LTBP-1mRNA and Protein Expression in Human Uterine Leiomyomas

Leiomyomas are composed of abundant fibrous connective tissue elements and extracellular matrix. TGFβ-1 has been shown to up-regulate the synthesis of many of the components of the extracellular matrix leading to fibrosis. LTBP-1 is an extracellular matrix glycoprotein which governs TGFβ-1 release and targets TGFβ-1 to the extracellular matrix from which the growth factor can be activated effectively. We hypothesized that LTBP-1 may play a dynamic role in the pathogenesis of leiomyoma. Our objective was to investigate LTBP-1 mRNA and protein expression in human leiomyomas and the myometrium, and correlate these with menstrual phase and leiomyoma size. Uterine leiomyomas and the adjacent normal myometrial tissues were collected from premenopausal women in both the proliferative and secretory phases, confirmed by endometrial histology. The women were then divided into three groups according to the size of their leiomyomas. LTBP-1 mRNA and protein in those tissues were evaluated by semi-quantitative RT-PCR and Western blot analysis. Localization of LTBP-1 protein expression was detected by immunohistochemical staining. Tissues were collected from premenopausal women, 12 of whom were in the proliferative, and 5 in the secretory phase of the menstrual cycle. These were divided into three groups by size of leiomyoma: ≤2cm, 3-5cm, and ≥6cm. The tissues were frozen in liquid nitrogen immediately after excision and stored at -80°C. Total RNA and protein were extracted. Semi-quantitative RT-PCR and Western blot analysis was used for mRNA and protein expression analysis. Localization of LTBP-1 protein expression was detected by immunohistochemical staining. Student’s t-test and analysis of variance (ANOVA) were used for statistical analysis between groups. P<0.05 was accepted as being statistically significant. Western blot analysis revealed that LTBP-1 protein expression was higher in leiomyomas in the proliferative phase (p=0.0035), while there was no difference in the secretory phase for size 3-5cm myomas. When compared to different size myomas, the LTBP-1 protein was higher in the 3-5cm group than in either the group ≥6cm or ≤2 cm (p=0.0022; p=0.0014), but no difference was seen between the size ≥6cm and ≤2cm (p=0.3050) in the proliferative phase. LTBP-1 was immunohistochemically detected in the extracellular matrix in human leiomyomas and myometria. There were no differences in LTBP-1 mRNA expression between myomas and myometria in either phase of the menstrual cycle using semi-quantitative RT-PCR. Up-regulation of LTBP-1 protein expression in the proliferative phase of the menstrual cycle in human uterine leiomyoma may be important in their pathogenesis. The increase in LTBP-1 protein expression in the 3-5cm myomas suggests that these myomas may be undergoing increased extracellular matrix accumulation compared to the ≤2cm and ≥6cm groups.