Lepr(db/db) Mice with Senescence Marker Protein-30 Knockout (Lepr(db/db)Smp30(Y/−)) Exhibit Increases in Small Dense-LDL and Severe Fatty Liver Despite Being Fed a Standard Diet

BACKGROUND/AIMS: The senescence marker protein-30 (SMP30) is a 34 kDa protein originally identified in rat liver that shows decreased levels with age. Several functional studies using SMP30 knockout (Smp30(Y/−)) mice established that SMP30 functions as an antioxidant and protects against apoptosis. To address the potential role of SMP30 in nonalcoholic fatty liver disease (NAFLD) pathogenesis, we established Smp30(Y/−) mice on a Lepr(db/db) background (Lepr(db/db)Smp30(Y/−) mice). RESEARCH DESIGN/PRINCIPAL FINDINGS: Male Lepr(db/db)Smp30(Y/−) mice were fed a standard diet (340 kcal/100 g, fat 5.6%) for 16 weeks whereupon the lipid/lipoprotein profiles, hepatic expression of genes related to lipid metabolism and endoplasmic reticulum stress markers were analyzed by HPLC, quantitative RT-PCR and western blotting, respectively. Changes in the liver at a histological level were also investigated. The amount of SMP30 mRNA and protein in livers was decreased in Lepr(db/db)Smp30(Y/+) mice compared with Lepr(db/+)Smp30(Y/+) mice. Compared with Lepr(db/db)Smp30(Y/+) mice, 24 week old Lepr(db/db)Smp30(Y/−) mice showed: i) increased small dense LDL-cho and decreased HDL-cho levels; ii) fatty liver accompanied by numerous inflammatory cells and increased oxidative stress; iii) decreased mRNA expression of genes involved in fatty acid oxidation (PPARα) and lipoprotein uptake (LDLR and VLDLR) but increased CD36 levels; and iv) increased endoplasmic reticulum stress. CONCLUSION: Our data strongly suggest that SMP30 is closely associated with NAFLD pathogenesis, and might be a possible therapeutic target for NAFLD.