Acid Sphingomyelinase (ASM) is a Negative Regulator of Regulatory T Cell (Treg) Development

Abstract

Background/Aims: Regulatory T cell (Treg) is required for the maintenance of tolerance to various tissue antigens and to protect the host from autoimmune disorders. However, Treg may, indirectly, support cancer progression and bacterial infections. Therefore, a balance of Treg function is pivotal for adequate immune responses. Acid sphingomyelinase (ASM) is a rate limiting enzyme involved in the production of ceramide by breaking down sphingomyelin. Previous studies in T-cells have suggested that ASM is involved in CD28 signalling, T lymphocyte granule secretion, degranulation, and vesicle shedding similar to the formation of phosphatidylserine-exposing microparticles from glial cells. However, whether ASM affects the development of Treg has not yet been described. Methods: Splenocytes, isolated Naive T lymphocytes and cultured T cells were characterized for various immune T cell markers by flow cytometery. Cell proliferation was measured by Carboxyfluorescein succinimidyl ester (CFSE) dye, cell cycle analysis by Propidium Iodide (PI), mRNA transcripts by q-RT PCR and protein expression by Western Blotting respectively. Results: ASM deficient mice have higher number of Treg compared with littermate control mice. In vitro induction of ASM deficient T cells in the presence of TGF-β and IL-2 lead to a significantly higher number of Foxp3⁺ induced Treg (iTreg) compared with control T-cells. Further, ASM deficient iTreg has less AKT (serine 473) phosphorylation and Rictor levels compared with control iTreg. Ceramide C6 led to significant reduction of iTreg in both ASM deficient and WT mice. The reduction in iTreg leads to induction of IL-1β, IL-6 and IL-17 but not IFN-γ mRNA levels. Conclusion: ASM is a negative regulator of natural and iTreg.

Concurrent CCR7 Overexpression and RelB Knockdown in Immature Dendritic Cells Induces Immune Tolerance and Improves Skin-Graft Survival in a Murine Model

“…CD4+CD25+Foxp3 Tregs, which constitute 5%-10% of peripheral CD4+ T cells, were considered to play a central role in inducing and maintaining tolerance by suppressing T-cell responses in several animal models and in a clinical trial of transplantation [23,24]. The therapeutic potential of Tregs, termed cellular immunotherapy, has been shown to be effective for controlling immune responses in the graft-versus-host disease.…”

Chloroquine Autophagic Inhibition Rebalances Th17/Treg-Mediated Immunity and Ameliorates Systemic Lupus Erythematosus

“…They also harbor a receptor protein, cytotoxic T-lymphocyteassociated protein 4 (CTLA-4), latently expressing TGF-β on the membrane surface [11]. Although a large number of signaling pathways participate in the regulation of Treg cells [12][13][14][15], forkhead box protein 3 (Foxp3) as Treg specific transcription factor is the most important one. Diminished expression of Foxp3 in CD4 + CD25 + Treg cells created dysfunction of Treg cells in SLE [16].…”

Regulation of Arthritis Severity by the Acid Sphingomyelinase

“…Previously, Asm-deficiency or Asm-inhibition has been linked to increased T reg frequencies in naïve mice [43, 44]. Here, we studied immunized mice and did not detect any differences in T reg cell number in lymph nodes of immunized Smpd1 -/- mice compared to immunized wild-type littermates (Fig.…”

“…Our study also included the analysis of regulatory T cells, whose frequency was not altered in Asm-deficient mice after immunization. Hollmann et al and Zhou et al have previously reported an increase of regulatory T cells upon Asm-deficiency in untreated mice [43, 44]. Zhou et al identified ASM as a negative regulator of T reg development, but also noted opposing effects based on the composition of the cytokine cocktail used for experimental T reg induction in their own and in another study by Kue et al [44, 49].…”