INCREASED COLLAGEN-SYNTHESIS AND INCREASED CONTENT OF TYPE-VI COLLAGEN IN MYOCARDIUM OF TIGHT-SKIN MICE

Objective: The tight skin mouse (TSK) is a mutant strain characterised by excessive collagen accumulation in skin and some internal organs such as the heart. The aims of this study were (1) to examine in vitro collagen synthesis in TSK myocardium; (2) to determine myocardial content of type VI collagen in the same model; and (3) to examine the expression of one of the genes for type VI collagen in cultured TSK myocardial fibroblasts. Methods: Individual hearts from 8 month old heterozygous male TSK and normal sex and age matched mice were incubated with C-14 proline. Total C-14 protein and C-14 collagen synthesis by myocardial tissues were determined with collagenase digestion and SDS gel electrophoresis. For determination of type VI collagen, hearts from 10 month old male TSK and normal mice were subjected to guanidine extraction followed by pepsin digestion, salt fractionation, and western blotting. Expression of the alpha2(VI) collagen gene was determined in myocardial fibroblasts cultured from TSK and normal mice, employing northern and dot blot hybridisations with a murine specific cDNA. Results: TSK hearts had up to twofold greater protein and collagen biosynthesis and 2.5-fold greater type VI collagen content (400 mug v 156 mug). Fibroblasts cultured from TSK mice hearts displayed up to threefold higher steady state concentrations of alpha2(VI) collagen mRNA than normal myocardial fibroblasts. Conclusions: Hearts from TSK mice showed increased protein and collagen biosynthesis and increased myocardial content of type VI collagen compared with hearts from age matched normal mice. Also, fibroblast cultures from TSK mice myocardium showed increased expression of the alpha2(VI) collagen gene, indicating that increased transcription of type VI collagen genes may be responsible for the accumulation of this collagen in myocardium from TSK mice.