Docosahexaenoic Acid Controls Pulmonary Macrophage Lipid Raft Size and Inflammation.

BACKGROUND: Docosahexaenoic acid (DHA) controls the biophysical organization of plasma membrane sphingolipid/cholesterol-enriched lipid rafts to exert anti-inflammatory effects, particularly in lymphocytes. However, the impact of DHA on the spatial arrangement of alveolar macrophage lipid rafts and inflammation is unknown. OBJECTIVES: The primary objective was to determine how DHA controls lipid raft organization and function of alveolar macrophages. As proof-of-concept, we also investigated DHA's anti-inflammatory effects on select pulmonary inflammatory markers with a murine influenza model. METHODS: MH-S cells, an alveolar macrophage line, were treated with 50 µM DHA or vehicle control and were used to study plasma membrane molecular organization with fluorescence-based methods. Biomimetic membranes and coarse grain molecular dynamic (MD) simulations were employed to investigate how DHA mechanistically controls lipid raft size. qRT-PCR, mass spectrometry, and ELISAs were used to quantify downstream inflammatory signaling transcripts, oxylipins, and cytokines, respectively. Lungs from DHA-fed influenza-infected mice were analyzed for specific inflammatory markers. RESULTS: DHA increased the size of lipid rafts while decreasing the molecular packing of the MH-S plasma membrane. Adding a DHA-containing phospholipid to a biomimetic lipid raft-containing membrane led to condensing, which was reversed with the removal of cholesterol. MD simulations revealed DHA nucleated lipid rafts by driving cholesterol and sphingomyelin into rafts. Downstream of the plasma membrane, DHA lowered the concentration of select inflammatory transcripts, oxylipins, and IL-6 secretion. DHA lowered pulmonary Il6 and Tnf-α mRNA expression and increased anti-inflammatory oxylipins of influenza-infected mice. CONCLUSIONS: The data suggest a model in which the localization of DHA acyl chains to nonrafts is driving sphingomyelin and cholesterol molecules into larger lipid rafts, which may serve as a trigger to impede signaling and lower inflammation. These findings also identify alveolar macrophages as a target of DHA and underscore the anti-inflammatory properties of DHA for lung inflammation.

Inhaled toxicants and pulmonary lipid metabolism: biological consequences and therapeutic interventions.

Inhaled toxicants drive the onset of and exacerbate preexisting chronic pulmonary diseases, however, the biological mechanisms by which this occurs are largely unknown. Exposure to inhaled toxicants, both environmental and occupational, drives pulmonary inflammation and injury. Upon activation of the inflammatory response, polyunsaturated fatty acids (PUFAs) are metabolized into predominately proinflammatory lipid mediators termed eicosanoids which recruit immune cells to the site of injury, perpetuating inflammation to clear the exposed toxicants. Following inflammation, lipid mediator class-switching occurs, a process that leads to increased metabolism of hydroxylated derivates of PUFAs. These mediators, which include mono-hydroxylated PUFA derivatives and specialized proresolving lipid mediators, initiate an active process of inflammation resolution by inhibiting the inflammatory response and activating resolution pathways to return the tissue to homeostasis. Exposure to inhaled toxicants leads to alterations in the synthesis of these proinflammatory and proresolving lipid mediator pathways, resulting in greater pulmonary inflammation and injury, and increasing the risk for the onset of chronic lung diseases. Recent studies have begun utilizing supplementation of PUFAs and their metabolites as potential therapeutics for toxicant-induced pulmonary inflammation and injury. Here we will review the current understanding of the lipid mediators in pulmonary inflammation and resolution as well as the impact of dietary fatty acid supplementation on lipid mediator-driven inflammation following air pollution exposure.

Functional Characterization of Organoids Derived From Irreversibly Damaged Liver of Patients With NASH.

BACKGROUND AND AIMS: NASH will soon become the leading cause of liver transplantation in the United States and is also associated with increased COVID-19 mortality. Currently, there are no Food and Drug Administration-approved drugs available that slow NASH progression or address NASH liver involvement in COVID-19. Because animal models cannot fully recapitulate human NASH, we hypothesized that stem cells isolated directly from end-stage liver from patients with NASH may address current knowledge gaps in human NASH pathology. APPROACH AND RESULTS: We devised methods that allow the derivation, proliferation, hepatic differentiation, and extensive characterization of bipotent ductal organoids from irreversibly damaged liver from patients with NASH. The transcriptomes of organoids derived from NASH liver, but not healthy liver, show significant up-regulation of proinflammatory and cytochrome p450-related pathways, as well as of known liver fibrosis and tumor markers, with the degree of up-regulation being patient-specific. Functionally, NASH liver organoids exhibit reduced passaging/growth capacity and hallmarks of NASH liver, including decreased albumin production, increased free fatty acid-induced lipid accumulation, increased sensitivity to apoptotic stimuli, and increased cytochrome P450 metabolism. After hepatic differentiation, NASH liver organoids exhibit reduced ability to dedifferentiate back to the biliary state, consistent with the known reduced regenerative ability of NASH livers. Intriguingly, NASH liver organoids also show strongly increased permissiveness to severe acute respiratory syndrome-coronavirus 2 (SARS-CoV-2) vesicular stomatitis pseudovirus as well as up-regulation of ubiquitin D, a known inhibitor of the antiviral interferon host response. CONCLUSION: Expansion of primary liver stem cells/organoids derived directly from irreversibly damaged liver from patients with NASH opens up experimental avenues for personalized disease modeling and drug development that has the potential to slow human NASH progression and to counteract NASH-related SARS-CoV-2 effects.