Intellectual disability (ID) is a pathological condition characterized by limited intellectual functioning and adaptive behaviors. It affects 1–3% of the worldwide population, and no pharmacological therapies are currently available. More than 1000 genes have been found mutated in ID patients pointing out that, despite the common phenotype, the genetic bases are highly heterogeneous and apparently unrelated. Bibliomic analysis reveals that ID genes converge onto a few biological modules, including cytoskeleton dynamics, whose regulation depends on Rho GTPases transduction. Genetic variants exert their effects at different levels in a hierarchical arrangement, starting from the molecular level and moving toward higher levels of organization, i.e., cell compartment and functions, circuits, cognition, and behavior. Thus, cytoskeleton alterations that have an impact on cell processes such as neuronal migration, neuritogenesis, and synaptic plasticity rebound on the overall establishment of an effective network and consequently on the cognitive phenotype. Systems biology (SB) approaches are more focused on the overall interconnected network rather than on individual genes, thus encouraging the design of therapies that aim to correct common dysregulated biological processes. This review summarizes current knowledge about cytoskeleton control in neurons and its relevance for the ID pathogenesis, exploiting in silico modeling and translating the implications of those findings into biomedical research.

Findings accumulated over time show that neurophysiological, neuropathological, and molecular alterations are present in CMT1A and support the dysmyelinating rather than demyelinating nature of this neuropathy. Moreover, uniform slowing of nerve conduction velocity is already manifest in CMT1A children and does not improve throughout their life. This evidence and our previous studies displaying aberrant myelin composition and structure in adult CMT1A rats prompt us to hypothesize a myelin and axon developmental defect in the CMT1A peripheral nervous system. Peripheral myelination begins during the early stages of development in mammals and, during this process, chemical and structural features of myelinated fibers (MFs) evolve towards a mature phenotype; deficiencies within this self-modulating circuit can cause its blockage. Therefore, to shed light on pathophysiological mechanisms that occur during development, and to investigate the relationship among axonal, myelin, and lipidome deficiencies in CMT1A, we extensively analyzed the evolution of both myelin lipid profile and MF structure in WT and CMT1A rats. Lipidomic analysis revealed a delayed maturation of CMT1A myelin already detectable at P10 characterized by a deprivation of sphingolipid species such as hexosylceramides and long-chain sphingomyelins, whose concentration physiologically increases in WT, and an increase in lipids typical of unspecialized plasma membranes, including phosphatidylcholines and phosphatidylethanolamines. Consistently, advanced morphometric analysis on more than 130,000 MFs revealed a delay in the evolution of CMT1A axon and myelin geometric parameters, appearing concomitantly with lipid impairment. We here demonstrate that, during normal development, MFs undergo a continuous maturation process in both chemical composition and physical structure, but these processes are delayed in CMT1A.

Purpose: The skeletal muscle has been proposed to contribute to the progressive loss of motor neurons typical of amyotrophic lateral sclerosis (ALS). However, this mechanism has not yet been clarified due to the lack of suitable imaging tools. Here, we aimed to verify whether PET imaging of the translocator protein 18 kDa (TSPO) can detect a muscular abnormality in an experimental model of ALS. Methods: In vivo biodistribution and kinetics of [¹⁸F]DPA-714 were analyzed in skeletal muscle and brain of SOD1^G93A transgenic mice and in wildtype (WT) littermates. Both cohorts were divided into three groups (n = 6 each) to be studied at 60, 90 and 120 days. After microPET imaging, animals were sacrificed to evaluate inflammatory infiltrates by hematoxylin/eosin staining and TSPO expression by immunohistochemistry and Western blot in both quadriceps and brain. Results: [¹⁸F]DPA-714 uptake was higher in the skeletal muscles of SOD1^G93A than in WT mice in the preclinical phase (60 and 90 days) and further increased up to the symptomatic late stage (120 days). Inflammatory cells were absent in the quadriceps of SOD1^G93A mice whose myocytes, instead, showed a progressive increase in TSPO expression with advancing age. By contrast, brain tracer uptake and TSPO expression were comparably low in both groups, regardless of age and genotype. Conclusion: Upregulation of TSPO expression is characteristic of skeletal muscle, but not the brain, in the experimental SOD1^G93A mouse model of ALS. Tracers targeting this pathway have been mostly proposed for the evaluation of inflammatory processes within the central nervous system. Nevertheless, the ubiquitous nature of TSPO expression and its responsiveness to various signals may broaden the diagnostic potential of these tracers to include disease conditions beyond inflammation.

1. Findings accumulated over time show that neurophysiological, neuropathological, and molecular alterations are present in CMT1A and support the dysmyelinating rather than demyelinating nature of this neuropathy. Moreover, uniform slowing of nerve conduction velocity is already manifest in CMT1A children and does not improve throughout their life. This evidence and our previous studies displaying aberrant myelin composition and structure in adult CMT1A rats prompt us to hypothesize a myelin and axon developmental defect in the CMT1A peripheral nervous system. Peripheral myelination begins during the early stages of development in mammals and, during this process, chemical and structural features of myelinated fibers (MFs) evolve towards a mature phenotype; deficiencies within this self-modulating circuit can cause its blockage. Therefore, to shed light on pathophysiological mechanisms that occur during development, and to investigate the relationship among axonal, myelin, and lipidome deficiencies in CMT1A, we extensively analyzed the evolution of both myelin lipid profile and MF structure in WT and CMT1A rats. Lipidomic analysis revealed a delayed maturation of CMT1A myelin already detectable at P10 characterized by deprivation of sphingolipid species such as hexosylceramides and long-chain sphingomyelins, whose concentration physiologically increases in WT, and an increase in lipids typical of unspecialized plasma membranes, including phosphatidylcholines and phosphatidylethanolamines. Consistently, advanced morphometric analysis on more than 130.000 MFs revealed a delay in the evolution of CMT1A axon and myelin geometric parameters, appearing concomitantly with lipid impairment. We here demonstrate that, during normal development, MFs undergo a continuous maturation process in both chemical composition and physical structure, but these processes are delayed in CMT1A.

Charcot–Marie–Tooth type 1A (CMT1A) is the most common inherited peripheral neuropathy, caused by duplication of the peripheral myelin protein 22 ( PMP22 ) gene and characterized by dysmyelination and defects in myelin maturation. Hypercellularity is a prominent feature of the disease, although its origin, persistence, and underlying mechanisms remain controversial. Here, we performed a longitudinal analysis of sciatic nerves from wild-type (WT) and CMT1A rats between 2 and 12 months of age. We demonstrated that CMT1A nerves exhibit persistent cellular proliferation extending into adulthood. This phenotype is confirmed by bulk RNA-seq data showing sustained enrichment of proliferation-associated gene signatures. Cell-type signature analysis identifies overrepresentation of immature, neural crest-related, and epithelial-mesenchymal transitional (EMT) transcriptional programs in CMT1A nerves. Among the most upregulated genes, RUNX2 showed strong and prolonged expression at both transcript and protein levels. Consistently with the key role of RUNX2 in the activation of the injury response, CMT1A nerves also showed a marked enrichment in SOX10 ⁺ /JUN ⁺ cells, that only partially overlap with SOX10 ⁺ /RUNX2 ⁺ cells, indicating a maladaptive activation of the injury-like Schwann cell (SC) program. Interestingly, we detected robust upregulation of SMOC2, an extracellular matrix protein selectively expressed by endoneurial fibroblasts, pointing to activation of non-canonical cell types and altered extracellular matrix remodeling. Together, these data demonstrate that CMT1A peripheral nerves are characterized by chronic hypercellularity driven by persistent proliferation, EMT, and dysregulated injury transcriptional programs, collectively pointing at progressive and multicellular nerve remodeling as a relevant pathomechanism in the disease. Highlights: CMT1A nerves exhibit persistent proliferation throughout adulthood CMT1A induces immature and injury prone transcriptional programs RUNX2 marks a distinct Schwann cell subpopulation in CMT1A nerves Endoneurial fibroblasts contribute to progressive nerve remodeling

Summary: Psychedelic compounds such as lysergic acid diethylamide (LSD) are increasingly studied for their neuroplastic effects and potential relevance to brain aging and neurodegeneration. However, the molecular mechanisms linking psychedelic-induced plasticity to age-associated cognitive decline remain unclear. Brain aging and dementia are characterized by coordinated transcriptional programs that underlie synaptic dysfunction and altered neuron-glia interactions. If psychedelic-induced plasticity engages opposing molecular programs, it could counteract these conserved trajectories. In computational drug discovery, this concept has been formalized as the principle of transcriptional signature reversal, whereby compounds inducing gene expression states opposite to disease-associated programs may exert a therapeutic effect by counteracting disease-associated phenotypes. Here, we combine cross-species transcriptomic analyses with experimental validation to test whether LSD opposes conserved signatures of brain aging and dementia. By comparing transcriptional profiles induced by chronic LSD treatment in rodents with age- and dementia-associated gene expression changes in the human prefrontal cortex, we show that LSD induces gene expression patterns strongly anti-correlated with aging and neurodegeneration programs. This reversal is specific compared to other pharmacological perturbations and is reproducible across datasets and species. Moreover, LSD counteracts amyloid-β-induced structural and molecular alterations in primary cortical neurons, linking transcriptomic opposition to functional rescue under neurodegenerative stress. Together, our findings suggest that LSD modulates molecular and cellular pathways associated with brain aging and neurodegeneration, linking systems-level gene expression changes to structural and functional resilience in neurodegeneration-relevant contexts.