L1 cell adhesion molecule is not required for small-diameter primary afferent sprouting after deafferentation

Abstract

L1 is a cell adhesion molecule associated with axonal outgrowth and fasciculation during spinal cord development and may reiterate its developmental role in adults following injury; L1 is upregulated on certain sprouting and regenerating axons in adults, but it is unclear if L1 expression is necessary for, or contributes to, regrowth of axons. This study asks if L1 is required for small-diameter primary afferents to sprout by conducting unilateral dorsal rhizotomies (6 segments; T10-L2) on both wildtype and L1 mutant mice. First we determined that L1 co-localizes substantially with the peptidergic (calcitonin gene-related peptide; CGRP) but minimally with the nonpeptidergic (isolectin B4; IB4) primary afferents in intact wild-type and L1 mutant mice. However, we encountered a complication using IB4 to identify primary afferents post-rhizotomy; we detected extensive abnormal IB4 expression in the dorsal horn and dorsal columns. Much of this aberrant IB4 labeling is associated with fibrous astrocytes and microglia. Five days after dorsal rhizotomy a large decrease in peptidergic and nonpeptidergic afferents is evident on the deafferented side in both wild-type and L1 mutants. Three months after surgery the peptidergic primary afferents sprouted into the center of the denervated dorsal horn in both wild-type and mutant mice, and quantitative analyses confirmed a sprouting density of similar magnitude in both genotypes. In contrast, we did not detect sprouting in the nonpeptidergic primary afferents in either genotype. These results suggest that the absence of L1 neither diminishes nor enhances sprouting of peptidergic small-diameter primary afferent axons following a dorsal rhizotomy. Keywordscell adhesion molecule; denervated; IB4; CGRP; nociceptors; rhizotomy The cell adhesion molecule L1 (L1 CAM) is an axonal glycoprotein and a member of the immunoglobulin superfamily (Kamiguchi et al., 1997). L1 plays a role in axonal outgrowth, fasciculation, and guidance during spinal cord development (Stallcup et al., 1985;Jessell, 1988;Stoeckli and Landmesser, 1995;Orlino et al., 2000;Tran and Phelps, 2000;Akopians et al., 2003) through homophilic and various heterophilic binding partners such as integrins (αVβ3 and α5β1) and the fibroblast growth factor receptor (Kamiguchi and Lemmon, 1997 Publisher's Disclaimer: This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final citable form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain. Lemmon, 1997;Castellani et al., 2000). NIH Public AccessMutations in X-linked L1 in humans cause major developmental errors and result in a group of symptoms that include corpus callosum hypoplasia, spastic paraplegia and hydrocephalus (Fran...

Differential distribution of diacylglycerol lipase‐alpha and N‐acylphosphatidylethanolamine‐specific phospholipase d immunoreactivity in the superficial spinal dorsal horn of rats

“…In contrast to some earlier reports demonstrating IB4-binding to astrocytes and microglial cells (Streit, 1990; Villeda et al, 2006; Runyan et al, 2007), we have never seen IB4-binding on glial cells in the present study (Supporting Information Figure 6). Despite the strong immunostaining and the substantial spatial overlap between the investigated profiles, the co-localization between axon terminals labeled with IB4-binding and puncta immunoreactive for DGLα or NAPE-PLD was very low.…”

Mouse olfactory ensheathing glia enhance axon outgrowth on a myelin substrate in vitro

“…Despite evidence that favored a contact-mediated role for L1 in OEG-enhanced regeneration, OEG stimulated axonal outgrowth regardless of the presence or absence of L1 in our assay. Our findings are consistent with those using the L1 mutant mouse model that report L1 expression is not essential for DRG sprouting following unilateral deafferentation (Runyan et al, 2007) or growth of the corticospinal tract into a contusion injury (Jakeman et al, 2006). These results suggest that other cell adhesion molecules or extracellular matrix proteins expressed by OEG, such as PSA-NCAM, must participate in contact-mediated growth promotion.…”

“…L1 is down-regulated on most axons during postnatal development (Akopians et al, 2003), but is maintained on adult small-diameter DRG nociceptors (Haney et al, 1999; Runyan et al, 2005; Runyan et al, 2007) and on the Schwann cells that ensheath these unmyelinated axons (Haney et al, 1999). Using L1-deficient mice Haney et al (1999) found that Schwann cells did not maintain ensheathment of DRG axons, due to the loss of axonal L1.…”

L1 cell adhesion molecule is essential for the maintenance of hyperalgesia after spinal cord injury

“…In accordance with this, we saw significantly increased CGRP + fiber sprouting in the lumbar dorsal horn after injury in WT mice when compared with uninjured WT controls. L1 and CGRP are co-expressed in these afferents (Runyan et al, 2005), and the influence of L1 as a growth molecule on CGRP+ fiber sprouting has been shown and discussed previously (Chaudhry et al, 2006; Runyan et al, 2007; Deumens et al, 2007; Yamanaka et al, 2007). Notably, L1 has also been shown to contribute to synapse formation and stabilization (Godenschwege et al, 2006; Triana-Baltzer et al, 2008) as well as the survival of small-diameter unmyelinated afferent axons in the periphery (Haney et al, 1999).…”