Eg. Eleftheriades et al., PROLYL HYDROXYLATION REGULATES INTRACELLULAR PROCOLLAGEN DEGRADATION IN CULTURED RAT CARDIAC FIBROBLASTS, Journal of Molecular and Cellular Cardiology, 27(8), 1995, pp. 1459-1473
To determine the regulatory role of prolyl hydroxylation in intracellu
lar cardiac procollagen turnover, we examined the effects of prolyl 4-
hydroxylase inhibitors (alpha,alpha'-dipyridil, 3,4-dihydroxybenzoic a
cid ethyl ester, pyridine 2,4-dicarboxylic acid ethyl ester) and ascor
bic acid on procollagen metabolism by cultured, neonatal rat cardiac f
ibroblasts. Ascorbate-deficient fibroblasts showed decreased rates of
prolyl hydroxylation and total collagen accumulation without a signifi
cant reduction in alpha(1)(I) and alpha(1)(III) mRNA levels. The fract
ion of newly synthesized procollagens degraded intracellularly was als
o substantially increased in ascorbate-deficient cells (50 +/- 7 v 30
+/- 3% in ascorbate-deficient v control fibroblasts; P<0.05). These fi
ndings were associated with increased intracellular accumulation of Ty
pe I procollagen, enhanced secretion of ''underhydroxylated'' pro alph
a(1)(I) polypeptide into the cell culture medium, and decreased extrac
ellular Type I collagen deposition, Similar results were obtained:by t
reating cells with alpha,alpha'-dipyridil (300 mu M), and 3,4-dihydrox
ybenzoic acid ethyl ester (400 mu M) in the presence of ascorbate. A m
ajor portion of the enhanced degradation of newly synthesized procolla
gens occurred within acidic intracellular compartments as indicated by
the inhibition of procollagen degradation by chloroquine (25 mu M). I
nhibition of procollagen secretion by colchicine (0.5 mu g/ml) enhance
d the diversion to, and subsequent intracellular degradation of underh
ydroxylated procollagens in cardiac fibroblast lysosomes, We conclude
that inactivation of prolyl 4-hydroxylase increases intracellular accu
mulation and intralysosomal degradation of newly synthesized cardiac p
rocollagen polypeptides. These observations suggest that procollagen p
rolyl hydroxylation may be important in the regulation of collagen acc
umulation by cardiac interstitial cells during fibrotic processes in v
ivo. (C) 1995 Academic Press Limited