Chiara Parisi

Dysregulated microRNAs in amyotrophic lateral sclerosis microglia modulate genes linked to neuroinflammation.

MicroRNAs (miRNAs) regulate gene expression at post-transcriptional level and are key modulators of immune system, whose dysfunction contributes to the progression of neuroinflammatory diseaseas such as amyotrophic lateral sclerosis (ALS), the most widespread motor neuron disorder. ALS is a non-cell-autonomous disease targeting motor neurons and neighboring glia, with microgliosis directly contributing to neurodegeneration. As limited information exists on miRNAs dysregulations in ALS, we examined this topic in primary microglia from superoxide dismutase 1-G93A mouse model. We compared miRNAs transcriptional profiling of non-transgenic and ALS microglia in resting conditions and after inflammatory activation by P2X7 receptor agonist. We identified upregulation of selected immune-enriched miRNAs, recognizing miR-22, miR-155, miR-125b and miR-146b among the most highly modulated. We proved that miR-365 and miR-125b interfere, respectively, with the interleukin-6 and STAT3 pathway determining increased tumor necrosis factor alpha (TNFα) transcription. As TNFα directly upregulated miR-125b, and inhibitors of miR-365/miR-125b reduced TNFα transcription, we recognized the induction of miR-365 and miR-125b as a vicious gateway culminating in abnormal TNFα release. These results strengthen the impact of miRNAs in modulating inflammatory genes linked to ALS and identify specific miRNAs as pathogenetic mechanisms in the disease.

The NADPH Oxidase Pathway Is Dysregulated by the P2X7 Receptor in the SOD1-G93A Microglia Model of Amyotrophic Lateral Sclerosis

Inflammation and oxidative stress are thought to play determinant roles in the pathogenesis of amyotrophic lateral sclerosis (ALS). Degenerating motor neurons produce signals that activate microglia to release reactive oxygen species (ROS) and proinflammatory cytokines, resulting in a vicious cycle of neurodegeneration. The ALS-causing mutant protein Cu+/Zn+ superoxide dismutase SOD1-G93A directly enhances the activity of the main ROS-producing enzyme in microglia, NADPH oxidase 2 (NOX2), a well-known player in the pathogenesis of ALS. Considering that extracellular ATP through P2X7 receptor constitutes a neuron-to-microglia alarm signal implicated in ALS pathology, we used primary microglial cells derived from transgenic SOD1-G93A mice and SOD1-G93A mice lacking the P2X7 receptor to investigate the effects of both pharmacological induction and genetic ablation of receptor activity on the NOX2 pathway. We observed that, in SOD1-G93A microglia, the stimulation of P2X7 receptor by 2′-3′-O-(benzoyl-benzoyl) ATP enhanced NOX2 activity in terms of translocation of p67phox to the membrane and ROS production; this effect was totally dependent on Rac1. We also found that, following P2X7 receptor stimulation, the phosphorylation of ERK1/2 was augmented in ALS microglia, and there was a mutual dependency between the NOX2 and ERK1/2 pathways. All of these microglia-mediated damaging mechanisms were prevented by knocking out P2X7 receptor and by the use of specific antagonists. These findings suggest a noxious mechanism by which P2X7 receptor leads to enhanced oxidative stress in ALS microglia and identify the P2X7 receptor as a promising target for the development of therapeutic strategies to slow down the progression of ALS.

Spinal cord pathology is ameliorated by P2X7 antagonism in a SOD1-mutant mouse model of amyotrophic lateral sclerosis

In recent years there has been an increasing awareness of the role of P2X7, a receptor for extracellular ATP, in modulating physiopathological mechanisms in the central nervous system. In particular, P2X7 has been shown to be implicated in neuropsychiatry, chronic pain, neurodegeneration and neuroinflammation. Remarkably, P2X7 has also been shown to be a ‘gene modifier’ in amyotrophic lateral sclerosis (ALS): the receptor is upregulated in spinal cord microglia in human and rat at advanced stages of the disease; in vitro, activation of P2X7 exacerbates pro-inflammatory responses in microglia that have an ALS phenotype, as well as toxicity towards neuronal cells. Despite this detrimental in vitro role of P2X7, in SOD1-G93A mice lacking P2X7, the clinical onset of ALS was significantly accelerated and disease progression worsened, thus indicating that the receptor might have some beneficial effects, at least at certain stages of disease. In order to clarify this dual action of P2X7 in ALS pathogenesis, in the present work we used the antagonist Brilliant Blue G (BBG), a blood-brain barrier permeable and safe drug that has already been proven to reduce neuroinflammation in traumatic brain injury, cerebral ischemia-reperfusion, neuropathic pain and experimental autoimmune encephalitis. We tested BBG in the SOD1-G93A ALS mouse model at asymptomatic, pre-symptomatic and late pre-symptomatic phases of disease. BBG at late pre-onset significantly enhanced motor neuron survival and reduced microgliosis in lumbar spinal cord, modulating inflammatory markers such as NF-κB, NADPH oxidase 2, interleukin-1β, interleukin-10 and brain-derived neurotrophic factor. This was accompanied by delayed onset and improved general conditions and motor performance, in both male and female mice, although survival appeared unaffected. Our results prove the twofold role of P2X7 in the course of ALS and establish that P2X7 modulation might represent a promising therapeutic strategy by interfering with the neuroinflammatory component of the disease.

MicroRNAs: Newcomers into the ALS Picture

Amyotrophic lateral sclerosis (ALS) causes neurodegeneration of both upper and lower motor neurons and progressive muscle impairment, atrophy and death within approximately five years from diagnosis. The aetiology is still not clear but evidence obtained in animal models of the disease indicates a non-cell-autonomous mechanism with the active contribution of non-neuronal cells such as microglia, astrocytes, muscle and T cells, which differently participate to the diverse phases of the disease. Clinically indistinguishable forms of ALS occur as sporadic disease in the absence of known mutation, or can be initiated by genetic mutations. About two-third of familial cases are triggered by mutations of four genes that are chromosome 9 open reading frame 72 (C9ORF72), Cu/Zn superoxide dismutase (SOD1), fused in sarcoma/translocated in liposarcoma (FUS/TLS), TAR-DNA binding protein 43 (TDP43). There is at present no succesfull treatment against ALS and the identification of novel signalling pathways, molecular mechanisms and cellular mediators are still a major task in the search for effective therapies. MiRNAs are conserved, endogenous, non-coding RNAs that post-transcriptionally regulate protein expression. Produced as long primary transcripts, they are exported to the cytoplasm and further modified to obtain the mature miRNAs, with each step of their biogenesis being a potential step of regulation. There are more than 1000 different known human miRNA sequences, and more than 20-30% of all human protein-coding genes are likely controlled by miRNAs. This earns to miRNAs the definition of fine regulators of genetic networks. The discovery of the involvement of ALS mutated proteins TDP43 and FUS/TLS in miRNAs biogenesis strongly suggests a role of miRNA dysregulation also in ALS and many efforts are thus directed toward understanding the role of these small RNA molecules in the pathogenesis of ALS. The overall objective of this review is thus to highlight the emerging involvement of miRNAs in ALS. After a brief description of miRNA biogenesis and function, we discuss the effects of miRNA dysregulation in cellular and molecular pathways that lead to ALS neuroinflammation and neurodegeneration. In the last part, we focus on the mechanistic insights of miRNAs that might have implications for the development of novel neuroprotective agents against ALS, and on recent attempts to establish new molecular miRNA-based therapies. Paving the way for more comparative studies on neuroinflammatory and neurodegenerative mechanisms, this strategy indeed promises a broader impact on ALS.

P2Y12 Receptor on the Verge of a Neuroinflammatory Breakdown

In the CNS, neuroinflammation occurring during pathologies as amyotrophic lateral sclerosis (ALS) and multiple sclerosis (MS) is the consequence of an intricate interplay orchestrated by various cell phenotypes. Among the molecular cues having a role in this process, extracellular nucleotides are responsible for intercellular communication and propagation of inflammatory stimuli. This occurs by binding to several receptor subtypes, defined P2X/P2Y, which are widespread in different tissues and simultaneously localized on multiple cells. For instance, the metabotropic P2Y12 subtype is found in the CNS on microglia, affecting activation and chemotaxis, on oligodendrocytes, possessing a hypothesized role in myelination, and on astrocytes. By comparative analysis, we have established here that P2Y12 receptor immunolabelled by antibodies against C-terminus or second intracellular loop, is, respectively, distributed and modulated under neuroinflammatory conditions on ramified microglia or myelinated fibers, in primary organotypic cerebellar cultures, tissue slices from rat striatum and cerebellum, spinal cord sections from symptomatic/end stage SOD1-G93A ALS mice, and finally autoptic cortical tissue from progressive MS donors. We suggest that modulation of P2Y12 expression might play a dual role as analytic marker of branched/surveillant microglia and demyelinating lesions, thus potentially acquiring a predictive value under neuroinflammatory conditions as those found in ALS and MS.

Modulation of P2X7 Receptor during Inflammation in Multiple Sclerosis

Multiple sclerosis (MS) is characterized by macrophage accumulation and inflammatory infiltrates into the CNS contributing to demyelination. Because purinergic P2X7 receptor (P2X7R) is known to be abundantly expressed on cells of the hematopoietic lineage and of the nervous system, we further investigated its phenotypic expression in MS and experimental autoimmune encephalomyelitis conditions. By quantitative reverse transcription polymerase chain reaction and flow cytometry, we analyzed the P2X7R expression in human mononuclear cells of peripheral blood from stable and acute relapsing-remitting MS phases. Human monocytes were also challenged in vitro with pro-inflammatory stimuli such as the lipopolysaccharide, or the P2X7R preferential agonist 2′(3′)-O-(4 Benzoylbenzoyl)adenosine 5′-triphosphate, before evaluating P2X7R protein expression. Finally, by immunohistochemistry and immunofluorescence confocal analysis, we investigated the P2X7R expression in frontal cortex from secondary progressive MS cases. We demonstrated that P2X7R is present and inhibited on peripheral monocytes isolated from MS donors during the acute phase of the disease, moreover it is down-regulated in human monocytes after pro-inflammatory stimulation in vitro. P2X7R is instead up-regulated on astrocytes in the parenchyma of frontal cortex from secondary progressive MS patients, concomitantly with monocyte chemoattractant protein-1 chemokine, while totally absent from microglia/macrophages or oligodendrocytes, despite the occurrence of inflammatory conditions. Our results suggest that inhibition of P2X7R on monocytes and up-regulation in astrocytes might contribute to sustain inflammatory mechanisms in MS. By acquiring further knowledge about P2X7R dynamics and identifying P2X7R as a potential marker for the disease, we expect to gain insights into the molecular pathways of MS.

M1 and M2 Functional Imprinting of Primary Microglia: Role of P2X7 Activation and miR-125b

Amyotrophic lateral sclerosis (ALS) is a most frequently occurring and severe form of motor neuron disease, causing death within 3–5 years from diagnosis and with a worldwide incidence of about 2 per 100,000 person-years. Mutations in over twenty genes associated with familial forms of ALS have provided insights into the mechanisms leading to motor neuron death. Moreover, mutations in two RNA binding proteins, TAR DNA binding protein 43 and fused in sarcoma, have raised the intriguing possibility that perturbations of RNA metabolism, including that of the small endogenous RNA molecules that repress target genes at the posttranscriptional level, that is, microRNAs, may contribute to disease pathogenesis. At present, the mechanisms by which microglia actively participate to both toxic and neuroprotective actions in ALS constitute an important matter of research. Among the pathways involved in ALS-altered microglia responses, in previous works we have uncovered the hyperactivation of P2X7 receptor by extracellular ATP and the overexpression of miR-125b, both leading to uncontrolled toxic M1 reactions. In order to shed further light on the complexity of these processes, in this short review we will describe the M1/M2 functional imprinting of primary microglia and a role played by P2X7 and miR-125b in ALS microglia activation.

New Kid on the Block: Does Histamine Get Along with Inflammation in Amyotrophic Lateral Sclerosis?

Results from amyotrophic lateral sclerosis (ALS) patients and pre-clinical studies strongly suggest that systemic and CNS-intrinsic immune activation plays a central role in ALS pathogenesis. Microglial cells are emerging in this context as master regulators with a bi-functional role in the progression of the pathological response. They foster a pro-inflammatory setting through the production of cytotoxic cytokines and chemokines (M1 phenotype), after an aborted effort to sustain an anti-inflammatory environment for motor neurons through the release of beneficial cytokines and growth factors (M2 phenotype). In this review, we gather information meant to propose that histamine and ATP, which are released from mast cells, microglia and damaged neurons at sites of injury where they function as transmitters, have to be considered as new players in the ALS neuroinflammatory arena. After all, abnormal histamine and ATP signalling in the brain are already documented in neurodegenerative/neuroinflammatory conditions such as multiple sclerosis, Alzheimer and Parkinsons disease and, at present, histamine- as well as ATP-related compounds are in clinical trial for these same pathologies. Concerning ALS, while emerging data are now available about purinergic mechanisms, the involvement of histamine is basically unexplored. The circumstantial evidence that we present here thus constitutes a solid background for formulating novel hypotheses, stimulating a scientific debate and, most of all, inspiring future research. We deem that a new potential role of histamine in the setting of ALS neuroinflammation might find a fertile ground where to thrive. ALS is still a disease without a cure: why not to play with a new kid on the block?