Aggregated and Hyperstable Damage-Associated Molecular Patterns Are Released During ER Stress to Modulate Immune Function

Antigen presentation plays positive roles in the regenerative response to cardiac injury in zebrafish

In contrast to adult mammals, adult zebrafish can fully regenerate injured cardiac tissue, and this regeneration process requires an adequate and tightly controlled immune response. However, which components of the immune response are required during regeneration is unclear. Here, we report positive roles for the antigen presentation-adaptive immunity axis during zebrafish cardiac regeneration. We find that following the initial innate immune response, activated endocardial cells (EdCs), as well as immune cells, start expressing antigen presentation genes. We also observe that T helper cells, a.k.a. Cd4+ T cells, lie in close physical proximity to these antigen-presenting EdCs. We targeted Major Histocompatibility Complex (MHC) class II antigen presentation by generating cd74a; cd74b mutants, which display a defective immune response. In these mutants, Cd4+ T cells and activated EdCs fail to efficiently populate the injured tissue and EdC proliferation is significantly decreased. cd74a; cd74b mutants exhibit additional defects in cardiac regeneration including reduced cardiomyocyte dedifferentiation and proliferation. Notably, Cd74 also becomes activated in neonatal mouse EdCs following cardiac injury. Altogether, these findings point to positive roles for antigen presentation during cardiac regeneration, potentially involving interactions between activated EdCs, classical antigen-presenting cells, and Cd4+ T cells.

Metformin-induced activation of Ca2+ signaling prevents immune infiltration/pathology in Sjogren's syndrome-prone mouse models

Immune cell infiltration and glandular dysfunction are the hallmarks of autoimmune diseases such as primary Sjogren's syndrome (pSS), however, the mechanism(s) is unknown. Our data show that metformin-treatment induces Ca2+ signaling that restores saliva secretion and prevents immune cell infiltration in the salivary glands of IL14α-transgenic mice (IL14α), which is a model for pSS. Mechanistically, we show that loss of Ca2+ signaling is a major contributing factor, which is restored by metformin treatment, in IL14α mice. Furthermore, the loss of Ca2+ signaling leads to ER stress in salivary glands. Finally, restoration of metformin-induced Ca2+ signaling inhibited the release of alarmins and prevented the activation of ER stress that was essential for immune cell infiltration. These results suggest that loss of metformin-mediated activation of Ca2+ signaling prevents ER stress, which inhibited the release of alarmins that induces immune cell infiltration leading to salivary gland dysfunction observed in pSS.

Immune regulation in neurovascular units after traumatic brain injury

Traumatic brain injury (TBI) is a major cause of death and disability worldwide. Survivors may experience movement disorders, memory loss, and cognitive deficits. However, there is a lack of understanding of the pathophysiology of TBI-mediated neuroinflammation and neurodegeneration. The immune regulation process of TBI involves changes in the peripheral and central nervous system (CNS) immunity, and intracranial blood vessels are essential communication centers. The neurovascular unit (NVU) is responsible for coupling blood flow with brain activity, and comprises endothelial cells, pericytes, astrocyte end-feet, and vast regulatory nerve terminals. A stable NVU is the basis for normal brain function. The concept of the NVU emphasizes that cell-cell interactions between different types of cells are essential for maintaining brain homeostasis. Previous studies have explored the effects of immune system changes after TBI. The NVU can help us further understand the immune regulation process. Herein, we enumerate the paradoxes of primary immune activation and chronic immunosuppression. We describe the changes in immune cells, cytokines/chemokines, and neuroinflammation after TBI. The post-immunomodulatory changes in NVU components are discussed, and research exploring immune changes in the NVU pattern is also described. Finally, we summarize immune regulation therapies and drugs after TBI. Therapies and drugs that focus on immune regulation have shown great potential for neuroprotection. These findings will help us further understand the pathological processes after TBI.

Transmissible ER stress between macrophages and tumor cells configures tumor microenvironment

Endoplasmic reticulum (ER) stress initiates the unfolded protein response (UPR) and is decisive for tumor cell growth and tumor microenvironment (TME) maintenance. Tumor cells persistently undergo ER stress and could transmit it to the neighboring macrophages and surroundings. Tumor infiltrating macrophages can also adapt to the microenvironment variations to fulfill their highly energy-demanding and biological functions via ER stress. However, whether the different macrophage populations differentially sense ER stress and transmit ER stress to surrounding tumor cells has not yet been elucidated. Here, we aimed to investigate the role of transmissible ER stress, a novel regulator of intercellular communication in the TME. Murine bone marrow-derived macrophage (BMDM) can be polarized toward distinct functional endpoints termed classical (M1) and alternative (M2) activation, and their polarization status has been shown to be tightly correlated with their functional significance. We showed that tumor cells could receive the transmissible ER stress from two differentially polarized macrophage populations with different extent of ER stress activation. The proinflammatory M1-like macrophages respond to ER stress with less extent, however they could transmit more ER stress to tumor cells. Moreover, by analyzing the secreted components of two ER-stressed macrophage populations, we identified certain damage-associated molecular patterns (DAMPs), including S100A8 and S100A9, which are dominantly secreted by M1-like macrophages could lead to significant recipient tumor cells death in synergy with transferred ER stress.

Mitochondrial damage-associated molecular patterns trigger arginase-dependent lymphocyte immunoregulation

Tissue damage leads to loss of cellular and mitochondrial membrane integrity and release of damage-associated molecular patterns, including those of mitochondrial origin (mitoDAMPs). Here, we describe the lymphocyte response to mitoDAMPs. Using primary cells from mice and human donors, we demonstrate that natural killer (NK) cells and T cells adopt regulatory phenotypes and functions in response to mitoDAMPs. NK cell-mediated cytotoxicity, interferon gamma (IFN-γ) production, T cell proliferation, and in vivo anti-viral T cell activation are all interrupted in the presence of mitoDAMPs or mitoDAMP-rich irradiated cells in in vitro and in vivo assays. Mass spectrometry analysis of mitoDAMPs demonstrates that arginase and products of its enzymatic activity are prevalent in mitoDAMP preparations. Functional validation by arginase inhibition and/or arginine add-back shows that arginine depletion is responsible for the alteration in immunologic polarity. We conclude that lymphocyte responses to mitoDAMPs reflect a highly conserved mechanism that regulates inflammation in response to tissue injury.

Artesunate Restrains Maturation of Dendritic Cells and Ameliorates Heart Transplantation-Induced Acute Rejection in Mice through the PERK/ATF4/CHOP Signaling Pathway

Background

Heart transplantation (HT) is the only effective treatment for end-stage heart failure because it can effectively improve the survival rate and quality of life of patients with heart failure. Artesunate (ART) is an artemisinin derivative, with good water solubility and higher oral bioavailability. The main aim of this study was to determine the role of ART in HT mice.

Methods

In animal experiments, mice were divided into the control group, HT group, low ART+HT group, and high ART+HT group. Next, inflammatory cell infiltration, oxidative stress injury, and myocardial cell apoptosis were determined in heart tissue. The proportion of multiple lymphocytes in spleen and lymph nodes was then determined using flow cytometry. In addition, cell experiments were conducted to determine the changes in expression of surface maturation markers of BMDC and changes in intracellular reactive oxygen species after LPS stimulation. Finally, western blot analysis was performed to determine the levels of endoplasmic reticulum stress-related proteins (CHOP/ATF4/PERK).

Results

The survival time of mice in the ART treatment group was significantly prolonged and was positively correlated with the dose. In animal experiments, ART significantly reduced inflammatory cell infiltration in heart tissue and the proportion of CD4+CD8+ T cells in spleens and lymph nodes. Moreover, ART treatment lowered the 8-OHdg in hearts and myocardial apoptosis. In cell experiments, ART treatment slowed down the development and maturation of BMDCs by inhibiting the expression of endoplasmic reticulum stress-related proteins. Furthermore, the treatment alleviated the oxidative stress damage of BMDCs.

Conclusion

ART can inhibit maturation of dendritic cells through the endoplasmic reticulum stress signaling pathway, thereby alleviating acute rejection in mice after heart transplantation.

The Emerging Role of the Innate Immune Response in Idiosyncratic Drug Reactions

Idiosyncratic drug reactions (IDRs) range from relatively common, mild reactions to rarer, potentially life-threatening adverse effects that pose significant risks to both human health and successful drug discovery. Most frequently, IDRs target the liver, skin, and blood or bone marrow. Clinical data indicate that most IDRs are mediated by an adaptive immune response against drug-modified proteins, formed when chemically reactive species of a drug bind to self-proteins, making them appear foreign to the immune system. Although much emphasis has been placed on characterizing the clinical presentation of IDRs and noting implicated drugs, limited research has focused on the mechanisms preceding the manifestations of these severe responses. Therefore, we propose that to address the knowledge gap between drug administration and onset of a severe IDR, more research is required to understand IDR-initiating mechanisms; namely, the role of the innate immune response. In this review, we outline the immune processes involved from neoantigen formation to the result of the formation of the immunologic synapse and suggest that this framework be applied to IDR research. Using four drugs associated with severe IDRs as examples (amoxicillin, amodiaquine, clozapine, and nevirapine), we also summarize clinical and animal model data that are supportive of an early innate immune response. Finally, we discuss how understanding the early steps in innate immune activation in the development of an adaptive IDR will be fundamental in risk assessment during drug development. SIGNIFICANCE STATEMENT: Although there is some understanding that certain adaptive immune mechanisms are involved in the development of idiosyncratic drug reactions, the early phase of these immune responses remains largely uncharacterized. The presented framework refocuses the investigation of IDR pathogenesis from severe clinical manifestations to the initiating innate immune mechanisms that, in contrast, may be quite mild or clinically silent. A comprehensive understanding of these early influences on IDR onset is crucial for accurate risk prediction, IDR prevention, and therapeutic intervention.

Damage-Associated Molecular Patterns and the Systemic Immune Consequences of Severe Thermal Injury

Thermal injury is often associated with a proinflammatory state resulting in serious complications. After a burn, the innate immune system is activated with subsequent immune cell infiltration and cytokine production. Although the innate immune response is typically beneficial, an excessive activation leads to cytokine storms, multiple organ failure, and even death. This overwhelming immune response is regulated by damage-associated molecular patterns (DAMPs). DAMPs are endogenous molecules that are actively secreted by immune cells or passively released by dead or dying cells that can bind to pathogen recognition receptors in immune and nonimmune cells. Recent studies involving animal models along with human studies have drawn great attention to the possible pathological role of DAMPs as an immune consequence of thermal injury. In this review, we outline DAMPs and their function in thermal injury, shedding light on the mechanism of sterile inflammation during tissue injury and identifying new immune targets for treating thermal injury.

[Thermo-chemotherapy enhances the immunogenicity of oral squamous cell carcinoma cells by inducing the expression of damage-associated molecular patterns]

OBJECTIVE

To investigate whether hyperthermia, chemotherapy and thermo-chemotherapy could trigger the expression of damage-associated molecular patterns (DAMPs).

METHODS

The optimal working concentration of pingyangmycin (PYM) was detected by CCK-8 assay, and temperatures of 39, 42, and 45 ℃ were applied to the oral squamous cell carcinoma CAL27, SCC-15, and Tca8113 cell lines. The effects of different treatments on the apoptosis, calreticulin (CRT) membrane expression and high-mobility group box 1 (HMGB1) secretion of the cells were detected by using Annexin V/propidium iodide (PI), flow cytometry and enzyme-linked immunosorbent assay (ELISA) assay. SPSS 20.0 software was used for statistical analysis.

RESULTS

Both hyperthermia and chemotherapy could increase the membrane expression of CRT and the secretion of HMGB1, and furthermore, thermo-chemotherapy group showed significantly increased in apoptosis, CRT membrane expression rate and HMGB1 secretion compared with chemotherapy group, and the difference was statistically significant (P<0.05).

CONCLUSIONS

Hyperthermia, chemotherapy and thermo-chemotherapy could induce oral squamous cell carcinoma cells succumb to death, and at the same time, they can effectively induce the membrane expression of CRT, and promote the secretion of HMGB1. Moreover, thermo-chemotherapy is significantly better than that of chemotherapy alone in the induction of cell apoptosis and DAMPs expression.

Danger signals in liver injury and restoration of homeostasis

Damage-associated molecular patterns are signalling molecules involved in inflammatory responses and restoration of homeostasis. Chronic release of these molecules can also promote inflammation in the context of liver disease. Herein, we provide a comprehensive summary of the role of damage-associated molecular patterns as danger signals in liver injury. We consider the role of reactive oxygen species and reactive nitrogen species as inducers of damage-associated molecular patterns, as well as how specific damage-associated molecular patterns participate in the pathogenesis of chronic liver diseases such as alcohol-related liver disease, non-alcoholic steatohepatitis, liver fibrosis and liver cancer. In addition, we discuss the role of damage-associated molecular patterns in ischaemia reperfusion injury and liver transplantation and highlight current studies in which blockade of specific damage-associated molecular patterns has proven beneficial in humans and mice.

Circulating miRNAs Associated With ER Stress and Organ Damage in a Preclinical Model of Trauma Hemorrhagic Shock

Circulating microRNAs (miRNA) alterations have been reported in severe trauma patients but the pathophysiological relevance of these changes is still unclear. miRNAs are critical biologic regulators of pathological events such as hypoxia and inflammation, which are known to induce endoplasmic reticulum (ER) stress. ER stress is emerging as an important process contributing to the development of single and/or multiple organ dysfunction after trauma hemorrhagic shock (THS) accompanied by impaired tissue microcirculation and inflammation. Here, we aim to bring new insights into the involvement of miRNAs associated with ER stress in THS. THS was induced in rats by a median laparotomy and blood withdrawal until mean arterial pressure (MAP) dropped to 30-35 mmHg followed by a restrictive (40 min) and full reperfusion (60 min) with Ringer's solution. Tunicamycin was used to induce ER stress. Blood samples were collected 24 h after THS for the determination of pathological changes in the blood (PCB) and circulating miRNAs. Plasma levels of circulating miRNAs were compared between THS, tunicamycin, and sham groups and correlated to biomarkers of PCB. MiRNA profile of THS animals showed that 40 out of 91 (44%) miRNAs were significantly upregulated compared to sham (p < 0.01). The data showed a very strong correlation between liver injury and miR−122-5p (r = 0.91, p < 0.00001). MiR-638, miR−135a-5p, miR−135b-5p, miR-668-3p, miR-204-5p, miR−146a-5p, miR−200a-3p, miR−17-5p, miR−30a-5p, and miR−214-3p were found positively correlated with lactate (r > 0.7, p < 0.05), and negatively with base excess (r ≤ 0.8, p < 0.05) and bicarbonate (r ≤ 0.8, p < 0.05), which are clinical parameters that reflected the shock severity. Tunicamycin significantly modified the microRNA profile of the animals, 33 out of 91 miRNAs were found differentially expressed. In addition, principal component analysis revealed that THS and tunicamycin induced similar changes in plasma miRNA patterns. Strikingly, the data showed that 15 (25.9%) miRNAs were regulated by both THS and tunicamycin (p < 0.01). This included miR−122-5p, a liver-specific microRNA, but also miR−17-5p and miR-125b-5p which are miRNAs remarkably involved in unfolded protein response (UPR)-mediating pro-survival signaling (IRE1α). Since miRNAs associated with ER stress are clearly correlated with THS, our data strongly suggest that interaction between miRNAs and ER stress is an important pathologic event occurring during THS. Overall, we consider that the miRNA profile developed in this study can provide a rationale for the development of bench-to-bedside strategies that target miRNAs in critical care diseases or be used as biomarkers in the prognosis of trauma patients.