Conditional knockout of Shank3 in the ventral CA1 by quantitative in vivo genome-editing impairs social memory in mice.

Individuals with autism spectrum disorder (ASD) have a higher prevalence of social memory impairment. A series of our previous studies revealed that hippocampal ventral CA1 (vCA1) neurons possess social memory engram and that the neurophysiological representation of social memory in the vCA1 neurons is disrupted in ASD-associated Shank3 knockout mice. However, whether the dysfunction of Shank3 in vCA1 causes the social memory impairment observed in ASD remains unclear. In this study, we found that vCA1-specific Shank3 conditional knockout (cKO) by the adeno-associated virus (AAV)- or specialized extracellular vesicle (EV)- mediated in vivo gene editing was sufficient to recapitulate the social memory impairment in male mice. Furthermore, the utilization of EV-mediated Shank3-cKO allowed us to quantitatively examine the role of Shank3 in social memory. Our results suggested that there is a certain threshold for the proportion of Shank3-cKO neurons required for social memory disruption. Thus, our study provides insight into the population coding of social memory in vCA1, as well as the pathological mechanisms underlying social memory impairment in ASD.

AMP-activated protein kinase mediates activity-dependent axon branching by recruiting mitochondria to axon.

During development, axons are guided to their target areas and provide local branching. Spatiotemporal regulation of axon branching is crucial for the establishment of functional connections between appropriate pre- and postsynaptic neurons. Common understanding has been that neuronal activity contributes to the proper axon branching; however, intracellular mechanisms that underlie activity-dependent axon branching remain elusive. Here, we show, using primary cultures of the dentate granule cells, that neuronal depolarization-induced rebalance of mitochondrial motility between anterograde versus retrograde transport underlies the proper formation of axonal branches. We found that the depolarization-induced branch formation was blocked by the uncoupler p-trifluoromethoxyphenylhydrazone, which suggests that mitochondria-derived ATP mediates the observed phenomena. Real-time analysis of mitochondrial movement defined the molecular mechanisms by showing that the pharmacological activation of AMP-activated protein kinase (AMPK) after depolarization increased anterograde transport of mitochondria into axons. Simultaneous imaging of axonal morphology and mitochondrial distribution revealed that mitochondrial localization preceded the emergence of axonal branches. Moreover, the higher probability of mitochondrial localization was correlated with the longer lifetime of axon branches. We qualitatively confirmed that neuronal ATP levels decreased immediately after depolarization and found that the phosphorylated form of AMPK was increased. Thus, this study identifies a novel role for AMPK in the transport of axonal mitochondria that underlie the neuronal activity-dependent formation of axon branches.

GABAergic excitation after febrile seizures induces ectopic granule cells and adult epilepsy.

Temporal lobe epilepsy (TLE) is accompanied by an abnormal location of granule cells in the dentate gyrus. Using a rat model of complex febrile seizures, which are thought to be a precipitating insult of TLE later in life, we report that aberrant migration of neonatal-generated granule cells results in granule cell ectopia that persists into adulthood. Febrile seizures induced an upregulation of GABA(A) receptors (GABA(A)-Rs) in neonatally generated granule cells, and hyperactivation of excitatory GABA(A)-Rs caused a reversal in the direction of granule cell migration. This abnormal migration was prevented by RNAi-mediated knockdown of the Na(+)K(+)2Cl(-) co-transporter (NKCC1), which regulates the excitatory action of GABA. NKCC1 inhibition with bumetanide after febrile seizures rescued the granule cell ectopia, susceptibility to limbic seizures and development of epilepsy. Thus, this work identifies a previously unknown pathogenic role of excitatory GABA(A)-R signaling and highlights NKCC1 as a potential therapeutic target for preventing granule cell ectopia and the development of epilepsy after febrile seizures.