Journal Club: Using cochlear implant to deliver electrical stimulation, aiding stem-cell based regenerative therapy for sensorineural hearing loss.

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Today's journal article

Chen W, Guo W, Li J, Ji F, Xu L, Yuan S, Ren L, Zhang L, Sun W, Yang SM. Cochlear-bioelectrode: Auditory response to cochlear implant can be improved by stem cell delivery into inner ear in a pig model. 

Why I picked this article

This study combines two exciting areas of auditory science,  cochlear implants and stem cell therapy, to explore whether hearing can be further restored by biologically repairing the auditory nerve region.

The cochlear implant is often described as the most successful neural prosthesis in medicine, and cochlear implant surgery is now routinely performed for those with profound hearing loss. A cochlear implant works by bypassing damaged parts of the inner ear and directly stimulating the auditory nerve with electrical signals, restoring the sense of hearing. Sound is captured by an external microphone, converted into digital signals, and then transmitted to an implanted electrode array inside the cochlea, where these signals activate nerve fibres that send sound information to the brain.

For cochlear implants to work, the health of the auditory nerve is very important. Auditory neurons in the cochlea are called the "spiral ganglion neurons". Once spiral ganglion neurons are lost, it is currently permanent. This study explores the concept of improved cochlear implants that they call "cochlear-bielectrodes", which have an additional feature to use electricity to guide cells into the cochlea to facilitate regeneration of spiral ganglion neurons. 

Figure 1A. Cochlear-biectrodes. Chen et al, (2025)

Some of the research findings

Animal model:

  • Adult Rongchang pigs (40-120 days old, 8-2 kg, both sex) 
  • Deaf group: The pigs with congenital deafness due to an MITF gene were used. 
  • A 3 × 3 mm window was made on the rear wall of the ear canal adjacent to the submandibular gland to gain visibility to the middle ear space. 
  • Round window was exposed, received stem cell delivery, sealed and the cochlear implant was inserted. 

Stem cell delivery: 

  • hiPSCs: Stem cells derived from female adult skin cells. 
  • 5th or 6th generation of cultured hiPSCs (10 μl, 1 × 106) were injected through the round window into the cochlear scala tympani. 
  • The round window was sealed afterwards and followed by cochlear implant insertion. 

Electrical stimulation by Cochlear bi-electrodes:

  • 24-channel cochlear implant (CS-10A, Nurotron, Hanzhou China) were used. 
  • After 3 hours of electrical stimulation, hiPSCs migrated towards the electrodes at a speed of 0.007 ± 0.002 μm/s at a current level (CL) of 50. 
  • Without electrical stimulation, hiPSCs showed random movement at a mean speed of 0.004 μm/s. (in vitro)

Findings about stem cell migration: 

  • With electrical stimulation, after 7 days, most implanted stem cells were seen in the same area as the spiral ganglion neurons. 
  • Without electrical stimulation, stem cells were found in the scala media and the scala tympani. 
  • With electrical stimulation, after 14 days, the implanted stem cells are starting to show signs of becoming neuron-like, as judged by the proteins it has. 
  • In the deaf pig, electrical stimulation with the stem cell group had better hearing, suggesting some functional recovery. 

Haruna's takeaway

The use of concurrent electrical stimulation as a guidance cue for stem cell migration is a very cool idea, as the injection and delivery strategy has been one of the challenges raised with regard to the stem cell therapy for hearing loss. It seems that the human-derived induced pluripotent stem cells can survive in the cochlea after implantation and manage to start differentiating into other cells. That's quite exciting. 

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This is Haruna's 35/100 of the 100-day challenge to post a science blog article every day! I love inner ear biology & cochlear physiology.