The Role of Progesterone in Cellular Apoptosis of Skin and Lung in a Bleomycin-injured Mouse Model

Systemic sclerosis is a female predominant, a fibrotic autoimmune disease in which disturbance in tissue homeostasis and cell turnover including cell apoptosis are central events in pathogenesis. Sex hormones are known as the important players in sexual dimorphism of autoimmune diseases and in tissue homeostasis. Progesterone influences autoimmune disease via its immunomodulatory effect or by its direct action on parenchymal cell function. On the other hand, this hormone impacts tissue homeostasis by acting on cell apoptosis in a different situation. The objective of this study was to examine the effect of progesterone on cellular apoptosis of skin and lung tissues in a mouse model of scleroderma. Four group of mice were involved in this study with 10 mice in each. The fibrotic model was induced by daily subcutaneous injection of bleomycin for 28 days. One week after initiation of fibrosis induction, mice received subcutaneous progesterone alone or with bleomycin for 21 days. Control group received only Phosphate buffered saline PBS. After 28 days, under lethal anesthesia skin and lung tissues were harvested for histological assessment and hydroxyproline measurement. Apoptosis in tissue sections was detected by TUNEL assay technique. Bleomycin administration induced fibrosis in skin and lung tissues. Severe apoptosis was seen in skin and lung tissues of the bleomycin-treated group (p<0.001 in the skin and p<0.05 in the lung). Progesterone injection either in the skin (p>0.05) or in the lung (p>0.05) did not alter apoptosis in bleomycin-treated animals. Our data confirm the role of apoptosis in the pathogenesis of fibrosis in this model; however, progesterone does not affect cellular apoptosis in skin and lung tissues of bleomycin-injured animals.