Claudins in the brain: Unconventional functions in neurons

Bonafide claudin proteins are functional and structural components of tight junctions and are largely responsible for barrier formation across epithelial and endothelial membranes. However, current advances in the understanding of claudin biology have revealed their unexpected functions in the brain. Apart from maintaining blood‐brain barriers in the brain, other functions of claudins in neurons and at synapses have been largely elusive and are just coming to light. In this review, we summarize the functions of claudins in the brain and their association in neuronal diseases. Further, we go on to cover some recent studies that show that claudins play signaling functions in neurons by regulating trafficking of postsynaptic receptors and controlling dendritic morphogenesis in the model organism Caenorhabditis elegans. The class of tetraspan proteins, called claudins, have been well studied for their function in epithelial integrity. It is only recently that claudin function in the brain is coming to light. This review gives an overview of our understanding on how claudins could be functioning in neurons and synapses.