Efferocytosis ő autophagy crosstalk in alveolar macrophages exposed to cigarette smoking (151.7)

Abstract

Alveolar macrophages (AM) apoptotic cell clearance function (efferocytosis) is dysregulated in COPD due to cigarette smoke (CS) exposure via production of ceramides and sphingosine (SHP). CS also alters the maturation of the autophagosomes (AP) blocking the autophagic flux. We hypothesized that impairment of both AP maturation and efferocytosis share an identical mechanism of cytoskeletal derangement linked to HDAC6 inactivation and sphingosine accumulation. AM obtained via bronchoalveolar lavage from human smoker and non‐smoker donors or from Sprague Dawley rats exposed to CS (3 months) were subject to engulfment assays quantified by flow cytometry. HDAC6 was evaluated by real‐time PCR or Western blot. Both CS and SPH significantly impaired efferocytosis in rat and human AM (50% and 80% inhibition; p<0.05, respectively). HDAC6 protein activity was markedly impaired by CS exposure. This effect was in part mediated by SPH production, since a ceramidase inhibitor, MAPP, restored both HDAC6 levels and improved autophagic flux. Moreover, HDAC6 inhibition with BML‐281 or siRNA significantly impaired efferocytosis, as well as bafilomycin treatment, an inhibitor of AP maturation (by up to 7‐fold; p<0.05). Whole protein HDAC6 overexpression significantly restored the efferocytosis impairment induced by CS but overexpression of the HDAC6 catalytic mutant did not. These results indicate a novel role of HDAC6 in efferocytosis. The impairment of both autophagic flux and efferocytosis may be mechanistically linked at the level of sphingolipid regulation of cytoskeletal effectors activity such as HDAC6. Improvement in AP maturation may help restore efferocytosis, an essential step in the resolution of pulmonary inflammation.Grant Funding Source: ALA RG‐1966666‐N and NIH‐HL077328