Targeted Inactivation of the Mouse α2-Macroglobulin Gene (∗)

The mouse α2-macroglobulin gene was inactivated in embryonic stem cells by homologous recombination. Liver α2-macroglobulin mRNA and plasma protein was absent in homozygotes and reduced to 50% in heterozygotes. α2-Macroglobulin-deficient mice were viable and produced normally sized litters with normal sex ratio over 3 generations. Characterization of adult homozygotes included diets with different fat content, treatments with endotoxin, bleomycin, carbon tetrachloride, and ethionine to test for immune system, lung, liver, and pancreas toxicity, respectively. Knock-out mice were more resistant to endotoxin but more sensitive to a choline-free diet supplemented with ethionine. Regulation of murinoglobulin mRNA expression during pregnancy was analyzed as a possible back-up mechanism for the deficiency in α2-macroglobulin. In addition, expression of mRNA was studied, coding for α2-macroglobulin receptor/lipoprotein receptor-related protein, low density lipoprotein receptor, and very low density lipoprotein receptor and for some common ligands, i.e. apolipoprotein E, lipoprotein lipase, and the 44-kDa heparin binding protein. Their differential regulation in the knock-out mice relative to C57Bl mice was evident and is discussed. The impressive 15-fold increase in maternal liver murinoglobulin mRNA at partum in the knock-out mice indicated increased consumption, compared to only 4-fold in normal mice. Thus, murinoglobulin appears as the major proteinase inhibitor around partum, obviously solicited to a much greater extend in α2-macroglobulin-deficient mice.