Procollagen production and procollagen messenger RNA levels and activity in human lung fibroblasts during periods of rapid and stationary growth.

The production of procollagen molecules by human diploid fetal lung fibroblasts (HFL-1 cells) remains constant in both rapid and stationary growth phases. However, log phase cells degrade 3-fold more newly synthesized collagen inside the cell prior to secretion than do stationary phase cells. Procollagen mRNA levels, measured by hybridization with a type I procollagen mRNA-specific complementary DNA, are approximately 2-fold higher in confluent cells than in log phase cells. There are no significant differences in the ability of either log phase or confluent HFL-1 cell procollagen mRNA to be translated in an in vitro cell-free translation system. Therefore, the ability of HFL-1 cells to maintain constant collagen production irrespective of the growth status of the cells results from the combined action of a number of regulatory mechanisms, including changes in procollagen mRNA levels, the utilization of procollagen mRNA, and intracellular procollagen degradation.

Control of collagen production by human diploid lung fibroblasts.

The fibroblast is a differentiated mesenchymal cell which produces and exports collagen, a macromolecule that plays a critical structural role in the function of most organs. To evaluate the control soft tissue fibroblasts have over collagen production, HFL-1, a diploid human lung cell strain, was studied during periods of rapid cell growth and relatively slow growth over 25 population doublings. To minimize environmental influences, the extracellular milieu of the cells was kept constant throughout the study period. Rates of collagen production per cell per unit time were quantitated by labeling HFL-1 with [14C]proline and measuring the production of [14C]hydroxyproline after taking into consideration the specific activity of [14C]proline within the free intracelllular proline pool and the per cent hydroxylation of proline residues in newly synthesized collagen. Although the specific activity of intracellular free proline and the per cent hydroxylation of proline in collagen varied considerably depending on the growth rates of the cells, collagen production by HFL-1 was constant, even during periods of rapid cell growth. Thus, under conditions of a stable environment, populations of soft tissue fibroblasts rigidly control their collagen production. In cultures that maintained a constant doubling time, this stability was maintained over at least 25 population doublings, suggesting that on the average, collagen production appears to be tightly controlled and dissociated from the events and sequelae of cell division.

Collagen in the lung: development of a technology applicable to human lung disease.

Techniques have been developed to quantitate in vitro the types, rates and fates of collagen synthesized by animal and human lung. Studies are continuing in our laboratory to apply these techniques to investigate important lung disorders, including: (1) classification of the fibrotic lung disorders by the types of collagen synthesized; (2) development of an in vitro drug evaluation system to determine, in a lung biopsy, which drugs are useful in reducing the fibrotic process for a patient with interstitial disease; and (3) investigations of the influence of serum proteins on lung connective tissue synthesis and proteolysis.

The metabolism of amino acids, peptides, and disulfides in lysosomes of fibroblasts cultured from normal individuals and those with cystinosis.

The metabolism of amino acids, peptides, and disulfides has been investigates in cultured skin fibroblasts from normal individuals and patients with cystinosis. Human fibroblast lysosomes closely resemble the lysosomes of mouse peritoneal macrophages in having an apparent permeability barrier to amino acids and peptides with molecular weights of greater than 220-230. Cystinotic and normal cells behave similarly in this regard. Normal cells do not undergo lysosomal swelling when exposed to cysteine-penicillamine disulfides, while cystinotic cells are prominently vacuolized under these conditions. Normal lysosomes may have a specific mechanism for the disposal of cystine, and deficient activity of this mechanism in cystinotic lysosomes could result in cystine storage therein. The demonstration that human fibroblasts can be used conveniently to study lysosomal metabolism of small substrates may facilitate investigations of these aspects of lysosomal function in a variety of genetic diseases of man.

Cystinosis: selective induction of vacuolation in fibroblasts by L-cysteine-D-penicillamine disulfide.

In cultured fibroblasts from individuals with cystinosis vacuolation is induced by exposure to L-cysteine-D-penicillamine disulfide. Normal fibroblasts do not show vacuolation on such exposure. These observations provide direct evidence that cystinotic cells have deficient activity of a lysosomal system for disulfide metabolism or transport. Induction of vacuolation by the mixed disulfide in cystinotic but not in normal cells furnishes a histological marker for cystinotic fibroblasts.

Cystine: compartmentalization within lysosomes in cystinotic leukocytes.

The large amount of cystine compartmentalized in cystinotic leukocytes cosediments in isopycnic sucrose density gradients with dense lysosomal particles, within which it is presumably contained. Such cystine appears to be primarily noncrystalline in these organelles.