Alkaline Cytosolic pH and High Sodium Hydrogen Exchanger 1 (NHE1) Activity in Th9 Cells

Abstract

CD4؉ T helper 9 (Th9) cells are a newly discovered Th cell subset that produce the pleiotropic cytokine IL-9. Th9 cells can protect against tumors and provide resistance against helminth infections. Given their pivotal role in the adaptive immune system, understanding Th9 cell development and the regulation of IL-9 production could open novel immunotherapeutic opportunities. The Na ؉ /H ؉ exchanger 1 (NHE1; gene name Slc9␣1)) is critically important for regulating intracellular pH (pH i ), cell volume, migration, and cell survival. The pH i influences cytokine secretion, activities of membrane-associated enzymes, ion transport, and other effector signaling molecules such as ATP and Ca 2؉ levels. However, whether NHE1 regulates Th9 cell development or IL-9 secretion has not yet been defined. The present study explored the role of NHE1 in Th9 cell development and function. Th cell subsets were characterized by flow cytometry and pH i was measured using 2,7-bis-(2-carboxyethyl)-5-(and-6)-carboxyfluorescein-acetoxymethyl ester (BCECF-AM) dye. NHE1 functional activity was estimated from the rate of realkalinization following an ammonium pulse. Surprisingly, in Th9 cells pH i and NHE1 activity were significantly higher than in all other Th cell subsets (Th1/Th2/Th17 and induced regulatory T cells (iTregs)). NHE1 transcript levels and protein abundance were significantly higher in Th9 cells than in other Th cell subsets. Inhibition of NHE1 by siRNA-NHE1 or with cariporide in Th9 cells down-regulated IL-9 and ATP production. NHE1 activity, Th9 cell development, and IL-9 production were further blunted by pharmacological inhibition of protein kinase Akt1/Akt2. Our findings reveal that Akt1/Akt2 control of NHE1 could be an important physiological regulator of Th9 cell differentiation, IL-9 secretion, and ATP production. CD4ϩ T cells participate in the regulation of the immune response during infections, autoimmunity, and cancer. CD4 ϩ T cells are an important and essential arm of the adaptive immune system (1). CD4 ϩ T cells can be divided into various subtypes based upon their cytokine secretion: T helper 1 (Th1) 4 cells produce IFN-␥ (1, 2), Th2 cells produce IL-4, IL-5, and IL-13 (3), Th17 cells produce IL-17 (4 -6), Th9 cells produce IL-9 (7-9), and suppressive regulatory T cells (Tregs) produce TGF-␤ and IL-10 (10). A great deal of experimental effort has been dedicated to decipher the development and function of various Th cell subsets. However, Th9 cell development and function remain incompletely understood.Th9 cells are a recently characterized Th cell subset recognized by their potent production of IL-9. Th9 cells play a pivotal role in health and disease. Th9 cells have been shown to exacerbate the airway allergic immune response by recruiting eosinophils and mast cells to the lungs, increasing mucus production, and production of serum IgE (11, 12). Th9 cells further contribute to the host-immune reaction against helminth infections and tumors (7, 13-23). The development and function of Th9 cells are regulated ...

Cell fate decisions: emerging roles for metabolic signals and cell morphology

“…A long‐held view is that pHi is constitutively maintained between 7.2 and 7.4 in normal mammalian cells and only dysregulated from this narrow range in diseases, including being constitutively increased in cancer and decreased in neurodegenerative disorders . However, emerging evidence indicates there are transient increases in pHi in normal mammalian cells during cell cycle progression , directional migration , and differentiation . Although the role of pHi dynamics in regulating cell fate decisions remains understudied, we highlight recent findings on this topic and emphasize questions that remain to be addressed (Fig ).…”

“…Considered more broadly, a role for pHi dynamics in differentiation, epithelial plasticity, and morphogenesis remains understudied. Increased pHi is reported to enable or be necessary for the differentiation of CD4 + T helper 9 (Th9) cells , epithelial‐to‐mesenchymal transition (EMT) , and neural fates from ectoderm during Xenopus development . In contrast, expression of the Cl‐HCO3 exchanger AE2, which as an acid loader facilitating HCO3 efflux should lower pHi, is necessary for clonal mouse macrophages to differentiate into osteoclasts , although a role for pHi dynamics was not determined.…”

Enhanced Reactive Oxygen Species Production, Acidic Cytosolic pH and Upregulated Na+/H+ Exchanger (NHE) in Dicer Deficient CD4+ T Cells

“…For instance, phosphorylation of Akt on both Ser473 and Thr308 after TCR activation with anti-CD3 and anti-CD28 antibodies is stronger in Dicer Δ/Δ CD4 + T cells than in than in Dicer fl/fl CD4 + T cells [35]. Akt activation could in turn lead to increase in NHE1 expression [27, 36]. In Dicer Δ/Δ CD4 + T cells, the enhanced Nhe1 expression could further result from acidic pHi.…”

“…In Dicer Δ/Δ CD4 + T cells, phosphorylation of Akt on both Ser473 and Thr308 after TCR activation is augmented [35]. Thus, Akt activation could lead to increase in Nhe1 expression [27, 36]. Furthermore, miR-15b/16 regulates phosphorylation of Akt by downregulating mTOR/Rictor [35].…”

1α,25(OH) 2D3 Sensitive Cytosolic pH Regulation and Glycolytic Flux in Human Endometrial Ishikawa Cells

“…Carriers particularly active in tumor cells include the Na + /H + exchanger (NHE1) [23, 24], the most common isoform of the Na + /H + exchanger family that is ubiquitously expressed in all mammalian cells [25]. Increased proliferation and energy consumption of tumor cells results in a tumor metabolic microenvironment that is hypoxic, acidic, and deprived of serum [26].…”