Gain-of-function cardiomyopathic mutations in RBM20 rewire splicing regulation and re-distribute ribonucleoprotein granules within processing bodies.

Mutations in the cardiac splicing factor RBM20 lead to malignant dilated cardiomyopathy (DCM). To understand the mechanism of RBM20-associated DCM, we engineered isogenic iPSCs with DCM-associated missense mutations in RBM20 as well as RBM20 knockout (KO) iPSCs. iPSC-derived engineered heart tissues made from these cell lines recapitulate contractile dysfunction of RBM20-associated DCM and reveal greater dysfunction with missense mutations than KO. Analysis of RBM20 RNA binding by eCLIP reveals a gain-of-function preference of mutant RBM20 for 3' UTR sequences that are shared with amyotrophic lateral sclerosis (ALS) and processing-body associated RNA binding proteins (FUS, DDX6). Deep RNA sequencing reveals that the RBM20 R636S mutant has unique gene, splicing, polyadenylation and circular RNA defects that differ from RBM20 KO. Super-resolution microscopy verifies that mutant RBM20 maintains very limited nuclear localization potential; rather, the mutant protein associates with cytoplasmic processing bodies (DDX6) under basal conditions, and with stress granules (G3BP1) following acute stress. Taken together, our results highlight a pathogenic mechanism in cardiac disease through splicing-dependent and -independent pathways.

Transcription factor overexpression drives reliable differentiation of retinal pigment epithelium from human induced pluripotent stem cells.

Age-related macular degeneration and genetic forms of blindness such as Best Disease and Retinitis Pigmentosa can be caused by degeneration of the Retinal Pigment Epithelium (RPE). RPE generated from patient-derived induced pluripotent stem cells (iPSCs) is valuable for both the study of disease mechanisms and development of therapeutic strategies. However, protocols to produce iPSC-derived RPE in vitro are often inefficient, labor-intensive, low-throughput, and highly variable between cell lines and within batches. Here, we report a robust, scalable method to generate iPSC-RPE using doxycycline-inducible expression of eye field transcription factors OTX2, PAX6 and MITF paired with RPE-permissive culture media. Doxycycline addition induces exogenous expression of these transcription factors in Best Disease patient- and wildtype iPSCs to efficiently produce monolayers of RPE with characteristic morphology and gene expression. Further, these RPE monolayers display functionality features including light absorption via pigmentation, polarity-driven fluid transport, and phagocytosis. With this method, we achieve a highly efficient and easily scalable differentiation without the need for mechanical isolation or enrichment methods, generating RPE cultures applicable for in vitro studies.

Spatiotemporal mosaic self-patterning of pluripotent stem cells using CRISPR interference.

Morphogenesis involves interactions of asymmetric cell populations to form complex multicellular patterns and structures comprised of distinct cell types. However, current methods to model morphogenic events lack control over cell-type co-emergence and offer little capability to selectively perturb specific cell subpopulations. Our in vitro system interrogates cell-cell interactions and multicellular organization within human induced pluripotent stem cell (hiPSC) colonies. We examined effects of induced mosaic knockdown of molecular regulators of cortical tension (ROCK1) and cell-cell adhesion (CDH1) with CRISPR interference. Mosaic knockdown of ROCK1 or CDH1 resulted in differential patterning within hiPSC colonies due to cellular self-organization, while retaining an epithelial pluripotent phenotype. Knockdown induction stimulates a transient wave of differential gene expression within the mixed populations that stabilized in coordination with observed self-organization. Mosaic patterning enables genetic interrogation of emergent multicellular properties, which can facilitate better understanding of the molecular pathways that regulate symmetry-breaking during morphogenesis.

A BAG3 chaperone complex maintains cardiomyocyte function during proteotoxic stress.

Molecular chaperones regulate quality control in the human proteome, pathways that have been implicated in many diseases, including heart failure. Mutations in the BAG3 gene, which encodes a co-chaperone protein, have been associated with heart failure due to both inherited and sporadic dilated cardiomyopathy. Familial BAG3 mutations are autosomal dominant and frequently cause truncation of the coding sequence, suggesting a heterozygous loss-of-function mechanism. However, heterozygous knockout of the murine BAG3 gene did not cause a detectable phenotype. To model BAG3 cardiomyopathy in a human system, we generated an isogenic series of human induced pluripotent stem cells (iPSCs) with loss-of-function mutations in BAG3. Heterozygous BAG3 mutations reduced protein expression, disrupted myofibril structure, and compromised contractile function in iPSC-derived cardiomyocytes (iPS-CMs). BAG3-deficient iPS-CMs were particularly sensitive to further myofibril disruption and contractile dysfunction upon exposure to proteasome inhibitors known to cause cardiotoxicity. We performed affinity tagging of the endogenous BAG3 protein and mass spectrometry proteomics to further define the cardioprotective chaperone complex that BAG3 coordinates in the human heart. Our results establish a model for evaluating protein quality control pathways in human cardiomyocytes and their potential as therapeutic targets and susceptibility factors for cardiac drug toxicity.

Miniaturized iPS-Cell-Derived Cardiac Muscles for Physiologically Relevant Drug Response Analyses.

Tissue engineering approaches have the potential to increase the physiologic relevance of human iPS-derived cells, such as cardiomyocytes (iPS-CM). However, forming Engineered Heart Muscle (EHM) typically requires >1 million cells per tissue. Existing miniaturization strategies involve complex approaches not amenable to mass production, limiting the ability to use EHM for iPS-based disease modeling and drug screening. Micro-scale cardiospheres are easily produced, but do not facilitate assembly of elongated muscle or direct force measurements. Here we describe an approach that combines features of EHM and cardiospheres: Micro-Heart Muscle (µHM) arrays, in which elongated muscle fibers are formed in an easily fabricated template, with as few as 2,000 iPS-CM per individual tissue. Within µHM, iPS-CM exhibit uniaxial contractility and alignment, robust sarcomere assembly, and reduced variability and hypersensitivity in drug responsiveness, compared to monolayers with the same cellular composition. µHM mounted onto standard force measurement apparatus exhibited a robust Frank-Starling response to external stretch, and a dose-dependent inotropic response to the ß-adrenergic agonist isoproterenol. Based on the ease of fabrication, the potential for mass production and the small number of cells required to form µHM, this system provides a potentially powerful tool to study cardiomyocyte maturation, disease and cardiotoxicology in vitro.

CRISPR Interference Efficiently Induces Specific and Reversible Gene Silencing in Human iPSCs.

Developing technologies for efficient and scalable disruption of gene expression will provide powerful tools for studying gene function, developmental pathways, and disease mechanisms. Here, we develop clustered regularly interspaced short palindromic repeat interference (CRISPRi) to repress gene expression in human induced pluripotent stem cells (iPSCs). CRISPRi, in which a doxycycline-inducible deactivated Cas9 is fused to a KRAB repression domain, can specifically and reversibly inhibit gene expression in iPSCs and iPSC-derived cardiac progenitors, cardiomyocytes, and T lymphocytes. This gene repression system is tunable and has the potential to silence single alleles. Compared with CRISPR nuclease (CRISPRn), CRISPRi gene repression is more efficient and homogenous across cell populations. The CRISPRi system in iPSCs provides a powerful platform to perform genome-scale screens in a wide range of iPSC-derived cell types, dissect developmental pathways, and model disease.

Automated Video-Based Analysis of Contractility and Calcium Flux in Human-Induced Pluripotent Stem Cell-Derived Cardiomyocytes Cultured over Different Spatial Scales.

Contractile motion is the simplest metric of cardiomyocyte health in vitro, but unbiased quantification is challenging. We describe a rapid automated method, requiring only standard video microscopy, to analyze the contractility of human-induced pluripotent stem cell-derived cardiomyocytes (iPS-CM). New algorithms for generating and filtering motion vectors combined with a newly developed isogenic iPSC line harboring genetically encoded calcium indicator, GCaMP6f, allow simultaneous user-independent measurement and analysis of the coupling between calcium flux and contractility. The relative performance of these algorithms, in terms of improving signal to noise, was tested. Applying these algorithms allowed analysis of contractility in iPS-CM cultured over multiple spatial scales from single cells to three-dimensional constructs. This open source software was validated with analysis of isoproterenol response in these cells, and can be applied in future studies comparing the drug responsiveness of iPS-CM cultured in different microenvironments in the context of tissue engineering.

Isolation of single-base genome-edited human iPS cells without antibiotic selection.

Precise editing of human genomes in pluripotent stem cells by homology-driven repair of targeted nuclease-induced cleavage has been hindered by the difficulty of isolating rare clones. We developed an efficient method to capture rare mutational events, enabling isolation of mutant lines with single-base substitutions without antibiotic selection. This method facilitates efficient induction or reversion of mutations associated with human disease in isogenic human induced pluripotent stem cells.

PI3K-AKT signaling is a downstream effector of retinoid prevention of murine basal cell carcinogenesis.

Basal cell carcinoma (BCC) is the most common human cancer. We have demonstrated previously that topical application of the retinoid prodrug tazarotene profoundly inhibits murine BCC carcinogenesis via retinoic acid receptor γ-mediated regulation of tumor cell transcription. Because topical retinoids can cause adverse cutaneous effects and because tumors can develop resistance to retinoids, we have investigated mechanisms downstream of tazarotene's antitumor effect in this model. Specifically we have used (i) global expression profiling to identify and (ii) functional cell-based assays to validate the phosphoinositide 3-kinase (PI3K)/AKT/mTOR pathway as a downstream target pathway of tazarotene's action. Crucially, we have demonstrated that pharmacologic inhibition of this downstream pathway profoundly reduces murine BCC cell proliferation and tumorigenesis both in vitro and in vivo. These data identify PI3K/AKT/mTOR signaling as a highly attractive target for BCC chemoprevention and indicate more generally that this pathway may be, in some contexts, an important mediator of retinoid anticancer effects.

A robust method to derive functional neural crest cells from human pluripotent stem cells.

Neural crest (NC) cells contribute to the development of many complex tissues of all three germ layers during embryogenesis, and its abnormal development accounts for several congenital birth defects. Generating NC cells-including specific subpopulations such as cranial, cardiac, and trunk NC cells-from human pluripotent stem cells will provide a valuable model system to study human development and disease. Here, we describe a rapid and robust NC differentiation method called "LSB-short" that is based on dual SMAD pathway inhibition. This protocol yields high percentages of NC cell populations from multiple human induced pluripotent stem and human embryonic stem cell lines in 8 days. The resulting cells can be propagated easily, retain NC marker expression over multiple passages, and can spontaneously differentiate into several NC-derived cell lineages, including smooth muscle cells, peripheral neurons, and Schwann cells. NC cells generated by this method represent cranial, cardiac and trunk NC subpopulations based on global gene expression analyses, are similar to in vivo analogues, and express a common set of NC alternative isoforms. Functionally, they are also able to migrate appropriately in response to chemoattractants such as SDF-1, FGF8b, and Wnt3a. By yielding NC cells that likely represent all NC subpopulations in a shorter time frame than other published methods, our LSB-short method provides an ideal model system for further studies of human NC development and disease.

Establishment of murine basal cell carcinoma allografts: a potential model for preclinical drug testing and for molecular analysis.

Dysregulated hedgehog (HH) signaling has been found in numerous cancers, suggesting that therapeutic targeting of this pathway may be useful versus a wide range of cancers. Basal cell carcinoma (BCC) is an excellent model system for studying the influence of the HH pathway on carcinogenesis because aberrant activation of HH signaling is crucial not only for the development of but also the maintenance of BCC. Genetically engineered BCC mouse models provide one important tool for the study of the biology of human BCCs and for evaluating therapeutic interventions, as these mice produce multiple genetically defined tumors within a relatively short period of time. However, these models remain expensive and cumbersome to use for large-scale preclinical drug testing. Here we report a method for growing allografts from murine BCC tumors in NOD/SCID mice. These allografts develop faster and reproduce the histology, immunophenotypes, and response to at least one anti-BCC drug of the parental autochthonous tumors from which they arise. Therefore, the allograft model provides a practical model for (i) studying BCC carcinogenesis and (ii) initial preclinical screening for anti-HH pathway and other anti-BCC drugs.

Vitamin D3 inhibits hedgehog signaling and proliferation in murine Basal cell carcinomas.

Constitutive Hedgehog (HH) signaling underlies several human tumors, including basal cell carcinoma (BCC). Recently, Bijlsma and colleagues reported a new biologic function for vitamin D3 in suppressing HH signaling in an in vitro model system. On the basis of that work, we have assessed effects of vitamin D3 on HH signaling and proliferation of murine BCCs in vitro and in vivo. We find that indeed in BCC cells, vitamin D3 blocks both proliferation and HH signaling as assessed by mRNA expression of the HH target gene Gli1. These effects of vitamin D3 on Gli1 expression and on BCC cell proliferation are comparable to the effects of cyclopamine, a known inhibitor of the HH pathway. These results are specific for vitamin D3, because the precursor 7-dehydrocholesterol and the downstream products 25-hydroxy vitamin D3 [25(OH)D] and 1,25-dihydroxy vitamin D3 [1,25(OH)(2)D] are considerably less effective in reducing either Gli1 mRNA or cellular proliferation. Moreover, these effects seem to be independent of the vitamin D receptor (VDR) because short hairpin RNA knockdown of VDR does not abrogate the anti-HH effects of D3 despite reducing expression of the VDR target gene 24-hydroxylase. Finally, topical vitamin D3 treatment of existing murine BCC tumors significantly decreases Gli1 and Ki67 staining. Thus, topical vitamin D3 acting via its HH inhibiting effect may hold promise as an effective anti-BCC agent.

Novel investigational drugs for basal cell carcinoma.

IMPORTANCE OF THE FIELD: In the United States, the annual incidence of basal cell carcinoma (BCC) is close to 1 million. Ultraviolet radiation exposure is the main risk factor; however, the availability of ever more potent sunscreens and education have not prevented the rise in BCC incidence. Therefore, concerted effects to identify novel preventive and therapeutic strategies are necessary. AREAS COVERED IN THIS REVIEW: This article summarizes our current understanding of the etiology and molecular mechanisms of BCC tumorigenesis and discusses the preclinical and clinical studies to identify agents with anti-BCC efficacy. WHAT THE READER WILL GAIN: The discovery that hyperactive Hh pathway signaling causes several cancers, including BCC, has spawned the development of many pharmacologic inhibitors of Hh signaling. Early clinical testing of the most advanced, GDC-0449, demonstrated impressive efficacy in patients with advanced BCC. Other promising anti-BCC chemopreventive strategies include drugs that are already FDA-approved for treating other diseases. TAKE HOME MESSAGE: Preclinical and clinical trials with pre-existing FDA-approved drugs suggest novel uses for BCC chemoprevention and treatment. Also, new chemical entities that inhibit the Hh pathway show promise, and in combination with other drugs may provide a nonsurgical cure for this most common cancer.

Basal cell carcinoma chemoprevention with nonsteroidal anti-inflammatory drugs in genetically predisposed PTCH1+/- humans and mice.

In vitro and epidemiologic studies favor the efficacy of nonsteroidal anti-inflammatory drugs (NSAID) in preventing skin squamous photocarcinogenesis, but there has been relatively little study of their efficacy in preventing the more common skin basal cell carcinoma (BCC) carcinogenesis. We first compared the relative anti-BCC effects of genetic deletion and NSAID pharmacologic inhibition of cyclooxygenase (COX) enzymes in the skin of Ptch1(+/-) mice. We then assessed the effects of celecoxib on the development of BCCs in a 3-year, double-blinded, randomized clinical trial in 60 (PTCH1(+/-)) patients with the basal cell nevus syndrome. In Ptch1(+/-) mice, genetic deletion of COX1 or COX2 robustly decreased (75%; P < 0.05) microscopic BCC tumor burden, but pharmacologic inhibition with celecoxib reduced microscopic BCCs less efficaciously (35%; P < 0.05). In the human trial, we detected a trend for oral celecoxib reducing BCC burden in all subjects (P = 0.069). Considering only the 60% of patients with less severe disease (<15 BCCs at study entry), celecoxib significantly reduced BCC number and burden: subjects receiving placebo had a 50% increase in BCC burden per year, whereas subjects in the celecoxib group had a 20% increase (P(difference) = 0.024). Oral celecoxib treatment inhibited BCC carcinogenesis in PTCH1(+/-) mice and had a significant anti-BCC effect in humans with less severe disease.

Primary cilia can both mediate and suppress Hedgehog pathway-dependent tumorigenesis.

Primary cilia are present on most mammalian cells and are implicated in transducing Hedgehog (Hh) signals during development; however, the prevalence of cilia on human tumors remains unclear, and the role of cilia in cancer has not been examined. Here we show that human basal cell carcinomas (BCCs) are frequently ciliated, and we test the role of cilia in BCC by conditionally deleting Kif3a (encoding kinesin family member 3A) or Ift88 (encoding intraflagellar transport protein 88), genes required for ciliogenesis, in two Hh pathway-dependent mouse tumor models. Ciliary ablation strongly inhibited BCC-like tumors induced by an activated form of Smoothened. In contrast, removal of cilia accelerated tumors induced by activated Gli2, a transcriptional effector of Hh signaling. These seemingly paradoxical effects are consistent with a dual role for cilia in mediating both the activation and the repression of the Hh signaling pathway. Our findings demonstrate that cilia function as unique signaling organelles that can either mediate or suppress tumorigenesis depending on the nature of the oncogenic initiating event.

Pharmacologic retinoid signaling and physiologic retinoic acid receptor signaling inhibit basal cell carcinoma tumorigenesis.

Basal cell carcinoma (BCC) is the most common human cancer. Patients with basal cell nevus syndrome (Gorlin syndrome) are highly susceptible to developing many BCCs as a result of a constitutive inactivating mutation in one allele of PATCHED 1, which encodes a tumor suppressor that is a major inhibitor of Hedgehog signaling. Dysregulated Hedgehog signaling is a common feature of both hereditary and sporadic BCCs. Recently, we showed remarkable anti-BCC chemopreventive efficacy of tazarotene, a retinoid with retinoic acid receptor (RAR) beta/gamma specificity, in Ptch1+/- mice when treatment was commenced before carcinogenic insults. In this study, we assessed whether the effect of tazarotene against BCC carcinogenesis is sustained after its withdrawal and whether tazarotene is effective against preexisting microscopic BCC lesions. We found that BCCs did not reappear for at least 5 months after topical drug treatment was stopped and that already developed, microscopic BCCs were susceptible to tazarotene inhibition. In vitro, tazarotene inhibited a murine BCC keratinocyte cell line, ASZ001, suggesting that its effect in vivo is by direct action on the actual tumor cells. Down-regulation of Gli1, a target gene of Hedgehog signaling and up-regulation of CRABPII, a target gene of retinoid signaling, were observed with tazarotene treatment. Finally, we investigated the effects of topical applications of other retinoid-related compounds on BCC tumorigenesis in vivo. Tazarotene was the most effective of the preparations studied, and its effect most likely was mediated by RARgamma activation. Furthermore, inhibition of basal RAR signaling in the skin promoted BCC carcinogenesis, suggesting that endogenous RAR signaling restrains BCC growth.

Novel Hedgehog pathway targets against basal cell carcinoma.

The Hedgehog signaling pathway plays a key role in directing growth and patterning during embryonic development and is required in vertebrates for the normal development of many structures, including the neural tube, axial skeleton, skin, and hair. Aberrant activation of the Hedgehog (Hh) pathway in adult tissue is associated with the development of basal cell carcinoma (BCC), medulloblastoma, and a subset of pancreatic, gastrointestinal, and other cancers. This review will provide an overview of what is known about the mechanisms by which activation of Hedgehog signaling leads to the development of BCCs and will review two recent papers suggesting that agents that modulate sterol levels might influence the Hh pathway. Thus, sterols may be a new therapeutic target for the treatment of BCCs, and readily available agents such as statins (HMG-CoA reductase inhibitors) or vitamin D might be helpful in reducing BCC incidence.

Long-term establishment, characterization and manipulation of cell lines from mouse basal cell carcinoma tumors.

There have been few reports of successful long-term culture of cells established from cutaneous basal cell carcinoma (BCC) tumors. Here, we describe techniques that have enabled us to establish three long-term cultures of BCC cells isolated from BCC tumors that arose in irradiated Patched 1 (Ptch1)(+/-) mice. All three cell lines showed cellular morphology similar to that of BCC tumors and could be propagated for at least 20 passages. In addition, similar to BCC tumors, all cell lines had lost the wildtype Ptch1 allele, expressed BCC molecular markers, and responded similarly to cyclopamine, a small molecule inhibitor of Hedgehog signaling. Finally, we describe an efficient electroporation technique for DNA transfection into the BCC cell lines and show that they have activated Hedgehog signaling activity, albeit at a level lower than that of murine BCCs in vivo. These data indicate that the cell lines are bona fide long-term cultures of BCC cells and that DNA plasmids can be introduced into the BCC cell lines with relatively high transfection efficiency using a modified electroporation technique.

Interactions between retinoic acid, nerve growth factor and sonic hedgehog signalling pathways in neurite outgrowth.

Many studies have shown a role of retinoid signalling in neurite outgrowth in vitro, and that the retinoic acid receptor (RAR) beta2 is critical for this process. We show here that RARbeta2 is expressed predominantly in dorsal root ganglia (DRG) neuronal subtypes that express neurofilament (NF) 200 and calcitonin gene-related peptide (CGRP), and that these neurons extend neurites in response to RA. We demonstrate that retinoid signalling has a role in neurite outgrowth in vivo, by showing that in a peripheral nerve crush model there is less neurite outgrowth from RARbeta null DRG compared to wild-type. We identify sonic hedgehog (Shh) as a downstream target of the RARbeta2 signalling pathway as it is expressed in the injured DRG of wild-type but not RARbeta null mice. This regulation is direct as when RARbeta2 is overexpressed in adult motoneurons Shh is induced in them. Finally we show that Shh alone cannot induce neurite outgrowth but potentiates RARbeta2 signalling in this process.

Adult stem cells: capturing youth from a bulge?

With the development of advanced cell-labeling technologies, fluorescence activated cell sorting (FACS), as well as improved understanding of mammalian gene expression, it is now possible to identify and isolate specific sub-populations of adult mammalian cells with good accuracy. Recent publications by Morris et al. and Tumbar et al. demonstrate the isolation of putative epithelial stem cells from the hair follicle bulge and Affymetrix expression arrays were employed to elucidate putative genes that might control stem cell fates.