Epithelial HO-1/STAT3 affords the protection of subanesthetic isoflurane against zymosan-induced lung injury in mice

The Nuclear Translocation of Heme Oxygenase-1 in Human Diseases

Heme oxygenase-1 (HO-1) is a rate-limiting enzyme in the degradation of heme to generate carbon monoxide (CO), free iron and biliverdin, which could then be converted to bilirubin by biliverdin reductase. HO-1 exhibits cytoprotective effects of anti-apoptosis, anti-oxidation, and anti-inflammation via these byproducts generated during the above process. In the last few years, despite the canonical function of HO-1 and possible biological significance of its byproducts, a noncanonical function, through which HO-1 exhibits functions in diseases independent of its enzyme activity, also has been reported. In this review, the noncanonical functions of HO-1 and its translocation in other subcellular compartments are summarized. More importantly, we emphasize the critical role of HO-1 nuclear translocation in human diseases. Intriguingly, this translocation was linked to tumorigenesis and tumor progression in lung, prostate, head, and neck squamous cell carcinomas and chronic myeloid leukemia. Given the importance of HO-1 nuclear translocation in human diseases, nuclear HO-1 as a novel target might be attractive for the prevention and treatment of human diseases.

ACE2 Promoted by STAT3 Activation Has a Protective Role in Early-Stage Acute Kidney Injury of Murine Sepsis

Sepsis-induced AKI (SIAKI) is the most common complication with unacceptable mortality in hospitalized and critically ill patients. The pathophysiology of the development of SIAKI is still poorly understood. Our recent work has demonstrated the role of signal transducer and activator of transcription 3 (STAT3) pathways in regulating inflammation and coagulation in sepsis. We hypothesized that STAT3 activation has a critical role in early-stage SIAKI. The early-stage SIAKI model was established in cecal ligation and puncture (CLP) mice, which recapitulates the clinical and renal pathological features of early-stage AKI patients. Brush border loss (BBL) was the specific pathological feature of acute tubular injury in early-stage AKI. The role of STAT3 signaling and angiotension system in early-stage SIAKI was evaluated. The STAT3 activation (increased pSTAT3) and increased angiotensin-converting enzyme 2 (ACE2) expressions were observed in CLP mice. The low responsive expressions of pSTAT3 and ACE2 to septic inflammation in CLP AKI mice were associated with BBL. Correlation analysis of proteins' expressions showed pSTAT3 expression was significantly positively related to ACE2 expression in CLP mice. Reduced pSTAT3 after S3I201 intervention, which blocked STAT3 phosphorylation, decreased ACE2 expression, and exacerbated tubular injury in early-stage SIAKI. Our data indicate that endogenous increase of ACE2 expression upregulated by STAT3 activation in early-stage SIAKI play protective role against acute tubular injury.

Targeting STAT3: A crucial modulator of sepsis

Signal transducer and activator of transcription 3 (STAT3) is a cellular signal transcription factor that has recently attracted a great deal of attention. It can trigger a variety of genes transcription in response to cytokines and growth factors stimulation, which plays an important role in many cellular biological processes involved in anti/proinflammatory responses. Sepsis is a life-threatening organ dysfunction resulting from dysregulated host responses to infection. As a converging point of multiple inflammatory responses pathways, accumulating studies have presented the elaborate network of STAT3 in sepsis pathophysiology; these results generally indicate a promising therapeutic application for targeting STAT3 in the treatment of sepsis. In the present review, we evaluated the published literature describing the use of STAT3 in the treatment of experimental and clinical sepsis. The information presented here may be useful for the design of future studies and may highlight the potential of STAT3 as a future biomarker and therapeutic target for sepsis.

Hemolysis inhibits humoral B-cell responses and modulates alloimmunization risk in patients with sickle cell disease

Red blood cell alloimmunization remains a barrier for safe and effective transfusions in sickle cell disease (SCD), but the associated risk factors remain largely unknown. Intravascular hemolysis, a hallmark of SCD, results in the release of heme with potent immunomodulatory activity, although its effect on SCD humoral response, specifically alloimmunization, remains unclear. Here, we found that cell-free heme suppresses human B-cell plasmablast and plasma cell differentiation by inhibiting the DOCK8/STAT3 signaling pathway, which is critical for B-cell activation, as well as by upregulating heme oxygenase 1 (HO-1) through its enzymatic byproducts, carbon monoxide and biliverdin. Whereas nonalloimmunized SCD B cells were inhibited by exogenous heme, B cells from the alloimmunized group were nonresponsive to heme inhibition and readily differentiated into plasma cells. Consistent with a differential B-cell response to hemolysis, we found elevated B-cell basal levels of DOCK8 and higher HO-1-mediated inhibition of activated B cells in nonalloimmunized compared with alloimmunized SCD patients. To overcome the alloimmunized B-cell heme insensitivity, we screened several heme-binding molecules and identified quinine as a potent inhibitor of B-cell activity, reversing the resistance to heme suppression in alloimmunized patients. B-cell inhibition by quinine occurred only in the presence of heme and through HO-1 induction. Altogether, these data suggest that hemolysis can dampen the humoral B-cell response and that B-cell heme responsiveness maybe a determinant of alloimmunization risk in SCD. By restoring B-cell heme sensitivity, quinine may have therapeutic potential to prevent and inhibit alloimmunization in SCD patients.

Isoflurane reduces septic neuron injury by HO‑1‑mediated abatement of inflammation and apoptosis

Sepsis-associated encephalopathy (SAE) frequently occurs in critically ill patients with severe systemic infections. Subanesthetic isoflurane (0.7% ISO) possesses anti-inflammatory, antioxidant and anti-apoptotic properties against a number of human diseases, including brain injury. The activation of heme oxygenase-1 (HO-1) impedes inflammation, oxidation and apoptosis, thus alleviating sepsis-induced brain damage. However, whether 0.7% ISO affords protection against septic neuronal injury involving HO-1 activation is unclear. The present study aimed to investigate the neuroprotective effects of 0.7% ISO and its potential underlying mechanisms in SAE using a mouse model established by cecal ligation and puncture (CLP). The results indicated that the expression and activity of HO-1 in the mouse hippocampus were increased by CLP, and further enhanced by ISO. ISO reduced the death rate, brain water content and blood-brain barrier disruption, but improved the learning and memory functions of CLP-treated mice. ISO significantly decreased the production of pro-inflammatory cytokines and the levels of oxidative indictors in the serum and hippocampus, as well as the number of apoptotic neurons and the expression of pro-apoptotic proteins in the hippocampus. Inversely, anti-inflammatory factors, antioxidative enzymes and anti-apoptotic proteins were markedly increased by ISO administration. However, the neuroprotective effects of ISO were abolished by a HO-1 inhibitor. Overall, these findings suggested that 0.7% ISO alleviated SAE via its anti-inflammatory, antioxidative and anti-apoptotic properties, which involved the activated form of HO-1.

The Role of Heme Oxygenase-1 in Remote Ischemic and Anesthetic Organ Conditioning

The cytoprotective effects of the heme oxygenase (HO) pathway are widely acknowledged. These effects are mainly mediated by degradation of free, pro-oxidant heme and the generation of carbon monoxide (CO) and biliverdin. The underlying mechanisms of protection include anti-oxidant, anti-apoptotic, anti-inflammatory and vasodilatory properties. Upregulation of the inducible isoform HO-1 under stress conditions plays a crucial role in preventing or reducing cell damage. Therefore, modulation of the HO-1 system might provide an efficient strategy for organ protection. Pharmacological agents investigated in the context of organ conditioning include clinically used anesthetics and sedatives. A review from Hoetzel and Schmidt from 2010 nicely summarized the effects of anesthetics on HO-1 expression and their role in disease models. They concluded that HO-1 upregulation by anesthetics might prevent or at least reduce organ injury due to harmful stimuli. Due to its clinical safety, anesthetic conditioning might represent an attractive pharmacological tool for HO-1 modulation in patients. Remote ischemic conditioning (RIC), first described in 1993, represents a similar secure option to induce organ protection, especially in its non-invasive form. The efficacy of RIC has been intensively studied herein, including on patients. Studies on the role of RIC in influencing HO-1 expression to induce organ protection are emerging. In the first part of this review, recently published pre-clinical and clinical studies investigating the effects of anesthetics on HO-1 expression patterns, the underlying signaling pathways mediating modulation and its causative role in organ protection are summarized. The second part of this review sums up the effects of RIC.

Dexmedetomidine ameliorates LPS induced acute lung injury via GSK-3β/STAT3-NF-κB signaling pathway in rats

Acute lung injury (ALI) is a serious complication of sepsis and an important cause of death in intensive care. Studies have shown that DEX can inhibit inflammation. However, the anti-inflammatory effect and protective mechanism of DEX in lipopolysaccharide (LPS) induced ALI are still unclear. ALI model was established by intraperitoneal injection of LPS (10 mg/kg) in Sprague-Dawley (SD) male rats. Firstly, at 4, 6, 8, 12 and 24 h after LPS treatment, lung injury including pathologic histology, lung edema, and inflammation were detected. The optimal time point for lung injury was determined to be 12 h, at which time DEX was added to further test. Furthermore, STAT3 inhibitor (NSC74859) and GSK-3β inhibitor (SB216763) were added to verify the role of STAT3, GSK-3β and NF-κB in ameliorated ALI. Our results show that DEX pretreatment significantly decreased lung Wet-to-Dry weight (W/D) ratio and MPO activity and ameliorated LPS induced lung histopathological alterations. In addition, we confirmed that DEX can increased the phosphorylation of STAT3 and GSK-3β, and inhibit the phosphorylation of nuclear factor-κB (NF-κB) p65 in the inflammatory response induced by LPS. What's more, NSC74859 inhibited the phosphorylation of STAT3 and reversed the protect effect of DEX on LPS. SB216763 inhibited the phosphorylation of NF-κB and reversed the damage effect of LPS and plays the same anti-inflammatory effect as DEX. In summary, our data demonstrated that DEX can ameliorate ALI induced by LPS through GSK-3β/STAT3-NF-κB pathway.