Lipocalin 2 functions as a negative regulator of red blood cell production in an autocrine fashion

Lipocalin 2-mediated growth suppression is evident in human erythroid and monocyte/macrophage lineage cells

Lipocalin 2 (LCN2), a secreted protein of the lipocalin family, induces apoptosis in some types of cells and inhibits bacterial growth by sequestration of the iron-laden bacterial siderophore. We have recently reported that LCN2 inhibits the production of red blood cells in the mouse. Here we analyzed the role of LCN2 in human hematopoiesis. Expression of LCN2 was observed not only in mature cells such as those of the granulocyte/macrophage and erythroid lineages but also in hematopoietic stem/progenitor cells. We also examined expression of two candidate receptors for LCN2, brain type organic cation transporter (BOCT) and megalin, in various cell types. BOCT showed relatively high levels of expression in erythroid and hematopoietic stem/progenitor cells but lower levels in granulocyte/macrophage and T lymphoid cells. Megalin was expressed at high levels in T lymphoid and erythroid cells but at lower levels in granulocyte/macrophage lineage cells. LCN2 suppressed the growth of erythroid and monocyte/macrophage lineages in vitro, but did not have this effect on cells of other lineages. In addition, immature hematopoietic stem/progenitor cells were not sensitive to LCN2. These results demonstrate a lineage-specific role for LCN2 in human hematopoiesis that is reminiscent of its effects upon mouse hematopoiesis and strongly suggest an important in vivo function of LCN2 in the regulation of human hematopoiesis.

Establishment of mouse embryonic stem cell-derived erythroid progenitor cell lines able to produce functional red blood cells

BACKGROUND

The supply of transfusable red blood cells (RBCs) is not sufficient in many countries. If erythroid cell lines able to produce transfusable RBCs in vitro were established, they would be valuable resources. However, such cell lines have not been established. To evaluate the feasibility of establishing useful erythroid cell lines, we attempted to establish such cell lines from mouse embryonic stem (ES) cells.

METHODOLOGY/PRINCIPAL FINDINGS

We developed a robust method to obtain differentiated cell lines following the induction of hematopoietic differentiation of mouse ES cells and established five independent hematopoietic cell lines using the method. Three of these lines exhibited characteristics of erythroid cells. Although their precise characteristics varied, each of these lines could differentiate in vitro into more mature erythroid cells, including enucleated RBCs. Following transplantation of these erythroid cells into mice suffering from acute anemia, the cells proliferated transiently, subsequently differentiated into functional RBCs, and significantly ameliorated the acute anemia. In addition, we did not observe formation of any tumors following transplantation of these cells.

CONCLUSION/SIGNIFICANCE

To the best of our knowledge, this is the first report to show the feasibility of establishing erythroid cell lines able to produce mature RBCs. Considering the number of human ES cell lines that have been established so far, the intensive testing of a number of these lines for erythroid potential may allow the establishment of human erythroid cell lines similar to the mouse erythroid cell lines described here. In addition, our results strongly suggest the possibility of establishing useful cell lines committed to specific lineages other than hematopoietic progenitors from human ES cells.

A dual role of lipocalin 2 in the apoptosis and deramification of activated microglia

Activated microglia are thought to undergo apoptosis as a self-regulatory mechanism. To better understand molecular mechanisms of the microglial apoptosis, apoptosis-resistant variants of microglial cells were selected and characterized. The expression of lipocalin 2 (lcn2) was significantly down-regulated in the microglial cells that were resistant to NO-induced apoptosis. lcn2 expression was increased by inflammatory stimuli in microglia. The stable expression of lcn2 as well as the addition of rLCN2 protein augmented the sensitivity of microglia to the NO-induced apoptosis, while knockdown of lcn2 expression using short hairpin RNA attenuated the cell death. Microglial cells with increased lcn2 expression were more sensitive to other cytotoxic agents as well. Thus, inflammatory activation of microglia may lead to up-regulation of lcn2 expression, which sensitizes microglia to the self-regulatory apoptosis. Additionally, the stable expression of lcn2 in BV-2 microglia cells induced a morphological change of the cells into the round shape with a loss of processes. Treatment of primary microglia cultures with the rLCN2 protein also induced the deramification of microglia. The deramification of microglia was closely related with the apoptosis-prone phenotype, because other deramification-inducing agents such as cAMP-elevating agent forskolin, ATP, and calcium ionophore also rendered microglia more sensitive to cell death. Taken together, our results suggest that activated microglia may secrete LCN2 protein, which act in an autocrine manner to sensitize microglia to the self-regulatory apoptosis and to endow microglia with an amoeboid form, a canonical morphology of activated microglia in vivo.

Neutrophil gelatinase-associated lipocalin as the real-time indicator of active kidney damage

Neutrophil gelatinase-associated lipocalin (Ngal, 24p3, SIP24, lipocalin 2, or siderocalin) was originally purified from neutrophils, but with unknown function. Recently, it was identified that Ngal activates nephron formation in the embryonic kidney, is rapidly and massively induced in renal failure and possesses kidney-protective activity. We would like to propose that blood, urine, and kidney Ngal levels are the real-time indicators of active kidney damage, rather than one of many markers of functional nephron number (as Forest Fire Theory). Ngal is a novel iron-carrier protein exerting pleiotropic actions including the upregulation of epithelial marker E-cadherin expression, opening an exciting field in cell biology.

Expression of the genes dual oxidase 2, lipocalin 2 and regenerating islet-derived 1 alpha in Crohn's disease

OBJECTIVE

A global gene expression profile of non-inflamed colonic mucosal cells from patients with Crohn's disease (CD) and of colonic mucosal cells from controls was performed.

MATERIAL AND METHODS

Tissue specimens from macroscopically non-inflamed descending colon were obtained colonoscopically from 33 CD patients and from 17 control subjects. All controls and 10 CD patients were medication-free at the time of colonoscopy. The Human Genome U133 Plus 2.0 GeneChip Array was used for gene profiling. Hybridization data were analysed with dChip software. Results were confirmed by real-time reverse transcriptase polymerase chain reaction (RT-PCR). Protein product expression of selected genes was assessed by immunohistochemistry using the Envision+ visualization technique.

RESULTS

The expression profile was not homogeneous with the statistical cut-point settings applied. In comparison with controls, it was found that 19 CD patients had three differentially expressed genes, two of them related to the innate immune system: dual oxidase 2 on chromosome 15 (DUOX2, fold change 4.1) and lipocalin 2 on chromosome 9 (LCN2, fold change 3.1). The third gene, regenerating islet-derived 1 alpha (REG1A, fold change 3.9), codes for a mitogenic protein; this could not be confirmed by RT-PCR. Medication-free patients had no differentially expressed genes as compared with controls. Immunohistochemistry indicated that these proteins were produced by epithelial cells (REG1A, LCN2) and leucocytes (DUOX2 and LCN2).

CONCLUSIONS

As compared with controls, non-inflamed colonic mucosal cells contain two up-regulated genes related to the innate immune system. Up-regulation of these genes, known to be induced by microorganisms, suggests either increased microflora antigenicity or an altered function in mucosal barrier defence.

Lipocalin-2 regulates the inflammatory response during ischemia and reperfusion of the transplanted heart

Ischemia and reperfusion (IR) are known to negatively affect early allograft function following solid organ transplantation. Lipocalin-2 (Lcn-2) has been described as a marker and potential positive modulator of acute inflammation during these processes. Using a heterotopic murine heart transplant model we previously found that IR resulted in a pronounced upregulation of Lcn-2 mRNA in the heart at 12 (22.7-fold increase) and 24 h (9.8-fold increase) of reperfusion. We now confirm this increase at the protein level and provide evidence for infiltrating polymorphonuclear cells as the primary source of Lcn-2 protein. Lcn-2 levels are increased 6.6-fold at 12 h, 11.4-fold at 24 h and 6.4 fold at 48 h after reperfusion. In Lcn-2(-/-) grafts the number of infiltrating granulocytes is reduced by 54% (p < 0.05) at 2 h, 79% (p < 0.01) at 12 h, 72% (p < 0.01) at 24 h and 52% (p < 0.01) at 48 h after reperfusion compared to Lcn-2(+/+) grafts, without any differences in cardiomyocyte apoptosis. These data suggest a function of Lcn-2 in the initiation of the inflammatory response. Moreover, an increase in Lcn-2 is not only restricted to the transplanted heart, but is also observed in the kidney, hinting at a possible involvement of Lcn-2 in the systemic response to IR.

Refinement of cytokine use in the in vitro expansion of erythroid cells

Blood transfusion is indispensable for many clinical applications. However, the supply of transfusable material is insufficient in many countries. Human cord blood contains many hematopoietic stem and progenitor cells, providing a promising resource for the production of transfusable material in vitro. In this study, we have refined a protocol to produce abundant red blood cells (RBC) from human cord blood in an in vitro culture system. We found that erythropoietin and interleukin-3 were most effective when they were added to the culture medium sequentially rather than simultaneously. Although insulin-like growth factor-I (IGF-1) has been reported to function as a positive regulator of RBC production in some in vitro culture systems, we found that IGF-1 had a negative effect upon RBC production. However, IGF-II appeared to function as a positive regulator of RBC production. Finally, stem cell factor functioned to both expand and accelerate the differentiation of immature erythroid cells.