Role of Asymmetric Methylarginine and Connexin 43 in the Regulation of Pulmonary Endothelial Function

Abstract

Circulating levels of asymmetric dimethylarginine (ADMA), a nitric oxide synthase inhibitor, are increased in patients with idiopathic pulmonary hypertension (IPAH). We hypothesized that ADMA abrogates gap junctional communication, required for the coordinated regulation of endothelial barrier function and angiogenesis, and so contributes to pulmonary endothelial dysfunction. The effects of ADMA on expression and function of gap junctional proteins were studied in human pulmonary artery endothelial cells; pulmonary endothelial microvascular cells from mice deficient in an enzyme metabolizing ADMA, dimethylarginine dimethylaminohydrolase I (DDAHI); and blood-derived endothelial-like cells from patients with IPAH. Exogenous and endogenous ADMA inhibited protein expression and membrane localization of connexin 43 (Cx43) in a nitric oxide/ soluble guanosine monophosphate/c-jun-dependent manner in pulmonary endothelial cells, resulting in the inhibition of gap junctional communication, increased permeability, and decreased angiogenesis. The effects of ADMA were prevented by overexpression of DDAHI or Cx43 and by treatment with rotigaptide. Blood-derived endothelial-like cells from IPAH patients displayed a distinct disease-related phenotype compared to cells from healthy controls, characterized by reduced DDAHI expression, increased ADMA production, and abnormal angiogenesis. In summary, we show that ADMA induces pulmonary endothelial dysfunction via changes in expression and activity of Cx43. Cells from IPAH patients exhibit abnormal DDAHI/Cx43 signaling as well as differences in gap junctional communication, barrier function, and angiogenesis. Strategies that promote DDAHI/Cx43 signaling may have an endothelium-protective effect and be beneficial in pulmonary vascular disease.

Connexin-mediated regulation of the pulmonary vasculature

“…Blood outgrowth endothelial cells from patients with PAH show abnormal gap junctional communication, whereas the nitric oxide synthase inhibitor asymmetric dimethyl arginine (ADMA), which is up-regulated in PAH patients, inhibits gap junctional communication in human PAECs. The effects of ADMA were prevented by overexpression of Cx43 or by treatment with rotigaptide, which enhances gap junction coupling [31]. In line with this, a recent study shows Cx37 and Cx40 expression is down-regulated in PAECs from PAH patients [32].…”

Asymmetric Dimethylarginine: Clinical Significance and Novel Therapeutic Approaches

“…In addition to vasoconstriction of pulmonary vessels, ADMA has also been reported to act via other mechanisms on the pulmonary endothelium. Particularly, ADMA inhibited protein expression and membrane localization of connexin 43, a gap junctional protein in the endothelium, increasing permeability, and decreasing angiogenesis [175]. Lastly, in pulmonary endothelium ADMA may act as a proproliferative molecule, since it has been reported to enhance urea production resulting in more viable cells [176].…”

The Role of Gap Junction in Regulating Vascular Function and Its Relationship with Hypertension

“…The regulation of gap junction function is significant for cell communication. Cytoplasmic pH, Ca 2+ , voltage, oncogenes, nucleotides, hormones, neurotransmitters, lipids, growth factors, and many exogenous chemicals can regulate function of gap junction by different levels including transcription, translation and post-translation modification, which is achieved by a variety of mechanisms [11][12][13][14].…”