Rbm39 ameliorates metabolic dysfunction-associated steatotic liver disease by regulating Apob and Fabp4

Excessive hepatic lipid accumulation is the hallmark of metabolic dysfunction-associated steatotic liver disease (MASLD), yet its underlying mechanisms still not fully understood. In this study, we identified RNA binding motif protein 39 (Rbm39) as a key modulator of hepatic lipid homeostasis during MASLD progression. To establish in vivo MASLD model, mice were fed either a high-fat diet (HFD) or a Gubra-Amylin NASH (GAN) diet. We employed adeno-associated virus to manipulate Rbm39 expression levels to assess its role in MASLD. Transcriptome analysis was conducted to pinpoint the genes targeted by Rbm39. Western blot, RT-PCR, dual-luciferase reporter gene assays, and alternative splicing analysis were utilized to delve into the molecular mechanisms. Our results showed that Rbm39 expression was notably decreased in the livers of MASLD mice. Knockdown of hepatic Rbm39 aggravated HFD-induced hepatic steatosis and GAN diet-induced MASH, along with a notable decrease in serum lipid levels. Conversely, overexpression of Rbm39 attenuated MASLD development and progression. RNA sequencing data analysis indicated that Rbm39 regulated the expression of apolipoprotein B (Apob) and fatty acid-binding protein 4 (Fabp4), both of which are crucial for lipid transport. Mechanistically, Rbm39 enhanced the transcription of Apob by upregulating hepatocyte nuclear factor 4α (Hnf4α), while it suppressed Fabp4 transcription by regulating alternative splicing of hypoxia inducible factor-1α (Hif-1α). These findings highlight the pivotal role of Rbm39 in maintaining hepatic lipid homeostasis and suggest its potential as a therapeutic target for MASLD.