Role of apoptosis and transforming growth factor beta 1 in fibroblast selection and activation in systemic sclerosis

Objective. We hypothesized that pathophysiologic events during the developm ent of systemic sclerosis (SSc) may lead to selection and propagation of ce rtain apoptosis-resistant fibroblast subpopulations. The aim of this study was to examine a possible role for apoptosis in fibroblast selection in SSc and the role of transforming growth factor beta 1 (TGF beta 1). Methods. We compared SSc and normal fibroblasts for their susceptibility to anti-Fas-induced apoptosis and analyzed 2 models that might lead to fibrob last resistance to apoptosis in this process: long-term exposure to either anti-Fas or TGF beta 1, Results. SSc-derived fibroblasts were resistant to anti-Fas-induced apoptos is, showing 5.5 +/- 17.2% (mean +/- SD) apoptosis, compared with 32.1 +/- 1 4.0% among normal fibroblasts (P < 0.05), Anti-Fas-selected normal fibrobla sts showed 9.0 +/- 3.7% apoptosis, compared with 21.6 +/- 5.9% for sham-tre ated cells, which is consistent with the elimination of apoptosis-susceptib le subpopulations. Normal fibroblasts subjected to 6 weeks of TGF beta 1 tr eatment showed not only resistance to apoptosis, but also proliferation (11 8.5 +/- 35.4%), after anti-Fas treatment, compared with sham-treated cells (35.1 +/- 11.1% apoptotic cell death). TGF beta 1 treatment also increased the proportion of myofibroblasts (47% versus 28% in controls). Cultured SSc fibroblasts had a greater proportion of myofibroblasts (32-83%) than did n ormal fibroblasts (4-25%). We also examined the relationship between collag en gene expression and the myofibroblast phenotype in normal and SSc skin s ections. Only 2 of 7 normal sections had alpha-smooth muscle actin (alpha-S MA)-positive cells (mean +/- SD score 0.29 +/- 0.49 on a scale of 0-3), but all SSc sections were positive for alpha-SMA, with a mean score of 1.90 +/ - 0.88 for lesional and 1.50 +/- 0.71 for nonlesional sections. Scores for alpha 1(I) procollagen messenger RNA (mRNA) in lesional skin (mean +/- SD 3 .30 +/- 0.82 on a scale of 1-4) were significantly higher than in normal (1 .43 +/- 0.79) or nonlesional (1.40 +/- 0.52) skin, but scores varied, and t here was no correlation between collagen mRNA and alpha-SMA levels. Conclusion. Our results show that resistance to apoptosis is an important p art of the SSc phenotype. TGF beta 1 may play a role by inducing apoptosis- resistant fibroblast populations, and also by inducing myofibroblasts and b y enhancing extracellular matrix synthesis.