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SMN-primed ribosomes modulate the translation of transcripts related to spinal muscular atrophy.

ABSTRACT: The contribution of ribosome heterogeneity and ribosome-associated proteins to the molecular control of proteomes in health and disease remains unclear. Here, we demonstrate that survival motor neuron (SMN) protein-the loss of which causes the neuromuscular disease spinal muscular atrophy (SMA)-binds to ribosomes and that this interaction is tissue-dependent. SMN-primed ribosomes are preferentially positioned within the first five codons of a set of mRNAs that are enriched for translational enhancer sequences in the 5' untranslated region (UTR) and rare codons at the beginning of their coding sequence. These SMN-specific mRNAs are associated with neurogenesis, lipid metabolism, ubiquitination, chromatin regulation and translation. Loss of SMN induces ribosome depletion, especially at the beginning of the coding sequence of SMN-specific mRNAs, leading to impairment of proteins that are involved in motor neuron function and stability, including acetylcholinesterase. Thus, SMN plays a crucial role in the regulation of ribosome fluxes along mRNAs encoding proteins that are relevant to SMA pathogenesis.

SUBMITTER: Lauria F

PROVIDER: S-EPMC7610479 | biostudies-literature |

REPOSITORIES: biostudies-literature

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Therapeutic strategies for spinal muscular atrophy: SMN and beyond.

Project description:Spinal muscular atrophy (SMA) is a devastating neuromuscular disorder characterized by loss of motor neurons and muscle atrophy, generally presenting in childhood. SMA is caused by low levels of the survival motor neuron protein (SMN) due to inactivating mutations in the encoding gene SMN1 A second duplicated gene, SMN2, produces very little but sufficient functional protein for survival. Therapeutic strategies to increase SMN are in clinical trials, and the first SMN2-directed antisense oligonucleotide (ASO) therapy has recently been licensed. However, several factors suggest that complementary strategies may be needed for the long-term maintenance of neuromuscular and other functions in SMA patients. Pre-clinical SMA models demonstrate that the requirement for SMN protein is highest when the structural connections of the neuromuscular system are being established, from late fetal life throughout infancy. Augmenting SMN may not address the slow neurodegenerative process underlying progressive functional decline beyond childhood in less severe types of SMA. Furthermore, individuals receiving SMN-based treatments may be vulnerable to delayed symptoms if rescue of the neuromuscular system is incomplete. Finally, a large number of older patients living with SMA do not fulfill the present criteria for inclusion in gene therapy and ASO clinical trials, and may not benefit from SMN-inducing treatments. Therefore, a comprehensive whole-lifespan approach to SMA therapy is required that includes both SMN-dependent and SMN-independent strategies that treat the CNS and periphery. Here, we review the range of non-SMN pathways implicated in SMA pathophysiology and discuss how various model systems can serve as valuable tools for SMA drug discovery.

| S-EPMC5560066 | biostudies-other

SMN dosage analysis and risk assessment for spinal muscular atrophy.

Project description: Not available

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SMN deficiency perturbs monoamine neurotransmitter metabolism in spinal muscular atrophy.

Project description:Beyond motor neuron degeneration, homozygous mutations in the survival motor neuron 1 (SMN1) gene cause multiorgan and metabolic defects in patients with spinal muscular atrophy (SMA). However, the precise biochemical features of these alterations and the age of onset in the brain and peripheral organs remain unclear. Using untargeted NMR-based metabolomics in SMA mice, we identify cerebral and hepatic abnormalities related to energy homeostasis pathways and amino acid metabolism, emerging already at postnatal day 3 (P3) in the liver. Through HPLC, we find that SMN deficiency induces a drop in cerebral norepinephrine levels in overt symptomatic SMA mice at P11, affecting the mRNA and protein expression of key genes regulating monoamine metabolism, including aromatic L-amino acid decarboxylase (AADC), dopamine beta-hydroxylase (DβH) and monoamine oxidase A (MAO-A). In support of the translational value of our preclinical observations, we also discovered that SMN upregulation increases cerebrospinal fluid norepinephrine concentration in Nusinersen-treated SMA1 patients. Our findings highlight a previously unrecognized harmful influence of low SMN levels on the expression of critical enzymes involved in monoamine metabolism, suggesting that SMN-inducing therapies may modulate catecholamine neurotransmission. These results may also be relevant for setting therapeutic approaches to counteract peripheral metabolic defects in SMA.

| S-EPMC10643621 | biostudies-literature

Decreasing disease severity in symptomatic, Smn(-/-);SMN2(+/+), spinal muscular atrophy mice following scAAV9-SMN delivery.

Project description:Spinal muscular atrophy (SMA), an autosomal recessive neuromuscular disorder, is the leading genetic cause of infant mortality. SMA is caused by the homozygous loss of Survival Motor Neuron-1 (SMN1). In humans, a nearly identical copy gene is present, SMN2. SMN2 is retained in all SMA patients and encodes the same protein as SMN1. However, SMN1 and SMN2 differ by a silent C-to-T transition at the 5' end of exon 7, causing alternative splicing of SMN2 transcripts and low levels of full-length SMN. SMA is monogenic and therefore well suited for gene-replacement strategies. Recently, self-complementary adeno-associated virus (scAAV) vectors have been used to deliver the SMN cDNA to an animal model of disease, the SMN?7 mouse. In this study, we examine a severe model of SMA, Smn(-/-);SMN2(+/+), to determine whether gene replacement is viable in a model in which disease development begins in utero. Using two delivery paradigms, intracerebroventricular injections and intravenous injections, we delivered scAAV9-SMN and demonstrated a two to four fold increase in survival, in addition to improving many of the phenotypic parameters of the model. This represents the longest extension in survival for this severe model for any therapeutic intervention and suggests that postsymptomatic treatment of SMA may lead to significant improvement of disease severity.

| S-EPMC3300100 | biostudies-literature

Blocking p62-dependent SMN degradation ameliorates spinal muscular atrophy disease phenotypes.

Project description:Spinal muscular atrophy (SMA), a degenerative motor neuron (MN) disease, caused by loss of functional survival of motor neuron (SMN) protein due to SMN1 gene mutations, is a leading cause of infant mortality. Increasing SMN levels ameliorates the disease phenotype and is unanimously accepted as a therapeutic approach for patients with SMA. The ubiquitin/proteasome system is known to regulate SMN protein levels; however, whether autophagy controls SMN levels remains poorly explored. Here, we show that SMN protein is degraded by autophagy. Pharmacological and genetic inhibition of autophagy increases SMN levels, while induction of autophagy decreases these levels. SMN degradation occurs via its interaction with the autophagy adapter p62 (also known as SQSTM1). We also show that SMA neurons display reduced autophagosome clearance, increased p62 and ubiquitinated proteins levels, and hyperactivated mTORC1 signaling. Importantly, reducing p62 levels markedly increases SMN and its binding partner gemin2, promotes MN survival, and extends lifespan in fly and mouse SMA models, revealing p62 as a potential new therapeutic target for the treatment of SMA.

| S-EPMC6025996 | biostudies-literature

Targeting SR proteins improves SMN expression in spinal muscular atrophy cells.

Project description:Spinal muscular atrophy (SMA) is one of the most common inherited causes of pediatric mortality. SMA is caused by deletions or mutations in the survival of motor neuron 1 (SMN1) gene, which results in SMN protein deficiency. Humans have a centromeric copy of the survival of motor neuron gene, SMN2, which is nearly identical to SMN1. However, SMN2 cannot compensate for the loss of SMN1 because SMN2 has a single-nucleotide difference in exon 7, which negatively affects splicing of the exon. As a result, most mRNA produced from SMN2 lacks exon 7. SMN2 mRNA lacking exon 7 encodes a truncated protein with reduced functionality. Improving SMN2 exon 7 inclusion is a goal of many SMA therapeutic strategies. The identification of regulators of exon 7 inclusion may provide additional therapeutic targets or improve the design of existing strategies. Although a number of regulators of exon 7 inclusion have been identified, the function of most splicing proteins in exon 7 inclusion is unknown. Here, we test the role of SR proteins and hnRNP proteins in SMN2 exon 7 inclusion. Knockdown and overexpression studies reveal that SRSF1, SRSF2, SRSF3, SRSF4, SRSF5, SRSF6, SRSF7, SRSF11, hnRNPA1/B1 and hnRNP U can inhibit exon 7 inclusion. Depletion of two of the most potent inhibitors of exon 7 inclusion, SRSF2 or SRSF3, in cell lines derived from SMA patients, increased SMN2 exon 7 inclusion and SMN protein. Our results identify novel regulators of SMN2 exon 7 inclusion, revealing potential targets for SMA therapeutics.

| S-EPMC4266657 | biostudies-literature

SMN Blood Levels in a Porcine Model of Spinal Muscular Atrophy.

Project description:BackgroundSpinal Muscular Atrophy (SMA) is an autosomal recessive motor neuron disease that results in loss of spinal motor neurons, muscular weakness and, in severe cases, respiratory failure and death. SMA is caused by a deletion or mutation of the SMN1 gene and retention of the SMN2 gene that leads to low SMN expression levels.The measurement of SMN mRNA levels in peripheral blood samples has been used in SMA clinical studies as a pharmacodynamic biomarker for response to therapies designed to increase SMN levels. We recently developed a postnatal porcine model of SMA by the viral delivery of a short-hairpin RNA (shRNA) targeting porcine SMN (pSMN). scAAV9-mediated knockdown of pSMN mRNA at postnatal day 5 results in denervation, weakness and motor neuron and ventral root axon loss that begins 3-4 weeks after viral delivery, and this phenotype can be ameliorated by subsequent viral delivery of human SMN (hSMN).ObjectiveTo determine if the effect of modulating SMN levels using gene therapy can be measured in blood.MethodsWe measured expression of pSMN mRNA and hSMN mRNA by quantitative droplet digital PCR (ddPCR).ResultsWe found that the endogenous expression of pSMN mRNA in blood increases in the first month of life. However, there were no significant differences in blood levels of pSMN mRNA after knock-down or of human SMN mRNA after gene therapy.ConclusionsOur results, obtained in a large animal model of SMA that is similar in size and anatomy to human infants, suggest that measurement of SMN mRNA levels in blood may not be informative in SMA clinical trials involving intrathecal delivery of SMN-modulating therapies.

| S-EPMC5531281 | biostudies-literature

SMN deficiency perturbs monoamine neurotransmitter metabolism in spinal muscular atrophy

Project description:<p>Beyond motor neuron degeneration, homozygous mutations in the survival motor neuron 1 (SMN1) gene cause multiorgan and metabolic defects in patients with spinal muscular atrophy (SMA). However, the precise biochemical features of these alterations and the age of onset in the brain and peripheral organs remain unclear. Using untargeted NMR-based metabolomics in SMA mice, we identify cerebral and hepatic abnormalities related to energy homeostasis pathways and amino acid metabolism, emerging already at postnatal day 3 (P3) in the liver. Through HPLC, we find that SMN deficiency induces a drop in cerebral norepinephrine levels in overt symptomatic SMA mice at P11, affecting the mRNA and protein expression of key genes regulating monoamine metabolism, including aromatic L-amino acid decarboxylase (AADC), dopamine beta-hydroxylase (DβH) and monoamine oxidase A (MAO-A). In support of the translational value of our preclinical observations, we also discovered that SMN upregulation increases cerebrospinal fluid norepinephrine concentration in Nusinersen-treated SMA1 patients. Our findings highlight a previously unrecognized harmful influence of low SMN levels on the expression of critical enzymes involved in monoamine metabolism, suggesting that SMN-inducing therapies may modulate catecholamine neurotransmission. These results may also be relevant for setting therapeutic approaches to counteract peripheral metabolic defects in SMA. </p>

2023-11-27 | MTBLS8784 | MetaboLights

ML372 blocks SMN ubiquitination and improves spinal muscular atrophy pathology in mice.

Project description:Spinal muscular atrophy (SMA) is an autosomal recessive neuromuscular disease and one of the leading inherited causes of infant mortality. SMA results from insufficient levels of the survival motor neuron (SMN) protein, and studies in animal models of the disease have shown that increasing SMN protein levels ameliorates the disease phenotype. Our group previously identified and optimized a new series of small molecules, with good potency and toxicity profiles and reasonable pharmacokinetics, that were able to increase SMN protein levels in SMA patient-derived cells. We show here that ML372, a representative of this series, almost doubles the half-life of residual SMN protein expressed from the SMN2 locus by blocking its ubiquitination and subsequent degradation by the proteasome. ML372 increased SMN protein levels in muscle, spinal cord, and brain tissue of SMA mice. Importantly, ML372 treatment improved the righting reflex and extended survival of a severe mouse model of SMA. These results demonstrate that slowing SMN degradation by selectively inhibiting its ubiquitination can improve the motor phenotype and lifespan of SMA model mice.

| S-EPMC5111506 | biostudies-literature

A survey of transcripts generated by spinal muscular atrophy genes.

Project description:Human Survival Motor Neuron (SMN) genes code for SMN, an essential multifunctional protein. Complete loss of SMN is embryonic lethal, while low levels of SMN lead to spinal muscular atrophy (SMA), a major genetic disease of children and infants. Reduced levels of SMN are associated with the abnormal development of heart, lung, muscle, gastro-intestinal system and testis. The SMN loci have been shown to generate a vast repertoire of transcripts, including linear, back- and trans-spliced RNAs as well as antisense long noncoding RNAs. However, functions of the majority of these transcripts remain unknown. Here we review the nature of RNAs generated from the SMN loci and discuss their potential functions in cellular metabolism.

| S-EPMC7302838 | biostudies-literature

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