Disturbed engram network caused by NPTX downregulation underlies aging-related contextual fear memory deficits.

Engram cells storing episodic memories are allocated to separate neuronal ensembles. However, how these ensembles maintain their stability to drive precise memory expression, and whether their destabilization contributes to aging-related memory deficits, remain elusive. Here, we show that during contextual fear memory consolidation, neuronal pentraxin 1 (NPTX1) in Fos transcription-dependent ensemble (F-RAM) of the dentate gyrus (DG) promotes memory expression in the fear context. NPTX1 facilitates K7.2 channel-mediated inhibition of engram cell hyperexcitability, thereby restricting the response of these cells to excitatory inputs from medial entorhinal cortex. Meanwhile, NPTX2 enhances the perisomatic inhibition of Npas4 transcription-dependent ensemble (N-RAM) by parvalbumin (PV) interneurons, thereby preventing fear memory overgeneralization. Pharmacological activation of K7.2 channels or chemogenetic activation of PV interneurons repaired memory deficits caused by engram-specific NPTX depletion. Contextual fear memory precision and NPTX expression in DG engram cells were decreased in aged mice. Overexpressing NPTX1 in F-RAM ensemble or the AMPAR-binding domain of NPTX2 in N-RAM ensemble rescued contextual fear memory deficits. These findings elucidate that the coordination of NPTX1 and NPTX2 prevents engram ensembles from becoming hyperactive and provide a causal link between engram network destabilization and aging-related contextual fear memory deficits.