Novel roles for metallothionein‐I + II (MT‐I + II) in defense responses, neurogenesis, and tissue restoration after traumatic brain injury: Insights from global gene expression profiling in wild‐type and MT‐I + II knockout mice

Abstract

Traumatic injury to the brain is one of the leading causes of injury-related death or disability, especially among young people. Inflammatory processes and oxidative stress likely underlie much of the damage elicited by injury, but the full repertoire of responses involved is not well known. A genomic approach, such as the use of microarrays, provides much insight in this regard, especially if combined with the use of gene-targeted animals. We report here the results of one of these studies comparing wild-type and metallothionein-I + II knockout mice subjected to a cryolesion of the somatosensorial cortex and killed at 0, 1, 4, 8, and 16 days postlesion (dpl) using Affymetrix genechips/oligonucleotide arrays interrogating approximately 10,000 different murine genes (MG_U74Av2). Hierarchical clustering analysis of these genes readily shows an orderly pattern of gene responses at specific times consistent with the processes involved in the initial tissue injury and later regeneration of the parenchyma, as well as a prominent effect of MT-I + II deficiency. The results thoroughly confirmed the importance of the antioxidant proteins MT-I + II in the response of the brain to injury and opened new avenues that were confirmed by immunohistochemistry. Data in KO, MT-I-overexpressing, and MT-II-injected mice strongly suggest a role of these proteins in postlesional activation of neural stem cells.

Effect of astrocyte‐targeted production of IL‐6 on traumatic brain injury and its impact on the cortical transcriptome

“…Therefore, cryolesion is a model that elicits an inflammatory response at the gene level, in agreement with previous results Penkowa et al, 2006). The effect of cryolesion at a transcriptome level has been already described by our group in animals lacking IL-6 (Poulsen et al, 2005), metallothioneins 1 and 2 (Penkowa et al, 2006), and TNFareceptor 1 or receptor 2 (Quintana et al, 2007).…”

“…As previously described in cryolesion (Poulsen et al, 2005;Penkowa et al, 2006;Quintana et al, 2007), a clear pattern of induction was observed, with genes up-regulated by the cryolesion at 1 day post lesion (dpl) (Fig. 4), both at 1-4 dpl (Fig.…”

“…We set a 1.2-fold change (that is, a 20% increase or decrease) and an absolute change in expression values of 100 expression units. With this procedure a list of 461 IDs (corresponding to 369 genes) was produced, therefore being comparable to previous experiments with the same model performed in our lab (Poulsen et al, 2005;Penkowa et al, 2006;Quintana et al, 2007).…”

Analysis of the Cerebral Transcriptome in Mice Subjected to Traumatic Brain Injury: Importance of IL-6

“…As expected [35][36][37] , a clear pattern of responses was observed, with genes being either up-or downregulated by the cryolesion readily identified by the hierarchical clustering analyses. Genes upregulated at 1 day after lesion constituted the largest cluster in our study, comprising 141 genes of a total of 174.…”

“…Gene knockouts in the laboratory mouse have produced particularly successful research, and efforts are being made to knockout each mouse gene for worldwide availability [34] . We have already shown results obtained in IL-6 knockout [35] , TNFR1 or TNFR2 knockout [36] and MtI&II knockout mice [37] that fully illustrate these points. A complementary approach is to analyze transgenic mice with overexpression of a given gene.…”