Fibroblasts: the missing link between fibrotic lung diseases of different etiologies?

Fibrotic lung disorders, either idiopathic, or associated with a specific etiology or a specific condition such as scleroderma, are increasingly recognized. As a whole they constitute a group of diseases characterized by the progressive destruction of the lung which ultimately leads to chronic respiratory failure and death. Improving the prognosis of these disorders requires the identification of drugs capable of inhibiting partially or totally the progression of lung fibrosis, and perhaps of reversing established fibrosis. This has been the focus of huge efforts from academic groups and pharma companies, and more than 20 different molecules are being investigated in clinical trials in idiopathic pulmonary fibrosis (IPF) a well defined and relatively frequent fibrotic lung disease of unknown etiology. However, until now, only one drug has been approved for lung fibrosis treatment. This drug, pirfenidone, has been shown to slow the decline of lung function in IPF, but no drug has demonstrated effects on survival in patients with lung fibrosis [1]. The effort must be prolonged and intensified. Beside IPF, scleroderma-associated lung fibrosis is a well recognized fibrotic disorder. With pulmonary hypertension, lung fibrosis is now the main cause of death of patients with scleroderma [2]. The nature and pathophysiology of lung fibrosis in IPF and scleroderma are different. For instance, scleroderma affects mainly women, whereas IPF predominates in men; usual interstitial pneumonia is the pathological pattern of IPF, whereas non specific interstitial pneumonia is the main pattern in patients with scleroderma; the MUC5B promotor polymorphism is associated with IPF whereas it is not observed in patients with IPF [3]; IPF is rapidly progressive disorder as compared with the slowly moving scleroderma-associated lung fibrosis [2]. Fibrotic lung diseases are characterized by the pathological accumulation of fibroblasts, which are thought to