Dual contribution of TRPV4 antagonism in the regulatory effect of vasoinhibins on blood-retinal barrier permeability: diabetic milieu makes a difference

Abstract

Breakdown of the blood-retinal barrier (BRB), as occurs in diabetic retinopathy and other chronic retinal diseases, results in vasogenic edema and neural tissue damage, causing vision loss. Vasoinhibins are N-terminal fragments of prolactin that prevent BRB breakdown during diabetes. They modulate the expression of some transient receptor potential (TRP) family members, yet their role in regulating the TRP vanilloid subtype 4 (TRPV4) remains unknown. TRPV4 is a calcium-permeable channel involved in barrier permeability, which blockade has been shown to prevent and resolve pulmonary edema. We found TRPV4 expression in the endothelium and retinal pigment epithelium (RPE) components of the BRB, and that TRPV4-selective antagonists (RN-1734 and GSK2193874) resolve BRB breakdown in diabetic rats. Using human RPE (ARPE-19) cell monolayers and endothelial cell systems, we further observed that (i) GSK2193874 does not seem to contribute to the regulation of BRB and RPE permeability by vasoinhibins under diabetic or hyperglycemic-mimicking conditions, but that (ii) vasoinhibins can block TRPV4 to maintain BRB and endothelial permeability. Our results provide important insights into the pathogenesis of diabetic retinopathy that will further guide us toward rationally-guided new therapies: synergistic combination of selective TRPV4 blockers and vasoinhibins can be proposed to mitigate diabetes-evoked BRB breakdown.

TRPV4 inhibition prevents increased water diffusion and blood-retina barrier breakdown in the retina of streptozotocin-induced diabetic mice

“…In both diabetic and nondiabetic mice, the right eye was injected with vehicle (PBS) and the left eye received GSK2193874 (17.3 pg, corresponding to 50 nM, as the estimated volume of mouse vitreous is 4.4 μl (Kaplan et al, 2010)). We previously demonstrated that PBS is an acceptable vehicle (Arredondo Zamarripa et al, 2017). Intravitreal injection was performed 24 hours before the end of the 4 weeks of diabetes to mimic a treatment scheme.…”

“…Eyes were then cryopreserved at 4 °C for 1 h 30 in 10 % and 20 % sucrose, respectively, in 30 % sucrose overnight, embedded in Tissue-Tek and frozen with liquid nitrogen. Cryostat was sectioned at 14 μm and mounted on slides for hematoxylin and eosin staining (Arredondo Zamarripa et al, 2017). Retinal layer thickness was quantified, as previously described (Arredondo Zamarripa et al, 2017).…”

“…Functionally coupled to acuaporin-4, TRPV4 is necessary for the regulatory volume decrease under hypo-osmotic conditions in retinal Müller glia endfeet (Jo et al, 2015). Furthermore, Trpv4 −/− mice show disrupted OLM (Arredondo Zamarripa et al, 2017). TRPV4 has also been implicated in the regulation of barrier permeability, but this is subject of debate.…”

“…Based on inconsistent observations in Trpv4 −/− mice, it has been suggested that the intricate role of TRPV4 may relate to its presence in different vascular beds and most cellular components of the neurogliovascular unit (Earley et al, 2009; Kim et al, 2016; Redmon et al, 2017). In the retina, TRPV4 is expressed in neurons, Müller glia, astrocytes, endothelial cells, and retinal pigment epithelium (Arredondo Zamarripa et al, 2017; Monaghan et al, 2015; Ryskamp et al, 2011; Zhao et al, 2015).…”

“…Indeed, TRPV4 activation mediates and amplifies inflammatory responses (Alessandri-Haber et al, 2006; Alessandri-Haber et al, 2004; Alessandri-Haber et al, 2005; Alessandri-Haber et al, 2003; Matsumoto et al, 2018; Okada et al, 2016; Reiter et al, 2006; Vergnolle et al, 2010), including edema (Reiter et al, 2006; Vergnolle et al, 2010). TRPV4 blockade resolves edema in several organs (Balakrishna et al, 2014; Cheung et al, 2017; Jie et al, 2015; Lu et al, 2017; Thorneloe et al, 2012; Zhao et al, 2018) and TRPV4 selective antagonists (RN-1734 and GSK2193874) mitigate BRB breakdown in diabetic rats (Arredondo Zamarripa et al, 2017). The role of TRPV4 in retinal hydro-ionic homeostasis should therefore be better characterized under control and diabetic conditions.…”