Zhi-Hua Chen

Background: Chronic obstructive pulmonary disease (COPD) is a progressive lung disease characterized by abnormal cellular responses to cigarette smoke, resulting in tissue destruction and airflow limitation. Autophagy is a degradative process involving lysosomal turnover of cellular components, though its role in human diseases remains unclear.

Chronic obstructive pulmonary disease (COPD) is a debilitating disease caused by chronic exposure to cigarette smoke (CS), which involves airway obstruction and alveolar loss (i.e., emphysema). The mechanisms of COPD pathogenesis remain unclear. Our previous studies demonstrated elevated autophagy in human COPD lung, and as a cellular and tissue response to CS exposure in an experimental model of emphysema in vivo. We identified the autophagic protein microtubule-associated protein 1 light chain-3B (LC3B) as a positive regulator of CS-induced lung epithelial cell death. We now extend these initial observations to explore the mechanism by which LC3B mediates CS-induced apoptosis and emphysema development in vivo. Here, we observed that LC3B(-/-) mice had significantly decreased levels of apoptosis in the lungs after CS exposure, and displayed resistance to CS-induced airspace enlargement, relative to WT littermate mice. We found that LC3B associated with the extrinsic apoptotic factor Fas in lipid rafts in an interaction mediated by caveolin-1 (Cav-1). The siRNA-dependent knockdown of Cav-1 sensitized epithelial cells to CS-induced apoptosis, as evidenced by enhanced death-inducing signaling complex formation and caspase activation. Furthermore, Cav-1(-/-) mice exhibited higher levels of autophagy and apoptosis in the lung in response to chronic CS exposure in vivo. In conclusion, we demonstrate a pivotal role for the autophagic protein LC3B in CS-induced apoptosis and emphysema, suggestive of novel therapeutic targets for COPD treatment. This study also introduces a mechanism by which LC3B, through interactions with Cav-1 and Fas, can regulate apoptosis.

Environmental ultrafine particulate matter (PM) is capable of inducing airway injury, while the detailed molecular mechanisms remain largely unclear. Here, we demonstrate pivotal roles of autophagy in regulation of inflammation and mucus hyperproduction induced by PM containing environmentally persistent free radicals in human bronchial epithelial (HBE) cells and in mouse airways. PM was endocytosed by HBE cells and simultaneously triggered autophagosomes, which then engulfed the invading particles to form amphisomes and subsequent autolysosomes. Genetic blockage of autophagy markedly reduced PM-induced expression of inflammatory cytokines, e.g. IL8 and IL6, and MUC5AC in HBE cells. Mice with impaired autophagy due to knockdown of autophagy-related gene Becn1 or Lc3b displayed significantly reduced airway inflammation and mucus hyperproduction in response to PM exposure in vivo. Interference of the autophagic flux by lysosomal inhibition resulted in accumulated autophagosomes/amphisomes, and intriguingly, this process significantly aggravated the IL8 production through NFKB1, and markedly attenuated MUC5AC expression via activator protein 1. These data indicate that autophagy is required for PM-induced airway epithelial injury, and that inhibition of autophagy exerts therapeutic benefits for PM-induced airway inflammation and mucus hyperproduction, although they are differentially orchestrated by the autophagic flux.

It is currently not understood whether cigarette smoke exposure facilitates sensitisation to self-antigens and whether ensuing auto-reactive T cells drive chronic obstructive pulmonary disease (COPD)-associated pathologies. To address this question, mice were exposed to cigarette smoke for 2 weeks. Following a 2-week period of rest, mice were challenged intratracheally with elastin for 3 days or 1 month. Rag1 −/− , Mmp12 −/− , and Il17a −/− mice and neutralising antibodies against active elastin fragments were used for mechanistic investigations. Human GVAPGVGVAPGV/HLA-A*02:01 tetramer was synthesised to assess the presence of elastin-specific T cells in patients with COPD. We observed that 2 weeks of cigarette smoke exposure induced an elastin-specific T cell response that led to neutrophilic airway inflammation and mucus hyperproduction following elastin recall challenge. Repeated elastin challenge for 1 month resulted in airway remodelling, lung function decline and airspace enlargement. Elastin-specific T cell recall responses were dose dependent and memory lasted for over 6 months. Adoptive T cell transfer and studies in T cells deficient Rag1 −/− mice conclusively implicated T cells in these processes. Mechanistically, cigarette smoke exposure-induced elastin-specific T cell responses were matrix metalloproteinase (MMP)12-dependent, while the ensuing immune inflammatory processes were interleukin 17A-driven. Anti-elastin antibodies and T cells specific for elastin peptides were increased in patients with COPD. These data demonstrate that MMP12-generated elastin fragments serve as a self-antigen and drive the cigarette smoke-induced autoimmune processes in mice that result in a bronchitis-like phenotype and airspace enlargement. The study provides proof of concept of cigarette smoke-induced autoimmune processes and may serve as a novel mouse model of COPD.