APLN and osteoporosis: In vitro experiments revealed that the expression levels of Wnt-target factors, specifically Axin2, CyclinD1, Smad6, and Wisp2, as well as downstream β-catenin, are significantly downregulated in primary bone cells isolated from Apelin-13−/− mice (88), indicating that Apelin-13 could be involved in regulating signaling via the canonical Wnt pathway to prevent osteoporosis.