Disease-associated polyalanine expansion mutations impair UBA6-dependent ubiquitination.

Expansion mutations in polyalanine stretches are associated with a growing number of diseases sharing a high degree of genotypic and phenotypic commonality. These similarities prompted us to query the normal function of physiological polyalanine stretches and to investigate whether a common molecular mechanism is involved in these diseases. Here, we show that UBA6, an E1 ubiquitin-activating enzyme, recognizes a polyalanine stretch within its cognate E2 ubiquitin-conjugating enzyme USE1. Aberrations in this polyalanine stretch reduce ubiquitin transfer to USE1 and, subsequently, polyubiquitination and degradation of its target, the ubiquitin ligase E6AP. Furthermore, we identify competition for the UBA6-USE1 interaction by various proteins with polyalanine expansion mutations in the disease state. The deleterious interactions of expanded polyalanine tract proteins with UBA6 in mouse primary neurons alter the levels and ubiquitination-dependent degradation of E6AP, which in turn affects the levels of the synaptic protein Arc. These effects are also observed in induced pluripotent stem cell-derived autonomic neurons from patients with polyalanine expansion mutations, where UBA6 overexpression increases neuronal resilience to cell death. Our results suggest a shared mechanism for such mutations that may contribute to the congenital malformations seen in polyalanine tract diseases.

Early maturation and hyperexcitability is a shared phenotype of cortical neurons derived from different ASD-associated mutations.

Autism Spectrum Disorder (ASD) is characterized mainly by social and sensory-motor abnormal and repetitive behavior patterns. Over hundreds of genes and thousands of genetic variants were reported to be highly penetrant and causative of ASD. Many of these mutations cause comorbidities such as epilepsy and intellectual disabilities (ID). In this study, we measured cortical neurons derived from induced pluripotent stem cells (iPSCs) of patients with four mutations in the genes GRIN2B, SHANK3, UBTF, as well as chromosomal duplication in the 7q11.23 region and compared them to neurons derived from a first-degree relative without the mutation. Using a whole-cell patch-clamp, we observed that the mutant cortical neurons demonstrated hyperexcitability and early maturation compared to control lines. These changes were characterized by increased sodium currents, increased amplitude and rate of excitatory postsynaptic currents (EPSCs), and more evoked action potentials in response to current stimulation in early-stage cell development (3-5 weeks post differentiation). These changes that appeared in all the different mutant lines, together with previously reported data, indicate that an early maturation and hyperexcitability may be a convergent phenotype of ASD cortical neurons.

Functional defects in hiPSCs-derived cardiomyocytes from patients with a PLEKHM2-mutation associated with dilated cardiomyopathy and left ventricular non-compaction.

Dilated cardiomyopathy (DCM) is a primary myocardial disease, leading to heart failure and excessive risk of sudden cardiac death with rather poorly understood pathophysiology. In 2015, Parvari's group identified a recessive mutation in the autophagy regulator, PLEKHM2 gene, in a family with severe recessive DCM and left ventricular non-compaction (LVNC). Fibroblasts isolated from these patients exhibited abnormal subcellular distribution of endosomes, Golgi apparatus, lysosomes and had impaired autophagy flux. To better understand the effect of mutated PLEKHM2 on cardiac tissue, we generated and characterized induced pluripotent stem cells-derived cardiomyocytes (iPSC-CMs) from two patients and a healthy control from the same family. The patient iPSC-CMs showed low expression levels of genes encoding for contractile functional proteins (α and ß-myosin heavy chains and 2v and 2a-myosin light chains), structural proteins integral to heart contraction (Troponin C, T and I) and proteins participating in Ca2+ pumping action (SERCA2 and Calsequestrin 2) compared to their levels in control iPSC-derived CMs. Furthermore, the sarcomeres of the patient iPSC-CMs were less oriented and aligned compared to control cells and generated slowly beating foci with lower intracellular calcium amplitude and abnormal calcium transient kinetics, measured by IonOptix system and MuscleMotion software. Autophagy in patient's iPSC-CMs was impaired as determined from a decrease in the accumulation of autophagosomes in response to chloroquine and rapamycin treatment, compared to control iPSC-CMs. Impairment in autophagy together with the deficiency in the expression of NKX2.5, MHC, MLC, Troponins and CASQ2 genes, which are related to contraction-relaxation coupling and intracellular Ca2+ signaling, may contribute to the defective function of the patient CMs and possibly affect cell maturation and cardiac failure with time.

PLEKHM2 Loss of Function Impairs the Activity of iPSC-Derived Neurons via Regulation of Autophagic Flux.

Pleckstrin Homology And RUN Domain Containing M2 (PLEKHM2) [delAG] mutation causes dilated cardiomyopathy with left ventricular non-compaction (DCM-LVNC), resulting in a premature death of PLEKHM2[delAG] individuals due to heart failure. PLEKHM2 is a factor involved in autophagy, a master regulator of cellular homeostasis, decomposing pathogens, proteins and other cellular components. Autophagy is mainly carried out by the lysosome, containing degradation enzymes, and by the autophagosome, which engulfs substances marked for decomposition. PLEKHM2 promotes lysosomal movement toward the cell periphery. Autophagic dysregulation is associated with neurodegenerative diseases' pathogenesis. Thus, modulation of autophagy holds considerable potential as a therapeutic target for such disorders. We hypothesized that PLEKHM2 is involved in neuronal development and function, and that mutated PLEKHM2 (PLEKHM2[delAG]) neurons will present impaired functions. Here, we studied PLEKHM2-related abnormalities in induced pluripotent stem cell (iPSC)-derived motor neurons (iMNs) as a neuronal model. PLEKHM2[delAG] iMN cultures had healthy control-like differentiation potential but exhibited reduced autophagic activity. Electrophysiological measurements revealed that PLEKHM2[delAG] iMN cultures displayed delayed functional maturation and more frequent and unsynchronized activity. This was associated with increased size and a more perinuclear lysosome cellular distribution. Thus, our results suggest that PLEKHM2 is involved in the functional development of neurons through the regulation of autophagic flux.

P450 oxidoreductase regulates barrier maturation by mediating retinoic acid metabolism in a model of the human BBB.

The blood-brain barrier (BBB) selectively regulates the entry of molecules into the central nervous system (CNS). A crosstalk between brain microvascular endothelial cells (BMECs) and resident CNS cells promotes the acquisition of functional tight junctions (TJs). Retinoic acid (RA), a key signaling molecule during embryonic development, is used to enhance in vitro BBB models' functional barrier properties. However, its physiological relevance and affected pathways are not fully understood. P450 oxidoreductase (POR) regulates the enzymatic activity of microsomal cytochromes. POR-deficient (PORD) patients display impaired steroid homeostasis and cognitive disabilities. Here, we used both patient-specific POR-deficient and CRISPR-Cas9-mediated POR-depleted induced pluripotent stem cell (iPSC)-derived BMECs (iBMECs) to study the role of POR in the acquisition of functional barrier properties. We demonstrate that POR regulates cellular RA homeostasis and that POR deficiency leads to the accumulation of RA within iBMECs, resulting in the impaired acquisition of TJs and, consequently, to dysfunctional development of barrier properties.

Generation and characterization of iPSC lines (UOHi003-A, UOHi002-A) from a patient with SHANK3 mutation and her healthy mother.

Phelan-McDermid syndrome (PMS) is a rare genetic condition that causes global developmental disability, delayed or absent speech, and an autism spectrum disorder. The loss of function of one copy of SHANK3, which codes for a scaffolding protein found in the postsynaptic density of synapses, has been identified as the main cause of PMS. We report the generation and characterization of two induced pluripotent stem cell (iPSC) lines derived from one patient with a SHANK3 mutation and the patient's mother as a control. Both lines expressed pluripotency markers, differentiated into the three germ layers, retained the disease-causing mutation, and displayed normal karyotypes.

The Effect of Sera from Children with Obstructive Sleep Apnea Syndrome (OSAS) on Human Cardiomyocytes Differentiated from Human Embryonic Stem Cells.

Obstructive sleep apnea syndrome (OSAS) patients suffer from cardiovascular morbidity, which is the leading cause of death in this disease. Based on our previous work with transformed cell lines and primary rat cardiomyocytes, we determined that upon incubation with sera from pediatric OSAS patients, the cell's morphology changes, NF-κB pathway is activated, and their beating rate and viability decreases. These results suggest an important link between OSAS, systemic inflammatory signals and end-organ cardiovascular diseases. In this work, we confirmed and expanded these observations on a new in vitro system of beating human cardiomyocytes (CM) differentiated from human embryonic stem cells (hES). Our results show that incubation with pediatric OSAS sera, in contrast to sera from healthy children, induces over-expression of NF-κB p50 and p65 subunits, marked reduction in CMs beating rate, contraction amplitude and a strong reduction in intracellular calcium signal. The use of human CM cells derived from embryonic stem cells has not been previously reported in OSAS research. The results further support the hypothesis that NF-κB dependent inflammatory pathways play an important role in the evolution of cardiovascular morbidity in OSAS. This study uncovers a new model to investigate molecular and functional aspects of cardiovascular pathology in OSAS.

Induced pluripotent stem cell (iPSC) lines from two individuals carrying a homozygous (BGUi007-A) and a heterozygous (BGUi006-A) mutation in ELP1 for in vitro modeling of familial dysautonomia.

Familial Dysautonomia (FD) is an autosomal recessive congenital neuropathy affecting the development and function of the peripheral nervous system. FD causing gene is IKBKAP, encoding IkappaB kinase complex-associated protein also named elongator complex like protein 1 (IKAP/ELP1). The most common mutation (IVS20 + 6 T > C) causes an exon 20 skipping, leading to a truncated protein. We report the generation of two induced pluripotent stem cell lines from an FD patient with a homozygous mutation in ELP1 and his heterozygous healthy family relative. Both lines highly express pluripotency markers, can differentiate into the three germ layers, retain the disease-causing mutation and display normal karyotypes.

Generation and characterization of three human induced pluripotent stem cell lines (iPSC) from two family members with dilated cardiomyopathy and left ventricular noncompaction (DCM-LVNC) and one healthy heterozygote sibling.

Autophagy serves as a master regulator of cellular homeostasis. Hence, expectedly autophagic dysfunction has been documented in many diseases such as cancer, neurodegeneration and cardiovascular disorders. A novel homozygous mutation in PLEKHM2 gene (mPLEKHM2) resulted in dilated cardiomyopathy with left ventricular noncompaction (DCM-LVNC), probably as result of impaired autophagy due to disruption of lysosomal movement assisted by PLEKHM2. Here we report a generation of three iPSC lines, four clones originated from two patients with homozygous mPLEKHM2 and two from a heterozygote sibling. All generated lines highly expressed pluripotency markers, spontaneously differentiated into three germ layers, retained the mutation after reprogramming and displayed normal karyotypes.

Reprogramming of two induced pluripotent stem cell lines from a heterozygous GRIN2D developmental and epileptic encephalopathy (DEE) patient (BGUi011-A) and from a healthy family relative (BGUi012-A).

The GLUN2D subunit of the N-methylD-aspartate receptor (NMDAR) is encoded by the GRIN2D gene. Mutations in GRIN2D have been associated with neurodevelopmental and epileptic encephalopathies. Access to patient samples harboring mutations in GRIN2D can contribute to understanding the role of NMDAR in neuronal development and function. We report the generation of induced pluripotent stem cell (iPSC) lines from a GRIN2D-developmental and epileptic encephalopathy (DEE) patient, carrying a de novo c.1999G>A heterozygous pathogenic variant, and his healthy parent. Generated lines highly expressed pluripotency markers, spontaneously differentiated into the three germ layers, retained the deficiency-causing mutation, and displayed normal karyotypes.

Generation of iPSC lines from two (BGUi002-A and BGUi003-A) homozygous p450 oxidoreductase-deficient patients and from one (BGUi001-A) heterozygous healthy family relative.

p450 oxidoreductase (POR) cytochromes are enzymes involved in the metabolism of steroids and sex hormones, in which POR acts as an electron donor. Inactivating mutations in the POR gene cause diverse deficiencies. Access to patient samples carrying these POR mutations can contribute to the understanding of metabolic and developmental processes. We report the generation of three iPSC lines from two POR-deficient patients carrying a rare G539R homozygous mutation, and one healthy heterozygous family relative. All generated lines highly expressed pluripotency markers, spontaneously differentiated into three germ layers, retained the deficiency causing mutation and displayed normal karyotypes.

Generation and characterization of iPSC lines (BGUi004-A, BGUi005-A) from two identical twins with polyalanine expansion in the paired-like homeobox 2B (PHOX2B) gene.

Congenital central hypoventilation syndrome (CCHS) is a rare life-threatening condition affecting the autonomic nervous system that usually presents shortly after birth as hypoventilation or central apnea during sleep. In the majority of cases, heterozygous polyalanine expansion mutations within the third exon of the paired-like homeobox 2B (PHOX2B) gene underlie CCHS. Here, we report the generation of two induced pluripotent stem cell (iPSC) lines from two identical twins with a heterozygous PHOX2B expansion mutation (+5 alanine residues). Both generated lines highly express pluripotency markers, can differentiate into the three germ layers, retain the disease-causing mutation and display normal karyotypes.

NKp44-Derived Peptide Binds Proliferating Cell Nuclear Antigen and Mediates Tumor Cell Death.

Proliferating cell nuclear antigen (PCNA) is considered as a hub protein and is a key regulator of DNA replication, repair, cell cycle control, and apoptosis. PCNA is overexpressed in many cancer types, and PCNA overexpression is correlated with cancer virulence. Membrane-associated PCNA is a ligand for the NKp44 (NCR2) innate immune receptor. The purpose of this study was to characterize the PCNA-binding site within NKp44. We have identified NKp44-derived linear peptide (pep8), which can specifically interact with PCNA and partly block the NKp44-PCNA interaction. We then tested whether NKp44-derived pep8 (NKp44-pep8) fused to cell-penetrating peptides (CPPs) can be employed for targeting the intracellular PCNA for the purpose of anticancer therapy. Treatment of tumor cells with NKp44-pep8, fused to R11-NLS cell-penetrating peptide (R11-NLS-pep8), reduced cell viability and promoted cell death, in various murine and human cancer cell lines. Administration of R11-NLS-pep8 to tumor-bearing mice suppressed tumor growth in the 4T1 breast cancer and the B16 melanoma in vivo models. We therefore identified the NKp44 binding site to PCNA and further developed an NKp44-peptide-based agent that can inhibit tumor growth through interfering with the function of intracellular PCNA in the tumor cell.

RSRC1 mutation affects intellect and behaviour through aberrant splicing and transcription, downregulating IGFBP3.

RSRC1, whose polymorphism is associated with altered brain function in schizophrenia, is a member of the serine and arginine rich-related protein family. Through homozygosity mapping and whole exome sequencing we show that RSRC1 mutation causes an autosomal recessive syndrome of intellectual disability, aberrant behaviour, hypotonia and mild facial dysmorphism with normal brain MRI. Further, we show that RSRC1 is ubiquitously expressed, and that the RSRC1 mutation triggers nonsense-mediated mRNA decay of the RSRC1 transcript in patients' fibroblasts. Short hairpin RNA (shRNA)-mediated lentiviral silencing and overexpression of RSRC1 in SH-SY5Y cells demonstrated that RSRC1 has a role in alternative splicing and transcription regulation. Transcriptome profiling of RSRC1-silenced cells unravelled specific differentially expressed genes previously associated with intellectual disability, hypotonia and schizophrenia, relevant to the disease phenotype. Protein-protein interaction network modelling suggested possible intermediate interactions by which RSRC1 affects gene-specific differential expression. Patient-derived induced pluripotent stem cells, differentiated into neural progenitor cells, showed expression dynamics similar to the RSRC1-silenced SH-SY5Y model. Notably, patient neural progenitor cells had 9.6-fold downregulated expression of IGFBP3, whose brain expression is affected by MECP2, aberrant in Rett syndrome. Interestingly, Igfbp3-null mice have behavioural impairment, abnormal synaptic function and monoaminergic neurotransmission, likely correlating with the disease phenotype.

Measles Virus Persistent Infection of Human Induced Pluripotent Stem Cells.

In this study, we found that the measles virus (MV) can infect human-induced pluripotent stem cells (hiPSCs). Wild-type MV strains generally use human signaling lymphocyte activation molecule (SLAM; CD150) as a cellular receptor, while vaccine strains such as the Edmonston strain can use both CD150 and CD46 as receptors. It is not yet known how early in the embryonal differentiation stages these receptors are expressed. We established two hiPSCs (BGU-iPSCs and EMF-iPSCs) which express CD46 and CD150. Both cell types can be infected by MV to form persistent, noncytopathic cell lines that release infectious MV particles. Following MV persistent infection, BGU-iPSCs and EMF-iPSCs remain pluripotent and can differentiate in vitro into the three germ layers. This includes cells expressing the neuronal differentiation markers: NF68 and miRNA-124. Since the MV does not integrate into the cell's genome, it can be utilized as a vehicle to systematically introduce genes into iPSC, to dissect and to define factors regulating lineage differentiation.

African descents are more sensitive than European descents to the antitumor compounds α-hederin and kalopanaxsaponin I.

α-Hederin, a natural triterpene saponin and its derivative kalopanaxsaponin I (ksI) exhibit cytotoxicity against various cancer cell lines and IN VIVO tumors. We studied the genetic variants contributing to the activity of these two anticancer compounds. Cell lines derived from 30 trios of European descent (Centre d'Etude du Polymorphisme Human, CEPH; CEU) and 30 trios of African descent (Yoruban, YRI) were used. Cytotoxicity was determined as inhibition of cell growth at increasing concentrations of α-hederin or ksI for 24 h. In comparison to the European, the Yoruban populations revealed a higher sensitivity to α-hederin and to ksI that can be attributed to several unique SNPs. These SNPs are located near 111 and 130 genes in the European and the Yoruban populations, respectively, raising the possibility that some of these genes contribute to the differential sensitivity to these compounds.