Publications by authors named "Rebeccah J Luu"

5 Publications

  • Page 1 of 1

Probing the subcellular nanostructure of engineered human cardiomyocytes in 3D tissue.

Microsyst Nanoeng 2021 27;7:10. Epub 2021 Jan 27.

Department of Mechanical Engineering, Boston University, Boston, MA 02215 USA.

The structural and functional maturation of human induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CMs) is essential for pharmaceutical testing, disease modeling, and ultimately therapeutic use. Multicellular 3D-tissue platforms have improved the functional maturation of hiPSC-CMs, but probing cardiac contractile properties in a 3D environment remains challenging, especially at depth and in live tissues. Using small-angle X-ray scattering (SAXS) imaging, we show that hiPSC-CMs matured and examined in a 3D environment exhibit a periodic spatial arrangement of the myofilament lattice, which has not been previously detected in hiPSC-CMs. The contractile force is found to correlate with both the scattering intensity (  = 0.44) and lattice spacing (  = 0.46). The scattering intensity also correlates with lattice spacing (  = 0.81), suggestive of lower noise in our structural measurement than in the functional measurement. Notably, we observed decreased myofilament ordering in tissues with a myofilament mutation known to lead to hypertrophic cardiomyopathy (HCM). Our results highlight the progress of human cardiac tissue engineering and enable unprecedented study of structural maturation in hiPSC-CMs.
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http://dx.doi.org/10.1038/s41378-020-00234-xDOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8433147PMC
January 2021

Force Generation via β-Cardiac Myosin, Titin, and α-Actinin Drives Cardiac Sarcomere Assembly from Cell-Matrix Adhesions.

Dev Cell 2018 01 8;44(1):87-96.e5. Epub 2018 Jan 8.

Department of Biomedical Engineering, Boston University, Boston, MA 02215, USA; The Wyss Institute for Biologically Inspired Engineering at Harvard University, Boston, MA 02115, USA. Electronic address:

Truncating mutations in the sarcomere protein titin cause dilated cardiomyopathy due to sarcomere insufficiency. However, it remains mechanistically unclear how these mutations decrease sarcomere content in cardiomyocytes. Utilizing human induced pluripotent stem cell-derived cardiomyocytes, CRISPR/Cas9, and live microscopy, we characterize the fundamental mechanisms of human cardiac sarcomere formation. We observe that sarcomerogenesis initiates at protocostameres, sites of cell-extracellular matrix adhesion, where nucleation and centripetal assembly of α-actinin-2-containing fibers provide a template for the fusion of Z-disk precursors, Z bodies, and subsequent striation. We identify that β-cardiac myosin-titin-protocostamere form an essential mechanical connection that transmits forces required to direct α-actinin-2 centripetal fiber assembly and sarcomere formation. Titin propagates diastolic traction stresses from β-cardiac myosin, but not α-cardiac myosin or non-muscle myosin II, to protocostameres during sarcomerogenesis. Ablating protocostameres or decoupling titin from protocostameres abolishes sarcomere assembly. Together these results identify the mechanical and molecular components critical for human cardiac sarcomerogenesis.
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http://dx.doi.org/10.1016/j.devcel.2017.12.012DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6421364PMC
January 2018

Lineage- and developmental stage-specific mechanomodulation of induced pluripotent stem cell differentiation.

Stem Cell Res Ther 2017 09 29;8(1):216. Epub 2017 Sep 29.

Department of Bioengineering, University of California-Riverside, Materials Science & Engineering Building 331, 900 University Avenue, Riverside, CA, 92521, USA.

Background: To maximize the translational utility of human induced pluripotent stem cells (iPSCs), the ability to precisely modulate the differentiation of iPSCs to target phenotypes is critical. Although the effects of the physical cell niche on stem cell differentiation are well documented, current approaches to direct step-wise differentiation of iPSCs have been typically limited to the optimization of soluble factors. In this regard, we investigated how temporally varied substrate stiffness affects the step-wise differentiation of iPSCs towards various lineages/phenotypes.

Methods: Electrospun nanofibrous substrates with different reduced Young's modulus were utilized to subject cells to different mechanical environments during the differentiation process towards representative phenotypes from each of three germ layer derivatives including motor neuron, pancreatic endoderm, and chondrocyte. Phenotype-specific markers of each lineage/stage were utilized to determine differentiation efficiency by reverse-transcription polymerase chain reaction (RT-PCR) and immunofluorescence imaging for gene and protein expression analysis, respectively.

Results: The results presented in this proof-of-concept study are the first to systematically demonstrate the significant role of the temporally varied mechanical microenvironment on the differentiation of stem cells. Our results demonstrate that the process of differentiation from pluripotent cells to functional end-phenotypes is mechanoresponsive in a lineage- and differentiation stage-specific manner.

Conclusions: Lineage/developmental stage-dependent optimization of electrospun substrate stiffness provides a unique opportunity to enhance differentiation efficiency of iPSCs for their facilitated therapeutic applications.
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http://dx.doi.org/10.1186/s13287-017-0667-2DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5622562PMC
September 2017

ROCK inhibitor primes human induced pluripotent stem cells to selectively differentiate towards mesendodermal lineage via epithelial-mesenchymal transition-like modulation.

Stem Cell Res 2016 09 4;17(2):222-227. Epub 2016 Aug 4.

Department of Bioengineering, University of California-Riverside, CA 92521, United States. Electronic address:

Robust control of human induced pluripotent stem cell (hIPSC) differentiation is essential to realize its patient-tailored therapeutic potential. Here, we demonstrate a novel application of Y-27632, a small molecule Rho-associated protein kinase (ROCK) inhibitor, to significantly influence the differentiation of hIPSCs in a lineage-specific manner. The application of Y-27632 to hIPSCs resulted in a decrease in actin bundling and disruption of colony formation in a concentration and time-dependent manner. Such changes in cell and colony morphology were associated with decreased expression of E-cadherin, a cell-cell junctional protein, proportional to the increased exposure to Y-27632. Interestingly, gene and protein expression of pluripotency markers such as NANOG and OCT4 were not downregulated by an exposure to Y-27632 up to 36h. Simultaneously, epithelial-to-mesenchymal (EMT) transition markers were upregulated with an exposure to Y-27632. These EMT-like changes in the cells with longer exposure to Y-27632 resulted in a significant increase in the subsequent differentiation efficiency towards mesendodermal lineage. In contrast, an inhibitory effect was observed when cells were subjected to ectodermal differentiation after prolonged exposure to Y-27632. Collectively, these results present a novel method for priming hIPSCs to modulate their differentiation potential with a simple application of Y-27632.
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http://dx.doi.org/10.1016/j.scr.2016.07.009DOI Listing
September 2016

Enhanced Lineage-Specific Differentiation Efficiency of Human Induced Pluripotent Stem Cells by Engineering Colony Dimensionality Using Electrospun Scaffolds.

Adv Healthc Mater 2016 06 17;5(12):1408-12. Epub 2016 May 17.

Department of Bioengineering, University of California-Riverside, Materials Science & Engineering Building 331, 900 University Avenue, Riverside, CA, 92521, USA.

Electrospun scaffolds with varied stiffness promote distinct colony morphology of human induced pluripotent stem cells, which affects their subsequent differentiation. On soft scaffolds, induced pluripotent stem cells develop 3D colonies due to the pliability of the electrospun fibrous networks, leading to greater differentiation tendency to ectodermal lineage.
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http://dx.doi.org/10.1002/adhm.201600141DOI Listing
June 2016
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