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 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.

CD11b regulates obesity-induced insulin resistance via limiting alternative activation and proliferation of adipose tissue macrophages.

Obesity-associated inflammation is accompanied by the accumulation of adipose tissue macrophages (ATMs), which is believed to predispose obese individuals to insulin resistance. CD11b (integrin αM) is highly expressed on monocytes and macrophages and is critical for their migration and function. We found here that high-fat diet-induced insulin resistance was significantly reduced in CD11b-deficient mice. Interestingly, the recruitment of monocytes to adipose tissue is impaired when CD11b is deficient, although the cellularity of ATMs in CD11b-deficient mice is higher than that in wild-type mice. We further found that the increase in ATMs is caused mainly by their vigorous proliferation in the absence of CD11b. Moreover, the proliferation and alternative activation of ATMs are regulated by the IL-4/STAT6 axis, which is inhibited by CD11b through the activity of phosphatase SHP-1. Thus, CD11b plays a critical role in obesity-induced insulin resistance by limiting the proliferation and alternative activation of ATMs.

An osteopontin-integrin interaction plays a critical role in directing adipogenesis and osteogenesis by mesenchymal stem cells.

An imbalance between normal adipogenesis and osteogenesis by mesenchymal stem cells (MSCs) has been shown to be related to various human metabolic diseases, such as obesity and osteoporosis; however, the underlying mechanisms remain elusive. We found that the interaction between osteopontin (OPN), an arginine-glycine-aspartate-containing glycoprotein, and integrin αv/ß1 plays a critical role in the lineage determination of MSCs. Although OPN is a well-established marker during osteogenesis, its role in MSC differentiation is still unknown. Our study reveals that blockade of OPN function promoted robust adipogenic differentiation, while inhibiting osteogenic differentiation. Re-expression of OPN restored a normal balance between adipogenesis and osteogenesis in OPN(-/-) MSCs. Retarded bone formation by OPN(-/-) MSCs was also verified by in vivo implantation with hydroxyapatite-tricalcium phosphate, a bone-forming matrix. The role of extracellular OPN in MSC differentiation was further demonstrated by supplementation and neutralization of OPN. Blocking well-known OPN receptors integrin αv/ß1 but not CD44 also affected MSC differentiation. Further studies revealed that OPN inhibits the C/EBPs signaling pathway through integrin αv/ß1. Consistent with these in vitro results, OPN(-/-) mice had a higher fat to total body weight ratio than did wild-type mice. Therefore, our study demonstrates a novel role for OPN-integrin αv/ß1 in regulating MSC differentiation.

miR-155 regulates immune modulatory properties of mesenchymal stem cells by targeting TAK1-binding protein 2.

MSCs possess potent immunosuppressive capacity. We have reported that mouse MSCs inhibit T cell proliferation and function via nitric oxide. This immune regulatory capacity of MSCs is induced by the inflammatory cytokines IFNγ together with either TNFα or IL-1ß. This effect of inflammatory cytokines on MSCs is extraordinary; logarithmic increases in the expression of iNOS and chemokines are often observed. To investigate the molecular mechanisms underlying this robust effect of cytokines, we examined the expression of microRNAs in MSCs before and after cytokine treatment. We found that miR-155 is most significantly up-regulated. Furthermore, our results showed that miR-155 inhibits the immunosuppressive capacity of MSCs by reducing iNOS expression. We further demonstrated that miR-155 targets TAK1-binding protein 2 (TAB2) to regulate iNOS expression. Additionally, knockdown of TAB2 reduced iNOS expression. In summary, our study demonstrated that miR-155 inhibits the immunosuppressive capacity of MSCs by reducing iNOS expression by targeting TAB2. Our data revealed a novel role of miR-155 in regulating the immune modulatory activities of MSCs.

Cholinergic control of Th17 cell pathogenicity in experimental autoimmune encephalomyelitis.

Experimental autoimmune encephalomyelitis (EAE) is a mouse model of multiple sclerosis (MS) in which Th17 cells have a crucial but unclear function. Here we show that choline acetyltransferase (ChAT), which synthesizes acetylcholine (ACh), is a critical driver of pathogenicity in EAE. Mice with ChAT-deficient Th17 cells resist disease progression and show reduced brain-infiltrating immune cells. ChAT expression in Th17 cells is linked to strong TCR signaling, expression of the transcription factor Bhlhe40, and increased Il2, Il17, Il22, and Il23r mRNA levels. ChAT expression in Th17 cells is independent of IL21r signaling but dampened by TGFß, implicating ChAT in controlling the dichotomous nature of Th17 cells. Our study establishes a cholinergic program in which ACh signaling primes chronic activation of Th17 cells, and thereby constitutes a pathogenic determinant of EAE. Our work may point to novel targets for therapeutic immunomodulation in MS.

Tumor-specific cholinergic CD4+ T lymphocytes guide immunosurveillance of hepatocellular carcinoma.

Cholinergic nerves are involved in tumor progression and dissemination. In contrast to other visceral tissues, cholinergic innervation in the hepatic parenchyma is poorly detected. It remains unclear whether there is any form of cholinergic regulation of liver cancer. Here, we show that cholinergic T cells curtail the development of liver cancer by supporting antitumor immune responses. In a mouse multihit model of hepatocellular carcinoma (HCC), we observed activation of the adaptive immune response and induction of two populations of CD4+ T cells expressing choline acetyltransferase (ChAT), including regulatory T cells and dysfunctional PD-1+ T cells. Tumor antigens drove the clonal expansion of these cholinergic T cells in HCC. Genetic ablation of Chat in T cells led to an increased prevalence of preneoplastic cells and exacerbated liver cancer due to compromised antitumor immunity. Mechanistically, the cholinergic activity intrinsic in T cells constrained Ca2+-NFAT signaling induced by T cell antigen receptor engagement. Without this cholinergic modulation, hyperactivated CD25+ T regulatory cells and dysregulated PD-1+ T cells impaired HCC immunosurveillance. Our results unveil a previously unappreciated role for cholinergic T cells in liver cancer immunobiology.

SHP1 Regulates Bone Mass by Directing Mesenchymal Stem Cell Differentiation.

Osteoblasts and adipocytes are derived from a common precursor, mesenchymal stem cells (MSCs). Alterations in the normal fate of differentiating MSCs are involved in the development of obesity and osteoporosis. Here, we report that viable motheaten (me(v)) mice, which are deficient in the SH2-domain-containing phosphatase-1 (SHP1), develop osteoporosis spontaneously. Consistently, MSCs from me(v)/me(v) mice exhibit significantly reduced osteogenic potential and greatly increased adipogenic potential. When MSCs were transplanted into nude mice, SHP1-deficient MSCs resulted in diminished bone formation compared with wild-type MSCs. SHP1 was found to bind to GSK3ß and suppress its kinase activity by dephosphorylating pY216, thus resulting in ß-catenin stabilization. Mice, in which SHP1 was deleted in MSCs using SHP1(fl/fl)Dermo1-cre, displayed significantly decreased bone mass and increased adipose tissue. Taken together, these results suggest a possible role for SHP1 in controlling tissue homeostasis through modulation of MSC differentiation via Wnt signaling regulation.

The roles of testicular c-kit positive cells in de novo morphogenesis of testis.

C-kit positive (c-kit(+)) cells are usual tissue-specific stem cells. However, in postnatal testis, undifferentiated spermatogonial stem cells (SSCs) are c-kit negative (c-kit(-)) and activation of c-kit represents the start of SSC differentiation, leaving an intriguing question whether other c-kit(+) cells exist and participate in the postnatal development of testis. To this end, a feasible system for testicular reconstitution, in which a specific type of cells can be manipulated, is needed. Here, we first establish de novo morphogenesis of testis by subcutaneous injection of testicular cells from neonatal testes into the backs of nude mice. We observe testicular tissue formation and spermatogenesis from all injected sites. Importantly, functional spermatids can be isolated from these testicular tissues. Using this system, we systemically analyze the roles of c-kit(+) cells in testicular reconstitution and identify a small population of cells (c-kit(+):CD140a(+):F4/80(+)), which express typical markers of macrophages, are critical for de novo morphogenesis of testis. Interestingly, we demonstrate that these cells are gradually replaced by peripheral blood cells of recipient mice during the morphogenesis of testis. Thus, we develop a system, which may mimic the complete developmental process of postnatal testis, for investigating the testicular development and spermatogenesis.