Cytosolic HMGB1 Mediates Autophagy Activation in an Emulsified Isoflurane Anesthesia Cell Model

Autophagy in Neuroinflammation: A Focus on Epigenetic Regulation

Neuroinflammation, characterized by the secretion of abundant inflammatory mediators, pro-inflammatory polarization of microglia, and the recruitment of infiltrating myeloid cells to foci of inflammation, drives or exacerbates the pathological processes of central nervous system disorders, especially in neurodegenerative diseases. Autophagy plays an essential role in neuroinflammatory processes, and the underlaying physiological mechanisms are closely correlated with neuroinflammation-related signals. Inhibition of mTOR and activation of AMPK and FOXO1 enhance autophagy and thereby suppress NLRP3 inflammasome activity and apoptosis, leading to the relief of neuroinflammatory response. And autophagy mitigates neuroinflammation mainly manifested by promoting the polarization of microglia from a pro-inflammatory to an anti-inflammatory state, reducing the production of pro-inflammatory mediators, and up-regulating the levels of anti-inflammatory factors. Notably, epigenetic modifications are intimately associated with autophagy and the onset and progression of various brain diseases. Non-coding RNAs, including microRNAs, circular RNAs and long noncoding RNAs, and histone acetylation have been reported to adjust autophagy-related gene and protein expression to alleviate inflammation in neurological diseases. The present review primarily focuses on the role and mechanisms of autophagy in neuroinflammatory responses, as well as epigenetic modifications of autophagy in neuroinflammation to reveal potential therapeutic targets in central nervous system diseases.

HMGB1 in the interplay between autophagy and apoptosis in cancer

Lysosome-mediated autophagy and caspase-dependent apoptosis are dynamic processes that maintain cellular homeostasis, ensuring cell health and functionality. The intricate interplay and reciprocal regulation between autophagy and apoptosis are implicated in various human diseases, including cancer. High-mobility group box 1 (HMGB1), a nonhistone chromosomal protein, plays a pivotal role in coordinating autophagy and apoptosis levels during tumor initiation, progression, and therapy. The regulation of autophagy machinery and the apoptosis pathway by HMGB1 is influenced by various factors, including the protein's subcellular localization, oxidative state, and interactions with binding partners. In this narrative review, we provide a comprehensive overview of the structure and function of HMGB1, with a specific focus on the interplay between autophagic degradation and apoptotic death in tumorigenesis and cancer therapy. Gaining a comprehensive understanding of the significance of HMGB1 as a biomarker and its potential as a therapeutic target in tumor diseases is crucial for advancing our knowledge of cell survival and cell death.

The Redox Protein High-Mobility Group Box 1 in Cell Death and Cancer

Significance: As a redox-sensitive protein, high-mobility group box 1 (HMGB1) is implicated in regulating stress responses to oxidative damage and cell death, which are closely related to the pathology of inflammatory diseases, including cancer. Recent Advances: HMGB1 is a nonhistone nuclear protein that acts as a deoxyribonucleic acid chaperone to control chromosomal structure and function. HMGB1 can also be released into the extracellular space and function as a damage-associated molecular pattern protein during cell death, including during apoptosis, necrosis, necroptosis, pyroptosis, ferroptosis, alkaliptosis, and cuproptosis. Once released, HMGB1 binds to membrane receptors to shape immune and metabolic responses. In addition to subcellular localization, the function and activity of HMGB1 also depend on its redox state and protein posttranslational modifications. Abnormal HMGB1 plays a dual role in tumorigenesis and anticancer therapy (e.g., chemotherapy, radiation therapy, and immunotherapy) depending on the tumor types and stages. Critical Issues: A comprehensive understanding of the role of HMGB1 in cellular redox homeostasis is important for deciphering normal cellular functions and pathological manifestations. In this review, we discuss compartmental-defined roles of HMGB1 in regulating cell death and cancer. Understanding these advances may help us develop potential HMGB1-targeting drugs or approaches to treat oxidative stress-related diseases or pathological conditions. Future Directions: Further studies are required to dissect the mechanism by which HMGB1 maintains redox homeostasis under different stress conditions. A multidisciplinary effort is also required to evaluate the potential applications of precisely targeting the HMGB1 pathway in human health and disease. Antioxid. Redox Signal. 39, 569-590.

4.8% sevoflurane induces activation of autophagy in human neuroblastoma SH-SY5Y cells by the AMPK/mTOR signaling pathway

Prolonged sevoflurane exposure leads to neurotoxicity. Autophagy plays an important role in promoting cell survival in different conditions. However, the role and mechanism of autophagy in sevoflurane-induced neurotoxicity were not fully elucidated. We attempted to indicate whether sevoflurane could activate the AMP-activated protein kinase (AMPK)/mechanistic target of rapamycin (mTOR)-mediated autophagy to attenuate anesthetics-induced neuronal injury in this study. Sevoflurane treatment significantly decreased the cell viability and induced apoptosis of SH-SY5Y cells. The expression level of Bcl-2 decreased, while that of Bax remarkably increased. Meanwhile, autophagy was activated by sevoflurane exposure as evidenced by increased expression levels of autophagy-related proteins (LC3-II and Atg5), decreased expression level of autophagic substrate P62, and increased autophagosomes and autolysosomes. Further autophagosomes and fewer autolysosomes were observed in the presence of Bafilomycin A1, an autolysosomes degradation inhibitor, suggesting that sevoflurane induced autophagic flux rather than inhibiting degradation of autophagy. Activation of autophagy by rapamycin partly reversed the sevoflurane-decreased cell viability. In contrast, inhibition of autophagy by 3-Methyladenine (3-MA) or Atg5-targeted small interfering RNA (siRNA) aggravated the sevoflurane-induced neurotoxicity. Further examination revealed that sevoflurane-induced autophagy was mediated by the AMPK/mTOR signaling pathway, with increased p-AMPK expression and decreased p-mTOR expression. Collectively, these results indicated that sevoflurane activates autophagy by regulating the AMPK/mTOR signaling pathway, which is protective against sevoflurane-induced damage in SH-SY5Y cells. Our results may assist clinicians to develop further promising therapeutic strategies for the neurotoxicity induced by inhaled anesthetics.

Autophagic degradation of CCN2 (cellular communication network factor 2) causes cardiotoxicity of sunitinib

Excessive macroautophagy/autophagy is one of the causes of cardiomyocyte death induced by cardiovascular diseases or cancer therapy, yet the underlying mechanism remains unknown. We and other groups previously reported that autophagy might contribute to cardiomyocyte death caused by sunitinib, a tumor angiogenesis inhibitor that is widely used in clinic, which may help to understand the mechanism of autophagy-induced cardiomyocyte death. Here, we found that sunitinib-induced autophagy leads to apoptosis of cardiomyocyte and cardiac dysfunction as the cardiomyocyte-specific Atg7^-/+ heterozygous mice are resistant to sunitinib. Sunitinib-induced maladaptive autophagy selectively degrades the cardiomyocyte survival mediator CCN2 (cellular communication network factor 2) through the TOLLIP (toll interacting protein)-mediated endosome-related pathway and cardiomyocyte-specific knockdown of Ccn2 through adeno-associated virus serotype 9 (AAV9) mimics sunitinib-induced cardiac dysfunction in vivo, suggesting that the autophagic degradation of CCN2 is one of the causes of sunitinib-induced cardiotoxicity and death of cardiomyocytes. Remarkably, deletion of Hmgb1 (high mobility group box 1) inhibited sunitinib-induced cardiomyocyte autophagy and apoptosis, and the HMGB1-specific inhibitor glycyrrhizic acid (GA) significantly mitigated sunitinib-induced autophagy, cardiomyocyte death and cardiotoxicity. Our study reveals a novel target protein of autophagic degradation in the regulation of cardiomyocyte death and highlights the pharmacological inhibitor of HMGB1 as an attractive approach for improving the safety of sunitinib-based cancer therapy.

HMGB1 Mediated Inflammation and Autophagy Contribute to Endometriosis

AIM

High mobility group box (HMGB)-1 has been implicated in endometriosis due to the important regulatory roles of inflammation in endometriosis. The aim of the present study was to explore the roles of HMGB-1 in endometriosis and to elucidate the underlying mechanism.

METHODS

Endometrial specimens were collected from women with endometriosis and healthy volunteers. Immunohistochemistry staining was used to determine the expression patterns and localization of HMGB-1 in the normal, eutopic and ectopic endometrial tissues. Western blotting and qRT-PCR were used to determine the mRNA and protein levels of inflammatory cytokines [interleukin (IL)-6, tumor necrosis factor (TNF)-α and IL-1β], autophagy-related markers [beclin-1, autophagy-related (atg)13, microtubule-associated protein light chain (LC)3-I, LC-II and p62] and HMGB-1, respectively. Spearman's rank correlation analysis was employed to investigate the correlation between HMGB-1 with inflammatory cytokines and beclin-1. Besides, human endometrial stromal cells (HESCs) were isolated from ectopic endometrium and subsequently transfected with shRNA against HMGB-1. After the transfected cells were subjected to hypoxia, ELISA was used to determine the levels of HMGB-1 and inflammatory cytokines in the cell supernatant. Western blotting was used to determine the expression levels of autophagy-related markers in the cells.

RESULTS

Positive correlations were observed between HMGB-1 and the inflammatory cytokines. In addition, a positive correlation was also identified between HMGB-1 and beclin-1 in the ectopic endometrium. Further results demonstrated that autophagy-related markers beclin-1, atg13 and p62 were significantly upregulated in the ectopic endometrium. In addition, HMGB-1 knockdown suppressed the levels of inflammatory cytokines IL-6, TNF-α and IL-1β and autophagy-related markers beclin-1 and atg13, while upregulated p62 in HESCs under hypoxic condition.

CONCLUSION

Knockdown of HMGB-1 under hypoxic condition regulated inflammatory cytokines and autophagy-related markers. HMGB-1 might contribute to the development of endometriosis in part through regulating inflammatory response and autophagy.

Beclin1-mediated ferroptosis activation is associated with isoflurane-induced toxicity in SH-SY5Y neuroblastoma cells

The widely used inhalation anesthetic, isoflurane, potentially induces neuronal injury in clinical practice. Previous studies showed multiple forms of cell death that resulted from isoflurane-induced cytotoxicity, but the precise underlying mechanism remains poorly understood. Ferroptosis has recently been identified as a non-apoptotic form of regulated cell death. Here, we found that ferroptosis inhibitors, ferrostatin-1 and deferoxamine mesylate (DFOM), showed great efficiency in maintaining cell viability in SH-SY5Y neuroblastoma cells exposed to a high concentration of isoflurane for 24 h. We also observed that cellular chelatable iron and lipid peroxidation were increased in a concentration-dependent manner in response to isoflurane. In addition, isoflurane upregulated Beclin1 phosphorylation, followed by the formation of a Beclin1-solute carrier family 7 member 11 (SLC7A11) complex, which affected the activity of cystine/glutamate antipoter and further regulated ferroptotic cell death. Accordingly, Beclin1 overexpression aggravated isoflurane-induced cell damage by upregulating ferroptosis. This phenomenon was significantly attenuated by silencing of Beclin1 in SH-SY5Y cells. These findings indicate that Beclin1 may regulate ferroptosis in a manner involving inhibition of glutamate exchange activity of system xc(-), which is implicated in isoflurane-induced toxicity. In particular, when isoflurane is administrated at high concentrations and for an extended duration, ferroptosis is more likely to play a crucial role in isoflurane-induced toxicity.