Efficient increase of the novel recombinant human plasminogen activator expression level and stability through the use of homozygote transgenic rabbits

Identification, purification, and pharmacological activity analysis of Desmodus rotundus salivary plasminogen activator alpha1 (DSPAα1) expressed in transgenic rabbit mammary glands

Desmodus rotundus plasminogen activator alpha 1(DSPAα1) is a thrombolytic protein with advantages, such as a long half-life, high accuracy and specificity for thrombolysis, wide therapeutic window, and no neurotoxicity. To date, DSPAα1 has only been expressed in the Chinese hamster ovary, insect cells, transgenic tobacco plants, and Pichia pastoris. To the best of our knowledge, we are the first to report the expression of DSPAα1 in transgenic rabbit mammary glands, extract the product, and analyze its pharmacology activity. An efficient mammary gland-specific expression vector pCL25/DSPAα1 was transferred to prokaryotic zygotes in rabbits by microinjection to generate six DSPAα1 transgenic rabbits. The recombinant DSPAα1 (rDSPAα1) expression in transgenic rabbit milk was 1.19 ± 0.26 mg/mL. The rDSPAα1 purification protocol included pretreatment, ammonium sulfate precipitation, benzamidine affinity chromatography, cation exchange chromatography, and Cibacron blue affinity chromatography; approximately 98% purity was achieved using gel electrophoresis. According to sequencing results, the primary structure of rDSPAα1 was consistent with the theoretical design sequence, and its molecular weight was consistent with that of the natural protein. N-terminal sequencing results indicated rDSPAα1 to be a mature protein, as the goat signal peptide sequence of the expression vector was no longer detected. The fibrinolytic activity of rDSPAα1 was estimated to be 773,333 IU/mg. Fibrin-agarose plate assay and in vitro rat blood clot degradation assay showed that rDSPAα1 had strong thrombolytic activity. In conclusion, we report recombinant DSPAα1 with high thrombolytic activity expressed in transgenic rabbit mammary glands.

Accurately cleavable goat β-lactoglobulin signal peptide efficiently guided translation of a recombinant human plasminogen activator in transgenic rabbit mammary gland

Poor expression is the key factor hampering the large-scale application of transgenic animal mammary gland bioreactors. A very different approach would be to evaluate the secretion of recombinant proteins into milk in response to a cleavable signal peptide of highly secreted lactoproteins.We previously reported rabbits harboring mammary gland-specific expression vector containing a fusion cDNA (goat β-lactoglobulin (BLG) signal peptide and recombinant human plasminogen activator (rhPA) coding sequences) expressed rhPA in the milk, but we did not realize the signal peptide contributed to the high rhPA concentration and did not mention it at that time. And the molecular structure and biological characteristics still remain unknown. So, rhPA in the milk was purified and characterized in the present study.rhPA was purified from the milk, and the purity of the recovered product was 98% with no loss of biological activity. Analysis of the N-terminal sequence, C-terminal sequence, and the molecular mass of purified rhPA revealed that they matched the theoretical design requirements. The active systemic anaphylaxis (ASA) reactions of the purified rhPA were negative. Taken together, these results indicated that the goat BLG signal peptide can efficiently mediate rhPA secretion into milk and was accurately cleaved off from rhPA by endogenous rabbit signal peptidase.We have reinforced the importance of a rhPA coding region fused to a cleavable heterologous signal peptide from highly secreted goat BLG to improve recombinant protein expression. It is anticipated that these findings will be widely applied to high-yield production of medically important recombinant proteins.