Promotion of self-renewal of embryonic stem cells by midkine

PRMT5 inhibition shows in vitro efficacy against H3K27M-altered diffuse midline glioma, but does not extend survival in vivo

H3K27-altered Diffuse Midline Glioma (DMG) is a universally fatal paediatric brainstem tumour. The prevalent driver mutation H3K27M creates a unique epigenetic landscape that may also establish therapeutic vulnerabilities to epigenetic inhibitors. However, while HDAC, EZH2 and BET inhibitors have proven somewhat effective in pre-clinical models, none have translated into clinical benefit due to either poor blood-brain barrier penetration, lack of efficacy or toxicity. Thus, there remains an urgent need for new DMG treatments. Here, we performed wider screening of an epigenetic inhibitor library and identified inhibitors of protein arginine methyltransferases (PRMTs) among the top hits reducing DMG cell viability. Two of the most effective inhibitors, LLY-283 and GSK591, were targeted against PRMT5 using distinct binding mechanisms and reduced the viability of a subset of DMG cells expressing wild-type TP53 and mutant ACVR1. RNA-sequencing and phenotypic analyses revealed that LLY-283 could reduce the viability, clonogenicity and invasion of DMG cells in vitro, representing three clinically important phenotypes, but failed to prolong survival in an orthotopic xenograft model. Together, these data show the challenges of DMG treatment and highlight PRMT5 inhibitors for consideration in future studies of combination treatments.

The uterine secretory cycle: recurring physiology of endometrial outputs that setup the uterine luminal microenvironment

Conserved in female reproduction across all mammalian species is the estrous cycle and its regulation by the hypothalamic-pituitary-gonadal (HPG) axis, a collective of intersected hormonal events that are crucial for ensuring uterine fertility. Nonetheless, knowledge of the direct mediators that synchronously shape the uterine microenvironment for successive yet distinct events, such as the transit of sperm and support for progressive stages of preimplantation embryo development, remain principally deficient. Toward understanding the timed endometrial outputs that permit luminal events as directed by the estrous cycle, we used Bovidae as a model system to uniquely surface sample and study temporal shifts to in vivo endometrial transcripts that encode for proteins destined to be secreted. The results revealed the full quantitative profile of endometrial components that shape the uterine luminal microenvironment at distinct phases of the estrous cycle (estrus, metestrus, diestrus, and proestrus). In interpreting this comprehensive log of stage-specific endometrial secretions, we define the "uterine secretory cycle" and extract a predictive understanding of recurring physiological actions regulated within the uterine lumen in anticipation of sperm and preimplantation embryonic stages. This repetitive microenvironmental preparedness to sequentially provide operative support was a stable intrinsic framework, with only limited responses to sperm or embryos if encountered in the lumen within the cyclic time period. In uncovering the secretory cycle and unraveling realistic biological processes, we present novel foundational knowledge of terminal effectors controlled by the HPG axis to direct a recurring sequence of vital functions within the uterine lumen.NEW & NOTEWORTHY This study unravels the recurring sequence of changes within the uterus that supports vital functions (sperm transit and development of preimplantation embryonic stages) during the reproductive cycle in female Ruminantia. These data present new systems knowledge in uterine reproductive physiology crucial for setting up in vitro biomimicry and artificial environments for assisted reproduction technologies for a range of mammalian species.

Differential Production of Midkine and Pleiotrophin by Innate APCs upon Stimulation through Nucleic Acid-Sensing TLRs

Midkine (MK) and pleiotrophin (PTN) belong to the same family of cytokines. They have similar sequences and functions. Both have important roles in cellular proliferation, tumors, and diseases. They regulate and are expressed by some immune cells. We have recently demonstrated MK production by some human innate antigen-presenting cells (iAPCs), i.e., monocyte-derived dendritic cells (MDDCs) and macrophages stimulated through Toll-like receptor (TLR)-4, and plasmacytoid dendritic cells (pDCs) stimulated through TLR 7. While PTN production was only documented in tissue macrophages. TLRs 3, 7, 8, and 9 are nucleic acid sensing (NAS) TLRs that detect nucleic acids from cell damage and infection and induce iAPC responses. We investigated whether NAS TLRs can induce MK and PTN production by human iAPCs, namely monocytes, macrophages, MDDCs, myeloid dendritic cells (mDCs), and pDCs. Our results demonstrated for the first time that PTN is produced by all iAPCs upon TLR triggering (p < 0.01). IAPCs produced more PTN than MK (p < 0.01). NAS TLRs and iAPCs had differential abilities to induce the production of MK, which was induced in monocytes and pDCs by all NAS TLRs (p < 0.05) and in MDDCs by TLRs 7/8 (p < 0.05). TLR4 induced a stronger MK production than NAS TLRs (p ≤ 0.05). Monocytes produced higher levels of PTN after differentiation to macrophages and MDDCs (p < 0.05). The production of MK and PTN differs among iAPCs, with a higher production of PTN and a selective induction of MK production by NAS TLR. This highlights the potentially important role of iAPCs in angiogenesis, tumors, infections, and autoimmunity through the differential production of MK and PTN upon TLR triggering.

Nasopharynx Battlefield: Cellular Immune Responses Mediated by Midkine in Nasopharyngeal Carcinoma and COVID-19

Clinical evidence suggests that the severe respiratory illness coronavirus disease 2019 (COVID-19) is often associated with a cytokine storm that results in dysregulated immune responses. Prolonged COVID-19 positivity is thought to disproportionately affect cancer patients. With COVID-19 disrupting the delivery of cancer care, it is crucial to gain momentum and awareness of the mechanistic intersection between these two diseases. This review discusses the role of the cytokine midkine (MK) as an immunomodulator in patients with COVID-19 and nasopharyngeal carcinoma (NPC), both of which affect the nasal cavity. We conducted a review and analysis of immunocellular similarities and differences based on clinical studies, research articles, and published transcriptomic datasets. We specifically focused on ligand-receptor pairs that could be used to infer intercellular communication, as well as the current medications used for each disease, including NPC patients who have contracted COVID-19. Based on our findings, we recommend close monitoring of the MK axis to maintain the desirable effects of therapeutic regimens in fighting both NPC and COVID-19 infections.

Dissecting the spermatogonial stem cell niche using spatial transcriptomics

Spermatogonial stem cells (SSCs) in the testis support the lifelong production of sperm. SSCs reside within specialized microenvironments called "niches," which are essential for SSC self-renewal and differentiation. However, our understanding of the molecular and cellular interactions between SSCs and niches remains incomplete. Here, we combine spatial transcriptomics, computational analyses, and functional assays to systematically dissect the molecular, cellular, and spatial composition of SSC niches. This allows us to spatially map the ligand-receptor (LR) interaction landscape in both mouse and human testes. Our data demonstrate that pleiotrophin regulates mouse SSC functions through syndecan receptors. We also identify ephrin-A1 as a potential niche factor that influences human SSC functions. Furthermore, we show that the spatial re-distribution of inflammation-related LR interactions underlies diabetes-induced testicular injury. Together, our study demonstrates a systems approach to dissect the complex organization of the stem cell microenvironment in health and disease.

OCT6 inhibits differentiation of porcine-induced pluripotent stem cells through MAPK and PI3K signaling regulation

As a transcription factor of the Pit-Oct-Unc (POU) domain family, octamer-binding transcription factor 6 ( OCT6) participates in various aspects of stem cell development and differentiation. At present, however, its role in porcine-induced pluripotent stem cells (piPSCs) remains unclear. Here, we explored the function of OCT6 in piPSCs. We found that piPSCs overexpressing OCT6 maintained colony morphology and pluripotency under differentiation conditions, with a similar gene expression pattern to that of non-differentiated piPSCs. Functional analysis revealed that OCT6 attenuated the adverse effects of extracellular signal-regulated kinase (ERK) signaling pathway inhibition on piPSC pluripotency by activating phosphatidylinositol 3-kinase-protein kinase B (PI3K-AKT) signaling activity. Our research sheds new light on the mechanism by which OCT6 promotes PSC maintenance.

Large-scale integration of single-cell transcriptomic data captures transitional progenitor states in mouse skeletal muscle regeneration

Skeletal muscle repair is driven by the coordinated self-renewal and fusion of myogenic stem and progenitor cells. Single-cell gene expression analyses of myogenesis have been hampered by the poor sampling of rare and transient cell states that are critical for muscle repair, and do not inform the spatial context that is important for myogenic differentiation. Here, we demonstrate how large-scale integration of single-cell and spatial transcriptomic data can overcome these limitations. We created a single-cell transcriptomic dataset of mouse skeletal muscle by integration, consensus annotation, and analysis of 23 newly collected scRNAseq datasets and 88 publicly available single-cell (scRNAseq) and single-nucleus (snRNAseq) RNA-sequencing datasets. The resulting dataset includes more than 365,000 cells and spans a wide range of ages, injury, and repair conditions. Together, these data enabled identification of the predominant cell types in skeletal muscle, and resolved cell subtypes, including endothelial subtypes distinguished by vessel-type of origin, fibro-adipogenic progenitors defined by functional roles, and many distinct immune populations. The representation of different experimental conditions and the depth of transcriptome coverage enabled robust profiling of sparsely expressed genes. We built a densely sampled transcriptomic model of myogenesis, from stem cell quiescence to myofiber maturation, and identified rare, transitional states of progenitor commitment and fusion that are poorly represented in individual datasets. We performed spatial RNA sequencing of mouse muscle at three time points after injury and used the integrated dataset as a reference to achieve a high-resolution, local deconvolution of cell subtypes. We also used the integrated dataset to explore ligand-receptor co-expression patterns and identify dynamic cell-cell interactions in muscle injury response. We provide a public web tool to enable interactive exploration and visualization of the data. Our work supports the utility of large-scale integration of single-cell transcriptomic data as a tool for biological discovery.

Midkine-a functions as a universal regulator of proliferation during epimorphic regeneration in adult zebrafish

Zebrafish have the ability to regenerate damaged cells and tissues by activating quiescent stem and progenitor cells or reprogramming differentiated cells into regeneration-competent precursors. Proliferation among the cells that will functionally restore injured tissues is a fundamental biological process underlying regeneration. Midkine-a is a cytokine growth factor, whose expression is strongly induced by injury in a variety of tissues across a range of vertebrate classes. Using a zebrafish Midkine-a loss of function mutant, we evaluated regeneration of caudal fin, extraocular muscle and retinal neurons to investigate the function of Midkine-a during epimorphic regeneration. In wildtype zebrafish, injury among these tissues induces robust proliferation and rapid regeneration. In Midkine-a mutants, the initial proliferation in each of these tissues is significantly diminished or absent. Regeneration of the caudal fin and extraocular muscle is delayed; regeneration of the retina is nearly completely absent. These data demonstrate that Midkine-a is universally required in the signaling pathways that convert tissue injury into the initial burst of cell proliferation. Further, these data highlight differences in the molecular mechanisms that regulate epimorphic regeneration in zebrafish.

TPGS-1000 exhibits potent anticancer activity for hepatocellular carcinoma in vitro and in vivo

D-alpha-tocopheryl polyethylene glycol 1000 succinate (TPGS1000) is the most active water-soluble derivative of vitamin E and has been widely used as a carrier of solvents, plasticizers, emulsifiers, absorbent agents and refractory drug delivery systems. However, its anti-hepatocellular carcinoma (HCC) properties have not been explored. HCC cells were treated with different concentrations of TPGS1000. Cell survival was tested by CCK8 assay, and cell migration was tested by wound healing and Transwell assay. EdU staining verified cell proliferation, and signalling pathway was assayed by Western blot analysis. The BALB/c-nu mouse xenograft model was established to test HCC cell growth in vivo. In vitro TPGS1000 significantly inhibited the viability and mobility of HCC cells (HepG2, Hep3B and Huh7) in a dose-dependent manner. Cell cycle analysis indicated that TPGS1000 treatment arrested the HCC cell cycle in the G0/G1 phase, and induction of cell apoptosis was confirmed by TUNEL and Annexin V-7-AAD staining. Further pharmacological analysis indicated that collapse of the transmembrane potential of mitochondria, increased ROS generation, PARP-induced cell apoptosis and FoxM1-p21-mediated cell cycle arresting, were involved in the anti-HCC activity of TPGS1000. Moreover, treatment in vivo with TPGS1000 effectively impaired the growth of HCC xenografts in nude mice.

Leukocyte receptor tyrosine kinase interacts with secreted midkine to promote survival of migrating neural crest cells

Neural crest cells migrate long distances throughout the embryo and rely on extracellular signals that attract, repel and/or stimulate survival to ensure proper contribution to target derivatives. Here, we show that leukocyte receptor tyrosine kinase (LTK), an ALK-type receptor tyrosine kinase, is expressed by neural crest cells during early migratory stages in chicken embryos. Loss of LTK in the cranial neural crest impairs migration and results in increased levels of apoptosis. Conversely, midkine, previously proposed as a ligand for ALK, is secreted by the non-neural ectoderm during early neural crest migratory stages and internalized by neural crest cells in vivo Similar to loss of LTK, loss of midkine reduces survival of the migratory neural crest. Moreover, we show by proximity ligation and co-immunoprecipitation assays that midkine binds to LTK. Taken together, these results suggest that LTK in neural crest cells interacts with midkine emanating from the non-neural ectoderm to promote cell survival, revealing a new signaling pathway that is essential for neural crest development.

MPA Modulates Tight Junctions' Permeability via Midkine/PI3K Pathway in Caco-2 Cells: A Possible Mechanism of Leak-Flux Diarrhea in Organ Transplanted Patients

Mycophenolic acid (MPA) is prescribed to prevent allograft rejection in organ transplanted patients. However, its use is sporadically linked to leak flux diarrhea and other gastrointestinal (GI) disturbances in around 75% of patients through yet unknown mechanisms. Recently, we identified Midkine as a modulator of tight junctions (TJs) permeability in MPA treated Caco-2 monolayer. In the present study, we investigated the possible involvement of Midkine dependent PI3K pathway in alteration of TJs under MPA treatment. Caco-2 cells were grown as monolayer to develop TJs and were treated for 72 h with DMSO (control) or MPA in presence and absence of Midkine inhibitor (iMDK) or PI3K inhibitors (LY/AMG). Caco-2 monolayer integrity was assessed by transepithelial electrical resistance (TEER) and FITC-dextran assays. Our functional assays showed that PI3K inhibitors (LY/AMG) can significantly inhibit the compromised TJs integrity of MPA-treated Caco-2 cells monolayer. Chromatin immunoprecipitation analyses showed a significant epigenetic activation of Midkine, PI3K, Cdx-2, and Cldn-2 genes and epigenetic repression of Cldn-1 gene after MPA treatment. The MPA-induced epigenetic alterations were further confirmed by mRNA and protein expression analysis. Collectively, our data shows that PI3K pathway as the downstream target of Midkine which in turn modulates p38MAPK and pAKT signaling to alter TJs permeability in Caco-2 cell monolayers treated with MPA. These results highlight the possible use of either Midkine or PI3K inhibitors as therapeutic agents to prevent MPA induced GI disturbances.

Expression of the heparin-binding growth factor midkine and its receptor, Ptprz1, in adult rat pituitary

Midkine (MK) belongs to a family of secreted heparin-binding growth factors and is highly expressed in various tissues during development. MK has multiple functions, such as regulation of cell proliferation, migration, survival and differentiation. We recently reported that MK mRNA is strongly expressed in the developing rat pituitary gland. In the adult pituitary, however, expression of MK and its receptor and the characteristics of the cells that produce them, have not been determined. Therefore, in this study, we investigate whether MK and its receptor, protein tyrosine phosphatase receptor-type Z (Ptprz1), are present in the adult rat pituitary. In situ hybridization, real-time reverse transcription-PCR and immunoblotting were performed to assess MK and Ptprz1 expression. We also characterize MK- and Ptprz1-expressing cells by double-staining with in situ hybridization and immunohistochemical techniques for each pituitary hormone or S100 protein [a marker of folliculostellate (FS) cells]. MK-expressing cells were located in the anterior and posterior lobes but not in the intermediate lobe. Double-staining and immunoblotting revealed that MK mRNA and protein were only expressed in FS cells in the anterior pituitary. Regarding Ptprz1 expression, Ptprz1 mRNA was detected in adrenocorticotropic hormone (ACTH) cells and growth hormone (GH) cells but not in prolactin cells, thyroid-stimulating hormone cells, luteinizing hormone cells, or FS cells. These findings suggest that MK produced in FS cells acts locally on ACTH cells and GH cells via Ptprz1 in the adult rat anterior pituitary.

Mesenchymal stem cells with overexpression of midkine enhance cell survival and attenuate cardiac dysfunction in a rat model of myocardial infarction

INTRODUCTION

Elevated midkine (MK) expression may contribute to ventricular remodeling and ameliorate cardiac dysfunction after myocardial infarction (MI). Ex vivo modification of signaling mechanisms in mesenchymal stem cells (MSCs) with MK overexpression may improve the efficacy of cell-based therapy. This study sought to assess the safety and efficacy of MSCs with MK overexpression transplantation in a rat model of MI.

METHODS

A pLenO-DCE vector lentivirus encoding MK was constructed and infected in MSCs. MSC migration activity and cytoprotection was examined in hypoxia-induced H9C2 cells using transwell insert in vitro. Rats were randomized into five groups: sham, MI plus injection of phosphate buffered saline (PBS), MSCs, MSCs-green fluorescent protein (MSCs-GFP) and MSCs-MK, respectively. Survival rates were compared among groups using log-rank test and left ventricular function was measured by echocardiography at baseline, 4, 8 and 12 weeks.

RESULTS

Overexpression of MK partially prevented hypoxia-induced MSC apoptosis and exerted MSC cytoprotection to anoxia induced H9C2 cells. The underlying mechanisms may be associated with the increased mRNA and protein levels of vascular endothelial growth factor (VEGF), transformation growth factor-β (TGF-β), insulin-like growth factor 1 (IGF-1) and stromal cell-derived factor 1 (SDF-1a) in MSCs-MK compared with isolated MSCs and MSCs-GFP. Consistent with the qPCR results, the culture supernatant of MSCs-MK had more SDF-1a (9.23 ng/ml), VEGF (8.34 ng/ml) and TGF-β1 (17.88 ng/ml) expression. In vivo, a greater proportion of cell survival was observed in the MSCs-MK group than in the MSCs-GFP group. Moreover, MSCs-MK administration was related to a significant improvement of cardiac function compared with other control groups at 12 weeks.

CONCLUSIONS

Therapies employing MSCs with MK overexpression may represent an effective treatment for improving cardiac dysfunction and survival rate after MI.

Midkine is associated with neuroendocrine differentiation in castration-resistant prostate cancer

BACKGROUND

Castration-resistant prostate cancer (CRPC) is an incurable disease and both androgen-deprivation therapy (ADT) and neuroendocrine differentiation (NED) are closely related to CRPC transition. More knowledge concerning neuroendocrine (NE)-transformed PC cells, the NED process and its association with CRPC, is needed. Expression of growth factor midkine (MDK) is correlated with poor clinical outcomes in various human cancers, including PC. In the present study, we have evaluated MDK expression and NED in two separate tumor groups: early and advanced PC.

METHODS

Immunohistochemical analysis of MDK, the neuronal marker tubulin-beta III (TUBB3) and the NE-marker chromogranin A (CGA) in a human archival material consisting of hormone naive (HN)/stage T1b (n = 29) and CRPC (n = 24) tumors. Triple immunofluorescent imaging was performed on a selection of specimens.

RESULTS

MDK, TUBB3, and CGA were upregulated in CRPC compared to HN tumors. MDK was highly associated to the expression of both CGA and TUBB3, and identified MDK-positive NE-like looking cells found to co-express CGA or, more commonly, CGA together with TUBB3. CGA and TUBB3 staining displayed a partial expression overlap, an overlap almost exclusively displaying also MDK expression.

CONCLUSIONS

MDK upregulation in CRPC is associated with NED (shown by its relation to CGA and TUBB3). The results suggest that MDK represents an over-bridging marker between different populations of NE-like tumor cells, possibly as part of the NED process and associated CRPC transition, something that needs to be evaluated experimentally as does the applicability of MDK as a future target.

Midkine-A functions upstream of Id2a to regulate cell cycle kinetics in the developing vertebrate retina

Background

Midkine is a small heparin binding growth factor expressed in numerous tissues during development. The unique midkine gene in mammals has two paralogs in zebrafish: midkine-a (mdka) and midkine-b (mdkb). In the zebrafish retina, during both larval development and adult photoreceptor regeneration, mdka is expressed in retinal stem and progenitor cells and functions as a molecular component of the retina’s stem cell niche. In this study, loss-of-function and conditional overexpression were used to investigate the function of Mdka in the retina of the embryonic zebrafish.

Results

The results show that during early retinal development Mdka functions to regulate cell cycle kinetics. Following targeted knockdown of Mdka synthesis, retinal progenitors cycle more slowly, and this results in microphthalmia, a diminished rate of cell cycle exit and a temporal delay of cell cycle exit and neuronal differentiation. In contrast, Mdka overexpression results in acceleration of the cell cycle and retinal overgrowth. Mdka gain-of-function, however, does not temporally advance cell cycle exit. Experiments to identify a potential Mdka signaling pathway show that Mdka functions upstream of the HLH regulatory protein, Id2a. Gene expression analysis shows Mdka regulates id2a expression, and co-injection of Mdka morpholinos and id2a mRNA rescues the Mdka loss-of-function phenotype.

Conclusions

These data show that in zebrafish, Mdka resides in a shared Id2a pathway to regulate cell cycle kinetics in retinal progenitors. This is the first study to demonstrate the function of Midkine during retinal development and adds Midkine to the list of growth factors that transcriptionally regulate Id proteins.

Artemisinin inhibits lipopolysaccharide-induced interferon-β production in RAW 264.7 cells: implications on signal transducer and activator of transcription-1 signaling and nitric oxide production

Artemisinin is a well-known anti-malarial drug and has been shown to inhibit nitric oxide (NO) production. In this study, we investigated the effect of artemisinin on lipopolysaccharide (LPS)-induced production of IFN-β and characterized the potential relationship between artemisinin-mediated inhibition of IFN-β and NO production. Artemisinin suppressed IFN-β production and mRNA expression in a dose-dependent manner in LPS-stimulated RAW 264.7 cells. LPS-induced phosphorylation of signal transducer and activator of transcription-1 (STAT-1) was also inhibited by artemisinin treatment in RAW 264.7 cells. In addition, artemisinin suppressed LPS-induced production of NO in RAW 264.7 cells. Further study demonstrated that artemisinin-mediated inhibition of NO production and STAT-1 phosphorylation was reversed by addition of exogenous IFN-β. Moreover, artemisinin does not affect IFN-β-induced STAT-1 phosphorylation in RAW 264.7 cells. Collectively, these results suggest that the inhibition of IFN-β production by artemisinin and concomitant attenuation of STAT-1 activation might be involved in artemisinin-mediated inhibition of NO production in macrophages.

Midkine promotes proliferation of primordial germ cells by inhibiting the expression of the deleted in azoospermia-like gene

Primordial germ cell (PGC) development is an area of research that is hampered by low cell numbers as well as difficulty in isolation. They are, however, required for the production of gametes and as such represent an important area of understanding that has widespread implications for fertility and reproductive technologies. Here we investigated the role of the heparin-binding growth factor midkine (MK) on PGC development, first using our established model of porcine stem cell-derived PGC-like cells and then confirming our findings in PGC. Our results show that MK has a mitogenic effect on PGC, mediated through an increased cell proliferation as well as decreased apoptosis. Upon further investigation, we found these effects concomitant with the decreased expression of the germ cell-specific gene deleted in azoospermia-like (DAZL). This decrease in DAZL expression, and consequent decreases in the meiosis-related genes SCP3 and DMC1, suggest a role for MK in preventing a shift in the PGC phenotype toward meiosis. MK instead increases activity of mitotic pathways in PGC, keeping them in a proliferative, less differentiated state. Lentiviral-mediated overexpression of DAZL further confirmed its role in promoting meiosis in and reducing proliferation of PGC. These effects were mitigated by the addition of MK, which was able to limit the effect of this DAZL overexpression. Furthermore, a loss-of-function study showed that a DAZL knockdown by small interfering RNA had the same effect as that induced by the addition of MK. Taken together, these data suggest that MK is able to maintain a proliferative PGC phenotype mediated by the suppression of DAZL in early germ cells.

Midkine prevented hypoxic injury of mouse embryonic stem cells through activation of Akt and HIF-1α via low-density lipoprotein receptor-related protein-1

Stem cell functions are dramatically altered by oxygen in tissue culture, which means the antioxidant/oxidant balance is critical for protection as well as toxicity. This study examined the effect of the heparin-binding growth factor midkine (MK) on hypoxia-induced apoptosis and related signal pathways in mouse embryonic stem cells (mESCs). Hypoxia (60 h) increased lactate dehydrogenase release and apoptosis, and reduced cell viability and proliferation. These effects were reversed by MK (100 ng/ml). MK also reversed hypoxia-induced increases of intracellular reactive oxygen species, c-Jun N-terminal kinase (JNK), and p38 mitogen-activated protein kinase (MAPK) phosphorylation. Blockage of JNK and p38 MAPK using small interference (si)RNAs produced a decrease in apoptosis. A loss of mitochondrial membrane potential, increases of cytochrome c release from mitochondria to cytosol, and cleaved caspase-3 expression, as well as decreases in cIAP-2 and Bcl-2 were also reversed by MK. Hypoxia alone and hypoxia with MK increased low-density lipoprotein receptor-related protein-1 (LRP-1) mRNA and protein expression. Hypoxia with MK rapidly increased serine/threonine protein kinase (Akt) phosphorylation which reversed by LRP-1 Ab (0.1 µg/ml) and prolonged heme oxygenase-1 (HO-1) expression. In addition, hypoxia with MK increased the expression of hypoxia-inducible factor-1α (HIF-1α). Moreover, inhibition of Akt, HO-1, and HIF-1α signaling pathways abolished the MK-induced blockage of apoptosis. In conclusion, MK partially prevented hypoxic injury of mESCs through activation of Akt, HO-1, and HIF-1α via LRP-1.

Intraclonal complexity in chronic lymphocytic leukemia: fractions enriched in recently born/divided and older/quiescent cells

The failure of chemotherapeutic regimens to eradicate cancers often results from the outgrowth of minor subclones with more dangerous genomic abnormalities or with self-renewing capacity. To explore such intratumor complexities in B-cell chronic lymphocytic leukemia (CLL), we measured B-cell kinetics in vivo by quantifying deuterium ((2)H)-labeled cells as an indicator of a cell that had divided. Separating CLL clones on the basis of reciprocal densities of chemokine (C-X-C motif) receptor 4 (CXCR4) and cluster designation 5 (CD5) revealed that the CXCR4(dim)CD5(bright) (proliferative) fraction contained more (2)H-labeled DNA and hence divided cells than the CXCR4(bright)CD5(dim) (resting) fraction. This enrichment was confirmed by the relative expression of two cell cycle-associated molecules in the same fractions, Ki-67 and minichromosome maintenance protein 6 (MCM6). Comparisons of global gene expression between the CXCR4(dim)CD5(bright) and CXCR4(bright)CD5(dim) fractions indicated higher levels of pro-proliferation and antiapoptotic genes and genes involved in oxidative injury in the proliferative fraction. An extended immunophenotype was also defined, providing a wider range of surface molecules characteristic of each fraction. These intraclonal analyses suggest a model of CLL cell biology in which the leukemic clone contains a spectrum of cells from the proliferative fraction, enriched in recently divided robust cells that are lymphoid tissue emigrants, to the resting fraction enriched in older, less vital cells that need to immigrate to lymphoid tissue or die. The model also suggests several targets preferentially expressed in the two populations amenable for therapeutic attack. Finally, the study lays the groundwork for future analyses that might provide a more robust understanding of the development and clonal evolution of this currently incurable disease.

Midkine: a promising molecule for drug development to treat diseases of the central nervous system

Midkine (MK) is a heparin-binding cytokine, and promotes growth, survival, migration and other activities of target cells. After describing the general properties of MK, this review focuses on MK and MK inhibitors as therapeutics for diseases in the central nervous system. MK is strongly expressed during embryogenesis especially at the midgestation period, but is expressed only at restricted sites in adults. MK expression is induced upon tissue injury such as ischemic brain damage. Since exogenously administered MK or the gene transfer of MK suppresses neuronal cell death in experimental systems, MK has the potential to treat cerebral infarction. MK might become important also in the treatment of neurodegenerative diseases such as Alzheimer's disease. MK is involved in inflammatory diseases by enhancing migration of leukocytes, inducing chemokine production and suppressing regulatory T cells. Since an aptamer to MK suppresses experimental autoimmune encephalitis, MK inhibitors are promising for the treatment of multiple sclerosis. MK is overexpressed in most malignant tumors including glioblastoma, and is involved in tumor invasion. MK inhibitors may be of value in the treatment of glioblastoma. Furthermore, an oncolytic adenovirus, whose replication is under the control of the MK promoter, inhibits the growth of glioblastoma xenografts. MK inhibitors under development include antibodies, aptamers, glycosaminoglycans, peptides and low molecular weight compounds. siRNA and antisense oligoDNA have proved effective against malignant tumors and inflammatory diseases in experimental systems. Practical information concerning the development of MK and MK inhibitors as therapeutics is described in the final part of the review.