Congratulations to our recent Ph.D. graduate, Dr. Alicia Allen, whose work was published in Tissue Engineering, Part A! The paper, titled “Temporal Impact of Substrate Anisotropy on Differentiating Cardiomyocyte Alignment and Functionality”, examines how differential fiber alignment on electrospun scaffolds affects the differentiation and final function of mESC-derived cardiomyocytes. The paper can be found here and the abstract is listed below:
Anisotropic biomaterials can affect cell function by driving cell alignment, which is critical for cardiac engineered tissues. Recent work, however, has shown that pluripotent stem cell-derived cardiomyocytes may self-align over long periods of time. To determine how the degree of biomaterial substrate anisotropy impacts differentiating cardiomyocyte structure and function, we differentiated mESCs to cardiomyocytes on non-aligned, semi-aligned, and aligned fibrous substrates and evaluated cell alignment, contractile displacement, and calcium transient synchronicity over time. Although cardiomyocyte gene expression was not affected by fiber alignment, we observed gradient- and threshold-based differences in cardiomyocyte alignment and function. Cardiomyocyte alignment increased with the degree of fiber alignment in a gradient-based manner at early time points and in a threshold-based manner at later time points. Calcium transient synchronization tightly followed cardiomyocyte alignment behavior, allowing highly anisotropic biomaterials to drive calcium transient synchronization within 8 days, while such synchronized cardiomyocyte behavior required 20 days of culture on non-aligned biomaterials. In contrast, cardiomyocyte contractile displacement had no directional preference on day 8 yet became anisotropic in the direction of fiber alignment on aligned fibers by day 20. Biomaterial anisotropy impact on differentiating cardiomyocyte structure and function is temporally-dependent.
We recently published our review by Crosby and Zoldan titled, “Mimicking the physical cues of the ECM in angiogenic biomaterials”, in the journal Regenerative Biomaterials. Thank you to chief editor and UT professor Dr. Nicholas Peppas for the opportunity to publish our summary and predictions for this burgeoning field! The abstract is listed below and the paper can be accessed here:
A functional microvascular system is imperative to build and maintain healthy tissue. Impaired microvasculature results in ischemia, thereby limiting the tissue’s intrinsic regeneration capacity. Therefore, the ability to regenerate microvascular networks is key to the development of effective cardiovascular therapies. To stimulate the formation of new microvasculature, researchers have focused on fabricating materials that mimic the angiogenic properties of the native extracellular matrix (ECM). Here, we will review biomaterials that seek to imitate the physical cues that are natively provided by the ECM to encourage the formation of microvasculature in engineered constructs and ischemic tissue in the body.
Congratulations to Cody Crosby whose publication, “Quantifying the vasculogenic potential of iPSC-derived EPs in collagen hydrogels”, was accepted and is now available online in Tissue Engineering, Part A! The abstract can be found below:
Induced pluripotent stem cell-derived endothelial progenitors (iPSC-EPs) have emerged as a promising candidate cell source for patient-specific ischemic therapies. Before these cells can be appropriately deployed in a clinical setting, it is imperative to study their assembly into functional vascular networks in extracellular matrix (ECM)-mimicking, three-dimensional microenvironments. To elucidate the interactions of iPSC-EPs with the ECM, we examined how in vitro modulation of structural protein density, the presence of angiogenic growth factors, and relative proteolytic activity affected the vasculogenic potential of these progenitors, i.e., their ability to self-assemble into vessel-like networks. We found that the addition of a ROCK pathway inhibitor and exogenous vascular endothelial growth factor (VEGF) are imperative for inducing robust iPSC-EP vasculogenesis in collagen hydrogels. Under these conditions, 3D vascular-like networks containing VE-cadherin-expressing lumens formed within a week of culture. To quantify this 3D vessel-like network, we developed a computational pipeline to analyze network length, connectivity, and average lumen diameter. Increasing the concentration of collagen in the hydrogels abrogated network formation and encouraged the formation of disconnected, large-diameter lumens. This phenomenon was in part related to the cells’ proteolytic capacity and the hydrogels’ properties, specifically hydrogel deformability and pore size. In conclusion, we demonstrate that the vasculogenic potential of iPSC-EPs is regulated by cell-matrix interactions and the matrix properties of collagen hydrogels.
Congratulations to Chengyi Tu, whose publication, “Commonly used thiol-containing antioxidants reduce cardiac differentiation and alter gene expression ratios of sarcomeric isoforms”, was recently accepted and is now published in Experimental Cell Research! The abstract can be found below:
Reactive oxygen species (ROS) scavengers such as beta-mercaptoethanol (BME) and monothiol glycerol (MTG) are extensively used in stem cell research to prevent cellular oxidative stress. However, how these antioxidant supplements impact stem cell cardiac differentiation, a process regulated by redox-signaling remains unknown. In this study, we found that removal of BME from the conventional high-glucose, serum-based differentiation medium improved cardiac differentiation efficiency by 2-3 fold. BME and MTG treatments during differentiation significantly reduced mRNA expression of cardiac progenitor markers (NKX2.5 and ISL1) as well as sarcomeric markers (MLC2A, MLC2V, TNNI3, MYH6 and MYH7), suggesting reduced cardiomyogenesis by BME or MTG. Moreover, BME and MTG altered the expression ratios between the sarcomeric isoforms. In particular, TNNI3 to TNNI1 ratio and MLC2V to MLC2A ratio were significantly lower in BME or MTG treated cells than untreated cells, implying altered cardiomyocyte phenotype and maturity. Lastly, BME and MTG treatments resulted in less frequent beating, slower contraction and relaxation velocities than untreated cells. Interestingly, none of the above-mentioned effects was observed with Trolox, a non-thiol based antioxidant, despite its strong antioxidant activity. This work demonstrates that commonly used antioxidant supplements may cause considerable changes to cellular redox state and the outcome of differentiation.
Chengyi Tu defended his thesis titled “Role of Reactive Oxygen Species in Pluripotent Stem Cells Cardiac Differentiation and Survival”. Congratulations Dr. Tu, we look forward to seeing what you do next!
We congratulate our two seniors, Elissa Barone (right) and Meghana Koleti (left), who each worked for more than two years in the Zoldan Lab and were authors on two publications. We won’t forget their hard work, and wish them all the best in their future careers!
Alicia Allen successfully defended her thesis, “Anisotropy in Cell Sheeting and Cardiac Differentiation”, thereby completing her PhD requirements and becoming the first graduate of the Zoldan Lab. Congrats Dr. Allen, we look forward to following your future career!
At the Society for Biomaterials conference in Atlanta, GA, Dr. Zoldan gave a talk titled “Matrix Anisotropy in Cardiac Differentiation”. Cody Crosby also presented his poster “Characterizing the Effect of Cell-Matrix Interactions on the Vasculogenesis of iPSC-derived Vascular Progenitor Cells” in the evening presentations.
The Zoldan lab was excited to hear Professor Jeff Hubbell’s talk on engineering novel protein-based immunotherapies to treat Type I diabetes. Wishing him and his lab the best going forward.
Olivia Conroy, who is working with Chengyi Tu, proposed to elucidate the role of ROS in cardiomyocyte proliferation via MAPK signaling. Deepti Valliappan, working with Cody Crosby, aimed to evaluate vascular network formation of endothelial progenitor cells in gelatin-CMC hydrogels. Congratulations to both!