Miguel A. Gama Sosa

Blast Exposure Induces Post-Traumatic Stress Disorder-Related Traits in a Rat Model of Mild Traumatic Brain Injury

Blast related traumatic brain injury (TBI) has been a major cause of injury in the wars in Iraq and Afghanistan. A striking feature of the mild TBI (mTBI) cases has been the prominent association with post-traumatic stress disorder (PTSD). However, because of the overlapping symptoms, distinction between the two disorders has been difficult. We studied a rat model of mTBI in which adult male rats were exposed to repetitive blast injury while under anesthesia. Blast exposure induced a variety of PTSD-related behavioral traits that were present many months after the blast exposure, including increased anxiety, enhanced contextual fear conditioning, and an altered response in a predator scent assay. We also found elevation in the amygdala of the protein stathmin 1, which is known to influence the generation of fear responses. Because the blast overpressure injuries occurred while animals were under general anesthesia, our results suggest that a blast-related mTBI exposure can, in the absence of any psychological stressor, induce PTSD-related traits that are chronic and persistent. These studies have implications for understanding the relationship of PTSD to mTBI in the population of veterans returning from the wars in Iraq and Afghanistan.

Selective expression of presenilin 1 in neural progenitor cells rescues the cerebral hemorrhages and cortical lamination defects in presenilin 1-null mutant mice

Mice with a null mutation of the presenilin 1 gene (Psen1–/–) die during late intrauterine life or shortly after birth and exhibit multiple CNS and non-CNS abnormalities, including cerebral hemorrhages and altered cortical development. The cellular and molecular basis for the developmental effects of Psen1 remain incompletely understood. Psen1 is expressed in neural progenitors in developing brain, as well as in postmitotic neurons. We crossed transgenic mice with either neuron-specific or neural progenitor-specific expression of Psen1 onto the Psen1–/– background. We show that neither neuron-specific nor neural progenitor-specific expression of Psen1 can rescue the embryonic lethality of the Psen1–/– embryo. Indeed neuron-specific expression rescued none of the abnormalities in Psen1–/– mice. However, Psen1 expression in neural progenitors rescued the cortical lamination defects, as well as the cerebral hemorrhages, and restored a normal vascular pattern in Psen1–/– embryos. Collectively, these studies demonstrate that Psen1 expression in neural progenitor cells is crucial for cortical development and reveal a novel role for neuroectodermal expression of Psen1 in development of the brain vasculature.

Molecular basis of late-life globoid cell leukodystrophy

Globoid cell leukodystrophy is an autosomal recessive inherited disease caused by deficiency of the lysosomal enzyme galactocerebrosidase (GALC). Although the severe, rapidly progressing infantile form is the most common, late‐onset forms have been described. We investigated the molecular basis of GALC deficiency in a patient with a late‐life mild form of globoid cell leukodystrophy who survived into the eighth decade. Since material suitable for mutation analysis was no longer available from the proband, her GALC genotype was reconstructed by analyzing this gene in her six obligate carrier offspring. One allele contained the mutation 809G>A (G270D) in the 1637C background, while the other allele contained three sequence variants: 1609G>A (G537R), 1873G>A (A625T), and 1650T>A (V550V) in the 1637T background. These mutations were confirmed in the probands genomic DNA isolated from a sural nerve biopsy. Expression studies indicated that the G537R is a disease‐causing mutation, as it resulted in no GALC activity, either alone or together with the A625T. This A625T sequence variant did not affect the enzyme activity, at least when expressed in the 1637T background. The mild clinical phenotype was likely to be associated with the 809G>A, since residual GALC activity, about 17% of the control activity, was detected in the expression studies of this mutation. This mutation has been found in several other patients with late‐onset GLD. Hum Mutat 14:256–262, 1999.

CORRELATION OF GLIOMA CELL REGRESSION WITH INHIBITION OF INSULIN-LIKE GROWTH FACTOR 1 AND INSULIN-LIKE GROWTH FACTOR-BINDING PROTEIN-2 EXPRESSION

To explore the antitumor effect of insulin-like growth factor 1 (IGF-I) antisense RNA and the interaction of IGF-I with insulin-like growth factor-binding proteins (IGFBPs) in glioma cells, a recombinant retrovirus expressing IGF-I antisense RNA was constructed and introduced into C6 glioma cells. IGF-I antisense RNA reverses the transformed phenotype in glioma cells and inhibits glioma cell growth by blocking overexpression of endogenous IGF-I. Expression of IGFBP-2 is increased in glioma cells as compared with normal adult glial cells. IGF-I antisense RNA also inhibits expression of IGFBP-2 in glioma cells, but does not influence expression of the other IGFBPs. Although IGFBP-2 in conditioned medium from wild-type C6 cell cultures itself does not directly influence glioma cell growth, it synergistically enhances exogenous IGF-I-mediated DNA synthesis in IGF-I-negative C6 cells. These findings indicate the inhibitory effect of IGF-I antisense RNA on growth and development of glioma cells. IGF-I-dependent glioma cell growth may, in some circumstances, require IGFBP-2 as a cofactor. The antitumor effect of IGF-I antisense RNA is also associated with inhibition of IGFBP-2 expression.

5-Fluorocytosine-mediated apoptosis and DNA damage in glioma cells engineered to express cytosine deaminase and their enhancement with interferon

To explore the antitumor mechanism of bacterial cytosine deaminase plus 5-fluorocytosine (CD/5-FCyt) in combination with interferons (IFNs), glioma cells were transduced with recombinant retroviruses expressing CD. The transduced glioma cells become sensitive to the nontoxic prodrug 5-FCyt. Apoptosis, DNA damage, bystander effect, and inhibition of thymidylate synthase (TS) and DNA synthesis are associated with CD/5-FCyt-mediated glioma cell killing. Furthermore, IFNs enhance this effect by increasing DNA damage and further inhibiting TS activity. The bystander effect is mediated by the release of cytotoxic metabolites of 5-FCyt into the extracellular milieu triggering apoptosis and DNA damage. Our data indicate that the use of CD/5-FCyt in combination with IFNs may provide a more effective approach for the treatment of brain tumors.

Chronic post-traumatic stress disorder-related traits in a rat model of low-level blast exposure

HighlightsBlast‐related traumatic brain injury (TBI) has been common in veterans of the recent conflicts in Iraq and Afghanistan.Blast‐related mild TBI (mTBI) has been frequently associated with post‐traumatic stress disorder (PTSD).Rats exposed to repetitive low‐level blast develop PTSD‐like behavioral traits in the absence of a psychological stressor.The presence of such traits 28–35 weeks after blast exposure suggests that blast induces chronic behavioral effects.These observations have implications for understanding the relationship of mTBI to PTSD in dual diagnosis veterans. ABSTRACT The postconcussion syndrome following mild traumatic brain injuries (mTBI) has been regarded as a mostly benign syndrome that typically resolves in the immediate months following injury. However, in some individuals, symptoms become chronic and persistent. This has been a striking feature of the mostly blast‐related mTBIs that have been seen in veterans returning from the recent conflicts in Iraq and Afghanistan. In these veterans a chronic syndrome with features of both the postconcussion syndrome and post‐traumatic stress disorder has been prominent. Animal modeling of blast‐related TBI has developed rapidly over the last decade leading to advances in the understanding of blast pathophysiology. However, most studies have focused on acute to subacute effects of blast on the nervous system and have typically studied higher intensity blast exposures with energies more comparable to that involved in human moderate to severe TBI. Fewer animal studies have addressed the chronic effects of lower level blast exposures that are more comparable to those involved in human mTBI or subclinical blast. Here we describe a rat model of repetitive low‐level blast exposure that induces a variety of anxiety and PTSD‐related behavioral traits including exaggerated fear responses that were present when animals were tested between 28 and 35 weeks after the last blast exposure. These animals provide a model to study the chronic and persistent behavioral effects of blast including the relationship of PTSD to mTBI in dual diagnosis veterans.

Presenilin 1 is necessary for neuronal, but not glial, EGFR expression and neuroprotection via γ-secretase-independent transcriptional mechanisms

Epidermal growth factor receptor (EGFR) plays pivotal roles in cell proliferation, differentiation, and tissue development, while EGFs protect neurons from toxic insults by binding EGFR and stimulating survival signaling. Furthermore, recent evidence implicates this receptor in neurometabolic disorders like Alzheimer disease and aging. Here we show that absence of presenilin 1 (PS1) results in dramatic decrease (>95%) of neuronal EGFR and that PS1‐null (PS1‐/‐) brains have reduced amounts of this receptor. PS1‐/‐ cortical neurons contain little EGFR and show no epidermal growth factor‐induced survival signaling or protection against excitotoxicity, but exogenous EGFR rescues both functions even in absence of PS1. EGFR mRNA is greatly reduced (>95%) in PS1‐/‐neurons, and PS1‐/‐ brains contain decreased amounts of this mRNA, although PS1 affects the stability of neither EGFR nor its mRNA. Exogenous PS1 increases neuronal EGFR mRNA, while down‐regulation of PS1 decreases this mRNA. These effects are neuron specific, as PS1 affects the EGFR of neither glial nor fibroblast cells. In addition, PS1 controls EGFR through novel mechanisms shared with neither γ‐secretase nor PS2. Our data reveal that PS1 functions as a positive transcriptional regulator of neuronal EGFR controlling its expression in a cell‐specific manner. Severe downregulation of EGFR may contribute to developmental abnormalities and lethal phenotype found in PS1, but not PS2, null mice. Furthermore, PS1 may affect neuroprotection and Alzheimer disease by controlling survival signaling of neuronal EGFR.—Bruban, J., Voloudakis, G., Huang, Q., Kajiwara, Y., Al Rahim, M., Yoon, Y., Shioi,J., Gama Sosa, M. A., Shao, Z., Georgakopoulos, A., Robakis, N. K. Presenilin 1 is necessary for neuronal, but not glial, EGFR expression and neuroprotection via 7‐secretase‐independent transcriptional mechanisms. FASEB J. 29, 3702‐3712 (2015). www.fasebj.org

Fibroblast growth factor rescues brain endothelial cells lacking presenilin 1 from apoptotic cell death following serum starvation.

Presenilin 1 (Psen1) is important for vascular brain development and is known to influence cellular stress responses. To understand the role of Psen1 in endothelial stress responses, we investigated the effects of serum withdrawal on wild type (wt) and Psen1−/− embryonic brain endothelial cells. Serum starvation induced apoptosis in Psen1−/− cells but did not affect wt cells. PI3K/AKT signaling was reduced in serum-starved Psen1−/− cells, and this was associated with elevated levels of phospho-p38 consistent with decreased pro-survival AKT signaling in the absence of Psen1. Fibroblast growth factor (FGF1 and FGF2), but not vascular endothelial growth factor (VEGF) rescued Psen1−/− cells from serum starvation induced apoptosis. Inhibition of FGF signaling induced apoptosis in wt cells under serum withdrawal, while blocking γ-secretase activity had no effect. In the absence of serum, FGF2 immunoreactivity was distributed diffusely in cytoplasmic and nuclear vesicles of wt and Psen1−/− cells, as levels of FGF2 in nuclear and cytosolic fractions were not significantly different. Thus, sensitivity of Psen1−/− cells to serum starvation is not due to lack of FGF synthesis but likely to effects of Psen1 on FGF release onto the cell surface and impaired activation of the PI3K/AKT survival pathway.

The human-specific CASP4 gene product contributes to Alzheimer-related synaptic and behavioural deficits

Recent studies have indicated that innate immune signalling molecules are involved in late-onset Alzheimers disease (LOAD) risk. Amyloid beta (Aβ) accumulates in AD brain, and has been proposed to act as a trigger of innate immune responses. Caspase-4 is an important part of the innate immune response. We recently characterized transgenic mice carrying human CASP4, and observed that the mice manifested profound innate immune responses to lipopolysaccharide (LPS). Since these inflammatory processes are important in the aetiology of AD, we have now analysed the correlation of expression of caspase-4 in human brain with AD risk genes, and studied caspase-4 effects on AD-related phenotypes in APPswe/PS1deltaE9 (APP/PS1) mice. We observed that the expression of caspase-4 was strongly correlated with AD risk genes including TYROBP, TREM2, CR1, PSEN1, MS4A4A and MS4A6A in LOAD brains. Caspase-4 expression was upregulated in CASP4/APP/PS1 mice in a region-specific manner, including hippocampus and prefrontal cortex. In APP/PS1 mice, caspase-4 expression led to impairments in the reversal phase of a Barnes maze task and in hippocampal synaptic plasticity, without affecting soluble or aggregated Aβ levels. Caspase-4 was expressed predominantly in microglial cells, and in the presence of CASP4, more microglia were clustered around amyloid plaques. Furthermore, our data indicated that caspase-4 modulates microglial cells in a manner that increases proinflammatory processes. We propose that microglial caspase-4 expression contributes to the cognitive impairments in AD, and that further study of caspase-4 will enhance our understanding of AD pathogenesis and may lead to novel therapeutic targets in AD.

Chapter 1 – Cellular Components of Nervous Tissue

This chapter provides general information on the various types of cells that compose nervous tissues and serves as an introduction to cellular neuroscience. Different classes of neurons are presented in terms of their function, morphology, neurochemistry, and place in neural circuits. Cortical pyramidal neurons and inhibitory interneuron subtypes are discussed together with examples of specialized neurons from subcortical regions. The structure of excitatory and inhibitory synapses is also reviewed. Each type of glial cell (astrocytes, oligodendrocytes, as well as microglia) is introduced in separate sections that review their particular function, structure, and interactions with neurons. A final section presents brain endothelial cells and their role in maintenance of the blood-brain barrier.