PKCζ Mediates Breakdown of Outer Blood-Retinal Barriers in Diabetic Retinopathy

Abstract

Aims/hypothesisDiabetic macular edema represents the main cause of visual loss in diabetic retinopathy. Besides inner blood retinal barrier breakdown, the role of the outer blood retinal barrier breakdown has been poorly analyzed. We characterized the structural and molecular alterations of the outer blood retinal barrier during the time course of diabetes, focusing on PKCζ, a critical protein for tight junction assembly, known to be overactivated by hyperglycemia.MethodsStudies were conducted on a type2 diabetes Goto-Kakizaki rat model. PKCζ level and subcellular localization were assessed by immunoblotting and immunohistochemistry. Cell death was detected by TUNEL assays. PKCζ level on specific layers was assessed by laser microdissection followed by Western blotting. The functional role of PKCζ was then evaluated in vivo, using intraocular administration of its specific inhibitor.ResultsPKCζ was localized in tight junction protein complexes of the retinal pigment epithelium and in photoreceptors inner segments. Strikingly, in outer segment PKCζ staining was restricted to cone photoreceptors. Short-term hyperglycemia induced activation and delocalization of PKCζ from both retinal pigment epithelium junctions and cone outer segment. Outer blood retinal barrier disruption and photoreceptor cone degeneration characterized long-term hyperglycemia. In vivo, reduction of PKCζ overactivation using a specific inhibitor, restored its tight-junction localization and not only improved the outer blood retinal barrier, but also reduced photoreceptor cell-death.ConclusionsIn the retina, hyperglycemia induced overactivation of PKCζ is associated with outer blood retinal barrier breakdown and photoreceptor degeneration. In vivo, short-term inhibition of PKCζ restores the outer barrier structure and reduces photoreceptor cell death, identifying PKCζ as a potential target for early and underestimated diabetes-induced retinal pathology.

Effects of white light‐emitting diode (LED) exposure on retinal pigment epithelium in vivo

“…The activation of PKC zeta leads to the opening of the outer blood–retinal barrier, as also seen in diabetes 29. Actually, as in diabetes, the use of a PKC inhibitor restores the outer BRB.…”

Retinal damage induced by commercial light emitting diodes (LEDs)

“…Among the possible responses of the retinal cells we investigated the PKC zeta-NFkB axis, because it was shown to be largely involved in other responses to retinal damage, as in diabetic retinopathy [37] and even in light damage (unpublished results). Following stress, activated PKC zeta phosphorylates IKK (Ikappa kinase B), which phosphorylates IKB leading to the release of NFkB and its nuclear translocation [38].…”

Diabetic retinopathy: current understanding, mechanisms, and treatment strategies

“…The notion that neuronal dysfunction and damage can promote clinical diabetic retinopathy, including microangiopathy, is supported by observational studies indicating that regional neuronal dysfunction ascertained by multifocal ERG predicts corresponding retinal locations that will develop retinopathy within 1-3 years (79,80). This potential pathogenic role for neurons has heightened interest in possible mechanisms for neuronal dysfunction and degeneration -including glutamate excitotoxicity, oxidative stress, and reduction of trophic support (81) -and prompted therapeutic strategies for DR based on neuroprotection (82,83).…”