Abstract
Cochlear spiral ligament fibrocytes (SLFs) play essential roles in the physiology of hearing including ion recycling and the generation of endocochlear potential. In adult animals, SLFs can repopulate after damages, yet little is known about the characteristics of proliferating cells that support SLFs’ self-renewal. Here we report in detail about the characteristics of cycling cells in the spiral ligament (SL). Fifteen P6 mice and six noise-exposed P28 mice were injected with 5-bromo-2′-deoxyuridine (BrdU) for 7 days and we chased BrdU retaining cells for as long as 60 days. Immunohistochemistry revealed that the BrdU positive IB4 (an endotherial marker) negative cells expressed an early SLF marker Pou3f4 but negative for cleaved-Caspase 3. Marker studies revealed that type 3 SLFs displayed significantly higher percentage of BrdU+ cells compared to other subtypes. Notably, the cells retained BrdU until P72, demonstrating they were dividing slowly.In the noise-damaged mice, in contrast to the loss of the other types, the number of type 3 SLFs did not altered and the BrdU incorporating- phosphorylated Histone H3 positive type 3 cells were increased from day 1 to 14 after noise exposure. Furthermore, the cells repopulating type 1 area, where the cells diminished profoundly after damage, were positive for the type 3 SLF markers. Collectively, in the latral wall of the cochlea, type 3 SLFs have the stem cell capacity and may contribute to the endogenous regeneration of lateral wall spiral ligament. Manipulating type 3 cells may be employed for potential regenerative therapies.
Highlights
Mammalian cochlear spiral ligament (SL) fibrocytes (SLFs) of the mesenchymal non-sensory regions play essential roles in the cochleae physiology of hearing, including the transport of potassium ions to generate an endocochlear potential in the endolymph [1,2,3]
The results reveal that the slow cycling cells, or potential stem cells, can be seen most frequently in the type 3 fibrocytes
Previous studies have shown that the stem cell capacities of the cochlear lateral wall cells are high in the neonatal stages and decrease dramatically by adulthood [10]
Summary
Mammalian cochlear spiral ligament (SL) fibrocytes (SLFs) of the mesenchymal non-sensory regions play essential roles in the cochleae physiology of hearing, including the transport of potassium ions to generate an endocochlear potential in the endolymph [1,2,3]. Recent studies indicate that SLFs are involved in acute and permanent sensorineural hearing loss [4, 5]. In mouse and gebil models of age-related hearing loss, loss of SLFs proceeds the degeneration of other cell-types within the cochlea [6, 7]. DFN3, an X chromosome-linked nonsyndromic mixed deafness, exhibits severe ultrastructural alterations in SLFs, which results in a dramatic reduction in endocochlear potential and a profound hearing loss [8, 9].
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