Decreased auditory function in the C3H/lpr autoimmune disease mouse

Cochlear Histopathologic Findings in Patients With Systemic Lupus Erythematosus: A Human Temporal Bone Study

HYPOTHESIS

We hypothesized that, in archived human temporal bone samples from patients with systemic lupus erythematosus (SLE), a pathologic condition exists in the stria vascularis and cochlear hair cells.

BACKGROUND

Sensorineural hearing loss is a common feature in SLE patients. However, the pathophysiologic mechanism of cochlear dysfunction is unclear.

METHODS

We examined 15 temporal bone samples from 8 SLE patients, along with 17 samples from 10 age-matched healthy control patients. The samples were serially sectioned in the horizontal plane and stained with hematoxylin and eosin. We determined the area of the stria vascularis in a midmodiolar section of each cochlear turn. Then, we made cytocochleograms and calculated the percentage of missing inner and outer hair cells.

RESULTS

The area of the stria vascularis in our SLE group was significantly smaller than in our control group. The number of remaining inner hair cells in our SLE group was smaller than in our control group; however, the difference did not reach statistical significance. The loss of outer hair cells in our SLE group was significantly higher than in our control group. There was a tendency toward a positive correlation between the loss of cochlear hair cells and the duration of SLE.

CONCLUSION

The stria vascularis and cochlear hair cells are affected in SLE patients. Our findings could provide the histopathologic basis for the cochlear dysfunction, including sensorineural hearing loss, experienced by SLE patients.

Glucocorticoid impact on cochlear function and systemic side effects in autoimmune C3.MRL-Faslpr and normal C3H/HeJ mice

Glucocorticoids are effective in reversing hearing loss, but their severe side effects limit long term management of many ear disorders. A clearer understanding of these side effects is critical for prolonged therapeutic control of hearing and vestibular dysfunction. Therefore, this study characterized the impact of the glucocorticoid prednisolone on cochlear dysfunction and systemic organ systems in C3.MRL-Fas(lpr) autoimmune mice and their normal C3H/HeJ parent strain. Following 3 months of treatment, autoimmune mice had better auditory thresholds and improved hematocrits, anti-nuclear antibodies, and immune complexes. Steroid treatment also lowered body and spleen weights, both of which rise with systemic autoimmune disease. Steroid treatment of the normal C3H/HeJ mice significantly elevated their blood hematocrits and lowered their body and spleen weights to abnormal levels. Thus, systemic autoimmune disease and its related hearing loss in C3.MRL-Fas(lpr) mice are steroid-responsive, but normal hemopoiesis and organ functions can be significantly compromised. This mouse model may be useful for studies of the detrimental side effects of steroid treatments for hearing loss.

Dystroglycan expression in the mouse cochlea

Viable dominant spotting (W(v)/W(v)) mice have a c-kit gene mutation, which impedes the migration of neural crest cells to the developing cochlea where they normally differentiate into intermediate cells (ICs). A prominent pathological feature shared by these mutants and the aging human and gerbil cochlea is thickening of the basement membrane (BM) of strial capillaries. Atrophy of strial capillaries in the aging gerbil has been associated with changes in the expression of dystroglycan (DG), a cell-surface receptor that regulates BM assembly. Here we evaluated the expression of DG in W(v)/W(v) mutant and C57BL/6J wild-type mice to investigate the possible role of ICs in regulating strial capillary BM homeostasis. The DG gene product was identified in lateral wall dissections from both W(v)/W(v) mutant and wild-type mice by reverse transcription-polymerase chain reaction. Subunit-specific antibodies were employed to localize the alpha and beta subunits of the DG heterodimer. Some sites in both wild-type and mutant mice, such as the subepithelial BM lining the scala media and regions of contact between selected epithelial cells, expressed alpha-DG alone. Other sites such as the perineural BM and the perivascular BM subtending strial capillaries and capillaries in the central portion of the auditory nerve coexpressed alpha- and beta-DG. The strong diffuse staining for alpha-DG along the basolateral membrane of strial marginal cells disappeared with advancing strial degeneration in abnormal turns of W(v)/W(v) mutants. Variations in staining intensity for both alpha- and beta-DG also occurred in the subendothelial BM of strial capillaries in turns lacking ICs and appeared to correspond with the degree of capillary atrophy. The results support the possibility that ICs play a role in the homeostasis of the strial capillary BM.

Spironolactone blocks glucocorticoid-mediated hearing preservation in autoimmune mice

HYPOTHESIS

Although autoimmune sensorineural hearing loss can be effectively treated with corticosteroids, little is known about how these drugs affect cochlear function. MRL/MpJ-Faslpr autoimmune mice treated with a mineralocorticoid (aldosterone) have previously been shown to have hearing improvement equal to those treated with a glucocorticoid (prednisolone). This suggested that the restoration of hearing with steroids was the result of an effect on sodium transport rather than an antiinflammatory or immunosuppressive role. We hypothesized that corticosteroids reverse autoimmune hearing loss through the mineralocorticoid receptor and that blocking the mineralocorticoid receptor will prevent glucocorticoid effects.

METHODS

Spironolactone, a mineralocorticoid receptor antagonist, was administered to MRL/MpJ-Faslpr autoimmune mice alone or in combination with corticosteroids. The four treatment groups were: spironolactone, spironolactone + aldosterone, spironolactone + prednisolone, and untreated water controls. Auditory brainstem response (ABR) thresholds were recorded before and during treatment (2, 3, and 4 mo) to measure the effect of steroids on hearing decline.

RESULTS

Hearing in spironolactone and spironolactone + prednisolone mice showed progressive decline in hearing similar to water controls. The hearing was preserved in spironolactone + aldosterone mice, presumably as a result of the fact that aldosterone has a higher affinity for the mineralocorticoid receptor than spironolactone. Thus, aldosterone was able to maintain cochlear function with autoimmune disease progression, similar to previous reports of aldosterone treatment effects.

CONCLUSIONS

Spironolactone effectively blocked prednisolone from improving hearing in MRL/MpJ-Faslpr autoimmune mice. This offers evidence that the inner ear mineralocorticoid receptor is the therapeutic target for corticosteroids used to treat autoimmune and sudden sensorineural hearing loss. Pharmacologic treatments that selectively target the mineralocorticoid receptor may provide greater clinical benefit with fewer systemic side effects than prednisone in patients with autoimmune sensorineural hearing loss.

Decreased cochlear DNA receptor staining in MRL.MpJ-Fas(lpr) autoimmune mice with hearing loss

OBJECTIVES

Previous studies of decreased cochlear DNA binding in autoimmune mice suggested that antibodies against a cochlear cell surface DNA receptor cause autoimmune hearing loss. However, the presence of a cochlear DNA receptor has not been determined. Therefore, immunohistochemistry with an anti-DNA receptor antibody was performed on MRL.MpJ-Fas(lpr) (MRL/lpr) autoimmune mice to determine 1) which inner ear structures contain DNA receptors and 2) whether the receptor staining pattern changes as autoimmune disease progresses and hearing thresholds increase.

STUDY DESIGN

A prospective study of the progression of hearing loss in autoimmune mice and correlated alterations in immunostaining for the inner ear DNA receptor.

METHODS

One group of MRL/lpr mice (n = 10) was allowed to develop autoimmune disease, and auditory brainstem response (ABR) audiometry was performed at 4, 6, and 9 months of age to measure the progression of hearing loss. A second group (n = 5) was tested for ABR thresholds at 2 months of age and immediately killed to assess receptor staining before the onset of autoimmune disease and hearing loss. The inner ears from all mice were immunohistochemically stained with an anti-DNA receptor antibody, and a qualitative analysis of the staining of cochlear structures was performed.

RESULTS

Auditory brainstem response audiometry revealed a significant 20- to 30-dB elevation of thresholds as systemic disease progressed. Anti-DNA receptor staining was heaviest in the spiral ligament and less intense in the spiral ganglion and cochlear nerve. Both groups showed a similar pattern of staining in these structures. The stria vascularis and hair cells also stained in both groups. However, the stria cells of normal-hearing mice showed diffuse intracellular immunoreactivity, whereas older mice displayed less staining that was confined to the cell membranes.

CONCLUSIONS

The inner ears of MRL/lpr mice contain DNA receptors. Autoimmune hearing loss was correlated with weaker overall intracellular staining in the stria vascularis and hair cells but increased staining of the cell membranes. This suggested DNA receptors have impaired endocytosis and more receptors remain on the cell membrane, possibly as a result of binding by circulating autoantibodies.

Aldosterone and prednisolone control of cochlear function in MRL/MpJ-Fas(lpr) autoimmune mice

Recently this laboratory showed aldosterone, a mineralocorticoid that only enhances sodium transport, was as effective as the glucocorticoid prednisolone in restoring cochlear function in autoimmune mice. To further test this relationship between sodium transport and autoimmune hearing loss, dosage comparisons were made of prednisolone and aldosterone control of the auditory dysfunction in autoimmune MRL/MpJ-Fas(lpr) mice. Mice were tested at 2 months of age to establish baseline auditory brainstem response (ABR) thresholds, hematocrit, serum immune complexes, and anti-nuclear antibodies. Mice were then given different doses of prednisolone or aldosterone in their drinking water for 2 months. After the treatment period, most untreated water controls showed elevation of ABR thresholds due to the ongoing autoimmune disease. However, the steroid groups had significantly more mice with improved or unchanged thresholds. Both steroids improved stria vascularis morphology, although aldosterone appeared to be more effective. The immune suppressive prednisolone caused a dose-related improvement in levels of serum immune complexes and hematocrit, hallmarks of systemic autoimmune disease. Aldosterone, which has no immune suppressive function, did not alter systemic disease. The comparable efficacy of prednisolone and aldosterone in restoring auditory function suggests steroid reversal of autoimmune hearing loss in mice is due to increasing stria vascularis sodium transport and not suppression of systemic autoimmune reactions.

Steroid treatment in young MRL.MpJ-Fas(lpr) autoimmune mice prevents cochlear dysfunction

Corticosteroid therapy reverses clinical autoimmune sensorineural hearing loss, although little is known of how steroids restore normal auditory function. If suppression of systemic autoimmune processes underlies hearing restoration, then preventing autoimmune symptoms from developing should prevent cochlear dysfunction. MRL. MpJ-Fas(lpr) autoimmune mice were used to test this potential mechanism by initiating oral prednisolone treatment at 6 weeks of age, prior to autoimmune disease and hearing loss onset. The steroid treatment group was given prednisolone in their drinking water, while untreated controls were given tap water. Treatment continued for 7 months with periodic evaluations of cochlear function with auditory brainstem response (ABR) audiometry. Autoimmune mice given the steroid lived longer and did not develop levels of serum immune complexes seen in their untreated controls. Also, their ABR thresholds remained near normal throughout the 7 months of treatment, while untreated controls showed progressive threshold elevations typical for autoimmune disease. This correlation of suppressed systemic autoimmune activity and maintenance of normal cochlear function identifies one potential mechanism for autoimmune hearing loss and hearing restoration with steroid therapy. The autoimmune mouse should serve as a valuable model for future studies of the cochlear mechanisms responsive to steroid treatment in autoimmune hearing loss.

Steroid treatment improves cochlear function in the MRL.MpJ-Fas(lpr) autoimmune mouse

Corticosteroid therapy is used to reverse autoimmune sensorineural hearing loss, although little is known of the mechanism by which this occurs. This has been due to the lack of a suitable animal model with spontaneous hearing loss that is steroid responsive. The present study examined the effects of prednisolone treatment on auditory thresholds in the MRL.MpJ-Fas(lpr) autoimmune mouse to determine its suitability as such a model. Autoimmune mice at 3.5-4. 5 months of age were evaluated by pure-tone auditory brainstem response (ABR) to establish threshold elevations due to the disease. The steroid treatment group was then given prednisolone in their drinking water for 2.5 months, while untreated controls were given tap water. Significantly more steroid treated mice survived to the time of post-treatment ABR evaluation. Half of the steroid treated ears demonstrated either improvement or no change in cochlear function compared to only 25% in the untreated controls. Overall, cochlear thresholds in the untreated controls increased by 14.7 dB, whereas no significant threshold increase was seen in the steroid treated group (4.3 dB) over the treatment period. No qualitative anatomical differences were seen in the ears of those mice surviving to the end of the study. These findings establish the autoimmune mouse as a model for studies of steroid responsive mechanisms within the ear. This could apply to autoimmune sensorineural hearing loss, as well as any hearing disorder for which steroid therapy is recommended.

Steroid-responsive cochlear dysfunction in the MRL/lpr autoimmune mouse

Corticosteroids historically have been used to treat autoimmune sensorineural hearing loss, although little is known of how steroids restore normal inner ear function. Therefore, to identify a potential model for this field of research, this study examined the effects of prednisolone on auditory brain stem response thresholds in the MRL/lpr mouse model of autoimmune sensorineural hearing loss. Mice treated with prednisolone after auditory threshold elevations demonstrated significant improvement and stabilization of thresholds compared with untreated controls. MRL/lpr mice treated with steroids before the onset of autoimmune disease and cochlear dysfunction demonstrated decreased serum immune complexes, higher survival rates, and lower auditory thresholds compared with untreated controls. These positive results suggest the autoimmune mouse may be useful for studies of steroid-responsive mechanisms of the cochlea in autoimmune sensorineural hearing loss, as well as any hearing disorder in which steroid therapy is currently used.

Induction of immune-mediated hearing loss in SCID mice by injection of MRL/lpr mouse spleen cells

Induction of immune-mediated hearing loss in SCID mice by injection of MRL/lpr mouse spleen cells The MRL/lpr mouse, which has a mutation in the Fas gene encoding a cell-surface receptor for apoptosis, shows an accumulation of abnormal immunocompetent cells and SLE-like disease. It has recently been reported that this mouse also manifests sensorineural hearing loss (SHL) with cochlear pathology at 20 weeks of age. We examined the effects of injecting MRL/lpr spleen cells on the development of SHL in severe combined immunodeficient (SCID) mice, which originally develop neither SHL nor cochlear pathology. Immune-mediated SHL and cochlear pathology were, indeed, transferred to the SCID mice by the injection of spleen cells from the MRL/lpr mice. These findings suggest that cell-mediated immunity is involved in the development of SHL and cochlear pathology.

Otitis Media Incidence and Impact on the Auditory Brain Stem Response in Lipopolysaccharide-Nonresponsive C3H/HeJ Mice

Although mice of the C3H strain normally respond to bacterial lipopolysaccharide with appropriate immune system activation, mice of the C3H/HeJ substrain do not because of a gene defect. This suggests they may be more susceptible to opportunistic bacterial infections and more likely to have otitis media than a normally responding substrain, such as the C3H/HeSnJ. Therefore these two substrains were evaluated for incidence of spontaneous middle ear disease at 2, 4, 6, 10, 12, 15, and 18 months of age. Auditory brain stem response audiometry to pure tones of 4, 8, 16, 24, and 32 kHz was performed to establish the impact of middle ear disease on auditory function. None of the lipopolysaccharide-responsive C3H/HeSnJ mice demonstrated middle ear disease. However, middle ear disease was present in 33% of the C3H/HeJ mice. The conductive loss caused by the otitis media resulted in auditory brain stem response threshold shifts of 15 to 40 dB SPL, lowered peak amplitudes, and increased latencies. Reduced lipopolysaccharide responsiveness by C3H/HeJ mice makes them less capable of reacting immunologically to bacterial infection and presumably underlies the failure to clear middle ear disease. The C3H/HeJ mouse may provide a valuable model in which to study lipopolysaccharide biologic activity and related middle ear inflammatory or immune mechanisms.

Cochlear Immunoglobulin in the C3H/lpr Mouse Model for Autoimmune Hearing Loss

Immunoglobulin staining was conducted in cochlear tissue from the C3H/ lpr autoimmune strain mouse to better understand the local immune processes underlying autoimmune inner ear disease. This mouse is a model for spontaneous systemic lupus erythematosus with coincident elevated cochlear thresholds. Cochleas were examined from C3H/ lpr mice at 2 months of age, before disease onset, and at 8 months of age, when systemic disease and hearing loss are manifested. Sections of these cochleas, along with cochlear sections from age-matched C3H/HeJ nonautoimmune controls, were immunocytochemically stained for IgG and IgM to identify areas of abnormal immunoglobulin activity. IgM immunoreactivity was similar in control and autoimmune cochlear tissue and did not appear to vary with disease progression. Staining was limited to the inside of capillaries in the stria vascularis and other areas within the cochlea. Similar staining patterns were seen in control animals stained for IgG. However, C3H/ lpr mice with autoimmune disease showed extensive IgG immunoreactivity spreading out from the stria vascularis capillaries into the extracapillary spaces. This increased permeability suggested that breakdown of the blood labyrinth barrier was coincident with systemic autoimmune disease.

Breakdown of Stria Vascularis Blood-Labyrinth Barrier in C3H/lpr Autoimmune Disease Mice

Sensorineural hearing loss related to autoimmune disease is a well-recognized condition, although the exact pathophysiologic mechanisms remain unclear. One current theory postulates immune complex-induced interference with blood-labyrinth barrier integrity in the stria vascularis. The C3H/ lpr autoimmune mouse was chosen to study the permeability of capillaries in the stria vascularis because this mouse model has demonstrated abnormalities of the stria vascularis and shifts in the auditory brain stem response threshold during active disease. C3H/ lpr mice with active disease were compared with younger mice without disease, as well as age-matched C3H/HeJ control mice. The mice were injected with the tracer ferritin and examined by transmission electron microscopy to evaluate the integrity of the capillary tight junctions in the stria vascularis. Four of five mice with active disease were noted to have extensive leakage of ferritin into the perivascular tissues. Neither the young, disease-free autoimmune mice nor the nonautoimmune control mice demonstrated vessel leakage. Thickening of the basement membrane was also noted in the diseased animals. The results imply that active disease leads to a breakdown in the blood-endolymph barrier, which could underlie the hearing loss accompanying autoimmune and other immune diseases.

Immunoglobulin deposition in thickened basement membranes of aging strial capillaries

The presence of immunoglobulins in the thickened basement membrane (BM) of aging strial capillaries was investigated as a possible indicator of autoimmunity in the genesis of atypical BM. Cochleas from young and old Mongolian gerbils raised in quiet were examined by immunostaining at the light microscopic level for IgG and IgM and for the BM components laminin (La) and type IV collagen (IV-C). Another age-graded series of cochleas was stained for IgG at the ultrastructural level. No immunoreactive IgG was detected in specimens from animals less than 6 months old. In contrast, 2 of 12 cochleas from 20- to 28-month-old gerbils and 11 of 20 cochleas from gerbils 30 months or older showed positive staining for IgG in strial capillary BM. IgM was not detected at any age. At the electron microscope level, no immunoreactive IgG was detected in the stria of cochleas younger than 30 months. However, labeling demonstrative of IgG was observed in the thickened BM of some strial capillaries in all six cochleas from gerbils older than 33 months. Lysosome-like granules in endothelial cells and the superiormost marginal cells also stained for content of IgG as did fibrillar material in edematous regions in the intrastrial space. In addition to showing accumulation of IgG, the findings confirm our prior demonstration of increased La deposition in the thickened strial capillary BM of all cochleas from old gerbils. The BM alterations appear confined to strial capillaries in old gerbils, since morphological observations and immunostaining for La and IgG failed to detect changes in BMs at any other site in a wide survey of aged gerbil organs including vessels in other regions of the affected cochleas. The results point more towards the development of an age-dependent permeability to IgG selectively in strial capillaries than to autoimmunity as an explanation of the IgG in BM.

Quantitative measures of hair cell loss in CBA and C57BL/6 mice throughout their life spans

The CBA mouse shows little evidence of hearing loss until late in life, whereas the C57BL/6 strain develops a severe and progressive, high-frequency sensorineural hearing loss beginning around 3-6 months of age. These functional differences have been linked to genetic differences in the amount of hair cell loss as a function of age; however, a precise quantitative description of the sensory cell loss is unavailable. The present study provides mean values of inner hair cell (IHC) and outer hair cell (OHC) loss for CBA and C57BL/6 mice at 1, 3, 8, 18, and 26 months of age. CBA mice showed little evidence of hair cell loss until 18 months of age. At 26 months of age, OHC losses in the apex and base of the cochlea were approximately 65% and 50%, respectively, and IHC losses were approximately 25% and 35%. By contrast, C57BL/6 mice showed approximately a 75% OHC and a 55% IHC loss in the base of the cochlea at 3 months of age. OHC and IHC losses increased rapidly with age along a base-to-apex gradient. By 26 months of age, more than 80% of the OHCs were missing throughout the entire cochlea; however, IHC losses ranged from 100% near the base of the cochlea to approximately 20% in the apex.

Inner ear DNA receptors in MRL/lpr autoimmune mice: potential 30 and 70 kDa link between autoimmune disease and hearing loss

Inner ear function and systemic autoimmune disease were evaluated in the MRL/lpr mouse to determine their relationship with alterations in cell surface DNA receptors of 28-30 and 68-70 kDa size. Auditory brainstem response thresholds in the autoimmune disease mice were significantly elevated as early as 2 months of age when compared to MRL/++ controls. Hearing thresholds continued to rise with progression of the disease, manifested as increasing spleen weights, antinuclear (anti-DNA) antibodies, and serum immune complexes. Cochlear membranous labyrinth cells in the autoimmune mice bound less DNA, suggesting the DNA receptors were abnormally occupied by circulating antibodies. Western blots of a murine T-cell line probed with autoimmune mouse sera demonstrated reactivity to 28-30 and 68-70 kDa proteins after disease onset. It is hypothesized that cell surface DNA binding molecules could be masked or down-regulated by circulating antibodies in autoimmune disease. This interference with DNA receptor activity may be occurring within the inner ear and underlie the cochlear dysfunction seen in autoimmune sensorineural hearing loss.