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TISSUE-SPECIFIC STEM CELLS

Ciliary Neurotrophic Factor-Mediated Signaling Regulates Neuronal Versus Glial Differentiation of Retinal Stem Cells/Progenitors by Concentration-Dependent Recruitment of Mitogen-Activated Protein Kinase and Janus Kinase-Signal Transducer and Activator of Transcription Pathways in Conjunction with Notch Signaling

Department of Ophthalmology and Visual Sciences, University of Nebraska Medical Center, Omaha, Nebraska, USA

Key Words. Ciliary neurotrophic factor • Notch • Retina • Stem cells/progenitors • Neurons • Glia • Müller cells

Correspondence: Correspondence: Iqbal Ahmad, Ph.D., Ophthalmology and Visual Sciences, 4044 Durham Research Center, Nebraska Medical Center, Omaha, Nebraska 68198-5840, USA. Telephone: 402-559-4091; Fax: 402-559-3251; e-mail: iahmad{at}unmc.edu

Received on March 4, 2008; accepted for publication on July 19, 2008.

First published online in STEM CELLS EXPRESS  July 31, 2008.

In the retina, as elsewhere in the central nervous system, neurogenesis precedes gliogenesis; that is, the only glia in the retina, Müller cells, are born when the majority of neurons have already been generated. However, our understanding of how the multipotent retinal stem cells/progenitors choose to differentiate along neuronal and glial lineages is unclear. This information is important in promoting directed differentiation of retinal stem cells/progenitors in an ex vivo or in vivo stem cell approach to treating degenerative retinal diseases. Here, using the neurosphere assay, we demonstrate that ciliary neurotrophic factor (CNTF), acting in a concentration-dependent manner, influences the simultaneous differentiation of retinal stem cells/progenitors into neurons or glia. At low CNTF concentrations differentiation of bipolar cells is promoted, whereas high CNTF concentrations facilitate Müller cell differentiation. The two concentrations of CNTF lead to differential activation of mitogen-activated protein kinase and Janus kinase-signal transducer and activator of transcription (Jak-STAT) pathways, with recruitment of the former and the latter for the differentiation of bipolar and Müller cells, respectively. The concentration-dependent recruitment of two disparate pathways toward neurogenesis and gliogenesis occurs in concert with Notch signaling. Furthermore, we demonstrate that the attenuation of Jak-STAT signaling along with Notch signaling facilitates the differentiation of retinal stem cells/progenitors along the rod photoreceptor lineage in vivo. Our observations posit CNTF-mediated signaling as a molecular switch for neuronal versus glial differentiation of retinal stem cells/progenitors and a molecular target for directed neuronal differentiation of retinal stem cells/progenitors as an approach to addressing degenerative changes in the retina.

Disclosure of potential conflicts of interest is found at the end of this article.