MFG-E8 Signaling Promotes Elastolysis and Calcification in the Aging Aortic Wall

Milk fat globule-EGF factor 8 (MFG-E8) protein increases with age and is mainly secreted by vascular smooth muscle cells in the arterial wall. Here, we investigated the role of MFG-E8 signaling during proinflammation, elastolysis, fibrosis, and calcification within the aging arterial wall. In vivo studies indicated that (1) Elastic lamina breaks collagen deposition and calcium-phosphorus products were markedly increased in the aging arterial wall of rats; (2) MFG-E8 protein abundance was markedly increased while intact tropoelastin (TPELN), an element of repair of the elastic fibers, was markedly decreased in the aging arterial wall of rats; (3) The absence of MFG-E8 markedly alleviated age-associated increases in elastic lamina breaks, collagen deposition and calcium-phosphorus products in mice; and (4) MFG-E8 deficiency significantly decreased age-associated increases in matrix metalloproteinase type II (MMP-2) activation, alkaline phosphatase, and runt-related transcription factor 1 (Runx1) expression in the aortic walls of mice. The in vitro studies demonstrated that (1) treating either young or old rat VSMCs with recombinant human MFG-E8 protein (rhMFG-E8) significantly reduced TPELN levels while MFG-E8 gene silencing significantly increased TPELN levels; (2) rhMFG-E8 treatment activated MMP-2 levels in both young and old VSMCs; and (3) MMP-2 bound to and cleaved TPELN secreted from VSMCs. Thus, these findings suggest that MFG-E8 signaling promotes age-associated adverse structural remodeling, including elastolysis, fibrosis, and calcification; however, MFG-E8 deficiency markedly mitigates these adverse effects in mice.