Human-specific signaling molecules

When this molecule absorbs light, it rapidly isomerizes (changes its structure) to the all-trans form. This specific chemical reaction is the central event in human vision. The molecule is bound within a protein (the combination is called rhodopsin), the isomerization triggers a series of later processes, ultimately leading to an electrical signal which is sent to the brain. 

The cell culture analog (CCA) system is one approach attempting to narrow this gap. It is developed to address the issues of reactive metabolite formation and tissue-tissue interaction through exchange of metabolites or signal molecules, and to evaluate potential efficacy and toxicity of pharmaceuticals and environmental chemicals. A CCA device can be considered as a simplified and minimized human/animal body, in which mammalian cell cultures are used to represent key functions of specific organs, and cell culture medium is used as a blood surrogate. 

Chemokine expression in the CNS by brain-specific cells was first described almost 20 years ago (for examples, see [20, 21). These results were obtained in an animal model for multiple sclerosis (MS), showing for the first time a disease-associated increase in chemokine expression by distinct subsets of brain cells [20, 22]. In the mean time, many in vitro and in vivo studies on functional expression of chemokines and their receptors in the CNS have been pubhshed. Chemokines are now discussed to be part of the repertoire of signaling molecules in the brain, with numerous functions in development, physiology and pathology of the CNS, not only in rodents but also in humans [7, 23-26]. 

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