Simultaneous analysis of multiple gene expression patterns as a function of development, injury or senescence

Developmental traumatic brain injury decreased brain derived neurotrophic factor expression late after injury

Pediatric traumatic brain injury (TBI) is a major cause of acquired cognitive dysfunction in children. Hippocampal Brain Derived Neurotrophic Factor (BDNF) is important for normal cognition. Little is known about the effects of TBI on BDNF levels in the developing hippocampus. We used controlled cortical impact (CCI) in the 17 day old rat pup to test the hypothesis that CCI would first increase rat hippocampal BDNF mRNA/protein levels relative to SHAM and Naïve rats by post injury day (PID) 2 and then decrease BDNF mRNA/protein by PID14. Relative to SHAM, CCI did not change BDNF mRNA/protein levels in the injured hippocampus in the first 2 days after injury but did decrease BDNF protein at PID14. Surprisingly, BDNF mRNA decreased at PID 1, 3, 7 and 14, and BDNF protein decreased at PID 2, in SHAM and CCI hippocampi relative to Naïve. In conclusion, TBI decreased BDNF protein in the injured rat pup hippocampus 14 days after injury. BDNF mRNA levels decreased in both CCI and SHAM hippocampi relative to Naïve, suggesting that certain aspects of the experimental paradigm (such as craniotomy, anesthesia, and/or maternal separation) may decrease the expression of BDNF in the developing hippocampus. While BDNF is important for normal cognition, no inferences can be made regarding the cognitive impact of any of these factors. Such findings, however, suggest that meticulous attention to the experimental paradigm, and possible inclusion of a Naïve group, is warranted in studies of BDNF expression in the developing brain after TBI.

Early and sustained increase in the expression of hippocampal IGF-1, but not EPO, in a developmental rodent model of traumatic brain injury

Pediatric traumatic brain injury (pTBI) is the leading cause of traumatic death and disability in children in the United States. Impaired learning and memory in these young survivors imposes a heavy toll on society. In adult TBI (aTBI) models, cognitive outcome improved after administration of erythropoietin (EPO) or insulin-like growth factor-1 (IGF-1). Little is known about the production of these agents in the hippocampus, a brain region critical for learning and memory, after pTBI. Our objective was to describe hippocampal expression of EPO and IGF-1, together with their receptors (EPOR and IGF-1R, respectively), over time after pTBI in 17-day-old rats. We used the controlled cortical impact (CCI) model and measured hippocampal mRNA levels of EPO, IGF-1, EPOR, IGF-1R, and markers of caspase-dependent apoptosis (bcl2, bax, and p53) at post-injury days (PID) 1, 2, 3, 7, and 14. CCI rats performed poorly on Morris water maze testing of spatial working memory, a hippocampally-based cognitive function. Apoptotic markers were present early and persisted for the duration of the study. EPO in our pTBI model increased much later (PID7) than in aTBI models (12 h), while EPOR and IGF-1 increased at PID1 and PID2, respectively, similar to data from aTBI models. Our data indicate that EPO expression showed a delayed upregulation post-pTBI, while EPOR increased early. We speculate that administration of EPO in the first 1-2 days after pTBI would increase hippocampal neuronal survival and function.

Differential role of tumor necrosis factor receptors in mouse brain inflammatory responses in cryolesion brain injury

Tumor necrosis factor-alpha (TNF-alpha) is one of the mediators dramatically increased after traumatic brain injury that leads to the activation, proliferation, and hypertrophy of mononuclear, phagocytic cells and gliosis. Eventually, TNF-alpha can induce both apoptosis and necrosis via intracellular signaling. This cytokine exerts its functions via interaction with two receptors: type-1 receptor (TNFR1) and type-2 receptor (TNFR2). In this work, the inflammatory response after a freeze injury (cryolesion) in the cortex was studied in wild-type (WT) animals and in mice lacking TNFR1 (TNFR1 KO) or TNFR2 (TNFR2 KO). Lack of TNFR1, but not of TNFR2, significantly decreased the inflammatory response and tissue damage elicited by the cryolesion at both 3 and 7 days postlesion, with decreased gliosis, lower IL-1beta immunostaining, and a reduction of apoptosis markers. Cryolesion produced a clear induction of the proinflammatory cytokines interleukin (IL)-1alpha, IL-1beta, IL-6, and TNF-alpha; this induction was significantly lower in the TNFR1 KO mice. Host response genes (ICAM-1, A20, EB22/5, and GFAP) were also induced by the cryolesion, but to a lesser extent in TNFR1 KO mice. Lack of TNFR1 signaling also affected the expression of apoptosis/cell death-related genes (Fas, Rip, p53), matrix metalloproteinases (MMP3, MMP9, MMP12), and their inhibitors (TIMP1), suggesting a role of TNFR1 in extracellular matrix remodeling after injury. However, GDNF, NGF, and BDNF expression were not affected by TNFR1 deficiency. Overall, these results suggest that TNFR1 is involved in the early establishment of the inflammatory response and that its deficiency causes a decreased inflammatory response and tissue damage following brain injury.

Gene expression in neurotrauma

It has been established that following injury to the central nervous system two types of damage take place, the initial insult and the secondary response to injury. This review will focus on the secondary molecular aspects of neurotrauma. These responses may be either deleterious or have protective effects upon the injured cell population. Molecular responses include the regulation of genes which change cellular architecture, up-regulate of growth factors, induce reparative stress responses, influence apoptosis and regulate the transcriptional process. The purpose of this study is to provide the reader with a brief overview of some of the molecular mechanisms which are activated following a neurological insult.

Temporal profile of expression and cellular localization of inducible nitric oxide synthase, interleukin-1beta and interleukin converting enzyme after cryogenic lesion of the rat parietal cortex

We used in situ hybridization, RT PCR and immunohistochemistry to study the time course of expression and the cellular localization of inducible nitric oxide synthase (iNOS) and interleukin-1beta (IL-1beta) during the first 7 days after induction of a standardized cryogenic lesion on the right parietal cortex in male rats. Cryogenic lesion induced iNOS mRNA in the lesioned hemisphere after 6 to 72 h with a maximum (15+/-2 cells/mm2, n=4, p<0.01 vs. sham) at 24 h. Microglia, invading monocytes and granulocytes in and around the lesion expressed iNOS immunoreactivity starting at 12 h and peaking (29+/-10 cells/mm2, n=4, p<0.05 vs. sham) at 24 h after lesion. Induction of IL-1beta mRNA expression was immediate with a peak (9+/-1 cells/mm2, n=4, p<0.01 vs. sham) at 24 h after cryogenic lesion. The number of round cells with IL-1beta immunoreactivity around the lesion was maximal (8+/-2 cells/0.1 mm2, n=3, p<0.01 vs. sham) at 24 h. A weak astrocytic expression of IL-1beta-immunoreactivity was seen in sham animal brains. Astrocytic IL-1beta-expression was significantly increased in the lesion hemisphere and both hippocampi. Interleukin converting enzyme (ICE) was expressed in astrocytes and microglia around the lesion 6 h after injury. The number of ICE immunoreactive cells (8+/-2 cells/0. 1 mm2, n=3, p<0.05 vs. sham) peaked at 72 h after lesion. Neuronal expression of ICE and IL-1beta was seen in the lesion periphery 72 h and 7 days after injury. At this time, morphological features of apoptosis were evident in cells in the lesion periphery. The data indicate an early activation of microglia and monocyte invasion into the lesion hemisphere leading to multicellular expression of iNOS, ICE, and IL-1beta. These events may contribute to the expansion of neuronal damage after brain injury.