Mitochondrial Adaptive Responses to Hypertriglyceridemia and Bioactive Lipids

Fenofibrate alleviates NAFLD by enhancing the PPARα/PGC-1α signaling pathway coupling mitochondrial function

BACKGROUND

To comprehend the influences of fenofibrate on hepatic lipid accumulation and mitochondrial function-related signaling pathways in mice with non-alcoholic fatty liver disease (NAFLD) secondary to high-fat diets together with free fatty acids-influenced HepG2 cells model.

MATERIALS AND METHODS

A random allocation of male 6-week C57BL/6J mice into three groups was done, including controls, model (14 weeks of a high-fat diet), and fenofibrate [similar to the model one with administered 0.04 g/(kg.d) fenofibrate by gavage at 11 weeks for 4 weeks] groups, which contained 10 mice each. This study verified NAFLD pathogenesis via mitochondrial functions in hepatic pathological abnormalities, liver index and weight, body weight, serum biochemical indexes, oxidative stress indicators, mitochondrial function indexes, and related signaling pathways. The effect of fenofibrate intervention was investigated in NAFLD model mice. In vitro, four groups based on HepG2 cells were generated, including controls, the FFA model (1.5 mmol/L FFA incubation for 24 h), LV-PGC-1α intervention (similar to the FFA model one after PPARGC1A lentivirus transfection), and LV control intervention (similar to the FFA model one after negative control lentivirus transfection) groups. The study investigated the mechanism of PGC-1α related to lipid decomposition and mitochondrial biosynthesis by Oil red O staining, colorimetry and western blot.

RESULTS

In vivo experiments, a high-fat diet achieved remarkable changes regarding liver weight, liver index, serum biochemical indicators, oxidative stress indicators, liver pathological changes, mitochondrial function indicators, and body weight of the NAFLD model mice while fenofibrate improved the objective indicators. In the HepG2 cells model, the lipid accumulation increased significantly within the FFA model group, together with aggravated hepatocytic damage and boosted oxidative stress levels. Moreover, FFA induced excessive mitosis into fragmented in mitochondrial morphology, ATP content in cells decreased, mtDNA replication fold decreased, the expression of lipid decomposition protein PPARα reduced, mitochondrial biosynthesis related protein PGC-1α, NRF-1 and TFAM decreased. PGC-1α overexpression inhibited lipid deposition by improving mitochondrial biosynthesis and lipid decomposition.

CONCLUSION

Fenofibrate up-regulated PPARα/PGC-1α signaling pathway, promoted mitochondrial β-oxidation, reduced oxidative stress damage and lipid accumulation of liver. PGC-1α overexpression enhanced mitochondrial biosynthesis and ATP production, and reduced HepG2 intracellular accumulation of lipids and oxidative stress.

Expanding the phenotypic spectrum of non-alcoholic fatty liver disease and hypertriglyceridemia

Background and aims

Hypertriglyceridemia is a common feature of metabolic syndrome (MetS), as well as of non-alcoholic fatty liver disease (NAFLD), which is considered the hepatic manifestation of MetS. Fat accumulation in hepatocytes may alter mitochondrial homeostasis predisposing to advanced liver disease. Here, we report a case of a 40-year-old woman with early aggressive NAFLD due to severe hypertriglyceridemia that ensued from a combination of genetic variants and additional metabolic risk factors.

Methods

Genetic screening was performed by using whole-exome sequencing (WES), and mitochondrial structures were evaluated by TEM.

Results

At presentation, the patient is reported to have hepatomegaly, hypertriglyceridemia, and raised transaminases. Genetic analysis revealed that the patient beard heritable alterations in genes implicated in lipid handling, among which APOB, APOE, CETP, and HSPG2, accompanied by missense mutations in genes involved in mitochondrial function, i.e., AK2, ALG6, ASPA, NDUFAF1, POLG, and TMEM70. Abdominal ultrasound (US) and transient elastography were suggestive of severe hepatic steatosis and fibrosis. A liver biopsy confirmed the diagnosis of non-alcoholic steatohepatitis (NASH)-related fibrosis. Thus, to better outline whether mutations involved in lipid remodeling and mitochondrial function may also affect organelles’ morphology, we exploited TEM. Along with multifaceted abnormalities of mitochondrial architecture that have been already observed in patients with NAFLD, astonishing ultrastructural defects, such as mitochondrial vacuolization, sub-compartmentalization, and onion-like mitochondria, were identified.

Conclusion

The anomalies reported may expand the phenotypic spectrum of mitochondrial abnormalities observed in patients with NAFLD, which may contribute to the switching toward a progressive disease.