Impaired Axonal Regeneration by Isolectin B4-Binding Dorsal Root Ganglion NeuronsIn Vitro

Abstract

The subpopulation of dorsal root ganglion (DRG) neurons recognized by Griffonia simplicifolia isolectin B4 (IB4) differ from other neurons by expressing receptors for glial cell line-derived neurotrophic factor (GDNF) rather than neurotrophins. Additionally, IB4-labeled neurons do not express the laminin receptor, ␣7-integrin (Gardiner et al., 2005), necessary for optimal axonal regeneration in the peripheral nervous system. In cultures of dissociated DRG neurons of adult mice on laminin, robust spontaneous neurite outgrowth from IB4-negative neurons occurs and is strongly enhanced by previous axotomy. In contrast, IB4-labeled neurons show little neurite outgrowth and do not express GAP 43, even after axotomy or culture with GDNF. Moreover, growth of their axons through collagen gels is impaired compared with other DRG neurons. To determine whether the sparse neurite outgrowth of IB4-labeled neurons is attributable to lack of integrin expression, DRG cultures were infected with a herpes simplex 1 vector encoding ␣7-integrin, but its forced expression failed to promote neurite outgrowth in either IB4-labeled or other DRG neurons or in cultured adult retinal ganglion cells. Forced coexpression of both ␣7-integrin and GAP 43 also failed to promote neurite outgrowth in IB4-labeled neurons. In addition, cultured sciatic nerve segments were found to release much lower levels of GDNF, demonstrated by ELISA, than nerve growth factor. These findings together with their impaired intrinsic axonal regeneration capacity may contribute to the known vulnerability of the IB4-labeled population of DRG neurons to peripheral nerve injury.

The role of glial cells in influencing neurite extension by dorsal root ganglion cells

“…In contrast, the GDNF-responsive IB4 þve cells required an extra day in culture to generate a comparable number of neurite-bearing neurons. The slower extension of neurites by GDNF-responsive cells compared to NGF-responsive cells has been previously reported (Tucker et al, 2006;Leclere et al, 2007).…”

“…Furthermore, morphometric analysis showed that only 10% of neurons in the IB4 2ve population were .30 mm in diameter, yet approximately 35% were NF200-positive. This discrepancy might be due to binding of anti-heavy neurofilament antibodies to IB4 þve neurons (Leclere et al, 2007).…”

“…Thus, dissociated DRG cells are useful tools for studying factors and pathways that control neurite extension and recovery (Lindsay, 1988;Kimpinski and Mearow, 2001; Leclere et al, 2007). We have previously shown that prostaglandin E 2 can stimulate neurite retraction in rat DRG neurons by activating EP 3 receptors (Wise, 2006).…”

PTEN Inhibition to Facilitate Intrinsic Regenerative Outgrowth of Adult Peripheral Axons

“…IB4 neurons are nociceptive and innervate the epidermis (Hunt and Mantyh, 2001;Lu et al, 2001). Interestingly, IB4 neurons have been shown to have a reduced ability to regenerate in vitro, and following nerve injury in vivo, the projections from IB4 neurons retreat, resulting in hyperalgesia (Doubell et al, 1997;Leclere et al, 2007). This reduced growth capacity could be a feature linked to the high PTEN expression we identified within them, suggesting that PTEN inhibition may have a prominent role in the recovery of nociception after nerve injury.…”

Chondroitin Sulfates in Axon Regeneration and Plasticity

“…Similarly, expressing α9 integrin subunit via a viral vector in adult neurons markedly enhanced their ability to extend axons on a substrate containing its binding partner, tenascin-C, which is also upregulated post-injury at lesion sites (112). However, a separate experiment expressing α7 subunit in adult isolectin B4 (IB4)-labelled DRG and retinal neurons did not produce any growth-promoting effect (113). This suggests that the effect of over-expressing integrin subunit may vary depending on the ligands available and/or neuronal type.…”