Hyperbaric oxygen therapy alleviates vascular dysfunction and amyloid burden in an Alzheimer's disease mouse model and in elderly patients.

Vascular dysfunction is entwined with aging and in the pathogenesis of Alzheimer's disease (AD) and contributes to reduced cerebral blood flow (CBF) and consequently, hypoxia. Hyperbaric oxygen therapy (HBOT) is in clinical use for a wide range of medical conditions. In the current study, we exposed 5XFAD mice, a well-studied AD model that presents impaired cognitive abilities, to HBOT and then investigated the therapeutical effects using two-photon live animal imaging, behavioral tasks, and biochemical and histological analysis. HBOT increased arteriolar luminal diameter and elevated CBF, thus contributing to reduced hypoxia. Furthermore, HBOT reduced amyloid burden by reducing the volume of pre-existing plaques and attenuating the formation of new ones. This was associated with changes in amyloid precursor protein processing, elevated degradation and clearance of Aß protein and improved behavior of 5XFAD mice. Hence, our findings are consistent with the effects of HBOT being mediated partially through a persistent structural change in blood vessels that reduces brain hypoxia. Motivated by these findings, we exposed elderly patients with significant memory loss at baseline to HBOT and observed an increase in CBF and improvement in cognitive performances. This study demonstrates HBOT efficacy in hypoxia-related neurological conditions, particularly in AD and aging.

Single Cortical Microinfarcts Lead to Widespread Microglia/Macrophage Migration Along the White Matter.

Loss of cognitive function with aging is a complex and poorly understood process. Recently, clinical research has linked the occurrence of cortical microinfarcts to cognitive decline. Cortical microinfarcts form following the occlusion of penetrating vessels and are considered to be restricted to the proximity of the occluded vessel. Whether and how such local events propagate and affect remote brain regions remain unknown. To this end, we combined histological analysis and longitudinal diffusion tensor imaging (DTI), following the targeted-photothrombotic occlusion of single cortical penetrating vessels. Occlusions resulted in distant tissue reorganization across the mouse brain. This remodeling co-occurred with the formation of a microglia/macrophage migratory path along subcortical white matter tracts, reaching the contralateral hemisphere through the corpus callosum and leaving a microstructural signature detected by DTI-tractography. CX3CR1-deficient mice exhibited shorter trail lengths, differential remodeling, and only ipsilateral white matter tract changes. We concluded that microinfarcts lead to brain-wide remodeling in a microglial CX3CR1-dependent manner.

Hotspots of dendritic spine turnover facilitate clustered spine addition and learning and memory.

Modeling studies suggest that clustered structural plasticity of dendritic spines is an efficient mechanism of information storage in cortical circuits. However, why new clustered spines occur in specific locations and how their formation relates to learning and memory (L&M) remain unclear. Using in vivo two-photon microscopy, we track spine dynamics in retrosplenial cortex before, during, and after two forms of episodic-like learning and find that spine turnover before learning predicts future L&M performance, as well as the localization and rates of spine clustering. Consistent with the idea that these measures are causally related, a genetic manipulation that enhances spine turnover also enhances both L&M and spine clustering. Biophysically inspired modeling suggests turnover increases clustering, network sparsity, and memory capacity. These results support a hotspot model where spine turnover is the driver for localization of clustered spine formation, which serves to modulate network function, thus influencing storage capacity and L&M.

Understanding the neurovascular unit at multiple scales: Advantages and limitations of multi-photon and functional ultrasound imaging.

Developing efficient brain imaging technologies by combining a high spatiotemporal resolution and a large penetration depth is a key step for better understanding the neurovascular interface that emerges as a main pathway to neurodegeneration in many pathologies such as dementia. This review focuses on the advances in two complementary techniques: multi-photon laser scanning microscopy (MPLSM) and functional ultrasound imaging (fUSi). MPLSM has become the gold standard for in vivo imaging of cellular dynamics and morphology, together with cerebral blood flow. fUSi is an innovative imaging modality based on Doppler ultrasound, capable of recording vascular brain activity over large scales (i.e., tens of cubic millimeters) at unprecedented spatial and temporal resolution for such volumes (up to 10µm pixel size at 10kHz). By merging these two technologies, researchers may have access to a more detailed view of the various processes taking place at the neurovascular interface. MPLSM and fUSi are also good candidates for addressing the major challenge of real-time delivery, monitoring, and in vivo evaluation of drugs in neuronal tissue.

JAKMIP1, a Novel Regulator of Neuronal Translation, Modulates Synaptic Function and Autistic-like Behaviors in Mouse.

Autism spectrum disorder (ASD) is a heritable, common neurodevelopmental disorder with diverse genetic causes. Several studies have implicated protein synthesis as one among several of its potential convergent mechanisms. We originally identified Janus kinase and microtubule-interacting protein 1 (JAKMIP1) as differentially expressed in patients with distinct syndromic forms of ASD, fragile X syndrome, and 15q duplication syndrome. Here, we provide multiple lines of evidence that JAKMIP1 is a component of polyribosomes and an RNP translational regulatory complex that includes fragile X mental retardation protein, DEAD box helicase 5, and the poly(A) binding protein cytoplasmic 1. JAKMIP1 loss dysregulates neuronal translation during synaptic development, affecting glutamatergic NMDAR signaling, and results in social deficits, stereotyped activity, abnormal postnatal vocalizations, and other autistic-like behaviors in the mouse. These findings define an important and novel role for JAKMIP1 in neural development and further highlight pathways regulating mRNA translation during synaptogenesis in the genesis of neurodevelopmental disorders.

The Autism Related Protein Contactin-Associated Protein-Like 2 (CNTNAP2) Stabilizes New Spines: An In Vivo Mouse Study.

The establishment and maintenance of neuronal circuits depends on tight regulation of synaptic contacts. We hypothesized that CNTNAP2, a protein associated with autism, would play a key role in this process. Indeed, we found that new dendritic spines in mice lacking CNTNAP2 were formed at normal rates, but failed to stabilize. Notably, rates of spine elimination were unaltered, suggesting a specific role for CNTNAP2 in stabilizing new synaptic circuitry.

Associative fear learning enhances sparse network coding in primary sensory cortex.

Several models of associative learning predict that stimulus processing changes during association formation. How associative learning reconfigures neural circuits in primary sensory cortex to "learn" associative attributes of a stimulus remains unknown. Using 2-photon in vivo calcium imaging to measure responses of networks of neurons in primary somatosensory cortex, we discovered that associative fear learning, in which whisker stimulation is paired with foot shock, enhances sparse population coding and robustness of the conditional stimulus, yet decreases total network activity. Fewer cortical neurons responded to stimulation of the trained whisker than in controls, yet their response strength was enhanced. These responses were not observed in mice exposed to a nonassociative learning procedure. Our results define how the cortical representation of a sensory stimulus is shaped by associative fear learning. These changes are proposed to enhance efficient sensory processing after associative learning.

Absence of CNTNAP2 leads to epilepsy, neuronal migration abnormalities, and core autism-related deficits.

Although many genes predisposing to autism spectrum disorders (ASD) have been identified, the biological mechanism(s) remain unclear. Mouse models based on human disease-causing mutations provide the potential for understanding gene function and novel treatment development. Here, we characterize a mouse knockout of the Cntnap2 gene, which is strongly associated with ASD and allied neurodevelopmental disorders. Cntnap2(-/-) mice show deficits in the three core ASD behavioral domains, as well as hyperactivity and epileptic seizures, as have been reported in humans with CNTNAP2 mutations. Neuropathological and physiological analyses of these mice before the onset of seizures reveal neuronal migration abnormalities, reduced number of interneurons, and abnormal neuronal network activity. In addition, treatment with the FDA-approved drug risperidone ameliorates the targeted repetitive behaviors in the mutant mice. These data demonstrate a functional role for CNTNAP2 in brain development and provide a new tool for mechanistic and therapeutic research in ASD.

Site-specific dephosphorylation of doublecortin (DCX) by protein phosphatase 1 (PP1).

Mutations in doublecortin (DCX) cause X-linked lissencephaly ("smooth brain") and double cortex syndrome in humans. DCX is highly phosphorylated in migrating neurons. Here, we demonstrate that dephosphorylation of specific sites phosphorylated by JNK is mediated by Neurabin II, which recruits the phosphatase PP1. During cortical development, the expression pattern of PP1 is widespread, while the expression of DCX and Neurabin II is dynamic, and they are coexpressed in migrating neurons. In vitro, DCX is site-specific dephosphorylated by PP1 without the presence of Neurabin II, this dephosphorylation requires an intact RVXF motif in DCX. Overexpression of the coiled-coil domain of Neurabin II, which is sufficient for interacting with DCX and recruiting the endogenous Neurabin II with PP1, induced dephosphorylation of DCX on one of the JNK-phosphorylated sites. We hypothesize that the transient recruitment of DCX to different scaffold proteins, JIP-1/2, which will regulate its phosphorylation by JNK, and Neurabin II, which will regulate its dephosphorylation by PP1, plays an important role in normal neuronal migration.

DCX's phosphorylation by not just another kinase (JNK).

The mammalian cortex is generally subdivided into six organized layers, which are formed during development in an organized fashion. This organized cortical layering is disrupted in case of mutations in the doublecortin (DCX) gene. DCX is a Microtubule Associated Protein (MAP). However, besides stabilization of microtubules, it may be involved in additional functions. The participation of this molecule in signal transduction is beginning to emerge via discovery of interacting molecules and its regulation by phosphorylation using several different kinases. We raise the hypothesis, that the combinatorial phosphorylation of DCX by different kinases and at different sites may be a molecular regulatory switch in the transition of a migrating neuron through multiple phases of migration. Our recent research has suggested the involvement of DCX in the JNK (Jun-N-terminal Kinase) pathway. The JNK pathway is linked to the reelin pathway, known to regulate cortical layering. Positioning of DCX in this signaling pathway opens up additional possibilities of understanding how migrating neurons are controlled.

DCX, a new mediator of the JNK pathway.

Mutations in the X-linked gene DCX result in lissencephaly in males, and abnormal neuronal positioning in females, suggesting a role for this gene product during neuronal migration. In spite of several known protein interactions, the involvement of DCX in a signaling pathway is still elusive. Here we demonstrate that DCX is a substrate of JNK and interacts with both c-Jun N-terminal kinase (JNK) and JNK interacting protein (JIP). The localization of this signaling module in the developing brain suggests its functionality in migrating neurons. The localization of DCX at neurite tips is determined by its interaction with JIP and by the interaction of the latter with kinesin. DCX is phosphorylated by JNK in growth cones. DCX mutated in sites phosphorylated by JNK affected neurite outgrowth, and the velocity and relative pause time of migrating neurons. We hypothesize that during neuronal migration, there is a need to regulate molecular motors that are working in the cell in opposite directions: kinesin (a plus-end directed molecular motor) versus dynein (a minus-end directed molecular motor).