Molecular Psychiatry (2020) 25:3380–3398 https://doi.org/10.1038/s41380-019-0483-4 ARTICLE Early restoration of parvalbumin interneuron activity prevents memory loss and network hyperexcitability in a mouse model of Alzheimer’s disease 1 2 3 4 4 2 Sara Hijazi ● Tim S. Heistek ● Philip Scheltens ● Ulf Neumann ● Derya R. Shimshek ● Huibert D. Mansvelder ● 1 1 August B. Smit ● Ronald E. van Kesteren Received: 6 June 2018 / Revised: 9 May 2019 / Accepted: 20 June 2019 / Published online: 20 August 2019 © The Author(s) 2019. This article is published with open access Abstract Neuronal network dysfunction is increasingly recognized as an early symptom in Alzheimer’s disease (AD) and may provide new entry points for diagnosis and intervention. Here, we show that amyloid-beta-induced hyperexcitability of hippocampal inhibitory parvalbumin (PV) interneurons importantly contributes to neuronal network dysfunction and memory impairment in APP/PS1 mice, a mouse model of increased amyloidosis. We demonstrate that hippocampal PV interneurons become hyperexcitable at ~16 weeks of age, when no changes are observed yet in the intrinsic properties of pyramidal cells. This 1234567890();,: 1234567890();,: hyperexcitable state of PV interneurons coincides with increased inhibitory transmission onto hippocampal pyramidal neurons and deficits in spatial learning and memory. We show that treatment aimed at preventing PV interneurons from becoming hyperexcitable is sufficient to restore PV interneuron properties to wild-type levels, reduce inhibitory input onto pyramidal cells, and rescue memory deficits in APP/PS1 mice. Importantly, we demonstrate that early intervention aimed at restoring PV interneuron activity has long-term beneficial effects on memory and hippocampal network activity, and reduces amyloid plaque deposition, a hallmark of AD pathology. Taken together, these findings suggest that early treatment of PV interneuron hyperactivity might be clinically relevant in preventing memory decline and delaying AD progression. Introduction Alzheimer’s disease (AD) accounts for the most common form of dementia with a population prevalence that increases rapidly. Recent clinical studies have described Supplementary information The online version of this article (https:// early prodromal AD stages that precede dementia, creating doi.org/10.1038/s41380-019-0483-4) contains supplementary material, which is available to authorized users. new opportunities for the development of novel treatment, and prevention strategies [1, 2]. Interestingly, early pro- * Ronald E. van Kesteren dromal symptoms include alterations in neuronal network [email protected] activity, as observed both in AD patients and in animal 1 Department of Molecular and Cellular Neurobiology, Center for models of AD, and these alterations may be responsible for Neurogenomics and Cognitive Research, Amsterdam early cognitive impairment [3–7]. As such, neuronal net- Neuroscience, VU University Amsterdam, Amsterdam, the work dysfunction might be a risk factor for AD, a biomarker Netherlands for identifying early stage AD or people at risk of devel- 2 Department of Integrative Neurophysiology, Center for oping AD, and a novel therapeutic entry point for effective Neurogenomics and Cognitive Research, Amsterdam treatment of AD [8–11]. Neuroscience, VU University Amsterdam, Amsterdam, the Netherlands Neuronal network alterations in AD have been identi- fied as impairments in both excitatory and inhibitory 3 Alzheimer Center and Department of Neurology, Amsterdam Neuroscience, VU University Medical Center, Amsterdam, the synaptic transmission [4, 12]. Typically, studies have Netherlands focused on aberrant increases in excitatory neuronal 4 Neuroscience Research, Novartis Institutes for BioMedical activity, exploring the hypothesis that enhanced gluta- Research, Basel, Switzerland matergic transmission is driving AD pathogenesis Early restoration of parvalbumin interneuron activity prevents memory loss and network. 3381 [12–14]. Indeed, epileptiform discharges and seizures are (Supplementary Fig. 1a, b). Also, aggregation of insoluble highly prevalent in AD patients [11, 15–17]andthe amyloid plaques in the hippocampus was detected at incidence of unprovoked seizures is more than fivefold 24 weeks and not yet at 16 weeks of age, similar as larger in late-onset sporadic AD patients compared with observed in APP/PS1 mice (Supplementary Fig. 1a, c, d). age-matched controls [11, 17, 18]. Likewise, animal To confirm the specific targeting of PV interneurons in this models of AD, in particular models with increased model, the hippocampal CA1 region was bilaterally injected amyloid-beta (Aβ) deposition, suffer from increased epi- with AAV5-expressing mCherry (hSyn-DIO-mCherry) leptic susceptibility and seizure incidence [12, 19, 20]. (Supplementary Fig. 2a–c). More than 84% of PV- Therefore, reducing glutamatergic transmission and con- expressing interneurons in the CA1 region showed trolling epileptic activity have been extensively tested as mCherry expression (Supplementary Fig. 2d) and all potential treatment strategies [15, 21–23]. While altera- mCherry-expressing cells recorded showed the typical fast- tions in inhibitory activity were also observed, they were spiking properties of PV interneurons (Supplementary initially suggested to reflect compensatory changes in Fig. 2e–h, Supplementary Table 1), confirming correct tar- response to glutamatergic dysfunction [12]. Recently, geting of the desired cell type. however, inhibitory network dysfunction has been We then expressed mCherry in hippocampal PV neurons emphasized as a potential causal event in early AD in APP/PS1-PV-Cre mice and PV-Cre control mice and pathogenesis [24–30]. subsequently performed whole-cell patch-clamp recordings. Parvalbumin (PV) neurons are abundant GABAergic We observed an early increase in the excitability of PV inhibitory interneurons that deliver feedback and feedfor- interneurons at 15–17 weeks of age compared with WT-PV- ward inhibition to excitatory pyramidal neurons in many Cre controls (Supplementary Table 2). In particular, PV brain areas, including the hippocampus [31, 32]. As such, interneurons of APP/PS1-PV-Cre mice had a significantly they play crucial roles in determining oscillatory network depolarized resting membrane potential (Fig. 1a) with activity and regulating plasticity following behavioral unaltered input resistance (Fig. 1b), a significantly larger learning [33–36]. PV interneuron dysfunction has pre- increase in action potential firing frequency with increasing viously been associated with AD [10, 27, 28, 37, 38]; current injections (Fig. 1c, d), and a significantly smaller however, it is still not clear how PV interneuron function is action potential half-width (Supplementary Table 2), indi- altered in early AD, or how these alterations contribute to cating a hyperexcitable PV interneuron phenotype. No AD progression. We here demonstrate that Aβ-induced changes in the excitability of pyramidal neurons was hyperexcitability of hippocampal PV interneurons plays a observed at this age (Fig. 1e–h, Supplementary Table 2), and causal role in the early cognitive deficits observed in APP/ neither PV interneurons nor pyramidal cells were affected at PS1 mice. We show that restoring PV interneuron function 7–9 weeks of age (Supplementary Fig. 3, Supplementary using chemogenetics rescues spatial memory impairments Table 3). We also quantified PV immunofluorescence levels in APP/PS1 mice. Our data furthermore indicate that early in hippocampal sections of 15–17-week-old APP/PS1 and reinstatement of PV interneuron activity has long-term APP/PS1-PV-Cre mice. PV immunofluorescence has been beneficial effects on hippocampal memory and network demonstrated to correlate well with GABA synthesis and function, reduces soluble Aβ levels, and delays the pro- reflect hippocampal PV interneuron activity [33]. Anti-PV gression of amyloid plaque pathology. Early hyperexcitable staining in the hippocampal CA1 area was overall sig- PV interneurons thus represent an interesting target for early nificantly increased in both mouse lines compared with their AD detection and treatment. respective WT controls, while no changes were detected in total number of PV neurons (Supplementary Fig. 4), sug- gesting that in 15–17-week-old APP/PS1 mice hippocampal Results PV interneurons are indeed also more active in vivo. To investigate whether the observed increase in PV APP/PS1 mice show hippocampal PV interneuron interneuron excitability would affect inhibitory transmis- hyperexcitability at 15–17 weeks of age sion in the hippocampus, we recorded spontaneous inhi- bitory postsynaptic currents (sIPSCs) from hippocampal APP/PS1 transgenic mice were crossed with PV-Cre pyramidal neurons. Consistent with increased PV inter- transgenic mice, generating an APP/PS1-PV-Cre mouse neuron activity, we observed a significant increase in the model that allows for the specific detection and genetic frequency of sIPSCs received by CA1 pyramidal neurons manipulation of PV interneurons in a progressive amyloi- of 15–17-week-old APP/PS1 mice compared with WT dosis background. Soluble Aβ levels in the hippocampus of controls (Fig. 1i, j). sIPSC amplitudes were not affected APP/PS1-PV-Cre mice at 16 weeks of age were found (Fig. 1k), suggesting an increase in either the number of similar to those measured in APP/PS1 mice of the same age inhibitory synaptic inputs or the firing frequency of 3382 S. Hijazi et al. a b c d 140 PV- APP/PS1- PV-Cre Cre PV-Cre n.s. 120 APP/PS1-PV-Cre -30 300 ) Ω 100 -40 200 80 *** PV-Cre -50 20 mV 0.2 s 60 -60 frequency (Hz) 100 P A 40 -70 input resistance (M 20 -80 0 ** PV- APP/PS1- 0 resting membrane potential (mV) Cre PV-Cre APP/PS1- 0 50 100 150 200 250 PV-Cre current injected (pA) e f g h 40 PV-Cre PV- APP/PS1- Cre PV-Cre APP/PS1-PV-Cre -30 n.s. 300 30 ) -40 Ω 200 PV-Cre -50 20 mV 20 0.2 s -60 frequency (Hz) P A 100 10 -70 input resistance (M -80 0 PV- APP/PS1- 0 n.s. 0 50 100 150 200 250 resting membrane potential (mV) Cre PV-Cre APP/PS1- PV-Cre current injected (pA) n.s. i j 1.5 k * 80 WT 1.0 60 40 0.5 APP/PS1 20 40 pA sIPSC frequency (HZ) sIPSC amplitude (pA) 200 ms 0.0 0 WT APP/PS1 WT APP/PS1 Fig.