Age-related differences in oligodendrogenesis across the dorsal-ventral axis of the mouse hippocampus

Neurogenesis drives hippocampal formation-wide spatial transcription alterations in health and Alzheimer's disease

The mechanism by which neurogenesis regulates the profile of neurons and glia in the hippocampal formation is not known. Further, the effect of neurogenesis on neuronal vulnerability characterizing the entorhinal cortex in Alzheimer's disease (AD) is unknown. Here, we used in situ sequencing to investigate the spatial transcription profile of neurons and glia in the hippocampal circuitry in wild-type mice and in familial AD (FAD) mice expressing varying levels of neurogenesis. This approach revealed that in addition to the dentate gyrus, neurogenesis modulates the cellular profile in the entorhinal cortex and CA regions of the hippocampus. Notably, enhancing neurogenesis in FAD mice led to partial restoration of neuronal and cellular profile in these brain areas, resembling the profile of their wild-type counterparts. This approach provides a platform for the examination of the cellular dynamics in the hippocampal formation in health and in AD.

S100A6 and Its Brain Ligands in Neurodegenerative Disorders

The S100A6 protein is present in different mammalian cells and tissues including the brain. It binds Ca²⁺ and Zn²⁺ and interacts with many target proteins/ligands. The best characterized ligands of S100A6, expressed at high level in the brain, include CacyBP/SIP and Sgt1. Research concerning the functional role of S100A6 and these two ligands indicates that they are involved in various signaling pathways that regulate cell proliferation, differentiation, cytoskeletal organization, and others. In this review, we focused on the expression/localization of these proteins in the brain and on their possible role in neurodegenerative diseases. Published results demonstrate that S100A6, CacyBP/SIP, and Sgt1 are expressed in various brain structures and in the spinal cord and can be found in different cell types including neurons and astrocytes. When it comes to their possible involvement in nervous system pathology, it is evident that their expression/level and/or subcellular localization is changed when compared to normal conditions. Among diseases in which such changes have been observed are Alzheimer’s disease (AD), amyotrophic lateral sclerosis (ALS), epileptogenesis, Parkinson’s disease (PD), Huntington’s disease (HD), and others.

Oligodendrocytes in intracerebral hemorrhage

Intracerebral hemorrhage (ICH) is a cerebrovascular disorder with high mortality and disability rates. Although a lot of effort has been put in ICH, there is still no effective treatment for this devastating disease. Recent studies suggest that oligodendrocytes play an important role in brain repair after ICH and thus may be targeted for the therapies of ICH. Here in this review, we first introduce the origin, migration, proliferation, differentiation, and myelination of oligodendrocytes under physiological condition. Second, recent findings on how ICH affects oligodendrocyte biology and function are reviewed. Third, potential crosstalk between oligodendrocytes and other cells in the brain is also summarized. Last, we discuss the therapeutic potential of oligodendrocyte‐based treatments in ICH. Our goal is to provide a comprehensive review on the biology and function of oligodendrocytes under both physiological and ICH conditions.

Age‑dependent alteration in the expression of oligodendrocyte‑specific protein in the gerbil hippocampus

Oligodendrocytes are myelin-forming cells in the central nervous system. Research into the effects of aging on oligodendrocyte protein expression remains limited. The present study aimed to determine the alterations in oligodendrocyte-specific protein (OSP) expression in the gerbil hippocampus at 1, 2, 3, 4, 6 and 24 months of age with western blot and immunohistochemistry analyses. OSP expression levels in the hippocampus were highest at 6 months of age. OSP immunoreactivity was identified in numerous cell bodies at 1 month, although the number of OSP immunoreactive cells was different according to hippocampal subregion. The number of OSP immunoreactive cells significantly decreased at 2 months and, thereafter, numbers decreased gradually. The detection of OSP immunoreactive fibers was negligible in all layers in the hippocampal subregions until 4 months. OSP immunoreactive fibers were abundant at 6 and 24 months, although the fiber distribution patterns in the CA1-3 areas and dentate gyrus were different. The results demonstrated that OSP expression in the gerbil hippocampus was age-dependent. The detection of OSP immunoreactive cell bodies and fibers was significantly different according to the layers of hippocampal subregions, indicating that myelination may be continuously altered in the hippocampus during normal aging.

Heterogeneity and function of hippocampal macroglia

The contribution of glial cells to normal and impaired hippocampal function is increasingly being recognized, although important questions as to the mechanisms that these cells use for their crosstalk with neurons and capillaries are still unanswered or lead to controversy. Astrocytes in the hippocampus are morphologically variable and a single cell contacts with its processes more than 100,000 synapses. They predominantly express inward rectifier K⁺ channels and transporters serving homeostatic function but may also release gliotransmitters to modify neuronal signaling and brain circulation. Intracellular Ca²⁺ transients are key events in the interaction of astrocytes with neurons and the vasculature. Hippocampal NG2 glia represent a population of cells with proliferative capacity throughout adulthood. Intriguingly, they receive direct synaptic input from pyramidal neurons and interneurons and express a multitude of ion channels and receptors. Despite in-depth knowledge about the features of these transmembrane proteins, the physiological impact of NG2 glial cells and their synaptic input remain nebulous. Because of the low abundance of oligodendrocytes in the hippocampus, limited information is available about their specific properties. Given the multitude of signaling molecules expressed by the various types of hippocampal glial cells (and because of space constraints), we focus, in this review, on those properties that are considered key for the interaction of the respective cell type with its neighborhood.

Parvalbumin neurons and perineuronal nets in the mouse prefrontal cortex

The prefrontal cortex (PFC) plays a key role in cognitive functions, memory, and attention. Alterations in parvalbumin interneurons (PV neurons) and perineuronal nets (PNNs) within the PFC have been implicated in schizophrenia and autism spectrum disorder pathology. However, it remains unclear why PV neurons and PNNs in the PFC are selectively impaired. Here we aimed to clarify if PV neurons and PNNs in the PFC have region-specific features. We found that PV neurons and PNNs were increased in a region-specific manner in the PFC during postnatal development. In the mature PFC, the expression of PV protein is lower than in other parts of the cortex. Furthermore, PNNs in the mature PFC are not typical lattice-like structures and do not have the major components of PNNs and tenascin-R. The present study indicates that PV neurons and PNNs have region-specific features, and our results suggest that PV neurons and PNNs have structural vulnerability within the PFC.

Aging affects new cell production in the adult hippocampus: A quantitative anatomic review

In the last century, cognitive impairment in elderly people was considered as the consequence of neuronal death. However, later analyses indicated that age-related reduction in neuron number was limited to specific regions of the central nervous system, and was irrelevant to brain dysfunction in both humans and non-human animals. Recent studies have indicated that progressive diminution of neural plasticity across an individual's life span may underlie age-related brain dysfunction. To date, various factors have been shown to contribute to neural plasticity. In particular, substantial data supports the importance of production of new cells in the adult brain: the rate of hippocampal neurogenesis wanes radically during aging; similarly, white matter homeostasis via oligodendrogenesis is also affected by aging. This review briefly summarizes quantitative studies on adult hippocampal neurogenesis and oligodendrogenesis. Although the hippocampus is traditionally recognized as the memory center of the brain, it has started to emerge as an integrator of cognition and emotion. One of the current research highlights is that diverse functions of the hippocampus are topographically embedded along its longitudinal and transverse axes. Here we discuss alterations in adult neurogenesis and oligodendrogenesis during aging from a topographic view point. The quantitative anatomic approach to age-related alterations in production of new cells in the hippocampus may give a novel insight into how brain functions suffer from aging.

Inhibition of Pediatric Glioblastoma Tumor Growth by the Anti-Cancer Agent OKN-007 in Orthotopic Mouse Xenografts

Pediatric glioblastomas (pGBM), although rare, are one of the leading causes of cancer-related deaths in children, with tumors essentially refractory to existing treatments. Here, we describe the use of conventional and advanced in vivo magnetic resonance imaging (MRI) techniques to assess a novel orthotopic xenograft pGBM mouse (IC-3752GBM patient-derived culture) model, and to monitor the effects of the anti-cancer agent OKN-007 as an inhibitor of pGBM tumor growth. Immunohistochemistry support data is also presented for cell proliferation and tumor growth signaling. OKN-007 was found to significantly decrease tumor volumes (p<0.05) and increase animal survival (p<0.05) in all OKN-007-treated mice compared to untreated animals. In a responsive cohort of treated animals, OKN-007 was able to significantly decrease tumor volumes (p<0.0001), increase survival (p<0.001), and increase diffusion (p<0.01) and perfusion rates (p<0.05). OKN-007 also significantly reduced lipid tumor metabolism in responsive animals [(Lip1.3 and Lip0.9)-to-creatine ratio (p<0.05)], as well as significantly decrease tumor cell proliferation (p<0.05) and microvessel density (p<0.05). Furthermore, in relationship to the PDGFRα pathway, OKN-007 was able to significantly decrease SULF2 (p<0.05) and PDGFR-α (platelet-derived growth factor receptor-α) (p<0.05) immunoexpression, and significantly increase decorin expression (p<0.05) in responsive mice. This study indicates that OKN-007 may be an effective anti-cancer agent for some patients with pGBMs by inhibiting cell proliferation and angiogenesis, possibly via the PDGFRα pathway, and could be considered as an additional therapy for pediatric brain tumor patients.