HELZ2 regulates APOB mRNA stability to modulate fatty liver disease and atherosclerosis
Background: Apolipoprotein B (APOB) is essential for lipoprotein assembly and secretion and plays a central role in the development of cardiovascular disease and metabolic dysfunction-associated steatotic liver disease (MASLD). While APOB protein degradation during very low-density lipoprotein (VLDL) maturation has been extensively studied, the regulation of APOB mRNA stability under physiological and pathological conditions remains unexplored. Methods: A forward genetic screen in randomly mutagenized mice identified helicase with zinc finger 2 (HELZ2) as a critical regulator of lipid metabolism. The metabolic effects of HELZ2 mutations or deficiency were evaluated in mice maintained on a chow diet or a high-fat diet (HFD). We also employed a doxycycline-inducible, liver-specific HELZ2 overexpression model to test the sufficiency of hepatocyte Helz2 upregulation. Biochemical assays were used to assess HELZ2 binding to APOB mRNA and its role in APOB mRNA degradation, while the effect of HELZ2 modulation on atherosclerosis was examined in Apoe-/- and Ldlr-/- mouse models. Results: We discovered a unique gain-of-function mutation in HELZ2 (L1833P, termed Colby) that promotes hepatic lipid accumulation independently of changes in body weight on a standard chow diet. Mechanistically, HELZ2 binds APOB mRNA and degrades it via its helicase activity, ensuring tight control of hepatic APOB levels. The Colby mutation enhances HELZ2 helicase activity, resulting in marked reductions in Apob expression and increased hepatic lipid accumulation. Conversely, Helz2-deficient mice show increased Apob mRNA levels and reduced hepatic triglycerides on a HFD. Notably, modest liver-restricted induction of HELZ2 was sufficient to decrease hepatic Apob mRNA and alter lipid handling, phenocopying the Helz2Colby state and supporting the gain-of-function mechanism. A single copy of the Helz2Colby mutation confers protection against atherosclerosis in Apoe-/- and Ldlr-/- mice. Conclusions: HELZ2 is a key regulator of APOB mRNA stability and lipid metabolism. Genetic or pharmacological modulation of HELZ2 activity represents a promising therapeutic strategy for cardiovascular disease and MASLD. Overall design: We performed RNA immunoprecipitation (RIP) with anti-Flag beads to pull down liver lysates from wild type (WT) and Helz2-3xFlag mice, and used RNA sequencing (RNA-seq) to identify HELZ2 interacting RNAs. There are two samples in total, rip_ctrl and rip_helz2.