Heat shock preconditioning protects against ER stress-induced apoptosis through the regulation of the BH3-only protein BIM

pH-Assisted multichannel heat shock monitoring in the endoplasmic reticulum with a pyridinium fluorophore

Heat shock is a global health concern as it causes permanent damage to living cells and has a relatively high mortality rate. Therefore, diagnostic tools that facilitate a better understanding of heat shock damage and the defense mechanism at the sub-cellular level are of great importance. In this report, we have demonstrated the use of a pyridinium-based fluorescent molecule, PM-ER-OH, as a 'multichannel' imaging probe to monitor the pH change associated with a heat shock in the endoplasmic reticulum. Among the three pyridinium derivatives synthesized, PM-ER-OH was chosen for study due to its excellent biocompatibility, good localization in the endoplasmic reticulum, and intracellular pH response signaled by a yellow fluorescence (λ max = 556 nm) at acidic pH and a far red fluorescence (λ max = 660 nm) at basic pH. By changing the excitation wavelength, we could modulate the fluorescence signal in 'turn-ON', single excitation ratiometric and 'turn-OFF' modes, making the fluorophore a 'multichannel' probe for both ex vitro and in vitro pH monitoring in the endoplasmic reticulum. The probe could efficiently monitor the pH change when heat shock was applied to cells either directly or in a pre-heated manner, which gives insight on cellular acidification caused by heat stress.

Endoplasmic Reticulum Stress in Hypertension and Salt Sensitivity of Blood Pressure

PURPOSE OF REVIEW

Hypertension is a principal risk factor for cardiovascular morbidity and mortality, with its severity exacerbated by high sodium intake, particularly in individuals with salt-sensitive blood pressure. However, the mechanisms underlying hypertension and salt sensitivity are only partly understood. Herein, we review potential interactions in hypertension pathophysiology involving the immune system, endoplasmic reticulum (ER) stress, the unfolded protein response (UPR), and proteostasis pathways; identify knowledge gaps; and discuss future directions.

RECENT FINDINGS

Recent advancements by our research group and others reveal interactions within and between adaptive and innate immune responses in hypertension pathophysiology. The salt-immune-hypertension axis is further supported by the discovery of the role of dendritic cells in hypertension, marked by isolevuglandin (IsoLG) formation. Alongside these broadened understandings of immune-mediated salt sensitivity, the contributions of T cells to hypertension have been recently challenged by groups whose findings did not support increased resistance of Rag-1-deficient mice to Ang II infusion. Hypertension has also been linked to ER stress and the UPR. Notably, a holistic approach is needed because the UPR engages in crosstalk with autophagy, the ubiquitin proteasome, and other proteostasis pathways, that may all involve hypertension. There is a critical need for studies to establish cause and effect relationships between ER stress and the UPR in hypertension pathophysiology in humans and to determine whether the immune system and ER stress function mainly to exacerbate or initiate hypertension and target organ injury. This review of recent studies proposes new avenues for future research for targeted therapeutic interventions.

Impact of Reactive Sulfur Species on Entamoeba histolytica: Modulating Viability, Motility, and Biofilm Degradation Capacity

Reactive sulfur species (RSS) like hydrogen sulfide (H2S) and cysteine persulfide (Cys-SSH) emerged as key signaling molecules with diverse physiological roles in the body, depending on their concentration and the cellular environment. While it is known that H2S and Cys-SSH are produced by both colonocytes and by the gut microbiota through sulfur metabolism, it remains unknown how these RSS affect amebiasis caused by Entamoeba histolytica, a parasitic protozoan that can be present in the human gastrointestinal tract. This study investigates H2S and Cys-SSH's impact on E. histolytica physiology and explores potential therapeutic implications. Exposing trophozoites to the H2S donor, sodium sulfide (Na2S), or to Cys-SSH led to rapid cytotoxicity. A proteomic analysis of Cys-SSH-challenged trophozoites resulted in the identification of >500 S-sulfurated proteins, which are involved in diverse cellular processes. Functional assessments revealed inhibited protein synthesis, altered cytoskeletal dynamics, and reduced motility in trophozoites treated with Cys-SSH. Notably, cysteine proteases (CPs) were significantly inhibited by S-sulfuration, affecting their bacterial biofilm degradation capacity. Immunofluorescence microscopy confirmed alterations in actin dynamics, corroborating the proteomic findings. Thus, our study reveals how RSS perturbs critical cellular functions in E. histolytica, potentially influencing its pathogenicity and interactions within the gut microbiota. Understanding these molecular mechanisms offers novel insights into amebiasis pathogenesis and unveils potential therapeutic avenues targeting RSS-mediated modifications in parasitic infections.

A Drosophila screen identifies a role for histone methylation in ER stress preconditioning

Stress preconditioning occurs when transient, sublethal stress events impact an organism's ability to counter future stresses. Although preconditioning effects are often noted in the literature, very little is known about the underlying mechanisms. To model preconditioning, we exposed a panel of genetically diverse Drosophila melanogaster to a sublethal heat shock and measured how well the flies survived subsequent exposure to endoplasmic reticulum (ER) stress. The impact of preconditioning varied with genetic background, ranging from dying half as fast to 4 and a half times faster with preconditioning compared to no preconditioning. Subsequent association and transcriptional analyses revealed that histone methylation, and transcriptional regulation are both candidate preconditioning modifier pathways. Strikingly, almost all subunits (7/8) in the Set1/COMPASS complex were identified as candidate modifiers of preconditioning. Functional analysis of Set1 knockdown flies demonstrated that loss of Set1 led to the transcriptional dysregulation of canonical ER stress genes during preconditioning. Based on these analyses, we propose a preconditioning model in which Set1 helps to establish an interim transcriptional "memory" of previous stress events, resulting in a preconditioned response to subsequent stress.

PP4R1 accelerates the malignant progression of NSCLC via up-regulating HSPA6 expression and HSPA6-mediated ER stress

Protein phosphatase 4 (PP4) plays an indispensable regulatory part in the development and malignant progression of multifarious tumors. Nevertheless, the function of protein phosphatase 4 regulatory subunit 1 (PP4R1), a vital regulatory subunit of PP4, in tumors especially in lung cancer remains blurred. Therefore, this study aimed to investigate the function and mechanism of PP4R1 in the development of non-small cell lung cancer (NSCLC). We analyzed the clinical correlation of PP4R1 based on the TCGA database by UALCAN (https://ualcan.path.uab.edu/index.html) and found that hyper-expression of PP4R1 mRNA was related to the severe prognosis in NSCLC. The subsequent cellular experiments confirmed that the proliferation, colony growth, migration as well as invasion of H1299 and HCC827 were significantly enhanced after PP4R1 overexpression treatment in vitro. Results from animal experiments pointed out that tumors exhibited stronger growth and lung metastatic capacities due to the overexpression of PP4R1. The bioinformatics analysis, including RNA-seq, showed us that PP4R1 significantly promoted the expression of several HSP70 family member genes, with a particularly marked increase in HSPA6, and the enrichment analyses illustrated that the differentially expressed genes (DEGs) were enriched in those pathways related to protein folding. More importantly, the overexpression of HSPA6 resulted in the same malignant progression of NSCLC as PP4R1 overexpression, and both concomitant with the activation of endoplasmic reticulum (ER) stress. In aggregate, PP4R1 contributed to the malignant progression of NSCLC via up-regulating HSPA6 expression and then activating ER stress.

A Drosophila screen identifies a role for histone methylation in ER stress preconditioning

Stress preconditioning occurs when transient, sublethal stress events impact an organism's ability to counter future stresses. Although preconditioning effects are often noted in the literature, very little is known about the underlying mechanisms. To model preconditioning, we exposed a panel of genetically diverse Drosophila melanogaster to a sublethal heat shock and measured how well the flies survived subsequent exposure to endoplasmic reticulum (ER) stress. The impact of preconditioning varied with genetic background, ranging from dying half as fast to four and a half times faster with preconditioning compared to no preconditioning. Subsequent association and transcriptional analyses revealed that histone methylation, transcriptional regulation, and immune status are all candidate preconditioning modifier pathways. Strikingly, almost all subunits (7/8) in the Set1/COMPASS complex were identified as candidate modifiers of preconditioning. Functional analysis of Set1 knockdown flies demonstrated that loss of Set1 led to the transcriptional dysregulation of canonical ER stress genes during preconditioning. Based on these analyses, we propose a model of preconditioning in which Set1 helps to establish an interim transcriptional 'memory' of previous stress events, resulting in a preconditioned response to subsequent stress.

Potential application of heat shock proteins as therapeutic targets in Parkinson's disease

Parkinson's disease (PD) is a common chronic neurodegenerative disease, and the heat shock proteins (HSPs) are proved to be of great value for PD. In addition, HSPs can maintain protein homeostasis, degrade and inhibit protein aggregation by properly folding and activating intracellular proteins in PD. This study mainly summarizes the important roles of HSPs in PD and explores their feasibility as targets. We introduced the structural and functional characteristics of HSPs and the physiological functions of HSPs in PD. HSPs can protect neurons from damage by degrading aggregates with three mechanisms, including the aggregation and removing α-Synuclein (α-Syn) aggregates, promotion the autophagy of abnormal proteins, and inhibition the apoptosis of degenerated neurons. This study underscores the importance of HSPs as targets in PD and helps to expand new mechanisms in PD treatment strategies.

Comparative Transcriptomic and Molecular Pathway Analyses of HL-CZ Human Pro-Monocytic Cells Expressing SARS-CoV-2 Spike S1, S2, NP, NSP15 and NSP16 Genes

The ongoing COVID-19 pandemic is a clear and present threat to global public health. Research into how the causative SARS-CoV-2 virus together with its individual constituent genes and proteins interact with target host cells can facilitate the development of improved strategies to manage the acute and long-term complications of COVID-19. In this study, to better understand the biological roles of critical SARS-CoV-2 proteins, we determined and compared the host transcriptomic responses of the HL-CZ human pro-monocytic cell line upon transfection with key viral genes encoding the spike S1 subunit, S2 subunit, nucleocapsid protein (NP), NSP15 (endoribonuclease), and NSP16 (2′-O-ribose-methyltransferase). RNA sequencing followed by gene set enrichment analysis and other bioinformatics tools revealed that host genes associated with topologically incorrect protein, virus receptor activity, heat shock protein binding, endoplasmic reticulum stress, antigen processing and presentation were up-regulated in the presence of viral spike S1 expression. With spike S2 expression, pro-monocytic genes associated with the interferon-gamma-mediated signaling pathway, regulation of phosphatidylinositol 3-kinase activity, adipocytokine signaling pathway, and insulin signaling pathway were down-regulated, whereas those associated with cytokine-mediated signaling were up-regulated. The expression of NSP15 induced the up-regulation of genes associated with neutrophil degranulation, neutrophil-mediated immunity, oxidative phosphorylation, prion disease, and pathways of neurodegeneration. The expression of NSP16 resulted in the down-regulation of genes associated with S-adenosylmethionine-dependent methyltransferase activity. The expression of NP down-regulated genes associated with positive regulation of neurogenesis, nervous system development, and heart development. Taken together, the complex transcriptomic alterations arising from these viral-host gene interactions offer useful insights into host genes and their pathways that potentially contribute to SARS-CoV-2 pathogenesis.

SARM1 promotes neuroinflammation and inhibits neural regeneration after spinal cord injury through NF-κB signaling

Axonal degeneration is a common pathological feature in many acute and chronic neurological diseases such as spinal cord injury (SCI). SARM1 (sterile alpha and TIR motif-containing 1), the fifth TLR (Toll-like receptor) adaptor, has diverse functions in the immune and nervous systems, and recently has been identified as a key mediator of Wallerian degeneration (WD). However, the detailed functions of SARM1 after SCI still remain unclear.

Methods: Modified Allen's method was used to establish a contusion model of SCI in mice. Furthermore, to address the function of SARM1 after SCI, conditional knockout (CKO) mice in the central nervous system (CNS), SARM1^Nestin-CKO mice, and SARM1^GFAP-CKO mice were successfully generated by Nestin-Cre and GFAP-Cre transgenic mice crossed with SARM1^flox/flox mice, respectively. Immunostaining, Hematoxylin-Eosin (HE) staining, Nissl staining and behavioral test assays such as footprint and Basso Mouse Scale (BMS) scoring were used to examine the roles of SARM1 pathway in SCI based on these conditional knockout mice. Drugs such as FK866, an inhibitor of SARM1, and apoptozole, an inhibitor of heat shock protein 70 (HSP70), were used to further explore the molecular mechanism of SARM1 in neural regeneration after SCI.

Results: We found that SARM1 was upregulated in neurons and astrocytes at early stage after SCI. SARM1^Nestin-CKO and SARM1^GFAP-CKO mice displayed normal development of the spinal cords and motor function. Interestingly, conditional deletion of SARM1 in neurons and astrocytes promoted the functional recovery of behavior performance after SCI. Mechanistically, conditional deletion of SARM1 in neurons and astrocytes promoted neuronal regeneration at intermediate phase after SCI, and reduced neuroinflammation at SCI early phase through downregulation of NF-κB signaling after SCI, which may be due to upregulation of HSP70. Finally, FK866, an inhibitor of SARM1, reduced the neuroinflammation and promoted the neuronal regeneration after SCI.

Conclusion: Our results indicate that SARM1-mediated prodegenerative pathway and neuroinflammation promotes the pathological progress of SCI and anti-SARM1 therapeutics are viable and promising approaches for preserving neuronal function after SCI.

Heat Shock Proteins and Autophagy Pathways in Neuroprotection: from Molecular Bases to Pharmacological Interventions

Neurodegenerative diseases (NDDs) such as Alzheimer's disease, Parkinson's disease and Huntington's disease (HD), amyotrophic lateral sclerosis, and prion diseases are all characterized by the accumulation of protein aggregates (amyloids) into inclusions and/or plaques. The ubiquitous presence of amyloids in NDDs suggests the involvement of disturbed protein homeostasis (proteostasis) in the underlying pathomechanisms. This review summarizes specific mechanisms that maintain proteostasis, including molecular chaperons, the ubiquitin-proteasome system (UPS), endoplasmic reticulum associated degradation (ERAD), and different autophagic pathways (chaperon mediated-, micro-, and macro-autophagy). The role of heat shock proteins (Hsps) in cellular quality control and degradation of pathogenic proteins is reviewed. Finally, putative therapeutic strategies for efficient removal of cytotoxic proteins from neurons and design of new therapeutic targets against the progression of NDDs are discussed.

Anastasis and the ER stress response: Solving the paradox of the unfolded protein response in cancer

In recent years, studies have suggested a novel pathway for cell survival, which faces scientific skepticism and interest in its concept of cell 'resurrection' - that is, the anastasis of cells at late-stage apoptosis. While biomarkers have been discovered, many of these are related to the endoplasmic reticulum (ER) stress response - acting also to promote cell survival in the presence of perturbation. The promises of anastasis, if accepted, will greatly impact translational medicine especially in the treatment of cancer, since apoptosis is generally irreversible in the late stages, and chemotherapy is performed to maximize tumor death and minimize off-target effects. As with all new concepts, there is a need to demarcate anastasis from a well-studied survival mechanism - the ER stress response - if the concept is to progress any further. In this article, it is proposed that anastasis and the ER stress response are one and the same mechanism, demarcated only by the presence of persistent stress. Further, anastasis solves the paradox of the unfolded protein response (UPR) in cancer by providing rationale in C/EBP homologous protein (CHOP)-induced tumor survival, such that CHOP-mediated apoptosis initiates genetic alterations in favor of its survival. After which, the cell regenerates through an enhanced ER stress response. Hence, anastatic cell recovery is the ER stress response post-apoptosis.

HSPB1 facilitates ERK-mediated phosphorylation and degradation of BIM to attenuate endoplasmic reticulum stress-induced apoptosis

BIM, a pro-apoptotic BH3-only protein, is a key regulator of the intrinsic (or mitochondrial) apoptosis pathway. Here, we show that BIM induction by endoplasmic reticulum (ER) stress is suppressed in rat PC12 cells overexpressing heat shock protein B1 (HSPB1 or HSP27) and that this is due to enhanced proteasomal degradation of BIM. HSPB1 and BIM form a complex that immunoprecipitates with p-ERK1/2. We found that HSPB1-mediated proteasomal degradation of BIM is dependent on MEK-ERK signaling. Other studies have shown that several missense mutations in HSPB1 cause the peripheral neuropathy, Charcot-Marie-Tooth (CMT) disease, which is associated with nerve degeneration. Here we show that cells overexpressing CMT-related HSPB1 mutants exhibited increased susceptibility to ER stress-induced cell death and high levels of BIM. These findings identify a novel function for HSPB1 as a negative regulator of BIM protein stability leading to protection against ER stress-induced apoptosis, a function that is absent in CMT-associated HSPB1 mutants.

Serial Changes of Heat Shock Protein 70 and Interleukin-8 in Burn Blister Fluid

Background

It has been reported that heat shock protein 70 (HSP70) and interleukin-8 (IL-8) play an important role in cells during the wound healing process. However, there has been no report on the effect of HSP70 and IL-8 on the blisters of burn patients.

Objective

This study aimed to evaluate the serial quantitative changes of HSP70 and IL-8 in burn blisters.

Methods

Twenty-five burn patients were included, for a total of 36 cases: twenty cases on the first day, six cases on the second, five cases on the third, three cases on the fourth, and two cases on the fifth. A correlation analysis was performed to determine the relationship between the concentration of HSP70 and IL-8 and the length of the treatment period.

Results

The HSP70 concentration was the highest on the first day, after which it decreased down to near zero. Most HSP70 was generated during the first 12 hours after the burn accident. There was no correlation between the concentration of HSP70 on the first day and the length of the treatment period. No measurable concentration of IL-8 was detected before 5 hours, but the concentration started to increase after 11 hours. The peak value was measured on the fourth day.

Conclusion

While HSP70 increased in the first few hours and decreased afterwards, IL-8 was produced after 11 hours and increased afterward in burn blister fluid. These findings provide new evidence on serial changes of inflammatory mediators in burn blister fluid.

Leishmania infantum Induces Mild Unfolded Protein Response in Infected Macrophages

The Leishmaniases are a group of parasitic diseases caused by protozoa of the Leishmania genus affecting both humans and other vertebrates. Leishmania is an intracellular pathogen able to confer resistance to apoptosis in the early phase of macrophages infection by activation of host PI3K/Akt pathway and inhibition of caspase-3 activation. Intracellular pathogens hijack organelles such as ER to facilitate survival and replication, thus eliciting ER stress and activating/modulating the unfolded protein response (UPR) in the host cell. The UPR is aimed to mitigate ER stress, thereby promoting cell survival. However, prolonged ER stress will activate the apoptotic pathway. The aim of this study was to investigate the ER stress response in Leishmania-infected macrophages to gain insights about the mechanisms underlying the apoptosis resistance in parasitized cells. Macrophages differentiated from human monocytic cell lines (U937 and THP-1) and murine primary macrophages were infected with Leishmania infantum MHOM/TN/80/IPT1 (WHO international reference strain). Several ER stress/autophagy expression markers, as well as cell survival/apoptosis markers (phospho-Akt and cleaved caspase-3) were evaluated by qPCR and/or by western blotting. As ER stress positive control, cells were treated with tunicamycin or dithiothreitol (DTT). The gene expression analyses showed a mild but significant induction of the ER stress/autophagy markers. The western blot analyses revealed that the Leishmania infection induced Akt phosphorylation and significantly inhibited the induction of caspase-3 cleavage, eIF2α phosphorylation and DDIT3/CHOP expression in tunicamycin and DTT treated cells. The mild but significant increase in ER stress expression markers and the delay/attenuation of the effects of ER stress inducers in infected cells support the hypothesis that L. infantum could promote survival of host cells by inducing a mild ER stress response. The host ER stress response could be not only a common pathogenic mechanism among Leishmania species but also a target for development of new drugs.

The antioxidant transcription factor Nrf2 contributes to the protective effect of mild thermotolerance (40°C) against heat shock-induced apoptosis

The exposure of cells to low doses of stress induces adaptive survival responses that protect cells against subsequent exposure to toxic stress. The ability of cells to resist subsequent toxic stress following exposure to low dose heat stress at 40°C is known as mild thermotolerance. Mild thermotolerance involves increased expression of heat shock proteins and antioxidants, but the initiating factors in this response are not understood. This study aims to understand the role of the Nrf2 antioxidant pathway in acquisition of mild thermotolerance at 40°C, and secondly, whether the Nrf2 pathway could be involved in the protective effect of thermotolerance against heat-shock (42°C)-induced apoptosis. During cell preconditioning at 40°C, protein expression of the Nrf2 transcription factor increased after 15-60min. In addition, levels of the Nrf2 targets MnSOD, catalase, heme oxygenase-1, glutamate cysteine ligase and Hsp70 increased at 40°C. Levels of these Nrf2 targets were enhanced by Nrf2 activator oltipraz and decreased by shRNA targeting Nrf2. Levels of pro-oxidants increased after 30-60min at 40°C. Pro-oxidant levels were decreased by oltipraz and increased by knockdown of Nrf2. Increased Nrf2 expression and catalase activity at 40°C were inhibited by the antioxidant PEG-catalase and by p53 inhibitor pifithrin-α. These results suggest that mild thermotolerance (40°C) increases cellular pro-oxidant levels, which in turn activate Nrf2 and its target genes. Moreover, Nrf2 contributes to the protective effect of thermotolerance against heat-shock (42°C)-induced apoptosis, because Nrf2 activation by oltipraz enhanced thermotolerance, whereas Nrf2 knockdown partly reversed thermotolerance. Improved knowledge about the different protective mechanisms that mild thermotolerance can activate is crucial for the potential use of this adaptive survival response to treat stress-related diseases.

Effect of cortisol on bovine oocyte maturation and embryo development in vitro

Glucocorticoids (GCs) are important mediators of key cellular events. Herein, we investigated the effect of adding cortisol to the IVM medium on the acquisition of developmental competency in bovine oocytes. Cortisol (0.01, 0.1, or 1 μg/mL) had no effect on cleavage rates or cell numbers of resulting blastocysts; however, supplementation with 0.1 μg/mL during IVM increased blastocyst rates of in vitro-fertilized bovine oocytes as compared to untreated controls (41 ± 10% vs. 21 ± 1.2%, P < 0.05, respectively). This concentration was chosen to assess changes in the relative expression of potential GC target genes. Oocytes matured in the presence of cortisol and their corresponding cumulus cells did not show changes in expression for genes analyzed as compared to untreated controls. Notably, blastocysts from oocytes matured in cortisol-supplemented medium expressed higher relative levels of glucose transporter 1 (GLUT1), fatty acid synthase (FASN), and heat shock protein 70 (HSP70). This study supports a role for cortisol in the acquisition of bovine oocyte competence. This is evidenced by increased blastocyst development rates and presumably related to elevated embryonic transcripts with roles in glucose and lipid metabolism, as well as the cellular response to stress.

Targeting Mitochondria and Reactive Oxygen Species-Driven Pathogenesis in Diabetic Nephropathy

Diabetic kidney disease is one of the major microvascular complications of both type 1 and type 2 diabetes mellitus. Approximately 30% of patients with diabetes experience renal complications. Current clinical therapies can only mitigate the symptoms and delay the progression to end-stage renal disease, but not prevent or reverse it. Oxidative stress is an important player in the pathogenesis of diabetic nephropathy. The activity of reactive oxygen and nitrogen species (ROS/NS), which are by-products of the diabetic milieu, has been found to correlate with pathological changes observed in the diabetic kidney. However, many clinical studies have failed to establish that antioxidant therapy is renoprotective. The discovery that increased ROS/NS activity is linked to mitochondrial dysfunction, endoplasmic reticulum stress, inflammation, cellular senescence, and cell death calls for a refined approach to antioxidant therapy. It is becoming clear that mitochondria play a key role in the generation of ROS/NS and their consequences on the cellular pathways involved in apoptotic cell death in the diabetic kidney. Oxidative stress has also been associated with necrosis via induction of mitochondrial permeability transition. This review highlights the importance of mitochondria in regulating redox balance, modulating cellular responses to oxidative stress, and influencing cell death pathways in diabetic kidney disease. ROS/NS-mediated cellular dysfunction corresponds with progressive disease in the diabetic kidney, and consequently represents an important clinical target. Based on this consideration, this review also examines current therapeutic interventions to prevent ROS/NS-derived injury in the diabetic kidney. These interventions, mainly aimed at reducing or preventing mitochondrial-generated oxidative stress, improving mitochondrial antioxidant defense, and maintaining mitochondrial integrity, may deliver alternative approaches to halt or prevent diabetic kidney disease.