Bias in the Boardroom: Psychological Foundations and Legal Implications of Corporate Cohesion

Brain trauma is known to activate inflammatory cells via various chemokine signals although their interactions remain to be characterized. Mice deficient in Ccl3, Ccr2 or Cxcl10 were compared with wildtype mice after controlled cortical impact injury. Expression of Ccl3 in wildtypes was rapidly upregulated in resident, regularly spaced reactive microglia. Ccl3-deficiency enhanced endothelial expression of platelet selectin and invasion of peripheral inflammatory cells. Appearance of Ccr2 transcripts, encoding the Ccl2 receptor, reflected invasion of lysozyme 2-expressing phagocytes and classical antigen-presenting dendritic cells expressing major histocompatibility complex class II. Ccr2 also directed clustered plasmacytoid dendritic cells positive for the T-cell attracting chemokine Cxcl10. A reduction in Ccr2 and dendritic cells was found in injured wildtype cortex after cyclophosphamide treatment resembling effects of Ccr2-deficiency. The findings demonstrate the feasibility to control inflammation in the injured brain by regulating chemokine-dependent pathways

Interacting Chemokine Signals Regulate Dendritic Cells in Acute Brain Injury

Brain trauma is known to activate inflammatory cells via various chemokine signals although their interactions remain to be characterized. Mice deficient in Ccl3, Ccr2 or Cxcl10 were compared with wildtype mice after controlled cortical impact injury. Expression of Ccl3 in wildtypes was rapidly upregulated in resident, regularly spaced reactive microglia. Ccl3-deficiency enhanced endothelial expression of platelet selectin and invasion of peripheral inflammatory cells. Appearance of Ccr2 transcripts, encoding the Ccl2 receptor, reflected invasion of lysozyme 2-expressing phagocytes and classical antigen-presenting dendritic cells expressing major histocompatibility complex class II. Ccr2 also directed clustered plasmacytoid dendritic cells positive for the T-cell attracting chemokine Cxcl10. A reduction in Ccr2 and dendritic cells was found in injured wildtype cortex after cyclophosphamide treatment resembling effects of Ccr2-deficiency. The findings demonstrate the feasibility to control inflammation in the injured brain by regulating chemokine-dependent pathways

Closed Head Injury in a Mouse Model Results in Molecular Changes Indicating Inflammatory Responses

Cerebral gene expression changes in response to traumatic brain injury will provide useful information in the search for future trauma treatment. In order to characterize the outcome of mild brain injury, we studied C57BL/6J mice in a weight-drop, closed head injury model. At various times post-injury, mRNA was isolated from neocortex and hippocampus and transcriptional alterations were studied using quantitative reverse transcriptase PCR and gene array analysis. At three days post-injury, the results showed unilateral injury responses, both in neocortex and hippocampus, with the main effect seen on the side of the skull hit by the dropping weight. Upregulated transcripts encoded products characterizing reactive astrocytes, phagocytes, microglia, and immune-reactive cells. Markers for oligodendrocytes and T-cells were not altered. Notably, strong differences in the responses among individual mice were seen (e.g., for the Gfap transcript expressed by reactive astrocytes and the chemokine Ccl3 transcript expressed by activated microglial cells). In conclusion, mild TBI chiefly activates transcripts leading to tissue signaling, inflammatory processes, and chemokine signaling, as in focal brain injury, suggesting putative targets for drug development

Inflammatory cells in the injured wt and <i>Ccr2</i>−/− cortex examined by flow cytometry and qRT-PCR.

<p>(<b>a</b>) Cells detected with FITC-CD45 in combination with either APC-PDCA-1 (<i>Bst2</i>) or APC-Cd11c (<i>Itgax</i>) in neocortex of wt or <i>Ccr2</i>−/− mice three days after injury. Upper panel left shows gating for Cd11c. The middle and right panels show wt and <i>Ccr2</i>−/− results, respectively, demonstrating reduced number of Cd11c-positive cells in the <i>Ccr2</i>−/− mice. Lower panel shows that PDCA-1 positive cells were reduced in <i>Ccr2</i>−/− brains. (<b>b</b>) Quantitative flow cytometry data from wt and <i>Ccr2</i>−/− mice three days postinjury. Isotype controls showed only trace signals. (<b>c</b>) Temporal expression patterns of six inflammatory-related transcripts (<i>Itgax</i>, <i>H2-Aa</i>, <i>Bst2</i>, <i>Cxcl10</i>, <i>Lyz2</i> and <i>Hmox1</i>) after injury in wt and <i>Ccr2</i>−/− brains.</p

Traumatic brain injury (TBI) in wildtype (wt) and chemokine-deficient (<i>Ccl3</i>−/− and <i>Ccr2</i>−/−) mice.

<p>(<b>a</b>) <i>In situ</i> hybridization revealed intense <i>Ccl3</i> expression in the perilesional zone four hours after trauma, in a pattern resembling distribution of activated microglial cells. (<b>b</b>) Temporal patterns of <i>Ccl3</i> and <i>Ccr2</i> transcript levels in the injured wt neocortex revealed by qRT-PCR. (<b>c</b>) The <i>Ccr2</i> transcript was further upregulated in <i>Ccl3</i>−/− mice as compared to wt mice three days postinjury. <i>Gfap</i> expression was also strongly upregulated but with no differences between the strains. (<b>d</b>) The <i>Ccl2</i> transcript, encoding a Ccr2 ligand, was upregulated after injury with no differences between wt and <i>Ccl3</i>−/− mice as shown by microarray analysis. In contrast, <i>Selp</i> transcript expressed by endothelial cells was more upregulated in <i>Ccl3</i>−/− compared to wt brains. (<b>e</b>) <i>Lyz2</i> expression and the microglial surface marker isolectin B4 (IB4) showed only partial overlap three days post-injury in wt brains (<i>in situ</i> hybridization and histochemistry). The <i>Bst2</i>, characterizing pDCs, exhibited a different expression pattern (insert). (<b>f</b>) At three days postinjury, the <i>Lyz2</i> increase shifted in opposite directions in the <i>Ccl3</i>−/− and <i>Ccr2</i>−/− compared to wt brains. (<b>g</b>) Cavity volume was reduced in the <i>Ccr2</i>−/− compared to wt mice seven days after injury in accordance with downregulation of inflammatory <i>Lyz2</i>-response.</p

Interactions among chemokine transcripts analyzed with qRT-PCR and <i>in situ</i> hybridization in neocortex three days after TBI.

<p>(<b>a</b>) The <i>Ccl3</i> transcript expression did not differ between <i>Ccr2</i>−/− and wt brains. (<b>b</b>) Compared to wt mice, <i>Cxcl10</i> transcript showed opposite changes in expression in <i>Ccl3</i>−/− and <i>Ccr2</i>−/− brains. (<b>c</b>) A clustered cell pattern was seen for the <i>Cxcl10</i> transcript by <i>in situ</i> hybridization in all injured brains, although with different intensities depending on genotype. Expression was stronger in the injured <i>Ccl3</i>−/− mice and weaker in the <i>Ccr2</i>−/− mice compared to wt brains. (<b>d</b>) <i>Ccl3</i> and <i>Ccr2</i> upregulation showed no differences in wt compared to <i>Cxcl10</i>−/− injured brains by qRT-PCR. (<b>e</b>) Suggested model of interactions among chemokine ligands Ccl3 and Cxcl10 and the chemokine receptor Ccr2 three days after brain injury.</p

Transcripts increased at least two-fold three days postinjury in wt cerebral cortex and with upregulation reduced by at least 50% in <i>Ccr2</i>−/− mice as well as in wt mice treated with cyclophosphamide.

<p>Transcripts increased at least two-fold three days postinjury in wt cerebral cortex and with upregulation reduced by at least 50% in <i>Ccr2</i>−/− mice as well as in wt mice treated with cyclophosphamide.</p

Cell sorting and immunodepletion of dendritic cells in neocortex three days after TBI in wt mice analyzed by qRT-PCR.

<p>(<b>a</b>) Cd11c-positive cells sorted on magnetic microbeads expressed enhanced <i>H2-Aa</i> and <i>Itgax</i> levels. In contrast, Bst2 was enriched in cells sorted on anti-PDCA-1 microbeads. (<b>b</b>) Cortical levels of inflammatory transcripts in mice injected with control immunoglobulin or with antibodies directed to PDCA-1. Depletion of pDCs was not accompanied by shifts in <i>Itgax</i> or <i>H2-Aa</i> transcript levels whereas a distinct reduction of <i>Bst2</i> and <i>Cxcl10</i> occurred.</p

Inflammatory-related transcripts measured in <i>Ccl3</i>−/− and <i>Ccr2</i>−/− mice with F2 hybrid background three days postinjury.

<p><i>Lyz2</i> expression was upregulated in homozygous <i>Ccl3</i> knockouts but downregulated in <i>Ccr2</i>−/− as in the parental strains, as was <i>Bst2</i>. Both <i>Itgax</i> and <i>Cxcl10</i> levels were less upregulated in the injured F2 Ccr2−/− brains. <i>Gfap</i> expression increased to the same extent in injured wt and F2 hybrid brains.</p