Differential NRF2 Methylation and PD-1 Expression in Normal Tissues of Colorectal Adenoma and Carcinoma across Sexes

Metachronous cancer following the cure of the primary cancer could be related with the tumor microenvironment. Recently it has been known that nuclear factor erythroid 2-related factor 2 (NRF2), a key transcription factor regulates immune checkpoint expression, including programmed cell death-ligand 1 (PD-L1), a well-known checkpoint molecule. The aim of this study was to investigate the roles of NRF2 and PD-1 in the tumor microenvironment using the normal colon tissue, with a focus on sex-specific differences.

A total of 280 participants were enrolled including 66 healthy controls (HC), 109 patients with colorectal adenoma (AD), and 105 patients with colorectal cancer (CRC). Quantitative real-time polymerase chain reaction (PCR) for NRF2 and PD-1 and methylation-specific PCR for NRF2 were performed with normal mucosal tissue above the 20 cm from anal verge.

NRF2 methylation levels were significantly lower in the AD and CRC groups compared to the HC in both sexes. PD-1 mRNA expression was significantly reduced in the AD and CRC groups compared to the HC group. In terms of sex males showed significantly lower PD-1 mRNA levels in the AD and CRC groups, whereas females displayed significantly higher PD-1 expression in the AD group but significantly lower levels in the CRC group. In conclusion there were significant differences in NRF2 methylation and PD-1 expression in the normal mucosal tissue among CRC, AD, and HC groups, suggesting that metachronous lesions might arise from this underlying tumor microenvironment.

Our results suggest that mRNA expressions of NRF2 and PD-L1 in the normal colon tissue may serve as early molecular markers in colorectal carcinogenesis with distinct sex-specific patterns.