Regenerating the brain from endogenous stem cells

1. Regenerating the brain from endogenous stem cells AI Ahmed1,2, M Zaben1,2, WP Gray1,2 1Clinical Neurosciences, University of Southampton and 2Wessex Neurological Centre, Southampton General Hospital, Tremona Road, Southampton, SO16 6YD

2. Key events in neural stem cell research Altman and Das identify dividing cells in the mammalian rodent nervous system EM studies confirm dividing cells are neurons Most studies of neurogenesis confined to the songbird 1992 Landmark paper in which cells from adult mammalian nervous system are isolated and divide to form free floating neurospheres. 1998 Erikson and colleagues identify new born neurons in adult humans 1960s 1970s 1980s 1990s 2000s

3. The neural stem cell cycle Neural Stem Cell SELF RENEWAL Progenitor Cell Glioblast Neuroblast DIFFERENTIATION Astrocyte Oligodendrocyte Neuron Neural stem cells have the key characteristics of self renewal and differentiation into all progeny subtypes. This includes Astrocytes, Oligodendrocytes and Neurons via intermediary progenitor cells.

4. Stem cell niches Defined as the microenvironment in which stem cells are found Influenced by growth factors, blood vessels, neurons, glia, extracellular matrix Permissive Niches Continued birth of neurons in adulthood Two well defined niches Subgranular zone of dentate gyrus of hippocampus Subventricular zone • Non Permissive niches • No new neurons in adulthood • Numerous including • Outer Cortex • Spinal Cord • Amygdala • Striatum Subventricular zone Hippocampus

5. Stem cells in the adult human brain Initial identification by Eriksson and colleagues1 Patients with terminal cancer given i.v. BRDU which incorporates into newly born cells Postmortem analysis reveals BRDU into neurons of dentate gyrus of hippocampus and subventricular zone Stem cells identified from surgical specimens both in permissive and non permissive niches • the subventricular zone2,3,4 • the periventricular subependymal zone5 • the hippocampus5 (our lab) • the olfactory bulb6 • the amygdala (our lab) • the insula cortex (our lab)

6. Stem cells in the adult human brain (2) Stem cells isolated from regions distinctly considered non-neurogenic • the spinal cord7 • the corpus callosum8 • the subcortical white matter9 In summary, there are cells with stem cell properties throughout the adult human brain

7. Understanding the regulatory mechanisms of stem cells The niche environment influences the stem cell. To manipulate the niche, an appreciation of the normal physiology is key. In the adult human brain, so far we can say: • Stem cells in different regions share common characteristics including proliferation and self-renewal • cells harboured in the adult human brain have the ability to develop into neurons • cells isolated from human tissue go through steps of morphological and electrophysiological development towards newly-born functional neurons • Cells expressing stem cell markers give rise to neurons • In animal studies, following targeted controlled cell death with a minimal inflammatory response, endogenous stem cells can perform a surprising level of anatomical repair both in permissive (hippocampus) and non-permissive (cortex) areas Human neural stem cells can be isolated from the adult brain and are capable of differentiating into functional neurons. If neurosurgeons are to contemplate using such cells in the treatment of neurological disorders, providing a source of cells that go on to survive is paramount

8. The next step Current therapeutic strategies use fetally derived stem cells for diseases such as Parkinson’s and spinal cord injury. Results have been disappointing. In this emerging field of ‘regenerative neurosurgery’, neurosurgeons could be involved in two distinct approaches to treatment • Following surgical resection, exogenous stem cells, derived from patients own cells, are expanded in culture and transplanted back • We can manipulate the stem cell niche with intrathecal or localised administration of medication, be it through a single procedure or a continuous delivery system.

9. How can a neurosurgeon effect repair? • Strategies to promote CNS repair. • Either • deployment of exogenous stem cells previously harvested • manipulation of endogenous stem cells Placement of drug delivery device (intrathecal or intraparenchymal catheter) Diagnosis of Disease TBI SCI Parkinson’s Stroke ALS stereotactic transplantation in vitro expansion

10. Conclusion • Stem cells are widespread in the adult human nervous system • Our understanding of the mechanistic processes is vital to effect repair • A neurosurgeon is poised to play a critical role in delivering factors or cells to manipulate the environment, and thus encourage repair

11. References • Eriksson, P.S. et al., Neurogenesis in the adult human hippocampus. Nat Med 4 (11), 1313-1317 (1998). • Ayuso-Sacido, A., Roy, N.S., Schwartz, T.H., Greenfield, J.P., & Boockvar, J.A., Long-term expansion of adult human brain subventricular zone precursors. Neurosurgery 62 (1), 223-229; discussion 229-231 (2008). • Moe, M.C. et al., A comparison of epithelial and neural properties in progenitor cells derived from the adult human ciliary body and brain. Exp Eye Res 88 (1), 30-38 (2009). • Westerlund, U. et al., Stem cells from the adult human brain develop into functional neurons in culture. Exp Cell Res 289 (2), 378-383 (2003). • Kukekov, V.G. et al., Multipotent stem/progenitor cells with similar properties arise from two neurogenic regions of adult human brain. Exp Neurol 156 (2), 333-344 (1999). • Casalbore, P. et al., Tumorigenic potential of olfactory bulb-derived human adult neural stem cells associates with activation of TERT and NOTCH1. PLoS ONE 4 (2), e4434 (2009). • Dromard, C. et al., Adult human spinal cord harbors neural precursor cells that generate neurons and glial cells in vitro. J Neurosci Res 86 (9), 1916-1926 (2008). • Chojnacki, A., Kelly, J.J., Hader, W., & Weiss, S., Distinctions between fetal and adult human platelet-derived growth factor-responsive neural precursors. Ann Neurol 64 (2), 127-142 (2008). • Nunes, M.C. et al., Identification and isolation of multipotential neural progenitor cells from the subcortical white matter of the adult human brain. Nat Med 9 (4), 439-447 (2003).