Department of Physiology and Pharmacology, University of Western Ontario, London, Ontario, Canada.
Cell Signal. 2012 Dec;24(12):2283-90. doi: 10.1016/j.cellsig.2012.07.025. Epub 2012 Aug 15.
Leptin, a product of the obesity gene, has been shown to produce cardiac hypertrophy. Although leptin's mechanism of action is poorly understood activation of the RhoA/ROCK pathway has been proposed as a contributing mechanism. The Ca(2+)-dependent phosphatase calcineurin plays a critical role in the hypertrophic program although it is not known whether leptin can activate this signaling pathway or whether there is a relationship between RhoA activation and calcineurin. Accordingly, we determined the effect of leptin on calcineurin activation and assessed the possible role of RhoA. Experiments were performed using cultured neonatal rat ventricular myocytes exposed to 50 ng/ml leptin for 24h which resulted in a robust hypertrophic response. Moreover, leptin significantly increased intracellular Ca(2+) and Na(+) concentrations which was associated with significantly reduced activity of the 3Na(+)-2K(+)ATPase. The hypertrophic response to leptin were completely abrogated by both C3 exoenzyme (C3), a RhoA inhibitor as well as the reverse mode 3Na(+)-1Ca(2+) exchange inhibitor KB-R7943 ((2-[2-[4-(4-nitrobenzyloxy)phenyl] ethyl]isothiourea methanesulfonate), however only the effect of the latter was associated with attenuation of intracellular Ca(2+) concentrations whereas Ca(2+) concentrations were unaffected by C3. Similarly, C3 and KB-R7943 significantly attenuated early leptin-induced increase in calcineurin activity as well as the increase in nuclear translocation of the transcriptional factor nuclear factor of activated T cells. The hypertrophic response to leptin was also associated with increased p38 and ERK1/2 MAPK phosphorylation and increased p38, but not ERK1/2, translocation into nuclei. Both p38 responses as well as hypertrophy were abrogated by KB-R7943 as well as the calcineurin inhibitor FK-506 although ERK1/2 phosphorylation was unaffected. Our study therefore demonstrates a critical role for the calcineurin pathway in mediating leptin-induced hypertrophy. Moreover, we report a novel RhoA-dependent leptin-induced calcineurin activation which acts independently of changes in intracellular Ca(2+) concentrations.
瘦素是肥胖基因的产物，已被证明可导致心肌肥厚。尽管瘦素的作用机制尚不清楚，但已经提出 RhoA/ROCK 途径的激活是一种促成机制。钙依赖性磷酸酶钙调神经磷酸酶在肥厚程序中起着关键作用，尽管尚不清楚瘦素是否可以激活这种信号通路，或者 RhoA 的激活与钙调神经磷酸酶之间是否存在关系。因此，我们确定了瘦素对钙调神经磷酸酶激活的影响，并评估了 RhoA 的可能作用。实验使用培养的新生大鼠心室肌细胞进行，将其暴露于 50ng/ml 的瘦素中 24 小时，导致强烈的肥厚反应。此外，瘦素显著增加细胞内 Ca2+和 Na+浓度，同时 3Na+-2K+ATP 酶的活性显著降低。C3 外切酶（C3），一种 RhoA 抑制剂以及反向模式 3Na+-1Ca2+交换抑制剂 KB-R7943（（2-[2-[4-（4-硝基苄氧基）苯基]乙基]异硫脲甲磺酸盐）完全阻断了瘦素引起的肥厚反应，然而，只有后者的作用与细胞内 Ca2+浓度的衰减有关，而 C3 则不影响 Ca2+浓度。同样，C3 和 KB-R7943 显著减弱了早期瘦素诱导的钙调神经磷酸酶活性增加以及转录因子激活的 T 细胞核易位的增加。瘦素引起的肥厚反应还与 p38 和 ERK1/2 MAPK 磷酸化的增加以及 p38 的转位有关，但 ERK1/2 没有转位。KB-R7943 以及钙调神经磷酸酶抑制剂 FK-506 均可阻断 p38 反应和肥厚，而 ERK1/2 磷酸化不受影响。因此，我们的研究证明了钙调神经磷酸酶途径在介导瘦素诱导的肥厚中的关键作用。此外，我们报告了一种新的 RhoA 依赖性瘦素诱导的钙调神经磷酸酶激活，该激活独立于细胞内 Ca2+浓度的变化。
