Since the first study reported the role of ferroptosis in LF (Sui et al., 2018), evidence of ferroptosis in the pathogenesis of LF has increased. In recent years, many clinical studies have found that severe pathological iron overload symptoms are often observed in LF patients, suggesting that pathological iron overload may play a critical role in the progression of LF. Yang et al. (2020) observed a significant increase in Fe2 + and also in the expression of GPX 4, TRF, and SLC7A11 proteins in the kidneys of fibrotic mice. TRF deficiency is an autosomal recessive metabolic disorder with low expression of TRF associated with severe anemia, hepatic iron overload, and fibrosis. Yu et al. (2020) reported that mice fed a high-iron diet showed iron accumulation in multiple organs with liver injury and LF. However, the involvement of SLC39A14 genes in TRF knockout mice, intracellular Fe2 + transport in the liver, and TRF-specific TRF and SLC39A14 double knockout mice demonstrate that hepatic TRF deficiency could induce cellular ferroptosis to induce LF. However, the involvement of the SLC39A14 gene in intracellular Fe2 + transport was further clarified in TRF knockout mice and in TRF-specific TRF and SLC39A14 double knockout mice, demonstrating that hepatic TRF deficiency induced ferroptosis to induce LF. Solute carrier family 39 member 14 (SLC39A14) is a key protein that causes non-transferrin-bound iron accumulation in hepatocytes in the absence of transferrin, and knockdown of SLC39A14 is able to completely reverse the LF caused by non-transferrin-bound iron deposition in hepatocytes. In the Bama mini-pig model of excessive iron-induced myocardial fibrosis, the amount of iron deposition was positively correlated with the degree of myocardial fibrosis (Yu et al., 2020). Solute carrier family 39 member 14 (SLC39A14) is a key protein causing non-transferrin-bound iron accumulation in hepatocytes in the absence of transferrin, and knockdown of SLC39A14 is able to completely reverse LF due to non-transferrin-bound iron deposition in hepatocytes.

A number of basic studies have shown that static HSCs do not express the transferrin receptor, while activated HSCs overexpress the transferrin receptor (Karvar et al., 2020). The transferrin receptor has a strong affinity for extracellular free iron and transports iron into activated HSCs via the endocytic pathway. Activated HSC intracellular iron can produce large amounts of free radicals through the Fenton response and induce the expression of inflammatory cytokines. These stimulators can continuously activate HSCs through autocrine or paracrine pathways. This pathological circulation may lead to a substantial accumulation of iron in the activated HSCs (Bridle et al., 2003; Ruddell et al., 2009; Yang et al., 2020). ELAV-like RNA-binding protein 1 (ELAVL1) (Zhang et al., 2018), bromodomain-containing protein 7 (BRD7) (Zhang et al., 2020b), ZFP36 ring finger protein (ZFP36) (Zhang et al., 2020a), and tripartite motif-containing protein 26 (TRIM26) (Zhu et al., 2021a) have been implicated in regulating ferroptosis of HSCs. Embryonic lethal abnormal vision, such as 1/human antigen R (ELAVL1/HuR), also plays a key role in promoting ferroptosis in LF cells. The upregulation of ELAVL1/HuR can induce ferroptosis in hematopoietic stem cells by stabilizing the expression of autophagy-related protein Beclin-1, promote the degradation of TRF, and release Fe2 +, leading to the imbalance of iron metabolism (Zhang et al., 2018). BRD7 has the ability to act as a ferroptosis inducer targeting HSCs (Zhang et al., 2020b). Another study showed that direct binding of BRD7 promotes p53 mitochondrial translocation, subsequently forming a complex with solute carrier family member 2,528 (SLC25A28) and enhancing its activity, causing excessive deposition of p53 mitochondrial translocation. Zhang et al. (2020b) further reported a critical role of the BRD7-p53-SLC25A28 axis in regulating ferroptosis in HSCs, with system Xc-inhibition, GPX4 inhibition, and GSH depletion mediated by BRD7 upregulation triggerring p53 mitochondrial translocation through direct binding to the N-terminal trans-activated structural domain, which exacerbates mitochondrial iron accumulation, electron transport chain hyperfunction, lipid peroxidation, and ultimately, iron-dependent ferroptosis. Zhang et al. (2020a) showed that the RNA-binding protein ZFP36 prevents ferroptosis by regulating the autophagy signaling pathway in HSCs. ZFP36 is an RNA-binding protein that disrupts autophagy-related 16-like 1 (ATG16L1) mRNA, thereby suppresses macroautophagy/autophagy activation and mediates ferroptosis resistance. TRIM26 is downregulated in the fibrotic tissue of liver tissue, and the overexpression of TRIM26 accelerates the degradation of lipid proteins by mediating SLC7A11 ubiquitination, promotes lipid peroxidation accumulation, and ultimately, leads to the death of ferritin in activated HSCs (Zhu et al., 2021a). In addition, N6-methyladenosine (m6A) modification is also associated with ferroptosis in liver HSCs, and FTO overexpression leads to the downregulation of m6A modification, which may damage autophagy and ferroptosis events. The m6A modification of BECN1 mRNA was significantly upregulated compared with other autophagy-related genes. YTHDF1 is a key reader protein for BECN1 mRNA stability, and the YTH domain extends the half-life of BECN1 mRNA, thereby activating autophagy and ultimately leading to ferroptosis in HSCs (Shen et al., 2021).

HSCs and hepatocytes play an important role in the physiological function of the liver, but few studies have reported the role of hepatocyte ferroptosis in the development of liver fibrosis. As liver parenchyma cells, liver cells have the largest number in the liver. Continuous hepatocyte injury and death can induce chronic inflammation and activation of HSCs, which is one of the initiations of the development of liver fibrosis (Gautheron et al., 2020). Iron overload is a driver of ferroptosis induction in hepatocytes, increasing the risk of developing liver fibrosis and cirrhosis. This excessive iron accumulation enhances ferroptosis in hepatocytes by inducing heme oxygenase-1 (HO-1) expression, which contributes to the progression of liver fibrosis, accompanied by the upregulation of FGF21 protein levels in vitro and in vivo (Wu et al., 2021). After iron overload induced ferroptosis, they release ROS and proinflammatory factors, transmit risk signals to surrounding cells including inflammatory cells and HSCs, and induce chronic inflammation and directly or indirectly induce the activation and proliferation of HSCs (Gautheron et al., 2020). Collagen synthesis after the activation of HSCs, ECM deposition, liver remodeling, and ultimately, fibrosis increased.

In the db/db mouse model of type 2 diabetes, the increased levels of TGF- β, collagen I, and collagen III in hepatocytes indicate a greater degree of hepatic fibrosis (Song et al., 2022). Ferroptosis activation was observed in hepatocytes; inhibition of GPX 4/GSH or impaired GSH synthesis increased ROS production (Yu et al., 2017); The Downregulation of SOD and upregulation of MDA, 4-HNE, and NOX4 increased the TfR1 expression, reduced the FPN 1 expression, and downregulated the SLC7A11 and Nrf 2/HO-1/ GPX4 signaling pathways (Song et al., 2022). Liraglutide suppresses hepatocyte ferroptosis and LF by increasing hepatic SLC7A11 and Nrf 2/HO-1/GPX 4 signaling expression. In addition, it reduces high glucose-induced LIP levels and intracellular lipid ROS levels in vitro, which is speculated to play a key role in reducing iron accumulation, oxidative damage, and ferroptosis (Song et al., 2022). Taken together, these findings suggest that the induction of ferroptosis in hepatocytes may be involved in the pathogenesis of liver fibrosis and can simultaneously promote liver fibrosis progression. However, the exact function of hepatocyte ferroptosis in the development and pathogenesis of liver fibrosis remains poorly understood. The molecular mechanisms regulating ferroptosis in hepatocytes remain largely unknown and require further investigation.

HSC activation is considered to be the core link of liver fibrosis, but it does not play an independent role in liver fibrosis and is regulated by the interaction network of hepatocytes and other non-parenchymal cells. It is crucial for the development and treatment of liver fibrosis to understand the difference of ferroptosis between HSCs and hepatocytes. Although these two cell classes play distinct roles in iron metabolism, their functions are tightly linked and interact. Therefore, further studies could reveal more detailed ferroptosis mechanisms between HSCs and hepatocytes, contributing to a comprehensive understanding of the pathway biology of liver disease and proposing more effective therapeutic strategies.

The effects of disorders of iron metabolism are significant and can effectively influence the course of LF by regulating iron levels or by influencing the occurrence of ferritinophagy and, thus, regulating the outcome of cellular ferroptosis.

The currently identified mechanisms of ferroptosis regulation based on lipid peroxidation mainly target systemic lipid peroxidation and lead to lipid peroxidation by inhibiting GSH production and, thus, GPX4 activity and ROS accumulation (Yu et al., 2021). Zhu et al. (2021a) reported that TRIM26 was downregulated in fibrotic liver tissues and that the overexpression of TRIM26 accelerates the degradation of this protein by mediating SLC7A11 ubiquitination, promoting lipid peroxidation and, ultimately, leading to the death of activated HSC iron, suggesting that mediating SLC7A11 may promote HSC ferroptosis.

Du K et al. (2021) showed that inhibiting xCT/SLC7A11 could inhibit the process of HSC transdifferentiation and intracellular GSH synthesis, thus inducing HSC ferroptosis and reducing LF. Sorafenib-triggered HSC ferroptosis is accompanied by the reduction in SLC7A11 and HIF-1 α proteins. Furthermore, the investigators found that reduced HIF-1α and SLC7A11 in HSC-T6 cells led to sorafenib-induced cellular ferroptosis and reduced ECM. Conversely, increasing the expression of HIF-1α and SLC7A11 suppressed ferroptosis in HSCs and attenuates the antifibrotic effects of sorafenib (Yuan et al., 2022a). Lang et al., (2023) found that GRh 2 upregulates IRF1 expression, leading to the inhibition of SLC7A11, thus resulting in ferroptosis and inactivation of HSCs. GRh2 improves liver fibrosis by enhancing HSC ferroptosis and suppressing hepatic inflammation. Therefore, targeting the downregulation of SLC7A11-induced HSC ferroptosis may be a new way to treat LF.

However, there is a problem that we may overlook, that is, lipid peroxidation itself is one of the causative factors of LF, and too much emphasis is placed on inducing lipid peroxidation in HSCs, which leads to ferroptosis and then HSC death, to alleviate LF. This strategy is over the top, so some researchers have started investigating the inhibition of lipid peroxidation. It was demonstrated that tβ4 specifically binds to G-actin and regulates actin polymerization, thereby promoting vascular regeneration, wound healing, and hair follicle regeneration (Kim et al., 2016). Zhu et al. (2021b) found that Tβ4 protects hepatocytes by inhibiting the GPX4-mediated ferroptosis pathway and also protects hepatocytes by upregulating GPX4 expression to inhibit ferroptosis, thereby reducing oxidative stress and lipid peroxidation in the liver, which further reduces the recruitment of hepatic inflammatory factors and activation of apoptotic signaling pathways. Moreover, treatment with Fer-1, a ferroptosis inhibitor, increased the protective effect of Tβ4, while elastin, a ferroptosis inducer, attenuated the protective effect of Tβ4.

GPX4 is one of the critical targets in the regulation of ferroptosis. GPX 4 reduces hydroperoxidized phospholipids and fatty acids and protects against LPO-mediated oxidative stress, and inhibition of GPX 4 activity can accumulate through LPO at the cell membrane and induce cellular ferroptosis (Huang et al., 2023). Kuo et al. (2020) found that chrysophanol inhibited HSC activation, reduced SLC7A11, increased ROS levels, and promoted ferroptosis and endoplasmic reticulum stress activation, especially HBx-mediated inhibition of cell death through HBx-induced HSC activation of the GPX4 pathway and HPX4-independent pathway through GPX4 activation. Chrysophanol may exert an effect on activated HSCSs, induce ferroptosis, and prevent LF. Wild bitter melon (WM) treatment induces ROS accumulation and HSC death by enhancing endoplasmic reticulum stress and triggering ferroptosis in LPS-activated HSCs, suggesting that WM treatment has antifibrotic effects on LPS-activated HSCs (Ho et al., 2021). Luo et al. (2021) reported that celastrol could regulate the expression levels of GPX4 and COX-2 in different cells, suggesting its effects on the induction of ferroptosis. ISL promotes ferroptosis in HSCs by increasing MDA content and inhibiting GPX4 expression (Li et al., 2022). Decurin also could promote ferroptosis of HSCs by decreasing the levels of Gpx 4 and GSH (Que et al., 2022).

Yi et al. (2021) found that BBR causes autophagy inhibition in hematopoietic stem cells, enhances ROS and oxidative stress, promotes ferritin degradation, and increases the risk of redox-active iron accumulation and ROS increasing from the Fenton response. The Fenton response triggers lipid peroxidation and glutathione depletion, leading to ferroptosis and alleviating LF symptoms; in conclusion, BBR attenuates LF by inducing ferroredox-activated ROS-mediated ferroptosis of HSCs. Tan et al. (2022) recently revealed that human umbilical cord mesenchymal stem cells (hucMSCs) and their secreted exosomes (MSC-ex) can deliver BECN1 proteins to HSCs to increase their BECN1 expression and subsequently inhibit SLC7A11/xCT transcription in the nucleus. Reduced SLC7A11/xCT led to cysteine deficiency and reduced GSH in HSCs, which resulted in reduced GPX4 and the onset of ferroptosis.

Based on the complex regulatory mechanisms of ferroptosis, multitargeted interventions are emerging as promising therapeutic strategies for LF. Exosomes are extracellular vesicles that contain proteins, DNA, and RNA of the cells that produce them and have also been found in recent years to have a vital role in the progression of LF (Dai et al., 2019; Kalluri et al., 2020). Transferrin receptor (TFRC) is a glycoprotein that can import iron, and silencing TFRC decreases total intracellular iron levels (Gammella et al., 2017). Exosomal miR-222 from HBV-infected hepatocytes promotes LF by inhibiting TFRC- and TFRC-induced HSC ferroptosis (Zhang et al., 2023).

Wogonoside (WG) improves LF through SOCS1/p53/SLC7A11 pathways to trigger the increase in SLC7A11, leading to the depletion of GPX 4 and GSH and an excess of ROS, finally inducing iron cell apoptosis in HSCs and inhibiting its activation during LF (Liu et al., 2022). Danshensu ameliorated LF by attenuating LPS-induced HSC activation by decreasing the expression of collagen І, CTGF, Gpx 4, SLC7A11, and LCN 2, and increasing the accumulation of lipid ROS (Wang et al., 2023). XCT-GSH-GPX 4 is an antioxidant signaling pathway. XCT consists of light-chain SLC7A11 and heavy-chain SCL3A2, which is a transmembrane amino acid transporter that participates in GSH synthesis through cystine uptake and glutamate excretion and promotes intracellular GSH synthesis (Yuan et al., 2022b). In acrylamide-induced infected cells, GPX4 and XCT expressions were decreased, and COX2 and GSH expressions were increased in HSC-T6 cells. Acrylamide-induced VDAC1 ensures mitochondrial integrity, regulated transport of substances and ions, and ROS production. This suggests that the induction of HSC ferroptosis by acrylamide is due to XCT-GSH-GPX4 antioxidant signaling and mitochondrial dysfunction (especially mtROS production) (Yuan et al., 2022b). Zhang et al. (2020b) found BRD7 upregulation, mitochondrial translocation of p53, a combination of SLC25A28 and p53, and ferroptosis induction in HSCs in patients with advanced hepatocellular carcinoma fibrosis treated with sorafenib. Concurrently, the HSC-specific blockade of the BRD7-p53-SLC25A28 axis abolished the erastin-induced HSC ferroptosis.

As a new therapeutic modality, ferroptosis has been confirmed to play an important role in multiple systemic diseases. By targeting HSCs, we can induce the occurrence of ferroptosis. In treating LF, we summarize the current targets of ferroptosis in HSCs in Table 1 and drugs, small molecules target HSCs ferroptosis to treat liver fibrosis in Table 2. We describe the mechanism of targeting ferroptosis in HSCs in Figure 2. In the future, more mechanisms can be studied through HSCs, and relevant targeted drugs can be developed; therefore, targeting HSC ferroptosis is expected to be an important target for the treatment of LF, which is a key to inhibit iron metabolism, lipid peroxidation, and regulation of oxidative stress.

The specific mechanism of LF ferroptosis has not been fully clarified; more detailed signal transduction pathway is still in further exploration. Many studies are still in the cell or animal experimental stage because of the lack of large samples, multicenter clinical randomized controlled studies, and evidence; we still need to conduct a more comprehensive and in-depth study to further explore the relationship between ferroptosis and LF. For targeting HSCs to treat LF, there is still a transformation gap; therefore, researchers should convert putative targets into effective clinical drugs. For disease treatment based on ferroptosis, induced ferroptosis may have the dual effect of injury and treatment, and according to the disease background, related treatment is needed to limit the occurrence of side effects. For the occurrence of ferroptosis mechanism development, new targeted drugs to regulate the occurrence of cell ferroptosis in different disease types is expected to become the new trend of disease treatment in the future.