Pioglitazone Therapy of Autoimmune Pulmonary Alveolar Proteinosis Autoimmune Pulmonary Alveolar Proteinosis

Pulmonary alveolar proteinosis (PAP) is a syndrome of surfactant accumulation, respiratory failure, and innate immune deficiency for which therapy remains limited to whole lung lavage (WLL), an invasive physical procedure to remove surfactant unavailable at most medical centers. While PAP occurs in multiple diseases affecting men, women, and children of all ages and ethnic origins, in 85% of patients, it occurs as an idiopathic disease associated with neutralizing GM-CSF autoantibodies. Basic science and translational research has shown that idiopathic PAP is an autoimmune disease in which disruption of GM-CSF signaling impairs the ability of alveolar macrophages to clear surfactant and perform host defense functions. Recently, it has been shown that cholesterol toxicity drives pathogenesis in alveolar macrophages from GM-CSF deficient (Csf2-/-) mice and patients with autoimmune PAP. Loss of GM-CSF signaling reduces PU.1/CEBP-mediated expression of PPARγ and its downstream target ABCG1 (a cholesterol exporter important in macrophages). The cell responds by esterifying and storing cholesterol in vesicles to reduce toxicity. Eventually, vesicles fill the cell, impair intracellular transport and reduce uptake and clearance of surfactant from the lung surface resulting in disease manifestations. Recent data indicates that pioglitazone, a PPARγ agonist currently approved by the FDA for human use, increases cholesterol/surfactant clearance by alveolar macrophages from autoimmune PAP patients and Csf2-/- mice. Importantly, pioglitazone significantly reduced the severity of PAP lung disease in Csf2-/- mice after several months of therapy. Together, these observations suggest pioglitazone could be 'repurposed' as pharmacologic therapy for PAP.