Determining The Role Of Ceramide And Sphingosine-1-phosphate In Light-induced Retinal Degeneration Of Albino Rats

Abstract

Purpose: : Sphingolipids/ceramides are essential components of every cell membrane and are especially important for development and maintenance of neural tissues. Ceramide (Cer) and sphingosine-1-phosphate (S1P), two bioactive signaling sphingolipids, are integrally related to each other for their metabolism, and functionally oppose each other’s action- Cer is involved in apoptosis and S1P in inflammation and neovascularization. Apoptosis and inflammation are common in many forms of retinal degenerative disorders. The purpose of this study was to delineate the intricate role of Cer and S1P in retinal degeneration using light-damaged models of albino rats.

Methods: : Sprague Dawley (SD) rats were light-stressed (2700 lux for 6 h) and the level of Cer, and S1P was determined in their retina at various time-points by GC- or LC-MS/MS analyses. In the harvested retinal tissue, expression of Cer-, S1P-metabolic and S1P receptor genes was determined by qRT-PCR; and the activity of Serine palmitoyl transferase (SPT) and Sphingomyelinases (SMase) enzymes were measured. A synthetic drug, FTY720, that is analogous to sphingosine and is known to act as an S1P mimic was administered intraperitoneally in SD rats before light-damage. Retinal structure and function was measured by ERG and histology.

Results: : Both Cer and S1P level increased significantly in the light-exposed retina before the onset of apoptosis. Significant increase in dihydro-ceramide indicates an induction of de novo biosynthesis. Also, the expression of de novo Cer biosynthetic genes, Sphingosine kinase 1, and the S1P receptors increased significantly. The SPT and SMase assays also indicate that it is the de novo biosynthesis that is activated in light-damaged retina. Interestingly, the activity of acidic SMase was significantly reduced in the light-damaged retina. Treatment of FTY720 before light-damage significantly protected the retina structurally and functionally.

Conclusions: : We determined the role and an integral involvement of signaling sphingolipids in light-induced retinal degeneration of albino rats. Both Cer and S1P play a crucial role in deciding the cell fate in a process that is otherwise called a sphingolipid rheostat. Furthermore, FTY720 could be a candidate for therapeutic protection of retinal degeneration.

Keywords: retinal degenerations: cell biology • lipids • gene/expression