The association between the gene encoding 5-lipoxygenase activating protein and abdominal aortic aneurysms

Genetic Variants in the Transcriptional Regulatory Region of the ALOX5AP gene and Susceptibility to Ischemic Stroke in Chinese Populations

No coding sequence variants of the ALOX5AP gene that lead to amino acid substitutions have been identified. A two-stage study design was used to explore the relationship between variants in the transcriptional regulatory region of ALOX5AP gene and ischemic stroke (IS) risk in Chinese populations. IS was determined using CT and/or MRI. First, 18 SNPs, located in the upstream promoter region of ALOX5AP gene, were genotyped in 200 IS patients and 200 controls. And one potential associated SNP (rs17222919) was identified (P = 0.005,OR = 0.623, 95% CI: 0.448~0.866). Next, another independent case-control cohort comprising 810 IS patients and 825 matched controls was recruited to investigate the role of rs17222919, rs9579646 polymorphisms and their haplotypes in IS risk. The G allele frequency of rs17222919 in the IS group was significantly lower than that in control group (P = 0.007, OR = 0.792, 95% CI: 0.669~0.937). T-A and G-A haplotypes were associated with IS (P = 0.001,OR = 1.282, 95% CI:1.100~1.495; P = 0.0001, OR = 0.712, 95% CI: 0.598~0.848; respectively). Our study providesevidence that rs17222919 is a potential genetic protective factor against IS. Furthermore, the T-A haplotype is a risk factor and the G-A haplotype is a protective factor against IS in Chinese population.

Oxidative stress and abdominal aortic aneurysm: potential treatment targets

Abdominal aortic aneurysm (AAA) is a significant cause of mortality in older adults. A key mechanism implicated in AAA pathogenesis is inflammation and the associated production of reactive oxygen species (ROS) and oxidative stress. These have been suggested to promote degradation of the extracellular matrix (ECM) and vascular smooth muscle apoptosis. Experimental and human association studies suggest that ROS can be favourably modified to limit AAA formation and progression. In the present review, we discuss mechanisms potentially linking ROS to AAA pathogenesis and highlight potential treatment strategies targeting ROS. Currently, none of these strategies has been shown to be effective in clinical practice.

Abdominal Aortic Aneurysm Genetic Associations: Mostly False? A Systematic Review and Meta-analysis

OBJECTIVE/BACKGROUND

Many associations between abdominal aortic aneurysm (AAA) and genetic polymorphisms have been reported. It is unclear which are genuine and which may be caused by type 1 errors, biases, and flexible study design. The objectives of the study were to identify associations supported by current evidence and to investigate the effect of study design on reporting associations.

METHODS

Data sources were MEDLINE, Embase, and Web of Science. Reports were dual-reviewed for relevance and inclusion against predefined criteria (studies of genetic polymorphisms and AAA risk). Study characteristics and data were extracted using an agreed tool and reports assessed for quality. Heterogeneity was assessed using I(2) and fixed- and random-effects meta-analyses were conducted for variants that were reported at least twice, if any had reported an association. Strength of evidence was assessed using a standard guideline.

RESULTS

Searches identified 467 unique articles, of which 97 were included. Of 97 studies, 63 reported at least one association. Of 92 studies that conducted multiple tests, only 27% corrected their analyses. In total, 263 genes were investigated, and associations were reported in polymorphisms in 87 genes. Associations in CDKN2BAS, SORT1, LRP1, IL6R, MMP3, AGTR1, ACE, and APOA1 were supported by meta-analyses.

CONCLUSION

Uncorrected multiple testing and flexible study design (particularly testing many inheritance models and subgroups, and failure to check for Hardy-Weinberg equilibrium) contributed to apparently false associations being reported. Heterogeneity, possibly due to the case mix, geographical, temporal, and environmental variation between different studies, was evident. Polymorphisms in nine genes had strong or moderate support on the basis of the literature at this time. Suggestions are made for improving AAA genetics study design and conduct.

A promoter polymorphism (rs17222919, -1316T/G) of ALOX5AP gene is associated with decreased risk of ischemic stroke in two independent Chinese populations

No coding sequence variants of the gene encoding 5-lipoxygenase-activating protein (ALOX5AP) leading to amino acid substitutions have been identified. Therefore, variants in the ALOX5AP promoter region have received attention recently. The purpose of this study was to explore whether the promoter polymorphism rs17222919 is involved in the etiology of ischemic stroke (IS) in the Chinese Han population. We investigated the rs17222919 polymorphism by TaqMan genotyping in two independent Chinese Han samples: the first comprised 910 IS patients and 925 healthy inhabitants from the northern Henan Province, while the second included 1003 IS patients and 889 healthy controls from the southern Henan Province. Functional characterization of rs17222919 was performed by an in vitro luciferase assay. After adjusting for conventional risk factors, the G allele frequencies in the IS groups were significantly lower than that in the control groups of the two independent Chinese cohorts (19.0% vs. 22.9%, P = 0.004, odds ratio (OR) = 0.792, 95% confidence interval (CI) = 0.675-0.929; 18.8% vs. 22.9%, P = 0.002, OR = 0.782, 95% CI = 0.668-0.915, respectively). This was also observed in the large-artery atherosclerosis (LAA) and stroke of other undetermined etiology (SUE) subtypes (P = 0.019, OR = 0.815, 95% CI = 0.687-0.967; P = 0.021, OR = 0.815, 95% CI = 0.685-0.970, respectively). Additionally, the TG genotype and G allele frequencies were significantly lower in the IS compared with the control group in two female cohorts (P<0.05). Finally, the in vitro luciferase assay demonstrated that the G allele has a significantly lower transcription activity than the T allele (P = 0.031). Our study provides evidence that the promoter single nucleotide polymorphism (SNP) rs17222919 is a potential genetic protective factor for IS in the Chinese Han population.

5-Lipoxygenase pathway in experimental abdominal aortic aneurysms

OBJECTIVE

The impact of leukotriene production by the 5-lipoxygenase (5-LO) pathway in the pathophysiology of abdominal aortic aneurysms (AAAs) has been debated. Moreover, a clear mechanism through which 5-LO influences AAA remains unclear.

APPROACH AND RESULTS

Aneurysm formation was attenuated in 5-LO(-/-) mice, and in lethally irradiated wild-type mice reconstituted with 5-LO(-/-) bone marrow in an elastase perfusion model. Pharmacological inhibition of 5-LO-attenuated aneurysm formation in both aortic elastase perfused wild-type and angiotensin II-treated LDLr(-/-) (low-density lipoprotein receptor) mice, with resultant preservation of elastin and fewer 5-LO and MMP9 (matrix metalloproteinase)-producing cells. Separately, analysis of wild-type mice 7 days after elastase perfusion showed that 5-LO inhibition was associated with reduced polymorphonuclear leukocyte infiltration to the aortic wall. Importantly, 5-LO inhibition initiated 3 days after elastase perfusion in wild-type mice arrested progression of small AAA. Human AAA and control aorta corroborated these elastin and 5-LO expression patterns.

CONCLUSIONS

Inhibition of 5-LO by pharmacological or genetic approaches attenuates aneurysm formation and prevents fragmentation of the medial layer in 2 unique AAA models. Administration of 5-LO inhibitor in small AAA slows progression of AAA. Targeted interruption of the 5-LO pathway is a potential treatment strategy in AAA.

Multiple-site activation of the cysteinyl leukotriene receptor 2 is required for exacerbation of ischemia/reperfusion injury

OBJECTIVE

Transgenic overexpression of the human cysteinyl leukotriene receptor 2 (CysLT2R) in murine endothelium exacerbates vascular permeability and ischemia/reperfusion injury. Here, we explore the underlying mechanisms of CysLT2R activation-mediated inflammation and delineate the relative contributions of endogenous murine CysLT2R and the transgene-derived receptor.

APPROACH AND RESULTS

We created a novel mouse with only endothelial-expressed CysLT2R (endothelium-targeted overexpression mice [EC]/CysLT2R-knockout mice [KO]) by crossing EC with KO to dissect the role of endothelial CysLT2R in tissue injury. Surprisingly, we discovered that damage in EC/KO mice was not elevated (24% versus 47% EC) after ischemia/reperfusion. We examined vascular permeability and leukocyte recruitment/rolling responses in the cremaster vasculature after cysteinyl leukotriene (cysLT) stimulation. Mice possessing transgenic endothelial CysLT2R overexpression, whether EC or EC/KO, when stimulated with cysLTs, exhibited vascular hyperpermeability, declining leukocyte flux, and a transient increase in slow-rolling leukocyte fraction. Mice lacking endogenous CysLT2R (both KO [20 ± 3 cells/min] EC/KO [24 ± 3]) showed lower-rolling leukocyte flux versus wild-type (38 ± 6) and EC (35 ± 6) mice under unstimulated conditions. EC/KO mice differed from EC counterparts in that vascular hyperpermeability was not present in the absence of exogenous cysLTs.

CONCLUSIONS

These results indicate that endothelial and nonendothelial CysLT2R niches have separate roles in mediating inflammatory responses. Endothelial receptor activation results in increased vascular permeability and leukocyte slow-rolling, facilitating leukocyte transmigration. Nonendothelial receptors, likely located on resident/circulating leukocytes, facilitate endothelial receptor activation and leukocyte transit. Activation of both receptor populations is required for injury exacerbation.

A novel risk haplotype of ALOX5AP gene is associated with ischemic stroke in Chinese Han population

Previous studies have implicated that two at-risk haplotypes (HapA and HapB) of gene-encoding 5-lipoxygenase-activating protein (ALOX5AP) were significantly associated with stroke. The aim of this study was to explore the association between haplotypes of ALOX5AP gene and risk for ischemic stroke (IS) in Chinese Han population. A total of 492 patients with IS and 490 matched control subjects were recruited. Six ALOX5AP SNPs (SG13S377, SG13S114, SG13S41, SG13S89, SG13S32 and SG13S35) were genotyped by SNaPshot minisequence technique. A common genetic variant SG13S114/AA in the ALOX5AP gene was associated with IS in this Chinese cohort (OR = 2.514, 95 % CI = 1.667 ~ 3.790). HapA (TGA) and HapB (AAAG) had no significant difference in the patients (36.3 and 18.5 %, respectively) and controls (37.6 and 16.3 %, respectively) (P = 0.631 and P = 0.375, respectively). But, the frequency of Hap (GAAG) was significantly higher in the patients than that in the controls after Bonferroni's adjustment (P = 0.006). To conclude, SG13S114/AA of the ALOX5AP gene was associated with an increased risk for IS. A novel risk haplotype, Hap (GAAG) was a genetic risk factor for IS in this Chinese population.

The leukotrienes: immune-modulating lipid mediators of disease

The leukotrienes are important lipid mediators with immune modulatory and proinflammatory properties. Classical bioactions of leukotrienes include chemotaxis, endothelial adherence, and activation of leukocytes, chemokine production, as well as contraction of smooth muscles in the microcirculation and respiratory tract. When formed in excess, these compounds play a pathogenic role in several acute and chronic inflammatory diseases, such as asthma, rheumatoid arthritis, and inflammatory bowel disease. An increasing number of diseases have been linked to inflammation implicating the leukotrienes as potential mediators. For example, recent investigations using genetic, morphological, and biochemical approaches have pointed to the involvement of leukotrienes in cardiovascular diseases including atherosclerosis, myocardial infarction, stroke, and abdominal aortic aneurysm. Moreover, new insights have changed our previous notion of leukotrienes as mediators of inflammatory reactions to molecules that can fine-tune the innate and adaptive immune response. Here, we review the most recent understanding of the leukotriene cascade with emphasis on recently identified roles in immune reactions and pathophysiology.