Tenascin‐R and axon growth‐promoting molecules are up‐regulated in the regenerating visual pathway of the lizard (Gallotia galloti)

Abstract

It is currently unclear whether retinal ganglion cell (RGC) axon regeneration depends on down-regulation of axon growth-inhibitory proteins, and to what extent outgrowth-promoting substrates contribute to RGC axon regeneration in reptiles. We performed an immunohistochemical study of the regulation of the axon growth-inhibiting extracellular matrix molecules tenascin-R and chondroitin sulphate proteoglycan (CSPG), the axon outgrowth-promoting extracellular matrix proteins fibronectin and laminin, and the axonal tenascin-R receptor protein F3/contactin during RGC axon regeneration in the lizard, Gallotia galloti. Tenascin-R and CSPG were expressed in an extracellular matrix-, oligodendrocyte/myelin- and neuron-associated pattern and up-regulated in the regenerating optic pathway. The expression pattern of tenascin-R was not indicative of a role in channeling or restriction of re-growing RGC axons. Up-regulation of fibronectin, laminin, and F3/contactin occurred in spatiotemporal patterns corresponding to tenascin-R expression. Moreover, we analyzed the influence of substrates containing tenascin-R, fibronectin, and laminin on outgrowth of regenerating lizard RGC axons. In vitro regeneration of RGC axons was not inhibited by tenascin-R, and further improved on mixed substrates containing tenascin-R together with fibronectin or laminin. These results indicate that RGC axon regeneration in Gallotia galloti does not require down-regulation of tenascin-R or CSPG. Presence of tenascin-R is insufficient to prevent RGC axon growth, and concomitant up-regulation of axon growth-promoting molecules like fibronectin and laminin may override the effects of neurite growth inhibitors on RGC axon regeneration. Up-regulation of contactin in RGCs suggests that tenascin-R may have an instructive function during axon regeneration in the lizard optic pathway.

Expression of neuronal markers, synaptic proteins, and glutamine synthetase in the control and regenerating lizard visual system

“…results) is consistent with the long-term axonal regrowth process in this species (Lang et al, 2002(Lang et al, , 2008. Implication of cAMP in the upregulation of beta-III tubulin is a possibility to be explored in our material, as detected in the regenerating DRG neurons (Han et al, 2004).…”

“…Furthermore, the recovery of GS staining at the lesion site is linked to the staining of GFAP þ astrocytes and decreased levels of fibronectin. However, the abundant GFAP þ astrogliosis observed on the regenerating side (Lang et al, 2002(Lang et al, , 2008 does not seem to significantly upregulate GS in response to the lesion, despite identifying GS þ /GFAP þ astrocytes in the lizard ON (Viñoly, 2005). Conversely, astrogliosis in mammals is generally characterized by the upregulation of GS, among other proteins, and by an accumulation of glutamine, which is suggested to contribute to astrocyte swelling in certain brain pathologies (Eddleston and Mucke, 1993).…”

“…Along these lines, our previous studies revealed that damaged RGCs upregulated the immediate early gene c-jun by up to a minimum of 9 months after optic nerve (ON) axotomy, thus reflecting the prolonged time course of axonal regrowth (Lang et al, 2002). Moreover, regrowing RGC axons in Gallotia galloti were insensitive both in vitro to the nonpermissiveness of rat oligodendrocytes and myelin (Lang et al, 1998) and in vivo to other putative inhibitory microenvironmental conditions such as the persistence of reactive gliosis and the upregulation of the extracellular matrix molecules tenascin-R and chondroitin sulfate proteoglycan (Lang et al, 2002(Lang et al, , 2008.…”

Ischemic injury leads to extracellular matrix alterations in retina and optic nerve

“…In general, tenascin-R represents a well-defined repellent, growth-inhibiting ECM component of optic nerve fibers in several species57585960. In this context, the epidermal growth factor family member CALEB, which is dynamically regulated after optic nerve lesion, represents a favorable interaction partner of tenascin-R during RGC axon regeneration61.…”

Development of astroglia heterogeneously expressing Pax2, vimentin and GFAP during the ontogeny of the optic pathway of the lizard (Gallotia galloti): an immunohistochemical and ultrastructural study

“…Unlike in mammals, the persistent astroglial scar, which, in lizard, expresses glial fibrillary acidic protein (GFAP; Lang et al 2002Lang et al , 2008 and neurotrophin-3 (NT-3; Santos et al 2008), is permissive to axon regrowth. The astroglial lineage of the optic tectum of G. galloti has been studied in detail during ontogeny (Monzón-Mayor et al 1990a, b, c, 1998Romero-Alemán et al 2003), whereas in the rest of the optic pathway, these cells are still poorly characterised (Alfayate et al 2011;Romero-Alemán et al 2003, 2010.…”