No abstract

The data suggest that 10 min after acid aspiration, damaged areas are characterized by increased pulmonary blood flow. The results may impact further treatment strategies, such as drug targeting.

Nitric oxide (NO)-cyclic GMP (cGMP) signaling is a vasoprotective pathway therapeutically targeted, for example, in pulmonary hypertension. Its dysregulation in disease is incompletely understood. Here we show in pulmonary artery endothelial cells that feedback inhibition by NO of the NO receptor, the cGMP forming soluble guanylate cyclase (sGC), may contribute to this. Both endogenous NO from endothelial NO synthase and exogenous NO from NO donor compounds decreased sGC protein and activity. This effect was not mediated by cGMP as the NO-independent sGC stimulator, or direct activation of cGMP-dependent protein kinase did not mimic it. Thiol-sensitive mechanisms were also not involved as the thiol-reducing agent N-acetyl-L-cysteine did not prevent this feedback. Instead, both in-vitro and in-vivo and in health and acute respiratory lung disease, chronically elevated NO led to the inactivation and degradation of sGC while leaving the heme-free isoform, apo-sGC, intact or even increasing its levels. Thus, NO regulates sGC in a bimodal manner, acutely stimulating and chronically inhibiting, as part of self-limiting direct feedback that is cGMP independent. In high NO disease conditions, this is aggravated but can be functionally recovered in a mechanism-based manner by apo-sGC activators that re-establish cGMP formation.

No abstract

(240 words)Endothelial nitric oxide (NO) stimulates the heme protein, soluble guanylyl cyclase (sGC) to form vasoprotective cyclic GMP (cGMP). In different disease states such as pulmonary hypertension, NO-cGMP signaling is pharmacologically augmented, yet the pathomechanisms leading to its dysregulation are incompletely understood. Here we show in pulmonary artery endothelial cells that endogenous NO or NO donor compounds acutely stimulate sGC activity, but chronically down-regulate both sGC protein and cGMP formation. Surprisingly, this endogenous feedback mechanism was independent of canonical cGMP signaling via cGMPdependent protein kinase. It did not involve thiol-dependent modulation, a process relevant for sGC maturation, either. Rather tonic NO exposure led to inactivation and degradation of NOsGC and without affecting NO-insensitive apo-sGC levels. Apo-sGC could be re-activated pharmacologically by the heme mimetic class of so-called sGC activators. Importantly, this noncanonical feedback was also observed in vivo. Specifically, it was induced by pathological high levels of NO in acute respiratory distress syndrome in which a similar self-limiting redox shift from NO-sensitive sGC to NO-insensitive apo-sGC occurred. Thus, our data establish a bimodal mechanism by which NO acutely stimulates sGC and chronically decreases sGC levels as part of a physiological and pathological self-limiting feedback. Of therapeutic importance in disease, our findings i) caution against any chronic use of classical NO donor drugs and ii) suggest that high NO-induced apo-sGC can be functionally fully recovered by sGC activator drugs to reestablish cGMP formation.All rights reserved. No reuse allowed without permission.(which was not peer-reviewed) is the author/funder, who has granted bioRxiv a license to display the preprint in perpetuity.The copyright holder for this preprint . http://dx.doi.org/10.1101/383208 doi: bioRxiv preprint first posted online Aug. 2, 2018; 3 Significance Statement (122 of 120) Dysfunctional nitric oxide (NO) signaling via the cyclic GMP (cGMP) forming heme-protein soluble guanylate cyclase (sGC) is a key cardiopulmonary disease mechanism. However, in particular during chronic use, NO donor drugs display limited therapeutic benefit. Here we identify a previously unrecognized non-canonical chemical feedback mechanism, which selflimits cGMP formation in response to NO donor drugs and endogenous NO, both in health and disease. Whilst NO acutely stimulates sGC, we find that exposure of sGC to either chronic NO or pathological NO overproduction reduces sGC and generates heme-free apo-sGC which is insensitive to NO but sensitive to heme-mimetic sGC activators. Importantly, this chemical feedback explains the limited applicability of NO-donor drugs for chronic treatment and explain their mechanism-based indication in vascular disease conditions.All rights reserved. No reuse allowed without permission.(which was not peer-reviewed) is the author/funder, who has granted bioRxiv a license to displ...