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Rebecca Rausch, Christopher P. Tanzie, Richard T Libby, Amy E. Kiernan; Cellular proliferation is correlated to morphological progression during murine trabecular meshwork development. Invest. Ophthalmol. Vis. Sci. 2016;57(12):4679.
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© ARVO (1962-2015); The Authors (2016-present)
The trabecular meshwork (TM) is the main site of aqueous humor outflow and a key target for the treatment of ocular hypertension in glaucoma patients. Despite its importance in ocular pathology, the molecular pathways controlling TM cellular development are not well understood. To elucidate this process, we characterized the morphologic development of the TM in conjunction with the proliferation of precursors that will generate TM cells.
C57BL/6J mice were used to study the TM at multiple time points from E15.5 to P21. The morphology of cells in the developing iridocorneal angle (IA) was assessed using 2µ plastic sections stained with H&E. To determine the time course of TM cell proliferation, twice-daily injections of BrdU were administered at six ages throughout early ocular morphogenesis (E15.5-P7). Animals were harvested at P21 (mature IA), and eyes were cryoprotected and sectioned at 14µ. Immunohistochemistry was used to label BrdU+ cells and presumptive TM cells using known markers. This experimental paradigm was used to determine when TM cells undergo their terminal differentiation.
Early in ocular development at E15.5, presumptive TM cells appear circular and condensed. The shape of these cells did not change until approximately P1 when they began to elongate. By P7, the TM cells appeared to have adopted the mature TM cell morphology and separation was observed between the trabecular beams (consistent with previously published work). A known marker for TM, α-smooth muscle actin, was found to be present in the IA from the earliest time point tested (E15.5). Upon analysis of P21 eyes from animals injected with BrdU early in development, TM cell proliferation was highest at E15.5 (12.54 ± 1.98 BrdU+ cells) and significantly declined by P1 (2.80 ± 0.50 BrdU+ cells; p=0.039).
Cells giving rise to the mature TM undergo a high rate of proliferation at E15.5. Proliferation declines thereafter, and is significantly reduced by P1, suggesting that TM cells undergo their terminal differentiation early postnatally. This finding correlated with the morphological changes observed at P1. Additional analysis at later time points to further characterize TM cell differentiation is ongoing. Understanding these developmental cellular processes will allow us to identify the critical factors regulating TM cell determination and differentiation.
This is an abstract that was submitted for the 2016 ARVO Annual Meeting, held in Seattle, Wash., May 1-5, 2016.
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