CT1812 Attenuates Surgery-Induced Cognitive Impairment and Modulates TMEM97- and PGRMC1-Associated Hippocampal Stress Responses in Aged Mice.

Postoperative neurocognitive disorders (PND) are common complications in older surgical patients, but druggable mechanisms linking surgical trauma to hippocampal synaptic and cognitive vulnerability remain poorly defined. The σ-2 receptor (σ-2R), encoded by transmembrane protein 97 (TMEM97), and progesterone receptor membrane component 1 (PGRMC1) intersect membrane lipid biology and synaptic stress signaling; CT1812, a pharmacological σ-2R complex modulator, has shown target engagement in early Alzheimer's disease trials, but whether this pathway participates in postoperative hippocampal injury is unknown. This study examined whether surgery-induced hippocampal stress in aged mice is associated with TMEM97 and PGRMC1 signaling and whether early CT1812 treatment can attenuate this response. Young adult (2-3 months) and aged (18-20 months) male C57BL/6J mice underwent sham operation or laparotomy; aged mice were further treated with vehicle or CT1812 (3 mg/kg, intravenous injection, days 0-3). Hippocampal molecular changes were assessed by western blotting and immunofluorescence on day 3, and behavior was evaluated by open field test (OFT) and Morris water maze (MWM) on days 6-10. Laparotomy increased hippocampal TMEM97 and PGRMC1 expression and induced anxiety-like and spatial-memory deficits preferentially in aged mice, without evidence that locomotor impairment explained the behavioral phenotype. TMEM97 and PGRMC1 were detected in neuronal nuclei (NeuN)-positive neurons, ionized calcium-binding adapter molecule 1 (Iba-1)-positive microglia, and glial fibrillary acidic protein (GFAP)-positive astrocytes in hippocampal cornu ammonis 1 (CA1), supporting multicellular pathway involvement. In aged surgical mice, CT1812 significantly reduced upregulation of TMEM97 and PGRMC1, improved OFT center-zone occupancy and MWM performance, and restored the synaptic markers postsynaptic density protein 95 (PSD95) and synaptophysin. CT1812 also normalized lipid-handling proteins, including apolipoprotein E (ApoE), ATP-binding cassette transporter A1 (ABCA1), cholesterol 24-hydroxylase (CYP46A1), and low-density lipoprotein receptor (LDLR), and reduced perilipin 2 (PLIN2) accumulation in neurons and microglia. In parallel, CT1812 attenuated a selective endoplasmic reticulum (ER) stress response involving binding immunoglobulin protein (BIP) and protein kinase R-like endoplasmic reticulum kinase (PERK)-eukaryotic initiation factor 2α (eIF2α) signaling in hippocampal neurons, and suppressed microglial nuclear factor κB (NF-κB)/NOD-like receptor family pyrin domain containing 3 (NLRP3) inflammatory activation, whereas C/EBP homologous protein (CHOP) was not significantly changed. These findings support a model in which postoperative injury in the aged hippocampus engages a lipid-proteostatic and inflammatory stress program associated with TMEM97 and PGRMC1, and suggest that CT1812 attenuates cognitive vulnerability by restraining this coupled response.