Leptin stimulates synaptogenesis in hippocampal neurons via KLF4 and SOCS3 inhibition of STAT3 signaling.

Normal development of neuronal connections in the hippocampus requires neurotrophic signals, including the cytokine leptin. During neonatal development, leptin induces formation and maturation of dendritic spines, the main sites of glutamatergic synapses in the hippocampal neurons. However, the molecular mechanisms for leptin-induced synaptogenesis are not entirely understood. In this study, we reveal two novel targets of leptin in developing hippocampal neurons and address their role in synaptogenesis. First target is Kruppel-Like Factor 4 (KLF4), which we identified using a genome-wide target analysis strategy. We show that leptin upregulates KLF4 in hippocampal neurons and that leptin signaling is important for KLF4 expression in vivo. Furthermore, KLF4 is required for leptin-induced synaptogenesis, as shKLF4 blocks and upregulation of KLF4 phenocopies it. We go on to show that KLF4 requires its signal transducer and activator of transcription 3 (STAT3) binding site and thus potentially blocks STAT3 activity to induce synaptogenesis. Second, we show that leptin increases the expression of suppressor of cytokine signaling 3 (SOCS3), another well-known inhibitor of STAT3, in developing hippocampal neurons. SOCS3 is also required for leptin-induced synaptogenesis and sufficient to stimulate it alone. Finally, we show that constitutively active STAT3 blocks the effects of leptin on spine formation, while the targeted knockdown of STAT3 is sufficient to induce it. Overall, our data demonstrate that leptin increases the expression of both KLF4 and SOCS3, inhibiting the activity of STAT3 in the hippocampal neurons and resulting in the enhancement of glutamatergic synaptogenesis during neonatal development.

海马体中神经元连接的正常发育需要神经营养信号，包括细胞因子瘦素。在新生儿发育期间，瘦素诱导树突棘的形成和成熟，树突棘是海马神经元中谷氨酸能突触的主要部位。然而，瘦素诱导突触发生的分子机制尚未完全清楚。在这项研究中，我们揭示了发育中的海马神经元中瘦素的两个新靶点，并阐述了它们在突触发生中的作用。第一个靶点是克鲁佩尔样因子4（KLF4），我们是通过全基因组靶点分析策略确定的。我们表明瘦素在海马神经元中上调KLF4，并且瘦素信号传导对体内KLF4的表达很重要。此外，KLF4是瘦素诱导突触发生所必需的，因为shKLF4会阻断这一过程，而KLF4的上调会产生类似的表型。我们进一步表明，KLF4需要其信号转导和转录激活因子3（STAT3）结合位点，因此可能阻断STAT3的活性以诱导突触发生。其次，我们表明瘦素增加了发育中的海马神经元中细胞因子信号传导抑制因子3（SOCS3）的表达，SOCS3是另一种众所周知的STAT3抑制剂。SOCS3也是瘦素诱导突触发生所必需的，并且单独就足以刺激这一过程。最后，我们表明持续激活的STAT3会阻断瘦素对树突棘形成的影响，而靶向敲低STAT3足以诱导树突棘形成。总体而言，我们的数据表明，瘦素增加了KLF4和SOCS3的表达，抑制了海马神经元中STAT3的活性，从而导致新生儿发育期间谷氨酸能突触发生的增强。