Effects of low-dose of TGF-β1 on maintaining bovine corneal stromal cell growth and retarding extra cellular matrix fibrosis in a three-dimensional culture model / 中华实验眼科杂志

ABSTRACT

Background Transforming growth factor-β1(TGF-β1) plays an important role in corneal woundhealing.The effects of TGF-β1 on the synthesis of extra cellular matrix (ECM) vary upon different concentrations.Previous studies focused on the effects of high concentration of TGF-β1 on keratocytes under the two-dimensional culture condition,and the effect of low concentration of TGF-β1 on the synthesis of ECM in keratocytes remains unclear.Objective This study was to investigate the growth of Pellet,a three-dimensional model of corneal stroma cells in vitro,and its ECM synthesis under a low concentration of TGF-β1.Methods Bovine corneal stromal cells were isolated from fresh bovine eyeballs by two-step digestion by collagenase and cultured using DMEM/F12 medium with 10％ fetal bovine serum (FBS).Pellets derived fresh bovine keratocytes with culture medium containing 0.25 ng/ml TGF-β1 +5％ FBS and 0.50 ng/ml TGF-β1 +5％ FBS were established,respectively.The morphology of Pellets was observed under the natural light at 48 hours,1 week,2 weeks and 3 weeks after culture.In 3 weeks after culture,the cell structures was observed by hematoxylin-eosin staining,and Calcein-AM/propidium (Calcein-AM/PI) staining was used to assay the cell viability.Real-time flurorescence quantitative PCR and immunofluorescence technology were applied to analyze the expressions of α-smooth muscle actin (α-SMA),fibronectin (FN),type Ⅰ collagen (Col Ⅰ) and type Ⅲ collagen (Col Ⅲ) mRNA and proteins.RT-PCR was employed to detect the expressions of lumican (LUM) mRNA and keratocan (KERA) mRNA in the cells.Results Cells in Pellet clustered throughout the culture duration.Hematoxylin-eosin staining showed the mass red-dyed collagen fibers in both 0.25 ng/ml TGF-β1 +5％ FBS group and 0.50 ng/ml TGF-β1 +5％ FBS group,and most cells possessed complete structures.The death rate of the cells was (33.60±1.65)％ in the 0.25 ng/ml TGF-β1 +5％ FBS group and (30.90±0.78) ％ in the 0.50 ng/ml TGF-β1 +5％ FBS group,showing an insignificant difference between them (t =0.144,P=0.887).The expressions of α-SMA,FN and Col Ⅲ proteins in 0.25 ng/ml TGF-β1 +5％ FBS group were lower than those in the 0.50 ng/ml TGF-β1 + 5 ％ FBS group (tα-SMA =4.622,P =0.010;tFN =2.973,P =0.040;tCol Ⅲ =7.845,P＜0.001),but the expression of Col Ⅰ in 0.25 ng/ml TGF-β1 +5％ FBS group was higher than that in 0.50 ng/ml TGF-β1+5％ FBS group (tColⅠ =4.022,P=0.016).The ratio of Col Ⅲ/Col Ⅰ in 0.25 ng/ml TGF-β1+5％ FBS group was lower than that in the 0.50 ng/ml TGF-β1 +5％ FBS group in both mRNA and protein level (tmRNA =-3.039,P =0.038;tprotein =3.215,P =0.032).The expression of LUM mRNA and KERA mRNA were detected in Pellet at different time points.The expression of LUM mRNA in 0.25 ng/ml TGF-β1 +5％ FBS group increased over time.While in 0.50 ng/ml TGF-β1 +5％ FBS group,the expression of LUM mRNA peaked at 1 week but declined at 2 weeks.The expression of KERA mRNA in two groups were all peaked at 1 week but declined at 2 weeks.Conclusions Low-dose TGF-β1 in Pellet can maintain the normal growth of keratocytes and synthesize ECM.The expression of ECM tends to the normal condition after reducing the concentration of TGF-β1,implying a scarless expression.