Der Einfluß des Diabetes mellitus auf das Hörorgan - Teil B: Spontaner Diabetes bei der Maus*

Abnormal basement membrane in the inner ear and the kidney of the Mpv17-/- mouse strain: ultrastructural and immunohistochemical investigations

The loss of the function of the peroxisomal Mpv17-protein and associated imbalanced radical oxygen species (ROS) homeostasis leads to an early onset of focal segmental glomerulosclerosis and sensorineural deafness associated with severe degeneration of cochlear structures. An excessive enlargement of basal laminae of the stria vascularis capillaries and glomeruli indicates numerous changes in their molecular composition. The basement membrane (BM) of the glomeruli and the stria vascularis are simultaneously affected in early stages of the disease and the lamination, splitting of the membrane and formation of the "basket weaving" seen at the onset of the disease in the kidney are similar to the ultrastructural alterations characteristic for Alporta9s syndrome. The progressive alteration of the BMs is accompanied by irregularity in the distribution of the collagen IV subunits and by an accumulation of the laminin B2(gamma1) in the inner ear and B(beta1) in the kidney. Since Mpv17 protein contributes to ROS homeostasis, further studies are necessary to elucidate downstream signaling molecules activated by ROS. These studies explain the cellular responses to missing Mpv17-protein, such as accumulation of the extracellular matrix, degeneration, and apoptosis in the inner ear.

Strial marginal cells play a role in basement membrane homeostasis: in vitro and in vivo evidence

The interaction of extracellular matrix and receptors plays a role in tissue homeostasis. The thickened strial capillary basement membrane (SCBM) reported in animal models of presbycusis and Alport's syndrome might be secondary to elevated synthesis and/or decreased turnover of specific basement membrane (BM) components. In this study, expression of specific BM proteins, integrin receptors and mediators of matrix turnover in the murine lateral wall were determined using cDNA probes and antibodies. The presence of collagen alpha1 and alpha2(IV) and laminin-8 in the SCBM was verified. The integrin subunits alpha3, alphav and beta1, cell surface receptors for the BM proteins, localized primarily to the SCBM and/or the strial marginal cells as did TIMP-3, a tissue inhibitor of matrix metalloproteinase. The epithelial cell line SV-k1, derived from the lateral wall of the 'immortomouse', showed expression of the same BM proteins as well as demonstrating the presence of markers specific to strial marginal cells, namely Na,K-ATPase alpha1 and beta2 subunits. Thus, the cultured cells are identified as deriving from marginal cells of the stria vascularis. Moreover, these data suggest that a culture system using this marginal cell line will be useful to delineate mechanisms underlying the pathologic accumulation of extracellular matrix in the SCBM.

Early Identification of Hearing Impairment in Patients With Type 1 Diabetes Mellitus

OBJECTIVE

The aim of this study was to evaluate the cochlear micromechanics and central auditory function in patients with type I diabetes mellitus and to identify the site of possible dysfunction.

METHODS

Cochlear activity was evaluated by recording distortion product otoacoustic emissions (DPOAEs). DPOAEs were performed using an ILO 92 Otodynamics Analyser. Functional changes in the retrocochlear auditory pathway were evaluated by auditory brainstem responses (ABRs). DPOAEs and ABRs were measured in 42 normally hearing patients with type 1 diabetes mellitus aged 21 to 42 years, and 33 age- and sex-matched nondiabetic control subjects.

RESULTS

Both of the groups (diabetic and control) had normal and undifferentiated results in tonal and impedance audiometry. ABR peripheral transmission time (wave I) and central transmission time (interpeak latencies I-V) were significantly delayed in the diabetic compared with normal subjects, and the mean amplitudes of various DPOAEs were significantly reduced in the diabetic patients compared with the control subjects.

CONCLUSIONS

Combined use of different procedures for monitoring central and peripheral portions of the auditory pathway in diabetic patients showed alterations in cochlear micromechanics and the retrocochlear auditory pathway. Hearing impairment in diabetic patients is usually mild and subclinical, and can be detected early by accurate and objective audiometric methods.