Most cited article - PubMed ID 29020454
The absence of brain-specific link protein Bral2 in perineuronal nets hampers auditory temporal resolution and neural adaptation in mice
The calyx of Held is a giant nerve terminal mediating high-frequency excitatory input to principal cells of the medial nucleus of the trapezoid body (MNTB). MNTB principal neurons are enwrapped by densely organized extracellular matrix structures, known as perineuronal nets (PNNs). Emerging evidence indicates the importance of PNNs in synaptic transmission at the calyx of Held. Previously, a unique differential expression of aggrecan and brevican has been reported at this calyceal synapse. However, the role of hyaluronan and proteoglycan binding link proteins (HAPLNs) in PNN formation and synaptic transmission at this synapse remains elusive. This study aimed to assess immunohistochemical evidence for the effect of HAPLN4 on differential PNN formation at the calyx of Held. Genetic deletion of Hapln4 exhibited a clear ectopic shift of brevican localization from the perisynaptic space between the calyx of Held terminals and principal neurons to the neuropil surrounding the whole calyx of Held terminals. In contrast, aggrecan expression showed a consistent localization at the surrounding neuropil, together with HAPLN1 and tenascin-R, in both gene knockout (KO) and wild-type (WT) mice. An in situ proximity ligation assay demonstrated the molecular association of brevican with HAPLN4 in WT and HAPLN1 in gene KO mice. Further elucidation of the roles of HAPLN4 may highlight the developmental and physiological importance of PNN formation in the calyx of Held.
Hapln4 is a link protein which stabilizes the binding between lecticans and hyaluronan in perineuronal nets (PNNs) in specific brain regions, including the medial nucleus of the trapezoid body (MNTB). The aim of this study was: (1) to reveal possible age-related alterations in the extracellular matrix composition in the MNTB and inferior colliculus, which was devoid of Hapln4 and served as a negative control, (2) to determine the impact of the Hapln4 deletion on the values of the ECS diffusion parameters in young and aged animals and (3) to verify that PNNs moderate age-related changes in the ECS diffusion, and that Hapln4-brevican complex is indispensable for the correct protective function of the PNNs. To achieve this, we evaluated the ECS diffusion parameters using the real-time iontophoretic method in the selected region in young adult (3 to 6-months-old) and aged (12 to 18-months-old) wild type and Hapln4 knock-out (KO) mice. The results were correlated with an immunohistochemical analysis of the ECM composition and astrocyte morphology. We report that the ECM composition is altered in the aged MNTB and aging is a critical point, revealing the effect of Hapln4 deficiency on the ECS diffusion. All of our findings support the hypothesis that the ECM changes in the MNTB of aged KO animals affect the ECS parameters indirectly, via morphological changes of astrocytes, which are in direct contact with synapses and can be influenced by the ongoing synaptic transmission altered by shifts in the ECM composition.
- Keywords
- Aging, Diffusion, Extracellular matrix, Extracellular space, Hapln4,
- MeSH
- Trapezoid Body metabolism pathology MeSH
- Diffusion * MeSH
- Extracellular Matrix Proteins deficiency MeSH
- Extracellular Matrix metabolism pathology MeSH
- Extracellular Space metabolism MeSH
- Mice, Inbred C57BL MeSH
- Mice, Knockout MeSH
- Mice MeSH
- Protein Deficiency metabolism pathology MeSH
- Organ Culture Techniques MeSH
- Peripheral Nerves metabolism pathology MeSH
- Nerve Tissue Proteins deficiency MeSH
- Auditory Pathways metabolism pathology MeSH
- Aging metabolism pathology MeSH
- Animals MeSH
- Check Tag
- Male MeSH
- Mice MeSH
- Female MeSH
- Animals MeSH
- Publication type
- Journal Article MeSH
- Names of Substances
- Extracellular Matrix Proteins MeSH
- Hapln4 protein, mouse MeSH Browser
- Nerve Tissue Proteins MeSH
