Netrin-1 drives cell-type-specific plasticity of human dopaminergic neurons during circuit integration in a Parkinsonian model

The survival of transplanted ventral midbrain (vm) dopaminergic neurons (DAn) and their innervation of host striatal tissue are crucial for ameliorating motor symptoms in Parkinson`s disease (PD). However, human pluripotent stem cells (hPSC) show inferior axonal plasticity compared to fetal donor tissue. While modulation of the host environment with trophic cues, such as glial cell-derived neurotrophic factor (GDNF), can improve graft outcomes, these cues lack specificity for DAn, resulting in plasticity of other neurons within the graft. Using single nuclei RNA sequencing, we identified axonal guidance pathways (Semaphorin, Netrin and Wnt) that were preferentially activated in DAn within the graft. Overexpression of Semaphorin3A/SEMA3A, Netrin1/NTN1 or WNT5A in the striatum of Parkinsonian mice following vm DA progenitor transplantation promoted A9-DA specification and selectively increased DA innervation of the host striatum, without off-target extrastriatal DA innervation observed in response to GDNF. In Parkinsonian rats, NTN1 overexpression promoted graft-induced motor recovery, selective DA plasticity and activation of postsynaptic striatal neurons without evidence of non-DAn plasticity. Further, snRNA-sequencing of NTN1 or GDNF-treated grafts confirmed the upregulation of DA-specific plasticity by NTN1, while GDNF promoted plasticity in both DA and non-DAn. These findings highlight the capacity to improve on-target integration of hPSC-derived DAn in grafts by selectively targeting DA-specific plasticity. Taken together, these results demonstrate the utility of DA-specific cues to promote functional recovery, improve graft predictability, and limit off-target innervation.