Bone Marrow Myeloid Cells Regulate Myeloid-Biased Hematopoietic Stem Cells via a Histamine-Dependent Feedback Loop.

Myeloid-biased hematopoietic stem cells (MB-HSCs) play critical roles in recovery from injury, but little is known about how they are regulated within the bone marrow niche. Here we describe an auto-/paracrine physiologic circuit that controls quiescence of MB-HSCs and hematopoietic progenitors marked by histidine decarboxylase (Hdc). Committed Hdc+ myeloid cells lie in close anatomical proximity to MB-HSCs and produce histamine, which activates the H2 receptor on MB-HSCs to promote their quiescence and self-renewal. Depleting histamine-producing cells enforces cell cycle entry, induces loss of serial transplant capacity, and sensitizes animals to chemotherapeutic injury. Increasing demand for myeloid cells via lipopolysaccharide (LPS) treatment specifically recruits MB-HSCs and progenitors into the cell cycle; cycling MB-HSCs fail to revert into quiescence in the absence of histamine feedback, leading to their depletion, while an H2 agonist protects MB-HSCs from depletion after sepsis. Thus, histamine couples lineage-specific physiological demands to intrinsically primed MB-HSCs to enforce homeostasis.

Histidine decarboxylase (HDC)-expressing granulocytic myeloid cells induce and recruit Foxp3+ regulatory T cells in murine colon cancer.

The colorectal tumor microenvironment contains a diverse population of myeloid cells that are recruited and converted to immunosuppressive cells, thus facilitating tumor escape from immunoediting. We have identified a genetically and functionally distinct subset of dynamic bone marrow myeloid cells that are characterized by histidine decarboxylase (HDC) expression. Lineage tracing in Hdc-CreERT2;R26-LSL-tdTomato mice revealed that in homeostasis, there is a strong bias by HDC+ myeloid cells toward the CD11b+Ly6Ghi granulocytic lineage, which was accelerated during azoxymethane/dextran sodium sulfate (AOM/DSS)-induced colonic carcinogenesis. More importantly, HDC+ myeloid cells strongly promoted colonic tumorigenesis, and colon tumor progression was profoundly suppressed by diphtheria toxin A (DTA)-mediated depletion of HDC+ granulocytic myeloid cells. In addition, tumor infiltration by Foxp3+ regulatory T cells (Tregs) was markedly impaired following HDC+ myeloid cell depletion. We identified an HDC+ myeloid-derived Cxcl13/Cxcr5 axis that mediated Foxp3 expression and Treg proliferation. Ablation of HDC+ myeloid cells or disruption of the Cxcl13/Cxcr5 axis by gene knockdown impaired the production and recruitment of Tregs. Cxcl13 induction of Foxp3 expression in Tregs during tumorigenesis was associated with Stat3 phosphorylation. Overall, HDC+ granulocytic myeloid cells affect CD8+ T cells directly and indirectly through the modulation of Tregs and thus appear to play key roles in suppressing tumoricidal immunity.

IL-17 producing mast cells promote the expansion of myeloid-derived suppressor cells in a mouse allergy model of colorectal cancer.

Food allergy can influence the development of colorectal cancer, although the underlying mechanisms are unclear. While mast cells (MC) store and secrete histamine, immature myeloid cells (IMC) are the major site of histidine decarboxylase (HDC) expression, the enzyme responsible for histamine production. From our earlier work, we hypothesized that histamine is central to the association between allergy and colorectal carcinogenesis through its influence on the MC-MDSC axis. Here, we show that in wild type (WT) mice, ovalbumin (OVA) immunization elicits a typical TH2 response. In contrast, in HDC-/- mice, the response to OVA allergy is skewed towards infiltration by IL-17 expressing MCs. This response is inhibited by histamine treatment. The HDC-/- allergic IL-17-expressing MCs promote MDSC proliferation and upregulation of Cox-2 and Arg-1. OVA allergy in HDC-/- mice increases the growth of colon tumor cells in both the MC38 tumor cell implantation model and the AOM/DSS carcinogenesis model. Taken together, our results show that histamine represses IL-17-expressing MCs and their subsequent activation of MDSCs, attenuating the risk of colorectal cancer in the setting of food allergy. Targeting the MC-MDSC axis may be useful for cancer prevention and treatment in patients, particularly in those with food allergy.

Evaluating the potential for halogen bonding in the oxyanion hole of ketosteroid isomerase using unnatural amino acid mutagenesis.

There has recently been an increasing interest in controlling macromolecular conformations and interactions through halogen bonding. Halogen bonds are favorable electrostatic interactions between polarized, electropositive chlorine, bromine, or iodine atoms and electronegative atoms such as oxygen or nitrogen. These interactions have been likened to hydrogen bonds in terms of their favored acceptor molecules, their geometries, and their energetics. We asked whether a halogen bond could replace a hydrogen bond in the oxyanion hole of ketosteroid isomerase, using semisynthetic enzymes containing para-halogenated phenylalanine derivatives to replace the tyrosine hydrogen bond donor. Formation of a halogen bond to the oxyanion in the transition state would be expected to rescue the effects of mutation to phenylalanine, but all of the halogenated enzymes were comparable in activity to the phenylalanine mutant. We conclude that, at least in this active site, a halogen bond cannot functionally replace a hydrogen bond.

Genetic ablation of NMDA receptor subunit NR3B in mouse reveals motoneuronal and nonmotoneuronal phenotypes.

NR3B is a modulatory subunit of the NMDA receptor, abundantly expressed in both cranial and spinal somatic motoneurons and at lower levels in other regions of the brain as well. Recently, we found the human NR3B gene (GRIN3B) to be highly genetically heterogeneous, and that approximately 10% of the normal European-American population lacks NR3B due to homozygous occurrence of a null allele in the gene. Therefore, it is especially important to understand the phenotypic consequences of the genetic loss of NR3B in both humans and animal models. We here provide results of behavioral analysis of mice genetically lacking NR3B, which is an ideal animal model due to homogeneity in genetic and environmental background. The NR3B(-/-) mice are viable and fertile. Consistent with the expression of NR3B in somatic motoneurons, the NR3B(-/-) mice showed a moderate but significant impairment in motor learning or coordination, and decreased activity in their home cages. Remarkably, the NR3B(-/-) mice showed a highly increased social interaction with their familiar cage mates in their home cage but moderately increased anxiety-like behaviour and decreased social interaction in a novel environment, consistent with the inhibitory role of NR3B on the functions of NMDA receptors. This work is the first reporting of the functional significance of NR3B in vivo and may give insight into the contribution of genetic variability of NR3B in the phenotypic heterogeneity among human population.

Inhibition, escape, and attenuated growth of severe acute respiratory syndrome coronavirus treated with antisense morpholino oligomers.

The recently emerged severe acute respiratory syndrome coronavirus (SARS-CoV) is a potent pathogen of humans and is capable of rapid global spread. Peptide-conjugated antisense morpholino oligomers (P-PMO) were designed to bind by base pairing to specific sequences in the SARS-CoV (Tor2 strain) genome. The P-PMO were tested for their capacity to inhibit production of infectious virus as well as to probe the function of conserved viral RNA motifs and secondary structures. Several virus-targeted P-PMO and a random-sequence control P-PMO showed low inhibitory activity against SARS coronavirus. Certain other virus-targeted P-PMO reduced virus-induced cytopathology and cell-to-cell spread as a consequence of decreasing viral amplification. Active P-PMO were effective when administered at any time prior to peak viral synthesis and exerted sustained antiviral effects while present in culture medium. P-PMO showed low nonspecific inhibitory activity against translation of nontargeted RNA or growth of the arenavirus lymphocytic choriomeningitis virus. Two P-PMO targeting the viral transcription-regulatory sequence (TRS) region in the 5' untranslated region were the most effective inhibitors tested. After several viral passages in the presence of a TRS-targeted P-PMO, partially drug-resistant SARS-CoV mutants arose which contained three contiguous base point mutations at the binding site of a TRS-targeted P-PMO. Those partially resistant viruses grew more slowly and formed smaller plaques than wild-type SARS-CoV. These results suggest PMO compounds have powerful therapeutic and investigative potential toward coronavirus infection.

Disulfide bonding arrangements in active forms of the somatomedin B domain of human vitronectin.

The N-terminal cysteine-rich somatomedin B (SMB) domain (residues 1-44) of the human glycoprotein vitronectin contains the high-affinity binding sites for plasminogen activator inhibitor-1 (PAI-1) and the urokinase receptor (uPAR). We previously showed that the eight cysteine residues of recombinant SMB (rSMB) are organized into four disulfide bonds in a linear uncrossed pattern (Cys(5)-Cys(9), Cys(19)-Cys(21), Cys(25)-Cys(31), and Cys(32)-Cys(39)). In the present study, we use an alternative method to show that this disulfide bond arrangement remains a major preferred one in solution, and we determine the solution structure of the domain using NMR analysis. The solution structure shows that the four disulfide bonds are tightly packed in the center of the domain, replacing the traditional hydrophobic core expected for a globular protein. The few noncysteine hydrophobic side chains form a cluster on the outside of the domain, providing a distinctive binding surface for the physiological partners PAI-1 and uPAR. The hydrophobic surface consists mainly of side chains from the loop formed by the Cys(25)-Cys(31) disulfide bond, and is surrounded by conserved acidic and basic side chains, which are likely to contribute to the specificity of the intermolecular interactions of this domain. Interestingly, the overall fold of the molecule is compatible with several arrangements of the disulfide bonds. A number of different disulfide bond arrangements were able to satisfy the NMR restraints, and an extensive series of conformational energy calculations performed in explicit solvent confirmed that several disulfide bond arrangements have comparable stabilization energies. An experimental demonstration of the presence of alternative disulfide conformations in active rSMB is provided by the behavior of a mutant in which Asn(14) is replaced by Met. This mutant has the same PAI-1 binding activity as rVN1-51, but its fragmentation pattern following cyanogen bromide treatment is incompatible with the linear uncrossed disulfide arrangement. These results suggest that active forms of the SMB domain may have a number of allowed disulfide bond arrangements as long as the Cys(25)-Cys(31) disulfide bond is preserved.