Expression of an engineered form of recombinant procollagen in mouse milk

We have examined the suitability of the mouse mammary gland for expression of novel recombinant procollagens that can be used for biomedical applications. We generated transgenic mouse lines containing cDNA constructs encoding recombinant procollagen, along with the α and β subunits of prolyl 4-hydroxylase, an enzyme that modifies the collagen into a form that is stable at body temperature. The lines expressed relatively high levels (50- 200 μg/ml) of recombinant procollagen in milk. As engineered, the recombinant procollagen was shortened and consisted of a proα2(I) chain capable of forming a triple-helical homotrimer not normally found in nature. Analysis of the product demonstrated that (1) the proα chains formed disulphide-linked trimers, (2) the trimers contained a thermostable triple- helical domain, (3) the N-propeptides were aligned correctly, and (4) the expressed procollagen was not proteolytically processed to collagen in milk.