Propionate alleviates fatty acid–induced mitochondrial dysfunction, oxidative stress, and apoptosis by upregulating PPARG coactivator 1 alpha in hepatocytes

Abstract

Reduced feed intake during the transition period renders cows unable to meet their energy needs for maintenance and lactation, leading to a state of negative energy balance. Severe negative energy balance initiates fat mobilization and increases circulating levels of free fatty acids (FFA), which could induce hepatic mitochondrial dysfunction, oxidative stress, and apoptosis. Enhancing the hepatic supply of propionate (major gluconeogenic substrate) is a feasible preventive and therapeutic strategy to alleviate hepatic metabolic disorders during the transition period. Whether propionate supply affects pathways beyond gluconeogenesis during high FFA loads is not well known. Thus, the objective of this study was to investigate whether propionate supply could protect calf hepatocytes from FFA-induced mitochondrial dysfunction, oxidative stress, and apoptosis. Hepatocytes were isolated from 5 healthy calves (1 d old, female, 30–40 kg, fasting) and treated with various concentrations of propionate (0, 1, 2, and 4 mM propionate for 12 h) or for different times (2 mM propionate for 0, 3, 6, 12 and 24 h). Furthermore, hepatocytes were treated with propionate (2 mM), fatty acids (1.2 mM), or both for 12 h with or without 50 nM PGC-1α (peroxisome proliferator-activated receptor-gamma coactivator-1 alpha) small interfering RNA. Compared with the control group, protein abundance of PGC-1α was greater with 2 and 4 mM propionate treatment groups. Furthermore, protein abundance of TFAM (mitochondrial function marker mitochondrial transcription factor A) and VDAC1 (voltage-dependent anion channel 1) was greater with 1, 2, and 4 mM propionate, and COX4 (cyclooxygenase 4) was greater with 2 and 4 mM propionate groups. In addition, propionate supply led to an increase in protein abundance of PGC-1α, TFAM, VDAC1, and COX4 over time. Flow cytometry revealed that propionate treatment increased the number of mitochondria in hepatocytes compared with control group, but inhibition of PGC-1α abolished these beneficial effects. The lower protein abundance of PGC-1α, TFAM, COX4, and VDAC1 and activities of superoxide dismutase and glutathione peroxidase, along with greater production of reactive oxygen species, malondialdehyde, and apoptosis rate in response to treatment with high concentrations of FFA suggested an impairment of mitochondrial function and induction of oxidative stress and apoptosis. In contrast, propionate treatment hastened these negative effects. Knockdown of PGC-1α by small interfering RNA impeded the beneficial role of propionate on FFA-induced mitochondrial dysfunction, oxidative stress, and apoptosis. Overall, results demonstrated that propionate supply alleviates mitochondrial dysfunction, oxidative stress, and apoptosis in FFA-treated calf hepatocytes by upregulating PGC-1α. Together, the data suggest that PGC-1α may be a promising target for preventing or improving hepatic function during periods such as the transition into lactation where the FFA load on the liver increases.