Dynamin-related protein 1 (DRP1) is a key molecule to regulate mitochondrial fission. DRP1 activity is modulated by phosphorylation and S-nitrosylation on serine and cysteine residues, respectively. However, it is still unexplored whether S-nitrosylation of DRP1 affects its phosphorylation. In the present study, we found that Nω-nitro-l-arginine methyl ester hydrochloride (l-NAME, a NOS inhibitor) abolished S-nitrosylated (SNO-DRP1) and DRP1-serine (S) 616 phosphorylation levels in CA1 neurons under physiological condition. l-NAME led to mitochondrial elongation. In spite of the sustained NO synthesis, status epilepticus (a prolonged seizure activity, SE) diminished SNO-DRP1 and DRP1-S616 levels in CA1 neurons, accompanied by the reduced protein disulfide isomerase (PDI) expression and mitochondrial elongation. SE did not influence thioredoxin 1 (Trx1, a denitrosylating enzyme) activity, which was unaffected by l-NAME under physiological and post-SE condition. PDI knockdown decreased SNO-DRP1 and DRP1-S616 levels concomitant with mitochondrial elongation in CA1 neurons without altered NO synthesis under physiological condition. These findings indicate that PDI may be a NO donor of DRP1 to regulate DRP1-S616 phosphorylation, independent of Trx1 activity. Therefore, we suggest that PDI-mediated S-nitrosylation of DRP1 may be one of the major regulatory modifications for mitochondrial dynamics.

Both α-amino-3-hydroxy-5-methylisoxazole-4-propionic acid receptor (AMPAR) and N-methyl-D-aspartate receptor (NMDAR) have been reported as targets for treatment of epilepsy. To investigate the roles and interactions of AMPAR and NMDAR in ictogenesis of epileptic hippocampus, we analyzed AMPAR antagonists (perampanel and GYKI 52466)-mediated phosphatase and tensin homolog deleted on chromosome 10 (PTEN) regulation and glutamate ionotropic receptor NMDA type subunit 2B (GluN2B) tyrosine (Y) 1472 phosphorylation in epilepsy rats. Both perampanel and GYKI 52466 increased PTEN expression and its activity (reduced phosphorylation), concomitant with decreased activities (phosphorylations) of Src family-casein kinase 2 (CK2) signaling pathway. Compatible with these, they also restored the upregulated GluN2B Y1472 and Ca2+/cAMP response element-binding protein (CREB) serine (S) 133 phosphorylations and surface expression of glutamate ionotropic receptor AMPA type subunit 1 (GRIA1) to basal level in the epileptic hippocampus. These effects of perampanel and GYKI 52466 are observed in responders (whose seizure activities are responsive to AMPAR antagonists), but not non-responders (whose seizure activities were uncontrolled by AMPAR antagonists). Therefore, our findings suggest that Src/CK2/PTEN-mediated GluN2B Y1472 and CREB S133 regulations may be one of the responsible signaling pathways for the generation of refractory seizures in non-responders to AMPAR antagonists.

Neuronal precursor cell expressed developmentally downregulated 4-2 (NEDD4-2) is an E3 ubiquitin ligase to regulate ion transport by controlling cellular trafficking/endocytosis and lysosomal degradation of ion channels and transporters. Thus, NEDD4-2 is relevant to neuronal excitability and epileptic encephalopathies in human patients. However, the regulatory molecules for NEDD4-2 dephosphorylation have been still elusive. Here, we demonstrate that pyridoxal-5′-phosphate phosphatase/chronophin (PLPP/CIN) specifically dephosphorylated NEDD4-2 serine (S) 448 site. PLPP/CIN deletion inhibited NEDD4-2 ubiquitination, and diminished the responsiveness of α‐amino‐3‐hydroxy‐5‐methyl‐4‐isoxazolepropionic acid receptor (AMPAR) by facilitating NEDD4-2-mediated ubiquitination of GluA1 subunit under physiological condition. PLPP/CIN overexpression reversed these effects. These PLPP/CIN-mediated processes were required for the increased seizure severity and its progression in response to kainic acid (KA). Therefore, we suggest the novel function of PLPP/CIN as a NEDD4-2 phosphatase, which may be a potential therapeutic target for NEDD4-2-associated diseases as well as various neurological and psychiatric disorders, including epilepsy.

Dendritic spines are dynamic structures whose efficacies and morphologies are modulated by activity-dependent synaptic plasticity. The actin cytoskeleton plays an important role in stabilization and structural modification of spines. However, the regulatory mechanism by which it alters the plasticity threshold remains elusive. Here, we demonstrate the role of pyridoxal-5′-phosphate phosphatase/chronophin (PLPP/CIN), one of the cofilin-mediated F-actin regulators, in modulating synaptic plasticity in vivo. PLPP/CIN transgenic (Tg) mice had immature spines with small heads, while PLPP/CIN knockout (KO) mice had gigantic spines. Furthermore, PLPP/CIN Tg mice exhibited enhanced synaptic plasticity, but KO mice showed abnormal synaptic plasticity. The PLPP/CIN-induced alterations in synaptic plasticity were consistent with the acquisition and the recall capacity of spatial learning. PLPP/CIN also enhanced N-methyl-D-aspartate receptor (GluN) functionality by regulating the coupling of GluN2A with interacting proteins, particularly postsynaptic density-95 (PSD95). Therefore, these results suggest that PLPP/CIN may be an important factor for regulating the plasticity threshold.

Calsenilin (CSEN) binds to Kv4.2 (an A-type K+ channel) as well as N-methyl-D-aspartate receptor (NMDAR), and modulates their activities. However, the regulatory mechanisms for CSEN-binding to Kv4.2 or NMDAR remain elusive. Here, we demonstrate the novel role of pyridoxal-5′-phosphate phosphatase/chronophin (PLPP/CIN), one of the cofilin-mediated F-actin regulators, in the CSEN binding to Kv4.2 or GluN1 (an NMDAR subunit). PLPP/CIN dephosphorylated CSEN in competition with casein kinase 1, independent of cofilin dephosphorylation. As compared to wild-type mice, PLPP/CIN transgenic (PLPP/CINTg) mice showed the enhancement of Kv4.2–CSEN binding, but the reduction in CSEN–GluN1 binding. In addition, PLPP/CINTg mice exhibited the higher intensity (severity), duration and progression of seizures, but the longer latency of seizure on-set in response to kainic acid. PLPP/CIN knockout mice reversed these phenomena. Therefore, we suggest that PLPP/CIN-mediated CSEN dephosphorylation may play an important role in the functional coupling of NMDAR and Kv4.2, which regulates the neuronal excitability.