Large-scale animal model study uncovers altered brain pH and lactate levels as a transdiagnostic endophenotype of neuropsychiatric disorders involving cognitive impairment.

Increased levels of lactate, an end-product of glycolysis, have been proposed as a potential surrogate marker for metabolic changes during neuronal excitation. These changes in lactate levels can result in decreased brain pH, which has been implicated in patients with various neuropsychiatric disorders. We previously demonstrated that such alterations are commonly observed in five mouse models of schizophrenia, bipolar disorder, and autism, suggesting a shared endophenotype among these disorders rather than mere artifacts due to medications or agonal state. However, there is still limited research on this phenomenon in animal models, leaving its generality across other disease animal models uncertain. Moreover, the association between changes in brain lactate levels and specific behavioral abnormalities remains unclear. To address these gaps, the International Brain pH Project Consortium investigated brain pH and lactate levels in 109 strains/conditions of 2294 animals with genetic and other experimental manipulations relevant to neuropsychiatric disorders. Systematic analysis revealed that decreased brain pH and increased lactate levels were common features observed in multiple models of depression, epilepsy, Alzheimer's disease, and some additional schizophrenia models. While certain autism models also exhibited decreased pH and increased lactate levels, others showed the opposite pattern, potentially reflecting subpopulations within the autism spectrum. Furthermore, utilizing large-scale behavioral test battery, a multivariate cross-validated prediction analysis demonstrated that poor working memory performance was predominantly associated with increased brain lactate levels. Importantly, this association was confirmed in an independent cohort of animal models. Collectively, these findings suggest that altered brain pH and lactate levels, which could be attributed to dysregulated excitation/inhibition balance, may serve as transdiagnostic endophenotypes of debilitating neuropsychiatric disorders characterized by cognitive impairment, irrespective of their beneficial or detrimental nature.

Identification of small molecule inhibitors of G3BP-driven stress granule formation.

Stress granule formation is triggered by the release of mRNAs from polysomes and is promoted by the action of the RNA-binding proteins G3BP1/2. Stress granules have been implicated in several disease states, including cancer and neurodegeneration. Consequently, compounds that limit stress granule formation or promote their dissolution have potential as both experimental tools and novel therapeutics. Herein, we describe two small molecules, G3BP inhibitor a and b (G3Ia and G3Ib), designed to bind to a specific pocket in G3BP1/2 that is targeted by viral inhibitors of G3BP1/2 function. In addition to disrupting the co-condensation of RNA, G3BP1, and caprin 1 in vitro, these compounds inhibit stress granule formation in cells treated prior to or concurrent with stress and dissolve pre-existing stress granules. These effects are consistent across multiple cell types and a variety of initiating stressors. Thus, these compounds represent powerful tools to probe the biology of stress granules and hold promise for therapeutic interventions designed to modulate stress granule formation.

RNA Foci in Two bi-Allelic RFC1 Expansion Carriers.

Cerebellar ataxia, neuropathy, vestibular areflexia syndrome (CANVAS) is a late-onset, autosomal recessive neurodegenerative disorder caused by biallelic AAGGG/ACAGG repeat expansion (AAGGG-exp/ACAGG-exp) in RFC1. The recent identification of patients with CANVAS exhibiting compound heterozygosity for AAGGG-exp and truncating variants supports the loss-of-function of RFC1 in CANVAS patients. We investigated the pathological changes in 2 autopsied patients with CANVAS harboring biallelic ACAGG-exp and AAGGG-exp. RNA fluorescence in situ hybridization of the 2 patients revealed CCTGT- and CCCTT-containing RNA foci, respectively, in neuronal nuclei of tissues with neuronal loss. Our findings suggest that RNA toxicity may be involved in the pathogenesis of CANVAS. ANN NEUROL 2024;95:607-613.

Identification of small molecule inhibitors of G3BP-driven stress granule formation.

Stress granule formation is triggered by the release of mRNAs from polysomes and is promoted by the action of the paralogs G3BP1 and G3BP2. G3BP1/2 proteins bind mRNAs and thereby promote the condensation of mRNPs into stress granules. Stress granules have been implicated in several disease states, including cancer and neurodegeneration. Consequently, compounds that limit stress granule formation or promote their dissolution have potential as both experimental tools and novel therapeutics. Herein, we describe two small molecules, referred to as G3BP inhibitor a and b (G3Ia and G3Ib), designed to bind to a specific pocket in G3BP1/2 that is known to be targeted by viral inhibitors of G3BP1/2 function. In addition to disrupting co-condensation of RNA, G3BP1, and caprin 1 in vitro, these compounds inhibit stress granule formation in cells treated prior to or concurrent with stress, and dissolve pre-existing stress granules when added to cells after stress granule formation. These effects are consistent across multiple cell types and a variety of initiating stressors. Thus, these compounds represent ideal tools to probe the biology of stress granules and hold promise for therapeutic interventions designed to modulate stress granule formation.

A murine model of hnRNPH2-related neurodevelopmental disorder reveals a mechanism for genetic compensation by Hnrnph1.

Mutations in HNRNPH2 cause an X-linked neurodevelopmental disorder with features that include developmental delay, motor function deficits, and seizures. More than 90% of patients with hnRNPH2 have a missense mutation within or adjacent to the nuclear localization signal (NLS) of hnRNPH2. Here, we report that hnRNPH2 NLS mutations caused reduced interaction with the nuclear transport receptor Kapß2 and resulted in modest cytoplasmic accumulation of hnRNPH2. We generated 2 knockin mouse models with human-equivalent mutations in Hnrnph2 as well as Hnrnph2-KO mice. Knockin mice recapitulated clinical features of the human disorder, including reduced survival in male mice, impaired motor and cognitive functions, and increased susceptibility to audiogenic seizures. In contrast, 2 independent lines of Hnrnph2-KO mice showed no detectable phenotypes. Notably, KO mice had upregulated expression of Hnrnph1, a paralog of Hnrnph2, whereas knockin mice failed to upregulate Hnrnph1. Thus, genetic compensation by Hnrnph1 may counteract the loss of hnRNPH2. These findings suggest that HNRNPH2-related disorder may be driven by a toxic gain of function or a complex loss of HNRNPH2 function with impaired compensation by HNRNPH1. The knockin mice described here are an important resource for preclinical studies to assess the therapeutic benefit of gene replacement or knockdown of mutant hnRNPH2.

Phosphorylated CRMP1, axon guidance protein, is a component of spheroids and is involved in axonal pathology in amyotrophic lateral sclerosis.

In amyotrophic lateral sclerosis (ALS), neurodegeneration is characterized by distal axonopathy that begins at the distal axons, including the neuromuscular junctions, and progresses proximally in a "dying back" manner prior to the degeneration of cell bodies. However, the molecular mechanism for distal axonopathy in ALS has not been fully addressed. Semaphorin 3A (Sema3A), a repulsive axon guidance molecule that phosphorylates collapsin response mediator proteins (CRMPs), is known to be highly expressed in Schwann cells near distal axons in a mouse model of ALS. To clarify the involvement of Sema3A-CRMP signaling in the axonal pathogenesis of ALS, we investigated the expression of phosphorylated CRMP1 (pCRMP1) in the spinal cords of 35 patients with sporadic ALS and seven disease controls. In ALS patients, we found that pCRMP1 accumulated in the proximal axons and co-localized with phosphorylated neurofilaments (pNFs), which are a major protein constituent of spheroids. Interestingly, the pCRMP1:pNF ratio of the fluorescence signal in spheroid immunostaining was inversely correlated with disease duration in 18 evaluable ALS patients, indicating that the accumulation of pCRMP1 may precede that of pNFs in spheroids or promote ALS progression. In addition, overexpression of a phospho-mimicking CRMP1 mutant inhibited axonal outgrowth in Neuro2A cells. Taken together, these results indicate that pCRMP1 may be involved in the pathogenesis of axonopathy in ALS, leading to spheroid formation through the proximal progression of axonopathy.

Inhibition of Crmp1 Phosphorylation at Ser522 Ameliorates Motor Function and Neuronal Pathology in Amyotrophic Lateral Sclerosis Model Mice.

Amyotrophic lateral sclerosis (ALS) is a rapidly progressive and fatal neurodegenerative disorder that affects upper and lower motor neurons; however, its pathomechanism has not been fully elucidated. Using a comprehensive phosphoproteomic approach, we have identified elevated phosphorylation of Collapsin response mediator protein 1 (Crmp1) at serine 522 in the lumbar spinal cord of ALS model mice overexpressing a human superoxide dismutase mutant (SOD1G93A). We investigated the effects of Crmp1 phosphorylation and depletion in SOD1G93A mice using Crmp1S522A (Ser522→Ala) knock-in (Crmp1ki/ki ) mice in which the S522 phosphorylation site was abolished and Crmp1 knock-out (Crmp1-/-) mice, respectively. Crmp1ki/ki /SOD1G93A mice showed longer latency to fall in a rotarod test while Crmp1-/-/SOD1G93A mice showed shorter latency compared with SOD1G93A mice. Survival was prolonged in Crmp1ki/ki /SOD1G93A mice but not in Crmp1-/-/SOD1G93A mice. In agreement with these phenotypic findings, residual motor neurons and innervated neuromuscular junctions (NMJs) were comparatively well-preserved in Crmp1ki/ki /SOD1G93A mice without affecting microglial and astroglial pathology. Pathway analysis of proteome alterations showed that the sirtuin signaling pathway had opposite effects in Crmp1ki/ki /SOD1G93A and Crmp1-/-/SOD1G93A mice. Our study indicates that modifying CRMP1 phosphorylation is a potential therapeutic strategy for ALS.

Ubiquitination is essential for recovery of cellular activities after heat shock.

Eukaryotic cells respond to stress through adaptive programs that include reversible shutdown of key cellular processes, the formation of stress granules, and a global increase in ubiquitination. The primary function of this ubiquitination is thought to be for tagging damaged or misfolded proteins for degradation. Here, working in mammalian cultured cells, we found that different stresses elicited distinct ubiquitination patterns. For heat stress, ubiquitination targeted specific proteins associated with cellular activities that are down-regulated during stress, including nucleocytoplasmic transport and translation, as well as stress granule constituents. Ubiquitination was not required for the shutdown of these processes or for stress granule formation but was essential for the resumption of cellular activities and for stress granule disassembly. Thus, stress-induced ubiquitination primes the cell for recovery after heat stress.

Clinical evidence that a dysregulated master neural network modulator may aid in diagnosing schizophrenia.

There are no validated biomarkers for schizophrenia (SCZ), a disorder linked to neural network dysfunction. We demonstrate that collapsin response mediator protein-2 (CRMP2), a master regulator of cytoskeleton and, hence, neural circuitry, may form the basis for a biomarker because its activity is uniquely imbalanced in SCZ patients. CRMP2's activity depends upon its phosphorylation state. While an equilibrium between inactive (phosphorylated) and active (nonphosphorylated) CRMP2 is present in unaffected individuals, we show that SCZ patients are characterized by excess active CRMP2. We examined CRMP2 levels first in postmortem brains (correlated with neuronal morphometrics) and then, because CRMP2 is expressed in lymphocytes as well, in the peripheral blood of SCZ patients versus age-matched unaffected controls. In the brains and, more starkly, in the lymphocytes of SCZ patients <40 y old, we observed that nonphosphorylated CRMP2 was higher than in controls, while phosphorylated CRMP2 remained unchanged from control. In the brain, these changes were associated with dendritic structural abnormalities. The abundance of active CRMP2 with insufficient opposing inactive p-CRMP2 yielded a unique lowering of the p-CRMP2:CRMP2 ratio in SCZ patients, implying a disruption in the normal equilibrium between active and inactive CRMP2. These clinical data suggest that measuring CRMP2 and p-CRMP2 in peripheral blood might reflect intracerebral processes and suggest a rapid, minimally invasive, sensitive, and specific adjunctive diagnostic aid for early SCZ: increased CRMP2 or a decreased p-CRMP2:CRMP2 ratio may help cinch the diagnosis in a newly presenting young patient suspected of SCZ (versus such mimics as mania in bipolar disorder, where the ratio is high).

SGTA associates with intracellular aggregates in neurodegenerative diseases.

Intracellular aggregates are a common pathological hallmark of neurodegenerative diseases such as polyglutamine (polyQ) diseases, amyotrophic lateral sclerosis (ALS), Parkinson's disease (PD), and multiple system atrophy (MSA). Aggregates are mainly formed by aberrant disease-specific proteins and are accompanied by accumulation of other aggregate-interacting proteins. Although aggregate-interacting proteins have been considered to modulate the formation of aggregates and to be involved in molecular mechanisms of disease progression, the components of aggregate-interacting proteins remain unknown. In this study, we showed that small glutamine-rich tetratricopeptide repeat-containing protein alfa (SGTA) is an aggregate-interacting protein in neurodegenerative diseases. Immunohistochemistry showed that SGTA interacted with intracellular aggregates in Huntington disease (HD) cell models and neurons of HD model mice. We also revealed that SGTA colocalized with intracellular aggregates in postmortem brains of patients with polyQ diseases including spinocerebellar ataxia (SCA)1, SCA2, SCA3, and dentatorubral-pallidoluysian atrophy. In addition, SGTA colocalized with glial cytoplasmic inclusions in the brains of MSA patients, whereas no accumulation of SGTA was observed in neurons of PD and ALS patients. In vitro study showed that SGTA bound to polyQ aggregates through its C-terminal domain and SGTA overexpression reduced intracellular aggregates. These results suggest that SGTA may play a role in the formation of aggregates and may act as potential modifier of molecular pathological mechanisms of polyQ diseases and MSA.

Case Report: Anti-MOG Antibody Seroconversion Accompanied by Dimethyl Fumarate Treatment.

Here we report three cases of anti-myelin oligodendrocyte glycoprotein (MOG) antibody-associated disease (MOGAD) mimicking multiple sclerosis in which seropositivity for anti-MOG antibodies occurred during disease-modifying drug dimethyl fumarate (DMF) treatment. These patients developed relapses with anti-MOG antibody seroconversion after switching from fingolimod or steroid pulse therapy to DMF, which was associated with peripheral lymphocyte recovery. MOGAD is considered a humoral immune disease, and DMF reportedly enhances Th2-skewed humoral immune activity. Therefore, we suggest that DMF, but not fingolimod, may exacerbate humoral immune imbalance and enhance autoantibody production, leading to aggravation of MOGAD.

Two distinct mechanisms of neuropathy in immunoglobulin light chain (AL) amyloidosis.

INTRODUCTION: Although polyneuropathy in patients with immunoglobulin light chain (AL) amyloidosis has been considered to be attributable to axonal degeneration resulting from amyloid deposition, patients with nerve conduction parameters indicating demyelination that mimics chronic inflammatory demyelinating polyneuropathy (CIDP) have also been reported anecdotally. METHODS: We evaluated the electrophysiological and pathological features of 8 consecutive patients with AL amyloidosis who were referred for sural nerve biopsy. RESULTS: Although findings of axonal neuropathy predominantly in the lower limbs were the cardinal feature, all patients showed one or more abnormalities of nerve conduction velocities or distal motor latencies. In particular, 2 of these patients fulfilled the definite electrophysiological for CIDP defined by the European Federation of Neurological Societies/Peripheral Nerve Society (EFNS/PNS). On electron microscopic examination of sural nerve biopsy specimens, Schwann cells apposed to amyloid fibrils became atrophic in all patients, suggesting that amyloid deposits directly affect neighboring tissues. Additionally, detachment of the neurilemma from the outermost compacted myelin lamella was seen where amyloid fibrils were absent in 4 patients. Electrophysiological findings suggestive of demyelination were more conspicuous in these patients compared with the other patients. The detachment of the neurilemma from the outermost compacted myelin lamella was particularly conspicuous in patients who fulfilled the definite EFNS/PNS electrophysiological criteria for CIDP. CONCLUSION: Abnormalities of myelinated fibers unrelated to amyloid deposition may frequently occur in AL amyloidosis. Disjunction between myelin and the neurilemma may induce nerve conduction abnormalities suggestive of demyelination.

Tonsillectomy Improved Therapeutic Response in Anti-SRP Myopathy With Chronic Tonsillitis.

Chronic tonsillitis has been attracted attention as a source of abnormal immune responses and a possible trigger of autoimmune diseases such as IgA nephritis, IgA vasculitis, palmoplantar pustulosis, psoriasis, rheumatoid arthritis, Behçet's disease, and myositis. Here we present the first report of anti-signal recognition particle antibody-associated necrotizing myopathy (anti-SRP myopathy) with IgA nephropathy and chronic tonsillitis in which the therapeutic response to intravenous immunoglobulin (IVIG) treatment was dramatically improved after tonsillectomy and accompanied by a rapid increase in ΔIgG, defined as the change in serum IgG levels 2 weeks after the start of IVIG treatment relative to pre-treatment levels. Moreover, serum anti-SRP antibody titers became undetectable after tonsillectomy even though the resected tonsils did not produce anti-SRP antibodies. Tonsillectomy should be considered when chronic tonsillitis is observed in patients with autoimmune diseases showing poor response to treatment, including anti-SRP myopathy.

De novo CACNA1G variants in developmental delay and early-onset epileptic encephalopathies.

INTRODUCTION: Variants of CACNA1G, which encodes CaV3.1, have been reported to be associated with various neurological disorders. METHODS: Whole-exome sequencing of genomic DNA from 348 Japanese patients with neurodevelopmental disorders and their parents was conducted, and de novo variants of CACNA1G were extracted. The electrophysiological properties of each mutant channel were investigated by voltage-clamp and current-clamp analyses of HEK293T cells overexpressing these channels. RESULTS: Two patients diagnosed with Rett syndrome and West syndrome were found to have known pathological CACNA1G mutations reported in cerebellar ataxia cohorts: c.2881G > A, p.Ala961Thr and c.4591A > G, p.Met1531Val, respectively. One patient with Lennox-Gastaut syndrome was revealed to harbor a previously unreported heterozygous variant: c.3817A > T, p.Ile1273Phe. Clinical symptoms of the two patients with known mutations included severe developmental delay without acquisition of the ability to walk independently. The patient with a potentially novel mutation showed developmental delay, intractable seizures, and mild cerebral atrophy on MRI, but the severity of symptoms was milder than in the former two cases. Electrophysiological study using HEK293T cells demonstrated significant changes of T-type Ca2+ currents by p.Ala961Thr and p.Met1531Val SNVs, which were likely to enhance oscillation of membrane potential at low frequencies. In contrast, p.Ile1273Phe showed no significant effects in our electrophysiological evaluations, with its pathogenesis remaining undetermined. CONCLUSION: De novo variants of CACNA1G explain some neurodevelopmental disorders. Our study further provides information to understand the genotype-phenotype correlations of patients with CACNA1G mutations.

[A case of subacute hypertrophic pachymeningitis caused by Pseudomonas aeruginosa infection presenting with subdural hygroma].

A 78-year-old woman with bilateral fungal sinusitis, which resulted in right orbital apex syndrome, underwent endoscopic sinus surgery and optic nerve decompression. Two months after the operation, she complained of anxiety and insomnia. Head CT showed subdural hematoma-like effusion and burr hole drainage was conducted. The collected fluid was not hematoma, but bloody, xanthochromic effusion with no pathogenic bacteria. Ten days later, she underwent drainage and dural biopsy after craniotomy because of relapse of subdural hygroma and progression of hypertrophic pachymeningitis associated with aggravation of psychiatric symptoms. A sample of the dura mater showed dense fibrosis with thickening, and Pseudomonas aeruginosa (P. aeruginosa) was detected by culture. Although otitis or sinusitis secondary to P. aeruginosa infection has been reported as a leading cause of infectious pachymeningitis, psychiatric symptoms alone and concomitant refractory subdural hygroma are atypical and unreported manifestations. In patients with pachymeningitis and a history of transnasal endoscopic surgery, P. aeruginosa infection should be considered, irrespective of an atypical clinical course and negative blood or fluid culture. Additionally, dural biopsy might help in detection of pathogenic bacteria.

CCR2 is localized in microglia and neurons, as well as infiltrating monocytes, in the lumbar spinal cord of ALS mice.

It remains controversial whether circulating monocytes expressing CCR2 infiltrate the central nervous system (CNS) and contribute to pathogenicity of amyotrophic lateral sclerosis (ALS). A previous report used conventional immunohistochemistry to show that CCR2 is exclusively expressed by astrocytes, but not infiltrating monocytes/microglia or neurons, in the spinal cords of ALS model mice. In this study, we assessed the cellular distribution of CCR2 in the CNS of ALS mice using CCR2-reporter mice (Ccr2rfp/+-Cx3cr1gfp/+-SOD1G93A Tg mice), a more sophisticated method for directly detecting the distribution of CCR2 protein. We found that infiltration of CCR2+ monocytes in the lumbar spinal cord increased over the course of disease progression. Moreover, from the middle stage of disease, CCR2 was partially distributed in microglia and neurons, but not astrocytes, in striking contrast to the previous findings. These novel observations suggested that CCR2+ monocyte infiltration leads to CNS environmental deterioration due to toxic conversion of microglia and neurons, creating a vicious cycle of neuroinflammation and leading to acceleration of ALS pathology. Our findings also show that this reporter mouse is a useful and powerful tool for obtaining new insights into the pathomechanisms of ALS.

Long-read sequencing identifies the pathogenic nucleotide repeat expansion in RFC1 in a Japanese case of CANVAS.

Recently, a recessively inherited intronic repeat expansion in replication factor C1 (RFC1) was identified in cerebellar ataxia with neuropathy and bilateral vestibular areflexia syndrome (CANVAS). Here, we describe a Japanese case of genetically confirmed CANVAS with autonomic failure and auditory hallucination. The case showed impaired uptake of iodine-123-metaiodobenzylguanidine and 123I-ioflupane in the cardiac sympathetic nerve and dopaminergic neurons, respectively, by single-photon emission computed tomography. Long-read sequencing identified biallelic pathogenic (AAGGG)n nucleotide repeat expansion in RFC1 and heterozygous benign (TAAAA)n and (TAGAA)n expansions in brain expressed, associated with NEDD4 (BEAN1). Enrichment of the repeat regions in RFC1 and BEAN1 using a Cas9-mediated system clearly distinguished between pathogenic and benign repeat expansions. The haplotype around RFC1 indicated that the (AAGGG)n expansion in our case was on the same ancestral allele as that of European cases. Thus, long-read sequencing facilitates precise genetic diagnosis of diseases with complex repeat structures and various expansions.

Proteomic analysis of exosome-enriched fractions derived from cerebrospinal fluid of amyotrophic lateral sclerosis patients.

Exosomes contain many proteins associated with neurodegenerative diseases. To identify new candidate biomarkers and proteins associated with amyotrophic lateral sclerosis (ALS), we performed liquid chromatography-tandem mass spectrometry proteomic analysis of exosome-enriched fractions isolated from cerebrospinal fluid (CSF) of sporadic ALS patients using gel filtration chromatography. Proteomic data revealed that three proteins were increased and 11 proteins were decreased in ALS patients. The protein with the greatest increase in exosome-enriched fractions of CSF derived from ALS was novel INHAT repressor (NIR), which is closely associated with nucleolar function. By immunohistochemical analysis, we found that NIR was reduced in the nucleus of motor neurons in ALS patients. Our results demonstrate the potential utility of our methodology for proteomic analysis of CSF exosomes and suggest that nucleolar stress might play a role in sporadic ALS pathogenesis through the dysfunction of NIR.