EFFECTS OF BACTERIAL LIPOPOLYSACCHARIDE AND SHIGA TOXIN ON INDUCED PLURIPOTENT STEM CELL-DERIVED MESENCHYMAL STEM CELLS.

ABSTRACT: Background : Mesenchymal stem cells (MSCs) can be activated by different bacterial toxins. Lipopolysaccharides and Shiga Toxin (Stx) are the main toxins necessary for hemolytic uremic syndrome development. The main etiological event in this disease is endothelial damage that causes glomerular destruction. Considering the repairing properties of MSC, we aimed to study the response of MSC derived from induced pluripotent stem cells (iPSC-MSC) to LPS and/or Stx and its effect on the restoration of injured endothelial cells. Methods : iPSC-MSC were treated with LPS and or/Stx for 24 h and secretion of cytokines, adhesion, and migration were measured in response to these toxins. In addition, conditioned media from treated iPSC-MSC were collected and used for proteomics analysis and evaluation of endothelial cell healing and tubulogenesis using human microvascular endothelial cells 1 as a source of endothelial cells. Results : The results obtained showed that LPS induced a proinflammatory profile on iPSC-MSC, whereas Stx effects were less evident, even though cells expressed the Gb 3 receptor. Moreover, LPS induced on iPSC-MSC an increment in migration and adhesion to a gelatin substrate. Addition of conditioned media of iPSC-MSC treated with LPS + Stx, decreased the capacity of human microvascular endothelial cells 1 to close a wound, and did not favor tubulogenesis. Proteomic analysis of iPSC-MSC treated with LPS and/or Stx revealed specific protein secretion patterns that support the functional results described. Conclusions : iPSC-MSC activated by LPS acquired a proinflammatory profile that induces migration and adhesion to extracellular matrix proteins but the addition of Stx did not activate any repair program to ameliorate endothelial damage, indicating that the use of iPSC-MSC to regenerate endothelial injury caused by LPS and/or Stx in hemolytic uremic syndrome could not be the best option to consider to regenerate a tissue injury.

Human embryonic stem cells display a pronounced sensitivity to the cyclin dependent kinase inhibitor Roscovitine.

BACKGROUND: The essentially unlimited expansion potential and the pluripotency of human embryonic stem cells (hESCs) make them attractive for cell-based therapeutic purposes. Although hESCs can indefinitely proliferate in culture, unlike transformed cancer cells, they are endowed with a cell-intrinsic property termed mitochondrial priming that renders them highly sensitive to apoptotic stimuli. Thus, all attempts to broaden the insights into hESCs apoptosis may be helpful for establishing pro-survival strategies valuable for its in vitro culture and further use in clinical applications. Cyclin-dependent kinases (CDKs), a family of serine/threonine protein kinases originally identified as regulators of the eukaryotic cell cycle, can also regulate transcription and differentiation. Moreover, there are compelling data suggesting that its activities are involved in certain apoptotic programs in different cell types. Currently, it is not completely determined whether CDKs regulate apoptotic processes in rapidly proliferating and apoptosis-prone hESCs. In this study, to elucidate the effect of CDKs inhibition in hESCs we used Roscovitine (ROSC), a purine analogue that selectively inhibits the activities of these kinases. RESULTS: Inhibition of CDKs by ROSC triggers programmed cell death in hESCs but not in proliferating somatic cells (human fibroblasts). The apoptotic process encompasses caspase-9 and -3 activation followed by PARP cleavage. ROSC treatment also leads to p53 stabilization, which coincides with site-specific phosphorylation at serine 46 and decreased levels of Mdm2. Additionally, we observed a transcriptional induction of p53AIP1, a repression of pro-survival factor Mcl-1 and an up-regulation of pro-apoptotic BH3-only proteins NOXA and PUMA. Importantly, we found that the role of CDK2 inhibition appears to be at best accessory as an active CDK2 is not required to ensure hESCs survival. CONCLUSION: Our experimental data reveal that hESCs, contrary to fibroblasts, exhibit a pronounced sensitivity to ROSC.

MicroRNA characterization in equine induced pluripotent stem cells.

Cell reprogramming has been well described in mouse and human cells. The expression of specific microRNAs has demonstrated to be essential for pluripotent maintenance and cell differentiation, but not much information is available in domestic species. We aim to generate horse iPSCs, characterize them and evaluate the expression of different microRNAs (miR-302a,b,c,d, miR-205, miR-145, miR-9, miR-96, miR-125b and miR-296). Two equine iPSC lines (L2 and L3) were characterized after the reprogramming of equine fibroblasts with the four human Yamanaka's factors (OCT-4/SOX-2/c-MYC/KLF4). The pluripotency of both lines was assessed by phosphatase alkaline activity, expression of OCT-4, NANOG and REX1 by RT-PCR, and by immunofluorescence of OCT-4, SOX-2 and c-MYC. In vitro differentiation to embryo bodies (EBs) showed the capacity of the iPSCs to differentiate into ectodermal, endodermal and mesodermal phenotypes. MicroRNA analyses resulted in higher expression of the miR-302 family, miR-9 and miR-96 in L2 and L3 vs. fibroblasts (p<0.05), as previously shown in human pluripotent cells. Moreover, downregulation of miR-145 and miR-205 was observed. After differentiation to EBs, higher expression of miR-96 was observed in the EBs respect to the iPSCs, and also the expression of miR-205 was induced but only in the EB-L2. In addition, in silico alignments of the equine microRNAs with mRNA targets suggested the ability of miR-302 family to regulate cell cycle and epithelial mesenchymal transition genes, miR-9 and miR-96 to regulate neural determinant genes and miR-145 to regulate pluripotent genes, similarly as in humans. In conclusion, we could obtain equine iPSCs, characterize them and determine for the first time the expression level of microRNAs in equine pluripotent cells.

Extracellular vesicles from pluripotent stem cell-derived mesenchymal stem cells acquire a stromal modulatory proteomic pattern during differentiation.

Mesenchymal stem/stromal cells (MSCs) obtained from pluripotent stem cells (PSCs) constitute an interesting alternative to classical MSCs in regenerative medicine. Among their many mechanisms of action, MSC extracellular vesicles (EVs) are a potential suitable substitute for MSCs in future cell-free-based therapeutic approaches. Unlike cells, EVs do not elicit acute immune rejection, and they can be produced in large quantities and stored until ready to use. Although the therapeutic potential of MSC EVs has already been proven, a thorough characterization of MSC EVs is lacking. In this work, we used a label-free liquid chromatography tandem mass spectrometry proteomic approach to identify the most abundant proteins in EVs that are secreted from MSCs derived from PSCs (PD-MSCs) and from their parental induced PSCs (iPSCs). Next, we compared both datasets and found that while iPSC EVs enclose proteins that modulate RNA and microRNA stability and protein sorting, PD-MSC EVs are rich in proteins that organize extracellular matrix, regulate locomotion, and influence cell-substrate adhesion. Moreover, compared to their respective cells, iPSCs and iPSC EVs share a greater proportion of proteins, while the PD-MSC proteome appears to be more specific. Correlation and principal component analysis consistently aggregate iPSCs and iPSC EVs but segregate PD-MSC and their EVs. Altogether, these findings suggest that during differentiation, compared with their parental iPSC EVs, PD-MSC EVs acquire a more specific set of proteins; arguably, this difference might confer their therapeutic properties.

Regulation of cyclin E1 expression in human pluripotent stem cells and derived neural progeny.

Human pluripotent stem cells (hPSCs), including embryonic and induced pluripotent stem cells (hESCs and hiPSCs) show unique cell cycle characteristics, such as a short doubling time due to an abbreviated G1 phase. Whether or not the core cell cycle machinery directly regulates the stemness and/or the differentiation potential of hPSCs remains to be determined. To date, several scenarios describing the atypical cell cycle of hPSCs have been suggested, and therefore there is still controversy over how cyclins, master regulators of the cell cycle, are expressed and regulated. Furthermore, the cell cycle profile and the expression pattern of major cyclins in hESCs-derived neuroprogenitors (NP) have not been studied yet. Therefore, herein we characterized the expression pattern of major cyclins in hPSCs and NP. We determined that all studied cyclins mRNA expression levels fluctuate along cell cycle. Particularly, after a thorough analysis of synchronized cell populations, we observed that cyclin E1 mRNA levels increased sharply in G1/S concomitantly with cyclin E1 protein accumulation in hPSCs and NP. Additionally, we demonstrated that cyclin E1 mRNA expression levels involves the activation of MEK/ERK pathway and the transcription factors c-Myc and E2Fs in hPSCs. Lastly, our results reveal that proteasome mediates the marked down-regulation (degradation) of cyclin E1 protein observed in G2/M by a mechanism that requires a functional CDK2 but not GSK3ß activity. ABBREVIATIONS: hPSCs: human pluripotent stem cells; hESCs: human embryonic stem cells; hiPSCs: human induced pluripotent stem cells; NP: neuroprogenitors; HF: human foreskin fibroblasts; MEFs: mouse embryonic fibroblasts; iMEFs: irradiated mouse embryonic fibroblasts; CDKs: cyclindependent kinases; CKIs: CDK inhibitors; CNS: central nervous system; Oct-4: Octamer-4; EB: embryoid body; AFP: Alpha-fetoprotein; cTnT: Cardiac Troponin T; MAP-2: microtubule-associated protein; TUJ-1: neuron-specific class III ß-tubulin; bFGF: basic fibroblastic growth factor; PI3K: Phosphoinositide 3-kinase; KSR: knock out serum replacement; CM: iMEF conditioned medium; E8: Essential E8 medium.

The Cell Cycle Inhibitors p21Cip1 and p27Kip1 Control Proliferation but Enhance DNA Damage Resistance of Glioma Stem Cells.

High-grade gliomas are the most prevalent and lethal primary brain tumors. They display a hierarchical arrangement with a population of self-renewing and highly tumorigenic cells called cancer stem cells. These cells are thought to be responsible for tumor recurrence, which make them main candidates for targeted therapies. Unbridled cell cycle progression may explain the selective sensitivity of some cancer cells to treatments. The members of the Cip/Kip family p21Cip1 and p27Kip1 were initially considered as tumor suppressors based on their ability to block proliferation. However, they are currently looked at as proteins with dual roles in cancer: one as tumor suppressor and the other as oncogene. Therefore, the aim of this study was to determine the functions of these cell cycle inhibitors in five patient-derived glioma stem cell-enriched cell lines. We found that these proteins are functional in glioma stem cells. They negatively regulate cell cycle progression both in unstressed conditions and in response to genotoxic stress. In addition, p27Kip1 is upregulated in nutrient-restricted and differentiating cells, suggesting that this Cip/Kip is a mediator of antimitogenic signals in glioma cells. Importantly, the lack of these proteins impairs cell cycle halt in response to genotoxic agents, rendering cells more vulnerable to DNA damage. For these reasons, these proteins may operate both as tumor suppressors, limiting cell proliferation, and as oncogenes, conferring cell resistance to DNA damage. Thus, deepening our knowledge on the biological functions of these Cip/Kips may shed light on how some cancer cells develop drug resistance.

AKT/GSK3ß signaling pathway is critically involved in human pluripotent stem cell survival.

Human embryonic and induced pluripotent stem cells are self-renewing pluripotent stem cells (PSC) that can differentiate into a wide range of specialized cells. Basic fibroblast growth factor is essential for PSC survival, stemness and self-renewal. PI3K/AKT pathway regulates cell viability and apoptosis in many cell types. Although it has been demonstrated that PI3K/AKT activation by bFGF is relevant for PSC stemness maintenance its role on PSC survival remains elusive. In this study we explored the molecular mechanisms involved in the regulation of PSC survival by AKT. We found that inhibition of AKT with three non-structurally related inhibitors (GSK690693, AKT inhibitor VIII and AKT inhibitor IV) decreased cell viability and induced apoptosis. We observed a rapid increase in phosphatidylserine translocation and in the extent of DNA fragmentation after inhibitors addition. Moreover, abrogation of AKT activity led to Caspase-9, Caspase-3, and PARP cleavage. Importantly, we demonstrated by pharmacological inhibition and siRNA knockdown that GSK3ß signaling is responsible, at least in part, of the apoptosis triggered by AKT inhibition. Moreover, GSK3ß inhibition decreases basal apoptosis rate and promotes PSC proliferation. In conclusion, we demonstrated that AKT activation prevents apoptosis, partly through inhibition of GSK3ß, and thus results relevant for PSC survival.

Granulocyte colony-stimulating factor (G-CSF) upregulates ß1 integrin and increases migration of human trophoblast Swan 71 cells via PI3K and MAPK activation.

Multiple cytokines and growth factors expressed at the fetal-maternal interface are involved in the regulation of trophoblast functions and placental growth, but the role of G-CSF has not been completely established. Based on our previous study showing that G-CSF increases the activity of matrix metalloproteinase-2 and the release of vascular endothelial growth factor in Swan 71 human trophoblast cells, in this work we explore the possible contribution of G-CSF to cell migration and the G-CSF-triggered signaling pathway. We found that G-CSF induced morphological changes on actin cytoskeleton consistent with a migratory cell phenotype. G-CSF also up-regulated the expression levels of ß1 integrin and promoted Swan 71 cell migration. By using selective pharmacological inhibitors and dominant negative mutants we showed that PI3K, Erk 1/2 and p38 pathways are required for promoting Swan 71 cell motility. It was also demonstrated that PI3K behaved as an upstream regulator of Erk 1/2 and p38 MAPK. In addition, the increase of ß1 integrin expression was dependent on PI3K activation. In conclusion, our results indicate that G-CSF stimulates ß1 integrin expression and Swan 71 cell migration by activating PI3K and MAPK signaling pathways, suggesting that G-CSF should be considered as an additional regulatory factor that contributes to a successful embryo implantation and to the placenta development.

Lysosomal and mitochondrial permeabilization mediates zinc(II) cationic phthalocyanine phototoxicity.

In order to find a novel photosensitizer to be used in photodynamic therapy for cancer treatment, we have previously showed that the cationic zinc(II) phthalocyanine named Pc13, the sulfur-linked dye 2,9(10),16(17),23(24)-tetrakis[(2-trimethylammonium) ethylsulfanyl]phthalocyaninatozinc(II) tetraiodide, exerts a selective phototoxic effect on human nasopharynx KB carcinoma cells and induces an apoptotic response characterized by an increase in the activity of caspase-3. Since the activation of an apoptotic pathway by chemotherapeutic agents contributes to the elimination of malignant cells, in this study we investigated the molecular mechanisms underlying the antitumor action of Pc13. We found that after light exposure, Pc13 induced the production of reactive oxygen species (ROS), which are mediating the resultant cytotoxic action on KB cells. ROS led to an early permeabilization of lysosomal membranes as demonstrated by the reduction of lysosome fluorescence with acridine orange and the release of lysosomal proteases to cytosol. Treatment with antioxidants inhibited ROS generation, preserved the integrity of lysosomal membrane and increased cell proliferation in a concentration-dependent manner. Lysosome disruption was followed by mitochondrial depolarization, cytosolic release of cytochrome C and caspases activation. Although no change in the total amount of Bax was observed, the translocation of Bax from cytosol to mitochondria, the cleavage of the pro-apoptotic protein Bid, together with the decrease of the anti-apoptotic proteins Bcl-XL and Bcl-2 indicated the involvement of Bcl-2 family proteins in the induction of the mitochondrial pathway. It was also demonstrated that cathepsin D, but not caspase-8, contributed to Bid cleavage. In conclusion, Pc13-induced cell photodamage is triggered by ROS generation and activation of the mitochondrial apoptotic pathway through the release of lysosomal proteases. In addition, our results also indicated that Pc13 induced a caspase-dependent apoptotic response, being activation of caspase-8, -9 and -3 the result of a post-mitochondrial event.

Peritumoral administration of granulocyte colony-stimulating factor induces an apoptotic response on a murine mammary adenocarcinoma.

The aim of the present study was to evaluate the in vivo effect of granulocyte colony-stimulating factor (G-CSF) on LM3 murine mammary adenocarcinoma cells subcutaneously implanted in Balb/c mice as experimental models. We showed that the peritumoral administration of 100 microg/kg of G-CSF diminished tumor progression, while no cytokine effect on LM3 cell proliferation was observed in vitro. Histological examination of G-CSF-treated tumors revealed infiltration of neutrophils and mononuclear cells. Apoptotic cells were identified by TUNEL assays. Western blot analysis of tumor lysates showed that G-CSF treatment increased the amount of Fas-L, TRAIL and Bax proteins, whereas decreased the expression of procaspase 3 and Bcl-2. In addition, cytokine arrays showed an increment in the amount of IL-12, IL-13 and TNFalpha. Our results suggest that the presence of G-CSF within tumor microenvironment would induce an immune response which eliminates tumor cells by apoptosis. Both death receptor and mitochondrial pathways would be involved in LM3 tumor cell death. We believe that the final local G-CSF concentration at the tumor site and each particular type of tumor should be carefully taken into account in order to evaluate the effect of the cytokine on tumor progression.