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High apolipoprotein B-containing (apoB-containing) low-density lipoproteins (LDLs) and low apoA1-containing high-density lipoproteins (HDLs) are associated with atherosclerotic cardiovascular diseases. In search of a molecular regulator that could simultaneously and reciprocally control both LDL and HDL levels, we screened a microRNA (miR) library using human hepatoma Huh-7 cells. We identified miR-541-3p that both significantly decreases apoB and increases apoA1 expression by inducing mRNA degradation of 2 different transcription factors, Znf101 and Casz1. We found that Znf101 enhances apoB expression, while Casz1 represses apoA1 expression. The hepatic knockdown of Casz1 in mice increased plasma apoA1, HDL, and cholesterol efflux capacity. The hepatic knockdown of Zfp961, an ortholog of Znf101, reduced lipogenesis and production of triglyceride-rich lipoproteins and atherosclerosis, without causing hepatic lipid accumulation. This study identifies hepatic Znf101/Zfp961 and Casz1 as potential therapeutic targets to alter plasma lipoproteins and reduce atherosclerosis without causing liver steatosis.

Lipid processing in the retinal pigment epithelium (RPE) is important for maintaining the health and function of the neural retina and the RPE itself. One mode of en mass lipid transport from the RPE is apolipoprotein B-containing lipoproteins (Blps), the assembly of which is regulated by microsomal triglyceride transfer protein (MTP). To gain an initial understanding of how the loss of MTP and, thereby, Blp secretion alters other lipid processing pathways in the RPE, we measured the expression of proteins associated with β-oxidation and lipid droplets in mice lacking MTP expression in the RPE (RPEΔMttp) and age-matched controls. Expression of perilipin 2, a lipid droplet-associated protein, nearly doubled in the RPE of RPEΔMttp, and its localization with neutral lipids also increased. Meanwhile, expression of CPT1A, which mediates the transport of fatty acids into the mitochondria for β-oxidation, was unaffected. These results suggest that the loss of Blp assembly alters intracellular lipid storage patterns. Future studies will examine the effects of the loss of RPE-specific MTP expression and Blp secretion on additional lipid processing pathways., (© 2025. The Author(s), under exclusive license to Springer Nature Switzerland AG.)

Microsomal triglyceride transfer protein (MTP) plays crucial roles in the assembly and secretion of apolipoprotein B-containing lipoproteins and loss of function MTP variants are associated with abetalipoproteinemia, a disease characterized by the absence of these lipoproteins. MTP is a heterodimeric protein of two subunits, MTP and protein disulfide isomerase (PDI). In this study, we report a proband with abetalipoproteinemia who was monitored annually for 10 years in her third decade and had very low plasma lipids and undetectable apoB-containing lipoproteins. Genetic testing revealed biallelic variants in the MTTP gene. She has a well-documented nonsense mutation Gly865∗ that does not interact with the PDI subunit. She also has a novel missense MTP mutation, Ile344Asn. We show that this mutation abrogates lipid transfer activity in MTP and does not support apolipoprotein B secretion. This residue is present in the central α-helical domain of MTP and the substitution of Ile with Asn at this position disrupts interactions between MTP and PDI subunits. Ile344 is away from the known MTP:PDI interacting sites identified in the crystal structure of MTP suggesting that MTP:PDI interactions are more dynamic than previously envisioned. Identification of more missense mutations will enhance our understanding of the structure-function of MTP and the role of critical residues in these interactions between the two subunits. This knowledge may guide us in developing novel treatment modalities to reduce plasma lipids and atherosclerosis., Competing Interests: Conflicts of Interest The authors declare that they have no conflicts of interest with the contents of this article., (Copyright © 2024 The Authors. Published by Elsevier Inc. All rights reserved.)