Cathelicidins are a family of antimicrobial proteins found in the peroxidase-negative granules of neutrophils. The known biologic functions reside in the C-terminus, which must be cleaved from the holoprotein to become active. Bovine and porcine cathelicidins are cleaved by elastase from the azurophil granules to yield the active antimicrobial peptides. The aim of this study was to identify the physiological setting for cleavage of the only human cathelicidin, hCAP-18, to liberate the antibacterial and cytotoxic peptide LL-37 and to identify the protease responsible for this cleavage. Immunoelectron microscopy demonstrated that both hCAP-18 and azurophil granule proteins were present in the phagolysosome. Immunoblotting revealed no detectable cleavage of hCAP-18 in cells after phagocytosis. In contrast, hCAP-18 was cleaved to generate LL-37 in exocytosed material. Of the 3 known serine proteases from azurophil granules, proteinase 3 was solely responsible for cleavage of hCAP-18 after exocytosis. This is the first detailed study describing the generation of a human antimicrobial peptide from a promicrobicidal protein, and it demonstrates that the generation of active antimicrobial peptides from common proproteins occurs differently in related species.

The human lung is exposed to a large number of airborne pathogens as a result of the daily inhalation of 10,000 litres of air. The observation that respiratory infections are nevertheless rare is testimony to the presence of an efficient host defence system at the mucosal surface of the lung.The airway epithelium is strategically positioned at the interface with the environment, and thus plays a key role in this host defence system. Recognition systems employed by airway epithelial cells to respond to microbial exposure include the action of the toll-like receptors.The airway epithelium responds to such exposure by increasing its production of mediators such as cytokines, chemokines and antimicrobial peptides. Recent findings indicate the importance of these peptides as effector molecules of innate immunity by killing microorganisms, but also as regulators of inflammation, immunity and wound repair. Finally, the clinical relevance of the functions of the airway epithelium in innate immunity is discussed.

Brown adipose tissue (BAT) combusts high amounts of fatty acids, thereby lowering plasma triglyceride levels and reducing obesity. However, the precise role of BAT in plasma cholesterol metabolism and atherosclerosis development remains unclear. Here we show that BAT activation by β3-adrenergic receptor stimulation protects from atherosclerosis in hyperlipidemic APOE*3-Leiden.CETP mice, a well-established model for human-like lipoprotein metabolism that unlike hyperlipidemic Apoe^−/− and Ldlr^−/− mice expresses functional apoE and LDLR. BAT activation increases energy expenditure and decreases plasma triglyceride and cholesterol levels. Mechanistically, we demonstrate that BAT activation enhances the selective uptake of fatty acids from triglyceride-rich lipoproteins into BAT, subsequently accelerating the hepatic clearance of the cholesterol-enriched remnants. These effects depend on a functional hepatic apoE-LDLR clearance pathway as BAT activation in Apoe^−/− and Ldlr^−/− mice does not attenuate hypercholesterolaemia and atherosclerosis. We conclude that activation of BAT is a powerful therapeutic avenue to ameliorate hyperlipidaemia and protect from atherosclerosis.

The airway epithelium is now considered to be central to the orchestration of pulmonary inflammatory and immune responses, and is also key to tissue remodelling. It acts as the first barrier in the defence against a wide range of inhaled challenges, and is critically involved in the regulation of both innate and adaptive immune responses to these challenges. Recent progress in our understanding of the developmental regulation of this tissue, the differentiation pathways, recognition of pathogens and antimicrobial responses is now exploited to help understand how epithelial cell function and dysfunction contributes to the pathogenesis of a variety of inflammatory lung diseases. Herein, advances in our knowledge of the biology of airway epithelium, as well as its role and (dys)function in asthma, chronic obstructive pulmonary fibrosis and cystic fibrosis will be discussed.

Cigarette smoking results in oxidative stress and inflammation in the lungs, which are involved in the pathogenesis of chronic obstructive pulmonary disease (COPD). 4-Hydroxy-2-nonenal (4-HNE), a highly reactive diffusible product of lipid peroxidation, is a key mediator of oxidant-induced cell signaling and apoptosis. 4-HNE has a high affinity toward cysteine, histidine, and lysine groups and forms direct protein adducts. We investigated the presence of 4-HNE–modified proteins in lung tissue obtained from subjects with and without COPD. We studied 23 current or ex-smokers with similar smoking histories with COPD (n = 11; FEV₁ < 70% predicted) or without COPD (n = 12; FEV₁ > 84% predicted) who had undergone lung resection. As 4-HNE and transforming growth factor-β₁ (TGF-β₁) can modulate γ-glutamylcysteine synthetase (γ-GCS) mRNA levels in lung cells, we assessed the relations between 4-HNE–modified protein levels, FEV₁, γ-GCS, and TGF-β₁. 4-HNE–modified protein levels were elevated in airway and alveolar epithelial cells, endothelial cells, and neutrophils in subjects with COPD, compared with the levels in subjects without COPD (p < 0.01). We also observed a significant inverse correlation between the levels of 4-HNE adducts in alveolar epithelium, airway endothelium, and neutrophils and FEV₁ (p < 0.05) and a positive correlation between 4-HNE adducts and TGF-β₁ protein and mRNA as well as γ-GCS mRNA levels in airway and alveolar epithelium (p < 0.01). The elevated levels of 4-HNE may play a role in the signaling events in lung inflammation leading to the imbalance of the expression of both proinflammatory mediators and protective antioxidant genes in COPD.

The epithelial lining of the airway forms the first barrier against environmental insults, such as inhaled cigarette smoke, which is the primary risk factor for the development of chronic obstructive pulmonary disease (COPD). The barrier is formed by airway epithelial junctions, which are interconnected structures that restrict permeability to inhaled pathogens and environmental stressors. Destruction of the epithelial barrier not only exposes subepithelial layers to hazardous agents in the inspired air, but also alters the normal function of epithelial cells, which may eventually contribute to the development of COPD. Of note, disruption of epithelial junctions may lead to modulation of signaling pathways involved in differentiation, repair, and proinflammatory responses. Epithelial barrier dysfunction may be particularly relevant in COPD, where repeated injury by cigarette smoke exposure, pathogens, inflammatory mediators, and impaired epithelial regeneration may compromise the barrier function. In the current review, we discuss recent advances in understanding the mechanisms of barrier dysfunction in COPD, as well as the molecular mechanisms that underlie the impaired repair response of the injured epithelium in COPD and its inability to redifferentiate into a functionally intact epithelium.