Neurodegenerative and neuroinflammatory mechanisms in neurological and psychiatric disorders

The central nervous system (CNS) displays remarkable structural and functional adaptability, allowing neural circuits to respond to environmental changes, injury, or disease. However, dysregulation of these processes can lead to maladaptive changes that contribute to the development and progression of neurological disorders. This thesis comprises three independent but conceptually related studies, each addressing a distinct pathological condition in which neuronal adaptability plays a key role. The first project investigated the role of perineuronal nets (PNN), condensed aggregates of extracellular matrix (ECM) enwrapping neurons in general and Parvalbumin-positive interneurons in particular, in neuropathic pain. In a mouse model of unilateral chronic constriction injury (CCI) of the sciatic nerve, we observed reduced mechanical and thermal pain thresholds accompanied by increased WFA⁺ (Wisteria Floribunda Agglutinin) PNNs density in several pain-related brain regions, including somatosensory cortex (SSC), medial prefrontal cortex (mPFC), reticular thalamic nuclei (RTN), and insular cortex. These structural changes were associated with increased expression of the proteoglycans brevican and neurocan in the SSC and mPFC. Enzymatic degradation of PNNs with chondroitinase ABC in the contralateral SSC or RTN attenuated CCI-induced hypersensitivity, whereas siRNA of the PNN-degrading enzyme, type-9 matrix metalloproteinase (MMP-9), lowered pain thresholds only in sham-operated mice. Overall, these findings suggest that enhanced formation or reduced degradation of PNNs within the pain matrix causally contributes to nociceptive sensitization and the persistence of chronic pain (Mascio et al., 2025). The second project explored the contribution of group II metabotropic glutamate receptors (mGlu2 and mGlu3) to methamphetamine use disorder (MUD), a condition characterized by persistent cognitive impairments and high relapse vulnerability. Repeated methamphetamine administration (1 mg/kg, i.p., once daily for 5 days) followed by a 7-day withdrawal period impaired novel object recognition (NOR) memory in wild-type mice. This effect was absent in mGlu2-/- and mGlu3-/- mice and was prevented by pharmacological blockades with selective negative allosteric modulators (NAMs) of mGlu2 (VU6001966) or mGlu3 (VU0650786) receptors. Methamphetamine upregulated the expression of mGlu2/3 receptors and presynaptic proteins involved in glutamate release, including vGlut1, Rab3A, and AGS3, in the PFC. Functionally, methamphetamine dysregulated mGlu2/3 receptor signaling: while it did not alter mGlu2/3-mediated inhibition of cAMP formation, it abolished the ability of postsynaptic mGlu3 receptors to potentiate mGlu5 receptor-mediated inositol phospholipid hydrolysis in PFC slices. Paradoxically, activation of presynaptic mGlu2/3 receptors amplified depolarization-evoked [³H]-D-aspartate release in PFC synaptosomes. These findings indicate that methamphetamine profoundly alters mGlu2/3 receptor expression and function, leading to dysregulated excitatory transmission in the PFC. Selective inhibition of these receptors may represent a promising therapeutic strategy to counteract methamphetamine-induced cognitive dysfunction (Busceti et al., 2024). Finally, the third project examined whether disease-modifying therapies (DMTs) commonly used in multiple sclerosis (MS) influence the expression of angiotensin-converting enzyme 2 (ACE2), the primary entry receptor for SARS-CoV-2. To determine whether MS drugs (fingolimod, cladribine, dimethyl fumarate, and teriflunomide) affect ACE2 mRNA and protein levels, we used two different human lung carcinoma cell lines (Calu-3 and A549-hACE2-TMPRSS2) under basal and interleukin-1β (IL-1β)-mediated pro-inflammatory conditions. In Calu-3 cells, fingolimod significantly reduced ACE2 protein levels under inflammatory conditions, whereas dimethyl fumarate and teriflunomide increased ACE2 expression under both basal and pro-inflammatory conditions, and cladribine increased ACE2 protein levels under basal conditions. In A549-hACE2-TMPRSS2 cells, fingolimod reduced ACE2 mRNA and protein expression under both basal and pro-inflammatory conditions. Treatment with cladribine or teriflunomide followed by IL-1β challenge, led to a significant reduction in ACE2 protein expression; however, teriflunomide concurrently increased ACE2 mRNA expression under both basal and inflammatory conditions. These findings suggest that MS therapies can differentially influence ACE2 expression and that fingolimod, in particular, may exert a protective effect against SARS-CoV-2 infection in treated MS patients, by downregulating ACE2 (Ginerete et al., manuscript under review). Together, these studies contribute to a broader understanding of the molecular and cellular mechanisms underlying CNS dysfunction across different neurological/psychiatric disorders, offering complementary perspectives that may guide the development of more targeted therapeutic strategies. Busceti CL, Di Menna L, Castaldi S, D'Errico G, Taddeucci A, Bruno V, Fornai F, Pittaluga A, Battaglia G, Nicoletti F. Adaptive Changes in Group 2 Metabotropic Glutamate Receptors Underlie the Deficit in Recognition Memory Induced by Methamphetamine in Mice. eNeuro. 2024; 11(8):ENEURO.0523-23.2024. Ginerete RP, Imbriglio T, Alborghetti M, Cannella M, Ceccherelli A, Castaldi S, Notartomaso S, Norma L, Battaglia G, Bruno V. Effects of Drugs for the Treatment of Multiple Sclerosis in Severe Acute Respiratory Syndrome Coronavirus 2 Infection on the Expression of Angiotensin-Converting Enzyme 2 in Vitro. Current Neuropharmacology. 2025, Manuscript under review. Mascio G, Notartomaso S, Ginerete RP, Imbriglio T, Bucci D, Liberatore F, Ceccherelli A, Castaldi S, Zampini G, Cannella M, Nicoletti F, Battaglia G, Bruno V. Formation of perineuronal nets within a thalamocortical circuit shapes mechanical and thermal pain thresholds in mice with neuropathic pain. Pain. 2025; 166(5):1128-1142.