Thioredoxin-interacting protein is required for endothelial NLRP3 inflammasome activation and cell death in a rat model of high-fat diet

Deletion of Thioredoxin-Interacting Protein (TXNIP) Abrogates High Fat Diet-induced Retinal Leukostasis, Barrier Dysfunction and Microvascular Degeneration in a Mouse Obesity Model

We have shown that a high fat diet (HFD) induces the activation of retinal NOD-like receptor protein (NLRP3)-inflammasome that is associated with enhanced expression and interaction with thioredoxin-interacting protein (TXNIP). Here, the specific contribution of TXNIP and the impact of HFD on retinal leukostasis, barrier dysfunction and microvascular degeneration were investigated. Wild-type (WT) and TXNIP knockout (TKO) mice were fed with normal diet or 60% HFD for 8–18 weeks. TXNIP was overexpressed or silenced in human retinal endothelial cells (REC). At 8 weeks, HFD significantly induced retinal leukostasis and breakdown of the blood–retina barrier in WT mice, but not in TKO mice. In parallel, HFD also induced retinal expression of adhesion molecules and cleaved IL-1β in WT mice, which were also abrogated in TKO mice. In culture, TXNIP overexpression induced NLRP3, IL-1β, and adhesion molecules expression, while TXNIP silencing inhibited them. Blocking the IL-1β receptor significantly suppressed TXNIP-induced expression of NLRP3-inflammasome and adhesion molecules in HREC. Ex-vivo assay showed that leukocytes isolated from WT-HFD, but not from TKO-HFD, induced leukostasis and cell death. At 18 weeks, HFD triggered development of degenerated (acellular) capillaries and decreased branching density in WT but not in TKO mice. Together, HFD-induced obesity triggered early retinal leukostasis and microvascular dysfunction at least in part via TXNIP-NLRP3-inflammasome activation.

Geniposide inhibits glucolipotoxicity and cooperates with Txnip knockdown to potentiate cell adaption to endoplasmic reticulum stress in pancreatic beta cells

Thioredoxin-interacting protein (Txnip), a negative regulator of thioredoxin, has become an attractive therapeutic target to alleviate metabolic diseases. Our previous data demonstrated that geniposide improved glucose-stimulated insulin secretion by accelerating Txnip degradation and prevented the early-stage apoptosis of pancreatic β cells induced by palmitate, but the underlying mechanisms are still unclear. The objective of this study is to identify the role of Txnip in geniposide preventing the apoptosis of pancreatic β cells induced by high glucose and palmitate (HG/PA). The results revealed that geniposide attenuated HG/PA-induced cell apoptosis and the expression of Bax and caspase-3, while increasing mitochondrial membrane potential and the anti-apoptotic protein levels of heme-oxygenase-1 (HO-1) and Bcl-2 in INS-1 rat pancreatic β cells. Knockdown of the Txnip gene raised the levels of anti-apoptotic proteins HO-1 and Bcl-2 and geniposide potentiated the effect of Txnip when the INS-1 cells were challenged by HG/PA. Furthermore, geniposide enhanced the adoptive unfolded protein response by increasing the phosphorylation of PERK/eIF2α and IRE1α in HG/PA-treated INS-1 cells. The results together suggest that geniposide might be useful to antagonize glucolipotoxicity and Txnip might be a pleiotropic cellular factor in pancreatic β cells.

The rOX-stars of inflammation: links between the inflammasome and mitochondrial meltdown

The nod‐like receptor protein 3 (NLRP3) inflammasome drives inflammation in response to mitochondrial dysfunction. As metabolic powerhouses with prokaryotic ancestry, mitochondria are a cache for danger‐associated molecular patterns and pathogen‐associated molecular pattern‐like molecules that elicit potent innate immune responses. Persistent mitochondrial damage caused by infection, or genetic or environmental factors, can lead to inappropriate or sustained inflammasome signalling. Here, we review the features of mitochondria that drive inflammatory signalling, with a particular focus on mitochondrial activation of the NLRP3 inflammasome. Given that mitochondrial network dynamics, metabolic activity and redox state are all intricately linked to each other and to NLRP3 inflammasome activity, we highlight the importance of a holistic approach to investigations of NLRP3 activation by dysfunctional mitochondria.

Cilostazol ameliorates high free fatty acid (FFA)-induced activation of NLRP3 inflammasome in human vascular endothelial cells

Cardiovascular disease is recognized as a leading cause of death worldwide, but the risk of death is 2-3 times higher for individuals with diabetes. NLRP3 inflammasome activation is a leading pathway of vascular damage, and new treatment methods are needed to reduce NLRP3 inflammasome expression, along with a detailed understanding of how those treatments work. In a series of assays on human vascular endothelial cells that were exposed to high concentrations of free fatty acids (FFA) to induce a diabetes-like environment, we found a significant impact of cilostazol, a vasodilator widely used to treat blood flow problems and well-tolerated medication. To our knowledge, this study is the first to demonstrate the effects of cilostazol in primary human aortic endothelial cells. We found that cilostazol significantly reduced NLRP3 inflammasome activation, as well as the activity of other related and harmful factors, including oxidative stress, expression of NADPH oxidase 4 (NOX-4), thioredoxin-interacting protein (TxNIP), high mobility group box 1 (HMGB-1), interleukin 1β (IL-1β) and IL-18. Cilostazol also protected the functionality of sirtuin 1 (SIRT1), which serves to restrict NLRP3 inflammasome activity, when exposure to FFAs would have otherwise impaired its function. Thus, it appears that cilostazol's mechanism of action in reducing NLRP3 inflammasome activation is an indirect one; it protects SIRT1, which then allows SIRT1 to perform its regulatory job. Cilostazol has potential as an already-available, well-tolerated preventive medication that may alleviate some of the adverse vascular effects of living with diabetes. The findings of the present study lay the groundwork for further research on the potential of cilostazol as a safe and effective treatment against diabetic endothelial dysfunction and vacular disease.

NOD-like Receptors in the Eye: Uncovering Its Role in Diabetic Retinopathy

Diabetic retinopathy (DR) is an ocular complication of diabetes mellitus (DM). International Diabetic Federations (IDF) estimates up to 629 million people with DM by the year 2045 worldwide. Nearly 50% of DM patients will show evidence of diabetic-related eye problems. Therapeutic interventions for DR are limited and mostly involve surgical intervention at the late-stages of the disease. The lack of early-stage diagnostic tools and therapies, especially in DR, demands a better understanding of the biological processes involved in the etiology of disease progression. The recent surge in literature associated with NOD-like receptors (NLRs) has gained massive attraction due to their involvement in mediating the innate immune response and perpetuating inflammatory pathways, a central phenomenon found in the pathogenesis of ocular diseases including DR. The NLR family of receptors are expressed in different eye tissues during pathological conditions suggesting their potential roles in dry eye, ocular infection, retinal ischemia, cataract, glaucoma, age-related macular degeneration (AMD), diabetic macular edema (DME) and DR. Our group is interested in studying the critical early components involved in the immune cell infiltration and inflammatory pathways involved in the progression of DR. Recently, we reported that NLRP3 inflammasome might play a pivotal role in the pathogenesis of DR. This comprehensive review summarizes the findings of NLRs expression in the ocular tissues with special emphasis on its presence in the retinal microglia and DR pathogenesis.

Role of Arginase 2 in Murine Retinopathy Associated with Western Diet-Induced Obesity

Western diet-induced obesity is linked to the development of metabolic dysfunctions, including type 2 diabetes and complications that include retinopathy, a leading cause of blindness. Aberrant activation of the inflammasome cascade leads to the progression of obesity-induced pathologies. Our lab showed the critical role of arginase 2 (A2), the mitochondrial isoform of this ureahydrolase, in obesity-induced metabolic dysfunction and inflammation. A2 deletion also has been shown to be protective against retinal inflammation in models of ischemic retinopathy and multiple sclerosis. We investigated the effect of A2 deletion on western diet-induced retinopathy. Wild-type mice fed a high-fat, high-sucrose western diet for 16 weeks exhibited elevated retinal expression of A2, markers of the inflammasome pathway, oxidative stress, and activation of microglia/macrophages. Western diet feeding induced exaggerated retinal light responses without affecting visual acuity or retinal morphology. These effects were reduced or absent in mice with global A2 deletion. Exposure of retinal endothelial cells to palmitate and high glucose, a mimic of the obese state, increased expression of A2 and inflammatory mediators and induced cell death. These effects, except for A2, were prevented by pretreatment with an arginase inhibitor. Collectively, our study demonstrated a substantial role of A2 in early manifestations of diabetic retinopathy.

The peroxisome proliferator-activated receptor-β/δ antagonist GSK0660 mitigates retinal cell inflammation and leukostasis

Diabetic retinopathy (DR) is triggered by retinal cell damage stimulated by the diabetic milieu, including increased levels of intraocular free fatty acids. Free fatty acids may serve as an initiator of inflammatory cytokine release from Müller cells, and the resulting cytokines are potent stimulators of retinal endothelial pathology, such as leukostasis, vascular permeability, and basement membrane thickening. Our previous studies have elucidated a role for peroxisome proliferator-activated receptor-β/δ (PPARβ/δ) in promoting several steps in the pathologic cascade in DR, including angiogenesis and expression of inflammatory mediators. Furthermore, PPARβ/δ is a known target of lipid signaling, suggesting a potential role for this transcription factor in fatty acid-induced retinal inflammation. Therefore, we hypothesized that PPARβ/δ stimulates both the induction of inflammatory mediators by Müller cells as well the paracrine induction of leukostasis in endothelial cells (EC) by Müller cell inflammatory products. To test this, we used the PPARβ/δ inhibitor, GSK0660, in primary human Müller cells (HMC), human retinal microvascular endothelial cells (HRMEC) and mouse retina. We found that palmitic acid (PA) activation of PPARβ/δ in HMC leads to the production of pro-angiogenic and/or inflammatory cytokines that may constitute DR-relevant upstream paracrine inflammatory signals to EC and other retinal cells. Downstream, EC transduce these signals and increase their synthesis and release of chemokines such as CCL8 and CXCL10 that regulate leukostasis and other cellular events related to vascular inflammation in DR. Our results indicate that PPARβ/δ inhibition mitigates these upstream (MC) as well as downstream (EC) inflammatory signaling events elicited by metabolic stimuli and inflammatory cytokines. Therefore, our data suggest that PPARβ/δ inhibition is a potential therapeutic strategy against early DR pathology.

Protective potential of klotho protein on diabetic retinopathy: Evidence from clinical and in vitro studies

AIMS/INTRODUCTION

The purpose of the present study was to observe the relationship between serum α-klotho (KL) protein level and diabetic retinopathy (DR), and to further examine the effects of KL protein on apoptosis induced by palmitic acid (PA) in human retinal endothelial cells.

MATERIALS AND METHODS

A total of 17 healthy people and 60 type 2 diabetes patients were included. According to the results from fundus fluorescein angiography, the diabetes patients were divided into three subgroups: without DR, non-proliferative DR and proliferative DR. Serum KL level was measured by enzyme-linked immunosorbent assay. In vitro, human retinal endothelial cells were exposed to PA with or without KL protein. Apoptosis rates were analyzed by flow cytometry analysis. Apoptotic-related protein expressions were detected by western blotting analysis.

RESULTS

Serum KL level was lower in diabetes patients than that in healthy participants (P = 0.007), and was gradually decreased among the without DR, non-proliferative DR and proliferative DR subgroups (P = 0.045). A logistic regression analysis showed that after adjusting for the other confounding factors, serum KL level was independently and negatively related with DR (P = 0.049). Furthermore, the increased apoptosis rates induced by PA were inhibited with the addition of KL protein. Consistently, KL protein reversed the expression levels of the increased pro-apoptotic protein Bax and the decreased anti-apoptotic protein Bcl-2 induced by PA. However, the anti-apoptotic effect of KL protein was attenuated by LY294002 through the phosphatidylinositol 3 kinase-serine∕threonine kinase pathway.

CONCLUSIONS

The data suggested that KL protein was probably a potential protective factor against retinopathy in type 2 diabetes patients.

Taurine Alleviates Schistosoma-Induced Liver Injury by Inhibiting the TXNIP/NLRP3 Inflammasome Signal Pathway and Pyroptosis

Schistosomiasis is a parasitic helminth disease that can cause severe inflammatory pathology, leading to organ damage, in humans. During a schistosomal infection, the eggs are trapped in the host liver, and products derived from eggs induce a polarized Th2 cell response, resulting in granuloma formation and eventually fibrosis. Previous studies indicated that the nucleotide-binding oligomerization domain-, leucine-rich repeat-, and pyrin domain-containing protein 3 (NLRP3) inflammasome is involved in schistosomiasis-associated liver fibrosis and that taurine could ameliorate hepatic granulomas and fibrosis caused by Schistosoma japonicum infection. Nevertheless, the precise role and molecular mechanism of the NLRP3 inflammasome and the protective effects of taurine in S. japonicum infection have not been extensively studied. In this study, we investigated the role of the NLRP3 inflammasome and the hepatoprotective mechanism of taurine in schistosoma-induced liver injury in mice. NLRP3 deficiency ameliorated S. japonicum-infection-induced hepatosplenomegaly, liver dysfunction, and hepatic granulomas and fibrosis; it also reduced NLRP3-dependent liver pyroptosis. Furthermore, taurine suppressed hepatic thioredoxin-interacting protein (TXNIP)/NLRP3 inflammasome activation in mice with S. japonicum infections, thereby inhibiting the activation of downstream inflammatory mediators such as interleukin-1β and subsequent pyroptosis. Our results suggest that the TXNIP/NLRP3 inflammasome pathway and mediating pyroptosis are involved in S. japonicum-induced liver injury and may be a potential therapeutic target for schistosomiasis treatment. In addition, taurine may be useful to alleviate or to prevent the occurrence of schistosomiasis-associated liver fibrosis.

NLRP3 inflammasome mediate palmitate-induced endothelial dysfunction

AIMS

Free fatty acids (FFA) is a key contributor to insulin resistance and endothelial dysfunction. However, the precise mechanism underlying the role of FFA remains elusive. This study aimed to investigate the role of NLRP3 (NOD-like receptor pyrin domain containing-3) inflammasome in FFA induced endothelial dysfunction.

MAIN METHODS

HUVECs were transfected with NLRP3 siRNA and then stimulated with LPS and palmitate. C57 BL/6 J mice transfected with NLRP3 Lenti-Virus were fed with a high-fat diet (HFD). The levels of NLRP3 inflammasome, AMPKα (AMP-activated protein kinase), endothelial nitric oxide synthase (eNOS) and the activity of the insulin signal pathway, in endothelial cells were determined via Western blotting. Endothelial function was determined by measuring the level of endothelium-dependent vasodilatation.

KEY FINDINGS

FFA could activate NLRP3 inflammasome and induce IL-1β release both in vitro. and in vivo. Using siRNA and Lenti-Virus to inhibit NLRP3 abolished palmitate-induced IL-1β release and restored impaired phosphorylation of IRS-1 (Tyr), Akt (Ser473) and eNOS (Ser1177) and ACh-mediated endothelium-dependent vasorelaxation induced by palmitate. AMPKα activator AICAR(5-aminoimidazole-4-carbox-amide-1-β-d-ribofuranoside) inhibited NLRP3 inflammasome activation and decreased IL-1β release and restored impaired insulin signal pathway induced by palmitate.

SIGNIFICANCE

NLRP3 inflammasome activation via AMPKα inactivation mediated palmitate-induced endothelial dysfunction through involves IL-1β-induced insulin signal pathway.

Modulating Expression of Thioredoxin Interacting Protein (TXNIP) Prevents Secondary Damage and Preserves Visual Function in a Mouse Model of Ischemia/Reperfusion

Retinal neurodegeneration, an early characteristic of several blinding diseases, triggers glial activation, resulting in inflammation, secondary damage and visual impairment. Treatments that aim only at neuroprotection have failed clinically. Here, we examine the impact of modulating thioredoxin interacting protein (TXNIP) to the inflammatory secondary damage and visual impairment in a model of ischemia/reperfusion (IR). Wild type (WT) and TXNIP knockout (TKO) mice underwent IR injury by increasing intraocular pressure for 40 min, followed by reperfusion. An additional group of WT mice received intravitreal TXNIP-antisense oligomers (ASO, 100 µg/2 µL) 2 days post IR injury. Activation of Müller glial cells, apoptosis and expression of inflammasome markers and visual function were assessed. IR injury triggered early TXNIP mRNA expression that persisted for 14 days and was localized within activated Müller cells in WT-IR, compared to sham controls. Exposure of Müller cells to hypoxia-reoxygenation injury triggered endoplasmic reticulum (ER) stress markers and inflammasome activation in WT cells, but not from TKO cells. Secondary damage was evident by the significant increase in the number of occluded acellular capillaries and visual impairment in IR-WT mice but not in IR-TKO. Intervention with TXNIP-ASO prevented ischemia-induced glial activation and neuro-vascular degeneration, and improved visual function compared to untreated WT. Targeting TXNIP expression may offer an effective approach in the prevention of secondary damage associated with retinal neurodegenerative diseases.

Right place, right time: localisation and assembly of the NLRP3 inflammasome

The NLRP3 inflammasome is a multimeric protein complex that cleaves caspase-1 and the pro-inflammatory cytokines interleukin 1 beta (IL-1β) and IL-18. Dysregulated NLRP3 inflammasome signalling is linked to several chronic inflammatory and autoimmune conditions; thus, understanding the activation mechanisms of the NLRP3 inflammasome is essential. Studies over the past few years have implicated vital roles for distinct intracellular organelles in both the localisation and assembly of the NLRP3 inflammasome. However, conflicting reports exist. Prior to its activation, NLRP3 has been shown to be resident in the endoplasmic reticulum (ER) and cytosol, although, upon activation, the NLRP3 inflammasome has been shown to assemble in the cytosol, mitochondria, and mitochondria-associated ER membranes by different reports. Finally, very recent work has suggested that NLRP3 may be localised on or adjacent to the Golgi apparatus and that release of mediators from this organelle may contribute to inflammasome assembly. Therefore, NLRP3 may be strategically placed on or in close proximity to these subcellular compartments to both sense danger signals originating from these organelles and use the compartment as a scaffold to assemble the complex. Understanding where and when NLRP3 inflammasome assembly occurs may help identify potential targets for treatment of NLRP3-related disorders.

Role of the thioredoxin interacting protein in diabetic nephropathy and the mechanism of regulating NOD‑like receptor protein 3 inflammatory corpuscle

Inflammatory response serves an important role in diabetic nephropathy (DN); however, the mechanism of inflammatory response results in renal damage is not yet clear. The aim of the present study was to investigate the role of the thioredoxin interacting protein (TXNIP)/NOD‑like receptor protein 3 (NLRP3) axis‑mediated activation of NLRP3 inflammasome in DN. A diabetic rat model was induced by streptozotocin injection. Hematoxylin and eosin (H&E) staining and streptavidin‑peroxidase staining were then used to examine the kidney tissue morphology, and TXNIP and NLRP3 protein expression levels, respectively. Furthermore, RNA interference technology was applied to silence the TXNIP gene. TXNIP and NLRP3 inflammasome activation‑associated proteins and mRNAs were detected by western blot analysis and RT‑qPCR, respectively. Enzyme‑linked immunosorbent assay was also used to examine interleukin (IL)‑1 and IL‑18 expression, while flow cytometry was performed to detect reactive oxygen species production. The data revealed that TXNIP and NLRP3 were overexpressed in kidney tissue of DN rats, and the level of antioxidant genes was downregulated. It was also observed that glucose promoted TXNIP expression and activation of NLRP3 inflammasome in a time‑dependent and dose‑dependent manner, therefore promoting inflammatory responses. Silencing of TXNIP gene resulted in the downregulation of NLRP3 inflammasome activation, and inhibited the expression levels of IL‑1 and IL‑18 in a high‑glucose environment. Furthermore, low expression of TXNIP promoted the levels of antioxidant genes and reduced the ROS levels. Taken together, the high‑glucose environment was able to upregulated the level of inflammatory factors by promoting the expression of TXNIP and the activation of NLRP3 inflammasome, consequently participating in DN.

NLRP3 inflammasome inhibition with MCC950 improves diabetes-mediated cognitive impairment and vasoneuronal remodeling after ischemia

Diabetes increases the risk and worsens the progression of cognitive impairment via the greater occurrence of small vessel disease and stroke. Yet, the underlying mechanisms are not fully understood. It is now accepted that cardiovascular health is critical for brain health and any neurorestorative approaches to prevent/delay cognitive deficits should target the conceptual neurovascular unit (NVU) rather than neurons alone. We have recently shown that there is augmented hippocampal NVU remodeling after a remote ischemic injury in diabetes. NLRP3 inflammasome signaling has been implicated in the development of diabetes and neurodegenerative diseases, but little is known about the impact of NLRP3 activation on functional and structural interaction within the NVU of hippocampus, a critical part of the brain that is involved in forming, organizing, and storing memories. Endothelial cells are at the center of the NVU and produce trophic factors such as brain derived neurotrophic factor (BDNF) contributing to neuronal survival, known as vasotrophic coupling. Therefore, the aims of this study focused on two hypotheses: 1) diabetes negatively impacts hippocampal NVU remodeling and worsens cognitive outcome after stroke, and 2) NLRP3 inhibition with MCC950 will improve NVU remodeling and cognitive outcome following stroke via vasotrophic (un)coupling between endothelial cells and hippocampal neurons. Stroke was induced through a 90-min transient middle cerebral artery occlusion (MCAO) in control and high-fat diet/streptozotocin-induced (HFD/STZ) diabetic male Wistar rats. Saline or MCC950 (3 mg/kg), an inhibitor of NLRP3, was injected at 1 and 3 h after reperfusion. Cognition was assessed over time and neuronal density, blood-brain barrier (BBB) permeability as well as NVU remodeling (aquaporin-4 [AQP4] polarity) was measured on day 14 after stroke. BDNF was measured in endothelial and hippocampal neuronal cultures under hypoxic and diabetes-mimicking condition with and without NLRP3 inhibition. Diabetes increased neuronal degeneration and BBB permeability, disrupted AQP4 polarity, impaired cognitive function and amplified NLRP3 activation after ischemia. Inhibition with MCC950 improved cognitive function and vascular integrity after stroke in diabetic animals and prevented hypoxia-mediated decrease in BDNF secretion. These results are the first to provide essential data showing MCC950 has the potential to become a therapeutic to prevent neurovascular remodeling and worsened cognitive decline in diabetic patients following stroke.

Inflammasome Activation Induces Pyroptosis in the Retina Exposed to Ocular Hypertension Injury

Mechanical stress and hypoxia during episodes of ocular hypertension (OHT) trigger glial activation and neuroinflammation in the retina. Glial activation and release of pro-inflammatory cytokines TNFα and IL-1β, complement, and other danger factors was shown to facilitate injury and loss of retinal ganglion cells (RGCs) that send visual information to the brain. However, cellular events linking neuroinflammation and neurotoxicity remain poorly characterized. Several pro-inflammatory and danger signaling pathways, including P2X7 receptors and Pannexin1 (Panx1) channels, are known to activate inflammasome caspases that proteolytically activate gasdermin D channel-formation to export IL-1 cytokines and/or induce pyroptosis. In this work, we used molecular and genetic approaches to map and characterize inflammasome complexes and detect pyroptosis in the OHT-injured retina. Acute activation of distinct inflammasome complexes containing NLRP1, NLRP3 and Aim2 sensor proteins was detected in RGCs, retinal astrocytes and Muller glia of the OHT-challenged retina. Inflammasome-mediated activation of caspases-1 and release of mature IL-1β were detected within 6 h and peaked at 12–24 h after OHT injury. These coincided with the induction of pyroptotic pore protein gasdermin D in neurons and glia in the ganglion cell layer (GCL) and inner nuclear layer (INL). The OHT-induced release of cytokines and RGC death were significantly decreased in the retinas of Casp1^−/−Casp4(11)^del, Panx1^−/− and in Wild-type (WT) mice treated with the Panx1 inhibitor probenecid. Our results showed a complex spatio-temporal pattern of innate immune responses in the retina. Furthermore, they indicate an active contribution of neuronal NLRP1/NLRP3 inflammasomes and the pro-pyroptotic gasdermin D pathway to pathophysiology of the OHT injury. These results support the feasibility of inflammasome modulation for neuroprotection in OHT-injured retinas.

NLRP3 inflammasome in NMDA-induced retinal excitotoxicity

N-methyl-D-aspartate (NMDA)-induced excitotoxicity is an acute form of experimental retinal injury as a result of overactivation of glutamate receptors. NLRP3 (nucleotide-binding domain, leucine-rich-repeat containing family, pyrin domain containing-3) inflammasome, one of the most studied sensors of innate immunity, has been reported to play a critical role in retinal neurodegeneration with controversial implications regarding neuroprotection and cell death. Thus far, it has not been elucidated whether NMDA-mediated excitotoxicity can trigger NLRP3 inflammasome in vivo. Moreover, it is unknown if NLRP3 is beneficial or detrimental to NMDA-mediated retinal cell death. Here, we employed a murine model of NMDA-induced retinal excitotoxicity by administering 100 nmoles of NMDA intravitreally, which resulted in massive TUNEL⁺ (TdT-dUTP terminal nick-end labelling) cell death in all retinal layers and especially in retinal ganglion cells (RGCs) 24 h post injection. NMDA insult in the retina potentiates macrophage/microglia cell infiltration, primes the NLRP3 inflammasome in a transcription-dependent manner and induces the expression of interleukin-1β (IL-1β). However, despite NLRP3 inflammasome upregulation, systemic deletion of Nlrp3 or Casp1 (caspase-1) did not significantly alter the NMDA-induced, excitotoxicity-mediated TUNEL⁺ retinal cell death at 24 h (acute phase). Similarly, the deletion of the two aforementioned genes did not alter the survival of the Brn3a⁺ (brain-specific homeobox/POU domain protein 3A) RGCs in a significant way at 3- or 7-days post injection (long-term phase). Our results indicate that NMDA-mediated retinal excitotoxicity induces immune cell recruitment and NLRP3 inflammasome activity even though inflammasome-mediated neuroinflammation is not a leading contributing factor to cell death in this type of retinal injury.

Verapamil Attenuated Prediabetic Neuropathy in High-Fat Diet-Fed Mice through Inhibiting TXNIP-Mediated Apoptosis and Inflammation

Diabetic neuropathy (DN) is a common and severe complication of diabetes mellitus. There is still a lack of an effective treatment to DN because of its complex pathogenesis. Thioredoxin-interacting protein (TXNIP), an endogenous inhibitor of thioredoxin, has been shown to be associated with diabetic retinopathy and nephropathy. Herein, we aim to investigate the role of TXNIP in prediabetic neuropathy and therapeutic potential of verapamil which has been shown to inhibit TXNIP expression. The effects of mediating TXNIP on prediabetic neuropathy and its exact mechanism were performed using high-fat diet- (HFD-) induced diabetic mice and palmitate-treated neurons. Our results showed that TXNIP upregulation is associated with prediabetic neuropathy in HFD-fed mice. TXNIP knockdown improved DN in HFD-induced prediabetic mice. Mechanistically, increased TXNIP in dorsal root ganglion is transferred into the cytoplasm and shuttled to the mitochondria. In cytoplasm, TXNIP binding to TRX1 results in the increased oxidative stress and inflammation. In mitochondria, TXNIP binding to TRX2 induced mitochondria dysfunction and apoptosis. TXNIP isolated from TRX2 then shuttles to the cytoplasm and binds to NLRP3, resulting in further increased TXNIP-NLRP3 complex, which induced the release of IL-1β and the development of inflammation. Thus, apoptosis and inflammation of dorsal root ganglion neuron eventually cause neural dysfunction. In addition, we also showed that verapamil, a known inhibitor of calcium channels, improved prediabetic neuropathy in the HFD-fed mice by inhibiting the upregulation of TXNIP. Our finding suggests that TXNIP might be a potential target for the treatment of neuropathy in prediabetic patients with dyslipidemia.

Thioredoxin-Interacting Protein (TXNIP) Associated NLRP3 Inflammasome Activation in Human Alzheimer's Disease Brain

Alzheimer's disease (AD) is the most common form of age-associated dementia characterized by amyloid-β plaques and neurofibrillary tangles. Recent studies have demonstrated that thioredoxin-interacting protein (TXNIP), an endogenous regulator of redox/glucose induced stress and inflammation, is now known to be upregulated in stroke, traumatic brain injury, diabetes and AD. We hypothesized that TXNIP overexpression sustains neurodegeneration through activation of the nucleotide binding and oligomerization domain-like receptor protein 3 in human AD brains. We analyzed TXNIP and the components of the NLRP3 inflammasome in the cortex of postmortem human brain samples by western blotting, real-time PCR, and immunohistochemical techniques in comparison with age-matched non-demented controls. Our results demonstrate that TXNIP protein as well as its mRNA levels in the cortex was significantly upregulated in AD compared to control brains. Moreover, using double immunofluorescence staining, TXNIP and interlukin-1β (IL-1β) were co-localized near Aβ plaques and p-tau. These results suggest an association between TXNIP overexpression levels and AD pathogenesis. Further, a significant increased expression of cleaved caspase-1 and IL-1β, the products of inflammasome activation, was detected in the cortex of AD brains. Together, these findings suggest that TXNIP, an upstream promising new therapeutic target, is a molecular link between inflammation and AD. The significant contribution of TXNIP to AD pathology suggests that strategies focusing on specific targeting of the TXNIP-NLRP3 inflammasome may lead to novel therapies for the management of AD and other age-related dementias.

Evidence and perspective for the role of the NLRP3 inflammasome signaling pathway in ischemic stroke and its therapeutic potential (Review)

Ischemic stroke is one of the main causes of death and disablement globally. The NLR family pyrin domain containing 3 (NLRP3) inflammasome is established as a sensor of detecting cellular damage and modulating inflammatory responses to injury during the progress of ischemic stroke. Inhibiting or blocking the NLRP3 inflammasome at different stages, including expression, assembly, and secretion, may have great promise to improve the neurological deficits during ischemic stroke. The current review provides a comprehensive summary of the current understanding in the literature of the molecular structure, expression, and assembly of the NLRP3 inflammasome, and highlights its potential as a novel therapeutic target for ischemic stroke.

Dysregulated Txnip-ROS-Wnt axis contributes to the impaired ischemic heart repair in diabetic mice

Hyperglycemia-induced impairment of angiogenesis contributes to the unfavorable prognosis of myocardial ischemia in long-standing diabetes mellitus. The underlying mechanism remains largely unknown and therapeutic strategies thereby limited. In the present study, we investigated the possible involvement of thioredoxin-interacting protein (TXNIP) and Wnt/β-catenin signaling in the context, and their possible relation was also explored. STZ induced diabetic mice were subjected to myocardial infarction (MI). Adenovirus expressing shTXNIP, shCtnnb1 (β-catenin) driven by VE-Cadherin promoter was administered intramyocardially immediately after MI. Cardiac function, histology, and molecular analyses were performed at predetermined time points. Increased endothelial expression of TXNIP was found in diabetic hearts, which correlated well with reduced nuclear β-catenin expression, insufficient angiogenesis, aggravated cardiac remodeling, and poor survival. Endothelial-specific knockdown of TXNIP significantly rescued β-catenin activity, together with increased angiogenesis, preserved cardiac function, and improved survival rate. Moreover, additional knockdown of β-catenin essentially reversed the beneficial effects of TXNIP downregulation. In vitro, high glucose treatment of human umbilical vein endothelial cells (HUVECs) increased TXNIP levels and ROS concentration, while it reduced β-catenin activity. Silencing TXNIP or ROS scavenger restored the high glucose induced reduction of Wnt/β-catenin activity in HUVECs. In addition, either reduction of TXNIP expression or supplementation of exogenous Wnt3a improved the HUVECs quantity and migration under high glucose conditions. Diabetes-induced increase of TXNIP expression in the endothelium contributes to impaired angiogenesis after MI, especially via the elevation of ROS and the impaired Wnt/β-catenin signaling. Targeting TXNIP-ROS-Wnt is a promising strategy in improving the prognosis.

Thioredoxin-interacting protein deficiency ameliorates kidney inflammation and fibrosis in mice with unilateral ureteral obstruction

Thioredoxin-interacting protein (TXNIP) is associated with inflammation, tubulointerstitial fibrosis, and oxidative stress in diabetic kidney disease, yet the potential role of TXNIP in nondiabetic renal injury is not well known. This study aimed to investigate the effect of TXNIP on renal injury by creating a unilateral ureteral obstruction (UUO) model in TXNIP knockout (TKO) mice. We performed sham or UUO surgery in 8-week-old TXNIP KO male mice and age and sex-matched wild-type (WT) mice. Animals were killed at 3, 5, 7, or 14 days after surgery, and renal tissues were obtained for RNA, protein, and other analysis. Our results show that the expression of TXNIP was increased in a time-dependent manner in the ligated kidneys. TXNIP deletion reduced renal fibrosis, apoptosis, α-SMA, TGF-β1 and CTGF expression, and activation of Smad3, p38 MAPK, and ERK1/2 in UUO kidneys. We also found UUO-induced renal F4/80+ macrophage infiltration, MCP-1 expression and activation of NF-κB and NLRP3 inflammasome were attenuated in TKO mice. Furthermore, our study revealed that TXNIP deficiency inhibited the expression of 8-OHdG, heme oxygenase-1 (HO-1) and NADPH oxidase 4 (Nox4) in UUO kidney. In summary, our study suggests that TXNIP plays a key role in the renal inflammation and fibrosis induced by UUO. Inhibition of TXNIP may be a strategy to slow the progression of chronic kidney diseases.

Melatonin inhibits endoplasmic reticulum stress-associated TXNIP/NLRP3 inflammasome activation in lipopolysaccharide-induced endometritis in mice

Endometritis, an inflammatory response of the uterus tissue, is characterized by the production of inflammatory cytokines and migration of neutrophil (PMN) into the uterus tissue. Melatonin has been demonstrated to have anti-inflammatory and antioxidant effects. The purpose of this study was to investigate the protective effects of melatonin on lipopolysaccharide (LPS)-induced endometritis in mice. An endometritis model was induced by LPS and melatonin was given 1 h before LPS treatment. The results showed that melatonin inhibited LPS-induced pathologic changes, Myeloperoxidase (MPO) activity, and levels of interleukin-1 beta (IL-1β). Melatonin also inhibited LPS-induced thioredoxin-interacting protein (TXNIP)/NOD-like receptor family, pyrin domain containing 3 (NLRP3) inflammasome and nuclear factor kappa B (NF-κB) activation, reactive oxygen species (ROS) production, and endoplasmic reticulum (ER) stress. Furthermore, melatonin was found to increase AMPK activity. In conclusion, our results demonstrated that melatonin inhibited ER stress-associated TXNIP/NLRP3 inflammasome activation with a regulation of adenosine monophosphate activated protein kinase (AMPK) in LPS-induced endometritis. Melatonin may serve as a promising nutritional supplement for the treatment of endometritis.

Salidroside Attenuates High-Fat Diet-Induced Nonalcoholic Fatty Liver Disease via AMPK-Dependent TXNIP/NLRP3 Pathway

Our previous studies suggested that salidroside could alleviate hepatic steatosis in type 2 diabetic C57BLKS/Lepr^db (db/db) mice. The aim of the present study was to evaluate the therapeutic effect of salidroside on high-fat diet- (HFD-) induced nonalcoholic fatty liver disease (NAFLD) by investigating underlying mechanisms. Mice were fed with HFD or regular diet, randomly divided into two groups, and treated with salidroside or vehicle for 8 weeks. Then, biochemical analyses and histopathological examinations were conducted in vivo and in vitro. Salidroside administration attenuated HFD-induced obesity, blood glucose variability, and hepatic lipid deposition, markedly increasing insulin sensitivity in HFD mice. In addition, salidroside suppressed oxidative stress, thioredoxin-interacting protein (TXNIP) expression, and NLRP3 inflammasome activation in the liver. In cultured hepatocytes, salidroside dose dependently regulated lipid accumulation, reactive oxygen species (ROS) generation, and NLRP3 inflammasome activation as well as improved AMP-activated protein kinase (AMPK) activity and insulin sensitivity. The inhibition of AMPK activation by inhibitor or short interfering RNA (siRNA) resulted in the suppression of the beneficial effects of salidroside in hepatocytes. Our findings demonstrated that salidroside protects against NAFLD by improving hepatic lipid metabolism and NLRP3 inflammasome activation, and these actions are related to the regulation of the oxidative stress and AMPK-dependent TXNIP/NLRP3 pathways.

Differential Expression of TXNIP Isoforms in the Peripheral Leukocytes of Patients with Acute Myocardial Infarction

Background

Acute myocardial infarction (AMI) is the most serious type of coronary atherosclerotic heart disease (CAD). The pathological changes are characterized by atherosclerosis. Oxidative stress plays an important role in atherosclerosis. Thioredoxin-interacting protein (TXNIP), an endogenous inhibitor and regulator of thioredoxin, could bind thioredoxin to regulate its expression and antioxidant activity negatively. The NCBI data show that there are two isoforms in TXNIP gene, namely, TXNIP1 and TXNIP2. Our previous studies have shown that TXNIP expression levels in patients with unstable angina pectoris (UAP) were increased compared with controls (CTR). However, no upregulation of TXNIP was detected in AMI patients.

Methods

The leucocytes were isolated from peripheral venous blood, and total RNA of the leucocytes was extracted. Then, real-time quantitative PCR was performed.

Results

mRNA levels of TXNIP2 in AMI were significantly increased compared with CTR (P < 0.05). However, the expression of TXNIP1 was downregulated in AMI, but the difference was not statistically significant (P > 0.05). Logistic regression analysis showed that TXNIP2 mRNA levels were significantly associated with AMI (OR = 2.207, P < 0.05).

Conclusions

The expression of TXNIP2, not TXNIP1, is upregulated in leukocytes of AMI patients, indicating that only TXNIP2 in circulating leucocytes may be involved in the pathogenesis of AMI.

The Function of Thioredoxin-Binding Protein-2 (TBP-2) in Different Diseases

Thioredoxin-binding protein-2 (TBP-2) has an important role in the redox system, but it plays a different role in many different diseases (e.g., various cancers, diabetes mellitus (DM), cardiovascular disease, and cataracts) by influencing cell proliferation, differentiation, apoptosis, autophagy, and metabolism. Distinct transcription factors (TFs) stimulated by different factors combine with binding sites or proteins to upregulate or downregulate TBP-2 expression, in order to respond to the change in the internal environment. Most research disclosed that the main function of TBP-2 is associating with thioredoxin (Trx) to inhibit the antioxidant capacity of Trx. Furthermore, the TBP-2 located in tissues, whether normal or abnormal, has the ability to cause the dysfunctioning of cells and even death through different pathways, such as shortening the cell cycle and inducing apoptosis or autophagy. Through these studies, we found that TBP-2 promoted the development of diseases which are involved in inflammatory and oxidative damage. To a certain extent, we believe that there is some hidden connection between the biological functions which TBP-2 participates in and some distinct diseases. This review presents only a summary of the roles that TBP-2 plays in cancer, DM, cataracts, and so on, as well as its universal mechanisms. Further investigations are needed for the cell signaling pathways of the effects caused by TBP-2. A greater understanding of the mechanisms of TBP-2 could produce potential new targets for the treatment of diseases, including cancer and diabetes, cardiovascular disease, and cataracts.

MicroRNA-20a protects human aortic endothelial cells from Ox-LDL-induced inflammation through targeting TLR4 and TXNIP signaling

MiR-20a has been previously reported to participate in the development of various human diseases. However, the role of miR-20a in the pathology of atherosclerosis remains elusive. The present study aimed to reveal the relationship between miR-20a expression and atherosclerosis using in vitro cell model. The expression level of miR-20a was detected in human aortic endothelial cells (HAECs) under Ox-LDL exposure. Meanwhile, the regulatory effects of miR-20a on predicted targets (TLR4 and TXNIP) were also determined. Moreover, the levels of key proteins and inflammatory mediators in TLR4 and NLRP3 signaling were detected to further confirm the regulatory effects of miR-20a. We found that miR-20a expression was repressed under Ox-LDL condition, and both TLR4 and TXNIP acted as regulatory targets of miR-20a. Overexpressed miR-20a reduced ROS generation under Ox-LDL treatment, and this effect was restored by forced expression of TLR4. Moreover, key molecules (including MyD88, TRIF, phosphorylated NF-κB (p65), NLRP3, ASC, cleaved caspase-1, ICAM-1 and IL-1β) in TLR4 and NLRP3 signaling were significantly repressed under miR-20a overexpression. In conclusion, miR-20a could negatively regulate TLR4 and NLRP3 signaling to protect HAECs from inflammatory injuries, which provides a new insight into the inhibition of atherosclerotic development.

Palmitic Acid Induces Müller Cell Inflammation that is Potentiated by Co-treatment with Glucose

Chronic hyperglycemia is thought to be the major stimulator of retinal dysfunction in diabetic retinopathy (DR). Thus, many diabetes-related systemic factors have been overlooked as inducers of DR pathology. Cell culture models of retinal cell types are frequently used to mechanistically study DR, but appropriate stimulators of DR-like factors are difficult to identify. Furthermore, elevated glucose, a gold standard for cell culture treatments, yields little to no response from many primary human retinal cells. Thus, the goal of this project was to demonstrate the effectiveness of the free fatty acid, palmitic acid and compare its use alone and in combination with elevated glucose as a stimulus for human Müller cells, a retinal glial cell type that is activated early in DR pathogenesis and uniquely responsive to fatty acids. Using RNA sequencing, we identified a variety of DR-relevant pathways, including NFκB signaling and inflammation, intracellular lipid signaling, angiogenesis, and MAPK signaling, that were stimulated by palmitic acid, while elevated glucose alone did not significantly alter any diabetes-relevant pathways. Co-treatment of high glucose with palmitic acid potentiated the expression of several DR-relevant angiogenic and inflammatory targets, including PTGS2 (COX-2) and CXCL8 (IL-8).

Deletion of Thioredoxin-interacting protein ameliorates high fat diet-induced non-alcoholic steatohepatitis through modulation of Toll-like receptor 2-NLRP3-inflammasome axis: Histological and immunohistochemical study

Endemic prevalence of obesity is associated with alarming increases in non-alcoholic steatohepatitis (NASH) with limited available therapeutics. Toll-like receptor2 (TLR2) and Nod-like receptor protein 3 (NLRP3) Inflammasome are implicated in hepatic steatosis, inflammation and fibrosis; the histological landmark stages of NASH. TXNIP, a member of α-arrestin family activates NLRP3 in response to various danger stimuli. The aim of current work was to investigate the effect of TXNIP genetic deletion on histological manifestations of high fat diet-induced steatohepatitis and activation of TLR2-NLRP3-inflammasome axis. Wild-type mice (WT) and TXNIP knock out (TKO) littermates were randomized to normal diet (WT-ND and TKO-ND) or high fat diet (HFD, 60% fat) (WT-HFD and TKO-HFD). After 8-weeks, liver samples from all groups were evaluated by histological, immunohistochemical and western blot analysis. HFD resulted in significant induction of micro and macrovesicular hepatic steatosis, that was associated with increased inflammatory immune cell infiltration in WT-HFD compared with WT-ND and TKO-ND controls, but not in TKO-HFD group. In parallel, WT-HFD group showed significant fibrosis and α-SMA expression; a marker of pro-fibrotic stellate-cell activation, in areas surrounding the central vein and portal circulation, versus all other groups. Western blot revealed increased activation of TLR2-NLRP3 inflammasome pathway and downstream IL-1β and TNFα in WT-HFD group, but not in TKO-HFD group. IL-1β expression coincided within the same areas of steatosis, inflammatory cell infiltration, collagen deposition and α-SMA expression in WT-HFD mice, that was significantly reduced in TKO-HFD mice. In conclusion, TXNIP deletion ameliorates the HFD-induced steatosis, inflammatory and fibrotic response via modulation of TLR2-NLRP3 inflammasome axis. Targeting TXNIP-TLR2-NLRP3 pathway may provide potential therapeutic modalities for NASH treatment.

Endoplasmic Reticulum Stress, a Driver or an Innocent Bystander in Endothelial Dysfunction Associated with Hypertension?

PURPOSE OF REVIEW

Hypertension (htn) is a polygenic disorder that effects up to one third of the US population. The endoplasmic reticulum (ER) stress response is a homeostatic pathway that regulates membrane structure, protein folding, and secretory function. Emerging evidence suggests that ER stress may induce endothelial dysfunction; however, it is unclear whether ER stress-associated endothelial dysfunction modulates htn.

RECENT FINDINGS

Exogenous and endogenous molecules activate ER stress in the endothelium, and ER stress mediates some forms of neurogenic htn, such as angiotensin II-dependent htn. Human studies suggest that ER stress induces endothelial dysfunction, though direct evidence that ER stress augments blood pressure in humans is lacking. However, animal and cellular models demonstrate direct evidence that ER stress influences htn. ER stress is likely one of many players in a complex interplay among molecular pathways that influence the expression of htn. Targeted activation of specific ER stress pathways may provide novel therapeutic opportunities.

Thioredoxin-Interacting Protein (TXNIP) in Cerebrovascular and Neurodegenerative Diseases: Regulation and Implication

Neurological diseases, including acute attacks (e.g., ischemic stroke) and chronic neurodegenerative diseases (e.g., Alzheimer's disease), have always been one of the leading cause of morbidity and mortality worldwide. These debilitating diseases represent an enormous disease burden, not only in terms of health suffering but also in economic costs. Although the clinical presentations differ for these diseases, a growing body of evidence suggests that oxidative stress and inflammatory responses in brain tissue significantly contribute to their pathology. However, therapies attempting to prevent oxidative damage or inhibiting inflammation have shown little success. Identification and targeting endogenous "upstream" mediators that normalize such processes will lead to improve therapeutic strategy of these diseases. Thioredoxin-interacting protein (TXNIP) is an endogenous inhibitor of the thioredoxin (TRX) system, a major cellular thiol-reducing and antioxidant system. TXNIP regulating redox/glucose-induced stress and inflammation, now is known to get upregulated in stroke and other brain diseases, and represents a promising therapeutic target. In particular, there is growing evidence that glucose strongly induces TXNIP in multiple cell types, suggesting possible physiological roles of TXNIP in glucose metabolism. Recently, a significant body of literature has supported an essential role of TXNIP in the activation of the NOD-like receptor protein (NLRP3)-inflammasome, a well-established multi-molecular protein complex and a pivotal mediator of sterile inflammation. Accordingly, TXNIP has been postulated to reside centrally in detecting cellular damage and mediating inflammatory responses to tissue injury. The majority of recent studies have shown that pharmacological inhibition or genetic deletion of TXNIP is neuroprotective and able to reduce detrimental aspects of pathology following cerebrovascular and neurodegenerative diseases. Conspicuously, the mainstream of the emerging evidences is highlighting TXNIP link to damaging signals in endothelial cells. Thereby, here, we keep the trend to present the accumulative data on CNS diseases dealing with vascular integrity. This review aims to summarize evidence supporting the significant contribution of regulatory mechanisms of TXNIP with the development of brain diseases, explore pharmacological strategies of targeting TXNIP, and outline obstacles to be considered for efficient clinical translation.

Reactive oxygen species promote tubular injury in diabetic nephropathy: The role of the mitochondrial ros-txnip-nlrp3 biological axis

NLRP3/IL-1β activation via thioredoxin (TRX)/thioredoxin-interacting protein (TXNIP) following mitochondria ROS (mtROS) overproduction plays a key role in inflammation. However, the involvement of this process in tubular damage in the kidneys of patients with diabetic nephropathy (DN) is unclear. Here, we demonstrated that mtROS overproduction is accompanied by decreases in TRX expression and TXNIP up-regulation. In addition, we discovered that mtROS overproduction is also associated with increases in NLRP3/IL-1β and TGF-β expression in the kidneys of patients with DN and db/db mice. We reversed these changes in db/db mice by administering a peritoneal injection of MitoQ, an antioxidant targeting mtROS. Similar results were observed in human tubular HK-2 cells subjected to high-glucose (HG) conditions and treated with MitoQ. Treating HK-2 cells with MitoQ suppressed the dissociation of TRX from TXNIP and subsequently blocked the interaction between TXNIP and NLRP3, leading to the inhibition of NLRP3 inflammasome activation and IL-1β maturation. The effects of MitoQ were enhanced by pretreatment with TXNIP siRNA and abolished by pretreatment with monosodium urate (MSU) and TRX siRNA in vitro. These results suggest that mitochondrial ROS-TXNIP/NLRP3/IL-1β axis activation is responsible for tubular oxidative injury, which can be ameliorated by MitoQ via the inhibition of mtROS overproduction.

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Reactive oxygen species promotes renal damage in diabetic nephropathy.

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Mitochondrial ROS- TXNIP-NLRP3 biological axis involved in tubular injury of DN.

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Inhibition of mitochondrial ROS by MitoQ ameliorated the renal tubular injury.

Reduced endothelial thioredoxin-interacting protein protects arteries from damage induced by metabolic stress in vivo

Although thioredoxin-interacting protein (TXNIP) is involved in a variety of biologic functions, the contribution of endothelial TXNIP has not been well defined. To investigate the endothelial function of TXNIP, we generated a TXNIP knockout mouse on the Cdh5-cre background (TXNIP^fl/fl cdh5^cre). Control (TXNIP^fl/fl) and TXNIP^fl/fl cdh5^cre mice were fed a high protein-low carbohydrate (HP-LC) diet for 3 mo to induce metabolic stress. We found that TXNIP^fl/fl and TXNIP^fl/fl cdh5^cre mice on an HP-LC diet displayed impaired glucose tolerance and dyslipidemia concretizing the metabolic stress induced. We evaluated the impact of this metabolic stress on mice with reduced endothelial TXNIP expression with regard to arterial structure and function. TXNIP^fl/fl cdh5^cre mice on an HP-LC diet exhibited less endothelial dysfunction than littermate mice on an HP-LC diet. These mice were protected from decreased aortic medial cell content, impaired aortic distensibility, and increased plasminogen activator inhibitor 1 secretion. This protective effect came with lower oxidative stress and lower inflammation, with a reduced NLRP3 inflammasome expression, leading to a decrease in cleaved IL-1β. We also show the major role of TXNIP in inflammation with a knockdown model, using a TXNIP-specific, small interfering RNA included in a lipoplex. These findings demonstrate a key role for endothelial TXNIP in arterial impairments induced by metabolic stress, making endothelial TXNIP a potential therapeutic target.-Bedarida, T., Domingues, A., Baron, S., Ferreira, C., Vibert, F., Cottart, C.-H., Paul, J.-L., Escriou, V., Bigey, P., Gaussem, P., Leguillier, T., Nivet-Antoine, V. Reduced endothelial thioredoxin-interacting protein protects arteries from damage induced by metabolic stress in vivo.

Silybin inhibits NLRP3 inflammasome assembly through the NAD+/SIRT2 pathway in mice with nonalcoholic fatty liver disease

Silybin is one of the effective, traditional Chinese medicines used as a hepatoprotective agent in nonalcoholic fatty liver disease (NAFLD) therapy worldwide, and the NOD-like receptor family pyrin domain-containing 3 (NLRP3) inflammasome has been recognized as an important factor involved in NAFLD development. However, little is known about the mechanisms of silybin in the regulation of high-fat diet (HFD)-induced liver inflammation. In our study, we found that silybin inhibited endoplasmic reticulum stress and NLRP3 inflammasome activation in the livers of HFD-fed mice and in cultured hepatocytes. Phosphorylation of inositol-requiring enzyme (IRE)1α and eIF2α, expression of thioredoxin-interacting protein and cleaved caspase-1, and release of IL-1β were reduced by silybin. In addition, silybin inhibited the approach of calreticulin and translocase of outer membrane 20 (Tom20), prevented assembly of the NLRP3 inflammasome complex, and suppressed the accumulation of acetylated α-tubulin in the perinuclear region. Both MEC-17 and sirtuin 2 (SIRT2) were influenced by palmitate and silybin, whereas histone deacetylase 6 was not affected. In addition, supplementing NAD⁺ directly or increasing NAD⁺ concentration with silybin could maintain the activity of SIRT2. The anti-inflammatory effect of silybin was blocked by SIRT2 silencing or by the SIRT2 inhibitor AGK2, as evidenced by NLRP3/ASC colocalization, AC-α-tubulin expression, and IL-1β release. These findings indicate that the NAD⁺/SIRT2 pathway is an important mediator through which silybin prevents NLRP3 inflammasome activation during NAFLD.-Zhang, B., Xu, D., She, L., Wang, Z., Yang, N., Sun, R., Zhang, Y., Yan, C., Wei, Q., Aa, J., Liu, B., Wang, G., Xie, Y. Silybin inhibits NLRP3 inflammasome assembly through the NAD⁺/SIRT2 pathway in mice with nonalcoholic fatty liver disease.

Altered Expression of TXNIP in the peripheral leukocytes of patients with coronary atherosclerotic heart disease

BACKGROUND

Coronary atherosclerotic heart disease (CAD) is mainly caused by atherosclerosis, an inflammatory disease characterized by plaque formation in arteries. Reactive oxygen species caused structural damage and dysfunction of arterial endothelial cells. Thioredoxin-interacting protein (TXNIP) is the endogenous inhibitor and regulator of thioredoxin, a major cellular antioxidant and antiapoptotic system. In order to explore the role of TXNIP in the occurrence and development of CAD, we detected the TXNIP expression and discussed its molecular mechanisms in CAD.

METHODS

The mRNA levels of TXNIP gene in peripheral leucocytes were detected in CAD and healthy controls (CTR) by quantitative real-time polymerase chain reaction. And TXNIP proteins were detected by western blotting.

RESULTS

TXNIP gene expression levels in patients with unstable angina pectoris (UAP, n = 96) were significantly increased compared with those of CTR (n = 192, P < .05). However, the situation is different in acute myocardial infarction (n = 96, P > .05). Logistic regression analysis showed that TXNIP levels were significantly positive correlated with UAP (OR = 1.728, P < .05).

CONCLUSIONS

TXNIP gene expression in the peripheral leucocytes was increased in patients with UAP, indicating that TXNIP in circulating leucocytes may be involved in the pathogenesis of UAP.

Silymarin attenuated paraquat-induced cytotoxicity in macrophage by regulating Trx/TXNIP complex, inhibiting NLRP3 inflammasome activation and apoptosis

Oxidative stress and inflammation are involved in paraquat-induced cytotoxicity. Silymarin can exert a potent antioxidative and anti-inflammatory effect in various pathophysiological processes. The aim of this current study is to explore the protective effect and potential mechanism of silymarin in paraquat-induced macrophage injury. Cells were pretreated with different doses of silymarin for 3h before exposure to paraquat. At 24h after exposure to paraquat, the paraquat-induced cytotoxicity to macrophage was measured via the MTT assay and LDH release. The levels of intracellular reactive oxygen species, GSH-Px, SOD, and lipid peroxidation product malondialdehyde were measured to evaluate the oxidative effect of paraquat. NLRP3 inflammasome and cytokines secretion in macrophage exposed to paraquat at 24h were measured via immunofluorescence microscopy, western blot or Elisa. Our results revealed that paraquat could dramatically cause cytotoxicity and reactive oxygen species generation, enhance TXNIP expression, and induce NLRP3 inflammasome activation and cytokines secretion. The pretreatment with silymarin could remarkably reduce the cytotoxicity, promote the expression of Trx and antioxidant enzymes, and suppress the TXNIP and NLRP3 inflammasome activation. In conclusion, silymarin attenuated paraquat-induced cytotoxicity in macrophage by inhibiting oxidative stress, NLRP3 inflammasome activation, cytokines secretion and apoptosis.

The NLPR3 inflammasome and obesity-related kidney disease

Over the past decade, the prevalence of obesity has increased, accompanied by a parallel increase in the prevalence of chronic kidney disease (CKD). Mounting evidence suggests that high body mass index (BMI) and obesity are important risk factors for CKD, but little is known about the mechanisms of obesity‐related kidney disease (ORKD). The NLRP3 inflammasome is a polyprotein complex that plays a crucial role in the inflammatory process, and numerous recent studies suggest that the NLRP3 inflammasome is involved in ORKD development and may serve as a key modulator of ORKD. Moreover, inhibiting activation of the NLRP3 inflammasome has been shown to attenuate ORKD. In this review, we summarize recent progress in understanding the link between the NLRP3 inflammasome and ORKD and discuss targeting the NLRP3 inflammasome as a novel therapeutic approach for ORKD.

The Role of Endoplasmic Reticulum Stress in Cardiovascular Disease and Exercise

Endoplasmic reticulum (ER) stress, which is highly associated with cardiovascular disease, is triggered by a disturbance in ER function because of protein misfolding or an increase in protein secretion. Prolonged disruption of ER causes ER stress and activation of the unfolded protein response (UPR) and leads to various diseases. Eukaryotic cells respond to ER stress via three major sensors that are bound to the ER membrane: activating transcription factor 6 (ATF6), inositol-requiring protein 1α (IRE1α), and protein kinase RNA-like ER kinase (PERK). Chronic activation of ER stress causes damage in endothelial cells (EC) via apoptosis, inflammation, and oxidative stress signaling pathways. The alleviation of ER stress has recently been accepted as a potential therapeutic target to treat cardiovascular diseases such as heart failure, hypertension, and atherosclerosis. Exercise training is an effective nonpharmacological approach for preventing and alleviating cardiovascular disease. We here review the recent viewing of ER stress-mediated apoptosis and inflammation signaling pathways in cardiovascular disease and the role of exercise in ER stress-associated diseases.

Deletion of TXNIP Mitigates High-Fat Diet-Impaired Angiogenesis and Prevents Inflammation in a Mouse Model of Critical Limb Ischemia

Background: Previous work demonstrated that high-fat diet (HFD) triggered thioredoxin-interacting protein (TXNIP) and that silencing TXNIP prevents diabetes-impaired vascular recovery. Here, we examine the impact of genetic deletion of TXNIP on HFD-impaired vascular recovery using hind limb ischemia model. Methods: Wild type mice (WT, C57Bl/6) and TXNIP knockout mice (TKO) were fed either normal chow diet (WT-ND and TKO-ND) or 60% high-fat diet (WT-HFD and TKO-HFD). After four weeks of HFD, unilateral hind limb ischemia was performed and blood flow was measured using Laser doppler scanner at baseline and then weekly for an additional three weeks. Vascular density, nitrative stress, infiltration of CD68+ macrophages, and expression of inflammasome, vascular endothelial growth factor (VEGF), VEGF receptor-2 were examined by slot blot, Western blot and immunohistochemistry. Results: By week 8, HFD caused similar increases in weight, cholesterol and triglycerides in both WT and TKO. At week 4 and week 8, HFD significantly impaired glucose tolerance in WT and to a lesser extent in TKO. HFD significantly impaired blood flow and vascular density (CD31 labeled) in skeletal muscle of WT mice compared to ND but not in TKO. HFD and ischemia significantly induced tyrosine nitration, and systemic IL-1β and infiltration of CD68+ cells in skeletal muscle from WT but not from TKO. HFD significantly increased cleaved-caspase-1 and IL-1 β compared to ND. Under both ND, ischemia tended to increase VEGF expression and increased VEGFR2 activation in WT only but not TKO. Conclusion: Similar to prior observation in diabetes, HFD-induced obesity can compromise vascular recovery in response to ischemic insult. The mechanism involves increased TXNIP-NLRP3 (nucleotide-binding oligomerization domain-like receptor protein 3) inflammasome activation, nitrative stress and impaired VEGFR2 activation. Deletion of TXNIP restored blood flow, reduced nitrative stress and blunted inflammasome-mediated inflammation; however, it did not impact VEGF/VEGFR2 in HFD. Targeting TXNIP-NLRP3 inflammasome can provide potential therapeutic target in obesity-induced vascular complication.

Acute fasting inhibits central caspase-1 activity reducing anxiety-like behavior and increasing novel object and object location recognition

BACKGROUND

Inflammation within the central nervous system (CNS) is frequently comorbid with anxiety. Importantly, the pro-inflammatory cytokine most commonly associated with anxiety is IL-1β. The bioavailability and activity of IL-1β are regulated by caspase-1-dependent proteolysis vis-a-vis the inflammasome. Thus, interventions regulating the activation or activity of caspase-1 should reduce anxiety especially in states that foster IL-1β maturation.

METHODS

Male C57BL/6j, C57BL/6j mice treated with the capase-1 inhibitor biotin-YVAD-cmk, caspase-1 knockout (KO) mice and IL-1R1 KO mice were fasted for 24h or allowed ad libitum access to food. Immediately after fasting, caspase-1 activity was measured in brain region homogenates while activated caspase-1 was localized in the brain by immunohistochemistry. Mouse anxiety-like behavior and cognition were tested using the elevated zero maze and novel object/object location tasks, respectively.

RESULTS

A 24h fast in mice reduced the activity of caspase-1 in whole brain and in the prefrontal cortex, amygdala, hippocampus, and hypothalamus by 35%, 25%, 40%, 40%, and 40% respectively. A 24h fast also reduced anxiety-like behavior by 40% and increased novel object and object location recognition by 21% and 31%, respectively. IL-1β protein, however, was not reduced in the brain by fasting. ICV administration of YVAD decreased caspase-1 activity in the prefrontal cortex and amygdala by 55%, respectively leading to a 64% reduction in anxiety like behavior. Importantly, when caspase-1 KO or IL1-R1 KO mice are fasted, no fasting-dependent reduction in anxiety-like behavior was observed.

CONCLUSIONS

Results indicate that fasting decrease anxiety-like behavior and improves memory by a mechanism tied to reducing caspase-1 activity throughout the brain.

High fat diet dysregulates microRNA-17-5p and triggers retinal inflammation: Role of endoplasmic-reticulum-stress

AIM

To elucidate how high diet-induced endoplasmic reticulum-stress upregulates thioredoxin interacting protein expression in Müller cells leading to retinal inflammation.

METHODS

Male C57Bl/J mice were fed either normal diet or 60% high fat diet for 4-8 wk. During the 4 wk study, mice received phenyl-butyric acid (PBA); endoplasmic reticulum-stress inhibitor; for 2 wk. Insulin resistance was assessed by oral glucose tolerance. Effects of palmitate-bovine serum albumin (BSA) (400 μmol/L) were examined in retinal Müller glial cell line and primary Müller cells isolated from wild type and thioredoxin interacting protein knock-out mice. Expression of thioredoxin interacting protein, endoplasmic reticulum-stress markers, miR-17-5p mRNA, as well as nucleotide-binding oligomerization domain-like receptor protein (NLRP3) and IL1β protein was determined.

RESULTS

High fat diet for 8 wk induced obesity and insulin resistance evident by increases in body weight and impaired glucose tolerance. By performing quantitative real-time polymerase chain reaction, we found that high fat diet triggered the expression of retinal endoplasmic reticulum-stress markers (P < 0.05). These effects were associated with increased thioredoxin interacting protein and decreased miR-17-5p expression, which were restored by inhibiting endoplasmic reticulum-stress with PBA (P < 0.05). In vitro, palmitate-BSA triggered endoplasmic reticulum-stress markers, which was accompanied with reduced miR-17-5p and induced thioredoxin interacting protein mRNA in retinal Müller glial cell line (P < 0.05). Palmitate upregulated NLRP3 and IL1β expression in primary Müller cells isolated from wild type. However, using primary Müller cells isolated from thioredoxin interacting protein knock-out mice abolished palmitate-mediated increase in NLRP3 and IL1β.

CONCLUSION

Our work suggests that targeting endoplasmic reticulum-stress or thioredoxin interacting protein are potential therapeutic strategies for early intervention of obesity-induced retinal inflammation.

Targeting Interleukin-1 beta to Suppress Sympathoexcitation in Hypothalamic Paraventricular Nucleus in Dahl Salt-Sensitive Hypertensive Rats

Findings from our laboratory indicate that expressions of some proinflammatory cytokines such as tumor necrosis factor, interleukin-6 and oxidative stress responses are increased in the hypothalamic paraventricular nucleus (PVN) and contribute to the progression of salt-sensitive hypertension. In this study, we determined whether interleukin-1 beta (IL-1β) activation within the PVN contributes to sympathoexcitation during development of salt-dependent hypertension. Eight-week-old male Dahl salt-sensitive (S) rats received a high-salt diet (HS, 8 % NaCl) or a normal-salt diet (NS, 0.3 % NaCl) for 6 weeks, and all rats were treated with bilateral PVN injection of gevokizumab (IL-1β inhibitor, 1 μL of 10 μg) or vehicle once a week. The mean arterial pressure (MAP), heart rate (HR) and plasma norepinephrine (NE) were significantly increased in high-salt-fed rats. In addition, rats with high-salt diet had higher levels of NOX-2, NOX-4 [subunits of NAD (P) H oxidase], IL-1β, NLRP3 (NOD-like receptor family pyrin domain containing 3), Fra-LI (an indicator of chronic neuronal activation) and lower levels of IL-10 in the PVN than normal-diet rats. Bilateral PVN injection of gevokizumab decreased MAP, HR and NE, attenuated the levels of oxidative stress and restored the balance of cytokines. These findings suggest that IL-1β activation in the PVN plays a role in salt-sensitive hypertension.

NF-κB Blockade in Hypothalamic Paraventricular Nucleus Inhibits High-Salt-Induced Hypertension Through NLRP3 and Caspase-1

High-salt-induced inflammation and oxidative stress in the hypothalamic paraventricular nucleus (PVN) contribute to the pathogenesis of salt-sensitive hypertension. In this study, we hypothesized that chronic inhibition of nuclear factor-κB (NF-κB) activity in the PVN delays the progression of hypertension by upregulating anti-inflammatory cytokines, reducing NLRP3 (NOD-like receptor family pyrin domain containing 3) and IL-1β and attenuating p-IKKβ, NF-κB p65 activity and NAD(P)H oxidase in the PVN of salt-sensitive hypertensive rats. Dahl salt-sensitive rats received a high-salt diet (HS, 8 % NaCl) or a normal-salt diet (NS, 0.3 % NaCl) for 6 weeks and were treated with bilateral PVN infusion with either vehicle or pyrrolidine dithiocarbamate (PDTC, 5 μg/h), a NF-κB inhibitor via osmotic minipump. The mean arterial pressure and plasma levels of norepinephrine (NE) and epinephrine (EPI) were significantly increased in high-salt-fed rats. In addition, rats with high-salt diet had higher levels of p-IKKβ, NF-κB p65 activity, Fra-like (Fra-LI) activity (an indicator of chronic neuronal activation), NOX-4 (subunits of NAD(P)H oxidase), NLRP3 and IL-1β, and lower levels of IL-10 in the PVN than normal diet rats. Bilateral PVN infusions of PDTC attenuated these high-salt-induced changes. These findings suggest that high-salt-induced NF-κB activation in the PVN caused hypertension via sympathoexcitation, which are associated with the increases of NLRP3, IL-1β and oxidative stress in the PVN; PVN inhibition of NF-κB activity attenuates NLRP3, IL-1β and oxidative stress in the PVN and thereby attenuates hypertension.

Nuclear receptors regulate lipid metabolism and oxidative stress markers in chondrocytes

Abstract

Joint homeostasis failure can result in osteoarthritis (OA). Currently, there are no treatments to alter disease progression in OA, but targeting early changes in cellular behavior has great potential. Recent data show that nuclear receptors contribute to the pathogenesis of OA and could be viable therapeutic targets, but their molecular mechanisms in cartilage are incompletely understood. This study examines global changes in gene expression after treatment with agonists for four nuclear receptor implicated in OA (LXR, PPARδ, PPARγ, and RXR). Murine articular chondrocytes were treated with agonists for LXR, PPARδ, PPARγ, or RXR and underwent microarray, qPCR, and cellular lipid analyses to evaluate changes in gene expression and lipid profile. Immunohistochemistry was conducted to compare two differentially expressed targets (Txnip, Gsta4) in control and cartilage-specific PPARδ knockout mice subjected to surgical destabilization of the medial meniscus (DMM). Nuclear receptor agonists induced different gene expression profiles with many responses affecting lipid metabolism. LXR activation downregulated gene expression of proteases involved in OA, whereas RXR agonism decreased expression of ECM components and increased expression of Mmp13. Functional assays indicate increases in cell triglyceride accumulation after PPARγ, LXR, and RXR agonism but a decrease after PPARδ agonism. PPARδ and RXR downregulate the antioxidant Gsta4, and PPARδ upregulates Txnip. Wild-type, but not PPARδ-deficient mice, display increased staining for Txnip after DMM. Collectively, these data demonstrate that nuclear receptor activation in chondrocytes primarily affects lipid metabolism. In the case of PPARδ, this change might lead to increased oxidative stress, possibly contributing to OA-associated changes.

Key message

Nuclear receptors regulate metabolic genes in chondrocytes.

Nuclear receptors affect triglyceride levels.

PPARδ mediates regulation of oxidative stress markers.

Nuclear receptors are promising therapeutic targets for osteoarthritis.

Electronic supplementary material

The online version of this article (doi:10.1007/s00109-016-1501-5) contains supplementary material, which is available to authorized users.

Homoplantaginin Inhibits Palmitic Acid-induced Endothelial Cells Inflammation by Suppressing TLR4 and NLRP3 Inflammasome

Palmitic acid (PA)-induced vascular endothelial inflammation plays a pivotal role in the occurrence and development of vascular diseases. The present study was conducted to examine the effect of homoplantaginin, a main flavonoid from a traditional Chinese medicine Salvia plebeia R. Br., on PA-treated human umbilical vein endothelial cells inflammation and the underlying molecular mechanism. Firstly, we found that homoplantaginin (0.1, 1, 10 μM) dose-dependently reduced expression of toll-like receptor-4 evoked by PA (100 μM). The inhibitory effect of homoplantaginin was further confirmed under lipopolysaccharide challenge. In addition, downstream adapted proteins including myeloid differentiation primary response gene 88, toll/interleukin-1 receptor-domain containing adaptor-inducing interferon-β and tumor necrosis factors receptor associated factor-6 were successfully inhibited by homoplantaginin under PA treatment. Also, we found that homoplantaginin tightly controlled PA-induced reactive oxygen species to prevent nucleotide-binding domain-like receptor 3 (NLRP3) inflammasome activation by suppressing reactive oxygen species-sensitive thioredoxin-interacting protein, NLRP3, and caspase-1. Meanwhile, protein and mRNA levels of inflammatory mediators (interleukin-1β, intercellular cell adhesion molecule-1, and monocyte chemotactic protein-1) were decreased by homoplantaginin. Furthermore, homoplantaginin restored PA-impaired nitric oxide generation. Taken together, these results indicated that homoplantaginin protected endothelial cells from ameliorating PA-induced endothelial inflammation via suppressing toll-like receptor-4 and NLRP3 pathways, and restoring nitric oxide generation, suggesting it may be a potential candidate for further development in the prevention and treatment of vascular diseases.