José-Enrique O'Connor

Human Endometrial Side Population Cells Exhibit Genotypic, Phenotypic and Functional Features of Somatic Stem Cells

During reproductive life, the human endometrium undergoes around 480 cycles of growth, breakdown and regeneration should pregnancy not be achieved. This outstanding regenerative capacity is the basis for womens cycling and its dysfunction may be involved in the etiology of pathological disorders. Therefore, the human endometrial tissue must rely on a remarkable endometrial somatic stem cells (SSC) population. Here we explore the hypothesis that human endometrial side population (SP) cells correspond to somatic stem cells. We isolated, identified and characterized the SP corresponding to the stromal and epithelial compartments using endometrial SP genes signature, immunophenotyping and characteristic telomerase pattern. We analyzed the clonogenic activity of SP cells under hypoxic conditions and the differentiation capacity in vitro to adipogenic and osteogenic lineages. Finally, we demonstrated the functional capability of endometrial SP to develop human endometrium after subcutaneous injection in NOD-SCID mice. Briefly, SP cells of human endometrium from epithelial and stromal compartments display genotypic, phenotypic and functional features of SSC.

The Human Blastocyst Regulates Endometrial Epithelial Apoptosis in Embryonic Adhesion

Abstract The implanting blastocyst must appose and adhere to the endometrial epithelium and, subsequently, invade it. Locally regulated uterine epithelial apoptosis induced by the embryo is a crucial step of the epithelial invasion in rodents. To address the physiological relevance of this process in humans, we investigated the effect of single human blastocysts on the regulation of apoptosis in cultured human endometrial epithelial cells (hEEC) in both apposition and adhesion phases of implantation. Here, we report a co-ordinated embryonic regulation of hEEC apoptosis. In the apposition phase, the presence of a blastocyst rescues hEEC from the apoptotic pathway. However, when the human blastocyst adheres to the hEEC monolayer, it induces a paracrine apoptotic reaction. Fas ligand (Fas-L) was present at the embryonic trophoectoderm. Fas was localized at the apical cell surface of hEEC, and flow cytometry revealed that 60% of hEEC express Fas. Neutralizing adhesion assays revealed that the Fas/Fas-L death system may be an important mechanism to cross the epithelial barrier, which is crucial for embryonic adhesion, and the manipulation of this system could have potential clinical implications as an interceptive mechanism.

Hypoxia Promotes Efficient Differentiation of Human Embryonic Stem Cells to Functional Endothelium

Early development of mammalian embryos occurs in an environment of relative hypoxia. Nevertheless, human embryonic stem cells (hESC), which are derived from the inner cell mass of blastocyst, are routinely cultured under the same atmospheric conditions (21% O2) as somatic cells. We hypothesized that O2 levels modulate gene expression and differentiation potential of hESC, and thus, we performed gene profiling of hESC maintained under normoxic or hypoxic (1% or 5% O2) conditions. Our analysis revealed that hypoxia downregulates expression of pluripotency markers in hESC but increases significantly the expression of genes associated with angio‐ and vasculogenesis including vascular endothelial growth factor and angiopoitein‐like proteins. Consequently, we were able to efficiently differentiate hESC to functional endothelial cells (EC) by varying O2 levels; after 24 hours at 5% O2, more than 50% of cells were CD34+. Transplantation of resulting endothelial‐like cells improved both systolic function and fractional shortening in a rodent model of myocardial infarction. Moreover, analysis of the infarcted zone revealed that transplanted EC reduced the area of fibrous scar tissue by 50%. Thus, use of hypoxic conditions to specify the endothelial lineage suggests a novel strategy for cellular therapies aimed at repair of damaged vasculature in pathologies such as cerebral ischemia and myocardial infarction. STEM CELLS 2010;28:407–418

Protective effect of L-carnitine on hyperammonemia

Inborn errors of the urea cycle, liver malfunction and drug‐induced hepatotoxicity are causes of life‐threatening encephalopathies arising from hyperammonemia. L‐Carnitine prevented entirely ammonia toxicity in mice when injected intraperitoneally 30 min before a lethal dose of ammonium acetate. Survival depends on the dose of L‐carnitine injected, e.g., 0, 60, 70, 80 and 100% with 0, 1, 2, 8 and 16 mmol L‐carnitine/kg, respectively. At the highest doses L‐carnitine abolishes the convulsions that accompany acute ammonia intoxication. At lower doses it delayed their onset. The protective effect was associated with a marked decrease of blood ammonia, while in unprotected mice ammonemia was lethal in less than 15 min. When sustained hyperammonemia was induced by urease injections, protection was also obtained. The mechanism of protection is under investigation, however, since L‐carnitine facilitates fatty acid entry into mitochondria, possibly ATP or reducing equivalents are increased.

An important role for CDK2 in G1 to S checkpoint activation and DNA damage response in human embryonic stem cells.

A precise understanding of mechanisms used by human embryonic stem cells (hESCs) to maintain genomic integrity is very important for their potential clinical applications. The G1 checkpoint serves to protect genomic integrity and prevents cells with damaged DNA from entering S‐phase. Previously, we have shown that downregulation of cyclin‐dependent kinase 2 (CDK2) in hESC causes G1 arrest, loss of pluripotency, upregulation of cell cycle inhibitors p21 and p27 and differentiation toward extraembryonic lineages. In this study, we investigate in detail the role of CDK2 in cellular processes, which are crucial to the maintenance of genomic stability in hESC such as G1 checkpoint activation, DNA repair, and apoptosis. Our results suggest that downregulation of CDK2 triggers the G1 checkpoint through the activation of the ATM‐CHK2‐p53‐p21 pathway. Downregulation of CDK2 is able to induce sustained DNA damage and to elicit the DNA damage response (DDR) as evidenced by the formation of distinct γ‐H2.AX and RAD52‐BRCA1 foci in hESC nuclei. CDK2 downregulation causes high apoptosis at the early time points; however, this is gradually decreased overtime as the DDR is initiated. Our mass spectrometry analysis suggest that CDK2 does interact with a large number of proteins that are involved in key cellular processes such as DNA replication, cell cycle progression, DNA repair, chromatin modeling, thus, suggesting a crucial role for CDK2 in orchestrating a fine balance between cellular proliferation, cell death, and DNA repair in hESC. STEM Cells 2011;29:651–659

Use of rhodamine 123 to investigate alterations in mitochondrial activity in isolated mouse liver mitochondria

The fluorescent dye Rhodamine-123, which selectively stains mitochondria depending on the mitochondrial membrane potential, was used with flow cytometry to evaluate alterations in activity of mitochondria isolated from mouse liver. Under in vitro conditions, with succinate and ADP present in the buffer, mitochondrial activity was affected by a variety of metabolic inhibitors that modify membrane potential. These results demonstrate clearly that flow cytometric techniques using Rhodamine-123 can be employed to study activity in isolated mitochondria.

Mitochondrial dysfunction, persistent oxidative damage, and catalase inhibition in immune cells of naïve and treated Crohn's disease

Background: Oxidative stress is considered a potential etiological factor for Crohns disease (CD). We characterized the reactive oxygen species (ROS) generated in immune peripheral cells of CD patients, as well as their antioxidant enzyme status and the presence of oxidative damage. In addition, mitochondrial function (&Dgr;&ggr;m) was analyzed to detect the possible origin of ROS. Methods: Cells were obtained from patients at the onset of disease, prior to any treatment. Experiments were repeated when patients were in clinical remission. A set of experiments was carried out in a group of CD patients in persistent morphological remission. Controls were healthy volunteers who were not receiving any treatment at the time. The generation of superoxide, hydrogen peroxide (H2O2) and nitric oxide, &Dgr;&ggr;m, superoxide dismutase (SOD) and catalase (CAT) activities, and concentrations of malondyaldehyde (MDA) and 8‐oxo‐deoxyguanosine (8‐oxo‐dG) were measured. Results: SOD activity and H2O2 production were significantly higher during active CD but returned to control levels in remission. &Dgr;&ggr;m was inhibited during active CD and, although it returned to control levels, its recovery took longer than clinical remission. CAT activity was permanently inhibited during CD, independent of the disease activity. MDA and 8‐oxo‐dG were permanently elevated. Conclusions: Oxidative stress during active CD depends on H2O2 production. The inhibition of &Dgr;&ggr;m suggests that this organelle is a source of ROS. CAT is permanently inhibited in CD, the biological significance of which is under study. The persistent oxidative damage detected may have implications for the evolution of the disease. Inflamm Bowel Dis 2010

Direct Toll-like receptor-mediated stimulation of hematopoietic stem and progenitor cells occurs in vivo and promotes differentiation toward macrophages.

As Toll‐like receptors (TLRs) are expressed by hematopoietic stem and progenitor cells (HSPCs), they may play a role in hematopoiesis in response to pathogens during infection. We show here that TLR2, TLR4, and TLR9 agonists (tripalmitoyl‐S‐glyceryl‐L‐Cys‐Ser‐(Lys)4 [Pam3CSK4], lipopolysaccharide [LPS], and CpG oligodeoxynucleotide [ODN]) induce the in vitro differentiation of purified murine lineage negative cells (Lin−) as well as HSPCs (identified as Lin− c‐Kit+ Sca‐1+ IL‐7Rα− [LKS] cells) toward macrophages (Mph), through a myeloid differentiation factor 88 (MyD88)‐dependent pathway. In order to investigate the possible direct interaction of soluble microorganism‐associated molecular patterns and TLRs on HSPCs in vivo, we designed a new experimental approach: purified Lin− and LKS cells from bone marrow of B6Ly5.1 mice (CD45.1 alloantigen) were transplanted into TLR2−/−, TLR4−/−, or MyD88−/− mice (CD45.2 alloantigen), which were then injected with soluble TLR ligands (Pam3CSK4, LPS, or ODN, respectively). As recipient mouse cells do not recognize the TLR ligands injected, interference by soluble mediators secreted by recipient cells is negligible. Transplanted cells were detected in the spleen and bone marrow of recipient mice, and in response to soluble TLR ligands, cells differentiated preferentially to Mph. These results show, for the first time, that HSPCs may be directly stimulated by TLR agonists in vivo, and that the engagement of these receptors induces differentiation toward Mph. Therefore, HSPCs may sense pathogen or pathogen‐derived products directly during infection, inducing a rapid generation of cells of the innate immune system. STEM CELLS2012;30:1486–1495

Flow Cytometric Kinetic Assay of Calcium Mobilization in Whole Blood Platelets Using Fluo-3 and CD41

BACKGROUND Platelet activation plays a major role in the physiology and pathology of hemostasis. Flow cytometry is a promising approach for the structural and functional analysis of platelets. However, the choice of adequate biological parameters and most technical issues are still under discussion. A rise in cytosolic free Ca2+ is a key early event that follows platelet stimulation and precedes several activation responses, including shape change, aggregation, secretion, and expression of procoagulant activity. Our objective was to set up a fast and sensitive flow cytometric method to determine the kinetics of intracellular Ca2+ mobilization in platelets, which could be performed with the least artifactual perturbation of platelet function. METHODS Anticoagulated blood was diluted in Tyrodes buffer and incubated with Fluo-3-acetoxymethyl ester prior to staining with phycoerytrin-conjugated antiplatelet GPIIb/IIIa complex monoclonal antibody. Platelets were identified by a gate including only CD41+ events. After the determination of baseline Fluo-3 green fluorescence on a flow cytometer (EPICS XL-MCL, Coulter Electronics, Hialeah, FL), adequate agonists were added and time-dependent changes in Fluo-3 fluorescence were recorded on-line for up to 3 min. RESULTS In these conditions, a very fast and transient increase of cytosolic-free Ca2+ was observed following the addition of thrombin, a strong platelet agonist. Stimulation with adenosine diphosphate (ADP), a weak agonist, also resulted in evident increase of Ca2+ levels. CONCLUSIONS Our results show that this flow cytometric kinetic method provides a simple and sensitive tool to assess in vitro the time course and intensity of signal transduction responses to different platelet agonists under near physiological conditions. In this way, it may be useful to evaluate the degree of platelet reactivity and thus to monitor antiplatelet therapy.

Prevention of ammonia toxicity by L-carnitine: metabolic changes in brain.

Abstractl-Carnitine when injected in mice 30 min before an LD100 of ammonium acetate (12 mmol/kg body weight, intraperitoneal) reduced mortality (100% survival with 16 mmoll-carnitine/kg) and prevented the appearance of symptoms of ammonia toxicity. Brain ammonia decreased in the animals givenl-carnitine. Ammonia decreased the levels of glutamate in brain; they were partially restored byl-carnitine, which also reduced the increase in brain glutamine in animals given only ammonia. The redox state of the brain was altered following ammonia intoxication. The ratio of lactate to pyruvate in the cytosol increased while that of glutamate to α-ketoglutarate in the mitochondria decreased. These ratios were partially restored byl-carnitine. The implications of these findings are discussed relative to the mechanism of ammonia toxicity.