Loss of lymphotoxin-α but not tumor necrosis factor-α reduces atherosclerosis in mice

Abstract

Inflammatory processes are involved with all phases of atherosclerotic lesion growth. Tumor necrosis factor-α (TNFα) is an inflammatory cytokine that is thought to contribute to lesion development. Lymphotoxin-α (LTα) is also a proinflammatory cytokine with homology to TNFα. However, its presence or function in lesion development has not been investigated. To study the role of these molecules in atherosclerosis, the expression of these cytokines in atherosclerotic lesions was examined. The presence of both cytokines was observed within aortic sinus fatty streak lesions. To determine the function of these molecules in regulating lesion growth, mice deficient for TNFα or LTα were examined for induction of atherosclerosis. Surprisingly, loss of TNFα did not alter lesion development compared with wild-type mice. This brings doubt to the generally held concept that TNFα is a "proatherogenic cytokine." However, LTα deficiency resulted in a 62% reduction in lesion size. This demonstrates an unexpected role for LTα in promoting lesion growth. The presence of LTα was observed in aortic sinus lesions suggesting a direct role of LTα in modulating lesion growth. To determine which receptor mediated these responses, diet-induced atherosclerosis in mice deficient for each of the TNF receptors, termed p55 and p75, was examined. Results demonstrated that loss of p55 resulted in increased lesion development, but loss of p75 did not alter lesion size. The disparity in results between ligand- and receptor-deficient mice suggests there are undefined members of the TNF ligand and receptor signaling pathway involved with regulating atherogenesis.