Lytic cell death in metabolic liver disease

“Ferroptosis can be induced either in a canonical way by a direct or indirect inactivation of the glutathione peroxidase 4 (GPX4), the major protective mechanism of biological membranes against peroxidation damage, or in a non-canonical manner by increasing the labile iron pool [48].”

“By indirectly blocking the Xc− transporter, erastin inhibits GSH synthesis, which is used by GPX4 to eliminate the production of phospholipid hydroperoxides (PL-OOH), the major mediator of chain reactions in lipoxygenases [53].”

“Caspases-1 and -11 cleave GSDMD into a 31-kDa N-terminal GSDMDNT fragment, which exhibits intrinsic pore-forming activity, and a 22-kDa C-terminal GSDMDCT fragment that binds to GSDMDNT to maintain the protein in an inhibitory state [40, 41].”

“Although metabolic alterations caused by free fatty acid overload is considered a major cause for hepatocyte damage, the mechanisms driving disease progression from simple steatosis to NASH remain incompletely understood [72].”

“Recently, the ferroptosis suppressor protein 1 (FSP1), previously known as apoptosis-inducing factor mitochondrial 2 (AIFM2), was identified as a key component of a non-mitochondrial CoQ10 (ubiquinone) antioxidant system that acts in parallel to the GPX4 canonical pathway to halt the progression of lipid peroxides [58…”

“Caspases-1 and -11 cleave GSDMD into a 31-kDa N-terminal GSDMDNT fragment, which exhibits intrinsic pore-forming activity, and a 22-kDa C-terminal GSDMDCT fragment that binds to GSDMDNT to maintain the protein in an inhibitory state [40, 41].”

“Pyroptosis is activated by canonical and non-canonical signalling pathways, which differ in the use of cytoplasmic multiprotein complexes named inflammasomes (Figure 2) [44, 45].”

“Nevertheless, secondary products of lipid peroxidation, such as malondialdehyde and 4-hydroxinonenal are utilized as oxidative stress markers in NASH patients [103], and Vitamin E, an antioxidant that suppresses lipid peroxidation, reduces serum ALT in NASH patients [104].”

“In this pathway, GSDMDNT also activates the NLRP3 inflammasome and thereby caspase-1-dependent maturation of IL-1β and IL-18.”

“Since this discovery, the number of pyroptotic caspases (as opposed to apoptotic caspases) has considerably increased, including caspase-1, caspase-11 and its human orthologs caspase-4 and 5 [35, 36], and even more surprisingly the apoptotic effector caspase-3 under specific circumstances [37, 38].”

“showed that necrostatin-1, a chemical compound that blocks the kinase activity of RIPK1, was able to inhibit cell death in TNF-treated cell lines [7].”

“However, further investigations are needed to identify which specific DAMPs might preferentially activate one lytic RCD or another.”

“Consequently, RIPK3 mediates the phosphorylation of MLKL, resulting in MLKL oligomerization and translocation to the plasma membrane [13].”

“Pyroptosis is activated by canonical and non-canonical signalling pathways, which differ in the use of cytoplasmic multiprotein complexes named inflammasomes (Figure 2) [44, 45].”

“Since this discovery, the number of pyroptotic caspases (as opposed to apoptotic caspases) has considerably increased, including caspase-1, caspase-11 and its human orthologs caspase-4 and 5 [35, 36], and even more surprisingly the apoptotic effector caspase-3 under specific circumstances [37, 38].”

“Since this discovery, the number of pyroptotic caspases (as opposed to apoptotic caspases) has considerably increased, including caspase-1, caspase-11 and its human orthologs caspase-4 and 5 [35, 36], and even more surprisingly the apoptotic effector caspase-3 under specific circumstances [37, 38].”

“In cells, cysteine is required for the synthesis of glutathione (GSH), a major redox regulatory system [52].”

“In the non-canonical pathway, increased iron uptake by transferrin receptor (TFRC) and reduced iron export by ferroportin promote oxidative damage and ferroptosis [60, 61].”

“A substantial number of DAMPs, including HMGB1, heat shock proteins (HSPs), ATP, and interleukins, have been differentially involved in pyroptosis, necroptosis or ferroptosis [65, 66].”

“However, recent findings highlight multiple forms of regulated necrotic modalities, including necroptosis, pyroptosis and ferroptosis, that share key morphologic features with passive necrosis yet have welldefined and regulated causal mechanisms [2, 3].”

“Although most of the gasdermins have been associated with the occurrence and development of various diseases, their precise function and molecular mechanism of activation remain largely unknown [43].”

“Since this discovery, the number of pyroptotic caspases (as opposed to apoptotic caspases) has considerably increased, including caspase-1, caspase-11 and its human orthologs caspase-4 and 5 [35, 36], and even more surprisingly the apoptotic effector caspase-3 under specific circumstances [37, 38].”

“Ferroptosis was originally observed in 2003 using erastin, a cell-permeable compound, which was only lethal to engineered human tumour cells expressing an oncogenic RAS mutation [47].”

“However, the term has emerged nearly a decade later, in 2001, when Cookson and Brennan demonstrated that Salmonellainduced macrophage death was dependent on caspase-1 [34].”

“Finally, MLKL forms pore in the plasma membrane [16, 17], and increases permeability via the activation of A disintegrin and metalloproteinase (ADAM) proteases [18], Ca2+ influx by targeting the cation channel transient receptor potential melastatin related 7 (TRPM7) [19], and phosphatidylserine externalization [20].”

“, who described a lytic form of cell death in Shigella flexneri-infected macrophages [33].”

“apoptosis, necroptosis and pyroptosis, and prevents tissue damage [67, 68].”

“Indeed, activation of IL-1β signalling, downstream of inflammasomes, drives liver inflammation and fibrosis in experimental NASH [93] and amplifies the response of other cytokines [100].”

“A substantial number of DAMPs, including HMGB1, heat shock proteins (HSPs), ATP, and interleukins, have been differentially involved in pyroptosis, necroptosis or ferroptosis [65, 66].”

“Although no specific necroptotic DAMPs have been identified so far, their release during necroptosis provokes a strong inflammatory response that has been linked to the development of many diseases [12].”

“Interestingly, compared to global NLRP3 knock-in mice, mice with myeloid-specific Nlrp3 mutations lack detectable pyroptotic hepatocyte cell death and have less severe liver inflammation, HSC activation, and fibrosis [101].”

“Cell injury, inflammation, oxidative stress, regeneration and bacterial translocation are key drivers of alcohol-induced liver injury [113].”

“On one hand, caspase-8 cleaves and inactivates RIPK1 and RIPK3, which has for consequence to suppress necroptosis [22, 23].”

“Finally, MLKL forms pore in the plasma membrane [16, 17], and increases permeability via the activation of A disintegrin and metalloproteinase (ADAM) proteases [18], Ca2+ influx by targeting the cation channel transient receptor potential melastatin related 7 (TRPM7) [19], and phosphatidylserine externalization [20].”

“The reactions involving iron and leading to the hydroxyl or alkoxyl (RO ̇) radical are traditionally called Fenton reactions [54].”

“, TLR3 and TLR4) [26], nucleic acid sensors (e.”

“Consistently, the hepatic PC/PE ratio is decreased in NASH patients [110, 111].”

“, RIPK3 kinase activity inhibited) [24, 25].”

“While it appears clear that ethanol-induced necroptosis involves RIPK3, it is not yet known if MLKL-independent pathways are involved as reported in models of autoimmune arthritis [118].”

“Moreover, inhibition of RIPK3 kinase often provokes apoptosis further confusing this approach in examining necroptosis in disease pertinent models [25].”

“Inflammasome activation triggers caspase activity and promotes inflammation and fibrosis in liver disease [97], while typical activators of inflammasomes such as fatty acids, DAMPs, and uric acid upregulate NLRP3 inflammasome components.”

“Finally, MLKL forms pore in the plasma membrane [16, 17], and increases permeability via the activation of A disintegrin and metalloproteinase (ADAM) proteases [18], Ca2+ influx by targeting the cation channel transient receptor potential melastatin related 7 (TRPM7) [19], and phosphatidylserine externalization [20].”

“Necroptosis is probably the best-understood form of regulated necrosis, since it shares multiple molecular components with the extrinsic apoptotic pathway and can act as a fail-safe mechanism to ensure cell death progression when apoptosis is abnormally inhibited, which may also be relevant in pathological conditions…”

“Third, caspase-8 limits necroptosis by proteolytically cleaving RIPK1 [138], and the genetic absence of caspase-8 in hepatocytes does not trigger widespread necroptosis [134].”

“In a recent study, ferroptosis inhibitors, trolox and deferiprone, suppressed necrotic cell death, infiltration of inflammatory cells, and inflammatory cytokine expression in the onset of steatohepatitis in the choline-deficient, ethionine-supplemented (CDE) diet model [108], in which hepatic cell death is an early ev…”

“Epigenetic silencing of RIPK3, in contrast, has been associated with malignant transformation in hepatocellular carcinoma cells, while reestablishment of RIPK3 expression by promoter demethylation resensitized cells to chemotherapy-induced necroptosis [89], again implying that induction of RIPK3 is context-dependent.”

“The canonical inflammasomes comprise a sensor protein belonging to the nucleotide-binding domain (NBD) and leucine-rich-repeat-(LRR)-containing (NLR) or the AIM2-like receptor (ALR) or pyrin family, an adaptor protein, apoptosis-associated speck-like protein containing a CARD (ASC), and an inactive zymogen, pro-caspas…”

“Cell death has been described as a clear and present danger for hepatocytes as they are directly exposed to portal blood from the intestines, participate in the xenobiotic metabolism of drugs and alcohol, play a central role in lipid, fatty acid, and bile acid metabolism, contact with prevalent hepatotropic viruses, a…”

“In addition, liver fibrosis was strongly attenuated in Gsdmd−/− mice after MCD feeding [99].”

“The Xc− transporter system is composed of a regulatory subunit solute carrier family 3 member 2 (SLC3A2) and a catalytic subunit solute carrier family 7 member 11 (SLC7A11), which promotes the cellular uptake of cystine, the plasma precursor of cysteine, by exchange with glutamate [51].”

“apoptosis, necroptosis and pyroptosis, and prevents tissue damage [67, 68].”

“Other functions of RIPK3 in hepatocarcinogenesis have been recognized [85], and its involvement in inflammatory signalling independent of necroptosis and mediation of cell death should not be neglected [86, 87].”

“Second, RIPK3 deficiency does not phenocopy MLKL deficiency, and hence studies with RIPK3 knockout or kinase dead knock-in mice, are not sufficient to invoke necroptosis as a cause of cell death, as RIPK3 has diverse functions [137].”

“Moreover, iron accumulation from metabolic dysfunction, aggravates NASH, such as in liver siderosis observed in some NASH patients [105], and primary hemochromatosis exacerbates NASH [106], while iron removal ameliorates liver damage and serum ALT [107].”

“Moreover, iron accumulation from metabolic dysfunction, aggravates NASH, such as in liver siderosis observed in some NASH patients [105], and primary hemochromatosis exacerbates NASH [106], while iron removal ameliorates liver damage and serum ALT [107].”

“JNK activation was implicated in RIPK3-dependent liver damage and fibrosis in methionine-choline deficient (MCD) diet-fed mice, since inhibition of JNK diminished RIPK3 levels in the liver [75].”

“These unexpected roles of caspase-8 involves the activation of the inflammasome and induction of pyroptosis under circumstances in which apoptosis and necroptosis are compromised, such as when the abundance of viral inhibitors may have driven the counteradaptation of pyroptosis as a host defence [70].”

“Necroptosis—The involvement of necroptosis has been suggested from studies where RIPK3 expression was induced in human ALD and in mice after ethanol exposure [84, 114].”

“In this regard, activation of resident Kupffer cells and infiltrating macrophages is a remarkable feature of NASH pathogenesis [95].”

“In the non-canonical pathway, increased iron uptake by transferrin receptor (TFRC) and reduced iron export by ferroportin promote oxidative damage and ferroptosis [60, 61].”

“Finally, we note that cell death per se may be a biomarker for stressed, proinflammatory hepatocytes as recently suggested in NASH [142], and therefore, precluding cell death may not have the major impact on liver injury that we anticipate.”

“Cleave of GSDMD occurs via a canonical inflammasome caspase-1 dependent mechanism, a non-canonical inflammasome pathway involving caspases 4, 5 or 11 [139], or in an inflammasome-independent caspase-8 mediated pathway [140].”

“Thus, in addition to immune cells, hepatocyte pyroptosis resulting from intrinsic inflammasome activation exacerbates inflammation and fibrosis in the liver, indicating that both immune cell- and liver-specific NLRP3 inflammasome activation are essential for liver injury [101, 102].”

“In addition to its enzymatic role in apoptosis and necroptosis, caspase-8 acts as a scaffolding protein that together with MLKL regulates NLRP3 inflammasome activation in macrophages [69].”

“Recently reported, caspase inhibition with Emricasan treatment did not improve clinical outcomes nor liver histology in patients with NASH fibrosis, resulting in more liver fibrosis and hepatocyte ballooning [143, 144].”

“demonstrated that alcohol elicits caspase-1-mediated pyroptosis through overexpression of thioredoxin-interacting protein (TXNIP), a member of the α-arrestin family, and this event is reversed by miR-148a [124].”

“For example, RIP kinases have diverse functions in addition to promoting necroptosis [90].”

“Consistently, NLRP3 deficiency ameliorated alcohol-driven liver stetaosis and injury [120], while caspase-4/11 was upregulated in liver tissue from patients with alcoholic hepatitis and in mice [121].”

“Interestingly, RIPK3 deficiency protected from liver injury, inflammation and fibrosis in MCD-fed mice [74, 75], but exacerbated liver steatosis and apoptosis, as well as adipose tissue inflammation, insulin resistance and glucose intolerance induced by high-fat diet [79, 81].”

“There are considerable crosstalk regulations between apoptosis and necroptosis in DR signalling pathways [21], and it seems that one cannot be achieved without inhibiting the other.”

“Schock SN, Chandra NV, Sun Y, Irie T, Kitagawa Y, Gotoh B, et al. Induction of necroptotic cell death by viral activation of the RIG-I or STING pathway.”

“Finally, MLKL forms pore in the plasma membrane [16, 17], and increases permeability via the activation of A disintegrin and metalloproteinase (ADAM) proteases [18], Ca2+ influx by targeting the cation channel transient receptor potential melastatin related 7 (TRPM7) [19], and phosphatidylserine externalization [20].”

“Indeed, Emricasan has previously been shown to shift cell death from apoptosis towards necroptosis in acute myeloid leukemia cells treated with birinapant, a second mitochondrial derived activator of caspases mimetic, which enhances cancer cell apoptosis [145].”

“Importantly, crossregulation by the effectors of different cell death pathways most likely influences liver inflammation in ALD.”

“Nevertheless, secondary products of lipid peroxidation, such as malondialdehyde and 4-hydroxinonenal are utilized as oxidative stress markers in NASH patients [103], and Vitamin E, an antioxidant that suppresses lipid peroxidation, reduces serum ALT in NASH patients [104].”

“In striking contrast, RIPK3-mediated necroptosis has been implicated in pathology of Gaucher’s disease [132].”

“Interestingly, RIPK3 deficiency protected from liver injury, inflammation and fibrosis in MCD-fed mice [74, 75], but exacerbated liver steatosis and apoptosis, as well as adipose tissue inflammation, insulin resistance and glucose intolerance induced by high-fat diet [79, 81].”

“Consistently, NLRP3 deficiency ameliorated alcohol-driven liver stetaosis and injury [120], while caspase-4/11 was upregulated in liver tissue from patients with alcoholic hepatitis and in mice [121].”

“RIPK3-deficient natural killer cells showed impaired immune responses to tumours and liver inflammation [88].”

“The NLRP3 inflammasome pathway is activated in hepatocytes in response to endotoxin challenge, a condition facilitated by alcohol intake [119].”

“The activation of necroptosis is not limited to DRs, and it can be triggered by multiple pathways, including toll-like receptors (e.g., TLR3 and TLR4) [26], nucleic acid sensors (e.g., Z-DNA-binding protein 1 [ZBP1, also known as DAI]) [27], retinoic acid inducible gene 1 protein (RIG1) [28], transmembrane protein 173…”

“, ferroptosis), their chronic stimulation can lead to an excessive inflammation that may be detrimental and start damaging healthy cells, tissues, and organs [62].”

“NAFLD is estimated to affect up to one-third of the general population worldwide [71].”

“Other functions of RIPK3 in hepatocarcinogenesis have been recognized [85], and its involvement in inflammatory signalling independent of necroptosis and mediation of cell death should not be neglected [86, 87].”

“Alcohol-associated liver disease (ALD) is a major health problem worldwide and a significant source of liver injury, characterized by a wide spectrum of hepatic lesions from steatosis, steatohepatitis and fibrosis that may progress to cirrhosis and even hepatocellular carcinoma [112].”

“High levels of core components of necroptosis were detected in liver, adipose tissue and muscle in diabetic mice, whereas targeting diabetic mice with RIPK1 inhibitors or depletion of MLKL prevented insulin resistance and glucose intolerance, despite no effect on inflammation [80].”

“MLKL inhibitors are being developed such as necrosulfonamide, which binds to the N-terminal 4 helical bundle of MLKL to prevent necroptosis [146, 147].”

“Similarly, in common bile duct ligation hepatic injury, necroptosis was induced and contributed to fibrosis [82], although the effects of necroptosis inhibition on different hepatic fibrosis models are yet to be consistently determined.”

“Finally, MLKL forms pore in the plasma membrane [16, 17], and increases permeability via the activation of A disintegrin and metalloproteinase (ADAM) proteases [18], Ca2+ influx by targeting the cation channel transient receptor potential melastatin related 7 (TRPM7) [19], and phosphatidylserine externalization [20].”

“First, there is vigorous controversy regarding the expression of RIPK3 by hepatocytes, but under basal conditions expression appears to be quite limited [135, 136].”

“Other studies reported that ethanol-induced decrease of Nrf2 expression was abrogated by curcumin or gallic acid treatment, by suppressing RIPK3 and RIPK1 expression as well as DAMP release [116, 117].”

“Nevertheless, inhibition of RIP1 kinase activity blunted Gao-binge alcohol-induced hepatic inflammation but did not protect against chronic ethanol feeding-induced steatosis and liver injury, suggesting that alcohol-induced RIPK3-mediated necroptosis is independent of RIPK1 [114].”

“, Z-DNA-binding protein 1 [ZBP1, also known as DAI]) [27], retinoic acid inducible gene 1 protein (RIG1) [28], transmembrane protein 173 (TMEM173, also known as STING) [29], and adhesion receptors [30].”

“Iron-induced liver damage is likely potentiated by coexisting inflammation, which culminates with hepatocyte cell death and drives fibrogenesis [127].”

“the expression of the viral cytokine response modifier A (CrmA), a caspase inhibitor [5].”

“Other functions of RIPK3 in hepatocarcinogenesis have been recognized [85], and its involvement in inflammatory signalling independent of necroptosis and mediation of cell death should not be neglected [86, 87].”

“Ablation of Ripk3 resulted in fewer CD68-positive Kupffer cells and decreased ALT activity, suggesting that hepatocyte injury was also attenuated.”

“RIPK3MLKL-mediated necroptosis contributed also to ischemia reperfusion injury of steatotic livers [83].”

“Nevertheless, corroborating the role of alternative RCD sub-routines, cellular death of NPC1 fibroblasts was not mitigated by treatment with caspase inhibitors [129] or following neuronal overexpression of Bcl-2 [130].”

“Nevertheless, corroborating the role of alternative RCD sub-routines, cellular death of NPC1 fibroblasts was not mitigated by treatment with caspase inhibitors [129] or following neuronal overexpression of Bcl-2 [130].”

“Interestingly, in shock models of liver injury, GSDMD germ line deficient mice display increased caspase-8 activation and apoptosis in the liver [141].”

“Similarly, MLKL pharmacological inhibition decreased hepatic de novo fat synthesis and chemokine ligand expression in NASH [91].”

“Other studies reported that ethanol-induced decrease of Nrf2 expression was abrogated by curcumin or gallic acid treatment, by suppressing RIPK3 and RIPK1 expression as well as DAMP release [116, 117].”

“Caspase-1 was also activated in hepatocytes of patients with alcoholic hepatitis [123].”

“In a recent study, ferroptosis inhibitors, trolox and deferiprone, suppressed necrotic cell death, infiltration of inflammatory cells, and inflammatory cytokine expression in the onset of steatohepatitis in the choline-deficient, ethionine-supplemented (CDE) diet model [108], in which hepatic cell death is an early ev…”

“Cleave of GSDMD occurs via a canonical inflammasome caspase-1 dependent mechanism, a non-canonical inflammasome pathway involving caspases 4, 5 or 11 [139], or in an inflammasome-independent caspase-8 mediated pathway [140].”

“Third, caspase-8 limits necroptosis by proteolytically cleaving RIPK1 [138], and the genetic absence of caspase-8 in hepatocytes does not trigger widespread necroptosis [134].”

“Indeed, lipotoxicity, oxidative stress, organelle dysfunction and inflammatory response exacerbate ballooning and increase hepatocyte cell death [73].”

“MLKL inhibitors are being developed such as necrosulfonamide, which binds to the N-terminal 4 helical bundle of MLKL to prevent necroptosis [146, 147].”

“Multiple types of cell death, including apoptosis, necroptosis, pyroptosis, and ferroptosis, as well as autophagy, are associated with the development of NAFL/ NASH.(72,293,294) Among targeting different formats of cell death, inhibition of apoptosis has achieved promising results, here we focus on anti-apoptosis agen…”

“New studies focused on the molecular basis of ferroptosis could help in deciphering the existing connections between the single components of the metabolic pathway.”