Inner ear content of glycosaminoglycans as shown by monoclonal antibodies

Functional Consequences of Keratan Sulfate Sulfation in Electrosensory Tissues and in Neuronal Regulation

Keratan sulfate (KS) is a functional electrosensory and neuro-instructive molecule. Recent studies have identified novel low sulfation KS in auditory and sensory tissues such as the tectorial membrane of the organ of Corti and the Ampullae of Lorenzini in elasmobranch fish. These are extremely sensitive proton gradient detection systems that send signals to neural interfaces to facilitate audition and electrolocation. High and low sulfation KS have differential functional roles in song learning in the immature male zebra song-finch with high charge density KS in song nuclei promoting brain development and cognitive learning. The conductive properties of KS are relevant to the excitable neural phenotype. High sulfation KS interacts with a large number of guidance and neuroregulatory proteins. The KS proteoglycan microtubule associated protein-1B (MAP1B) stabilizes actin and tubulin cytoskeletal development during neuritogenesis. A second 12 span transmembrane synaptic vesicle associated KS proteoglycan (SV2) provides a smart gel storage matrix for the storage of neurotransmitters. MAP1B and SV2 have prominent roles to play in neuroregulation. Aggrecan and phosphacan have roles in perineuronal net formation and in neuroregulation. A greater understanding of the biology of KS may be insightful as to how neural repair might be improved.

Gangliosides and hearing

Severe auditory impairment observed in GM3 synthase-deficient mice and humans indicates that glycosphingolipids, especially sialic-acid containing gangliosides, are indispensable for hearing. Gangliosides associate with glycoproteins to form membrane microdomains, the composition of which plays a special role in maintaining the structural and functional integrity of hair cells. These microdomains, also called lipid rafts, connect with intracellular signaling and cytoskeletal systems to link cellular responses to environmental cues. During development, ganglioside species are expressed in distinctive spatial and temporal patterns throughout the cochlea. In both mice and humans, blocking particular steps of ganglioside metabolism produces distinctive neurological and auditory phenotypes. Thus each ganglioside species may have specific, non-overlapping functions within the cochlea, central auditory network, and brain.

BODIPY-Conjugated Xyloside Primes Fluorescent Glycosaminoglycans in the Inner Ear of Opsanus tau

We report on a new xyloside conjugated to BODIPY, BX and its utility to prime fluorescent glycosaminoglycans (BX-GAGs) within the inner ear in vivo. When BX is administered directly into the endolymphatic space of the oyster toadfish (Opsanus tau) inner ear, fluorescent BX-GAGs are primed and become visible in the sensory epithelia of the semicircular canals, utricle, and saccule. Confocal and 2-photon microscopy of vestibular organs fixed 4 h following BX treatment, reveal BX-GAGs constituting glycocalyces that envelop hair cell kinocilium, nerve fibers, and capillaries. In the presence of GAG-specific enzymes, the BX-GAG signals are diminished, suggesting that chondroitin sulfates are the primary GAGs primed by BX. Results are consistent with similar click-xylosides in CHO cell lines, where the xyloside enters the Golgi and preferentially initiates chondroitin sulfate B production. Introduction of BX produces a temporary block of hair cell mechanoelectrical transduction (MET) currents in the crista, reduction in background discharge rate of afferent neurons, and a reduction in sensitivity to physiological stimulation. A six-degree-of-freedom pharmacokinetic mathematical model has been applied to interpret the time course and spatial distribution of BX and BX-GAGs. Results demonstrate a new optical approach to study GAG biology in the inner ear, for tracking synthesis and localization in real time.

Dual immunofluorescence staining of proteoglycans in human temporal bones

OBJECTIVES/HYPOTHESIS

Immunofluorescence staining methods have been developed to study the distribution of macromolecules in archival formalin-fixed celloidin-embedded human temporal bone tissues. The aim of this study was to investigate the feasibility of utilizing this approach to evaluate the codistribution of more than one molecule of interest in a single tissue section.

STUDY DESIGN

Retrospective study of proteoglycan codistribution in archival human temporal bone tissues.

METHODS

The chondroitin sulfate and keratan sulfate proteoglycans were selected for evaluating this methodology. Human tissues with known proteoglycan staining patterns were studied as controls. Thirty-one formalin-fixed celloidin-embedded archival human temporal bones were evaluated, and the observations in 11 specimens are described. A dual immunofluorescence staining method was developed using primary antibodies of differing isotypes and secondary antibodies labeled with fluorophores having nonoverlapping emission characteristics.

RESULTS

The specificity of the dual immunofluorescence technique for chondroitin sulfate and keratan sulfate proteoglycans was demonstrated in control tissues and confirmed through inhibition studies. The normal human tectorial membrane exhibited intense chondroitin sulfate staining. Cochlear and vestibular hair cells exhibited predominantly keratan sulfate staining. Keratan sulfate staining predominated in spiral ganglion cell bodies and fibers. Alterations in the normal distribution pattern of proteoglycans were observed in cases of presbycusis and otosclerosis.

CONCLUSIONS

The dual immunofluorescence staining methodology can be used to study archival formalin-fixed celloidin-embedded human temporal bone tissues. This technique may be applied to the evaluation of other molecules in archival human temporal bone tissues and lead to improvement in our understanding of the function of these molecules and their role in disease processes.

Physiopathological function of hematoside (GM3 ganglioside)

Since I was involved in the molecular cloning of GM3 synthase (SAT-I), which is the primary enzyme for the biosynthesis of gangliosides in 1998, my research group has been concentrating on our efforts to explore the physiological and pathological implications of gangliosides especially for GM3. During the course of study, we demonstrated the molecular pathogenesis of type 2 diabetes and insulin resistance focusing on the interaction between insulin receptor and gangliosides in membrane microdomains and propose a new concept: Life style-related diseases, such as type 2 diabetes, are a membrane microdomain disorder caused by aberrant expression of gangliosides. We also encountered an another interesting aspect indicating the indispensable role of gangliosides in auditory system. After careful behavioral examinations of SAT-I knockout mice, their hearing ability was seriously impaired with selective degeneration of the stereocilia of hair cells in the organ of Corti. This is the first observation demonstrating a direct link between gangliosides and hearing functions.

Inner ear pathology in the mucopolysaccharidosis VII mouse

Mucopolysaccharidosis type VII (MPS VII, Sly syndrome) is caused by dysfunction of the acid hydrolase beta-D-glucuronidase. The defect results in the accumulation of incompletely degraded glycosaminoglycans within lysosomes of a wide array of cell types. MPS VII is associated with mixed (conductive and sensorineural) hearing loss, vision defects, shortened stature, mental retardation and decreased lifespan. Whether the sensorineural component of hearing loss in MPS VII involves degeneration of cochlear sensory cells is not yet clear. The MPS VII mouse resembles its human counterpart in all major aspects, and has been the focus of extensive research seeking to correct MPS VII and other lysosomal storage diseases. The value of potential treatments for this hearing loss can be determined only if cochlear pathology in this model is well characterized. We examined threshold sensitivity, frequency tuning, hair cell density and the appearance of the cochlea and vestibular organs in MPS VII mice ranging from 1.0 to 7.5 months of age. At all ages, lysosomal storage is pronounced within cells of spiral limbus, spiral prominence, spiral ligament and glial cells, but not within organ of Corti, stria vascularis, or neurons. Within the vestibular maculae and cristae, both hair cells and supporting cells also show lysosomal storage. Although hearing thresholds are never normal, reduction in the sharpness of frequency tuning is not apparent until 2.5 months of age, suggesting that the sensorineural component of hearing loss begins in adulthood. No evidence was found for cell loss within the organ of Corti, or any other structure, however. Our results suggest that sensorineural hearing loss in the MPS VII mouse is not caused by degeneration, but may arise from alterations in mass and stiffness of cochlear structures or impaired sensory cell function. They also indicate a possible vestibular component in MPS VII.

Quantitative uronic acid analysis of the otoconial membrane of the guinea pig

Histochemical and biochemical studies have shown that the otoconial membrane, as well as the tectorial membrane and the cupula, contains glycoproteins and proteoglycans. However, uronic acids, which are essential elements of glycosaminoglycans (GAGs), have not so far been directly detected or quantitatively measured in inner ear samples. In the present study, we quantitatively analyzed the glucuronic acid (GlcA) content of the otoconial membrane of the guinea pig by methanolysis combined with reversed-phase high-performance liquid chromatography (RP-HPLC). The utricular otoconial membrane was treated with thermolysin to separate the supernatant (OM-sup; gelatinous layer) and precipitate (OM-ppt; otoconia). The samples were then subjected to methanolysis followed by brief TFA hydrolysis, incubated with 1-phenyl-3-methyl-5-pyrazolone for labeling, and then analyzed by RP-HPLC coupled with the detection of UV absorbance at 245 nm. The GlcA contents of OM-sup and OM-ppt were 2.1 and 5.8 pmol/100 ng protein, respectively. Based on this result, GlcA-containing GAGs estimated as (GlcA+monosulfo-N-acetylhexosamine)n would be 1.0% of protein in OM-sup and 2.61% of protein in OM-ppt, indicating that this type of glycoconjugate is a minor component in both fractions. It is, accordingly, presumed that both the gelatinous layer and otoconia of the otoconial membrane have totally different properties from those of the tectorial membrane and cartilaginous matrix, which contain abundant GAGs.