Direct Differentiation of Adult Ocular Progenitors into Striatal Dopaminergic Neurons

Parkinson's disease, characterized by motor dysfunction due to the loss of nigrostriatal dopaminergic neurons, is one of the most prevalent age-related neurodegenerative disorders. Given there is no current cure, the stem cell approach has emerged as a viable therapeutic option to replace the dopaminergic neurons that are progressively lost to the disease. The success of the approach is likely to depend upon accessible, renewable, immune compatible, and non-tumorigenic sources of neural progenitors from which stable dopaminergic neurons can be generated efficaciously. Here, we demonstrate that neural progenitors derived from limbus, a regenerative and accessible ocular tissue, represent a safe source of dopaminergic neurons. When the limbus-derived neural progenitors were subjected to a well-established protocol of directed differentiation under the influence of Shh and FGF8, they acquired the biochemical and functional phenotype of dopaminergic neurons that included the ability to synthesize dopamine. Their intrastriatal transplantation in the rat model of hemi-Parkinsonism was associated with a reduction in the amphetamine-induced rotation. No tumor formation was observed 6 weeks post-transplantation. Together, these observations posit limbus-derived neural progenitors as an accessible and safe source of dopaminergic neurons for a potential autologous ex-vivo stem cell approach to Parkinson's disease.

Putative stem cell markers in limbal epithelial cells cultured on intact & denuded human amniotic membrane.

BACKGROUND & OBJECTIVES: The ocular surface is an ideal region to study the epithelial stem cell (SC) biology because of the unique spatial arrangement of stem cells and transient amplifying cells. A major challenge in corneal SC biology is the ability to identify SC in vitro and in situ, and one of the major controversies in the field relates to reliable SC markers. This study was carried out to evaluate and compare the expression of the stem cell associated marker: ABCG2, keratinocyte stem cell marker: p63 and corneal differentiation markers: Cnx43 and K3/K12 on limbal explants cultured on human amniotic membrane (HAM) with intact epithelium and HAM denuded of its epithelium. METHODS: Human limbal biopsies obtained from the cadaveric donor eyes were used in this study. The cells were cultured over the HAM with intact and denuded epithelium. Reverse transcriptase PCR, immunohistochemistry, Western blotting for ABCG2, P63, Cnx43 and K3/K12 were done. RESULTS: The limbal epithelial cells cultured over intact HAM expressed the stem cell associated markers (ABCG2, p63) and showed reduced expression of the differentiation markers (Cnx43 and K3/K12) when compared to limbal epithelial cells cultured over denuded HAM, which expressed more differentiation markers at the end of three weeks. BrdU label retaining cells were observed in the limbal epithelial cells cultured over HAM with epihelium only. INTERPRETATION & CONCLUSIONS: Our results showed that the intact HAM supported the growth of limbal epithelial cells expressing stem cell associated markers, and allowing little differentiation of the limbal cells to cornea phenotype. Further studies are needed to understand the properties of the amniotic epithelium that retains the stemness in the cultured limbal stem cells.