Knocking Down Long Noncoding RNAs Using Antisense Oligonucleotide Gapmers.

Long noncoding RNAs (lncRNAs) are a class of RNA with 200 nucleotides or longer that are not translated into protein. lncRNAs are highly abundant; a study estimates that at least four times more lncRNAs are typically present than coding RNAs in humans. However, function of more than 95% of human lncRNAs are still unknown. Synthetic antisense oligonucleotides called gapmers are powerful tools for lncRNA loss-of-function studies. Gapmers contain a central DNA part, which activates RNase H-mediated RNA degradation, flanked by modified oligonucleotides, such as 2'-O-methyl RNA (2'OMe), 2'-O-methoxyethyl RNA (2'MOE), constrained ethyl nucleosides (cEt), and locked nucleic acids (LNAs). In contrast to siRNA or RNAi-based methods, antisense oligonucleotide gapmer-based knockdown is often more effective against nuclear-localized lncRNA targets, since RNase H is mainly localized in nuclei. As such, gapmers are also potentially a powerful tool for therapeutics targeting lncRNAs in various diseases, including cancer, cardiovascular diseases, lung fibrosis, and neurological/neuromuscular diseases. This chapter will discuss the development and applications of gapmers for lncRNA loss-of-function studies and tips to design effective antisense oligonucleotides.