Programmed cell death and the control of cell survival: lessons from the nervous system

Tocotrienol-rich fraction (TRF) protects against retinal cell apoptosis and preserves visual behavior in rats with streptozotocin-induced diabetic retinopathy

BACKGROUND

Tocotrienol is a vitamin E analogue that is known to exert anti-inflammatory and antioxidant effects. Hence, in the current study, the effects of TRF on the expression of pro- and anti-apoptotic proteins in the streptozotocin-induced diabetic rat retinas were investigated. The effect of TRF on the visual behaviour of rats was also studied.

METHODS

Diabetes was induced in rats by intraperitoneal injection of streptozotocin and was confirmed by a blood sugar level of at least 20 mmol/L, 48 h, post-injection. Diabetic rats were divided into a group treated with vehicle (DV) and the other treated with TRF (100 mg/kg; DT). A group of non-diabetic rats treated with vehicle (N) served as the control group. All treatments were administered orally for 12 weeks. Rats were then subjected to an assessment of general behaviour in an open field arena and a two-chamber mirror test to assess their visual behaviour. At the end of the experimental period, rats were sacrificed, and their retinas were isolated to measure the expression of pro- (Casp3, Bax) and anti-apoptotic (Bcl2) markers using RT-qPCR and ELISA. TUNEL staining was used to detect the apoptotic retinal cells.

RESULTS

Treatment with TRF lowered the retinal expression of Casp3 protein by 2.26-folds (p < 0.001) and Bax protein by 2.18-fold (p < 0.001) compared to vehicle-treated rats. The retinal anti-apoptotic protein Bcl2 expression was 1.87-fold higher in DT compared to DV rats (p < 0.001). Accordingly, the Bax/Bcl2 ratio in the TRF-treated group was significantly greater in DT compared to DV rats. Retinal Casp3, Bax, and Bcl2 gene expression, as determined by RT-qPCR, also showed changes corresponding to protein expression. In the open field test, DV rats showed greater anxiety-related behaviour than group N, while the behaviour of DT rats was similar to the N group of rats. DT rats and group N rats preferred the inverse mirror chamber over the mirror-containing chamber in the two-mirror chamber test (p < 0.01).

CONCLUSION

Oral TRF therapy for 12 weeks lowers retinal cell apoptosis by decreasing pro- and increasing anti-apoptotic markers. The preservation of visual behaviour in a two-chamber mirror test supported these retinal molecular alterations in diabetic rats.

Protective Effects of Polysaccharide of Atractylodes Macrocephala Koidz against Porcine Aortic Valve Endothelial Cells Damage Induced by di (2-ethylhexyl) Phthalate

The activation, injury, and dysfunction of endothelial cells are considered to be the initial key events in the development of atherosclerosis. Di (2-ethylhexyl) phthalate (DEHP), a prevalent organic pollutant, can cause damage to multiple organs. Polysaccharide of Atractylodes macrocephala Koidz (PAMK) is a bioactive compound extracted from A. macrocephala Koidz with various biological activities. This study investigates the protective effects of PAMK on porcine aortic valve endothelial cells (PAVEC) damaged by DEHP. PAVECs treated with DEHP alone or with PAMK showed reduced cell apoptosis and death in PAMK-pretreated cells. PAMK up-regulated Bcl-2 expression and down-regulated Bax protein, suppressing apoptosis. Flow cytometry analysis demonstrated that PAMK protected PAVECs from DEHP-induced damage. These findings suggest that PAMK inhibits cell apoptosis and protects against DEHP damage in endothelial cells.

p38γ MAPK delays myelination and remyelination and is abundant in multiple sclerosis lesions

Multiple sclerosis is a chronic inflammatory disease in which disability results from the disruption of myelin and axons. During the initial stages of the disease, injured myelin is replaced by mature myelinating oligodendrocytes that differentiate from oligodendrocyte precursor cells. However, myelin repair fails in secondary and chronic progressive stages of the disease and with ageing, as the environment becomes progressively more hostile. This may be attributable to inhibitory molecules in the multiple sclerosis environment including activation of the p38MAPK family of kinases. We explored oligodendrocyte precursor cell differentiation and myelin repair using animals with conditional ablation of p38MAPKγ from oligodendrocyte precursors. We found that p38γMAPK ablation accelerated oligodendrocyte precursor cell differentiation and myelination. This resulted in an increase in both the total number of oligodendrocytes and the migration of progenitors ex vivo and faster remyelination in the cuprizone model of demyelination/remyelination. Consistent with its role as an inhibitor of myelination, p38γMAPK was significantly downregulated as oligodendrocyte precursor cells matured into oligodendrocytes. Notably, p38γMAPK was enriched in multiple sclerosis lesions from patients. Oligodendrocyte progenitors expressed high levels of p38γMAPK in areas of failed remyelination but did not express detectable levels of p38γMAPK in areas where remyelination was apparent. Our data suggest that p38γ could be targeted to improve myelin repair in multiple sclerosis.

IOP and glaucoma damage: The essential role of optic nerve head and retinal mechanosensors

There are many unanswered questions on the relation of intraocular pressure to glaucoma development and progression. IOP itself cannot be distilled to a single, unifying value, because IOP level varies over time, differs depending on ocular location, and can be affected by method of measurement. Ultimately, IOP level creates mechanical strain that affects axonal function at the optic nerve head which causes local extracellular matrix remodeling and retinal ganglion cell death - hallmarks of glaucoma and the cause of glaucomatous vision loss. Extracellular tissue strain at the ONH and lamina cribrosa is regionally variable and differs in magnitude and location between healthy and glaucomatous eyes. The ultimate targets of IOP-induced tissue strain in glaucoma are retinal ganglion cell axons at the optic nerve head and the cells that support axonal function (astrocytes, the neurovascular unit, microglia, and fibroblasts). These cells sense tissue strain through a series of signals that originate at the cell membrane and alter cytoskeletal organization, migration, differentiation, gene transcription, and proliferation. The proteins that translate mechanical stimuli into molecular signals act as band-pass filters - sensing some stimuli while ignoring others - and cellular responses to stimuli can differ based on cell type and differentiation state. Therefore, to fully understand the IOP signals that are relevant to glaucoma, it is necessary to understand the ultimate cellular targets of IOP-induced mechanical stimuli and their ability to sense, ignore, and translate these signals into cellular actions.

Features, Fates, and Functions of Oligodendrocyte Precursor Cells

Oligodendrocyte precursor cells (OPCs) are a central nervous system resident population of glia with a distinct molecular identity and an ever-increasing list of functions. OPCs generate oligodendrocytes throughout development and across the life span in most regions of the brain and spinal cord. This process involves a complex coordination of molecular checkpoints and biophysical cues from the environment that initiate the differentiation and integration of new oligodendrocytes that synthesize myelin sheaths on axons. Outside of their progenitor role, OPCs have been proposed to play other functions including the modulation of axonal and synaptic development and the participation in bidirectional signaling with neurons and other glia. Here, we review OPC identity and known functions and discuss recent findings implying other roles for these glial cells in brain physiology and pathology.

The role of apoptosis in spinal cord injury: a bibliometric analysis from 1994 to 2023

Background

Apoptosis after spinal cord injury (SCI) plays a pivotal role in the secondary injury mechanisms, which cause the ultimate neurologic insults. A better understanding of the molecular and cellular basis of apoptosis in SCI allows for improved glial and neuronal survival via the administrations of anti-apoptotic biomarkers. The knowledge structure, development trends, and research hotspots of apoptosis and SCI have not yet been systematically investigated.

Methods

Articles and reviews on apoptosis and SCI, published from 1st January 1994 to 1st Oct 2023, were retrieved from the Web of Science™. Bibliometrix in R was used to evaluate annual publications, countries, affiliations, authors, sources, documents, key words, and hot topics.

Results

A total of 3,359 publications in accordance with the criterions were obtained, which exhibited an ascending trend in annual publications. The most productive countries were the USA and China. Journal of Neurotrauma was the most impactive journal; Wenzhou Medical University was the most prolific affiliation; Cuzzocrea S was the most productive and influential author. "Apoptosis," "spinal-cord-injury," "expression," "activation," and "functional recovery" were the most frequent key words. Additionally, "transplantation," "mesenchymal stemness-cells," "therapies," "activation," "regeneration," "repair," "autophagy," "exosomes," "nlrp3 inflammasome," "neuroinflammation," and "knockdown" were the latest emerging key words, which may inform the hottest themes.

Conclusions

Apoptosis after SCI may cause the ultimate neurological damages. Development of novel treatments for secondary SCI mainly depends on a better understanding of apoptosis-related mechanisms in molecular and cellular levels. Such therapeutic interventions involve the application of anti-apoptotic agents, free radical scavengers, as well as anti-inflammatory drugs, which can be targeted to inhibit core events in cellular and molecular injury cascades pathway.

Ciliary neurotrophic factor mediated growth of retinal ganglion cell axons on PGS/PCL scaffolds

Ciliary neurotrophic factor (CNTF) promotes survival and/or differentiation of a variety of neuronal cells including retinal ganglion cells (RGCs). Delivery of CNTF requires a suitable medium capable of mediating diffusion and premature release of CNTF within the target tissue. Polymeric tissue-engineered scaffolds have been readily used as substrates for cell transplantation, expansion, and differentiation and, as carriers of cell growth factors. Their functions to CNTF release for RGC proliferation have remained so far unexplored, especially to CNTF affinity to the scaffold and subsequent RGC fate. Electrospunpoly(glycerol sebacate)/poly(ϵ-caprolactone) (PGS/PCL) biopolymer scaffolds have recently shown promising results in terms of supporting regeneration of RGC neurites. This work explores covalent immobilization of CNTF on PGS/PCL scaffold and the way immobilised CNTF mediates growth of RGC axons on the scaffold. Anex-vivothree-dimensional model of rodent optic nerve on PGS/PCL revealed that RGC explants cultured in CNTF mediated environment increased their neurite extensions after 20 d of cell culture employing neurite outgrowth measurements. The CNTF secretion on PGS/PCL scaffold was found bio-mimicking natural extracellular matrix of the cell target tissue and, consequently, has shown a potential to improve the overall efficacy of the RGC regeneration process.

Feedback control of organ size precision is mediated by BMP2-regulated apoptosis in the Drosophila eye

Biological processes are intrinsically noisy, and yet, the result of development-like the species-specific size and shape of organs-is usually remarkably precise. This precision suggests the existence of mechanisms of feedback control that ensure that deviations from a target size are minimized. Still, we have very limited understanding of how these mechanisms operate. Here, we investigate the problem of organ size precision using the Drosophila eye. The size of the adult eye depends on the rates at which eye progenitor cells grow and differentiate. We first find that the progenitor net growth rate results from the balance between their proliferation and apoptosis, with this latter contributing to determining both final eye size and its variability. In turn, apoptosis of progenitor cells is hampered by Dpp, a BMP2/4 signaling molecule transiently produced by early differentiating retinal cells. Our genetic and computational experiments show how the status of retinal differentiation is communicated to progenitors through the differentiation-dependent production of Dpp, which, by adjusting the rate of apoptosis, exerts a feedback control over the net growth of progenitors to reduce final eye size variability.

The committed oligodendrocyte precursor cell, a newly-defined intermediate progenitor cell type in oligodendroglial lineage

In the central nervous system, oligodendrocytes (OLs) produce myelin sheaths that provide trophic support to neuronal axons and increase the propagation speed of action potential. OLs are constantly generated from OL precursor cells (OPCs) throughout life span. The production of myelinating OLs consists of three canonical stages: OPCs, newly-formed OLs (NFOs), and mature myelinating OLs. Recently, single-cell RNA transcriptomic analyses identified a new population of oligodendroglial cells, namely differentiation committed OPCs (COPs). COPs represent a critical intermediate population between OPCs and NFOs, as revealed by specific expression of G-protein coupled receptor 17 (GPR17). The dysregulation of COPs leads to the remyelination failure in demyelinating diseases and impairs the replacement of lost myelin sheaths due to aging. Hence, understanding the development of COPs and their underlying regulatory network will be helpful in establishing new strategies for promoting myelin repair in demyelinating diseases. This review summarizes the current knowledge on the development and functions of COPs under both physiological and pathological conditions. Overall, COPs function as "checkpoints" to prevent inappropriate precocious OL differentiation and myelination through expressing distinct regulatory factors. Deepening our understanding of COPs may not only advance our knowledge of how OL lineage progresses during development, but also open the door to new treatments for demyelinating diseases.

SNIP1 and PRC2 coordinate cell fates of neural progenitors during brain development

Stem cell survival versus death is a developmentally programmed process essential for morphogenesis, sizing, and quality control of genome integrity and cell fates. Cell death is pervasive during development, but its programming is little known. Here, we report that Smad nuclear interacting protein 1 (SNIP1) promotes neural progenitor cell survival and neurogenesis and is, therefore, integral to brain development. The SNIP1-depleted brain exhibits dysplasia with robust induction of caspase 9-dependent apoptosis. Mechanistically, SNIP1 regulates target genes that promote cell survival and neurogenesis, and its activities are influenced by TGFβ and NFκB signaling pathways. Further, SNIP1 facilitates the genomic occupancy of Polycomb complex PRC2 and instructs H3K27me3 turnover at target genes. Depletion of PRC2 is sufficient to reduce apoptosis and brain dysplasia and to partially restore genetic programs in the SNIP1-depleted brain in vivo. These findings suggest a loci-specific regulation of PRC2 and H3K27 marks to toggle cell survival and death in the developing brain.

Emerging mitochondrial-mediated mechanisms involved in oligodendrocyte development

Oligodendrocytes are the myelinating glia of the central nervous system and are generated after oligodendrocyte progenitor cells (OPCs) transition into pre-oligodendrocytes and then into myelinating oligodendrocytes. Myelin is essential for proper signal transmission within the nervous system and axonal metabolic support. Although the intrinsic and extrinsic factors that support the differentiation, survival, integration, and subsequent myelination of appropriate axons have been well investigated, little is known about how mitochondria-related pathways such as mitochondrial dynamics, bioenergetics, and apoptosis finely tune these developmental events. Previous findings suggest that changes to mitochondrial morphology act as an upstream regulatory mechanism of neural stem cell (NSC) fate decisions. Whether a similar mechanism is engaged during OPC differentiation has yet to be elucidated. Maintenance of mitochondrial dynamics is vital for regulating cellular bioenergetics, functional mitochondrial networks, and the ability of cells to distribute mitochondria to subcellular locations, such as the growing processes of oligodendrocytes. Myelination is an energy-consuming event, thus, understanding the interplay between mitochondrial dynamics, metabolism, and apoptosis will provide further insight into mechanisms that mediate oligodendrocyte development in healthy and disease states. Here we will provide a concise overview of oligodendrocyte development and discuss the potential contribution of mitochondrial mitochondrial-mediated mechanisms to oligodendrocyte bioenergetics and development.

Serotonergic regulation of bipolar cell survival in the developing cerebral cortex

One key factor underlying the functional balance of cortical networks is the ratio of excitatory and inhibitory neurons. The mechanisms controlling the ultimate number of interneurons are beginning to be elucidated, but to what extent similar principles govern the survival of the large diversity of cortical inhibitory cells remains to be investigated. Here, we investigate the mechanisms regulating developmental cell death in neurogliaform cells, bipolar cells, and basket cells, the three main populations of interneurons originating from the caudal ganglionic eminence and the preoptic region. We found that all three subclasses of interneurons undergo activity-dependent programmed cell death. However, while neurogliaform cells and basket cells require glutamatergic transmission to survive, the final number of bipolar cells is instead modulated by serotonergic signaling. Together, our results demonstrate that input-specific modulation of neuronal activity controls the survival of cortical interneurons during the critical period of programmed cell death.

Spatial and temporal heterogeneity in the lineage progression of fine oligodendrocyte subtypes

Background

Oligodendrocytes are glial cells that support and insulate axons in the central nervous system through the production of myelin. Oligodendrocytes arise throughout embryonic and early postnatal development from oligodendrocyte precursor cells (OPCs), and recent work demonstrated that they are a transcriptional heterogeneous cell population, but the regional and functional implications of this heterogeneity are less clear. Here, we apply in situ sequencing (ISS) to simultaneously probe the expression of 124 marker genes of distinct oligodendrocyte populations, providing comprehensive maps of the corpus callosum, cingulate, motor, and somatosensory cortex in the brain, as well as gray matter (GM) and white matter (WM) regions in the spinal cord, at postnatal (P10), juvenile (P20), and young adult (P60) stages. We systematically compare the abundances of these populations and investigate the neighboring preference of distinct oligodendrocyte populations.

Results

We observed that oligodendrocyte lineage progression is more advanced in the juvenile spinal cord compared to the brain, corroborating with previous studies. We found myelination still ongoing in the adult corpus callosum while it was more advanced in the cortex. Interestingly, we also observed a lateral-to-medial gradient of oligodendrocyte lineage progression in the juvenile cortex, which could be linked to arealization, as well as a deep-to-superficial gradient with mature oligodendrocytes preferentially accumulating in the deeper layers of the cortex. The ISS experiments also exposed differences in abundances and population dynamics over time between GM and WM regions in the brain and spinal cord, indicating regional differences within GM and WM, and we found that neighboring preferences of some oligodendroglia populations are altered from the juvenile to the adult CNS.

Conclusions

Overall, our ISS experiments reveal spatial heterogeneity of oligodendrocyte lineage progression in the brain and spinal cord and uncover differences in the timing of oligodendrocyte differentiation and myelination, which could be relevant to further investigate functional heterogeneity of oligodendroglia, especially in the context of injury or disease.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12915-022-01325-z.

Input-specific control of interneuron numbers in nascent striatal networks

The assembly of functional neuronal circuits requires appropriate numbers of distinct classes of neurons, but the mechanisms through which their relative proportions are established remain poorly defined. Investigating the mouse striatum, we found that the two most prominent subtypes of striatal interneurons, parvalbumin-expressing (PV+) GABAergic and cholinergic (ChAT+) interneurons, undergo extensive programmed cell death between the first and second postnatal weeks. Remarkably, the survival of PV+ and ChAT+ interneurons is regulated by distinct mechanisms mediated by their specific afferent connectivity. While long-range cortical inputs control PV+ interneuron survival, ChAT+ interneuron survival is regulated by local input from the medium spiny neurons. Our results identify input-specific circuit mechanisms that operate during the period of programmed cell death to establish the final number of interneurons in nascent striatal networks.

Extracellular and Intracellular Skeletons: How Do They Involve in Apoptosis

Apoptosis plays a key role in removing abnormal or senescent cells, maintaining the overall health of the tissue, and coordinating individual development. Recently, it has been discovered that the intracellular cytoskeleton plays a role in the apoptotic process. In addition, the regulatory role of extracellular matrix (ECM) fibrous proteins, which can be considered as the extracellular skeleton, in the process of apoptosis is rarely summarized. In this review, we collect the latest knowledge about how fibrous proteins inside and outside cells regulate apoptosis. We describe how ECM fibrous proteins participate in the regulation of death receptor and mitochondrial pathways through various signaling cascades mediated by integrins. We then explore the molecular mechanisms by which intracellular intermediate filaments regulate cell apoptosis by regulating death receptors on the cell membrane surface. Similarly, we report on novel supporting functions of microtubules in the execution phase of apoptosis and discuss their formation mechanisms. Finally, we discuss that the polypeptide fragments formed by caspase degradation of ECM fibrous proteins and intracellular intermediate filament act as local regulatory signals to play different regulatory roles in apoptosis.

Age and intraocular pressure in murine experimental glaucoma

Age and intraocular pressure (IOP) are the two most important risk factors for the development and progression of open-angle glaucoma. While IOP is commonly considered in models of experimental glaucoma (EG), most studies use juvenile or adult animals and seldom older animals which are representative of the human disease. This paper provides a concise review of how retinal ganglion cell (RGC) loss, the hallmark of glaucoma, can be evaluated in EG with a special emphasis on serial in vivo imaging, a parallel approach used in clinical practice. It appraises the suitability of EG models for the purpose of in vivo imaging and argues for the use of models that provide a sustained elevation of IOP, without compromise of the ocular media. In a study with parallel cohorts of adult (3-month-old, equivalent to 20 human years) and old (2-year-old, equivalent to 70 human years) mice, we compare the effects of elevated IOP on serial ganglion cell complex thickness and individual RGC dendritic morphology changes obtained in vivo. We also evaluate how age modulates the impact of elevated IOP on RGC somal and axonal density in histological analysis as well the density of melanopsin RGCs. We discuss the challenges of using old animals and emphasize the potential of single RGC imaging for understanding the pathobiology of RGC loss and evaluating new therapeutic avenues.

Synthesis and Antiproliferative Activity of New Thiosemicarboxamide Derivatives

To discover new anticancer agents, two series of thiosemicarboxamide derivatives were synthesized and evaluated for their antiproliferative activity against human cancer cells in vitro. Most target compounds (especially 3f, 3g, and 3h) exhibit potent antiproliferative activity against HeLa cells. Importantly, compound 3h, bearing a 4-methylphenyl substituent at N position of thiourea moiety, has significant and broad-spectrum inhibitory activities against cancer cells (HepG2, HeLa, MDA-MB231, A875, and H460 cells) with low IC₅₀ values (<5.0 μM) and shows low toxicity to normal LO2 and MRC-5 cells. Further studies show that compound 3h exerts high inhibitory activity in cancer cells by inducing the G2/M-phase arrest of cancer cells. Collectively, this study presents compound 3h as a new entity for the development of cell cycle arrest inducers for the treatment of cancer.

Inhibition of ERK/MAPK signaling as potential therapy to prevent optic pathway glioma in infants with neurofibromatosis type 1

Pediatric low-grade gliomas (pLGGs) arise primarily at early stages of development. The molecular mechanisms of pLGG gliomagenesis are unclear, as is the progenitor cell of origin. In this issue of Developmental Cell, Jecrois et al. show that NF1-associated optic pathway gliomas originate from migrating glial progenitors that have distinct MEK/ERK dependency.

Disruption of Transient SERT Expression in Thalamic Glutamatergic Neurons Alters Trajectory of Postnatal Interneuron Development in the Mouse Cortex

In mice, terminal differentiation of subpopulations of interneurons occurs in late postnatal stages, paralleling the emergence of the adult cortical architecture. Here, we investigated the effects of altered initial cortical architecture on later interneuron development. We identified that a class of somatostatin (SOM)-expressing GABAergic interneurons undergoes terminal differentiation between 2nd and 3rd postnatal week in the mouse somatosensory barrel cortex and upregulates Reelin expression during neurite outgrowth. Our previous work demonstrated that transient expression (E15-P10) of serotonin uptake transporter (SERT) in thalamocortical projection neurons regulates barrel elaboration during cortical map establishment. We show here that in thalamic neuron SERT knockout mice, these SOM-expressing interneurons develop at the right time, reach correct positions and express correct neurochemical markers, but only 70% of the neurons remain in the adult barrel cortex. Moreover, those neurons that remain display altered dendritic patterning. Our data indicate that a precise architecture at the cortical destination is not essential for specifying late-developing interneuron identities, their cortical deposition, and spatial organization, but dictates their number and dendritic structure ultimately integrated into the cortex. Our study illuminates how disruption of temporal-specific SERT function and related key regulators during cortical map establishment can alter interneuron development trajectory that persists to adult central nervous system.

Adult neurogenesis in the central nervous system of teleost fish: from stem cells to function and evolution

Adult neurogenesis, the generation of functional neurons from adult neural stem cells in the central nervous system (CNS), is widespread, and perhaps universal, among vertebrates. This phenomenon is more pronounced in teleost fish than in any other vertebrate taxon. There are up to 100 neurogenic sites in the adult teleost brain. New cells, including neurons and glia, arise from neural stem cells harbored both in neurogenic niches and outside these niches (such as the ependymal layer and parenchyma in the spinal cord, respectively). At least some, but not all, of the stem cells are of astrocytic identity. Aging appears to lead to stem cell attrition in fish that exhibit determinate body growth but not in those with indeterminate growth. At least in some areas of the CNS, the activity of the neural stem cells results in additive neurogenesis or gliogenesis - tissue growth by net addition of cells. Mathematical and computational modeling has identified three factors to be crucial for sustained tissue growth and correct formation of CNS structures: symmetric stem cell division, cell death and cell drift due to population pressure. It is hypothesized that neurogenesis in the CNS is driven by continued growth of corresponding muscle fibers and sensory receptor cells in the periphery to ensure a constant ratio of peripheral versus central elements. This 'numerical matching hypothesis' can explain why neurogenesis has ceased in most parts of the adult CNS during the evolution of mammals, which show determinate growth.

Building a (w)rapport between neurons and oligodendroglia: Reciprocal interactions underlying adaptive myelination

Myelin, multilayered lipid-rich membrane extensions formed by oligodendrocytes around neuronal axons, is essential for fast and efficient action potential propagation in the central nervous system. Initially thought to be a static and immutable process, myelination is now appreciated to be a dynamic process capable of responding to and modulating neuronal function throughout life. While the importance of this type of plasticity, called adaptive myelination, is now well accepted, we are only beginning to understand the underlying cellular and molecular mechanisms by which neurons communicate experience-driven circuit activation to oligodendroglia and precisely how changes in oligodendrocytes and their myelin refine neuronal function. Here, we review recent findings addressing this reciprocal relationship in which neurons alter oligodendroglial form and oligodendrocytes conversely modulate neuronal function.

Life-long oligodendrocyte development and plasticity

Oligodendrocyte precursor cells (OPCs) originate in localized germinal zones in the embryonic neural tube, then migrate and proliferate to populate the entire central nervous system, both white and gray matter. They divide and generate myelinating oligodendrocytes (OLs) throughout postnatal and adult life. OPCs express NG2 and platelet-derived growth factor receptor alpha subunit (PDGFRα), two functionally important cell surface proteins, which are also widely used as markers for OPCs. The proliferation of OPCs, their terminal differentiation into OLs, survival of new OLs, and myelin synthesis are orchestrated by signals in the local microenvironment. We discuss advances in our mechanistic understanding of paracrine effects, including those mediated through PDGFRα and neuronal activity-dependent signals such as those mediated through AMPA receptors in OL survival and myelination. Finally, we review recent studies supporting the role of new OL production and “adaptive myelination” in specific behaviours and cognitive processes contributing to learning and long-term memory formation. Our article is not intended to be comprehensive but reflects the authors’ past and present interests.

Intrinsic and Extrinsic Cell Apoptotic Pathways in Patients with HTLV-1-Associated Myelopathy/Tropical Spastic Paraparesis: A Systematic Review

We aimed to verify the influence of intrinsic and extrinsic cell apoptotic pathways on the inhibition of cellular apoptosis in patients with tropical spastic paralysis/myelopathy related to human T cell lymphotropic virus type 1. The databases accessed were PubMed, Scopus, Science Direct, and Web of Science. Neither the time of publishing nor the language of the articles was limited. The descriptors used for this systematic literature review were: Tropical Paraparesis, Proto-Oncogenic Protein C, Bcl-2, Bcl-X Protein, Bax protein, Fas ligand (FasL) protein, Fas receptor, TNF-related apoptosis-inducing ligand and Fas-associated protein with death domain (FADD)-like apoptosis regulating. The search resulted in 546 articles from which 9 articles were selected for analysis; ranging from serum levels of Bcl-2, Fas and tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) measured by enzyme-linked immunosorbent assay and the levels of cellular expression of Bcl-2 and Bcl-xL the TCD4+ lymphocytes accessed by western blot. Most studies accessed either gene expression or polymorphism of Fas, FasL, and TRAIL in patients with HTLV-1-associated myelopathy/tropical spastic paraparesis (HAM/TSP), whereas one study used flow cytometry and fluorescence to determine Fas expression. Increased Bcl-xL expression inhibited T lymphocyte apoptosis, whereas Bcl-2, serum levels, and cellular expression did not influence T lymphocyte apoptosis and serum levels of Fas were significantly higher and associated with markers of leukocyte activation in patients with HAM/TSP. In addition, Fas polymorphism (FAS-670AA) was associated with higher proviral load. There is a need for additional research on this issue since the number of patients was small and the studies presented higher heterogeneity.

Protective mechanism of kaempferol against Aβ25-35-mediated apoptosis of pheochromocytoma (PC-12) cells through the ER/ERK/MAPK signalling pathway

INTRODUCTION

Progressive accumulation of amyloid-β (Aβ) is a pathological trait of Alzheimer's disease (AD). Amyloid-β increases free radical production in neuronal cells, leading to neuronal cell death. Hormone replacement therapy can reduce the incidence of AD, and oestrogen significantly improves the clinical signs in patients with AD. However, the long-term use of oestrogen causes a variety of diseases. Phytoestrogens have been reported to bind and activate oestrogen receptors in mammals and humans to produce oestrogen-like or anti-oestrogen-like effects. Kaempferol is a flavonoid phytoestrogen that can produce a certain protective effect in neurons. However, the molecular mechanism of kaempferol in AD is unclear.

MATERIAL AND METHODS

This study used pheochromocytoma (PC-12) cells that were damaged by Aβ_25-35 as an in vitro model of AD, and oestradiol was a positive control. The cells were incubated with kaempferol alone or in combination with fulvestrant (an antagonist of ER) and U0126 (an inhibitor of ERK) in Aβ_25-35 culture. Cell activity was measured by the MTT method. Cell apoptosis was evaluated by flow cytometry. Gene and protein expression levels were tested by qRT-PCR and Western blotting.

RESULTS

This study demonstrated that kaempferol protected PC-12 cells from Aβ_25-35-induced cell death and apoptosis in a dose-dependent manner. Treatment with fulvestrant (an antagonist of ER) and U0126 (an inhibitor of ERK) significantly increased the apoptosis of PC-12 cells. Moreover, kaempferol promoted the expression of anti-apoptotic molecules and inhibited the expression of pro-apoptotic molecules, which were blocked by fulvestrant and U0126.

CONCLUSIONS

Kaempferol protected PC-12 cells against Aβ_25-35-induced cell apoptosis through the ER/ERK/MAPK signalling pathway.

Hepatic oxidative stress, up-regulation of pro-inflammatory cytokines, apoptotic and oncogenic markers following 2-methoxyethanol administrations in rats

2-methoxyethanol (2-ME) is an organic solvent widely used in the manufacture of brake fluids, paints, resins, varnish, nail polish, acetate cellulose, wood coloring, and as a plasticizer in plastics manufacturing. We therefore, investigated its effect on the liver, in a time-course study in male Wistar rats. Animals were orally administered 50 mg/kg body weight of 2-ME for a period of 7, 14, and 21 days. Following 7 days of administration of 2-ME, there was a significant increase in the level of Bax, c-Myc, K-Ras, TNF-α, IL-1β, IL-6, MDA and GPx activity, while the levels of Bcl-2, NO and GSH were significantly reduced compared with control. At the end of 14 days exposure, Bcl-2, and GSH levels, as well as GST activity, were significantly decreased, while levels of Bax, c-Myc, K-Ras, caspase-3, TNF-α, IL-1β, IL-6, MDA and NO were significantly increased compared with control. After 21 days of 2-ME administration, Bcl-2, IL-10, and GSH levels, as well as SOD and GST activities, were significantly decreased, while levels of Bax, c-Myc, K-Ras, caspase-3, p53, TNF-α, IL-1β, IL-6, MDA and NO were significantly increased compared with control. Lastly, liver histopathology confirmed and corroborated the biochemical findings reported above. We therefore, advised that exposures to 2-ME should be strictly avoided as it could trigger hepatic damage through the disorganization of the antioxidant system, up-regulation of inflammatory, apoptotic, and oncogenic markers in rats.

Role of glia in optic nerve

Glial cells are critically important for maintenance of neuronal activity in the central nervous system (CNS), including the optic nerve (ON). However, the ON has several unique characteristics, such as an extremely high myelination level of retinal ganglion cell (RGC) axons throughout the length of the nerve (with virtually all fibers myelinated by 7 months of age in humans), lack of synapses and very narrow geometry. Moreover, the optic nerve head (ONH) - a region where the RGC axons exit the eye - represents an interesting area that is morphologically distinct in different species. In many cases of multiple sclerosis (demyelinating disease of the CNS) vision problems are the first manifestation of the disease, suggesting that RGCs and/or glia in the ON are more sensitive to pathological conditions than cells in other parts of the CNS. Here, we summarize current knowledge on glial organization and function in the ON, focusing on glial support of RGCs. We cover both well-established concepts on the important role of glial cells in ON health and new findings, including novel insights into mechanisms of remyelination, microglia/NG2 cell-cell interaction, astrocyte reactivity and the regulation of reactive astrogliosis by mitochondrial fragmentation in microglia.

Targeting phosphatidylserine for Cancer therapy: prospects and challenges

Cancer is a leading cause of mortality and morbidity worldwide. Despite major improvements in current therapeutic methods, ideal therapeutic strategies for improved tumor elimination are still lacking. Recently, immunotherapy has attracted much attention, and many immune-active agents have been approved for clinical use alone or in combination with other cancer drugs. However, some patients have a poor response to these agents. New agents and strategies are needed to overcome such deficiencies. Phosphatidylserine (PS) is an essential component of bilayer cell membranes and is normally present in the inner leaflet. In the physiological state, PS exposure on the external leaflet not only acts as an engulfment signal for phagocytosis in apoptotic cells but also participates in blood coagulation, myoblast fusion and immune regulation in nonapoptotic cells. In the tumor microenvironment, PS exposure is significantly increased on the surface of tumor cells or tumor cell-derived microvesicles, which have innate immunosuppressive properties and facilitate tumor growth and metastasis. To date, agents targeting PS have been developed, some of which are under investigation in clinical trials as combination drugs for various cancers. However, controversial results are emerging in laboratory research as well as in clinical trials, and the efficiency of PS-targeting agents remains uncertain. In this review, we summarize recent progress in our understanding of the physiological and pathological roles of PS, with a focus on immune suppressive features. In addition, we discuss current drug developments that are based on PS-targeting strategies in both experimental and clinical studies. We hope to provide a future research direction for the development of new agents for cancer therapy.

Regulation of size and scale in vertebrate spinal cord development

All vertebrates have a spinal cord with dimensions and shape specific to their species. Yet how species‐specific organ size and shape are achieved is a fundamental unresolved question in biology. The formation and sculpting of organs begins during embryonic development. As it develops, the spinal cord extends in anterior–posterior direction in synchrony with the overall growth of the body. The dorsoventral (DV) and apicobasal lengths of the spinal cord neuroepithelium also change, while at the same time a characteristic pattern of neural progenitor subtypes along the DV axis is established and elaborated. At the basis of these changes in tissue size and shape are biophysical determinants, such as the change in cell number, cell size and shape, and anisotropic tissue growth. These processes are controlled by global tissue‐scale regulators, such as morphogen signaling gradients as well as mechanical forces. Current challenges in the field are to uncover how these tissue‐scale regulatory mechanisms are translated to the cellular and molecular level, and how regulation of distinct cellular processes gives rise to an overall defined size. Addressing these questions will help not only to achieve a better understanding of how size is controlled, but also of how tissue size is coordinated with the specification of pattern.

This article is categorized under:

Establishment of Spatial and Temporal Patterns > Regulation of Size, Proportion, and Timing

Signaling Pathways > Global Signaling Mechanisms

Nervous System Development > Vertebrates: General Principles

Revisiting the role of Dcc in visual system development with a novel eye clearing method

The Deleted in Colorectal Carcinoma (Dcc) receptor plays a critical role in optic nerve development. Whilst Dcc is expressed postnatally in the eye, its function remains unknown as Dcc knockouts die at birth. To circumvent this drawback, we generated an eye-specific Dcc mutant. To study the organization of the retina and visual projections in these mice, we also established EyeDISCO, a novel tissue clearing protocol that removes melanin allowing 3D imaging of whole eyes and visual pathways. We show that in the absence of Dcc, some ganglion cell axons stalled at the optic disc, whereas others perforated the retina, separating photoreceptors from the retinal pigment epithelium. A subset of visual axons entered the CNS, but these projections are perturbed. Moreover, Dcc-deficient retinas displayed a massive postnatal loss of retinal ganglion cells and a large fraction of photoreceptors. Thus, Dcc is essential for the development and maintenance of the retina.

The protective and therapeutic effects of vinpocetine, a PDE1 inhibitor, on oxidative stress and learning and memory impairment induced by an intracerebroventricular (ICV) injection of amyloid beta (aβ) peptide

Alzheimer's disease (AD) is a neurodegenerative disease leading to cognitive and memory impairment. This study aimed at investigating the therapeutic and preserving effects of vinpocetine on amyloid beta (Aβ)-induced rat model of AD. Sixty male adult Wistar rats were randomly divided into 6 groups (n = 10 per group) as follows: 1; control, 2; sham, 3; Aβ, 4; pre-treatment (vinpocetine + Aβ): oral gavage administration of vinpocetine at 4 mg/kg for 30 days followed by intracerebroventricular (ICV) injection of Aβ, 5; treatment (Aβ + vinpocetine): Aβ ICV injection followed by vinpocetine administration for 30 days, 6; pre-treatment + treatment (vinpocetine + Aβ + vinpocetine): vinpocetine administration for 30 days before and 30 days after AD induction. Following treatments, the animals' learning and memory were investigated using passive avoidance learning (PAL) task, Morris water maze (MWM), and novel object recognition (NOR) tests. The results demonstrated that Aβ significantly enhanced escape latency and the distance traveled in the MWM, decreased step-through latency, and increased time spent in the dark compartment in PAL. Vinpocetine ameliorated the Aβ-infused memory deficits in both MWM and PAL tests. Administration of vinpocetine in the Aβ rats increased the discrimination index of the NOR test. It also significantly diminished the nitric oxide and malondialdehyde levels and restored the reduced glutathione (GSH) levels. Vinpocetine can improve memory and learning impairment following Aβ infusion due to its different properties, including antioxidant effects, which indicates that vinpocetine administration can lead to the amelioration of cognitive dysfunction in AD.

Topographical profiles of macula and optic nerve head in concomitant strabismus patients as measured using OCT and CSLO

PURPOSE

Investigate morphological changes of macula and optic nerve head (ONH) in concomitant strabismic patients using optical coherence tomography (OCT) and confocal scanning laser ophthalmoscopy (CSLO).

METHODS

A cross-sectional study conducted from April 2017 to February 2018 at the Zhongshan Ophthalmic Center, Sun Yat-sen University. Spectral-domain (SD)-OCT and CSLO were used to observe morphological changes of macula and ONH in concomitant strabismic patients with normal vision and healthy controls. In each subject, a 6-mm diameter zone centered at the fovea was scanned and topographical images of the ONH and peripapillary retina were generated. Fundus parameters were recorded and analyzed.

RESULTS

A total of 138 cases, including 29 patients with concomitant esotropia (ET), 38 constant exotropia (XT), 42 intermittent exotropia (IXT), and 29 healthy controls, were recruited. Compared with controls, OCT revealed that the thickness of nasal intraretinal layers (IRLs) in ET patients was significantly increased, particularly in ganglion cell layer (GCL) and inner nuclear layer (INL). In XT patients, the temporal half of outer retinal layers (ORLs) showed significant increases in thickness. CSLO findings revealed significant changes in the ONH of ET patients consisting of a thinner retinal nerve fiber layer (RNFL) and a decreased RNFL cross-sectional area, height variation contour, maximum contour depression, and contour line modulation (CLM) temporal-superior area. The nasal-superior cup area and rim volume in XT patients were significantly increased.

CONCLUSION

Topographical profiles of the macula and ONH in concomitant strabismic patients with normal vision present with specific regularities.

Developmental cell death regulates lineage-related interneuron-oligodendroglia functional clusters and oligodendrocyte homeostasis

The first wave of oligodendrocyte precursor cells (firstOPCs) and most GABAergic interneurons share common embryonic origins. Cortical firstOPCs are thought to be replaced by other OPC populations shortly after birth, maintaining a consistent OPC density and making postnatal interactions between firstOPCs and ontogenetically-related interneurons unlikely. Challenging these ideas, we show that a cortical firstOPC subpopulation survives and forms functional cell clusters with lineage-related interneurons. Favored by a common embryonic origin, these clusters display unexpected preferential synaptic connectivity and are anatomically maintained after firstOPCs differentiate into myelinating oligodendrocytes. While the concomitant rescue of interneurons and firstOPCs committed to die causes an exacerbated neuronal inhibition, it abolishes interneuron-firstOPC high synaptic connectivity. Further, the number of other oligodendroglia populations increases through a non-cell-autonomous mechanism, impacting myelination. These findings demonstrate unprecedented roles of interneuron and firstOPC apoptosis in regulating lineage-related cell interactions and the homeostatic oligodendroglia density.

During cortical development the first wave of oligodendrocyte precursor cells (OPCs) completely disappear by programmed cell death, so that it is presumed that this OPC population does not play a role at postnatal stages. In this study, authors use lineage tracing in different transgenic mice to show that a subpopulation of OPCs from the first wave survives at postnatal stages and display a preferential synaptic connectivity with their ontogenetically-related interneurons compared to other OPCs or interneurons

Developmental Cell Death in the Cerebral Cortex

In spite of the high metabolic cost of cellular production, the brain contains only a fraction of the neurons generated during embryonic development. In the rodent cerebral cortex, a first wave of programmed cell death surges at embryonic stages and affects primarily progenitor cells. A second, larger wave unfolds during early postnatal development and ultimately determines the final number of cortical neurons. Programmed cell death in the developing cortex is particularly dependent on neuronal activity and unfolds in a cell-specific manner with precise temporal control. Pyramidal cells and interneurons adjust their numbers in sync, which is likely crucial for the establishment of balanced networks of excitatory and inhibitory neurons. In contrast, several other neuronal populations are almost completely eliminated through apoptosis during the first two weeks of postnatal development, highlighting the importance of programmed cell death in sculpting the mature cerebral cortex.

Small molecules enhance neurogenic differentiation of dental-derived adult stem cells

OBJECTIVE

Dental-derived stem cells originate from the embryonic neural crest, and exhibit high neurogenic potential. This study aimed to investigate whether a cocktail of eight small molecules (Valproic acid, CHIR99021, Repsox, Forskolin, SP600125, GO6983, Y-27632 and Dorsomorphin) can enhance the in vitro neurogenic differentiation of dental pulp stem cells (DPSCs), stem cells from apical papilla (SCAPs) and gingival mesenchymal stem cells (GMSCs), as a preliminary step towards clinical applications.

MATERIALS AND METHODS

Neural induction was carried out with a small molecule cocktail based two-step culture protocol, over a total duration of 14 days. At the 8 and 14 day timepoints, the cells were analyzed for expression of neural markers with immunocytochemistry, qRT-PCR and Western Blot. The Fluo 4-AM calcium flux assay was also performed after a further 14 days of neural maturation.

RESULTS

More pronounced morphological changes characteristic of the neural lineage (i.e. neuritogenesis) were observed in all three cell types treated with small molecules, as compared to the untreated controls. This was corroborated by the immunocytochemistry, qRT-PCR and western blot data, which showed upregulated expression of several early and mature neural markers in all three cell types treated with small molecules, versus the corresponding untreated controls. Finally, the Fluo-4 AM calcium flux assay showed consistently higher calcium transient (F/F_o) peaks for the small molecule-treated versus untreated control groups.

CONCLUSIONS

Small molecules can enhance the neurogenic differentiation of DPSCs, SCAPs and GMSCs, which offer much potential for therapeutic applications.

Optogenetic Stimulation of the Superior Colliculus Confers Retinal Neuroprotection in a Mouse Glaucoma Model

Glaucoma is characterized by a progressive loss of retinal ganglion cells (RGCs) in the eye, which ultimately results in visual impairment or even blindness. Because current therapies often fail to halt disease progression, there is an unmet need for novel neuroprotective therapies to support RGC survival. Various research lines suggest that visual target centers in the brain support RGC functioning and survival. Here, we explored whether increasing neuronal activity in one of these projection areas could improve survival of RGCs in a mouse glaucoma model. Prolonged activation of an important murine RGC target area, the superior colliculus (SC), was established via a novel optogenetic stimulation paradigm. By leveraging the unique channel kinetics of the stabilized step function opsin (SSFO), protracted stimulation of the SC was achieved with only a brief light pulse. SSFO-mediated collicular stimulation was confirmed by immunohistochemistry for the immediate-early gene c-Fos and behavioral tracking, which both demonstrated consistent neuronal activity upon repeated stimulation. Finally, the neuroprotective potential of optogenetic collicular stimulation was investigated in mice of either sex subjected to a glaucoma model and a 63% reduction in RGC loss was found. This work describes a new paradigm for optogenetic collicular stimulation and a first demonstration that increasing target neuron activity can increase survival of the projecting neurons.SIGNIFICANCE STATEMENT Despite glaucoma being a leading cause of blindness and visual impairment worldwide, no curative therapies exist. This study describes a novel paradigm to reduce retinal ganglion cell (RGC) degeneration underlying glaucoma. Building on previous observations that RGC survival is supported by the target neurons to which they project and using an innovative optogenetic approach, we increased neuronal activity in the mouse superior colliculus, a main projection target of rodent RGCs. This proved to be efficient in reducing RGC loss in a glaucoma model. Our findings establish a new optogenetic paradigm for target stimulation and encourage further exploration of the molecular signaling pathways mediating retrograde neuroprotective communication.

Targeted Oligodendrocyte Apoptosis in Optic Nerve Leads to Persistent Demyelination

The optic nerve represents one of the simplest regions of the CNS and has been useful in developing an understanding of glial development and myelination. While the visual system is frequently affected in demyelinating conditions, utilizing the optic nerve to model demyelination/remyelination studies has been difficult due to its accessibility, relatively small size, and dense nature that makes direct injections challenging. Taking advantage of the lack of oligodendrocytes and myelination in the mouse retina, we have developed a model in which the induction of apoptosis in mature oligodendrocytes allows for the selective, non-invasive generation of demyelinating lesions in optic nerve. Delivery of an inducer of oligodendrocyte apoptosis by intravitreous injection minimizes trauma to the optic nerve and allows for the assessment of oligodendrocyte death in the absence of injury related factors. Here we show that following induction of apoptosis, oligodendrocytes are lost within 3 days. The loss of oligodendrocytes is associated with limited microglial and astrocyte response, is patchy along the nerve, and results in localized myelin loss. Unlike in other regions of the murine CNS, where local demyelination stimulates activation of local oligodendrocyte precursors and remyelination, optic nerve demyelination induced by oligodendrocyte apoptosis fails to recover and results in persistent areas of myelin loss. Over time these chronic lesions change cellular composition and ultimately become devoid of GFAP+ astrocytes and OPCs. Why the optic nerve lesions fail to repair may reflect the lack of early immune responsiveness and provide a novel model of chronic demyelination.

Acute N-Acetylcysteine Administration Ameliorates Loss of Olfactory Neurons Following Experimental Injury In Vivo

The olfactory epithelium (OE) is the peripheral organ for the sense of smell, housing primary sensory neurons that project axons from the nose to the brain. Due to the presence of a basal stem cell niche, the adult mammalian OE is a dynamic tissue capable of replacing neurons following their loss. Nonetheless, certain conditions, such as blunt head trauma, can result in persistent olfactory loss, thought to be due to shearing of olfactory nerve filaments at the skull base, degeneration, and failures in proper regeneration/reinnervation. The identification of new treatment strategies aimed at preventing degeneration of olfactory neurons is, therefore, needed. In considering potential therapies, we have focused on N-acetylcysteine (NAC), a glutathione substrate shown to be neuroprotective, with a record of safe clinical use. Here, we have tested the use of NAC in an animal model of olfactory degeneration. Administered acutely, we found that NAC (100 mg/kg, twice daily) resulted in a reduction of olfactory neuronal loss from the OE of the nose following surgical ablation of the olfactory bulb. At 1 week postlesion, we identified 54 ± 8.1 mature neurons per 0.5 mm epithelium in NAC-treated animals vs. 28 ± 4.2 in vehicle-treated controls (P = 0.02). Furthermore, in an olfactory cell culture model, we have identified significant alterations in the expression of several genes involved in oxidative stress pathways following NAC exposure. Our results provide evidence supporting the potential therapeutic utility for NAC acutely following head trauma-induced olfactory loss. Anat Rec, 303:626-633, 2020. © 2019 American Association for Anatomy.

Spatiotemporal Control of CNS Myelination by Oligodendrocyte Programmed Cell Death through the TFEB-PUMA Axis

Nervous system function depends on proper myelination for insulation and critical trophic support for axons. Myelination is tightly regulated spatially and temporally, but how it is controlled molecularly remains largely unknown. Here, we identified key molecular mechanisms governing the regional and temporal specificity of CNS myelination. We show that transcription factor EB (TFEB) is highly expressed by differentiating oligodendrocytes and that its loss causes precocious and ectopic myelination in many parts of the murine brain. TFEB functions cell-autonomously through PUMA induction and Bax-Bak activation to promote programmed cell death of a subset of premyelinating oligodendrocytes, allowing selective elimination of oligodendrocytes in normally unmyelinated brain regions. This pathway is conserved across diverse brain areas and is critical for myelination timing. Our findings define an oligodendrocyte-intrinsic mechanism underlying the spatiotemporal specificity of CNS myelination, shedding light on how myelinating glia sculpt the nervous system during development.

Physical exercise enhances adult cortical plasticity in a neonatal rat model of hypoxic-ischemic injury: Evidence from BOLD-fMRI and electrophysiological recordings

Neuroplasticity is considered essential for recovery from brain injury in developing brains. Recent studies indicate that it is especially effective during early postnatal development and during the critical period. The current study used functional magnetic resonance imaging (fMRI) and local field potential (LFP) electrophysiological recordings in rats that experienced neonatal hypoxic-ischemic (HI) injury during the critical period to demonstrate that physical exercise (PE) can improve cortical plasticity even when performed during adulthood, after the critical period. We investigated to what extent the blood oxygen level-dependent (BOLD)-fMRI responses were increased in the contralesional spared cortex, and how these increases were related to the LFP electrophysiological measurements and the functional outcome. The balance of excitation and inhibition was assessed by measuring excitatory and inhibitory postsynaptic currents in stellate cells in the primary somatosensory (S1) cortex, which was compared with the BOLD-fMRI responses in the contralesional S1 cortex. The ratio of inhibitory postsynaptic current (IPSC) to excitatory postsynaptic current (EPSC) at the thalamocortical (TC) input to the spared S1 cortex was significantly increased by PE, which is consistent with the increased BOLD-fMRI responses and improved functional outcome. Our data clearly demonstrate in an experimental rat model of HI injury during the critical period that PE in adulthood enhances neuroplasticity and suggest that enhanced feed-forward inhibition at the TC input to the S1 cortex might underlie the PE-induced amelioration of the somatosensory deficits caused by the HI injury. In summary, the results of the current study indicate that PE, even if performed beyond the critical period or during adulthood, can be an effective therapy to treat neonatal brain injuries, providing a potential mechanism for the development of a potent rehabilitation strategy to alleviate HI-induced neurological impairments.

Injectable Neurotrophic Factor Delivery System Supporting Retinal Ganglion Cell Survival and Regeneration Following Optic Nerve Crush

In general, neurons belonging to the central nervous system (CNS), such as retinal ganglion cells (RGCs), do not regenerate. Due to this, strategies have emerged aimed at protecting and regenerating these cells. Neurotrophic factor (NTF) supplementation has been a promising approach but is limited by length of delivery and delivery vehicle. For this study, we tested a polymeric delivery system (sulfonated reverse thermal gel or SRTG) engineered to deliver cilliary neurotrophic factor (CNTF), while also being injectable. A rat optic nerve crush (ONC) model was used to determine the neuroprotective and regenerative capacity of our system. The results demonstrate that one single intravitreal injection of SRTG-CNTF following ONC showed significant protection of RGC survival at both 1 and 2 week time points, when compared to the control groups. Furthermore, there was no significant difference in the RGC count between the eyes that received the SRTG-CNTF following ONC and a healthy control eye. Intravitreal injection of the polymer system also induced noticeable axon regeneration 500 μm downstream from the lesion site compared to all other control groups. There was a significant increase in Müller cell response in groups that received the SRTG-CNTF injection following optic nerve crush also indicative of a regenerative response. Finally, higher concentrations of CNTF released from SRTG-CNTF showed a protective effect on RGCs and Müller cell response at a longer time point (4 weeks). In conclusion, we were able to show a neuroprotective and regenerative effect of this polymer SRTG-CNTF delivery system and the viability for treatment of neurodegenerations.

Multifarious Biologic Loaded Liposomes that Stimulate the Mammalian Target of Rapamycin Signaling Pathway Show Retina Neuroprotection after Retina Damage

A common event in optic neuropathies is the loss of axons and death of retinal ganglion cells (RGCs) resulting in irreversible blindness. Mammalian target of rapamycin (mTOR) signaling pathway agonists have been shown to foster axon regeneration and RGC survival in animal models of optic nerve damage. However, many challenges remain in developing therapies that exploit cell growth and tissue remodeling including (i) activating/inhibiting cell pathways synergistically, (ii) avoiding tumorigenesis, and (iii) ensuring appropriate physiological tissue function. These challenges are further exacerbated by the need to overcome ocular physiological barriers and clearance mechanisms. Here we present liposomes loaded with multiple mTOR pathway stimulating biologics designed to enhance neuroprotection after retina damage. Liposomes were loaded with ciliary neurotrophic factor, insulin-like growth factor 1, a lipopeptide N-fragment osteopontin mimic, and lipopeptide phosphatase tension homologue inhibitors for either the ATP domain or the c-terminal tail. In a mouse model of N-methyl-d-aspartic acid induced RGC death, a single intravitreal administration of liposomes reduced both RGC death and loss of retina electrophysiological function. Furthermore, combining liposomes with transplantation of induced pluripotent stem cell derived RGCs led to an improved electrophysiological outcome in mice. The results presented here show that liposomes carrying multiple signaling pathway modulators can facilitate neuroprotection and transplant electrophysiological outcome.

Progress in Gene Therapy to Prevent Retinal Ganglion Cell Loss in Glaucoma and Leber's Hereditary Optic Neuropathy

The eye is at the forefront of the application of gene therapy techniques to medicine. In the United States, a gene therapy treatment for Leber's congenital amaurosis, a rare inherited retinal disease, recently became the first gene therapy to be approved by the FDA for the treatment of disease caused by mutations in a specific gene. Phase III clinical trials of gene therapy for other single-gene defect diseases of the retina and optic nerve are also currently underway. However, for optic nerve diseases not caused by single-gene defects, gene therapy strategies are likely to focus on slowing or preventing neuronal death through the expression of neuroprotective agents. In addition to these strategies, there has also been recent interest in the potential use of precise genome editing techniques to treat ocular disease. This review focuses on recent developments in gene therapy techniques for the treatment of glaucoma and Leber's hereditary optic neuropathy (LHON). We discuss recent successes in clinical trials for the treatment of LHON using gene supplementation therapy, promising neuroprotective strategies that have been employed in animal models of glaucoma and the potential use of genome editing techniques in treating optic nerve disease.

Pyramidal cell regulation of interneuron survival sculpts cortical networks

Complex neuronal circuitries such as those found in the mammalian cerebral cortex have evolved as balanced networks of excitatory and inhibitory neurons. Although the establishment of appropriate numbers of these cells is essential for brain function and behaviour, our understanding of this fundamental process is limited. Here we show that the survival of interneurons in mice depends on the activity of pyramidal cells in a critical window of postnatal development, during which excitatory synaptic input to individual interneurons predicts their survival or death. Pyramidal cells regulate interneuron survival through the negative modulation of PTEN signalling, which effectively drives interneuron cell death during this period. Our findings indicate that activity-dependent mechanisms dynamically adjust the number of inhibitory cells in nascent local cortical circuits, ultimately establishing the appropriate proportions of excitatory and inhibitory neurons in the cerebral cortex.

Neuronal Homeostasis in Mammalian Olfactory Epithelium: A Review

The neuronal lineage of the olfactory epithelium (OE) is a cell lineage that includes the neuronal stem cell and its progeny (ultimately the mature olfactory receptor neuron [ORN]). Recent studies, including further characterization of the neuronal lineage of the OE, and of factors that influence proliferation, survival, and death of cells of this lineage, have contributed significantly to understanding of neuronal homeostasis, i.e., normal maintenance of neuronal number, in mammalian OE. Our recent studies indicate that in adult mice, all cell types of the neuronal lineage of the OE—neuronal precursors, immature ORNs and mature ORNs—undergo constitutive death, i.e., a normal, basal level of cell death, that is characteristic of programmed cell death or apoptosis. To some extent, constitutive cell death in this lineage may reflect random environmental insults; however, this may also be the result of an ongoing developmental program that acts to control both numbers and phenotypic organization of olfactory neurons. Although a variety of extrinsic and intrinsic factors are likely to contribute to cell death in the neuronal lineage of the OE, most have not been thoroughly studied. Detailed analysis of one of these factors, effects of target deprivation, suggests that survival of individual cell types of the neuronal lineage of the OE may be differentially regulated with mature ORNs, but not immature ORNs or neuronal precursors, dependent upon the olfactory bulb for their survival. Factors normally provided to cells of the ORN lineage, as in other neuronal systems, are likely to promote survival by inhibiting an endogenous genetic program of cell death. Whether candidate polypeptide growth factors, e.g., the neurotrophins, or other pharmacological inhibitors of apoptosis will eventually play a role in the treatment of specific anosmias remains to be determined.

Rough Titanium Oxide Coating Prepared by Micro-Arc Oxidation Causes Down-Regulation of hTERT Expression, Molecular Presentation, and Cytokine Secretion in Tumor Jurkat T Cells

The response of the human Jurkat T cell leukemia-derived cell line (Jurkat T cells) after 24 h of in vitro exposure to a titanium substrate (12 × 12 × 1 mm³) with a bilateral rough (R_a = 2.2–3.7 μm) titanium oxide coating (rTOC) applied using the micro-arc method in a 20% orthophosphoric acid solution was studied. A 1.5-fold down-regulation of hTERT mRNA expression and decreases in CD3, CD4, CD8, and CD95 presentation and IL-4 and TNFα secretion were observed. Jurkat T cell inactivation was not correlated with the generation of intracellular reactive oxygen species (ROS) and was not mediated by TiO₂ nanoparticles with a diameter of 14 ± 8 nm at doses of 1 mg/L or 10 mg/L. The inhibitory effect of the rTOC (R_a = 2.2–3.7 μm) on the survival of Jurkat T cells (Spearman’s coefficient r_s = −0.95; n = 9; p < 0.0001) was demonstrated by an increase in the necrotic cell count among the cell population. In turn, an elevation of the Ra index of the rTOC was accompanied by a linear increase (r = 0.6; p < 0.000001, n = 60) in the magnitude of the negative electrostatic potential of the titanium oxide surface. Thus, the roughness of the rTOC induces an electrostatic potential and decreases the viability of the immortalized Jurkat T cells through mechanisms unrelated to ROS generation. This may be useful for replacement surgery applications of rough TiO₂ implants in cancer patients.

Restorative effects of human neural stem cell grafts on the primate spinal cord

We grafted human spinal cord-derived neural progenitor cells (NPCs) into sites of cervical spinal cord injury in rhesus monkeys (Macaca mulatta). Under three-drug immunosuppression, grafts survived at least 9 months postinjury and expressed both neuronal and glial markers. Monkey axons regenerated into grafts and formed synapses. Hundreds of thousands of human axons extended out from grafts through monkey white matter and synapsed in distal gray matter. Grafts gradually matured over 9 months and improved forelimb function beginning several months after grafting. These findings in a 'preclinical trial' support translation of NPC graft therapy to humans with the objective of reconstituting both a neuronal and glial milieu in the site of spinal cord injury.

The STAT3/NFIL3 signaling axis-mediated chemotherapy resistance is reversed by Raddeanin A via inducing apoptosis in choriocarcinoma cells

Chemotherapy resistance is the major issue of choriocarcinoma. Apoptosis always is the ultimate outcome of chemotherapeutic drugs, which considered one of the reasons of resistance. We investigated the role of STAT3/NFIL3 signaling‐inhibited apoptosis in chemotherapy resistance and whether Raddeanin A (RA) could be a new drug to reverse resistance. Established three drug‐resistant cell lines as JEG‐3/MTX, JEG‐3/5‐FU, and JEG‐3/VP16. NFIL3 and STAT3 expression was evaluated in the cells. The IC₅₀ value, apoptosis rate and apoptins were observed with transfection of siNFIL3, Lenti‐OE™‐NFIL3, shSTAT3, and Lenti‐OE™‐STAT3 or RA treatment. In addition, the luciferase reporter analysis and co‐immunoprecipitation assays were used to investigate the relation of STAT3 and NFIL3. Hyper‐activation of STAT3 and NFIL3 expression were observed in three drug‐resistant cell lines. STAT3 enhanced NFIL3 transcriptional activity by binding the relative promoter region. Activated STAT3/NFIL3 pathway caused low rate of apoptosis which resulted in chemotherapy resistance. RA reduced the resistance index of resistant cells and induced caspase 3 dependent apoptosis, meanwhile it repressed the STAT3/NFIL3 activation. STAT3/NFIL3 axis‐inhibited apoptosis is a novel mechanism of chemotherapy resistance in choriocarcinoma. With the suppression of STAT3/NFIL3 axis and apoptosis induction, RA is a potential agent or lead candidate for improving chemotherapy.