RNase L

As the population ages, the incidence of neurodegenerative diseases such as Alzheimer's and Parkinson's are surging, presenting significant threats to public health and weighing on society. However, effective treatments for most neurodegenerative conditions remain elusive, with existing options merely providing symptomatic relief without targeting the root causes. While some biologic therapies have shown early promise in treating these diseases, developing small molecule drugs that are affordable and convenient continues to pose a major challenge.  The  ”undruggable” targets of neurodegenerative diseasesThe “undruggables”A key reason for this difficulty lies in the "undruggable" nature of proteins involved in neurodegeneration.  Unlike traditional drug targets that have enzymatic activity and binding sites for small molecules to modulate their functions, pathological proteins in neurodegenerative diseases are often misfolded, lacking sites that drugs could target, making medication development extremely hard. Despite decades of efforts, successes in developing effective neurodegenerative disease therapies like Alzheimer’s disease (AD), Parkinson’s disease (PD), Huntington’s disease (HD) and amyotrophic lateral sclerosis (ALS) remain scarce. The intricate disease etiology, unique target traits, and inherent obstacles in delivering therapeutics to the nervous system pose formidable challenges for drug development.  However, evidence from human genetics and animal models implicates amyloid-β (Aβ) and tau in Alzheimer's disease, α-synuclein in Parkinson's disease, TDP-43 in amyotrophic lateral sclerosis and frontotemporal dementia, and mutant huntingtin (mHTT) in Huntington's disease as central to the pathological processes and progression of these conditions. Together, they represent potential drug targets that can be addressed through various strategies.    Synapse record shows 11 drugs targeting TDP-43 for ALS Broadly speaking, these strategies fall into indirect or direct targeting approaches, and each category can then be further divided based on the pathways involved. Indirect approaches aim to modulate factors that influence protein levels or aggregation, while direct approaches seek to target pathogenic proteins or their interactions directly. Different strategies for drugging the “undruggable” targetsIndirect Targeting StrategiesWhile directly targeting "misfolded" pathogenic proteins is difficult, modifying upstream or downstream factors may be more feasible. For instance, through omics screens, researchers identified the upstream genes v-ATPase and GPR52 that modulate levels of Ataxin 2 (implicated in ALS and SCA2) and mutant huntingtin (mHTT). Follow-up studies have demonstrated that the utilization of small molecules to inhibit v-ATPase and GPR52 can efficiently and securely decrease Ataxin 2 and mHTT expression in both mouse and human neurons, leading to a notable enhancement of disease phenotypes associated with the condition. This approach involves designing drugs that specifically target the more "druggable" upstream modifiers of pathogenic proteins. However, as these upstream genes serve normal functions, the inhibition or activation of them can potentially lead to side effects, thereby limiting the effectiveness of this strategy. It will be crucial to establish a therapeutic window that enables the reduction of disease proteins without interfering with the essential functions of the modifiers. Alternatively, targeting downstream molecular pathways can also offer opportunities. Misfolded proteins can elicit neurodegeneration through complex mechanisms. Researchers have discovered that the inhibition of the p53-Puma pathway, which is activated in both ALS and FTD, effectively prevented neuronal death in both cell and animal models. These findings suggest that Puma inhibitors may have therapeutic potential for the treatment of these disorders. Likewise, the inhibition ofRIPK1, a crucial mediator of cell death and inflammation pathways in neurodegenerative disorders, has demonstrated safety both in preclinical and clinical studies. This presents opportunities for the treatment of diseases such as Alzheimer's, ALS, and multiple sclerosis. Overall, these strategies aim to target the aberrantly activated pathways in neurodegeneration, potentially with fewer side effects. However, targeting individual downstream proteins may also have limitations, since misfolded proteins trigger related diseases through diverse signaling routes, potentially interfering with or compensating for drugs against these pathways. Direct Targeting StrategiesAlthough directly reducing misfolded protein levels with small molecules is unfeasible, targeted protein degradation technologies, such as PROTACs and AUTOTACs, provide viable alternatives. These technologies function similarly, comprising three components: a ligand that binds to the target protein, a ligand for cellular degradation machinery components, and a linker that connects them.  329 drugs fall under the PROTAC category in Synapse.By acting as "molecular bridges," they facilitate interactions between targets and degradation elements, leading to the breakdown of the target. However, PROTACs and AUTOTACs are large, chimeric molecules with suboptimal drug properties. As chimeras, they often exhibit poor blood-brain barrier penetration, which poses challenges for treating neurodegenerative diseases. Recently, researchers proposed a new autophagy-targeting "molecular glue" strategy called ATTEC (AuTophagy-TEthering Compounds), which effectively addresses these issues. Studies have demonstrated that these "molecular glues" can degrade mutant huntingtin without affecting normal huntingtin, thereby rescuing Huntington's disease phenotypes in cells, flies, and mice. With molecular weights ranging from 250-500 Da, some "molecular glues" can cross the blood-brain barrier, exhibiting enhanced drug-like properties and representing potent tools for neurodegenerative drug discovery.  The ”molecular glue”Furthermore, "molecular glues" have uses beyond protein degradation; they can also elevate protein levels. For disorders caused by haploinsufficiency, upregulating wild-type protein levels may be desirable. In such cases, "molecular glues" can bind wild-type proteins to prevent their degradation by deubiquitinases. Small molecule induced protein degradationUnlike directly targeting neurodegenerative proteins, another strategy uses small molecule drugs against their encoding RNAs.  For example, small molecules can alter mRNA splicing. Novartis reported an orally available small molecule, branaplam, that lowers mutant huntingtin levels by introducing a termination codon into mRNA via splicing modulation, decreasing mutant and normal HTT production. This compound was previously reported to increased SMN protein in spinal muscular atrophy (SMA) by stabilizing SMN2 gene products, and a similar drug from Roche was approved by FDA in 2021 for SMA.    In addition to the aforementioned strategies, Matthew Disney's team has developed RNase recruitment bivalent oligonucleotides (RIBOTACs) that offer new RNA degradation options. RIBOTACs interact with target RNAs to recruit RNase L for degradation, and preclinical studies have shown their effectiveness in degrading RNAs with expanded repeats, thereby alleviating ALS/FTD phenotypes. However, the recognition of specific RNAs by small molecules is limited to specialized structures, usually in GC-rich repetitive sequences, and RIBOTACs are relatively large and unable to penetrate the brain effectively. Nonetheless, these results pave the way for future research directions. Aberrant organelles in neurodegeneration may also provide insights into drug development. Mitochondrial damage and lipid accumulation are prominent features, and while organelles have been difficult targets in the past, recent advancements have expanded degradation technologies to include organelles. Methods to degrade mitochondria (AUTAC4) and lipid droplets (LD·ATTEC) have been developed, but further studies are necessary to determine if these compounds can ameliorate disease phenotypes. Although developing small molecule drugs for neurodegenerative diseases is crucial, it has been challenging to target "undruggable" proteins. However, recent technological advancements have provided potential strategies for engaging with these difficult targets, offering hope for patients. Should these strategies prove successful, they could lead to transformative breakthroughs in neurodegenerative drug discovery and inform the targeting of "undruggable" proteins in other diseases as well. Reference Junmei Lu, Zhaoyang Li, Aaron D. Gitler, Boxun Lu. Drugging “undruggable” neurodegenerative disease targets with small molecules. Science Bulletin 2023.

A new study uncovers how a protein, APOBEC3B, could protects cells against many different types of RNA viruses like respiratory syncytial virus (RSV), SARS-CoV2, influenza virus, poliovirus and measles, helping to prevent disease. A new University of California, Irvine-led study uncovers how a protein, APOBEC3B, could protects cells against many different types of RNA viruses like respiratory syncytial virus (RSV), SARS-CoV2, influenza virus, poliovirus and measles, helping to prevent disease. The study was published in Nature Communications. Titled, "APOBEC3B drives PKR-mediated translation shutdown and protects stress granules in response to viral infection," the study findings provide an understanding of how lung cells, in particular, protect themselves against RNA viral infection. This new discovery is essential to developing future therapies to limit viral infection and improve the health of patients with chronic lung disease. Respiratory syncytial virus (RSV), SARS-CoV2, influenza virus, poliovirus, and measles -- all single-stranded RNA viruses -- are some examples of highly contagious diseases transmitted by respiratory aerosols that commonly infect lung cells. "Patients with chronic lung diseases, such as asthma, cystic fibrosis, chronic obstructive pulmonary disease and interstitial lung diseases, are more susceptible to respiratory lung infections. These viral infections can further contribute to disease progression," said Remi Buisson, PhD, assistant professor in the UCI School of Medicine Department of Biological Chemistry. "An exciting part of our finding fills a critical knowledge gap by illuminating how APOBEC3B can promote innate immune responses in host cells without generating mutations in the virus genomes and promoting viral evolution." In this study, graduate students Lavanya Manjunath and Sunwoo Oh, both at UCI School of Medicine in the Buisson Laboratory, utilized different RNA virus models, including Sendai virus, poliovirus, and Sindbis virus as tools to determine how APOBEC3B regulates innate immune signaling in response to viral infection. Moreover, they found that APOBEC3B is recruited to stress granules through its interaction with PABPC1 to prevent stress granule destabilization and protect mRNAs associated with stress granules from an RNA endonuclease RNase L that cleave RNAs in host cells. "We propose that APOBEC3B, in addition to its canonical role to edit viral genomes, functions with PABPC1 as important innate immunity mediators, protecting cells at different steps of the innate immune response against viral infections," said Buisson. More research is needed to develop strategies to prevent RNA viral infection. "Our next steps are to determine the detailed mechanism of how APOBEC3B recognizes viral genome to promote an innate immune response and prevent viral replication," said Buisson. "The goal is to identify how RNA viruses developed resistance mechanisms to counteract APOBEC3B functions and escape host cell defense." The study was funded by support from the National Institutes of Health.

一项新的研究首次揭示了一些感染了SARS-CoV-2的儿童会患上MIS-C的潜在遗传原因。相关研究结果于2022年12月20日在线发表在Science期刊上。 儿童多系统炎症综合征（Multisystem Inflammatory Syndrome in Children, MIS-C）是一种罕见但可能威胁生命的疾病。这种疾病通常在SARS-CoV-2感染大约四周后发生，具有广泛的症状，比如发烧、呕吐和心肌炎，可导致住院治疗。根据美国疾病控制与预防中心（CDC）的最新数字，各州已经报告了大约9000例MIS-C病例，有71例死亡。 一项新的研究首次揭示了一些感染了SARS-CoV-2的儿童会患上MIS-C的潜在遗传原因。相关研究结果于2022年12月20日在线发表在Science期刊上，论文标题为“Inborn errors of OAS–RNase L in SARS-CoV-2–related multisystem inflammatory syndrome in children”。 这一结果植根于克利夫兰诊所勒纳研究所癌症生物学系的Robert Silverman博士40多年的研究。这项新的研究发现，蛋白OAS和RNase L的基因突变增加了一些免疫细胞类型的炎症反应。这种变化可导致包括心脏、肺部、肾脏和胃肠道在内的多个器官的炎症。在这项研究中，在一小部分MIS-C患儿中发现了突变。 OAS蛋白是由干扰素诱导的，作为对抗病毒的第一道防线。在检测到病毒的双链RNA后，OAS蛋白激活RNase L以防止病毒增殖和扩散。 Silverman博士说，“RNase L就像剪刀一样，切割被翻译成蛋白---包括引起炎症的称为细胞因子的蛋白---的信使RNA（mRNA）。在MIS-C中，这些常染色体隐性突变要么阻止RNase L剪刀的运作（OAS突变），要么阻止RNase L剪刀的产生（RNase L突变）。这些发现提供了关于OAS-RNase L如何预防这种严重的无法解释的COVID-19并发症的重要见解。” Silverman博士的实验室研究干扰素在免疫反应中的作用，着重关注OAS-RNase L途径。Silverman团队与洛克菲勒大学的Jean-Laurent Casanova医学博士及其团队合作，部分上通过分析MIS-C患者的DNA序列数据，与其他感染了SARS-CoV-2但没有患上MIS-C的儿童进行对比，发现了这些突变。 MIS-C患者的OAS1, OAS2和RNASEL双等位基因变异。图片来自Science, 2022, doi:10.1126/science.abo3627。 Casanova博士说，“我们的发现通过阐明MIS-C的分子、细胞和免疫学基础，提高了对这种疾病的认识。我们通过分析MIS-C患者的DNA序列数据，与其他感染了SARS-CoV-2但没有患上MIS-C的儿童进行比较，确定了这些突变。其中一个关键的研究问题是，在携带这些突变的病例中，是病毒增殖增加还是过度的炎症反应导致了MIS-C。我们的结果支持了后一种解释。” 作为国际合作的一部分，Casanova团队确定了这些突变对OAS-RNase L途径的具体影响。这包括筛选几十个突变基因，确定对RNA的影响，然后将这些结果与这种疾病联系起来。 Silverman博士说，“我们的团队利用我多年来对这两种酶的了解来获得这项研究需要的功能数据。本质上，这验证了这些突变对功能的影响。” Silverman博士的实验室还贡献了非商业化的试剂，合成了一种激活RNase L并使它裂解RNA的小分子。这项研究确定这些突变在分子水平上导致了炎症反应的加剧。 有关这些突变以及它们如何影响免疫机制的知识可能为其他导致慢性炎症的疾病提供更多信息，比如临床表现与MIS-C相似的川崎病。（生物谷 Bioon.com） 参考资料： 1. Robert Silverman et al. Inborn errors of OAS–RNase L in SARS-CoV-2–related multisystem inflammatory syndrome in children. Science, 2022, doi:10.1126/science.abo3627. 2. Research identifies potential genetic cause for MIS-C complication following COVID-19 infectionhttps://medicalxpress.com/news/2022-12-potential-genetic-mis-c-complication-covid-.html