The involvement of endoplasmic reticulum stress response in immune dysfunction of dendritic cells after severe thermal injury in mice

Dysregulated dendritic cells in sepsis: functional impairment and regulated cell death

Sepsis is defined as life-threatening organ dysfunction caused by a dysregulated host response to infection. Studies have indicated that immune dysfunction plays a central role in the pathogenesis of sepsis. Dendritic cells (DCs) play a crucial role in the emergence of immune dysfunction in sepsis. The major manifestations of DCs in the septic state are abnormal functions and depletion in numbers, which are linked to higher mortality and vulnerability to secondary infections in sepsis. Apoptosis is the most widely studied pathway of number reduction in DCs. In the past few years, there has been a surge in studies focusing on regulated cell death (RCD). This emerging field encompasses various forms of cell death, such as necroptosis, pyroptosis, ferroptosis, and autophagy-dependent cell death (ADCD). Regulation of DC's RCD can serve as a possible therapeutic focus for the treatment of sepsis. Throughout time, numerous tactics have been devised and effectively implemented to improve abnormal immune response during sepsis progression, including modifying the functions of DCs and inhibiting DC cell death. In this review, we provide an overview of the functional impairment and RCD of DCs in septic states. Also, we highlight recent advances in targeting DCs to regulate host immune response following septic challenge.

Copper induced intestinal inflammation response through oxidative stress induced endoplasmic reticulum stress in Takifugu fasciatus

Copper (Cu) pollution in aquaculture water has seriously threatened the healthy and sustainable development of the aquaculture industry. Recently, many researchers have studied the toxic effects of Cu exposure on fish. However, the relationship between endoplasmic reticulum stress (ERS) and the inflammatory response, as well as its possible mechanisms, remain unclear. Particularly, information related to fish intestines must be expanded. Our study initially investigated the mechanisms underlying intestinal toxicity and inflammation resulting from Cu-induced ERS in vivo and in vitro in Takifugu fasciatus. In vivo study, T. fasciatus were treated with different concentrations (control, 20, and 100 µg/L) of Cu exposure for 28 days, causing intestinal oxidative stress, ERS, inflammatory responses, and histopathological and ultrastructural damage. Transcriptomic data further showed that Cu exposure caused ERS, as well as inflammatory responses, in the intestinal tracts of T. fasciatus. In vitro experiments on the intestinal cells of T. fasciatus showed that Cu exposure treatment (7.5 µg/mL) for 24 h induced ERS and increased mitochondrial numbers and inflammatory responses. In contrast, the addition of 4-phenylbutyric acid (4-PBA) alleviated ERS and inflammatory response in the Cu-exposed group. Furthermore, the reactive oxygen species (ROS) inhibitor, N-Acetyl-l-cysteine (NAC), effectively alleviated Cu-induced ERS. In conclusion, our in vivo and in vitro studies have confirmed that oxidative stress triggers the ERS pathway, which is involved in the intestinal inflammatory response. Our study provides new insights into the relationship among Cu-induced oxidative stress, ERS, and inflammatory responses in fish, as well as for the healthy culture of fish in aqueous environments.

Pink1/Parkin-Mediated Mitophagy Regulated the Apoptosis of Dendritic Cells in Sepsis

Dendritic cells (DCs) are vital antigen-presenting cells (APCs) in the immune system, whose apoptosis is closely related to the development of sepsis. Mitophagy is one of the necessary forms of selective autophagy that removes damaged or dysfunctional mitochondria to regulate immunity and inflammation. However, its effect on the apoptosis of DC in sepsis remains unknown. Here, we showed that sepsis activated the apoptosis and mitophagy of DC, and mitophagy had an anti-apoptotic effect on sepsis-induced DC apoptosis. In this study, we used cecal ligation and puncture (CLP) to simulate the pathophysiological state of sepsis. Apoptosis and mitophagy of DC were significantly enhanced in CPL mice compared with controls, and in the Pink1-KO (Pink1-knockout) mice CLP model, the level of apoptosis in DC was further increased while the level of mitophagy was decreased. In addition, more severe mitochondrial dysfunction was exhibited in DC of Pink1-KO mice CLP model compared to wild-type (WT) mice. The results suggest that Pink1/Parkin-mediated mitophagy is activated during sepsis and has an anti-apoptotic effect on DC, which regulates immune functions.

Sestrin2 protects against lethal sepsis by suppressing the pyroptosis of dendritic cells

Sepsis is defined as life-threatening organ dysfunction caused by a dysregulated host response to infection. Sestrin2 (SESN2), a highly evolutionarily conserved protein, is critically involved in the cellular response to various stresses and has been confirmed to maintain the homeostasis of the internal environment. However, the potential effects of SESN2 in regulating dendritic cells (DCs) pyroptosis in the context of sepsis and the related mechanisms are poorly characterized. In this study, we found that SESN2 was capable of decreasing gasdermin D (GSDMD)-dependent pyroptosis of splenic DCs by inhibiting endoplasmic reticulum (ER) stress (ERS)-related nucleotide-binding oligomerization domain-like receptor protein 3 (NLRP3)-mediated ASC pyroptosome formation and caspase-1 (CASP-1) activation. Furthermore, SESN2 deficiency induced NLRP3/ASC/CASP-1-dependent pyroptosis and the production of proinflammatory cytokines by exacerbating the PERK–ATF4–CHOP signaling pathway, resulting in an increase in the mortality of septic mice, which was reversed by inhibiting ERS. These findings suggest that SESN2 appears to be essential for inhibiting NLRP3 inflammasome hyperactivation, reducing CASP-1-dependent pyroptosis, and improving sepsis outcomes through stabilization of the ER. The present study might have important implications for exploration of novel potential therapeutic targets for the treatment of sepsis complications.

Circulating sFasL Levels Predict the Severity and Outcome of Burn Injury: A Prospective Observational Study

BACKGROUND

Severe burn injury activates shock, inflammation, and blood cell system, but inappropriate reactions may lead to adverse outcomes. Soluble Fas ligand (sFasL) participates in apoptosis and inflammatory response. The circulating sFasL levels we investigated in association with the burn severity, shock, inflammation, blood cells, and mortality in patients with severe burns.

METHODS

A total of 56 patients with severe burns were recruited. The levels of sFasL and the biomarkers reflecting shock, organ damage, inflammation, and blood cells at 48 h postburn were analyzed. We compared the practical situation of patients that stratified by median sFasL levels and investigated the predictive value of sFasL for mortality.

RESULTS

High circulating sFasL levels were associated with the higher degrees of burn index, shock index, lactate, N-terminal probrain natriuretic peptide, total bilirubin, blood urea nitrogen, creatinine, tumor necrosis factor-α, interleukin-1β, interleukin-8, intercellular adhesion molecule 1, and complement 3, and the lower degrees of oxygenation index, lymphocytes, and platelets. Multiple linear regression analysis showed that the higher tumor necrosis factor-α (P < 0.001) and the lower oxygenation index (P = 0.031) and lymphocytes (P = 0.043) were associated with the higher sFasL. High sFasL (a unit is 50 ng/L) (odds ratio [OR] 5.50 [95% CI 1.04-29.20], P = 0.045) was an independent predictor of increased mortality by multivariate logistic regression analysis.

CONCLUSIONS

High circulating sFasL at 48 h postburn in patients with severe burns reflect shock, proinflammatory response, organ damage, and lymphocyte reductions and predict 30-day mortality.

Engagement of Posthemorrhagic Shock Mesenteric Lymph on CD4+ T Lymphocytes In Vivo and In Vitro

BACKGROUND

Immune dysfunction is associated with posthemorrhagic shock mesenteric lymph (PHSML) return. To determine the proliferation and cytokine production capacity of CD4⁺ T lymphocytes, the effect of PHSML drainage on spleen CD4⁺ T lymphocytes in a mouse model of hemorrhagic shock was assessed.

METHODS

The normal spleen CD4⁺ T lymphocytes were in vitro incubated with either drained normal mesenteric lymph (NML), PHSML during hypotension (PHSML-H), or PHSML from 0 h to 3 h after resuscitation (PHSML-R) to verify direct proliferation effects of PHSML.

RESULTS

Hemorrhagic shock led to reduction of proliferation and mRNA expression of interleukin 2 (IL-2) and IL-2 receptor in CD4⁺ T lymphocytes and to decrease in IL-2 and interferon γ (IFN-γ) levels in supernatants. In contrast, the interleukin-4 levels were increased. These effects were reversed by PHSML drainage. Moreover, NML incubation promoted CD4⁺ T lymphocyte proliferation, whereas both PHSML-H and PHSML-R treatment had a biphasic effects on CD4⁺ T lymphocyte proliferation, exhibiting an enhanced effect at early stages and an inhibitory effect at later stages. Compared with NML, PHSML-H increased IL-2 expression at 12 h, but decreased expression of both IL-2 and IFN-γ at 24 h. By contrast, PHSML-R induced significant increases in IL-2 and IFN-γ levels at 24 h. Interleukin-4 expression in CD4⁺ T lymphocytes was reduced at 12 h, but augmented at 24 h after incubation with either PHSML-H or PHSML-R.

CONCLUSIONS

The results indicate that PHSML has a direct inhibitory effect on CD4⁺ T lymphocyte proliferation that induces an inflammatory response, which is associated with cellular immune dysfunction.

ER stress activates immunosuppressive network: implications for aging and Alzheimer's disease

The endoplasmic reticulum (ER) contains stress sensors which recognize the accumulation of unfolded proteins within the lumen of ER, and subsequently these transducers stimulate the unfolded protein response (UPR). The ER sensors include the IRE1, PERK, and ATF6 transducers which activate the UPR in an attempt to restore the quality of protein folding and thus maintain cellular homeostasis. If there is excessive stress, UPR signaling generates alarmins, e.g., chemokines and cytokines, which activate not only tissue-resident immune cells but also recruit myeloid and lymphoid cells into the affected tissues. ER stress is a crucial inducer of inflammation in many pathological conditions. A chronic low-grade inflammation and cellular senescence have been associated with the aging process and many age-related diseases, such as Alzheimer’s disease. Currently, it is known that immune cells can exhibit great plasticity, i.e., they are able to display both pro-inflammatory and anti-inflammatory phenotypes in a context-dependent manner. The microenvironment encountered in chronic inflammatory conditions triggers a compensatory immunosuppression which defends tissues from excessive inflammation. Recent studies have revealed that chronic ER stress augments the suppressive phenotypes of immune cells, e.g., in tumors and other inflammatory disorders. The activation of immunosuppressive network, including myeloid-derived suppressor cells (MDSC) and regulatory T cells (Treg), has been involved in the aging process and Alzheimer’s disease. We will examine in detail whether the ER stress-related changes found in aging tissues and Alzheimer’s disease are associated with the activation of immunosuppressive network, as has been observed in tumors and many chronic inflammatory diseases.

Sestrin2 protects dendritic cells against endoplasmic reticulum stress-related apoptosis induced by high mobility group box-1 protein

Sestrin2 (SESN2) is a highly evolutionary conserved protein and involved in different cellular responses to various stresses. However, the potential function of SESN2 in immune system remains unclear. The present study was designed to test whether dendritic cells (DCs) could express SESN2, and investigate the underlying molecular mechanism as well as its potential significance. Herein, we firstly reported that SESN2 was expressed in DCs after high mobility group box-1 protein (HMGB1) stimulation and the apoptosis of DCs was obviously increased when SESN2 gene silenced by siRNA. Cells undergone SESN2-knockdown promoted endoplasmic reticulum (ER) stress (ERS)-related cell death, markedly exacerbated ER disruption as well as the formation of dilated and aggregated structures, and they significantly aggravated the extent of ERS response. Conversely, overexpressing SESN2 DCs markedly decreased apoptotic rates and attenuated HMGB1-induced ER morphology fragment together with inhibition of ERS-related protein translation. Furthermore, sesn2^−/−-deficient mice manifested increased DC apoptosis and aggravated ERS extent in septic model. These results indicate that SESN2 appears to be a potential regulator to inhibit apoptotic ERS signaling that exerts a protective effect on apoptosis of DCs in the setting of septic challenge.

The impact of endoplasmic reticulum stress responses in dendritic cell immunobiology

Dendritic cells (DCs) are critical for bridging innate and adaptive immunity. They do so by presenting antigens to T cells, and by expressing diverse molecules that further promote T cell activation, differentiation and memory formation. During this process, intracellular and extracellular factors can perturb the protein-folding capacity of endoplasmic reticulum (ER) and induce a cellular state of "ER stress," which is controlled and resolved by the unfolded protein response (UPR). Interestingly, various studies have shown that DCs can activate UPR-related pathways even in the absence of global ER stress, and that this process can modulate their normal activity. In other settings, such as cancer, adverse microenvironmental conditions have been demonstrated to evoke severe ER stress and persistent activation of the UPR in tumor-infiltrating DCs. This process disrupts their metabolism and local antigen-presenting capacity, hence impeding the initiation and maintenance of anti-cancer immunity. Here, we review recent findings on how canonical and non-canonical UPR activation impacts DC immunobiology at the steady-state, upon activation via pattern recognition receptors, and under diverse pathological conditions. We also discuss the potential therapeutic implications that targeting the UPR in DCs may have in the context of cancer and in other pathologies such as graft-versus-host disease.

Mdivi-1 Protects CD4+ T Cells against Apoptosis via Balancing Mitochondrial Fusion-Fission and Preventing the Induction of Endoplasmic Reticulum Stress in Sepsis

Apoptosis of CD4⁺ T cells plays a central role in the progression of sepsis because it is associated with subsequent immunosuppression and the lack of specific treatment. Thus, developing therapeutic strategies to attenuate the apoptosis of CD4⁺ T cells in sepsis is critical. Several studies have demonstrated that Mdivi-1, which is a selective inhibitor of the dynamin-related protein 1 (Drp1), attenuates apoptosis of myocardial cells and neurons during various pathologic states. The present study revealed the impact of Mdivi-1 on the apoptosis of CD4⁺ T cells in sepsis and the potential underlying mechanisms. We used lipopolysaccharide (LPS) stimulation and cecal ligation and puncture (CLP) surgery as sepsis models in vitro and in vivo, respectively. Our results showed that Mdivi-1 attenuated the apoptosis of CD4⁺ T cells both in vitro and in vivo. The potential mechanism underlying the protective effect of Mdivi-1 involved Mdivi-1 reestablishing mitochondrial fusion-fission balance in sepsis, as reflected by the expression of the mitofusin 2 (MFN2) and optic atrophy 1 (OPA1) , Drp1 translocation, and mitochondrial morphology, as observed by electron microscopy. Moreover, Mdivi-1 treatment reduced reactive oxygen species (ROS) production and prevented the induction of endoplasmic reticulum stress (ERS) and associated apoptosis. After using tunicamycin to activate ER stress, the protective effect of Mdivi-1 on CD4⁺ T cells was reversed. Our results suggested that Mdivi-1 ameliorated apoptosis in CD4⁺ T cells by reestablishing mitochondrial fusion-fission balance and preventing the induction of endoplasmic reticulum stress in experimental sepsis.

Gut epithelial cell-derived exosomes trigger posttrauma immune dysfunction

BACKGROUND

Exosomes are extracellular vesicles that act as endogenous mediators of the immune response. We have previously shown that exosomes released into mesenteric lymph (ML) following trauma (T)/hemorrhagic shock (HS) induce proinflammatory cytokine production in macrophages and are involved in the pathogenesis of postshock acute lung injury. However, the cellular origin of ML exosomes and their role in the posttrauma immune response remains unclear. We hypothesized that exosomes released from damaged-intestinal epithelial cells contribute to posttrauma immune dysfunction by altering the function of dendritic cells (DCs), key regulators of the adaptive immunity.

METHODS

Male rats underwent cannulation of the femoral artery, jugular vein and ML duct. T/HS was induced by laparotomy and 60 minutes of hemorrhagic shock followed by resuscitation. The ML was collected before (preshock) and after T/HS (post-T/HS) for isolation of exosomes. Surface epitopes of exosomes isolated from ML were assessed by flow cytometry to determine their cellular origin and phenotypic changes. The immunomodulatory effects of ML exosomes on DCs were assessed by Annexin V apoptosis assay, expression of costimulatory molecules, and antigen-presenting capacity to lymphocytes.

RESULTS

Exosomes isolated from ML highly expressed CD63 (exosome marker) and epithelial cell-specific marker, suggesting their derivation from intestinal epithelial cells. The expression of immunomodulatory molecules, such as major histocompatibility complex class II and Fas ligand on ML exosomes, was significantly increased after T/HS. Coincubation of DCs with exosomes isolated from ML after T/HS increased DC apoptosis twofold compared with preshock ML exosomes. Furthermore, post-T/HS ML exosomes significantly suppressed lipopolysaccharide-mediated expression of CD80 and CD86 on DCs as well as decreased their antigen-presenting capacity to induce lymphocytes proliferation.

CONCLUSION

Gut epithelial cells release immunomodulatory exosomes into the ML after T/HS and resuscitation. Mesenteric lymph exosomes may be critical mediators of posttraumatic immunosuppression causing depletion and dysfunction of DCs.

Connexin32 plays a crucial role in ROS-mediated endoplasmic reticulum stress apoptosis signaling pathway in ischemia reperfusion-induced acute kidney injury

BACKGROUND

Ischemia-reperfusion (I/R)-induced acute kidney injury (AKI) not only prolongs the length of hospital stay, but also seriously affects the patient's survival rate. Although our previous investigation has verified that reactive oxygen species (ROS) transferred through gap junction composed of connexin32 (Cx32) contributed to AKI, its underlying mechanisms were not fully understood and viable preventive or therapeutic regimens were still lacking. Among various mechanisms involved in organs I/R-induced injuries, endoplasmic reticulum stress (ERS)-related apoptosis is currently considered to be an important participant. Thus, in present study, we focused on the underlying mechanisms of I/R-induced AKI, and postulated that Cx32 mediated ROS/ERS/apoptosis signal pathway activation played an important part in I/R-induced AKI.

METHODS

We established renal I/R models with Cx32+/+ and Cx32-/- mice, which underwent double kidneys clamping and recanalization. ROS scavenger (N-acetylcysteine, NAC) and ERS inhibitors (4-phenyl butyric acid, 4-PBA, and tauroursodeoxycholic acid, TUDCA) were used to decrease the content of ROS and attenuate ERS activation, respectively.

RESULTS

Renal damage was progressively exacerbated in a time-dependent manner at the reperfusion stage, that was consistent with the alternation of ERS activation, including glucose regulated protein 78 (BiP/GRP78), X box-binding protein1, and C/EBP homologous protein expression. TUDCA or 4-PBA application attenuated I/R-induced ERS activation and protected against renal tubular epithelial cells apoptosis and renal damage. Cx32 deficiency decreased ROS generation and distribution between the neighboring cells, which attenuated I/R-induced ERS activation, and improved cell apoptosis and renal damage.

CONCLUSION

Cx32 mediated ROS/ERS/apoptosis signal pathway activation played an important part in I/R-induced AKI. Cx32 deficiency, ROS elimination, and ERS inhibition all could protect against I/R-induced AKI.

Salubrinal attenuated retinal neovascularization by inhibiting CHOP-HIF1α-VEGF pathways

Retinal neovascularization (RNV) related disease is the leading cause of irreversible blindness in the world. The aim of this study is to identify whether salubrinal could attenuate RNV by inhibiting CCAAT/enhancer-binding protein (C/EBP) homologous protein (CHOP)- hypoxia inducible factors 1α (HIF1α) -vascular endothelial growth factor (VEGF) pathways in both mouse retinal microvascular endothelial cells (mRMECs) and oxygen-induced retinopathy (OIR) mouse model. After being treated with salubrinal (20μmol/L) or CHOP-siRNA, mRMECs were exposed to a hypoxia environment. OIR mice were intraperitoneally injected with salubrinal (0.5 mg/kg/day) from P12 to P17. With salubrinal or CHOP-siRNA treatment, the elevated CHOP protein and mRNA levels in hypoxia-induced mRMECs were significantly decreased. HIF1α-VEGF pathways were activated under hypoxia condition, then HIF1α protein was degraded and VEGF secretion was down-regulated after salubrinal or CHOP-siRNA treatment. In OIR mice, the areas of RNV were markedly decreased with salubrinal treatment. Moreover, elevated expressions of CHOP, HIF1α and VEGF in retinas of OIR mice were all reduced after salubrinal treatment. It suggested that salubrinal attenuated RNV in mRMECs and OIR mice by inhibiting CHOP-HIF1α-VEGF pathways and could be a potential therapeutic target for hypoxia-induced retinal microangiopathy.