Hepatic ferroptosis plays an important role as the trigger for initiating inflammation in nonalcoholic steatohepatitis

Abstract

Nonalcoholic steatohepatitis (NASH) is a metabolic liver disease that progresses from simple steatosis to the disease state of inflammation and fibrosis. Previous studies suggest that apoptosis and necroptosis may contribute to the pathogenesis of NASH, based on several murine models. However, the mechanisms underlying the transition of simple steatosis to steatohepatitis remain unclear, because it is difficult to identify when and where such cell deaths begin to occur in the pathophysiological process of NASH. In the present study, our aim is to investigate which type of cell death plays a role as the trigger for initiating inflammation in fatty liver. By establishing a simple method of discriminating between apoptosis and necrosis in the liver, we found that necrosis occurred prior to apoptosis at the onset of steatohepatitis in the choline-deficient, ethionine-supplemented (CDE) diet model. To further investigate what type of necrosis is involved in the initial necrotic cell death, we examined the effect of necroptosis and ferroptosis inhibition by administering inhibitors to wild-type mice in the CDE diet model. In addition, necroptosis was evaluated using mixed lineage kinase domain-like protein (MLKL) knockout mice, which is lacking in a terminal executor of necroptosis. Consequently, necroptosis inhibition failed to block the onset of necrotic cell death, while ferroptosis inhibition protected hepatocytes from necrotic death almost completely, and suppressed the subsequent infiltration of immune cells and inflammatory reaction. Furthermore, the amount of oxidized phosphatidylethanolamine, which is involved in ferroptosis pathway, was increased in the liver sample of the CDE diet-fed mice. These findings suggest that hepatic ferroptosis plays an important role as the trigger for initiating inflammation in steatohepatitis and may be a therapeutic target for preventing the onset of steatohepatitis.

Targeting ferroptosis alleviates methionine‐choline deficient (MCD)‐diet induced NASH by suppressing liver lipotoxicity

“…However, Fer‐1 treatment did not reverse the mRNA expression level of these genes (Figure 2F), in accordance with its role in directly scavenging lipid hydroperoxides. Finally, we examined ferroptotic cell death in vivo by PI staining, 28 which showed increased cell death in MCD‐diet mouse livers was suppressed by Fer‐1 treatment (Figure 2G). Collectively, we conclude that ferroptosis participates in MCD‐diet induced NASH in mice.…”

“…However, previous studies have reported a more complicated relationship between liver injury and steatosis. For instance, it has been shown that inhibiting triglyceride synthesis improves hepatic steatosis but exacerbates liver damage and fibrosis, 28 which indicates that improvement in liver function is not necessarily accompanied by reduction in steatosis. Thus, it is intriguing to elucidate how suppression of ferroptosis in NASH model may affect steatosis in addition to reducing liver injury.…”

“…During NASH progression, caspase‐dependent apoptosis has long been considered as the major form of cell death in hepatocytes, 41 although necrotic and pyroptotic cell death have also been implicated in NASH 10,42 . A recent study reported that in the choline‐deficient, ethionine‐supplemented diet induced NASH, which triggers severe inflammation and cell death in mouse liver within two days, ferroptosis was suggested as a trigger for this acute pathological process 28 . In our study, we first uncovered ferroptotic phenotypes in MCD‐diet induced NASH, including lipid ROS accumulation, morphological change of mitochondria, and upregulation of ferroptotic genes (Figure 2).…”

Pathogenesis of Nonalcoholic Steatohepatitis: An Overview

“…Free cholesterol accumulation in hepatocytes and cholesterol crystal formation in hepatocyte lipid droplets in subjects with NASH and not isolated steatosis is associated with aggregation of Kupffer cells (KCs) and fibrosis, suggesting that perhaps inflammasome activation may play a role in NASH . Similarly, ferroptosis, a form of cell death dependent on iron and oxygenated phosphatidyl ethanolamine (PE), is also reported in NASH . Oxygenated lipids, such as PE, may be a mediator or a correlate of lipotoxicity due to other lipids in these models.…”

“…(50,51) Similarly, ferroptosis, a form of cell death dependent on iron and oxygenated phosphatidyl ethanolamine (PE), is also reported in NASH. (52) Oxygenated lipids, such as PE, may be a mediator or a correlate of lipotoxicity due to other lipids in these models. Further, although necroptosis in hepatocytes with intact caspase signaling remains controversial, the receptor-interacting protein kinases are implicated in NASH.…”