Hyaluronic acid is present on specific perineuronal nets in the mouse cerebral cortex

In the central nervous system (CNS), extracellular matrix (ECM) molecules comprise more than 20% of the volume and are involved in neuronal plasticity, synaptic transmission, and differentiation. Perineuronal nets (PNNs) are ECM molecules that highly accumulate around the soma of neurons. The components of the ECM in the CNS include proteins, proteoglycans, and glycosaminoglycans. Although hyaluronic acid (HA) is considered a constituent element of PNNs, the distribution of HA in the cortex has not been clarified. To elucidate the cortical region-specific distribution of HA, we quantitatively analyzed HA binding protein (HABP)-positive PNNs in the mature mouse cerebral cortex. Our findings revealed that HABP-positive PNNs are present throughout the mouse cortex. The distribution of many HABP-positive PNNs differed from that of Wisteria floribunda agglutinin-positive PNNs. Furthermore, we observed granular-like HABP-positive PNNs in layer 1 of the cortex. These findings indicate that PNNs in the mouse cortex show region-dependent differences in composition. HABP-positive PNNs in layer 1 of the cortex may have different functions such as neuronal differentiation, proliferation, and migration unlike what has been reported for PNNs so far.