Cigarette Smoke Impairs Clearance of Apoptotic Cells through Oxidant-dependent Activation of RhoA

Abstract

Rationale: Cigarette smoke (CS) is the primary cause of chronic obstructive pulmonary disease (COPD), an effect that is, in part, due to intense oxidant stress. Clearance of apoptotic cells (efferocytosis) is a critical regulator of lung homeostasis, which is defective in smokers and in patients with COPD, suggesting a role in disease pathogenesis. Objectives: We hypothesized that CS would impair efferocytosis through oxidant-dependent activation of RhoA, a known inhibitor of this process. Methods: We investigated the effect of CS on efferocytosis in vivo and ex vivo, using acute, subacute, and long-term mouse exposure models. Measurements and Main Results: Acute and subacute CS exposure suppressed efferocytosis by alveolar macrophages in a dosedependent, reversible, and cell type-independent manner, whereas more intense CS exposure had an irreversible effect. In contrast, CS did not alter ingestion through the Fcg receptor. The inhibitory effect of CS on apoptotic cell clearance depended on oxidants, because the effect was blunted in oxidant-resistant ICR mice, and was prevented by either genetic or pharmacologic antioxidant strategies in vivo and ex vivo. CS inhibited efferocytosis through oxidant-dependent activation of the RhoA-Rho kinase pathway because (1) CS activated RhoA, (2) antioxidants prevented RhoA activation by CS, and (3) inhibitors of the RhoA-Rho kinase pathway reversed the suppressive effect of CS on apoptotic cell clearance in vivo and ex vivo. Conclusions: These findings advance the hypothesis that impaired efferocytosis may contribute to the pathogenesis of COPD and suggest the therapeutic potential of drugs targeting the RhoA-Rho kinase pathway.

Efferocytosis and Lung Disease

“…Cigarette smoke and other oxidant stresses reduce efferocytosis by activating RhoA (which inhibits Rac), 60 whereas antioxidant therapy has the converse effects. 61 Because the lung environment activates RhoA in AMøs 17 even in the absence of exogenous oxidants, local antioxidant therapy might be another means of increasing efferocytosis to reduce lung infl ammation ( Fig 3 ).…”

Enhancement of COPD biological networks using a web-based collaboration interface

“…The efferocytosis process of phagocytic uptake of apoptotic cells by macrophages is frequently disrupted in COPD tissue, and this disruption is thought to potentiate the chronic state of inflammation in the diseased lung 40– 42 . A new network model detailing components related to efferocytosis was constructed from information available in the published literature with the majority of edges coming from general macrophage experiments.…”

“…Apoptotic cells exhibit surface changes that distinguish them from viable cells, and these changes were recognized by efferocytic receptors including CD36 molecule (CD36), CD14 molecule (CD14), and Stabilin-1/2 (STAB1:STAB2) 39 . Reduced efferocytosis observed in COPD because of oxidant-driven and Rho-mediated inactivation increased the likelihood of aberrant antigen exposure from apoptotic cells, thereby perpetuating the chronic inflammatory state that is a hallmark of COPD 40– 42 . In adding efferocytosis mechanisms to the macrophage network, we focused on the surface receptors and bridge proteins such as CD36 and GAS6.…”

Second hand smoke and COPD: lessons from animal studies

“…The acute smoke exposure model is well-suited to examine cellular oxidative stress and mechanisms leading to increased inflammation (Valenca et al, 2008;Richens et al, 2009;Gould et al, 2010;Geraghty et al, 2011b;Lu et al, 2011). Within 6 h of smoke exposure, evidence of oxidative stress can be detected within the pulmonary vascular endothelium (Lu et al, 2011).…”