Susanna Amadio

Bio: Susanna Amadio is an academic researcher from University of Rome Tor Vergata. The author has contributed to research in topics: Receptor & Purinergic receptor. The author has an hindex of 29, co-authored 56 publications receiving 2251 citations.

Extracellular ATP and neurodegeneration.

Abstract: ATP is a potent signaling molecule abundantly present in the CNS. It elicits a wide array of physiological effects and is regarded as the phylogenetically most ancient epigenetic factor playing crucial biological roles in several different tissues. These can range from neurotransmission, smooth muscle contraction, chemosensory signaling, secretion and vasodilatation, to more complex phenomena such as immune responses, pain, male reproduction, fertilization and embryonic development. ATP is released into the extracellular space either exocytotically or from damaged and dying cells. It is often co-released with other neurotransmitters and it can interact with growth factors at both receptor- and/or signal transduction-level. Once in the extracellular environment, ATP binds to specific receptors termed P2. Based on pharmacological profiles, on selectivity of coupling to second-messenger pathways and on molecular cloning, two main subclasses with multiple subtypes have been distinguished. They are P2X, i.e. fast cation-selective receptor channels (Na+, K+, Ca2+), possessing low affinity for ATP and responsible for fast excitatory neurotransmission, and P2Y, i.e. slow G protein-coupled metabotropic receptors, possessing higher affinity for the ligand. In the nervous system, they are broadly expressed in both neurons and glial cells and can mediate dual effects: short-term such as neurotransmission, and long-term such as trophic actions. Since massive extracellular release of ATP often occurs after metabolic stress, brain ischemia and trauma, purinergic mechanisms are also correlated to and involved in the etiopathology of many neurodegenerative conditions. Furthermore, extracellular ATP per se is toxic for primary neuronal dissociated and organotypic CNS cultures from cortex, striatum and cerebellum and P2 receptors can mediate and aggravate hypoxic signaling in many CNS neurons. Conversely, several P2 receptor antagonists abolish the cell death fate of primary neuronal cultures exposed to excessive glutamate, serum/potassium deprivation, hypoglycemia and chemical hypoxia. In parallel with these detrimental effects, also trophic functions have been extensively described for extracellular purines (both for neuronal and non-neuronal cells), but these might either aggravate or ameliorate the normal cellular conditions. In summary, extracellular ATP plays a very complex role not only in the repair, remodeling and survival occurring in the nervous system, but even in cell death and this can occur either after normal developmental conditions, after injury, or acute and chronic diseases.

P2X7 Receptor Modulation on Microglial Cells and Reduction of Brain Infarct Caused by Middle Cerebral Artery Occlusion in Rat

Abstract: Adenosine 5'-triphosphate outflow increases after an ischemic insult in the brain and may induce the expression of P2X7 receptors in resting microglia, determining its modification into an activated state. To assess the effects of P2X7 receptor blockade in preventing microglia activation and ameliorating brain damage and neurological impairment, we delivered the P2 unselective antagonist Reactive Blue 2 to rats after middle cerebral artery occlusion. In sham-operated animals, devoid of brain damage, double immunofluorescence verified the absence of P2X7 immunoreactivity on resting microglia, astrocytes, and neurons, identified, respectively, by OX-42, glial fibrillary acid protein, and neuronal nuclei (NeuN) immunoreactivity. After ischemia, vehicle-treated rats showed monolateral sensorimotor deficit and tissue damage in striatum and frontoparietal cortex. Moreover, P2X7 immunoreactivity was de novo expressed on activated microglia in infarcted and surrounding areas, as well as on a reactive form of microglia, resting in shape but P2X7 immunoreactive, present in ipsi- and contralateral cingulate and medial frontal cortex. Reactive Blue 2 improved sensorimotor deficit and restricted the volume of infarction, without preventing the expression of P2X7, but inducing it in the microglia of contralateral frontal and parietal cortex and striatum, which had lost reciprocal connections with the remote infarct area. De novo expression of P2X7 occurred in both activated and reactive microglia, suggesting their differentiated roles in the area of infarct and in remote regions. Reactive Blue 2 reduced ischemic brain damage, likely blocking the function of activated microglia in the infarct area, but in the remote brain regions promoted the expression of P2X7 on reactive microglia, developing defense and reparative processes.

Metabotropic P2 receptor activation regulates oligodendrocyte progenitor migration and development

Abstract: To gain insights into the role of purinergic receptors in oligodendrocyte development, we characterized the expression and functional activity of P2 receptors in cultured rat oligodendrocyte progenitors and investigated the effects of ATP and its breakdown products on the migration and proliferation of this immature glial cell population. Using Western blot analysis, we show that oligodendrocyte progenitors express several P2X (P2X(1,2,3,4,7)) and P2Y (P2Y(1,2,4)) receptors. Intracellular Ca(2+) recording by Fura-2 video imaging allowed to determine the rank potency order of the P2 agonists tested: ADPbetaS = ADP = Benzoyl ATP > ATP > ATPgammaS > UTP, alpha,beta-meATP ineffective. Based on the above findings, on pharmacological inhibition by the antagonists oxATP and MRS2179, and on the absence of alpha,betameATP-induced inward current in whole-cell recording, P2X(7) and P2Y(1) were identified as the main ionotropic and metabotropic P2 receptors active in OPs. As a functional correlate of these findings, we show that ATP and, among metabotropic agonists, ADP and the P2Y(1)-specific agonist ADPbetaS, but not UTP, induce oligodendrocyte progenitor migration. Moreover, ATP and ADP inhibited the proliferation of oligodendrocyte progenitors induced by platelet-derived growth factor, both in purified cultures and in cerebellar tissue slices. The effects of ATP and ADP on cell migration and proliferation were prevented by the P2Y(1) antagonist MRS2179. By confocal laser scanning microscopy, P2Y(1) receptors were localized in NG2-labeled oligodendrocyte progenitors in the developing rat brain. These data indicate that ATP and ADP may regulate oligodendrocyte progenitor functions by a mechanism that involves mainly activation of P2Y(1) receptors.

Physiology of Microglia

Abstract: Microglial cells are the resident macrophages in the central nervous system. These cells of mesodermal/mesenchymal origin migrate into all regions of the central nervous system, disseminate through the brain parenchyma, and acquire a specific ramified morphological phenotype termed "resting microglia." Recent studies indicate that even in the normal brain, microglia have highly motile processes by which they scan their territorial domains. By a large number of signaling pathways they can communicate with macroglial cells and neurons and with cells of the immune system. Likewise, microglial cells express receptors classically described for brain-specific communication such as neurotransmitter receptors and those first discovered as immune cell-specific such as for cytokines. Microglial cells are considered the most susceptible sensors of brain pathology. Upon any detection of signs for brain lesions or nervous system dysfunction, microglial cells undergo a complex, multistage activation process that converts them into the "activated microglial cell." This cell form has the capacity to release a large number of substances that can act detrimental or beneficial for the surrounding cells. Activated microglial cells can migrate to the site of injury, proliferate, and phagocytose cells and cellular compartments.

Physiology and Pathophysiology of Purinergic Neurotransmission

Abstract: This review is focused on purinergic neurotransmission, i.e., ATP released from nerves as a transmitter or cotransmitter to act as an extracellular signaling molecule on both pre- and postjunctional membranes at neuroeffector junctions and synapses, as well as acting as a trophic factor during development and regeneration. Emphasis is placed on the physiology and pathophysiology of ATP, but extracellular roles of its breakdown product, adenosine, are also considered because of their intimate interactions. The early history of the involvement of ATP in autonomic and skeletal neuromuscular transmission and in activities in the central nervous system and ganglia is reviewed. Brief background information is given about the identification of receptor subtypes for purines and pyrimidines and about ATP storage, release, and ectoenzymatic breakdown. Evidence that ATP is a cotransmitter in most, if not all, peripheral and central neurons is presented, as well as full accounts of neurotransmission and neuromodulation in autonomic and sensory ganglia and in the brain and spinal cord. There is coverage of neuron-glia interactions and of purinergic neuroeffector transmission to nonmuscular cells. To establish the primitive and widespread nature of purinergic neurotransmission, both the ontogeny and phylogeny of purinergic signaling are considered. Finally, the pathophysiology of purinergic neurotransmission in both peripheral and central nervous systems is reviewed, and speculations are made about future developments.

Microglia in neurodegeneration.

Abstract: The neuroimmune system is involved in development, normal functioning, aging, and injury of the central nervous system Microglia, first described a century ago, are the main neuroimmune cells and have three essential functions: a sentinel function involved in constant sensing of changes in their environment, a housekeeping function that promotes neuronal well-being and normal operation, and a defense function necessary for responding to such changes and providing neuroprotection Microglia use a defined armamentarium of genes to perform these tasks In response to specific stimuli, or with neuroinflammation, microglia also have the capacity to damage and kill neurons Injury to neurons in Alzheimer’s, Parkinson’s, Huntington’s, and prion diseases, as well as in amyotrophic lateral sclerosis, frontotemporal dementia, and chronic traumatic encephalopathy, results from disruption of the sentinel or housekeeping functions and dysregulation of the defense function and neuroinflammation Pathways associated with such injury include several sensing and housekeeping pathways, such as the Trem2, Cx3cr1 and progranulin pathways, which act as immune checkpoints to keep the microglial inflammatory response under control, and the scavenger receptor pathways, which promote clearance of injurious stimuli Peripheral interference from systemic inflammation or the gut microbiome can also alter progression of such injury Initiation or exacerbation of neurodegeneration results from an imbalance between these microglial functions; correcting such imbalance may be a potential mode for therapy