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The inducible p25 overexpression mouse model recapitulate many hallmark features of Alzheimer's disase including progressive neuronal loss, elevated Aβ, tau pathology, cognitive dysfunction, and impaired synaptic plasticity. We chose p25 mice to evaluate the physical and functional integrity of the blood-brain barrier (BBB) in a context of Tau pathology (pTau) and severe neurodegeneration, at an early (3 weeks ON) and a late (6 weeks ON) stage of the pathology. Using in situ brain perfusion and confocal imaging, we found that the brain vascular surface area and the physical integrity of the BBB were unaltered in p25 mice. However, there was a significant 14% decrease in cerebrovascular volume in 6 weeks ON mice, possibly explained by a significant 27% increase of collagen IV in the basement membrane of brain capillaries. The function of the BBB transporters GLUT1 and LAT1 was evaluated by measuring brain uptake of d-glucose and phenylalanine, respectively. In 6 weeks ON p25 mice, d-glucose brain uptake was significantly reduced by about 17% compared with WT, without any change in the levels of GLUT1 protein or mRNA in brain capillaries. The brain uptake of phenylalanine was not significantly reduced in p25 mice compared with WT. Lack of BBB integrity, impaired BBB d-glucose transport have been observed in several mouse models of AD. In contrast, reduced cerebrovascular volume and an increased basement membrane thickness may be more specifically associated with pTau in mouse models of neurodegeneration., (Copyright © 2021 Elsevier Ltd. All rights reserved.)

Transient receptor potential vanilloid 1-4 (TRPV1-4) expression and functionality were investigated in brain microvessel endothelial cells (BMEC) forming the blood-brain barrier (BBB) from rat and human origins. In rat, Trpv1-4 were detected by qRT-PCR in the brain cortex, brain microvessels, and in primary cultures of brain microvessel endothelial cells [rat brain microvessel endothelial cells (rPBMEC)]. A similar Trpv1-4 expression profile in isolated brain microvessels and rPBMEC was found with the following order: Trpv4 > Trpv2 > Trpv3 > Trpv1 . In human, TRPV1-4 were detected in the BBB cell line human cerebral microvessel endothelial cells D3 cells (hCMEC/D3) and in primary cultures of BMEC isolated from human adult and children brain resections [human brain microvascular endothelial cells (hPBMEC)], showing a similar TRPV1-4 expression profile in both hCMEC/D3 cells and hPBMECs as follow: TRPV2 > > TRPV4 > TRPV1 > TRPV3 . Western blotting and immunofluorescence experiments confirmed that TRPV2 and TRPV4 are the most expressed TRPV isoforms in hCMEC/D3 cells with a clear staining at the plasma membrane. A fluorescent dye Fluo-4 AM ester was applied to record intracellular Ca 2+ levels. TRPV4 functional activity was demonstrated in mediating Ca 2+ influx under stimulation with the specific agonist GSK1016790A (ranging from 3 to 1000 nM, EC 50 of 16.2 ± 4.5 nM), which was inhibited by the specific TRPV4 antagonist, RN1734 (30 μM). In contrast, TRPV1 was slightly activated in hCMEC/D3 cells as shown by the weak Ca 2+ influx induced by capsaicin at a high concentration (3 μM), a highly potent and specific TRPV1 agonist. Heat-induced Ca 2+ influx was not altered by co-treatment with a selective potent TRPV1 antagonist capsazepine (20 μM), in agreement with the low expression of TRPV1 as assessed by qRT-PCR. Our present study reveals an interspecies difference between Rat and Human. Functional contributions of TRPV1-4 subtype expression were not identical in rat and human tissues reflective of BBB integrity. TRPV2 was predominant in the human whereas TRPV4 had a larger role in the rat. This interspecies difference from a gene expression point of view should be taken into consideration when modulators of TRPV2 or TRPV4 are investigated in rat models of brain disorders., (Copyright © 2020 Luo, Saubamea, Chasseigneaux, Cochois, Smirnova, Glacial, Perrière, Chaves, Cisternino and Declèves.)

The effect of cannabidiol (CBD), a high-affinity agonist of the transient receptor potential vanilloid-2 (TRPV2) channel, has been poorly investigated in human brain microvessel endothelial cells (BMEC) forming the blood-brain barrier (BBB). TRPV2 expression and its role on Ca 2+ cellular dynamics, trans-endothelial electrical resistance (TEER), cell viability and growth, migration, and tubulogenesis were evaluated in human primary cultures of BMEC (hPBMEC) or in the human cerebral microvessel endothelial hCMEC/D3 cell line. Abundant TRPV2 expression was measured in hCMEC/D3 and hPBMEC by qRT-PCR, Western blotting, nontargeted proteomics, and cellular immunofluorescence studies. Intracellular Ca 2+ levels were increased by heat and CBD and blocked by the nonspecific TRP antagonist ruthenium red (RR) and the selective TRPV2 inhibitor tranilast (TNL) or by silencing cells with TRPV2 siRNA. CBD dose-dependently induced the hCMEC/D3 cell number (EC 50 0.3 ± 0.1 μM), and this effect was fully abolished by TNL or TRPV2 siRNA. A wound healing assay showed that CBD induced cell migration, which was also inhibited by TNL or TRPV2 siRNA. Tubulogenesis of hCMEC/D3 cells in 3D matrigel cultures was significantly increased by 41 and 73% after a 7 or 24 h CBD treatment, respectively, and abolished by TNL. CBD also increased the TEER of hPBMEC monolayers cultured in transwell, and this was blocked by TNL. Our results show that CBD, at extracellular concentrations close to those observed in plasma of patients treated by CBD, induces proliferation, migration, tubulogenesis, and TEER increase in human brain endothelial cells, suggesting CBD might be a potent target for modulating the human BBB.

The modulation of histamine neuron activity by various non-competitive NMDA-receptor antagonists was evaluated by changes in tele-methylhistamine (t-MeHA) levels and histidine decarboxylase (hdc) mRNA expression induced in rodent brain. The NMDA open-channel blockers phencyclidine (PCP) and MK-801 enhanced t-MeHA levels in mouse brain by 50-60%. Ifenprodil, which interacts with polyamine sites of NR2B-containing NMDA receptors, had no effect. PCP also increased hdc mRNA expression in the rat tuberomammillary nucleus. The enhancement of t-MeHA levels elicited by MK-801 (ED50 of approximately 0.1 mg/kg) was observed in the hypothalamus, cerebral cortex, striatum and hippocampus. Control t-MeHA levels and the t-MeHA response to MK-801 were not different in male and female mice. Double immunostaining for HDC and NMDA receptor subunits showed that histamine neurons of the rat tuberomammillary nucleus express NMDA receptor subunit 1 (NR1) with NMDA receptor subunit 2A (NR2A) and NMDA receptor 2B subunit (NR2B). In addition, immunoreactivity for the neuronal glutamate transporter EAAC1 was observed near most histaminergic perikarya. Hence, these findings support the existence of histamine/glutamate functional interactions in the brain. The increase in histamine neuron activity induced by NMDA receptor antagonists further suggests a role of histamine neurons in psychotic disorders. In addition, the decrease in MK-801-induced hyperlocomotion observed in mice after administration of ciproxifan further strengthens the potential interest of H3-receptor antagonist/inverse agonists for the symptomatic treatment of schizophrenia.

The existence of mouse H3-receptor isoforms was investigated by PCR analysis and cDNA cloning. Splicing mechanisms previously reported in various species are conserved in the mouse. The retention/deletion of a fragment in the third intracellular loop of the mouse receptor leads to the existence of three isoforms designated mH(3(445)), mH(3(413)) and mH(3(397)) according to the length of their deduced amino acid sequence. PCR analysis showed that mouse H3-receptor isoforms display different expression patterns in the brain. Following expression in Cos-1 cells, [125I]iodoproxyfan binding indicated similar pharmacological profiles of the mH(3(445)), mH(3(413)) and mH(3(397)) isoforms. The pharmacological profile of the mouse H3 receptor is more similar to the rat receptor than to the human receptor, although some differences were also observed between the mouse and rat receptors. For example, the potency of thioperamide and ciproxifan is slightly higher at the mouse receptor than at the rat receptor but 40-100-fold higher than at the human receptor. In situ hybridization histochemistry showed that the distribution of H3-receptor mRNAs in the mouse brain is rather similar to that previously reported in the rat brain. However, the autoradiographic and cellular expression patterns observed in several brain areas such as the thalamus or hippocampus reveal important differences between the two species.

We cloned the full length guinea pig H3 receptor cDNA using RT-PCR amplification with primers from the human receptor and templates from brain areas. Evidence was obtained for two isoforms, designated H3L and H3S, differing by a 30 amino acid stretch within the third cytosolic loop, presumably generated by alternative splicing. In situ hybridization using a selective cRNA probe showed the gene transcripts to be highly expressed in discrete neuronal populations, e.g. pyramidal cells in the cerebral cortex or cerebellar Purkinje cells, in some instances already known to express other histamine receptor subtypes.