Supporting Cell Characteristics in Long-deafened Aged Mouse Ears

Abstract

Significant sensory hair cell loss leads to irreversible hearing and balance deficits in humans and other mammals. Future therapeutic strategies to repair damaged mammalian auditory epithelium may involve inserting stem cells into the damaged epithelium, inducing non-sensory cells remaining in the epithelium to transdifferentiate into replacement hair cells via gene therapy, or applying growth factors. Little is currently known regarding the status and characteristics of the non-sensory cells that remain in the deafened auditory epithelium, yet this information is integral to the development of therapeutic treatments. A single high-dose injection of the aminoglycoside kanamycin coupled with a single injection of the loop diuretic furosemide was used to kill hair cells in adult mice, and the mice were examined 1 year after the drug insult. Outer hair cells are lost throughout the entire length of the cochlea and less than a third of the inner hair cells remain in the apical turn. Over 20% and 55% of apical organ of Corti support cells and spiral ganglion cells are lost, respectively. We examined the expression of several known support cell markers to investigate for possible support cell dedifferentiation in the damaged ears. The support cell markers investigated included the microtubule protein acetylated tubulin, the transcription factor Sox2, and the Notch signaling ligand Jagged1. Non-sensory epithelial cells remaining in the organ of Corti retain acetylated tubulin, Sox2 and Jagged1 expression, even when the epithelium has a monolayer-like appearance. These results suggest a lack of marked SC dedifferentiation in these aged and badly damaged ears.

Methyl methacrylate embedding to study the morphology and immunohistochemistry of adult guinea pig and mouse cochleae

“…3G and H). Sox2 expression was shown in the nuclei of all subtypes of supporting cells in adult mouse cochleae (Oesterle and Campbell, 2009). Our findings showed a similar pattern ( Fig.…”

Changes in the adult vertebrate auditory sensory epithelium after trauma

“…However, in long-deafened aged animal models where the organ of Corti is severely damaged by aminoglycosides, differentiated support cells can be maintained for long periods of time in remnant organ of Corti in the absence of hair cells (Sugawara et al, 2005; Oesterle et al, 2009). The remnant organ of Corti has also been called the “repaired organ of Corti” or the “repaired columnar epithelium” (Taylor et al, 2012), and the latter term will be used here.…”

“…Light and electron microscopy studies have shown that the distinctive specializations of pillar and Deiters’ cells, such as the prominent intracellular bundles of closely packed microtubules that are acquired during late states of organ of Corti maturation (Forge et al, 1997; Souter et al, 1997), persist in the repaired organ when columnar support cells remain (Oesterle et al, 2008, Oesterle and Campbell, 2009; Taylor et al, 2012). Further, histochemical studies show that acetylated tubulin, a component of the distinctive intracellular bundles (Tannenbaum and Slepecky, 1997; Saha and Slepecky, 2000) is retained (Oesterle and Campbell, 2009; Taylor et al, 2012). Studies of KCC4, a plasma membrane protein involved in potassium uptake that is upregulated during the latter stages of organ of Corti maturation in inner border and Deiters’ cells (Boettger et al, 2002), indicate KCC4 is retained in repaired organ of Corti when columnar support cells remain despite massive or complete hair cell loss (Taylor et al, 2012).…”

“…Taylor and colleagues (2012) showed that the glutamate aspartate transporter (GLAST), whose expression increases in inner border, inner phalangeal, and Deiters’ cells during latter stages of organ of Corti development (Jin et al, 2003), is retained, and connexin expression patterns and gap-junctional intercellular connections, including compartmentalization of coupled cells within the organ, are retained in the repaired columnar epithelium (Taylor et al, 2012). Support cells in the repaired epithelium continue to express Sox2, a transcription factor expressed normally in all developing and mature organ of Corti support cell subtypes (Hume et al, 2007; Oesterle et al, 2008, Oesterle and Campbell, 2009). Interestingly, a recent study using tamoxifen-inducible CreER/loxP technologies to conditionally delete Sox2 in normal postnatal pillar and Deiters’ cells suggests that Sox2 may not be necessary to maintain their cell fate (Liu et al, 2012c).…”

“…Both damaged epithelial types may constitute the substrate for potential future therapy in clinical cases, and understanding the characteristics of the cells that remain after hair cell loss will be crucial to identifying feasible regenerative procedures. ( D–G ) Adult C57BL/6 mouse organ of Corti damaged by an aminoglycoside-diuretic combination described previously (single high-dose injection of kanamycin coupled with a single injection of furosemide, Oesterle et al, 2008; Oesterle and Campbell, 2009). Tissues were collected two months after the injections, prepared as whole mounts, immunolabeled for acetylated tubulin (green), and nuclei were counterstained with DAPI (blue) as described previously (Oesterle and Campbell, 2009).…”