Neuroprotective effect of TrkB agonist antibody in humanized TrkB rat

Abstract

Purpose : Tropomyosin receptor kinase B (TrkB) is a promising target for neuroprotection in neurodegenerative diseases such as glaucoma. The present study was undertaken to evaluate the neuroprotective effect of the endogenous TrkB agonist brain-derived neurotrophic factor (BDNF) and a TrkB agonist mAb in wild-type (WT) mice, rat and compared it with humanized TrkB mouse, rat.

Methods : Humanized TrkB mouse and rat (TrkB^hu/hu) were generated with Velocigene technology (Regeneron). The in vitro effects of BDNF and TrkB Ab were quantified by cell survival assays using differentiated human neuroblastoma cell line SH-SY5Y. TrkB phosphorylation was examined in cultured cortical neurons from TrkB^hu/hu mice. To test the in vivo neuroprotective effect, WT and humanized TrkB mice and rats were used. Animals received intravitreal (IVT) injections of BDNF or TrkB Ab on day 0, and day 3 (for mouse), or day 3 and 10 (for rat) post optic nerve transection. Retinal ganglion cell (RGC) number was quantified at 1 week for mouse or 2 weeks for rat after optic nerve transection by Brn3a IHC on retinal flatmounts.

Results : In vitro, BDNF or TrkB Ab significantly increased cell survival in retinoic acid differentiated SH-SY5Y cells. The effects showed bell shaped dose responses with the optimal dose of 1ug/ml for BDNF or 10ug/ml for TrkB Ab. RGC death in TrkB^hu/hu mice was similar to WT mice at 1 or 2 weeks after optic nerve transection. BDNF or TrkB Ab had small or no significant neuroprotective effect in WT or TrkB^hu/hu mouse. In contrast, there was significant RGC neuroprotection in TrkB^hu/hu rats with IVT TrkB Ab. A decrease in body weight was observed in TrkB^hu/hu mouse but not rat after IVT TrkB Ab treatment. BDNF had no effect on body weight in either mouse nor rat.

Conclusions : Intravitreal administration of TrkB agonist mAb shows a significant neuroprotective effect after optic nerve injury in humanized TrkB rat. Further studies will be needed to elucidate the possible differences in BDNF and TrkB Ab activation, distribution and clearance after IVT. The humanized TrkB rat will be a useful model to further test the efficacy of TrkB Ab in vivo.

This is an abstract that was submitted for the 2018 ARVO Annual Meeting, held in Honolulu, Hawaii, April 29 - May 3, 2018.