Increased Expression of Serum Amyloid A in Glaucoma and Its Effect on Intraocular Pressure

¹ Alcon Research, Ltd., Fort Worth, Texas, United States
² Ophthalmology, University of Iowa, Iowa City, Iowa, United States

^* To whom correspondence should be addressed. E-mail: iok-hou.pang{at}alconlabs.com.

	Abstract

Purpose: To search for and validate potential molecular pathogenic mechanisms in the trabecular meshwork (TM) responsible for the elevated intraocular pressure (IOP) associated with glaucoma. Methods: Affymetrix genechip arrays were used to identify differential gene expression in glaucomatous TM tissues. Serum amyloid A (SAA) upregulation was subsequently confirmed with quantitative PCR (QPCR) and ELISA. The effect of SAA on gene expression of cultured human TM cells was tested with genechip arrays and verified with ELISA, and its effect on IOP was evaluated in the human ocular perfusion organ culture. Results: Microarray analysis showed that the expression of SAA2 was increased in TM tissues from glaucoma donors. This finding was subsequently confirmed by QPCR. The SAA mRNA levels were increased in glaucoma TM tissues by more than 5 fold (p < 0.05) and in cultured TM cells derived from glaucoma donors by 25 fold (p < 0.05) compared to controls. SAA protein levels in the TM of glaucoma patients was also significantly (p < 0.05) elevated by 2.9 fold. Treatment of cultured human TM cells with recombinant SAA affected gene expression, including a 22 fold up-regulation of interleukin-8 (p < 0.001). SAA increased IOP by approximately 40% (p < 0.05) in the human ocular perfusion organ culture without any observable changes in the morphology of the tissues involved in aqueous outflow. Conclusions: These findings indicate that SAA, which is an acute phase apolipoprotein that plays important roles in infection, inflammation and tissue repair, may contribute to the pathogenic changes to the TM in glaucoma.

Key Words: glaucoma, trabecular meshwork, intraocular pressure, Serum Amyloid A