Extracellular concentration and enzyme activity of proteasome in BAL of patients with alveolar proteinosis

Introduction: Pulmonary alveolar proteinosis (PAP) is a rare disorder characterized by alveolar accumulation of surfactant lipoproteins. Proteasomes are responsible for nonlysosomal protein degradation. They are involved in apoptosis, stress response and inflammation. ARDS and sarcoidosis show elevated levels of extracellular proteasome. The aim of this study was to detect proteasome concentration and enzyme activity in BALF in PAP. Patients and methods: 22 PAP patients (20 with primary, 2 with secondary form) and 18 healthy controls were studied. 20S proteasome subunit (murine monoclonal antibody by Biomol Int. L.P., Exeter, UK) was measured by ELISA in BALF. The cleavage of 3 fluorogenic substrates (Suc-LLVY-AMC, BZ-VGR-AMC and Suc-LLE-AMC) was used to describe the specific enzyme activity (chymotrypsin-, trypsin- and caspase-like) of extracellular proteasome. Results: Proteasome concentration in BALF of PAP patients was 10-fold higher than in healthy subjects (699±422 vs 60±36 ng/mL, p<0.0001). Trypsin- and caspase-like activity of proteasome was significantly increased in PAP compared to healthy subjects (BZ-VGR-AMC 1.5±0.9 vs 0.26±0.27; Suc-LLE-AMC 0.62±0.7 vs 0.07±0.06 pkat/mL; p<0.01). Enzyme activity for all 3 substrates correlated directly with the total protein concentration in BALF (r=0.7, p= 0.002; r=-0.56, p=0.02; r=0.85, p<0.001) and inversely with TLCO (r=-0.72, p= 0.008; r=-0.7, p=0.014; r=-0.73, p=0.006). Conclusions: Proteasome alveolar concentration is higher in PAP than in healthy controls. This is associated with an increased trypsin- and caspase-like enzyme activity. Proteasome seems to be significantly involved in the alveolar protein degradation in PAP.