Neuroprotection & Axoprotection
Undifferentiated neural progenitor/stem cells (NPs) have previously been shown to provide pro-survival trophic support in both in vivo and in vitro systems. Our studies focus upon the capacity of grafted undifferentiated stem/progenitor cells to provide therapeutic molecules in the microenvironment and potentially stimulate dormant plasticity in the injured host brain that can yield neural repair. The goal was to use implanted NPs as a tool to find novel targets for therapeutic intervention. In a rat model of Parkinson’s disease, we proposed to examine whether implanted NPs could afford neuroprotection to dopamine (DA) neurons exposed to a 6-OHDA lesion and by what mechanism. Implanted undifferentiated NPs were found to provide neuroprotection for the nigrostriatal DA system [Madhavan et al., 2009, J Comp Neurol. 15:102-15]. An unexpected finding of implanting NPs was that it provoked the proliferation and migration of endogenous subventricular zone (SVZ) derived NPs. Through anti-mitotic treatments that prevented the proliferation of SVZ NPs, the neuroprotective response of the implanted NPs was reduced by ~50% [Madhavan et al., 2012, Eur J Neurosci. 35:883-95]. Similarly, by silencing one critical factor of several within NPs prior to their implantation (sonic hedgehog, SHH), a similar reduction in neuroprotection by ~50% was observed. This series of studies indicates that the observed neuroprotection is the result of communication/collaboration between grafted NPs and endogenous NPs. In addition, the studies suggest that SHH signaling is critical to induce the host response and guide an endogenous host repair response to the DA system.
Transplanted NPCs provide partial protection of the midbrain dopamine system that degenerates in Parkinson’s disease and in this rat 6-OHDA toxin model of parkinsonism.
Panels a, c & d illustrate the extent of loss of dopamine cell bodies in the midbrain (c), and dopamine terminals in the striatum (a) of control rats. Panels b, e & f illustrate the partial preservation of this system with grafted NPCs. Panel g = counts of substantia nigra dopamine neurons in the treatment groups.
Neuroprotection of the dopamine system by grafted NPCs is accompanied by proliferation of NPCs endogenous to the host brain in the subventricular zone and the extent of neuroprotection correlates with the magnitude of this host brain response. Panels a-d = staining for brdU, panels e-h = staining for nestin. Both are markers for NPCs resident in the host brain. a & e = baseline condition, b & f = following 6-OHDA lesion, c, d, g & h= proliferative response to NPC transplantation to induce neuroprotection. Panel i = counts of endogenous NPCs in treatment conditions. Panel j = correlation between enhanced dopamine neuron protection (TH cells) and enhanced proliferation of host NPCs (SVZ brdU cells).
Grafted NPCs (hPAP+) express glial cell line-derived neurotrophic factor (GDNF) and sonic hedgehog (SHH).
Inhibition of endogenous neurogenesis via treatment with Ara-C reduces the neuroprotective effects of grafted NPCs and diminishes behavioral recovery. Diminished neuroprotection is associated with a reduced number of grafted NPCs expressing nestin and sonic hedgehog (Shh). This finding suggests that the presence of endogenous neural stem cells is important for the expression of these molecules in grafted NPCs, and in turn, that expression of nestin and Shh are important for full neuroprotection of the dopamine system.
Diminished neuroprotection of dopamine neurons following inhibition of endogenous neurogenesis via treatment with Ara-C is associated with increased glial markers of inflammation.
Silencing (shRNA) SHH, or SHH + GDNF, in NPCs prior to grafting decreases neuroprotection for dopamine neurons and reduces behavioral benefit. Decreasing expression of SHH in transplanted NPCs preferentially reduces expression of nestin and increases the presence of markers for inflammation.
In Summary, the accomplishments of these studies moved the field as follows:
- Implantation of undifferentiated neural progenitor cells in a rat model of parkinsonism exert DA neuroprotection and induce proliferation and migration of progenitors from the host SVZ. First demonstration that neuroprotection provided by implanted progenitor cells in parkinsonian rats induce a response in host progenitor cells.
- Proliferation and migration of host SVZ progenitor cells is required for full DA neuroprotection provided by implanted progenitor cells. First demonstration that grafted progenitor cells and intrinsic progenitor cells collaborate in producing neuroprotection.
- Sonic hedgehog (SHH) expressed by grafted progenitor cells is critical for neuroprotection. First demonstration that graft-derived SHH is sufficient to induce proliferation and migration of host SVZ progenitors associated with DA neuroprotection.
- Dopamine neuroprotection produced by the interaction of grafted and endogenous neural progenitor cells is associated with reduced inflammation.
New Direction: Axoprotection
Madhavan L, Daley BF, Sortwell CE, Collier TJ (2012) Endogenous neural precursors influence grafted neural stem cells and contribute to neuroprotection in parkinsonian rat. Eur J Neurosci 35:883-95.
Madhavan L, Collier TJ (2010) A synergistic approach for neural repair: cell transplantation and induction of endogenous precursor cell activity. Neuropharmacol 58:835-44.
Madhavan L, Daley BF, Paumier KL, Collier TJ (2009) Transplantation of subventricular zone neural precursors induces an endogenous precursor cell response in a rat model of Parkinson’s disease. J Comp Neurol 515:102-15.
Udall Projects & Services
Director: Kathy Steece-Collier, Ph.D.
Director: Caryl E. Sortwell, Ph.D.
Director: Jack W. Lipton, Ph.D.
Director: Timothy J. Collier, Ph.D
Director: Fredric P. Manfredsson, Ph.D.
Director: Timothy J. Collier, Ph.D