RNA nanotechnology has promise for developing mRNA carriers with enhanced physicochemical and functional properties. However, the potential synergy for mRNA delivery of RNA nanotechnology in cooperation with established carrier systems remains unknown. This study proposes a combinational system of RNA nanotechnology and mRNA polyplexes, by focusing on mRNA steric structure inside the polyplexes. Firstly, several mRNA strands are bundled through hybridization with RNA oligonucleotide crosslinkers to obtain tight mRNA structure, and then the bundled mRNA is mixed with poly(ethylene glycol) (PEG)-polycation block copolymers to prepare PEG-coated polyplex micelles (PMs). mRNA bundling results in highly condensed mRNA packaging inside PM core with dense PEG chains on the surface, thereby, improving PM stability against polyion exchange reaction and ribonuclease (RNase) attack. Importantly, such stabilization effects are attributed to bundled structure of mRNA rather than the increase in total mRNA amount encapsulated in the PMs, as encapsulation of long mRNA strands without bundling fails to improve PM stability. Consequently, PMs loading bundled mRNA exhibit enhanced stability in mouse blood circulation, and induce efficient protein expression in cultured cells and mouse brain.

RNA纳米技术有望开发出具有增强的物理化学和功能特性的mRNA载体。然而，与已建立的载体系统合作，用于RNA纳米技术的mRNA递送的潜在协同作用仍然未知。这项研究提出了一种RNA纳米技术和mRNA多链体的组合系统，其重点是多链体内部的mRNA空间结构。首先，通过与RNA寡核苷酸交联剂杂交将几条mRNA链捆扎在一起，以获得紧密的mRNA结构，然后将捆绑的mRNA与聚乙二醇（PEG）-聚阳离子嵌段共聚物混合，以制备PEG包覆的多元胶束（PM）。mRNA捆绑导致PM核心内部高度浓缩的mRNA包装，表面上有密集的PEG链，因此，改善了针对多离子交换反应和核糖核酸酶（RNase）攻击的PM稳定性。重要的是，这种稳定作用归因于mRNA的束缚结构，而不是包封在PM中的总mRNA量增加，因为不捆绑的长mRNA链的封装不能提高PM的稳定性。因此，PMs捆绑的mRNA表现出增强的小鼠血液循环稳定性，并在培养的细胞和小鼠脑中诱导有效的蛋白表达。