Takekoshi K, Ishii K, Kawakami Y, Isobe K, Nanmoku T, Nakai T
Department of Clinical Pathology, Institute of Clinical Medicine, University of Tsukuba, Tsukuba, Ibaraki, 305-8575, Japan.
Endocrinology. 2001 Jan;142(1):290-8. doi: 10.1210/endo.142.1.7914.
Leptin acts as a satiety factor, but there is also evidence that it affects energy expenditure. Leptin's effects are mediated by its receptors, which function as activators of a Janus family of tyrosine kinases-signal transducer and activator of transcription (JAK-STAT) pathway. We have previously shown that murine recombinant leptin markedly induces both the release of catecholamine and tyrosine hydroxylase (TH) (rate-limiting enzyme in the biosynthesis of catecholamine)-messenger RNA (mRNA) levels, probably through Ob-Rb expressed in cultured porcine chromaffin cells. In the present study, we examined the effect of leptin on Ca(2+) mobilization, TH enzyme activity, and signaling. Ca(2+) channel blockers, nicardipine and omega-Conotoxin GVIA, each at 1 microM, were effective in inhibiting leptin-induced catecholamine secretion. When intracellular Ca(2+) (Ca(2+)) was measured in fura 2-loaded chromaffin cells, leptin was found to cause a sustained increase of Ca(2+) by mobilizing Ca(2+) from both extra- and intracellular pools. Additionally, leptin significantly stimulated inositol 1.4.5-triphosphate IP(3) production in a dose-dependent manner. TH-activity is regulated by both TH enzyme activity and increased TH-mRNA levels accompanied by increased TH protein synthesis. Leptin (>/=1 nM) significantly stimulated TH enzyme activity and increased the TH protein level, indicating that it stimulates catecholamine biosynthesis. In addition, removal of external Ca(2+) completely inhibited leptin (100 nM)-induced TH enzyme activity. Leptin (>/=1 nM) caused an increase in the activity of mitogen-activated protein kinases (MAPKs) that was accompanied by increased phosphorylation of STAT-3 and -5, but not STAT-1. Moreover, MAPK activity evoked by leptin(100 nM) and TH-mRNA caused by leptin (10 nM) were inhibited by 50 and 30 microM of PD-98059 (the MAP kinase kinase-1 inhibitor), respectively. These findings indicate that leptin activates voltage-dependent Ca(2+) channels (VDCC), presumably L-type and N-type Ca(2+) channels, as well as phospholipase C, and suggest that leptin-induced catecholamine secretion is mainly mediated by activation of VDCC. In addition, leptin stimulates the JAK-STAT pathway as well as increasing the levels of TH-mRNA levels through the MAPK pathway in porcine chromaffin cells.
瘦素作为一种饱腹感因子，但也有证据表明它会影响能量消耗。瘦素的作用是通过其受体介导的，这些受体作为酪氨酸激酶-信号转导和转录激活因子（JAK-STAT）通路的Janus家族激活剂发挥作用。我们之前已经表明，小鼠重组瘦素可能通过培养的猪嗜铬细胞中表达的Ob-Rb，显著诱导儿茶酚胺的释放以及酪氨酸羟化酶（TH）（儿茶酚胺生物合成中的限速酶）-信使核糖核酸（mRNA）水平。在本研究中，我们研究了瘦素对钙离子动员、TH酶活性和信号传导的影响。1微摩尔的钙离子通道阻滞剂尼卡地平和平贝毒素GVIA均能有效抑制瘦素诱导的儿茶酚胺分泌。当在负载fura 2的嗜铬细胞中测量细胞内钙离子（[Ca(2+)]i）时，发现瘦素通过从细胞外和细胞内池动员钙离子导致钙离子持续增加。此外，瘦素以剂量依赖的方式显著刺激肌醇1.4.5-三磷酸（IP(3)）的产生。TH活性受TH酶活性以及TH-mRNA水平增加和TH蛋白合成增加的调节。瘦素（≥1纳摩尔）显著刺激TH酶活性并增加TH蛋白水平，表明它刺激儿茶酚胺生物合成。此外，去除细胞外钙离子完全抑制了瘦素（100纳摩尔）诱导的TH酶活性。瘦素（≥1纳摩尔）导致丝裂原活化蛋白激酶（MAPKs）活性增加，同时伴随着STAT-3和-5磷酸化增加，但STAT-1没有增加。此外，瘦素（100纳摩尔）诱发的MAPK活性和瘦素（10纳摩尔）引起的TH-mRNA分别被50和30微摩尔的PD-98059（MAP激酶激酶-1抑制剂）抑制。这些发现表明瘦素激活电压依赖性钙离子通道（VDCC），可能是L型和N型钙离子通道，以及磷脂酶C，并表明瘦素诱导的儿茶酚胺分泌主要由VDCC的激活介导。此外，瘦素在猪嗜铬细胞中刺激JAK-STAT通路以及通过MAPK通路增加TH-mRNA水平。
