Abstract
Purpose :
Parthanatos is a caspase-independent cell death pathway whose contribution to retinal disease during the pathogenesis of acute retinal necrosis (ARN) or progressive outer retinal necrosis (PORN) caused by herpes simplex virus type 1 (HSV1) remains unclear. Grady et al (2012) showed that parthanatos is simulated during HSV1 infection of primary human fibroblasts. Our laboratory also has shown that key parthanatos proteins are stimulated within retinitis-susceptible eyes of mice with retrovirus-induced immunosuppression (MAIDS) after murine cytomegalovirus infection (Oh et al, 2019). These observations prompted us to investigate the possibility that parthanatos might also operate during HSV1 infection of human retinal cells. We, therefore, performed a pilot study to test the hypothesis that parthanatos-associated PARP-1 and PAR proteins are stimulated during HSV1 infection of ARPE-19 cells.
Methods :
Monolayers of ARPE-19 cells were inoculated with either HSV1 [KOS] (moi = 10) or maintenance medium (negative control) and harvested at 1, 2, and 3 days postinfection. Monolayers of uninfected ARPE-19 cells were treated with hydrogen peroxide (H2O2) (500 uM) for stimulation of parthanatos (positive control) and harvested at 2 hrs after treatment. HSV1-infected, mock-infected, and H2O2-treated cells were lysed and subjected to western blot analysis for detection of PARP-1 and PAR proteins.
Results :
H2O2-treated ARPE-19 cells showed stimulation of PARP-1 and especially PAR that is essential for the operation of parthanatos. Whereas PARP-1 protein was stimulated in both mock-infected and HSV1-infected ARPE-19 cells at relatively equal amounts at all times investigated, stimulation of PAR protein was not detected in either mock-infected or HSV1-infected ARPE-19 cells at all times investigated.
Conclusions :
Although parthanatos can operate in ARPE-19 cells as suggested by stimulation of PARP-1 and PAR following H2O2-treatment, we provide new evidence that HSV1 infection may inhibit the operation of parthanatos in ARPE-19 cells, possibly through virus-encoded suppressors as seen during apoptosis and necroptosis (Guo et al, 2015). Our findings also suggest that stimulation of parthanatos during HSV1 infection is cell-type specific. Our pilot study provides proof-of-principle for further investigations to determine the role of parthanatos during the pathogenesis of HSV1-induced ARN and PORN.
This abstract was presented at the 2022 ARVO Annual Meeting, held in Denver, CO, May 1-4, 2022, and virtually.