LSC - 2019 - Validating immunoproteasome activity as a potential biomarker in non-invasive samples from COPD patients

The immunoproteasome is the main protein degrading system in immune cells and is essential for the resolution of viral infections. Immunoproteasome activity is markedly decreased in end-stage COPD lung tissue and expression is reduced in early-stage BAL cells (Kammerl et al. AJRCCM 2016). This supports the concept that altered immunoproteasome function contributes to progression of COPD by increasing susceptibility to infections. Our study aims to evaluate if immunoproteasome activity may serve as a biomarker for COPD in non-invasive samples. Systemic immunoproteasome expression was determined by RT-qPCR, Western blot and proteome analysis in peripheral mononuclear cells of 28 COPD patients (GOLD II-IV) and 24 controls (6 smokers). Activity was analyzed using subunit-specific activity-based probes (ABPs) and native gel analysis. In COPD, expression of the immunoproteasome subunits LMP2, LMP7 and MECL1 was increased and activity was also slightly albeit non-significantly upregulated. We are currently analyzing local immune cells of the lung using induced sputum for immunoproteasome activity. Induced sputum of 13 controls (non-smokers), 9 COPD (status B-D) and 4 asthma patients was collected and immune cell composition analyzed via cytospins. Native proteins were extracted and immunoproteasome activity was analyzed using ABPs. Analysis is still ongoing. Contrarily to our findings from lung tissue and BAL cells, immunoproteasome activity seems to be upregulated systemically in PBMC of COPD patients. However, lung-specific determination of immunoproteasome activity is feasible also in non-invasive sputum samples and might be a more useful approach for biomarker profiling in COPD.