Brain link proteins: New insights for hyaluronan-binding proteoglycans in brain

Link protein is originally characterized as an abundant extracellular matrix protein in cartilage and named Crt11. It can stabilize aggregates of aggrecan and hyaluronan, giving cartilage its tensile strength. Similarly to the cartilage matrix, a high content of hyaluronan matrix has also been recognized in the brain matrix. Subsequently, several hyaluronan binding chondroitin sulphate proteoglycans, called lecticans, have been identified as the abundant extracellular matrix molecules in the developing and/or adult brain. Other than Crt11, brain-specific link protein gene, Bra11, was cloned recently. The two link proteins (LPs), old and new, are differentially expressed and seemed to be coordinately expressed with lecticans in the brain. In this review, we will focus on these brain link proteins that may play crucial roles in hyaluronan matrix.