THE EFFECT OF DIOXINS ON GLUCOSE HOMEOSTASIS IN MURINE TESTES

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DESCRIPTION (provided by applicant): Dioxins represent a class of highly toxic and widely dispersed environmental hazards that have been implicated in aberrations in male reproductive cell function and even adverse pregnancy outcomes associated with paternal exposure. Many of these effects take several years to manifest. Investigators have attempted to characterize the toxicity of dioxin binding at a cellular and molecular level, but to date the mechanism remains incompletely understood. The objective of this study is to determine whether the mechanism of action of dioxin exposure on male gametes involves communication between the aryl hydrocarbon receptor (AhR) and glucose transport. In addition we seek to determine if dioxin exposure affects gene expression in the germ cells and perhaps stem cells at different stages of spermatogenesis. These changes may not manifest until much later relative to exposure and thus may explain the paternal effects on offspring and pregnancy outcome. Previous studies suggest that the AhR receptor, also known as the "dioxin receptor," may play a role in decreased glucose utilization in epithelial cells in various other tissues of the body. Our preliminary data show that glucose transporters play a significant role in the testes and on spermatogenesis and that certain cell signaling proteins/receptors play a role in modulating glucose homeostasis in these germ cells at the various stages of spermatogenesis. Previous study in our lab has shown several functional detriments to spermatogenesis, sperm motility, and fertilization capability in mice affected with disruptions in glucose homeostasis. Moreover we have established a Laser Microdissection protocol for testis sections and have successful validate our techniques. We hypothesize that dioxin exposure disrupts spermatogenesis through activation of the AhR receptor and subsequent disruption of glucose transporter (GLUT) isoforms adversely affects essential cellular function and development. We address the following specific aims to investigate this hypothesis. SPECIFIC AIM 1: Which cell types, somatic and spermatogenic germ cell stages, in the testes express the Arylhydrocarbon Receptor? SPECIFIC AIM 2. Are protein and mRNA expression of GLUT8, GLUT9a and GLUT9b in the testes affected by exposure to TCDD? Is the location of the transporters altered? SPECIFIC AIM 3: Does a lack of AhR expression eliminate the effect of TCDD in the testes? Does AhR deficiency affect glucose transporter expression in the testes? ! The rationale for this proposal is that identifying the mechanism of toxic injury to male germ cells will lead to a better understanding the role of environmental toxins in paternal transmission of malformations and male infertility. If successful in completing these aims, we will have elucidated a novel major downstream effect of activation of the Aryl hydrocarbon receptor. Exogenous activation of the AhR by dioxins, resulting in decrease glucose utilization among cells in the testes would highlight a likely mechanism of action that could further our understanding of certain reproductive outcomes that have been linked to paternal toxic exposures. ! !