**2. Materials and Methods**

## *2.1. Cell Culture and Treatment*

Human male adult retinal pigment epithelium cells (ARPE-19 cells, passage 39; American Type Culture Collection, #CRL-2302) were cultivated for 6 days in cell culture flasks with Dulbecco's modified eagle medium (DMEM/F12; Sigma-Aldrich, Darmstadt, Germany), 10% fetal calf serum (FCS; PanBiotech, Aidenbach, Germany), and 1% penicillin/streptomycin (37 ◦C, 5% CO2). Cells were trypsinized (0.05% trypsin/0.02% ethylenediaminetetraacetic acid (EDTA)) and seeded in a concentration of 1.6 × 10<sup>5</sup> cells/cm<sup>2</sup> (passage 39) on mouse laminin-coated (5 μg/cm2, Sigma-Aldrich, Darmstadt, Germany) 0.4-μm-pore polyester membrane inserts (Corning, Corning, NY, USA). Cells were cultivated for 4 weeks with apical and basal media exchanges (first-day medium with 10% FCS), remaining time

medium with 5% FCS). Before treatment, the FCS concentration was reduced to 0% within 3 days (5%–2.5%–1.25%). ARPE-19 cells were treated with either 0.5 mM H2O2 for 1, 4, 24, and 48 h or with 0.5 mM H2O2 and 0.01 mM olaparib (Biomol, Hamburg, Germany) for 4 h.

#### *2.2. Immunohistochemistry and Terminal Deoxynucleotidyl Transferase dUTP Nick End Labeling (TUNEL) Assay*

Phosphate bu ffered saline (PBS)-washed, paraformaldehyde-fixated (4%, 20 min; Merck, Darmstadt, Germany) ARPE-19 cells were permeabilized (PBS/0.2% Tween20 (PBS-T), 45 min), and unspecific bindings were blocked (3% bovine serum albumin (BSA) (Carl Roth, Karlsruhe, Germany)/PBS-T, 1 h). Antigens were detected using a primary antibody (Supplementary Materials, Table S1, overnight, 3% BSA/PBS-T) and a fluorescence-conjugated antispecies antibody (Supplementary Materials, Table S1, 45 min, 3% BSA/PBS). The fluorochrome HOECHST 33342 (1:1000) was used to stain DNA. Cells were covered with fluorescence mounting medium (Dako, Agilent Technologies, Santa Clara, CA, USA). Images were taken with a confocal microscope (Zeiss, Jena, Germany).

The TUNEL assay was performed with a DeadEnd ™ Fluorometric TUNEL System (Promega, Madison, WI, USA) on paraformaldehyde-fixated, washed, and permeabilized (0.2% Triton X-100 in PBS) cells. Images were taken with a confocal microscope (Zeiss, Jena, Germany).

#### *2.3. Transepithelial Resistance (TER) and Cellular Capacitance*

TER and cell layer capacitance were recorded online using the established cellZscope device (nanoAnalytics, Münster, Germany), as previously described [36]. The dielectric properties of empty filter inserts were determined independently and were included in the equivalent circuit used for analysis. Fitting the parameters of the equivalent circuit to the experimental data was achieved via nonlinear least-squares optimization according to the Levenberg–Marquardt algorithm.

#### *2.4. Real-Time, Quantitative Polymerase Chain Reaction (RT-qPCR)*

Here, mRNA was isolated using a NucleoSpin ® RNA/Protein kit (Macherey-Nagel, Düren, Germany). Purified mRNA was transcribed into cDNA with a QuantiTect ®Reverse Transcription Kit (Qiagen, Hilden, Germany). Transcripts of complement components, receptors, and inflammation-associated markers were analyzed using a Rotor-Gene SYBR ®Green PCR Kit either with QuantiTect Primer Assays (Supplementary Materials, Table S2) or in-house-designed primer pairs (Metabion, Planegg, Germany) (described in the Supplementary Materials, Table S3) in a Rotor Gene Q 2plex cycler (Qiagen, Hilden, Germany). Data were analyzed using the delta delta Ct (ddCt) method. Values were depicted on a linear scale using log-transformed scores to equally visualize increases and decreases in expression levels.
