Frontline Science: D1 dopaminergic receptor signaling activates the AMPK-bioenergetic pathway in macrophages and alveolar epithelial cells and reduces endotoxin-induced ALI

Abstract

Catecholamines, including β-adrenergic and dopaminergic neurotransmitters, have an essential role in regulating the "fight or flight" reflex and also affects immune cell proinflammatory action. However, little is known about whether catecholamines prevent dysfunction of metabolic pathways associated with inflammatory organ injury, including development of acute lung injury (ALI). We hypothesize that selected catecholamines may reduce metabolic alterations in LPS-stimulated macrophages and in the lungs of mice subjected to endotoxin-induced ALI, a situation characterized by diminished activity of AMP-activated protein kinase (AMPK). We found that activation of the dopamine 1 receptor (D1R) with fenoldopam, but not stimulation of adrenergic receptors with norepinephrine, resulted in a robust activation of AMPK in peritoneal macrophages, human monocytes, or alveolar epithelial cells (AECs). Such AMPK activation was mediated by a phospholipase C (PLC)-dependent mechanism. Unlike norepinephrine, D1R activation also prevented Thr172-AMPK dephosphorylation and kinase inactivation in LPS-treated macrophages. Furthermore, we show that a culture of AECs with either fenoldopam or the AMPK activator metformin effectively diminished IL-1β-induced release of adverse paracrine signaling, which promotes the macrophage proinflammatory response. In vivo, fenoldopam reduced the severity of LPS-induced ALI, including development of pulmonary edema, lung permeability, and production of inflammatory cytokines TNF-α, MIP-2, or KC and HMGB1. Fenoldopam also prevented AMPK dephosphorylation in the lungs of LPS-treated mice and prevented loss of mitochondrial complexes NDUFB8 (complex I) and ATP synthase (complex V). Collectively, these results suggest that dopamine is coupled to AMPK activation, which provides a substantial anti-inflammatory and bioenergetic advantage and reduces the severity of endotoxin-induced ALI.

Mitochondrial Dysfunction and Immune Cell Metabolism in Sepsis

“…In activated macrophages, OxPhos is inactivated following the inducible form of nitric oxide synthase (iNOS) dependent NO production; NO competes with oxygen to inhibit the terminal electron acceptor (complex IV) of mitochondrial electron transport chain [8586]. Our recent studies indicate that preservation of major components of mitochondrial complexes is possible in a polymicrobial intra-abdominal model of sepsis [5087]. For example, metformin is major metabolic AMPK activator that promoted mitochondrial biogenesis and thus, decreased the severity of endotoxin induced acute lung injury [50].…”

Editorial: Therapeutics for acute lung injury: time to call in the DRs?

“…The study published by Bone et al [3] in this issue of the Journal of Leukocyte Biology adds to the growing body of evidence obtained from animal models for the targeting of DRs for the treatment of ALI. This study investigated the effects of the D1R agonist, fenoldopam, on peritoneal macrophages and alveolar epithelial cells derived from a murine model of LPS-induced lung injury.…”

“…This enzyme is a heterotrimer activated by AMP binding and phosphorylation of the Thr172 residue of the a-subunit. Bone et al [3] demonstrate that AMPK phosphorylation by fenoldopam was mediated by the PLC pathway in peritoneal macrophages using both a specific activator (m-3M3) and inhibitor (U73122) of this pathway. As the PLC pathway classically results in PKC activation, these results suggest a possible role for PKC in maintaining AMPK phosphorylation, as has been previously shown in the heart [5] (Fig.…”

“…1). Bone et al [3] further demonstrated that AMPK phosphorylation was inhibited by treatment of the peritoneal macrophages with LPS, but phosphorylation was maintained when cells were treated with fenoldopam before LPS exposure. This effect of the D1R agonist on AMPK also appears to be coupled to its antiinflammatory action, as the release of the proinflammatory cytokines TNF-a and MIP-2 into supernatants was decreased in LPS-stimulated macrophages pretreated with fenoldopam.…”

Macrophages and neutrophils: dynamic duo or partners in crime?

“…Thus, the Peiró  et al  study appears to give further weight to the pathological role of neutrophils in influenza infection by removing a critical brake on macrophage cytokine production. The IL-1β released from the activated macrophages can act in an autocrine fashion13 as well as in a paracrine positive feedback loop onto the lung epithelial cells14 causing further inflammatory cytokine release (figure 1). When combined with further neutrophil activation and cytokine release, this may explain the cytokine storm and acute lung injury/acute respiratory distress syndrome associated with the most severe influenza infections.…”