The neurodegeneration seen in diseases such as bovine spongiform encephalopathy may be linked to cholesterol levels in cell membranes, a study has suggested. Prions are widely believed to cause these diseases, but the their role in damaging brain cells is poorly understood. 
Summer school students at the Royal Veterinary College, Univesrsity of London, where the study is conducted
Photo: Royal Veterinary College
A study by the UK's Royal Veterinary College found that prion infection of neurons increases the free cholesterol content of cell membranes. These disturbances in cholesterol levels may be the mechanism by which damage occurs.
The researchers compared the levels of protein and cholesterol in prion-infected neuronal cell lines and primary cortical neurons with uninfected controls. Protein levels were similar, but the amount of total cholesterol (a mixture of free and esterified cholesterol) was higher in the infected cell lines.
The cholesterol balance was also affected: the amount of free cholesterol increased, while that of cholesterol esters fell, suggesting that prion infection affects cholesterol regulation. Free cholesterol is thought to affect the function of cell membranes, leading to abnormal activation of phospholipase A2, an enzyme implicated in the depletion of neurons in prion diseases and conditions such as Alzheimer's disease.
Dr Clive Bate, one of the study's authors, said: "Our observations raise the possibility that disturbances in membrane cholesterol induced by prions are major triggering events in the neuropathogenesis of prion diseases."
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