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Duplication of TBK1 Stimulates Autophagy in iPSC-derived Retinal Cells from a Patient with Normal Tension Glaucoma

Budd A Tucker, Frances Solivan-Timpe, Ben R Roos, Kristin R Anfinson, Alan L Robin, Luke A Wiley, Robert F Mullins and John H Fingert

Duplication of theTBK1 gene causes normal tension glaucoma (NTG); however the mechanism by which this copy number variation leads to retinal ganglion cell death is poorly understood. The ability to use skin-derived induced pluripotent stem cells (iPSCs) to investigate the function or dysfunction of a mutant gene product in inaccessible tissues such as the retina now provides us with that ability to interrogate disease pathophysiology in vitro. iPSCs were generated from dermal fibroblasts obtained from a patient with TBK1-associated NTG, via viral transduction of the transcription factors OCT4, SOX2, KLF4, and c-MYC. Retinal progenitor cells and subsequent retinal ganglion cell-like neurons were derived using our previously developed stepwise differentiation protocol. Differentiation to retinal ganglion-like cells was demonstrated via rt-PCR targeted against TUJ1, MAP2, THY1, NF200, and ATOH7 and immunohistochemistry targeted against NF200 and ATOH7. Western blot analysis demonstrated that both fibroblasts and retinal ganglion cell-like neurons derived from NTG patients with TBK1 gene duplication have increased levels of LC3-II protein (a key marker of autophagy). Duplication of TBK1 has been previously shown to increase expression of TBK1 and here we demonstrate that the same duplication leads to activation of LC3-II. This suggests that TBK1- associated glaucoma may be caused by dysregulation (over-activation) of this catabolic pathway.