Biology subjects

Pellizzoni, L.

Publications and source records attributed to Pellizzoni, L..

11 recordsLinked to original sources

bioRxiv2026

Incomplete cerebellar circuit restoration limits functional recovery following SMN therapy in severe spinal muscular atrophy

Spinal muscular atrophy (SMA) is caused by a deficiency in the survival motor neuron (SMN) protein, resulting in degeneration of spinal motor neurons (MNs). However, persistent neurological deficits despite postnatal SMN-restoring therapies suggest that recovery of sensorimotor and supraspinal circuits may be incomplete. The cerebellum has recently emerged as a supraspinal contributor to motor deficits in the severe SMN{Delta}7 mouse model, yet it remains unclear whether cerebellar pathology is a conserved and therapeutically reversible feature across severe SMA mouse models and clinical subtypes. Here, we identify cerebellar pathology in Taiwanese SMA mice, characterized by hypoplasia, disrupted organization and loss of Purkinje cells (PCs), altered synaptic circuitry, and impaired cerebellar cortical output. Unlike the previously described p53-dependent PC degeneration in SMN{Delta}7 mice, cerebellar pathology in Taiwanese SMA mice was associated with developmental disorganization and external granule layer (EGL)-restricted p53 activation. Human cerebellar tissue mirrored this distinction, with p53 activation found in PCs from SMA Type I and in the EGL from SMA Type 0 individuals, indicating that cerebellar pathology arises through distinct mechanisms across severe forms of SMA. Importantly, two SMN-restoring strategies produced divergent therapeutic outcomes. In SMN{Delta}7 mice, AAV9-SMN prevented PC degeneration yet incompletely restored cerebellar circuitry. AAV9-SMN-treated Taiwanese mice developed severe ataxia-like deficits, retained profound cerebellar pathology, and survived to approximately one month of age. In contrast, systemic risdiplam rescued cerebellar pathology, motor behavior, and survival in both models. Together, these findings identify cerebellar pathology as a conserved yet distinct feature across severe forms of SMA and reveal cell type-specific tropism as a critical determinant of therapeutic outcome. More broadly, these findings suggest that successful recovery requires restoration of distributed supraspinal circuit integrity in addition to rescue of spinal motor pathways.

neuroscience↗

bioRxiv2026

Intranucleolar Invasion of Cajal Body Remnants Suppresses Ribosomal Biogenesis in cis and Telomerase Functions in trans

Cellular processes are compartmentalized within immiscible heterotypic condensates, yet the functional consequences of losing their physical segregation remain unclear. Here, we show that genetic inactivation of the RNA chaperone SMN forces the aberrant intermixing of the two most prominent nuclear condensates: nucleolus and Cajal Body (CB). Upon SMN depletion, CB components invade the nucleolus and undergo reduced mobility and solubility consistent with a liquid-to-gel-like hardening transition. The CB-scaffold coilin aberrantly enriches at the nucleolar FC/DFC boundary and occupies rDNA chromatin, thereby locally suppressing rRNA production. Concurrently, this sequestration globally impairs coilin targeting to snRNA/snoRNA loci and limits telomerase access to telomeres, reducing telomeric synthesis. Crucially, genetic coilin depletion alone alleviates this mistargeting and rescues these functional impairments across condensates. Our findings reveal an inter-condensate rheostat model in which the loss of CB-nucleolar immiscibility is directly sensed, communicated, and executed by CB remnants, thereby proportionally coupling the functional outputs of otherwise distinct RNPs essential for splicing, translation, and genomic integrity.

molecular biology↗

bioRxiv2026

A p53-ΔNp73 signaling axis drives selective motor neuron degeneration in spinal muscular atrophy

Selective neuronal vulnerability is a hallmark of many neurodegenerative diseases, yet how ubiquitous genetic insults cause highly selective neuronal loss remains poorly understood. In spinal muscular atrophy (SMA), reduced SMN levels trigger degeneration of specific motor neuron pools. Although non-apoptotic, p53-mediated death pathways have been implicated, p53 is expressed in both vulnerable and resistant neurons, leaving the downstream determinants of selective vulnerability unresolved. Here, we identify a p53-{Delta}Np73 signaling axis as a previously unrecognized execution pathway driving motor neuron degeneration. Using differential transcriptional profiling of SMA motor neurons following pharmacological modulation of p53 activity, we uncover p73 as a critical downstream mediator of neuronal death. Notably, SMN deficiency induces cell-autonomous, p53-dependent expression of the {Delta}Np73 isoform selectively in vulnerable, but not resistant, motor neurons. {Delta}Np73 induction precisely parallels the spatial and temporal pattern of degeneration in mouse models and is also detected in motor neurons from SMA patients. Strikingly, despite its established role as a pro-survival antagonist of p53, depletion of {Delta}Np73 improves motor neuron survival and partially preserves neuromuscular junction integrity in SMA mice. These findings reveal a context-dependent, isoform-specific functional switch in p53 family signaling that redirects a canonical survival factor into a driver of neurodegeneration, identifying a novel molecular mechanism underlying selective neuronal vulnerability in SMA and a potential therapeutic target for neuroprotection.

neuroscience↗

bioRxiv2025

A chemical screen identifies p38 MAPK inhibition as a candidate neuroprotective strategy for combinatorial SMA therapy

Spinal muscular atrophy (SMA) is a neurodegenerative disease caused by ubiquitous deficiency in the survival motor neuron (SMN) protein. The identification of effectors and modifiers of pathogenic events downstream of SMN deficiency is key to understanding disease mechanisms and broadening the range of targets for developing SMA therapies that can complement SMN upregulation. Here, we report a cell-based phenotypic screen for chemical modifiers of SMN biology that identified inhibitors of p38 mitogen-activated protein kinase (p38 MAPK) as suppressors of proliferation defects induced by SMN deficiency in mouse fibroblasts. We further show that SMN deficiency induces p38 MAPK activation and that pharmacological inhibition of this pathway improves motor function in SMA mice through SMN-independent neuroprotective effects. Using a highly optimized p38 MAPK inhibitor (MW150) and a specific paradigm of combinatorial treatment in SMA mice, we observed synergistic enhancement of the phenotypic benefit induced by either MW150 or an SMN-inducing drug alone. By promoting survival of motor neurons, pharmacological inhibition of p38 MAPK synergizes with SMN induction and enables enhanced synaptic rewiring of motor neurons within sensory-motor spinal circuits, resulting in increased motor function, weight gain, and survival of SMA mice. Together, our studies identify the p38 MAPK pathway as a therapeutic target and MW150 as a candidate pharmacological approach for SMN-independent neuroprotection with clinical relevance for combination therapy in SMA.

neuroscience↗

bioRxiv2024

Dysregulated balance of D- and L-amino acids modulating glutamatergic neurotransmission in severe spinal muscular atrophy.

Spinal muscular atrophy (SMA) is a neuromuscular disorder caused by reduced expression of the survival motor neuron (SMN) protein. In addition to motor neuron survival, SMN deficiency affects the integrity and function of afferent synapses that provide glutamatergic excitatory drive essential for motor neuron firing and muscle contraction. However, it is unknown whether deficits in the metabolism of excitatory amino acids and their precursors contribute to neuronal dysfunction in SMA. To address this issue, we measured the levels of the main neuroactive D- and L-amino acids acting on glutamatergic receptors in the central nervous system of SMN{Delta}7 mice as well as the cerebrospinal fluid (CSF) of SMA patients of varying severity before and after treatment with the SMN-inducing drug Nusinersen. Our findings reveal that SMN deficiency disrupts glutamate and serine metabolism in the CSF of severe SMA patients, including decreased concentration of L-glutamate, which is partially corrected by Nusinersen therapy. Moreover, we identify dysregulated L-glutamine to L-glutamate conversion as a shared neurochemical signature of altered glutamatergic synapse metabolism that implicates astrocyte dysfunction in both severe SMA patients and mouse models. Lastly, consistent with a correlation of higher CSF levels of D-serine with better motor function in severe SMA patients, we show that daily supplementation with the NMDA receptor co-agonist D-serine improves neurological deficits in SMN{Delta}7 mice. Altogether, these findings provide direct evidence for dysregulation of D- and L-amino acid metabolism linked to glutamatergic neurotransmission in severe SMA and have potential implications for treating this neurological disorder.

neuroscience↗

bioRxiv2024

Synaptic imbalance and increased inhibition impair motor function in SMA

Movement is executed through the balanced action of excitatory and inhibitory neurotransmission in motor circuits of the spinal cord. Short-term perturbations in one of the two types of transmission are counteracted by homeostatic changes of the opposing type. Prolonged failure to balance excitatory and inhibitory drive results in dysfunction at the single neuron, as well as neuronal network levels. However, whether dysfunction in one or both types of neurotransmission leads to pathogenicity in neurodegenerative diseases characterized by select synaptic deficits is not known. Here, we used mouse genetics, functional assays, morphological methods, and viral-mediated approaches to uncover the pathogenic contribution of unbalanced excitation-inhibition neurotransmission in a mouse model of spinal muscular atrophy (SMA). We show that vulnerable motor circuits in the SMA spinal cord fail to respond homeostatically to the reduction of excitatory drive and instead increase inhibition. This imposes an excessive burden on motor neurons and further restricts their recruitment to activate muscle contraction. Importantly, genetic or pharmacological reduction of inhibitory synaptic drive improves neuronal function and provides behavioural benefit in SMA mice. Our findings identify the lack of excitation-inhibition homeostasis as a major maladaptive mechanism in SMA, by which the combined effects of reduced excitation and increased inhibition diminish the capacity of premotor commands to recruit motor neurons and elicit muscle contractions.

neuroscience↗

bioRxiv2022

Neuromuscular denervation and deafferentation but not motor neuron death are disease features in the Smn 2B/- mouse model of SMA

Spinal muscular atrophy (SMA) is a neurodegenerative disease characterized by loss of motor neurons and skeletal muscle atrophy which is caused by ubiquitous deficiency in the survival motor neuron (SMN) protein. Several cellular defects contribute to sensory-motor circuit pathology in SMA mice, but the underlying mechanisms have often been studied in one mouse model without validation in other available models. Here, we used Smn2B/- mice to investigate specific behavioral, morphological, and functional aspects of SMA pathology that we previously characterized in the SMN{Delta}7 model. Smn2B/- SMA mice on a pure FVB/N background display deficits in body weight gain and muscle strength with onset in the second postnatal week and median survival of 19 days. Morphological analysis revealed severe loss of proprioceptive synapses on the soma of motor neurons and prominent denervation of neuromuscular junctions (NMJs) in axial but not distal muscles. In contrast, no evidence of cell death emerged from analysis of several distinct pools of lumbar motor neurons known to be lost in the disease. Moreover, SMA motor neurons from Smn2B/- mice showed robust nuclear accumulation of p53 but lack of phosphorylation of serine 18 at its amino-terminal, which selectively marks degenerating motor neurons in the SMN{Delta}7 mouse model. These results indicate that NMJ denervation and deafferentation, but not motor neuron death, are conserved features of SMA pathology in Smn2B/- mice.

neuroscience↗

bioRxiv2021

SMN controls neuromuscular junction integrity through U7 snRNP

The neuromuscular junction (NMJ) is an essential synapse for animal survival whose loss is a key hallmark of neurodegenerative diseases such as amyotrophic lateral sclerosis (ALS) and spinal muscular atrophy (SMA). While insights into the function of the causative genes implicate RNA dysregulation in NMJ pathogenesis, the RNA-mediated mechanisms controlling the biology of this specialized synapse that go awry in disease remain elusive. Here, we show that activity of the SMA-determining SMN protein in the assembly of U7 small nuclear ribonucleoprotein (snRNP), which functions in the 3-end processing of replication-dependent histone mRNAs, is required for NMJ integrity. AAV9-mediated gene delivery of U7-specific Lsm10 and Lsm11 proteins selectively enhances U7 snRNP assembly, corrects histone mRNA processing defects, and rescues key structural and functional abnormalities of neuromuscular pathology in SMA mice - including NMJ denervation, reduced synaptic transmission, and skeletal muscle atrophy. Furthermore, U7 snRNP dysfunction induced by SMN deficiency drives selective loss of the synaptic organizing protein Agrin at NMJs innervating vulnerable axial muscles of SMA mice, revealing an unanticipated link between U7-dependent histone mRNA processing and motor neuron-derived expression of an essential factor for NMJ biology. Together, these findings establish a direct contribution of U7 snRNP dysfunction to the neuromuscular phenotype in SMA and the requirement of RNA-mediated histone gene regulation for maintaining functional synaptic connections between motor neurons and muscles.

neuroscience↗

bioRxiv2020

TGS1 controls snRNA 3' end processing, prevents neurodegeneration and ameliorates SMN-dependent neurological phenotypes in vivo

Trimethylguanosine synthase 1 (TGS1) is a highly conserved enzyme that converts the 5 mono-methylguanosine cap of snRNAs to a trimethylguanosine cap. Here, we show that loss of TGS1 in C. elegans, D. melanogaster and D. rerio results in neurological phenotypes similar to those caused by Survival Motor Neuron (SMN) deficiency. Importantly, expression of human TGS1 ameliorates the SMN-dependent neurological phenotypes in both flies and worms, revealing that TGS1 can partly counteract the effects of SMN deficiency. TGS1 loss in HeLa cells leads to the accumulation of immature U2 and U4atac snRNAs with long 3 tails that are often uridylated. snRNAs with defective 3 terminations also accumulate in Drosophila Tgs1 mutants. Consistent with defective snRNA maturation, TGS1 and SMN mutant cells also exhibit partially overlapping transcriptome alterations that include aberrantly spliced and readthrough transcripts. Together, these results identify a neuroprotective function for TGS1 and reinforce the view that defective snRNA maturation affects neuronal viability and function.

genetics↗

bioRxiv2019

Stasimon contributes to the loss of sensory synapses and motor neuron death in a mouse model of spinal muscular atrophy

Reduced expression of the SMN protein causes spinal muscular atrophy (SMA) - an inherited neurodegenerative disease characterized by multiple synaptic deficits and motor neuron loss. Here, we show that AAV9-mediated delivery of Stasimon - a gene encoding an ER-resident transmembrane protein regulated by SMN - improves motor function in a mouse model of SMA through multiple mechanisms. In proprioceptive neurons of SMA mice, Stasimon overexpression prevents the loss of afferent synapses on motor neurons and enhances sensory-motor neurotransmission. In SMA motor neurons, Stasimon suppresses the neurodegenerative process by selectively reducing phosphorylation but not upregulation of the tumor suppressor p53, both of which are converging events required to trigger neuronal death. We further show that Stasimon deficiency synergizes with SMA-related mechanisms of p53 upregulation to induce phosphorylation of p53. These findings identify Stasimon dysfunction induced by SMN deficiency as an upstream driver of cellular pathways that lead to synaptic loss and motor neuron degeneration, revealing a dual contribution of Stasimon to motor circuit pathology in SMA.

neuroscience↗

bioRxiv2018

The RNA demethylase FTO targets m6Am in snRNA to establish distinct methyl isoforms that influence splicing

Small nuclear RNAs (snRNAs) are core spliceosome components and mediate pre-mRNA splicing. During their biogenesis, snRNAs acquire several constitutive nucleotide modifications. Here we show that snRNAs also contain a regulated and reversible nucleotide modification causing them to exist as two different methyl isoforms, m1 and m2, reflecting the methylation state of the adenosine adjacent to the snRNA cap. We find that snRNA biogenesis involves the formation of an initial m1-isoform with a single-methylated adenosine (2-O-methyladenosine, Am), which is then converted to a dimethylated m2-isoform (N6,2-O-dimethyladenosine, m6Am). The relative m1- and m2-isoform levels are determined by the RNA demethylase FTO, which selectively demethylates the m2-isoform. We show FTO is inhibited by endogenous metabolites, resulting in increased m2-snRNA levels. Furthermore, cells that exhibit high m2-snRNA levels show altered patterns of alternative splicing. Together, these data reveal that FTO has a central role in snRNA biogenesis and controls a previously unknown step of snRNA processing involving reversible methylation, thereby providing a potential link between reversible RNA modifications and mRNA splicing.

molecular biology↗