Non-esterified Fatty Acid Induce Dairy Cow Hepatocytes Apoptosis via the Mitochondria-Mediated ROS-JNK/ERK Signaling Pathway.

Yu Li,Xiaobing Li,Xiliang Du,Guowen Liu,Jinchun Li,Xichun Wang,Hongyan Ding,Leihong Liu,Zhe Wang,Xinwei Li,Yuxiang Song,Jinjie Wu,Shibin Feng

doi:10.3389/fcell.2020.00245

Abstract

Elevated plasma non-esterified fatty acid (NEFA) levels and hepatocytes damage are characteristics of ketosis in dairy cows. Oxidative stress is associated with the pathogenesis of NEFA-induced liver damage. However, the exact mechanism by which oxidative stress mediates NEFA-induced hepatocytes apoptosis and liver injury remains poorly understood. The results of the present study demonstrated that NEFA contribute to reactive oxygen species (ROS) generation, resulting in an imbalance between oxidative and antioxidant species, transcriptional activation of p53, transcriptional inhibition of nuclear factor E2-related factor 2 (Nrf2), loss of mitochondria membrane potential (MMP) and release of apoptosis-inducing factor (AIF) and cytochrome c (cyt c) into the cytosol, leading to hepatocytes apoptosis. Besides, NEFA triggered apoptosis in dairy cow hepatocytes via the regulation of c-Jun N-terminal kinase (JNK), extracellular signal-regulated protein kinases 1 and 2 (ERK1/2), Bcl-2-associated X protein (Bax), B-cell lymphoma gene 2 (Bcl-2), caspase 9 and poly (ADP-ribose) polymerase (PARP). Pretreatment with the inhibitor SP600125 or PD98059 or the antioxidant N-acetylcysteine (NAC) revealed that NEFA-ROS-JNK/ERK-mediated mitochondrial signaling pathway plays a crucial role in NEFA-induced hepatocytes apoptosis. Moreover, the results suggested that the transcription factors p53 and Nrf2 function downstream of this NEFA-ROS-JNK/ERK pathway and are involved in NEFA-induced hepatocytes apoptosis. In conclusion, these findings indicate that the NEFA-ROS-JNK/ERK-mediated mitochondrial pathway plays an important role in NEFA-induced dairy cow hepatocytes apoptosis and strongly suggests that the inhibitors SP600125 and PD98059 and the antioxidant NAC may be developed as therapeutics to prevent hyperlipidemia-induced apoptotic damage in ketotic dairy cows.

Highlights

In dairy cows, ketosis is a metabolic disorder that occurs primarily during the transition period (21 days before and after parturition) (Melendez et al, 2006; Li et al, 2012)
The results of the present study demonstrated that non-esterified fatty acid (NEFA) contribute to reactive oxygen species (ROS) generation, resulting in an imbalance between oxidative and antioxidant species, transcriptional activation of p53, transcriptional inhibition of nuclear factor E2-related factor 2 (Nrf2), loss of mitochondria membrane potential (MMP) and release of apoptosis-inducing factor (AIF) and cytochrome c into the cytosol, leading to hepatocytes apoptosis
The results indicated that NEFA inhibited hepatocytes growth and increased LDH release from hepatocytes in a dosedependent manner (Figures 1A,B)

Summary

Introduction

Ketosis is a metabolic disorder that occurs primarily during the transition period (21 days before and after parturition) (Melendez et al, 2006; Li et al, 2012). A high concentration of NEFA is an important pathogenic factor that may be associated with the pathogenicity of some NEB-related metabolic disorders, such as ketosis and fatty liver. Clinical investigations have demonstrated that dairy cows with ketosis or with fatty liver display oxidative stress. Several lines of evidence in vivo and in vitro have demonstrated that a high-fat diet or high levels of NEFA induce oxidative stress, resulting in hepatocytes injury. Continuous, incomplete NEFA oxidation results in an abundance of oxygen radicals in the liver that induce hepatocytes damage. The underlying mechanism by which elevated NEFA levels induce hepatocytes injury remains unknown

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