Asthma is defined by airway inflammation and hyperresponsiveness, and contributes to morbidity and mortality worldwide. Although bronchodilation is a cornerstone of treatment, current bronchodilators become ineffective with worsening asthma severity. We investigated an alternative pathway that involves activating the airway smooth muscle enzyme, soluble guanylate cyclase (sGC). Activating sGC by its natural stimulant nitric oxide (NO), or by pharmacologic sGC agonists BAY 41-2272 and BAY 60-2770, triggered bronchodilation in normal human lung slices and in mouse airways. Both BAY 41-2272 and BAY 60-2770 reversed airway hyperresponsiveness in mice with allergic asthma and restored normal lung function. The sGC from mouse asthmatic lungs displayed three hallmarks of oxidative damage that render it NO-insensitive, and identical changes to sGC occurred in human lung slices or in human airway smooth muscle cells when given chronic NO exposure to mimic the high NO in asthmatic lung. Our findings show how allergic inflammation in asthma may impede NO-based bronchodilation, and reveal that pharmacologic sGC agonists can achieve bronchodilation despite this loss.A sthma is an inflammatory disease that causes airway hyperreactivity (AHR) and bronchoconstriction, which impedes daily life activities and, when severe, can cause death. It is the most common chronic disease of childhood, accounts for one in three emergency department visits daily, and asthma diagnoses are increasing worldwide (1). The leading treatment for relief and acute care is bronchodilation, which relies heavily on the β-adrenergic receptor-cAMP pathway. Nearly 70% of patients, however, develop resistance or tachyphylaxis to the existing β-agonist therapy (2), underscoring a need for new bronchodilators that can act through a different pharmacologic principle.The nitric oxide-soluble guanylate cyclase-cGMP pathway (NO-sGC-cGMP) is the primary signal transduction pathway for relaxing vascular smooth muscle (3). In contrast, a role for the NO-sGC-cGMP pathway in relaxing airway smooth muscle is less clear (4, 5), and bronchodilation was instead suggested to depend on glutathione nitrosothiol levels in the lung (6, 7). However, recent studies have shown that inflammation can desensitize sGC toward its natural activator, NO (8), and new drugs have become available that directly activate sGC, independent of NO (9). These developments encouraged us to re-examine the NO-sGC-cGMP pathway regarding its role in bronchodilation, its becoming damaged in inflammatory asthma, and its potential for alternative bronchodilator development under this circumstance. ResultsThe NO-sGC-cGMP Pathway Bronchodilates Human Lung. We first tested if stimulating the NO-sGC-cGMP pathway would dilate preconstricted small airways in human precision-cut lung slices (PCLS) obtained from healthy donor lungs (Fig. 1A and Table S1). Graded doses of the slow-release NO donor DETA/NO [3,3-Bis(aminoethyl)-1-hydroxy-2-oxo-1-triazene] produced bronchodilation in human PCLS similar to what was ...
Heme insertion is key during maturation of soluble guanylyl cyclase (sGC) because it enables sGC to recognize NO and transduce its multiple biological effects. Although sGC is often associated with the 90-kDa heat shock protein (hsp90) in cells, the implications are unclear. The present study reveals that hsp90 is required to drive heme insertion into sGC and complete its maturation. We used a mammalian cell culture approach and followed heme insertion into transiently and endogenously expressed heme-free sGC. We used pharmacological hsp90 inhibitors, an ATP-ase inactive hsp90 mutant, and heme-dependent or heme-independent sGC activators as tools to decipher the role of hsp90. Our findings suggest that hsp90 complexes with apo-sGC, drives heme insertion through its inherent ATPase activity, and then dissociates from the mature, heme-replete sGC. Together, this improves our understanding of sGC maturation and reveals a unique means to control sGC activity in cells, and it has important implications for hsp90 inhibitor-based cancer therapy.
Background: Heme insertion into souble guanylate cyclase (sGC) enables it to bind nitric oxide (NO) for cell signaling. Results: NO triggered a rapid, reversible, and hsp90-dependent heme insertion into sGC-1 and an association with sGC-␣1 subunit. sGC activator BAY 60-2770 did the same. Conclusion: NO dynamically impacts the maturation and stability of active sGC heterodimer. Significance: The data uncover new mechanisms that regulate cellular NO signaling cascades.
Soluble guanylyl cyclase (sGC) is a key component of NO–cGMP signaling in mammals. Although heme must bind in the sGC β1 subunit (sGCβ) for sGC to function, how heme is delivered to sGCβ remains unknown. Given that GAPDH displays properties of a heme chaperone for inducible NO synthase, here we investigated whether heme delivery to apo-sGCβ involves GAPDH. We utilized an sGCβ reporter construct, tetra-Cys sGCβ, whose heme insertion can be followed by fluorescence quenching in live cells, assessed how lowering cell GAPDH expression impacts heme delivery, and examined whether expressing WT GAPDH or a GAPDH variant defective in heme binding recovers heme delivery. We also studied interaction between GAPDH and sGCβ in cells and their complex formation and potential heme transfer using purified proteins. We found that heme delivery to apo-sGCβ correlates with cellular GAPDH expression levels and depends on the ability of GAPDH to bind intracellular heme, that apo-sGCβ associates with GAPDH in cells and dissociates when heme binds sGCβ, and that the purified GAPDH–heme complex binds to apo-sGCβ and transfers its heme to sGCβ. On the basis of these results, we propose a model where GAPDH obtains mitochondrial heme and then forms a complex with apo-sGCβ to accomplish heme delivery to sGCβ. Our findings illuminate a critical step in sGC maturation and uncover an additional mechanism that regulates its activity in health and disease.
Maturation of NOS enzymes requires that they incorporate heme to become active, but how this cellular process occurs is unclear. We investigated a role for chaperone heat shock protein 90 (hsp90) in enabling heme insertion into the cytokine-inducible mouse NOS. We used macrophage cell line RAW 264.7 and human embryonic kidney HEK293T cells and studied insertion of native heme during iNOS expression and insertion of exogenous heme into preformed apo-iNOS. Pulldown experiments showed that the hsp90-iNOS complex was present in cells, but the extent of their association was inversely related to iNOS heme content. Hsp90 was primarily associated with apo-iNOS monomer and was associated 11-fold less with heme-containing iNOS monomer or dimer in cells. Kinetic studies showed that hsp90 dissociation occurred coincident with cellular heme insertion into apo-iNOS (0.8 h(-1)). The hsp90 inhibitor radicicol or coexpression of an ATPase-defective hsp90 blocked heme insertion into apo-iNOS by 90 and 75%, respectively. The ATPase activity of hsp90 was not required for complex formation with iNOS but was essential for heme insertion to occur. We conclude that hsp90 plays a primary role in maturation of iNOS protein by interacting with the apoenzyme in cells and then driving heme insertion in an ATP-dependent manner.
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