Changes in collagen phenotypes during progression and regression of cardiac hypertrophy

Excessive deposition of collagen has been implied to be responsible for abnormal stiffness and altered cardiac function during hypertrophy and heart failure. In the present paper we studied the changes in collagen and their phenotypes during development of cardiac hypertrophy in spontaneously hypertensive rats (SHR) compared to age- and sex-matched Wistar Kyoto (WKY). We also studied the changes in collagen after regression of hypertrophy, with antihypertensive therapy with ACE inhibitors, captopril (C) and lisinopril (L).

Collagen was extracted from the heart tissue by cyanogen bromide (CNBr) digestion. Collagen phenotypes were separated and quantified by SDS-polyacrylamide gel electrophoresis. The transcript levels(mRNA) of collagen phenotypes were determined by Northern analysis.

Our studies showed that the ventricular collagen and their phenotypes did not alter in SHR during the first 6 months of progression of hypertrophy when compared to WKY. After 40 weeks, however, in SHR there was an unexpected rise in collagen content and the distribution of collagen phenotype differs compared to WKY, especially during the chronic phase of hypertrophy (65 weeks of age). In WKY during the aging process there was a gradual increase in type III collagen, whereas in SHR it plateaus after 40 weeks of age. Treatment with antihypertensive drugs captopril and lisinopril showed a similar degree of reduction in blood pressure (P < 0.001), regressed hypertrophy (P < 0.001), and reduced collagen, whereas decrease in type I to III ratio was found with captopril only, but not with lisinopril. This decrease in type I to III ratio due to captopril treatment is primarily due to an increase in type III collagen (both protein and transcript level) in SHR.

Our data showed, for the first time, that during the chronic phase of hypertrophy in SHR there is a gradual reduction in type I to III ratio, primarily due to a lack of increase in type III collagen during chronic phase of hypertrophy. This suggests that quality of collagen is an important factor in determining the degree of cardiac stiffness. Our data also showed that not all ACE inhibitors have similar actions on collagen phenotype production. This suggests that perhaps the mechanism of action of ACE inhibitors on collagen are independent of its effect on angiotensin II formation.