Targeting RNA-splicing for SMA treatment

Switching of RNA splicing regulators in immature neuroblasts during adult neurogenesis

The lateral wall of the mouse subventricular zone harbors neural stem cells (NSC, B cells) which generate proliferating transient-amplifying progenitors (TAP, C cells) that ultimately give rise to neuroblasts (NB, A cells). Molecular profiling at the single-cell level struggles to distinguish these different cell types. Here, we combined transcriptome analyses of FACS-sorted cells and single-cell RNAseq to demonstrate the existence of an abundant, clonogenic and multipotent population of immature neuroblasts (iNB cells) at the transition between TAP and migrating NB (mNB). iNB are reversibly engaged in neuronal differentiation. Indeed, they keep molecular features of both undifferentiated progenitors, plasticity and unexpected regenerative properties. Strikingly, they undergo important progressive molecular switches, including changes in the expression of splicing regulators leading to their differentiation in mNB subdividing them into two subtypes, iNB1 and iNB2. Due to their plastic properties, iNB could represent a new target for regenerative therapy of brain damage.

Molecular Mechanism of Resistance to Alternaria alternata Apple Pathotype in Apple by Alternative Splicing of Transcription Factor MdMYB6-like

As a fruit tree with great economic value, apple is widely cultivated in China. However, apple leaf spot disease causes significant damage to apple quality and economic value. In our study, we found that MdMYB6-like is a transcription factor without auto-activation activity and with three alternative spliced variants. Among them, MdMYB6-like-β responded positively to the pathogen infection. Overexpression of MdMYB6-like-β increased the lignin content of leaves and improved the pathogenic resistance of apple flesh callus. In addition, all three alternative spliced variants of MdMYB6-like could bind to the promoter of MdBGLU H. Therefore, we believe that MdMYB6-like plays an important role in the infection process of the pathogen and lays a solid foundation for breeding disease-resistant cultivars of apple in the future.

Function of two splicing variants of RcCPR5 in the resistance of Rosa chinensis to powdery mildew

Rosa chinensis is an important economic and ornamental crop, but powdery mildew greatly reduces its ornamental and economic value. The RcCPR5 gene, encoding a constitutive expressor of pathogenesis-related genes, has two splicing variants in R. chinensis. Compared with RcCPR5-1, RcCPR5-2 has a large C-terminal deletion. During disease development, RcCPR5-2 responded quickly and coordinated with RcCPR5-1 to resist the invasion of the powdery mildew pathogen. In virus-induced gene silencing experiments, down-regulation of RcCPR5 improved the resistance of R. chinensis to powdery mildew. This was confirmed to be broad-spectrum resistance. In the absence of pathogen infection, RcCPR5-1 and RcCPR5-2 formed homodimers and heterodimers to regulate plant growth; but when infected by the powdery mildew pathogen, the RcCPR5-1 and RcCPR5-2 complexes disassociated and released RcSIM/RcSMR to induce effector-triggered immunity, thereby inducing resistance to pathogen infection.

Computational assessment of saikosaponins as adjuvant treatment for COVID-19: molecular docking, dynamics, and network pharmacology analysis

Saikosaponins are major biologically active triterpenoids, usually as glucosides, isolated from Traditional Chinese Medicines (TCM) such as Bupleurum spp., Heteromorpha spp., and Scrophularia scorodonia with their antiviral and immunomodulatory potential. This investigation presents molecular docking, molecular dynamics simulation, and free energy calculation studies of saikosaponins as adjuvant therapy in the treatment for COVID19. Molecular docking studies for 23 saikosaponins on the crystal structures of the extracellular domains of human lnterleukin-6 receptor (IL6), human Janus Kinase-3 (JAK3), and dehydrogenase domain of Cylindrospermum stagnale NADPH-oxidase 5 (NOX5) were performed, and selected protein-ligand complexes were subjected to 100 ns molecular dynamics simulations. The molecular dynamics trajectories were subjected to free energy calculation by the MM-GBSA method. Molecular docking and molecular dynamics simulation studies revealed that IL6 in complex with Saikosaponin_U and Saikosaponin_V, JAK3 in complex with Saikosaponin_B4 and Saikosaponin_I, and NOX5 in complex with Saikosaponin_BK1 and Saikosaponin_C have good docking and molecular dynamics profiles. However, the Janus Kinase-3 is the best interacting partner for the saikosaponin compounds. The network pharmacology analysis suggests saikosaponins interact with the proteins CAT Gene CAT (Catalase) and Checkpoint kinase 1 (CHEK1); both of these enzymes play a major role in cell homeostasis and DNA damage during infection, suggesting a possible improvement in immune response toward COVID-19.

PacBio Iso-Seq Improves the Rainbow Trout Genome Annotation and Identifies Alternative Splicing Associated With Economically Important Phenotypes

Rainbow trout is an important model organism that has received concerted international efforts to study the transcriptome. For this purpose, short-read sequencing has been primarily used over the past decade. However, these sequences are too short of resolving the transcriptome complexity. This study reported a first full-length transcriptome assembly of the rainbow trout using single-molecule long-read isoform sequencing (Iso-Seq). Extensive computational approaches were used to refine and validate the reconstructed transcriptome. The study identified 10,640 high-confidence transcripts not previously annotated, in addition to 1,479 isoforms not mapped to the current Swanson reference genome. Most of the identified lncRNAs were non-coding variants of coding transcripts. The majority of genes had multiple transcript isoforms (average ∼3 isoforms/locus). Intron retention (IR) and exon skipping (ES) accounted for 56% of alternative splicing (AS) events. Iso-Seq improved the reference genome annotation, which allowed identification of characteristic AS associated with fish growth, muscle accretion, disease resistance, stress response, and fish migration. For instance, an ES in GVIN1 gene existed in fish susceptible to bacterial cold-water disease (BCWD). Besides, under five stress conditions, there was a commonly regulated exon in prolyl 4-hydroxylase subunit alpha-2 (P4HA2) gene. The reconstructed gene models and their posttranscriptional processing in rainbow trout provide invaluable resources that could be further used for future genetics and genomics studies. Additionally, the study identified characteristic transcription events associated with economically important phenotypes, which could be applied in selective breeding.

Drug screening with human SMN2 reporter identifies SMN protein stabilizers to correct SMA pathology

Spinal muscular atrophy (SMA), the leading genetic cause of infant mortality, is caused by reduced levels of functional survival motor neuron (SMN) protein. To identify therapeutic agents for SMA, we established a versatile SMN2-GFP reporter line by targeting the human SMN2 gene. We then screened a compound library and identified Z-FA-FMK as a potent candidate. Z-FA-FMK, a cysteine protease inhibitor, increased functional SMN through inhibiting the protease-mediated degradation of both full-length and exon 7-deleted forms of SMN. Further studies reveal that CAPN1, CAPN7, CTSB, and CTSL mediate the degradation of SMN proteins, providing novel targets for SMA. Notably, Z-FA-FMK mitigated mitochondriopathy and neuropathy in SMA patient-derived motor neurons and showed protective effects in SMA animal model after intracerebroventricular injection. E64d, another cysteine protease inhibitor which can pass through the blood-brain barrier, showed even more potent therapeutic effects after subcutaneous delivery to SMA mice. Taken together, we have successfully established a human SMN2 reporter for future drug discovery and identified the potential therapeutic value of cysteine protease inhibitors in treating SMA via stabilizing SMN proteins.

Discovery of Small Molecule Splicing Modulators of Survival Motor Neuron-2 (SMN2) for the Treatment of Spinal Muscular Atrophy (SMA)

Spinal muscular atrophy (SMA), a rare neuromuscular disorder, is the leading genetic cause of death in infants and toddlers. SMA is caused by the deletion or a loss of function mutation of the survival motor neuron 1 (SMN1) gene. In humans, a second closely related gene SMN2 exists; however it codes for a less stable SMN protein. In recent years, significant progress has been made toward disease modifying treatments for SMA by modulating SMN2 pre-mRNA splicing. Herein, we describe the discovery of LMI070/branaplam, a small molecule that stabilizes the interaction between the spliceosome and SMN2 pre-mRNA. Branaplam (1) originated from a high-throughput phenotypic screening hit, pyridazine 2, and evolved via multiparameter lead optimization. In a severe mouse SMA model, branaplam treatment increased full-length SMN RNA and protein levels, and extended survival. Currently, branaplam is in clinical studies for SMA.

Pharmacokinetics, pharmacodynamics, and efficacy of a small-molecule SMN2 splicing modifier in mouse models of spinal muscular atrophy

Spinal muscular atrophy (SMA) is caused by the loss or mutation of both copies of the survival motor neuron 1 (SMN1) gene. The related SMN2 gene is retained, but due to alternative splicing of exon 7, produces insufficient levels of the SMN protein. Here, we systematically characterize the pharmacokinetic and pharmacodynamics properties of the SMN splicing modifier SMN-C1. SMN-C1 is a low-molecular weight compound that promotes the inclusion of exon 7 and increases production of SMN protein in human cells and in two transgenic mouse models of SMA. Furthermore, increases in SMN protein levels in peripheral blood mononuclear cells and skin correlate with those in the central nervous system (CNS), indicating that a change of these levels in blood or skin can be used as a non-invasive surrogate to monitor increases of SMN protein levels in the CNS. Consistent with restored SMN function, SMN-C1 treatment increases the levels of spliceosomal and U7 small-nuclear RNAs and corrects RNA processing defects induced by SMN deficiency in the spinal cord of SMNΔ7 SMA mice. A 100% or greater increase in SMN protein in the CNS of SMNΔ7 SMA mice robustly improves the phenotype. Importantly, a ∼50% increase in SMN leads to long-term survival, but the SMA phenotype is only partially corrected, indicating that certain SMA disease manifestations may respond to treatment at lower doses. Overall, we provide important insights for the translation of pre-clinical data to the clinic and further therapeutic development of this series of molecules for SMA treatment.

SMN2 splice modulators enhance U1-pre-mRNA association and rescue SMA mice

Spinal muscular atrophy (SMA), which results from the loss of expression of the survival of motor neuron-1 (SMN1) gene, represents the most common genetic cause of pediatric mortality. A duplicate copy (SMN2) is inefficiently spliced, producing a truncated and unstable protein. We describe herein a potent, orally active, small-molecule enhancer of SMN2 splicing that elevates full-length SMN protein and extends survival in a severe SMA mouse model. We demonstrate that the molecular mechanism of action is via stabilization of the transient double-strand RNA structure formed by the SMN2 pre-mRNA and U1 small nuclear ribonucleic protein (snRNP) complex. The binding affinity of U1 snRNP to the 5' splice site is increased in a sequence-selective manner, discrete from constitutive recognition. This new mechanism demonstrates the feasibility of small molecule-mediated, sequence-selective splice modulation and the potential for leveraging this strategy in other splicing diseases.

Peptide nanoparticle delivery of charge-neutral splice-switching morpholino oligonucleotides

Oligonucleotide analogs have provided novel therapeutics targeting various disorders. However, their poor cellular uptake remains a major obstacle for their clinical development. Negatively charged oligonucleotides, such as 2′-O-Methyl RNA and locked nucleic acids have in recent years been delivered successfully into cells through complex formation with cationic polymers, peptides, liposomes, or similar nanoparticle delivery systems. However, due to the lack of electrostatic interactions, this promising delivery method has been unsuccessful to date using charge-neutral oligonucleotide analogs. We show here that lipid-functionalized cell-penetrating peptides can be efficiently exploited for cellular transfection of the charge-neutral oligonucleotide analog phosphorodiamidate morpholino. The lipopeptides form complexes with splice-switching phosphorodiamidate morpholino oligonucleotide and can be delivered into clinically relevant cell lines that are otherwise difficult to transfect while retaining biological activity. To our knowledge, this is the first study to show delivery through complex formation of biologically active charge-neutral oligonucleotides by cationic peptides.

Splicing and alternative splicing in rice and humans

Rice is a monocot gramineous crop, and one of the most important staple foods. Rice is considered a model species for most gramineous crops. Extensive research on rice has provided critical guidance for other crops, such as maize and wheat. In recent years, climate change and exacerbated soil degradation have resulted in a variety of abiotic stresses, such as greenhouse effects, lower temperatures, drought, floods, soil salinization and heavy metal pollution. As such, there is an extremely high demand for additional research, in order to address these negative factors. Studies have shown that the alternative splicing of many genes in rice is affected by stress conditions, suggesting that manipulation of the alternative splicing of specific genes may be an effective approach for rice to adapt to abiotic stress. With the advancement of microarrays, and more recently, next generation sequencing technology, several studies have shown that more than half of the genes in the rice genome undergo alternative splicing. This mini-review summarizes the latest progress in the research of splicing and alternative splicing in rice, compared to splicing in humans. Furthermore, we discuss how additional studies may change the landscape of investigation of rice functional genomics and genetically improved rice. [BMB Reports 2013; 46(9): 439-447]

PSF contacts exon 7 of SMN2 pre-mRNA to promote exon 7 inclusion

Spinal muscular atrophy (SMA) is an autosomal recessive genetic disease and a leading cause of infant mortality. Deletions or mutations of SMN1 cause SMA, a gene that encodes a SMN protein. SMN is important for the assembly of Sm proteins onto UsnRNA to UsnRNP. SMN has also been suggested to direct axonal transport of β-actin mRNA in neurons. Humans contain a second SMN gene called SMN2 thus SMA patients produce some SMN but not with sufficient levels. The majority of SMN2 mRNA does not include exon 7. Here we show that increased expression of PSF promotes inclusion of exon 7 in the SMN2 whereas reduced expression of PSF promotes exon 7 skipping. In addition, we present evidence showing that PSF interacts with the GAAGGA enhancer in exon 7. We also demonstrate that a mutation in this enhancer abolishes the effects of PSF on exon 7 splicing. Furthermore we show that the RNA target sequences of PSF and tra2β in exon 7 are partially overlapped. These results lead us to conclude that PSF interacts with an enhancer in exon 7 to promote exon 7 splicing of SMN2 pre-mRNA.

hnRNP M facilitates exon 7 inclusion of SMN2 pre-mRNA in spinal muscular atrophy by targeting an enhancer on exon 7

Spinal muscular atrophy (SMA) is an autosomal recessive genetic disease, which causes death of motor neurons in the anterior horn of the spinal cord. Genetic cause of SMA is the deletion or mutation of SMN1 gene, which encodes the SMN protein. Although SMA patients include SMN2 gene, a duplicate of SMN1 gene, predominant production of exon 7 skipped isoform from SMN2 pre-mRNA, fails to rescue SMA patients. Here we show that hnRNP M, a member of hnRNP protein family, when knocked down, promotes exon 7 skipping of both SMN2 and SMN1 pre-mRNA. By contrast, overexpression of hnRNP M promotes exon 7 inclusion of both SMN2 and SMN1 pre-mRNA. Significantly, hnRNP M promotes exon 7 inclusion in SMA patient cells. Thus, we conclude that hnRNP M promotes exon 7 inclusion of both SMN1 and SMN2 pre-mRNA. We also demonstrate that hnRNP M contacts an enhancer on exon 7, which was previously shown to provide binding site for tra2β. We present evidence that hnRNP M and tra2β contact overlapped sequence on exon 7 but with slightly different RNA sequence requirements. In addition, hnRNP M promotes U2AF65 recruitment on the flanking intron of exon 7. We conclude that hnRNP M promotes exon 7 inclusion of SMN1 and SMN2 pre-mRNA through targeting an enhancer on exon 7 through recruiting U2AF65. Our results provide a clue that hnRNP M is a potential therapeutic target for SMA.

Pressure-overload cardiac hypertrophy is associated with distinct alternative splicing due to altered expression of splicing factors

Chronic pressure-overload cardiac hypertrophy is associated with an increased risk of morbidity/mortality, largely due to maladaptive remodeling and dilatation that progresses to dilated cardiomyopathy. Alternative splicing is an important biological mechanism that generates proteomic complexity and diversity. The recent development of next-generation RNA sequencing has improved our understanding of the qualitative signatures associated with alternative splicing in various biological conditions. However, the role of alternative splicing in cardiac hypertrophy is yet unknown. The present study employed RNA-Seq and a bioinformatic approach to detect the RNA splicing regulatory elements involved in alternative splicing during pressure-overload cardiac hypertrophy. We found GC-rich exonic motifs that regulate intron retention in 5' UTRs and AT-rich exonic motifs that are involved in exclusion of the AT-rich elements that cause mRNA instability in 3' UTRs. We also identified motifs in the intronic regions involved in exon exclusion and inclusion, which predicted splicing factors that bind to these motifs. We found, through Western blotting, that the expression levels of three splicing factors, ESRP1, PTB and SF2/ASF, were significantly altered during cardiac hypertrophy. Collectively, the present results suggest that chronic pressure-overload hypertrophy is closely associated with distinct alternative splicing due to altered expression of splicing factors.

The sound of silence: autosomal recessive congenital ichthyosis caused by a synonymous mutation in ABCA12

Autosomal recessive congenital ichthyosis refers to a heterogeneous group of cornification disorders of major impact on patients' life. The disease has been linked so far to mutations in 8 distinct genes. We report a consanguineous family of Arab Muslim origin with several members displaying a severe form of congenital ichthyosiform erythroderma. Using a panel of polymorphic microsatellite markers, we identified a region of homozygosity shared by all patients on 2q34, in a region harbouring the ABCA12 gene. Direct sequencing of genomic DNA derived from a patient failed to reveal any obviously pathogenic change in the coding sequence of this gene. In contrast, cDNA sequence analysis revealed the existence of a 163-bp-long deletion in exon 24, thus pointing to a splicing defect. Careful reanalysis of the genomic DNA sequence revealed apart from several known single-nucleotide polymorphisms, a hitherto unreported homozygous synonymous mutation in exon 24 (c.3456G>A; p.S1152S), which was found to lead to the formation of a novel splicing acceptor site. Synonymous mutations have been shown to uncommonly cause inherited disorders in humans. Here, we present the first example of a congenital form of ichthyosis resulting from such a genetic defect.

Impact of EBV essential nuclear protein EBNA-3C on B-cell proliferation and apoptosis

For over 40 years, EBV infection has been implicated in the etiology of a variety of lymphoid malignancies with the exceptional ability to drive resting B cells to continuously proliferate by successfully overriding cellular apoptotic stimuli. EBV utilizes the normal physiology of B-cell differentiation to persist within the memory B-cell pool of the immunocompetent host and subsequently establishes a life-long latent infection. During latency, out of a subset of viral genes expressed, EBNA-3C is one of the essential antigens required for in vitro primary B-cell transformation. EBNA-3C acts as a transcriptional coregulator by interacting with various cellular and viral factors. For the last 10 years, we have been actively engaged in discerning the biological significance of these interactions and revealed that EBNA-3C primarily targets two important cellular pathways - cell cycle and apoptosis. This review aims to summarize our current knowledge on EBNA-3C-mediated functions and describe how EBNA-3C seizes these cellular pathways that eventually promote B-cell lymphomagenesis. A scrupulous understanding of the critical relationship between EBNA-3C and these cellular machineries will not only aid in elucidating EBV pathogenesis, but also largely facilitate the development of novel diagnostic, as well as therapeutic, strategies against a vast range of EBV-associated B-cell lymphomas.

Genome-wide analyses of Epstein-Barr virus reveal conserved RNA structures and a novel stable intronic sequence RNA

BACKGROUND

Epstein-Barr virus (EBV) is a human herpesvirus implicated in cancer and autoimmune disorders. Little is known concerning the roles of RNA structure in this important human pathogen. This study provides the first comprehensive genome-wide survey of RNA and RNA structure in EBV.

RESULTS

Novel EBV RNAs and RNA structures were identified by computational modeling and RNA-Seq analyses of EBV. Scans of the genomic sequences of four EBV strains (EBV-1, EBV-2, GD1, and GD2) and of the closely related Macacine herpesvirus 4 using the RNAz program discovered 265 regions with high probability of forming conserved RNA structures. Secondary structure models are proposed for these regions based on a combination of free energy minimization and comparative sequence analysis. The analysis of RNA-Seq data uncovered the first observation of a stable intronic sequence RNA (sisRNA) in EBV. The abundance of this sisRNA rivals that of the well-known and highly expressed EBV-encoded non-coding RNAs (EBERs).

CONCLUSION

This work identifies regions of the EBV genome likely to generate functional RNAs and RNA structures, provides structural models for these regions, and discusses potential functions suggested by the modeled structures. Enhanced understanding of the EBV transcriptome will guide future experimental analyses of the discovered RNAs and RNA structures.

Alternative splicing for diseases, cancers, drugs, and databases

Alternative splicing is a major diversification mechanism in the human transcriptome and proteome. Several diseases, including cancers, have been associated with dysregulation of alternative splicing. Thus, correcting alternative splicing may restore normal cell physiology in patients with these diseases. This paper summarizes several alternative splicing-related diseases, including cancers and their target genes. Since new cancer drugs often target spliceosomes, several clinical drugs and natural products or their synthesized derivatives were analyzed to determine their effects on alternative splicing. Other agents known to have modulating effects on alternative splicing during therapeutic treatment of cancer are also discussed. Several commonly used bioinformatics resources are also summarized.

The effect of 6-thioguanine on alternative splicing and antisense-mediated exon skipping treatment for duchenne muscular dystrophy

The severe muscle wasting disorder Duchenne muscular dystrophy (DMD) is caused by genetic defects in the DMD gene, leading to a complete absence of dystrophin protein. Of the therapeutic approaches addressing the underlying genetic defect, exon skipping through antisense oligonucleotides (AONs) is the closest to clinical application. Several strategies to improve the efficiency of this approach are currently being investigated, such as the use of small chemical compounds that improve AONmediated exon skipping levels. Recently, enhanced exon skipping in combination with a guanine analogue, 6-thioguanine (6TG) was reported for phosphorodiamidate morpholino oligomers (PMO). Here the effect of 6TG on the exon skipping efficacy of 2’-O-methyl phosphorothioate RNA (2OMePS) and PMO AONs in vitro and in vivo was further evaluated, as well as the effect of 6TG by itself. Results confirm an increase of exon skipping levels in vitro, however, in contrast to the previous report, no effect was observed in vivo. Importantly, 6TG treatment in vitro resulted in numerous additional DMD exon skipping events. This, in combination with the known cytotoxic effects of 6TG after incorporation in DNA, warrants reconsidering of the use of 6TG as enhancer of AON efficiency in DMD, were chronic treatment will be required.

Human osteopontin splicing isoforms: known roles, potential clinical applications and activated signaling pathways

Human osteopontin is subject to alternative splicing, which generates three isoforms, termed OPNa, OPNb and OPNc. These variants show specific expression and roles in different cell contexts. We present an overview of current knowledge of the expression profile of human OPN splicing isoforms (OPN-SIs), their tissue-specific roles, and the pathways mediating their functional properties in different pathophysiological conditions. We also describe their putative application as biomarkers, and their potential use as therapeutic targets by using antibodies, oligonucleotides or siRNA molecules. This synthesis provides new clues for a better understanding of human OPN splice variants, their roles in normal and pathological conditions, and their possible clinical applications.

Antisense oligonucleotide therapeutics for inherited neurodegenerative diseases

The rising median age of our population and the age-dependent risk of neurodegeneration translate to exponentially increasing numbers of afflicted individuals in the coming years. Although symptomatic treatments are available for some neurodegenerative diseases, most are only moderately efficacious and are often associated with significant side effects. The development of small molecule, disease-modifying drugs has been hindered by complex pathogenesis and a failure to clearly define the rate-limiting steps in disease progression. An alternative approach is to directly target the mutant gene product or a defined causative protein. Antisense oligonucleotides (ASOs) - with their diverse functionality, high target specificity, and relative ease of central nervous system (CNS) delivery - are uniquely positioned as potential therapies for neurological diseases. Here we review the development of ASOs for the treatment of inherited neurodegenerative diseases.