Lactation performance and milk composition studies in transgenic goats expressing recombinant proteins in the milk

Milk expression of recombinant proteins of pharmaceutical value in transgenic dairy animals is an emerging solution for molecules that cannot be made efficiently using the standard bioreactor platform. However, the expression of large quantities of recombinant proteins in the mammary gland can result in phenotypes with compromised lactation physiology. These negative consequences have been vaguely described in the literature and, in most cases they have not been studied in depth with view to understanding the mechanisms of mammary disruption by transgene expression. Therefore, using a transgenic herd of goats expressing recombinant human butyrylcholinesterase, the main goals of this research were to: (a) study the lactation performance and basic milk parameters (b) assess milk composition (c) explore the integrity of epithelial tight junctions, endoplasmic reticulum stress and accelerated cell death (d) investigate delayed lactogenesis and (e) assess the effects of "compensatory treatments" on transgenic lactation performance.Our findings showed that transgenic lactations were characterized by a slow/delayed start of milk production, a relatively normal milk volume at peak and a premature shutdown of milk production compared to controls. These compromised productivities were associated with a disrupted lipid secretion at the level of the secretory epithelium, and a dramatic raise in the presence of phagocytes in milk that was not associated with mammary infection. Milk composition studies indicated that transgenic goats produce lower quantities of caseins and short chain fatty acids. Through determination of serum album presence and Na:K ratio in milk we established the development of permeable tight junctions as an apparent mechanism of lactation disruption in the transgenic animals. Delayed expression of alpha-lactalbumin was proposed as a major determinant of the delayed lactogenesis observed in the transgenic goats. Immunohistochemistry studies revealed increased expression of ER-stress signalling molecules (ATF6 and Caspase 12) in transgenic goats. Finally, prepartum mammary priming as well as mammary stem cell stimulators were successfully applied to enhance milk production in transgenic goats. In conclusion, several mechanisms of mammary disruption in transgenic goats were established and this knowledge was applied to the development of treatments that can successfully improve productivity and recombinant protein output in transgenic goats.