Extracellular 20S proteasome in BAL and serum of patients with alveolar proteinosis

Background and objectivesPulmonary alveolar proteinosis (PAP) is characterized by alveolar accumulation of surfactant lipoproteins. Proteasomes are involved in the nonlysosomal protein degradation. We hypothesize that enzymatically active proteasome is increased in the alveolar space of PAP.Patients and methods31 PAP patients (29 with primary, 2 with secondary form), 14 disease controls (10 with COPD and 4 with emphysema) and 18 healthy controls were studied. 20S Proteasome was measured by ELISA in bronchoalveolar lavage fluid (BALF) and in serum. Enzyme activity of extracellular proteasome (pkat/mg) was measured through fluorogenic substrate cleavage.ResultsProteasome concentration in BAL was higher in PAP patients than in disease controls or healthy subjects (566 ± 420 vs 53 ± 27 vs 60 ± 42 ng/ml, respectively, p < 0.0001 for both). Serum proteasome levels were higher in PAP patients than in healthy controls (825 ± 712 vs 405 ± 176 ng/ml, p = 0.018). PAP patients with active disease had higher serum levels than those who achieved remission (1317 ± 1176 vs 439 ± 422 ng/ml, p = 0.008). Proteasomal enzyme activity was increased in BAL of PAP patients (p < 0.05).ConclusionsThe 20S proteasome is increased and active in BAL of patients with PAP. Extracellular proteasome may contribute to the alveolar degradation of accumulated proteins in PAP.