Study on Cerebral Amyloid Angiopathy (CAA) and the Level of Tight Junction Protein Claudin-5 in Microvessels

Background

Cerebral Amyloid Angiopathy (CAA) is a disease caused by the deposition of Amyloid-β (Aβ) in the cerebral blood vessels. Research indicates that approximately 23% of individuals over the age of 55 have moderate to severe CAA. CAA may lead to cognitive impairment and intracerebral hemorrhage (ICH), but it remains unclear what molecular mechanisms cause certain patients’ blood vessels to be more prone to rupture. Blood-brain barrier (BBB) dysfunction is associated with CAA and CAA-related ICH. Claudin-5 is a tight junction protein that plays a crucial role in regulating BBB permeability. Therefore, the authors hypothesize that a reduction in Claudin-5 in CAA may be associated with BBB dysfunction, thereby leading to the occurrence of ICH.

Source of the Paper

This research article was completed by the following team of authors: Lieke Jäkel, Kiki K. W. J. Claassen, Anna M. de Kort, Wilmar M. T. Jolink, Yannick Vermeiren, Floris H. B. M. Schreuder, Benno Küsters, Catharina J. M. Klijn, H. Bea Kuiperij, Marcel M. Verbeek. The institutions of the authors include Radboud University Medical Center in Nijmegen, the Netherlands, Isala Hospital in Zwolle, the Netherlands, Wageningen University & Research Center, the Department of Bioscience Engineering at the University of Antwerp, Belgium, Bunge Born Research Institute, Radboud University Medical Center in Nijmegen, and the Department of Neurology and the Department of Human Genetics at Radboud University Medical Center. This paper was published in Brain Pathology in 2024.

Research Process

Subjects and Methods

The study included brain tissue samples extracted from different patient groups: CAA-ICH cases (n=20), non-hemorrhagic CAA cases (CAA-NH, n=40), and control group (n=42). Immunohistochemistry was used to detect the expression of Claudin-5 in the microvessels of the occipital and temporal lobes, and Fiji software was used to analyze and compare the immunohistochemistry staining areas.

Experimental Steps

1. Sample Selection and Immunohistochemistry Detection:
   • Brain tissue samples from the occipital and temporal lobes were obtained from different patients.
   • Immunohistochemistry was used to detect the expression of Claudin-5 in the tissues.
2. Data Analysis:
   • Fiji software was used to calculate and compare the Claudin-5 stained areas in the CAA-ICH, CAA-NH, and control groups.
   • Statistical analyses (such as median, interquartile range, and p-values) were used to evaluate the differences in expression between the groups.

Results

1. Differences in Claudin-5 Expression:

   • In the gray matter of the occipital lobe, the Claudin-5 staining in the CAA-ICH group was significantly lower than in the CAA-NH group and the control group (p=0.027 and 0.003).
   • Similarly, in the white matter of the occipital lobe, the Claudin-5 expression in the CAA-ICH group was lower than in the CAA-NH and control groups (p=0.021 and 0.018).
   • In the gray matter of the temporal lobe, the Claudin-5 expression in the CAA-ICH group was also significantly lower than in the CAA-NH group (p=0.035).
   • Overall, the CAA-NH group showed higher expression than the control group, indicating that the reduction of Claudin-5 in CAA-ICH patients is a common phenomenon.

2. Correlation Between Regions:

   • In the CAA cases, there was a correlation in Claudin-5 expression between the gray matter of the occipital and temporal lobes (rs=0.36, p=0.008), whereas no correlation was found in the control group (rs=0.12, p=0.49).
   • Among CAA cases with different ICH severity, there was no significant difference in Claudin-5 expression, suggesting that the reduction is not an acute response to ICH.

Discussion

1. Comparison with Previous Studies:

   • The study found that the reduction in Claudin-5 expression in CAA-ICH patients is consistent with previous observations in Alzheimer’s disease patients, further supporting this associative mechanism.
   • Contrary to previous studies that did not report Claudin-5 expression in the context of CAA-ICH, this paper explicitly points out its widespread reduction in brain vessels of ICH patients.

2. Mechanism Speculation:

   • The authors speculate that the reduction of Claudin-5 may be one of the mechanisms causing the vulnerability of blood vessels in CAA patients. Additionally, the BBB leakage caused by CAA may lead to perivascular inflammation and vascular remodeling, further facilitating the occurrence of ICH.

Conclusion and Significance

By studying CAA-ICH patients, this paper reveals the widespread phenomenon of reduced Claudin-5 expression, indicating a significant link between Claudin-5, CAA, and ICH. This finding provides a scientific basis for future exploration of new treatment strategies to prevent ICH by regulating BBB function.

Research Highlights

• Discovered the widespread reduction of Claudin-5 expression in CAA-ICH patients, opening a new perspective for understanding the molecular mechanism of CAA.
• Emphasized the importance of Claudin-5 in BBB dysfunction, providing a potential therapeutic target.
• Utilized high-precision immunohistochemistry and detailed statistical analysis, ensuring the reliability of the research results.