Puttipong Sripinun
| Puttipong Sripinun |
Puttipong Sripinun1, Wennan Lu2, Jie He3, Venkata R. M. Chavali3, Claire H. Mitchell2
1Orthodontics, University of Pennsylvania, School of Dental Medicine; 2Basic and Translational Science, University of Pennsylvania; 3Ophthalmology, Scheie Eye Institute, University of Pennsylvania
Introduction
Throughout the body, mechanical stimuli are converted into electrochemical signals through the process of mechanotransduction. Excessive mechanical strain can manifest in various pathological changes. For example, the stretch of retinal tissue accompanying an increased intraocular pressure in glaucoma can lead to the degeneration and death of retinal ganglion cells (RGCs), causing irreversible visual impairment. While increased intraocular pressure remains one of the greatest risk factors for optic nerve damage, the cellular mechanisms underlying pressure transduction to retinal tissue remain elusive. Recent identification of Piezo ion channels as bona fide mechanosensitive channels suggests they may play an important step in the process. Herein, we examined the expression of the novel Piezo channels for their promising role as mechanosensing channels in retinal cells.
Methods
The expression and distribution of Piezo channels were identified by immunohistochemical staining of sections from retina of C57BL/6J mice and Long Evan rats. The location of Piezo channels was further investigated by co-labeling with astrocyte marker (Glial fibrillary acidic protein; GFAP) and RGC marker (β-tubulin III). Human-induced pluripotent stem cell-derived retinal ganglion cells (iPS-RGCs) and ARPE-19 cell lines were also used to further explore Piezo channel expression in retinal cells.
Results
Both Piezo channels were expressed primarily on the ganglion cell layer and sparsely in the inner plexiform layer. We found robust expression of Piezo2 in the soma and axons of RGCs in rodent eyes. Interestingly, little colocalization was found with GFAP, suggesting astrocytes did not express substantial levels of either Piezo1 or Piezo2. More detailed structural analysis was performed on human iPS-RGCs. Piezo1 and 2 stained nuclei, soma, and neurites, with the latter showing particular prominence. Piezo2 co-localized with β-tubulin III, in neutites/axons of iPS-RGCs as well as in the optic nerve of rodents. As β-tubulin III is a microtubule protein, this suggests a possible interaction between Piezo2 and the cytoskeleton in neurons. Both Piezo channels were also expressed in ARPE19 cells, suggesting a source of mechanosensitivity in the posterior eye.
Conclusion
Our data indicate the presence of Piezo channels in retinal cells, with RGCs showing the highest expression. Further study is needed to understand how Piezo channels communicate cytoskeletal and membrane strain to pathological downstream signaling pathways.