No abstract

Cognitive dysfunction and reactive microglia are hallmarks of traumatic brain injury (TBI), yet whether these cells contribute to cognitive deficits and secondary inflammatory pathology remains poorly understood. Here, we show that removal of microglia from the mouse brain has little effect on the outcome of TBI, but inducing the turnover of these cells through either pharmacologic or genetic approaches can yield a neuroprotective microglial phenotype that profoundly aids recovery. The beneficial effects of these repopulating microglia are critically dependent on interleukin-6 (IL-6) trans-signaling via the soluble IL-6 receptor (IL-6R) and robustly support adult neurogenesis, specifically by augmenting the survival of newborn neurons that directly support cognitive function. We conclude that microglia in the mammalian brain can be manipulated to adopt a neuroprotective and pro-regenerative phenotype that can aid repair and alleviate the cognitive deficits arising from brain injury.

One of the most important current scientific paradoxes is the economy with which nature uses genes. In all higher animals studied, we have found many fewer genes than we would have previously expected. The functional outputs of the eventual products of genes seem to be far more complex than the more restricted blueprint. In higher organisms, the functions of many proteins are modulated by post-translational modifications (PTMs). These alterations of amino-acid side chains lead to higher structural and functional protein diversity and are, therefore, a leading contender for an explanation for this seeming incongruity. Natural protein production methods typically produce PTM mixtures within which function is difficult to dissect or control. Until now it has not been possible to access pure mimics of complex PTMs. Here we report a chemical tagging approach that enables the attachment of multiple modifications to bacterially expressed (bare) protein scaffolds: this approach allows reconstitution of functionally effective mimics of higher organism PTMs. By attaching appropriate modifications at suitable distances in the widely-used LacZ reporter enzyme scaffold, we created protein probes that included sensitive systems for detection of mammalian brain inflammation and disease. Through target synthesis of the desired modification, chemistry provides a structural precision and an ability to retool with a chosen PTM in a manner not available to other approaches. In this way, combining chemical control of PTM with readily available protein scaffolds provides a systematic platform for creating probes of protein-PTM interactions. We therefore anticipate that this ability to build model systems will allow some of this gene product complexity to be dissected, with the aim of eventually being able to completely duplicate the patterns of a particular protein's PTMs from an in vivo assay into an in vitro system.

Multiple sclerosis (MS) is a disease of the central nervous system that is associated with leukocyte recruitment and subsequent inflammation, demyelination and axonal loss. Endothelial vascular cell adhesion molecule-1 (VCAM-1) and its ligand, α 4 β 1 integrin, are key mediators of leukocyte recruitment and new selective inhibitors that bind to the α 4 subunit of α 4 β 1 substantially reduce clinical relapse in MS. Urgently needed is a molecular imaging technique to accelerate diagnosis, quantify disease activity and guide specific therapy.We report in vivo detection of VCAM-1 in acute brain inflammation, using MRI in a mouse model, at a time when pathology is otherwise undetectable. Antibody-conjugated microparticles carrying a high payload of iron oxide provided potent, quantifiable contrast effects that delineated the architecture of activated cerebral blood vessels. Rapid clearance from blood resulted in minimal background contrast. This technology is adaptable to monitor expression of endovascular molecules in vivo in a range of pathologies.Multiple sclerosis (MS) is a disease of the central nervous system characterized by multifocal white matter lesions 1 . Current diagnostic criteria for MS, incorporating both clinical and magnetic resonance imaging (MRI) characteristics, require the demonstration of lesion dissemination in both time and space 2 , 3 T2-weighted and gadolinium-enhanced T1-weighted MRI detect some, but not all, lesions while advanced MRI techniques such as diffusion imaging 4 , magnetization transfer 5 and MR spectroscopy 6 may provide additional insights. However, these approaches are limited in two key respects: (1) they image downstream injury, reflecting relatively advanced pathology and (2) while providing an indication of severity, current imaging techniques can not accurately assess disease activity 7 .

In adult rats, 50,000 units of recombinant interleukin-1 beta (IL-1 beta) injected into the brain parenchyma produced an intense meningitis and disruption of the blood-CSF barrier by 4 h. No increase in vascular permeability to horseradish peroxidase or leukocyte recruitment was observed at the site of injection. By contrast, in juvenile rats, 100 units of IL-1 beta injected into the striatum gave rise to a large increase in blood-brain barrier permeability and recruitment of polymorphonuclear neutrophils into the tissue around the injection site by 4 h. This effect was also accompanied by a marked meningitis. The injection of 100 units of IL-1 beta into neonatal (2-h-old) rats gave rise to an increase in permeability of vessels to serum proteins in the meninges, but no increase in vascular permeability was observed at the injection site. The IL-1 beta-induced increases in vessel permeability in the meninges, parenchyma, and choroid plexus were polymorphonuclear neutrophil dependent, since leukocyte depletion by irradiation or polymorphonuclear neutrophil anti-serum pre-treatment eliminated the response in the juvenile animals and in the adults. Seventy-five thousand units of murine tumour necrosis factor-alpha injected into the parenchyma of both adults and juvenile animals failed to induce an increase in blood-brain barrier permeability or polymorphonuclear neutrophil recruitment, but did give rise to a mild meningitis. These findings demonstrate clear differences in the responsiveness of different CNS compartments to IL-1 beta. Furthermore, while tumour necrosis factor-alpha and IL-1 beta might have been expected to exhibit similar proinflammatory effects in the CNS, this is not the case. We also show, for the first time, that age has a significant effect on the response to a cytokine. The "window of susceptibility' to an inflammatory stimulus in juvenile rats, if paralleled in humans, may be a major factor in the increased susceptibility of children to trauma or to infectious insults to the CNS.