Jeongjin Kim

GIT1 is associated with ADHD in humans and ADHD-like behaviors in mice

Attention deficit hyperactivity disorder (ADHD) is a psychiatric disorder that affects ∼5% of school-aged children; however, the mechanisms underlying ADHD remain largely unclear. Here we report a previously unidentified association between G protein–coupled receptor kinase–interacting protein-1 (GIT1) and ADHD in humans. An intronic single-nucleotide polymorphism in GIT1, the minor allele of which causes reduced GIT1 expression, shows a strong association with ADHD susceptibility in humans. Git1-deficient mice show ADHD-like phenotypes, with traits including hyperactivity, enhanced electroencephalogram theta rhythms and impaired learning and memory. Hyperactivity in Git1−/− mice is reversed by amphetamine and methylphenidate, psychostimulants commonly used to treat ADHD. In addition, amphetamine normalizes enhanced theta rhythms and impaired memory. GIT1 deficiency in mice leads to decreases in ras-related C3 botulinum toxin substrate-1 (RAC1) signaling and inhibitory presynaptic input; furthermore, it shifts the neuronal excitation-inhibition balance in postsynaptic neurons toward excitation. Our study identifies a previously unknown involvement of GIT1 in human ADHD and shows that GIT1 deficiency in mice causes psychostimulant-responsive ADHD-like phenotypes.

Exosome engineering for efficient intracellular delivery of soluble proteins using optically reversible protein–protein interaction module

Nanoparticle-mediated delivery of functional macromolecules is a promising method for treating a variety of human diseases. Among nanoparticles, cell-derived exosomes have recently been highlighted as a new therapeutic strategy for the in vivo delivery of nucleotides and chemical drugs. Here we describe a new tool for intracellular delivery of target proteins, named ‘exosomes for protein loading via optically reversible protein–protein interactions’ (EXPLORs). By integrating a reversible protein–protein interaction module controlled by blue light with the endogenous process of exosome biogenesis, we are able to successfully load cargo proteins into newly generated exosomes. Treatment with protein-loaded EXPLORs is shown to significantly increase intracellular levels of cargo proteins and their function in recipient cells in vitro and in vivo. These results clearly indicate the potential of EXPLORs as a mechanism for the efficient intracellular transfer of protein-based therapeutics into recipient cells and tissues. Exosomes have been identified as promising vehicles for the in vivodelivery of therapeutic molecules. Here the authors design a system to load protein cargos into exosomes during their biogenesis using optogenetic control of protein-protein interactions between the cargo and an exosome-localized partner.

Alteration by p11 of mGluR5 localization regulates depression-like behaviors

Mood disorders and antidepressant therapy involve alterations of monoaminergic and glutamatergic transmission. The protein S100A10 (p11) was identified as a regulator of serotonin receptors, and it has been implicated in the etiology of depression and in mediating the antidepressant actions of selective serotonin reuptake inhibitors. Here we report that p11 can also regulate depression-like behaviors via regulation of a glutamatergic receptor in mice. p11 directly binds to the cytoplasmic tail of metabotropic glutamate receptor 5 (mGluR5). p11 and mGluR5 mutually facilitate their accumulation at the plasma membrane, and p11 increases cell surface availability of the receptor. Whereas p11 overexpression potentiates mGluR5 agonist-induced calcium responses, overexpression of mGluR5 mutant, which does not interact with p11, diminishes the calcium responses in cultured cells. Knockout of mGluR5 or p11 specifically in glutamatergic neurons in mice causes depression-like behaviors. Conversely, knockout of mGluR5 or p11 in GABAergic neurons causes antidepressant-like behaviors. Inhibition of mGluR5 with an antagonist, 2-methyl-6-(phenylethynyl)pyridine (MPEP), induces antidepressant-like behaviors in a p11-dependent manner. Notably, the antidepressant-like action of MPEP is mediated by parvalbumin-positive GABAergic interneurons, resulting in a decrease of inhibitory neuronal firing with a resultant increase of excitatory neuronal firing. These results identify a molecular and cellular basis by which mGluR5 antagonism achieves its antidepressant-like activity.

Thalamic T-Type Ca2+ Channels Mediate Frontal Lobe Dysfunctions Caused by a Hypoxia-Like Damage in the Prefrontal Cortex

Hypoxic damage to the prefrontal cortex (PFC) has been implicated in the frontal lobe dysfunction found in various neuropsychiatric disorders. The underlying subcortical mechanisms, however, have not been well explored. In this study, we induced a PFC-specific hypoxia-like damage by cobalt-wire implantation to demonstrate that the role of the mediodorsal thalamus (MD) is critical for the development of frontal lobe dysfunction, including frontal lobe-specific seizures and abnormal hyperactivity. Before the onset of these abnormalities, the cross talk between the MD and PFC nuclei at theta frequencies was enhanced. During the theta frequency interactions, burst spikes, known to depend on T-type Ca2+ channels, were increased in MD neurons. In vivo knockout or knockdown of the T-type Ca2+ channel gene (CaV3.1) in the MD substantially reduced the theta frequency MD–PFC cross talk, frontal lobe-specific seizures, and locomotor hyperactivity in this model. These results suggest a two-step model of prefrontal dysfunction in which the response to a hypoxic lesion in the PFC results in abnormal thalamocortical feedback driven by thalamic T-type Ca2+ channels, which, in turn, leads to the onset of neurological and behavioral abnormalities. This study provides valuable insights into preventing the development of neuropsychiatric disorders arising from irreversible PFC damage.

Comparative three-dimensional connectome map of motor cortical projections in the mouse brain

The motor cortex orchestrates simple to complex motor behaviors through its output projections to target areas. The primary (MOp) and secondary (MOs) motor cortices are known to produce specific output projections that are targeted to both similar and different target areas. These projections are further divided into layer 5 and 6 neuronal outputs, thereby producing four cortical outputs that may target other areas in a combinatorial manner. However, the precise network structure that integrates these four projections remains poorly understood. Here, we constructed a whole-brain, three-dimensional (3D) map showing the tract pathways and targeting locations of these four motor cortical outputs in mice. Remarkably, these motor cortical projections showed unique and separate tract pathways despite targeting similar areas. Within target areas, various combinations of these four projections were defined based on specific 3D spatial patterns, reflecting anterior-posterior, dorsal-ventral, and core-capsular relationships. This 3D topographic map ultimately provides evidence for the relevance of comparative connectomics: motor cortical projections known to be convergent are actually segregated in many target areas with unique targeting patterns, a finding that has anatomical value for revealing functional subdomains that have not been classified by conventional methods.

Optogenetic Mapping of Functional Connectivity in Freely Moving Mice via Insertable Wrapping Electrode Array Beneath the Skull

Spatiotemporal mapping of neural interactions through electrocorticography (ECoG) is the key to understanding brain functions and disorders. For the entire brain cortical areas, this approach has been challenging, especially in freely moving states, owing to the need for extensive craniotomy. Here, we introduce a flexible microelectrode array system, termed iWEBS, which can be inserted through a small cranial slit and stably wrap onto the curved cortical surface. Using iWEBS, we measured dynamic changes of signals across major cortical domains, namely, somatosensory, motor, visual and retrosplenial areas, in freely moving mice. iWEBS robustly displayed somatosensory evoked potentials (SEPs) in corresponding cortical areas to specific somatosensory stimuli. We also used iWEBS for mapping functional interactions between cortical areas in the propagation of spike-and-wave discharges (SWDs), the neurological marker of absence seizures, triggered by optogenetic inhibition of a specific thalamic nucleus. This demonstrates that iWEBS represents a significant improvement over conventional ECoG recording methodologies and, therefore, is a competitive recording system for mapping wide-range brain connectivity under various behavioral conditions.

Lack of CaV3.1 channels causes severe motor coordination defects and an age-dependent cerebellar atrophy in a genetic model of essential tremor

T-type Ca(2+) channels have been implicated in tremorogenesis and motor coordination. The α1 subunit of the Ca(V)3.1 T-type Ca(2+) channel is highly expressed in motor pathways in the brain, but knockout of the Ca(V)3.1 gene (α(1G)(-/-)) per se causes no motor defects in mice. Thus, the role of Ca(V)3.1 channels in motor control remains obscure in vivo. Here, we investigated the effect of the Ca(V)3.1 knockout in the null genetic background of α1 GABA(A) receptor (α1(-/-)) by generating the double mutants (α1(-/-)/α(1G)(-/-)). α1(-/-)/α(1G)(-/-) mice showed severer motor abnormalities than α1(-/-) mice as measured by potentiated tremor activities at 20Hz and impaired motor learning. Propranolol, an anti-ET drug that is known to reduce the pathologic tremor in α1(-/-) mice, was not effective for suppressing the potentiated tremor in α1(-/-)/α(1G)(-/-) mice. In addition, α1(-/-)/α(1G)(-/-) mice showed an age-dependent loss of cerebellar Purkinje neurons. These results suggest that α1(-/-)/α(1G)(-/-) mice are a novel mouse model for a distinct subtype of ET in human and that Ca(V)3.1 T-type Ca(2+) channels play a role in motor coordination under pathological conditions.

The potential roles of T-type Ca2+ channels in motor coordination

Specific behavioral patterns are expressed by complex combinations of muscle coordination. Tremors are simple behavioral patterns and are the focus of studies investigating motor coordination mechanisms in the brain. T-type Ca2+ channels mediate intrinsic neuronal oscillations and rhythmic burst spiking, and facilitate the generation of tremor rhythms in motor circuits. Despite substantial evidence that T-type Ca2+ channels mediate pathological tremors, their roles in physiological motor coordination and behavior remain unknown. Here, we review recent progress in understanding the roles that T-type Ca2+ channels play under pathological conditions, and discuss the potential relevance of these channels in mediating physiological motor coordination.

Age-dependent gait abnormalities in mice lacking the Rnf170 gene linked to human autosomal-dominant sensory ataxia

Really interesting new gene (RING) finger protein 170 (RNF170) is an E3 ubiquitin ligase known to mediate ubiquitination-dependent degradation of type-I inositol 1,4,5-trisphosphate receptors (ITPR1). It has recently been demonstrated that a point mutation of RNF170 gene is linked with autosomal-dominant sensory ataxia (ADSA), which is characterized by an age-dependent increase of walking abnormalities, a rare genetic disorder reported in only two families. Although this mutant allele is known to be dominant, the functional identity thereof has not been clearly established. Here, we generated mice lacking Rnf170 (Rnf170(-/-)) to evaluate the effect of its loss of function in vivo. Remarkably, Rnf170(-/-) mice began to develop gait abnormalities in old age (12 months) in the form of asynchronous stepping between diagonal limb pairs with a fixed step sequence during locomotion, while age-matched wild-type mice showed stable gait patterns using several step sequence repertoires. As reported in ADSA patients, they also showed a reduced sensitivity for proprioception and thermal nociception. Protein blot analysis revealed that the amount of Itpr1 protein was significantly elevated in the cerebellum and spinal cord but intact in the cerebral cortex in Rnf170(-/-) mice. These results suggest that the loss of Rnf170 gene function mediates ADSA-associated phenotypes and this gives insights on the cure of patients with ADSA and other age-dependent walking abnormalities.

p11 regulates the surface localization of mGluR5.

p11 (S100A10), a member of a large family of S100 proteins, regulates the intracellular localization of metabotropic glutamate receptor 5 (mGluR5) and mGluR5 signaling, and is required for the antidepressant-like effect of mGluR5 antagonism. p11 is primarily localized in the cytoplasm and the plasma membrane (top panel). A dramatic redistribution of endogenous p11 from the cytoplasm to the plasma membrane was observed in human embryonic kidney 293 (HEK293) cells transfected with wild-type mGluR5 (middle panel). In contrast, when cells were transfected with the mutant form of mGluR5, which cannot bind to p11, p11 was partially present in the membrane but a significant portion remained in the cytoplasm (bottom panel). Bright-field imaging was performed to display the cell membrane and nucleus without labeling (first column). Color coding is as follows: red, immunofluorescence labeling of mGluR5 (second column); green, immunofluorescence labeling of p11 (third column). Merge of images of the first, second and third columns is displayed in the fourth column. Specific pixel-by-pixel colocalization of mGluR5 and p11 is represented with an intensity heat map in the fifth column. For more information on this topic, please refer to the article by Lee et al. on pages 1546–1556.