Department of Internal Medicine, University of Michigan, Ann Arbor, MI, USA.
Department of Internal Medicine, University of Michigan, Ann Arbor, MI, USA; Department of Molecular and Integrative Physiology, University of Michigan, Ann Arbor, MI, USA.
Mol Metab. 2020 Feb;32:168-175. doi: 10.1016/j.molmet.2019.12.013. Epub 2020 Jan 3.
Leptin acts via its receptor, LepRb, on specialized neurons in the brain to modulate energy balance and glucose homeostasis. LepRb→STAT3 signaling plays a crucial role in leptin action, but LepRb also mediates an additional as-yet-unidentified signal (Signal 2) that is important for leptin action. Signal 2 requires LepRb regions in addition to those required for JAK2 activation but operates independently of STAT3 and LepRb phosphorylation sites.
To identify LepRb sequences that mediate Signal 2, we used CRISPR/Cas9 to generate five novel mouse lines containing COOH-terminal truncation mutants of LepRb. We analyzed the metabolic phenotype and measures of hypothalamic function for these mouse lines.
We found that deletion of LepRb sequences between residues 921 and 960 dramatically worsens metabolic control and alters hypothalamic function relative to smaller truncations. We also found that deletion of the regions including residues 1013-1053 and 960-1013 each decreased obesity compared to deletions that included additional COOH-terminal residues.
LepRb sequences between residues 921 and 960 mediate the STAT3 and LepRb phosphorylation-independent second signal that contributes to the control of energy balance and metabolism by leptin/LepRb. In addition to confirming the inhibitory role of the region (residues 961-1013) containing Tyr, we also identified the region containing residues 1013-1053 (which contains no Tyr residues) as a second potential mediator of LepRb inhibition. Thus, the intracellular domain of LepRb mediates multiple Tyr-independent signals.
瘦素通过其受体 LepRb 作用于大脑中的特定神经元，调节能量平衡和葡萄糖稳态。LepRb→STAT3 信号在瘦素作用中起着至关重要的作用，但 LepRb 还介导了一种尚未确定的额外信号（信号 2），这对瘦素作用很重要。信号 2 需要 LepRb 区域，除了那些激活 JAK2 所需的区域，但独立于 STAT3 和 LepRb 磷酸化位点操作。
为了确定介导信号 2 的 LepRb 序列，我们使用 CRISPR/Cas9 生成了包含 LepRb COOH 端截断突变体的五个新型小鼠系。我们分析了这些小鼠系的代谢表型和下丘脑功能的测量结果。
我们发现，与较小的截断相比，LepRb 序列缺失 921 到 960 位残基会显著恶化代谢控制并改变下丘脑功能。我们还发现，与包含其他 COOH 端残基的缺失相比，缺失包括残基 1013-1053 和 960-1013 的区域会导致肥胖减少。
LepRb 序列缺失 921 到 960 位残基介导了 STAT3 和 LepRb 磷酸化非依赖性的第二信号，该信号有助于瘦素/LepRb 对能量平衡和代谢的控制。除了确认包含 Tyr 的区域（残基 961-1013）的抑制作用外，我们还确定了包含残基 1013-1053 的区域（不含 Tyr 残基）为 LepRb 抑制的另一个潜在介质。因此，LepRb 的细胞内结构域介导多种 Tyr 非依赖性信号。
