention to the function of BAT at other sites. Here, we investigated the function of BAT at different sites of the body during cold acclimation in a small rodent species. As expected, Brandt's voles (Lasiopodomys brandtii) consumed more food and reduced the body mass gain when they were exposed to cold. The voles increased resting metabolic rate and maintained a relatively lower body temperature in the cold (36.5 ± 0.27 °C) compared to those in the warm condition (37.1 ± 0.36 °C). During cold acclimation, the uncoupling protein 1 (UCP1) increased in aBAT (axillary), cBAT (anterior cervical), iBAT (interscapular), nBAT (supraclavicular), and sBAT (suprascapular). The levels of proliferating cell nuclear antigen (PCNA), a marker for cell proliferation, were higher in cBAT and iBAT in the cold than in the warm group. The pAMPK/AMPK and pCREB/CREB were increased in cBAT and iBAT during cold acclimation, respectively. These data indicate that these different sites of BAT play the cold-induced thermogenic function for small mammals.

Temporal Trends in Body Composition and Metabolic Markers Prior to Diagnosis of Pancreatic Ductal Adenocarcinoma

BACKGROUND & AIMS

Changes in body composition and metabolic factors may serve as biomarkers for the early detection of pancreatic ductal adenocarcinoma (PDAC). The aim of this study was to capture the longitudinal changes in body composition and metabolic factors before diagnosis of PDAC.

METHODS

We performed a retrospective cohort study in which all patients (≥18 years) diagnosed with PDAC from 2002 to 2021 were identified. We collected all abdominal computed tomography scans and 10 different blood-based biomarkers up to 36 months before diagnosis. We applied a fully automated abdominal segmentation algorithm previously developed by our group for 3-dimensional quantification of body composition on computed tomography scans. Longitudinal trends of body composition and blood-based biomarkers before PDAC diagnosis were estimated using linear mixed models, compared across different time windows, and visualized using spline regression.

RESULTS

We included 1690 patients in body composition analysis, of whom 516 (30.5%) had ≥2 prediagnostic computed tomography scans. For analysis of longitudinal trends of blood-based biomarkers, 3332 individuals were included. As an early manifestation of PDAC, we observed a significant decrease in visceral and subcutaneous adipose tissue (β = -1.94 [95% confidence interval (CI), -2.39 to -1.48] and β = -2.59 [95% CI, -3.17 to -2.02]) in area (cm2)/height (m2) per 6 months closer to diagnosis, accompanied by a decrease in serum lipids (eg, low-density lipoprotein [β = -2.83; 95% CI, -3.31 to -2.34], total cholesterol [β = -2.69; 95% CI, -3.18 to -2.20], and triglycerides [β = -1.86; 95% CI, -2.61 to -1.11]), and an increase in blood glucose levels. Loss of muscle tissue and bone volume was predominantly observed in the last 6 months before diagnosis.

CONCLUSIONS

This study identified significant alterations in a variety of soft tissue and metabolic markers that occur in the development of PDAC. Early recognition of these metabolic changes may provide an opportunity for early detection.

Developing MiR-133a Zipper Nanoparticles for Targeted Enhancement of Thermogenic Adipocyte Generation

Existing delivery methods for RNAi therapeutics encounter challenges, including stability, specificity, and off-target effects, which restrict their clinical effectiveness. In this study, a novel miR-133a zipper nanoparticle (NP) system that integrates miRNA zipper technology with rolling circle transcription (RCT) to achieve targeted delivery and specific regulation of miR-133a in adipocytes, is presented. This innovative approach can greatly enhance the delivery and release of miR-133a zippers, increasing the expression of thermogenic genes and mitochondrial biogenesis. he miR-133a zipper NP is utilized for the delivery of miRNA zipper-blocking miR-133a, an endogenous inhibitor of Prdm16 expression, to enhance the thermogenic activity of adipocytes by modulating their transcriptional program. Inhibition of miR-133a through the miR-133a zipper NP leads to more significant upregulation of thermogenic gene expression (Prdm16 and Ucp1) than with the free miR-133a zipper strand. Furthermore, miR-133a zipper NPs increase the number of mitochondria and induce heat production, reducing the size of 3D adipose spheroids. In short, this study emphasizes the role of RNA NPs in improving RNAi stability and specificity and paves the way for broader applications in gene therapy. Moreover, this research represents a significant advancement in RNAi-based treatments, pointing toward a promising direction for future therapeutic strategies.

Unravelling the function of prdm16 in human tumours: A comparative analysis of haematologic and solid tumours

Extensive research has shown that PR domain 16 (PRDM16) plays a critical role in adipose tissue metabolism, including processes such as browning and thermogenesis of adipocytes, beigeing of adipocytes, and adipogenic differentiation of myoblasts. These functions have been associated with diseases such as obesity and diabetes. Additionally, PRDM16 has been correlated with various other conditions, including migraines, heterochromatin abnormalities, metabolic syndrome, cardiomyopathy, sarcopenia, nonsyndromic cleft lip, and essential hypertension, among others. However, there is currently no systematic or comprehensive conclusion regarding the mechanism of PRDM16 in human tumours, including haematologic and solid tumours. The aim of this review is to provide an overview of the research progress on PRDM16 in haematologic and solid tumours by incorporating recent literature findings. Furthermore, we explore the prospects of PRDM16 in the precise diagnosis and treatment of human haematologic and solid tumours.

Mechanistic insights into metabolic function of dynamin-related protein 1

Dynamin-related protein 1 (DRP1) plays crucial roles in mitochondrial and peroxisome fission. However, the mechanisms underlying the functional regulation of DRP1 in adipose tissue during obesity remain unclear. To elucidate the metabolic and pathological significance of diminished DRP1 in obese adipose tissue, we utilized adipose tissue-specific DRP1 KO mice challenged with a high-fat diet. We observed significant metabolic dysregulations in the KO mice. Mechanistically, DRP1 exerts multifaceted functions in mitochondrial dynamics and endoplasmic reticulum (ER)-lipid droplet crosstalk in normal mice. Loss of function of DRP1 resulted in abnormally giant mitochondrial shapes, distorted mitochondrial membrane structure, and disrupted cristae architecture. Meanwhile, DRP1 deficiency induced the retention of nascent lipid droplets in ER, leading to perturbed overall lipid dynamics in the KO mice. Collectively, dysregulation of the dynamics of mitochondria, ER, and lipid droplets contributes to whole-body metabolic disorders, as evidenced by perturbations in energy metabolites. Our findings demonstrate that DRP1 plays diverse and critical roles in regulating energy metabolism within adipose tissue during the progression of obesity.

Role of protein arginine methyltransferase 1 in obesity-related metabolic disorders: Research progress and implications

Obesity has become a major global problem that significantly confers an increased risk of developing life-threatening complications, including type 2 diabetes mellitus, fatty liver disease and cardiovascular diseases. Protein arginine methyltransferases (PRMTs) are enzymes that catalyse the methylation of target proteins. They are ubiquitous in eukaryotes and regulate transcription, splicing, cell metabolism and RNA biology. As a key, epigenetically modified enzyme, protein arginine methyltransferase 1 (PRMT1) is involved in obesity-related metabolic processes, such as lipid metabolism, the insulin signalling pathway, energy balance and inflammation, and plays an important role in the pathology of obesity-related metabolic disorders. This review summarizes recent research on the role of PRMT1 in obesity-related metabolic disorders. The primary objective was to comprehensively elucidate the functional role and regulatory mechanisms of PRMT1. Moreover, this study attempts to review the pathogenesis of PRMT1-mediated obesity-related metabolic disorders, thereby offering pivotal information for further studies and clinical treatment.

Comparative functional analysis reveals differential nucleotide sensitivity between human and mouse UCP1

AIM

Mitochondrial uncoupling protein 1 (UCP1) is a unique protein of brown adipose tissue. Upon activation by free fatty acids, UCP1 facilitates a thermogenic net proton flux across the mitochondrial inner membrane. Non-complexed purine nucleotides inhibit this fatty acid-induced activity of UCP1. The most available data have been generated from rodent model systems. In light of its role as a putative pharmacological target for treating metabolic disease, in-depth analyses of human UCP1 activity, regulation, and structural features are essential.

METHODS

In the present study, we established a doxycycline-regulated cell model with inducible human or murine UCP1 expression and conducted functional studies using respirometry comparing wild-type and mutant variants of human UCP1.

RESULTS

We demonstrate that human and mouse UCP1 exhibit similar specific fatty acid-induced activity but a different inhibitory potential of purine nucleotides. Mutagenesis of non-conserved residues in human UCP1 revealed structural components in α-helix 56 and α-helix 6 crucial for uncoupling function.

CONCLUSION

Comparative studies of human UCP1 with other orthologs can provide new insights into the structure-function relationship for this mitochondrial carrier and will be instrumental in searching for new activators.

Lactating striped hamsters (Cricetulus barabensis) do not decrease the thermogenic capacity to cope with extreme cold temperature

For small non-hibernating mammals, a high thermogenic capacity is important to increase activity levels in the cold. It has been previously reported that lactating females decrease their thermogenic activity of brown adipose tissue (BAT), whereas their capacity to cope with extreme cold remains uncertain. In this study we examined food intake, body temperature and locomotor behavior, resting metabolic rate, non-shivering thermogenesis, and cytochrome c oxidase activity, and the rate of state 4 respiration of liver, skeletal muscle, and BAT in striped hamsters (Cricetulus barabensis) at peak lactation and non- breeding hamsters (controls). The lactating hamsters and non- breeding controls were acutely exposed to -15°C, and several markers indicative of thermogenic capacity were examined. In comparison to non-breeding females, lactating hamsters significantly increased food intake and body temperature, but decreased locomotor behavior, and the BAT mass, indicative of decreased BAT thermogenesis at peak lactation. Unexpectedly, lactating hamsters showed similar body temperature, resting metabolic rate, non-shivering thermogenesis with non-breeding females after acute exposure to -15°C. Furthermore, cytochrome c oxidase activity of liver, skeletal muscle and BAT, and serum thyroid hormone concentration, and BAT uncoupling protein 1 expression, in lactating hamsters were similar with that in non-breeding hamsters after acute extreme cold exposure. This suggests that lactating females have the same thermogenic capacity to survive cold temperatures compared to non-breeding animals. This is particularly important for females in the field to cope with cold environments during the period of reproduction. Our findings indicate that the females during lactation, one of the highest energy requirement periods, do not impair their thermogenic capacity in response to acute cold exposure.

The Different Shades of Thermogenic Adipose Tissue

PURPOSE OF REVIEW

By providing a concise overview of adipose tissue types, elucidating the regulation of adipose thermogenic capacity in both physiological contexts and chronic wasting diseases (a protracted hypermetabolic state that precipitates sustained catabolism and consequent progressive corporeal atrophy), and most importantly, delving into the ongoing discourse regarding the role of adipose tissue thermogenic activation in chronic wasting diseases, this review aims to provide researchers with a comprehensive understanding of the field.

RECENT FINDINGS

Adipose tissue, traditionally classified as white, brown, and beige (brite) based on its thermogenic activity and potential, is intricately regulated by complex mechanisms in response to exercise or cold exposure. This regulation is adipose depot-specific and dependent on the duration of exposure. Excessive thermogenic activation of adipose tissue has been observed in chronic wasting diseases and has been considered a pathological factor that accelerates disease progression. However, this conclusion may be confounded by the detrimental effects of excessive lipolysis. Recent research also suggests that such activation may play a beneficial role in the early stages of chronic wasting disease and provide potential therapeutic effects. A more comprehensive understanding of the changes in adipose tissue thermogenesis under physiological and pathological conditions, as well as the underlying regulatory mechanisms, is essential for the development of novel interventions to improve health and prevent disease.

Adipose thermogenic mechanisms by cold, exercise and intermittent fasting: Similarities, disparities and the application in treatment

Given its nonnegligible role in metabolic homeostasis, adipose tissue has been the target for treating metabolic disorders such as obesity, diabetes and cardiovascular diseases. Besides its lipolytic function, adipose thermogenesis has gained increased interest due to the irreplaceable contribution to dissipating energy to restore equilibrium, and its therapeutic effects have been testified in various animal models. In this review, we will brief about the canonical cold-stimulated adipose thermogenic mechanisms, elucidate on the exercise- and intermittent fasting-induced adipose thermogenic mechanisms, with a focus on the similarities and disparities among these signaling pathways, in an effort to uncover the overlapped and specific targets that may yield potent therapeutic efficacy synergistically in improving metabolic health.

Relative sarcolipin (SLN) and sarcoplasmic reticulum Ca2+ ATPase (SERCA1) transcripts levels in closely related endothermic and ectothermic scombrid fishes: Implications for molecular basis of futile calcium cycle non-shivering thermogenesis (NST)

Regional endothermy is the ability of an animal to elevate the temperature of specific regions of the body above that of the surrounding environment and has evolved independently among several fish lineages. Sarcolipin (SLN) is a small transmembrane protein that uncouples the sarcoplasmic reticulum calcium ATPase pump (SERCA1b) resulting in futile Ca2+ cycling and is thought to play a role in non-shivering thermogenesis (NST) in cold-challenged mammals and possibly some fishes. This study investigated the relative expression of sln and serca1 transcripts in three regionally-endothermic fishes (the skipjack, Katsuwonus pelamis, and yellowfin tuna, Thunnus albacares, both of which elevate the temperatures of their slow-twitch red skeletal muscle (RM) and extraocular muscles (EM), as well as the cranial endothermic swordfish, Xiphias gladius), and closely related ectothermic scombrids (the Eastern Pacific bonito, Sarda chiliensis, and Pacific chub mackerel, Scomber japonicus). Using Reverse Transcription quantitative PCR (RT-qPCR) and species-specific primers, relative sln expression trended higher in both the RM and EM for all four scombrid species compared to white muscle. In addition, relative serca1 expression was found to be higher in RM of skipjack and yellowfin tuna in comparison to white muscle. However, neither sln nor serca1 transcripts were higher in swordfish RM, EM or cranial heater tissue in comparison to white muscle. A key phosphorylation site in sarcolipin, threonine 5, is conserved in the swordfish, but is mutated to alanine or valine in tunas and the endothermic smalleye Pacific opah, Lampris incognitus, which should result in increased uncoupling of the SERCA pump. Our results support the role of potential SLN-NST in endothermic tunas and the lack thereof for swordfish.

Adaptive Induction of Nonshivering Thermogenesis in Muscle Rather Than Brown Fat Could Counteract Obesity

Warm-blooded animals such as birds and mammals are able to protect stable body temperature due to various thermogenic mechanisms. These processes can be facultative (occurring only under specific conditions, such as acute cold) and adaptive (adjusting their capacity according to long-term needs). They can represent a substantial part of overall energy expenditure and, therefore, affect energy balance. Classical mechanisms of facultative thermogenesis include shivering of skeletal muscles and (in mammals) non-shivering thermogenesis (NST) in brown adipose tissue (BAT), which depends on uncoupling protein 1 (UCP1). Existence of several alternative thermogenic mechanisms has been suggested. However, their relative contribution to overall heat production and the extent to which they are adaptive and facultative still needs to be better defined. Here we focus on comparison of NST in BAT with thermogenesis in skeletal muscles, including shivering and NST. We present indications that muscle NST may be adaptive but not facultative, unlike UCP1-dependent NST. Due to its slow regulation and low energy efficiency, reflecting in part the anatomical location, induction of muscle NST may counteract development of obesity more effectively than UCP1-dependent thermogenesis in BAT.

Misaligned feeding uncouples daily rhythms within brown adipose tissue and between peripheral clocks

Extended food consumption during the rest period perturbs the phase relationship between circadian clocks in the periphery and the brain, leading to adverse health effects. Beyond the liver, how metabolic organs respond to a timed hypocaloric diet is largely unexplored. We investigated how feeding schedules impacted circadian gene expression in epididymal white and brown adipose tissue (eWAT and BAT) compared to the liver and hypothalamus. We restricted food to either daytime or nighttime in C57BL/6J male mice, with or without caloric restriction. Unlike the liver and eWAT, rhythmic clock genes in the BAT remained insensitive to feeding time, similar to the hypothalamus. We uncovered an internal split within the BAT in response to conflicting environmental cues, displaying inverted oscillations on a subset of metabolic genes without modifying its local core circadian machinery. Integrating tissue-specific responses on circadian transcriptional networks with metabolic outcomes may help elucidate the mechanism underlying the health burden of eating at unusual times.

Proper micro-environment alleviates mortality in laboratory mouse breeding induced by litter overlap and older dams

The ongoing worldwide effort to reduce animal numbers in research often omits the issue of pre-weaning mortality in mouse breeding. A conservative estimate of 20% mortality would mean approximately 1.1 M mice die annually in the EU before scientific use. We hypothesize that pre-weaning mortality in laboratory mouse breeding is associated with cage social and macro/micro-environment conditions. Here we count pups from 509 C57BL/6J litters daily for accurate detection of mortality, and monitor cage micro-environment for 172 C57BL/6J litters. Probability of pups to die increases with the increase in dam age, number and age of older pups in the cage (of overlapped/cohabitating litters), and in small (<6 pups) and large (>11 pups) focal litters. Higher temperatures (>23.6 °C) and nest scores (>3.75) compensate for some of the socially-associated risks for pup death. These findings can be implemented in strategies for reducing pre-weaning mouse mortality, a more welfare-friendly and sustainable approach for science.