Constitutive expression of toll-like receptor genes and signaling pathways in stallion testis and epididymis

Abstract

Toll-like receptors (TLRs) expression pattern and their associated molecules have not been described in stallions. Understanding the TLR expression and their responses to activation is key in interpreting the interactions between immune system and reproductive system in healthy and ill animals. Objective of this study was to describe the constitutive expression pattern of TLRs and their signaling pathways in stallion’s testis and epididymis. It was hypothesized that all TLRs and downstream signaling molecules are constitutively expressed in these tissues in reproductively normal stallions. Transcriptome analysis was performed in testicular and epididymal samples from reproductively normal stallions (n = 8). A detectable constitutive expression of all TLRs, costimulatory molecules, and most downstream adaptors and effectors was identified in stallion reproductive tissues. Most significant pathways were associated with TLR3, TLR2/TLR1, TLR2/TLR6, and the effector molecules C-C motif ligand 5 (CCL5) and CD40. Most genes were overexpressed in the epididymis compared to testis. Widespread and abundant expression of these genes supports an important function of the innate immunity in testicular and epididymal defense. These TLRs may also have a physiological role in maintaining the tolerogenic environment, supporting posttesticular maturation, or removing defective sperm from the tubular system.