| Abstract No.: | A-D1141 |
| Country: | Canada |
| | |
| Title: | EVIDENCE THAT NETRIN-DCC INTERACTIONS ARE INVOLVED IN PERIPHERAL NERVE REGENERATION |
| | |
| Authors/Affiliations: | 1 Christine Webber*; 1 Chu Chen; 1 Kimberly Vanneste; 1 Jose Martinez; 1 Douglas Zochodne;
1 University of Calgary, AB, Canada
|
| | |
| Content: | Background: Adult regenerating sensory neurons can be guided in vitro and it is likely that such guidance could play critical roles in regenerative success of injured axons in vivo. The guidance factor netrin-1 attracts embryonic Xenopus commissural and retinal axons when they express the deleted in colo-rectal cancer (DCC) receptor and these same axons are repelled by this ligand when they express the uncoordinated 5h (Unc5h) receptor. In the adult rat, studies have shown netrin-1 and the Unc5h1-3 receptor isoforms, but not the DCC mRNAs are present in dorsal root ganglia (DRG).
Objectives: To determine the expression pattern of netrin-1 and its receptors DCC and Unc5h1-3 during peripheral nerve regeneration. We explore the function of DCC during regenerative pathfinding in adult peripheral neurons in vivo.
Materials and Methods: Adult male Sprague-Dawley rats were sham-injured, or the left sciatic nerve was transected at mid-thigh levels for 3 or 7 days. Uninjured or lesioned sciatic nerves and their DRGs were used for immunohistochemistry and qRT-PCR of neuron-purified DRGs was used to analyze mRNA expression. Proximal and distal stumps of cut sciatic nerves were placed in either ends of a silicone conduit with a T connection to a subcutaneous access port. DCC-siRNA or scrambled (control) siRNA were injected into the chamber at 1, 3 and 5 days post-injury and on day 7 outgrowth of axons and Schwann cells (SCs) into the regenerative bridge was assessed.
Results: In control and lesioned animals, DCC protein was expressed within the sciatic nerve and in the small and medium-sized DRG neurons. Low levels of DCC mRNA were seen in the uninjured state, and there was an increase in DCC mRNA expression in DRG neurons following a 3 day sciatic nerve injury. The mRNAs for the Unc5h1-3 receptors were highly expressed in the adult DRG and all isoforms decreased at 3 and 7 days post-injury. There was no significant change in netrin-1 mRNA expression following sciatic nerve injury. Moreover, reduced DCC mRNA expression in vivo, by DCC siRNA injection into the regeneration chamber altered the normal trajectory of regenerating axons from the proximal nerve stump. Fewer axons extended across the regeneration bridges, which formed across the transection gap compared to axons that were exposed to control siRNA. When exposed to the DCC siRNA construct, SC processes were also misdirected and had impaired growth into regenerative bridges.
Conclusion: We show netrin-1 may play an important role in the PNS during regeneration. The DCC mRNA and protein, and mRNA of the Unc5h1-3 receptors are found in the adult DRG in the injured and uninjured state. DCC mRNA levels increase in the DRG following nerve injury and there is a decrease in Unc5h1-3 levels, supporting a role for the DCC receptor during nerve regeneration. The decrease of DCC mRNA at the injury site is associated with misdirected growth and impaired entry into regenerative bridges by both axons and SC processes.
|
| | |
| Back |
|
