Activating transcription factor 6 regulates cystathionine to increase autophagy and restore memory in Alzheimer’ s disease model mice

Activating transcription factor 6 alleviates secondary brain injury by increasing cystathionine γ-lyase expression in a rat model of intracerebral hemorrhage

BACKGROUND

Intracerebral hemorrhage (ICH) comprises primary and secondary injuries, the latter of which induces increased inflammation and apoptosis and is more severe. Activating transcription factor 6 (ATF6) is a type-II transmembrane protein in the endoplasmic reticulum (ER). ATF6 target genes could improve ER homeostasis, which contributes to cryoprotection. Hence, we predict that ATF6 will have a protective effect on brain tissue after ICH.

METHOD

The ICH rat model was generated through autologous blood injection into the right basal ganglia, the expression of ATF6 after ICH was determined by WB and IF. The expression of ATF6 was effectively controlled by means of intervention, and a series of measures was used to detect cell death, neuroinflammation, brain edema, blood-brain barrier and other indicators after ICH. Finally, the effects on long-term neural function of rats were measured by behavioral means.

RESULT

ATF6 was significantly increased in the ICH-induced brain tissues. Further, ATF6 was found to modulate the expression of cystathionine γ-lyase (CTH) after ICH. Upregulation of ATF6 attenuated neuronal apoptosis and inflammation in ICH rats, along with mitigation of ICH-induced brain edema, blood-brain barrier deterioration, and cognitive behavior defects. Conversely, ATF6 genetic knockdown induced effects counter to those aforementioned.

CONCLUSIONS

This study thereby emphasizes the crucial role of ATF6 in secondary brain injury in response to ICH, indicating that ATF6 upregulation may potentially ameliorate ICH-induced secondary brain injury. Consequently, ATF6 could serve as a promising therapeutic target to alleviate clinical ICH-induced secondary brain injuries.

Endoplasmic reticulum stress and therapeutic strategies in metabolic, neurodegenerative diseases and cancer

The accumulation of unfolded or misfolded proteins within the endoplasmic reticulum (ER), due to genetic determinants and extrinsic environmental factors, leads to endoplasmic reticulum stress (ER stress). As ER stress ensues, the unfolded protein response (UPR), comprising three signaling pathways-inositol-requiring enzyme 1, protein kinase R-like endoplasmic reticulum kinase, and activating transcription factor 6 promptly activates to enhance the ER's protein-folding capacity and restore ER homeostasis. However, prolonged ER stress levels propels the UPR towards cellular demise and the subsequent inflammatory cascade, contributing to the development of human diseases, including cancer, neurodegenerative disorders, and diabetes. Notably, increased expression of all three UPR signaling pathways has been observed in these pathologies, and reduction in signaling molecule expression correlates with decreased proliferation of disease-associated target cells. Consequently, therapeutic strategies targeting ER stress-related interventions have attracted significant research interest. In this review, we elucidate the critical role of ER stress in cancer, metabolic, and neurodegenerative diseases, offering novel therapeutic approaches for these conditions.

Dietary conjugated linoleic acid downregulates the AlCl3-induced hyperactivation of compensatory and maladaptive signalling in the mouse brain cortex

Oxidative stress, hyperactivation of compensatory mechanisms (unfolded protein response, UPR; nuclear factor erythroid 2-related factor 2, Nrf2) and the stimulation of maladaptive response (inflammation/apoptosis) are interconnected pathogenic processes occurring during Alzheimer's disease (AD) progression. The neuroprotective ability of dietary Conjugated linoleic acid (CLAmix) in a mouse model of AlCl3-induced AD was recently described but, the effects of AlCl3 or CLAmix intake on these pathogenic processes are still unknown. The effects of dietary AlCl3 or CLAmix - alone and in combination - were examined in the brain cortex of twenty-eight BalbC mice divided into 4 groups (n = 7 each). The neurotoxic effects of AlCl3 were investigated in animals treated for 5 weeks with 100 mg/kg/day (AL). CLAmix supplementation (600 mg/kg bw/day) for 7 weeks (CLA) was aimed at evaluating its modulatory effects on the Nrf2 pathway while its co-treatment with AlCl3 during the last 5 weeks of CLAmix intake (CLA + AL) was used to investigate its neuroprotective ability. Untreated mice were used as controls. In the CLA group, the NADPH oxidase (NOX) activation in the brain cortex was accompanied by the modulation of the Nrf2 pathway. By contrast, in the AL mice, the significant upregulation of oxidative stress markers, compensatory pathways (UPR/Nrf2), proinflammatory cytokines (IL-6, TNFα) and the proapoptotic protein Bax levels were found as compared with control. Notably, in CLA + AL mice, the marked decrease of oxidative stress, UPR/Nrf2 markers and proinflammatory cytokines levels were associated with the significant increase of the antiapoptotic protein Bcl2. The involvement of NOX in the adaptive response elicited by CLAmix along with its protective effects against the onset of several pathogenic processes triggered by AlCl3, broadens the knowledge of the mechanism underlying the pleiotropic activity of Nrf2 activators and sheds new light on their potential therapeutic use against neurodegenerative disorders.

Metabolic changes in the plasma of mild Alzheimer's disease patients treated with Hachimijiogan

Background: Alzheimer's disease (AD), the most prevalent form of dementia, is a debilitating, progressive neurodegeneration. Amino acids play a wide variety of physiological and pathophysiological roles in the nervous system, and their levels and disorders related to their synthesis have been related to cognitive impairment, the core feature of AD. Our previous multicenter trial showed that hachimijiogan (HJG), a traditional Japanese herbal medicine (Kampo), has an adjuvant effect for Acetylcholine estelase inhibitors (AChEIs) and that it delays the deterioration of the cognitive dysfunction of female patients with mild AD. However, there are aspects of the molecular mechanism(s) by which HJG improves cognitive dysfunction that remain unclear. Objectives: To elucidate through metabolomic analysis the mechanism(s) of HJG for mild AD based on changes in plasma metabolites. Methods: Sixty-seven patients with mild AD were randomly assigned to either an HJG group taking HJG extract 7.5 g/day in addition to AChEI or to a control group treated only with AChEI (HJG:33, Control:34). Blood samples were collected before, 3 months, and 6 months after the first drug administration. Comprehensive metabolomic analyses of plasma samples were done by optimized LC-MS/MS and GC-MS/MS methods. The web-based software MetaboAnalyst 5.0 was used for partial least square-discriminant analysis (PLS-DA) to visualize and compare the dynamics of changes in the concentrations of the identified metabolites. Results: The VIP (Variable Importance in Projection) score of the PLS-DA analysis of female participants revealed a significantly higher increase in plasma metabolite levels after HJG administration for 6 months than was seen in the control group. In univariate analysis, the aspartic acid level of female participants showed a significantly higher increase from baseline after HJG administration for 6 months when compared with the control group. Conclusion: Aspartic acid was a major contributor to the difference between the female HJG and control group participants of this study. Several metabolites were shown to be related to the mechanism of HJG effectiveness for mild AD.

Protective Roles of Hydrogen Sulfide in Alzheimer's Disease and Traumatic Brain Injury

The gaseous signaling molecule hydrogen sulfide (H₂S) critically modulates a plethora of physiological processes across evolutionary boundaries. These include responses to stress and other neuromodulatory effects that are typically dysregulated in aging, disease, and injury. H₂S has a particularly prominent role in modulating neuronal health and survival under both normal and pathologic conditions. Although toxic and even fatal at very high concentrations, emerging evidence has also revealed a pronounced neuroprotective role for lower doses of endogenously generated or exogenously administered H₂S. Unlike traditional neurotransmitters, H₂S is a gas and, therefore, is unable to be stored in vesicles for targeted delivery. Instead, it exerts its physiologic effects through the persulfidation/sulfhydration of target proteins on reactive cysteine residues. Here, we review the latest discoveries on the neuroprotective roles of H₂S in Alzheimer's disease (AD) and traumatic brain injury, which is one the greatest risk factors for AD.

The potential roles of ATF family in the treatment of Alzheimer's disease

Activating transcription factors, ATFs, is a family of transcription factors that activate gene expression and transcription by recognizing and combining the cAMP response element binding proteins (CREB). It is present in various viruses as a cellular gene promoter. ATFs is involved in regulating the mammalian gene expression that is associated with various cell physiological processes. Therefore, ATFs play an important role in maintaining the intracellular homeostasis. ATF2 and ATF3 is mostly involved in mediating stress responses. ATF4 regulates the oxidative metabolism, which is associated with the survival of cells. ATF5 is presumed to regulate apoptosis, and ATF6 is involved in the regulation of endoplasmic reticulum stress (ERS). ATFs is actively studied in oncology. At present, there has been an increasing amount of research on ATFs for the treatment of neurological diseases. Here, we have focused on the different types of ATFs and their association with Alzheimer's disease (AD). The level of expression of different ATFs have a significant difference in AD patients when compared to healthy control. Recent studies have suggested that ATFs are implicated in the pathogenesis of AD, such as neuronal repair, maintenance of synaptic activity, maintenance of cell survival, inhibition of apoptosis, and regulation of stress responses. In this review, the potential role of ATFs for the treatment of AD has been highlighted. In addition, we have systematically reviewed the progress of research on ATFs in AD. This review will provide a basic and innovative understanding on the pathogenesis and treatment of AD.

Crosstalk between endoplasmic reticulum stress response and autophagy in human diseases

Cells activate protective mechanisms to overcome stressful conditions that threaten cellular homeostasis, including imbalances in calcium, redox, and nutrient levels. Endoplasmic reticulum (ER) stress activates an intracellular signaling pathway, known as the unfolded protein response (UPR), to mitigate such circumstances and protect cells. Although ER stress is sometimes a negative regulator of autophagy, UPR induced by ER stress typically activates autophagy, a self-degradative pathway that further supports its cytoprotective role. Sustained activation of ER stress and autophagy is known to trigger cell death and is considered a therapeutic target for certain diseases. However, ER stress-induced autophagy can also lead to treatment resistance in cancer and exacerbation of certain diseases. Since the ER stress response and autophagy affect each other, and the degree of their activation is closely related to various diseases, understanding their relationship is very important. In this review, we summarize the current understanding of two fundamental cellular stress responses, the ER stress response and autophagy, and their crosstalk under pathological conditions to help develop therapies for inflammatory diseases, neurodegenerative disorders, and cancer.

Protein persulfidation: Rewiring the hydrogen sulfide signaling in cell stress response

The past few decades have witnessed significant progress in the discovery of hydrogen sulfide (H₂S) as a ubiquitous gaseous signaling molecule in mammalian physiology, akin to nitric oxide and carbon monoxide. As the third gasotransmitter, H₂S is now known to exert a wide range of physiological and cytoprotective functions in the biological systems. However, endogenous H₂S concentrations are usually low, and its potential biologic mechanisms responsible have not yet been fully clarified. Recently, a growing body of evidence has demonstrated that protein persulfidation, a posttranslational modification of cysteine residues (RSH) to persulfides (RSSH) elicited by H₂S, is a fundamental mechanism of H₂S-mediated signaling pathways. Persulfidation, as a biological switch for protein function, plays an important role in the maintenance of cell homeostasis in response to various internal and external stress stimuli and is also implicated in numerous diseases, such as cardiovascular and neurodegenerative diseases and cancer. In this review, the biological significance of protein persulfidation by H₂S in cell stress response is reviewed providing a framework for understanding the multifaceted roles of H₂S. A mechanism-guided perspective can help open novel avenues for the exploitation of therapeutics based on H₂S-induced persulfidation in the context of diseases.

Saikosaponin D Inducing Apoptosis and Autophagy through the Activation of Endoplasmic Reticulum Stress in Glioblastoma

Saikosaponin D (SSD), a saponin derivative, is extracted from Bupleurum falcatum. It exhibits an inhibitory effect on a number of tumor cells and is relatively safe when used at therapeutic doses. However, its effects on glioblastoma multiforme (GBM) have not been fully explored. This study is aimed at investigating the cytotoxic effects of SSD in GBM cell lines. SSD induces apoptosis and autophagy by activating endoplasmic reticulum (ER) stress in GBM cells. GBM cell proliferation activity and morphology were observed using the Cell Counting Kit-8 assay and hematoxylin and eosin staining. Hoechst 33258 fluorescence staining and flow cytometry were performed to assess apoptosis. Western blotting and immunocytochemical staining were used to detect protein expression and distribution. SSD significantly inhibited the proliferation of RG-2, U87-MG, and U251 cells in a dose-dependent manner, and the proportion of apoptotic cells increased significantly. Additionally, the expressions of ER-, apoptosis-, and autophagy-related proteins were significantly upregulated and distributed in the cytoplasm and nucleus. Therefore, SSD may be considered a novel treatment option for GBM. This study demonstrated the anti-GBM effect of SSD from the perspectives of cell apoptosis and autophagy.