Microrna-31 Regulates T-Cell Metabolism Via HIF1α and Promotes Effector Function
Authors: Wu Yongxia , Zhang Mengmeng , Bastian David , Sofi Mohammed Hanief , Schutt Steven Douglas , Choi Hee-Jin , Mealer Corey , Nguyen Hung D , Tian Linlu , Yu Xue-Zhong 
Published: February 2020

MicroRNAs (miRs) repress gene expression at the post-transcriptional level via binding target mRNAs subsequently promoting mRNA degradation or impeding translation. Certain miRs influence the survival, differentiation, and function of T cells in cancer, infections, and autoimmunity. Uncontrolled T-cell allogeneic responses contribute to chronic graft-versus-host disease (cGVHD), a major cause of non-relapse mortality following allogeneic hematopoietic stem-cell transplantation (allo-HCT). Dysregulation of miR-31 is implicated in cancer, but how miR-31 impacts allogeneic T-cell response is unclear. Using oligonucleotide array, we found miR-31 was dramatically up-regulated in T cells under alloantigen-driven vs. homeostatic proliferation in recipient mice following bone marrow transplantation (BMT) (Figure 1A-B).
To understand how miR-31 regulates T-cell responses to alloantigens, we utilized murine models of allogeneic BMT and donor mice with miR-31 conditional knock-out on their T cells. In a sclerodermatous cGVHD model (B6→BDF1), we observed that the recipients transferred with donor T cells deficient for miR-31 exhibited significantly alleviated disease (Figure 1C), reflected by attenuated fibrosis and pathologic damage in skin. In a bronchiolitis obliterans cGVHD model (B6→B10.BR), we found that the recipients of miR-31-deficient T cells had reduced airway resistance, elastance (Figure 1D) and pathological damage in the lungs as compared with those of WT T cells. The role of miR-31 in promoting T-cell pathogenicity was further confirmed when miR-31 was inhibited by administration of specific antagomir (locked nuclear acid anti-miR-31).
We used mass cytometry to analyze donor immune cell reconstitution in recipient spleens after BMT. Consistent with attenuated disease manifestation, the recipients of miR-31-deficient T cells displayed improved reconstitution of donor T- and B- lymphocytes. The follicular T helper cells (TFH) instruct germinal center (GC) B-cell expansion, affinity maturation, and plasma cell differentiation, whereas follicular regulatory T cells (TFR) inhibit TFH -mediated B-cell activation and antibody production. We found that miR-31 deficient T cells differentiated into more TFR, but fewer TFH during alloresponses. As a result, the differentiation and activation of GC B cells and the generation of plasma cells were attenuated in the recipients of miR-31-deficient T cells.
Furthermore, miR-31-deficient T cells exhibited defects in proliferation and survival in allogeneic recipients, resulting in fewer donor T cells in recipient thymus, skin and lungs. In the absence of miR-31, T cells differentiated less into Th17 cells but more towards Tregs (Figure 1E) in vivo. Those miR-31-deficient Tregs expressed higher levels of Neuropilin 1 and PD-L1, the markers associated with superior stability and suppressive function of Tregs. While miR-31 played little role on Th1 cell differentiation, it facilitated alloantigen-reactive iTregs losing Foxp3 and producing IFNγ after being transferred into allogeneic recipients.
Hypoxia, a hallmark of inflamed and damaged tissue, can drive fibrosis and disease development through immune cell dysregulation. Upon activation, T cells rapidly increase their metabolic rate and switch from oxidative phosphorylation to aerobic glycolysis. We found that miR-31-deficient T cells exhibited reduced hypoxia-inducible factor 1α (HIF1α) signaling (glycolysis promotor), surface GLUT1 expression, and glucose uptake, but increased lipid droplet accumulation in allogeneic recipients, suggesting that miR-31 promotes metabolic switch from fatty acid β-oxidation to aerobic glycolysis in allo-reactive T cells (Figure 1F). Furthermore, under hypoxia (3% oxygen) but not normoxia (21% oxygen) conditions, miR-31 increased Th17 but decreased iTreg differentiation from naïve CD4 T cells in the presence of IL-6 and TGFβ in vitro.
Taken together, miR-31 regulates T-cell expansion, differentiation, and metabolism via promoting HIF1α expression and hypoxia adaptation in allo-reactive T cells, which enhances T-cell effector function and pathogenicity after allogeneic BMT.

Disclosures
No relevant conflicts of interest to declare.