The investigation of the function of plasma membrane domains in follicle stimulating hormone signal transduction

The human reproductive hormone, follicle stimulating hormone (hFSH) acts in females on granulosa cells in the ovaries to stimulate egg maturation. In males FSH promotes spermatogenesis by stimulating Sertoli cells of the testes. The human FSH receptor (hFSHR) is a G protein-coupled receptor that is known to stimulate the production of cAMP as well as the p44/42 MAP kinase pathway. The multiple signaling responses of this hormone receptor complex may be due to its location in special membrane domains known as lipid rafts. Lipid rafts are rigid domains of the plasma membrane that are enriched in cholesterol, glycolipids and sphingomyelin. Previous studies have shown that disruption of these domains by removing cholesterol inhibits the hFSHR cAMP response but interestingly not the p44/42 MAP Kinase pathway activation. My research investigated if degradation of lipid rafts by an enzyme called sphyingomyelinase (SMase) caused any changes in the signaling ability of hFSHR. SMase breaks down sphingomyelin destabilizing the lipid raft. Epithelial cells expressing hFSHR were pretreated with SMase followed by hFSH treatment and signal transduction was measured. Surprisingly, SMase did not inhibit cAMP production the same way removal of cholesterol did. Further experiments will be required to elucidate this difference.

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