KCC2 Regulates Dendritic Spine Formation in a Brain-Region Specific and BDNF Dependent Manner

Abstract

KCC2 is the major chloride extruder in neurons. The spatiotemporal regulation of KCC2 expression orchestrates the developmental shift towards inhibitory GABAergic drive and the formation of glutamatergic synapses. Whether KCC2’s role in synapse formation is similar in different brain regions is unknown. First, we found that KCC2 subcellular localization, but not overall KCC2 expression levels, differed between cortex and hippocampus during the first postnatal week. We performed site-specific in utero electroporation of KCC2 cDNA to target either hippocampal CA1 or somatosensory cortical pyramidal neurons. We found that a premature expression of KCC2 significantly decreased spine density in CA1 neurons, while it had the opposite effect in cortical neurons. These effects were cell autonomous, because single-cell biolistic overexpression of KCC2 in hippocampal and cortical organotypic cultures also induced a reduction and an increase of dendritic spine density, respectively. In addition, we found that the effects of its premature expression on spine density were dependent on BDNF levels. Finally, we showed that the effects of KCC2 on dendritic spine were dependent on its chloride transporter function in the hippocampus, contrary to what was observed in cortex. Altogether, these results demonstrate that KCC2 regulation of dendritic spine development, and its underlying mechanisms, are brain-region specific.

KCC2 is required for the survival of mature neurons but not for their development

“…This was demonstrated by immunoblotting with N-and Cterminal antibodies and suggests that either the truncated form of KCC2 protein is unstable and does not accumulate, or that the altered gene sequence results in premature transcriptional or translational termination. This is contrary to previous work (9,10), and likely represents the differences associated with endogenous versus overexpression systems. We were not able to completely ablate KCC2 expression in vitro or in vivo under these experimental conditions.…”

“…A recent study demonstrated that the genetic removal of KCC2 during neuronal migration induces the apoptosis of embryonic neocortical projection neurons (23). Yet, the functional consequences of KCC2 removal during postnatal neuronal development have not been investigated and are of great interest as a number of studies have suggested that KCC2 plays a transport independent role in determining spine morphology (9,10). These studies used overexpression of a KCC2 construct devoid of its cytoplasmic tail (residues Q911-Q1096) or a DNA construct modified with a GFP reporter which may act to stabilize this truncated form of KCC2 (9, 10).…”

Delayed maturation of GABAergic signaling in the Scn1a and Scn1b mouse models of Dravet Syndrome

“…5, panels I–L). Similar to previously published results 25 , at both P10 (Fig. 5I, arrow) and P17 (Fig.…”

Pannexin 1 Regulates Network Ensembles and Dendritic Spine Development in Cortical Neurons

“…The mechanisms governing spine formation and plasticity are poorly understood (for review, see Yoshihara et al, 2009; Murakoshi and Yasuda, 2012), and are developmental age- and brain region-specific, making it difficult to directly compare these previous studies with our own. For example the major chloride extruder in neurons, KCC2, differentially regulates brain-derived neurotrophic factor (BDNF)-dependent dendritic spine development in CA1 and somatosensory neurons during the first postnatal week (Awad et al, 2018). This study suggests molecular mechanisms of dendritic spine formation in different brain regions might not be completely generalizable.…”