Victor Ndaw

TGF-β1 Suppresses IL-33–Induced Mast Cell Function

TGF-β1 is involved in many pathological conditions, including autoimmune disorders, cancer, and cardiovascular and allergic diseases. We have previously found that TGF-β1 can suppress IgE-mediated mast cell activation of human and mouse mast cells. IL-33 is a member of the IL-1 family capable of inducing mast cell responses and enhancing IgE-mediated activation. In this study, we investigated the effects of TGF-β on IL-33–mediated mast cell activation. Bone marrow–derived mast cells cultured in TGF-β1, β2, or β3 showed reduced IL-33–mediated production of TNF, IL-6, IL-13, and MCP-1 in a concentration-dependent manner. TGF-β1 inhibited IL-33–mediated Akt and ERK phosphorylation as well as NF-κB– and AP-1–mediated transcription. These effects were functionally important, as TGF-β1 injection suppressed IL-33–induced systemic cytokines in vivo and inhibited IL-33–mediated cytokine release from human mast cells. TGF-β1 also suppressed the combined effects of IL-33 and IgE-mediated activation on mouse and human mast cells. The role of IL-33 in the pathogenesis of allergic diseases is incompletely understood. These findings, consistent with our previously reported effects of TGF-β1 on IgE-mediated activation, demonstrate that TGF-β1 can provide broad inhibitory signals to activated mast cells.

Fluvastatin Suppresses Mast Cell and Basophil IgE Responses: Genotype-Dependent Effects

Mast cell (MC)– and basophil-associated inflammatory diseases are a considerable burden to society. A significant portion of patients have symptoms despite standard-of-care therapy. Statins, used to lower serum cholesterol, have immune-modulating activities. We tested the in vitro and in vivo effects of statins on IgE-mediated MC and basophil activation. Fluvastatin showed the most significant inhibitory effects of the six statins tested, suppressing IgE-induced cytokine secretion among mouse MCs and basophils. The effects of fluvastatin were reversed by mevalonic acid or geranylgeranyl pyrophosphatase, and mimicked by geranylgeranyl transferase inhibition. Fluvastatin selectively suppressed key FcεRI signaling pathways, including Akt and ERK. Although MCs and basophils from the C57BL/6J mouse strain were responsive to fluvastatin, those from 129/SvImJ mice were completely resistant. Resistance correlated with fluvastatin-induced upregulation of the statin target HMG-CoA reductase. Human MC cultures from eight donors showed a wide range of fluvastatin responsiveness. These data demonstrate that fluvastatin is a potent suppressor of IgE-mediated MC activation, acting at least partly via blockade of geranyl lipid production downstream of HMG-CoA reductase. Importantly, consideration of statin use for treating MC–associated disease needs to incorporate genetic background effects, which can yield drug resistance.

Lactic Acid Suppresses IL-33–Mediated Mast Cell Inflammatory Responses via Hypoxia-Inducible Factor-1α–Dependent miR-155 Suppression

Lactic acid (LA) is present in tumors, asthma, and wound healing, environments with elevated IL-33 and mast cell infiltration. Although IL-33 is a potent mast cell activator, how LA affects IL-33–mediated mast cell function is unknown. To investigate this, mouse bone marrow–derived mast cells were cultured with or without LA and activated with IL-33. LA reduced IL-33–mediated cytokine and chemokine production. Using inhibitors for monocarboxylate transporters (MCT) or replacing LA with sodium lactate revealed that LA effects are MCT-1– and pH-dependent. LA selectively altered IL-33 signaling, suppressing TGF-β–activated kinase-1, JNK, ERK, and NF-κB phosphorylation, but not p38 phosphorylation. LA effects in other contexts have been linked to hypoxia-inducible factor (HIF)-1α, which was enhanced in bone marrow–derived mast cells treated with LA. Because HIF-1α has been shown to regulate the microRNA miR-155 in other systems, LA effects on miR-155-5p and miR-155-3p species were measured. In fact, LA selectively suppressed miR-155-5p in an HIF-1α–dependent manner. Moreover, overexpressing miR-155-5p, but not miR-155-3p, abolished LA effects on IL-33–induced cytokine production. These in vitro effects of reducing cytokines were consistent in vivo, because LA injected i.p. into C57BL/6 mice suppressed IL-33–induced plasma cytokine levels. Lastly, IL-33 effects on primary human mast cells were suppressed by LA in an MCT-dependent manner. Our data demonstrate that LA, present in inflammatory and malignant microenvironments, can alter mast cell behavior to suppress inflammation.