Targeted Inactivation of the Mouse α2-Macroglobulin Gene

The mouse alpha(2)-macroglobulin gene was inactivated in embryonic stem cells by homologous recombination, Liver alpha(2)-macroglobulin mRNA and plasma protein was absent in homozygotes and reduced to 50% in heterozygotes, alpha(2)-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 alpha(2)-macroglobulin. In addition, expression of mRNA was studied, coding for alpha(2)-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 knockout 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 alpha(2)-macroglobulin-deficient mice.