Donnai-Barrow综合征,与LRP2(低密度脂蛋白受体2/megalin)突变相关的遗传性疾病,以无法解释的神经症状和智力缺陷为特征。Megalin是一种多功能的内吞清除细胞表面受体,主要在上皮细胞中描述。这种受体也在中枢神经系统中表达,主要在神经元中,参与神经突生长和神经保护机制。然而,中枢神经系统中megalin调节的机制知之甚少。使用转甲状腺素基因敲除小鼠,一个megalin配体,我们发现,在不同的中枢神经系统区域,运甲状腺素蛋白正调节神经元的megalin水平,特别是在海马区。转甲状腺素蛋白甚至能够挽救转甲状腺素蛋白敲除海马神经元培养物中的megalin下调,通过megalin的正反馈机制。重要的是,转甲状腺素蛋白激活了神经元巨蛋白的受调节的细胞内蛋白水解机制,产生一个胞内结构域,它被转移到细胞核,揭示megalinC末端作为潜在的转录因子,能够调节基因表达。我们揭示了神经元megalin减少会影响生理神经元活动,导致神经突数量减少,长度和分支,增加神经元对毒性损伤的敏感性。最后,我们揭示了巨蛋白在突触可塑性中的一个新的意想不到的作用,通过促进树突棘的形成和成熟,并有助于建立活跃的突触,在体外和体内海马神经元。此外,megalin的这些结构和突触作用对学习和记忆机制的影响,因为megalin杂合子小鼠在一些行为测试中表现出与海马相关的记忆和学习缺陷。总之,我们揭示了megalin在生理神经元活动中的全新作用,主要表现在突触可塑性,影响学习和记忆。重要的是,我们有助于揭示与megalin基因病理相关的认知和智力障碍的分子机制。
Donnai-Barrow syndrome, a genetic disorder associated to LRP2 (low-density lipoprotein receptor 2/megalin) mutations, is characterized by unexplained neurological symptoms and intellectual deficits. Megalin is a multifunctional endocytic clearance cell-surface receptor, mostly described in epithelial cells. This receptor is also expressed in the CNS, mainly in neurons, being involved in neurite outgrowth and neuroprotective mechanisms. Yet, the mechanisms involved in the regulation of megalin in the CNS are poorly understood. Using transthyretin knockout mice, a megalin ligand, we found that transthyretin positively regulates neuronal megalin levels in different CNS areas, particularly in the hippocampus. Transthyretin is even able to rescue megalin downregulation in transthyretin knockout hippocampal neuronal cultures, in a positive feedback mechanism via megalin. Importantly, transthyretin activates a regulated intracellular proteolysis mechanism of neuronal megalin, producing an intracellular domain, which is translocated to the nucleus, unveiling megalin C-terminal as a potential transcription factor, able to regulate gene expression. We unveil that neuronal megalin reduction affects physiological neuronal activity, leading to decreased neurite number, length and branching, and increasing neuronal susceptibility to a toxic insult. Finally, we unravel a new unexpected role of megalin in synaptic plasticity, by promoting the formation and maturation of dendritic spines, and contributing for the establishment of active synapses, both in in vitro and in vivo hippocampal neurons. Moreover, these structural and synaptic roles of megalin impact on learning and memory mechanisms, since megalin heterozygous mice show hippocampal-related memory and learning deficits in several behaviour tests. Altogether, we unveil a complete novel role of megalin in the physiological neuronal activity, mainly in synaptic plasticity with impact in learning and memory. Importantly, we contribute to disclose the molecular mechanisms underlying the cognitive and intellectual disabilities related to megalin gene pathologies.