This month’s featured article is from the labs of Z-B Jin and F Lu of the Lab for Stem Cells and Retinal Regeneration at Wenzhou Medical University in Wenzhou, China. The article was published 29 February 2016 in the journal Cell Death Discovery. This study investigates the mechanisms of light-induced apoptosis in retinal epithelial cells. More specifically, the study focuses on blue-light intensive LED lights, which are becoming more common in homes and businesses due to their low energy consumption and long life. LED light is problematic, however, because it delivers blue light that is more intense than normal daylight, and this could potentially cause damage to the retina. Light-induced damage to the retina is one of the leading factors behind macular degeneration and other retinopathies.
Central to this study was the development of a temperature-controlled instrument capable of delivering tunable LED light. The authors found that light ranges from 10,000 to 12,000 Lux resulted in cell death of cultured ARPE-19 cells. Using a treatment of 10,000 Lux, they found that ARPE-19 cells died in a time-responsive manner, while cultured human fibroblasts were not affected. They next showed evidence that cell death proceeded via apoptosis, and treatment of 10,000 Lux for 9 hours resulted in late stage apoptosis/necrosis. To understand the molecular mechanisms of light-induced apoptosis, the authors used Phalanx Biotech’s Human OneArray Whole Genome Microarray. They compared the gene expression profile of light-treated cells to non-light-exposed cells and found hundreds of differentially expressed genes (see Volcano Plot above). Gene Ontology and pathway enrichment analysis of these differnetially expressed genes revealed enriched pathways associated with apoptosis, cell cycle arrest, and DNA repair. Notably, GADD45α showed an 8-fold upregulation during light exposure (see Heat Map above).
GADD45α is known regulator of cell cycle arrest and apoptosis, so the authors focused on this gene further. Over-expression of GADD45α in ARPE-19 cells resulted in a dose-dependent decrease is cell viability, and the same scenario in light-exposed ARPE-19 cells led to worsened cell death. These increases in cell death due to over-expression of GADD45α could be reversed by treating the cells with a shRNA targeting GADD45α. Lastly, the authors further elucidated the GADD45α apoptosis pathway in retinal cells by showing that dephosphorylation of AKT was associated with light-induced cell death.
In summary, the authors developed an instrument to deliver controlled exposures to LED light, and they used this apparatus to determine the molecular mechanisms underlying LED light-induced apoptosis in human retinal epithelial cells. Ultimately, GADD45α represents a novel therapeutic target for the treatment of retinal diseases.
Reference
Gao M-L et al. Upregulation of GADD45α in light-damaged retinal pigment epithelial cells (2016). Cell Death Discovery 2:16013.