Date of Award
Medical Doctor (MD)
Stephen M. Strittmatter
Disorders affecting the CNS are significantly disabling and often carry a poor prognosis of functional recovery. Pharmacotherapies that promote functional improvement via neuroregeneration have proven to be an elusive goal. Factors intrinsic to the neuronal microenvironment, particularly myelin-associated proteins such as Nogo-A, MAG, and OMgp, have been shown to be important in inhibiting such regeneration through neuronal NgR1. Additionally, LPA signaling through LPA1 has also shown to be important in inhibiting neuroregeneration through mechanisms that are currently being researched.
It has been previously shown that application of a NgR1 decoy receptor (AA-NgR(310)ecto-Fc) increases sprouting below the site of the lesion in rats with spinal cord contusion injuries. Likewise, application of this same decoy receptor effectively disinhibited functional recovery as exemplified by the increase in percentage of weight-bearing rats treated with the decoy receptor. Noting the more ideal synthetic properties of a small molecule pharmaceutical, here we attempt to use a small molecule inhibitor of NgR1 to induce the in vitro regeneration of axons following scrape injury as well as in an in vivo model of mice with SCI. Additionally, noting the importance of LPA1 as shown through previous studies, we also attempt to utilize a small molecule inhibitor of LPA1 to promote axonal regeneration.
Our results show that inhibition of NgR1 with the small molecule inhibitor YU-NR-008 did not significantly improve axonal regeneration in vitro. Application of the NgR1 inhibitor YU-NR-008 alone showed a trend toward improved axonal regeneration, albeit insignificant (mean signal intensity for YU-NR-008 treated animals at 1.243 ± 0.128 vs. control 1.00 ± 0.00, p = 0.0787). Co-treatment with YU-NR-008 and Nogo-22 did not rescue Nogo-22-mediated inhibition of axonal regeneration (Nogo-22 0.771 ± 0.051 vs. Nogo-22 with YU-NR-008 at 0.801 ± 0.073). Additionally, functional recovery as measured by the Basso Mouse Scale (BMS) was not improved with the administration of YU-NR-008 following SCI for 2 or 4 weeks (D32 BMS scores were 4.643 ± 0.713 (SEM) for control vs. 3.550 ± 0.669 for animals treated with YU-NR-008 for 4 weeks). Likewise, administration of the LPA1 antagonist AM095 did not improve functional recovery following SCI (mean BMS at 54 days for AM095-treated animals was 3.182 ± 0.532 vs. 5.033 ± 0.448 for vehicle-treated animals). We conclude that the tested doses of YU-NR-008 and AM095 were ineffective in promoting recovery in a rodent model spinal cord injury. Additional studies will be needed to determine whether axonal growth was stimulated by these doses, or if drug doses failed to achieve the cellular target effect following spinal cord injury.
Naiditch, Hiam, "The Application Of Small Molecule Inhibitors Of Ngr1 And Lpa1 Towards The Goal Of Neuroregeneration In The Central Nervous System" (2017). Yale Medicine Thesis Digital Library. 2158.