Transcriptomic differences in cochlear cells isolated from mice implanted with dexamethason-eluting electrode arrays or standard electrode arrays

The inflammatory foreign body response (FBR) following cochlear implantation (CI) can negatively impact CI outcomes, including increased electrode impedances. This study aims to investigate the long-term efficacy of dexamethasone eluting cochlear implant and locally delivered dexamethasone, a potent anti-inflammatory glucocorticoid, on the intracochlear FBR and electrical impedance post-implantation in a murine model. The left ears of CX3CR1+/GFP Thy1+/YFP (macrophage-neuron dual reporter) mice were implanted with dexamethasone-eluting cochlear implants (Dex-CI) or standard implant (Standard-CI) while the right ear served as unoperated control. Another group of dual reporter mice was implanted with a standard CI electrode array followed by injection of dexamethasone in the middle ear to mimic current clinical practice (Dex-local). Mouse implants were electrically stimulated with serial measurement of electrical impedance. Dex-CI reduced electrical impedance and inflammatory FBR in the murine model for an extended period. Dex-local in the murine model is ineffective for long-term reduction of FBR and electrode impedance. Our data suggest that dexamethasone eluting arrays are more effective than the current clinical practice of locally applied dexamethasone in reducing FBR and electrical impedance. Overall design: Following cochlear implantation (CI), mice were euthanized at 33 days post-CI, implanted and contralateral cochlea were microdissected, tissues collected separately in DMEM F-12 media and lysed with accutase at 37°C for 30 minutes on a shaker. The media was replaced with 2 mL of DMEM F-12 containing 5% FBS to stop the lysis. The tissue was triturated for 2 minutes and filtered through a 20 µm filter (pluriSelect Life Science, El Cajon, CA, United States). The filtered cells were centrifuged at 300 x g for 3 minutes and resuspended in 90 µL MACS buffer (0.5% BSA in PBS). 10 µL of CD11b microbeads (71-097-142, Miltenyi Biotec, Auburn, Ca, USA) were added to the cell suspension and incubated for 15 minutes at 4°C, washed in MACS buffer followed by centrifugation 350 x g for 5 minutes resuspended in 500 µL MACS buffer. Cell suspension was then applied to a prewashed column in a magnetic holder to collect flow-through containing Cd11b negative cells. Column was then washed 3 times with 500 µL MACS buffer with negative flow-through captured each time. The CD11b microbead-bound cells were then eluted with 1 mL MACS buffer. Samples were centrifuged at 300 x g for 3 minutes and adjusted with MACS buffer to 3 x 106 cells/mL. Samples at this concentration were used for 10x cell capture. Single-cell captures were performed following the manufacturer's recommendations on a 10x Genomics Controller. The targeted number of captured cells ranged from 3231 to 3572 per run. Library preparation was performed according to the instructions in the 10x Genomics Chromium Single Cell c' Chip Kit V2. Libraries were sequenced on a Nextseq 500 instrument (Illumina, San Diego, CA) and reads were subsequently processed using 10x Genomics CellRanger analytical pipeline using default settings and 10x Genomics downloadable mm10 genome as previously described.