Liver-Specific Bmal1 Depletion Reverses the Beneficial Effects of Nobiletin on Liver Cholesterol Homeostasis in Mice Fed with High-Fat Diet

Abstract

Nobiletin (NOB), a naturally occurring small-molecule compound abundant in citrus peels, has displayed potential lipid-lowering and circadian-enhancing properties in preclinical studies. However, the requirement of specific clock genes for the beneficial effects of NOB is not well understood. In the current study, mice with a liver-specific deletion of the core clock component, Bmal1—Bmal1LKO—were fed a high-fat diet (HFD) ad libitum for eight weeks, while NOB (200 mg/kg) was administered by daily oral gavage from the fifth week and throughout the last four weeks. NOB decreased liver triglyceride (TG) alongside the decreasing mRNA levels of de novo lipogenesis (DNL) genes in both Bmal1flox/flox and Bmal1LKO mice. NOB increased serum very low-density lipoprotein (VLDL) levels in Bmal1LKO mice, which was consistent with higher liver Shp and lower Mttp mRNA expression levels, the key genes that facilitate VLDL assembly and secretion. NOB decreased liver and serum cholesterol levels in the Bmal1flox/flox mice, consistent with lower Hmgcr and higher Cyp7a1, Cyp8b1, Gata4 and Abcg5 mRNA levels in the liver. In contrast, in the Bmal1LKO mice, NOB increased Hmgcr mRNA levels and had no effect on the above-mentioned genes related to bile acid synthesis and cholesterol excretion, which might contribute to the elevation of liver and serum cholesterol levels in NOB-treated Bmal1LKO mice. NOB inhibited hepatic DNL and decreased liver TG levels in HFD-fed mice independently of liver Bmal1, whereas liver-specific Bmal1 depletion reversed the beneficial effects of NOB on liver cholesterol homeostasis. The complex interactions between NOB, the circadian clock and lipid metabolism in the liver warrant further research.

Nobiletin from citrus peel: a promising therapeutic agent for liver disease-pharmacological characteristics, mechanisms, and potential applications

“…Studies confirm NOB’s role in treating NAFLD and NASH ( Morin et al, 2008 ; Lin et al, 2011 ; Lee et al, 2013 ; Tung et al, 2016 ; Kim et al, 2017 ; Peng et al, 2018 ; Qi et al, 2018 ; Morrow et al, 2020 ; Bunbupha et al, 2021 ; Wang et al, 2021 ; Zhang et al, 2021 ; Li ML. et al, 2022 ; Li S. et al, 2022 ; Huang et al, 2022 ; Larion et al, 2022 ; Lin et al, 2022 ; Yang et al, 2022 ; Yang X. et al, 2023 ; Ke et al, 2023 ; Li et al, 2023 ; Lu et al, 2023 ).…”

“…Biological rhythms might be involved in NAFLD by regulating triglyceride accumulation, inflammation, oxidative stress, and mitochondrial dysfunction ( Reinke and Asher, 2016 ). Recent studies have shown that NOB modulates circadian rhythm disruption to influence the onset and progression of NAFLD ( He B. et al, 2016 ; Qi et al, 2018 ; Nohara et al, 2019 ; Lu et al, 2023 ). Lu et al (2023) examined the effects of NOB on biorhythms in HFD-induced liver-specific mice without a core clock component (Bmal1-Bmal1LKO).…”

“…Recent studies have shown that NOB modulates circadian rhythm disruption to influence the onset and progression of NAFLD ( He B. et al, 2016 ; Qi et al, 2018 ; Nohara et al, 2019 ; Lu et al, 2023 ). Lu et al (2023) examined the effects of NOB on biorhythms in HFD-induced liver-specific mice without a core clock component (Bmal1-Bmal1LKO). Their findings showed that NOB (200 mg/kg) was orally administered daily and decreased liver and serum cholesterol levels for 4 weeks, increasing serum very low-density lipoprotein levels.…”

Metabolic Profile and Lipid Metabolism Phenotype in Mice with Conditional Deletion of Hepatic BMAL1

“…Sci. 2024, 25, 6070 2 of 13 mostly focused on external zeitgebers (such as restricted feeding) [14,15] or non-alcoholic fatty liver disease (NAFLD) induced by a high-fat diet (HFD) [7,8,11]. There is a scarcity of comprehensive research on the effects of BMAL1 on liver metabolism under normal physiological conditions (unrestricted access to food and water with a standard chow diet).…”

“…The liver is integral to lipid metabolism, with hepatocytes intricately regulating processes such as fatty acid uptake, oxidation, synthesis, and release under the precise control of CCGs [ 9 ]. Bmal1 plays a regulatory role in hepatic lipid synthesis, encompassing lipoprotein synthesis [ 10 , 11 ]. In our previously study, we found that exposure to ambient fine particulate matter (PM 2.5 ) disturbed hepatic Bmal1 circadian oscillations at ZT0 and disrupted hepatic lipid metabolism at ZT12 [ 12 ].…”