Arterial Elastin Synthesis in the Growing Chick

Abstract

In the growing chick a marked stimulation in soluble and mature arterial elastin synthesis occurs 2 and 5 weeks after hatching. Measurement of [³H]valine and [³H] proline incorporation into arterial soluble protein during this period indicated that most of the label is found in a 70,000 dalton protein subunit. The labeled soluble subunit had the characteristics of native soluble elastin or tropoelastin. During the period in which the greatest percentage increase in mature elastin occurs, the highest specific activities of soluble [³H]valine-labeled protein were observed. These changes were striking and suggest a developmental period for the growing chick in which factors related to elastin metabolism may be more easily studied. For example, one of our interests has been the effects of diet on vascular wall metabolism. The aortas from birds fed 1% cholesterol in their diets appear to synthesize soluble elastin (the 70,000 dalton subunlt) at rates 2–3 times that of controls. This newly synthesized soluble elastin also appears to be incorporated very quickly and quantitatively into insoluble elastin. Furthermore, pulse labeling with as much as a three hour chase does not appear to alter significantly the nature of the soluble elastin subunlt, i.e., significant proteolysis does not occur with respect to the remaining non-incorporated soluble elastin. Also, in some of the experiments Proteinase inhibitors were used (EDTA, ε-aminocaproic acid, N-ethylmaleimide, phenylmethylsulfonyl fluoride). No indication of a “pro”-tropoelastin was observed, which suggests that in the growing chick this form of elastin must be very short lived. Quantitation of soluble elastin in the extracts was also performed using a radioimmunoassay.