Endothelin-1 mediated regulation of extracellular matrix collagens in cells of human lamina cribrosa

Abstract

Endothelin-1(ET-1), a potent vaso-active peptide, mediates extracellular matrix regulation resulting in an increase in collagen deposition in various cell types and tissues and has been proposed to play a key role in glaucoma pathology. The role of ET-1 in the regulation of extracellular matrix collagens at the level of optic nerve head is not known. In this study we have examined the role of ET-1 in extracellular matrix collagen regulation in primary cultures of human lamina cribrosa cells. Our hypothesis is that ET-1 increases remodeling of the ECM of cells of the lamina cribrosa. Such actions could contribute to the development of optic neuropathy. QPCR analysis revealed that ET-1 mediated an increase in mRNA levels of collagen type I alpha 1 and collagen type VI alpha 1 chains at all doses of ET-1 with a significant increase at 1nM and 10nM concentration in LC cells. A dose dependent increase in collagen type I and type VI protein deposition and secretion was also observed by Western blot in response to ET-1 and was significant at 10nM and 100nM concentrations of ET-1. ET-1 increased the [ 3 H] proline uptake in LC cells suggesting that ET-1 contributed to an increase in total collagen synthesis in LC cells. ET-1 -mediated increase in collagen type I, type VI and total collagen synthesis was significantly blocked by the ET A receptor antagonist, BQ610, as well as with the ET B receptor antagonist, BQ788, suggesting the involvement of both receptor subtypes in ET-1 mediated collagen synthesis in LC cells. These results suggest that ET-1 regulates extra cellular matrix-collagen synthesis in LC cells and may contribute to ECM remodeling at the level of LC of POAG subjects who have elevated plasma and aqueous humor levels of endothelin-1.

The Role of Inflammation in the Pathogenesis of Glaucoma

“…22 Interestingly, ET-1, which has been shown to be up-regulated during glaucoma, also enhances expression of MMP-2, which further mediates a concentration-dependant increase of collagen type I alpha 1 and collagen type VI alpha 1 production through stimulation of lamina cribrosa cells. 23,62,75 Because collagen induction is a marker of tissue fibrosis, this may lead to RGC death. Collagen up-regulation may lead to compromised astrocyte function and thereby secondarily RGC death.…”

The role of endothelin in the pathophysiology of glaucoma

“…ET-1 has also been found to contribute to the disruption of anterograde axonal transport, another key area of impairment in glaucomatous eyes [50,51]. Interestingly, one study found that ET-1, acting through activation of both ET A and ET B , caused increases in collagen synthesis in lamina cribrosa (LC) cells, suggesting that ET-1 mediates ECM remodeling at the level of the ONH, possibly contributing to increased collagen deposition, reduced aqueous humor outflow and progressive damage to the ONH [52]. In a study on rabbits, intravitreal injection of ET-1 resulted in significant elevation of synthesis of NO, a potent substance known to cause oxidative damage to the ONH [53].…”

A biomechanical paradigm for axonal insult within the optic nerve head in aging and glaucoma

“…While endothelin has been proposed to be a model of ischemic optic neuropathy in a variety of species (Chauhan et al, 2004; Cioffi et al, 1995; Orgul et al, 1996a; Orgul et al, 1996b), a robust literature has called into question its actual mechanisms (He et al, 2007; Murphy et al, 2010; Rao et al, 2008; Stokely et al, 2002; Wang et al, 2008; Yorio et al, 2002)and there are no definitive studies that establish the “glaucomatous” nature of the neuropathy (Chauhan et al, 2004; Oku et al, 1999). One paper has reported the “glaucomatous” loss of retinal ganglion cells in rats following systemic exposure to retinal heat shock proteins, but documentation of the “glaucomatous” nature of the neuropathy has not been provided (Wax et al, 2008).…”