Impaired Human Cardiac Cell Development due to NOTCH1 Deficiency.

BACKGROUND: NOTCH1 pathogenic variants are implicated in multiple types of congenital heart defects including hypoplastic left heart syndrome, where the left ventricle is underdeveloped. It is unknown how NOTCH1 regulates human cardiac cell lineage determination and cardiomyocyte proliferation. In addition, mechanisms by which NOTCH1 pathogenic variants lead to ventricular hypoplasia in hypoplastic left heart syndrome remain elusive. METHODS: CRISPR (Clustered Regularly Interspaced Short Palindromic Repeats)/Cas9 genome editing was utilized to delete NOTCH1 in human induced pluripotent stem cells. Cardiac differentiation was carried out by sequential modulation of WNT signaling, and NOTCH1 knockout and wild-type differentiating cells were collected at day 0, 2, 5, 10, 14, and 30 for single-cell RNA-seq. RESULTS: Human NOTCH1 knockout induced pluripotent stem cells are able to generate functional cardiomyocytes and endothelial cells, suggesting that NOTCH1 is not required for mesoderm differentiation and cardiovascular development in vitro. However, disruption of NOTCH1 blocks human ventricular-like cardiomyocyte differentiation but promotes atrial-like cardiomyocyte generation through shortening the action potential duration. NOTCH1 deficiency leads to defective proliferation of early human cardiomyocytes, and transcriptomic analysis indicates that pathways involved in cell cycle progression and mitosis are downregulated in NOTCH1 knockout cardiomyocytes. Single-cell transcriptomic analysis reveals abnormal cell lineage determination of cardiac mesoderm, which is manifested by the biased differentiation toward epicardial and second heart field progenitors at the expense of first heart field progenitors in NOTCH1 knockout cell populations. CONCLUSIONS: NOTCH1 is essential for human ventricular-like cardiomyocyte differentiation and proliferation through balancing cell fate determination of cardiac mesoderm and modulating cell cycle progression. Because first heart field progenitors primarily contribute to the left ventricle, we speculate that pathogenic NOTCH1 variants lead to biased differentiation of first heart field progenitors, blocked ventricular-like cardiomyocyte differentiation, and defective cardiomyocyte proliferation, which collaboratively contribute to left ventricular hypoplasia in hypoplastic left heart syndrome.

MAF protein mediates innate resistance to proteasome inhibition therapy in multiple myeloma.

Multiple myeloma (MM) patients with the t(14;16) translocation have a poor prognosis, and unlike other molecular subgroups, their outcome has not improved with the introduction of bortezomib (Bzb). The mechanism underlying innate resistance of MM to Bzb is unknown. In the present study, we have investigated how MAF overexpression impacts resistance to proteasome inhibitor (PI) therapy (Bzb and carfilzomib). High levels of MAF protein were found in t(14;16) cell lines; cell lines from the t(4;14) subgroup had intermediate levels, whereas cell lines from the other subgroups had low levels. High expression of MAF protein in t(14;16) was associated with significantly higher PI half-maximum inhibitory concentration values compared with other molecular subgroups. PI exposure abrogated glycogen synthase kinase 3ß (GSK3ß)-mediated degradation of MAF protein, resulting in increased MAF protein stability and PI resistance. Subsequent studies using loss-of-function and gain-of-function models showed that silencing MAF led to increased sensitivity to PIs, enhanced apoptosis, and activation of caspase-3, -7, -8, -9, poly (ADP-ribose) polymerase, and lamin A/C. In contrast, overexpression of MAF resulted in increased resistance to PIs and reduced apoptosis. These results define the role of MAF and GSK3 in the resistance of t(14;16) MM to PIs and identifies a novel mechanism by which MAF protein levels are regulated by PIs, which in turn confers resistance to PIs.

MAFb protein confers intrinsic resistance to proteasome inhibitors in multiple myeloma.

BACKGROUND: Multiple myeloma (MM) patients with t(14;20) have a poor prognosis and their outcome has not improved following the introduction of bortezomib (Bzb). The mechanism underlying the resistance to proteasome inhibitors (PIs) for this subset of patients is unknown. METHODS: IC50 of Bzb and carfilzomib (CFZ) in human myeloma cell lines (HMCLs) were established by MTT assay. Gene Expression profile (GEP) analysis was used to determine gene expression in primary myeloma cells. Immunoblotting analysis was performed for MAFb and caspase family proteins. Immunofluorescence staining was used to detect the location of MAFb protein in MM cells. Lentiviral infections were used to knock-down MAFb expression in two lines. Apoptosis detection by flow cytometry and western blot analysis was performed to determine the molecular mechanism MAFb confers resistance to proteasome inhibitors. RESULTS: We found high levels of MAFb protein in cell lines with t(14;20), in one line with t(6;20), in one with Igλ insertion into MAFb locus, and in primary plasma cells from MM patients with t(14;20). High MAFb protein levels correlated with higher IC50s of PIs in MM cells. Inhibition of GSK3ß activity or treatment with Bzb or CFZ prevented MAFb protein degradation without affecting the corresponding mRNA level indicating a role for GSK3 and proteasome inhibitors in regulation of MAFb stability. Silencing MAFb restored sensitivity to Bzb and CFZ, and enhanced PIs-induced apoptosis and activation of caspase-3, - 8, - 9, PARP and lamin A/C suggesting that high expression of MAFb protein leads to insensitivity to proteasome inhibitors. CONCLUSION: These results highlight the role of post-translational modification of MAFb in maintaining its protein level, and identify a mechanism by which proteasome inhibitors induced stabilization of MAFb confers resistance to proteasome inhibitors, and provide a rationale for the development of targeted therapeutic strategies for this subset of patients.

Ubiquitin E3 Ligase LNX2 is Critical for Osteoclastogenesis In Vitro by Regulating M-CSF/RANKL Signaling and Notch2.

The Notch signaling pathway plays a crucial role in skeletal development and homeostasis by regulating the proliferation and differentiation of osteoblasts and osteoclasts. However, the molecular mechanisms modulating the level and activity of Notch receptors in bone cells remain unknown. In this study, we uncovered that LNX2, an E3 ubiquitin ligase and Notch inhibitor Numb binding protein, was up-regulated during osteoclast differentiation. Knocking-down LNX2 expression in bone marrow macrophages by lentivirus-mediated short hairpin RNAs markedly inhibited osteoclast formation. Decreased LNX2 expression attenuated macrophage colony-stimulating factor (M-CSF)-induced ERK and AKT activation and RANKL-stimulated activation of NF-κB and JNK pathways; therefore, accelerated osteoclast apoptosis. Additionally, loss of LNX2 led to an increased accumulation of Numb, which promoted the degradation of Notch and caused a reduction of the expression of the Notch downstream target gene, Hes1. We conclude that LNX2 regulates M-CSF/RANKL and the Notch signaling pathways during osteoclastogenesis.

Steap4 plays a critical role in osteoclastogenesis in vitro by regulating cellular iron/reactive oxygen species (ROS) levels and cAMP response element-binding protein (CREB) activation.

Iron is essential for osteoclast differentiation, and iron overload in a variety of hematologic diseases is associated with excessive bone resorption. Iron uptake by osteoclast precursors via the transferrin cycle increases mitochondrial biogenesis, reactive oxygen species production, and activation of cAMP response element-binding protein, a critical transcription factor downstream of receptor activator of NF-κB-ligand-induced calcium signaling. These changes are required for the differentiation of osteoclast precursors to mature bone-resorbing osteoclasts. However, the molecular mechanisms regulating cellular iron metabolism in osteoclasts remain largely unknown. In this report, we provide evidence that Steap4, a member of the six-transmembrane epithelial antigen of prostate (Steap) family proteins, is an endosomal ferrireductase with a critical role in cellular iron utilization in osteoclasts. Specifically, we show that Steap4 is the only Steap family protein that is up-regulated during osteoclast differentiation. Knocking down Steap4 expression in vitro by lentivirus-mediated short hairpin RNAs inhibits osteoclast formation and decreases cellular ferrous iron, reactive oxygen species, and the activation of cAMP response element-binding protein. These results demonstrate that Steap4 is a critical enzyme for cellular iron uptake and utilization in osteoclasts and, thus, indispensable for osteoclast development and function.

Suppression of autophagy in osteocytes mimics skeletal aging.

Bone mass declines with age but the mechanisms responsible remain unclear. Here we demonstrate that deletion of a conditional allele for Atg7, a gene essential for autophagy, from osteocytes caused low bone mass in 6-month-old male and female mice. Cancellous bone volume and cortical thickness were decreased, and cortical porosity increased, in conditional knock-out mice compared with control littermates. These changes were associated with low osteoclast number, osteoblast number, bone formation rate, and wall width in the cancellous bone of conditional knock-out mice. In addition, oxidative stress was higher in the bones of conditional knock-out mice as measured by reactive oxygen species levels in the bone marrow and by p66(shc) phosphorylation in L6 vertebra. Each of these changes has been previously demonstrated in the bones of old versus young adult mice. Thus, these results demonstrate that suppression of autophagy in osteocytes mimics, in many aspects, the impact of aging on the skeleton and suggest that a decline in autophagy with age may contribute to the low bone mass associated with aging.

Downregulation of Notch modulators, tetraspanin 5 and 10, inhibits osteoclastogenesis in vitro.

Genetic studies in human and mice have pinpointed an essential role of Notch signaling in osteoblast and osteoclast differentiation during skeletal development and bone remodeling. However, the factors and pathways regulating Notch activation in bone cells remain largely unknown. In this in vitro study, we have provided evidence that two of the TspanC8 subfamily members of tetraspanins, Tspan-5 and Tspan-10, are up-regulated during osteoclast differentiation and knockdown of their expression by shRNAs dramatically inhibits osteoclastogenesis. Loss of Tspan-5 and Tspan-10 in osteoclast lineage cells results in attenuation of ADAM10 maturation and Notch activation. Therefore, these two tetraspanins play a critical role in osteoclast formation, at least in part, by modulating Notch signaling pathway.

Generation and characterization of a human induced pluripotent stem cell line heterozygous for a NOTCH1 mutation (NCHi014-A).

NOTCH1 signaling is crucial for cardiovascular development. Numerous studies have identified heterozygous NOTCH1 loss of function and missense variants associated with a spectrum of congenital heart diseases (CHD). We generated induced pluripotent stem cells (iPSC) from a healthy individual to develop a model for NOTCH1+/- iPSC to study the molecular pathogenesis of CHD. NOTCH1+/-iPSC (NCHi014-A) have normal morphology and karyotype, are identical to the parental cell line, express pluripotency markers and have the ability to differentiate to the three germ layers. NOTCH1+/- iPSC can be used as a tool to study the cellular and molecular mechanisms underlying NOTCH1-associated human CHD.

Generation of iPSC line NCHi015-A from a patient with truncus arteriosus carrying heterozygous variants in KMT2D and NOTCH1.

Truncus arteriosus (TA) is a congenital heart defect where one main blood vessel emerges from the heart, instead of individual aorta and pulmonary artreries. Peripheral mononuclear cells (PBMCs) of a male infant with TA were reporogrammed using Sendai virus. The resultant iPSC line (NCHi015-A) displayed normal colony formation, expressed pluripotency markers, and differentiated into cells from three germ layers. NCHi015-A was matched to the patient's genetic profile, had normal karyotype, retained genetic variants in KMT2D and NOTCH1, and tested negative for reprogramming transgene. This iPSC line can be used for studying congenital heart defects associated with genetic variants in KMT2D and NOTCH1.

Generation of an induced pluripotent stem cell line (NCHi010-A) from a 6-year-old female with Down syndrome and without congenital heart disease.

Down syndrome is a genetic anomaly that manifests when there is a mistake during cell division, resulting in an additional chromosome 21. Down syndrome can impact cognitive capabilities and physical development, giving rise to diverse developmental disparities and an elevated likelihood of certain health issues. The iPSC line NCHi010-A was generated from peripheral blood mononuclear cells of a 6-year-old female with Down syndrome and without congenital heart disease using Sendai virus reprogramming. NCHi010-A displayed a morphology of pluripotent stem cells, expressed pluripotency markers, retained trisomy 21 karyotype, and demonstrated potential to differentiate into cells representative of the three germ layers.

Creation of iPSC line NCHi004-A from a patient with down syndrome and congenital heart defects.

Down syndrome is a congenital disorder resulting from an extra full or partial chromosome 21, which is characterized by a spectrum of systemic developmental abnormalities, including those affecting the cardiovascular system. Here, we generated an iPSC line from peripheral blood mononuclear cells of a male adolescent with Down syndrome-associated congenital heart defects through Sendai virus-mediated transfection of 4 Yamanaka factors. This line exhibited normal morphology, expressed pluripotency markers, trisomy 21 karyotype, and could be differentiated into three germ layers. This iPSC line can be used for studying cellular and developmental etiologies of congenital heart defects induced by aneuploidy of chromosome 21.

Establishment of NCHi009-A, an iPSC line from a patient with hypoplastic left heart syndrome (HLHS) carrying a heterozygous NOTCH1 mutation.

Hypoplastic left heart syndrome (HLHS) is a congenital heart malformation clinically characterized by an underdeveloped left ventricle, mitral or aortic valve stenosis or atresia, and narrowed ascending aorta. Although genetic etiology of HLHS is heterogenous, recurrent NOTCH1 variants have been associated with this defect. We report generation of an iPSC line derived from a female with HLHS with a heterozygous missense NOTCH1 (c.2058G > A; p.Gly661Ser) mutation within the conserved EGF-like repeat 17. This iPSC line exhibited typical cellular morphology, normal karyotype, high expression of pluripotent markers, and trilineage differentiation potential; and can be leveraged to dissect the complex NOTCH1-mediated HLHS disease mechanism.

Characterization of an induced pluripotent stem cell line NCHi011-A from a 23-year-old female with Alagille Syndrome harboring a heterozygous JAG1 pathogenic variant.

Alagille syndrome (ALGS) is a multisystem disease with high variability in clinical features. ALGS is predominantly caused by pathogenic variants in the Notch ligand JAG1. An iPSC line, NCHi011-A, was generated from a ALGS patient with complex cardiac phenotypes consisting of pulmonic valve and branch pulmonary artery stenosis. NCHi011-A is heterozygous for a single base duplication causing a frameshift in the JAG1 gene. This iPSC line demonstrates normal cellular morphology, expression of pluripotency markers, trilineage differentiation potential, and identity to the source patient. NCHi011-A provides a resource for modeling ALGS and investigating the role of Notch signaling in the disease.

Generation of iPSC line NCHi012-A from a patient with Alagille syndrome and heterozygous pathogenic variant in the JAG1 gene.

Alagille syndrome (ALGS) is an autosomal dominant disease affecting the liver, heart and other organs with high variability. About 95% of ALGS cases are associated with pathogenic variants in JAG1, encoding the Jagged1 ligand that binds to Notch receptors. The iPSC line NCHi012-A was derived from an ALGS patient with cholestatic liver disease and mild pulmonary stenosis, who is heterozygous for a 2 bp deletion in the JAG1 coding sequence. We report here an initial characterization of NCHi012-A to evaluate its morphology, pluripotency, differentiation potential, genotype, karyotype and identity to the source patient.

Generation of Cardiomyocytes and Endothelial Cells from Human iPSCs by Chemical Modulation of Wnt Signaling.

The generation of cardiomyocytes (CMs) and endothelial cells (ECs) from human induced pluripotent stem cells (iPSCs) allows for precise modeling of cardiovascular disease using clinically relevant and patient-specific cells. Differentiation of human iPSCs into cardiomyocytes (iPSC-CMs) and endothelial cells (iPSC-ECs) is governed by small molecules that regulate the WNT signaling pathway. Here we outline the detailed steps to generate iPSC-CMs and iPSC-ECs through small molecule-mediated monolayer differentiation.

Generation and characterization of a human induced pluripotent stem cell (iPSC) line from a patient with congenital heart disease (CHD).

Epstein-Barr virus (EBV) immortalized lymphoblastoid cell lines (LCLs) are widely used for banking. This bioresource could be leveraged for creating human iPSC lines to model diseases including CHD. We generated an LCL-derived iPSC line (NCHi001-A) from a patient with congenital aortic valve stenosis. NCHi001-A was EBV and transgenes free, exhibited stem cell-like morphology, expressed pluripotency markers, has a normal karyotype, and could be differentiated into cells of three germ layers in vitro. Relationship inference via a microarray-based analysis showed NCHi001-A is identical to the parental cell line. NCHi001-A can be used for disease modeling, drug discovery, and cell therapy development.

Generation of an induced pluripotent stem cell line NCHi003-A from a 11-year-old male with pulmonary atresia with intact ventricular septum (PA-IVS).

Pulmonary atresia with intact ventricular septum (PA-IVS) is a rare congenital heart defect defined by membranous or muscular atresia of the right ventricular outflow tract where patients display varying degrees of hypoplasia of the right ventricle. This condition results in cyanosis due to an inability of blood to flow from the right ventricle to the pulmonary arteries, thus requiring immediate surgical intervention after birth. An iPSC line was generated from peripheral blood mononuclear cells of a 11-year-old male patient diagnosed with PA-IVS through Sendai virus-mediated reprogramming. This disease-specific iPSC line was characterized by immunocytochemistry, STR analysis, karyotype analysis, and mycoplasma testing.

Characterization of an iPSC line NCHi006-A from a patient with hypoplastic left heart syndrome (HLHS).

Hypoplastic left heart syndrome (HLHS) is a severe congenital heart defect characterized by underdeveloped structures on the left side of the heart, including hypoplasia of the left ventricle and stenosis or atresia of the aortic and mitral valves. Here, we generated an iPSC line from the peripheral blood mononuclear cells of a male patient with HLHS through Sendai virus-mediated transfection of 4 Yamanaka factors. This iPSC line exhibited normal morphology, expressed pluripotency markers, had a normal karyotype, and could differentiate into cells of three germ layers. This iPSC line can be used for studying cellular and developmental etiologies of HLHS.

Generation and Expansion of Human Cardiomyocytes from Patient Peripheral Blood Mononuclear Cells.

Generating patient-specific cardiomyocytes from a single blood draw has attracted tremendous interest in precision medicine on cardiovascular disease. Cardiac differentiation from human induced pluripotent stem cells (iPSCs) is modulated by defined signaling pathways that are essential for embryonic heart development. Numerous cardiac differentiation methods on 2-D and 3-D platforms have been developed with various efficiencies and cardiomyocyte yield. This has puzzled investigators outside the field as the variety of these methods can be difficult to follow. Here we present a comprehensive protocol that elaborates robust generation and expansion of patient-specific cardiomyocytes from peripheral blood mononuclear cells (PBMCs). We first describe a high-efficiency iPSC reprogramming protocol from a patient's blood sample using non-integration Sendai virus vectors. We then detail a small molecule-mediated monolayer differentiation method that can robustly produce beating cardiomyocytes from most human iPSC lines. In addition, a scalable cardiomyocyte expansion protocol is introduced using a small molecule (CHIR99021) that could rapidly expand patient-derived cardiomyocytes for industrial- and clinical-grade applications. At the end, detailed protocols for molecular identification and electrophysiological characterization of these iPSC-CMs are depicted. We expect this protocol to be pragmatic for beginners with limited knowledge on cardiovascular development and stem cell biology.