SPINE Volume 35, Number 11, pp 1116 –1121 ©2010, Lippincott Williams & Wilkins Differentiation of Endogenous Progenitors in an Animal Model of Post-Traumatic Syringomyelia Jian Tu, MBBS, PhD,*† Jinxin Liao, MBBS, PhD,† Marcus A. Stoodley, PhD, FRACS,*† and Anne M. Cunningham, PhD, FRACP‡ Study Design. An in vivo study to examine the differ- entiation of endogenous neural progenitor cells in an adult rat model of post-traumatic syringomyelia. Objective. To quantitatively evaluate the phenotypic fate of endogenous neural progenitor cells in post-trau- matic syringomyelia. Summary of Background Data. Although neural pro- genitors have been identified in the central nervous system, their differentiation in experimental post-traumatic syringo- myelia and possible role in the pathophysiology of this con- dition have not been investigated. Methods. Bromodeoxyuridine was used to label pro- liferating cells in a time-dependent rat model of post- traumatic syringomyelia. Eight neural markers were quantitatively analyzed to phenotype the cellular fate of these cells by double labeling immunohistochemistry. Results. Following syrinx induction, cell proliferation rate increased to 25–115 times that of cells in the intact and sham-operated controls with a peak at day 14 post- injury. In the earliest time points post-syrinx induction, ED1-expressing inflammatory cells formed a significant proportion of the proliferating population. Proliferating neural progenitor cells predominantly differentiated into NG2-expressing immature oligodendrocytes at all stages post-syrinx induction, except the final time point of 56 days. At this time, there was a peak in the number of newly generated astrocytes identified to have developed from labeled proliferating precursor cells. Conclusions. Endogenous neural progenitors prolifer- ate markedly following induction of post-traumatic sy- ringomyelia which consists of two stages, initial cyst formation and progressive cyst enlargement. During the former stage, macrophages proliferate in situ and contribute to the inflammatory process. The predominant cell type formed from progeny of the induced neural pro- genitors was characterized to be immature oliggodendro- cytes. However, during the latter stage of cyst development, there was an increase in astrocytic progeny which may represent an environment more conductive to glial scar formation acting to limit further cyst enlargement. Key words: adult progenitor/stem cell, astrocyte, dif- ferentiation, macrophage, rat, spinal cord injury, syringo- myelia, trauma. Spine 2010;35:1116 –1121 Post-traumatic syringomyelia (PTS) occurs in 20% of patients following spinal cord injury. 1 It causes progres- sive neurologic deficits in patients who often already have disabilities. Half of the patients do not respond to surgical treatment. 2 Advances in stem cell biology have demonstrated that endogenous progenitors can differen- tiate into astrocytes and oligodendrocytes in the adult spinal cord, 3 and the progenitors isolated from the spinal cord parenchyma are able to differentiate into neurons and glial cells in vitro. 4,5 There is therefore the theoretical possibility of stimulating cell prolifer- ation and differentiation resulting in sufficient neural progenitor cells to replace lost tissue and repair deficits caused by syrinxes. This strategy may offer an alterna- tive therapeutic option for the treatment of PTS in the future. Neural progenitors are those derived from the ner- vous system and have the capacity to divide and dif- ferentiate into neurons and glial cells. It was originally thought that the fully developed mammalian adult central nervous system (CNS) lacked significant regen- erative capacity. The differentiation of progenitors to neurons and glia in the adult brain, 6 intact spinal cord, 3 and animal models of spinal cord injury 7–9 has recently been demonstrated. However, whether the same is true in PTS is unknown. The pathophysiology of PTS is believed to consist of 2 stages: initial cyst formation and subsequently enlarge- ment. Initial cyst formation is likely caused by inflamma- tion, hematoma, infarction, or excitatory amino acid overproduction after trauma. 10 –13 In our previous re- port, 14,15 we have studied an animal model of PTS that shares many characteristics with human PTS. In this model, excitatory amino acid triggers inflammation, cel- lular injury, neuronal death, and contributes to initial cyst formation. Subsequently, an imbalance between ce- rebrospinal fluid inflow and outflow causes syrinx en- largement. 16,17 In our animal model of PTS, we focused on the question of whether progenitors exhibit in situ differentiation, and the phenotypic fate of these cells. From the *The Australian School of Advanced Medicine, Macquarie University, Sydney, New South Wales, Australia; †Prince of Wales Medical Research Institute, University of New South Wales, Sydney, New South Wales, Australia; and ‡School of Women’s and Children’s Health, University of New South Wales, Sydney, New South Wales, Australia. Acknowledgment date: March 30, 2009. Acceptance date: August 3, 2009. The manuscript submitted does not contain information about medical device(s)/drug(s). Foundation funds were received in support of this work. No benefits in any form have been or will be received from a commercial party related directly or indirectly to the subject of this manuscript. J.L. and J.T. contributed equally to this manuscript. Supported by a project grant from Australian Brain Foundation. This work was performed, in part, in the Westfield Research Labora- tory, Sydney Children’s Hospital. Address correspondence and reprint requests to Marcus Stoodley, PhD, FRACS, The Australian School of Advanced Medicine, Macquarie Uni- versity, Level 1, Dow Corning Building, 3 Innovation Rd, Sydney, NSW 2109, Australia; E-mail: marcus@teamneuro.com 1116