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C5a-C5AR1 axis as a potential trigger of the rupture of intracranial aneurysms

ABSTRACT: Subarachnoid hemorrhage due to rupture of intracranial aneurysm (IA) still has poor prognosis once after the onset in spite of modern technical advancement in medical care. The development of the novel therapeutic strategy based on molecular machineries regulating the rupture is thus mandatory for social health. Here, recent studies have clarified the potential role of neutrophil-mediated inflammatory responses in the process leading to rupture. Thereby, factors mediating the recruitment of neutrophils in situ could be the therapeutic targets to prevent rupture of IAs. In the present study, complement C5a receptor 1 (C5AR1) was picked up as the candidates from comprehensive gene expression profile data. The induction of C5AR1 in IA lesions exclusively in rupture-prone or ruptured lesions was then confirmed in immunohistochemistry. The ligand of C5AR1, C5a, was induced through the enzymatic digestion by tissue-type Plasminogen Activator and, intriguingly, forms the auto-amplification in C5a-C5AR1 axis to exacerbate neutrophil infiltration and resultant neutrophil-mediated inflammation in situ, which triggers rupture of IAs. In conclusion, we have, in the present study, examined potential factors mediating the infiltration of neutrophils into IA lesions and then identified C5a-C5AR1 axis. This cascade could become the therapeutic target to prevent rupture of IAs.

ORGANISM(S): Rattus norvegicus

PROVIDER: GSE242795 | GEO | 2025/09/08

REPOSITORIES: GEO

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Project description:The complement system is part of the innate immune system that works to clear pathogens and cellular debris. In the central nervous system (CNS) complement activation can promote synaptic pruning clearance of neuronal blebs recruitment of phagocytes and protection from pathogens. However in a neuropathologic environment complement activation may contribute to inflammatory pathways neuronal dysfunction and in the Alzheimer’s disease (AD) brain cognitive decline. If complement activation proceeds to the cleavage of C5 and thus generation of C5a engagement of C5a with the receptor C5aR1 can instigate a feed-forward loop of inflammation injury and neuronal death thus making this molecule a potential target for modulation in AD therapeutics. The Arctic (Arc) AD mouse model known to rapidly accumulate fibrillar amyloid plaques was crossed to a model that lacks the receptor for C5a (ArcC5aR1KO) or to a transgenic mouse that generates C5a under the GFAP promoter (ArcC5a+). ArcticC5a+ mice showed accelerated loss of spatial memory compared to Arc mice. While eliminating C5aR1 did not alter amyloid plaque accumulation in this AD model C5aR1KO delayed or prevented the expression of important AD-associated genes in the hippocampus indicating a separation between those genes induced by amyloid plaques and those influenced by C5a-C5aR1 signaling. C5ar1 deletion also reduced/delayed the expression of select pan-reactive and A1 reactive astrocyte genes. ArcC5aR1KO showed delayed expression of genes enriched for biological processes that are significant in the AD context such as regulation of inflammatory signaling microglial cell activation astrocyte migration and lysosome pathway. Interestingly overexpression of C5a also delayed the increase of some AD- complement and astrocyte-associated genes perhaps mediated by C5aR2 and emphasizing the importance of selectively suppressing C5aR1. Immunohistochemical investigation further confirmed that modulation of C5a-C5aR1 either delayed or reduced some reactive microglial markers in the Arc hippocampus including CD11b and CD11c. These results suggest that C5a-C5aR1 signaling in the context of AD largely exerts its effects by suppressing those microglial activation pathways that accelerate disease enhancing pathways. Given the highly focused modulation of a common driver of neurotoxicity pharmacological inhibition of this C5aR1 signaling pathway is a promising therapeutic strategy to treat AD.

Project description:<p>Our long-term objective is to identify susceptibility genes that are related to the formation of intracranial aneurysms (IA). Rupture of IAs occurs in 16,000 to 17,000 persons in the U.S. annually and nearly half of affected persons are dead within the first 30 days. An additional 6,000 to 7,000 persons with unruptured IAs are identified each year. Accumulated evidence indicates that a genetic component plays an important role in the development of IAs, but specific loci affecting the risk of IA have not been identified. The primary hypothesis of this study is that there are specific human chromosomal regions that are associated with an increased risk of IAs. Specific Aims of are: <ol> <li>Recruitment of 400 (475) families with multiple individuals who have an IA through 23 (25) referral centers throughout North America, Australia, and New Zealand that represent 35 (40) recruitment sites.</li> <li>Ascertainment of interviews and blood samples from all affected family members as well as their first-degree relatives. White blood cells from living persons with an IA will be cryopreserved at Coriell Institute for Medical Research for future immortalization of cells lines as indicated.</li> <li>Identification of unruptured IAs by obtaining MRAs in selected asymptomatic siblings (of affected individuals).</li> <li>Completion of a 10 cM genome series in persons with IAs as well as the spouses and children of persons with an IA who are deceased. We will perform finer mapping of chromosomal regions with suggestive evidence of linkage in the genome screen.</li> <li>Performance of a nonparametric (allele sharing) linkage analysis, including relevant environmental factors such as smoking, to identify chromosomal regions linked to IA. Reconstruction of the genotypes of deceased affected family members will be performed.</li> </ol> </p> <p>Identification of individuals who are genetically at high risk for the development of IAs would enable targeted and effective screening/prevention/treatment strategies to reduce the substantial mortality and morbidity associated with this devastating type of stroke. Only a multidisciplinary, collaborative effort to identify, accrue, and genotype FIA families will be successful in identifying sufficient high-risk families to characterize the genetic underpinnings of IA.</p>

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C5a-C5AR1 axis as a potential trigger of the rupture of intracranial aneurysms

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