Silibinin’s regulation of proliferation and collagen gene expressions of rat pancreatic β-cells cultured on types I and V collagen involves β-catenin nuclear translocation

Extracellular matrix (ECM) molecules have multiple functions; prevention of cytotoxicity, provision of mechanical support, cell adhesive substrates and structural integrity in addition to mediation of cellular signaling. In this study, we report that the proliferation of INS-1 cells cultured on collagen I-coated dishes is enhanced, but it is inhibited on collagen V-coated dishes. Inhibitory proliferation on collagen V-coated is not due to apoptosis induction. Silibinin decreases hepatic glucose production and protects pancreatic β-cells, as a potential medicine for type II diabetes. Silibinin up-regulates the proliferation of cells cultured on both collagen I- and V-coated dishes. Collagen-coating regulates gene expression of collagen in a collagen type-related manner. Silibinin increases mRNA expression of collagen I in the cells on collagen I- and V-coated dishes; however, silibinin decreases collagen V mRNA expression on collagen I- and V-coated dishes. Collagen I-coating significantly enhances nuclear translocation of β-catenin, while collagen V-coating reduces it. Differential effects of silibinin on collagen I mRNA and collagen V mRNA can be accounted for by the finding that silibinin enhances nuclear translocation of β-catenin on both collagen I- and V-coated dishes, since phenomenologically nuclear translocation of β-catenin enhances collagen I mRNA but represses collagen V mRNA. These results demonstrate that nuclear translocation of β-catenin up-regulates proliferation and collagen I gene expression, whereas it down-regulates collagen V gene expression of INS-1 cells. Differential gene expressions of collagen I and V by nuclear β-catenin could be important for understanding fibrosis where collagen I and V may have differential effects.

细胞外基质（Extracellular matrix, ECM）分子具有多种功能：除介导细胞信号传导外，还可抵御细胞毒性、提供机械支撑、作为细胞黏附底物并维持结构完整性。本研究发现，在包被I型胶原（collagen I）的培养皿中培养的INS-1细胞增殖能力增强，而在包被V型胶原（collagen V）的培养皿中其增殖则受到抑制。V型胶原包被所介导的增殖抑制并非由细胞凋亡诱导所致。水飞蓟宾（Silibinin）可降低肝脏葡萄糖生成并保护胰腺β细胞，是一种潜在的2型糖尿病治疗药物。水飞蓟宾可提升在I型和V型胶原包被培养皿中培养的细胞的增殖能力。胶原包被可依据胶原类型调控胶原基因的表达模式：在I型和V型胶原包被的培养细胞中，水飞蓟宾均可上调I型胶原的mRNA表达水平；但与此同时，水飞蓟宾会下调I型和V型胶原包被培养细胞中V型胶原的mRNA表达水平。I型胶原包被可显著增强β-连环蛋白（β-catenin）的核转位，而V型胶原包被则会抑制该过程。水飞蓟宾在I型和V型胶原包被的培养细胞中均可增强β-连环蛋白的核转位，这一发现可解释其对I型和V型胶原mRNA表达的差异化调控作用——从现象上看，β-连环蛋白的核转位可上调I型胶原mRNA的表达，同时抑制V型胶原mRNA的表达。上述结果表明，β-连环蛋白的核转位可上调INS-1细胞的增殖能力与I型胶原基因表达，同时下调V型胶原基因的表达。核β-连环蛋白对I型与V型胶原的差异化基因调控作用，或有助于理解纤维化进程中I型和V型胶原所发挥的差异化功能。