Constitutive Expression of Inducible Cyclic Adenosine Monophosphate Early Repressor (ICER) in Cycling Quiescent Hematopoietic Cells: Implications for Aging Hematopoietic Stem Cells.

Despite extensive insights on the interaction between hematopoietic stem cells (HSCs) and the supporting bone marrow (BM) stroma in hematopoietic homeostasis there remains unanswered questions on HSC regulation. We report on the mechanism by which HSCs attain cycling quiescence by addressing a role for inducible cyclic AMP early repressor (ICER). ICER negatively transcriptional regulators of cAMP activators such as CREM and CREB. These activators can be induced by hematopoietic stimulators such as cytokines. We isolated subsets of hematopoietic cells from ten healthy donors: CD34+CD38-/c-kit + (primitive progenitor), CD34+CD38+/c-kitlow (mature progenitor) and CD34-CD38+/-/c-kitlow/- (differentiated lineage-). The relative maturity of the progenitors were verified in long-term culture initiating assay. Immunoprecipitation indicated the highest level of ICER in the nuclear extracts of CD34+/CD38- cells. Phospho (p)-CREM was also present suggesting a balance between ICER and p-CREM in HSC. ICER seems to be responsible for decrease in G1 transition, based on reduced Cdk4 protein, decreased proliferation and functional studies with propidium iodide. There were no marked changes in the cycling inhibitors, p15 and p-Rb, suggesting that ICER may act independently of other cycling inhibitors. The major effects of ICER were validated with BM mononuclear cells (BMNCs) in which ICER was ectopically expressed, and with BMNCs resistant to 5-fluorouracil- or cyclophosphamide. In total, this study ascribes a novel role for ICER in G1 checkpoint regulation in HSCs. These findings are relevant to gene therapy that require engineering of HSCs, age-related disorders that are associated with hematopoietic dysfunction and other hematological disorders.

Preexisting helminth infection induces inhibition of innate pulmonary anti-tuberculosis defense by engaging the IL-4 receptor pathway.

Tuberculosis and helminthic infections coexist in many parts of the world, yet the impact of helminth-elicited Th2 responses on the ability of the host to control Mycobacterium tuberculosis (Mtb) infection has not been fully explored. We show that mice infected with the intestinal helminth Nippostrongylus brasiliensis (Nb) exhibit a transitory impairment of resistance to airborne Mtb infection. Furthermore, a second dose of Nb infection substantially increases the bacterial burden in the lungs of co-infected mice. Interestingly, the Th2 response in the co-infected animals did not impair the onset and development of the protective Mtb-specific Th1 cellular immune responses. However, the helminth-induced Th2 environment resulted in the accumulation of alternatively activated macrophages (AAMs) in the lung. Co-infected mice lacking interleukin (IL) 4Rα exhibited improved ability to control Mtb infection, which was accompanied by significantly reduced accumulation of AAMs. Moreover, IL-4Rα(-/-) mice adoptively transferred with wild-type macrophages had a significantly higher Mtb load in their lungs compared with those that received IL-4Rα(-/-) macrophages, suggesting a direct contribution for the IL-4R pathway to the heightened susceptibility of co-infected animals. The Th2 response can thus enhance the intracellular persistence of Mtb, in part by mediating the alternative activation of macrophages via the IL-4Rα signaling pathway.

A paradoxical role for IFN-gamma in the immune properties of mesenchymal stem cells during viral challenge.

OBJECTIVE: The functional "plasticity" and immune-suppressive effects of human bone marrow (BM)-derived mesenchymal stem cells (MSC) provide them with the potential to be used across allogeneic barriers. The immunosuppressive properties of MSC may be detrimental in a clinical setting in which viral exposure is common. The study hypothesizes that MSC-derived IFN-gamma could offset the immune-suppressive functions of MSC and mediate partial CTL responses during viral infection. METHODS: CTL responses were studied in bioassays with (51)Cr-P815 targets and PBMC (uninfected or infected) as effectors. Immunofluorescence studied the relative expression of CD8(+) cells. Cytokine analyses were performed with microarrays. Roles for IFN-gamma in CTL responses were studied with IFNgammaRI mAb or with MSC knockdown for IFN-gamma by siRNA (pPMSKH1-IFNgamma). RESULTS: MSC showed no significant effect on circulating CTL of healthy subjects. For virus-induced CTL, MSC demonstrated approximately 50% suppression. CD8(+) cell expansion could not explain the suppressive effects of MSC. Soluble factors produced by MSC were responsible for the retention of 50% CTL responses. Cytokine microarray analyses, noncontact cultures, and functional assays identified a role for IFN-gamma. MSC were identified as the relevant source of IFN-gamma. CONCLUSION: The results show a facilitating role of IFN-gamma on CTL responses, although paradoxical in light of the veto properties of MSC. This report shows that in cases where MSC are used in transplantation for repair of damaged tissue, they can exert an additional role by protecting the host to viral challenges and thereby protect from its immunosuppressive properties.

Facilitating role of preprotachykinin-I gene in the integration of breast cancer cells within the stromal compartment of the bone marrow: a model of early cancer progression.

Despite early detection of breast cancer, patients' survival may be compromised if the breast cancer cells (BCCs) enter the bone marrow (BM). It is highly probable that BCCs enter the BM long before clinical detection. An in vitro coculture model with BM stroma and BCCs (cell lines; primary cells from stage III BC, n = 7, and stage M0, n = 3) mimicked early entry of BCCs into the BM. In coculture, BCCs exhibit contact inhibition and do not require otherwise needed growth supplements. Stromal growth rate was increased 2-fold in coculture. The inclusion of BCCs in stromal support of long-term culture-initiating cell assay frequencies show no difference (38 +/- 3 versus 36 +/- 6). Nontumorigenic breast cells (patients and cell lines) did not survive in coculture, suggesting that the model could select for malignant population in surgical breast tissues. Cocultures were able to select cells with 73 +/- 7% cloning efficiencies and with the ability to form cocultures with BM stroma. Preprotachykinin-I (PPT-I), a gene that is conserved by evolution, facilitates BCC integration as part of the stromal compartment. This was deduced as follows: (a) nontumorigenic breast cells (n = 4) genetically engineered to express PPT-I and led to anchorage-independent growth, foci formation, and formation of cocultures; and (b) suppression of PPT-I in BCCs (n = 5) with pPMSKH1-PPT-I small interfering RNA reverted the cells to nontumorigenic phenotypes and was undetectable in the BM nude mice. The evidence supports that the PPT-I gene facilitates the integration of BCCs in the stromal compartment during a period before clinical detection, without disrupting hematopoietic activity.

Veto-like activity of mesenchymal stem cells: functional discrimination between cellular responses to alloantigens and recall antigens.

Trans-differentiation of stem cells shows promise for use in tissue repair medicine. Although poorly defined, mesenchymal stem cells (MSC) appear useful for applications in repair medicine. Despite the low frequency of MSC, they are relatively easy to expand. The expression of MHC class II on MSC, however, could deter their use in repair medicine, since these molecules could stimulate an allogeneic host response. This study sought to compare the immune stimulatory and suppressive effects of MSC. Primary human MSC were cultured from bone marrow aspirates and then passaged at least three times before use in assays. Morphologically, MSC were symmetrical; were SH2(+), MHC class II(+), CD45(-), CD44(+), CD31(-), CD14(-), proly-4-hydroxylase(-); and showed normal karyotype patterns and elevated telomerase activities. MSC elicited significant stimulatory responses when cocultured with allogeneic PBMC. Despite the production of different types of growth factors, allogeneic effects of MSC could not be explained by the production of these growth factors. One-way MLR reactions were significantly blunted by third-party MSC. Similar suppression was not observed for responses to three different recall Ags. Based on these functional differences by MSC in responses to allo- and recall Ags, we examined whether MSC could exert veto-like functions. We showed that MSC could blunt the cytotoxic effects of allogeneic-induced effectors to mitogen-activated targets. The results showed that although MSC elicited allogeneic responses in a model that mimics a graft-vs-host reaction, they also exerted veto-like activity, but caused no effect on responses to recall Ags.

Crosstalk between neurokinin receptors is relevant to hematopoietic regulation: cloning and characterization of neurokinin-2 promoter.

Neurokinin (NK)-1 and NK-2 receptors regulate hematopoiesis by interacting with neurotransmitters that belong to the tachykinin. This report studies the relationship between NK-1 and NK-2 in primary human bone marrow (BM) stroma, which supports hematopoiesis. Use of NK receptor antagonists and deficient stromal cells indicate that the neurotransmitter, substance P (SP), could exert dual hematopoietic effects (inhibitory or stimulatory), depending on the interacting receptor and crosstalk between NK-1 and NK-2. Cloning and identification of the minimal promoter for NK-2 and comparison with NK-1 promoter showed that the hematopoietic functions of NK receptors involve receptor crosstalk and the particular cytokine (IL-3, GM-CSF, TGF-beta or IL-1alpha). Crosstalk between NK-1 and NK-2 adds to communication within neural-hematopoietic axis.