Impacts of health insurance on tympanostomy tube outcomes in the pediatric population.

OBJECTIVES: Tympanostomy tube (TT) placement is a common surgical procedure for treating pediatric patients with chronic otitis media with effusion (COME) with or without recurrent acute otitis media (rAOM). Prior work suggests children from low-income families face significant disparities in access to care for rAOM or COME. The impact of these health disparities in the care of children with rAOM or COME has yet to be investigated in a state with an expanded public health insurance model. We seek to examine differences in care for patients with rAOM and COME based on insurance status and socioeconomic status (SES) in Massachusetts. METHODS: Retrospective review of 560 pediatric patients referred for TT insertion at a tertiary academic medical center between 2017 and 2019. Demographic data collected included age, ethnicity, insurance type (public, private, none) and zip code. Otologic history collected included prior AOM episodes, time to postoperative follow-up, postoperative "no-show" appointments, and number of postoperative audiograms. Multinomial logistic regression was used to isolate the effects of race and ethnicity. RESULTS: We found no major differences in preoperative outcome measures between cohorts. Postoperatively, public insurance was independently associated with decreased odds of undergoing an audiogram (OR 0.35, 95% Cl 0.16-0.76) and increased odds of "no-showing" for an appointment (OR 3.1, 95% CI 1.8-5.3). SES was not independently associated with differences in postoperative outcomes. CONCLUSION: In a state with an early expanded public health insurance model, access to care for rAOM and COME is comparable despite differences in insurance type and SES. However, enrollment in public health insurance is associated with worse measures of follow up care. Despite improvements in access to care with expanded health insurance models, retention continues to be a challenge for vulnerable populations.

Online Reputations: Comparing Hospital- and Patient-Generated Ratings in Academic Otolaryngology.

OBJECTIVES: This study compares hospital-generated online ratings to patient-generated online ratings in academic otolaryngology and evaluates physician factors influencing these results. METHODS: Websites of academic otolaryngologists were assessed for inclusion of hospital-generated Press Ganey surveys. Corresponding scores on Healthgrades and Vitals.com were identified via internet search. Hospital ratings were compared with patient-generated ratings, including score, demographics, and number of ratings. All data was collected between July 15th 2019 and August 22nd 2019. RESULTS: 742 academic otolaryngologists with hospital-generated ratings were identified. Mean hospital-generated rating was significantly higher ((4.70, 95% CI 4.69-4.72) than patient-generated rating (Vitals:4.26, 95% CI 4.18-4.34, and Healthgrades:4.02, 95% CI 3.87-4.18; P < .001). In patient-generated rating, an increased number of rating scores (>20) was associated with male gender, professor ranking, and >30 years in practice (P < .005). Physician demographics did not impact number of ratings in hospital-generated setting. With patient-generated, lower aggregate score was associated with professor ranking (P = .001). In hospital-generated, lower score was associated with >30+ years in practice (P = .023). Across all platforms, comprehensive otolaryngologists and neurotologists/otologists were rated lower in comparison to other specialties (PGS:P < .001,Vitals:P = .027,Healthgrades:P = .016). CONCLUSION: Hospital-generated ratings yield higher mean scores than patient-generated platforms. Between sources, Healthgrades.com scores were lower than those of Vitals.com. Professors with >30 years of practice generated more reviews in patient-generated ratings, and these physicians were generally rated lower. Access to patient-generated ratings is universal and physicians should be aware of variability between online rating platforms as scores may affect referrals and practice patterns.

Women and Minorities in Otolaryngology: A Historical Perspective and Analysis of Current Representation.

Over the course of the last century, otolaryngology-head and neck surgery has made significant medical and surgical advancements. Several of these efforts are credited to women and minorities despite their having faced systemic barriers to entering medical schools and the medical professions. This article highlights some of these pioneering doctors and their contributions to the field. Additionally, the current representation of women and minorities in otolaryngology residency programs and the gender and racial disparities in academic positions are reviewed. The need for mentorship during undergraduate medical education to improve diversity and inclusion within this surgical subspecialty is reinforced.

Women in Otolaryngology: Experiences of Being Female in the Specialty.

OBJECTIVES: A broad survey of women otolaryngologists on the current state of the field, including opportunities for advancement, support of family leave, and prevalence of harassment, has not been performed since 1998. An update on the experiences of female otolaryngologists is vital to continue to advance the specialty. STUDY DESIGN: Anonymous web-based survey. METHODS: Survey of members of the Women in Otolaryngology (WIO) section of the American Academy of Otolaryngology-Head and Neck Surgery (all members of the AAO-HNS that identify as female are automatically members of this section). Distributed via AAO-HNS. RESULTS: Five hundred thirty-five responses out of 2303 total WIO members (response rate of 23.2%). Respondents ranged in age from 25 to >65 years. Respondents reported that in the residency programs they attended, 29% of residents, 13% of faculty, and 7% of department leaders were women. Forty-four percent disagreed that their department leaders and 39% disagreed that their male co-residents were supportive of women starting families in training. Younger respondents were more likely to feel that their department leaders were supportive of female residents, maternity leave, etc. Harassment in the current work environment did not differ by age; 53% reported harassment-free, 31% subtle undertones, 8% noticeable tones, 2% significant harassment. Harassment in the workplace varied by region; the greatest level of harassment was in the Midwest. CONCLUSIONS: Women otolaryngologists continue to experience harassment in the workplace. It is encouraging that younger otolaryngologists feel more supported by their departments in both their careers and their personal lives. This survey highlights critical areas for continued growth within our specialty. LEVEL OF EVIDENCE: IV Laryngoscope, 131:E380-E387, 2021.

Gender Representation in Otolaryngology-Head and Neck Surgery Recognition Awards.

OBJECTIVE: The proportion of women in otolaryngology-head and neck surgery (OHNS) has steadily increased in recent years. This study examines gender representation in recognition awards given by OHNS societies between 2009 and 2019. STUDY DESIGN: Retrospective analysis of recognition awards given by 10 OHNS societies between 2009 and 2019. SETTING: Retrospective review of web-based, public records. METHODS: Data from 19 awards were analyzed for recipient gender ratio, society, subspecialty, award type (research, achievement, or humanitarian), and change over time. RESULTS: Of 184 awards given by societies in otolaryngology-head and neck surgery, 59 (28%) were given to women. Women received 49 (28%) research awards, 9 (31%) humanitarian awards, and 1 (2.8%) achievement award. Women represented 31% of award winners in rhinology/skull base, 30% of award winners in head and neck surgery, 8% in neurotology, and 6% in facial plastic surgery. The American Head and Neck Society Prevention and Early Detection award had the highest representation of women at 43%. Some awards had no female awardees over the past decade. No temporal trends were observed. CONCLUSION: From 2009 to 2019, women received recognition awards at a higher percentage than overall gender representation in OHNS. Comparison of research, humanitarian, and achievement awards revealed the disparity of women receiving fewer achievement awards relative to men. Gender representation of award recipients varied by subspecialty, which may be partially determined by gender distribution within the fields.

Satisfaction in Academic Otolaryngology: Do Physician Demographics Impact Press Ganey Survey Scores?

OBJECTIVES/HYPOTHESIS: Patient satisfaction is increasingly emphasized and measured in healthcare delivery. However, patient satisfaction is multifactorial and difficult to comprehensively assess. The objective of this study was to assess for correlation between patient satisfaction measured by Press Ganey surveys (PGS) and physician demographics of gender, years in practice, academic rank, and specialty in academic otolaryngology. STUDY DESIGN: Review of publicly available PGS scores in academic otolaryngology practice. METHODS: Public websites of academic otolaryngology departments were assessed for inclusion of PGS scores. Individual physician profiles were queried for years in practice, academic rank, and specialty. Gender was determined by picture or profile pronouns. Univariate and multivariate analyses compared PGS scores with studied variables. RESULTS: Forty-seven of 113 (42.8%) academic practices publicly reported physician PGS score. Of 1,360 affiliated otolaryngologists, 742 (54.6%,592 male:150 female) revealed PGS scores. Average PGS score for male and female providers was equivalent (PGS = 4.73, P = .84). There was no significant difference in PGS scores by academic rank (P = .28). A weak statistically significant decrease in mean PGS scores was associated with longer duration of practice (r = -0.11, P = .018). Head and neck oncologic surgeons had higher mean PGS score in comparison to other specialties (PGS = 4.81, P < .05). General/comprehensive otolaryngologists had lower average PGS score (PGS = 4.66) in comparison to specialists (P < .05). CONCLUSIONS: Physician gender and academic rank do not correlate with patient satisfaction in academic otolaryngology as measured by publicly reported PGS scores. Head and neck oncology is rated more highly than other specialties, and physicians in practice for longer demonstrate decreased PGS scores. With PGS scores tied to physician evaluation and reimbursement, investigation into the generalizability of PGS in otolaryngology is warranted. LEVEL OF EVIDENCE: NA Laryngoscope, 130: 1902-1906, 2020.

Long-Term Otologic and Audiometric Outcomes in Patients with Cleft Palate.

Objective Describe longitudinal audiometric and otologic outcomes in patients with cleft palates. Study Design Case series with chart review. Setting Single academic medical center. Methods Charts of 564 patients with a diagnosis of cleft palate (59% syndromic etiology, 41% nonsyndromic) from 1998 to 2014 were reviewed. Patients without at least 1 audiometric follow-up were excluded from analysis. Patient demographics, surgeries, audiometric tests, and otologic data were recorded for 352 patients. Results Forty-five percent had isolated cleft palates, 34% had unilateral cleft lip and palate, and 21% had bilateral cleft lip and palate. Patients were followed for a mean of 50.3 months with a mean of 3.2 separate audiograms performed. Patients received a mean of 2.93 pressure equalization tubes. Increased number of pressure equalization tubes was not associated with incidence of cholesteatoma, which was identified in only 4 patients. Nine patients underwent eventual tympanoplasty with an 89% closure rate. Analysis of mean air-bone gap by cleft type did not reveal significant differences ( P = .08), but conductive losses and abnormal tympanometry persisted into teenage years. Conclusions Patients with cleft palates have eustachian tube dysfunction, which, in our cohort, resulted in persistent conductive hearing loss, highlighting the importance of long-term follow-up. Cholesteatoma incidence was low and not associated with number of tubes, which at our institution were placed prophylactically. Tympanoplasty was successful in those with persistent perforations.

Microbiology of the Upper and Lower Airways in Pediatric Cystic Fibrosis Patients.

Objective To evaluate the microbiology of the upper and lower airways in pediatric cystic fibrosis (CF) patients who underwent sinus surgery. Study Design Retrospective case series with chart review. Setting Tertiary care children's hospital. Subjects and Methods A total of 201 paired sinus and pulmonary cultures from 105 CF patients were identified between 1996 and 2014. Demographics and culture results were analyzed. Results The mean age of patients was 11.2 ± 5.4 years (range, 1-27 years), and approximately one-half were female. Methicillin-sensitive Staphylococcus aureus was the most common pathogen overall. A significantly higher prevalence of Pseudomonas aeruginosa (32% for pulmonary and 37% for sinus cultures) was observed in older patients versus younger patients ( P < .001). There was low to moderate agreement between sinus and pulmonary cultures (Kappa statistic range, 0.03-0.56). The prevalence of methicillin-resistant S aureus (MRSA) increased significantly for lower respiratory tract culture (from 5% to 16%) and sinus culture (from 5% to 27%) between 1996-2004 and 2010-2014 ( P = .016 and P < .001, respectively). The prevalence of positive sinus cultures increased from 40% to 85% between 1996-2004 and 2010-2014 ( P = .018). Patients with pulmonary MRSA were more likely to be coinfected with pulmonary P aeruginosa (risk ratio, 2.4; 95% CI, 1.2-4.8; P = .015) or Aspergillus fumigatus (risk ratio, 2.2; 95% CI, 1.2-4.8; P = .035). Conclusions There is low to moderate correlation between pulmonary and sinus pathogens in CF patients. This is important to consider when treating infections. The prevalence of MRSA in sinus cultures has increased over time and warrants further investigation.

Maxillofacial injuries among National Collegiate Athletic Association athletes: 2004-2014.

OBJECTIVE: Participation in National Collegiate Athletic Association (NCAA) sports increases annually, yet the risk of maxillofacial injuries among these athletes is unknown. We report the incidence and trends in maxillofacial injuries among NCAA athletes. STUDY DESIGN: Retrospective study of the NCAA Injury Surveillance System (ISS) representing athletes from seven men's and eight women's sports across Divisions 1, 2, and 3. Incidence of maxillofacial injuries by sport, gender, anatomic location, and injuries requiring surgery were measured. METHODS: Athlete exposure data from 2004 to 2005 through 2013 to 2014 were analyzed, along with maxillofacial injuries recorded in the NCAA-ISS. RESULTS: There were 2,017 injuries recorded, which projects to 41,204 injuries from 202,087,229 athlete events, or 2.04 injuries per 10,000 athlete events (95% confidence interval [CI], 1.68 to 2.40). Women had higher injury rates, 2.06 versus 2.03 (P = 0.016 [95% CI 0.22 to 2.09]). Highest rates were noted in men's wrestling 7.02 (95% CI, 2.84 to 11.19) and men's basketball 4.80 (95% CI, 3.57 to 6.02), and were lowest in women's ice hockey 0.61 (95% CI, 0.17 to 1.06) and women's volleyball 0.43 (95% CI, 0.20 to 0.66). No gender differences in fractures or need for surgery, but men sustained more operative fractures, 27.85% versus 17.04% (P = 0.035 [95% CI, 0.79 to 20.82]). Men's football, women's ice hockey, women's volleyball, and women's gymnastics had consistently low fracture rates. CONCLUSION: Maxillofacial injuries represent approximately 3.4% of all injuries sustained by NCAA athletes. Women had a higher injury rate, whereas men had a higher rate of operative facial fractures. Awareness and improved facial protection, especially among noncontact sports, will be crucial in reducing the incidence of these injuries. LEVEL OF EVIDENCE: 4. Laryngoscope, 127:1296-1301, 2017.

Impostor syndrome and burnout among American medical students: a pilot study.

Objectives: To describe levels of burnout and impostor syndrome (IS) in medical students, and to recognize demographic differences in those experiencing burnout and IS. Methods: Anonymous survey administered online in 2014 that included demographic data, the Maslach Burnout Inventory and an IS screening questionnaire. Main outcome measures were level of burnout, and presence or absence of imposter syndrome. The presence of IS and burnout components were analyzed across age, gender, race, year of training, intention to pursue fellowship training, and greater than one year of work experience outside of medicine using chi-squared tests. The association between burnout and IS was also compared using chi-squared tests. Results: One hundred and thirty-eight students completed the questionnaire. Female gender was significantly associated with IS (χ2(3)=10.6, p=0.004) with more than double the percentage of females displaying IS than their male counterparts (49.4% of females versus 23.7% of males). IS was significantly associated with the burnout components of exhaustion (χ2 (2)=5.9, p=0.045), cynicism (χ2(2)=9.4, p=0.004), emotional exhaustion (χ2(2)=8.0, p=0.018), and depersonalization (χ2 (2)=10.3, p=0.006). The fourth year of medical school was significantly associated with IS (χ2(3)=10.5, p=0.015). Conclusions: Almost a quarter of male medical students and nearly half of female students experience IS and IS was found to be significantly associated with burnout indices. Given the high psychological morbidity of these conditions, this association cannot be ignored. It behooves us to reconsider facets of medical education (i.e. shame-based learning and overall teaching style) and optimize the medical learning environment.

Intraoperative hypotension associated with massive deep space neck abscesses in a 9-month old: A case report.

The neck is divided into multiple compartments by cervical fasciae. The deep space compartments, which all have a potential for becoming infected, are interconnected, providing a mechanism for the spread of infections. Thus, infections of the deep spaces can lead to devastating consequences, especially when there is extension to the mediastinum. Here we report a case of intraoperative hypotension in a 9-month-old child with extensive bilateral parapharyngeal and retropharyngeal abscesses with mediastinal extension with a focus on when hemodynamic monitoring should be considered.

Incidence of Concussion in Patients With Isolated Mandible Fractures.

IMPORTANCE: This study examines the association between isolated mandible fractures and mild traumatic brain injury (mTBI). OBJECTIVE: To determine the rates of mTBI in patients who have sustained isolated mandible fractures. DESIGN, SETTING, AND PARTICIPANTS: A prospective study was conducted among patients who sustained isolated mandible fractures within 24 hours of presentation. Patients were administered the Military Acute Concussion Evaluation (MACE). Recorded data included demographics, time since injury, use of alcohol or illicit drugs, nonfacial pain, and mechanism of injury. All patients were evaluated in the emergency department of a level I trauma center between June 20, 2013, and June 20, 2014. In addition, discharge data from the Nationwide Inpatient Sample database was analyzed to identify current rates of patients with a diagnosis of both mandible fractures and concussions. MAIN OUTCOMES AND MEASURES: Rates of concussion. Patients with a MACE score of less than 25 were considered to have mTBI. RESULTS: Sixteen patients met the study criteria over a 1-year period. Fourteen patients (88%) were male, and mean age was 27.5 years. The mean time since injury was 11.25 hours (range, 3-21 hours). The mechanism of injury was assault in 12 patients (75%), sports in 2 patients (13%), all-terrain vehicle crash in 1 patient (6%), and biking in 1 patient (6%). Eight patients (50%) admitted to the use of alcohol, and none reported the use of illicit drugs. Eleven patients (69%) reported loss of consciousness. Twelve patients (75%) met criteria for concussion according to the MACE. Among these 12 patients, 7 (58%) admitted to the use of alcohol at the time of injury. There was no relationship between the rates of concussion and the use of alcohol. CONCLUSIONS AND RELEVANCE: Mandible fractures are often sustained after high-force impacts during altercations between men. In our study, a 75% (12 of 16) rate of concussions associated with isolated mandible fractures was identified. Patients with isolated mandible fractures may benefit from being screened for concussion and referred to a concussion clinic. LEVEL OF EVIDENCE: 4.

Trends of online ratings of otolaryngologists: what do your patients really think of you?

IMPORTANCE: The otolaryngologist's online reputation is of increasing importance. Physician rating websites are becoming increasingly prevalent, and patients are using them to evaluate their current and future physicians. OBJECTIVE: To evaluate patterns in online ratings of otolaryngologists. DESIGN, SETTING, AND PARTICIPANTS: From May 1, 2013, through June 1, 2013, lists of academic program faculty members in the Northeastern United States were compiled, and academic allopathic otolaryngologists from the Eastern Section of the Triological Society were identified. Each faculty member's name was searched using the Google search engine to link to profiles on the Healthgrades.com and Vitals.com websites. MAIN OUTCOMES AND MEASURES: State, program, academic position, years in practice, subspecialty, ratings, and reviews were recorded. Ratings were compared using analysis of variance. RESULTS: A total of 281 faculty members from 25 programs were identified. A total of 266 otolaryngologists (94.7%) had a profile on Healthgrades, and 247 (87.9%) had a profile on Vitals. Of those with profiles, 186 (69.9%) and 202 (81.8%) had patient reviews on Healthgrades and Vitals, respectively. The mean score was 4.4 of 5.0 on Healthgrades and 3.4 of 4.0 on Vitals. On Vitals, 179 profiles (63.7%) had comments associated with them. Overall, 49 comments (27.3%) were determined to be negative, and 138 otolaryngologists (49.1%) had at least 1 negative comment. Academic position and subspecialty affected reviews on Healthgrades. State and years in practice did not influence reviews. CONCLUSIONS AND RELEVANCE: Most patients use online resources for information on health care professionals. Physician perceptions of these sites tend to be negative. Awareness of the content and rating patterns may help physicians better manage their online reputation.

Spontaneous carotid-cavernous fistula: challenges in clinical and radiologic diagnosis.

We present a 47-year-old female patient with spontaneous carotid-cavernous fistula without comorbidities. The symptoms of a carotid-cavernous fistula may be confused with other pathology in the region of the orbit and cavernous sinus such as cavernous sinus thrombosis. Carotid-cavernous fistulas most commonly result from direct injury to the internal carotid artery, as with skull base or surgical trauma, but it can also result from weakness in the arterial wall, as with an aneurysm. Because of the high flow of the internal carotid artery, carotid-cavernous fistulas typically present with rapidly progressive symptoms. The case study presented demonstrates the usefulness of radiologic studies in distinguishing between these similarly presenting disease processes. Clinically, cavernous sinus thrombosis generally presents bilaterally and carotid-cavernous fistula presents unilaterally; however, there are a number of exceptions in the literature. The use of a variety of radiologic and angiographic studies will help differentiate between these pathologies. On magnetic resonance imaging, both pathologies can appear as an enlargement of cavernous sinus. Magnetic resonance angiography sequence can reveal aneurysms communicating with the cavernous sinus, and magnetic resonance venography will define thrombosis within the cavernous sinus. Differentiating between cavernous sinus thrombosis and carotid-cavernous fistula can be clinically difficult, and a team approach including emergency physicians, neurosurgeons, ophthalmologists, and otolaryngologists will be called upon to assist in diagnosis. Prompt diagnosis and management can allow for potentially vision and lifesaving interventions.

Laryngotracheal reconstruction in infants and children: are single-stage anterior and posterior grafts a reliable intervention at all pediatric hospitals?

OBJECTIVE: To review outcomes of pediatric laryngotracheal stenosis treated by single-stage laryngotracheal reconstruction with anterior and posterior cartilage grafts and compare decannulation rate for single-stage laryngotracheal reconstruction with rates published at larger (>200 beds) pediatric tertiary care hospitals. METHODS: A 4-year retrospective chart review (2004-2008) of all patients undergoing procedures coded with 2008 CPT codes 31582 (laryngoplasty for laryngeal stenosis with graft or core mold, including tracheotomy) and 31587 (laryngoplasty, cricoid split) for a pediatric, tertiary-care hospital. Interventions were single-stage laryngotracheal reconstruction with anterior and posterior cartilage grafts, and the main outcome measure was the decannulation rate after single-stage laryngotracheal reconstruction. RESULTS: We identified 44 patients with subglottic stenosis, of whom 13 underwent single-stage laryngotracheal reconstruction with anterior and posterior cartilage grafts. The mean age at surgery was 2.2 years (range, 5 months to 4 years). Twelve of 13 children had Cotton-Myer grade III stenosis. Ninety-two percent (12 of 13) of children remain decannulated. The mean follow up was 52 months. CONCLUSIONS: Single-stage laryngotracheal reconstruction with anterior and posterior cartilage grafts appears to be a safe and effective technique for managing patients with high-grade subglottic stenosis at intermediate size children's hospitals. Our overall decannulation rate of 92% compares favorably to that reported in the literature (84-96%).

Mutant huntingtin impairs vesicle formation from recycling endosomes by interfering with Rab11 activity.

Huntingtin (Htt) localizes to endosomes, but its role in the endocytic pathway is not established. Recently, we found that Htt is important for the activation of Rab11, a GTPase involved in endosomal recycling. Here we studied fibroblasts of healthy individuals and patients with Huntington's disease (HD), which is a movement disorder caused by polyglutamine expansion in Htt. The formation of endocytic vesicles containing transferrin at plasma membranes was the same in control and HD patient fibroblasts. However, HD fibroblasts were delayed in recycling biotin-transferrin back to the plasma membrane. Membranes of HD fibroblasts supported less nucleotide exchange on Rab11 than did control membranes. Rab11-positive vesicular and tubular structures in HD fibroblasts were abnormally large, suggesting that they were impaired in forming vesicles. We used total internal reflection fluorescence imaging of living fibroblasts to monitor fluorescence-labeled transferrin-carrying transport intermediates that emerged from recycling endosomes. HD fibroblasts had fewer small vesicles and more large vesicles and long tubules than did control fibroblasts. Dominant active Rab11 expressed in HD fibroblasts normalized the recycling of biotin-transferrin. We propose a novel mechanism for cellular dysfunction by the HD mutation arising from the inhibition of Rab11 activity and a deficit in vesicle formation at recycling endosomes.

Polyglutamine expansion in huntingtin alters its interaction with phospholipids.

Huntingtin has an expanded polyglutamine tract in patients with Huntington's disease. Huntingtin localizes to intracellular and plasma membranes but the function of huntingtin at membranes is unknown. Previously we reported that exogenously expressed huntingtin bound pure phospholipids using protein-lipid overlays. Here we show that endogenous huntingtin from normal (Hdh(7Q/7Q)) mouse brain and mutant huntingtin from Huntington's disease (Hdh(140Q/140Q)) mouse brain bound to large unilamellar vesicles containing phosphoinositol (PI) PI 3,4-bisphosphate, PI 3,5-bisphosphate, and PI 3,4,5-triphosphate [PI(3,4,5)P3]. Huntingtin interactions with multivalent phospholipids were similar to those of dynamin. Mutant huntingtin associated more with phosphatidylethanolamine and PI(3,4,5)P3 than did wild-type huntingtin, and associated with other phospholipids not recognized by wild-type huntingtin. Wild-type and mutant huntingtin also bound to large unilamellar vesicles containing cardiolipin, a phospholipid specific to mitochondrial membranes. Maximal huntingtin-phospholipid association required inclusion of huntingtin amino acids 171-287. Endogenous huntingtin recruited to the plasma membrane in cells that incorporated exogenous PI 3,4-bisphosphate and PI(3,4,5)P3 or were stimulated by platelet-derived growth factor or insulin growth factor 1, which both activate PI 3-kinase. These data suggest that huntingtin interacts with membranes through specific phospholipid associations and that mutant huntingtin may disrupt membrane trafficking and signaling at membranes.

Lysosomal proteases are involved in generation of N-terminal huntingtin fragments.

N-terminal mutant huntingtin (N-mhtt) fragments form inclusions and cause cell death in vitro. Mutant htt expression stimulates autophagy and increases levels of lysosomal proteases. Here, we show that lysosomal proteases, cathepsins D, B and L, affected mhtt processing and levels of cleavage products (cp) known as A and B, which form inclusions. Adding inhibitors of cathepsin D, B and L to clonal striatal cells reduced mhtt, especially mhtt fragment cp A. Mutant htt fully degraded in cathepsin-L-treated lysates but formed stable N-mhtt fragments upon exposure to cathepsin D. Mutagenesis analysis of htt cDNA suggested that cathepsin D and the protease for cp A may cleave htt in the same region. Brain lysates from HD knock-in mice expressed N-mhtt fragments that accumulated with cathepsin D treatment and declined with aspartyl protease inhibition. Findings implicate lysosomal proteases in formation of N-mhtt fragments and clearance of mhtt.

Huntingtin associates with acidic phospholipids at the plasma membrane.

We have identified a domain in the N terminus of huntingtin that binds to membranes. A three-dimensional homology model of the structure of the binding domain predicts helical HEAT repeats, which emanate a positive electrostatic potential, consistent with a charge-based mechanism for membrane association. An amphipathic helix capable of inserting into pure lipid bilayers may serve to anchor huntingtin to the membrane. In cells, N-terminal huntingtin fragments targeted to regions of plasma membrane enriched in phosphatidylinositol 4,5-bisphosphate, receptor bound-transferrin, and endogenous huntingtin. N-terminal huntingtin fragments with an expanded polyglutamine tract aberrantly localized to intracellular regions instead of plasma membrane. Our data support a new model in which huntingtin directly binds membranes through electrostatic interactions with acidic phospholipids.