Enzymatic disruption of extracellular matrix promotes dendritic growth and branching of spinal dorsal horn neurons

.Dendritic arborisation of neurons largely determines their synaptic input- and membrane characteristics. While spinal superficial dorsal horn (SDH) neurons derive from a single progenitor population they later present substantial morphological heterogeneity in their cell type specific dendritic tree. This finding raises the possibility that coordinated dendritic growth is mostly determined by environmental over intrinsic factors in late born SDH neurons. Such extrinsic environmental factors include extracellular matrix (ECM) macromolecules, like chondroitin-sulphate and hyaluronan. Levels of these ECM molecules are increased in the dorsal horn at the same time when SDH neurons terminate their migration and initiate their dendritic differentiation.
Thus, to clarify the function of ECM macromolecules in dendritic development we investigated the effect of chondroitinase ABC, AC and hyaluronidase treatment on embryonic organotypic spinal cord tissue cultures in which the late born population of Ptf1a progenitors was labelled with GFP by in utero electroporation of mice embryos (E12). Spinal cords were then maintained in organotypic slice culture in enzymatic treated and enzyme free conditions. GFP labelled cells were reconstructed by the Neurolucida software and a morphometric analysis of the newly formed processes was performed.
Sholl analysis revealed that all types of enzymatic treatment caused dramatic increase in branchpoint numbers, length and the total dendritic surface. Total dendritic length increased with 124% in samples treated with a combination of chondroitinase AC and hyaluronidase, while branching was more facilitated when treated with either chondroitinase ABC or hyaluronidase alone.
Our data suggest that extracellular macromolecules hyaluronan and chondroitin-sulphate proteoglycans acting alone or together with other molecules are non-permissive for dendritic development and that they contribute to proper differentiation of SDH neurons. At the same time, enzymatic manipulation of the levels of ECM macromolecules may also be a potential strategy in promoting neuronal regeneration after spinal cord injury.