Excess macrophage elastase MMP-12 is a major driver of chronic obstructive pulmonary disease. Here the authors show that the endolysosomal ion channel TRPML3 is a regulator of the cellular reuptake... Show moreExcess macrophage elastase MMP-12 is a major driver of chronic obstructive pulmonary disease. Here the authors show that the endolysosomal ion channel TRPML3 is a regulator of the cellular reuptake of MMP-12, thus neutralizing harmful MMP-12 in the lung.Lung emphysema and chronic bronchitis are the two most common causes of chronic obstructive pulmonary disease. Excess macrophage elastase MMP-12, which is predominantly secreted from alveolar macrophages, is known to mediate the development of lung injury and emphysema. Here, we discovered the endolysosomal cation channel mucolipin 3 (TRPML3) as a regulator of MMP-12 reuptake from broncho-alveolar fluid, driving in two independently generated Trpml3(-/-) mouse models enlarged lung injury, which is further exacerbated after elastase or tobacco smoke treatment. Mechanistically, using a Trpml3(IRES-Cre/eR26-tau GFP) reporter mouse model, transcriptomics, and endolysosomal patch-clamp experiments, we show that in the lung TRPML3 is almost exclusively expressed in alveolar macrophages, where its loss leads to defects in early endosomal trafficking and endocytosis of MMP-12. Our findings suggest that TRPML3 represents a key regulator of MMP-12 clearance by alveolar macrophages and may serve as therapeutic target for emphysema and chronic obstructive pulmonary disease. Show less
RATIONALE Chronic obstructive pulmonary disease patients and in particular smokers are more susceptible to respiratory infections contributing to acute exacerbations of disease. The... Show moreRATIONALE Chronic obstructive pulmonary disease patients and in particular smokers are more susceptible to respiratory infections contributing to acute exacerbations of disease. The immunoproteasome is a specialized type of proteasome destined to improve major histocompatibility complex (MHC) class I-mediated antigen presentation for the resolution of intracellular infections. OBJECTIVES To characterize immunoproteasome function in COPD and its regulation by cigarette smoke. METHODS Immunoproteasome expression and activity were determined in bronchoalveolar lavage (BAL) and lungs of human donors, COPD, and IPF patients, as well as in cigarette smoke-exposed mice. Smoke-mediated alteration of immunoproteasome activity and MHC I surface expression were analysed in human blood-derived macrophages. Immunoproteasome-specific MHC I antigen presentation was evaluated in spleen and lung immune cells that had been smoke-exposed in vitro or in vivo. MEASUREMENTS AND MAIN RESULTS Immunoproteasome and MHC I mRNA expression was reduced in BAL cells of COPD patients and in isolated alveolar macrophages of COPD and IPF patients. Exposure of immune cells to cigarette smoke extract in vitro reduced immunoproteasome activity and impaired immunoproteasome-specific MHC I antigen presentation. In vivo, acute cigarette smoke exposure dynamically regulated immunoproteasome function and MHC I antigen presentation in mouse BAL cells. End-stage COPD lungs showed markedly impaired immunoproteasome activities. CONCLUSIONS We here show for the first time that the activity of the immunoproteasome is impaired by cigarette smoke resulting in reduced MHC I antigen presentation. Regulation of immunoproteasome function by cigarette smoke may thus alter adaptive immune responses and add to prolonged infections and exacerbations in COPD and IPF. Show less
