Despite antiretroviral therapy (ART), HIV infection promotes cognitive dysfunction and neurodegeneration through persistent inflammation and neurotoxin release from infected and/or activated macrophages/microglia. Furthermore, inflammation and immune activation within both the central nervous system (CNS) and periphery correlate with disease progression and morbidity in ART-treated individuals. Accordingly, drugs targeting these pathological processes in the CNS and systemic compartments are needed for effective, adjunctive therapy. Using our in vitro model of HIV-mediated neurotoxicity, in which HIV infected monocyte-derived macrophages (MDM) release excitatory neurotoxins, we show that HIV infection dysregulates the macrophage antioxidant response and reduces levels of heme oxygenase-1 (HO-1). Furthermore, restoration of HO-1 expression in HIV-infected MDM reduces neurotoxin release without altering HIV replication. Given these novel observations, we have identified dimethyl fumarate (DMF), used to treat psoriasis and showing promising results in clinical trials for multiple sclerosis, as a potential neuroprotectant and HIV disease-modifying agent. DMF, an immune modulator and inducer of the antioxidant response, suppresses HIV replication and neurotoxin release. Two distinct mechanisms are proposed; inhibition of NF-κB nuclear translocation and signaling, which could contribute to the suppression of HIV replication, and induction of HO-1, which is associated with decreased neurotoxin release. Finally, we found that DMF attenuates CCL2-induced monocyte chemotaxis, suggesting that DMF could decrease recruitment of activated monocytes to the CNS in response to inflammatory mediators. We propose that dysregulation of the antioxidant response during HIV infection drives macrophage-mediated neurotoxicity and that DMF could serve as an adjunctive neuroprotectant and HIV disease modifier in ART-treated individuals.

The 5 -phosphoinositol phosphatase SHIP negatively regulates signaling pathways triggered by antigen, cytokine and Fc receptors in both lymphocytes and myeloid cells. Mice with germ-line (null) deletion of SHIP develop a myeloproliferative-like syndrome that causes early lethality. Lymphocyte anomalies have been observed in SHIP-null mice, but it is unclear whether they are due to an intrinsic requirement of SHIP in these cells or a consequence of the severe myeloid pathology. To precisely address the function of SHIP in T cells, we have generated mice with T cell-specific deletion of SHIP. In the absence of SHIP, we found no differences in thymic selection or in the activation state and numbers of regulatory T cells in the periphery. In contrast, SHIP-deficient T cells do not skew efficiently to Th2 in vitro. Mice with T cell-specific deletion of SHIP show poor antibody responses on Alum/NP-CGG immunization and diminished Th2 cytokine production when challenged with Schistosoma mansoni eggs. The failure to skew to Th2 responses may be the consequence of increased basal levels of the Th1-associated transcriptional factor T-bet, resulting from enhanced sensitivity to cytokine-mediated T-bet induction. SHIP-deficient CD8 ؉ cells show enhanced cytotoxic responses, consistent with elevated T-bet levels in these cells. Overall our experiments indicate that in T cells SHIP negatively regulates cytokine-mediated activation in a way that allows effective Th2 responses and limits T cell cytotoxicity.cytotoxicity ͉ T-bet T he 5Ј-inositol phosphatase SHIP is a well characterized inhibitory molecule that regulates cell responses in lymphocytes and myeloid cells by its ability to hydrolyze the second messenger PI(3,4,5) trisphosphate (1-4). SHIP is recruited by engagement of the inhibitory Fc receptor in B cells and mast cells (5)(6)(7)(8) or by the engagement of FcRs (Fc RI and Fc␥RIII), cytokine [interleukin 3 (IL3), granulocyte-macrophage colony-stimulating factor (GM-CSF), and TGF␤], and growth factor (steel factor and M-CSF) receptors in myeloid cells (2, 9). Once SHIP is recruited to the membrane by the signaling complexes, its enzymatic activity depletes PI(3,4,5)P 3 and prevents membrane localization of PHdomain-containing factors such as Tec kinases, Akt, and PLC␥ (10-13). This inhibitory effect ultimately leads to reduced calcium influx and prevents cellular activation (14).Germ-line deletion of SHIP in mice leads to early mortality from a myeloproliferative-like syndrome characterized by profound splenomegaly and massive myeloid infiltration of the lung (15). B cells develop abnormally in SHIP-null mice, with an activated phenotype and specifically lacking the marginal zone B cell population (16,17). The absence of marginal-zone B cells in SHIP-null mice has been explained not as a B cell primary defect, but as a consequence of macrophage dysregulation in the spleen of these animals (17). Macrophages from SHIP-null mice are skewed toward an M2-activated phenotype showing high levels of arginase I (ArgI) and Ym1. R...

Notch signaling regulates myriad cellular functions by activating transcription, yet how Notch selectively activates different transcriptional targets is poorly understood. The core Notch transcriptional activation complex can bind DNA as a monomer, but it can also dimerize on DNA-binding sites that are properly oriented and spaced. However, the significance of Notch dimerization is unknown. Here, we show that dimeric Notch transcriptional complexes are required for T-cell maturation and leukemic transformation but are dispensable for T-cell fate specification from a multipotential precursor. The varying requirements for Notch dimerization result from the differential sensitivity of specific Notch target genes. In particular, c-Myc and pre-T-cell antigen receptor α (Ptcra) are dimerization-dependent targets, whereas Hey1 and CD25 are not. These findings identify functionally important differences in the responsiveness among Notch target genes attributable to the formation of higher-order complexes. Consequently, it may be possible to develop a new class of Notch inhibitors that selectively block outcomes that depend on Notch dimerization (e.g., leukemogenesis).

SummaryT cells develop in the thymus. Previous work suggested an early separation of lymphoid from myeloerythroid lineages during hematopoiesis, and hypothesized the thymus was settled exclusively by lymphoid-restricted hematopoietic progenitors. Recent data have instead established the existence of lymphoid-myeloid progenitors, which possess lymphoid and myeloid lineage potentials but lack erythroid potential. Myeloid and lymphoid potentials are present at the clonal level in early thymic progenitors, confirming that progenitors settling the thymus include lymphoid-myeloid progenitors. These results revise our view of the T lineage branch of hematopoiesis, and focus attention on the generation, circulation, and homing of lymphoid-myeloid progenitors to the thymus.

Common myeloid progenitors (CMPs) were first identified as progenitors that were restricted to myeloid and erythroid lineages. However, it was recently demonstrated that expression of both lymphoidand myeloid-related genes could be detected in myeloid progenitors. Furthermore, these progenitors were able to give rise to T and B lymphocytes, in addition to myeloid cells. Yet, it was not known whether these progenitors were multipotent at the clonogenic level or there existed heterogeneity within these progenitors with different lineage potential. Here we report that previously defined CMPs possess T-lineage potential, and that this is exclusively found in the Flt3 ؉ CD150 -subset of CMPs at the clonal level. In contrast, we did not detect B-lineage potential in CMP subsets. Therefore, these IntroductionAll blood lineages ultimately arise from hematopoietic stem cells (HSCs). HSCs, along with downstream multipotent progenitors (MPPs) and lymphoid-primed MPPs (LMPPs), are present within a small pool of bone marrow (BM) cells with the surface phenotype of LSK (Lineage-marker Ϫ Sca1 ϩ Kit ϩ ). 1,2 Outside of LSK progenitors, a population of BM progenitors characterized as Lin -Sca1 -Kit ϩ CD34 ϩ Fc␥R low was found to be able to give rise to myeloid or erythroid cells, but appeared to lack the ability to generate lymphoid cells in in vivo and in vitro assays. 3 Thus it appeared these cells were restricted to myeloid/erythroid lineages. Because myeloid and erythroid potential was present at the clonogenic level within this population, these progenitors were termed common myeloid progenitors, or CMPs. 3 Granulocyte/monocyte progenitors (GMPs) and megakaryocyte/erythrocyte progenitors (MEPs) were also identified. As GMPs and MEPs possessed a more restricted developmental potential than CMPs, it was postulated that GMPs and MEPs were downstream of CMPs and that CMPs gave rise to myeloid cells or erythroid cells via GMPs or MEPs, respectively. 3 More recent work has suggested that a degree of lymphoid potential persists in myeloid progenitors. First, myeloid progenitors transduced with stabilized ␤-catenin were able to give rise to T and B lymphocytes. 4 Using Ikaros-reporter mice, 5 expression of both lymphoid-and myeloid-related genes was detected in Lin -Sca1 -Kit ϩ GFP Ikarosϩ BM cells, suggesting the existence of lymphoidmyeloid progenitors within the previously thought myeloid/ erythroid-restricted progenitor compartment. 6 It was further shown that some of these progenitors were able to give rise to T and B lymphocytes, in addition to myeloid cells, at the population level. 6 However, it was not known whether individual cells within this population were multipotent at the clonal level. Alternatively, there might be heterogeneity within this population where subsets of progenitors possess different lineage potentials. Indeed, recent work has clearly established heterogeneity for myeloid and erythroid lineage potentials among CMPs. CMPs can be subdivided into CD150 -(preGM) and CD150 ϩ (preMegE) populations, with ...