Paul Lu, Ph.D.
Assistant Research Scientist
My primary research is focused on combinatorial approaches to promote axon regeneration after spinal cord injury. Combinatorial treatments include testing neurotrophic factor delivery into and beyond spinal cord lesions in conjunction with augmenting intrinsic gene expression within injured neurons. Previous studies have shown that cAMP-mediated signaling pathways can induce an axonal growth state that is able to overcome local myelin inhibition. Combining cAMP stimulation of neuronal cell bodies, implants of autologous bone marrow stromal cells (BMS) into spinal cord lesion cavities to form a growth-supporting cellular matrix in the lesion cavity , and growth factor delivery into and beyond lesion sites in the spinal cord we observed, in our own hands for the first time, convincing evidence of axonal bridging in mid-cervical spinal cord lesion sites (Journal of Neuroscience, 2004). Somal stimulation with cAMP, a growth factor beyond the lesion site, and a cellular bridge in the lesion site are all required to achieve bridging regeneration; omission of any of these components eliminates bridging for significant distances.
We further tested two systemically-administered phosphodiesterase (PDE) inhibitors, rolipram (PDE IV) and milrinone (PDE III) to determine whether peripheral pharmacological strategies can replicate the effects of direct cAMP injections. Our results show that rolipram and milrinone are less effective in promoting axon regeneration than direct administration of cAMP into dorsal root ganglia. This is probably due to PDE inhibitors causing only transient elevations of cAMP levels. We currently aim to identify other agents that can elevate intrinsic cAMP levels in CNS neurons.
Using similar combinatorial approaches, our preliminary experiments show that motor axons, such as reticulospinal axons and rubrospinal axons, also regenerate into and beyond hemisection-lesioned cell graft sites in the cervical spinal cord. We are currently using a model of complete spinal cord transection to confirm motor axon regeneration beyond a lesion site.
Triple label for CTB-labeled sensory axons (red), implanted MSCs (green, expressing GFP), and astrocytes (GFAP, blue). Click to view complete figure in a new window.
In addition, we are extending our combinatorial approach to study axon regeneration in the chronically injured spinal cord. We initially found that an extensive glial and extracellular "scar" persists at a chronic, 3-month post-lesion stage of spinal cord injury, but that resection of this scar is not necessary to elicit axonal growth beyond the scarred region and into a lesion cavity. Furthermore, the addition of a growth factor augments regeneration of chronically-injured axons without scar removal. In the chronic injury paradigm, we use the combinatorial approach described above to test whether axons can regenerate beyond the lesion site through the chronic scar to enter the intact, inhibitory environment distal to the lesion site. With post-conditioning lesions of peripheral nerve and delivery of neurotrophins into and beyond mid-cervical lesion sites, sensory axons regenerate not only into the lesion site, but beyond and into host white matter for several millimeters. These data indicate that conditioning lesions performed long after central injury can effectively stimulate the intrinsic growth capacity of sensory neurons, and that only a combinatorial approach is sufficiently potent to elicit bridging axonal regeneration beyond chronic lesion sites.
Lu P, Jones LL, Tuszynski MH. Axon regeneration through scars and into sites of chronic spinal cord injury. Experimental Neurology (2007): 203:8-21.
Lu P, Yang H, Culbertson M, Graham L, Roskams AJ, Tuszynski MH. Olfactory ensheathing cells do not exhibit unique migratory or axonal growth-promoting properties after spinal cord injury. Journal of Neuroscience (2006): 26:11120-11130.
Lu P, Jones LL, Tuszynski MH. BDNF-expressing marrow stromal cells support extensive axonal growth at sites of spinal cord injury. Experimental Neurology (2005): 191:344-360.
Lu P, Yang H, Jones LL, Filbin MT, Tuszynski MH. Combinatorial therapy with neurotrophins and cAMP promotes axonal regeneration beyond sites of spinal cord injury. Journal of Neuroscience (2004): 24:6402-6409.
Lu P, Blesch A, Tuszynski MH. Induction of bone marrow stromal cells to neurons: differentiation, transdifferentiation, or artifact? Journal of Neuroscience Research(2004): 77:174-191.
Lu P, Jones LL, Snyder EY, and Tuszynski MH. Neural stem cells constitutively secrete neurotrophic factors and promote extensive host axonal growth after spinal cord injury. Experimental Neurology (2003): 181: 115-129.
Lu P, Tuszynski MH. Stem cells for spinal cord injury. In: Neural Stem Cells for Brain and Spinal Cord Repair (2002). Zigova T, Snyder EY and Sanberg PR, eds. Humana Press, Totowa, NJ.
Lu, P, Blesch, A., and Tuszynski, MH. Neurotrophism without neurotropism: BDNF promotes survival but not growth of lesioned corticospinal neurons. Journal of Comparative Neurology (2001): 436: 456-470.