Schwartz M W, Erickson J C, Baskin D G, Palmiter R D
Department of Medicine, University of Washington, and Puget Sound Veterans Affairs Health Care System, Seattle 98108, USA.
Endocrinology. 1998 May;139(5):2629-35. doi: 10.1210/endo.139.5.6000.
Neuropeptide Y (NPY), a peptide synthesized in the hypothalamic arcuate nucleus, is implicated in the physiologic control of food intake and body weight. Because both genetic (e.g. in obese ob/ob mice) and acquired leptin deficiency (e.g. fasting in normal mice) increase hypothalamic NPY accumulation, and as leptin administration reverses this effect, we hypothesized that leptin inhibits transcription of the NPY gene by arcuate nucleus neurons. To test this hypothesis, we studied mice with a targeted mutation of the NPY gene (NPY knockout mice), in which the lacZ reporter gene was inserted into the first exon of the NPY gene. As a result, these mice express beta-galactosidase (beta gal; the enzyme encoded by lacZ) in neurons that normally express the NPY gene. To determine whether beta gal staining provides a valid measure of lacZ expression, we used a histochemical method to count the number of beta gal+ neurons in coronal sections of brain tissue from mice bearing either one (NPY+/-) or two (NPY-/-) mutant alleles. In both the arcuate nucleus and the thalamic reticular nucleus, beta gal+ cell number was 260% higher in NPY-/- than in NPY+/- mice (P < 0.05). Fasting for 48 h also increased the mean beta gal+ cell number in the arcuate nucleus of NPY+/- mice by 260% (P < 0.001), but had no effect in the thalamic reticular nucleus. Similarly, obese leptin-deficient ob/ob, NPY+/- mice had a 67.3% increase in arcuate nucleus beta gal+ cell number compared with lean ob/+, NPY+/- littermates (P < 0.05), and this effect was attenuated 36.6% (P < 0.05) by leptin administration (70 microg/day, i.p., for 4 days). Based on the results of this novel method for measuring NPY gene transcription in vivo, we conclude that both fasting and genetic leptin deficiency increase NPY gene transcription in the arcuate nucleus and that this transcriptional response is attenuated by leptin administration in ob/ob, NPY+/- mice.
神经肽Y（NPY）是一种在下丘脑弓状核合成的肽，与食物摄入和体重的生理控制有关。由于遗传因素（如肥胖的ob/ob小鼠）和后天性瘦素缺乏（如正常小鼠禁食）都会增加下丘脑NPY的积累，且给予瘦素可逆转这种效应，我们推测瘦素可抑制弓状核神经元中NPY基因的转录。为验证这一假设，我们研究了NPY基因发生靶向突变的小鼠（NPY基因敲除小鼠），其中lacZ报告基因被插入到NPY基因的第一个外显子中。结果，这些小鼠在正常表达NPY基因的神经元中表达β-半乳糖苷酶（β-gal；由lacZ编码的酶）。为确定β-gal染色是否能有效测量lacZ的表达，我们采用组织化学方法对携带一个（NPY+/-）或两个（NPY-/-）突变等位基因的小鼠脑组织冠状切片中β-gal+神经元的数量进行计数。在弓状核和丘脑网状核中，NPY-/-小鼠的β-gal+细胞数量比NPY+/-小鼠高260%（P<0.05）。禁食48小时也使NPY+/-小鼠弓状核中β-gal+细胞的平均数量增加了260%（P<0.001），但对丘脑网状核没有影响。同样，肥胖的瘦素缺乏型ob/ob、NPY+/-小鼠的弓状核β-gal+细胞数量比瘦的ob/ +、NPY+/-同窝小鼠增加了67.3%（P<0.05），而给予瘦素（70微克/天，腹腔注射，共4天）后，这种效应减弱了36.6%（P<0.05）。基于这种在体内测量NPY基因转录的新方法的结果，我们得出结论，禁食和遗传性瘦素缺乏都会增加弓状核中NPY基因的转录，且在ob/ob、NPY+/-小鼠中，给予瘦素可减弱这种转录反应。
