Localization and proteomic characterization of cholesterol-rich membrane microdomains in the inner ear.

Biological membranes organize and compartmentalize cell signaling into discrete microdomains, a process that often involves stable, cholesterol-rich platforms that facilitate protein-protein interactions. Polarized cells with distinct apical and basolateral cell processes rely on such compartmentalization to maintain proper function. In the cochlea, a variety of highly polarized sensory and non-sensory cells are responsible for the early stages of sound processing in the ear, yet little is known about the mechanisms that traffic and organize signaling complexes within these cells. We sought to determine the prevalence, localization, and protein composition of cholesterol-rich lipid microdomains in the cochlea. Lipid raft components, including the scaffolding protein caveolin and the ganglioside GM1, were found in sensory, neural, and glial cells. Mass spectrometry of detergent-resistant membrane (DRM) fractions revealed over 600 putative raft proteins associated with subcellular localization, trafficking, and metabolism. Among the DRM constituents were several proteins involved in human forms of deafness including those involved in ion homeostasis, such as the potassium channel KCNQ1, the co-transporter SLC12A2, and gap junction proteins GJA1 and GJB6. The presence of caveolin in the cochlea and the abundance of proteins in cholesterol-rich DRM suggest that lipid microdomains play a significant role in cochlear physiology. BIOLOGICAL SIGNIFICANCE: Although mechanisms underlying cholesterol synthesis, homeostasis, and compartmentalization in the ear are poorly understood, there are several lines of evidence indicating that cholesterol is a key modulator of cochlear function. Depletion of cholesterol in mature sensory cells alters calcium signaling, changes excitability during development, and affects the biomechanical processes in outer hair cells that are responsible for hearing acuity. More recently, we have established that the cholesterol-modulator beta-cyclodextrin is capable of inducing significant and permanent hearing loss when delivered subcutaneously at high doses. We hypothesize that proteins involved in cochlear homeostasis and otopathology are partitioned into cholesterol-rich domains. The results of a large-scale proteomic analysis point to metabolic processes, scaffolding/trafficking, and ion homeostasis as particularly associated with cholesterol microdomains. These data offer insight into the proteins and protein families that may underlie cholesterol-mediated effects in sensory cell excitability and cyclodextrin ototoxicity.

Applications of targeted gene capture and next-generation sequencing technologies in studies of human deafness and other genetic disabilities.

The goal of sequencing the entire human genome for $1000 is almost in sight. However, the total costs including DNA sequencing, data management, and analysis to yield a clear data interpretation are unlikely to be lowered significantly any time soon to make studies on a population scale and daily clinical uses feasible. Alternatively, the targeted enrichment of specific groups of disease and biological pathway-focused genes and the capture of up to an entire human exome (~1% of the genome) allowing an unbiased investigation of the complete protein-coding regions in the genome are now routine. Targeted gene capture followed by sequencing with massively parallel next-generation sequencing (NGS) has the advantages of 1) significant cost saving, 2) higher sequencing accuracy because of deeper achievable coverage, 3) a significantly shorter turnaround time, and 4) a more feasible data set for a bioinformatic analysis outcome that is functionally interpretable. Gene capture combined with NGS has allowed a much greater number of samples to be examined than is currently practical with whole-genome sequencing. Such an approach promises to bring a paradigm shift to biomedical research of Mendelian disorders and their clinical diagnoses, ultimately enabling personalized medicine based on one's genetic profile. In this review, we describe major methodologies currently used for gene capture and detection of genetic variations by NGS. We will highlight applications of this technology in studies of genetic disorders and discuss issues pertaining to applications of this powerful technology in genetic screening and the discovery of genes implicated in syndromic and non-syndromic hearing loss.

Stylohyoid complex syndrome: a new diagnostic classification.

OBJECTIVE: To describe stylohyoid complex syndrome (SHCS) as a new diagnostic classification of all lateral neck and/or facial pain conditions resulting from an elongated styloid process, ossified stylohyoid ligament, or elongated hyoid bone. All of these pathologic conditions result in tension and reduced distensibility of the stylohyoid complex (SHC), with resultant irritation of the surrounding cervical structures with movement of the complex. DESIGN: A retrospective medical chart review was performed to identify a cohort of patients who underwent surgical intervention for lateral neck and/or facial pain due to pathologic SHCS. Follow-up time of greater than 1 year is reported in 5 of 7 patients. SETTING: Tertiary, academic referral center. PATIENTS: Patients included were those given a diagnosis of SHCS who underwent surgical intervention from June 2006 through September 2009. There were 7 patients, 5 of whom were female. The age range was 38 to 53 years at time of presentation (mean age, 45.3 years). Common presenting complaints were lateral neck and oropharyngeal pain exacerbated by tongue and head movements. INTERVENTION: The pathologic areas were surgically addressed through transoral or cervical approaches. MAIN OUTCOME MEASURE: Symptoms following surgical intervention. RESULTS: Seven patients (8 sides) were identified as having SHCS. Computed tomographic findings included elongated styloid processes (3 sides), ossified stylohyoid ligaments (2 sides), and elongated hyoid bones (3 sides). Computed tomographic scan, frequently with volume-rendered 3-dimensional reconstructions, identified the pathologic condition. All patients experienced clinically significant relief of presenting symptoms following surgical intervention. CONCLUSIONS: Stylohyoid complex syndrome includes all lateral neck and/or facial pain conditions resulting from an elongated styloid process, ossified stylohyoid ligament, or elongated hyoid bone. Surgical intervention directed at any pathologic point to disrupt this complex relieves tension and offers patients relief of symptoms.