Glucose-derived glutamate drives neuronal terminal differentiation in vitro

Neuronal maturation is the phase during which neurons acquire their final characteristics in terms of morphology, electrical activity, and metabolism. However, little is known about the metabolic pathways governing neuronal maturation. Here, we investigate the contribution of the main metabolic pathways, namely glucose, glutamine, and fatty acid oxidation, during the maturation of primary rat hippocampal neurons. Blunting glucose oxidation through the genetic and chemical inhibition of the mitochondrial pyruvate transporter reveals that this protein is critical for the production of glutamate, which is required for neuronal arborization, proper dendritic elongation, and spine formation. Glutamate supplementation in the early phase of differentiation restores morphological defects and synaptic function in mitochondrial pyruvate transporter-inhibited cells. Furthermore, the selective activation of metabotropic glutamate receptors restores the impairment of neuronal differentiation due to the reduced generation of glucose-derived glutamate and rescues synaptic local translation. Fatty acid oxidation does not impact neuronal maturation. Whereas glutamine metabolism is important for mitochondria, it is not for endogenous glutamate production. Our results provide insights into the role of glucose-derived glutamate as a key player in neuronal terminal differentiation.

New Views of the DNA Repair Protein Ataxia-Telangiectasia Mutated in Central Neurons: Contribution in Synaptic Dysfunctions of Neurodevelopmental and Neurodegenerative Diseases

Ataxia-Telangiectasia Mutated (ATM) is a serine/threonine protein kinase principally known to orchestrate DNA repair processes upon DNA double-strand breaks (DSBs). Mutations in the Atm gene lead to Ataxia-Telangiectasia (AT), a recessive disorder characterized by ataxic movements consequent to cerebellar atrophy or dysfunction, along with immune alterations, genomic instability, and predisposition to cancer. AT patients show variable phenotypes ranging from neurologic abnormalities and cognitive impairments to more recently described neuropsychiatric features pointing to symptoms hardly ascribable to the canonical functions of ATM in DNA damage response (DDR). Indeed, evidence suggests that cognitive abilities rely on the proper functioning of DSB machinery and specific synaptic changes in central neurons of ATM-deficient mice unveiled unexpected roles of ATM at the synapse. Thus, in the present review, upon a brief recall of DNA damage responses, we focus our attention on the role of ATM in neuronal physiology and pathology and we discuss recent findings showing structural and functional changes in hippocampal and cortical synapses of AT mouse models. Collectively, a deeper knowledge of ATM-dependent mechanisms in neurons is necessary not only for a better comprehension of AT neurological phenotypes, but also for a higher understanding of the pathological mechanisms in neurodevelopmental and degenerative disorders involving ATM dysfunctions.

POS0430 SYNOVIAL FLUID-DERIVED EXTRACELLULAR VESICLES FROM RHEUMATOID ARTHRITIS AND OSTEOARTHRITIS MODULATE DIFFERENT HIPPOCAMPAL SYNAPTIC ACTIVITIES

Background

Accumulating evidence suggests that poor mental health is one of the most common comorbidities of both rheumatoid arthritis (RA) and osteoarthritis (OA) [1]. Even if underpinning RA and OA are different genetic, structural, mechanical, and immunologic pathways involved in their pathogenesis, poor mental health, and joint involvement are intertwined and negatively affect their mutual course by contributing to global disability. Thus, new insights into mechanisms that link these disorders are needed to identify new actionable biomarkers to drive more personalized therapeutic strategies. Amidst potential mediators, extracellular vesicles (EVs) play a central role in terms of communication between cells, they cross the blood-brain barrier and based on their cargos can affect the recipient cell function [2].

Objectives

To isolate EVs from synovial fluid (SF) in RA and OA patients and to evaluate if and how these EVs can alter in vitro synaptic transmission of murine hippocampal neurons.

Methods

In this cross-sectional pilot study, consecutive adult RA and primary OA who were referred to the Rheumatology Unit for aspiration of joint effusion were enrolled. Demographic and clinical variables and mental health rating scales were collected. Discarded SF were collected and EVs were isolated and analyzed by Malvern NanoSight NS300 system to obtain information on their number and size. Afterwards, DIV14 cultured wild-type hippocampal neurons were exposed for two hours to OA- and RA-EVs at low and high concentration EVs. Thus, miniature excitatory and inhibitory postsynaptic currents (mEPSCs and mIPSCs), which reflects glutamatergic and GABA-ergic activity respectively, were examined by exploiting patch-clamp recordings in the whole-cell configuration. Frequency and amplitude were analyzed to evaluate potential changes at the presynaptic or postsynaptic compartment. Mann Whitney test was used to compare two different samples.

Results

Eight RA patients (7 female, mean age 57 yrs), and 5 primary OA (4 female, mean age 60 yrs) were recruited for SF aspiration. The mean VAS pain was 7.25 in RA and 6.5 in OA. No statistically significant differences were found between the two groups in mean rating scale scores although patients affected by RA had more severe depressive symptoms (Montgomery Asberg Depression Rating Scale -MADRS- means scores: 16.57) with respect OA group (MADRS mean scores: 10). The Nanoparticle tracking analysis showed that RA-EVs were significantly more in number compared to OA-EVs (Figure 1 A), mimicking more inflammation, while no significant difference in size was observed. Analysis of miniature events revealed the occurrence of two different changes. High concentration of OA-EVs has led to an increased amplitude of excitatory events, meaning an increased susceptibility of neurons to glutamate in the post-synaptic compartment (Figure 1 B). Whereas low concentration of RA-EVs has led to a decreased frequency of inhibitory events, which reflects a reduced function of GABA-ergic synapse in the pre-synaptic compartment (Figure 1 C).

Figure 1.

Conclusion

Our results suggest that SF-derived EVs from OA and RA patients lead to different specific changes of neurotransmission, with different concentration needed to alter neuronal spontaneous activity in post-synaptic and pre-synaptic compartment, respectively. EVs may provide insight into the pathogenesis of joint-brain communication in RA and OA, unraveling specific pathways thus allowing targeted therapies for neuropsychiatric involvement.

References

[1]Lancet 2017;390(10100): 1211–1259

[2]FASEB Bioadv 2021;3(9):665-675

Disclosure of Interests

Lavinia A. Coletto: None declared, Francesca Ingegnoli: None declared, Clara Cambria: None declared, Laura Cantone: None declared, Orazio De Lucia: None declared, Roberto Caporali Speakers bureau: Abbvie, Amgen, BMS, Celltrion, Galapagos, Lilly, Pfizer, Fresenius-Kabi, MSD, UCB, Roche,Janssen, Novartis, Sandoz, Consultant of: Abbvie, Amgen, BMS, Celltrion, Galapagos, Lilly, Pfizer, MSD, UCB, Janssen, Novartis, Sandoz, Valentina Bollati: None declared, Massimiliano Buoli: None declared, Flavia Antonucci: None declared.

The DNA repair protein ATM as a target in autism spectrum disorder

Impairment of the GABAergic system has been reported in epilepsy, autism, attention deficit hyperactivity disorder, and schizophrenia. We recently demonstrated that ataxia telangiectasia mutated (ATM) directly shapes the development of the GABAergic system. Here, we show for the first time to our knowledge how the abnormal expression of ATM affects the pathological condition of autism. We exploited 2 different animal models of autism, the methyl CpG binding protein 2-null (Mecp2y/-) mouse model of Rett syndrome and mice prenatally exposed to valproic acid, and found increased ATM levels. Accordingly, treatment with the specific ATM kinase inhibitor KU55933 (KU) normalized molecular, functional, and behavioral defects in these mouse models, such as (a) delayed GABAergic development, (b) hippocampal hyperexcitability, (c) low cognitive performances, and (d) social impairments. Mechanistically, we demonstrate that KU administration to WT hippocampal neurons leads to (a) higher early growth response 4 activity on Kcc2b promoter, (b) increased expression of Mecp2, and (c) potentiated GABA transmission. These results provide evidence and molecular substrates for the pharmacological development of ATM inhibition in autism spectrum disorders.

LSD1 is an environmental stress-sensitive negative modulator of the glutamatergic synapse

Along with neuronal mechanisms devoted to memory consolidation –including long term potentiation of synaptic strength as prominent electrophysiological correlate, and inherent dendritic spines stabilization as structural counterpart– negative control of memory formation and synaptic plasticity has been described at the molecular and behavioral level. Within this work, we report a role for the epigenetic corepressor Lysine Specific Demethylase 1 (LSD1) as a negative neuroplastic factor whose stress-enhanced activity may participate in coping with adverse experiences. Constitutively increasing LSD1 activity via knocking out its dominant negative splicing isoform neuroLSD1 (neuroLSD1^KO mice), we observed extensive structural, functional and behavioral signs of excitatory decay, including disrupted memory consolidation. A similar LSD1 increase, obtained with acute antisense oligonucleotide-mediated neuroLSD1 splicing knock down in primary neuronal cultures, dampens spontaneous glutamatergic transmission, reducing mEPSCs. Remarkably, LSD1 physiological increase occurs in response to psychosocial stress-induced glutamatergic signaling. Since this mechanism entails neuroLSD1 splicing downregulation, we conclude that LSD1/neuroLSD1 ratio modulation in the hippocampus is instrumental to a negative homeostatic feedback, restraining glutamatergic neuroplasticity in response to glutamate. The active process of forgetting provides memories with salience. With our work, we propose that softening memory traces of adversities could further represent a stress-coping process in which LSD1/neuroLSD1 ratio modulation may help preserving healthy emotional references.