Interferon-β1a protects neurons against mitochondrial toxicity via modulation of STAT1 signaling: electrophysiological evidence

Implications of immunometabolism for smouldering MS pathology and therapy

Clinical symptom worsening in patients with multiple sclerosis (MS) is driven by inflammation compartmentalized within the CNS, which results in chronic neuronal damage owing to insufficient repair mechanisms. The term 'smouldering inflammation' summarizes the biological aspects underlying this chronic, non-relapsing and immune-mediated mechanism of disease progression. Smouldering inflammation is likely to be shaped and sustained by local factors in the CNS that account for the persistence of this inflammatory response and explain why current treatments for MS do not sufficiently target this process. Local factors that affect the metabolic properties of glial cells and neurons include cytokines, pH value, lactate levels and nutrient availability. This Review summarizes current knowledge of the local inflammatory microenvironment in smouldering inflammation and how it interacts with the metabolism of tissue-resident immune cells, thereby promoting inflammatory niches within the CNS. The discussion highlights environmental and lifestyle factors that are increasingly recognized as capable of altering immune cell metabolism and potentially responsible for smouldering pathology in the CNS. Currently approved MS therapies that target metabolic pathways are also discussed, along with their potential for preventing the processes that contribute to smouldering inflammation and thereby to progressive neurodegenerative damage in MS.

Type I interferon detection in autoimmune diseases: challenges and clinical applications

INTRODUCTION

Accumulating data highlights that the dysregulation of type I interferon (IFN) pathways plays a central role in the pathogenesis of several systemic and organ-specific autoimmune diseases. Advances in understanding the role of type I IFNs in these disorders can lead to targeted drug development as well as establishing potential disease biomarkers.

AREAS COVERED

Here, we summarize current knowledge regarding the role of type I IFNs in the major systemic, as well as organ-specific, autoimmune disorders, including prominent inflammatory CNS disorders like multiple sclerosis.

EXPERT OPINION

Type I IFN involvement and its clinical associations in a wide spectrum of autoimmune diseases represents a promising area for research aiming to unveil common pathogenetic pathways in systemic and organ-specific autoimmunity.

Neuro-Immune Cross-Talk in the Striatum: From Basal Ganglia Physiology to Circuit Dysfunction

The basal ganglia network is represented by an interconnected group of subcortical nuclei traditionally thought to play a crucial role in motor learning and movement execution. During the last decades, knowledge about basal ganglia physiology significantly evolved and this network is now considered as a key regulator of important cognitive and emotional processes. Accordingly, the disruption of basal ganglia network dynamics represents a crucial pathogenic factor in many neurological and psychiatric disorders. The striatum is the input station of the circuit. Thanks to the synaptic properties of striatal medium spiny neurons (MSNs) and their ability to express synaptic plasticity, the striatum exerts a fundamental integrative and filtering role in the basal ganglia network, influencing the functional output of the whole circuit. Although it is currently established that the immune system is able to regulate neuronal transmission and plasticity in specific cortical areas, the role played by immune molecules and immune/glial cells in the modulation of intra-striatal connections and basal ganglia activity still needs to be clarified. In this manuscript, we review the available evidence of immune-based regulation of synaptic activity in the striatum, also discussing how an abnormal immune activation in this region could be involved in the pathogenesis of inflammatory and degenerative central nervous system (CNS) diseases.

Interferon-β suppresses inflammatory pain through activating µ-opioid receptor

Interferons (IFNs) are cytokines secreted by infected cells that can interfere with viral replication. Besides activating antiviral defenses, type I IFNs also exhibit diverse biological functions. IFN-β has been shown to have a protective effect against neurotoxic and inflammatory insults on neurons. Therefore, we aimed to investigate the possible role of IFN-β in reducing mechanical allodynia caused by Complete Freund's Adjuvant (CFA) injection in rats. We assessed the antinociceptive effect of intrathecal IFN-β in naïve rats and the rats with CFA-induced inflammatory pain. After the behavioral test, the spinal cords of the rats were harvested for western blot and immunohistochemical double staining. We found that intrathecal administration of IFN-β in naïve rats can significantly increase the paw withdrawal threshold and paw withdrawal latency. Further, the intrathecal injection of a neutralizing IFN-β antibody can reduce the paw withdrawal threshold and paw withdrawal latency, suggesting that IFN-β is produced in the spinal cord in normal conditions and serves as a tonic inhibitor of pain. In addition, intrathecal injection of IFN-β at dosages from 1000 U to 10000 U demonstrates a significant transient dose-dependent inhibition of CFA-induced inflammatory pain. This analgesic effect is reversed by intrathecal naloxone, suggesting that IFN-β produces an analgesic effect through central opioid receptor-mediated signaling. Increased expression of phospho-µ-opioid receptors after IFN-β injection was observed on western blot, and immunohistochemical staining showed that µ-opioids co-localized with IFN-α/βR in the dorsal horn of the spinal cord. The findings of this study demonstrate that the analgesic effect of IFN-β is through µ-opioid receptors activation in spial cord.

Dopamine D2 receptor-mediated neuroprotection in a G2019S Lrrk2 genetic model of Parkinson's disease

Parkinson's disease (PD) is a neurodegenerative disorder in which genetic and environmental factors synergistically lead to loss of midbrain dopamine (DA) neurons. Mutation of leucine-rich repeated kinase2 (Lrrk2) genes is responsible for the majority of inherited familial cases of PD and can also be found in sporadic cases. The pathophysiological role of this kinase has to be fully understood yet. Hyperactivation of Lrrk2 kinase domain might represent a predisposing factor for both enhanced striatal glutamatergic release and mitochondrial vulnerability to environmental factors that are observed in PD. To investigate possible alterations of striatal susceptibility to mitochondrial dysfunction, we performed electrophysiological recordings from the nucleus striatum of a G2019S Lrrk2 mouse model of PD, as well as molecular and morphological analyses of G2019S Lrrk2-expressing SH-SY5Y neuroblastoma cells. In G2019S mice, we found reduced striatal DA levels, according to the hypothesis of alteration of dopaminergic transmission, and increased loss of field potential induced by the mitochondrial complex I inhibitor rotenone. This detrimental effect is reversed by the D2 DA receptor agonist quinpirole via the inhibition of the cAMP/PKA intracellular pathway. Analysis of mitochondrial functions in G2019S Lrrk2-expressing SH-SY5Y cells revealed strong rotenone-induced oxidative stress characterized by reduced Ca2+ buffering capability and ATP synthesis, production of reactive oxygen species, and increased mitochondrial fragmentation. Importantly, quinpirole was able to prevent all these changes. We suggest that the G2019S-Lrrk2 mutation is a predisposing factor for enhanced striatal susceptibility to mitochondrial dysfunction induced by exposure to mitochondrial environmental toxins and that the D2 receptor stimulation is neuroprotective on mitochondrial function, via the inhibition of cAMP/PKA intracellular pathway. We suggest new possible neuroprotective strategies for patients carrying this genetic alteration based on drugs specifically targeting Lrrk2 kinase domain and mitochondrial functionality.

Type I interferon pathway in CNS homeostasis and neurological disorders

Type I interferons (IFNs), IFN-α and IFN-β, represent the major effector cytokines of the host immune response against viruses and other intracellular pathogens. These cytokines are produced via activation of numerous pattern recognition receptors, including the Toll-like receptor signaling network, retinoic acid-inducible gene-1 (RIG-1), melanoma differentiation-associated protein-5 (MDA-5) and interferon gamma-inducible protein-16 (IFI-16). Whilst the contribution of type I IFNs to peripheral immunity is well documented, they can also be produced by almost every cell in the central nervous system (CNS). Furthermore, IFNs can reach the CNS from the periphery to modulate the function of not only microglia and astrocytes, but also neurons and oligodendrocytes, with major consequences for cognition and behavior. Given the pleiotropic nature of type I IFNs, it is critical to determine their exact cellular impact. Inappropriate upregulation of type I IFN signaling and interferon-stimulated gene expression have been linked to several CNS diseases termed "interferonopathies" including Aicardi-Goutieres syndrome and ubiquitin specific peptidase 18 (USP18)-deficiency. In contrast, in the CNS of mice with virus-induced neuroinflammation, type I IFNs can limit production of other cytokines to prevent potential damage associated with chronic cytokine expression. This capacity of type I IFNs could also explain the therapeutic benefits of exogenous type I IFN in chronic CNS autoimmune diseases such as multiple sclerosis. In this review we will highlight the importance of a well-balanced level of type I IFNs for healthy brain physiology, and to what extent dysregulation of this cytokine system can result in brain 'interferonopathies'.

Nutraceuticals against Neurodegeneration: A Mechanistic Insight

The mechanisms underlying neurodegenerative disorders are complex and multifactorial; however, accumulating evidences suggest few common shared pathways. These common pathways include mitochondrial dysfunction, intracellular Ca²⁺ overload, oxidative stress and inflammation. Often multiple pathways co-exist, and therefore limit the benefits of therapeutic interventions. Nutraceuticals have recently gained importance owing to their multifaceted effects. These food-based approaches are believed to target multiple pathways in a slow but more physiological manner without causing severe adverse effects. Available information strongly supports the notion that apart from preventing the onset of neuronal damage, nutraceuticals can potentially attenuate the continued progression of neuronal destruction. In this article, we i) review the common pathways involved in the pathogenesis of the toxicants-induced neurotoxicity and neurodegenerative disorders with special emphasis on Alzheimer's disease (AD), Parkinson's disease (PD), Huntington's disease (HD), Multiple sclerosis (MS) and Amyotrophic lateral sclerosis (ALS), and ii) summarize current research advancements on the effects of nutraceuticals against these detrimental pathways.

Interferon alpha inhibits spinal cord synaptic and nociceptive transmission via neuronal-glial interactions

It is well known that interferons (IFNs), such as type-I IFN (IFN-α) and type-II IFN (IFN-γ) are produced by immune cells to elicit antiviral effects. IFNs are also produced by glial cells in the CNS to regulate brain functions. As a proinflammatory cytokine, IFN-γ drives neuropathic pain by inducing microglial activation in the spinal cord. However, little is known about the role of IFN-α in regulating pain sensitivity and synaptic transmission. Strikingly, we found that IFN-α/β receptor (type-I IFN receptor) was expressed by primary afferent terminals in the superficial dorsal horn that co-expressed the neuropeptide CGRP. In the spinal cord IFN-α was primarily expressed by astrocytes. Perfusion of spinal cord slices with IFN-α suppressed excitatory synaptic transmission by reducing the frequency of spontaneous excitatory postsynaptic current (sEPSCs). IFN-α also inhibited nociceptive transmission by reducing capsaicin-induced internalization of NK-1 and phosphorylation of extracellular signal-regulated kinase (ERK) in superficial dorsal horn neurons. Finally, spinal (intrathecal) administration of IFN-α reduced inflammatory pain and increased pain threshold in naïve rats, whereas removal of endogenous IFN-α by a neutralizing antibody induced hyperalgesia. Our findings suggest a new form of neuronal-glial interaction by which IFN-α, produced by astrocytes, inhibits nociceptive transmission in the spinal cord.

Interferon-β1a modulates glutamate neurotransmission in the CNS through CaMKII and GluN2A-containing NMDA receptors

Interferons (IFNs) are widely expressed cytokines with antiviral and immune-modulating effects and have been utilised for the treatment of several human pathological conditions. In particular, the immune-modulatory drug IFN-β is utilized in the treatment of multiple sclerosis (MS), a chronic autoimmune and neurodegenerative disorder of the central nervous system (CNS). Although the effects of IFN-β on immune cells functions have been widely investigated, information about the ability of the drug to modulate neuronal transmission in the CNS is still largely lacking. The aim of this study was to investigate the ability of IFN-β1a to modulate excitatory synaptic transmission in the CNS. Whole cell patch-clamp electrophysiological recordings were performed in the nucleus striatum, one of the CNS grey matter structures that is prone to degenerate during the course of MS. We demonstrate that the drug IFN-β1a, independently from its known peripheral immune-modulating action, is able to directly modulate synaptic transmission. In particular, we demonstrated that IFN-β1a reduces the amplitude of striatal excitatory post-synaptic currents, indicating an inhibitory effect on glutamate neurotransmission, and in particular on its NMDA component. The inhibitory effect of IFN-β1a on striatal glutamate neurotransmission was found to be mediated by a novel post-synaptic mechanism requiring Ca(2+), CaMKII and the GluN2A subunit of the NMDA receptor, without the involvement of the classic STAT1 pathway. The evidence of a novel neuro-modulating effect of IFN-β shed light on the mechanisms of action of the drug and on the complex bidirectional interaction occurring between the immune and the nervous system. This article is part of the Special Issue entitled 'Synaptopathy--from Biology to Therapy'.

Therapeutic strategies for relapsing-remitting multiple sclerosis: a special focus on reduction of grey matter damage as measured by brain atrophy

In the past two decades, several pathological and radiological findings convincingly demonstrated that damage of the cortical and deep grey matter is a key issue in multiple sclerosis with a significant impact on physical and cognitive disability. Moreover, it has become increasingly evident that the effect of available therapies on the inflammatory white matter damage is not a guarantee of a meaningful effect on the neurodegenerative process mainly affecting the grey matter. Despite the efficacy of all approved disease-modifying drugs should be measured considering such a relevant aspect of the disease, data from clinical trials are few, scattered and heterogeneous. The aim of this review is to summarize the evidence so far acquired on the effect of reducing grey matter damage produced by current and emerging disease-modifying therapies for multiple sclerosis.

Interferon receptor signaling in malignancy: a network of cellular pathways defining biological outcomes

IFNs are cytokines with important antiproliferative activity and exhibit key roles in immune surveillance against malignancies. Early work initiated over three decades ago led to the discovery of IFN receptor activated Jak-Stat pathways and provided important insights into mechanisms for transcriptional activation of IFN-stimulated genes (ISG) that mediate IFN biologic responses. Since then, additional evidence has established critical roles for other receptor-activated signaling pathways in the induction of IFN activities. These include MAPK pathways, mTOR cascades, and PKC pathways. In addition, specific miRNAs appear to play a significant role in the regulation of IFN signaling responses. This review focuses on the emerging evidence for a model in which IFNs share signaling elements and pathways with growth factors and tumorigenic signals but engage them in a distinctive manner to mediate antiproliferative and antiviral responses.