Il-Hoan Oh

The myb gene family in cell growth, differentiation and apoptosis.

The myb gene family consists of three members, named A, B and c-myb which encode nuclear proteins that function as transcriptional transactivators. Proteins encoded by these three genes exhibit a tripartate structure with an N-terminal DNA-binding domain, a central transactivation domain and a C-terminal regulatory domain. These proteins exhibit highest homology in their DNA binding domains and appear to bind DNA with overlapping sequence specificities. Transactivation by myb gene family varies considerably depending on cell type and promoter context suggesting a dependence on interaction with other cell type specific co-factors. While the C-terminal domains of A-Myb and c-Myb proteins exert a negative regulatory effect on their transcriptional transactivation function, the C-terminal domain of B-Myb appears to function as a positive regulator of this activity. One or more of these proteins interact with other transcription factors such as Ets-2, CEBP and NF-M. In addition, expression of these genes is cell cycle-regulated and inhibition of their expression with anti-sense oligonucleotides has been found to affect cell cycle-progression, cell division and/or differentiation. Members of the myb gene family exhibit different temporal and spatial expression patterns suggesting a distinctive function for each of these genes. Gene knockout experiments show that these genes play an essential role in development. Loss of c-myb function results in embryonic lethality due to failure of fetal hepatic hematopoiesis. A-myb null mutant mice, on the other hand are viable but exhibit growth abnormalities, and defects in spermatogenesis and female breast development. While the role of c-myb in oncogenesis is well established, future experiments are likely to provide further clues regarding the role of A-myb and B-myb in tumorigenesis.

Mesenchymal stem cells overexpressing interleukin-10 attenuate collagen-induced arthritis in mice

Mesenchymal stem cells (MSCs) have the inherent ability to migrate to multiple organs and to exert immunosuppressive activity. The aim of this study was to investigate the anti‐arthritogenic effects of interleukin (IL)‐10‐transduced MSCs (IL‐10‐MSC) on the development of inflammatory arthritis. DBA/1 mice were immunized with type II collagen (CII) to induce inflammatory arthritis and then injected weekly three times with IL‐10‐MSCs 21 days after primary immunization. Control mice received vehicle or MSCs alone. Serum anti‐CII antibody and T cell response to CII were determined. The results showed that cultured IL‐10‐MSCs were able to secrete high amounts of IL‐10 in vitro. Injection of IL‐10‐MSCs decreased the severity of arthritis significantly. However, there was no difference in arthritis severity between mice treated with MSC and vehicle alone. Anti‐CII antibody titres in the sera and T cell proliferative response to CII in lymph node cells were decreased significantly in mice treated with IL‐10‐MSCs compared with vehicle‐treated mice. Serum IL‐6 level was also decreased by the administration of IL‐10‐MSCs. In contrast, spleen cells of IL‐10‐MSC‐treated mice produced higher amounts of IL‐4 than those of control mice. Interestingly, although not as potent as IL‐10‐MSCs, injection of naive MSCs alone decreased serum levels of IL‐6 and anti‐CII antibody, while increasing IL‐4 production from cultured splenic cells. Taken together, systemic administration of genetically modified MSCs overexpressing IL‐10 inhibits experimental arthritis not only by suppressing autoimmune response to CII but also by regulating cytokine production, and thus would be a new strategy for treating rheumatoid arthritis.

Identification of a Stroma‐Mediated Wnt/β‐Catenin Signal Promoting Self‐Renewal of Hematopoietic Stem Cells in the Stem Cell Niche

With contrasting observations on the effects of β‐catenin on hematopoietic stem cells (HSCs), the precise role of Wnt/β‐catenin signals on HSC regulation remains unclear. Here, we show a distinct mode of Wnt/β‐catenin signal that can regulate HSCs in a stroma‐dependent manner. Stabilization of β‐catenin in the bone marrow stromal cells promoted maintenance and self‐renewal of HSCs in a contact‐dependent manner, whereas direct stabilization in hematopoietic cells caused loss of HSCs. Interestingly, canonical Wnt receptors and β‐catenin accumulation were predominantly enriched in the stromal rather than the hematopoietic compartment of bone marrows. Moreover, the active form of β‐catenin accumulated selectively in the trabecular endosteum in “Wnt 3a‐stimulated” or “irradiation‐stressed,” but not in “steady‐state” marrows. Notably, notch ligands were induced in Wnt/β‐catenin activated bone marrow stroma and downstream notch signal activation was seen in the HSCs in contact with the activated stroma. Taken together, Wnt/β‐catenin activated stroma and their cross‐talk with HSCs may function as a physiologically regulated microenvironmental cue for HSC self‐renewal in the stem cell niche. STEM CELLS 2009;27:1318–1329

Concise Review: Multiple Niches for Hematopoietic Stem Cell Regulations†‡§

Two types of stem cell niches in bone marrow (BM), endosteal osteoblastic, and vascular niches are involved in the microenvironmental regulation of hematopoietic stem cells (HSCs). Recently, redundant features of the two niches were identified, based on their common cellular origins or chemical mediators being produced in each niche. In contrast, studies have also revealed that HSCs are localized differentially in the niches with respect to their distinct functional status, and that the biological activity of each niche is differentially influenced by extrinsic conditions. An important question is, therefore, whether these two niches play distinct roles in regulating HSCs and whether they respond differentially to environmental stimuli/stress for “compartmentalized” niche organization in BM. In this review, recent discoveries related to the characteristics of each type of niche and their common or unique features are discussed, along with the possibility of multiniche regulation of HSCs in BM. STEM CELLS 2010;28:1243–1249

Mesenchymal Stromal Cells Expanded in Human Allogenic Cord Blood Serum Display Higher Self-Renewal and Enhanced Osteogenic Potential

Recent clinical trials using ex vivo expanded mesenchymal stromal cells (MSCs) have raised interest in the safety and function of cultured MSCs. Here, to assess the feasibility of using allogenic human umbilical cord blood serum (CBS) for humanized clinical-grade expansion of MSCs, we characterized MSCs expanded in CBS and compared them to MSCs expanded in fetal bovine serum (FBS). MSCs in CBS exhibited a higher preservation of colony-forming cells and an accelerated expansion over serial passages with increased Oct-4 expression compared to those cultured in FBS. Notably, CBS-expanded MSCs exhibited a unique differentiation potential characterized by a shift from adipogenic to osteogenic differentiation. The differentiation shift was associated with enhanced basal and Runx2-mediated transcriptional activation of the osteocalcin promoter, as well as increased accumulation of beta-catenin and the yes-associated protein (YAP) which was independent of changes in TAZ (transcriptional co-activator with PDZ-binding motif) levels. Interestingly, the phenotypes were reversed when the FBS and CBS media were switched, suggesting the unique stimulatory effects of CBS rather than the selection of heterogeneous MSC subpopulations. The distinct regulatory effects of CBS on MSC included selective activation of platelet-derived growth factor and epidermal growth factor signals in MSCs, but not in FBS. Taken together, these results provide insight into the dynamic regulation of MSCs during ex vivo culture and show that the ex vivo culture of MSCs in allogenic human CBS provides a novel tool for the accelerated expansion of a population of MSCs that exhibit a higher self-renewal and an enhanced osteogenic potential.

Overexpression of a dominant negative form of STAT3 selectively impairs hematopoietic stem cell activity.

STAT3 is a key downstream signaling intermediate of gp130, a receptor previously shown to activate hematopoietic stem cell (HSC) self-renewal divisions. These findings prompted us to investigate if the STAT3 pathway is important to HSC activity in vivo. Initial semi-quantitative RT–PCR analyses showed STAT3 to be expressed at slightly higher levels in primitive subsets of both human and murine adult bone marrow cells. To test the effect of abrogating STAT3 activity in HSCs, primitive murine fetal liver cells were transduced at high efficiency with either a bicistronic dominant-negative (dn) or wild-type (wt) STAT3-IRES-GFP retrovirus. Dn STAT3-transduced HSCs showed markedly and permanently reduced in vivo lympho-myeloid reconstituting ability relative to co-transplanted non-transduced HSCs or HSCs transduced with a control (GFP-only) vector. In contrast, the activity of dn STAT3-transduced cells with short term in vivo (CFU-S) or in vitro (CFC) proliferation potential was not affected. Overexpression of wt-STAT3 had very little effect on either HSCs or shorter term progenitors. These findings suggest HSCs express non-limiting levels of STAT3 which, nevertheless, play an important stage-specific and non-redundant role in maintaining the function of HSCs stimulated to divide in adult marrow tissue.

Microenvironmental Remodeling as a Parameter and Prognostic Factor of Heterogeneous Leukemogenesis in Acute Myelogenous Leukemia

Acute myelogenous leukemia (AML) is a heterogeneous disorder characterized by clonal proliferation of stem cell-like blasts in bone marrow (BM); however, their unique cellular interaction within the BM microenvironment and its functional significance remain unclear. Here, we assessed the BM microenvironment of AML patients and demonstrate that the leukemia stem cells induce a change in the transcriptional programming of the normal mesenchymal stromal cells (MSC). The modified leukemic niche alters the expressions of cross-talk molecules (i.e., CXCL12 and JAG1) in MSCs to provide a distinct cross-talk between normal and leukemia cells, selectively suppressing normal primitive hematopoietic cells while supporting leukemogenesis and chemoresistance. Of note, AML patients exhibited distinct heterogeneity in the alteration of mesenchymal stroma in BM. The distinct pattern of stromal changes in leukemic BM at initial diagnosis was associated with a heterogeneous posttreatment clinical course with respect to the maintenance of complete remission for 5 to 8 years and early or late relapse. Thus, remodeling of mesenchymal niche by leukemia cells is an intrinsic self-reinforcing process of leukemogenesis that can be a parameter for the heterogeneity in the clinical course of leukemia and hence serve as a potential prognostic factor.

Efficacy and safety of stem cell therapies for patients with stroke: a systematic review and single arm meta-analysis.

Background and Objectives: Stem cell-based therapy is a potential new approach in the treatment of stroke. However, the efficacy and safety of these treatments are not yet fully understood. Therefore, we performed a meta-analysis of available single-arm studies using stem cell-based therapy in patients with stroke. Methods: We searched MEDLINE, EMBASE, and the Cochrane database for studies of stem cell therapy in patients with stroke from its inception through July 2014. The articles included in the search were restricted to the English language, studies with at least 5 patients, and those using cell-based therapies for treating stroke. Results: Fourteen studies included in the meta-analysis. The pooled mean difference in National Institutes of Health Stroke Scale (NIHSS) scores from baseline to follow-up points was 5.7 points (95%CI: −8.2 to −3.2, I2=91.5%) decreased. Also the pooled mean difference in modified Bathel index (BI) score was increased by 31.5 points (95%CI: 35.6∼14.9, I2=52.7%) and the pooled incidence rate to achieve on modified Rankin score (mRS)≤2 was 40% (95% CI: 30%∼51%, I2=35.4%) at follow-up points. The pooled incidence rates of death, seizure, and infection were 13% (95%CI, 8∼23%), 15% (95%CI, 8∼25%), and 15% (95%CI, 8∼23%), respectively. Conclusions: The published data suggest that stem cell-based therapy for patients with stroke can be judged as effective based on single arm clinical studies. However, clinical benefits of stem cell therapy for patients with stroke need further investigation and reevaluation to test the clinical efficacy.

Increased SCF/c‐kit by hypoxia promotes autophagy of human placental chorionic plate‐derived mesenchymal stem cells via regulating the phosphorylation of mTOR

Hypoxia triggers physiological and pathological cellular processes, including proliferation, differentiation, and death, in several cell types. Mesenchymal stem cells (MSCs) derived from various tissues have self‐renewal activity and can differentiate towards multiple lineages. Recently, it has been reported that hypoxic conditions tip the balance between survival and death by hypoxia‐induced autophagy, although the underlying mechanism is not clear. The objectives of this study are to compare the effect of hypoxia on the self‐renewal of bone marrow‐derived mesenchymal stem cells (BM‐MSCs) and placental chorionic plate‐derived mesenchymal stem cells (CP‐MSCs) and to investigate the regulatory mechanisms of self‐renewal in each MSC type during hypoxia. The expression of self‐renewal markers (e.g., Oct4, Nanog, Sox2) was assessed in both cell lines. PI3K and stem cell factor (SCF) expression gradually increased in CP‐MSCs but were markedly downregulated in BM‐MSCs by hypoxia. The phosphorylation of ERK and mTOR was augmented by hypoxia in CP‐MSCs compared to control. Also, the expression of LC3 II, a component of the autophagosome and the hoof‐shaped autophagosome was detected more rapidly in CP‐MSCs than in BM‐MSCs under hypoxia. Hypoxia induced the expression of SCF in CP‐MSCs and increased SCF/c‐kit pathway promotes the self‐renewal activities of CP‐MSCs via an autocrine/paracrine mechanism that balances cell survival and cell death events by autophagy. These activities occur to a greater extent in CP‐MSCs than in BM‐MSCs through regulating the phosphorylation of mTOR. These findings will provide useful guidelines for better understanding the function of SCF/c‐kit in the self‐renewal and autophagy‐regulated mechanisms that promote of MSC survival. J. Cell. Biochem. 114: 79–88, 2012.

Concise Review: Multidimensional Regulation of the Hematopoietic Stem Cell State†‡§

Hematopoietic stem cells (HSCs) are characterized by their unique function to produce all lineages of blood cells throughout life. Such tissue‐specific function of HSC is attributed to their ability to execute self‐renewal and multilineage differentiation. Accumulating evidence indicates that the undifferentiated state of HSC is characterized by dynamic maintenance of chromatin structures and epigenetic plasticity. Conversely, quiescence, self‐renewal, and differentiation of HSCs are dictated by complex regulatory mechanisms involving specific transcription factors and microenvironmental crosstalk between stem cells and multiple compartments of niches in bone marrows. Thus, multidimensional regulatory inputs are integrated into two opposing characters of HSCs—maintenance of undifferentiated state analogous to pluripotent stem cells but execution of tissue‐specific hematopoietic functions. Further studies on the interplay of such regulatory forces as “cell fate determinant” will likely shed the light on diverse spectrums of tissue‐specific stem cells. STEM CELLS 2012;30:82–88