Regulation of hematopoiesis in a sea of chemokine family members with a plethora of redundant activities

CCL3 in the bone marrow microenvironment causes bone loss and bone marrow adiposity in aged mice

The central physiological role of the bone marrow renders bone marrow stromal cells (BMSCs) particularly sensitive to aging. With bone aging, BMSCs acquire a differentiation potential bias in favor of adipogenesis over osteogenesis, and the underlying molecular mechanisms remain unclear. Herein, we investigated the factors underlying age-related changes in the bone marrow and their roles in BMSCs' differentiation. Antibody array revealed that CC chemokine ligand 3 (CCL3) accumulation occurred in the serum of naturally aged mice along with bone aging phenotypes, including bone loss, bone marrow adiposity, and imbalanced BMSC differentiation. In vivo Ccl3 deletion could rescue these phenotypes in aged mice. CCL3 improved the adipogenic differentiation potential of BMSCs, with a positive feedback loop between CCL3 and C/EBPα. CCL3 activated C/EBPα expression via STAT3, while C/EBPα activated CCL3 expression through direct promoter binding, facilitated by DNA hypomethylation. Moreover, CCL3 inhibited BMSCs' osteogenic differentiation potential by blocking β-catenin activity mediated by ERK-activated Dickkopf-related protein 1 upregulation. Blocking CCL3 in vivo via neutralizing antibodies ameliorated trabecular bone loss and bone marrow adiposity in aged mice. This study provides insights regarding age-related bone loss and bone marrow adiposity pathogenesis and lays a foundation for the identification of new targets for senile osteoporosis treatment.

DEK, a nuclear protein, is chemotactic for hematopoietic stem/progenitor cells acting through CXCR2 and Gαi signaling

Few cytokines/growth modulating proteins are known to be chemoattractants for hematopoietic stem (HSC) and progenitor cells (HPC); stromal cell-derived factor 1α (SDF1α/CXCL12) being the most potent known such protein. DEK, a nuclear DNA-binding chromatin protein with hematopoietic cytokine-like activity, is a chemotactic factor attracting mature immune cells. Transwell migration assays were performed to test whether DEK serves as a chemotactic agent for HSC/HPC. DEK induced dose- and time-dependent directed migration of lineage negative (Lin- ) Sca-1+ c-Kit+ (LSK) bone marrow (BM) cells, HSCs and HPCs. Checkerboard assays demonstrated that DEK's activity was chemotactic (directed), not chemokinetic (random migration), in nature. DEK and SDF1α compete for HSC/HPC chemotaxis. Blocking CXCR2 with neutralizing antibodies or inhibiting Gαi protein signaling with Pertussis toxin pretreatment inhibited migration of LSK cells toward DEK. Thus, DEK is a novel and rare chemotactic agent for HSC/HPC acting in a direct or indirect CXCR2 and Gαi protein-coupled signaling-dependent manner.

CXCL15/Lungkine has suppressive activity on proliferation and expansion of multi-potential, erythroid, granulocyte and macrophage progenitors in S-phase specific manner

Cytokines/chemokines regulate hematopoiesis, most having multiple cell actions. Numerous but not all chemokine family members act as negative regulators of hematopoietic progenitor cell (HPC) proliferation, but very little is known about such effects of the chemokine, CXCL15/Lungkine. We found that CXCL15/Lungkine-/- mice have greatly increased cycling of multi cytokine-stimulated bone marrow and spleen hematopoietic progenitor cells (HPCs: CFU-GM, BFU-E, and CFU-GEMM) and CXCL15 is expressed in many bone marrow progenitor and other cell types. This suggests that CXCL15/Lungkine acts as a negative regulator of the cell cycling of these HPCs in vivo. Recombinant murine CXCL15/Lungkine, decreased numbers of functional HPCs during cytokine-enhanced ex-vivo culture of lineage negative mouse bone marrow cells. Moreover, CXCL15/Lungkine, through S-Phase specific actions, was able to suppress in vitro colony formation of normal wildtype mouse bone marrow CFU-GM, CFU-G, CFU-M, BFU-E, and CFU-GEMM. This clearly identifies the negative regulatory activity of CXCL15/Lungkine on proliferation of multiple types of mouse HPCs.

Сord blood hematopoietic stem cells ex vivo enhance the bipotential commitment of adipose mesenchymal stromal progenitors

AIMS

Stroma-dependent ex vivo expansion of hematopoietic stem progenitor cells (HSPCs) is a valid approach for cell therapy needs. Our goal was to verify whether HSPCs can affect stromal cells to optimize their functions during ex vivo expansion.

MAIN METHODS

HSPCs from cord blood (cb) were cocultured with growth-arrested adipose mesenchymal stromal cells (MSCs). Commitment-related transcriptional and secretory profiles as well as hematopoiesis-supportive activity of intact and osteo-induced MSCs were examined.

KEY FINDINGS

During expansion, cbHSPCs affected the functional state of MSCs, contributing to the formation of early stromal progenitors with a bipotential osteo-adipogenic profile. This was evidenced by the upregulation of certain MSC genes of osteo- and adipodifferentiation (ALPL, RUNX2, BGLAP, CEBPA, ADIPOQ), as well as by elevated alkaline phosphatase activity and altered osteoprotein patterns. Joint paracrine profiles upon coculture were characterized by a balance of "positive" (GM-SCF) and "negative" (IP-10, MIP-1α, MCP-3) myeloid regulators, effectively supporting expansion of both committed and primitive cbHSPCs. Short-term (72 h) osteoinduction prior to coculture resulted in more pronounced shift of the bipotential transcriptomic and osteoprotein profiles. The increased proportions of late primitive CD133^-/CD34⁺cbHSPCs and unipotent CFUs suggested that cbHSPCs after expansion on osteo-MSCs were more committed versus cbHSPCs from coculture with non-differentiated MSCs.

SIGNIFICANCE

During ex vivo expansion, cbHSPCs can drive the bipotential osteo-adipogenic commitment of MSCs, providing a specific hematopoiesis-supportive milieu. Short-term preliminary osteo-induction enhanced the development of the bipotential profile, leading to more pronounced functional polarization of cbHSPCs, which may be of interest in an applied context.

Platelets Boost Recruitment of CD133+ Bone Marrow Stem Cells to Endothelium and the Rodent Liver-The Role of P-Selectin/PSGL-1 Interactions

We previously demonstrated that clinical administration of mobilized CD133⁺ bone marrow stem cells (BMSC) accelerates hepatic regeneration. Here, we investigated the potential of platelets to modulate CD133⁺BMSC homing to hepatic endothelial cells and sequestration to warm ischemic livers. Modulatory effects of platelets on the adhesion of CD133⁺BMSC to human and mouse liver-sinusoidal- and micro- endothelial cells (EC) respectively were evaluated in in vitro co-culture systems. CD133⁺BMSC adhesion to all types of EC were increased in the presence of platelets under shear stress. This platelet effect was mostly diminished by antagonization of P-selectin and its ligand P-Selectin-Glyco-Ligand-1 (PSGL-1). Inhibition of PECAM-1 as well as SDF-1 receptor CXCR4 had no such effect. In a model of the isolated reperfused rat liver subsequent to warm ischemia, the co-infusion of platelets augmented CD133⁺BMSC homing to the injured liver with heightened transmigration towards the extra sinusoidal space when compared to perfusion conditions without platelets. Extravascular co-localization of CD133⁺BMSC with hepatocytes was confirmed by confocal microscopy. We demonstrated an enhancing effect of platelets on CD133⁺BMSC homing to and transmigrating along hepatic EC putatively depending on PSGL-1 and P-selectin. Our insights suggest a new mechanism of platelets to augment stem cell dependent hepatic repair.

Ubiquitous overexpression of CXCL12 confers radiation protection and enhances mobilization of hematopoietic stem and progenitor cells

C-X-C motif chemokine ligand 12 (CXCL12; aka SDF1α) is a major regulator of a number of cellular systems, including hematopoiesis, where it influences hematopoietic cell trafficking, proliferation, and survival during homeostasis and upon stress and disease. A variety of constitutive, temporal, ubiquitous, and cell-specific loss-of-function models have documented the functional consequences on hematopoiesis upon deletion of Cxcl12. Here, in contrast to loss-of-function experiments, we implemented a gain-of-function approach by generating a doxycycline-inducible transgenic mouse model that enables spatial and temporal overexpression of Cxcl12. We demonstrated that ubiquitous CXCL12 overexpression led to an increase in multipotent progenitors in the bone marrow and spleen. The CXCL12+ mice displayed reduced reconstitution potential as either donors or recipients in transplantation experiments. Additionally, we discovered that Cxcl12 overexpression improved hematopoietic stem and progenitor cell mobilization into the blood, and conferred radioprotection by promoting quiescence. Thus, this new CXCL12+ mouse model provided new insights into major facets of hematopoiesis and serves as a versatile resource for studying CXCL12 function in a variety of contexts.

Regulation of hematopoiesis by the chemokine system

Although chemokines are best known for their role in directing cell migration, accumulating evidence indicate their involvement in many other processes. This review focus on the role of chemokines in hematopoiesis with an emphasis on myelopoiesis. Indeed, many chemokine family members are an important component of the cytokine network present in the bone marrow that controls proliferation, retention, and mobilization of hematopoietic progenitors.

Secreted nuclear protein DEK regulates hematopoiesis through CXCR2 signaling

The nuclear protein DEK is an endogenous DNA-binding chromatin factor regulating hematopoiesis. DEK is one of only 2 known secreted nuclear chromatin factors, but whether and how extracellular DEK regulates hematopoiesis is not known. We demonstrated that extracellular DEK greatly enhanced ex vivo expansion of cytokine-stimulated human and mouse hematopoietic stem cells (HSCs) and regulated HSC and hematopoietic progenitor cell (HPC) numbers in vivo and in vitro as determined both phenotypically (by flow cytometry) and functionally (through transplantation and colony formation assays). Recombinant DEK increased long-term HSC numbers and decreased HPC numbers through a mechanism mediated by the CXC chemokine receptor CXCR2 and heparan sulfate proteoglycans (HSPGs) (as determined utilizing Cxcr2-/- mice, blocking CXCR2 antibodies, and 3 different HSPG inhibitors) that was associated with enhanced phosphorylation of ERK1/2, AKT, and p38 MAPK. To determine whether extracellular DEK required nuclear function to regulate hematopoiesis, we utilized 2 mutant forms of DEK: one that lacked its nuclear translocation signal and one that lacked DNA-binding ability. Both altered HSC and HPC numbers in vivo or in vitro, suggesting the nuclear function of DEK is not required. Thus, DEK acts as a hematopoietic cytokine, with the potential for clinical applicability.

Chemokines as a Conductor of Bone Marrow Microenvironment in Chronic Myeloid Leukemia

All blood lineage cells are generated from hematopoietic stem cells (HSCs), which reside in bone marrow after birth. HSCs self-renew, proliferate, and differentiate into mature progeny under the control of local microenvironments including hematopoietic niche, which can deliver regulatory signals in the form of bound or secreted molecules and from physical cues such as oxygen tension and shear stress. Among these mediators, accumulating evidence indicates the potential involvement of several chemokines, particularly CXCL12, in the interaction between HSCs and bone marrow microenvironments. Fusion between breakpoint cluster region (BCR) and Abelson murine leukemia viral oncogene homolog (ABL)-1 gene gives rise to BCR-ABL protein with a constitutive tyrosine kinase activity and transforms HSCs and/or hematopoietic progenitor cells (HPCs) into disease-propagating leukemia stem cells (LSCs) in chronic myeloid leukemia (CML). LSCs can self-renew, proliferate, and differentiate under the influence of the signals delivered by bone marrow microenvironments including niche, as HSCs can. Thus, the interaction with bone marrow microenvironments is indispensable for the initiation, maintenance, and progression of CML. Moreover, the crosstalk between LSCs and bone marrow microenvironments can contribute to some instances of therapeutic resistance. Furthermore, evidence is accumulating to indicate the important roles of bone marrow microenvironment-derived chemokines. Hence, we will herein discuss the roles of chemokines in CML with a focus on bone marrow microenvironments.

Dysregulation of Chemokine/Chemokine Receptor Axes and NK Cell Tissue Localization during Diseases

Chemokines are small chemotactic molecules that play key roles in physiological and pathological conditions. Upon signaling via their specific receptors, chemokines regulate tissue mobilization and trafficking of a wide array of immune cells, including natural killer (NK) cells. Current research is focused on analyzing changes in chemokine/chemokine receptor expression during various diseases to interfere with pathological trafficking of cells or to recruit selected cell types to specific tissues. NK cells are a heterogeneous lymphocyte population comprising several subsets endowed with distinct functional properties and mainly representing distinct stages of a linear development process. Because of their different functional potential, the type of subset that accumulates in a tissue drives the final outcome of NK cell-regulated immune response, leading to either protection or pathology. Correspondingly, chemokine receptors, including CXCR4, CXCR3, and CX₃CR1, are differentially expressed by NK cell subsets, and their expression levels can be modulated during NK cell activation. At first, this review will summarize the current knowledge on the contribution of chemokines to the localization and generation of NK cell subsets in homeostasis. How an inappropriate chemotactic response can lead to pathology and how chemokine targeting can therapeutically affect tissue recruitment/localization of distinct NK cell subsets will also be discussed.

Modulation of Hematopoietic Chemokine Effects In Vitro and In Vivo by DPP-4/CD26

Dipeptidyl peptidase 4 (DPP4)/CD26 truncates certain proteins, and this posttranslational modification can influence their activity. Truncated (T) colony-stimulating factors (CSFs) are decreased in potency for stimulating proliferation of hematopoietic progenitor cells (HPCs). T-CXCL12, a modified chemokine, is inactive as an HPC chemotactic, survival, and enhancing factor for replating or ex-vivo expansion of HPCs. Moreover, T-CSFs and T-CXCL12 specifically downmodulates the positively acting effects of their own full-length molecule. Other chemokines have DPP4 truncation sites. In the present study, we evaluated effects of DPP4 inhibition (by Diprotin A) or gene deletion of HPC on chemokine inhibition of multicytokine-stimulated HPC, and on chemokine-enhancing effects on single CSF-stimulated HPC proliferation, as well as effects of DPP4 treatment of a number of chemokines. Myelosuppressive effects of chemokines with, but not without, a DPP4 truncation site were greatly enhanced in inhibitory potency by pretreating target bone marrow (BM) cells with Diprotin A, or by assaying their activity on dpp4/cd26(-/-) BM cells. DPP4 treatment of myelosuppressive chemokines containing a DPP4 truncation site produced a nonmyelosuppressive molecule, but one which had the capacity to block suppression by that unmodified chemokine both in vitro and in vivo. Additionally, DPP4 treatment ablated the single cytokine-stimulated HPC-enhancing activity of CCL3/MIP-1α and CCL4/MIP-1β, and blocked the enhancing activity of each unmodified molecule, in vitro and in vivo. These results highlight the functional posttranslational modulating effects of DPP4 on chemokine activities, and information offering additional biological insight into chemokine regulation of hematopoiesis.

Differential expression of CXCR4 and CXCR7 with various stem cell markers in paired human primary and recurrent glioblastomas

The chemokine CXCL12 (also termed SDF-1, stromal cell-derived factor-1) and its receptors CXCR4 and CXCR7 are known to play a pivotal role in tumor progression including glioblastomas (GBM). Previous investigations focused on the expression and functional roles of CXCR4 and CXCR7 in different GBM cell subpopulations, but comparative analysis in matched primary versus recurrent GBM samples are still lacking. Thus, here we investigated the expression of CXCR4 and CXCR7 on mRNA and protein level using matched primary and recurrent GBM pairs. Additionally, as GBM CXCR4-positive stem-like cells are supposed to give rise to recurrence, we compared the expression of both receptors in primary and recurrent GBM cells expressing either neural (MUSASHI-1) or embryonic stem cell markers (KLF-4, OCT-4, SOX-2, NANOG). We were able to show that both CXCR4 and CXCR7 were expressed at considerable mRNA and protein levels. CXCR7 was downregulated in relapse cases, and different groups regarding CXCR4/CXCR7 expression differences between primary and recurrent samples could be distinguished. A co-expression of both receptors was rare. In line with this, CXCR4 was co-expressed with all investigated neural and embryonic stem cell markers in both primary and recurrent tissues, whereas CXCR7 was mostly found on stem cell marker-negative cells, but was co-expressed with KLF-4 on a distinct GBM cell subpopulation. These results point to an individual role of CXCR4 and CXCR7 in stem cell marker-positive GBM cells in glioma progression and underline the opportunity to develop new therapeutic tools for GBM intervention.

The combined use of cytokine-induced killer cells and cyclosporine a for the treatment of aplastic anemia in a mouse model

In this study, we investigated the combined use of cytokine-induced killer (CIK) cells and cyclosporine A (CsA) to treat a mouse model of aplastic anemia (AA). CIK cells were cultured and injected alone or in combination with CsA into mice that had previously been induced into AA by busulfan and mouse interferon-γ (IFN-γ). The CIK cell-treated group had a survival rate of 55%, which was similar to the 60% survival rate observed in the CsA-treated group. The combination group showed a survival rate as high as 90%, while none of the mice in the no-treatment group survived to the end of the experiment. The CIK cells produced multiple cytokines, including several hematopoietic growth factors, which could promote the expansion of mouse bone marrow mononuclear cells in vitro. CsA reduced the proportion of CD4(+) T cells and the level of IFN-γ. The combined CIK cell and CsA treatment exhibited the best curative effect, a finding that might be due to the influence of these factors on both hematopoiesis and immunity. These data suggest that the combination of CIK cells and immunosuppressive therapy might be a candidate therapy for AA in the future.

Expansion and homing of umbilical cord blood hematopoietic stem and progenitor cells for clinical transplantation

The successful expansion of hematopoietic stem and progenitor cells (HSPCs) from umbilical cord blood (UCB) for transplantation could revolutionize clinical practice by improving transplantation-related outcomes and making available UCB units that have suboptimal cell doses for transplantation. New cytokine combinations appear able to promote HSPC growth with minimal differentiation into mature precursors and new agents, such as insulin-like growth factor-binding protein 2, are being used in clinical trials. Molecules that simulate the HSPC niche, such as Notch ligand, have also shown promise. Further improvements have been made with the use of mesenchymal stromal cells, which have made possible UCB expansion without a potentially deleterious prior CD34/CD133 cell selection step. Chemical molecules, such as copper chelators, nicotinamide, and aryl hydrocarbon antagonists, have shown excellent outcomes in clinical studies. The use of bioreactors could further add to HSPC studies in future. Drugs that could improve HSPC homing also appear to have potential in improving engraftment times in UCB transplantation. Technologies to expand HSPC from UCB and to enhance the homing of these cells appear to have attained the goal of accelerating hematopoietic recovery. Further discoveries and clinical studies are likely to make the goal of true HSPC expansion a reality for many applications in future.

Leukocyte chemoattractant receptors in human disease pathogenesis

Combinations of leukocyte attractant ligands and cognate heptahelical receptors specify the systemic recruitment of circulating cells by triggering integrin-dependent adhesion to endothelial cells, supporting extravasation, and directing specific intratissue localization via gradient-driven chemotaxis. Chemoattractant receptors also control leukocyte egress from lymphoid organs and peripheral tissues. In this article, we summarize the fundamental mechanics of leukocyte trafficking, from the evolution of multistep models of leukocyte recruitment and navigation to the regulation of chemoattractant availability and function by atypical heptahelical receptors. To provide a more complete picture of the migratory circuits involved in leukocyte trafficking, we integrate a number of nonchemokine chemoattractant receptors into our discussion. Leukocyte chemoattractant receptors play key roles in the pathogenesis of autoimmune diseases, allergy, inflammatory disorders, and cancer. We review recent advances in our understanding of chemoattractant receptors in disease pathogenesis, with a focus on genome-wide association studies in humans and the translational implications of mechanistic studies in animal disease models.

Modeling cell-cell interactions in regulating multiple myeloma initiating cell fate

Cancer initiating cells have been documented in multiple myeloma and believed to be a key factor that initiates and drives tumor growth, differentiation,metastasis, and recurrence of the diseases. Although myeloma initiating cells (MICs) are likely to share many properties of normal stem cells, the underlying mechanisms regulating the fate of MICs are largely unknown. Studies designed to explore such communication are urgently needed to enhance our ability to predict the fate decisions of ICs (self-renewal, differentiation, and proliferation). In this study, we developed a novel system to understand the intercellular communication between MICs and their niche by seamlessly integrating experimental data and mathematical model. We first designed dynamic cell culture experiments and collected three types of cells (side population cells, progenitor cells, and mature myeloma cells) under various cultural conditions with flow cytometry. Then we developed a lineage model with ordinary differential equations by considering secreted factors, self-renewal, differentiation, and other biological functions of those cells, to model the cell–cell interactions among the three cell types. Particle swarm optimization was employed to estimate the model parameters by fitting the experimental data to the lineage model. The theoretical results show that the correlation coefficient analysis can reflect the feedback loops among the three cell types, the intercellular feedback signaling can regulate cell population dynamics, and the culture strategies can decide cell growth. This study provides a basic framework of studying cell–cell interactions in regulating MICs fate.

HGF and SDF-1-mediated mobilization of CD133+ BMSC for hepatic regeneration following extensive liver resection

BACKGROUND

The molecular mechanisms of haematopoietic stem cells (HSC) mobilization and homing to the liver after partial hepatectomy (PH) remain largely unexplored.

METHODS

Functional liver volume loss and regain was determined by computerized tomography (CT) volumetry in 30 patients following PH. Peripheral HSC mobilization was investigated by fluorescence-activated cell sorting (FACS) analyses and cytokine enzyme-linked immunosorbent assay assays. Migration of purified HSC towards hepatic growth factor (HGF) and stroma-derived factor-1 (SDF-1) gradients was tested in vitro. Mice after 70% PH were examined for HSC mobilization by FACS and cytokine mRNA expression in the liver. FACS-sorted HSC were administered after PH and hepatocyte proliferation was evaluated by immunohistochemical staining for Ki67.

RESULTS

Impaired liver function was noted after extended hepatic resection when compared to smaller resections. Patients with large liver resections were characterized by significantly higher levels of peripheral HSC which were positively correlated with the extent of resected liver volume and its regain after 3 weeks. Increased plasma levels of HGF, SDF-1 and insulin like growth factor (IGF-1) were evident within the first 6 hours post resection. Migration assays of human HSC in vitro showed a specific target-demonstrated migration towards recombinant HGF and SDF-1 gradients in a concentration and specific receptor (c-Met and CXCR4) dependent manner. The evaluation of peripheral human alpha foetoprotein expression demonstrated pronounced stemness following increased CD133(+) HSC in the course of liver regeneration following PH. Our human data were further validated in a murine model of PH and furthermore demonstrated increased hepatocyte proliferation subsequent to CD133(+) HSC treatment.

CONCLUSION

HGF and SDF-1 are required for effective HSC mobilization and homing to the liver after hepatic resection. These findings have significant implications for potential therapeutic strategies targeting chemotactant modulation and stem cell mobilization for liver protection and regeneration.

Increasing hematopoietic stem cell yield to develop mice with human immune systems

Hematopoietic stem cells (HSCs) are unique in their capacity to give rise to all mature cells of the immune system. For years, HSC transplantation has been used for treatment of genetic and neoplastic diseases of the hematopoietic and immune systems. The sourcing of HSCs from human umbilical cord blood has salient advantages over isolation from mobilized peripheral blood. However, poor sample yield has prompted development of methodologies to expand HSCs ex vivo. Cytokines, trophic factors, and small molecules have been variously used to promote survival and proliferation of HSCs in culture, whilst strategies to lower the concentration of inhibitors in the culture media have recently been applied to promote HSC expansion. In this paper, we outline strategies to expand HSCs in vitro, and to improve engraftment and reconstitution of human immune systems in immunocompromised mice. To the extent that these “humanized” mice are representative of the endogenous human immune system, they will be invaluable tools for both basic science and translational medicine.

Targeting chemokines in proteinuria-induced renal disease

INTRODUCTION

Proteinuria is a common finding in glomerular diseases that contributes to the progression of chronic kidney injury. Tubular cells reabsorb the excess of albumin and other plasma proteins from the tubular lumen, triggering several pathophysiologic responses, such as overexpression of fibrogenic mediators and inflammatory chemokines. Chemokines are implicated both in the recruitment of inflammatory infiltrate and in a number of physiological and pathological processes related to protein overload.

AREAS COVERED

In recent years, the specific chemokines and their receptors and the intracellular signaling pathways involved in proteinuria-induced renal damage have been identified. This review provides an overview of the role of chemokines and their receptors in proteinuria-related renal disease and summarizes novel therapeutic approaches to restrain the progression of renal damage.

EXPERT OPINION

Inhibition of chemokine-induced biological activities is a promising therapeutic strategy in proteinuric disorders. Neutralizing antibodies and small organic molecules targeting chemokines and chemokine receptors have been proven to prevent inflammation and renal damage in experimental models of protein overload. Some of these compounds are currently being tested in human clinical trials.

Hematopoietic stem cell mobilization: updated conceptual renditions

Despite its specific clinical relevance, the field of hematopoietic stem cell mobilization has received broad attention, owing mainly to the belief that pharmacologic stem cell mobilization might provide clues as to how stem cells are retained in their natural environment, the bone marrow 'niche'. Inherent to this knowledge is also the desire to optimally engineer stem cells to interact with their target niche (such as after transplantation), or to lure malignant stem cells out of their protective niches (in order to kill them), and in general to decipher the niche's structural components and its organization. Whereas, with the exception of the recent addition of CXCR4 antagonists to the armamentarium for mobilization of patients refractory to granulocyte colony-stimulating factor alone, clinical stem cell mobilization has not changed significantly over the last decade or so, much effort has been made trying to explain the complex mechanism(s) by which hematopoietic stem and progenitor cells leave the marrow. This brief review will report some of the more recent advances about mobilization, with an attempt to reconcile some of the seemingly inconsistent data in mobilization and to interject some commonalities among different mobilization regimes.

Rapid expansion of human hematopoietic stem cells by automated control of inhibitory feedback signaling

Clinical hematopoietic transplantation outcomes are strongly correlated with the numbers of cells infused. Anticipated novel therapeutic implementations of hematopoietic stem cells (HSCs) and their derivatives further increase interest in strategies to expand HSCs ex vivo. A fundamental limitation in all HSC-driven culture systems is the rapid generation of differentiating cells and their secreted inhibitory feedback signals. Herein we describe an integrated computational and experimental strategy that enables a tunable reduction in the global levels and impact of paracrine signaling factors in an automated closed-system process by employing a controlled fed-batch media dilution approach. Application of this system to human cord blood cells yielded a rapid (12-day) 11-fold increase of HSCs with self-renewing, multilineage repopulating ability. These results highlight the marked improvements that control of feedback signaling can offer primary stem cell culture and demonstrate a clinically relevant rapid and relatively low culture volume strategy for ex vivo HSC expansion.

Chemokine receptor requirements for epidermal T-cell trafficking

Inflamed skin contains CD4 T-cell subsets that express chemokine receptors CCR4, CCR6, and/or CCR10. Prior attempts to reveal the distinct role(s) of each receptor in T-cell trafficking to skin have not produced a coherent story. Different conclusions drawn by separate research groups are difficult to reconcile because of the disparate inflammation models used. Here we directly compare CD4 T cells from wild-type, CCR4(-/-), CCR6(-/-), and CCR10(-/-) mice in parallel assays of trafficking to skin. Our models require direct competition between wild-type and receptor-deficient populations for access to inflamed cutaneous sites. Major histocompatibility complex-peptide tetramers allowed us to identify antigen-specific endogenous long-term memory CD4 T cells within skin after multiple topical immunizations. We separately analyzed cells from the dermal and epidermal layers, allowing us to assess the involvement of each receptor in trafficking between dermis and epidermis. We found that CCR4 deficiency reduces accumulation of memory CD4 T cells in skin by approximately 20-fold, but neither CCR6 nor CCR10 deficiency yielded any detectable effects. Strikingly, no differences in dermal versus epidermal localization were observed for cells lacking any of these three receptors. Our findings raise the possibility that CCR6 and CCR10 play (as yet) unknown roles in cutaneous T-cell immunology, unrelated to skin-specific trafficking.

Dynamic interaction networks in a hierarchically organized tissue

We have integrated gene expression profiling with database and literature mining, mechanistic modeling, and cell culture experiments to identify intercellular and intracellular networks regulating blood stem cell self-renewal.

Blood stem cell fate in vitro is regulated non-autonomously by a coupled positive–negative intercellular feedback circuit, composed of megakaryocyte-derived stimulatory growth factors (VEGF, PDGF, EGF, and serotonin) versus monocyte-derived inhibitory factors (CCL3, CCL4, CXCL10, TGFB2, and TNFSF9).

The antagonistic signals converge in a core intracellular network focused around PI3K, Raf, PLC, and Akt.

Model simulations enable functional classification of the novel endogenous ligands and signaling molecules.

Intercellular (between cell) communication networks are required to maintain homeostasis and coordinate regenerative and developmental cues in multicellular organisms. Despite the recognized importance of intercellular networks in regulating adult stem and progenitor cell fate, the specific cell populations involved, and the underlying molecular mechanisms are largely undefined. Although a limited number of studies have applied novel bioinformatic approaches to unravel intercellular signaling in other cell systems (Frankenstein et al, 2006), a comprehensive analysis of intercellular communication in a stem cell-derived, hierarchical tissue network has yet to be reported.

As a model system to explore intercellular communication networks in a hierarchically organized tissue, we cultured human umbilical cord blood (UCB)-derived stem and progenitor cells in defined, minimal cytokine-supplemented liquid culture (Madlambayan et al, 2006). To systematically explore the molecular and cellular dynamics underlying primitive progenitor growth and differentiation, gene expression profiles of primitive (lineage negative; Lin⁻) and mature (lineage positive; Lin⁺) populations were generated during phases of stem cell expansion versus depletion. Parallel phenotypic and subproteomic experiments validated that mRNA expression correlated with complex measures of proteome activity (protein secretion and cell surface expression). Using a curated list of secreted ligand–receptor interactions and published expression profiles of purified mature blood populations, we implemented a novel algorithm to reconstruct the intercellular signaling networks established between stem cells and multi-lineage progeny in vitro. By correlating differential expression patterns with stem cell growth, we predict cell populations, pathways, and secreted ligands associated with stem cell self-renewal and differentiation (Figure 3A).

We then tested the correlative predictions in a series of cell culture experiments. UCB progenitor cell cultures were supplemented with saturating amounts of 18 putative regulatory ligands, or cocultured with purified mature blood lineages (megakaryocytes, monocytes, and erythrocytes), and analyzed for effects on total cell, progenitor, and primitive progenitor growth. At the primitive progenitor level, 3/5 novel predicted stimulatory ligands (EGF, PDGFB, and VEGF) displayed significant positive effects, 5/7 predicted inhibitory factors (CCL3, CCL4, CXCL10, TNFSF9, and TGFB2) displayed negative effects, whereas only 1/5 non-correlated ligand (CXCL7) displayed an effect. Also consistent with predictions from gene expression data, megakaryocytes and monocytes were found to stimulate and inhibit primitive progenitor growth, respectively, and these effects were attributable to differential secretome profiles of stimulatory versus inhibitory ligands.

Cellular responses to external stimuli, particularly in heterogeneous and dynamic cell populations, represent complex functions of multiple cell fate decisions acting both directly and indirectly on the target (stem cell) populations. Experimentally distinguishing the mode of action of cytokines is thus a difficult task. To address this we used our previously published interactive model of hematopoiesis (Kirouac et al, 2009) to classify experimentally identified regulatory ligands into one of four distinct functional categories based on their differential effects on cell population growth. TGFB2 was classified as a proliferation inhibitor, CCL4, CXCL10, SPARC, and TNFSF9 as self-renewal inhibitors, CCL3 a proliferation stimulator, and EGF, VEGF, and PDGFB as self-renewal stimulators.

Stem and progenitor cells exposed to combinatorial extracellular signals must propagate this information through intracellular molecular networks, and respond appropriately by modifying cell fate decisions. To explore how our experimentally identified positive and negative regulatory signals are integrated at the intracellular level, we constructed a blood stem cell self-renewal signaling network through extensive literature curation and protein–protein interaction (PPI) network mapping. We find that signal transduction pathways activated by the various stimulatory and inhibitory ligands converge on a limited set of molecular control nodes, forming a core subnetwork enriched for known regulators of self-renewal (Figure 6A). To experimentally test the intracellular signaling molecules computationally predicted as regulators of stem cell self-renewal, we obtained five small molecule antagonists against the kinases Phosphatidylinositol 3-kinase (PI3K), Raf, Akt, Phospholipase C (PLC), and MEK1. Liquid cultures were supplemented with the five molecules individually, and resultant cell population outputs compared against model simulations to deconvolute the functional effects on proliferation (and survival) versus self-renewal. This analysis classifies inhibition of PI3K and Raf activity as selectively targeting self-renewal, PLC as selectively targeting survival, and Akt as selectively targeting proliferation; MEK inhibition appears non-specific for these processes.

This represents the first systematic characterization of how cell fate decisions are regulated non-autonomously through lineage-specific interactions with differentiated progeny. The complex intercellular communication networks can be approximated as an antagonistic positive–negative feedback circuit, wherein progenitor expansion is modulated by a balance of megakaryocyte-derived stimulatory factors (EGF, PDGF, VEGF, and possibly serotonin) versus monocyte-derived inhibitory factors (CCL3, CCL4, CXCL10, TGFB2, and TNFSF9). This complex milieu of endogenous regulatory signals is integrated and processed within a core intracellular signaling network, resulting in modulation of cell-level kinetic parameters (proliferation, survival, and self-renewal). We reconstruct a stem cell associated intracellular network, and identify PI3K, Raf, Akt, and PLC as functionally distinct signal integration nodes, linking extracellular and intracellular signaling. These findings lay the groundwork for novel strategies to control blood stem cell self-renewal in vitro and in vivo.

Intercellular (between cell) communication networks maintain homeostasis and coordinate regenerative and developmental cues in multicellular organisms. Despite the importance of intercellular networks in stem cell biology, their rules, structure and molecular components are poorly understood. Herein, we describe the structure and dynamics of intercellular and intracellular networks in a stem cell derived, hierarchically organized tissue using experimental and theoretical analyses of cultured human umbilical cord blood progenitors. By integrating high-throughput molecular profiling, database and literature mining, mechanistic modeling, and cell culture experiments, we show that secreted factor-mediated intercellular communication networks regulate blood stem cell fate decisions. In particular, self-renewal is modulated by a coupled positive–negative intercellular feedback circuit composed of megakaryocyte-derived stimulatory growth factors (VEGF, PDGF, EGF, and serotonin) versus monocyte-derived inhibitory factors (CCL3, CCL4, CXCL10, TGFB2, and TNFSF9). We reconstruct a stem cell intracellular network, and identify PI3K, Raf, Akt, and PLC as functionally distinct signal integration nodes, linking extracellular, and intracellular signaling. This represents the first systematic characterization of how stem cell fate decisions are regulated non-autonomously through lineage-specific interactions with differentiated progeny.

Mobilization of hematopoietic stem cells for use in autologous transplantation

Autologous hematopoietic stem cell transplantation (HSCT) is a potentially curative therapeutic approach for various malignant hematologic and lymphoid diseases. Hematopoietic stem cells (HSCs) may be collected from the blood or the bone marrow. HSCs are capable of self-renewal and give rise to progenitor cells, multipotent cells that differentiate and proliferate into the mature cells of the blood and immune system. HSCs and progenitor cells are released from the bone marrow into the peripheral blood through a process called mobilization. HSCs then are collected from the blood in a process called apheresis and cryopreserved for administration following the high-dose preparative regimen. This article reviews stem cell biology, current mobilization strategies, use of novel mobilization agents, and nursing care of patients during the mobilization phase of autologous HSCT. Understanding the biology and process of HSC mobilization is critical for transplantation nurses to deliver and coordinate care during this complex phase of autologous HSCT.

Recruited peripheral blood monocytes participate in the liver extramedullary hematopoietic milieu

The hematopoietic microenvironment has been investigated and well defined in the bone marrow. However, there is a lack of studies on the extramedullary hematopoietic milieu such as in the liver, to which hematopoietic stem cells migrate and there commence hematopoiesis under pathological conditions such as bone marrow failure. We induced extramedullary hematopoiesis by phenylhydrazine in the adult mouse liver and investigated the immunohistochemical, ultrastructural, and molecular changes within this organ. Using an intravital lectin injection technique, we found numerous monocytes attached to the central vein prior to hematopoietic foci formation. These cells were later incorporated into the hematopoietic foci. An increase in the mRNA expressions of the monocyte attracting chemokine CCL-2 (MCP-1) was noted in the central vein region as well as in cells within the hematopoietic foci. Together with local liver components, we regard these monocytes as components of the extramedullary hematopoietic milieu. We conclude that the recruitment of extra-hepatic monocytes is an important event during extramedullary hematopoiesis in the liver and that these monocytes participate in the liver hematopoietic microenvironment.

Cell-cell interaction networks regulate blood stem and progenitor cell fate

Communication networks between cells and tissues are necessary for homeostasis in multicellular organisms. Intercellular (between cell) communication networks are particularly relevant in stem cell biology, as stem cell fate decisions (self-renewal, proliferation, lineage specification) are tightly regulated based on physiological demand. We have developed a novel mathematical model of blood stem cell development incorporating cell-level kinetic parameters as functions of secreted molecule-mediated intercellular networks. By relation to quantitative cellular assays, our model is capable of predictively simulating many disparate features of both normal and malignant hematopoiesis, relating internal parameters and microenvironmental variables to measurable cell fate outcomes. Through integrated in silico and experimental analyses, we show that blood stem and progenitor cell fate is regulated by cell–cell feedback, and can be controlled non-cell autonomously by dynamically perturbing intercellular signalling. We extend this concept by demonstrating that variability in the secretion rates of the intercellular regulators is sufficient to explain heterogeneity in culture outputs, and that loss of responsiveness to cell–cell feedback signalling is both necessary and sufficient to induce leukemic transformation in silico.

Targeted disruption of Zfp36l2, encoding a CCCH tandem zinc finger RNA-binding protein, results in defective hematopoiesis

Members of the tristetraprolin family of tandem CCCH finger proteins can bind to AU-rich elements in the 3'-untranslated region of mRNAs, leading to their deadenylation and subsequent degradation. Partial deficiency of 1 of the 4 mouse tristetraprolin family members, Zfp36l2, resulted in complete female infertility because of early embryo death. We have now generated mice completely deficient in the ZFP36L2 protein. Homozygous Zfp36l2 knockout (KO) mice died within approximately 2 weeks of birth, apparently from intestinal or other hemorrhage. Analysis of peripheral blood from KO mice showed a decrease in red and white cells, hemoglobin, hematocrit, and platelets. Yolk sacs from embryonic day 11.5 (E11.5) Zfp36l2 KO mice and fetal livers from E14.5 KO mice gave rise to markedly reduced numbers of definitive multilineage and lineage-committed hematopoietic progenitors. Competitive reconstitution experiments demonstrated that Zfp36l2 KO fetal liver hematopoietic stem cells were unable to adequately reconstitute the hematopoietic system of lethally irradiated recipients. These data establish Zfp36l2 as a critical modulator of definitive hematopoiesis and suggest a novel regulatory pathway involving control of mRNA stability in the life cycle of hematopoietic stem and progenitor cells.

SDF-1 and PDGF enhance alphavbeta5-mediated ERK activation and adhesion-independent growth of human pre-B cell lines

CD23 acts through the alphavbeta5 integrin to promote growth of human pre-B cell lines in an adhesion-independent manner. alphavbeta5 is expressed on normal B-cell precursors in the bone marrow. Soluble CD23 (sCD23), short CD23-derived peptides containing the arg-lys-cys (RKC) motif recognized by alphavbeta5 and anti-alphavbeta5 monoclonal antibodies (MAbs) all sustain growth of pre-B cell lines. The chemokine stromal cell-derived factor-1 (SDF-1) regulates key processes during B-cell development. SDF-1 enhanced the growth-sustaining effect driven by ligation of alphavbeta5 with anti-alphavbeta5 MAb 15F-11, sCD23 or CD23-derived RKC-containing peptides. This effect was restricted to B-cell precursors and was specific to SDF-1. The enhancement in growth was associated with the activation of extracellular signal-regulated kinase (ERK) and both these responses were attenuated by the MEK inhibitor U0126. Finally, platelet-derived growth factor also enhanced both alphavbeta5-mediated cell growth and ERK activation. The data suggest that adhesion-independent growth-promoting signals delivered to B-cell precursors through the alphavbeta5 integrin can be modulated by cross-talk with receptors linked to both G-protein and tyrosine kinase-coupled signalling pathways.

Infection with Anaplasma phagocytophilum induces multilineage alterations in hematopoietic progenitor cells and peripheral blood cells

Infection with Anaplasma phagocytophilum, a gram-negative, lipopolysaccharide (LPS)-negative, obligate intracellular bacterium, results in multiple peripheral blood cytopenias. We hypothesized that infection with this organism would result in decreased bone marrow (BM) function and shifts in hematopoietic progenitor cells (HPCs) and lineage-committed cells in a well-established murine model of infection. HPCs and lineage-committed progenitors were enumerated in the BM and spleen during acute infection. BM cytokine production and BM CXCL12 expression were determined. Infection resulted in peripheral blood bicytopenia, marked decreases in the number of lineage-committed HPCs in the BM along with concurrent increases in the number of lineage-committed HPCs in the spleen, and a mixed, predominantly myelosuppressive BM cytokine environment. There was significant downregulation of CXCL12 in BM cells that may have been partially responsible for changes in HPC trafficking observed. Changes occurred in the absence of direct pathogen infection of BM cells. Hematopoietic lineage assessment demonstrated that there was loss of erythrocytes and B lymphocytes from the BM along with increased granulopoiesis. These changes were accompanied by splenomegaly due to lymphoid hyperplasia and increased hematopoiesis, most notably erythropoiesis. These changes largely mimic well-described inflammation and endotoxin-mediated effects on the BM and spleen; however, the numbers of peripheral blood neutrophils appear to be independently modulated as granulocytic hyperplasia does not result in neutrophilia. Our findings highlight a well-conserved series of events that we demonstrate can be instigated by an LPS-negative pathogen in the absence of an endotoxin-mediated acute proinflammatory response.

Human periosteum-derived progenitor cells express distinct chemokine receptors and migrate upon stimulation with CCL2, CCL25, CXCL8, CXCL12, and CXCL13

For bone repair, transplantation of periosteal progenitor cells (PCs), which had been amplified within supportive scaffolds, is applied clinically. More innovative bone tissue engineering approaches focus on the in situ recruitment of stem and progenitor cells to defective sites and their subsequent use for guided tissue repair. Chemokines are known to induce the directed migration of bone marrow CD34(-) mesenchymal stem cells (MSCs). The aim of our study was to determine the chemokine receptor expression profile of human CD34(-) PCs and to demonstrate that these cells migrate upon stimulation with selected chemokines. PCs were isolated from periosteum of the mastoid bone and displayed a homogenous cell population presenting an MSC-related cell-surface antigen profile (ALCAM(+), SH2(+), SH3(+), CD14(-), CD34(-), CD44(+), CD45(-), CD90(+)). The expression profile of chemokine receptors was determined by real-time PCR and immunohistochemistry. Both methods consistently demonstrated that PCs express receptors of all four chemokine subfamilies CC, CXC, CX(3)C, and C. Migration of PCs and a dose-dependent migratory effect of the chemokines CCL2 (MCP1), CCL25 (TECK), CXCL8 (IL8), CXCL12 (SDF1alpha), and CXCL13 (BCA1), but not CCL22 (MDC) were demonstrated using a 96-multiwell chemotaxis assay. In conclusion, for the first time, here we report that human PCs express chemokine receptors, present their profile, and demonstrate a dose-dependent migratory effect of distinct chemokines on these cells. These results are promising towards in situ bone repair therapies based on guiding PCs to bone defects, and encourage further in vivo studies.

SDF-1/CXCL12 enhances in vitro replating capacity of murine and human multipotential and macrophage progenitor cells

Hematopoietic progenitor cells (HPCs) manifest a limited self-renewal capacity, as determined by a surrogate assay involving replating capacity of single colonies in vitro with generation of secondary colonies. Stromal cell-derived factor-1 (SDF-1/CXCL12), has been implicated in regulation of hematopoiesis through its modulation of hematopoietic stem cell (HSC) and HPC migration, homing, mobilization, and survival. We used bone marrow cells from SDF-1/CXCL12 transgenic and littermate control mice, and culture of normal mouse bone marrow and human cord blood cells plated in the presence or absence of recombinant SDF-1/CXCL12 to evaluate a role for SDF-1/CXCL12 in the replating capability in vitro of multipotential [colony-forming units (CFU)-GEMM] and macrophage (CFU-M) progenitor cells. Competitive repopulating capacity of mouse HSCs was assessed in lethally irradiated mice. Transgenic or exogenous SDF-1/CXCL12 significantly enhanced numbers of secondary colonies formed from primary CFU-GEMM or CFU-M colonies. In the limited setting of our in vivo studies, the SDF-1/CXCL12 transgene did not influence HSC competitive repopulation. However, the results suggest that SDF-1/CXCL12 enhances in vitro replating/self-renewal of HPCs, which may contribute to myelopoiesis in vivo. This information may be of value to ex vivo expansion of HPCs/HSCs.

Stimulation of osteoclastogenesis by enhanced levels of MIP-1alpha in BALB/c mice in vitro

OBJECTIVES

We compared osteoclast (OC) formation in bone marrow-derived macrophages (BMM) from C57BL/6 (B/6) and BALB/c (B/c) mice. After stimulation of receptor activator of nuclear factor-kappaB ligand (RANKL), enhanced OC formation and higher level of macrophage inflammatory protein-1alpha (MIP-1alpha) were observed in the BMM from B/c mice. In this study, we determined whether MIP-1alpha is responsible for stimulated OC formation in the BMM.

MATERIALS AND METHODS

OC formation was evaluated in BMM. Expression of MIP-1alpha during OC formation was analyzed at the mRNA and protein levels. Apoptosis of mature OCs was evaluated by observing the degradation of DNA. Activation of nuclear factor-kappaB (NF-kappaB) was measured by electrophoretic mobility shift assay.

RESULTS

After stimulation by RANKL expression of MIP-1alpha at the mRNA and protein levels was much higher in BMM from B/c mice than in BMM from B/6 mice. Transcripts of the MIP-1alpha receptors, CCR1 and CCR5, were present at similar levels in unstimulated BMM of the two strains. Blockade of MIP-1alpha inhibited OC formation, and exogenously added MIP-1alpha stimulated it in RANKL-stimulated BMM. MIP-1alpha affected not only the early precursors but also mature OCs. It prevented apoptosis of mature OCs by activating NF-kappaB, and the effect of RANKL on survival was dependent on its ability to induce MIP-1alpha.

CONCLUSIONS

MIP-1alpha, induced by RANKL during OC differentiation, increases OC formation by acting on OC progenitor cells, and prolongs survival of mature OC via signaling through NF-kappaB. The enhanced OC formation in BMM from B/c mice could be due to, at least in part, to their higher levels of MIP-1alpha.

Aberrant regulation of hematopoiesis by T cells in BAZF-deficient mice

The BAZF (BCL-6b) protein is highly similar to the BCL-6 transcriptional repressor. While BCL-6 has been characterized extensively, relatively little is known about the normal function of BAZF. In order to understand the physiological role of BAZF, we created BAZF-deficient mice. Unlike BCL-6-deficient mice, BAZF-deficient mice are healthy and normal in size. However, BAZF-deficient mice have a hematopoietic progenitor phenotype that is almost identical to that of BCL-6-deficient mice. Compared to wild-type mice, both BAZF-deficient and BCL-6-deficient mice have greatly reduced numbers of cycling hematopoietic progenitor cells (HPC) in the BM and greatly increased numbers of cycling HPC in the spleen. In contrast to HPC from wild-type mice, HPC from BAZF-deficient and BCL-6-deficient mice are resistant to chemokine-induced myelosuppression and do not show a synergistic growth response to granulocyte-macrophage colony-stimulating factor plus stem cell factor. Depletion of CD8 T cells in BAZF-deficient mice reverses several of the hematopoietic defects in these mice. Since both BAZF- and BCL-6-deficient mice have defects in CD8 T-cell differentiation, we hypothesize that both BCL-6 and BAZF regulate HPC homeostasis by an indirect pathway involving CD8 T cells.

Synergistic inhibition in vivo of bone marrow myeloid progenitors by myelosuppressive chemokines and chemokine-accelerated recovery of progenitors after treatment of mice with Ara-C

OBJECTIVE

Selected chemokines suppress proliferation of hematopoietic progenitor cells (HPCs) in vitro; some of these have demonstrated inhibition of myelopoiesis in vivo. Because myelosuppressive chemokines synergize in vitro with other myelosuppressive chemokines, we sought to determine whether additional chemokines active in vitro were myelosuppressive in vivo and whether combinations of myelosuppressive chemokines synergized in vivo to dampen myelopoiesis. We also evaluated three chemokines in vivo for myeloprotection against Ara-C-induced decreases in HPCs.

METHODS

C3H/HeJ mice were used for analysis of in vivo influence of chemokines, with the end points being effects on absolute numbers and cycling status of HPCs.

RESULTS

When used alone, CCL2, CCL3, CCL19, CCL20, CXCL4, CXCL5, CXCL8, CXCL9, and XCL1 caused dose-dependent significant decreases in absolute numbers and cycling status of HPCs in vivo. The following combinations of two chemokines resulted in in vivo myelosuppression at concentrations much lower than that induced by each chemokine alone: CCL3 plus either CXCL8 or CXCL4, CXCL8 plus CXCL4, CCL2 plus either CCL20 or CXCL9, CCL20 plus CXCL9, CXCL5 plus either XCL1 or CCL19, XCL1 plus CCL19, and CCL3 plus CCL19. Also, mice injected with CXCL8, CXCL4, or the chimeric CXCL8/CXCL4 protein CXCL8M1 manifested accelerated recovery of absolute numbers of HPCs in response to the toxic effects of Ara-C administration.

CONCLUSIONS

A number of chemokines shown previously to manifest inhibitory effects in vitro for proliferation of HPCs are now demonstrated to also induce myelosuppression in vivo. Moreover, combinations of low dosages of two myelosuppressive chemokines when administered together demonstrate synergistic suppression in vivo. Additionally, chemokines, including a CXCL8M1 chimeric protein previously shown to manifest enhanced suppression of HPC proliferation in vitro and in vivo, accelerate HPC recovery after treatment of mice with Ara-C. These results may be of use for future clinical utility of chemokines in a myelosuppressive/myeloprotective setting.

Chemoattractants, extracellular proteases, and the integrated host defense response

The host response to tissue injury and/or infection is dependent on the action of numerous extracellular proteases. Proteolytic cascades trigger blood clotting, fibrinolysis, and complement activation, while proteases released upon leukocyte degranulation are integral to the processes of inflammation and immunity. Modulation of effector protein activity by proteases provides a critical layer of posttranslational control that enables rapid enzymatic regulation of target proteins. This report reviews the emerging literature describing a novel class of proteolytic targets, leukocyte chemoattractants, and, in particular, chemerin, a dendritic cell and macrophage chemoattractant activated by serine proteases of the coagulation, fibrinolytic, and inflammatory cascades. As chemoattractants are critical for both systemic leukocyte positioning by triggering integrin activation and subsequent recruitment from circulation, and local intratissue leukocyte positioning via chemotaxis, modulation of attractant activities by proteases may have profound effects on the immune response.

Class II transactivator-mediated regulation of major histocompatibility complex class II antigen expression is important for hematopoietic progenitor cell suppression by chemokines and iron-binding proteins

OBJECTIVE

Iron-binding proteins H-ferritin (HF) and lactoferrin (LF), as well as chemokines, tumor necrosis factor (TNF)-alpha, and interferon (IFN)-gamma suppress hematopoietic progenitor cell (HPC) proliferation. Major histocompatibility complex (MHC) class II antigens have been associated with suppressive effects of HF and LF. Because the transcription factor class II transactivator (CIITA) regulates expression of MHC class II antigens, we evaluated influences of CIITA and MHC class II antigens on suppression of colony formation by murine bone marrow HPC in response to HF, LF, CC, and CXC chemokines, TNF-alpha, and IFN-gamma. We also evaluated hematopoiesis in mice deficient in both CIITA and MHC class II antigens (CIITA -/-), in mice deficient in MHC class II antigens but not in CIITA (MHC class II -/-), and in mice deficient in CIITA but not in MHC class II antigens (CIITA-IE).

MATERIALS AND METHODS

HF, LF, CCL3/MIP-1alpha, CXCL5/ENA-78, CXCL8/IL-8, CCL5/RANTES, TNF-alpha, and IFN-gamma were assessed for effects on colony formation by bone marrow HPC (colony-forming unit granulocyte-macrophage, burst-forming unit erythroid, and colony-forming unit multipotential) stimulated in vitro by combinations of growth factors including erythropoietin, stem cell factor, pokeweed mitogen mouse spleen cell conditioned medium, and hemin. Bone marrow cells were from CIITA -/-, MHC class II antigen -/-, CIITA-IE, and littermate control mice. We also evaluated cycling status (percent cells in S-phase) and absolute numbers of marrow and spleen HPC in these mice.

RESULTS

Multiple growth factor-stimulated colony formation by control bone marrow HPC was significantly suppressed by HF, LF, CCL3, CXCL5, CXCL8, TNF-alpha, and IFN-gamma, but not by CCL5. However, HPC from CIITA -/- and MHC class II antigen -/- mouse marrow was insensitive to inhibition by HF, LF, CCL3, CXCL5, CXCL8, and CCL5; these HPC were inhibited by TNF-alpha and IFN-gamma. Restoration of MHC class II expression in CIITA -/- (CIITA-IE) mice restored responsiveness of HPC to inhibition by HF, LF, CCL3, CXCL5, and CXCL8. Increased cycling of splenic HPC in CIITA -/- and MHC class II antigen -/-, compared to control and CIITA-IE, mice was noted.

CONCLUSIONS

Myelosuppressive effects of iron-binding proteins HF and LF and chemokines CCL3, CXCL5, and CXCL8 on mouse bone marrow HPC require expression of MHC class II antigens, and CIITA is involved in this responsiveness through its regulation of expression of MHC class II antigens.

Significance of macrophage inflammatory protein-1 alpha (MIP-1alpha) in multiple myeloma

Macrophage inflammatory protein-1 alpha (MIP-1alpha) is a member of the CC chemokine family and is primarily associated with cell adhesion and migration. It is produced by myeloma (MM) cells and directly stimulates osteoclast formation and differentiation in a dose dependent way. MIP-1alpha protein levels were elevated in the bone marrow plasma of MM patients and correlated with disease stage and activity. MIP-1alpha was also elevated in the serum of myeloma patients with severe bone disease and correlated positively with bone resorption markers providing evidence for a causal role of MIP-1alpha in the development of lytic bone lesions in MM. MIP-1alpha has also been found to stimulate proliferation, migration and survival of plasma cells. Mice, which were inoculated with myeloma cells and treated with a monoclonal rat anti-mouse MIP-1alpha antibody, showed a reduction of both paraprotein and lytic lesions. In addition, MIP-1alpha enhanced adhesive interactions between myeloma and marrow stromal cells, increasing the expression of RANKL and IL-6, which further increased bone destruction and tumor burden. Myeloma patients with high MIP-1alpha serum levels have poor prognosis. The positive correlation between MIP-1alpha and beta(2)-microglobulin that has been observed in MM patients at diagnosis further supports the notion that MIP-1alpha is not only a chemokine with osteoclast activity function but is also implicated in myeloma growth and survival. Therefore, MIP-1alpha pathway may serve as a target for the development of novel anti-myeloma therapies.

CCL23/myeloid progenitor inhibitory factor-1 inhibits production and release of polymorphonuclear leukocytes and monocytes from the bone marrow

OBJECTIVE

CCL23/Myeloid progenitor inhibitory factor-1 is a human CC chemokine with potent in vitro suppressor effects on both human and murine myeloid progenitor cells. This study concerns in vivo inhibitory effect of CCL23 on production of polymorphonuclear leukocytes (PMNs) and monocytes in the bone marrow and their release into the circulation.

METHODS

5'-Bromo-2'-deoxyuridine (BrdU; 100 mg/kg) was used to label dividing PMNs and monocytes in the bone marrow, and BrdU-labeled cells were followed for 10 days in the circulation and identified using immunocytochemistry. Rabbits were given CCL23 (100 mug/kg, n = 5) or saline (control: n = 5) intravenously daily for 3 days before labeling with BrdU. Turnover of PMNs and monocytes in the bone marrow and their transit times through the bone marrow were calculated.

RESULTS

CCL23 treatment tended to prolong transit time of PMN (98.4 +/- 4.3 hours vs 111.2 +/- 3.8 hours, control vs CCL23, p = 0.06) through the bone marrow and decreased the size of the bone marrow mitotic pool of PMN (p < 0.01). CCL23 treatment also prolonged the transit time of monocyte (43.4 +/- 3.1 hours vs 54.2 +/- 1.3 hours, control vs CCL23, p < 0.05) through the bone marrow and decreased turnover and pool size of monocytes in the bone marrow (p < 0.05).

CONCLUSION

We conclude that CCL23 suppresses PMN and monocyte progenitors, decreases the pool size and slows their turnover in the bone marrow.

Elevated plasma chemokine CCL18/PARC in β-thalassemia

Plasma CCL18/PARC, a member of the CC chemokine family, has been found to be several ten-fold increased in symptomatic Gaucher type I patients. Elevated plasma chitotriosidase levels are a well-known abnormality in Gaucher patients, however, its diagnostic use is limited by the frequent genetic deficiency in the protein. Like the situation in Gaucher disease, lipids accumulate in macrophages of patients suffering from beta-thalassemia, and, in both conditions, increased chitotriosidase levels occur. We here report that plasma CCL18/PARC is also significantly increased in patients with beta-thalassemia major (range 76.8-4977.8, median=650.8 ng/ml, n=36 and control range 10-72, median=33 ng/ml n=36 respectively, P<0.001). The CCL18/PARC levels are lower than in Gaucher patients (range 174.8-10798.7, median 2538.2 ng/ml, n=28, P<0.001). In our cohort of beta-thalassemic patients, CCL18/PARC showed a significant negative correlation to iron chelation therapy and a significant positive correlation to ferritin and chitotriosidase levels, the latter only in the patients with the wild type genotype for the enzyme. Our study demonstrates that beta-thalassemic patients have increased CCL18/PARC levels that could be of value in monitoring iron overload and compliance to therapy.

Quantum proteolytic activation of chemokine CCL15 by neutrophil granulocytes modulates mononuclear cell adhesiveness

Monocyte infiltration into inflammatory sites is generally preceded by neutrophils. We show here that neutrophils may support this process by activation of CCL15, a human chemokine circulating in blood plasma. Neutrophils were found to release CCL15 proteolytic activity in the course of hemofiltration of blood from renal insufficiency patients. Processing of CCL15 immunoreactivity (IR) in the pericellular space is suggested by a lack of proteolytic activity in blood and blood filtrate, but a shift of the retention time (t(R)) of CCL15-IR, detected by chromatographic separation of CCL15-IR in blood and hemofiltrate. CCL15 molecules with N-terminal deletions of 23 (delta23) and 26 (delta26) aa were identified as main proteolytic products in hemofiltrate. Neutrophil cathepsin G was identified as the principal protease to produce delta23 and delta26 CCL15. Also, elastase displays CCL15 proteolytic activity and produces a delta21 isoform. Compared with full-length CCL15, delta23 and delta26 isoforms displayed a significantly increased potency to induce calcium fluxes and chemotactic activity on monocytes and to induce adhesiveness of mononuclear cells to fibronectin. Thus, our findings indicate that activation of monocytes by neutrophils is at least in part induced by quantum proteolytic processing of circulating or endothelium-bound CCL15 by neutrophil cathepsin G.

Cord blood hematopoietic progenitor cell concentration and infant sex

BACKGROUND

Characterization of cord blood facilitates understanding of the factors affecting cord blood transplant quality and improvement of transplantation results. Cord blood obtained from male and female infants has not been thoroughly characterized.

STUDY DESIGN AND METHODS

A study was performed to test the hypothesis that the cord blood hematopoietic progenitor cell content-of which the CD34+ cell and colony-forming unit (CFU) concentrations were taken as markers-would not only associate with birth weight but also with sex. The hematopoietic progenitor cell concentrations of 1999 healthy infants (47% female) were analyzed in a cord blood bank setting.

RESULTS

Male infants had significantly higher median CD34+ cell concentrations than female infants (31.8/microL vs. 30.2/microL, respectively; p = 0.03). Although the disparity in absolute concentrations was small, it was 5.3 percent. In CFU subgroup analysis, the median CFU-mixed concentration of male infants (11.1/microL) was higher than in female infants (9.9/microL; p = 0.03). The difference was more pronounced when cumulative frequencies of the CFU-mixed concentrations from cesarean section deliveries were compared. In multivariate linear regression analysis, the positive influence of male sex on the CD34+ cell concentration was significant (p < 0.05). The expected higher median nucleated cell concentration of female compared to male infants (13.9 x 10(9)/L vs. 13.3 x 10(9)/L, respectively; p = 0.0001) was mainly due to the higher neutrophil concentration of female infants (7.1 x 10(9)/L vs. 6.5 x 10(9)/L, respectively, p < 0.0001).

CONCLUSION

Cord blood hematopoietic progenitor cell concentration was higher in male infants, even after correcting for birth weight. Sex may affect the hematopoietic potential of cord blood transplants.

Stromal Cell-Derived Factor-1/CXCL12 Selectively Counteracts Inhibitory Effects of Myelosuppressive Chemokines on Hematopoietic Progenitor Cell Proliferation In Vitro

A variety of cytokines and chemokines exert potent myelosuppressive effects that play a role in the maintenance of hematopoiesis, which, if unchecked, may result in pathological impairment of blood cell production. Processes that modulate these myelosuppressive effects are not well defined. Here we demonstrate that stromal cell-derived factor-1 (SDF-1/CXCL12), known for its ability to attract and to promote survival of hematopoietic progenitor cells (HPCs) and stem cells, blocks the effects of a broad range of myelosuppressive chemokines on proliferation of HPCs in vitro. The regulatory effects of SDF/CXCL12 on colony formation by mouse bone marrow granulocyte-macrophage (CFUGM), erythroid (BFU-E), and multipotential (CFU-GEMM) progenitor cells were assessed. These cells were stimulated to proliferate by combinations of growth factors, such that responses of immature HPCs could be assessed. SDF-1/CXCL12 potently blocked myelosuppressive responses induced by CCL2/MCP-1, CCL3/MIP-1alpha, CCL19/CKbeta-11, CCL25/TECK, CXCL4/PF4, CXCL8/IL-8, CXCL10/IP-10, and XCL1/Lymphotactin. However, SDF/CDL12 did not influence myelosuppression induced by tumor necrosis factor (TNF)-alpha, interferon (IFN)-gamma, transforming growth factor (TGF)-beta or the iron-binding proteins H-ferritin or lactoferrin (LF). LF, previously shown to suppress release of growth factors, is shown here to also suppress proliferation of immature subsets of HPCs. HPCs from marrows of mice expressing an SDF-1/CXCL12 transgene were insensitive to inhibition by SDF/CXCL12-sensitive myelosuppressive chemokines, but not to SDF/CCL12-insensitive cytokines (TNF-alpha, IFN-gamma, TGF-beta, H-Ferritin, or LF). Thus, SDF-1/CXCL12 differentially and selectively regulates suppression of HPC proliferation by chemokines. These effects may counter myelosuppressive effects of certain chemokines in vivo, where proliferation of HPCs must be sustained.

Enhancement of cell survival by stromal cell-derived factor-1/CXCL12 involves activation of CREB and induction of Mcl-1 and c-Fos in factor-dependent human cell line MO7e

Stromal cell-derived factor-1 (SDF-1/CXCL12) enhances the survival of hematopoietic stem and progenitor cells in synergy with other cytokines such as granulocyte-macrophage colony-stimulating factor (GM-CSF), steel factor, and thrombopoietin (TPO), and both the PI3K/Akt and MAPK pathways have been linked to this survival. To further evaluate intracellular signaling involved in SDF-1/CXCL12 survival effects, we investigated modulation of downstream signaling molecules. The synergistic survival enhancement of SDF-1/CXCL12 plus other cytokines were directly linked to enhanced phosphorylation of p70/85S6K and cAMP responsive element binding protein (CREB), as well as enhanced induction of the Bcl-2 family member Mcl-1. Most prominently, c-Fos, a component of AP1 transcription factor, was synergistically induced by SDF-1/CXCL12 plus other cytokines. These results suggest that SDF-1/CXCL12 enhanced cell survival in synergy with other cytokines involves activation of CREB and induction of Mcl-1 and c-Fos.

Chemokine networks and in vivo T-lymphocyte trafficking in nonhuman primates

T-lymphocyte migratory circuits in human and nonhuman primates remain largely unexplored due to the difficulty of defining cell trafficking in vivo. However, this knowledge may reveal critical aspects of immunity and T-lymphocyte homeostasis in both health and disease. Furthermore, in vivo T-lymphocyte trafficking studies may facilitate defining mechanism(s) of immune dysfunction in the nonhuman primate model for acquired immunodeficiency syndrome (AIDS). Here, we developed a model for in vivo T-lymphocyte trafficking in nonhuman primates, and delineated homing characteristics of unstimulated peripheral blood mononuclear cells (PBMCs) to lymphoid and nonlymphoid compartments in healthy rhesus macaques. T-lymphocyte homing of autologous, carboxyfluorescein diacetate succinimidyl ester (CFSE)-labeled PBMCs was defined within 48 h of intravenous transfer. The highest relative frequency of CFSE+ T lymphocytes was observed in peripheral blood and spleen. Expression of chemokine receptor CCR7 and its ligands correlated with recirculation of T lymphocytes through the periphery and homing to paracortical regions of lymph node, where cells remained largely excluded from B-cell follicles. T-lymphocyte trafficking was also detected to the liver and bone marrow, and at low levels to the thymus and small intestine. The liver contained the highest proportion of CD45RA- T lymphocytes, consistent with homing of activated/memory T lymphocytes to this nonlymphoid site. Our data suggest that lymphoid and nonlymphoid organs are under continuous immunosurveillance in healthy macaques, and that this model may serve to investigate aberrant patterns in disease.

Stromal cell-derived factor-1alpha/CXCL12-induced chemotaxis of T cells involves activation of the RasGAP-associated docking protein p62Dok-1

Events mediating stromal cell-derived factor-1 (SDF-1alpha/CXCL12) chemotaxis of lymphocytes are not completely known. We evaluated intracellular signaling through RasGAP-associated protein p62Dok-1 (downstream of tyrosine kinase [Dok-1]) and associated proteins. SDF-1alpha/CXCL12 stimulated Dok-1 tyrosine phosphorylation and association with RasGAP, adaptor protein p46Nck, and Crk-L in Jurkat T cells. The phosphorylation of Dok-1 was blocked by pretreatment of cells with the src kinase inhibitor PP2. Src kinase family member Lck was implicated. SDF-1alpha/CXCL12 did not phosphorylate Dok-1 in J.CaM1.6 cells, a Jurkat derivative not expressing Lck, but did phosphorylate Dok-1 in J.CaM1.6 cells expressing Lck. SDF-1alpha/CXCL12 induced the tyrosine phosphorylation of Pyk2 and the association of Pyk2 with zeta chain-associated protein-70 kilodaltons (Zap-70) and Vav. SDF-1alpha/CXCL12 enhanced the association of RasGAP with Pyk2. CXCR4-expressing NIH3T3 and Baf3 cells transfected with full-length Dok-1 cDNA were suppressed in their responses to SDF-1alpha/CXCL12-induced chemotaxis; mitogen-activated protein (MAP) kinase activity was also decreased. Chemotaxis to SDF-1/CXCL12 was significantly enhanced in Dok-1(-/-) CD4+ and CD8+ splenic T cells. These results implicate Dok-1, Nck, Crk-L, and Src kinases-especially Lck, Pyk2, Zap-70, Vav, and Ras-GAP-in intracellular signaling by SDF-1alpha/CXCL12, and they suggest that Dok-1 plays an important role in SDF-1alpha/CXCL12-induced chemotaxis in T cells.

Chemokines promote quiescence and survival of human neural progenitor cells

Many cell types in the brain express chemokines and chemokine receptors under homeostatic conditions, arguing for a role of these proteins in normal brain processes. Because chemokines have been shown to regulate hematopoietic progenitor cell proliferation, we hypothesized that chemokines would regulate neural progenitor cell (NPC) proliferation as well. Here we show that chemokines activating CXCR4 or CCR3 reversibly inhibit NPC proliferation in isolated cells, neurospheres, and in hippocampal slice cultures. Cells induced into quiescence by chemokines maintain their multipotential ability to form both neurons and astrocytes. The mechanism of chemokine action appears to be a reduction of extracellular signal-related kinase phosphorylation as well as an increase in Reelin expression. The inhibitory effects of chemokines are blocked by heparan sulfate and apolipoprotein E3 but not apolipoprotein E4, suggesting a regulatory role of these molecules on the effects of chemokines. Additionally, we found that the chemokine fractalkine promotes survival of NPCs. In addition to their role in chemotaxis, chemokines affect both the survival and proliferation of human NPCs in vitro. The presence of constitutively expressed chemokines in the brain argues that under homeostatic conditions, chemokines promote survival but maintain NPCs in a quiescent state. Our studies also suggest a link between inflammatory chemokine production and the inhibition of neurogenesis.