Analysis of Cyclooxygenase 2, Programmed Cell Death Ligand 1, and Arginase 1 Expression in Human Pituitary Adenoma

Cyclooxygenase 2 (COX-2) is a key enzyme in the synthesis of prostaglandins. Recent studies have shown that overexpression of COX-2 can reduce the antitumor effect of the immune system by inhibiting the proliferation of B and T lymphocytes. Programmed cell death ligand 1 (PD-L1) was the first functionally characterized ligand of programmed cell death protein 1. It plays an important role in maintaining peripheral and central immune tolerance by combining with programmed cell death protein 1. Arginase 1 (ARG1) can process L-arginine in the local microenvironment and affect the function of T cells, resulting in immune escape. In this study, COX-2, PD-L1, and ARG1 expression in human pituitary adenoma (PA) and their relationship were investigated, which provided an initial theoretic basis for further study of the immune escape mechanism in PA in cellular and animal experiments.

The protein expression of COX-2, PD-L1, and ARG1 in 55 PA samples was detected by immunohistochemistry, with 10 normal brain tissues as the control group. The location of COX-2, PD-L1, and ARG1 in PA cells was studied by double immunofluorescence colocalization. The results of immunohistochemistry were further verified by Western blot.

The expression of COX-2, PD-L1, and ARG1 in PA was significantly higher than that in normal brain tissue. In functional PA (FPA) and nonfunctional PA (NFPA), there was no significant difference in the expression of COX-2 and PD-L1, whereas ARG1 was higher in NFPA. Moreover, the protein expression level of COX-2 was positively correlated with that of PD-L1 and ARG1, and the expression of PD-L1 was positively correlated with that of ARG1. Immunofluorescence confocal imaging showed that COX-2, PD-L1, and ARG1 were all expressed in the cytoplasm of PA cells, and the physical positions of COX-2, PD-L1, and ARG1 were partially coincident.

These findings indicate that overexpression of COX-2, PD-L1, and ARG1 may be involved in the pathogenesis of PA. ARG1 plays a more important role in the development of NFPA. By upregulating the expression of PD-L1, COX-2 may promote the expression of ARG1, forming the COX-2/PD-L1/ARG1 signal pathway in promoting the occurrence and development of PA. Perhaps further study of the pathogenesis of PA can start with the mechanism of immune escape.