The RNA-binding protein vigilin regulates VLDL secretion through modulation of Apob mRNA translation

Abstract

The liver is essential for the synthesis of plasma proteins and integration of lipid metabolism. While the role of transcriptional networks in these processes is increasingly understood, less is known about post-transcriptional control of gene expression by RNA-binding proteins (RBPs). Here, we show that the RBP vigilin is upregulated in livers of obese mice and in patients with fatty liver disease. By using in vivo, biochemical and genomic approaches, we demonstrate that vigilin controls very-low-density lipoprotein (VLDL) secretion through the modulation of apolipoproteinB/Apob mRNA translation. Crosslinking studies reveal that vigilin binds to CU-rich regions in the mRNA coding sequence of Apob and other proatherogenic secreted proteins, including apolipoproteinC-III/Apoc3 and fibronectin/Fn1. Consequently, hepatic vigilin knockdown decreases VLDL/low-density lipoprotein (LDL) levels and formation of atherosclerotic plaques in Ldlr À / À mice. These studies uncover a role for vigilin as a key regulator of hepatic Apob translation and demonstrate the therapeutic potential of inhibiting vigilin for cardiovascular diseases. 4 , and vigilin has been found to be associated with cytoplasmic mRNA 5 and tRNA 6 . Vigilin has been implicated in diverse biological processes such as sterol metabolism 5,7-10 , carcinogenesis 11,12 , control of translation 13,14 , formation of heterochromatin [15][16][17] , nuclear export of tRNA 18 , cytoplasmic transport of RNA 19 and metabolism of specific mRNAs 7,[20][21][22] . Yet, very few mRNA targets and no precise RNA recognition element (RRE) have been reported in mammals. Furthermore, its function in mice and human has not been addressed in a systematic and unbiased manner.Here, through unbiased approaches using photoactivatable ribonucleoside-enhanced crosslinking and immunoprecipitation (PAR-CLIP), RNA sequencing, as well as label-free quantification by mass spectrometry, we identify vigilin as a translational regulator of a subset of genes encoding for secreted liver proteins. We report that vigilin binds to CU-rich regions in the mRNA coding sequence of Apob and other proatherogenic secreted proteins, including apolipoproteinC-III/Apoc3 and fibronectin/Fn1. Expression of vigilin also correlated with lipid accumulation in patients with non-alcoholic fatty liver disease (NAFLD) and non-alcoholic steatohepatitis (NASH) as well as livers of insulin-resistant obese mice. Lastly, we show that silencing of vigilin in the liver reduces atherosclerotic plaque formation in Ldlr À / À mice, suggesting a critical role of vigilin in hepatic metabolism and a possible therapeutic approach for the prevention of cardiovascular diseases. ResultsVigilin regulates hepatic lipid metabolism. Vigilin is ubiquitously expressed with highest levels in organs with preferential endodermal cell origin, including the liver (Fig. 1a), and is predominantly localized to the cytoplasm in hepatocytes (Fig. 1b). To assess its relevance in metabolic disorders, we investigated if vigilin was deregulated in obes...

Global Tudor‐SN transgenic mice are protected from obesity‐induced hepatic steatosis and insulin resistance

“…It has been reported that knocking down hepatic Insr expression in WT mice reduced VLDL secretion (35). We thus speculated that the phenotype of reduced hepatic steatosis in HFD-Tg mice is related to active insulin signaling.…”

“…6B). Given that insulin signaling benefits VLDL secretion (34,35), we sought to detect the capacity of VLDL secretion Figure 3. Identification of unregulated Tudor-SN-related genes involved in metabolism.…”

Identification of Receptor Ligands in Apo B100 Reveals Potential Functional Domains

“…LLTP molecules are involved in extracellular transport of hydrophobic lipids and triglycerides (9, 10), binding nucleic acids (15–17), and appear to be involved in the immune response (12–14). LLTPs, including apo B100, share a common ancestor (9) and therefore contain similar primary structures that impart similar functions.…”

“…LLTPs, including apo B100, share a common ancestor (9) and therefore contain similar primary structures that impart similar functions. For example, Vigilin contains 13 K-homology nucleic acid binding domains as compared to 11 similar sequences in apo B100, both molecules have been shown to bind RNA (25, 15–17). VTG A2 also contains 10 K-homology RNA binding motifs.…”

“…Non-apo B100 LLTPs are known to have multiple roles, including protein-protein interactions in immune response (12–14) and mRNA binding (15–17). Apo B100 is a massive, semi-hydrophobic molecule of 4,536 amino acids and, like other LLTPs, contains a variety of short sequence motifs indicative of potential function (7, 8, 18, 19).…”