The hidden bioactive molecules: miRNAs loaded in extracellular vesicles might act as bioactive constituents in European mistletoe

草药产品被全球公认为药物或食品补充剂形式的有效补充治疗系统。通常，它们的生物活性成分和与人类的相应相互作用尚未得到全面表征。世界各地的各种研究已经启动，以开发基于科学证据的草药疗法。新的植物生物活性分子正在被发现。microRNA（miRNAs）是一类约22个核苷酸的单链非编码RNA，在基因表达中起着重要作用。近年来，跨植物界的miRNAs研究引起了人们极大的兴趣。例如，水稻miRNAs被认为可以进入哺乳动物的血液，并在哺乳动物的新陈代谢中发挥功能作用。植物来源的miR159可以靶向人类基因，并在体外和体内抑制乳腺癌细胞生长。这些研究表明，膳食植物miRNAs可以调控人类基因，为药用植物miRNAs可能是调节人类健康和疾病的潜在生物活性物质提供了令人振奋的线索。槲寄生（Viscum album L.）几个世纪以来，在欧洲传统上一直用于治疗癌症和心血管疾病，但其科学背景仍有争议。通过高通量Illumina测序和生物信息学分析，我们前期的研究表明槲寄生miRNAs可能参与槲寄生的药理作用。目前迫切需要进一步的实验验证来确认这些植物miRNAs的生物活性。考虑到植物miRNAs在酶环境中不稳定，如草药提取物和哺乳动物体液，被封装到细胞外囊泡（EV）中，细胞释放的膜封闭的纳米尺寸颗粒，可以提供miRNAs纳米穿梭机，允许它们长距离旅行。在此，我们提出槲寄生miRNAs可能作为一个独立的活性成分类别，并可能负责或至少有助于槲寄生的药理作用（如抗肿瘤作用）。槲寄生EV可能作为有效的载体来递送具有完整功能的miRNAs，并介导槲寄生miRNAs的跨界调节。拟议的研究将集中在跨王国的调控miRNA的分析，哺乳动物靶标的鉴定和槲寄生EV介导的miRNA递送的可视化。如果我们的假设得到证实，将促进我们对药用植物中基于miRNA的生物活性成分的了解，为民间药用和药用植物的临床应用提供科学支持。更重要的是，它将为开发基于miRNA的疗法以预防或治疗人类疾病开辟新的途径。

Herbal products are globally accepted as a valid complementary system of therapy in the form of pharmaceuticals or food supplements. Often their bioactive constituents and corresponding interactions with human have not been comprehensively characterized. Various studies around the world have been initiated to develop scientific evidence-based herbal therapies. New plant bioactive molecules are being discovered. MicroRNAs (miRNAs) are a class of approximately 22 nucleotides single-stranded non-coding RNAs that play crucial roles in gene expression. Recently, the cross-kingdom of plant derived miRNAs has attracted great attraction. For example, the rice miRNAs have been suggested to enter mammalian bloodstream and have a functional role in mammalian metabolism. Plant-derived miR159 can target human genes and suppress breast cancer cell growth in vitro and in vivo. These studies suggested that human genes can be regulated by dietary plant miRNAs, providing thrilling clues that medicinal plants miRNAs might be the hidden bioactive compounds regulating human health and diseases. Mistletoe (Viscum album L.) has been used traditionally in Europe for centuries for the treatment of cancer and cardiovascular diseases but their scientific background is still controversially discussed. By using high-throughput Illumina sequencing and bioinformatics analysis, our previous study indicated that mistletoe miRNAs might be involved in the pharmacological effects of mistletoe. Further experimental validations are currently urgent to confirm the bioactivities of these plant miRNAs. Considering plant miRNAs are not stable in enzymatic environment such as herb extracts and mammalian body fluids, being encapsulated into extracellular vesicles (EVs) that are membrane-enclosed nano-sized particles released by cells, could offer miRNAs nano-shuttles allowing them to travel long distances. Herein, we propose that mistletoe miRNAs might serve as an independent category of active ingredients and might be responsible for or at least contribute to the pharmacological effects (e.g. anti-tumor effect) of mistletoe. Mistletoe EVs might act as effective vehicles to deliver miRNAs with intact functionality, and mediate the cross-kingdom regulation of mistletoe miRNAs. Proposed investigations will be focused on the profiling of cross-kingdom regulatory miRNAs, identification of mammalian targets and visualization of mistletoe EVs mediated miRNA delivery. If our hypothesis is proven, it will promote our understanding of miRNA-based bioactive ingredients in medicinal plants provide scientific support for folk medicinal use and clinical use of medicinal plants. More importantly, it will open new ways for the development of miRNA-based therapies to prevent or treat human diseases.