A novel transcription factor combination for direct reprogramming to a spontaneously contracting human cardiomyocyte-like state

The reprogramming of somatic cells to a spontaneously contracting cardiomyocyte-like state using defined transcription factors has proven successful in mouse fibroblasts. However, this process has been less successful in human cells, thus limiting the potential clinical applicability of this technology in regenerative medicine. We hypothesized that this issue is due to a lack of cross-species concordance between the required transcription factor combinations for mouse and human cells. To address this issue, we identified novel transcription factor candidates to induce cell conversion between human fibroblasts and cardiomyocytes, using the network-based algorithm Mogrify. We developed an automated, high-throughput method for screening transcription factor, small molecule, and growth factor combinations, utilizing acoustic liquid handling and high-content kinetic imaging cytometry. Using this high-throughput platform, we screened the effect of 4960 unique transcription factor combinations on direct conversion of 24 patient-specific primary human cardiac fibroblast samples to cardiomyocytes. Our screen revealed the combination of MYOCD, SMAD6, and TBX20 (MST) as the most successful direct reprogramming combination, which consistently produced up to 40% TNNT2+ cells in just 25 days. Addition of FGF2 and XAV939 to the MST cocktail resulted in reprogrammed cells with spontaneous contraction and cardiomyocyte-like calcium transients. Gene expression profiling of the reprogrammed cells also revealed the expression of cardiomyocyte associated genes. Together, these findings indicate that cardiac direct reprogramming in human cells can be achieved at similar levels to those attained in mouse fibroblasts. This progress represents a step forward towards the clinical application of the cardiac direct reprogramming approach.

Nutritional requirements of human induced pluripotent stem cells

The nutritional requirements for human induced pluripotent stem cell (hiPSC) growth have not been extensively studied. Here, building on our prior work that established the suitable non-basal medium components for hiPSC growth, we develop a simplified basal medium consisting of just 39 components, demonstrating that many ingredients of DMEM/F12 are either not essential or are at suboptimal concentrations. This new basal medium along with the supplement, which we call BMEM, enhances the growth rate of hiPSCs over DMEM/F12-based media, supports derivation of multiple hiPSC lines, and allows differentiation to multiple lineages. hiPSCs cultured in BMEM consistently have enhanced expression of undifferentiated cell markers such as POU5F1 and NANOG, along with increased expression of markers of the primed state and reduced expression of markers of the naive state. This work describes titration of the nutritional requirements of human pluripotent cell culture and identifies that suitable nutrition enhances the pluripotent state.

A Novel Transcription Factor Combination for Direct Reprogramming to a Spontaneously Contracting Human Cardiomyocyte-like State

The reprogramming of somatic cells to a spontaneously contracting cardiomyocyte-like state using defined transcription factors has proven successful in mouse fibroblasts. However, this process has been less successful in human cells, thus limiting the potential clinical applicability of this technology in regenerative medicine. We hypothesized that this issue is due to a lack of cross-species concordance between the required transcription factor combinations for mouse and human cells. To address this issue, we identified novel transcription factor candidates to induce cell conversion between human fibroblasts and cardiomyocytes, using the network-based algorithm Mogrify. We developed an automated, high-throughput method for screening transcription factor, small molecule, and growth factor combinations, utilizing acoustic liquid handling and high-content kinetic imaging cytometry. Using this high-throughput platform, we screened the effect of 4,960 unique transcription factor combinations on direct conversion of 24 patient-specific primary human cardiac fibroblast samples to cardiomyocytes. Our screen revealed the combination of MYOCD , SMAD6 , and TBX20 (MST) as the most successful direct reprogramming combination, which consistently produced up to 40% TNNT2 ⁺ cells in just 25 days. Addition of FGF2 and XAV939 to the MST cocktail resulted in reprogrammed cells with spontaneous contraction and cardiomyocyte-like calcium transients. Gene expression profiling of the reprogrammed cells also revealed the expression of cardiomyocyte associated genes. Together, these findings indicate that cardiac direct reprogramming in human cells can be achieved at similar levels to those attained in mouse fibroblasts. This progress represents a step forward towards the clinical application of the cardiac direct reprogramming approach.

HIGHLIGHTS

Using network-based algorithm Mogrify, acoustic liquid handling, and high-content kinetic imaging cytometry we screened the effect of 4,960 unique transcription factor combinations. Using 24 patient-specific human fibroblast samples we identified the combination of MYOCD , SMAD6 , and TBX20 (MST) as the most successful direct reprogramming combination. MST cocktail results in reprogrammed cells with spontaneous contraction, cardiomyocyte-like calcium transients, and expression of cardiomyocyte associated genes.

Abstract P1031: A Novel Transcription Factor Combination For Direct Reprogramming To A Spontaneously Contracting Human Cardiomyocyte-Like State

The reprogramming of somatic cells to a spontaneously contracting cardiomyocyte-like state using defined transcription factors has proven successful in mouse fibroblasts, but has been less successful with human cells, limiting the potential clinical applicability of this technology in regenerative medicine. We hypothesized that this issue is due to a lack of cross-species concordance between the required transcription factor combinations. Despite a decade of research, direct myocardial reprogramming still relies on overexpression of reprogramming factors first identified in mice: GATA4, MEF2C, TBX5. Using the Mogrify algorithm, we identified new candidate transcription factor combinations to induce cell conversion between human fibroblasts and cardiomyocytes. We developed an automated, high-throughput method for screening transcription factors, small molecules, and growth factors utilizing acoustic liquid handling and high-content kinetic imaging cytometry. Using this high-throughput platform we identified the combination of MYOCD, SMAD6, and TBX20 (MST) that can produce 40% TNNT2+MYH6+ cells in just 6 days and consistently produce spontaneous cardiomyocyte-like calcium transients and spontaneous contraction at just 25 days. These findings indicate that human cardiac direct reprogramming is feasible at similar levels to that achieved in the mouse and represents a step forward towards the possible clinical application of this direct cardiacreprogramming approach.

Identification of Drug Transporter Genomic Variants and Inhibitors That Protect Against Doxorubicin-Induced Cardiotoxicity

BACKGROUND

Multiple pharmacogenomic studies have identified the synonymous genomic variant rs7853758 (G > A, L461L) and the intronic variant rs885004 in SLC28A3 (solute carrier family 28 member 3) as statistically associated with a lower incidence of anthracycline-induced cardiotoxicity. However, the true causal variant(s), the cardioprotective mechanism of this locus, the role of SLC28A3 and other solute carrier (SLC) transporters in anthracycline-induced cardiotoxicity, and the suitability of SLC transporters as targets for cardioprotective drugs has not been investigated.

METHODS

Six well-phenotyped, doxorubicin-treated pediatric patients from the original association study cohort were recruited again, and human induced pluripotent stem cell-derived cardiomyocytes were generated. Patient-specific doxorubicin-induced cardiotoxicity (DIC) was then characterized using assays of cell viability, activated caspase 3/7, and doxorubicin uptake. The role of SLC28A3 in DIC was then queried using overexpression and knockout of SLC28A3 in isogenic human-induced pluripotent stem cell-derived cardiomyocytes using a CRISPR/Cas9 (Clustered Regularly Interspaced Short Palindromic Repeats/CRISPR-associated protein 9). Fine-mapping of the SLC28A3 locus was then completed after SLC28A3 resequencing and an extended in silico haplotype and functional analysis. Genome editing of the potential causal variant was done using cytosine base editor. SLC28A3-AS1 overexpression was done using a lentiviral plasmid-based transduction and was validated using stranded RNA-sequencing after ribosomal RNA depletion. Drug screening was done using the Prestwick Chemical Library (n = 1200), followed by in vivo validation in mice. The effect of desipramine on doxorubicin cytotoxicity was also investigated in 8 cancer cell lines.

RESULTS

Here, using the most commonly used anthracycline, doxorubicin, we demonstrate that patient-derived cardiomyocytes recapitulate the cardioprotective effect of the SLC28A3 locus and that SLC28A3 expression influences the severity of DIC. Using Nanopore-based fine-mapping and base editing, we identify a novel cardioprotective single nucleotide polymorphism, rs11140490, in the SLC28A3 locus; its effect is exerted via regulation of an antisense long noncoding RNA (SLC28A3-AS1) that overlaps with SLC28A3. Using high-throughput drug screening in patient-derived cardiomyocytes and whole organism validation in mice, we identify the SLC competitive inhibitor desipramine as protective against DIC.

CONCLUSIONS

This work demonstrates the power of the human induced pluripotent stem cell model to take a single nucleotide polymorphism from a statistical association through to drug discovery, providing human cell-tested data for clinical trials to attenuate DIC.

Negligible-Cost and Weekend-Free Chemically Defined Human iPSC Culture

Human induced pluripotent stem cell (hiPSC) culture has become routine, yet the cost of pluripotent cell media, frequent medium changes, and the reproducibility of differentiation have remained restrictive. Here, we describe the formulation of a hiPSC culture medium (B8) as a result of the exhaustive optimization of medium constituents and concentrations, establishing the necessity and relative contributions of each component to the pluripotent state and cell proliferation. The reagents in B8 represent only 3% of the costs of commercial media, made possible primarily by the in-lab generation of three E. coli-expressed, codon-optimized recombinant proteins: fibroblast growth factor 2, transforming growth factor β3, and neuregulin 1. We demonstrate the derivation and culture of 34 hiPSC lines in B8 as well as the maintenance of pluripotency long term (over 100 passages). This formula also allows a weekend-free feeding schedule without sacrificing capacity for differentiation.