Investigating the implications of CFTR exon skipping using a Cftr exon 9 deleted mouse model

Introduction: Severity and disease progression in people with Cystic Fibrosis (CF) is typically dependent on their genotype. One potential therapeutic strategy for people with specific mutations is exon skipping with antisense oligonucleotides (AO). CFTR exon 9 is an in-frame exon and hence the exclusion of this exon would excise only 31 amino acids but not alter the reading frame of the remaining mRNA. Splice mutations 1209 + 1 G > C and 1209 + 2 T > G were documented to cause CFTR exon 9 skipping and these variants were reported to manifest as a milder CF disease, therefore exon 9 skipping could be beneficial for people with class I mutations that affect exon 9 such as p.Trp401X. While the impact of exon 9 skipping on gene expression and cellular pathways can be studied in cells in vitro, trace amount of full-length normal or mutated material could confound the evaluation. To overcome this limitation, the impact of CFTR exon 9 skipping on disease phenotype and severity is more effectively evaluated in a small animal model. It was hypothesised that antisense oligonucleotide-mediated skipping this particular exon could result in a “mild mouse CF phenotype”. Methods: Cftr exon 9 deleted mice were generated using homologous recombination. Survival of homozygous (CftrΔ9/Δ9) and heterozygous (CftrΔ9/+) mice was compared to that of other CF mouse models, and lung and intestinal organ histology examined for any pathologies. Primary airway epithelial cells (pAECs) were harvested from CftrΔ9/Δ9 mice and cultured at the Air Liquid Interface for CFTR functional assessment using Ussing Chamber analysis. Results: A CftrΔ9/Δ9 mouse model presented with intestinal obstructions, and at time of weaning (21 days). CftrΔ9/Δ9 mice had a survival rate of 83% that dropped to 38% by day 50. Histological sections of the small intestine from CftrΔ9/Δ9 mice showed more goblet cells and mucus accumulation than samples from the CftrΔ9/+ littermates. Airway epithelial cell cultures established from CftrΔ9/Δ9 mice were not responsive to forskolin stimulation. Summary: The effect of Cftr exon 9 deletion on Cftr function was assessed and it was determined that the encoded Cftr isoform did not result in a milder “mouse CF disease phenotype,” suggesting that Cftr exon 9 is not dispensable, although further investigation in human CF pAECs would be required to confirm this observation

Antisense suppression of donor splice site mutations in the dystrophin gene transcript

We describe two donor splice site mutations, affecting dystrophin exons 16 and 45 that led to Duchenne muscular dystrophy (DMD), through catastrophic inactivation of the mRNA. These gene lesions unexpectedly resulted in the retention of the downstream introns, thereby increasing the length of the dystrophin mRNA by 20.2 and 36 kb, respectively. Splice-switching antisense oligomers targeted to exon 16 excised this in-frame exon and the following intron from the patient dystrophin transcript very efficiently in vitro, thereby restoring the reading frame and allowing synthesis of near-normal levels of a putatively functional dystrophin isoform. In contrast, targeting splice-switching oligomers to exon 45 in patient cells promoted only modest levels of an out-of-frame dystrophin transcript after transfection at high oligomer concentrations, whereas dual targeting of exons 44 and 45 or 45 and 46 resulted in more efficient exon skipping, with concomitant removal of intron 45. The splice site mutations reported here appear highly amenable to antisense oligomer intervention. We suggest that other splice site mutations may need to be evaluated for oligomer interventions on a case-by-case basis

Outcome in patients perceived as receiving excessive care across different ethical climates: a prospective study in 68 intensive care units in Europe and the USA

Purpose: Whether the quality of the ethical climate in the intensive care unit (ICU) improves the identification of patients receiving excessive care and affects patient outcomes is unknown. Methods: In this prospective observational study, perceptions of excessive care (PECs) by clinicians working in 68 ICUs in Europe and the USA were collected daily during a 28-day period. The quality of the ethical climate in the ICUs was assessed via a validated questionnaire. We compared the combined endpoint (death, not at home or poor quality of life at 1 year) of patients with PECs and the time from PECs until written treatment-limitation decisions (TLDs) and death across the four climates defined via cluster analysis. Results: Of the 4747 eligible clinicians, 2992 (63%) evaluated the ethical climate in their ICU. Of the 321 and 623 patients not admitted for monitoring only in ICUs with a good (n = 12, 18%) and poor (n = 24, 35%) climate, 36 (11%) and 74 (12%), respectively were identified with PECs by at least two clinicians. Of the 35 and 71 identified patients with an available combined endpoint, 100% (95% CI 90.0–1.00) and 85.9% (75.4–92.0) (P = 0.02) attained that endpoint. The risk of death (HR 1.88, 95% CI 1.20–2.92) or receiving a written TLD (HR 2.32, CI 1.11–4.85) in patients with PECs by at least two clinicians was higher in ICUs with a good climate than in those with a poor one. The differences between ICUs with an average climate, with (n = 12, 18%) or without (n = 20, 29%) nursing involvement at the end of life, and ICUs with a poor climate were less obvious but still in favour of the former. Conclusion: Enhancing the quality of the ethical climate in the ICU may improve both the identification of patients receiving excessive care and the decision-making process at the end of life

Prevalence of stroke in Parkinson's disease: A postmortem study

The results of previous epidemiological studies of the relationship between Parkinson's disease and stroke have been conflicting; some showing a reduced risk of ischaemic and haemorrhagic stroke during life, and others indicating an increased likelihood of stroke-related death. We compared the frequency of cerebral infarcts and haemorrhages at postmortem in 100 cases of pathologically verified idiopathic Parkinson's disease and 100 age-matched control brains. No significant differences were found in the numbers of infarcts or haemorrhages or stroke-related deaths between the two groups. Our findings do not indicate either a protective effect against stroke, or a greater susceptibility to death from stroke, in the population studied

Mismatched single stranded antisense oligonucleotides can induce efficient dystrophin splice switching

Background Antisense oligomer induced exon skipping aims to reduce the severity of Duchenne muscular dystrophy by redirecting splicing during pre-RNA processing such that the causative mutation is by-passed and a shorter but partially functional Becker muscular dystrophy-like dystrophin isoform is produced. Normal exons are generally targeted to restore the dystrophin reading frame however, an appreciable subset of dystrophin mutations are intra-exonic and therefore have the potential to compromise oligomer efficiency, necessitating personalised oligomer design for some patients. Although antisense oligomers are easily personalised, it remains unclear whether all patient polymorphisms within antisense oligomer target sequences will require the costly process of producing and validating patient specific compounds. Methods Here we report preclinical testing of a panel of splice switching antisense oligomers, designed to excise exon 25 from the dystrophin transcript, in normal and dystrophic patient cells. These patient cells harbour a single base insertion in exon 25 that lies within the target sequence of an oligomer shown to be effective at removing exon 25. Results It was anticipated that such a mutation would compromise oligomer binding and efficiency. However, we show that, despite the mismatch an oligomer, designed and optimised to excise exon 25 from the normal dystrophin mRNA, removes the mutated exon 25 more efficiently than the mutation-specific oligomer. Conclusion This raises the possibility that mismatched AOs could still be therapeutically applicable in some cases, negating the necessity to produce patient-specific compounds

Investigation of age-related changes in LMNA splicing and expression of progerin in human skeletal muscles

Age-related changes in splice-forms of LMNA, which encodes the nuclear lamina proteins lamin A/C, have not been investigated in skeletal muscle. In the rare premature ageing disease, Hutchinson-Gilford progeria syndrome (HGPS), de novo point mutations in LMNA activate a cryptic splice site in exon 11, resulting in a 150 base deletion in LMNA mRNA and accumulation of a truncated protein isoform, progerin. The LMNA ∆150 progerin transcript has also been found in trace quantities in tissues of healthy people and its implication in ‘natural’ ageing has been proposed. We therefore investigated the expression of progerin and lamin A/C in normal human and mouse skeletal muscles of different ages. LMNA ∆150 was detected in most muscle samples from healthy individuals aged 16-71 years, but was not present in any mouse muscle samples up to the age of 18 months. Real time qPCR of human muscle samples showed that there was an age-related increase in both the full length lamin A and LMNA ∆150 transcripts, whereas their protein levels did not change significantly with age. These findings indicate that there is a basal level of mis-splicing during LMNA expression that does not change with ageing in human muscle, but at levels that do not result in increased aberrant protein. The significance of these findings in the pathophysiology of muscle ageing is uncertain and warrants further investigation

Antisense oligonucleotide induction of progerin in human myogenic cells

We sought to use splice-switching antisense oligonucleotides to produce a model of accelerated ageing by enhancing expression of progerin, translated from a mis-spliced lamin A gene ( LMNA) transcript in human myogenic cells. The progerin transcript (LMNA Δ150) lacks the last 150 bases of exon 11, and is translated into a truncated protein associated with the severe premature ageing disease, Hutchinson-Gilford progeria syndrome (HGPS). HGPS arises from de novo mutations that activate a cryptic splice site in exon 11 of LMNA and result in progerin accumulation in tissues of mesodermal origin. Progerin has also been proposed to play a role in the 'natural' ageing process in tissues. We sought to test this hypothesis by producing a model of accelerated muscle ageing in human myogenic cells. A panel of splice-switching antisense oligonucleotides were designed to anneal across exon 11 of the LMNA pre-mRNA, and these compounds were transfected into primary human myogenic cells. RT-PCR showed that the majority of oligonucleotides were able to modify LMNA transcript processing. Oligonucleotides that annealed within the 150 base region of exon 11 that is missing in the progerin transcript, as well as those that targeted the normal exon 11 donor site induced the LMNA Δ150 transcript, but most oligonucleotides also generated variable levels of LMNA transcript missing the entire exon 11. Upon evaluation of different oligomer chemistries, the morpholino phosphorodiamidate oligonucleotides were found to be more efficient than the equivalent sequences prepared as oligonucleotides with 2′-O-methyl modified bases on a phosphorothioate backbone. The morpholino oligonucleotides induced nuclear localised progerin, demonstrated by immunostaining, and morphological nuclear changes typical of HGPS cells. We show that it is possible to induce progerin expression in myogenic cells using splice-switching oligonucleotides to redirect splicing of LMNA. This may offer a model to investigate the role of progerin in premature muscle ageing