Interferon-γ causes mood abnormalities by altering cannabinoid CB1 receptor function in the mouse striatum

Interleukin-9 protects from microglia- and TNF-mediated synaptotoxicity in experimental multiple sclerosis

BACKGROUND

Multiple sclerosis (MS) is a progressive neurodegenerative disease of the central nervous system characterized by inflammation-driven synaptic abnormalities. Interleukin-9 (IL-9) is emerging as a pleiotropic cytokine involved in MS pathophysiology.

METHODS

Through biochemical, immunohistochemical, and electrophysiological experiments, we investigated the effects of both peripheral and central administration of IL-9 on C57/BL6 female mice with experimental autoimmune encephalomyelitis (EAE), a model of MS.

RESULTS

We demonstrated that both systemic and local administration of IL-9 significantly improved clinical disability, reduced neuroinflammation, and mitigated synaptic damage in EAE. The results unveil an unrecognized central effect of IL-9 against microglia- and TNF-mediated neuronal excitotoxicity. Two main mechanisms emerged: first, IL-9 modulated microglial inflammatory activity by enhancing the expression of the triggering receptor expressed on myeloid cells-2 (TREM2) and reducing TNF release. Second, IL-9 suppressed neuronal TNF signaling, thereby blocking its synaptotoxic effects.

CONCLUSIONS

The data presented in this work highlight IL-9 as a critical neuroprotective molecule capable of interfering with inflammatory synaptopathy in EAE. These findings open new avenues for treatments targeting the neurodegenerative damage associated with MS, as well as other inflammatory and neurodegenerative disorders of the central nervous system.

rTMS ameliorates depression/anxiety-like behaviors in experimental autoimmune encephalitis by inhibiting neurotoxic reactive astrocytes

One third of patients with multiple sclerosis (MS) suffered from depressive symptoms. The pathogenesis of depression in MS patients has been related to innate immune activation in certain regions of the brain such as hippocampus. However, pharmacotherapy lacks sufficient evidence for beneficial effects on depression in MS patients, urging for a novel treatment modality for this mental disorder. Treatment effects of rTMS on depression/anxiety-like behaviors in mice with experimental autoimmune encephalomyelitis (EAE) were assessed by behavioral tests. The role of innate immune response was examined by RNA sequencing, quantitative RT-PCR, and immunofluorescence techniques. Depressive symptom severity and astroglial activation in patients with MS were assessed by Beck Depression Inventory and serum glial fibrillary acidic protein (GFAP), respectively. EAE mice displayed depression/anxiety-like behaviors, which were ameliorated by rTMS. Transcriptome and gene-specific expression analysis of the hippocampus showed significant reduction in transcript levels associated with neurotoxic reactive astrocytes in EAE mice after rTMS treatment. This was confirmed by immunofluorescence studies. Complement component 3d, a marker of neurotoxic reactive astrocytes, was highly expressed in EAE hippocampus, but was reduced to a basal level after rTMS treatment. In patients with MS, astroglial activation, indicated by serum GFAP levels, was significantly elevated in those with moderate or major depressive symptoms. These findings support that the suppression of neurotoxic reactive astrocytes might be a potential target for treatment of depression in patients with MS, and suggest the potential of using rTMS as a potential therapeutic treatment for this disorder.

Selected Biomarkers of Depression: What Are the Effects of Cytokines and Inflammation?

Depression is one of the leading mental illnesses worldwide and lowers the quality of life of many. According to WHO, about 5% of the worldwide population suffers from depression. Newer studies report a staggering global prevalence of 27.6%, and it is rising. Professionally, depression belonging to affective disorders is a psychiatric illness, and the category of major depressive disorder (MDD) comprises various diagnoses related to persistent and disruptive mood disorders. Due to this fact, it is imperative to find a way to assess depression quantitatively using a specific biomarker or a panel of biomarkers that would be able to reflect the patients' state and the effects of therapy. Cytokines, hormones, oxidative stress markers, and neuropeptides are studied in association with depression. The latest research into inflammatory cytokines shows that their relationship with the etiology of depression is causative. There are stronger cytokine reactions to pathogens and stressors in depression. If combined with other predisposing factors, responses lead to prolonged inflammatory processes, prolonged dysregulation of various axes, stress, pain, mood changes, anxiety, and depression. This review focuses on the most recent data on cytokines as markers of depression concerning their roles in its pathogenesis, their possible use in diagnosis and management, their different levels in bodily fluids, and their similarities in animal studies. However, cytokines are not isolated from the pathophysiologic mechanisms of depression or other psychiatric disorders. Their effects are only a part of the whole pathway.

Pro-Inflammatory Cytokines: Potential Links between the Endocannabinoid System and the Kynurenine Pathway in Depression

Substance use/abuse is one of the main causes of depressive symptoms. Cannabis and synthetic cannabinoids in particular gained significant popularity in the past years. There is an increasing amount of clinical data associating such compounds with the inflammatory component of depression, indicated by the up-regulation of pro-inflammatory cytokines. Pro-inflammatory cytokines are also well-known to regulate the enzymes of the kynurenine pathway (KP), which is responsible for metabolizing tryptophan, a precursor in serotonin synthesis. Enhanced pro-inflammatory cytokine levels may over-activate the KP, leading to tryptophan depletion and reduced serotonin levels, which can subsequently precipitate depressive symptoms. Therefore, such mechanism might represent a possible link between the endocannabinoid system (ECS) and the KP in depression, via the inflammatory and dysregulated serotonergic component of the disorder. This review will summarize the data regarding those natural and synthetic cannabinoids that increase pro-inflammatory cytokines. Furthermore, the data on such cytokines associated with KP activation will be further reviewed accordingly. The interaction of the ECS and the KP has been postulated and demonstrated in some studies previously. This review will further contribute to this yet less explored connection and propose the KP to be the missing link between cannabinoid-induced inflammation and depressive symptoms.

Inflammation-Associated Synaptic Alterations as Shared Threads in Depression and Multiple Sclerosis

In the past years, several theories have been advanced to explain the pathogenesis of Major Depressive Disorder (MDD), a neuropsychiatric disease that causes disability in general population. Several theories have been proposed to define the MDD pathophysiology such as the classic "monoamine-theory" or the "glutamate hypothesis." All these theories have been recently integrated by evidence highlighting inflammation as a pivotal player in developing depressive symptoms. Proinflammatory cytokines have been indeed claimed to contribute to stress-induced mood disturbances and to major depression, indicating a widespread role of classical mediators of inflammation in emotional control. Moreover, during systemic inflammatory diseases, peripherally released cytokines circulate in the blood, reach the brain and cause anxiety, anhedonia, social withdrawal, fatigue, and sleep disturbances. Accordingly, chronic inflammatory disorders, such as the inflammatory autoimmune disease multiple sclerosis (MS), have been associated to higher risk of MDD, in comparison with overall population. Importantly, in both MS patients and in its experimental mouse model, Experimental Autoimmune Encephalomyelitis (EAE), the notion that depressive symptoms are reactive epiphenomenon to the MS pathology has been recently challenged by the evidence of their early manifestation, even before the onset of the disease. Furthermore, in association to such mood disturbance, inflammatory-dependent synaptic dysfunctions in several areas of MS/EAE brain have been observed independently of brain lesions and demyelination. This evidence suggests that a fine interplay between the immune and nervous systems can have a huge impact on several neurological functions, including depressive symptoms, in different pathological conditions. The aim of the present review is to shed light on common traits between MDD and MS, by looking at inflammatory-dependent synaptic alterations associated with depression in both diseases.

Interferon-γ acutely augments inhibition of neocortical layer 5 pyramidal neurons

BACKGROUND

Interferon-γ (IFN-γ, a type II IFN) is present in the central nervous system (CNS) under various conditions. Evidence is emerging that, in addition to its immunological role, IFN-γ modulates neuronal morphology, function, and development in several brain regions. Previously, we have shown that raising levels of IFN-β (a type I IFN) lead to increased neuronal excitability of neocortical layer 5 pyramidal neurons. Because of shared non-canonical signaling pathways of both cytokines, we hypothesized a similar neocortical role of acutely applied IFN-γ.

METHODS

We used semi-quantitative RT-PCR, immunoblotting, and immunohistochemistry to analyze neuronal expression of IFN-γ receptors and performed whole-cell patch-clamp recordings in layer 5 pyramidal neurons to investigate sub- and suprathreshold excitability, properties of hyperpolarization-activated cyclic nucleotide-gated current (I_h), and inhibitory neurotransmission under the influence of acutely applied IFN-γ.

RESULTS

We show that IFN-γ receptors are present in the membrane of rat's neocortical layer 5 pyramidal neurons. As expected from this and the putative overlap in IFN type I and II alternative signaling pathways, IFN-γ diminished I_h, mirroring the effect of type I IFNs, suggesting a likewise activation of protein kinase C (PKC). In contrast, IFN-γ did neither alter subthreshold nor suprathreshold neuronal excitability, pointing to augmented inhibitory transmission by IFN-γ. Indeed, IFN-γ increased electrically evoked inhibitory postsynaptic currents (IPSCs) on neocortical layer 5 pyramidal neurons. Furthermore, amplitudes of spontaneous IPSCs and miniature IPSCs were elevated by IFN-γ, whereas their frequency remained unchanged.

CONCLUSIONS

The expression of IFN-γ receptors on layer 5 neocortical pyramidal neurons together with the acute augmentation of inhibition in the neocortex by direct application of IFN-γ highlights an additional interaction between the CNS and immune system. Our results strengthen our understanding of the role of IFN-γ in neocortical neurotransmission and emphasize its impact beyond its immunological properties, particularly in the pathogenesis of neuropsychiatric disorders.

CB1 enhanced the osteo/dentinogenic differentiation ability of periodontal ligament stem cells via p38 MAPK and JNK in an inflammatory environment

Objectives

Periodontitis is an inflammatory immune disease that causes periodontal tissue loss. Inflammatory immunity and bone metabolism are closely related to periodontitis. The cannabinoid receptor I (CB1) is an important constituent of the endocannabinoid system and participates in bone metabolism and inflammation tissue healing. It is unclear whether CB1 affects the mesenchymal stem cell (MSC) function involved in periodontal tissue regeneration. In this study, we revealed the role and mechanism of CB1 in the osteo/dentinogenic differentiation of periodontal ligament stem cells (PDLSCs) in an inflammatory environment.

Materials and methods

Alkaline phosphatase (ALP) activity, Alizarin Red staining, quantitative calcium analysis and osteo/dentinogenic markers were used to assess osteo/dentinogenic differentiation. Real‐time RT‐PCR and Western blotting were employed to detect gene expression.

Results

CB1 overexpression or CB1 agonist (10 µM R‐1 Meth) promoted the osteo/dentinogenic differentiation of PDLSCs. Deletion of CB1 or the application of CB1 antagonist (10 µM AM251) repressed the osteo/dentinogenic differentiation of PDLSCs. The activation of CB1 enhanced the TNF‐α‐ and INF‐γ‐impaired osteo/dentinogenic differentiation potential in PDLSCs. Moreover, CB1 activated p38 MAPK and JNK signalling and repressed PPAR‐γ and Erk1/2 signalling. Inhibition of JNK signalling could block CB1‐activated JNK and p38 MAPK signalling, while CB1 could activate p38 MAPK and JNK signalling, which was inhibited by TNF‐α and INF‐γ stimulation.

Conclusions

CB1 was able to enhance the osteo/dentinogenic differentiation ability of PDLSCs via p38 MAPK and JNK signalling in an inflammatory environment, which might be a potential target for periodontitis treatment.

Toxoplasmosis: A pathway to neuropsychiatric disorders

Toxoplasma gondii is an obligate intracellular parasite that resides, in a latent form, in the human central nervous system. Infection with Toxoplasma drastically alters the behaviour of rodents and is associated with the incidence of specific neuropsychiatric conditions in humans. But the question remains: how does this pervasive human pathogen alter behaviour of the mammalian host? This fundamental question is receiving increasing attention as it has far reaching public health implications for a parasite that is very common in human populations. Our current understanding centres on neuronal changes that are elicited directly by this intracellular parasite versus indirect changes that occur due to activation of the immune system within the CNS, or a combination of both. In this review, we explore the interactions between Toxoplasma and its host, the proposed mechanisms and consequences on neuronal function and mental health, and discuss Toxoplasma infection as a public health issue.

Exploiting the Multifaceted Effects of Cannabinoids on Mood to Boost Their Therapeutic Use Against Anxiety and Depression

The endocannabinoid system (ECS) has been recently recognized as a prominent promoter of the emotional homeostasis, mediating the effects of different environmental signals including rewarding and stressing stimuli. The ECS modulates the rewarding effects of environmental stimuli, influencing synaptic transmission in the dopaminergic projections to the limbic system, and mediates the neurophysiological and behavioral consequences of stress. Notably, the individual psychosocial context is another key element modulating the activity of the ECS. Finally, inflammation represents an additional factor that could alter the cannabinoid signaling in the CNS inducing a "sickness behavior," characterized by anxiety, anhedonia, and depressive symptoms. The complex influences of the ECS on both the environmental and internal stimuli processing, make the cannabinoid-based drugs an appealing option to treat different psychiatric conditions. Although ample experimental evidence shows beneficial effects of ECS modulation on mood, scarce clinical indication limits the use of cannabis-based treatments. To better define the possible clinical indications of cannabinoid-based drugs in psychiatry, a number of issues should be better addressed, including genetic variability and psychosocial factors possibly affecting the individual response. In particular, better knowledge of the multifaceted effects of cannabinoids could help to understand how to boost their therapeutic use in anxiety and depression treatment.

Interplay Between Age and Neuroinflammation in Multiple Sclerosis: Effects on Motor and Cognitive Functions

Aging is one of the main risk factors for the development of many neurodegenerative diseases. Emerging evidence has acknowledged neuroinflammation as potential trigger of the functional changes occurring during normal and pathological aging. Two main determinants have been recognized to cogently contribute to neuroinflammation in the aging brain, i.e., the systemic chronic low-grade inflammation and the decline in the regulation of adaptive and innate immune systems (immunosenescence, ISC). The persistence of the inflammatory status in the brain in turn may cause synaptopathy and synaptic plasticity impairments that underlie both motor and cognitive dysfunctions. Interestingly, such inflammation-dependent synaptic dysfunctions have been recently involved in the pathophysiology of multiple sclerosis (MS). MS is an autoimmune neurodegenerative disease, typically affecting young adults that cause an early and progressive deterioration of both cognitive and motor functions. Of note, recent controlled studies have clearly shown that age at onset modifies prognosis and exerts a significant effect on presenting phenotype, suggesting that aging is a significant factor associated to the clinical course of MS. Moreover, some lines of evidence point to the different impact of age on motor disability and cognitive deficits, being the former most affected than the latter. The precise contribution of aging-related factors to MS neurological disability and the underlying molecular and cellular mechanisms are still unclear. In the present review article, we first emphasize the importance of the neuroinflammatory dependent mechanisms, such as synaptopathy and synaptic plasticity impairments, suggesting their potential exacerbation or acceleration with advancing age in the MS disease. Lastly, we provide an overview of clinical and experimental studies highlighting the different impact of age on motor disability and cognitive decline in MS, raising challenging questions on the putative age-related mechanisms involved.