Graphene oxide prevents lateral amygdala dysfunctional synaptic plasticity and reverts long lasting anxiety behavior in rats

Regulation of depressive-like behaviours by palmitoylation: Role of AKAP150 in the basolateral amygdala

BACKGROUND AND PURPOSE

Protein palmitoylation is involved in learning and memory, and in emotional disorders. Yet, the underlying mechanisms in these processes remain unclear. Herein, we describe that A-kinase anchoring protein 150 (AKAP150) is essential and sufficient for depressive-like behaviours in mice via a palmitoylation-dependent mechanism.

EXPERIMENTAL APPROACH

Depressive-like behaviours in mice were induced by chronic restraint stress (CRS) and chronic unpredictable mild stress (CUMS). Palmitoylated proteins in the basolateral amygdala (BLA) were assessed by an acyl-biotin exchange assay. Genetic and pharmacological approaches were used to investigate the role of the DHHC2-mediated AKAP150 palmitoylation signalling pathway in depressive-like behaviours. Electrophysiological recording, western blotting and co-immunoprecipitation were performed to define the mechanistic pathway.

KEY RESULTS

Chronic stress successfully induced depressive-like behaviours in mice and enhanced AKAP150 palmitoylation in the BLA, and a palmitoylation inhibitor was enough to reverse these changes. Blocking the AKAP150-PKA interaction with the peptide Ht-31 abolished the CRS-induced AKAP150 palmitoylation signalling pathway. DHHC2 expression and palmitoylation levels were both increased after chronic stress. DHHC2 knockdown prevented CRS-induced depressive-like behaviours, as well as attenuating AKAP150 signalling and synaptic transmission in the BLA in CRS-treated mice.

CONCLUSION AND IMPLICATIONS

These results delineate that DHHC2 modulates chronic stress-induced depressive-like behaviours and synaptic transmission in the BLA via the AKAP150 palmitoylation signalling pathway, and this pathway may be considered as a promising novel therapeutic target for major depressive disorder.

MoS2 2D materials induce spinal cord neuroinflammation and neurotoxicity affecting locomotor performance in zebrafish

MoS2 nanosheets belong to an emerging family of nanomaterials named bidimensional transition metal dichalcogenides (2D TMDCs). The use of such promising materials, featuring outstanding chemical and physical properties, is expected to increase in several fields of science and technology, with an enhanced risk of environmental dispersion and associated wildlife and human exposures. In this framework, the assessment of MoS2 nanosheets toxicity is instrumental to safe industrial developments. Currently, the impact of the nanomaterial on the nervous tissue is unexplored. In this work, we use as in vivo experimental model the early-stage zebrafish, to investigate whether mechano-chemically exfoliated MoS2 nanosheets reach and affect, when added in the behavioral ambient, the nervous system. By high throughput screening of zebrafish larvae locomotor behavioral changes upon exposure to MoS2 nanosheets and whole organism live imaging of spinal neuronal and glial cell calcium activity, we report that sub-acute and prolonged ambient exposures to MoS2 nanosheets elicit locomotor abnormalities, dependent on dose and observation time. While 25 μg mL-1 concentration treatments exerted transient effects, 50 μg mL-1 ones induced long-lasting changes, correlated to neuroinflammation-driven alterations in the spinal cord, such as astrogliosis, glial intracellular calcium dysregulation, neuronal hyperactivity and motor axons retraction. By combining integrated technological approaches to zebrafish, we described that MoS2 2D nanomaterials can reach, upon water (i.e. ambient) exposure, the nervous system of larvae, resulting in a direct neurological damage.

Few-layered graphene increases the response of nociceptive neurons to irritant stimuli

The unique properties of few-layered graphene (FLG) make it interesting for a variety of applications, including biomedical applications, such as tissue engineering and drug delivery. Although different studies focus on applications in the central nervous system, its interaction with the peripheral nervous system has been so far overlooked. Here, we investigated the effects of exposure to colloidal dispersions of FLG on the sensory neurons of the rat dorsal root ganglia (DRG). We found that the FLG flakes were actively internalized by sensory neurons, accumulated in large intracellular vesicles, and possibly degraded over time, without major toxicological concerns, as neuronal viability, morphology, protein content, and basic electrical properties of DRG neurons were preserved. Interestingly, in our electrophysiological investigation under noxious stimuli, we observed an increased functional response upon FLG treatment of the nociceptive subpopulation of DRG neurons in response to irritants specific for chemoreceptors TRPV1 and TRPA1. The observed effects of FLG on DRG neurons may open-up novel opportunities for applications of these materials in specific disease models.

Regulation of anxiety-like behaviors by S-palmitoylation and S-nitrosylation in basolateral amygdala

Protein posttranslational modification regulates synaptic protein stability, sorting and trafficking, and is involved in emotional disorders. Yet the molecular mechanisms regulating emotional disorders remain unelucidated. Here we report unknown roles of protein palmitoylation/nitrosylation crosstalk in regulating anxiety-like behaviors in rats. According to the percentages of open arm duration in the elevated plus maze test, the rats were divided into high-, intermediate- and low-anxiety groups. The palmitoylation and nitrosylation levels were detected by acyl-biotin exchange assay, and we found low palmitoylation and high nitrosylation levels in the basolateral amygdala (BLA) of high-anxiety rats. Furthermore, we observed that 2-bromopalmitate (2-BP), a palmitoylation inhibitor, induced anxiety-like behaviors, accompanied with decreased amplitude and frequency of mEPSCs and mIPSCs in the BLA. Additionally, we also found that inhibiting nNOS activity with 7-nitroindazole (7-NI) in the BLA caused anxiolytic effects and reduced the synaptic transmission. Interestingly, diazepam (DZP) rapidly elevated the protein palmitoylation level and attenuated the protein nitrosylation level in the BLA. Specifically, similar to DZP, the voluntary wheel running exerted DZP-like anxiolytic action, and induced high palmitoylation and low nitrosylation levels in the BLA. Lastly, blocking the protein palmitoylation with 2-BP induced an increase in protein nitrosylation level, and attenuating the nNOS activity by 7-NI elevated the protein palmitoylation level. Collectively, these results show a critical role of protein palmitoylation/nitrosylation crosstalk in orchestrating anxiety behavior in rats, and it may serve as a potential target for anxiolytic intervention.

Graphene Oxide Nanosheets Hamper Glutamate Mediated Excitotoxicity and Protect Neuronal Survival In An In vitro Stroke Model

Small graphene oxide (s-GO) nanosheets reversibly downregulate central nervous system (CNS) excitatory synapses, with potential developments as future therapeutic tools to treat neuro-disorders characterized by altered glutamatergic transmission. Excitotoxicity, namely cell death triggered by exceeding ambient glutamate fueling over-activation of excitatory synapses, is a pathogenic mechanism shared by several neural diseases, from ischemic stroke to neurodegenerative disorders. In this work, CNS cultures were exposed to oxygen-glucose deprivation (OGD) to mimic ischemic stroke in vitro, and it is show that the delivery of s-GO following OGD, during the endogenous build-up of secondary damage and excitotoxicity, improved neuronal survival. In a different paradigm, excitotoxicity cell damage was reproduced through exogenous glutamate application, and s-GO co-treatment protected neuronal integrity, potentially by directly downregulating the synaptic over-activation brought about by exogenous glutamate. This proof-of-concept study suggests that s-GO may find novel applications in therapeutic developments for treating excitotoxicity-driven neural cell death.

Delivery of graphene oxide nanosheets modulates glutamate release and normalizes amygdala synaptic plasticity to improve anxiety-related behavior

Graphene oxide nanosheets (GO) were reported to alter neurobiological processes involving cell membrane dynamics. GO ability to reversibly downregulate specifically glutamatergic synapses underpins their potential in future neurotherapeutic developments. Aberrant glutamate plasticity contributes to stress-related psychopathology and drugs which target dysregulated glutamate represent promising treatments. We find that in a rat model of post-traumatic stress disorder (PTSD), a single injection of GO to the lateral amygdala following the stressful event induced PTSD-related behavior remission and reduced dendritic spine densities. We explored from a mechanistic perspective how GO could impair glutamate synaptic plasticity. By simultaneous patch clamp pair recordings of unitary synaptic currents, live-imaging of presynaptic vesicle release and confocal microscopy, we report that GO nanosheets altered the probability of release enhancing the extinction of synaptic plasticity in the amygdala. These findings show that the modulation of presynaptic glutamate release might represent an unexplored target for (nano)pharmacological interventions of stress-related disorders.

Unravelling the Link between Psychological Distress and Liver Disease: Insights from an Anxiety-like Rat Model and Metabolomics Analysis

Psychological distress is associated with an increase in liver disease mortality. This association highlights the close relationship between psychological and physical health. The underlying mechanism of this association needs to be elucidated. In this study, a rat model of anxiety was developed via compound stress. Changes in the HPA axis and inflammatory factors in the brains of the rats were evaluated for behavioral tests and liver function, respectively. The liver metabolic profiles of the rats were characterized through liquid chromatography-mass spectrometry (LC-MS). Differential metabolites were screened based on the conditions of p < 0.05 and VIP > 1. A pathway enrichment analysis was performed on the metabolomics data using the Ingenuity Pathway Analysis (IPA). Immunofluorescence (IF), immunohistochemistry (IHC), and Western blotting assays were performed to examine the expression of the screened target epidermal growth factor receptor (EGFR) and to elucidate the pathway associated with the mechanism. The results showed the impairment of liver function among the rats in an anxiety-like state. Additionally, 61 differential metabolites in the control and anxiety groups were screened using metabolomics (p < 0.05, VIP > 1). The results of the IPA analysis showed that the key target was EGFR. We also found that an anxiety-like state in rats may cause liver injury through the EFGR/PI3K/AKT/NF-κB pathway, which can lead to the production of inflammatory factors in the liver. Our results revealed a mechanism by which anxiety-like behavior leads to liver damage in rats. The findings of this study provided new insights into the deleterious effects of psychological problems on physical health.

Interfacing reduced graphene oxide with an adipose-derived extracellular matrix as a regulating milieu for neural tissue engineering

Enthralling evidence of the potential of graphene-based materials for neural tissue engineering is motivating the development of scaffolds using various structures related to graphene such as graphene oxide (GO) or its reduced form. Here, we investigated a strategy based on reduced graphene oxide (rGO) combined with a decellularized extracellular matrix from adipose tissue (adECM), which is still unexplored for neural repair and regeneration. Scaffolds containing up to 50 wt% rGO relative to adECM were prepared by thermally induced phase separation assisted by carbodiimide (EDC) crosslinking. Using partially reduced GO enables fine-tuning of the structural interaction between rGO and adECM. As the concentration of rGO increased, non-covalent bonding gradually prevailed over EDC-induced covalent conjugation with the adECM. Edge-to-edge aggregation of rGO favours adECM to act as a biomolecular physical crosslinker to rGO, leading to the softening of the scaffolds. The unique biochemistry of adECM allows neural stem cells to adhere and grow. Importantly, high rGO concentrations directly control cell fate by inducing the differentiation of both NE-4C cells and embryonic neural progenitor cells into neurons. Furthermore, primary astrocyte fate is also modulated as increasing rGO boosts the expression of reactivity markers while unaltering the expression of scar-forming ones.

Graphene Oxide Nanosheets Reduce Astrocyte Reactivity to Inflammation and Ameliorate Experimental Autoimmune Encephalomyelitis

In neuroinflammation, astrocytes play multifaceted roles that regulate the neuronal environment. Astrocytes sense and respond to pro-inflammatory cytokines (CKs) and, by a repertoire of intracellular Ca²⁺ signaling, contribute to disease progression. Therapeutic approaches wish to reduce the overactivation in Ca²⁺ signaling in inflammatory-reactive astrocytes to restore dysregulated cellular changes. Cell-targeting therapeutics might take advantage by the use of nanomaterial-multifunctional platforms such as graphene oxide (GO). GO biomedical applications in the nervous system involve therapeutic delivery and sensing, and GO flakes were shown to enable interfacing of neuronal and glial membrane dynamics. We exploit organotypic spinal cord cultures and optical imaging to explore Ca²⁺ changes in astrocytes, and we report, when spinal tissue is exposed to CKs, neuroinflammatory-associated modulation of resident glia. We show the efficacy of GO to revert these dynamic changes in astrocytic reactivity to CKs, and we translate this potential in an animal model of immune-mediated neuroinflammatory disease.

Bonding of Neuropeptide Y on Graphene Oxide for Drug Delivery Applications to the Central Nervous System

Nanoscale graphene-based materials (GBMs) enable targeting subcellular structures of the nervous system, a feature crucial for the successful engineering of alternative nanocarriers to deliver drugs and to treat neurodisorders. Among GBMs, graphene oxide (GO) nanoflakes, showing good dispersibility in water solution and being rich of functionalizable oxygen groups, are ideal core structures for carrying biological active molecules to the brain, such as the neuropeptide Y (NPY). In addition, when unconjugated, these nanomaterials have been reported to modulate neuronal function per se. Although some GBM-based nanocarriers have been tested both in vitro and in vivo, a thorough characterization of covalent binding impact on the biological properties of the carried molecule and/or of the nanomaterial is still missing. Here, a copper(I)-catalyzed alkyne-azide cycloaddition strategy was employed to synthesize the GO-NPY complex. By investigating through electrophysiology the impact of these conjugates on the activity of hippocampal neurons, we show that the covalent modification of the nanomaterial, while making GO an inert platform for the vectorized delivery, enhances the duration of NPY pharmacological activity. These findings support the future use of GO for the development of smart platforms for nervous system drug delivery.

Biomaterials for Regenerative Medicine in Italy: Brief State of the Art of the Principal Research Centers

Regenerative medicine is the branch of medicine that effectively uses stem cell therapy and tissue engineering strategies to guide the healing or replacement of damaged tissues or organs. A crucial element is undoubtedly the biomaterial that guides biological events to restore tissue continuity. The polymers, natural or synthetic, find wide application thanks to their great adaptability. In fact, they can be used as principal components, coatings or vehicles to functionalize several biomaterials. There are many leading centers for the research and development of biomaterials in Italy. The aim of this review is to provide an overview of the current state of the art on polymer research for regenerative medicine purposes. The last five years of scientific production of the main Italian research centers has been screened to analyze the current advancement in tissue engineering in order to highlight inputs for the development of novel biomaterials and strategies.

Bidirectional Modulation of Neuronal Cells Electrical and Mechanical Properties Through Pristine and Functionalized Graphene Substrates

In recent years, the quest for surface modifications to promote neuronal cell interfacing and modulation has risen. This course is justified by the requirements of emerging technological and medical approaches attempting to effectively interact with central nervous system cells, as in the case of brain-machine interfaces or neuroprosthetic. In that regard, the remarkable cytocompatibility and ease of chemical functionalization characterizing surface-immobilized graphene-based nanomaterials (GBNs) make them increasingly appealing for these purposes. Here, we compared the (morpho)mechanical and functional adaptation of rat primary hippocampal neurons when interfaced with surfaces covered with pristine single-layer graphene (pSLG) and phenylacetic acid-functionalized single-layer graphene (fSLG). Our results confirmed the intrinsic ability of glass-supported single-layer graphene to boost neuronal activity highlighting, conversely, the downturn inducible by the surface insertion of phenylacetic acid moieties. fSLG-interfaced neurons showed a significant reduction in spontaneous postsynaptic currents (PSCs), coupled to reduced cell stiffness and altered focal adhesion organization compared to control samples. Overall, we have here demonstrated that graphene substrates, both pristine and functionalized, could be alternatively used to intrinsically promote or depress neuronal activity in primary hippocampal cultures.

Nanomedicine and graphene-based materials: advanced technologies for potential treatments of diseases in the developing nervous system

The interest in graphene-based nanomaterials (GBNs) application in nanomedicine, in particular in neurology, steadily increased in the last decades. GBNs peculiar physical-chemical properties allow the design of innovative therapeutic tools able to manipulate biological structures with subcellular resolution. In this review, we report GBNs applications to the central nervous system (CNS) when these nanomaterials are engineered as potential therapeutics to treat brain pathologies, with a focus on those of the pediatric age. We revise the state-of-the art studies addressing the impact of GBNs in the CNS, showing that the design of GBNs with different dimensions and chemical compositions or the use of specific administration routes and doses can limit unwanted side effects, exploiting GBNs efficacy in therapeutic approaches. These features favor the development of GBNs-based multifunctional devices that may find applications in the field of precision medicine for the treatment of disorders in the developing CNS. In this framework, we address the suitability of GBNs to become successful therapeutic tools, such as drug nano-delivery vectors when being chemically decorated with pharmaceutical agents and/or other molecules to obtain a high specific targeting of the diseased area and to achieve a controlled release of active molecules. IMPACT: The translational potential of graphene-based nanomaterials (GBNs) can be used for the design of novel therapeutic approaches to treat pathologies affecting the brain with a focus on the pediatric age. GBNs can be chemically decorated with pharmaceutical agents and molecules to obtain a highly specific targeting of the diseased site and a controlled drug release. The type of GBNs, the selected functionalization, the dose, and the way of administration are factors that should be considered to potentiate the therapeutic efficacy of GBNs, limiting possible side effects. GBNs-based multifunctional devices might find applications in the precision medicine and theranostics fields.