Stress-associated purinergic receptors code for fatal suicidality in the hippocampal-hypothalamic-prefrontal circuit

Imbalanced purine metabolism is a key neurological basis for suicide and mood disorders (MD), wherein purinergic receptors in stress-sensitive cerebral regions are thought to be differentially activated. A hippocampal network that links the hypothalamus and prefrontal cortex implements an affective sensation of stress. We discovered that the hippocampus encoded fatal suicidal ideations in the dentate gyrus (DG) by a considerable amount of the granule cell nuclei with P2X purinoceptor 7 (P2RX7) expression, irrespective of the underlying MD. Compared to controls, patients with MD showed microglial dyshomeostasis throughout the hippocampal formation. Strikingly, P2Y purinoceptor 12 (P2RY12)-expressing microglia with segmented processes were remarkably present in the superficial layers of the medial entorhinal cortex (mEnt) in individuals with fatal suicidality. In the hypothalamic stress-sensitive nuclei, P2RY12+ microglia were more expressed in the supraoptic nucleus in MD and even higher when fatal suicidality was present. In the prefrontal cortex, P2RX7 transcripts sharply dropped in suicidal individuals, possibly removing the prefrontal inhibition of the hippocampus and hypothalamus. Confounder analysis showed that the suicide-specific molecular features faded when the postmortem delay was prolonged. Our findings imply that fatal suicidality presents with unique neuropathological alterations. The DG and mEnt are two crucial areas for deciphering the suicidal consequences. By including brain samples from legal euthanasia donors, suicide-specific biosignatures can be maximally retained. Decoding the bioactive framework through key genes, brain regions and neurological processes involved in suicide neuropathology may provide novel therapeutic strategies for suicidal individuals who are beyond the reach of mental health care.