Age-associated loss of lymphatic vessels promotes cardiac inflammation.

Aging is a major risk factor for cardiovascular disease, but the role of the cardiac lymphatic vasculature in this process remains poorly understood. Here we show that aging reduces cardiac lymphatic vessel density in humans and mice and induces structural remodeling characterized by tighter, zipper-like endothelial junctions. These changes are associated with immune cell infiltration, fibrinogen and amyloid accumulation, and myocardial edema. Selective reduction of cardiac lymphatics in young mice, through Flt4 (VEGFR3) depletion or soluble Flt4 overexpression, recapitulates key features of cardiac aging, including inflammation and impaired lymphatic integrity. Mechanistically, aging induces selective upregulation of nuclear interleukin-33 (IL-33) in lymphatic endothelial cells. Unlike extracellular IL-33, nuclear IL-33 promotes lymphatic endothelial cell death and junctional remodeling. We identify VEGFC as an age-sensitive regulator that declines with aging and suppresses IL-33. Cardiac Vegfc overexpression or Il33 silencing restores lymphatic density and tissue homeostasis in aged hearts, identifying a potential therapeutic target for age-related cardiac dysfunction.