Oleic acid availability impacts thymocyte preprogramming and subsequent peripheral Treg cell differentiation.

The nature of activation signals is essential in determining T cell subset differentiation; however, the features that determine T cell subset preference acquired during intrathymic development remain elusive. Here we show that naive CD4+ T cells generated in the mouse thymic microenvironment lacking Scd1, encoding the enzyme catalyzing oleic acid (OA) production, exhibit enhanced regulatory T (Treg) cell differentiation and attenuated development of experimental autoimmune encephalomyelitis. Scd1 deletion in K14+ thymic epithelia recapitulated the enhanced Treg cell differentiation phenotype of Scd1-deficient mice. The dearth of OA permitted DOT1L to increase H3K79me2 levels at the Atp2a2 locus of thymocytes at the DN2-DN3 transition stage. Such epigenetic modification persisted in naive CD4+ T cells and facilitated Atp2a2 expression. Upon T cell receptor activation, ATP2A2 enhanced the activity of the calcium-NFAT1-Foxp3 axis to promote naive CD4+ T cells to differentiate into Treg cells. Therefore, OA availability is critical for preprogramming thymocytes with Treg cell differentiation propensities in the periphery.

MHC class Ib-restricted CD8+ T cells possess strong tumoricidal activities.

The importance of classical CD8+ T cells in tumor eradication is well acknowledged. However, the anti-tumor activity of MHC (major histocompatibility complex) Ib-restricted CD8+ T (Ib-CD8+ T) cells remains obscure. Here, we show that CX3CR1-expressing Ib-CD8+ T cells (Ib-restricted CD8+ T cells) highly express cytotoxic factors, austerely resist exhaustion, and effectively eliminate various tumors. These Ib-CD8+ T cells can be primed by MHC Ia (MHC class Ia molecules) expressed on various cell types for optimal activation in a Tbet-dependent manner. Importantly, MHC Ia does not allogeneically activate Ib-CD8+ T cells, rather, sensitizes these cells for T cell receptor activation. Such effects were observed when MHC Ia+ cells were administered to tumor-bearing Kb-/-Db-/-mice. A similar population of tumoricidal CX3CR1+CD8+ T cells was identified in wild-type mice and melanoma patients. Adoptive transfer of Ib-CD8+ T cells to wild-type mice inhibited tumor progression without damaging normal tissues. Taken together, we demonstrate that MHC class Ia can prime Ib-CD8+ T cells for robust tumoricidal activities.

SCD1 Sustains Homeostasis of Bulge Niche via Maintaining Hemidesmosomes in Basal Keratinocytes.

Niche for stem cells profoundly influences their maintenance and fate during tissue homeostasis and pathological disorders; however, the underlying mechanisms and tissue-specific features remain poorly understood. Here, it is reported that fatty acid desaturation catabolized by stearoyl-coenzyme A desaturase 1 (SCD1) regulates hair follicle stem cells (HFSCs) and hair growth by maintaining the bulge, niche for HFSCs. Scd1 deletion in mice results in abnormal hair growth, an effect exerted directly on keratin K14+ keratinocytes rather than on HFSCs. Mechanistically, Scd1 deficiency impairs the level of integrin α6ß4 complex and thus the assembly of hemidesmosomes (HDs). The disruption of HDs allows the aberrant activation of focal adhesion kinase and PI3K in K14+ keratinocytes and subsequently their differentiation and proliferation. The overgrowth of basal keratinocytes results in downward extension of the outer root sheath and interruption of bulge formation. Then, inhibition of PI3K signaling in Scd1-/- mice normalizes the bulge, HFSCs, and hair growth. Additionally, supplementation of oleic acid to Scd1-/- mice reestablishes HDs and the homeostasis of bulge niche, and restores hair growth. Thus, SCD1 is critical in regulating hair growth through stabilizing HDs in basal keratinocytes and thus sustaining bulge for HFSC residence and periodic activity.

Mesenchymal stromal cells equipped by IFNα empower T cells with potent anti-tumor immunity.

Cancer treatments have been revolutionized by the emergence of immune checkpoint blockade therapies. However, only a minority of patients with various tumor types have benefited from such treatments. New strategies focusing on the immune contexture of the tumor tissue microenvironment hold great promises. Here, we created IFNα-overexpressing mesenchymal stromal cells (IFNα-MSCs). Upon direct injection into tumors, we found that these cells are powerful in eliminating several types of tumors. Interestingly, the intra-tumoral injection of IFNα-MSCs could also induce specific anti-tumor effects on distant tumors. These IFNα-MSCs promoted tumor cells to produce CXCL10, which in turn potentiates the infiltration of CD8+ T cells in the tumor site. Furthermore, IFNα-MSCs enhanced the expression of granzyme B (GZMB) in CD8+ T cells and invigorated their cytotoxicity in a Stat3-dependent manner. Genetic ablation of Stat3 in CD8+ T cells impaired the effect of IFNα-MSCs on GZMB expression. Importantly, the combination of IFNα-MSCs and PD-L1 blockade induced an even stronger anti-tumor immunity. Therefore, IFNα-MSCs represent a novel tumor immunotherapy strategy, especially when combined with PD-L1 blockade.

IGF2R-initiated proton rechanneling dictates an anti-inflammatory property in macrophages.

Metabolic traits of macrophages can be rewired by insulin-like growth factor 2 (IGF2); however, how IGF2 modulates macrophage cellular dynamics and functionality remains unclear. We demonstrate that IGF2 exhibits dual and opposing roles in controlling inflammatory phenotypes in macrophages by regulating glucose metabolism, relying on the dominant activation of the IGF2 receptor (IGF2R) by low-dose IGF2 (L-IGF2) and IGF1R by high-dose IGF2. IGF2R activation leads to proton rechanneling to the mitochondrial intermembrane space and enables sustained oxidative phosphorylation. Mechanistically, L-IGF2 induces nucleus translocation of IGF2R that promotes Dnmt3a-mediated DNA methylation by activating GSK3α/ß and subsequently impairs expression of vacuolar-type H+-ATPase (v-ATPase). This sequestrated assembly of v-ATPase inhibits the channeling of protons to lysosomes and leads to their rechanneling to mitochondria. An IGF2R-specific IGF2 mutant induces only the anti-inflammatory response and inhibits colitis progression. Together, our findings highlight a previously unidentified role of IGF2R activation in dictating anti-inflammatory macrophages.

Scd1 controls de novo beige fat biogenesis through succinate-dependent regulation of mitochondrial complex II.

Preadipocytes can give rise to either white adipocytes or beige adipocytes. Owing to their distinct abilities in nutrient storage and energy expenditure, strategies that specifically promote "beiging" of adipocytes hold great promise for counterbalancing obesity and metabolic diseases. Yet, factors dictating the differentiation fate of adipocyte progenitors remain to be elucidated. We found that stearoyl-coenzyme A desaturase 1 (Scd1)-deficient mice, which resist metabolic stress, possess augmentation in beige adipocytes under basal conditions. Deletion of Scd1 in mature adipocytes expressing Fabp4 or Ucp1 did not affect thermogenesis in mice. Rather, Scd1 deficiency shifted the differentiation fate of preadipocytes from white adipogenesis to beige adipogenesis. Such effects are dependent on succinate accumulation in adipocyte progenitors, which fuels mitochondrial complex II activity. Suppression of mitochondrial complex II by Atpenin A5 or oxaloacetic acid reverted the differentiation potential of Scd1-deficient preadipocytes to white adipocytes. Furthermore, supplementation of succinate was found to increase beige adipocyte differentiation both in vitro and in vivo. Our data reveal an unappreciated role of Scd1 in determining the cell fate of adipocyte progenitors through succinate-dependent regulation of mitochondrial complex II.

Kynurenic acid, an IDO metabolite, controls TSG-6-mediated immunosuppression of human mesenchymal stem cells.

Mesenchymal stem cells (MSCs) have been demonstrated to be anti-inflammatory against various immune disorders through several factors, including indoleamine 2,3-dioxygenase (IDO) and TNF-stimulated gene 6 (TSG-6). However, little is known about the necessity for both of these key immunosuppressive factors. Here we employed the mouse lipopolysaccharide (LPS)-induced acute lung injury (ALI) model, and found that IDO is necessary to achieve the effect of human umbilical cord-derived MSC (hUC-MSC)-based treatment on ALI. Notably, when IDO was deleted or inhibited, the expression of TSG-6 was decreased. This specific IDO-mediated regulation of TSG-6 expression was found to be exerted through its metabolite, kynurenic acid (KYNA), as inhibition of KYNA production led to decreased TSG-6 expression. Importantly, KYNA pretreatment of human MSCs enhanced their therapeutic effect on ALI. Mechanistically, KYNA activates aryl hydrocarbon receptor (AhR), which directly binds to the TSG-6 promoter to enhance TSG-6 expression. Therefore, our study has uncovered a novel link between IDO and TSG-6, and demonstrates that a metabolite of IDO controls the TSG-6-mediated anti-inflammatory therapeutic effects of human MSCs.

Isocitrate lyase is required for urediniospore germination of Puccinia striiformis f. sp. tritici.

The PstICL1 gene, which encodes isocitrate lyase, a key enzyme in the glyoxylate cycle, was cloned and characterized in the biotrophic wheat pathogen Puccinia striiformis f. sp. tritici (Pst). Expression analyses of PstICL1 exhibited high levels of transcripts in ungerminated urediniospores, which showed low isocitrate lyase enzyme activity. In planta, PstICL1 expression was continuously down-regulated upon germination. During the later stages of the infection of wheat, the level of PstICL1 expression was extremely low. The function of PstICL1 was identified via mutant complementation. The expression of PstICL1 in Saccharomyces cerevisiae can complement the defects of the △ICL mutant. Using 3-nitropropionate, we observed that inactivation of isocitrate lyase greatly reduced the germination rate of urediniospores, indicating that PstICL1 plays a key role during Pst germination. Furthermore, analysis of lipid bodies revealed that lipid components continuously enter the germ tube from the urediniospore cell during germ tube elongation. Moreover, during this period, the lipid contents continuously decreased, and the total carbohydrates markedly increased, demonstrating that the lipids are being converted into carbohydrates. These results suggest that PstICL1 is required for Pst germination.