Functional expression of the ATP-gated P2X7 receptor in human iPSC-derived astrocytes.

Activation of the ATP-gated P2X7 receptor (P2X7R), implicated in numerous diseases of the brain, can trigger diverse responses such as the release of pro-inflammatory cytokines, modulation of neurotransmission, cell proliferation or cell death. However, despite the known species-specific differences in its pharmacological properties, to date, most functional studies on P2X7R responses have been analyzed in cells from rodents or immortalised cell lines. To assess the endogenous and functional expression of P2X7Rs in human astrocytes, we differentiated human-induced pluripotent stem cells (hiPSCs) into GFAP and S100 ß-expressing astrocytes. Immunostaining revealed prominent punctate P2X7R staining. P2X7R protein expression was also confirmed by Western blot. Importantly, stimulation with the potent non-selective P2X7R agonist 2',3'-O-(benzoyl-4-benzoyl)-adenosine 5'- triphosphate (BzATP) or endogenous agonist ATP induced robust calcium rises in hiPSC-derived astrocytes which were blocked by the selective P2X7R antagonists AFC-5128 or JNJ-47965567. Our findings provide evidence for the functional expression of P2X7Rs in hiPSC-derived astrocytes and support their in vitro utility in investigating the role of the P2X7R and drug screening in disorders of the central nervous system (CNS).

Increased expression of the ATP-gated P2X7 receptor reduces responsiveness to anti-convulsants during status epilepticus in mice.

BACKGROUND AND PURPOSE: Refractory status epilepticus is a clinical emergency associated with high mortality and morbidity. Increasing evidence suggests neuroinflammation contributes to the development of drug-refractoriness during status epilepticus. Here, we have determined the contribution of the ATP-gated P2X7 receptor, previously linked to inflammation and increased hyperexcitability, to drug-refractory status epilepticus and its therapeutic potential. EXPERIMENTAL APPROACH: Status epilepticus was induced via a unilateral microinjection of kainic acid into the amygdala in adult mice. Severity of status epilepticus was compared in animals with overexpressing or knock-out of the P2X7 receptor, after inflammatory priming by pre-injection of bacterial lipopolysaccharide (LPS) and in mice treated with P2X7 receptor-targeting and anti-inflammatory drugs. KEY RESULTS: Mice overexpressing P2X7 receptors were unresponsive to several anticonvulsants (lorazepam, midazolam, phenytoin and carbamazepine) during status epilepticus. P2X7 receptor expression increased in microglia during status epilepticus, at times when responses to anticonvulsants were reduced. Overexpression of P2X7 receptors induced a pro-inflammatory phenotype in microglia during status epilepticus and the anti-inflammatory drug minocycline restored normal responses to anticonvulsants in mice overexpressing P2X7 receptors. Pretreatment of wild-type mice with LPS increased P2X7 receptor levels in the brain and reduced responsiveness to anticonvulsants during status epilepticus, which was overcome by either genetic deletion of P2X7 receptors or treatment with the P2X7 receptor antagonists, AFC-5128 or ITH15004. CONCLUSION AND IMPLICATIONS: Our results demonstrate that P2X7 receptor-induced pro-inflammatory effects contribute to resistance to pharmacotherapy during status epilepticus. Therapies targeting P2X7 receptors could be novel adjunctive treatments for drug-refractory status epilepticus.

Chronic high dose P2X7 receptor inhibition exacerbates cancer-induced bone pain.

The functional role of P2X7 receptor (P2X7R) inhibition in cancer-induced bone pain has been highly contradictory. Whereas knockout studies have suggested pro-nociceptive effects, pharmacological studies suggest anti-nociceptive or no effect. The discrepancy is likely linked to the highly polymorphic nature of the P2X7R and the related functional differences in different tissue and conditions. In this study we tested the analgesic potential of AFC5261, a selective P2X7R antagonist, in a rat model of cancer-induced bone pain to evaluate if the opposing pro- and anti-nociceptive effects could be a consequence of long vs. short term inhibition of the P2X7R. Following intratibial inoculation of MRMT-1 carcinoma cells, movement-evoked and background pain was assessed with the limb use and weight-bearing test, and the effect of acute and chronic AFC5261-treatement evaluated. Bone degradation and tumor progression was in addition evaluated with x-ray densitometry and bioluminescence, respectively. In an acute treatment regime, a single administration of 300 mg/kg AFC5261 had no effect on either weight-bearing or limb use deficits. In contrast, morphine significantly increased both the limb use and weight-bearing ratio. In a chronic treatment study, BID administration of 300 mg/kg AFC5261 exacerbated the pain-related behavior, demonstrated by an earlier onset of both limb use and weight-bearing deficits without affecting the overall bone degradation or tumor progression. In contrast, 50 mg/kg and 100 mg/kg AFC5261 had no effect on the pain-related behavior. Overall, the data suggest that whereas acute P2X7R inhibition has no effect on the pain-related behavior, chronic inhibition exacerbate the cancer-induced bone pain.

TRPC4/TRPC5 channels mediate adverse reaction to the cancer cell cytotoxic agent (-)-Englerin A.

(-)-Englerin A (EA) is a natural product which has potent cytotoxic effects on renal cell carcinoma cells and other types of cancer cell but not non-cancer cells. Although selectively cytotoxic to cancer cells, adverse reaction in mice and rats has been suggested. EA is a remarkably potent activator of ion channels formed by Transient Receptor Potential Canonical 4 and 5 proteins (TRPC4 and TRPC5) and TRPC4 is essential for EA-mediated cancer cell cytotoxicity. Here we specifically investigated the relevance of TRPC4 and TRPC5 to the adverse reaction. Injection of EA (2 mg.kg-1 i.p.) adversely affected mice for about 1 hour, manifesting as a marked reduction in locomotor activity, after which they fully recovered. TRPC4 and TRPC5 single knockout mice were partially protected and double knockout mice fully protected. TRPC4/TRPC5 double knockout mice were also protected against intravenous injection of EA. Importance of TRPC4/TRPC5 channels was further suggested by pre-administration of Compound 31 (Pico145), a potent and selective small-molecule inhibitor of TRPC4/TRPC5 channels which did not cause adverse reaction itself but prevented adverse reaction to EA. EA was detected in the plasma but not the brain and so peripheral mechanisms were implicated but not identified. The data confirm the existence of adverse reaction to EA in mice and suggest that it depends on a combination of TRPC4 and TRPC5 which therefore overlaps partially with TRPC4-dependent cancer cell cytotoxicity. The underlying nature of the observed adverse reaction to EA, as a consequence of TRPC4/TRPC5 channel activation, remains unclear and warrants further investigation.

Identification of an (-)-englerin A analogue, which antagonizes (-)-englerin A at TRPC1/4/5 channels.

BACKGROUND AND PURPOSE: (-)-Englerin A (EA) is a potent cytotoxic agent against renal carcinoma cells. It achieves its effects by activation of transient receptor potential canonical (TRPC)4/TRPC1 heteromeric channels. It is also an agonist at channels formed by the related protein, TRPC5. Here, we sought an EA analogue, which might enable a better understanding of these effects of EA. EXPERIMENTAL APPROACH: An EA analogue, A54, was synthesized by chemical elaboration of EA. The effects of EA and A54 on the activity of human TRPC4 or TRPC5 channels overexpressed on A498 and HEK 293 cells were investigated, firstly, by measuring intracellular Ca2+ and, secondly, current using whole-cell patch clamp recordings. KEY RESULTS: A54 had weak or no agonist activity at endogenous TRPC4/TRPC1 channels in A498 cells or TRPC4 or TRPC5 homomeric channels overexpressed in HEK 293 cells. A54 strongly inhibited EA-mediated activation of TRPC4/TRPC1 or TRPC5 and weakly inhibited activation of TRPC4. Studies of TRPC5 showed that A54 shifted the EA concentration-response curve to the right without changing its slope, consistent with competitive antagonism. In contrast, Gd3+ -activated TRPC5 or sphingosine-1-phosphate-activated TRPC4 channels were not inhibited but potentiated by A54. A54 did not activate TRPC3 channels or affect the activation of these channels by the agonist 1-oleoyl-2-acetyl-sn-glycerol. CONCLUSIONS AND IMPLICATIONS: This study has revealed a new tool compound for EA and TRPC1/4/5 channel research, which could be useful for characterizing endogenous TRPC1/4/5 channels and understanding EA-binding sites and their physiological relevance.

P2 receptor antagonist trinitrophenyl-adenosine-triphosphate protects hippocampus from oxygen and glucose deprivation cell death.

In this work, we mainly used the organotypic model of rat hippocampus to demonstrate the protective role of the P2 receptor antagonist trinitrophenyl-adenosine-triphosphate (TNP-ATP) during oxygen/glucose deprivation. Among the P2X receptors that TNP-ATP specifically blocks, mainly P2X1 seems to be involved in the processes of cell damage after oxygen/glucose deprivation. P2X1 receptor is strongly and transiently up-regulated in 24 h after an ischemic insult on structures likely corresponding to mossy fibers and Schaffer collaterals of CA1-3 and dentate gyrus. Furthermore, P2X1 receptor is down-regulated by pharmacological treatment with TNP-ATP, which is also found neuroprotective against ischemic cell death. Morphological studies conducted through immunofluorescence and confocal analysis in primary organotypic, in dissociated cultures, and in adult rat in vivo demonstrated the neuronal colocalization of P2X1 protein with neurofilament light chain and neuronal nuclei immunoreactivity in myelinated and unmyelinated fibers of both granular and pyramidal neurons. In conclusion, with this work, we proved the neuronal distribution of P2X1 receptor in hippocampus, and we presented evidence for a potential disadvantageous role of its expression during the path of in vitro ischemia.

Glucocorticoids worsen excitotoxin-induced expression of pro-inflammatory cytokines in hippocampal cultures.

Glucocorticoids (GCs), the adrenal steroid hormones released during stress, have well-known anti-inflammatory actions. Despite that, there is increasing evidence that GCs are not uniformly anti-inflammatory in the injured nervous system and, in fact, can be pro-inflammatory. The present report continues this theme. Primary hippocampal cultures were treated with GC concentrations approximating basal, acute (1 h) stress or chronic (24 h) stress conditions and were then exposed to the excitotoxin kainic acid (KA). KA induced expression of the pro-inflammatory cytokines IL-1 beta and TNF-alpha, and chronic high dose GC exposure excacerbated this induction. In a second study, cultures were exposed to the physiological range of GC concentrations for 24 h prior to KA treatment. Low- to mid-range GC concentrations were anti-inflammatory, decreasing expression of IL-1 beta and TNF-alpha, while the highest GC doses either failed to be anti-inflammatory or even potentiated expression further. These findings add to the growing picture of these classically anti-inflammatory hormones potentially having pro-inflammatory effects in the injured CNS.

Novel glucocorticoid effects on acute inflammation in the CNS.

The CNS can mount an inflammatory reaction to excitotoxic insults that contributes to the emerging brain damage. Therefore, anti-inflammatory drugs should be beneficial in neurological insults. In contrast, glucocorticoids (GCs), while known for their anti-inflammatory effects, can exacerbate neurotoxicity in the hippocampus after excitotoxic insults. We investigated the effect of GCs on the inflammatory response after a neurological insult. Intact control (INT; intact stress response GC profile), adrenalectomized/GC-supplemented (ADX; low basal GC profile) and GC-treated (COR; chronically high GC profile) rats were injected with kainic acid into the hippocampal CA3 region. Lesion size was determined 8-72 h later. The inflammatory response was characterized using immunohistochemistry, RNAse protection assay and ELISA. The INT and COR rats developed larger CA3 lesions than ADX rats. We found that GCs surprisingly caused an increase in relative numbers of inflammatory cells (granulocytes, monocytes/macrophages and microglia). Additionally, mRNA and protein (IL-1beta and TNF-alpha) levels of the pro-inflammatory cytokines IL-1alpha, IL-1beta and TNF-alpha were elevated in COR rats compared with INT and ADX rats. These data strongly question the traditional view of GCs being uniformly anti-inflammatory and could further explain how GCs worsen the outcome of neurological insults.

Stiff-man syndrome: identification of 17 beta-hydroxysteroid dehydrogenase type 4 as a novel 80-kDa antineuronal antigen.

Stiff-man syndrome (SMS) is a rare autoimmune disorder of the central nervous system associated with autoantibodies to glutamate decarboxylase (GAD). We isolated five brain-reactive human monoclonal antibodies, with reactivity distinct from GAD, from peripheral blood of a patient newly diagnosed with SMS. Two antibodies reacted with both Purkinje cells and ependymal cells, and precipitated an 80-kDa protein from rat neuronal primary cultures, which was also recognized by 12% (3/25) of SMS sera and 13% (2/15) of SMS cerebrospinal fluid (CSF) samples. The corresponding antigen was identified as 17 beta-hydroxysteroid dehydrogenase type 4 and may represent a possible novel target of autoimmunity in SMS.