Stem cell therapy in stroke: strategies in basic study and clinical application

Acta Neurochir Suppl (2006) 99: 137–139

# Springer-Verlag 2006 Printed in Austria

Stem cell therapy in stroke: strategies in basic study and clinical application

D. D. Liu

, W. C. Shyu

, and S. Z. Lin

1

Department of Dentistry, Tzu-Chi Buddhist General Hospital, Tzu-Chi University, Hualien, Taiwan

2

Neuro-Medical Scientific Center, Tzu-Chi Buddhist General Hospital, Tzu-Chi University, Hualien, Taiwan

Summary

Stem cell therapies are an important strategy for the treatment of stroke. Bone marrow-derived stem cells (BMSCs) may promote struc- tural and functional repair in several organs via stem cell plasticity. The tissue damage could stimulate the stem cells migration, and they track into the site of damage and then undergo differentiation. The plasticity functions of BMSCs in an injuries tissue are dependent on the specific signals present in the local environment of the damaged tissue. Recent studies have also identified the specific molecular signals, such as SDF- 1 =CXCR4, required for the interaction of BMSCs and damaged host tissues. This review summarizes the current understanding of how BMSCs reach and function in cerebral ischemic tissues.

Keywords: Stroke; stem cells; homing; therapy.

Introduction

Atherosclerosis of cerebral vessels leads to focal ischemic stroke and subsequent degeneration in the re- stricted central nervous system region with acute loss of neurons, astrocytes and oligodendrocytes [1]. This pro- cess finally results in tissue necrosis and possibly irre- versible impairment of brain functions. In neurological disorders the aim of cell therapy is to replace, repair or enhance the biological function of damaged cells in order to restore brain function.

Several different types of stem cells, such as those from peripheral blood, bone marrow, and embryonic stem cells, have been successfully used to induce neu- rogenesis and functional recovery in various experimen- tal models of ischemia [2, 3].

This functional recovery of the damaged brain is de- pendent on the response to specific signals present in the local ischemic tissue micro-environment. The beneficial effects are considered to be mediated by two factors: (1) increasing endogenous angiogenic, neurogenic and anti-

apoptotic factors due to interactions between BMSCs and host brain parenchymal cells [2, 4, 5]; (2) differen- tiation of BMSCs themselves directly into both neuronal and endothelial cells that restore brain function [2].

Thus, BMSCs have neuroprotective effects not only directly, through their differentiation, but also through their ability to induce angiogenic, neurogenic and anti- apoptotic factors either by themselves or by interaction with host cells.

This review will focus on our recent studies on stem cell-based therapies for application in stroke patients, the possible mechanisms that may be involved in stem cell-based therapies, and how stem cells reach the site of cerebral ischemia and function there in the context of stem cell plasticity.

Granulocyte-colony stimulating factor (G-CSF) and stem-cell based therapy

Granulocyte colony-stimulating factor (G-CSF), a 20- kDa glycoprotein, is able to mobilize stem cells from bone marrow into the peripheral blood (PB) [6]. Recom- binant G-CSF is also a common treatment after hema- tologic disease, or chemotherapy, when white blood cell counts tend to be dangerously low and there is a risk of infection [7]. G-CSF is also widely used to induce mobi- lization of blood precursors in different clinical settings such as chemotherapy-induced myelosuppression and peripheral blood stem cell recollection for autologous and allogeneic bone marrow transplantation [8].

We have recently demonstrated that G-CSF can en-

hance tissue regeneration and improve the survival rate

after stroke by mobilizing BMSCs from bone marrow

into peripheral blood [9]. Our earlier study showed that subcutaneous injections of G-CSF, starting one day after cerebral ischemia and continuing for up to 5 days, pro- mote BMSC migration to the injured brain and enhance neural repair in rats suffering from cerebral ischemia [9].

Infarction volume was markedly reduced, and there was also significant recovery of neurological dysfunc- tion. G-CSF may enhance this process by increasing the number of circulating BMSCs, and their infiltration into the CNS. In addition, a sufficient number of BMSCs, mobilized by G-CSF, could home in on cerebral ische- mic injuries to promote neuronal repair and recovery of brain function; this would provide a basis for the development of a non-invasive autologous therapy for cerebral ischemia. If G-CSF treatment can mobilize autologous BMSCs into circulation, enhance their trans- location into the ischemic brain and thus significantly improve lesion repair, it represents an attractive strategy for the development of a clinically significant non-inva- sive stroke therapy. Our recent pilot clinical trial demon- strated that G-CSF could mobilize BMSCs in patients after acute stroke in a safe, feasible manner and provide a neurological outcome superior to conventional treat- ment (Shyu et al. manuscript submitted).

Chemotaxic factor of SDF-1 =CXCR4

SDF-1 is a strong chemo-attractant for CD34

cells that express CXCR4, the receptor for SDF-1, and it plays an important role in BMSC trafficking between peripheral circulation and bone marrow [10]. SDF-1 regulates adhesion =chemotaxis of bone marrow hemato- poietic progenitor cells through activation =regulation of specific integrin molecules [11–13]. Over-expression of SDF-1 in ischemic tissues has recently been found to enhance BMSC recruitment from PB and to induce neo- angiogenesis [14, 15]. Since mobilized peripheral blood stem cells are increasingly used for clinical cell trans- plantation, it is becoming clear that proteolytic degrada- tion of SDF-1 and CXCR4 on stem cells is an important step in stem cell release and homing [16].

Since SDF-1 receptors are present on bone marrow stem cells [17], up-regulation of SDF-1 in the local ischemic damage after injury [18–20] may be related to homing and engraftment of stem cell to the injured tissue. Hill et al. [21] recently demonstrated that up- regulation of SDF-1 was associated with endothelial cells when GFP-bone marrow transplanted mice under- went temporary middle cerebral artery occlusion (MCAo).

We hypothesize that SDF-1 is up-regulated in ischemic

tissues and that ischemia-associated hypoxia causes an imbalance between plasma and bone marrow SDF-1 concentration, resulting in the transient establishment of an SDF-1 gradient that favors stem cell translocation into ischemic tissue, thereby enhancing angiogenesis and functional recovery.

Function of stem cells in ischemic brain

It is possible that BMSCs migrating to the ischemic hemisphere create local chemical gradients and =or local- ized chemokine accumulation, dictating a directional response in endothelial, neuronal and glial progenitor cells [14]. For example, SDF-1 might also stimulate host endothelium progenitor cell (EPC) differentiation from pre-existing blood vessels and =or host EPCs derived from bone marrow [22]. In the ideal transplantation sce- nario, stem cells implanted directly into or around the damaged area would differentiate in situ into those ori- ginal host cells that have died. The optimum strategy would probably be to combine transplantation of neural stem cells (NSCs) close to the damaged area with sti- mulation of neurogenesis from endogenous NSCs form- ing a ‘‘new neuron network’’.

The results of our recent study suggested that mobi- lized EPCs contributed to ‘‘collateral circulation’’, and could even ‘‘line-up’’ and ‘‘build’’ new vessels in the ischemic brain [23].

Conclusion

Definitely, cell therapy may serve as a future restora- tive therapy for stroke. Further studies are necessary to examine whether stem cells can have a therapeutic role as, supportive cells, a sole treatment and =or as vehicles of gene delivery; and to what extent these cells are capa- ble of neuronal remodeling. Moreover, it remains to be shown how transplanted cells are integrated into neuro- nal circuits and promote functional recovery, and whether grafts survive for long periods of time.

References

1. Blau HM, Brazelton TR, Weimann JM (2001) The evolving concept of a stem cell: entity or function ? Cell 105: 829–841

2. Chen J, Li Y, Wang L, Zhang Z, Lu D, Lu M, Chopp M (2001) Therapeutic benefit of intravenous administration of bone marrow stromal cells after cerebral ischemia in rats. Stroke 32: 1005–1011 3. Li Y, Chen J, Chen XG, Wang L, Gautam SC, Xu YX, Katakowski M, Zhang LJ, Lu M, Janakiraman N, Chopp M (2002) Human marrow stromal cell therapy for stroke in rat: neurotrophins and functional recovery. Neurology 59: 514–523

138 D. D. Liu et al.

4. Sun Y, Jin K, Xie L, Childs J, Mao XO, Logvinova A, Greenberg DA (2003) VEGF-induced neuroprotection, neurogenesis, and angiogenesis after focal cerebral ischemia. J Clin Invest 111:

1843–1851

5. Lu D, Mahmood A, Wang L, Li Y, Lu M, Chopp M (2001) Adult bone marrow stromal cells administered intravenously to rats after traumatic brain injury migrate into brain and improve neurological outcome. Neuroreport 12: 559–563

6. Demetri GD, Griffin JD (1991) Granulocyte colony-stimulating factor and its receptor. Blood 78: 2791–2808

7. Wong SF, Chan HO (2005) Effects of a formulary change from granulocyte colony-stimulating factor to granulocyte-macrophage colony-stimulating factor on outcomes in patients treated with myelosuppressive chemotherapy. Pharmacotherapy 25: 372–378 8. Law P, Lane TA (2002) Mobilization of allogeneic peripheral blood

progenitor cells. Cancer Treat Res 110: 51–77

9. Shyu WC, Lin SZ, Yang HI, Tzeng YS, Pang CY, Yen PS, Li H (2004) Functional recovery of stroke rats induced by granulocyte colony-stimulating factor-stimulated stem cells. Circulation 110:

1847–1854

10. Petit I, Szyper-Kravitz M, Nagler A, Lahav M, Peled A, Habler L, Ponomaryov T, Taichman RS, Arenzana-Seisdedos F, Fujii N, Sandbank J, Zipori D, Lapidot T (2002) G-CSF induces stem cell mobilization by decreasing bone marrow SDF-1 and up-regulating CXCR4. Nat Immunol 3: 687–694

11. Wright DE, Bowman EP, Wagers AJ, Butcher EC, Weissman IL (2002) Hematopoietic stem cells are uniquely selective in their migratory response to chemokines. J Exp Med 195: 1145–1154 12. Peled A, Kollet O, Ponomaryov T, Petit I, Franitza S, Grabovsky V,

Slav MM, Nagler A, Lider O, Alon R, Zipori D, Lapidot T (2000) The chemokine SDF-1 activates the integrins LFA-1, VLA-4, and VLA-5 on immature human CD34( þ) cells: role in transendothe- lial =stromal migration and engraftment of NOD=SCID mice. Blood 95: 3289–3296

13. Jo DY, Rafii S, Hamada T, Moore MA (2000) Chemotaxis of primitive hematopoietic cells in response to stromal cell-derived factor-1. J Clin Invest 105: 101–111

14. Yamaguchi J, Kusano KF, Masuo O, Kawamoto A, Silver M, Murasawa S, Bosch-Marce M, Masuda H, Losordo DW, Isner JM, Asahara T (2003) Stromal cell-derived factor-1 effects on ex vivo expanded endothelial progenitor cell recruitment for ischemic neovascularization. Circulation 107: 1322–1328

15. Hiasa K, Ishibashi M, Ohtani K, Inoue S, Zhao Q, Kitamoto S, Sata M, Ichiki T, Takeshita A, Egashira K (2004) Gene transfer of stromal cell-derived factor-1alpha enhances ischemic vasculogen- esis and angiogenesis via vascular endothelial growth factor=

endothelial nitric oxide synthase-related pathway: next-generation chemokine therapy for therapeutic neovascularization. Circulation 109: 2454–2461

16. Levesque JP, Hendy J, Takamatsu Y, Simmons PJ, Bendall LJ (2003) Disruption of the CXCR4 =CXCL12 chemotactic interaction during hematopoietic stem cell mobilization induced by GCSF or cyclophosphamide. J Clin Invest 111: 187–196

17. Rodgers KE, Xiong S, Steer R, diZerega GS (2000) Effect of angiotensin II on hematopoietic progenitor cell proliferation. Stem Cells 18: 287–294

18. Yamagishi H, Kim S, Nishikimi T, Takeuchi K, Takeda T (1993) Contribution of cardiac renin-angiotensin system to ventricular remodelling in myocardial-infarcted rats. J Mol Cell Cardiol 25:

1369–1380

19. Sawa H, Kawaguchi H, Mochizuki N, Endo Y, Kudo T, Tokuchi F, Fijioka Y, Nagashima K, Kitabatake A (1994) Distribution of angiotensinogen in diseased human hearts. Mol Cell Biochem 132: 15–23

20. Hirsch AT, Talsness CE, Schunkert H, Paul M, Dzau VJ (1991) Tissue-specific activation of cardiac angiotensin converting enzyme in experimental heart failure. Circ Res 69: 475–482

21. Hill WD, Hess DC, Martin-Studdard A, Carothers JJ, Zheng J, Hale D, Maeda M, Fagan SC, Carroll JE, Conway SJ (2004) SDF-1 (CXCL12) is upregulated in the ischemic penumbra following stroke: association with bone marrow cell homing to injury. J Neuropathol Exp Neurol 63: 84–96

22. Chen J, Zhang ZG, Li Y, Wang L, Xu YX, Gautam SC, Lu M, Zhu Z, Chopp M (2003) Intravenous administration of human bone marrow stromal cells induces angiogenesis in the ischemic bound- ary zone after stroke in rats. Circ Res 92: 692–699

23. Buschmann IR, Hossmann KA (2005) Letter regarding article by Shyu et al, ‘‘functional recovery of stroke rats induced by granu- locyte colony-stimulating factor-stimulated stem cells’’. Circula- tion 111: e297–e298; author reply e297–e298

Correspondence: Shinn-Zong Lin, Neuro-Medical Scientific Center, Tzu-Chi Buddhist General Hospital, Tzu-Chi University, Hualien, Taiwan. e-mail: szlin@tzuchi.org.tw

Stem cell therapy in stroke 139