The influence of genetics on intracranial aneurysm formation and rupture: current knowledge and its possible impact on future treatment

Intracranial Aneurysms and Lipid Metabolism Disorders: From Molecular Mechanisms to Clinical Implications

Many vascular diseases are linked to lipid metabolism disorders, which cause lipid accumulation and peroxidation in the vascular wall. These processes lead to degenerative changes in the vessel, such as phenotypic transformation of smooth muscle cells and dysfunction and apoptosis of endothelial cells. In intracranial aneurysms, the coexistence of lipid plaques is often observed, indicating localized lipid metabolism disorders. These disorders may impair the function of the vascular wall or result from it. We summarize the literature on the relationship between lipid metabolism disorders and intracranial aneurysms below.

Gene Expression in Intracranial Aneurysms-Comparison Analysis of Aneurysmal Walls and Extracranial Arteries with Real-Time Polymerase Chain Reaction and Immunohistochemistry

BACKGROUND

This study was aimed at evaluating the gene expression levels of 4 genes in the intracranial aneurysm wall and comparing them with extracranial arteries. The analysis was done using real-time polymerase chain reaction (RT-PCR) and immunohistochemistry (IHC). Also, a correlation of the differential genetic expression was done with various patient clinical and radiologic factors.

METHODS

The quantitative assessment of ribonucleic acid levels was done with RT-PCR and was validated with IHC. The genes studied were collagen 1A2 (COL1A2), tissue inhibitor of metalloproteinase 4 (TIMP4), cathepsin B (CTSB), and alpha-1 antitrypsin (α-1 AT). The analysis was done on 24 aneurysm sacs and superficial temporal/occipital artery samples from patients undergoing surgical clipping.

RESULTS

The mean fold change of COL1A2 in the aneurysm sample was 8.89, that of TIMP4 was 10.16, that of CTSB was 1.02, and that of α-1 AT was 1.46 when compared with normal control vessel on PCR. On semiquantitative IHC, COL1A2 was 94.44%, α-1 AT was 77.8% overexpressed, CTSB was positive in 50%, and the expression of TIMP4 was 94.4% underexpressed in aneurysmal walls. There was no statistically significant correlation between patient profile and gene expression.

CONCLUSIONS

On RT-PCR and IHC analysis, COL1A2 and α-1 AT were overexpressed, CTSB was marginally overexpressed, and TIMP4 had equivocal expression in the aneurysmal sac when compared with the normal extracranial vessel. This is the first study of its kind in the Indian population with the largest sample size on live human patients.

Genetic Risk Assessment of Elastin Gene Polymorphisms with Intracranial Aneurysm in Koreans

Elastin encoded by elastin gene (ELN) is a crucial extracellular matrix protein responsible for arterial resilience. The objective of this study was to identify single nucleotide polymorphisms (SNPs) of ELN gene susceptible to intracranial aneurysm (IA) in Korean population. Two SNPs of ELN gene, rs2071307 (Gly422Ser) and rs2856728 (intron), were genotyped in 90 patients with IA and 90 age and frequency matched controls. Fisher’s exact test was conducted to evaluate allelic association with IA. Of the two SNPs in ELN gene, T allele of rs2856728 (intron) showed statistically significant association with increased development of IA (odds ratio [OR]: 2.34, 95% confidence interval [CI]: 1.44–3.81, P = 7.6 × 10⁻⁴). However, G allele of rs2071307 (Gly422Ser) had no significant association with the development of IA (OR: 1.27, 95% CI: 1.44–3.81, P = 0.607). Interestingly, the odds of having rs2856728 variant was approximately 2-fold higher in males than that in females (OR: 3.46 vs. 1.88, P < 0.05). However, none of SNPs showed difference between single and multiple IA in this study. This preliminary study implies that the rs2856728 variant in ELN gene polymorphisms might play crucial roles in the development and pathogenesis of IA in Korean population.

Aneurysmal subarachnoid hemorrhage: relationship to solar activity in the United States, 1988-2010

Aneurysmal subarachnoid hemorrhage (SAH) is a common condition treated by neurosurgeons. The inherent variability in the incidence and presentation of ruptured cerebral aneurysms has been investigated in association with seasonality, circadian rhythm, lunar cycle, and climate factors. We aimed to identify an association between solar activity (solar flux and sunspots) and the incidence of aneurysmal SAH, all of which appear to behave in periodic fashions over long time periods. The Nationwide Inpatient Sample (NIS) provided longitudinal, retrospective data on patients hospitalized with SAH in the United States, from 1988 to 2010, who underwent aneurysmal clipping or coiling. Solar activity and SAH incidence data were modeled with the cosinor methodology and a 10-year periodic cycle length. The NIS database contained 32,281 matching hospitalizations from 1988 to 2010. The acrophase (time point in the cycle of highest amplitude) for solar flux and for sunspots were coincident. The acrophase for aneurysmal SAH incidence was out of phase with solar activity determined by non-overlapping 95% confidence intervals (CIs). Aneurysmal SAH incidence peaks appear to be delayed behind solar activity peaks by 64 months (95% CI; 56-73 months) when using a modeled 10-year periodic cycle. Solar activity (solar flux and sunspots) appears to be associated with the incidence of aneurysmal SAH. As solar activity reaches a relative maximum, the incidence of aneurysmal SAH reaches a relative minimum. These observations may help identify future trends in aneurysmal SAH on a population basis.

Body pigmentation as a risk factor for the formation of intracranial aneurysms

Recent studies demonstrated pigmented cells both in the murine heart, in pulmonary veins, and in brain arteries. Moreover, a role for melanocytes in the downregulation of inflammatory processes was suggested. As there is increasing evidence that inflammation is contributing significantly to the pathogenesis of intracranial aneurysms, melanocyte-like cells may be relevant in preventing age-related impairment of vessels. As pigmentation of the heart reflects that of coat color, aspects of body pigmentation might be associated with the incidence of intracranial aneurysms. We performed a case-control study to evaluate associations between the pigmentation of hair and eyes and the formation of aneurysms. In addition to hair and eye color, constitutive and facultative skin pigmentation were assessed in a replication study as well as individual handedness which can be seen as a neurophysiological correlate of developmental pigmentation processes. Hair pigmentation was highly associated with intracranial aneurysms in both samples, whereas eye pigmentation was not. In the replication cohort, facultative but not constitutive skin pigmentation proved significant. The strongest association was observed for individual handedness. Results indicate a significant association of intracranial aneurysms with particular aspects of body pigmentation as well as handedness, and imply clinical usefulness for screening of aneurysms and possible interventions.

Association of Kallikrein gene polymorphisms with sporadic intracranial aneurysms in the Chinese population

OBJECT

Variants of Kallikreins have been shown to be risk factors for intracranial aneurysm (IA) in a Finnish population. In the present study, the authors investigated the correlation between polymorphisms in the Kallikrein gene cluster and IAs in the Chinese population.

METHODS

The association of Kallikrein variants (rs1722561 and rs1701946) with sporadic IAs was tested in 308 cases and 443 controls. The differences in allelic frequencies between patients and the control group were evaluated with the chi-square test.

RESULTS

The C allele of rs1722561 showed a significant reduction in the risk of sporadic IA (OR 0.71, 95% CI 0.53-0.95; p = 0.023). However, no association of the variant rs1701946 with sporadic IA was found (OR 0.78, 95% CI 0.57-1.06; p = 0.115).

CONCLUSIONS

The variant rs1722561 of Kallikreins might reduce the risk of sporadic IAs among individuals of Chinese Han ethnicity. This study confirms the association between Kallikreins and IAs.

Cerebral aneurysms: formation, progression, and developmental chronology

The prevalence of unruptured intracranial aneurysms (UIAs) in the general population is up to 3%. Existing epidemiological data suggests that only a small fraction of UIAs progress towards rupture over the lifetime of an individual, but the surrogates for subsequent rupture and the natural history of UIAs are discussed very controversially at present. In case of rupture of an UIA, the case fatality is up to 50%, which therefore continues to stimulate interest in the pathogenesis of cerebral aneurysm formation and progression. Actual data on the chronological development of cerebral aneurysm has been especially difficult to obtain and, until recently, the existing knowledge in this respect is mainly derived from animal or mathematical models or short-term observational studies. Here, we review the current data on cerebral aneurysm formation and progression as well as a novel approach to investigate the developmental chronology of cerebral aneurysms.

MicroRNA/mRNA profiling and regulatory network of intracranial aneurysm

Background

Intracranial aneurysm (IA) is one of the most lethal forms of cerebrovascular diseases characterized by endothelial dysfunction, vascular smooth muscle cell phenotypic modulation, inflammation and consequently loss of vessel cells and extracellular matrix degradation. Besides environmental factors, genetics seem to be a very important factor in the genesis of this disease. Previous mRNA expression studies revealed a large number of differentially expressed genes between IA and control tissue. However, microRNAs (miRNA), small non-coding RNAs which are post-transcriptional regulators of gene expression, have been barely studied. Studying miRNAs could provide a hypothetical mechanism underlying rupture of IA.

Methods

A microarray study was carried out to determine difference in microRNAs and mRNA between patients’ IA tissues and controls. Quantitative RT-PCR assay compared the expression level between two groups (14 IA domes vs. 14 controls) were used for validation. Validated miRNAs were analyzed using Ingenuity Pathway Analysis (IPA) to identify the networks and pathways.

Results

18 miRNAs were confirmed by qPCR to be robustly down-regulated in 14 ruptured IA patients including hsa-mir-133b, hsa-mir-133a, hsa-mir-1, hsa-mir-143-3p, hsa-mir-145-3p, hsa-mir-145-5p, hsa-mir-455-5p, hsa-mir-143-5p, hsa-mir-23b-3p etc., of which 11 miRNAs are clusters: hsa-mir-1/has-mir-133a, hsa-mir-143/hsa-mir-145, hsa-mir-23b/hsa-mir-24-1, and hsa-mir-29b-2/hsa-mir-29c. 12 predicted functions were generated using IPA which showed significant associations with migration of phagocytes, proliferation of mononuclear leukocytes, cell movement of mononuclear leukocytes, cell movement of smooth muscle cells etc.

Conclusion

These data support common disease mechanisms that may be under miRNA control and provide exciting directions for further investigations aimed at elucidating the miRNA mechanisms and targets that may yield new therapies for IA.

The expression of SPARC in human intracranial aneurysms and its relationship with MMP-2/-9

Objective

SPARC is a key determinant of invasion and metastasis in some tumors, such as gliomas, melanomas and prostate tumors. SPARC can change the composition and structure of the matrix and promote angiogenesis; these effects are closely related to clinical stage and the prognosis of tumors such as meningiomas. However, little is known about the expression of SPARC in intracranial aneurysms. The goal of this study was to establish the role of SPARC in human intracranial aneurysms.

Methods

Thirty-one intracranial aneurysms were immunohistochemically stained for SPARC, MMP-2 and MMP-9. As controls, normal Circle of Willis arteries were similarly immunostained. All specimens were retrieved during autopsies and were embedded in paraffin. To evaluate the expression levels of SPARC, MMP-2 and MMP-9, western blotting was also performed in three available intracranial aneurysm specimens. The limited availability of fresh intracranial aneurysm tissue was the result of the majority of patients choosing endovascular embolization.

Results

The results showed that SPARC, MMP-2 and MMP-9 were strongly expressed in intracranial aneurysm tissues; however, these proteins were expressed minimally or not at all in normal Circle of Willis arteries. The western blot results showed that the expression levels of SPARC, MMP-2 and MMP-9 were significantly up-regulated in intracranial aneurysms relative to the expression levels in the normal Circle of Willis arteries. Data analysis showed that SPARC was significantly correlated with MMP-2 and MMP-9, also with age and risk factors but not with the Hunt-Hess grade or with sex.

Conclusion

The results indicate that SPARC is widely expressed in human intracranial aneurysms, and its expression correlates with MMP-2 and MMP-9 expression, age and risk factors but not with the Hunt-Hess grade. The results of this study suggest that SPARC has a pathogenic role in the alteration of the extracellular matrix of intracranial arteries during aneurysm formation.