Defining the signaling mechanisms through which dopamine stimulates Akt activation in primary human macrophages

Dayna Robinson

doi:10.17918/00001821

Macrophages are innate immune cells that regulate a variety of essential processes in the immune response. We and others have connected several of the pathways underlying these processes to dopamine receptor activation, demonstrating that dopamine drives inflammation in primary human monocyte derived macrophages (hMDMs). Prior data from our lab have shown that exposure of hMDM to elevated dopamine levels increases the activation of the transcription factor NF-[kappa]B and the production of inflammatory cytokines such as IL-6 and IL-1[beta]. The signaling mechanisms underlying these effects are not clear, although our data have previously shown that dopamine does activate canonical cAMP signaling in human macrophages. To examine whether these effects are mediated by dopamine driven Akt signaling, we treated hMDMs with either dopamine or dopamine receptor agonists or antagonists and evaluated changes in Akt phosphorylation by Western blot. Akt activation requires phosphorylation at both serine 473 and threonine 308, and our data show that dopamine significantly increases phosphorylation at both sites. Phosphorylation was also induced by the D1-like receptor agonists SKF 38389 and A68930, but not the D2-like receptor agonist Quinpirole. To further define the pathway by which dopamine receptors act on Akt, we used the phosphoinositide kinase 3 (PI3K) inhibitor, Buparlisib (BKM 120) and the protein phosphatase 2A (PP2A) inhibitor, okadaic acid (OA). BKM 120 eliminated the capacity of dopamine to phosphorylate Akt, but dopamine had no effect on OA mediated changes in Akt phosphorylation. This suggests that dopamine may act on Akt via activation of D1-like dopamine receptors that stimulate PI3K signaling. However, additional treatments with dopamine or A68930 in the presence of the pan-dopamine antagonist Flupenthixol show that dopamine can also increase Akt phosphorylation when dopamine receptors are blocked. This suggests that dopamine could act on Akt through both dopamine receptor dependent and independent pathways, such as adrenergic receptor activation. Future studies using receptor agonists and antagonists for dopamine and adrenergic receptors will further define and verify these processes. These data add clarity to the mechanisms by which dopamine drives macrophage immune function, potentially enabling the manipulation of dopamine-driven inflammatory activity.

Defining the signaling mechanisms through which dopamine stimulates Akt activation in primary human macrophages

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Defining the signaling mechanisms through which dopamine stimulates Akt activation in primary human macrophages

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