Efficacy of Tezepelumab in Patients with Severe, Uncontrolled Asthma Across Multiple Clinically Relevant Subgroups in the NAVIGATOR Study.

INTRODUCTION: Many patients with severe asthma continue to experience symptoms and exacerbations despite treatment with standard-of-care therapy. In the phase 3 NAVIGATOR study, tezepelumab significantly reduced exacerbations over 52 weeks compared with placebo in patients with severe, uncontrolled asthma. This analysis assessed the efficacy of tezepelumab in reducing asthma exacerbations in various clinically relevant subgroups of patients in NAVIGATOR. METHODS: NAVIGATOR was a phase 3, multicentre, randomized, double-blind, placebo-controlled study. Participants (12-80 years old) with severe, uncontrolled asthma were randomized 1:1 to receive tezepelumab 210 mg or placebo subcutaneously every 4 weeks for 52 weeks. Pre-specified and post hoc analyses were performed to evaluate the annualized asthma exacerbation rate (AAER) over 52 weeks in clinically relevant subgroups of patients defined by baseline patient characteristics, medical history, exacerbation triggers, medication eligibility and medication use before and during the study. RESULTS: Tezepelumab reduced the AAER over 52 weeks compared with placebo across a wide range of patient subgroups assessed. Reductions in exacerbations were similar across subgroups defined by baseline patient characteristics, ranging from 48% (95% confidence interval [CI]: 21, 65) to 60% (95% CI: 44, 71) in subgroups analysed by sex, smoking history and body mass index. Among the asthma-related comorbidity subgroups investigated, patients with aspirin or NSAID sensitivity had the greatest reductions in AAER with tezepelumab compared with placebo (83%; 95% CI: 66, 91). In patients eligible to receive dupilumab, tezepelumab reduced exacerbations compared with placebo by 64% (95% CI: 54, 71). Reductions in the AAER with tezepelumab compared with placebo were also observed irrespective of exacerbation trigger category and the number of asthma controller medications patients were receiving at baseline. CONCLUSION: These findings further support the benefits of tezepelumab in patients with severe, uncontrolled asthma and can help to inform healthcare providers' treatment decisions. CLINICAL TRIAL REGISTRATION: NAVIGATOR (NCT03347279).

Efficacy of Biologics in Patients with Allergic Severe Asthma, Overall and by Blood Eosinophil Count: A Literature Review.

Patients with uncontrolled, allergic severe asthma may be prescribed biologic therapies to reduce exacerbations and improve disease control. Randomized controlled trials (RCTs) of these therapies have differed in design, with varying results overall and by baseline blood eosinophil count (BEC). This study describes published annualized asthma exacerbation rate (AAER) reductions from RCTs in patients with allergic severe asthma, overall and by baseline BEC category. A literature search was performed to identify published phase 3 RCT data of US Food and Drug Administration-approved biologics for severe asthma in patients with severe, uncontrolled asthma and confirmed sensitization to perennial aeroallergens. Analyses focused on AAER reduction versus placebo in the overall population and/or in those with an elevated or low BEC at baseline or screening. Baseline serum total immunoglobulin E levels varied between RCT populations. In patients with allergic severe asthma across all BEC categories, data were available for tezepelumab, dupilumab, benralizumab and omalizumab only; the greatest AAER reduction was observed with tezepelumab. In patients with allergic severe asthma and BECs of ≥ 260 cells/µL or ≥ 300 cells/µL, AAER reductions were observed with all biologics (tezepelumab, dupilumab, mepolizumab, benralizumab and omalizumab); the greatest AAER reduction was observed with tezepelumab and the smallest AAER reduction was observed with omalizumab. In patients with allergic severe asthma and BECs of < 260 cells/µL or < 300 cells/µL (regardless of historical BEC), an AAER reduction was observed with tezepelumab but not with benralizumab or omalizumab. Differential mechanisms of action may explain the differences in results observed between biologics. Among patients with allergic severe asthma, the efficacy of biologics in RCTs varied considerably overall and by BEC. Tezepelumab was the only biologic to demonstrate AAER reductions consistently across all subgroups. These differences can inform provider treatment decisions when selecting biologic treatments for patients with allergic severe asthma.

Effect of Tezepelumab on Lung Function in Patients With Severe, Uncontrolled Asthma in the Phase 3 NAVIGATOR Study.

INTRODUCTION: Severe asthma is associated with airway inflammation and airway obstruction. In the phase 3 NAVIGATOR study, tezepelumab treatment significantly improved pre-bronchodilator forced expiratory volume in 1 s (FEV1) compared with placebo in patients with severe, uncontrolled asthma. This analysis assessed the effect of tezepelumab versus placebo on additional lung function parameters in patients from NAVIGATOR. METHODS: NAVIGATOR was a multicenter, randomized, double-blind, placebo-controlled study. Patients (12-80 years old) receiving medium- or high-dose inhaled corticosteroids and at least one additional controller medication, with or without oral corticosteroids, were randomized 1:1 to tezepelumab 210 mg or placebo subcutaneously every 4 weeks for 52 weeks. Changes from baseline to week 52 in pre-bronchodilator FEV1, post-bronchodilator FEV1, forced vital capacity (FVC), pre-bronchodilator FEV1/FVC ratio, pre-bronchodilator forced expiratory flow between 25 and 75% of vital capacity (FEF25-75), and morning and evening peak expiratory flow (PEF) were assessed. RESULTS: Tezepelumab treatment improved all evaluated lung function parameters over 52 weeks compared with placebo [least-squares mean difference (95% confidence interval): pre-bronchodilator FEV1, 0.13 (0.08, 0.18) L; post-bronchodilator FEV1, 0.12 (0.07, 0.16) L; FVC, 0.13 (0.07, 0.19) L; FEV1/FVC ratio, 2.06% (1.22%, 2.90%); FEF25-75, 0.13 (0.07, 0.19) L/s; morning PEF, 16.6 (8.1, 25.1) L/min; and evening PEF, 14.9 (6.3, 23.4) L/min]. Improvements were observed as early as weeks 1-2 and were maintained over 52 weeks. Greater improvements in lung function compared with placebo were observed in patients with a disease duration of less than 20 years, those with baseline post-bronchodilator FEV1 reversibility of at least 20%, and in patients with a baseline post-bronchodilator FEV1/FVC ratio of less than 0.7. CONCLUSION: These findings further support the benefits of tezepelumab treatment in improving airflow limitation in patients with severe, uncontrolled asthma. CLINICAL TRIAL REGISTRATION: NAVIGATOR (NCT03347279).

Effect of tezepelumab on healthcare utilization in patients with severe, uncontrolled asthma: The NAVIGATOR study.

BACKGROUND: Tezepelumab, a human monoclonal antibody, blocks thymic stromal lymphopoietin. In the phase 3 NAVIGATOR study, tezepelumab reduced exacerbations and improved lung function, asthma control, and health-related quality of life compared with placebo in patients with severe, uncontrolled asthma. However, little is known about the impact of tezepelumab on healthcare utilization (HCU) in these patients. OBJECTIVE: To evaluate to what extent tezepelumab reduces patients' HCU. METHODS: In NAVIGATOR, patients were randomized to receive subcutaneous tezepelumab 210 mg or placebo, every 4 weeks for 52 weeks. For this analysis, the main outcomes of interest were asthma-related HCU. A blinded, systematic analysis of the symptoms and HCU recorded in the investigator-reported narratives describing exacerbation-related hospitalizations was also conducted; the narratives included blinded ratings of event intensity, recorded as mild, moderate, or severe. RESULTS: Recipients of tezepelumab (n = 528) required fewer asthma-related unscheduled specialist visits (tezepelumab, 285 events; placebo, 406 events), telephone calls with a healthcare provider (tezepelumab, 234; placebo, 599), ambulance transports (tezepelumab, 5; placebo, 22), emergency department visits (without subsequent hospitalization; tezepelumab, 16; placebo, 37), hospitalizations (tezepelumab, 14; placebo, 78), and intensive care days (tezepelumab, 0; placebo, 31) than did recipients of placebo (n = 531). Among patients with asthma exacerbation-related hospitalizations, 38% of those hospitalized and receiving tezepelumab (5/13) had an event rated as severe, compared with 82% of those hospitalized and receiving placebo (32/39). CONCLUSION: Tezepelumab substantially reduced HCU across all outcomes measured compared with placebo, in addition to the severity of asthma exacerbations requiring hospitalization. Tezepelumab can reduce the overall burden of disease of severe, uncontrolled asthma. CLINICAL TRIAL REGISTRATION: ClinicalTrials.gov (https://clinicaltrials.gov/ct2/home), identifier: NCT03347279.

Efficacy and safety of tezepelumab in patients recruited in Japan who participated in the phase 3 NAVIGATOR study.

BACKGROUND: Tezepelumab, a human monoclonal antibody, blocks the activity of thymic stromal lymphopoietin. In the phase 3 NAVIGATOR study (NCT03347279), tezepelumab reduced exacerbations by 56% compared with placebo in adults and adolescents with severe, uncontrolled asthma. This analysis evaluated the efficacy and safety of tezepelumab in NAVIGATOR patients recruited in Japan. METHODS: NAVIGATOR was a phase 3, multicenter, randomized, double-blind, placebo-controlled study. Patients (12-80 years old) were randomized 1:1 to receive tezepelumab 210 mg or placebo subcutaneously every 4 weeks for 52 weeks. Endpoints assessed included: the annualized asthma exacerbation rate (AAER) over 52 weeks (primary endpoint) and the change from baseline to week 52 in pre-bronchodilator forced expiratory volume in 1 s (FEV1) and Asthma Control Questionnaire (ACQ)-6 score. The safety of tezepelumab was also assessed. RESULTS: Overall, 97 patients recruited in Japan were randomized (tezepelumab, n = 58; placebo, n = 39). The AAER over 52 weeks was 1.54 (95% confidence interval [CI]: 0.90, 2.64) with tezepelumab compared with 3.12 (95% CI: 1.82, 5.35) with placebo (rate ratio: 0.49 [95% CI: 0.25, 0.99]; 51% reduction). For tezepelumab and placebo, the least-squares mean (standard error) change from baseline to week 52 for pre-bronchodilator FEV1 was 0.23 (0.06) L and 0.19 (0.07) L and the ACQ-6 score was -1.12 (0.15) and -0.97 (0.19), respectively. The frequency of adverse events was similar between treatment groups (tezepelumab, 86.2%; placebo, 87.2%). CONCLUSIONS: Tezepelumab reduced exacerbations compared with placebo, and was well tolerated, in NAVIGATOR patients with severe, uncontrolled asthma recruited in Japan.

Microvasculopathy in spinal muscular atrophy is driven by a reversible autonomous endothelial cell defect.

Spinal muscular atrophy (SMA) is a neuromuscular disorder due to degeneration of spinal cord motor neurons caused by deficiency of the ubiquitously expressed SMN protein. Here, we present a retinal vascular defect in patients, recapitulated in SMA transgenic mice, driven by failure of angiogenesis and maturation of blood vessels. Importantly, the retinal vascular phenotype was rescued by early, systemic SMN restoration therapy in SMA mice. We also demonstrate in patients an unfavorable imbalance between endothelial injury and repair, as indicated by increased circulating endothelial cell counts and decreased endothelial progenitor cell counts in blood circulation. The cellular markers of endothelial injury were associated with disease severity and improved following SMN restoration treatment in cultured endothelial cells from patients. Finally, we demonstrated autonomous defects in angiogenesis and blood vessel formation, secondary to SMN deficiency in cultured human and mouse endothelial cells, as the underlying cellular mechanism of microvascular pathology. Our cellular and vascular biomarker findings indicate microvasculopathy as a fundamental feature of SMA. Our findings provide mechanistic insights into previously described SMA microvascular complications, and highlight the functional role of SMN in the periphery, including the vascular system, where deficiency of SMN can be addressed by systemic SMN-restoring treatment.

Income Responses to the Affordable Care Act: Evidence from a Premium Tax Credit Notch.

We examine responses to the ACA subsidy for Marketplace health insurance in the first year of subsidy availability. Drawing on federal tax data and focusing on a notch in the schedule where eligibility is lost, we document that taxpayers lowered their income to remain eligible for the subsidy. The observed bunching is modest relative to the size of the notch, which, consistent with larger responses we detect in additional analyses among certain subgroups, is likely explained by significant optimization frictions. Finally, we find suggestive evidence that increased deductions drive some of the response, while reduced labor supply also plays a role.

Evaluation of Antibody Properties and Clinically Relevant Immunogenicity, Anaphylaxis, and Hypersensitivity Reactions in Two Phase III Trials of Tralokinumab in Severe, Uncontrolled Asthma.

INTRODUCTION: Tralokinumab is a monoclonal antibody (mAb) that neutralizes interleukin (IL)-13, a cytokine involved in the pathogenesis of asthma. OBJECTIVE: The objectives of this study were to characterize the potential immunogenic properties of tralokinumab and report data for anti-drug antibodies (ADAs) and hypersensitivity reactions from two phase III clinical trials. METHODS: The oligosaccharide structure of tralokinumab, Fab-arm exchange, and ADAs were characterized by standard techniques. Hypersensitivity adverse events (AEs) were evaluated in two pivotal clinical trials of tralokinumab in severe, uncontrolled asthma: STRATOS 1 and 2 (NCT02161757 and NCT02194699). RESULTS: No galactose-α-1,3-galactose (α-Gal) epitopes were found in the Fab region of tralokinumab and only 4.5% of glycoforms contained α-Gal in the Fc region. Under non-reducing conditions, Fab-arm exchange did not take place with another immunoglobulin (Ig) G4 mAb (mavrilimumab). However, following glutathione reduction, a hybrid antibody with monovalent bioactivity was detected. ADA incidences (titers) were as follows: STRATOS 1-every 2 weeks (Q2 W) 0.8% (26.0), every 4 weeks (Q4 W) 0.5% (26.0), placebo 0.8% (52.0); STRATOS 2-Q2 W 1.2% (39.0), placebo 0.8% (13.0). Participant-reported hypersensitivity AE rates were as follows: STRATOS 1-Q2 W 25.9%, Q4 W 25.0%, placebo 25.5%; STRATOS 2-Q2 W 13.2%, placebo 9.0%. External evaluation for anaphylaxis by Sampson criteria found no tralokinumab-related severe hypersensitivity or anaphylaxis reactions. CONCLUSION: Preclinical assessments suggested a low likelihood of immunogenicity for tralokinumab. In STRATOS 1 and 2, ADA incidence was low, no differences were found between tralokinumab-treated and placebo groups in reporting of hypersensitivity reactions, and there were no Sampson criteria-evaluated anaphylaxis events with tralokinumab treatment. Together, the results suggest that tralokinumab treatment would not increase the risk for severe hypersensitivity or anaphylactic reactions.

Systemic restoration of UBA1 ameliorates disease in spinal muscular atrophy.

The autosomal recessive neuromuscular disease spinal muscular atrophy (SMA) is caused by loss of survival motor neuron (SMN) protein. Molecular pathways that are disrupted downstream of SMN therefore represent potentially attractive therapeutic targets for SMA. Here, we demonstrate that therapeutic targeting of ubiquitin pathways disrupted as a consequence of SMN depletion, by increasing levels of one key ubiquitination enzyme (ubiquitin-like modifier activating enzyme 1 [UBA1]), represents a viable approach for treating SMA. Loss of UBA1 was a conserved response across mouse and zebrafish models of SMA as well as in patient induced pluripotent stem cell-derive motor neurons. Restoration of UBA1 was sufficient to rescue motor axon pathology and restore motor performance in SMA zebrafish. Adeno-associated virus serotype 9-UBA1 (AAV9-UBA1) gene therapy delivered systemic increases in UBA1 protein levels that were well tolerated over a prolonged period in healthy control mice. Systemic restoration of UBA1 in SMA mice ameliorated weight loss, increased survival and motor performance, and improved neuromuscular and organ pathology. AAV9-UBA1 therapy was also sufficient to reverse the widespread molecular perturbations in ubiquitin homeostasis that occur during SMA. We conclude that UBA1 represents a safe and effective therapeutic target for the treatment of both neuromuscular and systemic aspects of SMA.

Restoration of SMN in Schwann cells reverses myelination defects and improves neuromuscular function in spinal muscular atrophy.

Spinal muscular atrophy (SMA) is a neuromuscular disease caused by low levels of SMN protein, primarily affecting lower motor neurons. Recent evidence from SMA and related conditions suggests that glial cells can influence disease severity. Here, we investigated the role of glial cells in the peripheral nervous system by creating SMA mice selectively overexpressing SMN in myelinating Schwann cells (Smn-/-;SMN2tg/0;SMN1SC). Restoration of SMN protein levels restricted solely to Schwann cells reversed myelination defects, significantly improved neuromuscular function and ameliorated neuromuscular junction pathology in SMA mice. However, restoration of SMN in Schwann cells had no impact on motor neuron soma loss from the spinal cord or ongoing systemic and peripheral pathology. This study provides evidence for a defined, intrinsic contribution of glial cells to SMA disease pathogenesis and suggests that therapies designed to include Schwann cells in their target tissues are likely to be required in order to rescue myelination defects and associated disease symptoms.

The Impact of the ACA on Premiums: Evidence from the Self-Employed.

This article examines the impact of the Affordable Care Act on premiums by studying a segment of the nongroup market, the self-employed. Because self-employed health insurance premiums are deductible, tax data contain comprehensive individual-level information on the premiums paid by this group prior to the establishment of health insurance exchanges. We compare these prior premiums to reference silver premiums available on the exchanges and find that exchange premiums are 4.2 percent higher on average among the entire sample but 42.3 percent lower on average after taxes and subsidies. We also examine which type of exchange coverage would cost less than the individual's prior health insurance premiums and find that almost 60 percent of families could purchase bronze plans for less than their prior premiums, though only about a quarter could purchase platinum plans. After taxes and subsidies, the fractions increase to over 85 percent for bronze plans and over half for platinum plans.

Alleles that increase risk for type 2 diabetes mellitus are not associated with increased risk for Alzheimer's disease.

Although epidemiological studies suggest that type 2 diabetes mellitus (T2DM) increases the risk of late-onset Alzheimer's disease (LOAD), the biological basis of this relationship is not well understood. The aim of this study was to examine the genetic comorbidity between the 2 disorders and to investigate whether genetic liability to T2DM, estimated by a genotype risk scores based on T2DM associated loci, is associated with increased risk of LOAD. This study was performed in 2 stages. In stage 1, we combined genotypes for the top 15 T2DM-associated polymorphisms drawn from approximately 3000 individuals (1349 cases and 1351 control subjects) with extracted and/or imputed data from 6 genome-wide studies (>10,000 individuals; 4507 cases, 2183 controls, 4989 population controls) to form a genotype risk score and examined if this was associated with increased LOAD risk in a combined meta-analysis. In stage 2, we investigated the association of LOAD with an expanded T2DM score made of 45 well-established variants drawn from the 6 genome-wide studies. Results were combined in a meta-analysis. Both stage 1 and stage 2 T2DM risk scores were not associated with LOAD risk (odds ratio = 0.988; 95% confidence interval, 0.972-1.004; p = 0.144 and odds ratio = 0.993; 95% confidence interval, 0.983-1.003; p = 0.149 per allele, respectively). Contrary to expectation, genotype risk scores based on established T2DM candidates were not associated with increased risk of LOAD. The observed epidemiological associations between T2DM and LOAD could therefore be a consequence of secondary disease processes, pleiotropic mechanisms, and/or common environmental risk factors. Future work should focus on well-characterized longitudinal cohorts with extensive phenotypic and genetic data relevant to both LOAD and T2DM.

Label-free quantitative proteomic profiling identifies disruption of ubiquitin homeostasis as a key driver of Schwann cell defects in spinal muscular atrophy.

Low levels of survival of motor neuron (SMN) protein cause the neuromuscular disease spinal muscular atrophy (SMA), characterized by degeneration of lower motor neurons and atrophy of skeletal muscle. Recent work demonstrated that low levels of SMN also trigger pathological changes in Schwann cells, leading to abnormal axon myelination and disrupted deposition of extracellular matrix proteins in peripheral nerve. However, the molecular pathways linking SMN depletion to intrinsic defects in Schwann cells remained unclear. Label-free proteomics analysis of Schwann cells isolated from SMA mouse peripheral nerve revealed widespread changes to the Schwann cell proteome, including disruption to growth/proliferation, cell death/survival, and molecular transport pathways. Functional clustering analyses revealed significant disruption to a number of proteins contributing to ubiquitination pathways, including reduced levels of ubiquitin-like modifier activating enzyme 1 (Uba1). Pharmacological suppression of Uba1 in Schwann cells was sufficient to reproduce the defective myelination phenotype seen in SMA. These findings demonstrate an important role for SMN protein and ubiquitin-dependent pathways in maintaining Schwann cell homeostasis and provide significant additional experimental evidence supporting a key role for ubiquitin pathways and, Uba1 in particular, in driving SMA pathogenesis across a broad range of cells and tissues.

The influence of storage parameters on measurement of survival motor neuron (SMN) protein levels: implications for pre-clinical studies and clinical trials for spinal muscular atrophy.

Spinal muscular atrophy (SMA) is caused by low levels of survival motor neuron (SMN) protein. A growing number of potential therapeutic strategies for SMA are entering pre-clinical and clinical testing, including gene therapy and antisense oligonucleotide-based approaches. For many such studies SMN protein levels are used as one major readout of treatment efficacy, often necessitating comparisons between samples obtained at different times and/or using different protocols. Whether differences in tissue sampling strategies or storage parameters have an influence on measurable SMN levels remains to be determined. We assessed murine SMN protein immunoreactivity over time and under differing tissue storage conditions. SMN protein levels, measured using sensitive quantitative fluorescent western blotting, declined rapidly over a period of several days following sample collection, especially when protein was extracted immediately and stored at -20°C. Storage of samples at lower temperatures (-80°C), and as intact tissue, led to significantly better preservation of SMN immunoreactivity. However, considerable deterioration in measurable SMN levels occurred, even under optimal storage conditions. These issues need to be taken into consideration when designing and interpreting pre-clinical and clinical SMA studies where SMN protein levels are being measured.

Increased levels of UCHL1 are a compensatory response to disrupted ubiquitin homeostasis in spinal muscular atrophy and do not represent a viable therapeutic target.

AIM: Levels of ubiquitin carboxyl-terminal hydrolase L1 (UCHL1) are robustly increased in spinal muscular atrophy (SMA) patient fibroblasts and mouse models. We therefore wanted to establish whether changes in UCHL1 contribute directly to disease pathogenesis, and to assess whether pharmacological inhibition of UCHL1 represents a viable therapeutic option for SMA. METHODS: SMA mice and control littermates received a pharmacological UCHL1 inhibitor (LDN-57444) or DMSO vehicle. Survival and weight were monitored daily, a righting test of motor performance was performed, and motor neurone loss, muscle fibre atrophy and neuromuscular junction pathology were all quantified. Ubiquitin-like modifier activating enzyme 1 (Uba1) was then pharmacologically inhibited in neurones in vitro to examine the relationship between Uba1 levels and UCHL1 in SMA. RESULTS: Pharmacological inhibition of UCHL1 failed to improve survival, motor symptoms or neuromuscular pathology in SMA mice and actually precipitated the onset of weight loss. LDN-57444 treatment significantly decreased spinal cord mono-ubiquitin levels, further exacerbating ubiquitination defects in SMA mice. Pharmacological inhibition of Uba1, levels of which are robustly reduced in SMA, was sufficient to induce accumulation of UCHL1 in primary neuronal cultures. CONCLUSION: Pharmacological inhibition of UCHL1 exacerbates rather than ameliorates disease symptoms in a mouse model of SMA. Thus, pharmacological inhibition of UCHL1 is not a viable therapeutic target for SMA. Moreover, increased levels of UCHL1 in SMA likely represent a downstream consequence of decreased Uba1 levels, indicative of an attempted supportive compensatory response to defects in ubiquitin homeostasis caused by low levels of SMN protein.

Dysregulation of ubiquitin homeostasis and ß-catenin signaling promote spinal muscular atrophy.

The autosomal recessive neurodegenerative disease spinal muscular atrophy (SMA) results from low levels of survival motor neuron (SMN) protein; however, it is unclear how reduced SMN promotes SMA development. Here, we determined that ubiquitin-dependent pathways regulate neuromuscular pathology in SMA. Using mouse models of SMA, we observed widespread perturbations in ubiquitin homeostasis, including reduced levels of ubiquitin-like modifier activating enzyme 1 (UBA1). SMN physically interacted with UBA1 in neurons, and disruption of Uba1 mRNA splicing was observed in the spinal cords of SMA mice exhibiting disease symptoms. Pharmacological or genetic suppression of UBA1 was sufficient to recapitulate an SMA-like neuromuscular pathology in zebrafish, suggesting that UBA1 directly contributes to disease pathogenesis. Dysregulation of UBA1 and subsequent ubiquitination pathways led to ß-catenin accumulation, and pharmacological inhibition of ß-catenin robustly ameliorated neuromuscular pathology in zebrafish, Drosophila, and mouse models of SMA. UBA1-associated disruption of ß-catenin was restricted to the neuromuscular system in SMA mice; therefore, pharmacological inhibition of ß-catenin in these animals failed to prevent systemic pathology in peripheral tissues and organs, indicating fundamental molecular differences between neuromuscular and systemic SMA pathology. Our data indicate that SMA-associated reduction of UBA1 contributes to neuromuscular pathogenesis through disruption of ubiquitin homeostasis and subsequent ß-catenin signaling, highlighting ubiquitin homeostasis and ß-catenin as potential therapeutic targets for SMA.

SMN-dependent intrinsic defects in Schwann cells in mouse models of spinal muscular atrophy.

Low levels of survival of motor neuron (SMN) protein lead to spinal muscular atrophy (SMA). The major pathological hallmark of SMA is a loss of lower motor neurons from spinal cord and peripheral nerve. However, recent studies have revealed pathological changes in other cells and tissues of the neuromuscular system. Here, we demonstrate intrinsic, SMN-dependent defects in Schwann cells in SMA. Myelination in intercostal nerves was perturbed at early- and late-symptomatic stages of disease in two mouse models of SMA. Similarly, maturation of axo-glial interactions at paranodes was disrupted in SMA mice. In contrast, myelination of motor axons in the corticospinal tract of the spinal cord occurred normally. Schwann cells isolated from SMA mice had significantly reduced levels of SMN and failed to express key myelin proteins following differentiation, likely due to perturbations in protein translation and/or stability rather than transcriptional defects. Myelin protein expression was restored in SMA Schwann cells following transfection with an SMN construct. Co-cultures of healthy neurons with diseased Schwann cells revealed deficient myelination, suggestive of intrinsic defects in Schwann cells, as well as reduced neurite stability. Alongside myelination defects, SMA Schwann cells failed to express normal levels of key extracellular matrix proteins, including laminin α2. We conclude that Schwann cells require high levels of SMN protein for their normal development and function in vivo, with reduced levels of SMN resulting in myelination defects, delayed maturation of axo-glial interactions and abnormal composition of extracellular matrix in peripheral nerve.

Label-free proteomics identifies Calreticulin and GRP75/Mortalin as peripherally accessible protein biomarkers for spinal muscular atrophy.

BACKGROUND: Spinal muscular atrophy (SMA) is a neuromuscular disease resulting from mutations in the survival motor neuron 1 (SMN1) gene. Recent breakthroughs in preclinical research have highlighted several potential novel therapies for SMA, increasing the need for robust and sensitive clinical trial platforms for evaluating their effectiveness in human patient cohorts. Given that most clinical trials for SMA are likely to involve young children, there is a need for validated molecular biomarkers to assist with monitoring disease progression and establishing the effectiveness of therapies being tested. Proteomics technologies have recently been highlighted as a potentially powerful tool for such biomarker discovery. METHODS: We utilized label-free proteomics to identify individual proteins in pathologically-affected skeletal muscle from SMA mice that report directly on disease status. Quantitative fluorescent western blotting was then used to assess whether protein biomarkers were robustly changed in muscle, skin and blood from another mouse model of SMA, as well as in a small cohort of human SMA patient muscle biopsies. RESULTS: By comparing the protein composition of skeletal muscle in SMA mice at a pre-symptomatic time-point with the muscle proteome at a late-symptomatic time-point we identified increased expression of both Calreticulin and GRP75/Mortalin as robust indicators of disease progression in SMA mice. We report that these protein biomarkers were consistently modified in different mouse models of SMA, as well as across multiple skeletal muscles, and were also measurable in skin biopsies. Furthermore, Calreticulin and GRP75/Mortalin were measurable in muscle biopsy samples from human SMA patients. CONCLUSIONS: We conclude that label-free proteomics technology provides a powerful platform for biomarker identification in SMA, revealing Calreticulin and GRP75/Mortalin as peripherally accessible protein biomarkers capable of reporting on disease progression in samples of muscle and skin.