The Role of Endoplasmic Reticulum Stress and NLRP3 Inflammasome in Liver Disorders

Emerging insights into the role of NLRP3 inflammasome and endoplasmic reticulum stress in renal diseases

NLRP3 inflammasome is a key component of the innate immune system, mediating the activation of caspase-1, and the maturity and secretion of the pro-inflammatory cytokine interleukin (IL)-1beta (IL-1β) and IL-18 to cope with microbial infections and cell injury. The NLRP3 inflammasome is activated by various endogenous danger signals, microorganisms and environmental stimuli, including urate, extracellular adenosine triphosphate (ATP) and cholesterol crystals. Increasing evidence indicates that the abnormal activation of NLRP3 is involved in multiple diseases including renal diseases. Hence, clarifying the mechanism of action of NLRP3 inflammasome in different diseases can help prevent and treat various diseases. Endoplasmic reticulum (ER) is an important organelle which participates in cell homeostasis maintenance and protein quality control. The unfolded protein response (UPR) and ER stress are caused by the excessive accumulation of unfolded or misfolded proteins in ER to recover ER homeostasis. Many factors can cause ER stress, including inflammation, hypoxia, environmental toxins, viral infections, glucose deficiency, changes in Ca2+ level and oxidative stress. The dysfunction of ER stress participates in multiple diseases, such as renal diseases. Many previous studies have shown that NLRP3 inflammasome and ER stress play an important role in renal diseases. However, the relevant mechanisms are not yet fully clear. Herein, we focus on the current understanding of the role and mechanism of ER stress and NLRP3 inflammasome in renal diseases, hoping to provide theoretical references for future related researches.

The Involvement of Calcium Channels in the Endoplasmic Reticulum Membrane in Nonalcoholic Fatty Liver Disease Pathogenesis

Nonalcoholic fatty liver disease (NAFLD) is a prevalent and complex condition that affects millions of people globally. It occurs when fat, primarily triglycerides, accumulates in liver cells, leading to inflammation and damage. Calcium, an essential mineral, is involved in various physiological processes, including the regeneration process following liver injury. The endoplasmic reticulum (ER), a complex organelle involved in protein synthesis and lipid metabolism, regulates intracellular calcium levels. Dysregulation of this process can lead to calcium overload, oxidative stress, and cellular damage, all of which are hallmarks of NAFLD. Inositol 1,4,5-trisphosphate receptor (IP3R), a type of calcium ion channel, is found throughout the body, including the liver. IP3R is classified into three subtypes: IP3R1, IP3R2, and IP3R3, and it plays a critical role in regulating intracellular calcium levels. However, excessive calcium accumulation in the mitochondria due to an overload of calcium ions or increased IP3R activity can lead to NAFLD. Therefore, targeting calcium channels in the ER membrane may represent a promising therapeutic strategy for preventing and treating this increasingly prevalent metabolic disorder. It may help prevent mitochondrial calcium accumulation and reduce the risk of hepatic damage. This review article aimed to review the relationship between IP3R modulation and the pathogenicity of NAFLD, providing valuable insights to help researchers develop more effective treatments for the condition.

Resveratrol improves emamectin benzoate-induced pyroptosis and inflammation of Ctenopharyngodon idellus hepatic cells by alleviating oxidative stress/endoplasmic reticulum stress

Emamectin benzoate (EMB) is the most widely used pesticide in the world and contributes to water pollution. Owing to the lack of a specific antidote, EMB has a severe negative impact on the health of aquatic organisms. Resveratrol (RES), a substance with antioxidant capacity, is secreted by the fruits of many plants. This study was to explore the protection of RES against EMB-induced pyroptosis and inflammatory response in grass carp (Ctenopharyngodon idellus) hepatic liver (L8824) cells by oxidative stress/endoplasmic reticulum (ER) stress. The results showed that compared to the CON group, EMB induced oxidative stress in L8824 cells with the increase of reactive oxygen species (ROS), methane dicarboxylic aldehyde (MDA), and hydrogen peroxide (H2O2) contents and the decrease of total superoxide dismutase (t-sod) and glutathione peroxidase (gsh-px) activities (P < 0.05). In addition, EMB triggered ERS, increasing the relative mRNA expression of protein kinase R-like endoplasmic reticulum kinase (perk), inositol requiring enzyme 1 alpha (ire1α), glucose-regulated protein 78 (grp78), activating transcription factor 4 (atf4), activating transcription factor 6 (atf6), and CCAAT-enhancer-binding protein homologous protein (chop) and the protein expression of eukaryotic initiation factor 2α (eif2α), chop, atf6, and atf4. Meanwhile, EMB further induced pyroptosis by upregulating the mRNA and protein expression of nlrp3, aptamer protein (asc), caspase-1, gsdmd, interleukin-1β (il-1β), and interleukin-18 (il-18). EMB also induced inflammation in L8824 cells by increasing the mRNA expression of interleukin-2 (il-2), interleukin-6 (il-6), tumor necrosis factor-α (tnf-α), and ifn-γ and decreasing the content of interleukin-10 (il-10). However, compared to the EMB group, the oxidant indices and expression of genes related to ER stress, pyroptosis, and pro-inflammatory factors were significantly down-regulated (P < 0.05), whereas the antioxidant indicators and anti-inflammatory factor were significantly up-regulated in the EMB + RES group (P < 0.05). In conclusion, EMB caused hepatocytes pyroptosis and inflammation in grass carp, and RES could alleviate EMB-induced pyroptosis and inflammation in L8824 cells by ameliorating oxidative stress/ER stress.

Polysaccharides Extracted from Dendrobium officinale Grown in Different Environments Elicit Varying Health Benefits in Caenorhabditis elegans

Dendrobium officinale is one of the most widely used medicinal herbs, especially in Asia. In recent times, the polysaccharide content of D. officinale has garnered attention due to the numerous reports of its medicinal properties, such as anticancer, antioxidant, anti-diabetic, hepatoprotective, neuroprotective, and anti-aging activities. However, few reports of its anti-aging potential are available. Due to high demand, the wild D. officinale is scarce; hence, alternative cultivation methods are being employed. In this study, we used the Caenorhabditis elegans model to investigate the anti-aging potential of polysaccharides extracted from D. officinale (DOP) grown in three different environments; tree (TR), greenhouse (GH), and rock (RK). Our findings showed that at 1000 µg/mL, GH-DOP optimally extended the mean lifespan by 14% and the maximum lifespan by 25% (p < 0.0001). TR-DOP and RK-DOP did not extend their lifespan at any of the concentrations tested. We further showed that 2000 µg/mL TR-DOP, GH-DOP, or RK-DOP all enhanced resistance to H₂O₂-induced stress (p > 0.05, p < 0.01, and p < 0.01, respectively). In contrast, only RK-DOP exhibited resistance (p < 0.01) to thermal stress. Overall, DOP from the three sources all increased HSP-4::GFP levels, indicating a boost in the ability of the worms to respond to ER-related stress. Similarly, DOP from all three sources decreased α-synuclein aggregation; however, only GH-DOP delayed β-amyloid-induced paralysis (p < 0.0001). Our findings provide useful information on the health benefits of DOP and also provide clues on the best practices for cultivating D. officinale for maximum medicinal applications.

The Role of the NLRP3 Inflammasome and Programmed Cell Death in Acute Liver Injury

Acute liver injury (ALI) is a globally important public health issue that, when severe, rapidly progresses to acute liver failure, seriously compromising the life safety of patients. The pathogenesis of ALI is defined by massive cell death in the liver, which triggers a cascade of immune responses. Studies have shown that the aberrant activation of the nod-like receptor protein 3 (NLRP3) inflammasome plays an important role in various types of ALI and that the activation of the NLRP3 inflammasome causes various types of programmed cell death (PCD), and these cell death effectors can in turn regulate NLRP3 inflammasome activation. This indicates that NLRP3 inflammasome activation is inextricably linked to PCD. In this review, we summarize the role of NLRP3 inflammasome activation and PCD in various types of ALI (APAP, liver ischemia reperfusion, CCl₄, alcohol, Con A, and LPS/D-GalN induced ALI) and analyze the underlying mechanisms to provide references for future relevant studies.

A perspective study of the possible impact of obeticholic acid against SARS-CoV-2 infection

The causative agent of CoV disease 2019 is a new coronavirus CoV type 2, affecting the respiratory tract with severe manifestations (SARS-CoV-2). Covid-19 is mainly symptomless, with slight indications in about 85% of the affected cases. Many efforts were done to face this pandemic by testing different drugs and agents to make treatment protocols in different countries. However, the use of these proposed drugs is associated with the development of adverse events. Remarkably, the successive development of SARS-CoV-2 variants which could affect persons even they were vaccinated, prerequisite wide search to find efficient and safe agents to face SARS-CoV-2 infection. Obeticholic acid (OCA), which has anti-inflammatory effects, may efficiently treat Covid-19. Thus, the goal of this perspective study is to focus on the possible medicinal effectiveness in managing Covid-19. OCA is a powerful farnesoid X receptor (FXR) agonist possessing marked antiviral and anti-inflammatory effects. FXR is dysregulated in Covid-19 resulting in hyper-inflammation with concurrent occurrence of hypercytokinemia. Interestingly, OCA inhibits the reaction between this virus and angiotensin-converting enzyme type 2 (ACE2) receptors. FXR agonists control the expression of ACE2 and the inflammatory signaling pathways in this respiratory syndrome, which weakens the effects of Covid-19 disease and accompanied complications. Taken together, FXR agonists like OCA may reveal both direct and indirect impacts in the modulation of immune reaction in SARS-CoV-2 conditions. It is highly recommended to perform many investigations regarding different phases of the discovery of new drugs.

Hydrogen sulfide plays an important role by regulating endoplasmic reticulum stress in myocardial diseases

Endoplasmic reticulum (ER) is an important organelle for protein translation, folding and translocation, as well as the post-translational modification and assembly of newly synthesized secreted proteins. When the excessive accumulation of misfolded and/or unfolded proteins exceeds the processing capacity of ER, ER stress is triggered. The integrated intracellular signal cascade, namely the unfolded protein response, is induced to avoid ER stress. ER stress is involved in many pathological and physiological processes including myocardial diseases. For a long time, hydrogen sulfide (H₂S) has been considered as a toxic gas with the smell of rotten eggs. However, more and more evidences indicate that H₂S is an important gas signal molecule after nitric oxide and carbon monoxide, and regulates a variety of physiological and pathological processes in mammals. In recent years, increasing studies have focused on the regulatory effects of H₂S on ER stress in myocardial diseases, however, the mechanism is not very clear. Therefore, this review focuses on the role of H₂S regulation of ER stress in myocardial diseases, and deeply analyzes the relevant mechanisms so as to lay the foundation for the future researches.

Lycopene Alleviates Chronic Stress-Induced Liver Injury by Inhibiting Oxidative Stress-Mediated Endoplasmic Reticulum Stress Pathway Apoptosis in Rats

The liver is the major organ of metabolism and is extremely vulnerable to chronic stress. Lycopene (LYC) is a natural carotenoid with potent antioxidant and chronic disease potential. However, whether LYC protects against chronic restraint stress (CRS)-induced liver injury and the underlying mechanisms remain unclear. In this study, rats were restrained for 21 days for 6 h per day, with or without gavage of LYC (10 mg/kg). Serum ALT (85.99 ± 4.07 U/L) and AST (181.78 ± 7.35 U/L) and scores of liver injury were significantly increased in the CRS group. LYC significantly promoted the nuclear translocation of Nrf2, elevated the expression of antioxidant genes, and attenuated reactive oxygen radicals (ROS) levels within the liver. Cellular thermal shift assay (CETSA) and molecular docking results indicated that LYC competitively binds to Keap1 with the lowest molecule affinity of -9.0 kcal/mol. Moreover, LYC significantly relieved the hepatic endoplasmic reticulum swelling and decreased the expression of endoplasmic reticulum stress (ERS) hallmarks like GRP78, CHOP, and cleaved caspase-12. Meanwhile, LYC also mitigated CRS-induced hepatocyte apoptosis. Interestingly, every other day, the intraperitoneal injection of the Nrf2 inhibitor brusatol (0.4 mg/kg) significantly counteracted the protective effect of LYC. In conclusion, LYC protects against CRS-induced liver injury by activating the Nrf2 signaling pathway, scavenging ROS, and further attenuating ERS-associated apoptosis pathways.

GRP94 Inhabits the Immortalized Porcine Hepatic Stellate Cells Apoptosis under Endoplasmic Reticulum Stress through Modulating the Expression of IGF-1 and Ubiquitin

Endoplasmic reticulum stress (ERS) is closely related to the occurrence and progression of metabolic liver disease. The treatment targeting glucose-regulated protein 94 (GRP94) for liver disease has gotten much attention, but the specific effect of GRP94 on hepatocyte apoptosis is still unclear. So far, all the studies on GRP94 have been conducted in mice or rats, and little study has been reported on pigs, which share more similarities with humans. In this study, we used low-dose (LD) and high-dose (HD) tunicamycin (TM) to establish ERS models on piglet livers and immortalized porcine hepatic stellate cells (HSCs). On the piglet ERS model we found that ERS could significantly (p < 0.01) stimulate the secretion and synthesis of insulin-like growth factor (IGF-1), IGF-1 receptor (IGF-1R), and IGF-binding protein (IGFBP)-1 and IGFBP-3; however, with the increase in ERS degree, the effect of promoting secretion and synthesis significantly (p < 0.01) decreased. In addition, the ubiquitin protein and ubiquitination-related gene were significantly increased (p < 0.05) in the LD group compared with the vehicle group. The protein level of Active-caspase 3 was significantly increased (p < 0.01) in the HD group, however, the TUNEL staining showed there was no significant apoptosis in the piglet liver ERS model. To explore the biofunction of ER chaperone GRP94, we used shRNA to knock down the expression of GRP94 in porcine HSCs. Interestingly, on porcine HSCs, the knockdown of GRP94 significantly (p < 0.05) decreased the secretion of IGF-1, IGFBP-1 and IGFBP-3 under ERS, but had no significant effect on these under normal condition, and knockdown GRP94 had a significant (p < 0.01) effect on the UBE2E gene and ubiquitin protein from the analysis of two-way ANOVA. On porcine HSCs apoptosis, the knockdown of GRP94 increased the cell apoptosis in TUNEL staining, and the two-way ANOVA analysis shows that knockdown GRP94 had a significant (p < 0.01) effect on the protein levels of Bcl-2 and Caspase-3. For CCK-8 assay, ERS had a significant inhibitory(p < 0.05) effect on cell proliferation when treated with ERS for 24 h, and both knockdown GRP94 and ERS had a significant inhibitory(p < 0.05) effect on cell proliferation when treated with ERS for 36 h and 48 h. We concluded that GRP94 can protect the cell from ERS-induced apoptosis by promoting the IGF-1 system and ubiquitin. These results provide valuable information on the adaptive mechanisms of the liver under ERS, and could help identify vital functional genes to be applied as possible diagnostic biomarkers and treatments for diseases induced by ERS in the future.

Study on the Mechanism of Mesaconitine-Induced Hepatotoxicity in Rats Based on Metabonomics and Toxicology Network

Mesaconitine (MA), one of the main diterpenoid alkaloids in Aconitum, has a variety of pharmacological effects, such as analgesia, anti-inflammation and relaxation of rat aorta. However, MA is a highly toxic ingredient. At present, studies on its toxicity are mainly focused on the heart and central nervous system, and there are few reports on the hepatotoxic mechanism of MA. Therefore, we evaluated the effects of MA administration on liver. SD rats were randomly divided into a normal saline (NS) group, a low-dose MA group (0.8 mg/kg/day) and a high-dose MA group (1.2 mg/kg/day). After 6 days of administration, the toxicity of MA on the liver was observed. Metabolomic and network toxicology methods were combined to explore the effect of MA on the liver of SD rats and the mechanism of hepatotoxicity in this study. Through metabonomics study, the differential metabolites of MA, such as L-phenylalanine, retinyl ester, L-proline and 5-hydroxyindole acetaldehyde, were obtained, which involved amino acid metabolism, vitamin metabolism, glucose metabolism and lipid metabolism. Based on network toxicological analysis, MA can affect HIF-1 signal pathway, MAPK signal pathway, PI3K-Akt signal pathway and FoxO signal pathway by regulating ALB, AKT1, CASP3, IL2 and other targets. Western blot results showed that protein expression of HMOX1, IL2 and caspase-3 in liver significantly increased after MA administration (p < 0.05). Combined with the results of metabonomics and network toxicology, it is suggested that MA may induce hepatotoxicity by activating oxidative stress, initiating inflammatory reaction and inducing apoptosis.