Multicenter expanded access program for access to investigational products for amyotrophic lateral sclerosis

INTRODUCTION/AIMS

Expanded access (EA) is a Food and Drug Administration-regulated pathway to provide access to investigational products (IPs) to individuals with serious diseases who are ineligible for clinical trials. The aim of this report is to share the design and operations of a multicenter, multidrug EA program for amyotrophic lateral sclerosis (ALS) across nine US centers.

METHODS

A central coordination center was established to design and conduct the program. Templated documents and processes were developed to streamline study design, regulatory submissions, and clinical operations across protocols. The program included three protocols and provided access to IPs that were being tested in respective regimens of the HEALEY ALS Platform Trial (verdiperstat, CNM-Au8, and pridopidine). Clinical and safety data were collected in all EA protocols (EAPs). The program cohorts comprised participants who were not eligible for the platform trial, including participants at advanced stages of disease progression and with long disease duration.

RESULTS

A total of 85 participants were screened across the 3 EAPs from July 2021 to September 2022. The screen failure rate was 3.5%. Enrollment for the regimens of the platform trial was completed as planned and results informed the duration of the corresponding EAP. The verdiperstat EAP was concluded in December 2022. Mean duration of participation in the verdiperstat EAP was 5.8 ± 4.1 months. The CNM-Au8 and pridopidine EAPs are ongoing.

DISCUSSION

Multicenter EAPs conducted in parallel to randomized clinical trials for ALS can successfully enroll participants who do not qualify for clinical trials.

Systemic delivery of mutant huntingtin lowering antisense oligonucleotides to the brain using apolipoprotein A-I nanodisks for Huntington disease

Efficient delivery of therapeutics to the central nervous system (CNS) remains a major challenge for the treatment of neurological diseases. Huntington disease (HD) is a dominantly inherited neurodegenerative disorder caused by a CAG trinucleotide expansion mutation in the HTT gene which codes for a toxic mutant huntingtin (mHTT) protein. Pharmacological reduction of mHTT in the CNS using antisense oligonucleotides (ASO) ameliorates HD-like phenotypes in rodent models of HD, with such therapies being investigated in clinical trials for HD. In this study, we report the optimization of apolipoprotein A-I nanodisks (apoA-I NDs) as vehicles for delivery of a HTT-targeted ASO (HTT ASO) to the brain and peripheral organs for HD. We demonstrate that apoA-I wild type (WT) and the apoA-I K133C mutant incubated with a synthetic lipid, 1,2-dimyristoyl-sn-glycero-3-phosphocholine, can self-assemble into monodisperse discoidal particles with diameters <20 nm that transmigrate across an in vitro blood-brain barrier model of HD. We demonstrate that apoA-I NDs are well tolerated in vivo, and that apoA-I K133C NDs show enhanced distribution to the CNS and peripheral organs compared to apoA-I WT NDs following systemic administration. ApoA-I K133C conjugated with HTT ASO forms NDs (HTT ASO NDs) that induce significant mHTT lowering in the liver, skeletal muscle and heart as well as in the brain when delivered intravenously in the BACHD mouse model of HD. Furthermore, HTT ASO NDs increase the magnitude of mHTT lowering in the striatum and cortex compared to HTT ASO alone following intracerebroventricular administration. These findings demonstrate the potential utility of apoA-I NDs as biocompatible vehicles for enhancing delivery of mutant HTT lowering ASOs to the CNS and peripheral organs for HD.

Reducing huntingtin by immunotherapy delays disease progression in a mouse model of Huntington disease

In Huntington disease (HD), the mutant huntingtin (mtHTT) protein is the principal cause of pathological changes that initiate primarily along the cortico-striatal axis. mtHTT is ubiquitously expressed and there is, accordingly, growing recognition that HD is a systemic disorder with functional interplay between the brain and the periphery. We have developed a monoclonal antibody, C6-17, targeting an exposed region of HTT near the aa586 Caspase 6 cleavage site. As recently published, mAB C6-17 can block cell-to-cell propagation of mtHTT in vitro. In order to reduce the burden of the mutant protein in vivo, we queried whether extracellular mtHTT could be therapeutically targeted in YAC128 HD mice. In a series of proof of concept experiments, we found that systemic mAB C6-17 treatment resulted in the distribution of the mAB C6-17 to peripheral and CNS tissues and led to the reduction of HTT protein levels. Compared to CTRL mAB or vehicle treated mice, the mAB C6-17 treated YAC128 animals showed improved body weight and motor behaviors, a delayed progression in motor deficits and reduced striatal EM48 immunoreactivity. These results provide the first proof of concept for the feasibility and therapeutic efficacy of an antibody-based anti-HTT passive immunization approach and suggest this modality as a potential new HD treatment strategy.

Huntingtin Decreases Susceptibility to a Spontaneous Seizure Disorder in FVN/B Mice

Huntington disease (HD) is an adult-onset neurodegenerative disorder that is caused by a trinucleotide CAG repeat expansion in the HTT gene that codes for the protein huntingtin (HTT in humans or Htt in mice). HTT is a multi-functional, ubiquitously expressed protein that is essential for embryonic survival, normal neurodevelopment, and adult brain function. The ability of wild-type HTT to protect neurons against various forms of death raises the possibility that loss of normal HTT function may worsen disease progression in HD. Huntingtin-lowering therapeutics are being evaluated in clinical trials for HD, but concerns have been raised that decreasing wild-type HTT levels may have adverse effects. Here we show that Htt levels modulate the occurrence of an idiopathic seizure disorder that spontaneously occurs in approximately 28% of FVB/N mice, which we have called FVB/N Seizure Disorder with SUDEP (FSDS). These abnormal FVB/N mice demonstrate the cardinal features of mouse models of epilepsy including spontaneous seizures, astrocytosis, neuronal hypertrophy, upregulation of brain-derived neurotrophic factor (BDNF), and sudden seizure-related death. Interestingly, mice heterozygous for the targeted inactivation of Htt (Htt+/- mice) exhibit an increased frequency of this disorder (71% FSDS phenotype), while over-expression of either full length wild-type HTT in YAC18 mice or full length mutant HTT in YAC128 mice completely prevents it (0% FSDS phenotype). Examination of the mechanism underlying huntingtin's ability to modulate the frequency of this seizure disorder indicated that over-expression of full length HTT can promote neuronal survival following seizures. Overall, our results demonstrate a protective role for huntingtin in this form of epilepsy and provide a plausible explanation for the observation of seizures in the juvenile form of HD, Lopes-Maciel-Rodan syndrome, and Wolf-Hirschhorn syndrome. Adverse effects caused by decreasing huntingtin levels have ramifications for huntingtin-lowering therapies that are being developed to treat HD.

Limitations of Dual-Single Guide RNA CRISPR Strategies for the Treatment of Central Nervous System Genetic Disorders

Huntington's disease (HD) is a fatal neurodegenerative disorder caused by a toxic gain-of-function CAG expansion in the first exon of the huntingtin (HTT) gene. The monogenic nature of HD makes mutant HTT (mHTT) inactivation a promising therapeutic strategy. Single nucleotide polymorphisms frequently associated with CAG expansion have been explored to selectively inactivate mHTT allele using the CRISPR/Cas9 system. One of such allele-selective approaches consists of excising a region flanking the first exon of mHTT by inducing simultaneous double-strand breaks at upstream and downstream positions of the mHTT exon 1. The removal of the first exon of mHTT deletes the CAG expansion and important transcription regulatory sites, leading to mHTT inactivation. However, the frequency of deletion events is yet to be quantified either in vitro or in vivo. Here, we developed accurate quantitative digital polymerase chain reaction-based assays to assess HTT exon 1 deletion in vitro and in fully humanized HU97/18 mice. Our results demonstrate that dual-single guide RNA (sgRNA) strategies are efficient and that 67% of HTT editing events are leading to exon 1 deletion in HEK293T cells. In contrast, these sgRNA actively cleaved HTT in HU97/18 mice, but most editing events do not lead to exon 1 deletion (10% exon 1 deletion). We also showed that the in vivo editing pattern is not affected by CAG expansion but may potentially be due to the presence of multiple copies of wildtype (wt)/mHTT genes HU97/18 mice as well as the slow kinetics of AAV-mediated CRISPR/Cas9 delivery.

Preclinical Development and Characterization of Novel Adeno-Associated Viral Vectors for the Treatment of Lipoprotein Lipase Deficiency

Lipoprotein lipase deficiency (LPLD) results from mutations within the lipoprotein lipase (LPL) gene that lead to a complete lack of catalytically active LPL protein. Glybera was one of the first adeno-associated virus (AAV) gene replacement therapy to receive European Medicines Agency regulatory approval for the treatment of LPLD. However, Glybera is no longer marketed potentially due to a combination of economical, manufacturing, and vector-related issues. The aim of this study was to develop a more efficacious AAV gene therapy vector for LPLD. Following preclinical biodistribution, efficacy and non-Good Laboratory Practice toxicity studies with novel AAV1 and AAV8-based vectors in mice, we identified AAV8 pVR59. AAV8 pVR59 delivered a codon-optimized, human gain-of-function hLPLS447X transgene driven by a CAG promoter in an AAV8 capsid. AAV8 pVR59 was significantly more efficacious, at 10- to 100-fold lower doses, compared with an AAV1 vector based on Glybera, when delivered intramuscularly or intravenously, respectively, in mice with LPLD. Efficient gene transfer was observed within the injected skeletal muscle and liver following delivery of AAV8 pVR59, with long-term correction of LPLD phenotypes, including normalization of plasma triglycerides and lipid tolerance, for up to 6 months post-treatment. While intramuscular delivery of AAV8 pVR59 was well tolerated, intravenous administration augmented liver pathology. These results highlight the feasibility of developing a superior AAV vector for the treatment of LPLD and provide critical insight for initiating studies in larger animal models. The identification of an AAV gene therapy vector that is more efficacious at lower doses, when paired with recent advances in production and manufacturing technologies, will ultimately translate to increased safety and accessibility for patients.

Delivery of mutant huntingtin-lowering antisense oligonucleotides to the brain by intranasally administered apolipoprotein A-I nanodisks

Lowering mutant huntingtin (mHTT) in the central nervous system (CNS) using antisense oligonucleotides (ASOs) is a promising approach currently being evaluated in clinical trials for Huntington disease (HD). However, the therapeutic potential of ASOs in HD patients is limited by their inability to cross the blood-brain barrier (BBB). In non-human primates, intrathecal infusion of ASOs results in limited brain distribution, with higher ASO concentrations in superficial regions and lower concentrations in deeper regions, such as the basal ganglia. To address the need for improved delivery of ASOs to the brain, we are evaluating the therapeutic potential of apolipoprotein A-I nanodisks (apoA-I NDs) as novel delivery vehicles for mHTT-lowering ASOs to the CNS after intranasal administration. Here, we have demonstrated the ability of apoA-I nanodisks to bypass the BBB after intranasal delivery in the BACHD model of HD. Following intranasal administration of apoA-I NDs, apoA-I protein levels were elevated along the rostral-caudal brain axis, with highest levels in the most rostral brain regions including the olfactory bulb and frontal cortex. Double-label immunohistochemistry indicates that both the apoA-I and ASO deposit in neurons. Most importantly, a single intranasal dose of apoA-I ASO-NDs significantly reduces mHTT levels in the brain regions most affected in HD, namely the cortex and striatum. This approach represents a novel non-invasive means for improving delivery and brain distribution of oligonucleotide therapies and enhancing likelihood of efficacy. Improved ASO delivery to the brain has widespread application for treatment of many other CNS disorders.

Axonal ER Ca2+ Release Selectively Enhances Activity-Independent Glutamate Release in a Huntington Disease Model

Action potential (AP)-independent (miniature) neurotransmission occurs at all chemical synapses but remains poorly understood, particularly in pathologic contexts. Axonal endoplasmic reticulum (ER) Ca2+ stores are thought to influence miniature neurotransmission, and aberrant ER Ca2+ handling is implicated in progression of Huntington disease (HD). Here, we report elevated mEPSC frequencies in recordings from YAC128 mouse (HD-model) neurons (from cortical cultures and striatum-containing brain slices, both from male and female animals). Pharmacological experiments suggest that this is mediated indirectly by enhanced tonic ER Ca2+ release. Calcium imaging, using an axon-localized sensor, revealed slow AP-independent ER Ca2+ release waves in both YAC128 and WT cultures. These Ca2+ waves occurred at similar frequencies in both genotypes but spread less extensively and were of lower amplitude in YAC128 axons, consistent with axonal ER Ca2+ store depletion. Surprisingly, basal cytosolic Ca2+ levels were lower in YAC128 boutons and YAC128 mEPSCs were less sensitive to intracellular Ca2+ chelation. Together, these data suggest that elevated miniature glutamate release in YAC128 cultures is associated with axonal ER Ca2+ depletion but not directly mediated by ER Ca2+ release into the cytoplasm. In contrast to increased mEPSC frequencies, cultured YAC128 cortical neurons showed less frequent AP-dependent (spontaneous) Ca2+ events in soma and axons, although evoked glutamate release detected by an intensity-based glutamate-sensing fluorescence reporter in brain slices was similar between genotypes. Our results indicate that axonal ER dysfunction selectively elevates miniature glutamate release from cortical terminals in HD. This, together with reduced spontaneous cortical neuron firing, may cause a shift from activity-dependent to -independent glutamate release in HD, with potential implications for fidelity and plasticity of cortical excitatory signaling.SIGNIFICANCE STATEMENT Miniature neurotransmitter release persists at all chemical neuronal synapses in the absence of action potential firing but remains poorly understood, particularly in disease states. We show enhanced miniature glutamate release from cortical neurons in the YAC128 mouse Huntington disease model. This effect is mediated by axonal ER Ca2+ store depletion, but is not obviously due to elevated ER-to-cytosol Ca2+ release. Conversely, YAC128 cortical pyramidal neurons fired fewer action potentials and evoked cortical glutamate release was similar between WT an YAC128 preparations, indicating axonal ER depletion selectively enhances miniature glutamate release in YAC128 mice. These results extend our understanding of action potential independent neurotransmission and highlight a potential involvement of elevated miniature glutamate release in Huntington disease pathology.

A PET-CT study on neuroinflammation in Huntington's disease patients participating in a randomized trial with laquinimod

Microglia activation, an indicator of central nervous system inflammation, is believed to contribute to the pathology of Huntington's disease. Laquinimod is capable of regulating microglia. By targeting the translocator protein, 11C-PBR28 PET-CT imaging can be used to assess the state of regional gliosis in vivo and explore the effects of laquinimod treatment. This study relates to the LEGATO-HD, multi-centre, double-blinded, Phase 2 clinical trial with laquinimod (US National Registration: NCT02215616). Fifteen patients of the UK LEGATO-HD cohort (mean age: 45.2 ± 7.4 years; disease duration: 5.6 ± 3.0 years) were treated with laquinimod (0.5 mg, N = 4; 1.0 mg, N = 6) or placebo (N = 5) daily. All participants had one 11C-PBR28 PET-CT and one brain MRI scan before laquinimod (or placebo) and at the end of treatment (12 months apart). PET imaging data were quantified to produce 11C-PBR28 distribution volume ratios. These ratios were calculated for the caudate and putamen using the reference Logan plot with the corpus callosum as the reference region. Partial volume effect corrections (Müller-Gartner algorithm) were applied. Differences were sought in Unified Huntington's Disease Rating Scale scores and regional distribution volume ratios between baseline and follow-up and between the two treatment groups (laquinimod versus placebo). No significant change in 11C-PBR28 distribution volume ratios was found post treatment in the caudate and putamen for both those treated with laquinimod (N = 10) and those treated with placebo (N = 5). Over time, the patients treated with laquinimod did not show a significant clinical improvement. Data from the 11C-PBR28 PET-CT study indicate that laquinimod may not have affected regional translocator protein expression and clinical performance over the studied period.

Allele-specific quantitation of ATXN3 and HTT transcripts in polyQ disease models

BACKGROUND

The majority of genes in the human genome is present in two copies but the expression levels of both alleles is not equal. Allelic imbalance is an aspect of gene expression relevant not only in the context of genetic variation, but also to understand the pathophysiology of genes implicated in genetic disorders, in particular, dominant genetic diseases where patients possess one normal and one mutant allele. Polyglutamine (polyQ) diseases are caused by the expansion of CAG trinucleotide tracts within specific genes. Spinocerebellar ataxia type 3 (SCA3) and Huntington's disease (HD) patients harbor one normal and one mutant allele that differ in the length of CAG tracts. However, assessing the expression level of individual alleles is challenging due to the presence of abundant CAG repeats in the human transcriptome, which make difficult the design of allele-specific methods, as well as of therapeutic strategies to selectively engage CAG sequences in mutant transcripts.

RESULTS

To precisely quantify expression in an allele-specific manner, we used SNP variants that are linked to either normal or CAG expanded alleles of the ataxin-3 (ATXN3) and huntingtin (HTT) genes in selected patient-derived cell lines. We applied a SNP-based quantitative droplet digital PCR (ddPCR) protocol for precise determination of the levels of transcripts in cellular and mouse models. For HD, we showed that the process of cell differentiation can affect the ratio between endogenous alleles of HTT mRNA. Additionally, we reported changes in the absolute number of the ATXN3 and HTT transcripts per cell during neuronal differentiation. We also implemented our assay to reliably monitor, in an allele-specific manner, the silencing efficiency of mRNA-targeting therapeutic approaches for HD. Finally, using the humanized Hu128/21 HD mouse model, we showed that the ratio of normal and mutant HTT transgene expression in brain slightly changes with the age of mice.

CONCLUSIONS

Using allele-specific ddPCR assays, we observed differences in allele expression levels in the context of SCA3 and HD. Our allele-selective approach is a reliable and quantitative method to analyze low abundant transcripts and is performed with high accuracy and reproducibility. Therefore, the use of this approach can significantly improve understanding of allele-related mechanisms, e.g., related with mRNA processing that may be affected in polyQ diseases.

Full-length huntingtin is palmitoylated at multiple sites and post-translationally myristoylated following caspase-cleavage

Introduction: Huntington disease is an autosomal dominant neurodegenerative disorder which is caused by a CAG repeat expansion in the HTT gene that codes for an elongated polyglutamine tract in the huntingtin (HTT) protein. Huntingtin is subjected to multiple post-translational modifications which regulate its cellular functions and degradation. We have previously identified a palmitoylation site at cysteine 214 (C214), catalyzed by the enzymes ZDHHC17 and ZDHHC13. Reduced palmitoylation level of mutant huntingtin is linked to toxicity and loss of function. Moreover, we have described N-terminal myristoylation by the N-myristoyltransferases of a short fragment of huntingtin (HTT553-586) at glycine 553 (G553) following proteolysis at aspartate 552 (D552). Results: Here, we show that huntingtin is palmitoylated at numerous cysteines: C105, C433, C3134 and C3144. In addition, we confirm that full-length huntingtin is cleaved at D552 and post-translationally myristoylated at G553. Importantly, blocking caspase cleavage at the critical and pathogenic aspartate 586 (D586) significantly increases posttranslational myristoylation of huntingtin. In turn, myristoylation of huntingtin promotes the co-interaction between C-terminal and N-terminal huntingtin fragments, which is also protective. Discussion: This suggests that the protective effect of inhibiting caspase-cleavage at D586 may be mediated through post-translational myristoylation of huntingtin at G553.

Restoration of c-Src/Fyn Proteins Rescues Mitochondrial Dysfunction in Huntington's Disease

Aims: Huntington's disease (HD) is an autosomal-dominant neurodegenerative disorder with no effective therapies. Mutant huntingtin protein (mHTT), the main HD proteinaceous hallmark, has been linked to reactive oxygen species (ROS) formation and mitochondrial dysfunction, among other pathological mechanisms. Importantly, Src-related kinases, c-Src and Fyn, are activated by ROS and regulate mitochondrial activity. However, c-Src/Fyn involvement in HD is largely unexplored. Thus, in this study, we aimed at exploring changes in Src/Fyn proteins in HD models and their role in defining altered mitochondrial function and dynamics and redox regulation. Results: We show, for the first time, that c-Src/Fyn phosphorylation/activation and proteins levels are decreased in several human and mouse HD models mainly due to autophagy degradation, concomitantly with mHtt-expressing cells showing enhanced TFEB-mediated autophagy induction and autophagy flux. c-Src/Fyn co-localization with mitochondria is also reduced. Importantly, the expression of constitutive active c-Src/Fyn to restore active Src kinase family (SKF) levels improves mitochondrial morphology and function, namely through improved mitochondrial transmembrane potential, mitochondrial basal respiration, and ATP production, but it did not affect mitophagy. In addition, constitutive active c-Src/Fyn expression diminishes the levels of reactive species in cells expressing mHTT. Innovation: This work supports a relevant role for c-Src/Fyn proteins in controlling mitochondrial function and redox regulation in HD, revealing a potential HD therapeutic target. Conclusion: c-Src/Fyn restoration in HD improves mitochondrial morphology and function, precluding the rise in oxidant species and cell death. Antioxid. Redox Signal. 38, 95-114.

Huntingtin Overexpression Does Not Alter Overall Survival in Murine Cancer Models

A reduced incidence of various forms of cancer has been reported in Huntington's disease patients and may be due to pro-apoptotic effects of mutant huntingtin. We tested this hypothesis by assessing the effects of huntingtin protein overexpression on survival in two murine cancer models. We generated YAC HD mice containing human huntingtin transgenes with various CAG tract lengths (YAC18, YAC72, YAC128) on either an Msh2 or p53 null background which have increased cancer incidence. In both mouse models of cancer, the overexpression of either mutant or wild-type huntingtin had no significant effect on overall survival. These results do not support the hypothesis that mutant huntingtin expression is protective against cancer.

Cerebrospinal fluid biomarkers for assessing Huntington disease onset and severity

The identification of molecular biomarkers in CSF from individuals affected by Huntington disease may help improve predictions of disease onset, better define disease progression and could facilitate the evaluation of potential therapies. The primary objective of our study was to investigate novel CSF protein candidates and replicate previously reported protein biomarker changes in CSF from Huntington disease mutation carriers and healthy controls. Our secondary objective was to compare the discriminatory potential of individual protein analytes and combinations of CSF protein markers for stratifying individuals based on the severity of Huntington disease. We conducted a hypothesis-driven analysis of 26 pre-specified protein analytes in CSF from 16 manifest Huntington disease subjects, eight premanifest Huntington disease mutation carriers and eight healthy control individuals using parallel-reaction monitoring mass spectrometry. In addition to reproducing reported changes in previously investigated CSF biomarkers (NEFL, PDYN, and PENK), we also identified novel exploratory CSF proteins (C1QB, CNR1, GNAL, IDO1, IGF2, and PPP1R1B) whose levels were altered in Huntington disease mutation carriers and/or across stages of disease. Moreover, we report strong associations of select CSF proteins with clinical measures of disease severity in manifest Huntington disease subjects (C1QB, CNR1, NEFL, PDYN, PPP1R1B, and TTR) and with years to predicted disease onset in premanifest Huntington disease mutation carriers (ALB, C4B, CTSD, IGHG1, and TTR). Using receiver operating characteristic curve analysis, we identified PENK as being the most discriminant CSF protein for stratifying Huntington disease mutation carriers from controls. We also identified exploratory multi-marker CSF protein panels that improved discrimination of premanifest Huntington disease mutation carriers from controls (PENK, ALB and NEFL), early/mid-stage Huntington disease from premanifest mutation carriers (PPP1R1B, TTR, CHI3L1, and CTSD), and late-stage from early/mid-stage Huntington disease (CNR1, PPP1R1B, BDNF, APOE, and IGHG1) compared with individual CSF proteins. In this study, we demonstrate that combinations of CSF proteins can outperform individual markers for stratifying individuals based on Huntington disease mutation status and disease severity. Moreover, we define exploratory multi-marker CSF protein panels that, if validated, may be used to improve the accuracy of disease-onset predictions, complement existing clinical and imaging biomarkers for monitoring the severity of Huntington disease, and potentially for assessing therapeutic response in clinical trials. Additional studies with CSF collected from larger cohorts of Huntington disease mutation carriers are needed to replicate these exploratory findings.

Haploinsufficiency of CYP8B1 associates with increased insulin sensitivity in humans

BACKGROUNDCytochrome P450 family 8 subfamily B member 1 (CYP8B1) generates 12α-hydroxylated bile acids (BAs) that are associated with insulin resistance in humans.METHODSTo determine whether reduced CYP8B1 activity improves insulin sensitivity, we sequenced CYP8B1 in individuals without diabetes and identified carriers of complete loss-of-function (CLOF) mutations utilizing functional assays.RESULTSMutation carriers had lower plasma 12α-hydroxylated/non-12α-hydroxylated BA and cholic acid (CA)/chenodeoxycholic acid (CDCA) ratios compared with age-, sex-, and BMI-matched controls. During insulin clamps, hepatic glucose production was suppressed to a similar magnitude by insulin, but glucose infusion rates to maintain euglycemia were higher in mutation carriers, indicating increased peripheral insulin sensitivity. Consistently, a polymorphic CLOF CYP8B1 mutation associated with lower fasting insulin in the AMP-T2D-GENES study. Exposure of primary human muscle cells to mutation-carrier CA/CDCA ratios demonstrated increased FOXO1 activity, and upregulation of both insulin signaling and glucose uptake, which were mediated by increased CDCA. Inhibition of FOXO1 attenuated the CDCA-mediated increase in muscle insulin signaling and glucose uptake. We found that reduced CYP8B1 activity associates with increased insulin sensitivity in humans.CONCLUSIONOur findings suggest that increased circulatory CDCA due to reduced CYP8B1 activity increases skeletal muscle insulin sensitivity, contributing to increased whole-body insulin sensitization.FUNDINGBiomedical Research Council/National Medical Research Council of Singapore.

Pridopidine rescues BDNF/TrkB trafficking dynamics and synapse homeostasis in a Huntington disease brain-on-a-chip model

Huntington disease (HD) is a neurodegenerative disorder caused by polyglutamine-encoding CAG repeat expansion in the huntingtin (HTT) gene. HTT is involved in the axonal transport of vesicles containing brain-derived neurotrophic factor (BDNF). In HD, diminished BDNF transport leads to reduced BDNF delivery to the striatum, contributing to striatal and cortical neuronal death. Pridopidine is a selective and potent sigma-1 receptor (S1R) agonist currently in clinical development for HD. The S1R is located at the endoplasmic reticulum (ER)-mitochondria interface, where it regulates key cellular pathways commonly impaired in neurodegenerative diseases. We used a microfluidic device that reconstitutes the corticostriatal network, allowing the investigation of presynaptic dynamics, synaptic morphology and transmission, and postsynaptic signaling. Culturing primary neurons from the HD mouse model Hdh^CAG140/+ provides a "disease-on-a-chip" platform ideal for investigating pathogenic mechanisms and drug activity. Pridopidine rescued the trafficking of BDNF and TrkB resulting in an increased neurotrophin signaling at the synapse. This increased the capacity of HD neurons to release glutamate and restored homeostasis at the corticostriatal synapse. These data suggest that pridopidine enhances the availability of corticostriatal BDNF via S1R activation, leading to neuroprotective effects.

Neuroprotection of retinal ganglion cells by the sigma-1 receptor agonist pridopidine in models of experimental glaucoma

Optic neuropathies such as glaucoma are characterized by retinal ganglion cell (RGC) degeneration and death. The sigma-1 receptor (S1R) is an attractive target for treating optic neuropathies as it is highly expressed in RGCs, and its absence causes retinal degeneration. Activation of the S1R exerts neuroprotective effects in models of retinal degeneration. Pridopidine is a highly selective and potent S1R agonist in clinical development. We show that pridopidine exerts neuroprotection of retinal ganglion cells in two different rat models of glaucoma. Pridopidine strongly binds melanin, which is highly expressed in the retina. This feature of pridopidine has implications to its ocular distribution, bioavailability, and effective dose. Mitochondria dysfunction is a key contributor to retinal ganglion cell degeneration. Pridopidine rescues mitochondrial function via activation of the S1R, providing support for the potential mechanism driving its neuroprotective effect in retinal ganglion cells.

Gene expression profiles complement the analysis of genomic modifiers of the clinical onset of Huntington disease

Huntington disease (HD) is a neurodegenerative disorder that is caused by a CAG repeat expansion in HTT. The length of this repeat, however, only explains a proportion of the variability in age of onset in patients. Genome-wide association studies have identified modifiers that contribute toward a proportion of the observed variance. By incorporating tissue-specific transcriptomic information with these results, additional modifiers can be identified. We performed a transcriptome-wide association study assessing heritable differences in genetically determined expression in diverse tissues, with genome-wide data from over 4000 patients. Functional validation of prioritized genes was undertaken in isogenic HD stem cells and patient brains. Enrichment analyses were performed with biologically relevant gene sets to identify the core pathways. HD-associated gene coexpression modules were assessed for associations with neurological phenotypes in an independent cohort and to guide drug repurposing analyses. Transcriptomic analyses identified genes that were associated with age of HD onset and displayed colocalization with gene expression signals in brain tissue (FAN1, GPR161, PMS2, SUMF2), with supporting evidence from functional experiments. This included genes involved in DNA repair, as well as novel-candidate modifier genes that have been associated with other neurological conditions. Further, cortical coexpression modules were also associated with cognitive decline and HD-related traits in a longitudinal cohort. In summary, the combination of population-scale gene expression information with HD patient genomic data identified novel modifier genes for the disorder. Further, these analyses expanded the pathways potentially involved in modifying HD onset and prioritized candidate therapeutics for future study.

Rescue of aberrant huntingtin palmitoylation ameliorates mutant huntingtin-induced toxicity

Huntington disease (HD) is a neurodegenerative disorder caused by a CAG expansion in the HTT gene that codes for an elongated polyglutamine tract in the huntingtin (HTT) protein. HTT is subject to multiple post-translational modifications (PTMs) that regulate its cellular function. Mutating specific PTM sites within mutant HTT (mHTT) in HD mouse models can modulate disease phenotypes, highlighting the key role of HTT PTMs in the pathogenesis of HD. These findings have led to increased interest in developing small molecules to modulate HTT PTMs in order to decrease mHTT toxicity. However, the therapeutic efficacy of pharmacological modulation of HTT PTMs in preclinical HD models remains largely unknown. HTT is palmitoylated at cysteine 214 by the huntingtin-interacting protein 14 (HIP14 or ZDHHC17) and 14-like (HIP14L or ZDHHC13) acyltransferases. Here, we assessed if HTT palmitoylation should be regarded as a therapeutic target to treat HD by (1) investigating palmitoylation dysregulation in rodent and human HD model systems, (2) measuring the impact of mHTT-lowering therapy on brain palmitoylation, and (3) evaluating if HTT palmitoylation can be pharmacologically modulated. We show that palmitoylation of mHTT and some HIP14/HIP14L-substrates is decreased early in multiple HD mouse models, and that mHTT palmitoylation decreases further with aging. Lowering mHTT in the brain of YAC128 mice is not sufficient to rescue aberrant palmitoylation. However, we demonstrate that mHTT palmitoylation can be normalized in COS-7 cells, in YAC128 cortico-striatal primary neurons and HD patient-derived lymphoblasts using an acyl-protein thioesterase (APT) inhibitor. Moreover, we show that modulating palmitoylation reduces mHTT aggregation and mHTT-induced cytotoxicity in COS-7 cells and YAC128 neurons.

Pridopidine reduces mutant huntingtin-induced endoplasmic reticulum stress by modulation of the Sigma-1 receptor

The endoplasmic reticulum (ER)-localized Sigma-1 receptor (S1R) is neuroprotective in models of neurodegenerative diseases, among them Huntington disease (HD). Recent clinical trials in HD patients and preclinical studies in cellular and mouse HD models suggest a therapeutic potential for the high-affinity S1R agonist pridopidine. However, the molecular mechanisms of the cytoprotective effect are unclear. We have previously reported strong induction of ER stress by toxic mutant huntingtin (mHtt) oligomers, which is reduced upon sequestration of these mHtt oligomers into large aggregates. Here, we show that pridopidine significantly ameliorates mHtt-induced ER stress in cellular HD models, starting at low nanomolar concentrations. Pridopidine reduced the levels of markers of the three branches of the unfolded protein response (UPR), showing the strongest effects on the PKR-like endoplasmic reticulum kinase (PERK) branch. The effect is S1R-dependent, as it is abolished in cells expressing mHtt in which the S1R was deleted using CRISPR/Cas9 technology. mHtt increased the level of the detergent-insoluble fraction of S1R, suggesting a compensatory cellular mechanism that responds to increased ER stress. Pridopidine further enhanced the levels of insoluble S1R, suggesting the stabilization of activated S1R oligomers. These S1R oligomeric species appeared in ER-localized patches, and not in the mitochondria-associated membranes nor the ER-derived quality control compartment. The colocalization of S1R with the chaperone BiP was significantly reduced by mHtt, and pridopidine restored this colocalization to normal, unstressed levels. Pridopidine increased toxic oligomeric mHtt recruitment into less toxic large sodium dodecyl sulfate-insoluble aggregates, suggesting that this in turn reduces ER stress and cytotoxicity.

Reliable Resolution of Full-Length Huntingtin Alleles by Quantitative Immunoblotting

BACKGROUND

Therapeutics that lower mutant huntingtin (mHTT) have shown promise in preclinical studies and are in clinical development for the treatment of Huntington's disease (HD). Multiple assays have been developed that either quantify mHTT or total HTT but may not accurately measure levels of wild type HTT (wtHTT) in biological samples.

OBJECTIVE

To optimize a method that can be used to resolve, quantify and directly compare levels of full length wtHTT and mHTT in HD samples.

METHODS

We provide a detailed quantitative immunoblotting protocol to reproducibly resolve full length wtHTT and mHTT in multiple HD mouse and patient samples.

RESULTS

We show that this assay can be modified, depending on the sample, to resolve wtHTT and mHTT with a wide range of polyglutamine differences (ΔQs 22-179). We also demonstrate that this method can be used to quantify allele-selective lowering of mHTT using an antisense oligonucleotide in HD patient-derived cells.

CONCLUSION

This quantitative immunoblotting method can be used to reliably resolve full length HTT alleles with ΔQs≥22 and allows for direct comparison of wtHTT and mHTT levels in HD samples.

Sigma-1 Receptor (S1R) Interaction with Cholesterol: Mechanisms of S1R Activation and Its Role in Neurodegenerative Diseases

The sigma-1 receptor (S1R) is a 223 amino acid-long transmembrane endoplasmic reticulum (ER) protein. The S1R modulates the activity of multiple effector proteins, but its signaling functions are poorly understood. S1R is associated with cholesterol, and in our recent studies we demonstrated that S1R association with cholesterol induces the formation of S1R clusters. We propose that these S1R-cholesterol interactions enable the formation of cholesterol-enriched microdomains in the ER membrane. We hypothesize that a number of secreted and signaling proteins are recruited and retained in these microdomains. This hypothesis is consistent with the results of an unbiased screen for S1R-interacting partners, which we performed using the engineered ascorbate peroxidase 2 (APEX2) technology. We further propose that S1R agonists enable the disassembly of these cholesterol-enriched microdomains and the release of accumulated proteins such as ion channels, signaling receptors, and trophic factors from the ER. This hypothesis may explain the pleotropic signaling functions of the S1R, consistent with previously observed effects of S1R agonists in various experimental systems.

The Sigma-1 Receptor Mediates Pridopidine Rescue of Mitochondrial Function in Huntington Disease Models

Pridopidine is a selective Sigma-1 receptor (S1R) agonist in clinical development for Huntington disease (HD) and amyotrophic lateral sclerosis. S1R is a chaperone protein localized in mitochondria-associated endoplasmic reticulum (ER) membranes, a signaling platform that regulates Ca2+ signaling, reactive oxygen species (ROS) and mitochondrial fission. Here, we investigate the protective effects of pridopidine on various mitochondrial functions in human and mouse HD models. Pridopidine effects on mitochondrial dynamics were assessed in primary neurons from YAC128 HD mice expressing the mutant human HTT gene. We observe that pridopidine prevents the disruption of mitochondria-ER contact sites and improves the co-localization of inositol 1,4,5-trisphosphate receptor (IP3R) and its chaperone S1R with mitochondria in YAC128 neurons, leading to increased mitochondrial activity, elongation, and motility. Increased mitochondrial respiration is also observed in YAC128 neurons and in pridopidine-treated HD human neural stem cells (hNSCs). ROS levels were assessed after oxidative insult or S1R knockdown in pridopidine-treated YAC128 neurons, HD hNSCs, and human HD lymphoblasts. All HD models show increased ROS levels and deficient antioxidant response, which are efficiently rescued with pridopidine. Importantly, pridopidine treatment before H2O2-induced mitochondrial dysfunction and S1R presence are required for HD cytoprotection. YAC128 mice treated at early/pre-symptomatic age with pridopidine show significant improvement in motor coordination, indicating a delay in symptom onset. Additionally, in vivo pridopidine treatment reduces mitochondrial ROS levels by normalizing mitochondrial complex activity. In conclusion, S1R-mediated enhancement of mitochondrial function contributes to the neuroprotective effects of pridopidine, providing insight into its mechanism of action and therapeutic potential.