Pulmonary fibrosis (PF) is a chronic, progressive and life-threatening lung disease with a poor prognosis.
It is the most common type of interstitial lung disease, characterized by thick and stiff lung tissue that scars over time. The scarring hampers the movement of oxygen from the lungs to the bloodstream. Reduced oxygen supply in the body causes such complications as shortness of breath, persistent, dry and hacking cough, fatigue, unexplained weight loss, aching muscles and joints, and a deformity known as clubbed fingernails.
Most PF cases are classified as idiopathic, meaning doctors don’t fully understand the cause. Doctors are able to identify reasons why the disease develops in some cases, however. They include exposure to pollutants, the use of specific medications, radiation therapy, connective tissue diseases, and interstitial lung disease.
Several factors increase the risk of PF, such as age, gender, smoking, certain occupations, cancer treatments, and genetics.
PF is more common in men than women, but the question of which sex has a better survival rate has yet to be resolved. One study showed that women have a better survival rate, while another showed the opposite.
Research published in 2016 showed gender differences in the expression of SPP1, a protein whose levels increase in PF. SPP1 differences in male and female mice contributed to differences in their susceptibility to developing silica-induced fibrosis, the study showed.
Studies had shown that mice lacking SPP1 develop less severe fibrosis after exposure to bleomycin, a chemical used to induce fibrosis in experimental animals. So the researchers who did the study published in 2016 decided to explored the effects of silica in these mutant mice.
Surprisingly, the team discovered that mutant male and female mice had the same number of inflammatory cells in their bronchoalveolar lavage fluid. The study in the journal Environmental Health Perspectives noted, however, that female mice lacking the SPP1 gene had fewer inflammatory cells in their bronchoalveolar lavage fluid than normal female mice. That difference did not appear in male mice. But male mice lacking SPP1 had lower levels of the fibrosis marker hydroxyproline in their lungs than normal male mice.
To further explore gender differences in PF, the team treated male mice with estrogen and removed the ovaries of female mice. Estrogen treatment did not lead to changes in SPP1 signaling in the male mice, but female mice without ovaries had more SPP1 in their lungs.
The study suggested that gender differences in SPP1 expression may contribute to the differences in male and female mice’s susceptibility to silica exposure. Researchers said more studies were necessary to confirm the finding. If it is confirmed, scientists might try to develop sex-specific treatments for fibrosis.
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