Dilated cardiomyopathy (DCM) is a common cause of heart failure and sudden cardiac death. It has ... more Dilated cardiomyopathy (DCM) is a common cause of heart failure and sudden cardiac death. It has been estimated that up to half of DCM cases are hereditary. Mutations in more than 50 genes, primarily autosomal dominant, have been reported. Although rare, recessive mutations are thought to contribute considerably to DCM, especially in young children. Here we identified a novel recessive mutation in the striated muscle enriched protein kinase (SPEG, p. E1680K) gene in a family with nonsyndromic, early onset DCM. To ascertain the pathogenicity of this mutation, we generated SPEG E1680K homozygous mutant human induced pluripotent stem cell derived cardiomyocytes (iPSC-CMs) using CRISPR/Cas9-mediated genome editing. Functional studies in mutant iPSC-CMs showed aberrant calcium homeostasis, impaired contractility, and sarcomeric disorganization, recapitulating the hallmarks of DCM. By combining genetic analysis with human iPSCs, genome editing, and functional assays, we identified SPEG E1680K as a novel mutation associated with early onset DCM and provide evidence for its pathogenicity in vitro. Our study provides a conceptual paradigm for establishing genotype-phenotype associations in DCM with autosomal recessive inheritance.
Rationale: Human embryonic stem cells can form cardiomyocytes when cultured under differentiation... more Rationale: Human embryonic stem cells can form cardiomyocytes when cultured under differentiation conditions. Although the initiating step of mesoderm formation is well characterized, the subsequent steps that promote for cardiac lineages are poorly understood and limit the yield of cardiomyocytes. Objective: Our aim was to develop a human embryonic stem cell–based high-content screening assay to discover small molecules that drive cardiogenic differentiation after mesoderm is established to improve our understand-ing of the biology involved. Screening of libraries of small-molecule pathway modulators was predicted to provide insight into the cellular proteins and signaling pathways that control stem cell cardiogenesis. Methods and Results: Approximately 550 known pathway modulators were screened in a high-content screen-ing assay, with hits being called out by the appearance of a red fluorescent protein driven by the promoter of the cardiac-specific MYH6 gene. One potent small mole...
Invariant patterning of left-right asymmetry during embryogenesis depends upon a cascade of induc... more Invariant patterning of left-right asymmetry during embryogenesis depends upon a cascade of inductive and repressive interactions between asymmetrically expressed genes. Different cascades of asymmetric genes distinguish the left and right sides of the embryo and are maintained by a midline barrier. As such, the left and right sides of an embryo can be viewed as distinct and autonomous fields. Here we describe a series of experiments that indicate that the initiation of these programs requires communication between the two sides of the blastoderm. When deprived of either the left or the right lateral halves of the blastoderm, embryos are incapable of patterning normal left-right gene expression at Hensen's node. Not only are both flanks required, suggesting that there is no single signaling source for LR pattern, but the blastoderm must be intact. These results are consistent with our previously proposed model in which the orientation of LR asymmetry in the frog, Xenopus laevis,...
Induced pluripotent stem cell-derived cardiomyocytes (iPSC-CMs) have enormous potential for the s... more Induced pluripotent stem cell-derived cardiomyocytes (iPSC-CMs) have enormous potential for the study of human cardiac disorders. However, their physiological immaturity severely limits their utility as a model system and their adoption for drug discovery. Here, we describe maturation media designed to provide oxidative substrates adapted to the metabolic needs of human iPSC (hiPSC)-CMs. Compared with conventionally cultured hiPSC-CMs, metabolically matured hiPSC-CMs contract with greater force and show an increased reliance on cardiac sodium (Na + ) channels and sarcoplasmic reticulum calcium (Ca 2+ ) cycling. The media enhance the function, long-term survival, and sarcomere structures in engineered heart tissues. Use of the maturation media made it possible to reliably model two genetic cardiac diseases: long QT syndrome type 3 due to a
Highlights d RBM20 mutant DCM iPSC-cardiomyocytes show mRNA splicing and contractile defects d RB... more Highlights d RBM20 mutant DCM iPSC-cardiomyocytes show mRNA splicing and contractile defects d RBM20 P633L variant causes the phenotypes of the disease d All-trans retinoic acid upregulates RBM20 mRNA and protein expression d Pharmacological RBM20 upregulation ameliorates DCM phenotypes in vitro
NOTCH plays a pivotal role during normal development and in congenital disorders and cancer. γ-se... more NOTCH plays a pivotal role during normal development and in congenital disorders and cancer. γ-secretase inhibitors are commonly used to probe NOTCH function, but also block processing of numerous other proteins. We discovered a new class of small molecule inhibitor that disrupts the interaction between NOTCH and RBPJ, which is the main transcriptional effector of NOTCH signaling. RBPJ Inhibitor-1 (RIN1) also blocked the functional interaction of RBPJ with SHARP, a scaffold protein that forms a transcriptional repressor complex with RBPJ in the absence of NOTCH signaling. RIN1 induced changes in gene expression that resembled siRNA silencing of RBPJ rather than inhibition at the level of NOTCH itself. Consistent with disruption of NOTCH signaling, RIN1 inhibited the proliferation of hematologic cancer cell lines and promoted skeletal muscle differentiation from C2C12 myoblasts. Thus, RIN1 inhibits RBPJ in its repressing and activating contexts, and can be exploited for chemical biology and therapeutic applications. NOTCH proteins are trans-membrane receptors that transduce signals from cell-bound JAGGED (JAG) and Delta-like (DLL) families of ligands to mediate cell-cell interactions in processes as diverse as fetal development, heart disease and cancer 1,2 . Upon interaction with ligand, NOTCH is cleaved by γ-secretase to release an intracellular domain (NICD) that binds the transcriptional effector RBPJ [recombination signal-binding protein for immunoglobulin κ J region, also known as CSL and CBF1] 3,4 . There is only one small molecule reported to selectively inhibit NOTCH signaling and none known to target RBPJ 5 . γ-secretase inhibitors (GSIs) have been used widely to block the proteolytic activation of NOTCH, but are inherently unselective since they also block the processing of >90 other substrates, including the amyloid precursor protein (APP), ErbB4, and E-cadherin . Although newer generation GSIs exhibit a biased inhibition of APP over NOTCH , there are no NOTCH-selective GSIs. Clinical use of GSIs cause numerous side effects, notably intestinal crypt cell proliferation 11 , and skin rashes and tumors 12 . These undesirable effects have led to the early termination of a phase III clinical trial of Semagacestat for treatment of Alzheimer's Disease 13 . The NOTCH ICD:RBPJ complex contains co-activators MAML (mastermind-like protein) and histone acetyltransferases (HATs) to activate downstream genes including members of the structurally related HES (Hairy/ Enhancer of Split) and HEY/HRT (Hairy/Enhancer of Split-related) family 14 . The transcriptional effects of NICD are mediated primarily through the interaction with RBPJ, which recruits NICD to recognition sites in promoter regions as well as to more distally located superenhancers 15 . Thus, antagonism of RBPJ would be a desirable point to modulate NOTCH signaling, making it a useful probe and potential clinical candidate since it could provide additional selectivity over targeting γ-secretases or NOTCH itself. To develop a novel chemical inhibitor of NOTCH, we evaluated the feasibility of selectively targeting the RBPJ protein to perturb its interaction with the NOTCH ICD. Although protein-protein interactions can be challenging to inhibit with small molecules, the binding interface between RBPJ and NOTCH is small hence we reasoned that it might be possible to disrupt it with a small
Cardiovascular disease remains the largest single cause of mortality in the Western world, despit... more Cardiovascular disease remains the largest single cause of mortality in the Western world, despite significant advances in clinical management over the years. Unfortunately, the development of new cardiovascular medicines is stagnating and can in part be attributed to the difficulty of screening for novel therapeutic strategies due to a lack of suitable models. The advent of human induced pluripotent stem cells and the ability to make limitless numbers of cardiomyocytes could revolutionize heart disease modeling and drug discovery. This review summarizes the state of the art in the field, describes the strengths and weaknesses of the technology, and applications where the model system would be most appropriate.
Proceedings of the National Academy of Sciences, 2012
Unique insights for the reprograming of cell lineages have come from embryonic development in the... more Unique insights for the reprograming of cell lineages have come from embryonic development in the ascidian Ciona , which is dependent upon the transcription factors Ci -ets1/2 and Ci -mesp to generate cardiac progenitors. We tested the idea that mammalian v-ets erythroblastosis virus E26 oncogene homolog 2 (ETS2) and mesoderm posterior (MESP) homolog may be used to convert human dermal fibroblasts into cardiac progenitors. Here we show that murine ETS2 has a critical role in directing cardiac progenitors during cardiopoiesis in embryonic stem cells. We then use lentivirus-mediated forced expression of human ETS2 to convert normal human dermal fibroblasts into replicative cells expressing the cardiac mesoderm marker KDR + . However, although neither ETS2 nor the purported cardiac master regulator MESP1 can by themselves generate cardiac progenitors de novo from fibroblasts, forced coexpression of ETS2 and MESP1 or cell treatment with purified proteins reprograms fibroblasts into card...
The adult human heart is an ideal target for regenerative intervention since it does not function... more The adult human heart is an ideal target for regenerative intervention since it does not functionally restore itself after injury yet has a modest regenerative capacity that could be enhanced by innovative therapies. Adult cardiac cells with regenerative potential share gene expression signatures with early fetal progenitors that give rise to multiple cardiac cell types, suggesting that the evolutionarily conserved regulatory networks that drive embryonic heart development might also control aspects of regeneration. Here we discuss commonalities of development and regeneration, and the application of the rich developmental biology heritage to achieve therapeutic regeneration of the human heart.
Rationale: The transforming growth factor-β (TGFβ) family member Nodal promotes cardiogenesis, bu... more Rationale: The transforming growth factor-β (TGFβ) family member Nodal promotes cardiogenesis, but the mechanism is unclear despite the relevance of TGFβ family proteins for myocardial remodeling and regeneration. Objective: To determine the function(s) of TGFβ family members during stem cell cardiogenesis. Methods and Results: Murine embryonic stem cells were engineered with a constitutively active human type I Nodal receptor (caACVR1b) to mimic activation by Nodal and found to secrete a paracrine signal that promotes cardiogenesis. Transcriptome and gain- and loss-of-function studies identified the factor as TGFβ2. Both Nodal and TGFβ induced early cardiogenic progenitors in embryonic stem cell cultures at day 0 to 2 of differentiation. However, Nodal expression declines by day 4 due to feedback inhibition, whereas TGFβ persists. At later stages (days 4–6), TGFβ suppresses the formation of cardiomyocytes from multipotent Kdr + progenitors while promoting the differentiation of vas...
Rationale: Human embryonic stem cells can form cardiomyocytes when cultured under differentiation... more Rationale: Human embryonic stem cells can form cardiomyocytes when cultured under differentiation conditions. Although the initiating step of mesoderm formation is well characterized, the subsequent steps that promote for cardiac lineages are poorly understood and limit the yield of cardiomyocytes. Objective: Our aim was to develop a human embryonic stem cell–based high-content screening assay to discover small molecules that drive cardiogenic differentiation after mesoderm is established to improve our understanding of the biology involved. Screening of libraries of small-molecule pathway modulators was predicted to provide insight into the cellular proteins and signaling pathways that control stem cell cardiogenesis. Methods and Results: Approximately 550 known pathway modulators were screened in a high-content screening assay, with hits being called out by the appearance of a red fluorescent protein driven by the promoter of the cardiac-specific MYH6 gene. One potent small molecu...
The cellular signals controlling the formation of cardiomyocytes, vascular smooth muscle, and end... more The cellular signals controlling the formation of cardiomyocytes, vascular smooth muscle, and endothelial cells from stem cell-derived mesoderm are poorly understood. To identify these signals, a mouse embryonic stem cell (ESC)-based differentiation assay was screened against a small molecule library resulting in a 1,4-dihydropyridine inducer of type II TGF-b receptor (TGFBR2) degradation-1 (ITD-1). ITD analogs enhanced proteasomal degradation of TGFBR2, effectively clearing the receptor from the cell surface and selectively inhibiting intracellular signaling (IC 50 $0.4-0.8 mM). ITD-1 was used to evaluate TGF-b involvement in mesoderm formation and cardiopoietic differentiation, which occur sequentially during early development, revealing an essential role in both processes in ESC cultures. ITD-1 selectively enhanced the differentiation of uncommitted mesoderm to cardiomyocytes, but not to vascular smooth muscle and endothelial cells. ITD-1 is a highly selective TGF-b inhibitor and reveals an unexpected role for TGF-b signaling in controlling cardiomyocyte differentiation from multipotent cardiovascular precursors.
knockdown. Notably, 9 of these factors affected erythroid development whereas 8 factors affected ... more knockdown. Notably, 9 of these factors affected erythroid development whereas 8 factors affected myeloid development. More than half of these factors were predicted to regulate the specific lineage based on the sequence or expressionbased model. Moreover, two of these factors, HIF3A and AFF1 (encoding the AF9 protein), were not previously implicated in erythropoiesis but emerged from this study based on their expression profile. The scope of the analysis performed in this study on human hematopoietic progenitors provides a rich resource for identifying regulatory networks controlling HSC self-renewal, differentiation, and lineage determination.
Developmental biologists have defined many of the diffusible and transcription factors that contr... more Developmental biologists have defined many of the diffusible and transcription factors that control muscle differentiation, yet we still have only rudimentary knowledge of the mechanisms that dictate whether a myogenic progenitor cell forms muscle versus alternate lineages, including those that can be pathological in a state of disease or degeneration. Clues about the molecular basis for lineage determination in muscle progenitors are only now emerging from studies of chromatin modifications that avail myogenic genes for transcription, together with analysis of the composition and activities of the chromatin-modifying complexes themselves. Here we review recent progress on muscle determination and explore a unifying theme that environmental cues from the stem or progenitor niche control the selection of specific subunit variants of the switch/sucrose nonfermentable (SWI/SNF) chromatin-modifying complex, creating a combinatorial code that dictates whether cells adopt myogenic versus ...
For adult women in the United States, breast cancer is the most prevalent form of cancer. Compoun... more For adult women in the United States, breast cancer is the most prevalent form of cancer. Compounds that target dysregulated signal transduction can be efficacious anti-cancer therapies. A prominent signaling pathway frequently dysregulated in breast cancer cells is the Wingless-related integration site (Wnt) pathway. The purpose of the work was to optimize a "hit" from a screening campaign. 76,000 compounds were tested in a Wnt transcription assay and revealed potent and reproducible "hit," compound 1. Medicinal chemistry optimization of 1 led to more potent and drug-like molecules, 19, 24 and 25 (i.e., Wnt pathway IC values = 11, 18 and 7 nM, respectively). The principal results showed compounds 19, 24 and 25 were potent anti-proliferative agents in breast cancer cell lines, MCF-7 (i.e., IC values = 10, 7 and 4 nM, respectively) and MDA-MB 231 (i.e., IC values = 13, 13 and 16 nM, respectively). Compound 19 synergized anti-proliferation with chemotherapeutic Dox...
Understanding the mechanisms that control human cardiomyocyte proliferation might be applicable t... more Understanding the mechanisms that control human cardiomyocyte proliferation might be applicable to regenerative medicine. We screened a whole genome collection of human miRNAs, identifying 96 to be capable of increasing proliferation (DNA synthesis and cytokinesis) of human iPSC-derived cardiomyocytes. Chemical screening and computational approaches indicated that most of these miRNAs (67) target different components of the Hippo pathway and that their activity depends on the nuclear translocation of the Hippo transcriptional effector YAP. 53 of the 67 miRNAs are present in human iPSC cardiomyocytes, yet anti-miRNA screening revealed that none are individually essential for basal proliferation of hiPSC cardiomyocytes despite the importance of YAP for proliferation. We propose a model in which multiple endogenous miRNAs redundantly suppress Hippo signaling to sustain the cell cycle of immature cardiomyocytes.
Molecular therapy : the journal of the American Society of Gene Therapy, Jan 26, 2017
MicroRNAs are promising therapeutic targets, because their inhibition has the potential to normal... more MicroRNAs are promising therapeutic targets, because their inhibition has the potential to normalize gene expression in diseased states. Recently, our group found that miR-25 is a key SERCA2a regulating microRNA, and we showed that multiple injections of antagomirs against miR-25 enhance cardiac contractility and function through SERCA2a restoration in a murine heart failure model. However, for clinical application, a more stable suppressor of miR-25 would be desirable. Tough Decoy (TuD) inhibitors are emerging as a highly effective method for microRNA inhibition due to their resistance to endonucleolytic degradation, high miRNA binding affinity, and efficient delivery. We generated a miR-25 TuD inhibitor and subcloned it into a cardiotropic AAV9 vector to evaluate its efficacy. The AAV9 TuD showed selective inhibition of miR-25 in vitro cardiomyoblast culture. In vivo, AAV9-miR-25 TuD delivered to the murine pressure-overload heart failure model selectively decreased expression of ...
The ability to produce unlimited numbers of human induced pluripotent stem cell derived cardiomyo... more The ability to produce unlimited numbers of human induced pluripotent stem cell derived cardiomyocytes (hiPSC-CMs) harboring disease and patient-specific gene variants creates a new paradigm for modeling congenital heart diseases (CHDs) and predicting proarrhythmic liabilities of drug candidates. However, a major roadblock to implementing hiPSC-CM technology in drug discovery is that conventional methods for monitoring action potential (AP) kinetics and arrhythmia phenotypes in vitro have been too costly or technically challenging to execute in high throughput. Herein, we describe the first large-scale, fully automated and statistically robust analysis of AP kinetics and drug-induced proarrhythmia in hiPSC-CMs. The platform combines the optical recording of a small molecule fluorescent voltage sensing probe (VoltageFluor2.1.Cl), an automated high throughput microscope and automated image analysis to rapidly generate physiological measurements of cardiomyocytes (CMs). The technique c...
The expression of nearly all smooth muscle genes are controlled by serum response factor binding ... more The expression of nearly all smooth muscle genes are controlled by serum response factor binding sites in their promoter regions. However, SRF alone is not sufficient for regulating smooth muscle cell development. It associates with other cardiovascular specific cofactors to regulate smooth muscle gene expression. Previously, we showed that the transcription co-factor CRP2 was a regulator of smooth muscle gene expression. Here, we report that CSRP2BP, a coactivator for CRP2, is a histone acetyltransferase and a driver of smooth muscle gene expression. CSRP2BP directly interacted with SRF, CRP2 and myocardin. CSRP2BP synergistically activated smooth muscle gene promoters in an SRF-dependent manner. A combination of SRF, GATA6 and CRP2 required CSRP2BP for robust smooth muscle gene promoter activity. Knock-down of Csrp2bp in smooth muscle cells resulted in reduced smooth muscle gene expression. We conclude that the CSRP2BP histone acetyltransferase is a coactivator for CRP2 that works...
Dilated cardiomyopathy (DCM) is a common cause of heart failure and sudden cardiac death. It has ... more Dilated cardiomyopathy (DCM) is a common cause of heart failure and sudden cardiac death. It has been estimated that up to half of DCM cases are hereditary. Mutations in more than 50 genes, primarily autosomal dominant, have been reported. Although rare, recessive mutations are thought to contribute considerably to DCM, especially in young children. Here we identified a novel recessive mutation in the striated muscle enriched protein kinase (SPEG, p. E1680K) gene in a family with nonsyndromic, early onset DCM. To ascertain the pathogenicity of this mutation, we generated SPEG E1680K homozygous mutant human induced pluripotent stem cell derived cardiomyocytes (iPSC-CMs) using CRISPR/Cas9-mediated genome editing. Functional studies in mutant iPSC-CMs showed aberrant calcium homeostasis, impaired contractility, and sarcomeric disorganization, recapitulating the hallmarks of DCM. By combining genetic analysis with human iPSCs, genome editing, and functional assays, we identified SPEG E1680K as a novel mutation associated with early onset DCM and provide evidence for its pathogenicity in vitro. Our study provides a conceptual paradigm for establishing genotype-phenotype associations in DCM with autosomal recessive inheritance.
Rationale: Human embryonic stem cells can form cardiomyocytes when cultured under differentiation... more Rationale: Human embryonic stem cells can form cardiomyocytes when cultured under differentiation conditions. Although the initiating step of mesoderm formation is well characterized, the subsequent steps that promote for cardiac lineages are poorly understood and limit the yield of cardiomyocytes. Objective: Our aim was to develop a human embryonic stem cell–based high-content screening assay to discover small molecules that drive cardiogenic differentiation after mesoderm is established to improve our understand-ing of the biology involved. Screening of libraries of small-molecule pathway modulators was predicted to provide insight into the cellular proteins and signaling pathways that control stem cell cardiogenesis. Methods and Results: Approximately 550 known pathway modulators were screened in a high-content screen-ing assay, with hits being called out by the appearance of a red fluorescent protein driven by the promoter of the cardiac-specific MYH6 gene. One potent small mole...
Invariant patterning of left-right asymmetry during embryogenesis depends upon a cascade of induc... more Invariant patterning of left-right asymmetry during embryogenesis depends upon a cascade of inductive and repressive interactions between asymmetrically expressed genes. Different cascades of asymmetric genes distinguish the left and right sides of the embryo and are maintained by a midline barrier. As such, the left and right sides of an embryo can be viewed as distinct and autonomous fields. Here we describe a series of experiments that indicate that the initiation of these programs requires communication between the two sides of the blastoderm. When deprived of either the left or the right lateral halves of the blastoderm, embryos are incapable of patterning normal left-right gene expression at Hensen's node. Not only are both flanks required, suggesting that there is no single signaling source for LR pattern, but the blastoderm must be intact. These results are consistent with our previously proposed model in which the orientation of LR asymmetry in the frog, Xenopus laevis,...
Induced pluripotent stem cell-derived cardiomyocytes (iPSC-CMs) have enormous potential for the s... more Induced pluripotent stem cell-derived cardiomyocytes (iPSC-CMs) have enormous potential for the study of human cardiac disorders. However, their physiological immaturity severely limits their utility as a model system and their adoption for drug discovery. Here, we describe maturation media designed to provide oxidative substrates adapted to the metabolic needs of human iPSC (hiPSC)-CMs. Compared with conventionally cultured hiPSC-CMs, metabolically matured hiPSC-CMs contract with greater force and show an increased reliance on cardiac sodium (Na + ) channels and sarcoplasmic reticulum calcium (Ca 2+ ) cycling. The media enhance the function, long-term survival, and sarcomere structures in engineered heart tissues. Use of the maturation media made it possible to reliably model two genetic cardiac diseases: long QT syndrome type 3 due to a
Highlights d RBM20 mutant DCM iPSC-cardiomyocytes show mRNA splicing and contractile defects d RB... more Highlights d RBM20 mutant DCM iPSC-cardiomyocytes show mRNA splicing and contractile defects d RBM20 P633L variant causes the phenotypes of the disease d All-trans retinoic acid upregulates RBM20 mRNA and protein expression d Pharmacological RBM20 upregulation ameliorates DCM phenotypes in vitro
NOTCH plays a pivotal role during normal development and in congenital disorders and cancer. γ-se... more NOTCH plays a pivotal role during normal development and in congenital disorders and cancer. γ-secretase inhibitors are commonly used to probe NOTCH function, but also block processing of numerous other proteins. We discovered a new class of small molecule inhibitor that disrupts the interaction between NOTCH and RBPJ, which is the main transcriptional effector of NOTCH signaling. RBPJ Inhibitor-1 (RIN1) also blocked the functional interaction of RBPJ with SHARP, a scaffold protein that forms a transcriptional repressor complex with RBPJ in the absence of NOTCH signaling. RIN1 induced changes in gene expression that resembled siRNA silencing of RBPJ rather than inhibition at the level of NOTCH itself. Consistent with disruption of NOTCH signaling, RIN1 inhibited the proliferation of hematologic cancer cell lines and promoted skeletal muscle differentiation from C2C12 myoblasts. Thus, RIN1 inhibits RBPJ in its repressing and activating contexts, and can be exploited for chemical biology and therapeutic applications. NOTCH proteins are trans-membrane receptors that transduce signals from cell-bound JAGGED (JAG) and Delta-like (DLL) families of ligands to mediate cell-cell interactions in processes as diverse as fetal development, heart disease and cancer 1,2 . Upon interaction with ligand, NOTCH is cleaved by γ-secretase to release an intracellular domain (NICD) that binds the transcriptional effector RBPJ [recombination signal-binding protein for immunoglobulin κ J region, also known as CSL and CBF1] 3,4 . There is only one small molecule reported to selectively inhibit NOTCH signaling and none known to target RBPJ 5 . γ-secretase inhibitors (GSIs) have been used widely to block the proteolytic activation of NOTCH, but are inherently unselective since they also block the processing of >90 other substrates, including the amyloid precursor protein (APP), ErbB4, and E-cadherin . Although newer generation GSIs exhibit a biased inhibition of APP over NOTCH , there are no NOTCH-selective GSIs. Clinical use of GSIs cause numerous side effects, notably intestinal crypt cell proliferation 11 , and skin rashes and tumors 12 . These undesirable effects have led to the early termination of a phase III clinical trial of Semagacestat for treatment of Alzheimer's Disease 13 . The NOTCH ICD:RBPJ complex contains co-activators MAML (mastermind-like protein) and histone acetyltransferases (HATs) to activate downstream genes including members of the structurally related HES (Hairy/ Enhancer of Split) and HEY/HRT (Hairy/Enhancer of Split-related) family 14 . The transcriptional effects of NICD are mediated primarily through the interaction with RBPJ, which recruits NICD to recognition sites in promoter regions as well as to more distally located superenhancers 15 . Thus, antagonism of RBPJ would be a desirable point to modulate NOTCH signaling, making it a useful probe and potential clinical candidate since it could provide additional selectivity over targeting γ-secretases or NOTCH itself. To develop a novel chemical inhibitor of NOTCH, we evaluated the feasibility of selectively targeting the RBPJ protein to perturb its interaction with the NOTCH ICD. Although protein-protein interactions can be challenging to inhibit with small molecules, the binding interface between RBPJ and NOTCH is small hence we reasoned that it might be possible to disrupt it with a small
Cardiovascular disease remains the largest single cause of mortality in the Western world, despit... more Cardiovascular disease remains the largest single cause of mortality in the Western world, despite significant advances in clinical management over the years. Unfortunately, the development of new cardiovascular medicines is stagnating and can in part be attributed to the difficulty of screening for novel therapeutic strategies due to a lack of suitable models. The advent of human induced pluripotent stem cells and the ability to make limitless numbers of cardiomyocytes could revolutionize heart disease modeling and drug discovery. This review summarizes the state of the art in the field, describes the strengths and weaknesses of the technology, and applications where the model system would be most appropriate.
Proceedings of the National Academy of Sciences, 2012
Unique insights for the reprograming of cell lineages have come from embryonic development in the... more Unique insights for the reprograming of cell lineages have come from embryonic development in the ascidian Ciona , which is dependent upon the transcription factors Ci -ets1/2 and Ci -mesp to generate cardiac progenitors. We tested the idea that mammalian v-ets erythroblastosis virus E26 oncogene homolog 2 (ETS2) and mesoderm posterior (MESP) homolog may be used to convert human dermal fibroblasts into cardiac progenitors. Here we show that murine ETS2 has a critical role in directing cardiac progenitors during cardiopoiesis in embryonic stem cells. We then use lentivirus-mediated forced expression of human ETS2 to convert normal human dermal fibroblasts into replicative cells expressing the cardiac mesoderm marker KDR + . However, although neither ETS2 nor the purported cardiac master regulator MESP1 can by themselves generate cardiac progenitors de novo from fibroblasts, forced coexpression of ETS2 and MESP1 or cell treatment with purified proteins reprograms fibroblasts into card...
The adult human heart is an ideal target for regenerative intervention since it does not function... more The adult human heart is an ideal target for regenerative intervention since it does not functionally restore itself after injury yet has a modest regenerative capacity that could be enhanced by innovative therapies. Adult cardiac cells with regenerative potential share gene expression signatures with early fetal progenitors that give rise to multiple cardiac cell types, suggesting that the evolutionarily conserved regulatory networks that drive embryonic heart development might also control aspects of regeneration. Here we discuss commonalities of development and regeneration, and the application of the rich developmental biology heritage to achieve therapeutic regeneration of the human heart.
Rationale: The transforming growth factor-β (TGFβ) family member Nodal promotes cardiogenesis, bu... more Rationale: The transforming growth factor-β (TGFβ) family member Nodal promotes cardiogenesis, but the mechanism is unclear despite the relevance of TGFβ family proteins for myocardial remodeling and regeneration. Objective: To determine the function(s) of TGFβ family members during stem cell cardiogenesis. Methods and Results: Murine embryonic stem cells were engineered with a constitutively active human type I Nodal receptor (caACVR1b) to mimic activation by Nodal and found to secrete a paracrine signal that promotes cardiogenesis. Transcriptome and gain- and loss-of-function studies identified the factor as TGFβ2. Both Nodal and TGFβ induced early cardiogenic progenitors in embryonic stem cell cultures at day 0 to 2 of differentiation. However, Nodal expression declines by day 4 due to feedback inhibition, whereas TGFβ persists. At later stages (days 4–6), TGFβ suppresses the formation of cardiomyocytes from multipotent Kdr + progenitors while promoting the differentiation of vas...
Rationale: Human embryonic stem cells can form cardiomyocytes when cultured under differentiation... more Rationale: Human embryonic stem cells can form cardiomyocytes when cultured under differentiation conditions. Although the initiating step of mesoderm formation is well characterized, the subsequent steps that promote for cardiac lineages are poorly understood and limit the yield of cardiomyocytes. Objective: Our aim was to develop a human embryonic stem cell–based high-content screening assay to discover small molecules that drive cardiogenic differentiation after mesoderm is established to improve our understanding of the biology involved. Screening of libraries of small-molecule pathway modulators was predicted to provide insight into the cellular proteins and signaling pathways that control stem cell cardiogenesis. Methods and Results: Approximately 550 known pathway modulators were screened in a high-content screening assay, with hits being called out by the appearance of a red fluorescent protein driven by the promoter of the cardiac-specific MYH6 gene. One potent small molecu...
The cellular signals controlling the formation of cardiomyocytes, vascular smooth muscle, and end... more The cellular signals controlling the formation of cardiomyocytes, vascular smooth muscle, and endothelial cells from stem cell-derived mesoderm are poorly understood. To identify these signals, a mouse embryonic stem cell (ESC)-based differentiation assay was screened against a small molecule library resulting in a 1,4-dihydropyridine inducer of type II TGF-b receptor (TGFBR2) degradation-1 (ITD-1). ITD analogs enhanced proteasomal degradation of TGFBR2, effectively clearing the receptor from the cell surface and selectively inhibiting intracellular signaling (IC 50 $0.4-0.8 mM). ITD-1 was used to evaluate TGF-b involvement in mesoderm formation and cardiopoietic differentiation, which occur sequentially during early development, revealing an essential role in both processes in ESC cultures. ITD-1 selectively enhanced the differentiation of uncommitted mesoderm to cardiomyocytes, but not to vascular smooth muscle and endothelial cells. ITD-1 is a highly selective TGF-b inhibitor and reveals an unexpected role for TGF-b signaling in controlling cardiomyocyte differentiation from multipotent cardiovascular precursors.
knockdown. Notably, 9 of these factors affected erythroid development whereas 8 factors affected ... more knockdown. Notably, 9 of these factors affected erythroid development whereas 8 factors affected myeloid development. More than half of these factors were predicted to regulate the specific lineage based on the sequence or expressionbased model. Moreover, two of these factors, HIF3A and AFF1 (encoding the AF9 protein), were not previously implicated in erythropoiesis but emerged from this study based on their expression profile. The scope of the analysis performed in this study on human hematopoietic progenitors provides a rich resource for identifying regulatory networks controlling HSC self-renewal, differentiation, and lineage determination.
Developmental biologists have defined many of the diffusible and transcription factors that contr... more Developmental biologists have defined many of the diffusible and transcription factors that control muscle differentiation, yet we still have only rudimentary knowledge of the mechanisms that dictate whether a myogenic progenitor cell forms muscle versus alternate lineages, including those that can be pathological in a state of disease or degeneration. Clues about the molecular basis for lineage determination in muscle progenitors are only now emerging from studies of chromatin modifications that avail myogenic genes for transcription, together with analysis of the composition and activities of the chromatin-modifying complexes themselves. Here we review recent progress on muscle determination and explore a unifying theme that environmental cues from the stem or progenitor niche control the selection of specific subunit variants of the switch/sucrose nonfermentable (SWI/SNF) chromatin-modifying complex, creating a combinatorial code that dictates whether cells adopt myogenic versus ...
For adult women in the United States, breast cancer is the most prevalent form of cancer. Compoun... more For adult women in the United States, breast cancer is the most prevalent form of cancer. Compounds that target dysregulated signal transduction can be efficacious anti-cancer therapies. A prominent signaling pathway frequently dysregulated in breast cancer cells is the Wingless-related integration site (Wnt) pathway. The purpose of the work was to optimize a "hit" from a screening campaign. 76,000 compounds were tested in a Wnt transcription assay and revealed potent and reproducible "hit," compound 1. Medicinal chemistry optimization of 1 led to more potent and drug-like molecules, 19, 24 and 25 (i.e., Wnt pathway IC values = 11, 18 and 7 nM, respectively). The principal results showed compounds 19, 24 and 25 were potent anti-proliferative agents in breast cancer cell lines, MCF-7 (i.e., IC values = 10, 7 and 4 nM, respectively) and MDA-MB 231 (i.e., IC values = 13, 13 and 16 nM, respectively). Compound 19 synergized anti-proliferation with chemotherapeutic Dox...
Understanding the mechanisms that control human cardiomyocyte proliferation might be applicable t... more Understanding the mechanisms that control human cardiomyocyte proliferation might be applicable to regenerative medicine. We screened a whole genome collection of human miRNAs, identifying 96 to be capable of increasing proliferation (DNA synthesis and cytokinesis) of human iPSC-derived cardiomyocytes. Chemical screening and computational approaches indicated that most of these miRNAs (67) target different components of the Hippo pathway and that their activity depends on the nuclear translocation of the Hippo transcriptional effector YAP. 53 of the 67 miRNAs are present in human iPSC cardiomyocytes, yet anti-miRNA screening revealed that none are individually essential for basal proliferation of hiPSC cardiomyocytes despite the importance of YAP for proliferation. We propose a model in which multiple endogenous miRNAs redundantly suppress Hippo signaling to sustain the cell cycle of immature cardiomyocytes.
Molecular therapy : the journal of the American Society of Gene Therapy, Jan 26, 2017
MicroRNAs are promising therapeutic targets, because their inhibition has the potential to normal... more MicroRNAs are promising therapeutic targets, because their inhibition has the potential to normalize gene expression in diseased states. Recently, our group found that miR-25 is a key SERCA2a regulating microRNA, and we showed that multiple injections of antagomirs against miR-25 enhance cardiac contractility and function through SERCA2a restoration in a murine heart failure model. However, for clinical application, a more stable suppressor of miR-25 would be desirable. Tough Decoy (TuD) inhibitors are emerging as a highly effective method for microRNA inhibition due to their resistance to endonucleolytic degradation, high miRNA binding affinity, and efficient delivery. We generated a miR-25 TuD inhibitor and subcloned it into a cardiotropic AAV9 vector to evaluate its efficacy. The AAV9 TuD showed selective inhibition of miR-25 in vitro cardiomyoblast culture. In vivo, AAV9-miR-25 TuD delivered to the murine pressure-overload heart failure model selectively decreased expression of ...
The ability to produce unlimited numbers of human induced pluripotent stem cell derived cardiomyo... more The ability to produce unlimited numbers of human induced pluripotent stem cell derived cardiomyocytes (hiPSC-CMs) harboring disease and patient-specific gene variants creates a new paradigm for modeling congenital heart diseases (CHDs) and predicting proarrhythmic liabilities of drug candidates. However, a major roadblock to implementing hiPSC-CM technology in drug discovery is that conventional methods for monitoring action potential (AP) kinetics and arrhythmia phenotypes in vitro have been too costly or technically challenging to execute in high throughput. Herein, we describe the first large-scale, fully automated and statistically robust analysis of AP kinetics and drug-induced proarrhythmia in hiPSC-CMs. The platform combines the optical recording of a small molecule fluorescent voltage sensing probe (VoltageFluor2.1.Cl), an automated high throughput microscope and automated image analysis to rapidly generate physiological measurements of cardiomyocytes (CMs). The technique c...
The expression of nearly all smooth muscle genes are controlled by serum response factor binding ... more The expression of nearly all smooth muscle genes are controlled by serum response factor binding sites in their promoter regions. However, SRF alone is not sufficient for regulating smooth muscle cell development. It associates with other cardiovascular specific cofactors to regulate smooth muscle gene expression. Previously, we showed that the transcription co-factor CRP2 was a regulator of smooth muscle gene expression. Here, we report that CSRP2BP, a coactivator for CRP2, is a histone acetyltransferase and a driver of smooth muscle gene expression. CSRP2BP directly interacted with SRF, CRP2 and myocardin. CSRP2BP synergistically activated smooth muscle gene promoters in an SRF-dependent manner. A combination of SRF, GATA6 and CRP2 required CSRP2BP for robust smooth muscle gene promoter activity. Knock-down of Csrp2bp in smooth muscle cells resulted in reduced smooth muscle gene expression. We conclude that the CSRP2BP histone acetyltransferase is a coactivator for CRP2 that works...
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Papers by Mark Mercola