Dynamic changes in glypican‐1 expression in dorsal root ganglion neurons after peripheral and central axonal injury

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Abstract
Glypican‐1, a glycosyl phosphatidyl inositol (GPI)‐anchored heparan sulphate proteoglycan expressed in the developing and mature cells of the central nervous system, acts as a coreceptor for diverse ligands, including slit axonal guidance proteins, fibroblast growth factors and laminin. We have examined its expression in primary sensory dorsal root ganglion (DRG) neurons and spinal cord after axonal injury. In noninjured rats, glypican‐1 mRNA and protein are constitutively expressed at low levels in lumbar DRGs. Sciatic nerve transection results in a two‐fold increase in mRNA and protein expression. High glypican‐1 expression persists until the injured axons reinnervate their peripheral targets, as in the case of a crushed nerve. Injury to the central axons of DRG neurons by either a dorsal column injury or a dorsal root transection also up‐regulates glypican‐1, a feature that differs from most DRG axonal injury‐induced genes, whose regulation changes only after peripheral and not central axonal injury. After axonal injury, the cellular localization of glypican‐1 changes from a nuclear pattern restricted to neurons in noninjured DRGs, to the cytoplasm and membrane of injured neurons, as well as neighbouring non‐neuronal cells. Sciatic nerve transection also leads to an accumulation of glypican‐1 in the proximal nerve segment of injured axons. Glypican‐1 is coexpressed with robo 2 and its up‐regulation after axonal injury may contribute to an altered sensitivity to axonal growth or guidance cues.