Relationship Between Mast Cell Subtypes and Cyclooxygenase-2 Expression in Uterine Leiomyomas

Abstract

Objective: Mast cells (MCs) have been proved to be multifunctional cells which are known to be located at peri-and intra-tumoral sites, playing an active role physiologically or pathologically. In humans, MCs are subtyped by the difference in their neutral protease content. MCs that have granules containing tryptase alone (MCT) are predominantly found at mucosal sites. MCs whose granules possess tryptase along with chymase (MCTC) are found especially within connective tissue. MC mediators have different functions and the coexistence of both MC subtypes contributes to tissue homeostasis. Furthermore, cyclooxygenase-2 (COX-2) is an enzyme associated with inflammation, cell growth and differentiation, prevention of apoptosis and tumorigenesis. Recent studies show the clinical significance of COX-2 expression in different tumor types. However, to our knowledge, there is no data assessing the relationship between COX-2 and MC density in uterine leiomyomas. We aimed to investigate the relation between the expression of COX-2, MC density, and proportional changes of MC phenotypes in human leiomyoma uteri and control cases, and also their possible correlations between each other. Methods: We performed a retrospective study of 34 cases carried out on parafin-embedded samples obtained from 14 control (group 1) and 20 leiomyoma uteri (group 2) patients who had undergone curative hysterectomy. These specimens were investigated immunohistochemically by using anti-cyclooxygenase-2 (COX-2) antibodies to stain COX-2; anti-tryptase antibodies to stain MCT and anti-chymase antibodies to stain MCTC. Results: In leiomyoma, the median value of COX-2 staining grade was 2 (min:1-max:3) which was statistically lower than that of controls with a median value of 3 (min:2-max:4) (p=0.001). The median value of tryptase expression was 12 (min:10-max:16) in the control myometrium, slightly higher than that of the leiomyoma group which had a median value of 10.5 (min:6-max:15). On the other hand, the median value of chymase expression was 7 (min:4-max:13) in the control myometrium, which was significantly higher (p=0.001) than that of the leiomyoma group with a median value of 5 (min:2max:8). Thus, in the leiomyoma group, the mast cell subtypes, including tryptase÷chymase proportion, was found to be significantly higher than the controls (p=0.032). Moreover, COX-2, tryptase and chymase expressions showed no correlation in both groups. Conclusion: This study has demonstrated that expressions of COX-2 and mast cell subtypes are reduced in leiomyoma, and the proportion of mast cell subtypes of MCT÷MCTC increases in leiomyoma compared to the control group. However, MC subtypes neither correlated with each other nor with COX-2 expression in the leiomyoma and control series. Understanding the mechanisms for MC functions and the secretory molecules will provide a basis for a rational approach to the development of antitumoral therapy in patients with leiomyoma and other tumors. (JAREM 2011; 1: 44-8)