Elevated intraocular pressure is the main risk factor in primary open-angle glaucoma, involving an increased resistance to aqueous humor outflow in the juxtacanalicular region of the conventional outflow pathway which includes the trabecular meshwork (TM) and the inner wall of Schlemm's canal (SC). Previously, sphingosine-1-phosphate (S1P) was shown to decrease outflow facility in porcine and human eyes, thus increasing outflow resistance and intraocular pressure. Owing to S1P's known effect of increasing barrier function in endothelial cells and the robust expression of the S1P1 receptor on the inner wall of SC, we hypothesized that S1P1 receptor activation promotes junction formation and decreases outflow facility. The effects of subtype-specific S1P receptor compounds were tested in human and porcine whole-eye perfusions and human primary cultures of SC and TM cells to determine the receptor responsible for S1P effects on outflow resistance. The S1P1-specific agonist SEW2871 failed to both mimic S1P effects in paired human eye perfusions, as well as increase myosin light chain (MLC) phosphorylation in cell culture, a prominent outcome in S1P-treated SC and TM cells. In contrast, the S1P2 antagonist JTE-013, but not the S1P1 or S1P1,3 antagonists, blocked the S1P-promoted increase in MLC phosphorylation. Moreover, JTE-013 prevented S1P-induced decrease in outflow facility in perfused human eyes ( P < 0.05, n = 6 pairs). Similarly, porcine eyes perfused with JTE-013 + S1P did not differ from eyes with JTE-013 alone ( P = 0.53, n = 3). These results demonstrate that S1P2, and not S1P1 or S1P3, receptor activation increases conventional outflow resistance and is a potential target to regulate intraocular pressure.
S1P2 receptor regulation of sphingosine-1-phosphate effects on conventional outflow physiology