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.

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.