ERRγ enhances cardiac maturation with T-tubule formation in human iPSC-derived cardiomyocytes

One of the earliest maturation steps in cardiomyocytes (CMs) is the sarcomere protein isoform switch between TNNI1 and TNNI3 (fetal and neonatal/adult troponin I). Here, we generate human induced pluripotent stem cells (hiPSCs) carrying a TNNI1EmGFP and TNNI3mCherry double reporter to monitor and isolate mature sub-populations during cardiac differentiation. Extensive drug screening identifies two compounds, an estrogen-related receptor gamma (ERRγ) agonist and an S-phase kinase-associated protein 2 inhibitor, that enhances cardiac maturation and a significant change to TNNI3 expression. Expression, morphological, functional, and molecular analyses indicate that hiPSC-CMs treated with the ERRγ agonist show a larger cell size, longer sarcomere length, the presence of transverse tubules, and enhanced metabolic function and contractile and electrical properties. Here, we show that ERRγ-treated hiPSC-CMs have a mature cellular property consistent with neonatal CMs and are useful for disease modeling and regenerative medicine.

Oncogenic mutation or overexpression of oncogenic KRAS or BRAF is not sufficient to confer oncogene addiction

Oncogene addiction is a cellular property by which cancer cells become highly dependent on the expression of oncogenes for their survival. Oncogene addiction can be exploited to design molecularly targeted drugs that kill only cancer cells by inhibiting the specific oncogenes. Genes and cell lines exhibiting oncogene addiction, as well as the mechanisms by which cell death is induced when addicted oncogenes are suppressed, have been extensively studied. However, it is still not fully understood how oncogene addiction is acquired in cancer cells. Here, we take a synthetic biology approach to investigate whether oncogenic mutation or oncogene expression suffices to confer the property of oncogene addiction to cancer cells. We employed human mammary epithelium-derived MCF-10A cells expressing the oncogenic KRAS or BRAF. MCF-10A cells harboring an oncogenic mutation in a single-allele of KRAS or BRAF showed weak transformation activity, but no characteristics of oncogene addiction. MCF-10A cells overexpressing oncogenic KRAS demonstrated the transformation activity, but MCF-10A cells overexpressing oncogenic BRAF did not. Neither cell line exhibited any oncogene addiction properties. These results indicate that the introduction of oncogenic mutation or the overexpression of oncogenes is not sufficient for cells to acquire oncogene addiction, and that oncogene addiction is not associated with transformation activity.

Oncogenic mutation or overexpression of oncogenic KRAS or BRAF is not sufficient to confer oncogene addiction

Oncogene addiction is a cellular property by which cancer cells become highly dependent on the expression of oncogenes for their survival. Oncogene addiction can be exploited to design molecularly targeted drugs that kill only cancer cells by inhibiting the specific oncogenes. Genes and cell lines exhibiting oncogene addiction, as well as the mechanisms by which cell death is induced when addicted oncogenes are suppressed, have been extensively studied. However, it is still not fully understood how oncogene addiction is acquired in cancer cells. Here, we take a synthetic biology approach to investigate whether oncogenic mutation or oncogene expression suffices to confer the property of oncogene addiction to cancer cells. We employed human mammary epithelium-derived MCF-10A cells expressing the oncogenic KRAS or BRAF. MCF-10A cells harboring an oncogenic mutation in a single-allele of KRAS or BRAF showed weak tumorigenic activity, but no characteristics of oncogene addiction. MCF-10A cells overexpressing oncogenic KRAS demonstrated the tumorigenic activity, but MCF-10A cells overexpressing oncogenic BRAF did not. Neither cell line exhibited any oncogene addiction properties. These results indicate that the introduction of oncogenic mutation or the overexpression of oncogenes is not sufficient for cancer cells to acquire oncogene addiction, and that oncogene addiction is not associated with tumorigenic potential.

Cortical cell stiffness is independent of substrate mechanics

Cortical stiffness is an important cellular property that changes during migration, adhesion, and growth. Previous atomic force microscopy (AFM) indentation measurements of cells cultured on deformable substrates suggested that cells adapt their stiffness to that of their surroundings. Here we show that the force applied by AFM onto cells results in a significant deformation of the underlying substrate if it is softer than the cells. This ‘soft substrate effect’ leads to an underestimation of a cell’s elastic modulus when analyzing data using a standard Hertz model, as confirmed by finite element modelling (FEM) and AFM measurements of calibrated polyacrylamide beads, microglial cells, and fibroblasts. To account for this substrate deformation, we developed the ‘composite cell-substrate model’ (CoCS model). Correcting for the substrate indentation revealed that cortical cell stiffness is largely independent of substrate mechanics, which has significant implications for our interpretation of many physiological and pathological processes.

A positive feedback at the cellular level promotes robustness and modulation at the circuit level

This article highlights the role of a positive feedback gating mechanism at the cellular level in the robustness and modulation properties of rhythmic activities at the circuit level. The results are presented in the context of half-center oscillators, which are simple rhythmic circuits composed of two reciprocally connected inhibitory neuronal populations. Specifically, we focus on rhythms that rely on a particular excitability property, the postinhibitory rebound, an intrinsic cellular property that elicits transient membrane depolarization when released from hyperpolarization. Two distinct ionic currents can evoke this transient depolarization: a hyperpolarization-activated cation current and a low-threshold T-type calcium current. The presence of a slow activation is specific to the T-type calcium current and provides a slow positive feedback at the cellular level that is absent in the cation current. We show that this slow positive feedback is required to endow the network rhythm with physiological modulation and robustness properties. This study thereby identifies an essential cellular property to be retained at the network level in modeling network robustness and modulation.

Abstract 860: Phenotypic Characterization Of Murine And Human Cardiac-resident Progenitor Cells Isolated On Basis Of Aldehyde-dehydrogenase Activity

Identification of stem cells based on hematopoietic stem cell (HSC) surface markers, such as stem cell antigen-1 (Sca-1) and the c-kit receptor, has limited specificity. High aldehyde-dehydrogenase (ALDH) activity is a general cellular property of stem cells shared by HSC, neural, and intestinal stem cells. The presence of cells with high ALDH activity in the adult heart has not been investigated. Methods: Cells were isolated from adult mouse hearts, and from atrial appendage samples from humans with ischemic or valvular heart disease. Myocyte-depleted mouse Sca-1+, and lineage (Lin)-negative/c-kit+ human heart cells were purified with immunomagnetic beads. ALDH-high cells were identified using a specific fluorescent substrate, and sorted by FACS. Cell surface marker analysis was performed by flow cytometry. Results: Myocyte-depleted mouse heart cells contained 4.8+/−3.2% ALDH-high/SSC-low and 32.6+/−1.6% Sca-1+ cells. ALDH-high cells were Lin-negative, Sca-1+ CD34+ CD105+ CD106+, contained small CD44+ (27%) and CD45+ (15%) subpopulations, and were essentially negative for c-kit (2%), CD29, CD31, CD133 and Flk-1. After several passages in culture, ~20% of ALDH-high cells remained ALDH-high. Myocyte-depleted human atrial cells contained variable numbers of ALDH-high cells ranging from 0.5% to 11%, and 4% Lin-negative/c-kit+ cells. ALDH-high cells were CD29+ CD105+, contained a small c-kit+ subpopulation (5%), and were negative for CD31, CD45 and CD133. After 5 passages in culture, the majority of ALDH-high cells remained ALDH-high. Conclusions: Adult mouse and human hearts contain significant numbers of cells with high ALDH activity, a general cellular property that stem cells possess in different organs, and express stem cell markers (Sca-1 and CD34 in the mouse). The immunophenotype of cardiac-resident ALDH-high cells differs from that previously described for bone marrow ALDH-high HSC, and suggests that this cell population may be enriched in mesenchymal progenitors. Analysis of lineage differentiation potential of ALDH-high cells is in progress. ALDH activity provides a new, practical approach to purifying cardiac-resident progenitor cells.