Abstract
Inflammatory response alter traumatic brain injury is orchestrated by cytokines, a complex group of proteins implicated in intercellular signalling, such as interleukin (IL)-6 or tumoral necrosis factor (TNF)-α. Although these two factors were originally described to mediate the pro-apoptotic responses of inflammation, they have recently been described to exert beneficial actions in both the cell survival and tissue recovery after injury. Among the factors induced by IL-6 one can find metallothioneins (MTs), low-weight, cysteine-rich proteins with antioxidant, antiapoptotic and neuroprotective actions; which could mediate, at least in part, the beneficial actions of IL-6.The use of genetically modified mice has allowed us to gain insight in the role of IL-6, TNF-α and MTs in the pathophysiology of the central nervous system. We have used animals lacking the IL-6 gene (IL6KO), mice overexpressing IL-6 in the brain (GFAP-IL6 mice), mice lacking either TNF-α receptor 1 or receptor 2 (TNFR1KO and TNFR2KO) and animals lacking MT-I and MT-II (MTKO mice) treated with saline solution or with exogenous MTs. All of these mice were subjected to a focal freeze injury such as cryolesion, placing a dry ice pellet for 30 seconds on the parietal bone.
The neurohistological status of these animals was assessed by means of immunohistochemistry. Gene expression of several apoptotis, survival and inflammatory response markers was assessed by in situ hybridization, microarray and ribonuclease protection assay (RPA). The functional status of these mice was also assessed by behavioural tests, namely elevated plus maze (EPM), hole board (HB) and horizontal ladder beam (HLB).
Our present results show that although chronic IL-6 expression is detrimental, GFAP-IL6 mice show reduced cell death and lower oxidative stress, suggesting a role for IL-6 in survival, which may be mediated by inducing antioxidant and antiapoptotic factors. IL6KO animals, on the other hand, show a decreased inflammatory response but an increase in cell death after lesion. In this regard, MTKO mice present a similar phenotype after injury which can be reverted by exogenous MT administration, an effect which does not depend on the homology of the different MT isoforms and mice, suggesting a receptor-independent action, opening a possible therapeutic use for MTs.
Deficiency in TNF-α signalling, by lack of either receptor 1 or 2, involves a reduction in the tissue damage, with a reduction in genes involved in cellular response to lesion altogether with reduced pro-inflammatory markers and lower activation of pro-apoptotic pathways. This reduced damage correlates with a better functional response. Behaviourally, both TNFR1KO and TNFR2KO mice show an increased exploratory activity compared to the control mice.
In conclusion, our results give new insights in the importance of TNF-α and IL-6 in inflammatory processes, and their dual role, being mediators both of pro-apoptotic and survival responses, being the alter in part mediated by MTs. This dual response may depend on the level of expression and, very likely, on the cell where it is acting.
| Date of Award | 19 Dec 2007 |
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| Original language | Spanish |
| Awarding Institution |
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| Supervisor | Maria Amalia Molinero Egea (Director) |