Increased transglutaminase in the aortas of cholesterol-fed rabbits: occurrence of buffer soluble and insoluble forms and an inhibitor.

Rabbits were fed for 10-12 weeks on a normal pellet diet or on the same diet containing 1% cholesterol and 6% peanut oil. The animals were killed and the aortas divided into three layers which were homogenized and extracted. The extracts and the insoluble residues were assayed for transglutaminase activity and tissue transglutaminase antigen. When compared with normal aortas, the inner and middle layers of aortas with atherosclerotic lesions from cholesterol-fed rabbits showed higher transglutaminase activities in the buffer-soluble fraction without a corresponding increase in antigen. The buffer extracts showed two peaks (I and II) of activity and antigen on DE 52 chromatography; peak I was also found, together with lipid, in Triton X-100 extracts of the buffer-insoluble residue. The Triton X-100 insoluble fraction showed higher concentrations of both activity and antigen in the inner and middle layers of atherosclerotic aortas than in normal aortas, but the activity per nanogram of antigen was lower than in the buffer-soluble fraction. The activity in this insoluble residue was largely extracted, together with an inhibitor, by an NaCl-sucrose-dithiothreitol-Triton X-100 solution. DE 52 chromatography of this extract showed a third peak of activity and antigen (peak III) and an inhibitor peak that was distinct from the activity peaks.

Transglutaminase-catalysed cross-linking: a potential mechanism for the interaction of fibrinogen, low density lipoprotein and arterial type III procollagen.

Bovine type III [3H]procollagen or its [125I]aminopropeptide were shown by chromatography under dissociating conditions to form very high molecular weight compounds with excess bovine fibrinogen after incubation with purified tissue transglutaminase, though none is formed with other major plasma proteins. Larger compounds of this type formed from fibrinogen or fibrin monomer can be separated by centrifugation and they are insoluble on washing with 1% SDS. Ultracentrifugation showed that a significant fraction of [3H]procollagen III forms a low density complex on incubation with transglutaminase plus excess IDL or LDL, but not HDL. SDS polyacrylamide gel electrophoresis showed that type III collagen [125I]aminopropeptide forms high molecular weight compounds after incubation with transglutaminase plus excess IDL or LDL but not with HDL. It is hypothesized that, in the presence of excessive concentrations of LDL and/or fibrinogen and of tissue transglutaminase, crosslinking reactions of the type demonstrated may interfere with normal injury-repair processes and stimulate the formation of atherosclerotic lesions in arteries.