Biology subjects

Mentis, G. Z.

Publications and source records attributed to Mentis, G. Z..

7 recordsLinked to original sources

bioRxiv2026

A standardized framework resolves ambiguity in motor neuron loss across neurodegenerative diseases

Motor neuron (MN) loss is a hallmark of neurodegenerative disorders, yet its assessment remains variable, confounding mechanistic and therapeutic interpretation. To address this, we conducted a systematic review and meta-analysis of spinal muscular atrophy (SMA) mouse studies, revealing 60% variability in reported MN loss, largely attributable to nonspecific spinal cord sampling. Using a whole-segment approach with tissue clearing, MN tracing, and multimodal imaging, we confirmed segment-dependent differences in MN counts. Common MN markers (SMI-32, Nissl) lacked specificity, whereas choline acetyltransferase (ChAT) provided robust labeling in murine and human spinal cords. Deep learning-based whole-mount segmentation enabled unbiased MN quantification and validated manual counts. Integrating analysis with computational modeling established segment sampling as a key driver of variability and revealed degeneration patterns: widespread MN loss in amyotrophic lateral sclerosis (ALS), selective MN loss in severe SMA, and preservation in mild SMA models. These findings establish a framework for reproducible MN quantification. HighlightsO_LISpinal cord segment-specific analysis reduces variability and allows accurate MN quantification C_LIO_LIChAT is the most reliable MN marker in murine and human spinal cords C_LIO_LIDeep learning-based segmentation enables unbiased MN quantification in intact spinal cords C_LIO_LIMN degeneration is widespread in ALS but restricted to pools innervating proximal muscles in severe SMA C_LI

neuroscience↗

bioRxiv2025

A mouse model of CHCHD10 p.R15L familial ALS presents mild, age-related motor neuron degeneration without protein instability or mitochondrial dysfunction

Mutations in the mitochondrial protein CHCHD10 (D10) cause a spectrum of hereditary neurodegenerative disorders. Among these, the p.R15L variant is linked to a slowly progressive, late-onset familial form of amyotrophic lateral sclerosis (ALS) with unclear pathogenic mechanisms. To better understand this, we investigated a knock-in (KI) mouse model carrying the p.R15L mutation in the endogenous protein. Unlike previously described mutant D10 KI models, p.R15L KI mice exhibited normal D10 protein levels, with no evidence of large protein aggregates. Mitochondrial respiration and hydrogen peroxide emission in mitochondria isolated from muscle and brain were unaltered. Similarly, fibroblasts from human p.R15L carriers exhibited normal D10 levels and unchanged oxidative phosphorylation function. Histochemical analyses of p.R15L KI muscle revealed mild increases in mitochondrial enzymatic activity in a subset of muscle fibers and muscle transcriptomics showed elevated expression of PGC-1, suggesting enhanced mitochondrial biogenesis. p.R15L KI mice developed subtle, late-onset phenotypes, including reduced body weight and motor activity and increased anxiety-like behavior. Importantly, in aged mice electrophysiological studies demonstrated decreased amplitude of the compound muscle action potential, commensurate with a moderate loss of spinal cord motor neurons and elevated serum neurofilament light levels, indicative of neurodegeneration. Together, these results indicate that the p.R15L mutation produces a mild, late-onset motor neuron phenotype in mice, partially recapitulating the human disease, without mitochondrial functional or morphological alterations. The findings indicate that p.R15L D10 selectively impairs mouse motor neurons through a gain-of-function mechanism, providing a genetically accurate yet mild in vivo model of familial ALS.

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↗

bioRxiv2023

C3 and CD47 dependent mechanisms in the refinement of sensory-motor circuits during spinal cord development

Overground movement in mammals requires the assembly and refinement of sensory-motor circuits. Within the spinal cord, sensory neurons, interneurons and motor neurons form intricate neuronal circuits to ensure proper motor control. In the developing brain, supernumerary synapses are initially formed and subsequently pruned making way for the emergence of mature circuits. However, whether this occurs within spinal sensory-motor circuits, it has not been firmly established. Moreover, it is also unknown if a combination of distinct molecules are required to refine spinal cord neuronal circuits. Here, we demonstrate the presence of supernumerary synapses which form inappropriate contacts, resulting in miswired immature spinal neuronal circuits. We determined that inappropriate synapses are of proprioceptive sensory origin and are functional, leading to impaired motor behavior. Using mouse genetics, viral-mediated neuronal map strategies, electrophysiology, and behavioral assessments, we demonstrate that two molecularly distinct mechanisms are responsible for the refinement of spinal circuits. First, we identify C3 as a major contributing factor through classical complement activation. Second, a CD47-dependent mechanism, operating in parallel to classical complement, causing elimination of inappropriate synapses. This finding underlies an unexpected function for CD47 within the spinal cord, in striking contrast to its function in the brain. Our study demonstrates that during early development, the natural course of elimination of inappropriately-generated synapses utilizes a dual fail-safe system to ensure the emergence of normal spinal reflexes and proper behavior in 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

Molecular development of muscle spindle and Golgi tendon organ sensory afferents revealed by single proprioceptor transcriptome analysis

Anatomical and physiological analyses have long revealed differences between proprioceptive groups Ia, II, and Ib sensory neurons, yet the molecular correlates of these three muscle afferent subtypes remain unknown. We performed single cell RNA sequencing of genetically identified adult proprioceptors and, using unbiased bioinformatics approaches, detected five molecularly distinct neuronal clusters. Validation of cluster-specific transcripts in dorsal root ganglia (DRG) and skeletal muscle provides evidence these clusters correspond to functionally distinct muscle spindle (MS) or Golgi tendon organ (GTO) afferent proprioceptors. Remarkably, while we uncovered just one type of GTO afferents, four of the five clusters represent MS afferents, thus demonstrating a previously unappreciated diversity among these muscle proprioceptors. In vitro electrophysiological recordings reveal just two broadly distinct proprioceptor types, and suggest that the refinement of functional subtype diversity may occur along multiple axes of maturation. Lineage analysis between proprioceptor transcriptomes at different developmental stages show little or no correlation for transcripts that define adult MS or GTO afferents, supporting the idea that proprioceptor subtype identity emerges late in development. Together, our data provide the first comprehensive molecular signature for groups Ia and II MS afferents and group Ib GTO afferents, and offer new strategies for genetic interrogation of the role of these individual proprioceptor subtypes in regulating voluntary motor behavior.

neuroscience↗

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↗