Sequential Changes in the Localization of the Type IV Collagen α Chain in the Infarct Zone: Immunohistochemical Study of Experimental Myocardial Infarction in the Rat

Collagen, as a component or the extracenuiar matrix, have a role in the healing process after myocardial infarction (MI). For type IV collagen, a major structural protein present in the basal membrane of myocytes, six α chains [α1(IV)–α6(IV)] have been identified. We examined the sequential changes in the appearance and localization of the α1(IV)–α5(IV) after experimental MI in rats. Hearts were excised from 1 day to 8 weeks after permanent left coronary artery ligation. Immunohistochemical staining with monoclonal antibodies was performed. On day 3, staining for both α1(IV) and α2(IV) first appeared, forming a wavy pattern in the infarct peripheral zone, and the staining was not restricted to the cell membrane. The staining intensity and distribution for both α1 (IV) and α(IV) in the peripheral zone then gradually increased, reaching a maximum around day 7. The distribution progressed from the peripheral to the central zone of the infarct for 1–2 days, reaching the center point after 2 weeks. The staining distribution gradually decreased after reaching the maximum, but the staining had not completely disappeared at 8 weeks. In contrast, no positive staining for α3(IV), α4(IV)or α5(IV) was observed at any time during the 8-week observation period. Thus, the present results demonstrated that in rats, type IV collagen consisting of α1 and α2 chains appears in the infarct zone at a relatively early phase after MI, indicating that type IV collagen composed of α1 and α2 chains contributes to infarct healing.