Antisense oligonucleotides: the next frontier for treatment of neurological disorders

Non-coding RNA in C9orf72-related amyotrophic lateral sclerosis and frontotemporal dementia: A perfect storm of dysfunction

A hexanucleotide repeat expansion in the first intron/promoter region of C9orf72 is the most common genetic cause of amyotrophic lateral sclerosis (ALS) and frontotemporal dementia (FTD). Both sense and antisense transcripts exist at the C9orf72 locus but the function of the antisense lncRNA is unknown. RNA toxicity of the transcribed repeat expansion has been implicated in the pathogenesis of C9orf72-related ALS/FTD, not only through direct sequestration of important RNA binding proteins but also indirectly through non-ATG dependent translation into dipeptide repeats. Formation of RNA/DNA hybrid R-loops may also play a key role in the pathogenesis of this condition and this mechanism could provide a link between the repeat expansion, DNA damage, repeat instability and deficiency of RNA binding proteins. Non-coding C9orf72 antisense transcripts could also act to epigenetically regulate gene expression at the locus. The potential effects of such non-coding RNAs should be considered in the design of antisense oligonucleotide therapeutics for C9orf72-related ALS/FTD. Furthermore, the mechanisms of RNA dysregulation exemplified by C9orf72-related disease may help illustrate more broadly how a “perfect storm” of dysfunction occurs in ALS/FTD and how targeting these factors could lead to corrective or preventative therapies.

Muscle Wasting Diseases: Novel Targets and Treatments

Adequate skeletal muscle plasticity is an essential element for our well-being, and compromised muscle function can drastically affect quality of life, morbidity, and mortality. Surprisingly, however, skeletal muscle remains one of the most under-medicated organs. Interventions in muscle diseases are scarce, not only in neuromuscular dystrophies, but also in highly prevalent secondary wasting pathologies such as sarcopenia and cachexia. Even in other diseases that exhibit a well-established risk correlation of muscle dysfunction due to a sedentary lifestyle, such as type 2 diabetes or cardiovascular pathologies, current treatments are mostly targeted on non-muscle tissues. In recent years, a renewed focus on skeletal muscle has led to the discovery of various novel drug targets and the design of new pharmacological approaches. This review provides an overview of the current knowledge of the key mechanisms involved in muscle wasting conditions and novel pharmacological avenues that could ameliorate muscle diseases.

The global role of biotechnology for non communicable disorders

The World Health Organization (WHO) has tagged non-communicable diseases (NCDs) as one of the twenty-first century's major development challenges. NCDs account for over 15 million deaths annually and over 80% of those deaths occur in developing countries and among the poorest populations. Biotechnology presents unique opportunities to improve the early diagnosis and the treatment of NCDs. This review describes the major applications of biotechnology for a better clinical management of NCDs, i.e. the implementation of innovative diagnostic approaches and the production of innovative treatments, including those based on monoclonal antibodies, recombinant proteins, regulatory nucleic acids and cell-based therapies for regenerative medicine. In this context, it also examines the major challenges faced by biotechnology in developing countries.

Convective influx/glymphatic system: tracers injected into the CSF enter and leave the brain along separate periarterial basement membrane pathways

Tracers injected into CSF pass into the brain alongside arteries and out again. This has been recently termed the “glymphatic system” that proposes tracers enter the brain along periarterial “spaces” and leave the brain along the walls of veins. The object of the present study is to test the hypothesis that: (1) tracers from the CSF enter the cerebral cortex along pial-glial basement membranes as there are no perivascular “spaces” around cortical arteries, (2) tracers leave the brain along smooth muscle cell basement membranes that form the Intramural Peri-Arterial Drainage (IPAD) pathways for the elimination of interstitial fluid and solutes from the brain. 2 μL of 100 μM soluble, fluorescent fixable amyloid β (Aβ) were injected into the CSF of the cisterna magna of 6–10 and 24–30 month-old male mice and their brains were examined 5 and 30 min later. At 5 min, immunocytochemistry and confocal microscopy revealed Aβ on the outer aspects of cortical arteries colocalized with α-2 laminin in the pial-glial basement membranes. At 30 min, Aβ was colocalised with collagen IV in smooth muscle cell basement membranes in the walls of cortical arteries corresponding to the IPAD pathways. No evidence for drainage along the walls of veins was found. Measurements of the depth of penetration of tracer were taken from 11 regions of the brain. Maximum depths of penetration of tracer into the brain were achieved in the pons and caudoputamen. Conclusions drawn from the present study are that tracers injected into the CSF enter and leave the brain along separate periarterial basement membrane pathways. The exit route is along IPAD pathways in which Aβ accumulates in cerebral amyloid angiopathy (CAA) in Alzheimer’s disease. Results from this study suggest that CSF may be a suitable route for delivery of therapies for neurological diseases, including CAA.

Synthesis, Affinity for Complementary RNA and DNA, and Enzymatic Stability of Triazole-Linked Locked Nucleic Acids (t-LNAs)

Dinucleoside phosphoramidites containing a triazole internucleotide linkage flanked by locked nucleic acid (LNA) were synthesized and incorporated into oligonucleotides (ONs). ONs bearing both LNA and triazole at multiple sites were obtained and their biophysical properties including enzymatic stability and binding affinity for RNA and DNA targets were studied. t-LNAs with four incorporations of a dinucleoside monomer having LNA on either side of the triazole linkage bind to their RNA target with significantly higher affinity and greater specificity than unmodified oligonucleotides, and are remarkably stable to nuclease degradation. A similar but reduced effect on enzymatic stability and binding affinity was noted for LNA only on the 3'-side of the triazole linkage. Thus, by combining unnatural triazole linkages and LNA in one unit (t-LNA), we produced a promising class of ONs with reduced anionic charge and potential for antisense applications.

Molecular Therapies for Muscular Dystrophies

PURPOSE OF REVIEW

To construct a framework to understand the different molecular interventions for muscular dystrophy.

RECENT FINDINGS

The recent approval of antisense oligonucleotides treatment for Duchenne muscular dystrophy and spinal muscular atrophy and current clinical trials using recombinant adeno-associated virus for the treatment of those diseases suggests that we are at a tipping point where we are able to treat and potentially cure muscular dystrophies. Understanding the basic molecular pathogenesis of muscular dystrophies and the molecular biology of the treatment allows for critical evaluation of the proposed therapies.

Intracellular Trafficking and Endosomal Release of Oligonucleotides: What We Know and What We Don't

Understanding the cellular uptake and intracellular trafficking of oligonucleotides provides an important basic underpinning for the developing field of oligonucleotide-based therapeutics. Whether delivered as "free" oligonucleotides, as ligand-oligonucleotide conjugates, or in association with various nanocarriers, all forms of oligonucleotide enter cells by endocytosis and are initially ensconced within membrane-limited vesicles. Accordingly, the locus and extent of release to the cytosol and nucleus are key determinants of the pharmacological actions of oligonucleotides. A number of recent studies have explored the intracellular trafficking of various forms of oligonucleotides and their release from endomembrane compartments. These studies reveal a surprising convergence on an early-intermediate compartment in the trafficking pathway as the key locus of release for oligonucleotides administered in "free" form as well as those delivered with lipid complexes. Thus, oligonucleotide release from multivesicular bodies or from late endosomes seems to be the crucial endogenous process for attaining pharmacological effects. This intrinsic process of oligonucleotide release may be amplified by delivery agents such as lipid complexes or small molecule enhancers.

Synthesis of O-Amino Sugars and Nucleosides

Nucleic acids and carbohydrates are essential biomolecules involved in numerous biological and pathological processes. Development of multifunctional building blocks based on nucleosides and sugars is in high demand for the generation of novel oligonucleotide mimics and glycoconjugates for biomedical applications. Recently, aminooxyl-functionalized compounds have attracted increasing research interest because of their easy derivatization through oxime ligation or N-oxyamide formation reactions. Various biological applications have been reported for O-amino carbohydrate- and nucleoside-derived compounds. Here, we report our efforts in the design and synthesis of glyco-, glycosyl, nucleoside- and nucleo-aminooxy acid derivatives from readily available sugars and amino acids, and their use for the generation of N-oxyamide-linked oligosaccharides, glycopeptides, glycolipids, oligonucleosides and nucleopeptides as novel glycoconjugates or oligonucleotide mimics. Delicate and key points in the synthesis will be emphasized.

Regulation of Tak1 alternative splicing by splice-switching oligonucleotides

Alternative splicing (AS) generates multiple isoforms from a single precursor mRNA, and these isoforms usually exhibit different tissue distributions and functions. Aberrant protein isoforms can lead to abnormalities in protein function and may even result in genetic disorders or cancer. In recent years, splice-switching oligonucleotides (SSOs) have emerged as a promising therapeutic strategy for several neurological diseases, but the efficacy of this strategy in other organs is less reported. In this study, we designed and synthesized SSOs targeting the splicing regulators of exon 12 of the Tak1 gene, inducing variant switching between Tak1-A and Tak1-B. We also designed SSOs capable of knockdown both Tak1 variants by inducing the aberrant splicing of exon 4. The Vivo-morpholino SSOs showed significant splice-switching of Tak1 in mouse liver, with a persistence of at least 10 days after initial SSOs delivery. Bioinformatics analysis indicated a lipid metabolism-related function for Tak1-B but not Tak1-A. The conversion of Tak1-B to Tak1-A consistently led to significant accumulation of lipids in cultured AML12 cells, as well as the dysregulation of several lipid metabolism-related genes in mouse liver. Different functional properties of the two isoforms may explain the conflicting functions previously reported for Tak1. In conclusion, our research clarified the different functions of Tak1 isoforms, and provided an efficient strategy for the functional research of the AS isoforms.

Shape selective bifacial recognition of double helical DNA

An impressive array of antigene approaches has been developed for recognition of double helical DNA over the past three decades; however, few have exploited the 'Watson-Crick' base-pairing rules for establishing sequence-specific recognition. One approach employs peptide nucleic acid as a molecular reagent and strand invasion as a binding mode. However, even with integration of the latest conformationally-preorganized backbone design, such an approach is generally confined to sub-physiological conditions due to the lack of binding energy. Here we report the use of a class of shape-selective, bifacial nucleic acid recognition elements, namely Janus bases, for targeting double helical DNA or RNA. Binding occurs in a highly sequence-specific manner under physiologically relevant conditions. The work may provide a foundation for the design of oligonucleotides for targeting the secondary and tertiary structures of nucleic acid biopolymers.