Although GPR3 plays pivotal roles in both the nervous system and metabolic processes, such as cold-induced thermogenesis, its endogenous ligand remains elusive. Here, by combining structural approach (including cryo-electron microscopy), mass spectrometry analysis, and functional studies, we identify oleic acid (OA) as an endogenous ligand of GPR3. Our study reveals a hydrophobic tunnel within GPR3 that connects the extracellular side of the receptor to the middle of plasma membrane, enabling fatty acids to readily engage the receptor. Functional studies demonstrate that OA triggers downstream G_s signaling, whereas lysophospholipids fail to activate the receptor. Moreover, our research reveals that cold stimulation induces the secretion of OA in mice, subsequently activating G_s/cAMP/PKA signaling in brown adipose tissue. Notably, brown adipose tissues from Gpr3 knockout mice do not respond to OA during cold stimulation, reinforcing the significance of GPR3 in this process. Finally, we propose a “born to be activated and cold to enhance” model for GPR3 activation. Our study provides a starting framework for the understanding of GPR3 signaling in cold-stimulated thermogenesis.

尽管 GPR3 在神经系统和代谢过程（例如寒冷诱导的产热）中发挥着关键作用，但其内源配体仍然难以捉摸。在这里，通过结合结构方法（包括冷冻电子显微镜）、质谱分析和功能研究，我们确定油酸（OA）是 GPR3 的内源配体。我们的研究揭示了 GPR3 内的疏水通道，该通道将受体的细胞外侧与质膜中部连接起来，使脂肪酸能够轻松地与受体结合。功能研究表明，OA 会触发下游 G _s信号传导，而溶血磷脂则无法激活受体。此外，我们的研究表明，冷刺激会诱导小鼠 OA 的分泌，随后激活棕色脂肪组织中的 G _s /cAMP/PKA 信号传导。值得注意的是， Gpr3敲除小鼠的棕色脂肪组织在冷刺激期间不会对 OA 做出反应，这强化了 GPR3 在此过程中的重要性。最后，我们提出了“生来激活，冷来增强”的GPR3激活模型。我们的研究为理解冷刺激生热作用中的 GPR3 信号传导提供了一个起始框架。