Spinal cord injury-induced up-regulation of AHNAK, expressed in cells delineating cystic cavities, and associated with neoangiogenesis Ysander von Boxberg, Claudio Salim, Sylvia Soares, Hasna Baloui, Jeanine Alterio, Miche ` le Ravaille-Veron and Fatiha Nothias Neurobiology of Intercellular Signaling, CNRS UMR 7101, universite ´ Paris VI Pierre et Marie Curie, 7 quai Saint Bernard, 75005 Paris, France Keywords: barrier formation, cavitation, inflammation, neoangiogenesis, Wistar rat Abstract To investigate the molecular basis for the poor regenerative capacity of the mammalian central nervous system (CNS) after injury, we searched for genes whose expression was affected by an adult rat spinal cord hemi-section. Differential screening of a rat spinal cord expression library was performed using polyclonal antibodies raised against lesioned spinal cord tissue. A striking overexpression was found for ahnak, encoding a 700-kDa protein, in normal CNS present only in the blood–brain barrier (BBB) forming vascular endothelial cells. Indeed, very early after spinal cord injury (SCI), high levels of membrane-associated AHNAK are observed on non- neuronal cells invading the lesion site. With time, AHNAK distribution spreads rostrally and caudally concomitant with the process of tissue inflammation and axon degeneration, delineating the interior surface of cystic cavities, mainly in front of barrier-forming astrocytes. Strong overexpression is also observed on vascular endothelial cells reacting to BBB breakdown. Based on our detailed analysis of its spatiotemporal and cellular expression, and its previously described function in BBB, we suggest that AHNAK expression is associated with cell types displaying tissue–protective barrier properties. Our study may thus contribute to the elucidation of the precise molecular and cellular events that eventually render traumatic spinal cord tissue non-permissive for regeneration. Introduction Recovery from spinal cord trauma in adult mammals is impeded by rapid formation at the lesion site of a molecular and physical barrier to axon growth, the glial scar (Silver & Miller, 2004), and a partial incapacity of injured adult cenral nervous system (CNS) neurons to reactivate the molecular machinery implicated in developmental axon growth (Mason et al., 2003). In contrast, a lesion of peripheral nervous system (PNS) is usually followed by precisely controlled degenerative events (Wallerian degeneration) that clear the way for successful axon regrowth and functional restoration of the neuronal circuitry (Stoll et al., 2002). This difference in the regenerative capacities of CNS vs. PNS is likely to be reflected on the gene expression level. Several recent studies employed the DNA array technology to perform a large-scale screen for genes whose expression is changed upon mechanical, or ischemic lesions of adult CNS (Song et al., 2001; Velardo et al., 2004; Zhang et al., 2004; Di Giovanni et al., 2005; reviewed in Bareyre & Schwab, 2003). Thus, molecules responsible for the axon growth-inhibitory properties of the adult CNS environment have become targets for the development of novel therapeutic strategies to treat CNS injury (David & Lacroix, 2003; Schwab, 2004; Ramer et al., 2005). Nevertheless, it seems crucial to understand better the complex molecular events underlying the differential reaction of PNS vs. CNS to injury, including protective barrier formation, regrowth or arrest of lesioned axons, and cell survival. Here, using antibodies generated against lesioned spinal cord tissue, we screened a rat spinal cord cDNA library for genes up-regulated after a spinal cord hemi-section (cf. von Boxberg & Kemmner, 1994). One of the critical genes detected by our approach codes for the ‘giant’ (700 kDa) protein AHNAK (desmoyokin), first described as a component of desmosomal plaques (Hieda et al., 1989). Independ- ently, ahnak had been identified in a screen for genes whose transcription is repressed in non-differentiated tumours of neural crest origin (Shtivelman & Bishop, 1993). Human AHNAK is transcribed from an apparently intron-less gene located at chromosome 11q12– q13, and displays a peculiar structure with a large central part composed of 128 amino acid (aa) ‘central repeat units’ (CRU; approximately 4600 aa), flanked by non-repetitive N-terminal and C-terminal sequences of 251, and 1002 aa, respectively. While the exact function of AHNAK is unknown, its distribution and several of its potential binding partners have been thoroughly studied in lining epithelial and endothelial cells, and in the heart (see Discussion). In adult CNS, AHNAK is detected only in blood vessels, in particular those forming the BBB (Gentil et al., 2005). Here, we describe for the Correspondence: Dr Ysander von Boxberg, as above. E-mail: ysander.boxberg@snv.jussieu.fr or:Dr Fatiha Nothias, as above. E-mail: fatiha.nothias@snv.jussieu.fr Received 1 March 2004, revised 23 May 2006, accepted 12 June 2006 European Journal of Neuroscience, Vol. 24, pp. 1031–1041, 2006 doi:10.1111/j.1460-9568.2006.04994.x ª The Authors (2006). Journal Compilation ª Federation of European Neuroscience Societies and Blackwell Publishing Ltd