Advances in Recombinant Gonadotropin Production for Use in Bovine Superovulation

Abstract

Bovine ovarian hyperstimulation is a process that currently relies on pituitary-derived follicle stimulating hormone (FSH) to facilitate the maturation of multiple follicles to achieve dominance and eventual ovulation. The prevalence of this process, also called superovulation, has more than doubled in the past 10 years, but the efficiency of recovered transferable embryos has remained low at ~6 per collection. The use of pituitary-derived products presents other problems including contamination from other hormones, inconsistencies within and among batches, and the possibility of the spread of disease-transmitting agents. Recombinant gonadotropins have been engineered to yield varieties of FSH and luteinizing hormone from a myriad of heterologous hosts with the resulting products demonstrating various levels of biological activity. Research has also been devoted to alternative delivery methods to reduce the frequency of injections required in current superovulatory protocols. Together, recombinant gonadotropins and alternative delivery approaches potentially provide an economical alternative to the use of pituitary-derived products.

Trends in recombinant protein use in animal production

“…Animal reproduction is one of the areas where production of recombinant protein is broadly used [4, 12, 13]. Reproductive hormones have a critical role in the regulation of the male reproductive function, female reproductive cycle, and the maintenance of pregnancy in the dams.…”

“…Despite being a widespread practice, it has significant associated problems such as: (i) batch-to-batch inconsistencies leading to variations in the superovulatory responses between animals [17, 18], (ii) purity problems because of the presence of other hormones contaminating the sample [16], and (iii) the possible contamination with disease-transmitting agents (for a more detailed review see [13]). All these require the development and application of cumbersome purification protocols to concentrate and purify the protein to guarantee the quality of the final product.…”

“…Furthermore, the 2 subunits of gonadotropins are glycosylated after translation generating pools of different glycoforms (gonadotropin varieties) with different half-lives and activity efficiencies [25, 26]. Thus, since reproductive hormones require a N-glycosylation [20], recombinant production has been carried out mainly in mammalian or insect cells [13, 27]. However, the production of proteins in large amounts in these eukaryotic systems is expensive, difficult, and time-consuming.…”

“…These extra glycosylation sites have been fused to FSH [6, 19, 32–34] and LH [21, 24, 57–59], which do not naturally contain this sequence, to achieve long-acting hormones. This allowed the reduction in the number of injections for superovulation treatments [13, 36, 40]. Interestingly, given the similarities between the LH and CG, both hormones bind to the LH receptor.…”

“…This, together with the fact that other hormones, such as growth hormones from different origins have been broadly studied in this recombinant system (buffalo [78], caprine [78], bovine [79], ovine [80] and porcine [81]), showing activities equivalent to those found in natural hormones, suggests that E. coli has a bold potential in this field. Although, thus far, mammalian cells have been the gonadotropin producers per excellence [13, 27], articles published show that microbes can be used as a real alternative for the production of biologically active CG and LH through economic and facile processes [36–39, 49, 67, 70]. …”