Abstract
Aging is the main risk factor for cardiovascular diseases, but the associated molecular mechanisms are poorly understood. The Wnt signaling pathway was shown to be induced during aging in muscle and in the skin, but the regulation and role of Wnt signaling in the aged vessel have not yet been addressed. While screening for age-related changes in gene expression in the intima/media of human mammary arteries, we observed that the expression of frizzled 4 (Fzd4), a Wnt receptor, and of several targets of the Wnt/β-catenin/TCF signaling pathway [Wnt-inducible secreted protein 1 (WISP1), versican, osteopontin (SPP1), insulin-like growth factor binding protein 2 (IGFBP-2), and p21] were modified with age, suggesting an activation of the Wnt/β-catenin pathway. In contrast, we did not observe any regulation of forkhead transcription factor (FoxO) target genes. Beta-catenin-activating phosphorylation at position Ser675 was increased in aging mammary arteries, confirming the activation of this pathway. We confirmed in vitro that Wnt3a or Wnt1 treatment of human vascular smooth muscle cells (VSMCs) induced β-catenin phosphorylation at Ser675 and WISP1, SPP1, and IGFBP-2 expression. In vitro, Wnt treatment induced proliferation and cyclin D1 expression in VSMC from young (6 weeks old) rats but not in cells from older rats (8 months old), even though low-density lipoprotein receptor-related protein 6 and β-catenin phosphorylation, and β-catenin nuclear translocation demonstrated β-catenin activation in both cell types. Beta-catenin silencing demonstrated that Wnt induction of cyclin D1 expression is β-catenin dependent. Altogether, our data show that the Wnt/β-catenin/TCF pathway is activated in aging human mammary artery cells, but fails to induce the proliferation of aging vascular cells.