Researchers have discovered that Chlamydia pneumoniae, a bacterium commonly causing pneumonia and sinus infections, may contribute to Alzheimer's disease by invading the retina and brain. The study found higher levels of the bacterium in Alzheimer's patients, particularly those with the APOE4 gene variant, associated with greater cognitive decline. This suggests potential new treatment avenues targeting infection and inflammation.
A team at Cedars-Sinai Medical Center has identified a possible connection between Chlamydia pneumoniae and Alzheimer's disease. The bacterium, known for respiratory infections, can persist in the eye and brain, triggering inflammation, nerve cell death, and accumulation of amyloid-beta protein, a key feature of Alzheimer's.
The research, published in Nature Communications, analyzed retinal tissue from 104 individuals, including those with normal cognition, mild cognitive impairment, and Alzheimer's. Results showed significantly higher levels of Chlamydia pneumoniae in the retinas and brains of Alzheimer's patients compared to those with normal cognition. These elevated levels correlated with more severe brain damage and accelerated cognitive decline, especially in carriers of the APOE4 gene variant, which raises Alzheimer's risk.
In laboratory tests on human nerve cells and in mouse models of Alzheimer's, infection with the bacterium increased inflammation, promoted nerve cell loss, and boosted amyloid-beta production, worsening cognitive issues.
"Seeing Chlamydia pneumoniae consistently across human tissues, cell cultures and animal models allowed us to identify a previously unrecognized link between bacterial infection, inflammation and neurodegeneration," stated Maya Koronyo-Hamaoui, PhD, professor of Neurosurgery, Neurology, and Biomedical Sciences at Cedars-Sinai and senior author.
She added, "The eye is a surrogate for the brain, and this study shows that retinal bacterial infection and chronic inflammation can reflect brain pathology and predict disease status, supporting retinal imaging as a noninvasive way to identify people at risk for Alzheimer's."
Co-corresponding author Timothy Crother, PhD, noted, "This discovery raises the possibility of targeting the infection-inflammation axis to treat Alzheimer's."
The findings, led in part by co-first authors Bhakta Gaire, PhD, and Yosef Koronyo, MSc, propose that addressing chronic bacterial infections and resulting inflammation could offer new therapeutic strategies. They also bolster the use of retinal imaging for early detection and monitoring of Alzheimer's. The study received funding from the NIH/NIA and the Alzheimer's Association.
