Seasonal Variation in TLR4 Expression in The Testis and Epididymis of Anatolian Ground Squirrels (Spermophilus xanthoprymnus): Insights from Non-Breeding Period of Pre-Hibernation and Hibernation

Abstract

This study investigates the modulation of Toll-like receptor 4 (TLR4) expression within the testis and epididymis of Anatolian ground squirrels (Spermophilus xanthoprymnus) during the non-breeding period of pre-hibernation and hibernation. Immunohistochemical investigation showed that TLR4 was not detected in germ cells, Leydig cells, or Sertoli cells in the testicular tissue during the pre-hibernation period. Nevertheless, there was a presence of TLR4 in the vessels walls and certain interstitial cells within the intertubular regions. Epithelial cells in the caput, corpus, and cauda regions of the epididymis showed no TLR4 expression. However, it was observed in the vessel walls, smooth muscle layers, and some interstitial cells. TLR4 expression was seen in spermatogonia and primary spermatocytes during hibernation, with strong labeling observed in the vessel walls of the intertubular area. In contrast, TLR4 was detected in the epididymal epithelium, as well as in the smooth muscle layers and vessel walls throughout all segments. A notable upregulation in the expression of TLR4 in the testis was identified through quantitative image analysis during hibernation as compared to pre-hibernation. During pre-hibernation, the cauda segment of the epididymis exhibited the highest expression of TLR4, whereas during hibernation, the corpus segment demonstrated the highest expression. These findings suggest a dynamic modulation of TLR4 in response to hibernation, highlighting its potential role in reproductive function and immune adaptation.