O-GlcNAc site-mapping of liver X receptor-α and O-GlcNAc transferase.

The Liver X Receptor α (LXRα) belongs to the nuclear receptor superfamily and plays an essential role in regulating cholesterol, lipid and glucose metabolism and inflammatory responses. We have previously shown that LXRα is post-translationally modified by O-linked ß-N-acetyl-glucosamine (O-GlcNAc) with increased transcriptional activity. Moreover, we showed that LXRα associates with O-GlcNAc transferase (OGT) in vitro and in vivo in mouse liver. In this study, we report that human LXRα is O-GlcNAc modified in its N-terminal domain (NTD) by identifying a specific O-GlcNAc site S49 and a novel O-GlcNAc modified peptide 20LWKPGAQDASSQAQGGSSCILRE42. However, O-GlcNAc site-mutations did not modulate LXRα transactivation of selected target gene promoters in vitro. Peptide array and co-immunoprecipitation assays demonstrate that LXRα interacts with OGT in its NTD and ligand-binding domain (LBD) in a ligand-independent fashion. Moreover, we map two new O-GlcNAc sites in the longest OGT isoform (ncOGT): S437 in the tetratricopeptide repeat (TPR) 13 domain and T1043 in the far C-terminus, and a new O-GlcNAc modified peptide (amino acids 826-832) in the intervening region (Int-D) within the catalytic domain. We also map four new O-GlcNAc sites in the short isoform sOGT: S391, T393, S399 and S437 in the TPRs 11-13 domain. Future studies will reveal the biological role of identified O-GlcNAc sites in LXRα and OGT.

TCDD-inducible poly-ADP-ribose polymerase (TIPARP/PARP7) mono-ADP-ribosylates and co-activates liver X receptors.

Members of the poly-ADP-ribose polymerase (PARP) family catalyse the ADP-ribosylation of target proteins and are known to play important roles in many cellular processes, including DNA repair, differentiation and transcription. The majority of PARPs exhibit mono-ADP-ribosyltransferase activity rather than PARP activity; however, little is known about their biological activity. In the present study, we report that 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD)-inducible poly-ADP-ribose polymerase (TIPARP), mono-ADP-ribosylates and positively regulates liver X receptor α (LXRα) and LXRß activity. Overexpression of TIPARP enhanced LXR-reporter gene activity. TIPARP knockdown or deletion reduced LXR regulated target gene expression levels in HepG2 cells and in Tiparp(-/-)mouse embryonic fibroblasts (MEFs) respectively. Deletion and mutagenesis studies showed that TIPARP's zinc-finger and catalytic domains were required to enhance LXR activity. Protein interaction studies using TIPARP and LXRα/ß peptide arrays revealed that LXRs interacted with an N-terminal sequence (a.a. 209-236) of TIPARP, which also overlapped with a putative co-activator domain of TIPARP (a.a. 200-225). Immunofluorescence studies showed that TIPARP and LXRα or LXRß co-localized in the nucleus.In vitroribosylation assays provided evidence that TIPARP mono-ADP-ribosylated both LXRα and LXRß. Co-immunoprecipitation (co-IP) studies revealed that ADP-ribosylase macrodomain 1 (MACROD1), but not MACROD2, interacted with LXRs in a TIPARP-dependent manner. This was complemented by reporter gene studies showing that MACROD1, but not MACROD2, prevented the TIPARP-dependent increase in LXR activity. GW3965-dependent increases in hepatic Srebp1 mRNA and protein expression levels were reduced in Tiparp(-/-)mice compared with Tiparp(+/+)mice. Taken together, these data identify a new mechanism of LXR regulation that involves TIPARP, ADP-ribosylation and MACROD1.

The molecular basis of emerin-emerin and emerin-BAF interactions.

Emerin is a conserved membrane component of nuclear lamina structure. Here, we report an advance in understanding the molecular basis of emerin function: intermolecular emerin-emerin association. There were two modes: one mediated by association of residues 170-220 in one emerin molecule to residues 170-220 in another, and the second involving residues 170-220 and 1-132. Deletion analysis showed residues 187-220 contain a positive element essential for intermolecular association in cells. By contrast, deletion of residues 168-186 inactivated a proposed negative element, required to limit or control association. Association of GFP-emerin with nuclear BAF in cells required the LEM domain (residues 1-47) and the positive element. Emerin peptide arrays revealed direct binding of residues 170-220 to residues 206-225 (the proposed positive element), residues 147-174 (particularly P(153)MYGRDSAYQSITHYRP(169)) and the LEM domain. Emerin residues 1-132 and 159-220 were each sufficient to bind lamin A or B1 tails in vitro, identifying two independent regions of molecular contact with lamins. These results, and predicted emerin intrinsic disorder, support the hypothesis that there are multiple 'backbone' and LEM-domain configurations in a proposed intermolecular emerin network at the nuclear envelope.

Liver X receptor regulates hepatic nuclear O-GlcNAc signaling and carbohydrate responsive element-binding protein activity.

Liver X receptor (LXR)α and LXRß play key roles in hepatic de novo lipogenesis through their regulation of lipogenic genes, including sterol regulatory element-binding protein (SREBP)-1c and carbohydrate responsive element-binding protein (ChREBP). LXRs activate lipogenic gene transcription in response to feeding, which is believed to be mediated by insulin. We have previously shown that LXRs are targets for glucose-hexosamine-derived O-linked ß-N-acetylglucosamine (O-GlcNAc) modification enhancing their ability to regulate SREBP-1c promoter activity in vitro. To elucidate insulin-independent effects of feeding on LXR-mediated lipogenic gene expression in vivo, we subjected control and streptozotocin-treated LXRα/ß(+/+) and LXRα/ß(-/-) mice to a fasting-refeeding regime. We show that under hyperglycemic and hypoinsulinemic conditions, LXRs maintain their ability to upregulate the expression of glycolytic and lipogenic enzymes, including glucokinase (GK), SREBP-1c, ChREBPα, and the newly identified shorter isoform ChREBPß. Furthermore, glucose-dependent increases in LXR/retinoid X receptor-regulated luciferase activity driven by the ChREBPα promoter was mediated, at least in part, by O-GlcNAc transferase (OGT) signaling in Huh7 cells. Moreover, we show that LXR and OGT interact and colocalize in the nucleus and that loss of LXRs profoundly reduced nuclear O-GlcNAc signaling and ChREBPα promoter binding activity in vivo. In summary, our study provides evidence that LXRs act as nutrient and glucose metabolic sensors upstream of ChREBP by modulating GK expression, nuclear O-GlcNAc signaling, and ChREBP expression and activity.

Injury and protection of spiral ganglion neurons.

ABSTRACT: Cochlear spiral ganglion neurons (SGNs) are bipolar ganglion cells and are the first neurons in the auditory transduction pathway. They transmit complex acoustic information from hair cells to second-order sensory neurons in the cochlear nucleus for sound processing. Injury to SGNs causes largely irreversible hearing impairment because these neurons are highly differentiated cells and cannot regenerate, making treatment of sensorineural hearing loss (SNHL) arising from SGN injury difficult. When exposed to ototoxic drugs or damaging levels of noise or when there is loss of neurotrophic factors (NTFs), aging, and presence of other factors, SGNs can be irreversibly damaged, resulting in SNHL. It has been found that NTFs and stem cells can induce regeneration among dead spiral ganglion cells. In this paper, we summarized the present knowledge regarding injury, protection, and regeneration of SGNs.

Bioinformatics analysis and verification of key candidate genes influencing the pathogenesis of chronic rhinosinusitis with nasal polyps.

OBJECTIVES: Chronic rhinosinusitis (CRS) with nasal polyps (CRSwNP) is a prominent public health issue. Furthermore, the prognosis of eosinophilic CRSwNP is poor, with a high recurrence rate. The underlying molecular mechanisms of eosinophilic CRSwNP remain unclear. Therefore, in this study, we sought to determine the crucial genes underlying eosinophil infiltration in eosinophilic CRSwNP pathogenesis. METHODS: We used the Gene Expression Omnibus database (GEO) (GSE36830 and GSE23552 datasets) to mine gene expression profiles of CRSwNP patients and normal subjects. Differentially expressed genes (DEGs) between normal and CRSwNP tissues were identified and subjected to the Kyoto Encyclopedia of Genes and Genomes (KEGG) and Gene Ontology (GO) enrichment analyses. Co-expression networks were established using a weighted gene co-expression network analysis (WGCNA) and single-sample gene set enrichment analysis (GSEA). Protein-protein interaction networks were developed to detect functional protein modules. Based on the common DEGs, candidate miRNAs and related lncRNAs were predicted using the mirTarBase and StarBase databases. Finally, we generated immune cell subtypes of CRSwNP. RESULTS: A total of 146 DEGs were identified. Of these, 131 genes were upregulated, whereas 15 were downregulated. GO analysis indicated that DEGs primarily participated in leukocyte chemotaxis and migration as well as cell chemotaxis. KEGG pathway analysis suggested that DEGs participated in the interactions between cytokines and viral proteins, osteoclast differentiation, and cytokine-cytokine receptor interactions. Real-time quantitative polymerase chain reaction analysis showed that Complement C5a Receptor 1 (C5AR1), C-C Motif Chemokine Receptor 3 (CCR3), Complement C3a Receptor 1 (C3AR1), and C-C Motif Chemokine Ligand 13 (CCL13) expression levels were significantly upregulated in nasal polyps, whereas C-C Motif Chemokine Ligand 4 (CCL4) expression levels were significantly downregulated. CONCLUSIONS: The candidate genes identified in this study may influence the activation and accumulation of eosinophils, cell chemotaxis, and inflammatory responses, thereby potentially representing molecular targets for future studies of CRSwNP.

Cardiac O-GlcNAc signaling is increased in hypertrophy and heart failure.

Reversible protein O-GlcNAc modification has emerged as an essential intracellular signaling system in several tissues, including cardiovascular pathophysiology related to diabetes and acute ischemic stress. We tested the hypothesis that cardiac O-GlcNAc signaling is altered in chronic cardiac hypertrophy and failure of different etiologies. Global protein O-GlcNAcylation and the main enzymes regulating O-GlcNAc, O-GlcNAc transferase (OGT), O-GlcNAcase (OGA), and glutamine-fructose-6-phosphate amidotransferase (GFAT) were measured by immunoblot and/or real-time RT-PCR analyses of left ventricular tissue from aortic stenosis (AS) patients and rat models of hypertension, myocardial infarction (MI), and aortic banding (AB), with and without failure. We show here that global O-GlcNAcylation was increased by 65% in AS patients, by 47% in hypertensive rats, by 81 and 58% post-AB, and 37 and 60% post-MI in hypertrophic and failing hearts, respectively (P < 0.05). Noticeably, protein O-GlcNAcylation patterns varied in hypertrophic vs. failing hearts, and the most extensive O-GlcNAcylation was observed on proteins of 20-100 kDa in size. OGT, OGA, and GFAT2 protein and/or mRNA levels were increased by pressure overload, while neither was regulated by myocardial infarction. Pharmacological inhibition of OGA decreased cardiac contractility in post-MI failing hearts, demonstrating a possible role of O-GlcNAcylation in development of chronic cardiac dysfunction. Our data support the novel concept that O-GlcNAc signaling is altered in various etiologies of cardiac hypertrophy and failure, including human aortic stenosis. This not only provides an exciting basis for discovery of new mechanisms underlying pathological cardiac remodeling but also implies protein O-GlcNAcylation as a possible new therapeutic target in heart failure.

Heterozygous MYH9 Mutations in 2 Children With Cochlear Nerve Canal Stenosis.

MYH9 is a gene that encodes for a subunit of the myosin heavy chain IIA protein. Mutations in MYH9 are associated with hematologic abnormalities, renal dysfunction, and hearing loss. Bony cochlear nerve canal stenosis (CNCS), which is diagnosed on computed tomography (CT) imaging, has been associated with congenital deafness, cochlear nerve aplasia/hypoplasia, and inner ear malformations. We report two cases of CNCS presenting with profound congenital hearing loss whom we diagnosed with mutations in MYH9 and discuss the genotype-phenotype association and implications for management.

Clinical characteristics in unilateral cochlear nerve canal stenosis.

OBJECTIVE: To characterize the clinical features of patients with congenital hearing loss and unilateral cochlear nerve canal stenosis (CNCS). METHODS: A retrospective review of 12 patients with unilateral CNCS diagnosed between January 2018 and December 2019 at a tertiary referral hospital was performed. RESULTS: Of the 12 patients identified, there were 6 males and 6 females. All patients presented with hearing loss, with no other chief complaints. Two patients had accessory auricles. Eleven patients had a severe to profound sensorineural hearing loss on the affected side, while 1 patient had an isolated high-frequency hearing loss. Nine patients demonstrated atresia of the cochlear nerve canal (CNC), while three patients had a stenotic, but patent, CNC. CONCLUSION: Prompt radiologic diagnosis of patients with unilateral CNCS is important for patient counseling and appropriate rehabilitation.

Nuclear receptor liver X receptor is O-GlcNAc-modified in response to glucose.

Post-translational modification of nucleocytoplasmic proteins by O-linked beta-N-acetylglucosamine (O-GlcNAc) has for the last 25 years emerged as an essential glucose-sensing mechanism. The liver X receptors (LXRs) function as nutritional sensors for cholesterol-regulating lipid metabolism, glucose homeostasis, and inflammation. LXRs are shown to be post-translationally modified by phosphorylation, acetylation, and sumoylation, affecting their target gene specificity, stability, and transactivating and transrepressional activity, respectively. In the present study, we show for the first time that LXRalpha and LXRbeta are targets for glucose-hexosamine-derived O-GlcNAc modification in human Huh7 cells. Furthermore, we observed increased hepatic LXRalpha O-GlcNAcylation in vivo in refed mice and in streptozotocin-induced refed diabetic mice. Importantly, induction of LXRalpha O-GlcNAcylation in both mouse models was concomitant with increased expression of the lipogenic gene SREBP-1c (sterol regulatory element-binding protein 1c). Furthermore, glucose increased LXR/retinoic acid receptor-dependent activation of luciferase reporter activity driven by the mouse SREBP-1c promoter via the hexosamine biosynthetic pathway in Huh7 cells. Altogether, our results suggest that O-GlcNAcylation of LXR is a novel mechanism by which LXR acts as a glucose sensor affecting LXR-dependent gene expression, substantiating the crucial role of LXR as a nutritional sensor in lipid and glucose metabolism.

[Prediction of facial nerve fronting with temporal bone high resolution computed tomograph].

Objective:To report a new CT measurement to predict the exposure of round window niche during facial nerve recess surgery. Methods:Forty CT scans were measured by conventional facial-round window line and limiting facial-round window line method, and compared with the exposure of round window niche after the opening of the facial recess. Results:There was no significant difference in the sensitivity and specificity of the two CT measurement methods to predict the exposure degree of the round window niche, and the Kappa consistency test of the two methods also showed a strong correlation. Conclusion:The new measurement method can predict the exposure of the round window niche pre-operation, and in practice, it can predict the maximum exposure of the round window niche.

Recording of electrocochleography from the facial nerve canal in mice.

BACKGROUND: The ever-expanding arsenal of genetically modified mice has created experimental models for studying various mechanisms of deafness. Electrocochleography (ECochG) is a recording technique of cochlear potentials evoked by sound stimulation, which was widely used to evaluate the cochlear hearing function. However, there is currently a lack of information on long-term recording technology of ECochG in mice. NEW METHOD: We describe in detail the surgical procedure of implanting electrode into the facial nerve canal in C57BL/6J mice for ECochG recording. The results of ECochG recorded by electrode in the facial nerve canal were compared with ECochG guided by electrode on the round window niche. RESULTS: The surgical method of inserting the electrode into the facial nerve canal is relatively simple and can be completed within 15 min. The electrode inserted into the elongated facial nerve canal is stable and close to the auditory nerve trunk, so it is conducive to long-term auditory function monitoring. Hence, the ECochG guided by the electrode from the facial nerve canal can maintain a stable response for more than two weeks. In contrast, the ECochG guided by the electrode in the round window niche can only be maintained for a maximum of 20 min. COMPARISON WITH EXISTING METHODS: In mice, existing recording techniques of ECochG from round window niche is limited by conductive hearing loss due to middle ear effusion or surgical damage. CONCLUSIONS: ECochG recording from the facial nerve canal is suitable for long-term recording in mice. This electrode approach provides a repeatable and reliable measurement of ECochG.

Auditory and speech performance after unilateral cochlear implantation for cochlear nerve canal stenosis.

To explore the correlation between the width of the bony cochlear nerve canal (CNC) and long-term auditory rehabilitation after unilateral cochlear implantation (CI) in pediatric patients with congenital deafness and bilateral cochlear nerve canal stenosis (CNCS). A retrospective review was performed on 10 patients with bilateral CNCS and bilateral congenital profound hearing loss who each underwent unilateral cochlear implantation. The width of the CNC was determined on computed tomography (CT) imaging and following CI, auditory and speech performance following CI were graded using categories of auditory performance (CAP), speech intelligibility rating (SIR), and the meaningful auditory integration scale (MAIS) at 24 months following implantation. No correlation was noted between CAP score and CNCS at 24 months post CI (P > .05). A positive correlation was noted between SIR score and CNC width (ρ = .81, P < .05). Similarly, a positive correlation was noted between MAIS and CNC width (ρ = .71, P < .05). The width of the CNC in patients with CNCS is positively correlated with some long-term auditory and speech outcomes after CI.

Cochlear Nerve Canal Stenosis: Association With MYH14 and MYH9 Genes.

The bony cochlear nerve canal transmits the cochlear nerve as it passes from the fundus of the internal auditory canal to the cochlea. Stenosis of the cochlear nerve canal, defined as a diameter less than 1.0 mm in transverse diameter, is associated with inner ear anomalies and severe to profound congenital hearing loss. We describe an 11-month-old infant with nonsyndromic congenital sensorineural hearing loss with cochlear nerve canal stenosis. Next-generation sequencing revealed heterozygous mutations in MYH9 and MYH14, encoding for the inner ear proteins myosin heavy chain IIA and IIC. The patient's hearing was rehabilitated with bilateral cochlear implantation.

[Clinical analysis of 8 cases of delayed facial paralysis after middle ear surgery].

Objective:To investigate the possible causes, prevention, treatment and recovery of delayed facial paralysis after middle ear surgery. Method:A retrospectively analysis of the data of 8 patients with delayed facial paralysis after middle ear surgery under general anesthesia, including one case of tympanoplasty （type Ⅰ） , one case of tympanotomy+tympanoplasty c（type Ⅰ） , one case ofepitympanotomy+reconstruction of attic lateral wall+tympanoplasty （type Ⅱ ）, four cases of canal wall down+tympanoplasty （ type Ⅱ） and one case of canal wall up mastoidectomy. After discovering the facial paralysis, the stuffing in the surgical cavity was released and removed for all patients immediately. Necessary stuffing was replaced by dexamethasone gauze （not press hardl）. Meanwhile, patients took methylprednisolone orally and were intramuscularly injected with mecobalamine. Result:Among eight patients, there were six patients with horizontal exposure of facial nerve and two patients with pyramis exposure of facial nerve. There was one case, five cases and two cases of delayed facial paralysis at five days, one week and two weeks after operation respectively. There were six patients suffering from the facial paralysis of HB Ⅱ grade and two patients suffering from the facial paralysis of HB Ⅲ grade. Four patients recovered four weeks and the remaining four patients returned to normal six weeks after surgery. Conclusion:Delayed facial paralysis is one of complications of the middle ear surgery, and most of patients can recover completely after conservative treatment.

[Clinical features and surgical treatment of external auditory canal cholesteatoma in 149 cases].

Objective:The aim of this study is to explore the clinical characteristics, surgical management and treatment results of type Ⅰto type Ⅳ external auditory canal cholesteatoma（EACC）. Method:One hundred and forty-nine patients（150 ears） with EACC underwent different surgical approach according to the classification of EACC and the lesion range: ① 44 ears: external auditory canal lesion resection with or without reconstruction of external auditory canal ② 23 ears: external auditory canal lesion resection with reconstruction of external auditory canal and the tympanoplasty（TypesⅠto Ⅲ）; ③ 32 ears: external auditory canal lesion resection with reconstruction of external auditory canal and modified mastoidectomy and reconstruction of the posterior wall of external auditory canal; ④ 28 ears: external auditory canal lesion resection with reconstruction of external auditory canal and tympanoplasty（Types Ⅰ to Ⅲ） and modified mastoidectomy and reconstruction of the posterior wall of external auditory canal; ⑤12 ears: canal wall down mastoidectomy （CWD） with plasty of the cavity of auricular concha; ⑥ 11 ears: epitympanum dectomy and reconstruction with tympanoplasty. Result:In the 150 ears, there were 38 ears classified as Type Ⅰ, 52 as Type Ⅱ, 58 as Type Ⅲ and 2 as Type Ⅳ based on the Shin classification. All patients were followed up for more than half a year. The postoperative outcomes were satisfactory with low rate of cholesteatoma recurrence and the hearing was improved to varying degrees. Conclusion:Base on the variety of lesions, the surgical treatment method of choice depends on the extent of the lesion. Effective postoperative follow-up can reduce recurrence and avoid the second operation.

LXRα Regulates ChREBPα Transactivity in a Target Gene-Specific Manner through an Agonist-Modulated LBD-LID Interaction.

The cholesterol-sensing nuclear receptor liver X receptor (LXR) and the glucose-sensing transcription factor carbohydrate responsive element-binding protein (ChREBP) are central players in regulating glucose and lipid metabolism in the liver. More knowledge of their mechanistic interplay is needed to understand their role in pathological conditions like fatty liver disease and insulin resistance. In the current study, LXR and ChREBP co-occupancy was examined by analyzing ChIP-seq datasets from mice livers. LXR and ChREBP interaction was determined by Co-immunoprecipitation (CoIP) and their transactivity was assessed by real-time quantitative polymerase chain reaction (qPCR) of target genes and gene reporter assays. Chromatin binding capacity was determined by ChIP-qPCR assays. Our data show that LXRα and ChREBPα interact physically and show a high co-occupancy at regulatory regions in the mouse genome. LXRα co-activates ChREBPα and regulates ChREBP-specific target genes in vitro and in vivo. This co-activation is dependent on functional recognition elements for ChREBP but not for LXR, indicating that ChREBPα recruits LXRα to chromatin in trans. The two factors interact via their key activation domains; the low glucose inhibitory domain (LID) of ChREBPα and the ligand-binding domain (LBD) of LXRα. While unliganded LXRα co-activates ChREBPα, ligand-bound LXRα surprisingly represses ChREBPα activity on ChREBP-specific target genes. Mechanistically, this is due to a destabilized LXRα:ChREBPα interaction, leading to reduced ChREBP-binding to chromatin and restricted activation of glycolytic and lipogenic target genes. This ligand-driven molecular switch highlights an unappreciated role of LXRα in responding to nutritional cues that was overlooked due to LXR lipogenesis-promoting function.

Suprameatal approach for cochlear implantation in 45 Chinese children.

OBJECTIVE: To investigate the feasibility of applying the suprameatal approach (SMA) for cochlear implantation in Chinese children with profound sensory hearing loss, and to demonstrate a technical modification incorporated in the procedure due to an observed racial difference. STUDY DESIGN: Retrospective study. SETTING: University hospital. PATIENTS: Forty-five Chinese children (total 47 ears) with profound sensory hearing loss were surgically treated from May 2005 to May 2006. The patients were followed anywhere from 1 month to 20 months post-surgery, with 30 patients being followed for more than 6 months. INTERVENTIONS: All patients received cochlear implantation through the suprameatal approach. In this procedure, the cochleostomy was performed in one stage after the suprameatal tunnel was finished, rather than the two-stage approach described by Kronenberg (who firstly introduced the suprameatal approach). Three patients with low-lying dura (which is considered to be the contraindication for cochlear implantation with SMA) were treated with a further modified surgical approach. RESULTS: Among the 47 ears, full electrode pairs were completely inserted in 45 ears without surgical difficulties, but 1 ear was only fitted with 9 pairs of electrodes because of an ossified cochlea, and another with just 8 pairs of electrodes due to serious cochlear dysplasia. An intraoperative "gusher" occurred in the dysplasia case, and a small piece of temporalis muscle was used, along with biology glue, to seal the cochleostomy and prevent further leakage. In 1 case, the electrode was inserted into the cochlea through the tunnel lateral to the chorda tympani because adhesion had occurred between the incus and chorda tympani. There were no postoperative complications in any case. Thirty cases exhibited better hearing or speech development from cochlear implantation after more than 6 months of follow-up. CONCLUSIONS: The SMA was found to be a simple and safe technique for cochlear implantation in Chinese children. It enables wide exposure of the middle ear, and is especially suitable for cases with a narrow facial recess, an anteriorly located facial nerve, or an ossified cochlea. It is almost impossible to injure the facial nerve or the chorda tympani nerve. The cochleostomy can be performed in one stage in those patients with a normal cochlea. With some modifications, a low-lying dura will not be the absolute contraindication of SMA.

Characteristics of electrically evoked auditory brainstem responses in patients with cochlear nerve canal stenosis receiving cochlear implants.

OBJECTIVE: To explore the characteristics of the electrically evoked auditory brainstem responses (EABR) in children with cochlear nerve canal stenosis (CNCs) following cochlear implantation (CI), and the EABR thresholds in children with stenotic versus normal cochlear nerve canals. METHOD: Sixteen children with profound sensorineural hearing loss were included in this study: 8 with CNCs (CNCs group) and 8 with normal cochlear nerve canals (control group). All children underwent cochlear implantation with full insertion of all electrodes. EABR was performed 6 months postoperatively in both groups. RESULTS: The EABR extraction rate was 100% in children with normal cochlear nerve canals and only 50% in children with CNCs. EABR thresholds were significantly higher in children with CNCs of electrodes No. 11and 22 than in children with normal cochlear nerve canals (P < 0.05 for both comparisons). There was no significant difference in EABR thresholds among electrode No. 1, 11 and 22 in CNCs group (P > 0.05 for all comparisons); while in the control group, the EABR threshold at electrode No 22 was lower than those at both electrodes No. 11 and 1 (P < 0.05 for both comparisons), and the EABR threshold at electrode No. 11 was also lower than that at electrode No. 1 (P < 0.05). CONCLUSION: The EABR thresholds in children with normal cochlear nerve canals vary according to the different locations of electrodes in the cochlea; while in children with CNCs, there was no significant difference among different electrode locations. The EABR thresholds in CNCs children were higher than those of children with normal cochlear nerve canals at electrode 11 and 22.

OGT (O-GlcNAc Transferase) Selectively Modifies Multiple Residues Unique to Lamin A.

The LMNA gene encodes lamins A and C with key roles in nuclear structure, signaling, gene regulation, and genome integrity. Mutations in LMNA cause over 12 diseases ('laminopathies'). Lamins A and C are identical for their first 566 residues. However, they form separate filaments in vivo, with apparently distinct roles. We report that lamin A is ß-O-linked N-acetylglucosamine-(O-GlcNAc)-modified in human hepatoma (Huh7) cells and in mouse liver. In vitro assays with purified O-GlcNAc transferase (OGT) enzyme showed robust O-GlcNAcylation of recombinant mature lamin A tails (residues 385⁻646), with no detectable modification of lamin B1, lamin C, or 'progerin' (Δ50) tails. Using mass spectrometry, we identified 11 O-GlcNAc sites in a 'sweet spot' unique to lamin A, with up to seven sugars per peptide. Most sites were unpredicted by current algorithms. Double-mutant (S612A/T643A) lamin A tails were still robustly O-GlcNAc-modified at seven sites. By contrast, O-GlcNAcylation was undetectable on tails bearing deletion Δ50, which causes Hutchinson⁻Gilford progeria syndrome, and greatly reduced by deletion Δ35. We conclude that residues deleted in progeria are required for substrate recognition and/or modification by OGT in vitro. Interestingly, deletion Δ35, which does not remove the majority of identified O-GlcNAc sites, does remove potential OGT-association motifs (lamin A residues 622⁻625 and 639⁻645) homologous to that in mouse Tet1. These biochemical results are significant because they identify a novel molecular pathway that may profoundly influence lamin A function. The hypothesis that lamin A is selectively regulated by OGT warrants future testing in vivo, along with two predictions: genetic variants may contribute to disease by perturbing OGT-dependent regulation, and nutrient or other stresses might cause OGT to misregulate wildtype lamin A.