Ultrastructural localization of calcyon in the primate cortico-basal ganglia-thalamocortical loop

Dynein binds and stimulates axonal motility of the endosome adaptor and NEEP21 family member, calcyon

The neuron-enriched, endosomal protein Calcyon (Caly) regulates endocytosis and vesicle sorting, and is important for synaptic plasticity and brain development. In the current investigation of Caly interacting proteins in brain, the microtubule retrograde motor subunit, cytoplasmic dynein 1 heavy chain (DYNC1H), and microtubule structural proteins, α and β tubulin, were identified as Caly associated proteins by MALDI-ToF/ToF. Direct interaction of the Caly-C terminus with dynein and tubulin was further confirmed in in vitro studies. In Cos-7 cells, mCherry-Caly moved along the microtubule network in organelles largely labeled by the late endosome marker Rab7. Expression of the dynein inhibitor CC1, produced striking alterations in Caly distribution, consistent with retrograde motors playing a prominent role in Caly localization and movement. In axons of cultured adult rat sensory neurons, Caly-positive organelles co-localized with dynein intermediate chain (DYNC1I1-isoform IC-1B) and the dynein regulator, lissencephaly 1 (LIS1), both of which co-precipitated from brain with the Caly C-terminus. Manipulation of dynein function in axons altered the motile properties of Caly indicating that Caly vesicles utilize the retrograde motor. Altogether, the current evidence for association with dynein motors raises the possibility that the endocytic and cargo sorting functions of Caly in neurons could be regulated by interaction with the microtubule transport system.

Complementary roles of the neuron-enriched endosomal proteins NEEP21 and calcyon in neuronal vesicle trafficking

Understanding mechanisms governing the trafficking of transmembrane (TM) cargoes to synapses and other specialized membranes in neurons represents a long-standing challenge in cell biology. Investigation of the neuron-enriched endosomal protein of 21 kDa (NEEP21, or NSG1or P21) and Calcyon (Caly, or NSG3) indicates that the emergence of the NEEP21/Caly/P19 gene family could play a vital role in the success of these mechanisms in vertebrates. The upshot of a sizeable body of work is that the NEEP21 and Caly perform distinct endocytic and recycling functions, which impact (i) α amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid-type glutamate receptor trafficking at excitatory synapses; (ii) transport to/in neuronal axons; as well as (iii) proteolytic processing of amyloid precursor protein and neuregulin 1, suggesting roles in neuron development, synaptic function, and neurodegeneration. We argue that their distinct effects on cargo endocytosis and recycling depend on interactions with vesicle trafficking and synaptic scaffolding proteins. As they play complementary, but opposing roles in cargo endocytosis, recycling, and degradation, balancing NEEP21 and Caly expression levels or activity could be important for homeostasis in a variety of signaling pathways, and also lead to a novel therapeutic strategy for disorders like Alzheimer's disease and schizophrenia. This review focuses on two closely related, neuron-enriched endosomal proteins: NEEP21 and Calcyon which perform distinct roles in regulating receptor endocytosis, recycling, and degradation. Based on an in-depth examination of the literature, we argue that these two proteins carry out complementary yet sometimes opposing vesicle trafficking functions that impact excitatory transmission, transcytosis, axonal transport, and also proteolytic processing by beta-secretase I (BACE1). Finally, we propose that balancing NEEP21 and Calcyon expression and/or activity could be important for homeostasis in a variety of signaling pathways, and also lead to a novel therapeutic strategy for disorders like Alzheimer's disease and schizophrenia. AMPA = α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptor; NMDA = N-Methyl-D-aspartate.

Calcyon upregulation in adolescence impairs response inhibition and working memory in adulthood

Calcyon regulates activity-dependent internalization of α-amino-3-hydroxyl-5-methyl-4-isoxazole-propionate (AMPA) glutamate receptors and long-term depression of excitatory synapses. Elevated levels of calcyon are consistently observed in brains from schizophrenic patients, and the calcyon gene is associated with attention-deficit hyperactivity disorder. Executive function deficits are common to both disorders, and at least for schizophrenia, the etiology appears to involve both heritable and neurodevelopmental factors. Here, we show with calcyon-overexpressing Cal(OE) transgenic mice that lifelong calcyon upregulation impairs executive functions including response inhibition and working memory, without producing learning and memory deficits in general. As response inhibition and working memory, as well as the underlying neural circuitry, continue to mature into early adulthood, we functionally silenced the transgene during postnatal days 28-49, a period corresponding to adolescence. Remarkably, the response inhibition and working memory deficits including perseverative behavior were absent in adult Cal(OE) mice with the transgene silenced in adolescence. Suppressing the calcyon transgene in adulthood only partially rescued the deficits, suggesting calcyon upregulation in adolescence irreversibly alters development of neural circuits supporting mature response inhibition and working memory. Brain regional immunoblots revealed a prominent downregulation of AMPA GluR1 subunits in hippocampus and GluR2/3 subunits in hippocampus and prefrontal cortex of the Cal(OE) mice. Silencing the transgene in adolescence prevented the decrease in hippocampal GluR1, further implicating altered fronto-hippocampal connectivity in the executive function deficits observed in the Cal(OE) mice. Treatments that mitigate the effects of high levels of calcyon during adolescence could preempt adult deficits in executive functions in individuals at risk for serious mental illness.

Deficits in fine motor skills in a genetic animal model of ADHD

Background

In an attempt to model some behavioral aspects of Attention Deficit/Hyperactivity Disorder (ADHD), we examined whether an existing genetic animal model of ADHD is valid for investigating not only locomotor hyperactivity, but also more complex motor coordination problems displayed by the majority of children with ADHD.

Methods

We subjected young adolescent Spontaneously Hypertensive Rats (SHRs), the most commonly used genetic animal model of ADHD, to a battery of tests for motor activity, gross motor coordination, and skilled reaching. Wistar (WIS) rats were used as controls.

Results

Similar to children with ADHD, young adolescent SHRs displayed locomotor hyperactivity in a familiar, but not in a novel environment. They also had lower performance scores in a complex skilled reaching task when compared to WIS rats, especially in the most sensitive measure of skilled performance (i.e., single attempt success). In contrast, their gross motor performance on a Rota-Rod test was similar to that of WIS rats.

Conclusion

The results support the notion that the SHR strain is a useful animal model system to investigate potential molecular mechanisms underlying fine motor skill problems in children with ADHD.

Effects of antenatal dexamethasone treatment on glucocorticoid receptor and calcyon gene expression in the prefrontal cortex of neonatal and adult common marmoset monkeys

BACKGROUND

Synthetic glucocorticoids such as dexamethasone (DEX) are commonly used to promote fetal lung maturation in at-risk preterm births, but there is emerging evidence of subsequent neurobehavioral abnormalities in these children e.g. problems with inattention/hyperactivity. However, molecular pathways mediating effects of glucocorticoid overexposure on motor and cognitive development are poorly understood.

METHODS

In this study with common marmoset monkeys, we investigated for neonatal and adulthood effects of antenatal DEX treatment on the expression of the corticosteroid receptors and also calcyon, a risk gene for attention-deficit/hyperactivity disorder, in the prefrontal cortex (PFC). Pregnant marmosets were exposed to DEX (5 mg/kg body weight) or vehicle during early (days 42-48) or late (days 90-96) stages of the 144-day pregnancy.

RESULTS

In neonates, relative to controls, glucocorticoid receptor (GR) mRNA levels were significantly reduced after the late DEX treatment in the medial, orbital and dorsal PFC and after the early DEX treatment in the dorsal PFC. The early DEX exposure, specifically, resulted in significant reduction in calcyon mRNA expression in the medial, orbital, dorsal and lateral PFC relative to controls. Mineralocorticoid receptor (MR) mRNA levels were not significantly affected by DEX treatment. In adults, PFC GR, calcyon, and MR mRNA levels were not significantly affected by early or late prenatal DEX treatment.

CONCLUSION

These findings indicate that antenatal DEX treatment could lead to short-term alterations in PFC expression of the GR and calcyon genes, with possible neurodevelopmental functional consequences.