Endothelial Cells Are Able to Synthesize and Release Catecholamines Both In Vitro and In Vivo

Abstract

Abstract-Recently it has been demonstrated that catecholamines are produced and used by macrophages and mediate immune response. The aim of this study is to verify whether endothelial cells (ECs), which are of myeloid origin, can produce catecholamines. We demonstrated that genes coding for tyrosine hydroxylase, Dopa decarboxylase, dopamine ␤ hydroxylase (D␤H), and phenylethanolamine-N-methyl transferase, enzymes involved in the synthesis of catecholamines, are all expressed in basal conditions in bovine aorta ECs, and their expression is enhanced in response to hypoxia. Moreover, hypoxia enhances catecholamine release. To evaluate the signal transduction pathway that regulates catecholamine synthesis in ECs, we overexpressed in bovine aorta ECs either protein kinase A (PKA) or the transcription factor cAMP response element binding, because PKA/cAMP response element binding activation induces tyrosine hydroxylase transcription and activity in response to stress. Both cAMP response element binding and PKA overexpression enhance D␤H and phenylethanolamine-N-methyl transferase gene expression and catecholamine release, whereas H89, inhibitor of PKA, exerts the opposite effect, evidencing the role of PKA/cAMP response element binding transduction pathway in the regulation of catecholamine release in bovine aorta ECs. We then evaluated by immunohistochemistry the expression of tyrosine hydroxylase, Dopa decarboxylase, D␤H, and phenylethanolamine-N-methyl transferase in femoral arteries from hindlimbs of C57Bl/6 mice 3 days after removal of the common femoral artery to induce chronic ischemia. Ischemia evokes tyrosine hydroxylase, Dopa decarboxylase, D␤H, and phenylethanolamine-N-methyl transferase expression in the endothelium. Finally, the pharmacological inhibition of catecholamine release by fusaric acid, an inhibitor of D␤H, reduces the ability of ECs to form network-like structures on Matrigel matrix. In conclusion, our study demonstrates for the first time that ECs are able to synthesize and release catecholamines in response to ischemia. Key Words: catecholamines Ⅲ ischemia Ⅲ endothelium Ⅲ angiogenesis E ndothelial cells (ECs) cover the interior surface of blood vessels throughout the entire circulatory system, and they are involved in many aspects of vascular biology.1-4 Indeed, angiogenesis is a phenomenon intimately associated with EC migration and proliferation during embryonic development. 5Similarly, ECs play major roles in immune and inflammatory reactions by regulating lymphocyte and leukocyte migration into tissues by means of direct interaction with ECs.6 Moreover, ECs have an important role in the regulation of the vascular tone by releasing vasoactive agents controlling smooth muscle cell proliferation and contractility.Indeed, ECs are known to release both vasodilators (NO) and vasoconstrictors (thromboxane, platelet-derived growth factor, and endothelin 1) in response to local and circulating stimuli. [7][8][9][10][11][12][13][14] To this purpose, the endothelium is regulated in a fine way by a s...

Ischemic Emergency?

“…In addition, CAs are known to be elevated in response to vascular injury and to contribute to arteriogenesis and neoangiogenesis in response to hindlimb ischemia, possibly via increased vascular endothelial growth factor production induced by activation of the EC membrane-residing ␤ 2 ARs (as the same authors had shown previously 8 and again in this study 7 ). Thus, it appears that this capability of ECs to produce and release their own CAs serves primarily as a homeostatic, self-protective mech-anism to defend the cell against vascular injury/stress and ischemia (Figure).…”

“…Macrophages, for instance, not only respond to CAs but can also produce them, essentially operating an autocrine feedback loop in which CAs produced and released by the macrophage activate ARs on the surface of the very same macrophage to regulate production of the key proinflammatory cytokine interleukin 1␤. 6 Now, ECs have been added to this expanding list: in a very interesting and elegant study reported in this issue of Hypertension, Sorriento et al 7 found that such an autocrine feedback system of CAs is present also in ECs regulating their function ( Figure). Working with bovine aorta-derived ECs in culture, the authors found surprisingly that ECs express naturally all the enzymes of the entire CA biosynthetic pathway, from tyrosine hydroxylase all the way down to phenylethanolamine N-methyl transferase, are capable of synthesizing all 3 natural CAs and of releasing (at least) NE and Epi into their extracellular environment, and, finally, are also capable of metabolizing NE and Epi because they also express catechol-O-methyl-transferase and monoamine oxidase.…”

“…Working with bovine aorta-derived ECs in culture, the authors found surprisingly that ECs express naturally all the enzymes of the entire CA biosynthetic pathway, from tyrosine hydroxylase all the way down to phenylethanolamine N-methyl transferase, are capable of synthesizing all 3 natural CAs and of releasing (at least) NE and Epi into their extracellular environment, and, finally, are also capable of metabolizing NE and Epi because they also express catechol-O-methyl-transferase and monoamine oxidase. In addition, it appears that this autocrine feedback catecholaminergic loop of the ECs is a positive feedback one, that is, it leads to further enhancement of CA synthesis and secretion, because ␤ 2 ARs present in EC membranes can also stimulate CA synthesis via coupling to the classic G s protein-adenylyl cyclase-cAMP-protein kinase A-cAMP-responsive element binding protein signaling pathway 7 ( Figure). Therefore, the CAs released by the EC can activate these ␤ 2 ARs on its surface and further stimulate their own production ( Figure).…”

Adrenal Signaling in Heart Failure

“…5 Of course, this model represents a streamlined point of view of the whole story because adrenal gland is not the exclusive site of production of catecholamines. 6 Likewise, the same group had previously 2 shown that turning down via a gene therapy approach the adrenal levels of GRK2, a master regulator of cardiac βAR desensitization alongside with β-arrestins, 3 cardiac function after myocardial infarction was substantially improved. Ergo, modulation of βAR signaling via β-arrestin-1 and GRK2 inhibition from both the heart and the adrenal (Figure) seems to lead to a reduced neurohumoral burden, halting the myocardial adverse remodeling and increasing the inotropic reserves.…”

“…Supporting a potential role for β-arrestin-1 in the regulation of these activities, β 2 AR has been shown recently to partake in all the above-mentioned processes. 6,8,9 Equally important, growing evidence indicates that loss or dysfunction of β-arrestin-2 results in profound disturbance of insulin …”