Inflammatory changes in the CNS in association with chronic experimental atherosclerosis in mice

Caroline Drake, Adam Denes, Barry McColl, Nancy Rothwell, Stuart Allan. University of Manchester, Manchester, United Kingdom.

Stroke is caused by the occlusion of an artery supplying blood to the brain and is one of the leading causes of death and disability worldwide. Epidemiological studies highlight an increased susceptibility to stroke in patients with pre-existing conditions such as atherosclerosis, obesity and diabetes. These conditions are all associated with chronic peripheral inflammation. Interleukin-1 is an inflammatory molecule and has been shown to worsen stroke outcome and also act as an atherogenic molecule in animal models of atherosclerosis. Studies in animals with co-morbidities have demonstrated worsening of outcome after experimental stroke. It is however unclear as to how a chronic peripheral inflammatory disease impacts upon CNS function and stroke incidence and outcome.

In this project an experimental model of atherosclerosis has been used. Apoliopoprotein E (Apo E) knock out mice aged three months were fed either a chow or Paigen diet for eight weeks to develop plaques in major peripheral arteries. To investigate changes in the CNS, the brain was removed and free floating immunohistochemistry was performed for several inflammatory markers. Vascular adhesion molecule-1 (VCAM-1) and intercellular adhesion molecule-1 (ICAM-1) were found to be upregulated in ApoE-/- animals on Paigen diet (n=5) compared with Apo E-/-chow-fed controls (n=3) indicating endothelial activation. Paigen diet also induced activation of Iba1-positive microglia in various brain sites. In some of these mice, Oil red O staining indicated focal lipid deposition and pathology in the parenchyma, which was confirmed on parallel hematoxylin-eosin stained sections. Infiltration and accumulation of CD45-positive leukocytes into highly lipid laden areas in the lateral ventricle were observed only in Apo E-/- animals fed Paigen diet. CNS inflammatory changes and cerebrovascular pathology seem to be IL-1 receptor-dependent, as none of the above mentioned alterations were observed in Apo E-/-/IL-1 receptor-/- mice fed a Paigen diet. These findings indicate that Paigen diet induces brain cerebrovascular pathology and a brain immunological response dependent on the IL-1 receptor. This highlights the importance of chronic inflammatory diseases in the possible generation inflammatory alterations in the brain and indicates possible mechanisms for the increased risk of stroke in patients with atherosclerotic disease.