Browsing by Author "Yoder, Mervin"

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    Diabetes reduces bone marrow and circulating porcine endothelial progenitor cells, an effect ameliorated by atorvastatin and independent of cholesterol
    (Wiley, 2009-01) Mohler III, Emile R.; Shi, Yuquan; Moore, Jonni; Bantly, Andrew; Hamamdzic, Damir; Yoder, Mervin; Rader, Daniel J.; Putt, Mary; Zhang, Lifeng; Parmacek, Michael; Wilensky, Robert L.; Pediatrics, School of Medicine
    Bone marrow derived endothelial progenitor cells (EPCs) are early precursors of mature endothelial cells which replenish aging and damaged endothelial cells. The authors studied a diabetic swine model to determine if induction of DM adversely affects either bone marrow or circulating EPCs and whether a HMG-CoA reductase inhibitor (statin) improves development and recruitment of EPCs in the absence of cholesterol lowering. Streptozotocin was administered to Yorkshire pigs to induce DM. One month after induction, diabetic pigs were treated with atorvastatin (statin, n = 10), ezetimibe (n = 10) or untreated (n = 10) and evaluated for number of bone marrow and circulating EPCs and femoral artery endothelial function. There was no effect of either medication on cholesterol level. One month after induction of DM prior to administration of drugs, the number of bone marrow and circulating EPCs significantly decreased (P < 0.0001) compared to baseline. Three months after DM induction, the mean proportion of circulating EPCs significantly increased in the atorvastatin group, but not in the control or ezetimibe groups. The control group showed progressive reduction in percentage of flow mediated vasodilatation (no dilatation at 3 months) whereas the atorvastatin group and ezetimibe exhibited vasodilatation, 6% and 4% respectively. DM results in significant impairment of bone marrow and circulating EPCs as well as endothelial function. The effect is ameliorated, in part, by atorvastatin independent of its cholesterol lowering effect. These data suggest a model wherein accelerated atherosclerosis seen with DM may, in part, result from reduction in EPCs which may be ameliorated by treatment with a statin.
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    Endogenous Transmembrane TNF-Alpha Protects Against Premature Senescence in Endothelial Colony Forming Cells
    (American Heart Association, 2016-05) Green, Linden A.; Njoku, Victor; Mund, Julie; Case, Jaime; Yoder, Mervin; Murphy, Michael P.; Clauss, Matthias; Cellular and Integrative Physiology, School of Medicine
    RATIONALE: Transmembrane tumor necrosis factor-α (tmTNF-α) is the prime ligand for TNF receptor 2, which has been shown to mediate angiogenic and blood vessel repair activities in mice. We have previously reported that the angiogenic potential of highly proliferative endothelial colony-forming cells (ECFCs) can be explained by the absence of senescent cells, which in mature endothelial cells occupy >30% of the population, and that exposure to a chronic inflammatory environment induced premature, telomere-independent senescence in ECFCs. OBJECTIVE: The goal of this study was to determine the role of tmTNF-α in the proliferation of ECFCs. METHODS AND RESULTS: Here, we show that tmTNF-α expression on ECFCs selects for higher proliferative potential and when removed from the cell surface promotes ECFC senescence. Moreover, the induction of premature senescence by chronic inflammatory conditions is blocked by inhibition of tmTNF-α cleavage. Indeed, the mechanism of chronic inflammation-induced premature senescence involves an abrogation of tmTNF/TNF receptor 2 signaling. This process is mediated by activation of the tmTNF cleavage metalloprotease TNF-α-converting enzyme via p38 MAP kinase activation and its concurrent export to the cell surface by means of increased iRhom2 expression. CONCLUSIONS: Thus, we conclude that tmTNF-α on the surface of highly proliferative ECFCs plays an important role in the regulation of their proliferative capacity.
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    The role of Bruton's tyrosine kinase and PI3K p110δ in mutant SHP2-induced juvenile myelomonocytic leukemia
    (2018) Deng, Lisa; Chan, Rebecca, J.; Kapur, Reuben; Herbert, Brittney-Shea; Ware, Stephanie M.; Yoder, Mervin
    Juvenile myelomonocytic leukemia (JMML) is an aggressive myeloproliferative neoplasm that lacks effective chemotherapies. Most commonly, patients have gain-of-function (GOF) oncogenic mutations in SHP2, leading to hyperactivation of ERK and AKT and hyperproliferation of cells in response to granulocyte macrophage-colony stimulating factor (GM-CSF). Our lab previously showed that p110δ, the hematopoietic-specific catalytic subunit of phosphoinositide 3-kinase, is a crucial mediator of mutant Shp2-induced GM-CSF hypersensitivity in vitro. We treated oncogenic Shp2-expressing mice with a p110δ inhibitor and showed that the strong effect our lab observed in vitro translated into reduced splenomegaly and prolonged survival in vivo. We investigated molecules potentially cooperating with p110δ signaling and discovered that Bruton’s tyrosine kinase (BTK) is hyperphosphorylated in GOF Shp2 myeloid cells. We used specific BTK and p110δ inhibitors to demonstrate that BTK cooperates with p110δ to hyperactivate Akt/Erk and to promote hyperproliferation. GOF Shp2-expressing mice treated in vivo with the drug combination targeting p110δ and BTK have significantly decreased splenomegaly and WBC counts. We also explored the mechanism of BTK signaling and hypothesized that B cell adaptor for PI3K (BCAP) mediated BTK upregulation of PI3K activity. In mutant Shp2 macrophages, we observed BCAP phosphorylation specifically in the larger isoforms needed for PI3K activation, and BTK inhibition led to a dose-dependent reduction in this phosphorylation. We also demonstrated reduced interaction between BCAP and the PI3K regulatory p85α subunit bearing mutated SH2 domains. Finally, we investigated the effects of mutated DNA methyltransferase 3A (Dnmt3a) in conjunction with GOF Shp2. Double mutant mice quickly became moribund with pronounced splenomegaly and leukocytosis. There was an expansion of mature myeloid cells in the periphery and myeloid progenitors in the bone marrow, plus anemia with evidence of compensatory erythropoiesis in the spleen. Our findings show that the myeloproliferative neoplasm caused by GOF Shp2 is due to hyperactive p110δ, and this is further promoted by BTK, which forms a positive feedback loop with PI3K and BCAP, thus leading to more Akt/Erk hyperphosphorylation and more hyperproliferation in response to GM-CSF. The dual inhibition of p110δ and BTK represents a novel effective treatment strategy for JMML and other diseases induced by oncogenic Shp2.
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    STIFFNESS OF 3D COLLAGEN MATRICES REGULATES CDC42 ACTIVITY OF ENDOTHELIAL COLONY FORMING CELLS DURING EARLY VACUOLE
    (Office of the Vice Chancellor for Research, 2012-04-13) Kim, Seung Joon; Voytik-Harbin, Sherry; Yoder, Mervin; Na, Sungsoo
    Recent preclinical reports have provided evidence that endothelial colony forming cells (ECFCs), a subset of endothelial progenitor cells, significantly improve vessel formation, largely due to their robust vasculogenic potential. While it has been known that the Rho family GTPase Cdc42 is involved in this ECFC-driven vessel formation process, the effect of extracellular matrix (ECM) stiffness on its activity during vessel formation is largely unknown. Using a fluorescence resonance energy transfer (FRET)-based Cdc42 biosen-sor, we examined the spatio-temporal activity of Cdc42 of ECFCs in three-dimensional (3D) collagen matrices with varying stiffness. The result re-vealed that ECFCs exhibited an increase in Cdc42 activity in a soft (150 Pa) matrix, while they were much less responsive in a stiff (1000 Pa) matrix. In both soft and stiff matrices, Cdc42 was highly activated near vacuoles; how-ever, its activity is higher in a soft matrix than that in a stiff matrix. The ob-served Cdc42 activity was closely associated with vacuole area. Soft matri-ces induced higher Cdc42 activity, faster vacuole formation, and larger vac-uole area than stiff matrices. Time courses of Cdc42 activity and vacuole formation data revealed that Cdc42 activity proceeds vacuole formation. Collectively, these results suggest that matrix stiffness is critical in regulat-ing Cdc42 activity in ECFCs and its activation is an important step in early vacuole formation.