The authors assess the role of N6-methyladenosine in T cell development and function, and show that RNA methylation controls T cell homeostasis by regulating IL-7-mediated STAT5 activation. N3-methyladenosine is a common modification of messenger RNA responsible for the regulation of mRNA metabolism such as turnover and stability. Here, Richard Flavell and colleagues assess its physiological role in T cell development and function, and show that RNA methylation controls T cell homeostasis by regulating IL-7-mediated STAT5 activation. N6-methyladenosine (m6A) is the most common and abundant messenger RNA modification, modulated by ‘writers’, ‘erasers’ and ‘readers’ of this mark1,2. In vitro data have shown that m6A influences all fundamental aspects of mRNA metabolism, mainly mRNA stability, to determine stem cell fates3,4. However, its in vivo physiological function in mammals and adult mammalian cells is still unknown. Here we show that the deletion of m6A ‘writer’ protein METTL3 in mouse T cells disrupts T cell homeostasis and differentiation. In a lymphopaenic mouse adoptive transfer model, naive Mettl3-deficient T cells failed to undergo homeostatic expansion and remained in the naive state for up to 12 weeks, thereby preventing colitis. Consistent with these observations, the mRNAs of SOCS family genes encoding the STAT signalling inhibitory proteins SOCS1, SOCS3 and CISH were marked by m6A, exhibited slower mRNA decay and showed increased mRNAs and levels of protein expression in Mettl3-deficient naive T cells. This increased SOCS family activity consequently inhibited IL-7-mediated STAT5 activation and T cell homeostatic proliferation and differentiation. We also found that m6A has important roles for inducible degradation of Socs mRNAs in response to IL-7 signalling in order to reprogram naive T cells for proliferation and differentiation. Our study elucidates for the first time, to our knowledge, the in vivo biological role of m6A modification in T-cell-mediated pathogenesis and reveals a novel mechanism of T cell homeostasis and signal-dependent induction of mRNA degradation.

The identification of m ⁶ A demethylases and high-throughput sequencing analysis of methylated transcriptome corroborated m ⁶ A RNA epigenetic modification as a dynamic regulation process, and reignited its investigation in the past few years. Many basic concepts of cytogenetics have been revolutionized by the growing understanding of the fundamental role of m ⁶ A in RNA splicing, degradation and translation. In this review, we summarize typical features of methylated transcriptome in mammals, and highlight the ‘writers’, ‘erasers’ and ‘readers’ of m ⁶ A RNA modification. Moreover, we emphasize recent advances of biological functions of m ⁶ A and conceive the possible roles of m ⁶ A in the regulation of immune response and related diseases.

Psoriasis is a severe disease associated with the disturbance of metabolism and inflammation, but the molecular mechanisms underlying these aspects of psoriasis pathology are poorly understood. Here, we report that glutaminase 1–mediated (GLS1-mediated) glutaminolysis was aberrantly activated in patients with psoriasis and in psoriasis-like mouse models, which promoted Th17 and γδ T17 (IL-17A–producing γδ T) cell differentiation through enhancement of histone H3 acetylation of the Il17a promoter, thereby contributing to the immune imbalance and development of psoriasis. We further demonstrate that mucosa-associated lymphoid tissue lymphoma translocation protein 1 (MALT1) protease was constitutively active in psoriatic CD4⁺ and γδ T cells, thereby supporting GLS1 expression by stabilizing c-Jun, which directly binds to the GLS1 promoter region. Blocking the activity of either GLS1 or MALT1 protease resolved Th17 and γδ T17 cell differentiation and epidermal hyperplasia in the psoriasis-like mouse models. Finally, IL-17A enhanced GLS1 expression via the MALT1/cJun pathway in keratinocytes, resulting in hyperproliferation of and chemokine production by keratinocytes. Our findings identify the role of the MALT1/cJun/GLS1/glutaminolysis/H3 acetylation/T17 axis in psoriasis pathogenesis and reveal potential therapeutic targets for this disease.

Immune responses and neuroinflammation are critically involved in spinal cord injury (SCI). γδ T cells, a small subset of T cells, regulate the inflammation process in many diseases, yet their function in SCI is still poorly understood. In this paper, we demonstrate that mice deficient in γδ T cells (TCRδ^−/−) showed improved functional recovery after SCI. γδ T cells are detected at the lesion sites within 24 hours after injury and are predominantly of the Vγ4 subtype and express the inflammatory cytokine IFN-γ. Inactivating IFN-γ signaling in macrophages results in a significantly reduced production of proinflammatory cytokines in the cerebrospinal fluid (CSF) of mice with SCIs and improves functional recovery. Furthermore, treatment of SCI with anti-Vγ4 antibodies has a beneficial effect, similar to that obtained with anti–TNF-α. In SCI patients, γδ T cells are detected in the CSF, and most of them are IFN-γ positive. In conclusion, manipulation of γδ T cell functions may be a potential approach for future SCI treatment. Graphical Abstract