<i>INKILN</i> is a Novel Long Noncoding RNA Promoting Vascular Smooth Muscle Inflammation via Scaffolding MKL1 and USP10.

Abstract

Activation of vascular smooth muscle cell (VSMC) inflammation is vital to initiate vascular disease. The role of human-specific long noncoding RNAs in VSMC inflammation is poorly understood. Bulk RNA sequencing in differentiated human VSMCs revealed a novel human-specific long noncoding RNA called inflammatory MKL1 (megakaryoblastic leukemia 1) interacting long noncoding RNA (<i>INKILN</i>). <i>INKILN</i> expression was assessed in multiple in vitro and ex vivo models of VSMC phenotypic modulation as well as human atherosclerosis and abdominal aortic aneurysm. The transcriptional regulation of <i>INKILN</i> was verified through luciferase reporter and chromatin immunoprecipitation assays. Loss-of-function and gain-of-function studies and multiple RNA-protein and protein-protein interaction assays were used to uncover a mechanistic role of <i>INKILN</i> in the VSMC proinflammatory gene program. Bacterial artificial chromosome transgenic mice were used to study <i>INKILN</i> expression and function in ligation injury-induced neointimal formation. <i>INKILN</i> expression is downregulated in contractile VSMCs and induced in human atherosclerosis and abdominal aortic aneurysm. <i>INKILN</i> is transcriptionally activated by the p65 pathway, partially through a predicted NF-κB (nuclear factor kappa B) site within its proximal promoter. <i>INKILN</i> activates proinflammatory gene expression in cultured human VSMCs and ex vivo cultured vessels. <i>INKILN</i> physically interacts with and stabilizes MKL1, a key activator of VSMC inflammation through the p65/NF-κB pathway. <i>INKILN</i> depletion blocks interleukin-1β-induced nuclear localization of both p65 and MKL1. Knockdown of <i>INKILN</i> abolishes the physical interaction between p65 and MKL1 and the luciferase activity of an NF-κB reporter. Furthermore, <i>INKILN</i> knockdown enhances MKL1 ubiquitination through reduced physical interaction with the deubiquitinating enzyme USP10 (ubiquitin-specific peptidase 10). <i>INKILN</i> is induced in injured carotid arteries and exacerbates ligation injury-induced neointimal formation in bacterial artificial chromosome transgenic mice. These findings elucidate an important pathway of VSMC inflammation involving an <i>INKILN</i>/MKL1/USP10 regulatory axis. Human bacterial artificial chromosome transgenic mice offer a novel and physiologically relevant approach for investigating human-specific long noncoding RNAs under vascular disease conditions.