Optic Nerve Astrocytes Under Pressure Decrease Synthesis and Secretion of Transforming Growth Factor-ß1

Abstract

Abstract: : Purpose: To investigate mRNA expression and protein synthesis of transforming growth factor (TGF)-ß1 by optic nerve astrocytes exposed to varying levels of hydrostatic pressure. Methods: First-passage porcine astrocytes harvested from freshly excised optic nerves incubated in 0.5% serum-supplemented culture medium were exposed to: (1) gradually elevated hydrostatic pressure from 15 mmHg to 40 mmHg during 72 hrs; (2) acute elevation of pressure from 15 mmHg to 40 mmHg for 24 hrs; and (3) 15 mmHg for 24 hrs, as control. We extracted total RNA, performed RT-PCR using primer pairs specific for porcine TGF-ß1 and glyceraldehyde-3-phosphate dehydrogenase and quantified the products. We utilized ELISA to detect and quantify TGF-ß1 protein in the conditioned media. Results: Ethidium bromide-stained gels demonstrated a prominent band with the expected size of 412 bps from control cells exposed to 15 mmHg. Semi-quantitative analysis revealed that, compared to control cells, the mRNA of expression of TGF-ß1 was down-regulated 39% in cells exposed to a gradually elevated pressure and 1% in cells exposed to acutely raised pressure. The amount of TGF-ß1 secreted into the medium was 34.78 pg/ml/24 hrs by control cells, 22.32 pg/ml/24 hrs by cells exposed to gradually elevated pressure, and 26.61 pg/ml/24 hrs by cells exposed to an acute increase of pressure. Conclusions: Increased hydrostatic pressure down-regulates the synthesis and secretion of TGF-ß1 by astrocytes. Because this cytokine has important neurotrophic actions, its decreased level may contribute to the degeneration of ganglion cells and their axons in the optic nerve of glaucomatous eyes with raised intraocular pressure.

Keywords: growth factors/growth factor receptors • microglia • ganglion cells