Differential expression of nitric oxide synthases in porcine aortic endothelial cells during LPS-induced apoptosis

Background: It is well known that nitric oxide (NO) is generated by a family of constitutively (nNOS and eNOS) or inducibly (iNOS) expressed enzymes and takes part in different aspects of the inflammatory response; nevertheless, its effective role in the pathogenesis of multiple organ dysfunction and septic shock is not fully understood. Methods: To investigate the Nitric Oxide Synthases (NOSs) expression in endothelial cells during endotoxin exposure and the involvement of NO in lipopolysaccharide (LPS)-induced apoptosis, primary cultures of porcine Aortic Endothelial Cells (pAECs) were exposed to LPS for different time periods (1-24 h) and to LPS + L-NAME (15 h). Results: Lipopolysaccharide induced an increase in mRNA and protein iNOS expression; on the contrary, the expression of eNOS was decreased. Furthermore, NOSs localisation was in part modified by LPS treatment. No alteration in the total level of Nitric Oxide was observed. L-NAME (5 mM) addition determined a slight decrease of LPS-induced apoptosis. Conclusions: Endotoxin treatment strongly influenced NOS expression with an upregulation of iNOS and a simultaneous down regulation of eNOS. Moreover, in our model, the involvement of NO on LPS-induced apoptosis is very modest, suggesting that different pathways are involved in the regulation of this process.