Neurodevelopmental and synaptic defects in DNAJC6 parkinsonism, amenable to gene therapy

DNAJC6 encodes auxilin, a co-chaperone protein involved in clathrin-mediated endocytosis (CME) at the presynaptic terminal. Biallelic mutations in DNAJC6 cause a complex, early-onset neurodegenerative disorder characterized by rapidly progressive parkinsonism-dystonia in childhood. The disease is commonly associated with additional neurodevelopmental, neurological and neuropsychiatric features. Currently, there are no disease-modifying treatments for this condition, resulting in significant morbidity and risk of premature mortality. To investigate the underlying disease mechanisms in childhood-onset DNAJC6 parkinsonism, we generated induced pluripotent stem cells (iPSC) from three patients harboring pathogenic loss-of-function DNAJC6 mutations and subsequently developed a midbrain dopaminergic (mDA) neuronal model of disease. When compared to age-matched and CRISPR-corrected isogenic controls, the neuronal cell model revealed disease-specific auxilin deficiency as well as disturbance of synaptic vesicle (SV) recycling and homeostasis. We also observed neurodevelopmental dysregulation affecting ventral midbrain patterning and neuronal maturation. In order to explore the feasibility of a viral vector-mediated gene therapy approach, iPSC-derived neuronal cultures were treated with lentiviral DNAJC6 gene transfer, which restored auxilin expression and rescued CME. Our patient-derived neuronal model provides deeper insights into the molecular mechanisms of auxilin deficiency as well as a robust platform for the development of targeted precision therapy approaches.

Expression of gain-of-function CFTR in cystic fibrosis airway cells restores epithelial function better than wild-type or codon-optimized CFTR

Class Ia/b cystic fibrosis transmembrane regulator (CFTR) variants cause severe lung disease in 10% of cystic fibrosis (CF) patients and are untreatable with small-molecule pharmaceuticals. Genetic replacement of CFTR offers a cure, but its effectiveness is limited in vivo. We hypothesized that enhancing protein levels (using codon optimization) and/or activity (using gain-of-function variants) of CFTR would more effectively restore function to CF bronchial epithelial cells. Three different variants of the CFTR protein were tested: codon optimized (high codon adaptation index [hCAI]), a gain-of-function (GOF) variant (K978C), and a combination of both (hˆK978C). In human embryonic kidney (HEK293T) cells, initial results showed that hCAI and hˆK978C produced greater than 10-fold more CFTR protein and displayed ∼4-fold greater activity than wild-type (WT) CFTR. However, functionality was profoundly different in CF bronchial epithelial cells. Here, K978C CFTR more potently restored essential epithelial functions (anion transport, airway surface liquid height, and pH) than WT CFTR. hCAI and hˆK978C CFTRs had limited impact because of mislocalization in the cell. These data provide a proof of principle showing that GOF variants may be more effective than codon-optimized forms of CFTR for CF gene therapy.

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Optimized lentiviral vector to restore full-length dystrophin via a cell-mediated approach in a mouse model of Duchenne muscular dystrophy

Duchenne muscular dystrophy (DMD) is a muscle wasting disorder caused by mutations in the DMD gene. Restoration of full-length dystrophin protein in skeletal muscle would have therapeutic benefit, but lentivirally mediated delivery of such a large gene in vivo has been hindered by lack of tissue specificity, limited transduction, and insufficient transgene expression. To address these problems, we developed a lentiviral vector, which contains a muscle-specific promoter and sequence-optimized full-length dystrophin, to constrain dystrophin expression to differentiated myotubes/myofibers and enhance the transgene expression. We further explored the efficiency of restoration of full-length dystrophin in vivo, by grafting DMD myoblasts that had been corrected by this optimized lentiviral vector intramuscularly into an immunodeficient DMD mouse model. We show that these lentivirally corrected DMD myoblasts effectively reconstituted full-length dystrophin expression in 93.58% ± 2.17% of the myotubes in vitro. Moreover, dystrophin was restored in 64.4% ± 2.87% of the donor-derived regenerated muscle fibers in vivo, which were able to recruit members of the dystrophin-glycoprotein complex at the sarcolemma. This study represents a significant advance over existing cell-mediated gene therapy strategies for DMD that aim to restore full-length dystrophin expression in skeletal muscle.

Transiently expressed CRISPR/Cas9 induces wild-type dystrophin in vitro in DMD patient myoblasts carrying duplications

Among the mutations arising in the DMD gene and causing Duchenne Muscular Dystrophy (DMD), 10–15% are multi-exon duplications. There are no current therapeutic approaches with the ability to excise large multi-exon duplications, leaving this patient cohort without mutation-specific treatment. Using CRISPR/Cas9 could provide a valid alternative to achieve targeted excision of genomic duplications of any size. Here we show that the expression of a single CRISPR/Cas9 nuclease targeting a genomic region within a DMD duplication can restore the production of wild-type dystrophin in vitro. We assessed the extent of dystrophin repair following both constitutive and transient nuclease expression by either transducing DMD patient-derived myoblasts with integrating lentiviral vectors or electroporating them with CRISPR/Cas9 expressing plasmids. Comparing genomic, transcript and protein data, we observed that both continuous and transient nuclease expression resulted in approximately 50% dystrophin protein restoration in treated myoblasts. Our data demonstrate that a high transient expression profile of Cas9 circumvents its requirement of continuous expression within the cell for targeting DMD duplications. This proof-of-concept study therefore helps progress towards a clinically relevant gene editing strategy for in vivo dystrophin restoration, by highlighting important considerations for optimizing future therapeutic approaches.

Aromatic l-amino acid decarboxylase deficiency: a patient-derived neuronal model for precision therapies

Aromatic l-amino acid decarboxylase (AADC) deficiency is a complex inherited neurological disorder of monoamine synthesis which results in dopamine and serotonin deficiency. The majority of affected individuals have variable, though often severe cognitive and motor delay, with a complex movement disorder and high risk of premature mortality. For most, standard pharmacological treatment provides only limited clinical benefit. Promising gene therapy approaches are emerging, though may not be either suitable or easily accessible for all patients. To characterize the underlying disease pathophysiology and guide precision therapies, we generated a patient-derived midbrain dopaminergic neuronal model of AADC deficiency from induced pluripotent stem cells. The neuronal model recapitulates key disease features, including absent AADC enzyme activity and dysregulated dopamine metabolism. We observed developmental defects affecting synaptic maturation and neuronal electrical properties, which were improved by lentiviral gene therapy. Bioinformatic and biochemical analyses on recombinant AADC predicted that the activity of one variant could be improved by l-3,4-dihydroxyphenylalanine (l-DOPA) administration; this hypothesis was corroborated in the patient-derived neuronal model, where l-DOPA treatment leads to amelioration of dopamine metabolites. Our study has shown that patient-derived disease modelling provides further insight into the neurodevelopmental sequelae of AADC deficiency, as well as a robust platform to investigate and develop personalized therapeutic approaches.

Gene therapy for inherited metabolic diseases

Over the last two decades, gene therapy has been successfully translated to many rare diseases. The number of clinical trials is rapidly expanding and some gene therapy products have now received market authorisation in the western world. Inherited metabolic diseases (IMD) are orphan diseases frequently associated with a severe debilitating phenotype with limited therapeutic perspective. Gene therapy is progressively becoming a disease-changing therapeutic option for these patients. In this review, we aim to summarise the development of this emerging field detailing the main gene therapy strategies, routes of administration, viral and non-viral vectors and gene editing tools. We discuss the respective advantages and pitfalls of these gene therapy strategies and review their application in IMD, providing examples of clinical trials with lentiviral or adeno-associated viral gene therapy vectors in rare diseases. The rapid development of the field and implementation of gene therapy as a realistic therapeutic option for various IMD in a short term also require a good knowledge and understanding of these technologies from physicians to counsel the patients at best.

Effects of Mini-Dystrophin on Dystrophin-Deficient, Human Skeletal Muscle-Derived Cells

BACKGROUND

We are developing a novel therapy for Duchenne muscular dystrophy (DMD), involving the transplantation of autologous, skeletal muscle-derived stem cells that have been genetically corrected to express dystrophin. Dystrophin is normally expressed in activated satellite cells and in differentiated muscle fibres. However, in past preclinical validation studies, dystrophin transgenes have generally been driven by constitutive promoters that would be active at every stage of the myogenic differentiation process, including in proliferating muscle stem cells. It is not known whether artificial dystrophin expression would affect the properties of these cells.

AIMS

Our aims are to determine if mini-dystrophin expression affects the proliferation or myogenic differentiation of DMD skeletal muscle-derived cells.

METHODS

Skeletal muscle-derived cells from a DMD patient were transduced with lentivirus coding for mini-dystrophins (R3-R13 spectrin-like repeats (ΔR3R13) or hinge2 to spectrin-like repeats R23 (ΔH2R23)) with EGFP (enhanced green fluorescence protein) fused to the C-terminus, driven by a constitutive promoter, spleen focus-forming virus (SFFV). Transduced cells were purified on the basis of GFP expression. Their proliferation and myogenic differentiation were quantified by ethynyl deoxyuridine (EdU) incorporation and fusion index. Furthermore, dystrophin small interfering ribonucleic acids (siRNAs) were transfected to the cells to reverse the effects of the mini-dystrophin. Finally, a phospho-mitogen-activated protein kinase (MAPK) array assay was performed to investigate signalling pathway changes caused by dystrophin expression.

RESULTS

Cell proliferation was not affected in cells transduced with ΔR3R13, but was significantly increased in cells transduced with ΔH2R23. The fusion index of myotubes derived from both ΔR3R13- and ΔH2R23 -expressing cells was significantly compromised in comparison to myotubes derived from non-transduced cells. Dystrophin siRNA transfection restored the differentiation of ΔH2R23-expressing cells. The Erk1/2- signalling pathway is altered in cells transduced with mini-dystrophin constructs.

CONCLUSIONS

Ectopic expression of dystrophin in cultured human skeletal muscle-derived cells may affect their proliferation and differentiation capacity. Caution should be taken when considering genetic correction of autologous stem cells to express dystrophin driven by a constitutive promoter.

SUN-112 Arcuate 11-Betahydroxysteroid Dehydrogenase Type1 Regulates Energy Homeostasis

Introduction: Despite the ongoing increase in the prevalence of obesity, there are few licensed anti-obesity medications, and these therapies have limited efficacy and significant side effects. Therefore, new treatments are being developed, including 11-βhydroxysteroid dehydrogenase type1 (11βHSD1) inhibitors. In vivo, the enzyme 11-βhydroxysteroid dehydrogenase type1 (11βHSD1), converts the inactive glucocorticoid, 11-dehydrocorticosterone, to its active form (corticosterone). Tissue-specific 11βHSD1 has been reported to be important in the development of obesity. 11βHSD1 is expressed in the arcuate nucleus (ARC), a major hypothalamic centre which regulates energy homeostasis. We investigated the effect of modulation of intra-ARC 11βHSD1 expression on appetite and body weight in rodents. Methods: Experiments were performed using adult male Wistar rats fed a standard chow diet. In the overexpression experiment, recombinant adeno-associated virus (rAAV) encoding 11βHSD1 (rAAV-S11βHSD1) was injected bilaterally into the ARC of 12 rats and rAAV expressing green fluorescent protein (rAAV-GFP) was injected bilaterally into the ARC of 12 control rats. In the underexpression experiment, rAAV encoding small interfering RNA to 11βHSD1 (rAAV-si11βHSD1) was injected bilaterally into the ARC of 12 rats and rAAV-GFP injected into the ARC of 12 control rats. Starting 1 week post-surgery, body weight and food intake were measured three times a week for 10 weeks. At the end of the experiments, tissues and plasma were collected for gene expression and hormone analysis. Results and Conclusions: Compared to controls, ARC 11βHSD1 overexpression increased ARC corticosterone levels (iARC-S11βHSD1 243±34pg/mg vs iARC-GFP 89±39pg/mg, p<0.05), resulting in hyperphagia and 6% greater weight gain. ARC 11βHSD1 underexpression decreased ARC corticosterone levels by 47% (iARC-si11βHSD1 124.9±14.59pg/mg vs iARC-GFP 262.1±47.3pg/mg, p=0.01), resulting in 5% lower weight gain and a 1.7-fold increase in interscapular brown adipose tissue uncoupling protein-1 expression compared to controls. Corticosterone levels were unchanged in the neighbouring paraventricular nucleus. Additonally, systemic ACTH and corticosterone were unaffected by altered ARC 11βHSD1 expression. Our results suggest ARC 11βHSD1 plays a significant role in the regulation of energy homeostasis. Therefore, the novel class of therapies, 11βHSD1 inhibitors, may require central activity for maximal anti-obesity efficacy. Sources of Support: MRC MR/M004171/1, NIHR RP-2014-05-001, BBSRC BB/E52708X, FP7- HEALTH- 2009- 241592 EuroCHIP Grant

Acute coronary syndromes following abrupt cessation of oral propranolol therapy

Abrupt cessation of oral propranolol therapy was followed by 15 acute coronary events in 14 patients with severe angina who had been receiving propranolol in daily doses of 80 to 400 mg for periods of 7 days to 6 years. Propranolol had been stopped 1 to 14 days before each acute event because of angiographic study (seven patients), increasing symptoms (three), acute coronary insufficiency (one), asymptomatic bradycardia (one), elective surgery (one) and unknown reasons (two). Before abrupt cessation of propranolol treatment anginal symptoms had been stable in six instances but had increased in the other nine. Cessation was followed by rapid progression of symptoms prior to 11 of the 15 acute events. There were six acute transmural myocardial infarctions with three deaths, three intramural myocardial infarctions, one with ventricular fibrillation, and six episodes of acute coronary insufficiency, Unstable angina followed nine of the events and responded to propranolol therapy (160 to 320 mg/d) in eight instances. Three other patients underwent aortocoronary bypass surgery; perioperative acute myocardial infarction occurred in two. These data suggest that in a minority of patients abrupt cessation of propranolol may be hazardous, particularly in severe or unstable disease. Cessation or propranolol therapy in such patients should be gradual and closely observed. Recurrent symptoms respond to reinstitution of propranolol therapy.