nArgBP2 regulates excitatory synapse formation by controlling dendritic spine morphology

Abstract

Neural Abelson-related gene-binding protein 2 (nArgBP2) was originally identified as a protein that directly interacts with synapseassociated protein 90/postsynaptic density protein 95-associated protein 3 (SAPAP3), a postsynaptic scaffolding protein critical for the assembly of glutamatergic synapses. Although genetic deletion of nArgBP2 in mice leads to manic/bipolar-like behaviors resembling many aspects of symptoms in patients with bipolar disorder, the actual function of nArgBP2 at the synapse is completely unknown. Here, we found that the knockdown (KD) of nArgBP2 by specific small hairpin RNAs (shRNAs) resulted in a dramatic change in dendritic spine morphology. Reintroducing shRNA-resistant nArgBP2 reversed these defects. In particular, nArgBP2 KD impaired spinesynapse formation such that excitatory synapses terminated mostly at dendritic shafts instead of spine heads in spiny neurons, although inhibitory synapse formation was not affected. nArgBP2 KD further caused a marked increase of actin cytoskeleton dynamics in spines, which was associated with increased Wiskott-Aldrich syndrome protein-family verprolin homologous protein 1 (WAVE1)/p21-activated kinase (PAK) phosphorylation and reduced activity of cofilin. These effects of nArgBP2 KD in spines were rescued by inhibiting PAK or activating cofilin combined with sequestration of WAVE. Together, our results suggest that nArgBP2 functions to regulate spine morphogenesis and subsequent spine-synapse formation at glutamatergic synapses. They also raise the possibility that the aberrant regulation of synaptic actin filaments caused by reduced nArgBP2 expression may contribute to the manifestation of the synaptic dysfunction observed in manic/bipolar disorder. nArgBP2 | dendritic spines | excitatory synapse | actin | bipolar disorder T he postsynaptic enriched adaptor protein neural Abelsonrelated gene-binding protein 2 (nArgBP2), a neural-specific splice variant of the ubiquitous ArgBP2, was originally identified as a binding partner of synapse-associated protein 90/postsynaptic density protein 95-associated protein 3 (SAPAP3) (1). It belongs to a family of adaptor proteins that are involved in the regulation of cell adhesion, actin cytoskeleton organization, and growth factor receptor signaling (2). This protein family is characterized by a sorbin homology (SoHo) domain in the NH 2 -terminal region and three Src homology 3 (SH3) domains in the COOH-terminal region (3). Although the SoHo domain remains poorly characterized, the SH3 domains bind signaling protein kinases, the ubiquitin ligase, and protein involved in the regulation of focal adhesions and adhering junctions (1, 4-6). The NH 2 -terminal region of nArgBP2, which contains the SoHo domain, interacts with spectrin, whereas the COOH-terminal SH3 domains bind dynamin, synaptojanin, Wiskott-Aldrich syndrome protein-family verprolin homologous protein (WAVE) isoforms, and WAVE regulatory proteins (3), all of which participate in the regulation of the actin cytoskeleton. We also found that the down-re...

TSPAN5 Enriched Microdomains Provide a Platform for Dendritic Spine Maturation through Neuroligin-1 Clustering

“…In pyramidal neurons most excitatory synapses form on dendritic spines, but previous work has shown excitatory synapses on dendritic shafts in physiological conditions both in vitro and in vivo (Harris et al, 1992;Trachtenberg et al, 2002). The proportion of shaft synapses varies during neuronal maturation (Harris et al, 1992) and can be affected by genetic manipulation of proteins involved in dendritic spine formation (Aoto et al, 2007;Lee et al, 2016;Niesmann et al, 2011).…”

Peptide regulation of cofilin activity in the CNS: A novel therapeutic approach for treatment of multiple neurological disorders

“…In dendritic spines, the postsynaptic structures on excitatory synapses in the hippocampus and cortex, actin dynamics modulate the insertion of ion channels and the morphological changes associated with long-term potentiation (LTP) and long-term depression (LTD), electrophysiological correlates for memory formation. Morphological and functional alterations in dendritic spines are observed in human subjects and/or genetic mouse models of AD (Calabrese et al, 2006; Rust, 2015; Dorostkar et al, 2015), Down syndrome (Belichenko et al, 2004), Fragile X syndrome (Grossman et al, 2010), schizophrenia and autism (Blundell et al, 2010; Qiao et al, 2014; Foote et al, 2015; Copf, 2016; Liu et al, 2016), sleep deprivation (Havekes et al, 2016), and manic/bipolar disorder (Zhang Q, et al, 2016; Lee et al, 2016). …”

“…Cofilin phosphoregulation is significantly shifted from the norm in rodent models of many neurological disorders, including AD (Zhao et al, 2006; Woo et al, 2015a; Woo et al, 2015b), autism (Duffney et al, 2015; Liu et al, 2016), manic/bipolar disorder (Lee et al, 2016), sleep deprivation (Havekes et al, 2016), neonatal isolation (Tada et al, 2016), and neuropathic pain (Qiu et al, 2016) (Table 1). Dendritic spine shrinkage occurs as a result of cofilin hyperactivation (dephosphorylation) and has been observed in hippocampal neurons during establishment of long-term depression (Figure 2; Zhou et al, 2004), and in neurons of the hippocampus but not the prefrontal cortex of sleep deprived mice (Havekes et al, 2016).…”

“…Deletion of neural Abelson-related gene-binding protein 2 (nArgBP2) in mice results in impaired spine development and memory along with manic/bipolar behaviors (Zhang Q, et al, 2016; Lee et al, 2016). nArgBP2 knock-down mice develop excitatory glutamatergic synapses along dendritic shafts but not in spine heads, suggesting altered synaptic receptor trafficking.…”

“…WAVE1 enhances actin filament branching by Arp2/3 complex (Sloane and Vartanian, 2007), suggesting that excessive branched filament formation may be causing the defect. Normal spine function can be rescued in these mice by inhibiting Pak, or by expressing an active (non-phosphorylatable) cofilin (S3A) while sequestering WAVE1 by targeting it to mitochondria (Lee et al, 2016). …”