Tunicamycin Induces Hepatic Stellate Cell Apoptosis Through Calpain-2/Ca2 +-Dependent Endoplasmic Reticulum Stress Pathway

Liver Fibrosis Resolution: From Molecular Mechanisms to Therapeutic Opportunities

The liver is a critical system for metabolism in human beings, which plays an essential role in an abundance of physiological processes and is vulnerable to endogenous or exogenous injuries. After the damage to the liver, a type of aberrant wound healing response known as liver fibrosis may happen, which can result in an excessive accumulation of extracellular matrix (ECM) and then cause cirrhosis or hepatocellular carcinoma (HCC), seriously endangering human health and causing a great economic burden. However, few effective anti-fibrotic medications are clinically available to treat liver fibrosis. The most efficient approach to liver fibrosis prevention and treatment currently is to eliminate its causes, but this approach's efficiency is too slow, or some causes cannot be fully eliminated, which causes liver fibrosis to worsen. In cases of advanced fibrosis, the only available treatment is liver transplantation. Therefore, new treatments or therapeutic agents need to be explored to stop the further development of early liver fibrosis or to reverse the fibrosis process to achieve liver fibrosis resolution. Understanding the mechanisms that lead to the development of liver fibrosis is necessary to find new therapeutic targets and drugs. The complex process of liver fibrosis is regulated by a variety of cells and cytokines, among which hepatic stellate cells (HSCs) are the essential cells, and their continued activation will lead to further progression of liver fibrosis. It has been found that inhibiting HSC activation, or inducing apoptosis, and inactivating activated hepatic stellate cells (aHSCs) can reverse fibrosis and thus achieve liver fibrosis regression. Hence, this review will concentrate on how HSCs become activated during liver fibrosis, including intercellular interactions and related signaling pathways, as well as targeting HSCs or liver fibrosis signaling pathways to achieve the resolution of liver fibrosis. Finally, new therapeutic compounds targeting liver fibrosis are summarized to provide more options for the therapy of liver fibrosis.

An ER-Horse Detonating Stress Cascade for Hepatocellular Carcinoma Nanotherapy

Persisting and excessive endoplasmic reticulum stress (ERS) can evoke rapid cell apoptosis. Therapeutic interference of ERS signaling holds enormous potential for cancer nanotherapy. Herein, a hepatocellular carcinoma (HCC) cell-derived ER vesicle (ERV) encapsulating siGRP94, denoted as ER-horse, has been developed for precise HCC nanotherapy. Briefly, ER-horse, like the Trojan horse, was recognized via homotypic camouflage, imitated the physiological function of ER, and exogenously opened the Ca²⁺ channel. Consequently, the mandatory pouring-in of extracellular Ca²⁺ triggered the aggravated stress cascade (ERS and oxidative stress) and apoptosis pathway with the inhibition of unfolded protein response by siGRP94. Collectively, our findings provide a paradigm for potent HCC nanotherapy via ERS signaling interference and exploring therapeutic interference of physiological signal transduction pathways for precision cancer therapy.

Calpain-2 Facilitates Autophagic/Lysosomal Defects and Apoptosis in ARPE-19 Cells and Rats Induced by Exosomes from RPE Cells under NaIO3 Stimulation

Although accumulated evidence supports the notion that calpain contributes to eye disease, the mechanisms by which calpain promotes RPE injury are not defined. The present study is aimed at investigating whether the effect of NaIO₃-exos (exosomes derived from RPE cells under NaIO₃ stimulation) on the dysfunction of the autophagy-lysosomal pathway (ALP) and apoptosis is based on its regulation of calpain activation in ARPE-19 cells and rats. The results showed that calpain-2 activation, ALP dysfunction, and apoptosis were induced by NaIO₃-exos in ARPE-19 cells. NaIO₃-exo significantly increased autophagic substrates by activating lysosomal dysfunction. ALP dysfunction and apoptosis in vitro could be eliminated by knocking down calpain-2 (si-C2) or the inhibitor calpain-2-IN-1. Further studies indicated that NaIO₃-exo enhanced calpain-2 expression, ALP dysfunction, apoptosis, and retinal damage in rats. In summary, these results demonstrate for the first time that calpain-2 is one of the key players in the NaIO₃-exo-mediated ALP dysfunction, apoptosis, and retinal damage and identify calpain-2 as a promising target for therapies aimed at age-related macular degeneration (AMD).

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.

Melatonin alleviates PM2.5 -induced glucose metabolism disorder and lipidome alteration by regulating endoplasmic reticulum stress

Exposure to fine particulate matter (PM_2.5 ) was associated with an increased incidence of liver metabolic disease. Melatonin has been shown to prevent liver glucolipid metabolism disorders. However, whether melatonin could rescue PM_2.5 -induced liver metabolic abnormalities remains uncertain. This study was to evaluate the mitigating effect of melatonin on PM_2.5 -accelerated hepatic glucose metabolism imbalance in vivo and in vitro. Schiff periodic acid shiff staining and other results showed that PM_2.5 led to a decrease in hepatic glycogen reserve and an increase in glucose content, which was effectively alleviated by melatonin. Targeted lipidomics is used to identify lipid biomarkers associated with this process, including glycerolipids, glycerophospholipids, and sphingolipids. In addition, gene microarray and quantitative polymerase chain reaction analysis of ApoE^-/- mice liver suggested that PM_2.5 activated the miR-200a-3p and inhibited DNAJB9, and the targeting relationship was verified by luciferase reports for the first time. Further investigation demonstrated that DNAJB9 might motivate endoplasmic reticulum (ER) stress by regulating Ca²⁺ homeostasis, thus altering the protein expression of GSK3B, FOXO1, and PCK2. Meanwhile, melatonin effectively inhibited miR-200a-3p and glucose metabolism disorder. Knockout of miR-200a-3p in L02 cells revealed that miR-200a-3p is indispensable in the damage of PM_2.5 and the therapeutic effect of melatonin. In summary, melatonin alleviated PM_2.5 -induced liver metabolic dysregulation by regulating ER stress via miR-200a-3p/DNAJB9 signaling pathway. Our data provide a prospective targeted therapy for air pollution-related liver metabolism disorders.

Bisimidazolium Salt Glycosyltransferase Inhibitors Suppress Hepatocellular Carcinoma Progression In Vitro and In Vivo

Hepatocellular carcinoma is a leading cause of cancer death, and the disease progression has been related to glycophenotype modifications. Previously synthesized bisimidazolium salts (C20 and C22) have been shown to selectively inhibit the activity of glycosyltransferases in cultured cancer cell homogenates. The current study investigated the anticancer effects of C20/C22 and the possible pathways through which these effects are achieved. The therapeutic value of C20/C22 in terms of inhibiting cancer cell proliferation, metastasis, and angiogenesis, as well as inducing apoptosis, were examined with hepatic cancer cell line HepG2 and a xenograft mouse model. C20/C22 treatment downregulated the synthesis of SLex and Ley sugar epitopes and suppressed selectin-mediated cancer cell metastasis. C20/C22 inhibited HepG2 proliferation, induced cell-cycle arrest, increased intracellular ROS level, led to ER stress, and eventually induced apoptosis through the intrinsic pathway. Furthermore, C20/C22 upregulated the expressions of death receptors DR4 and DR5, substantially increasing the sensitivity of HepG2 to TRAIL-triggered apoptosis. In vivo, C20/C22 effectively inhibited tumor growth and angiogenesis in the xenograft mouse model without adverse effects on major organs. In summary, C20 and C22 are new promising anti-hepatic cancer agents with multiple mechanisms in controlling cancer cell growth, metastasis, and apoptosis, and they merit further development into anticancer drugs.