Studies have recently demonstrated that a caspase-2-mediated cleavage of human tau (htau) at asparate-314 (D314) is responsible for cognitive deficits and neurodegeneration in mice modeling frontotemporal dementia (FTD). However, these animal studies may be confounded by flaws in their model systems, such as endogenous functional gene disruption and inequivalent transgene expression. To avoid these weaknesses, we examined the pathogenic role of this site-specific htau cleavage in FTD using genetically matched htau targeted-insertion mouse lines: rT2 and rT3. Both male and female mice were included in this study. rT2 mice contain a single copy of the FTD-linked htau proline-to-leucine mutation at amino acid 301 (htau P301L), inserted into a neutral site to avoid dysregulation of host gene expression. The similarly constructed rT3 mice harbor an additional D314-to-glutamate (D314E) mutation that blocks htau cleavage. We demonstrate that htau transgene expression occurs primarily in the forebrain at similar levels in rT2 and rT3 mice. Importantly, expression of the cleavage-resistant D314E mutant delays transgene-induced tau accumulation in the postsynaptic density, brain atrophy, hippocampal neurodegeneration, and spatial memory impairment, without altering age-related progression of pathologic tau conformation and phosphorylation. Our comprehensive investigation of age-dependent disease phenotypes associated with the htau P301L variant in precisely engineered FTD-modeling mice unveils a transiently protective effect of blocking htau cleavage at D314. Findings of this study advance our understanding of the contribution of this tau cleavage to the pathogenesis of FTD, and aid the development of effective dementia-targeting therapies.

SIGNIFICANCE STATEMENT A site-specific and caspase-2-mediated cleavage of human tau plays a pathologic role in dementia. In this study, we investigate the contribution of this cleavage to the pathogenesis of frontotemporal dementia (FTD) using two genetically matched, tau-transgene targeted-insertion mouse lines that differ only by a cleavage-resistant mutation. The use of these mice avoids confounding effects associated with the random integration of tau transgenes to the mouse genome and allows us to comprehensively evaluate the impact of the tau cleavage on FTD phenotypes. Our data reveal that blocking this tau cleavage delays memory impairment and neurodegeneration of FTD-modeling mice. These findings improve our understanding of the pathogenic mechanisms underlying FTD and will facilitate the development of effective therapeutics.

最近的研究表明，caspase-2 介导的人类 tau (htau) 在天冬氨酸 314 (D314) 上的切割是造成额颞叶痴呆 (FTD) 模型小鼠的认知缺陷和神经变性的原因。然而，这些动物研究可能会因其模型系统中的缺陷而混淆，例如内源性功能基因破坏和不等价的转基因表达。为了避免这些弱点，我们使用基因匹配的 htau 靶向插入小鼠系：rT2 和 rT3 检查了这种位点特异性 htau 切割在 FTD 中的致病作用。本研究包括雄性和雌性小鼠。rT2 小鼠在氨基酸 301 (htau P301L) 处包含 FTD 连接的 htau 脯氨酸到亮氨酸突变的单拷贝，插入中性位点以避免宿主基因表达的失调。类似构建的 rT3 小鼠具有额外的 D314 至谷氨酸 (D314E) 突变，可阻断 htau 切割。我们证明 htau 转基因表达主要发生在 rT2 和 rT3 小鼠的前脑中，水平相似。重要的是，抗切割 D314E 突变体的表达延迟了转基因诱导的 tau 在突触后密度、脑萎缩、海马神经变性和空间记忆障碍中的积累，而不会改变与年龄相关的病理性 tau 构象和磷酸化的进展。我们对精确设计的 FTD 建模小鼠中与 htau P301L 变体相关的年龄依赖性疾病表型的全面研究揭示了在 D314 阻断 htau 切割的瞬时保护作用。

重要性声明人类 tau 的位点特异性和 caspase-2 介导的切割在痴呆中起病理作用。在这项研究中，我们使用两个基因匹配的 tau 转基因靶向插入小鼠系来研究这种分裂对额颞叶痴呆 (FTD) 发病机制的贡献，这些小鼠系的区别仅在于抗分裂突变。使用这些小鼠避免了与 tau 转基因随机整合到小鼠基因组相关的混淆效应，并使我们能够全面评估 tau 切割对 FTD 表型的影响。我们的数据表明，阻断这种 tau 裂解会延缓 FTD 建模小鼠的记忆障碍和神经变性。这些发现提高了我们对 FTD 致病机制的理解，并将促进有效疗法的开发。