Solomon, L. A. | bioRxiv Science

bioRxiv2019

A role for ATP Citrate Lyase in cell cycle regulation during myeloid differentiation

Differentiation of myeloid progenitor cells into macrophages is accompanied by increased PU.1 concentration and increasing cell cycle length, culminating in cell cycle arrest. Induction of PU.1 expression in a cultured myeloid cell line expressing low PU.1 concentration results in decreased levels of mRNA encoding ATP-Citrate Lyase (ACL) and cell cycle arrest. ACL is an essential enzyme for generating acetyl-CoA, a key metabolite for the first step in fatty acid synthesis as well as for histone acetylation. We hypothesized that ACL may play a role in cell cycle regulation in the myeloid lineage. In this study, we found that acetyl-CoA or acetate supplementation was sufficient to rescue cell cycle progression in cultured BN cells treated with an ACL inhibitor or induced for PU.1 expression. Acetyl-CoA supplementation was also sufficient to rescue cell cycle progression in BN cells treated with a fatty acid synthase (FASN) inhibitor. We demonstrated that acetyl-CoA was utilized in both fatty acid synthesis and histone acetylation pathways to promote proliferation. Finally, we found that Acly mRNA transcript levels decrease during normal macrophage differentiation from bone marrow precursors. Our results suggest that regulation of ACL activity is a potentially important point of control for cell cycle regulation in the myeloid lineage.

immunology↗

bioRxiv2018

IL-2 Modulates Th2 cell Responses to Glucocorticoid: A Cause of Persistent Type 2 Inflammation?

BackgroundInhaled glucocorticosteroids (GCs) are the main treatment for asthma as they reduce type 2 cytokine (IL-4, IL-5 and IL-13) expression and induce apoptosis. Asthma severity is associated with GC insensitivity, increased type 2 inflammation and circulating Th2 cells. Since IL-2 is a T cell survival factor, we assessed whether IL-2 levels associate with the proportion of Th2 cells and/or correlate with clinical features of asthma severity.\n\nMethodsPeripheral blood from asthma patients (n=18) was obtained and Th2 cell numbers determined by flow cytometry. Peripheral blood cells were activated with mitogen (24hrs) and supernatant levels of IL-2 and IL-13 measured by ELISA. In vitro differentiated Th2 cells were treated with dexamethasone and IL-2 and assessed for apoptosis by flow cytometry staining of Annexin V. Level of mRNA for anti-apoptotic (BCL-2) and pro-apoptotic (BIM) genes as well as IL-13 were determined by qRT-PCR.\n\nResultsIL-2 produced by activated peripheral blood cells correlated negatively with lung function (FEV1) and positively with daily dose of inhaled GC. When patients were stratified based on IL-2 level, high IL-2 producers made more IL-13 and had more circulating Th2 cells. In vitro, increasing the level of IL-2 in the culture media was associated with resistance to DEX-induced apoptosis, more BCL-2 and less BIM mRNA. Th2 cells cultured with higher IL-2 also had more IL-13 mRNA and required higher concentrations of DEX for cytokine suppression.\n\nConclusions and Clinical RelevanceIL-2 modulates Th2 cell responses to GC, supporting both their survival and pro-inflammatory capacity, suggesting that a patients potential to produce IL-2 may be a determinant in asthma severity.

immunology↗