EO, Rounds S. Cigarette smoke causes lung vascular barrier dysfunction via oxidative stress-mediated inhibition of RhoA and focal adhesion kinase.

Epidemiologic evidence indicates that cigarette smoke (CS) is associated with the development of acute lung injury (ALI). We have previously shown that brief CS exposure exacerbates lipopolysaccharide (LPS)-induced ALI in vivo and endothelial barrier dysfunction in vitro. In this study, we found that CS also exacerbated Pseudomonas-induced ALI in mice. We demonstrated that lung microvascular endothelial cells (ECs) isolated from mice exposed to CS had a greater permeability or incomplete recovery after challenges by LPS and thrombin. Histone deacetylase (HDAC) 6 deacetylates proteins essential for maintenance of endothelial barrier function. We found that HDAC6 phosphorylation at serine-22 was increased in lung tissues of mice exposed to CS and in lung ECs exposed to cigarette smoke extract (CSE). Inhibition of HDAC6 attenuated CSE-induced increases in EC permeability and CS priming of ALI. Similar barrier protection was provided by the microtubule stabilizer taxol, which preserved α-tubulin acetylation. CSE decreased α-tubulin acetylation and caused microtubule depolymerization. In coordination with increased HDAC6 phosphorylation, CSE inhibited Akt and activated glycogen synthase kinase (GSK)-3β; these effects were ameliorated by the antioxidant N-acetyl cysteine. Our results suggest that CS increases lung EC permeability, thereby enhancing susceptibility to ALI, likely through oxidative stress-induced Akt inactivation and subsequent GSK-3β activation. Activated GSK-3β may activate HDAC6 via phosphorylation of serine-22, leading to α-tubulin deacetylation and microtubule disassembly. Inhibition of HDAC6 may be a novel therapeutic option for ALI in cigarette smokers.

Extracellular ATP, adenosine (Ado), and adenosine plus homocysteine (Ado/HC) cause apoptosis of cultured pulmonary artery endothelial cells through the enhanced formation of intracellular S-adenosylhomocysteine and disruption of focal adhesion complexes. Because an increased intracellular ratio of S-adenosylhomocysteine/S-adenosylmethionine favors inhibition of methylation, we hypothesized that Ado/HC might act by inhibition of isoprenylcysteine-O-carboxyl methyltransferase (ICMT). We found that N-acetyl-S-geranylgeranyl-l-cysteine (AGGC) and Nacetyl-S-farnesyl-l-cysteine (AFC), which inhibit ICMT by competing with endogenous substrates for methylation, caused apoptosis. Transient overexpression of ICMT inhibited apoptosis caused by Ado/HC, UV light exposure, or tumor necrosis factor-␣. Because the small GTPase, Ras, is a substrate for ICMT and may modulate apoptosis, we also hypothesized that inhibition of ICMT with Ado/HC or AGGC might cause endothelial apoptosis by altering Ras activation. We found that ICMT inhibition decreased Ras methylation and activity and the activation of the downstream signaling molecules Akt, ERK-1, and ERK-2. Furthermore, overexpression of wild-type or dominant active H-Ras blocked Ado/HC-induced apoptosis. These findings suggest that inhibition of ICMT causes endothelial cell apoptosis by attenuation of Ras GTPase methylation and activation and its downstream antiapoptotic signaling pathway. INTRODUCTIONVascular injury has been implicated in the pathogenesis of disorders such as sepsis and acute respiratory distress syndrome (ARDS). Endothelial cell apoptosis, or programmed cell death, may be important in vascular injury and repair. Apoptotic cells have been identified in increased quantities in the lungs of patients with ARDS, indicating that apoptosis occurs in this syndrome (Polunovsky et al., 1993). Apoptosis can be triggered by disruption of cell-extracellular matrix communication (anoikis) (Frisch and Francis, 1994) or by extracellular factors, such as lipopolysaccharide (Han and Wyche, 1994;Hoyt et al., 1995;Mebmer et al., 1999), tumor necrosis factor (TNF)-␣ (Polunovsky et al., 1994), or UV light (Chatterjee and Wu, 2001). We have previously demonstrated that increased extracellular ATP causes endothelial cell apoptosis after conversion to adenosine and uptake into cells. Moreover, apoptosis caused by intracellular adenosine was enhanced by homocysteine (Dawicki et al., 1997). In subsequent work, we found that increased concentrations of adenosine and homocysteine or inhibition of Sadenosylhomocysteine hydrolase resulted in enhanced levels of S-adenosylhomocysteine (SAH) (Rounds et al., 1998). Because enhanced intracellular concentrations of SAH may result in product inhibition of S-adenosylmethionine (SAM)-dependent methyltransferases (Perna et al., 1997) (Figure 1), we postulated that methyltransferase activity is important in the modulation of endothelial cell apoptosis.Among the methyltransferases is isoprenylcysteine-O-carboxyl methyltransferase (ICMT), the substrates ...

No abstract