Optic nerve head astrocytes contribute to vascular associated effects

Abstract

PurposeThis study was conducted in order to test the expression of vasoactive substances within rat lamina cribrosa (LC) and optic nerve head (ONH) astrocytes, so as to investigate the role and potential mechanism of ONH astrocytes in vascular associated effects.MethodsLC tissue sections and primary cultured ONH astrocytes were obtained from adult Sprague-Dawley (SD) rats. Immunofluorescent staining was then used to detect the expression of vasoactive substances. Hyperoxia exposure was carried out both in vivo and in vitro, after which nitric oxide (NO) levels in LC tissue and cell supernatant were detected. The variations of protein and gene expression associated with vasoactive substances were subsequently tested. ONH astrocytes and vascular smooth muscle cells (VSMCs) were then incubated in a direct co-culture manner. Morphological parameters of VSMCs were finally analyzed in order to evaluate cell contraction.ResultsEndothelin-1 (ET-1), nitric oxide synthase (NOS) and renin-angiotensin system (RAS) were detected in both LC tissue and ONH astrocytes. Retinal vessel diameter was found obviously decreased following hyperoxia exposure. Moreover, hyperoxia inhibited NO production both in vivo and in vitro. ET-1 and RAS elements were observed to be upregulated, whereas NOS was downregulated. In ONH astrocytes and VSMCs co-culture system, the length-to-width ratio of VSMCs was shown to significantly increase on days 3 and 7 in hyperoxia compared with normoxia.ConclusionsThere is an abundance of expression of vasoactive substances within LC tissue and ONH astrocytes. The contractile response of VSMCs in the co-culture system provided direct evidence for the involvement of ONH astrocytes in vascular associated effects, which may signify a potentially novel direction for future research.

Morphological Changes of Glial Lamina Cribrosa of Rats Suffering from Chronic High Intraocular Pressure

“…The changes in the morphology of the LC under the effect of chronic elevated IOP could be researched using rodent hypertensive glaucoma models [ 21 ]. By injection of microbeads, laser photocoagulation, or episcleral vein cauterization, a chronic high intraocular pressure animal model can be induced [ 11 , 31 , 32 , 35 ]. We induced the model by cauterizing episcleral veins with 5-Fluorouracil subconjunctival injection, which might elevate the episcleral venous pressure and then obstruct the outflow of aqueous humor.…”

“…We hope to obtain the typical feature of morphological changes of animal LC at the different sustained times of high IOP to map the course of glaucoma. The elevated IOP could be sustained from 10d to 24 w [ 11 , 21 , 31 , 32 , 35 ]. Considering that the change in LC morphology occurred the early stage of injury, we have studied the axonal transport of the optic nerve using a confocal laser scanning microscope and the morphology of the optic nerve head of a rat after 4 w of high IOP using hematoxylin–eosin (HE) staining, immunofluorescence staining, and transmission electron microscopy (TEM) [ 12 ].…”

“…Several imaging methods can be used in vivo to study the morphology or structure of the LC [ 4 , 39 ], including confocal scanning laser ophthalmoscopy [ 40 ], ultrasound [ 15 ], and optical coherence tomography (OCT) with several modalities such as spectral-domain OCT, swept-source OCT, and enhanced depth imaging OCT [ 41 , 42 , 43 ]. Since the measurement resolution of LC pores using OCT in vivo is often lower than that of using a confocal microscope in vitro, many investigations [ 5 , 32 ] prefer to apply a confocal microscope. Further, [ 5 , 44 ] showed that the 200 μm thick region near the BMO in the rat ONH was found to be an unmyelinated region with strong GFAP immunoreactivity.…”

“…However, the thickness of rodent glial LC and pre-laminar region in the unmyelinated area is still inconclusive [ 19 , 37 ]. A previous study regarded the region where the shape of glial LC was circular as the “pre-laminar” region [ 32 ]. In order to separate the pre-laminar region from the ONH and quantify the glial LC morphology features, we fit the minimum external rectangle of it for aspect ratio calculation, which is applicable for regular or irregular figures in many fields [ 45 , 46 ].…”

“…The ONH was sectioned from the Bruch’s membrane opening (BMO) and was divided into two regions: the pre-laminar region and the glial LC region [ 32 ]. According to the aspect ratio results ( Figure 4 a), the pre-laminar region was defined by a distance of 0 to 40 μm from the BMO, and the morphology of the ONH was closest to the circle type ( Figure 4 b,c).…”