Selective expression of hyaluronan and receptor for hyaluronan mediated motility (Rhamm) in the adult mouse subventricular zone and rostral migratory stream and in ischemic cortex

Hyaluronan is a large glycosaminoglycan, which is abundant in the extracellular matrix of the developing rodent brain. In the adult brain however, levels of hyaluronan are significantly reduced. In this study, we used neurocan-GFP as a histochemical probe to analyze the distribution of hyaluronan in the adult mouse subventricular zone (SVZ), as well as in the rostral migratory stream (RMS). Interestingly, we observed that hyaluronan is generally downregulated in the adult brain, but notably remains at high levels in the SVZ and RMS; areas in which neural stem/progenitor cells (NSPCs) persist, proliferate and migrate throughout life. In addition, we found that the receptor for hyaluronan-mediated motility (Rhamm) was expressed in migrating neuroblasts in these areas, indicating that Rhamm could be involved in regulating hyaluronan-mediated cell migration. Hyaluronan levels are balanced by synthesis through hyaluronan synthases (Has) and degradation by hyaluronidases (Hyal). We found that Has1 and Has2, as well as Hyal1 and Hyal2 were expressed in GFAP positive cells in the adult rodent SVZ and RMS, indicating that astrocytes could be regulating hyaluronan-mediated functions in these areas. We also demonstrate that hyaluronan levels are substantially increased at six weeks following a photothrombotic stroke lesion to the adult mouse cortex. Furthermore, GFAP positive cells in the peri-infarct area express Rhamm. Thus, hyaluronan may be involved in regulating cell migration in the normal SVZ and RMS and could also be responsible for priming the peri-infarct area following an ischemic lesion for cell migration