LIVER SPECIFIC TRANSGENIC EXPRESSION OF OXYSTEROL 7α-HYDROXYLASE ATTENUATES OXYSTEROL DRIVEN STEATOTIC LIVER DISEASE PROGRESSION

Background: Hepatocellular (25R)26-Hydroxycholesterol (26HC) and 3β-Hydroxy-5-cholestenoic acid (3βHCA) accumulations due to chronic oxysterol 7α-hydroxylase (CYP7B1) suppression represent a major driving force for the transition from metabolic dysfunction-associated steatotic liver (MASL) to steatohepatitis (MASH) [PMID: 33008924]. Recently we reported dietary coffee [PMID: 36193897] or berberine administration [PMID: 33494295] upregulated liver Cyp7b1 levels with subsequent reduced hepatic 26HC/3βHCA accumulations, attenuating Western diet (WD)-induced MASH progression in mice. These results prompted us to hypothesize that liver-specific Cyp7b1 upregulation could protect against MASLD progression; outlining for the first time a mechanistic pathway on which to focus novel strategies in early MASH interventions.
Methods: CAG-lox-STOP-lox-Cyp7b1 (+); Alb-Cre (+) double overexpressing mice were initially generated on a C57Bl/6J background, and were subsequently backcrossed onto a B6/129 background for >5 generations. The 13-week-old liver-specific Cyp7b1 transgenic (TG) mice (n=12, each sex) were fed an ad libitum Western diet (WD) for six weeks. Age-matched B6/129 background CAG-LSL-Cyp7b1 (-); Alb-Cre (-) double negative mice (Wild type: WT) were used for control (n=6, each sex). Serum biomarkers, liver lipids, and hepatic gene expression were analyzed.
Results: On a standard chow diet, hepatic Cyp7b1 protein levels of male and female TG mice were 15-fold higher than WT counterparts. In male TG mice early WD-induced hepatotoxicity was attenuated as evidenced by reduced serum ALTs (44 IU/l vs 90 IU/l of WT, P<0.05) and hepatic Tnfα mRNA levels (4-fold lower vs WT, P<0.05). Mass spectrometry analysis in male WD-fed TG mice revealed significantly lower hepatic 26HC (433±152 ng/g) and 3βHCA (1.4±1.6 ng/g) levels as compared to those (26HC: 1650±219 ng/g, 3βHCA: 31±3.9 ng/g) of WT mice. Hepatic cholesterol also trended down in the male TG mice (17±3.0 mg/g) compared to WT counterparts (25±5.9 mg/g). Hepatic bile acid levels were 18% elevated in the WD-fed TG mice with slightly higher muricholic acid proportions as compared to WT counterparts. Improvements were less pronounced in the female TG mice fed a WD in early limited studies.
Discussion: Liver-specific Cyp7b1 overexpression in the WD-induced MASLD mice enhances 26HC/3βHCA metabolism. This study represents a “proof-of-concept” that restoring hepatic Cyp7b1 activity reduces 26HC/3βHCA-driven liver toxicity and attenuates MASLD progression. Female mouse liver has higher oxysterol detoxification enzymatic activity (i.e. Sult2b1), and therefore, the effect of transgenic Cyp7b1 overexpression on their MASH attenuation was likely reduced. In conclusion, our results could open the door to direct focused treatment approaches for early MASH.