Atherosclerosis remains a major cause of morbidity and mortality despite substantial therapeutic interventions. Evidence suggests that the ever-more sedentary lifestyle of Americans is undermining the benefits of lipid- lowering therapy. It is widely accepted that tissue deposition and modification of lipoproteins induce inflammation and atherosclerosis;we and others are now showing that the same mechanism underlies vascular calcification and bone loss. It is well known that the interstitial spaces of tissues are normally cleared by fluid circulation through the lymphatic circulatory system, and that lymphatic circulation, which has no pump, depends on physical activity. Interestingly, cardiovascular disease is reduced by even mild physical activity -- below levels that promote aerobic capacity -- through mechanisms that are not known. One promising area of atherosclerosis research is reverse cholesterol transport, which focuses on removing lipoprotein deposits from the interstitial spaces of the artery wall to the circulation for hepatic clearance. However, if sedentary behavior impairs lymphatic circulation, enhancing reverse cholesterol transport at the molecular level may not translate to clinical benefit. Integrative physiological approaches are needed to complement the current molecular approach to reverse cholesterol transport. We hypothesize that enhancing lymphatic clearance reduces stagnation of lipoproteins in the interstitial spaces and prevents vascular and bone inflammation and disease. To test this novel hypothesis, we will develop interventions to maximize and minimize lymphatic flow in a mouse model of atherosclerosis and osteoporosis. We will use three interventions to induce changes in lymphatic clearance in mice: 1) Lyve1 deficiency, which enhances baseline lymphatic circulation, 2) controlled physical activity, to increase lymphatic flow, and 3) sedatives to reduce lymphatic flow.
In Specific Aim 1, we will explore the effects of maximal vs. minimal lymphatic clearance on vascular disease using diet-induced atherosclerosis and vascular calcification in hyperlipidemic mice.
In Specific Aim 2, we will explore the effects of maximal vs. minimal lymphatic clearance on bone disease using diet-induced osteoporosis in hyperlipidemic mice. In this pilot study, we will explore the levels of frequency and intensity of activity required to induce lymphatic flow, and test whether maximizing lymphatic circulation prevents vascular and bone disease. Findings of this work could introduce a promising new direction of research and greatly benefit prevention and treatment of atherosclerosis and osteoporosis.
Prolonged sedentary behavior, which leads to poor lymphatic clearance, may be a key mechanism for accumulation and oxidation of lipids in the artery wall and even in bone. Lymphatic circulation is needed to clear inflammatory and oxidized lipids, but it fails without physical activity. This study will test whether promoting lymphatic clearance by physical activity can prevent chronic inflammatory diseases of the heart and bone such as atherosclerosis and osteoporosis.
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