Induction of Heat Shock Protein 70 in Mouse RPE as an In Vivo Model of Transpupillary Thermal Stimulation

Abstract

The induction of heat shock response in the macula has been proposed as a useful therapeutic strategy for retinal neurodegenerative diseases by promoting proteostasis and enhancing protective chaperone mechanisms. We applied transpupillary 1064 nm long-duration laser heating to the mouse (C57Bl/6J) fundus to examine the heat shock response in vivo. The intensity and spatial distribution of heat shock protein (HSP) 70 expression along with the concomitant probability for damage were measured 24 h after laser irradiation in the mouse retinal pigment epithelium (RPE) as a function of laser power. Our results show that the range of heating powers for producing heat shock response while avoiding damage in the mouse RPE is narrow. At powers of 64 and 70 mW, HSP70 immunostaining indicates 90 and 100% probability for clearly elevated HSP expression while the corresponding probability for damage is 20 and 33%, respectively. Tunel staining identified the apoptotic regions, and the estimated 50% damaging threshold probability for the heating (ED50) was ~72 mW. The staining with Bestrophin1 (BEST1) demonstrated RPE cell atrophy with the most intense powers. Consequently, fundus heating with a long-duration laser provides an approachable method to develop heat shock-based therapies for the RPE of retinal disease model mice.

Hormetic Heat Shock Enhances Autophagy through HSF1 in Retinal Pigment Epithelium Cells

“…The emphasis of these studies has been to apply temperature increases in order to activate the HSR yet to prevent cellular damage [ 23 , 24 , 25 ]. Previous studies have demonstrated the induction of HSPs in the RPE cells after transpupillary laser irradiation [ 24 , 25 , 26 , 27 , 28 , 29 ], which could lead to therapeutical effects [ 24 , 25 , 30 , 31 , 32 ]. However, the molecular mechanisms underlying the beneficial effects of HHS in RPE cells have not been fully unraveled yet.…”

Retinal Temperature Determination Based on Photopic Porcine Electroretinogram

“…The laser-induced therapeutic effect and the retinal damage seems to be defined by the delivered thermal dose rather than chosen treatment modality and parameters [39], [44], [45]. Although the main hypothesis is that the treatment effect is induced by the heating of the RPE [3], [23], [24], [40], it is unclear whether limiting the therapeutic effect to the RPE is necessary or even beneficial if safety concerns associated with SLT could be alleviated. The introduced ERG-based temperature control would enable the optimal thermal dose to be delivered reliably without significant risks for adverse events for long pulse laser treatments such as TTT [21], [40].…”

“…Although there is uncertainty about the key mechanisms responsible for delivering the therapeutic effect, the ratio between laser power causing increased HSP70 production and the laser power causing cell death in the irradiated site has been most extensively studied. Laser powers between 50 and 80% of the power causing cellular damage have been reported to trigger increased HSP70 production in the RPE and choroid [22]- [24].…”

An imbalance in autophagy contributes to retinal damage in a rat model of oxygen‐induced retinopathy

“…The rapid fluctuations in oxygen cause a substantial stress to the retina tissue, which can activate apoptotic pathways that lead to retinal cell death 7 . In line with these findings, an expansion of studies suggests that autophagy is involved in retinal diseases and contributes to the progressive visual dysfunction 8,9 …”

“… 7 In line with these findings, an expansion of studies suggests that autophagy is involved in retinal diseases and contributes to the progressive visual dysfunction. 8 , 9 …”