The progression of NF-кB in intestinal ischemia-reperfusion injury

Yu-Hua Zhang,Peng-Fei Zhu,Meng Wang,Yun-Jie Zhang,Jian Ding

1Graduate School of Shandong Traditional Chinese Medicine University,Shandong,China.2Thoracic Surgery Department3,Affiliated Hospital of Shandong University of Traditional Chinese Medicine,Shandong,China.General Surgery Department,Affiliated Hospital of Shandong University of Traditional Chinese Medicine,Shandong,China.

Abstract

Key words: Nuclear factor κB; Intestinal ischemia-reperfusion; Tumor necrosis factor

Intestinal ischemia-reperfusion injury (IIR)

Summary of IIR

IIR is a syndrome of intestinal ischemia,hypoxia and even ischemia necrosis caused by primary intestinal diseases or secondary intestinal diseases.In an ischemic state,in order to maintain perfusion of important organs such as the heart and brain,the body initiates a self-injury repair mechanism,at which time the intestinal tract becomes the earliest ischemia damaged organ.When the blood flow is re-perfused,not only can the symptoms of tissue ischemia and hypoxia not be alleviated quickly,but also the tissue and organ injury will be further aggravated.The re-perfusion injury is far more serious than the injury caused by ischemia itself.IIR not only damages intestinal tissue itself,but also has a serious impact on the functions of distant organs such as liver,lung,brain and other important organs [1-3].Severe cases can lead to systemic inflammatory response syndrome (SIRS) and multiple organ dysfunction syndrome (MODS),leading to multiple organ failure (MOF).

IIR pathogenesis

The pathogenesis of IIR is extremely complex and has not yet been fully elucidated.However,many recent studies have made new interpretations of IIR.At present,the mainstream theories are mainly summarized into the following three levels: (1) Pathophysiological level: Under the condition of ischemia and anoxia,a large amount of calcium ions flow in,the active oxygen radicals in the body are extremely active and unstable,and the lipid oxidation reaction of the cell membrane is affected,resulting in structural changes of the cell membrane,increased intestinal mucosa permeability,abnormal intestinal mucosa barrier function,and a large amount of endotoxin translocation,which also become one of the important causes of sepsis [4].Schellekens DH et al.found that the expression of serum intestinal fatty acid binding protein (I-FABP) increased significantly after intestinal mucosal permeability increased and barrier function was damaged,thus I-FABP could be used as a diagnostic index for IIR [5-6]; (2) cellular mechanism level: Apoptosis is a process of programmed cell death due to the influence of various factors inside and outside the receptor,which triggers the pre-stored death procedure in the cell.There are two main pathways in this process: one is the extracellular death receptor pathway,which activates P53,Bcl-2,NF-KB and other genes by stimulating factors,and activates Casepase-8 mediated by TNF family receptors.Another way is the mitochondrial pathway in cells.This pathway relies on stimulation factors to affect the mitochondrial membrane potential and promote a large amount of ion inflow.In addition,due to the attack of a large amount of oxygen free radicals,mitochondria swell and structural damage,which eventually lead to decomposition,thus promoting the release of cytochrome C peptide in mitochondria and activating Casepase-9.The two pathways finally activate Casepase-3 and further activate endonuclease,causing DNA strand breakage and cell structure disintegration,thus completing the whole process of cell apoptosis; (3) molecular level: Inflammatory reaction is one of the important mechanisms of IIR.Inflammatory mediators such as cytokines and adhesion factors can be destroyed by adhesion with endothelial cells,aggravating the damage of intestinal epithelial cells.Inflammatory cells mainly composed of leukocytes can block small blood vessels,resulting in secondary intestinal tissue hypoperfusion.The release of oxygen free radicals and vasoconstrictor substances increases vascular permeability,causing intestinal tissue edema and exacerbating intestinal tissue ischemia and hypoxia symptoms.

In recent years,there have been more and more researches on signal pathway in IIR pathogenesis,including both protective molecular mechanism and damaging molecular mechanism. Protective molecular mechanisms are as follows: SIRT1/p53 mechanism [7].SIRT1,as a member of Sirtuin family,deacetylates lysine sites on tumor-related protein p53 through acetylation,thus reducing the binding capacity of p53,weakening its ability to interfere with normal cell cycle and promote cell apoptosis,thus inhibiting or reducing cell apoptosis.Damaged molecular mechanisms, such as IκB-α/NF-κB/ICAM-1 pathway dominated by cytokines [8],PI3K/Akt/NF-κB pathway dominated by inflammatory factors [9],JAK2/STAT3 pathway dominated by inflammation and apoptosis [10],etc.Both the damaging molecular mechanism and the protective molecular mechanism have made a new exposition of IIR at the signal pathway level,and NF-кB plays an irreplaceable role in IIR damage among many signal pathways.

IIR prevention research

With the in-depth study on the pathogenesis of IIR,it provides strong support for timely and effective prevention and treatment.Prevention and treatment measures mainly include anti-inflammation,anti-apoptosis,anti-oxidative stress,anti-oxygen free radicals,regulation of related immune reactions,energy therapy,ischemic preconditioning and post-treatment,etc.In recent years,traditional Chinese medicine has also been widely used in IIR injury prevention and treatment [11].Regulating the activation of NF-кB is one of the important strategies to effectively reduce IIR damage to the body [12].It can not only affect intestinal inflammatory response by regulating inflammatory factors,but also affectintestinal epithelial cell regeneration by regulating apoptosis.

NF-κB

About NF-κB

NF-κB,as an important transcription regulator in cells,is an intermediate hub of intracellular signal transduction [13],and can participate in various biological processes of the body by regulating the expression of various genes,such as inflammatory response,apoptosis,immune response,tumor occurrence,tissue damage and repair,etc.Among them,NF-κB plays a two-way regulatory role on cell apoptosis,which can not only inhibit cell apoptosis through IAP family and Bcl-2 family,but also promote cell apoptosis through NF-κB self-activation.Under normal circumstances,NF-κB exists in the form of a trimer in an inactive state in the cytoplasm.The latter is formed by combining two members of NF-κB monomers and the inhibitory factor IKB.Under the stimulation of factors such as cytokines or endotoxin,NF-κB is activated and functions after being subjected to various translation and modification controls such as phosphorylation,acetylation,methylation and ubiquitination [14].

Application of NF-κB

NF-κB is widely present in a variety of tissues and cells,and specifically binds with a variety of gene promoters to participate in transcription regulation of various pathophysiological processes in the body.In recent studies,NF-κB has been widely used.Through its transcriptional regulation function,NF-κB exerts its regulation function on various organs of the body to varying degrees.NF-кB signal pathway plays an important role in the protection of brain injury and can slow down neurodegenerative brain diseases [15].NF-кB is also widely present in myocardial cells,especially after ischemia reperfusion,it is widely involved in the course of myocarditis,myocardial cell apoptosis and cardiac function decline.Besides playing an important role in important organs such as heart and brain,NF-κB can participate in the expression of cancer and many immune diseases by regulating many inflammatory cytokines [16].Moreover,it is also a core participant in maintaining innate immune homeostasis in the intestinal tract,which can reduce the damage of inflammation to the intestinal tract [17].Especially in IIR,NF-κB can affect the expression regulation of many cytokines and adhesion factors,induce intestinal inflammatory response or aggravate the original inflammatory response,and aggravate the multiple organ function damage caused by intestinal ischemia reperfusion.A better understanding and application of NF-κB can provide targeted intervention therapy for IIR-induced inflammatory injury [18].

Application of NF-κB in IIR injury

IIR- intestinal injury

Inflammation is one of the important pathogenesis of intestinal ischemia-reperfusion injury.Intestinal ischemia-reperfusion can significantly improve the sensitivity of endotoxin attack,leaving neutrophils and monocytes/macrophages in a sensitive state.Therefore,inhibiting the activation and release of various cytokines and inflammatory mediators is one of the important means to reduce IIR,and inhibiting the inflammatory reaction mediated by NF-кB signaling pathway plays an important role in this process.Liu QS et al.[19] pointed out that activation of PPAR-γ can regulate TLR-4/NF-κB signaling pathway,and rosiglitazone,as one of PPAR-γ agonists,can reduce intestinal inflammatory response after IIR and a series of pathological changes such as intestinal congestion and edema by inhibiting activation of the signaling pathway.Meng QT et al [20] proposed to control the overexpression of inflammatory cytokines and caspase-3 protein by inhibiting Nrf2/NF-κB signaling pathway,so as to reduce intestinal inflammatory response and intestinal cell apoptosis.Therefore,starting from the molecular mechanism level,playing the role of NF-κB in inflammatory response can effectively alleviate and alleviate intestinal injury caused by reperfusion.

Apoptosis is one of the other important pathogenesis of IIR.Its endogenous pathway mainly depends on stimulating factors to activate P53,NF-кB and so on,and finally activates endonuclease to cause cell disintegration and apoptosis.We can improve the survival rate of intestinal epithelial cells and reduce cell apoptosis by regulating the expression of anti-apoptosis genes and blocking the activation of NF-κ B.He X et al.[21] experiments prove that after up-regulating miR-146a in IIR rat IEC-6 cells,TLR4/TRAF6/NF-κB pathway is down-regulated and caspase 3 cleavage is reduced,Therefore,it is concluded that TLR4/TRAF6/NF-κB signaling pathway can reduce NF-κB p65 nuclear translocation and caspase 3 cleavage,thus improving the survival rate of intestinal epithelial cells and reducing cell apoptosis.The research of Wu ZM et al.[22] alleviates the apoptosis of intestinal epithelial cells by using hydrogen sulfide (H2S) to promote the phosphorylation of NF-κ B.All the above studies have confirmed that NF-κB plays an important role in cell apoptosis.We can reduce cell apoptosis by regulating NF-κB and play its protective role in IIR.At the same time,Tu I et al.[23] pretreated rats with intestinal ischemia-reperfusion by using S- nitrosoglutathione (GSNO).The results show that GSNO can reduce intestinal inflammatory reaction and oxidative stress reaction by inhibiting NF-κBactivation and reducing iNOS expression.In addition,studies by Jin Xiaosheng and others [24] prove that chitosan oligosaccharide inhibits NF-κB activity and alleviates intestinal mucosal damage by scavenging intestinal free radicals.Gingerol (6G),as the main active ingredient of ginger,also has a protective effect on IIR-induced intestinal mucosal injury.Li Y et al.believe that it may be related to inhibition of p38 MAPK/NF-κB signaling pathway [25].

To sum up,after IIR,NF-κB plays a protective role on intestinal tract by mediating multiple signal pathways.

IIR-distant organ injury

After IIR,it not only aggravates the damage of intestinal tissue itself,but also causes secondary damage to lung,liver,kidney,brain and other tissues and organs.NF-κB,as an important transcription factor,also plays an indispensable role.

IIR-lung injuryIIR can trigger systemic inflammatory reaction,and excessive inflammatory reaction is the important cause of acute lung injury.NF-κB plays a central role in this process.NF-κB and TNF-α form a positive feedback loop,and the two activate each other,eventually causing waterfall inflammatory reaction and aggravating lung injury.Liao Meijuan et al.also confirmed this point [26].Through curcumin pretreatment,the expression levels of TNF-α and IL-6 in lung tissue were significantly reduced,thus reducing the activation of NF-κB and further reducing the secondary lung injury degree of IIR.Chu L et al.also indicated that baicalein can reduce the level of TNF-α in lung tissue after intestinal ischemia reperfusion by inhibiting the activation of NF-κB [2].In other related studies,after IIR,the lung tissue will undergo histopathological changes,with congestion and edema in lung tissue and interstitial lung,and a large number of neutrophils widely infiltrating in alveolar and interstitial lung.NF-кBp65 is highly expressed in both alveolar stroma and nucleus,and NF-κB activity in lung tissue is significantly enhanced [27].The results showed that lung injury caused by IIR was closely related to the expression and activation of NF-κB.Under normal circumstances,N-myc downstream regulatory gene 2(NDRG2) is highly expressed in lung tissue.Yang Bo et al.pointed out that after IIR,the expression of NDRG2 in lung tissue is down-regulated,aggravating lung injury caused by IIR [28].NDRG2 is a stress-responsive gene,which mainly inhibits the degradation of IKBα by down-regulating IKB α/β,thus inhibiting the activation of NF-κB conduction pathway and eventually inhibiting cell apoptosis,thus playing a role in reducing the degree of lung injury caused by IIR.

IIR-liver injuryAfter IIR,intestinal mucosa causes intestinal epithelial cell damage,necrosis and shedding due to ischemia and hypoxia,inflammatory media,oxygen free radicals and other factors,intestinal mucosal barrier function is destroyed,permeability increases,enteric bacteria and toxins enter portal vein with blood,promoting the release of intestinal inflammatory media into blood circulation,causing liver cell damage.By activating Kupffer cells and neutrophils to release a large amount of proinflammatory factors and inflammatory media,NF-κB signaling pathway is activated,aggravating the degree of liver injury [29].After glutamine (Gln) was pretreated on intestinal ischemia-reperfusion injury rats,the expression levels of AST,ALT,NF-κB and SOD,GSH in serum were significantly decreased,and the expression levels of SOD,GSH and other were significantly increased [30],which indicated that Gln could reduce oxidative damage and inflammatory medium expression by inhibiting the expression of NF-κB,thus playing a role in reducing liver injury.Zhe Fan et al.experiments show that curcumin can significantly reduce MPO activity in liver and TNF-α level in serum [1].Its mechanism of action can be attributed to the anti-oxidation and anti-inflammatory effects by inhibiting NF-κB pathway,thus achieving the purpose of protecting liver.Wu ZM also pointed out that H2S can inhibit hepatocyte apoptosis by down-regulating the gene expression of caspase-3 and Bax,up-regulating the gene expression of Bcl-2,and inhibiting the release of cytochrome C from mitochondria to cytoplasm,thus playing a good protective role on liver injury caused by intestinal ischemia reperfusion [22].

IIR-kidney injuryDue to hypotension and oxidative stress caused by IIR,kidney has become an important target organ of IIR.Research by Sun Qian et al.found that after intestinal ischemia reperfusion for 2 hours,renal tubular epithelial cells produced a large number of edema,necrosis and vacuolation phenomena,and SOD activity in renal tissue decreased while MDA content increased [31].The above phenomena indicated that IIR could cause renal injury,and its mechanism may be closely related to IIR causing systemic oxidative stress reaction and large accumulation of renal oxygen free radicals.After IIR,oxygen free radicals in the body accumulate explosively,and free radicals in renal tubular epithelial cells also multiply,causing membrane lipid peroxidation,calcium ion influx,and initiating mitochondrial pathway of cell apoptosis.In this process,NF-кB plays a key role in regulating many genes in cells, especially immune inflammatory response,and plays an important role in B cell proliferation,glomerular activation and mesangial proliferation.

IIR-brain injuryThe main mechanism of IIR-induced brain injury is to induce lipid peroxidation by activating microglia in brain tissue,activating NOS and promoting ROS generation.Microglia TLR4/My D88 signaling pathway plays an important role in IIR renal injury [3].Yang B pointed out that melatonin can inhibit TLR4/My D88 signaling pathway,affect the expression levels of NF-кB,TNF-α,IL-6 and IL-1β,and further play anti-inflammation,anti-oxidation and anti-apoptosis roles,thus playing a protective role in IIR-induced brain injury.The process of body pain is often accompanied by the expression of phosphorylated NF-кB p65 in the central nervous system,increased nuclear translocation and activation of NF-кB signaling pathway,while IIR can aggravate the degree of body pain and intensify many inflammatory factors.Basic and clinical studies have found that the use of NF-кB inhibitor can effectively relieve the degree of inflammatory pain.Hong JQ et al.pointed out that paeoniflorin extract can inhibit Akt/NF-κB signaling pathway by inhibiting the release of inflammatory factors and activation of spinal microglia,thus achieving the purpose of relieving inflammatory pain and also reducing central nerve pain caused by intestinal ischemia reperfusion [32].

IIR- myocardial injuryThe longer the reperfusion time is,the more serious the congestion and edema of intestinal wall will be.Endotoxic shock characterized by hypotension can affect myocardial perfusion and lead to dysfunction of myocardial energy metabolism.IIR injury to myocardium can be reflected in activating NF-кB,thus stimulating inflammatory response, oxidative stress and apoptosis in myocardial cells [33].Therefore,NF-кB inhibitor is also one of the effective methods to reduce IIR-induced myocardial cell injury.

Discussion

To sum up,IIR is a complex pathophysiological process,which includes both primary injury at the initial stage of ischemia and secondary injury caused by reperfusion.In this process,NF-кB plays a role through the regulation of multiple targets,which has important implications for IIR and multiple organ injury caused by IIR.In recent years,although great progress has been made in the study of IIR,its mechanism of action is complex and its pathophysiology is varied.At present,there is still a lack of clinical verification,which makes it impossible to organically combine the research results with clinical studies.There is also a lack of large-scale,long-term,controlled and prospective clinical studies.Therefore,on the one hand,we need to make full use of modern advanced means,carry out basic research,collect a large number of samples,and discuss the role of NF-кB in IIR from multiple angles and in depth.On the other hand,the theoretical research results should be combined with clinical practice to better guide the treatment of clinical IIR.