Chronic systemic inflammation, as an independent risk factor, can promote the development of atherosclerosis. It can interfere with physiological hemostasis, induce hypercoagulability, and lead to thrombosis[16]. Therefore, chronic inflammatory diseases are usually associated with a high risk of thromboembolism[29, 30].
Ischemic stroke, one of the world's highest-risk brain injuries, has been described as an inflammatory bowel disease complication that can manifest as narrowing, occlusion or acute circulatory disturbance of the cerebral arteries[31, 32]. The pathogenesis of IS is complex and can be caused by a variety of systemic symptoms, such as arteriosclerosis, cardiovascular inflammation, arrhythmias and brain dysfunction caused by thrombosis[10, 33]. With the growth of cerebral artery embolus, the intracellular environment is destroyed, resulting in serious blood shortage, thus promoting a variety of immune signals, such as chemokines, cytokines and matrix metalloproteinases (MMPs) 1, 2 and 9, which are discharged from the brain and flow into the intestine[34, 35]. Subsequent reperfusion increases blood cell infiltration, including allowing natural neutrophil, killer cell (NK), monocytes, or lymphocyte to enter the damaged brain parenchyma. In this process, inflammation is triggered because these signals or immune factors are transmitted to other organs[36]. Many cases have been elucidated that the intestine, as the most versatile human organ, can induce different intestinal pathology while continuously obtaining the immune signals released by the brain injured area[37–39]. Brain-gut axis is also regarded as an effective channel for small immune molecules (including interleukins, interferons, neurotransmitters, peptides and chemokines) that can penetrate the mesentery and brain barrier (BBB) because of its special fulcrum role in human circulation[40, 41].during the development of IS, Hypoxic ischemia interferes with the release and communication of molecular signals, thereby providing feedback to the intestinal tract, leading to pituitary and neural dysfunction[42]. Long-term exposure to this disease may disrupt the homeostasis of the peripheral system and may also lead to various intestinal complications, including CD[30, 42].
IS and CD might have overlapping pathogenic pathways, Inflammatory and immune regulatory pathways, such as nod like receptor protein 3 (NLRP3)/IL-17A pathways are linked to the pathogenesis of both diseases[43, 44]. At present, NLRP3 inhibitors are commonly used to treat IS[45, 46]. The aim of this study was to determine the hub genes in IS and CD. For this reason, we explored the shared molecular biological functions and pathways between IS and CD in order to determine their relationship. In this study, the common hub genes and pathways of IS and CD were explored through the combination of public database mining and bioinformatics analysis. CXCL1 and FCGR1A were significantly up regulated in patients with IS and CD, and they were identified as hub genes.
Chemokine (C-X-C motif) ligand 1(CXCL1) is a secreted single-chain protein with chemotactic properties belonging to the CXC chemokine family, also known as grown-regulated oncogene α (GRO α)[47, 48]. Previous studies have shown that increased expression of CXCL1 gene and protein is significantly correlated with the occurrence of ischemic stroke, and positively correlated with brain infiltrating neutrophils. This is due to the presence of an ELR (glutamic leucine arginine) functional region on the amino acid sequence of CXCL1, which gives it strong chemotactic activity against neutrophils and is involved in the development of inflammatory damage in the brain[49]. In addition, CXCL1 can promote the activation and release of NLRP3 inflammasome in macrophages by binding to CXCR2 after different brain injuries such as inflammation, injury, hypoxia and ischemia[50–53], promoting the occurrence of inflammatory response. Therefore, many scholars believe that the combination of CXCL1 and CXCL2 is a chemotactic agent for T cells, monocytes and neutrophils in the brain[52, 54]. A study has shown that reducing the expression of CXCL1 and blocking the combination of CXCL1 and CXCR2 can effectively improve the chemical attraction and infiltration mechanism of neutrophils after stroke, thus achieving therapeutic goals[55]. In addition, some scholars utilized the negative correlation between miR-532-5p and CXCL1 to increase the level of miR-532-5p in SH-SY5Y brain tissue of rats, thereby inhibiting CXCL1/CXCR2 signaling pathway and alleviated in vivo and in vitro cerebral ischemia reperfusion injury (CI/RI)[56]. Other studies on CD also found that CXCL1 expression in CD was significantly increased compared with the intestinal mucosal tissues of normal patients and was closely related to the progression of CD activity. The e manner in which CXCL1 interferes with neutrophil infiltration has also been demonstrated in the treatment of experimental IBD mouse models[57]. In addition, CXCL1 has been found to be essential to produce reactive oxygen species, which further regulate inflammation, induce the activation and assembly of NLRP3 inflammasome, and regulate the maturation, secretion and immune response of IL-1β and IL-18 [53, 58]. Th17 cells are thought to play an important immunomodulatory role in CD. New studies have shown that CXCL1 is involved in the differentiation of Th17 [59], and stimulates the chemotaxis of neutrophils and Th17 cells to inflammatory sites[60, 61]. Moreover, IL-17A, which inhibits Th17 cell secretion, also reduces the inflammatory burden and inflammatory cell infiltration in plaques, significantly stops the progression of atherosclerosis, and improves plaque stability in apolipoprotein E-deficient mice [62]. These studies reveal the direction of our future work and suggest the need to examine the time course of serum CXCL1 levels in patients with IS and CD, focusing on its role in inflammatory response and recruitment of immune cells.
FCGR1A is an IgG receptor associated with the early stages of inflammation and is also known as CD64[63, 64]. Under normal physiological conditions, CD64 is expressed constitutively on macrophages, monocytes, and eosinophils, but it may not be as active on a resting neutrophil[65]. However, in the case of infection or inflammation, A rapid increase in CD64 expression on neutrophil surfaces can occur in cases of infection or inflammation, even by up to 10 times[66]. Therefore, The CD64 receptor serves as a bridge between humoral immunity and cellular immunity in the onset and maintenance of chronic diseases. Aside from regulating phagocytosis, it also interferes immune complex clearance (such as inhibiting IFN- γ And TLR4 signal transduction), affect antigen presentation and stimulate the release of inflammatory mediators[65]. Previous studies have found that CD64 activates NF- κ B through the phosphoinositide 3-kinase (PI3K) / protein kinase B (Akt) cascade and is involved in the regulation its downstream molecules, including NLRP3[66, 67]. Upon interaction with the ligand apoptosis associated speck like protein (ASC), NLRP3 is allowed to be recruited by NF- κ B activates the produced caspase-1 and triggers the maturation process of IL-1 β and IL-18, Leading to irreversible tissue decline and immune activation disorders[67, 68]. Accumulating evidence suggests that CD64 is a regulator of microbial attack in intestinal mucositis[69], which can undermine host tolerance and induce aberrant immune responses leading to CD[70].In a clinical study, it was found that the proportion of CD64 expression in polymorphonuclear neutrophils (PMNs) of CD patients was significantly higher than that of healthy people[71, 72]. Due to the change of intestinal permeability, the luminal antigens of CD patients can penetrate the mucosal epithelium and cause the activation of B cells in the lamina propria, which triggers the release of IgG and the binding of CD64, and finally causes a series of cytotoxic reactions in the transferred PMN[72]. In addition, it has been reported that CD64 can be used as a biomarker for the diagnosis of gastrointestinal tract in CD patients, and it’s up-regulation is related to clinical and biological parameters of inflammation in CD patients[69], Compared with other laboratory markers, it has stronger correlation and specificity with CD activity index, and its clinical value is more significant[72]. Currently, few experiments have directly revealed the relationship between FCGR1A and IS development, which is also a novel finding in this study. Previous studies have shown that FCGR1A gene knockout can significantly block the expression of NF-κ B p65, inhibit the activation of NLRP3 inflammasome, and down-regulate the release of inflammatory factors from macrophages[66]. We believe that mediating inflammation plays an indispensable role in IS[68], so FCGR1A may cause inflammatory response and affect the development of IS by participating in the expression of related proteins mediated by this pathway. The pathophysiological role of FCGR1A in IS and CD is still unclear, which is one of the focuses in subsequent studies.
In this study, GO enrichment analysis indicated that the neutrophil migration is common pathogenesis of IS and CD. Furthermore, neutrophil migration has been suggested to be the mechanism behind both IS and CD, according to published research.
Neutrophils, the most abundant white blood cells in the blood, promote repair by forming a first line of defense against invading cells by pathogens and deploying an effective enzymatic and chemical weapon to neutralize and therefore remove invaders and necrotic tissue[73, 74]. Once abnormal recruitment and activation occur and lead to impaired clearance, this will aggravate the initial inflammatory response and continue to be prolonged and worsened[74–76]. The persistent inflammatory response is considered a major component of many diseases, including cardiovascular disease and inflammatory bowel disease[76, 77].Activated neutrophils damage the blood-brain barrier, migrate and infiltrate with a large amount of protein leakage into the brain tissue, release neurotoxic substances to destroy brain homeostasis and aggravate neuronal death[35, 41, 78–80]. In addition, after 3 days of reperfusion, the ischemic hemisphere was almost completely inundated by it, and its recruitment in the infarct area was also a direct cause of poor neurological outcome[81–84]. Platelets play a key role in the prevention of thrombotic stroke, and neutrophils bind to them as dependent recruiters to release ROS, triggering neural and endothelial cytotoxic effects and altering BBB permeability[85–87]. Alternatively, in a high-cutting environment, their combination can directly increase blood vessel coagulation, which IS also critical for IS injury[85, 87]. Studies have confirmed that MMP-9 can disrupt the ischemic blood-brain barrier, causing leukocyte infiltration and secondary brain injury, and neutrophils are the main source of MMP-9 after IS[40]. An in vitro experiment using NRG1-β to treat human brain microvascular endothelial cells found that NRG1-β could reduce the level of IL1-β-activated neutrophil adhesion to brain microvascular endothelial cells, fundamentally reducing the recruitment and migration of neutrophils in IS patients, thereby playing a neuroprotective role[81]. Therefore, treatment of stroke by rebalancing the proportion of senescent versus immunosuppressed neutrophils or reducing reverse neutrophil transport or both is a potential means.[88]. Previous studies have shown that neutrophil dysfunction is also associated with intestinal inflammation. In many immune cells involved in CD, neutrophils are the first to infiltrate[89], It may destroy the epithelial barrier through oxidation and proteolysis, and release cytokines and chemokines related to proinflammatory effects to perpetuate inflammation[90, 91]. Of course, in addition to phagocytosis and chemotaxis, the most important thing is that neutrophils can form extracellular traps (nets) similar to reticular structures, which undoubtedly act as traps to increase tissue damage. NETosis, as a unique mode of NETs formation[92], also happens to be a promoter of neutrophil activation and endothelial cell injury[91, 93, 94]. In patients with active CD, the levels of cell-free DNA (cfDNA) and MPO-DNA complexes are significantly increased, suggesting disease, inflammation and tissue damage[95, 96]. cfDNA endogenous damage NETs, which regulate the non-classical signaling pathway mediated Toll-like (TLR9) pathway to trigger NETosis, induce the release of pro-inflammatory chromatin network[92, 97, 98], active the innate and adaptive immunity[92, 95].As a hallmark of inflammatory diseases[99]. migrating neutrophils, releasing mediators such as IL-8, TNF-α and leukotriene B4, activate inflammatory pathways and damage the epithelial barrier while recruiting more neutrophils into the gut[91]. Excessive recruitment and accumulation can delay neutrophil lysis and continuously induce mucosal destruction[91, 100]. The presence of intestinal mucosal neutrophils in remission in clinical CD patients is also considered a marker of disease recurrence, whereas mucosal neutrophil loss and reduction indicate tissue healing[101, 102]. Taken together, neutrophil migration and recruitment may contribute to the development of IS and CD by inducing immunity and regulating inflammatory responses.
Interestingly, many studies have revealed that changes in intestinal microbiota are one of the risk factors for atherosclerosis and are associated with cardiovascular diseases[7]. The metabolic potential of intestinal microbiota is also considered to be an element contributing to the occurrence of IS[103]. Trimethylamine N-oxide (TMAO), a hepatic oxidation product of the microbial metabolite by trimethylamine (TMA), which was found to accelerate atherosclerosis in experimental models[104]. TMAO was involved in the development of stroke, leading to high platelet reactivity, promoting thrombosis, and increasing the risk of IS. Although aberrant microbial composition had also been found in IBD, TMAO of IBD patients was lower than that of the control group, at which point it with a protective effect on the heart and considered a beneficial factor[105]. Thus, the role of gut microbiota in IBD may not be achieved by regulating metabolites such as TMAO, but rather by affecting inflammation and immune activity[13]. In this theory, no genes related to intestinal microbial metabolites were found, supporting the above theory.
Although many previous studies have separately explored the hub genes related to Ischemic stroke and Crohn’s Disease. However, few studies used advanced bioinformatics methods to explore their common molecular mechanisms. In this study, we first explored and identified common DEGs, hub genes and Immune Infiltration of IS and CD, which will help to further clarify the pathogenesis of both. However, our research also has some limitations. First of all, there is a lack of databases containing two diseases at the same time, so we can only analyze through the data set of a single disease; Secondly, in the present retrospective study, the function and pathways of hub genes have not been validated in experiments and need to be confirmed in vitro models, which will be the focus of our future investigations. To conclude, we identified common DEGs between IS and CD, performed enrichment, and analyzed the PPI network. There is a possible relationship between IS and CD in terms of pathogenic mechanisms that may be mediated by specific hub genes. This study indicates a potential direction for further investigation into the molecular mechanisms underlying IS and CD.