The effect of quercetin on phosphorylated p38, Smad7, Smad2/3 nuclear translocation and collagen type I of keloid fibroblast culture

Keloid is connective skin tissue overgrowth resulting from abnormal wound healing activated by transforming growth factor-β (TGF-β) through particularly TGF-β/Smad signaling pathway which translocate Smad2/3 into nucleus to induce type I collagen synthesis and normally regulated by inhibitory Smad7. The expression of Smad2/3 are increased while Smad7 is decreased in keloid fibroblast. The keloid fibroblast phosphorylated p38 (p-p38) increased and inhibited Smad7 expression. Those biomolecular findings cause keloid recurrence. Therefore, studies on keloid recurrence prevention must be developed. Quercetin is a flavonoid found in many fruits and vegetables. Previous studies showed that quercetin inhibited p-p38 which provided opportunity increasing Smad7, decreasing nuclear Smad2/3, and preventing keloid recurrence. This study aimed to determine the quercetin effect on p-p38, Smad7, Smad2/3, and collagen type I levels in human keloid fibroblasts. Four replicates three-passages primary human keloid fibroblast culture incubated with 5, 10, 20 µg/mL quercetin were conducted with culture media as control for 48 hours. The expressions of p-p38, Smad7, and Smad2/3 were measured using western blotting. The level of collagen type I was measured using enzyme-linked immunosorbent assay (ELISA). Mean comparisons between multiple groups were analyzed using one-way analysis of variance (ANOVA) or Kruskal-Wallis test. Mean comparison between two groups were analyzed using independent T-test or Mann-Whitney test. The results showed that 10 µg/mL quercetin group showed lower p-p38 expression than that of control group (P < 0.05). The 10 and 20 µg/mL quercetin groups showed lower Smad7 expression than that of control (P < 0.05). The 20 µg/mL quercetin group showed lower nuclear Smad2/3 expression than that of control (P < 0.05). All quercetin groups demonstrated lower nuclear Smad2/3 compared to cytoplasmic Smad2/3 expression (P < 0.05), while control group did not show nuclear and cytoplasmic Smad2/3 expression significant difference. This study confirmed that quercetin could regulate keloid fibroblast TGF-β/Smad pathway by inhibiting p-p38 and Smad2/3 nuclear translocation and could be used, as biomolecular basis, for keloid prevention in wound healing process.