Sphingosine-1-phosphate is a key regulator of proliferation and differentiation in retina photoreceptors.
OBJECTIVE
Identifying the cues required for the survival and development of photoreceptors is essential for treating retinal neurodegeneration. The authors previously established that glial-derived neurotrophic factor (GDNF) stimulates proliferation and that docosahexaenoic acid (DHA) promotes photoreceptor survival and differentiation. Later findings that ceramide triggers photoreceptor apoptosis suggested sphingolipids might also control photoreceptor development. The present study investigated whether sphingosine-1-phophate (S1P), which promotes survival and differentiation in several cell types, regulates photoreceptor proliferation and differentiation and whether it is a mediator in GDNF and DHA effects.


METHODS
Rat retina neuronal cultures were supplemented at day 0 or 1 with S1P, GDNF, or DHA and were treated with DL-threo-dihydrosphingosine to inhibit S1P synthesis or with brefeldin A (BFA) to block intracellular trafficking. Proliferation was quantified to determine bromodeoxyuridine uptake and number of mitotic figures. Opsin, peripherin, and sphingosine kinase (SphK), the enzyme required for S1P synthesis, were quantified by immunocytochemistry and Western blot analysis.


RESULTS
S1P increased the proliferation of photoreceptor progenitors. It also stimulated the formation of apical processes, enhanced opsin and peripherin expression, and promoted their localization in these processes; DHA had similar effects. BFA prevented S1P and DHA enhancement of apical process formation without affecting opsin expression. GDNF and DHA enhanced SphK expression in photoreceptors, while inhibiting S1P synthesis blocked GDNF mitogenic effects and DHA effects on differentiation.


CONCLUSIONS
The authors propose S1P as a key regulator in photoreceptor development. GDNF and DHA might upregulate SphK levels to promote S1P synthesis, which would initially promote proliferation and then advance photoreceptor differentiation.
Miranda
Gisela E
GE
Instituto de Investigaciones Bioquímicas de Bahía Blanca, Universidad Nacional del Sur-CONICET, Bahía Blanca, Buenos Aires, Argentina.
Abrahan
Carolina E
CE
Politi
Luis E
LE
Rotstein
Nora P
NP
D000818:Animals; D015153:Blotting, Western; D020126:Brefeldin A / Q000494:pharmacology; D002454:Cell Differentiation / Q000502:physiology*; D049109:Cell Proliferation; D002470:Cell Survival; D004281:Docosahexaenoic Acids / Q000494:pharmacology; D004791:Enzyme Inhibitors / Q000494:pharmacology; D051100:Glial Cell Line-Derived Neurotrophic Factor / Q000494:pharmacology; D007150:Immunohistochemistry; D007381:Intermediate Filament Proteins / Q000378:metabolism; D008246:Lysophospholipids / Q000037:antagonists & inhibitors / Q000494:pharmacology / Q000502:physiology*; D008562:Membrane Glycoproteins / Q000378:metabolism; D009419:Nerve Tissue Proteins / Q000378:metabolism; D055355:Opsins / Q000378:metabolism; D064531:Peripherins; D017853:Phosphotransferases (Alcohol Group Acceptor) / Q000378:metabolism; D020419:Photoreceptor Cells, Vertebrate / Q000166:cytology* / Q000187:drug effects / Q000378:metabolism; D051381:Rats; D017208:Rats, Wistar; D013110:Sphingosine / Q000031:analogs & derivatives* / Q000037:antagonists & inhibitors / Q000494:pharmacology / Q000502:physiology; D000099157:Sphingosine Kinase
D020126:Brefeldin A; D004281:Docosahexaenoic Acids; D004791:Enzyme Inhibitors; D051100:Glial Cell Line-Derived Neurotrophic Factor; D007381:Intermediate Filament Proteins; D008246:Lysophospholipids; D008562:Membrane Glycoproteins; D009419:Nerve Tissue Proteins; D055355:Opsins; D064531:Peripherins; D017853:Phosphotransferases (Alcohol Group Acceptor); D013110:Sphingosine; D000099157:Sphingosine Kinase; C060506:sphingosine 1-phosphate; C005682:safingol