Meeting Abstract
P2.12 Tuesday, Jan. 5 Biological activity of mammalian thyrotropins in goldfish MILLER, TC*; MACKENZIE, D; JAQUES, JT; DELOVIO, ML; Dept. of Biology, Texas AM University; Dept. of Biology, Texas AM University; Texas Veterinary Medical Diagnostic Laboratory; Texas Veterinary Medical Diagnostic Laboratory tcmiller@tamu.edu
Little is known about the structure or function of teleost thyrotropin (TSH), a glycosylated pituitary hormone that stimulates the thyroid gland. As a first step towards production of recombinant teleost TSHs, we developed a bioassay which could be used to assess the in vivo biological activity of mammalian TSH. Goldfish received a single injection of TSH and resulting plasma TSH and thyroxine (T4) were measured by immunoassay. Time course studies found that circulating TSH peaks between 2-5 hours after bovine TSH (bTSH) injection and that resulting T4 is elevated from 5-20 hours. The linear T4 dose response (from 0.1-10 mU bTSH/gBW) at 5 hours post-injection was consistent across 9 assays using the same group of fish over 2 years. Because TSH can be synthesized by expression systems using various cell lines which differ in their ability to glycosylate TSH, we examined the effects of glycosylation on the T4 response. The removal of carbohydrates from bTSH increased the clearance rate of TSH while abolishing the T4 response. Recombinant canine TSH (rcTSH) expressed using a baculovirus system with enhanced glycosylation capabilities produced a dose dependent increase in T4 between 1 and 20 ng/gBW at 5 hours post-injection. In contrast, rcTSH produced using a baculovirus system without the capability of processing carbohydrate moieties into mature mammalian forms had 9% as much biological activity. Thus, the goldfish TSH bioassay is a sensitive and stable bioassay which can be used to determine the biological activity of both pituitary-derived TSH and recombinant TSH. Moreover, these experiments demonstrate that the carbohydrate composition of TSH is important for in vivo biological function in goldfish as in mammals.
