Mory G, Wiel M, Adli H, Diot-Dupuy F, Ferré P, Bazin R
INSERM U 465, Centre Biomédical des Cordeliers, Paris, France.
Int J Obes Relat Metab Disord. 2001 Nov;25(11):1592-8. doi: 10.1038/sj.ijo.0801811.
In fa/fa Zucker rats, leptin receptor deficiency is responsible for both a deficit of energy expenditure and hyperphagia which lead to massive obesity and insulin resistance in adulthood. This obesity is also characterised by alterations of the beta-adrenergic signaling pathway.
To determine whether alterations in beta-adrenergic pathway could occur at the onset of obesity when fa/fa rats are not yet hyperinsulinemic.
Fourteen-day-old suckling fa/fa and Fa/fa littermates (from heterozygous lean (Fa/fa) female and homozygous obese (fa/fa) male mating).
Membranes were prepared from isolated adipocytes after collagenase treatment of inguinal adipose tissue. The response of adenylyl-cyclase activity to stimulation by isoprenaline, GTPgamma-S or forskolin was studied. Bmax and Kd of (beta1+beta2) and of beta3 adrenoceptors were measured using 3H-CGP saturation binding experiments. mRNA concentration of beta1- and beta3-AR was determined by semi-quantitative RT-PCR. G(s)alpha protein was quantified by Western blotting and Gi protein by ADP-ribosylation.
Despite an almost normal body weight, inguinal fat pad weight was increased two-fold by the expression of fa mutation. This increase was entirely accounted for by fat cell hypertrophy (x2.5 in volume). In fa/fa compared to Fa/fa pups, response of adenylyl cyclase to isoprenaline was decreased two-fold but responses to GTPgammaS or forskolin were unchanged. Density of (beta1+beta2) and beta3-AR was not affected by the fa/fa genotype, as well as G(s)alpha and Gi concentration.
Response of inguinal fat cells to catecholamines was decreased without any quantitative modifications of the different elements of the adenylyl cyclase cascade. This suggests an alteration in the coupling between beta-AR and G proteins. Due to the important increase in fat cell volume we hypothesize that changes in the physical properties of plasma membranes and/or changes in cytoskeleton-extracellular-matrix interactions could disturb the beta-adrenergic pathway responsiveness. In addition to the excess of lipid storage, which occurs very early at the onset of obesity, the impairment of the responsiveness to catecholamines reported in this study might worsen the obesity syndrome.
在fa/fa Zucker大鼠中，瘦素受体缺乏导致能量消耗不足和食欲亢进，进而在成年期引发严重肥胖和胰岛素抵抗。这种肥胖还表现为β-肾上腺素能信号通路的改变。
确定在fa/fa大鼠尚未出现高胰岛素血症的肥胖初期，β-肾上腺素能通路是否会发生改变。
14日龄的哺乳fa/fa和Fa/fa同窝仔鼠（来自杂合子瘦型（Fa/fa）雌性和纯合子肥胖型（fa/fa）雄性的交配）。
用胶原酶处理腹股沟脂肪组织后，从分离的脂肪细胞制备细胞膜。研究腺苷酸环化酶活性对异丙肾上腺素、GTPγ-S或福斯高林刺激的反应。使用3H-CGP饱和结合实验测量（β1+β2）和β3肾上腺素能受体的Bmax和Kd。通过半定量RT-PCR测定β1-和β3-AR的mRNA浓度。通过蛋白质免疫印迹法定量G(s)α蛋白，通过ADP-核糖基化法定量Gi蛋白。
尽管体重几乎正常，但fa突变的表达使腹股沟脂肪垫重量增加了两倍。这种增加完全是由脂肪细胞肥大（体积增加2.5倍）所致。与Fa/fa幼崽相比，fa/fa幼崽中腺苷酸环化酶对异丙肾上腺素的反应降低了两倍，但对GTPγS或福斯高林的反应未改变。（β1+β2）和β3-AR的密度以及G(s)α和Gi浓度不受fa/fa基因型的影响。
腹股沟脂肪细胞对儿茶酚胺的反应降低，而腺苷酸环化酶级联反应的不同元件没有任何定量变化。这表明β-肾上腺素能受体与G蛋白之间的偶联发生了改变。由于脂肪细胞体积显著增加，我们推测质膜物理性质的改变和/或细胞骨架-细胞外基质相互作用的改变可能会干扰β-肾上腺素能通路的反应性。除了在肥胖初期很早就出现的脂质储存过多外，本研究中报道的对儿茶酚胺反应性的损害可能会使肥胖综合征恶化。
