Systemic Identification of Functionally Conserved Long Noncoding RNA Metabolic Regulators in Human and Mouse Livers.

BACKGROUND & AIMS: Unlike protein-coding genes, most human long noncoding RNAs (lncRNAs) lack conservation based on their sequences, posing a challenge for investigating their role in a pathophysiological context for clinical translation. This study explores the hypothesis that nonconserved lncRNAs in human and mouse livers may share similar metabolic functions, giving rise to functionally conserved lncRNA metabolic regulators (fcLMRs). METHODS: We developed a sequence-independent strategy to select putative fcLMRs and performed extensive analysis to determine the functional similarities of putative human and mouse (h/m)LMR pairs. RESULTS: We found that several pairs of putative fcLMRs share similar functions in regulating gene expression. We further demonstrated that a pair of fcLMRs, h/mLMR1, robustly regulated triglyceride levels by modulating the expression of a similar set of lipogenic genes. Mechanistically, h/mLMR1 binds to poly(A)-binding protein cytoplasmic 1 (PABPC1), a regulator of protein translation, via short motifs on either lncRNA with divergent sequences but similar structures. This interaction inhibits protein translation, activating an amino acid- mechanistic target of rapamycin (mTOR)-sterol regulatory element-binding transcription factor 1 (SREBP1) axis to regulate lipogenic gene expression. Intriguingly, PABPC1-binding motifs on each lncRNA fully rescued the functions of their corresponding LMRs in the opposite species. Given the elevated expression of h/mLMR1 in humans and mice with hepatic steatosis, the PABPC1-binding motif on hLMR1 emerges as a potential nonconserved human drug target whose functions can be fully validated in a physiologically relevant setting before clinical studies. CONCLUSIONS: Our study supports that fcLMRs represent a novel and prevalent biological phenomenon and that deep phenotyping of genetic mLMR mouse models constitutes a powerful approach to understand the pathophysiological role of lncRNAs in the human liver.