Adeno-associated Virus 9-mediated Small RNA Interference of TLR4 Alleviates Myocardial Ischemia and Reperfusion Injury by Inhibition of the NF-κB and MAPK Signaling Pathways in Rats

TLR4 signalling in ischemia/reperfusion injury: a promising target for linking inflammation, oxidative stress and programmed cell death to improve organ transplantation outcomes

Transplantations represent the principal therapeutic interventions for terminal organ failure, a procedure that has salvaged myriad lives annually. Ischemia/reperfusion injury (IRI) is frequently correlated with an unfavourable prognosis and is relevant for early graft dysfunction and graft survival. IRI constitutes a complex pathological state influenced by a series of factors such as oxidative stress, metabolic stress, leukocytic infiltration, programmed cell death pathways, and inflammatory immune responses. Reducing ischemia/reperfusion injury is one of the main directions of transplantation research. Toll-like receptors (TLRs) are important pattern-recognition receptors expressed on various organs that orchestrate the immune responses upon recognising PAMPs and DAMPs. Targeting the TLR4 signalling has recently been suggested as a promising approach for alleviating IRI by affecting inflammation, oxidative stress and programmed cell death (PCD). In this minireview, we summarise the role of TLR4 signalling in regulating inflammation, oxidative stress and PCD in organ transplantation and discuss their interactions during IRI. A detailed understanding of the multiple functions of TLR4 in IRI provides novel insights into developing therapies to improve organ transplantation outcomes.

Inhibition of Myocardial Cell Apoptosis Is Important Mechanism for Ginsenoside in the Limitation of Myocardial Ischemia/Reperfusion Injury

Ischemic heart disease has a high mortality, and the recommended therapy is reperfusion. Nevertheless, the restoration of blood flow to ischemic tissue leads to further damage, namely, myocardial ischemia/reperfusion injury (MIRI). Apoptosis is an essential pathogenic factor in MIRI, and ginsenosides are effective in inhibiting apoptosis and alleviating MIRI. Here, we reviewed published studies on the anti-apoptotic effects of ginsenosides and their mechanisms of action in improving MIRI. Each ginsenoside can regulate multiple pathways to protect the myocardium. Overall, the involved apoptotic pathways include the death receptor signaling pathway, mitochondria signaling pathway, PI3K/Akt signaling pathway, NF-κB signaling pathway, and MAPK signaling pathway. Ginsenosides, with diverse chemical structures, regulate different apoptotic pathways to relieve MIRI. Summarizing the effects and mechanisms of ginsenosides contributes to further mechanism research studies and structure–function relationship research studies, which can help the development of new drugs. Therefore, we expect that this review will highlight the importance of ginsenosides in improving MIRI via anti-apoptosis and provide references and suggestions for further research in this field.

Exosomal microRNA-98-5p from hypoxic bone marrow mesenchymal stem cells inhibits myocardial ischemia-reperfusion injury by reducing TLR4 and activating the PI3K/Akt signaling pathway

OBJECTIVE

MicroRNAs (miRNAs) are essential biomarkers during development of human diseases. We aimed to explore the role of hypoxia-induced bone marrow mesenchymal stem cells (BMSCs)-derived exosomal miR-98-5p in myocardial ischemia-reperfusion injury (MI/RI).

METHODS

BMSCs were isolated, cultured, stimulated by hypoxia and transfected with adenovirus expressing miR-98-5p. The exosomes were extracted from BMSCs and named as BMSC-exos. The rat MI/RI models were established by ligation of left anterior descending artery and were respectively injected. Then, hemodynamic indices, myocardial enzymes, oxidative stress factors, inflammatory factors, macrophage infiltration and infarct size in these rats were determined. Expression of miR-98-5p, toll-like receptor 4 (TLR4) and the phosphatidylinositol-3-kinase/protein kinase B (PI3K/Akt) signaling pathway-related proteins was assessed. The target relation between miR-98-5p and TLR4 was confirmed by bioinformatic method and dual luciferase report gene assay.

RESULTS

MiR-98-5p was downregulated, TLR4 was upregulated and the PI3K/Akt signaling pathway was inactivated in MI/RI rat myocardial tissues. Exosomal miR-98-5p from hypoxic BMSCs promoted cardiac function and suppressed myocardial enzyme levels, oxidative stress, inflammation response, macrophage infiltration and infarct size in I/R myocardial tissues. Moreover, TRL4 was targeted by miR-98-5p and miR-98-5p activated PI3K/Akt signaling pathway.

CONCLUSION

Hypoxia-induced BMSC-exos elevated miR-98-5p to protect against MI/RI. This study may be helpful for treatment of MI/RI.

Astragaloside IV prevents acute myocardial infarction by inhibiting the TLR4/MyD88/NF-κB signaling pathway

Although astragaloside IV protects from acute myocardial infarction (AMI)-induced chronic heart failure (CHF), the underlying mechanism of action is unclear. We determined the potential therapeutic effect of astragaloside IV using molecular docking approaches and validated the findings by the ligation of the left anterior descending (LAD) coronary artery-induced AMI rat model. The interaction between astragaloside IV and myeloid differentiation factor 88 (MyD88) was evaluated by SwissDock. To explore the mechanisms underlying the beneficial effects of astragaloside IV in the LAD coronary artery ligation-induced AMI model, we administered the rats with astragaloside IV for 4 weeks. Hemodynamic indexes were used to evaluate the degree of myocardial injury in model rats. The histopathological changes in myocardium were detected by hematoxylin & eosin (H&E) staining and Masson's staining. Myocardium homogenate contents of collagen I and collagen III were evaluated by ELISA. The level of myocardial hydroxyproline (HYP) was determined by alkaline hydrolysis. Immunohistochemistry was used to examine collagen I. Western blotting was used to examine relevant proteins. As per the molecular docking study results, astragaloside IV may act on MyD88. Furthermore, astragaloside IV improved hemodynamic disorders, alleviated pathological changes, and reduced abnormal collagen deposition and myocardial HYP in vivo. Astragaloside IV significantly reduced the overexpression of TLR4, MyD88, NF-Κb, and TGF-β, which further validated the molecular docking findings. Hence, astragaloside IV ameliorates AMI by reducing inflammation and blocking TLR4/MyD88/NF-κB signaling. These results indicate that astragaloside IV may alleviate AMI. PRACTICAL APPLICATIONS: Astragaloside IV, a small active substance extracted from Astragalus membranaceus, has demonstrated potent protective effects against cardiovascular ischemia/reperfusion, diabetic nephropathy, and other diseases. Molecular docking experiments showed that astragaloside IV might act on the myeloid differentiation factor 88 (MyD88). Astragaloside IV can effectively reduce the overexpression of TLR4, MyD88, and NF-κB p65, indicating that astragaloside IV inhibits inflammation via TLR4/MyD88/NF-κB signaling pathway. These results indicate that astragaloside IV may alleviate acute myocardial infarction.

Toll-like Receptor 4 Deficiency Aggravates Airway Hyperresponsiveness and Inflammation by Impairing Neutrophil Apoptosis in a Toluene Diisocyanate-Induced Murine Asthma Model

PURPOSE

Accumulating evidence has suggested that toll-like receptor 4 (TLR4) is critically involved in the pathogenesis of asthma. The aim of this study was to investigate the role of TLR4 in toluene diisocyanate (TDI)-induced allergic airway inflammation.

METHODS

TLR4^-/- and wild-type (WT) C57BL/10J mice were sensitized and challenged with TDI to generate a TDI-induced asthma model. B-cell lymphoma 2 (Bcl-2) inhibitors, ABT-199 (4 mg/kg) and ABT-737 (4 mg/kg), were intranasally given to TDI-exposed TLR4^-/- mice after each challenge.

RESULTS

TDI exposure led to increased airway hyperresponsiveness (AHR), granulocyte flux, bronchial epithelial shedding and extensive submucosal collagen deposition, which were unexpectedly aggravated by TLR4 deficiency. Following TDI challenge, TLR4^-/- mice exhibited down-regulated interleukin-17A and increased colony-stimulating factor 3 in bronchoalveolar lavage fluid (BALF), while WT mice did not. In addition, TLR4 deficiency robustly suppressed the expression of NOD-like receptor family pyrin domain containing 3 and NLR family CARD domain containing 4, decreased caspase-1 activity in TDI-exposed mice, but had no effect on the level of high mobility group box 1 in BALF. Flow cytometry revealed that TDI hampered both neutrophil and eosinophil apoptosis, of which neutrophil apoptosis was further inhibited in TDI-exposed TLR4^-/- mice, with marked up-regulation of Bcl-2. Moreover, inhibition of Bcl-2 with either ABT-199 or ABT-737 significantly alleviated neutrophil recruitment by promoting apoptosis.

CONCLUSIONS

These data indicated that TLR4 deficiency promoted neutrophil infiltration by impairing its apoptosis via up-regulation of Bcl-2, thereby resulting in deteriorated AHR and airway inflammation, which suggests that TLR4 could be a negative regulator of TDI-induced neutrophilic inflammation.