Paolo Gelosa

The orphan receptor GPR17 identified as a new dual uracil nucleotides/cysteinyl-leukotrienes receptor

Nucleotides and cysteinyl‐leukotrienes (CysLTs) are unrelated signaling molecules inducing multiple effects through separate G‐protein‐coupled receptors: the P2Y and the CysLT receptors. Here we show that GPR17, a Gi‐coupled orphan receptor at intermediate phylogenetic position between P2Y and CysLT receptors, is specifically activated by both families of endogenous ligands, leading to both adenylyl cyclase inhibition and intracellular calcium increases. Agonist‐response profile, as determined by [35S]GTPγS binding, was different from that of already known CysLT and P2Y receptors, with EC50 values in the nanomolar and micromolar range, for CysLTs and uracil nucleotides, respectively. Both rat and human receptors are highly expressed in the organs typically undergoing ischemic damage, that is, brain, heart and kidney. In vivo inhibition of GPR17 by either CysLT/P2Y receptor antagonists or antisense technology dramatically reduced ischemic damage in a rat focal ischemia model, suggesting GPR17 as the common molecular target mediating brain damage by nucleotides and CysLTs. In conclusion, the deorphanization of GPR17 revealed a dualistic receptor for two endogenous unrelated ligand families. These findings may lead to dualistic drugs of previously unexplored therapeutic potential.

The Recently Identified P2Y-Like Receptor GPR17 Is a Sensor of Brain Damage and a New Target for Brain Repair

Deciphering the mechanisms regulating the generation of new neurons and new oligodendrocytes, the myelinating cells of the central nervous system, is of paramount importance to address new strategies to replace endogenous damaged cells in the adult brain and foster repair in neurodegenerative diseases. Upon brain injury, the extracellular concentrations of nucleotides and cysteinyl-leukotrienes (cysLTs), two families of endogenous signaling molecules, are markedly increased at the site of damage, suggesting that they may act as “danger signals” to alert responses to tissue damage and start repair. Here we show that, in brain telencephalon, GPR17, a recently deorphanized receptor for both uracil nucleotides and cysLTs (e.g., UDP-glucose and LTD4), is normally present on neurons and on a subset of parenchymal quiescent oligodendrocyte precursor cells. We also show that induction of brain injury using an established focal ischemia model in the rodent induces profound spatiotemporal-dependent changes of GPR17. In the lesioned area, we observed an early and transient up-regulation of GPR17 in neurons expressing the cellular stress marker heat shock protein 70. Magnetic Resonance Imaging in living mice showed that the in vivo pharmacological or biotechnological knock down of GPR17 markedly prevents brain infarct evolution, suggesting GPR17 as a mediator of neuronal death at this early ischemic stage. At later times after ischemia, GPR17 immuno-labeling appeared on microglia/macrophages infiltrating the lesioned area to indicate that GPR17 may also acts as a player in the remodeling of brain circuitries by microglia. At this later stage, parenchymal GPR17+ oligodendrocyte progenitors started proliferating in the peri-injured area, suggesting initiation of remyelination. To confirm a specific role for GPR17 in oligodendrocyte differentiation, the in vitro exposure of cortical pre-oligodendrocytes to the GPR17 endogenous ligands UDP-glucose and LTD4 promoted the expression of myelin basic protein, confirming progression toward mature oligodendrocytes. Thus, GPR17 may act as a “sensor” that is activated upon brain injury on several embryonically distinct cell types, and may play a key role in both inducing neuronal death inside the ischemic core and in orchestrating the local remodeling/repair response. Specifically, we suggest GPR17 as a novel target for therapeutic manipulation to foster repair of demyelinating wounds, the types of lesions that also occur in patients with multiple sclerosis.

Stimulation of AT2 receptor exerts beneficial effects in stroke-prone rats : focus on renal damage

Background and aim Angiotensin II acts through two major receptors: AT1-R and AT2-R. It is known that the stimulation of AT1-R mediates vasoconstriction, cell proliferation and fibrosis, aldosterone release and inflammatory response but, although the stimulation of AT2-R is thought to promote vasodilation and anti-inflammatory effects, its real in-vivo functions are still unclear. The aim of this study was to investigate the effects of specific and selective AT2-R stimulation on the pathological events occurring in spontaneously hypertensive stroke-prone rats (SHRSPs). Methods and results SHRSPs who were fed a high-salt diet underwent long-term treatment with vehicle or compound 21 (C21), a nonpeptide selective AT2-R agonist, at doses of 0.75, 5 and 10 mg/kg per day. The vehicle-treated rats developed brain abnormalities detectable by magnetic resonance imaging after 42.5 ± 7.5 days, and died 43 ± 9.5 days after the start of the dietary treatment. The highest C21 dose delayed the occurrence of brain damage (P < 0.001 vs. vehicle-treated SHRSPs) and prolonged survival (P < 0.001) without affecting blood pressure. These beneficial effects of C21 were abolished by the administration of PD123319, an AT2-R antagonist. C21 treatment preserved renal structure by preventing inflammatory cell infiltration, collagen accumulation, and the neo-expression of vimentin; it also prevented the increased plasma renin activity and accumulation of urinary acute-phase proteins observed in the vehicle-treated rats. Conclusion Specific and selective AT2-R stimulation has beneficial effects on the pathological events occurring in SHRSPs. These data indicate a new avenue for the pharmacological treatment of diseases in which modulation of the renin–angiotensin system is required.

Statins: Multiple Mechanisms of Action in the Ischemic Brain

Although substantial epidemiological studies have failed to find a correlation between cholesterol levels and stroke, clinical trials have shown that HMG-CoA reductase inhibitors (or statins, the most potent hypocholesterolemic drugs available) greatly reduce the incidence of stroke. These clinical observations have opened the way to a number of studies of the non—cholesterol-dependent (or pleiotropic) effects in animal models of stroke, indicating that the neuroprotection is attributable to multiple activities. One of the main protective mechanisms elicited by statin administration is the increase in nitric oxide bioavailability that regulates cerebral perfusion and improves endothelial function, but others include antioxidant properties, the inhibition of inflammatory responses, immunomodulatory actions, the regulation of progenitor cells, and the stabilization of atherosclerotic plaques. Many of these effects are due to the inhibited synthesis of isoprenoid intermediates, which serve as lipid attachments for a variety of intracellular signaling molecules. This article describes the mechanisms involved in the neuroprotective effects of statins. NEUROSCIENTIST 13(3):208—213, 2007.

Rosuvastatin, but not Simvastatin, Provides End-Organ Protection in Stroke-Prone Rats by Antiinflammatory Effects

Objective—Brain abnormalities, preceded by a systemic inflammation, develop in spontaneously hypertensive stroke-prone rats (SHRSP). In this model, we investigated whether the hydrophilic statin, rosuvastatin, influences the development of inflammation associated with brain abnormalities. Because differences in hydrophilicity/hydrophobicity contribute to the differences in statin pharmacology, we also evaluated the effects of simvastatin, a lipophilic molecule Methods and Results—SHRSP, fed a high-salt diet, were treated long-term with vehicle or rosuvastatin (1 and 10 mg/kg per day). Brain abnormalities developed after 40±5 days and after 60±5 days of salt loading, in vehicle-treated and in rosuvastatin-treated (1 mg/kg per day) SHRSP, respectively. After 100 days of treatment, no damage was detectable in 30% of the rats treated with the highest dose of the drug. In comparison with vehicle-treated SHRSP, rosuvastatin treatment attenuated the transcription of monocyte chemoattractant protein-1, transforming growth factor-&bgr;1, IL-1&bgr;, and tumor necrosis factor-&agr; in the kidney, and of P-selectin in brain vessels and increased the transcription of endothelial nitric oxide synthase mRNA in the aorta. Urinary excretion of acute-phase proteins increased with time in vehicle-treated animals but remained negligible in drug-treated animals. These effects are independent of changes in physiological parameters. Treatment of SHRSP with simvastatin (2 to 20 mg/kg per day) did not exert any protective effect. Conclusions—Rosuvastatin attenuates inflammatory processes associated with cerebrovascular disease.

Bovine serum albumin-based magnetic nanocarrier for MRI diagnosis and hyperthermic therapy: a potential theranostic approach against cancer.

The scientific communityis seeking to exploit the intrinsic properties of magneticnanoparticles (MNPs) to obtain medical breakthroughs indiagnosisandtherapy.OneofthemainadvantagesofmagneticNPs is that they can be visualized acting as magnetic contrastagents(CA)formagneticresonanceimaging(MRI).Heatedina high-frequency magnetic field they trigger drug release orproducehyperthermia/ablationoftissues,currentlyreportedasmagnetic fluid hyperthermia (MFH). Accordingly, the termtheranostic nanomedicine has been defined as an integratednanotherapeutic system, which can diagnose, provide targetedtherapy and monitor the response to therapy.

Analysis of pathological events at the onset of brain damage in stroke‐prone rats: A proteomics and magnetic resonance imaging approach

Spontaneously hypertensive stroke‐prone rats (SHRSP) develop brain abnormalities invariably preceded by the accumulation of acute‐phase proteins in body fluids. This study describes the sequence of pathological events, and in particular the involvement of inflammation, at the onset of brain injury in this animal model. In SHRSP subjected to permissive dietary treatment, the appearance of brain damage and of altered permeability of the blood–brain barrier (BBB) was monitored over time by magnetic resonance imaging (MRI) after intravenous injection of gadolinium. The protein content in cerebrospinal fluid and brain extracts was analyzed by two‐dimensional electrophoresis. Gadolinium diffusion showed impairment of the BBB after 42 ± 3 days from the start of salt loading, simultaneously with the detection of brain abnormalities by MRI. Tissue lesions were initially localized at one or more small foci and then spread throughout the brain in the form of fibrinoid necrosis. This type of lesion is characterized by fibrin deposition, in particular around the vessels; loss of tissue texture; and infiltration of macrophages and lymphocytes. High levels of plasma‐derived proteins of molecular mass up to >130 kDa were detected in the cerebrospinal fluid after MRI had revealed brain abnormalities. Plasma proteins extravasated from brain vessels were immunodetected in tissue homogenates from affected areas. The results obtained in this study provide new insights into the pathogenesis of the spontaneous brain damage in SHRSP and in particular on the involvement of the inflammatory cascade. These studies may be useful in evaluating new pharmacological strategies aimed at preventing/treating brain diseases.

Activation of NF-kB and ERK1/2 after permanent focal ischemia is abolished by simvastatin treatment

We investigated the effects of simvastatin treatment on the expression of IL-1beta and MCP-1, the activity of NF-kB, and the signaling pathways related to NF-kB activation in a rat model of permanent middle cerebral artery occlusion (pMCAO). IL-1beta and MCP-1 expression, determined using RT-PCR, was enhanced by pMCAO; this effect was inhibited by the administration of simvastatin before ischemia. Pre-treatment with simvastatin abolished the ischemia-induced activation of NF-kB observed in vehicle-treated animals. The evaluation of signal transduction pathways, including extracellular signal-regulated kinase (ERK1/2), SAPK/JNK 46/54 and p38, indicated that only ERK1/2 phosphorylation was enhanced by ischemia, and this activation was prevented by simvastatin. ERK1/2-inhibitor, U0126, reduced brain ischemia but not cytokine induction. These results provide evidence that the HMG-CoA reductase inhibitor induces its effect in the protection of ischemic brain damage with a more complex mechanism which also involve anti-inflammatory properties rather than simple inhibition of ERK1/2 signaling pathway.

Treatment with LXR agonists after focal cerebral ischemia prevents brain damage

Stroke is characterized by massive inflammation in areas surrounding the injury that magnifies damage to the brain. The liver X receptors (LXRs) are nuclear receptors that regulate cholesterol, lipid, and glucose metabolism. Synthetic LXR agonists have potent anti‐inflammatory properties in a variety of settings, including neuroinflammation. However, the ability of LXR agonists to suppress stroke‐associated inflammation has not been evaluated. Here, we have used time‐lapse magnetic resonance imaging (MRI) to show that a single dose of an LXR ligand administered post‐injury dramatically reduces brain damage in a model of acute brain ischemia. Neuroprotection was associated with suppression of neuroinflammation.

Proepileptic Influence of a Focal Vascular Lesion Affecting Entorhinal Cortex-CA3 Connections After Status Epilepticus

In limbic seizures, neuronal excitation is conveyed from the entorhinal cortex directly to CA1 and subicular regions. This phenomenon is associated with a reduced ability of CA3 to respond to entorhinal cortex inputs. Here, we describe a lesion that destroys the perforant path in CA3 after status epilepticus (SE) induced by pilocarpine injection in 8-week-old rats. Using magnetic resonance imaging, immunohistochemical, and ultrastructural analyses, we determined that this lesion develops after 30 minutes of SE and is characterized by microhemorrhages and ischemia. After a longer period of SE, the lesion invariably involves the upper blade of the dentate gyrus. Adult rats treated with subcutaneous diazepam (20 mg kg−1 for 3 days) did not develop the dentate gyrus lesion and had less frequent spontaneous recurrent seizures (p < 0.01). Young (3-week-old) rats rarely (20%) developed the CA3 lesion, and their spontaneous seizures were delayed (p < 0.01). To investigate the role of the damaged CA3 in seizure activity, we reinduced SE in adult and young epileptic rats. Using FosB/&Dgr;FosB markers, we found induction of FosB/&Dgr;FosB immunopositivity in CA3 neurons of young but not in adult rats. These experiments indicate that SE can produce a focal lesion in the perforant path that may affect the roles of the hippocampus in epileptic rats.