Wnt proteins retard macrophage foam cell formation and oxidised LDL induced apoptosis

Abstract

Increased macrophage-derived foam cell formation and apoptosis are associated with atherosclerotic plaque instability. The role of Wnt proteins in foam cell formation and apoptosis is unclear. Our previous experiments demonstrated Wnt3a, Wnt4 and Wnt5a proteins in human atherosclerotic plaques. We isolated human monocytes from healthy volunteers’ blood, differentiated them into macrophages, treated concurrently with 20mg/ml oxidised LDL (Ox-LDL) and 250ng/ml Wnt proteins, and then lipid content and apoptosis were measured by oil red-O staining and cleaved caspase-3 immunocytochemistry, respectively. Recombinant Wnt3a, Wnt4 and Wnt5a significantly suppressed lipid content by 90±4%, 83±3% and 74±6%, respectively (n=4, p<0.05). In addition, treatment with recombinant Wnt3a, Wnt4 and Wnt5a significantly reduced Ox-LDL induced apoptosis by 73±7%, 63±4% and 67±10% respectively. To further investigate the effect of the Wnt proteins on lipid content and apoptosis macrophages were pre-treated with Wnt proteins or Ox-LDL for 24hours, before addition of Ox-LDL or Wnt proteins, respectively. We observed that addition of Wnt3a, Wnt4 and Wnt5a proteins for 24hours before Ox-LDL treatment retained the protective effect on lipid uptake, reducing it by 44±9%, 57%±3% and 50±3%, respectively (n=4, p<0.05). In addition Ox-LDL induced apoptosis was also reduced in a similar manner to concurrent treatment, reducing it by 54±7%, 60±9% and 62±6% respectively (n=4, p<0.05). Conversely when Ox-LDL was given before Wnts their protective effects, both on uptake and apoptosis, were not observed. In summary this suggests that these Wnt proteins may have profound effects on foam cell formation and apoptosis, in particular modulating Ox-LDL uptake rather than lipid clearance.