mTORC2 in adipocytes is essential to increase cold-induced thermogenic capacity and improve insulin sensitivity induced by cold and high-fat diet rich in omega 3 fatty acids.

Rictor é um componente essencial do complexo 2 da mTOR (mTORC2) que controla o crescimento, a proliferação e o metabolismo celular. Quando ativado por insulina, Rictor/mTORC2 promove, principalmente via fosforilação e ativação da Akt, a captação de glicose e a lipogênese de novo em adipócitos. Neste estudo, nós investigamos o envolvimento de mTORC2 em adipócitos como possível mediador do aumento da capacidade termogênica, captação de glicose no tecido adiposo e melhora na homeostase da glicose induzidos pela aclimatação ao frio por 14 dias (Capítulo 2), tratamento com o agonista de PPAR γ pioglitazona (Capítulo 3), e ingestão de dieta hiperlipídica rica em ácidos graxos ômega 3 (Capítulo 4). Para atingir estes objetivos camundongos com deleção de Rictor exclusivamente em adipócitos (ARicKO, Rictor flox/flox adiponectina Cre +) e irmãos controles (ARicWT, Rictor flox/flox) foram ou mantidos à 30°C ou a 10°C por 14 dias (Capítulo 2); ou alimentados com dieta hiperlipídica (60% de lipídeos) suplementada ou não com o agonista de PPARγ pioglitazona (Pio, 30 mg/ kg massa corporal/ dia) por 8 semanas a 23°C (Capítulo 3); ou alimentados com dietas hiperlipídicas isocalóricas (60% de lipídeos) produzidas usando como fonte de gordura a banha de porco (HFD) ou óleo de peixe (HFn3) por 8 semanas a 23°C (Capítulo 4). Foram avaliados a massa corporal, gasto energético por calorimetria indireta, metabólitos séricos, consumo de oxigênio tecidual, homeostase da glicose e o metabolismo glicídico e lipídico. Nossos principais achados foram que camundongos ARicKO aclimatados a 10°C são resistentes à insulina, apresentam redução da massa do tecido adiposo marrom (TAM), do Browning do tecido adiposo branco (TAB) inguinal, do conteúdo total da proteína desacopladora UCP-1 e da capacidade termogênica estimulada por agonista do receptor β3-adrenérgico. Deficiência de Rictor em adipócitos, entretanto, não interferiu com o aumento da captação de glicose no TAM e TAB inguinal induzidos pela aclimatação ao frio. ARicKO alimentados com HFD apresentam resistência à insulina e esteatose hepática, apesar do menor ganho de massa corporal e redução das massas dos TAM e TAB. O tratamento com Pio, por sua vez, não interfere com o ganho de massa corporal, mas melhora a sensibilidade à insulina e exacerba a esteatose hepática em ARicKO. ARicKO alimentados com HFn3 têm maior ganho de massa corporal, redução do Browning e do consumo de oxigênio no TAB inguinal, também apresentam resistência à insulina, mas são protegidos do desenvolvimento de esteatose hepática. Em conjunto, nossos resultados demonstram que Rictor/mTORC2 em adipócitos é um importante mediador da expansão da massa do TAM e do Browning do TAB inguinal induzidos pela aclimatação ao frio, o que resulta em reduzida capacidade termogênica. mTORC2 é também um importante mediador da expansão do TAB induzida pela ingestão de dieta hiperlipídica HFD e da melhora da sensibilidade à insulina induzida pela dieta hiperlipídica rica em ácidos graxos ômega 3, mas não participa da melhora da sensibilidade à insulina induzida pelo tratamento com pioglitazona. Nossos dados também indicam que Rictor/mTORC2 em adipócitos é membro de um eixo de comunicação com o fígado de controle da sensibilidade à insulina, por mecanismos que ainda precisam ser elucidados.Rictor is an essential component of mTOR complex 2 (mTORC2) that regulates cell growth, proliferation and metabolism. Upon activation by insulin, Rictor/mTORC2 promotes mainly through the phosphorylation and activation of Akt, glucose uptake and de novo lipogenesis in adipocytes. We investigated herein the involvement of adipocyte mTORC2 as a possible mediator of the increases in thermogenic capacity, glucose uptake in adipose tissue and improvement in glucose homeostasis induced by cold acclimation for 14 days (Chapter 2), treatment with the PPAR γ ligand pioglitazone (Chapter 3) and intake of high-fat diet enriched with omega 3 fatty acids (Chapter 4). For this, mice with Rictor deletion exclusively in adipocytes (ARicKO, Rictor flox/flox adiponectina Cre+) and littermate controls (ARicWT, Rictor flox/flox) were maintained at 30°C or acclimated to cold (10°C) for 14 days (Chapter 2); or fed with a high-fat diet supplemented or not with pioglitazone (Pio, 30 mg/ kg body weight/ day) during 8 weeks at 23°C (Chapter 3); or fed with high-fat diets produced using either lard (HFD) or fish oil (HFn3) as fat source for 8 weeks at 23°C (Chapter 4). Mice were evaluated for body mass, energy expenditure, serum metabolites, tissue oxygen consumption, glucose homeostasis and lipid and glucose metabolism. Our main findings indicate that ARicKO mice acclimated to cold (10°C) are insulin intolerant, and display impairments in brown adipose tissue mass (BAT) and inguinal white adipose tissue (iWAT) browning and total UCP-1 content and therefore thermogenic capacity stimulated by agonist β3-adrenergic. Adipocyte Rictor deficiency, however, did not affect the increase in BAT and iWAT glucose uptake induced by cold acclimation. Furthermore, ARicKO fed with a high-fat diet displayed insulin resistance and hepatic steatosis, despite the lower body weight gain and reduced adiposity. Treatment with Pio did not affect body weight, but improved insulin sensitivity in ARicKO, despite exacerbating hepatic steatosis. ARicKO fed with HFn3 are insulin resistant, display higher body weight gain, and reduced iWAT browning and oxygen consumption than ARicWT and reduced hepatic steatosis when compared to HFD-fed ARicKO. In conclusion, our findings indicate that adipocyte Rictor/mTORC2 is an important mediator of BAT expansion and iWAT browning induced by cold acclimation, which results in an impaired total UCP-1 content and mediated thermogenic capacity. Rictor/mTORC2 is also an important mediator of iWAT expansion induced by intake of HFD, and mediate the improvement in insulin sensitivity induced by HFn3, but not by Pio. Our findings also indicate that adipocyte Rictor/mTORC2 is involved in AT-liver communication axis, through unknown molecular mechanisms

Leaf Dynamics of Panicum maximum under Future Climatic Changes.

Panicum maximum Jacq. 'Mombaça' (C4) was grown in field conditions with sufficient water and nutrients to examine the effects of warming and elevated CO2 concentrations during the winter. Plants were exposed to either the ambient temperature and regular atmospheric CO2 (Control); elevated CO2 (600 ppm, eC); canopy warming (+2°C above regular canopy temperature, eT); or elevated CO2 and canopy warming (eC+eT). The temperatures and CO2 in the field were controlled by temperature free-air controlled enhancement (T-FACE) and mini free-air CO2 enrichment (miniFACE) facilities. The most green, expanding, and expanded leaves and the highest leaf appearance rate (LAR, leaves day(-1)) and leaf elongation rate (LER, cm day(-1)) were observed under eT. Leaf area and leaf biomass were higher in the eT and eC+eT treatments. The higher LER and LAR without significant differences in the number of senescent leaves could explain why tillers had higher foliage area and leaf biomass in the eT treatment. The eC treatment had the lowest LER and the fewest expanded and green leaves, similar to Control. The inhibitory effect of eC on foliage development in winter was indicated by the fewer green, expanded, and expanding leaves under eC+eT than eT. The stimulatory and inhibitory effects of the eT and eC treatments, respectively, on foliage raised and lowered, respectively, the foliar nitrogen concentration. The inhibition of foliage by eC was confirmed by the eC treatment having the lowest leaf/stem biomass ratio and by the change in leaf biomass-area relationships from linear or exponential growth to rectangular hyperbolic growth under eC. Besides, eC+eT had a synergist effect, speeding up leaf maturation. Therefore, with sufficient water and nutrients in winter, the inhibitory effect of elevated CO2 on foliage could be partially offset by elevated temperatures and relatively high P. maximum foliage production could be achieved under future climatic change

Accumulated number of expanded (A), expanding (B), and senescent (C) leaves; and the mean number of cut-expanded leaves (D) per tiller of <i>Panicum maximum</i> growing under different atmospheric conditions.

<p>A—Regular concentration of CO₂ and canopy temperature (Control). B—Elevated CO₂ concentration of 600 ppm (eC). C—Elevated canopy temperature of +2°C (eT). D—Combination of treatments (eC+eT). The days of measurement were August 22 and 29, and September 3, 9, 12, and 20, 2013.</p

The leaf/stem biomass ratio (A) and leaf nitrogen content (B) of <i>Panicum maximum</i> under regular concentration of CO₂ and canopy temperature (Control), under elevated CO₂ concentration of 600 ppm (eC), under elevated canopy temperature of +2°C (eT), and under both treatments (eC+eT).

<p>Bars show average values and lines at the top of the bars the standard error. Different letters above the bars indicate significant differences among the datasets after the Mann-Whitney test at p < 0.1.</p

Leaf appearance rate (A), leaf elongation rate (B), leaf area (C), and leaf biomass (D) per tiller of <i>Panicum maximum</i> under regular CO₂ and canopy temperature (Control), under elevated CO₂ concentration of 600 ppm (eC), under elevated canopy temperature of +2°C (eT), and under both treatments (eC+eT).

<p>Bars show average values and lines at the top of the bars show the standard error. Different letters above bars indicate significant differences among datasets according to a Mann-Whitney test at p < 0.05.</p

Average values of leaf biomass as a function of leaf area per tiller of <i>Panicum maximum</i> under regular atmospheric CO₂ concentration and canopy temperature (Control, A), under elevated atmospheric CO₂ concentration of 600 ppm (eC, B), under elevated canopy temperature of +2°C (eT, C), and under both treatments (eC+eT, D).

<p>Average values of leaf biomass as a function of leaf area per tiller of <i>Panicum maximum</i> under regular atmospheric CO₂ concentration and canopy temperature (Control, A), under elevated atmospheric CO₂ concentration of 600 ppm (eC, B), under elevated canopy temperature of +2°C (eT, C), and under both treatments (eC+eT, D).</p