David Tai Leong

Publications (36) View all

• Article: Insights into the Role of Focal Adhesion Modulation in Myogenic Differentiation of Human Mesenchymal Stem Cells.

  Haiyang Yu, Yuan Siang Lui, Sijing Xiong, Wen Shing Leong, Feng Wen, Himawan Nurkahfianto, Sravendra Rana, David Tai Leong, Kee Woei Ng, Lay Poh Tan
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  ABSTRACT: We report the establishment of a novel platform to induce myogenic differentiation of human mesenchymal stem cells (hMSCs) via focal adhesion (FA) modulation, giving insights into the role of FA on stem cell differentiation. Micropatterning of collagen type I on a polyacrylamide gel with a stiffness of 10.2 kPa efficiently modulated elongated FA. This elongated FA profile preferentially recruited the β(3) integrin cluster and induced specific myogenic differentiation at both transcription and translation levels with expression of myosin heavy chain and α-sarcomeric actin. This was initiated with elongation of FA complexes that triggered the RhoA downstream signaling toward a myogenic lineage commitment. This study also illustrates how one could partially control myogenic differentiation outcomes of similar-shaped hMSCs by modulating FA morphology and distribution. This technology increases our toolkit choice for controlled differentiation in muscle engineering.
  Stem cells and development 07/2012; · 4.15 Impact Factor
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  Available from: David Tai Leong

  Article: The role of the tumor suppressor p53 pathway in the cellular DNA damage response to zinc oxide nanoparticles.

  Kee Woei Ng, Stella P K Khoo, Boon Chin Heng, Magdiel I Setyawati, Eng Chok Tan, Xinxin Zhao, Sijing Xiong, Wanru Fang, David T Leong, Joachim S C Loo
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  ABSTRACT: In this paper, we explored how ZnO nanoparticles cross-interact with a critical tumor suppressive pathway centered around p53, which is one of the most important known tumor suppressors that protects cells from developing cancer phenotypes through its control over major pathways like apoptosis, senescence and cell cycle progression. We showed that the p53 pathway was activated in BJ cells (skin fibroblasts) upon ZnO nanoparticles treatment with a concomitant decrease in cell numbers. This suggests that cellular responses like apoptosis in the presence of ZnO nanoparticles require p53 as the molecular master switch towards programmed cell death. This also suggests that in cells without robust p53, protective response can be tipped towards carcinogenesis when stimulated by DNA damage inducing agents like ZnO nanoparticles. We observed this precarious tendency in the same BJ cells with p53 knocked down using endogeneous expressing shRNA. These p53 knocked down BJ cells became more resistant to ZnO nanoparticles induced cell death and increased cell progression. Collectively, our results suggest that cellular response towards specific nanoparticle induced cell toxicity and carcinogenesis is not only dependent on specific nanoparticle properties but also (perhaps more importantly) the endogenous genetic, transcriptomic and proteomic landscape of the target cells.
  Biomaterials 07/2011; 32(32):8218-25. · 7.40 Impact Factor
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  Available from: David Tai Leong

  Article: Cancer-related ectopic expression of the bone-related transcription factor RUNX2 in non-osseous metastatic tumor cells is linked to cell proliferation and motility.

  David T Leong, Joleen Lim, Xuewei Goh, Jitesh Pratap, Barry P Pereira, Hui Si Kwok, Saminathan Suresh Nathan, Jason R Dobson, Jane B Lian, Yoshiaki Ito, P Mathijs Voorhoeve, Gary S Stein, Manuel Salto-Tellez, Simon M Cool, Andre J van Wijnen
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  ABSTRACT: Metastatic breast cancer cells frequently and ectopically express the transcription factor RUNX2, which normally attenuates proliferation and promotes maturation of osteoblasts. RUNX2 expression is inversely regulated with respect to cell growth in osteoblasts and deregulated in osteosarcoma cells. Here, we addressed whether the functional relationship between cell growth and RUNX2 gene expression is maintained in breast cancer cells. We also investigated whether the aberrant expression of RUNX2 is linked to phenotypic parameters that could provide a selective advantage to cells during breast cancer progression. We find that, similar to its regulation in osteoblasts, RUNX2 expression in MDA-MB-231 breast adenocarcinoma cells is enhanced upon growth factor deprivation, as well as upon deactivation of the mitogen-dependent MEK-Erk pathway or EGFR signaling. Reduction of RUNX2 levels by RNAi has only marginal effects on cell growth and expression of proliferation markers in MDA-MB-231 breast cancer cells. Thus, RUNX2 is not a critical regulator of cell proliferation in this cell type. However, siRNA depletion of RUNX2 in MDA-MB-231 cells reduces cell motility, while forced exogenous expression of RUNX2 in MCF7 cells increases cell motility. Our results support the emerging concept that the osteogenic transcription factor RUNX2 functions as a metastasis-related oncoprotein in non-osseous cancer cells.
  Breast cancer research: BCR 10/2010; 12(5):R89. · 5.24 Impact Factor
• Article: Direct laser machining-induced topographic pattern promotes up-regulation of myogenic markers in human mesenchymal stem cells.

  Huaqiong Li, Feng Wen, Yee Shan Wong, Freddy Yin Chiang Boey, Venkatraman S Subbu, David Tai Leong, Kee Woei Ng, Gary Ka Lai Ng, Lay Poh Tan
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  ABSTRACT: The engineering of tissue is preferably done with stem cells, which can be differentiated into the tissue of interest using biochemical or physical cues. While much effort has been focused on using biological factors to regulate stem cell differentiation, recently interest in the contribution of physical factors has increased. In this work, three-dimensional (3-D) microchannels with topographic micropatterns were fabricated by femtosecond laser machining on a biodegradable polymer (poly(L-lactide-co-ε-caprolactone)) substrate. Two substrates with narrow and wide channels respectively were created. Human mesenchymal stem cells (hMSCs) were cultured on the scaffolds for cell proliferation and cellular organization. Gene expression and the immunostaining of myogenic and neurogenic markers were studied. Both scaffolds improved the cell alignment along the channels as compared to the control group. Microfilaments within hMSCs were more significantly aligned and elongated on the narrower microchannels. The gene expression study revealed significant up-regulation of several hallmark markers associated with myogenesis for hMSCs cultured on the scaffold with narrow microchannels, while osteogenic and neurogenic markers were down-regulated or remained similar to the control at day 14. Immunostaining of myogen- and neurogen-specific differentiation markers were used to further confirm the specific differentiation towards a myogenic lineage. This study demonstrates that femtosecond laser machining is a versatile tool for generating controllable 3-D microchannels with topographic features that can be used to induce specific myogenic differentiation of hMSCs in vitro, even in the absence of biological factors.
  Acta biomaterialia 02/2012; 8(2):531-9. · 3.98 Impact Factor
• Article: Bio-inspired micropatterned platform to steer stem cell differentiation.

  Chor Yong Tay, Mintu Pal, Haiyang Yu, Wen Shing Leong, Nguan Soon Tan, Kee Woei Ng, Subbu Venkatraman, Freddy Boey, David Tai Leong, Lay Poh Tan
  Small 05/2011; 7(10):1416-21. · 8.35 Impact Factor