High expression of the cGMP‐specific phosphodiesterase, PDE9A, in sickle cell disease (SCD) and the effects of its inhibition in erythroid cells and SCD neutrophils

Abstract

Summary Modulation of intracellular cyclic guanosine monophosphate (cGMP) may characterize a therapeutic target for sickle cell disease (SCD); cGMP‐dependent signalling may be important for erythroid foetal haemoglobin induction and exert anti‐inflammatory functions in leucocytes. As the inhibition of phosphodiesterases (PDEs), which regulate intracellular cGMP, can result in tissue‐specific elevation of cGMP, we studied the gene expressions of cGMP‐specific PDEs (−1A, −5A and −9A) in the reticulocytes and neutrophils of healthy controls, steady‐state SCD patients and SCD patients on hydroxycarbamide therapy (SCDHC). PDE9A gene expression was found in numerous cell types; however, high expression was found in neutrophils, reticulocytes, CD34+‐derived erythroid cells and K562 erythroleukaemic cells, indicating a high haematopoietic cell expression. PDE9A gene expression was, however, significantly higher in the reticulocytes and neutrophils of SCD individuals, compared to control cells; Western blotting confirmed the production of PDE9A protein in SCD neutrophils and K562 cells. Inhibition of PDE9A enzyme with the specific inhibitor, BAY73‐6691, significantly increased production of the γ‐globin gene (HBG) in K562 cells and reversed the increased adhesive properties of SCD neutrophils. Since elevation of haematopoietic intracellular cGMP may be beneficial in SCD, the relatively limited tissue distribution of PDE9A suggests that it could represent a novel drug target worthy of further study.

Hydroxyurea and a cGMP-amplifying agent have immediate benefits on acute vaso-occlusive events in sickle cell disease mice

“…Accordingly, circulating cGMP levels were found to be significantly elevated in the circulation of SCD mice after the administration of the 2 drugs. The PDE9 enzyme constitutes an attractive therapeutic target, because of its relatively restricted tissue distribution profile, being highly expressed in the brain 41 and hematopoietic cells, 28 and with very low-level basal expression in other tissues. 28 BAY73-6691, a potent inhibitor of PDE9, 42 has demonstrated significant effects in vitro, inducing erythroid cell HBG gene production and decreasing leukocyte adhesive properties and adhesion molecule expression.…”

“…The PDE9 enzyme constitutes an attractive therapeutic target, because of its relatively restricted tissue distribution profile, being highly expressed in the brain 41 and hematopoietic cells, 28 and with very low-level basal expression in other tissues. 28 BAY73-6691, a potent inhibitor of PDE9, 42 has demonstrated significant effects in vitro, inducing erythroid cell HBG gene production and decreasing leukocyte adhesive properties and adhesion molecule expression. 28,29 In our SCD mouse model, BAY73-6691 amplified the cGMPdependent effects of HU in the absence of any apparent vasodilatory effect (possibly because of the limited tissue expression of PDE9).…”

“…28 BAY73-6691, a potent inhibitor of PDE9, 42 has demonstrated significant effects in vitro, inducing erythroid cell HBG gene production and decreasing leukocyte adhesive properties and adhesion molecule expression. 28,29 In our SCD mouse model, BAY73-6691 amplified the cGMPdependent effects of HU in the absence of any apparent vasodilatory effect (possibly because of the limited tissue expression of PDE9). TNF-␣-stimulated SCD mice that received HU and BAY73-6691 presented a diminished expression of endothelial surface adhesion molecules in venules that may have contributed to reduced leukocyte recruitment to the vessel wall.…”

“…27 Recent data demonstrate that the cGMPdegrading enzyme, phosphodiesterase 9 (PDE9), is highly expressed in hematopoietic cells, possibly providing a more tissuespecific drug target (see scheme, Figure 1). 28 The specific PDE9 inhibitor, BAY73-6691, has been reported to increase HBG ␥-globin expression in K562 erythroleukemic cells, and also to reduce SCD neutrophil adhesive properties in vitro. 28,29 The aim of this study was to investigate the effects of the acute administration of HU alone, and in combination with the PDE9-inhibiting agent, BAY73-6691, in an in vivo model of inflammationinduced vaso-occlusion in SCD mice, and to further determine whether these effects are mediated through a cGMP-dependent pathway.…”

Nitric Oxide / Cyclic Nucleotide Regulation of Globin Genes in Erythropoiesis

“…In addition, PDE9A gene expression is increased in CD34 + -derived erythroid cells and K562 erythroleukemic cells. Inhibition of PDE9A enzyme significantly increased production of the Ǒ-globin gene in K562 cells (Almeida et al, 2008).…”