TABLE 1.
Microglial P2Y12 receptors in healthy and diseased brain.
| Specie/age/brain region | Experimental techniques | Main findings | References |
|---|---|---|---|
| Animal models | |||
| Mice/45–180 days/hippocampus Rat/2 weeks | In vivo two-photon imaging; immunofluorescence; rat primary microglia live imaging; western blot | Activation of P2Y12 receptors triggers extension of microglial processes | Bernier et al. (2019) |
| Rats/neonatal/forebrain | Real time RT-PCR; calcium imaging; western blot; immunocytochemistry | Stimulation of P2Y12 receptors instigated processes extension towards the source of ADP | Tozaki-Saitoh et al. (2017) |
| Mice/P1/cortex | Immunocytochemistry; IB4 staining; quantitative PCR; western blot | P2Y12 receptors-mediated Ca2+ signalling regulate the migration and phagocytic ability of microglia during post-natal brain development | Sunkaria et al. (2016) |
| Mice/P21–P23/hippocampus | Primary microglia culture; in vitro phagocytosis assay; calcium imaging; FACS sorting; gene expression arrays; real-time qPCR | Genetic deletion of P2Y12 receptors affected microglial phagocytosis and neurogenesis suggesting active role of microglia in regulation of this process | Diaz-Aparicio et al. (2020) |
| Mice/ventral hippocampus CA1 | Constitutive and induced microglia-specific knockout of P2Y12 receptors; behaviour tests (open field, elevated plus maze, light/dark box, fear conditioning); in vivo two-photon imaging; electrophysiology; immunocytochemistry | P2Y12 receptors contribute to microglia-dependent suppression of neuronal excitability as well as to innate fear behaviours | Peng et al. (2019) |
| Mice/6–8 weeks/somatosensory cortex | Photothrombotic stroke; two-photon imaging; immunocytochemistry and confocal imaging | Expression of P2Y12 receptors declined significantly 14 days after stroke; which correlated with the development of secondary neurodegeneration and neuronal damage | Kluge et al. (2019) |
| Rats/neonatal/cerebral cortex | Facial nerve axotomy; primary cell culture; northern blot; in situ hybridisation; immunocytochemistry | P2Y12 receptors are expressed selectively in microglia. Number of P2Y12 receptor expressing cells increased following facial nerve axotomy | Sasaki et al. (2003) |
| Mice/12–14 weeks/cortex | Electrophysiology; immunofluorescence; STORM super-resolution microscopy | Spreading depolarisation increased the density of microglial P2Y12 receptors and increased association of microglial processes to neurones in P2Y12-dependent manner | Varga et al. (2020) |
| Mice/5, 12 weeks/hippocampus dentate gyrus | Sleep deprivation; behavioural tests (open field test; novel object recognition test; elevated plus maze test); histological examinations; RT-PCR; immunocytochemistry; western blot | Sleep deprivation resulted in a decrease in microglial P2Y12 receptors | Tuan and Lee (2019) |
| Rat/prelimbic cortex, central amygdala, perifornical lateral hypothalamic area, and dorsal raphe nucleus | Immunocytochemistry; densitometry and cell counts; histology; qRT-PCR | Sleep deprivation increased Iba1 staining, but did not affect immunoreactivity of P2Y12 receptors and pro-inflammatory cytokines | Hall et al. (2020) |
| Humans, tissues and cells | |||
| Humans/23–92 years/post-mortem tissue of MDD patients (5) and mentally healthy controls (5)/frontal lobe, temporal lobe, thalamus, subventricular zone | Freshly isolated microglial cell suspension; purified with CD11b− assisted multiplexed single-cell mass cytometry. Immunocytochemistry | A subpopulation of microglia from MDD brains have increased expression of P2Y12 receptors, arguably associated with an increase in homeostatic and neuroprotective capacity of microglial cells in the diseased nervous tissue | Bottcher et al. (2020) |
| Humans/recent-onset schizophrenia patients (20) and 20 non-psychiatric controls (20)/myeloid cell | Monocytes induced into microglia-like cells; RNA isolation and sequencing; mass cytometry; phagocytosis assay; immunocytochemistry and microscopy | P2Y12 receptors mRNA was enriched in a sub-population of cells from schizophrenia patients | Ormel et al. (2020) |
| Humans/dermal fibroblast cells | Human induced pluripotent stem cells (iPSCs); immunocytochemistry; scanning electron microscopy; flow cytometry; engraftment assays electrophysiology; PCR | Microglia derived from iPSCs displayed ramified morphology and 100% expression of P2Y12 receptors. Stimulation of these cells with lipopolysaccharide resulted in downregulation of P2Y12 receptors expression | Banerjee et al. (2020) |
| Humans/60–80 years old/occipitalcortex, corpus callosum, choroid plexus | Freshly isolated microglial cell; quantitative RT-PCR; IRF8 + isolation and sorting of nuclei; immunocytochemistry; western blot analysis; flow cytometry | P2Y12 receptor expression is unaltered in normal-appearing tissue from MS patients indicating overall preservation of microglia homeostatic phenotype | van der Poel et al. (2019) |
| Human patients with AD/70–90 years old | Immunocytochemistry, confocal microscopy | The P2Y12 positive microglial cells of heterogeneous morphology populated outer regions of senile plaques | Walker et al. (2020) |
| Human patients with MS/rats (8–11 weeks)/tissue | Experimental autoimmune encephalomyelitis in rats; human microglia isolation; immunocytochemistry; q-PCR; western blot; autoradiography | P2Y12 receptors were associated with an anti-inflammatory phenotype; expression of P2Y12 receptors was decreased in tissues with active MS lesions | Beaino et al. (2017) |
| Humans/newborns (5), children (4), adults (5), elderly individuals (5)/cortex, hippocampus | Immunocytochemistry; microscopy | Expression of P2Y12 receptors in the brain microglia is stable throughout human lifespan. Density of P2Y12 expressing microglia is similarly constant throughout life. CNS pathologies are associated with a decrease in P2Y12 immunoreactivity | Mildner et al. (2017) |
| Human/foetal brain tissue | Human monocyte-derived macrophages culture; immunocytochemistry; quantitative real time PCR; flow cytometry; calcium imaging; cell migration assays; ELISA | P2Y12 is selectively expressed on human microglia and elevated under neuropathological conditions that promote Th2 responses, such as parasitic CNS infection | Moore et al. (2015) |
| Humans/59–78 years old/MCA area mice/12–18 weeks/ | MCAO; histology; cloning; in utero electroporation; in vivo two-photon imaging; calcium imaging; immunocytochemistry; STORM super-resolution imaging; immunoelectrone microscopy; electron tomography | P2Y12 receptors support formation and maintenance of somatic microglia-neurone junctions and mediate microglial neuroprotection in ischaemia | Cserep et al. (2020) |
| Humans/59–78 years old/Mice/8–12 weeks/hypothalamic paraventricular nucleus | In vivo pharmacological treatments and chemogenetics; histology; cloning; in utero electroporation; isolation of microglial cells; quantification of ATP; in vivo two-photon imaging; immunocytochemistry; confocal laser scanning microscopy | Microglial P2Y12 receptors are instrumental in defence against neurotropic viruses | Fekete et al. (2018) |
| Human/30–97 years old/white matter | Post-mortem immunocytochemistry | Activated microglia in the active and slowly expanding lesion sites in the white matter of MS patients demonstrated significant down-regulation of P2Y12 receptors, in the inactive lesions however the P2Y12 positive microglia re-emerged | Zrzavy et al. (2017) |