Transforming Growth Factor-β1 Decreases Expression of the Epithelial Sodium Channel αENaC and Alveolar Epithelial Vectorial Sodium and Fluid Transport via an ERK1/2-dependent Mechanism

Abstract

Acute lung injury (ALI) is characterized by the flooding of the alveolar airspaces with protein-rich edema fluid and diffuse alveolar damage. We have previously reported that transforming growth factor-␤1 (TGF-␤1) is a critical mediator of ALI after intratracheal administration of bleomycin or Escherichia coli endotoxin, at least in part due to effects on lung endothelial and alveolar epithelial permeability. In the present study, we hypothesized that TGF-␤1 would also decrease vectorial ion and water transport across the distal lung epithelium. Therefore, we studied the effect of active TGF-␤1 on 22 Na ؉ uptake across monolayers of primary rat and human alveolar type II (ATII) cells. TGF-␤1 significantly reduced the amiloride-sensitive fraction of 22 Na ؉ uptake and fluid transport across monolayers of both rat and human ATII cells. TGF-␤1 also significantly decreased ␣ENaC mRNA and protein expression and inhibited expression of a luciferase reporter downstream of the ␣ENaC promoter in lung epithelial cells. The inhibitory effect of TGF-␤1 on sodium uptake and ␣ENaC expression in ATII cells was mediated by activation of the MAPK, ERK1/2. Consistent with the in vitro results, TGF-␤1 inhibited the amiloride-sensitive fraction of the distal airway epithelial fluid transport in an in vivo rat model at a dose that was not associated with any change in epithelial protein permeability. These data indicate that increased TGF-␤1 activity in the distal airspaces during ALI promotes alveolar edema by reducing distal airway epithelial sodium and fluid clearance. This reduction in sodium and fluid transport is attributable in large part to a reduction in apical membrane ␣ENaC expression mediated through an ERK1/2-dependent inhibition of the ␣ENaC promoter activity. Acute lung injury (ALI)1 is a devastating syndrome characterized by flooding of alveolar spaces with a protein-rich exudate that impairs pulmonary gas exchange, leading to arterial hypoxemia and respiratory failure (1). Epithelial injury can contribute to alveolar flooding, because the epithelial barrier is much less permeable under normal conditions than the endothelial barrier. Injury to alveolar epithelial cells can also disrupt normal epithelial fluid transport, impairing the removal of edema fluid from the alveolar space. Clinical studies have demonstrated that impaired alveolar fluid clearance is a characteristic feature of clinical lung injury (2, 3), but the mechanisms for this decrease in epithelial fluid transport have not been well worked out. The removal of edema fluid from the airspaces occurs via an active transport-dependent sodium concentration gradient across the distal lung epithelium. The ratelimiting step in the transport of fluid across the lung epithelium is the movement of sodium and chloride across the apical plasma membrane, specifically the movement of sodium through amiloride-sensitive and -insensitive channels (4). Among the sodium channels at the apical membrane of lung epithelial cells, amiloride-sensitive channels represent 50 -60% ...

Transforming Growth Factor β1 Inhibits Cystic Fibrosis Transmembrane Conductance Regulator-dependent cAMP-stimulated Alveolar Epithelial Fluid Transport via a Phosphatidylinositol 3-Kinase-dependent Mechanism

“…We have also shown that increased TGF-␤1 activity in the distal airspaces during ALI promotes alveolar edema by reducing distal airspace epi-thelial sodium and fluid clearance. This reduction occurred mainly by a loss of apical membrane ␣-ENaC expression in lung epithelial cells mediated through an ERK1/2-dependent inhibition of the ␣-ENaC promoter activity (22). Although we have shown that TGF-␤1 inhibits basal and corticosteroid-stimulated alveolar fluid transport (22), the potential effect of TGF-␤1 on the ␤-adrenergic-stimulated alveolar fluid transport is still unknown.…”

“…This reduction occurred mainly by a loss of apical membrane ␣-ENaC expression in lung epithelial cells mediated through an ERK1/2-dependent inhibition of the ␣-ENaC promoter activity (22). Although we have shown that TGF-␤1 inhibits basal and corticosteroid-stimulated alveolar fluid transport (22), the potential effect of TGF-␤1 on the ␤-adrenergic-stimulated alveolar fluid transport is still unknown. Recent experimental evidence convincingly demonstrated in mice and humans a role for the cystic fibrosis transmembrane conductance regulator (CFTR) in the ␤ 2 AR agonist-mediated stimulation of the alveolar epithelial fluid transport (23)(24)(25)(26)(27)(28)(29).…”

Initial interrogation, confirmation and fine mapping of modifying genes: STAT3, IL1B and IFNGR1 determine cystic fibrosis disease manifestation

“…Several cytokines have been identified to alter secretory properties of epithelial cells [48][49][50][51] resulting in altered ion and fluid transport upon activation of host defense pathways. This has been interpreted as an unspecific host response to pathogens as the surface liquid is increased on the epithelium upon induction of a hypersecretory state by inflammatory stimuli, 49 and consequently mucociliary clearance of the intruding pathogen will be alleviated.…”

“…This hypothesis is in accordance with the findings that cytokines such as TNFa and IFNg, both of which are known to utilize STAT3 signaling among other signal transduction pathways 46,47 have been reported to directly influence the CFTR expression and function. 48 The gold standard for genetic association studies has always been the replication of findings in different study populations. For IL1B, described recently as a modifier by a North-American consortium, 27 we have compared both studies (author's comment: by chance, the two SNPs rs1143634 (Levy et al) and rs1143643 (this work) differ by the last two digits only -discriminative ciphers have been underlined for your convenience).…”

Allogeneic human mesenchymal stem cells for treatment of E. coli endotoxin-induced acute lung injury in the ex vivo perfused human lung

“…Catecholamine-independent pathways can also up-regulate AFC including growth factors, thyroid hormone, and glucocorticoids (7,10,11). Multiple pathways can reduce alveolar epithelial fluid transport and impair the resolution of alveolar edema, including hypoxia, high tidal volume ventilation, and pro-inflammatory cytokines in the pulmonary edema fluid (7,(12)(13)(14)(15)(16).…”