RESUMEN
Thermogenic adipocytes possess a therapeutically appealing, energy-expending capacity, which is canonically cold-induced by ligand-dependent activation of ß-adrenergic G protein-coupled receptors (GPCRs). Here, we uncover an alternate paradigm of GPCR-mediated adipose thermogenesis through the constitutively active receptor, GPR3. We show that the N terminus of GPR3 confers intrinsic signaling activity, resulting in continuous Gs-coupling and cAMP production without an exogenous ligand. Thus, transcriptional induction of Gpr3 represents the regulatory parallel to ligand-binding of conventional GPCRs. Consequently, increasing Gpr3 expression in thermogenic adipocytes is alone sufficient to drive energy expenditure and counteract metabolic disease in mice. Gpr3 transcription is cold-stimulated by a lipolytic signal, and dietary fat potentiates GPR3-dependent thermogenesis to amplify the response to caloric excess. Moreover, we find GPR3 to be an essential, adrenergic-independent regulator of human brown adipocytes. Taken together, our findings reveal a noncanonical mechanism of GPCR control and thermogenic activation through the lipolysis-induced expression of constitutively active GPR3.
Asunto(s)
Tejido Adiposo Pardo/metabolismo , Receptor de Androstano Constitutivo/metabolismo , Lipólisis , Receptores Acoplados a Proteínas G/metabolismo , Termogénesis , Adipocitos/metabolismo , Animales , Células COS , Células Cultivadas , Chlorocebus aethiops , Frío , Grasas de la Dieta/farmacología , Humanos , Ratones Endogámicos C57BL , Fenotipo , Receptores Acoplados a Proteínas G/genética , Transducción de Señal , Sistema Nervioso Simpático/metabolismo , Transcripción GenéticaRESUMEN
In mammals, O2 and CO2 levels are tightly regulated and are altered under various pathological conditions. While the molecular mechanisms that participate in O2 sensing are well characterized, little is known regarding the signaling pathways that participate in CO2 signaling and adaptation. Here, we show that CO2 levels control a distinct cellular transcriptional response that differs from mere pH changes. Unexpectedly, we discovered that CO2 regulates the expression of cholesterogenic genes in a SREBP2-dependent manner and modulates cellular cholesterol accumulation. Molecular dissection of the underlying mechanism suggests that CO2 triggers SREBP2 activation through changes in endoplasmic reticulum (ER) membrane cholesterol levels. Collectively, we propose that SREBP2 participates in CO2 signaling and that cellular cholesterol levels can be modulated by CO2 through SREBP2.
Asunto(s)
Dióxido de Carbono , Colesterol , Animales , Colesterol/metabolismo , Transducción de Señal , Proteína 2 de Unión a Elementos Reguladores de Esteroles/genética , Proteína 2 de Unión a Elementos Reguladores de Esteroles/metabolismo , Mamíferos/metabolismoRESUMEN
Molecular clocks in the periphery coordinate tissue-specific daily biorhythms by integrating input from the hypothalamic master clock and intracellular metabolic signals. One such key metabolic signal is the cellular concentration of NAD+, which oscillates along with its biosynthetic enzyme, nicotinamide phosphoribosyltransferase (NAMPT). NAD+ levels feed back into the clock to influence rhythmicity of biological functions, yet whether this metabolic fine-tuning occurs ubiquitously across cell types and is a core clock feature is unknown. Here, we show that NAMPT-dependent control over the molecular clock varies substantially between tissues. Brown adipose tissue (BAT) requires NAMPT to sustain the amplitude of the core clock, whereas rhythmicity in white adipose tissue (WAT) is only moderately dependent on NAD+ biosynthesis, and the skeletal muscle clock is completely refractory to loss of NAMPT. In BAT and WAT, NAMPT differentially orchestrates oscillation of clock-controlled gene networks and the diurnality of metabolite levels. NAMPT coordinates the rhythmicity of TCA cycle intermediates in BAT, but not in WAT, and loss of NAD+ abolishes these oscillations similarly to high-fat diet-induced circadian disruption. Moreover, adipose NAMPT depletion improved the ability of animals to defend body temperature during cold stress but in a time-of-day-independent manner. Thus, our findings reveal that peripheral molecular clocks and metabolic biorhythms are shaped in a highly tissue-specific manner by NAMPT-dependent NAD+ synthesis.
Asunto(s)
NAD , Nicotinamida Fosforribosiltransferasa , Animales , NAD/metabolismo , Nicotinamida Fosforribosiltransferasa/genética , Nicotinamida Fosforribosiltransferasa/metabolismo , Ritmo Circadiano/fisiología , Tejido Adiposo Pardo/metabolismo , Obesidad/metabolismo , Citocinas/metabolismoRESUMEN
Non-identical copies of mitochondrial DNA (mtDNA) compete with each other within a cell and the ultimate variant of mtDNA present depends on their relative replication rates. Using yeast Saccharomyces cerevisiae cells as a model, we studied the effects of mitochondrial inhibitors on the competition between wild-type mtDNA and mutant selfish mtDNA in heteroplasmic zygotes. We found that decreasing mitochondrial transmembrane potential by adding uncouplers or valinomycin changes the competition outcomes in favor of the wild-type mtDNA. This effect was significantly lower in cells with disrupted mitochondria fission or repression of the autophagy-related genes ATG8, ATG32 or ATG33, implying that heteroplasmic zygotes activate mitochondrial degradation in response to the depolarization. Moreover, the rate of mitochondrially targeted GFP turnover was higher in zygotes treated with uncoupler than in haploid cells or untreated zygotes. Finally, we showed that vacuoles of zygotes with uncoupler-activated autophagy contained DNA. Taken together, our data demonstrate that mitochondrial depolarization inhibits clonal expansion of selfish mtDNA and this effect depends on mitochondrial fission and autophagy. These observations suggest an activation of mitochondria quality control mechanisms in heteroplasmic yeast zygotes.
Asunto(s)
ADN Mitocondrial/metabolismo , Potencial de la Membrana Mitocondrial , Mitocondrias/metabolismo , Saccharomyces cerevisiae/metabolismo , Cigoto/metabolismo , Autofagia/efectos de los fármacos , Carbonil Cianuro p-Trifluorometoxifenil Hidrazona/farmacología , Células Clonales , Diploidia , Potencial de la Membrana Mitocondrial/efectos de los fármacos , Potenciales de la Membrana/efectos de los fármacos , Mitocondrias/efectos de los fármacos , Mitocondrias/ultraestructura , Dinámicas Mitocondriales/efectos de los fármacos , Mitofagia/efectos de los fármacos , Saccharomyces cerevisiae/efectos de los fármacos , Saccharomyces cerevisiae/ultraestructura , Cigoto/efectos de los fármacos , Cigoto/ultraestructuraRESUMEN
ABC-transporters with broad substrate specificity are responsible for pathogenic yeast resistance to antifungal compounds. Here we asked whether highly hydrophobic chemicals with delocalized positive charge can be used to overcome the resistance. Such molecules efficiently penetrate the plasma membrane and accumulate inside the cells. We reasoned that these properties can convert an active efflux of the compounds into a futile cycle thus interfering with the extrusion of the antibiotics. To test this, we studied the effects of several alkylated rhodamines on the drug resistance of yeast Saccharomyces cerevisiae We found that octylrhodamine synergetically increases toxicity of Pdr5p substrate-clotrimazole, while the others were less effective. Next, we compared the contributions of three major pleiotropic ABC-transporters (Pdr5p, Yor1p, Snq2p) on the accumulation of the alkylated rhodamines. While all of the tested compounds were extruded by Pdr5p, Yor1p and Snq2p showed narrower substrate specificity. Interestingly, among the tested alkylated rhodamines, inactivation of Pdr5p had the strongest effect on the accumulation of octylrhodamine inside the cells, which is consistent with the fact that clotrimazole is a substrate of Pdr5p. As alkylated rhodamines were shown to be non-toxic on mice, our study makes them potential components of pharmacological antifungal compositions.
Asunto(s)
Transportadoras de Casetes de Unión a ATP/antagonistas & inhibidores , Antifúngicos/farmacología , Compuestos de Benzalconio/farmacología , Clotrimazol/farmacología , Inhibidores Enzimáticos/metabolismo , Rodaminas/metabolismo , Saccharomyces cerevisiae/efectos de los fármacos , Sinergismo Farmacológico , Viabilidad Microbiana/efectos de los fármacosRESUMEN
Multiple drug resistance pumps are potential drug targets. Here we asked whether the lipophilic cation dodecyltriphenylphosphonium (C12TPP) can interfere with their functioning. First, we found that suppression of ABC transporter gene PDR5 increases the toxicity of C12TPP in yeast. Second, C12TPP appeared to prevent the efflux of rhodamine 6G - a fluorescent substrate of Pdr5p. Moreover, C12TPP increased the cytostatic effects of some other known Pdr5p substrates. The chemical nature of C12TPP suggests that after Pdr5p-driven extrusion the molecules return to the plasma membrane and then into the cytosol, thus effectively competing with other substrates of the pump.
Asunto(s)
Farmacorresistencia Microbiana/efectos de los fármacos , Resistencia a Múltiples Medicamentos/efectos de los fármacos , Compuestos Organofosforados/farmacología , Saccharomyces cerevisiae/efectos de los fármacos , Farmacorresistencia Microbiana/genética , Resistencia a Múltiples Medicamentos/genética , Saccharomyces cerevisiae/genéticaRESUMEN
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.
Asunto(s)
Adaptación Fisiológica , Calcio , Músculo Esquelético , Obesidad , Condicionamiento Físico Animal , Animales , Femenino , Condicionamiento Físico Animal/fisiología , Músculo Esquelético/metabolismo , Ratones , Obesidad/metabolismo , Obesidad/fisiopatología , Calcio/metabolismo , Adaptación Fisiológica/fisiología , Ratones Endogámicos C57BL , Respuesta al Choque por Frío/fisiología , Ratones Obesos , Frío , Adiposidad/fisiologíaRESUMEN
Exercise training is a powerful means to combat metabolic diseases. Mice are extensively used to investigate the benefits of exercise, but mild cold stress induced by ambient housing temperatures may confound translation to humans. Thermoneutral housing is a strategy to make mice more metabolically similar to humans but its effects on exercise adaptations are unknown. Here we show that thermoneutral housing blunts exercise-induced improvements in insulin action in muscle and adipose tissue and reduces the effects of training on energy expenditure, body composition, and muscle and adipose tissue protein expressions. Thus, many reported effects of exercise training in mice are likely secondary to metabolic stress of ambient housing temperature, making it challenging to translate to humans. We conclude that adaptations to exercise training in mice critically depend upon housing temperature. Our findings underscore housing temperature as a critical parameter in the design and interpretation of murine exercise training studies.
Asunto(s)
Adaptación Fisiológica/fisiología , Vivienda para Animales , Condicionamiento Físico Animal/fisiología , Tejido Adiposo/efectos de los fármacos , Animales , Composición Corporal , Metabolismo Energético , Femenino , Microbioma Gastrointestinal , Insulina/farmacología , Ratones , Ratones Endogámicos C57BL , Músculo Esquelético/efectos de los fármacos , Estrés Fisiológico , TemperaturaRESUMEN
OBJECTIVE: The ability of adipose tissue to expand and contract in response to fluctuations in nutrient availability is essential for the maintenance of whole-body metabolic homeostasis. Given the nutrient scarcity that mammals faced for millions of years, programs involved in this adipose plasticity were likely evolved to be highly efficient in promoting lipid storage. Ironically, this previously advantageous feature may now represent a metabolic liability given the caloric excess of modern society. We speculate that nicotinamide adenine dinucleotide (NAD+) biosynthesis exemplifies this concept. Indeed NAD+/NADH metabolism in fat tissue has been previously linked with obesity, yet whether it plays a causal role in diet-induced adiposity is unknown. Here we investigated how the NAD+ biosynthetic enzyme nicotinamide phosphoribosyltransferase (NAMPT) supports adipose plasticity and the pathological progression to obesity. METHODS: We utilized a newly generated Nampt loss-of-function model to investigate the tissue-specific and systemic metabolic consequences of adipose NAD+ deficiency. Energy expenditure, glycemic control, tissue structure, and gene expression were assessed in the contexts of a high dietary fat burden as well as the transition back to normal chow diet. RESULTS: Fat-specific Nampt knockout (FANKO) mice were completely resistant to high fat diet (HFD)-induced obesity. This was driven in part by reduced food intake. Furthermore, HFD-fed FANKO mice were unable to undergo healthy expansion of adipose tissue mass, and adipose depots were rendered fibrotic with markedly reduced mitochondrial respiratory capacity. Yet, surprisingly, HFD-fed FANKO mice exhibited improved glucose tolerance compared to control littermates. Removing the HFD burden largely reversed adipose fibrosis and dysfunction in FANKO animals whereas the improved glucose tolerance persisted. CONCLUSIONS: These findings indicate that adipose NAMPT plays an essential role in handling dietary lipid to modulate fat tissue plasticity, food intake, and systemic glucose homeostasis.
Asunto(s)
Tejido Adiposo/metabolismo , Citocinas/metabolismo , NAD/biosíntesis , Nicotinamida Fosforribosiltransferasa/metabolismo , Obesidad/metabolismo , Animales , Células Cultivadas , Citocinas/genética , Dieta Alta en Grasa/efectos adversos , Metabolismo Energético , Glucosa/metabolismo , Mutación con Pérdida de Función , Masculino , Ratones , Ratones Endogámicos C57BL , Nicotinamida Fosforribosiltransferasa/genética , Obesidad/etiologíaRESUMEN
Activation of energy expenditure in thermogenic fat is a promising strategy to improve metabolic health, yet the dynamic processes that evoke this response are poorly understood. Here we show that synthesis of the mitochondrial phospholipid cardiolipin is indispensable for stimulating and sustaining thermogenic fat function. Cardiolipin biosynthesis is robustly induced in brown and beige adipose upon cold exposure. Mimicking this response through overexpression of cardiolipin synthase (Crls1) enhances energy consumption in mouse and human adipocytes. Crls1 deficiency in thermogenic adipocytes diminishes inducible mitochondrial uncoupling and elicits a nuclear transcriptional response through endoplasmic reticulum stress-mediated retrograde communication. Cardiolipin depletion in brown and beige fat abolishes adipose thermogenesis and glucose uptake, which renders animals insulin resistant. We further identify a rare human CRLS1 variant associated with insulin resistance and show that adipose CRLS1 levels positively correlate with insulin sensitivity. Thus, adipose cardiolipin has a powerful impact on organismal energy homeostasis through thermogenic fat bioenergetics.