Biology subjects

Wirth, B.

Publications and source records attributed to Wirth, B..

9 recordsLinked to original sources

bioRxiv2026

Endogenous SMN Heterogeneity Defines Dynamic States of Motor Neuron Vulnerability and Resilience

Selective neuronal vulnerability, whereby some neurons degenerate while others remain resilient despite a shared genetic and disease context, is a defining feature of neurodegenerative diseases, yet the intrinsic mechanisms underlying these divergent fates remain poorly understood. Here, we identify naturally occurring heterogeneity in endogenous Survival Motor Neuron (SMN) protein abundance as a determinant of dynamic motor neuron (MN) vulnerability states that predict neuronal fate. Longitudinal live-cell imaging of human SMN-Clover reporter MNs shows that neurons with high endogenous SMN survive significantly longer than neighboring low-SMN neurons across healthy, spinal muscular atrophy (SMA) and amyotrophic lateral sclerosis (ALS) genetic backgrounds. These vulnerability states are not fixed: a substantial proportion of MNs progressively increase endogenous SMN abundance, transitioning toward a more resilient state associated with enhanced survival. Low-SMN neurons also exhibit increased spontaneous activity, linking endogenous SMN abundance to neuronal physiology and survival. In vivo, selectively vulnerable MN populations display corresponding shifts in endogenous SMN abundance during disease progression, supporting the relevance of SMN-defined vulnerability states beyond in vitro models. Integrated transcriptomic and proteomic analyses reveal distinct molecular programs associated with resilient and vulnerable states, including RNA metabolism, proteostasis, cytoskeletal organization, neuronal activity and stress responses. Among conserved molecular differences, the anti-apoptotic regulator LMO3 emerged as a candidate mediator of resilience. LMO3 overexpression reduced expression of p53-responsive genes, increased MN survival and shifted neurons toward higher endogenous SMN states. Together, these findings establish endogenous protein heterogeneity as a determinant of dynamic neuronal vulnerability and reveal neuronal resilience as a plastic molecular state that can be identified and therapeutically reinforced.

neuroscience↗

bioRxiv2026

System-Wide Proteomic Remodeling in Spinal Muscular Atrophy Reveals Tissue-Specific Responses and Partial Rescue by SMN Restoration

Spinal muscular atrophy (SMA), traditionally defined as a neuromuscular disorder characterized by degeneration of lower motor neurons, is increasingly recognized as a multi-organ disease. SMA is caused by deficiency of the survival motor neuron (SMN) protein below a critical threshold required for cellular homeostasis. While motor neurons are particularly vulnerable, the ubiquitous expression and fundamental functions of SMN result in widespread perturbations across multiple tissues. Here, we generated a label-free quantitative proteomics atlas of spinal cord, heart, and gastrocnemius muscle from wild-type, heterozygous, and SMA mice at the symptomatic stage, including cohorts treated, at postnatal day 1 (P1), with a systemic suboptimal dose of SMN antisense oligonucleotides (SMN-ASOs), resulting in partial SMN restoration. SMN deficiency induced pronounced, tissue-specific proteome remodeling, with peripheral tissues exhibiting broader molecular alterations than spinal cord. Cross-tissue analyses revealed limited overlap, although heart and muscle showed partial convergence in metabolic and mitochondrial-associated pathways. SMN-ASO treatment partially repositioned these proteomes toward control states; however, restoration was incomplete and strongly tissue-dependent, with persistent dysregulation of mitochondrial and metabolic pathways. These findings demonstrate that SMN deficiency drives systemic yet heterogeneous proteome remodeling and that partial SMN restoration does not fully reverse established molecular alterations. Graphical Abstract O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=99 SRC="FIGDIR/small/715402v1_ufig1.gif" ALT="Figure 1"> View larger version (35K): org.highwire.dtl.DTLVardef@114d73borg.highwire.dtl.DTLVardef@13e8c13org.highwire.dtl.DTLVardef@15e4ba0org.highwire.dtl.DTLVardef@1b70fb8_HPS_FORMAT_FIGEXP M_FIG C_FIG

cell biology↗

bioRxiv2026

Pharmacological Activation of NRF2 by Omaveloxolone Upregulates NRF2-Target Proteins in SMA Type I Human Fibroblasts

Spinal muscular atrophy (SMA) is caused by loss of SMN protein and is increasingly recognized as a multisystem disorder involving molecular pathology beyond motor neurons. Recently, we identified NRF2-KEAP1 signaling as dysregulated in SMA mice. Because NRF2 coordinates transcriptional programs that maintain cellular redox homeostasis and adaptive stress responses, we investigated whether NRF2 signaling is similarly altered in SMA type I patient-derived fibroblasts and whether it can be pharmacologically engaged. Compared with control fibroblasts, SMA fibroblasts displayed reduced basal expression of NRF2 target proteins, including NQO1 and xCT (SLC7A11), along with decreased levels of PGC1. Omaveloxolone (OMAV), a pharmacological NRF2 activator approved for the treatment of Friedreichs ataxia, increased cell viability and upregulated NRF2 target proteins in both control and SMA fibroblasts. Notably, OMAV produced a modest increase in SMN protein abundance and PGC1 levels selectively in SMA cells. Together, these findings support diminished NRF2 pathway output as a feature of SMA fibroblasts and demonstrate that OMAV induces NRF2 target proteins in this human SMA cellular model, consistent with enhanced cytoprotective signaling. Graphical abstract O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=104 SRC="FIGDIR/small/712434v1_ufig1.gif" ALT="Figure 1"> View larger version (33K): org.highwire.dtl.DTLVardef@19b82b0org.highwire.dtl.DTLVardef@a11691org.highwire.dtl.DTLVardef@1d089e9org.highwire.dtl.DTLVardef@e48ef_HPS_FORMAT_FIGEXP M_FIG C_FIG

cell biology↗

bioRxiv2026

SMN deficiency disrupts hepatic mitochondrial iron homeostasis and NRF2-dependent redox control in spinal muscular atrophy

Spinal muscular atrophy (SMA), classically defined as a motor neuron disorder caused by deficiency of the survival motor neuron (SMN) protein, is increasingly recognized as a multi-system disease. Among peripheral organs, the liver, essential for metabolic regulation and xenobiotic processing, remains underexplored despite growing evidence of dysfunction. Defining hepatic contributions may be critical for understanding systemic disease progression and optimizing therapeutic strategies. Here, we performed integrative profiling of liver pathology in SMA by combining unbiased proteomics from wild-type (WT), heterozygous (HET), and SMA mice at the late symptomatic stage (postnatal day 10; P10) with targeted analyses of mitochondrial function, iron metabolism, and redox homeostasis. To resolve temporal dynamics, key pathways were examined at early symptomatic disease (P5), and the reversibility of identified defects was evaluated following SMN-restoring antisense oligonucleotide (ASO) therapy. We uncover early (P5) activation of the heme biosynthetic pathway, marked by increased ferrochelatase (FECH), preceding overt metabolic disruption. By P10, SMA liver shows a coordinated loss of mitochondrial Complex II integrity, pathological mitochondrial iron accumulation, disruption of the NRF2-KEAP1 antioxidant axis, and heightened susceptibility to ferroptotic redox stress. ASO treatment robustly restored mitochondrial and redox phenotypes, yet FECH remained elevated, indicating sustained heme pathway activation despite SMN rescue. HET mice displayed mild redox abnormalities, revealing a dosage-sensitive hepatic phenotype. Collectively, these findings delineate a mitochondrial-iron-redox axis uniquely vulnerable in SMA liver, identify ferroptotic sensitivity as an early and therapeutically responsive feature, and highlight persistent heme biosynthesis activation as a target to complement SMN-directed therapies.

cell biology↗

bioRxiv2025

Clinical relevance of zebrafish for gene variants testing. Proof-of-principle with SMN1/SMA.

Spinal muscular atrophy (SMA) results from SMN1 gene loss-of-function (LOF), with disease severity directly linked to the level of remaining SMN protein. Nusinersen, risdiplam and onasemnogene abeparvovec are revolutionary treatments but should ideally be implemented before clinical symptoms appear. Because of this, prenatal and newborn screenings are increasingly used to identify common SMN1 mutations and patients requiring therapy. However, for novel mutations, clinicians lack robust analytic tools to predict pathogenicity before irreversible damage occurs. To address this gap, we deployed a zebrafish model presenting smn1-LOF, exhibiting progressive motor defects and death by only six days of age. We evaluated two SMN1-variants (VUS) identified in newborn patients awaiting definite diagnosis and treatment recommendations. We demonstrated that while known pathogenic variants did not change the disease course, wild-type SMN1 and both patient variants rescued SMA hallmarks in zebrafish, demonstrating the relevance of this approach for VUS-testing within a crucial timeframe for patients. Both VUS turned out to be non-pathogenic, and therapeutic costs of >US$2 million per child were avoided. Beyond SMA, this study provides robust proof-of-principle that the zebrafish represents a powerful translational tool for VUS-analysis, and that such approaches should be considered in clinical settings for supporting diagnosis and treatment decisions.

neuroscience↗

bioRxiv2023

CLUH maintains functional mitochondria and translation in motoneuronal axons and prevents peripheral neuropathy

Transport and local translation of mRNAs in distal axonal compartments are essential for neuronal viability. Local synthesis of nuclear-encoded mitochondrial proteins protects mitochondria from damage during their long journey along the axon, however the regulatory factors involved are largely unknown. Here, we show that CLUH, a cytosolic protein that binds mRNAs encoding mitochondrial proteins, is essential for preventing axonal degeneration of spinal motoneurons and maintaining motor behavior in the mouse. We demonstrate that CLUH is enriched in the growth cone of developing spinal motoneurons and is required for their growth. The absence of CLUH affects the abundance of target mRNAs and the corresponding mitochondrial proteins more prominently in axons, leading to ATP deficits specifically in the growth cone. CLUH binds ribosomal subunits, translation initiation and ribosome recycling components, and preserves axonal translation. Overexpression of the ribosome recycling factor ABCE1 rescues the growth cone and translation defects in CLUH-deficient motoneurons. In conclusion, we demonstrate a role for CLUH in mitochondrial quality control and translational regulation in axons, which are essential for their development and long-term integrity and function.

cell biology↗

bioRxiv2023

An isogenic human iPSC model unravels neurodevelopmental abnormalities in SMA

Whether neurodevelopmental defects underlie the selective neuronal death that characterizes neurodegenerative diseases is becoming an intriguing question. To address it, we focused on the motor neuron (MN) disease Spinal Muscular Atrophy (SMA), caused by reduced levels of the ubiquitous protein SMN. Taking advantage of the first isogenic human induced pluripotent stem cell-derived SMA model that we have generated and a spinal cord organoid system, here we report that the relative and temporal expression of early neural progenitor and MN markers is altered in SMA. Furthermore, the corrected isogenic controls only partially reverse these abnormalities. These findings raise the relevant clinical implication that SMN-increasing treatments might not fully amend SMA pathological phenotypes. The approach we have taken demonstrates that the discovery of new disease mechanisms is greatly improved by using human isogenic models. Moreover, our study implies that SMA has a developmental component that might trigger the MN degeneration.

neuroscience↗

bioRxiv2022

Autophagy regulates neuronal excitability by controlling cAMP/Protein Kinase A signaling

Autophagy provides nutrients during starvation and eliminates detrimental cellular components. However, accumulating evidence indicates that autophagy is not merely a housekeeping process. Here, we show that the protein AuTophaGy 5 (ATG5) functions in neurons to regulate the cAMP-dependent protein kinase A (PKA)-mediated phosphorylation of a synapse-confined proteome. This function of ATG5 is independent of bulk turnover of synaptic proteins and requires the targeting of PKA inhibitory R1 subunits to autophagosomes. Neuronal loss of ATG5 causes synaptic accumulation of PKA R1, which sequesters the PKA catalytic subunit and diminishes the cAMP/PKA-dependent phosphorylation of postsynaptic cytoskeletal proteins mediating AMPAR trafficking. Glutamatergic neurons-confined ATG5 deletion augments AMPAR-dependent excitatory neurotransmission and causes the appearance of spontaneous recurrent seizures in mice. Our findings identify a novel role of autophagy in regulating PKA signaling at glutamatergic synapses and suggest the PKA as a target for restoration of synaptic function in neurodegenerative conditions with autophagy dysfunction.

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↗