LRRK2 as a target for the treatment of Parkinson’s disease

抑制LRRK2的小分子是保护神经元免受帕金森病(PD)病理影响的有希望的新药候选。然而，帕金森病是一种由多个亚型组成的异质性神经退行性疾病，患者的症状和进展差异很大，这使得临床试验很难找到有效的药物。因此，迫切需要生物标记物来确定对LRRK2抑制剂有反应的患者亚群，以及监测靶点接触的生物标记物。为了识别这些生物标志物，首先有必要了解LRRK2影响神经退行性变的机制。使用从突变的LRRK2患者的诱导多能干细胞(IPSCs)分化的神经元和等基因突变校正的对照，我们已经开发出第一批利用轴突运输的强大的神经退行性表型之一，这种运输缺陷通过LRRK2抑制剂治疗完全挽救。利用定量磷酸化蛋白质组学，我们发现LRRK2的活性与微管相关蛋白(MAPs)的磷酸化增加有关，这会导致细胞骨架的破坏，导致轴突变性。这些变化很可能是间接的，因为LRRK2的表达水平非常低，而且许多已知的激酶介导了MAP的磷酸化。Rab蛋白已被证明直接被LRRK2磷酸化，并与轴突运输有关，使它们成为靶向参与的良好候选生物标记物。在这里，我们建议：(1)用LRRK2G2019S鉴定介导神经元轴突表型和MAP异常磷酸化的特异性磷酸化Rab(S)，(2)评估磷酸化Rab和磷酸化MAP作为IPSC源性神经元中LRRK2抑制剂靶向参与的可能生物标志物，(3)使用来自患者队列的样本来验证LRRK2靶向参与的候选生物标志物，以及(4)使用基于IPSC的特发性帕金森病(IPD)模型，根据常见的LRRK2风险多态分层来确定LRRK2抑制剂是否也可以在IPD患者的亚群中有效。由于我们建议将重点放在正在进行I期临床试验的化合物上，我们认为我们的提议将对临床试验的结构产生直接影响，这可能导致第一个被批准的有效预防帕金森病发病机制的药物。

Small molecules inhibiting LRRK2 are promising new drug candidates to protect neurons against Parkinson’s disease (PD) pathology. However, PD is a heterogeneous neurodegenerative disorder consisting of multiple subtypes with patients differing widely in their symptoms and progression, making it very difficult for a clinical trial to detect an effective drug. Thus, biomarkers are urgently needed to identify patient subgroups that would respond to LRRK2 inhibitors as well as biomarkers of to monitor target engagement. In order to identify these biomarkers, it is first necessary to understand the mechanism by which LRRK2 affects neurodegeneration. Using neurons differentiated from induced pluripotent stem cells (iPSCs) from patients with mutant LRRK2 and isogenic mutation-corrected controls, we have developed one of the first robust neurodegenerative phenotypes using axonal trafficking, and this trafficking defect is completely rescued by treating with LRRK2 inhibitors. Using quantitative phospho-proteomics, we found that LRRK2 activity is associated with increased phosphorylation of microtubule associated proteins (MAPs), which leads to disruption of the cytoskeleton, causing axonal degeneration. It is likely that these changes are indirect since LRRK2 is expressed at very low levels, and many kinases are known to mediate MAP phosphorylation. Rab proteins have been shown to be directly phosphorylated by LRRK2 and have been linked to axonal trafficking, making them good candidate biomarkers for target engagement. Here, we propose: (1) identifying the specific phospho-Rab(s) mediating axonal phenotypes and aberrant phosphorylation of MAPs in neurons with LRRK2 G2019S, (2) assessing phospho-Rab and phospho-MAPs as possible biomarkers of target engagement for LRRK2 inhibitors in iPSCs-derived neurons, (3) validating the candidate biomarkers of LRRK2 target engagement using samples from patient cohorts, and (4) using iPSC-based models of idiopathic PD (iPD) stratified by common LRRK2 risk polymorphisms to determine if LRRK2 inhibitors could also be effective in subsets of iPD patients. Because we propose focusing on compounds that are being tested in phase I clinical trials, we argue that our proposal is poised to have a direct impact on the structure of clinical trials, which could lead to the first approved drug that effectively protects against PD pathogenesis.