C9ORF72 GGGGCC repeat-associated non-AUG translation is upregulated by stress through eIF2α phosphorylation.

Hexanucleotide repeat expansion in C9ORF72 is the most frequent cause of both amyotrophic lateral sclerosis (ALS) and frontotemporal dementia (FTD). Here we demonstrate that the repeat-associated non-AUG (RAN) translation of (GGGGCC) n -containing RNAs into poly-dipeptides can initiate in vivo without a 5'-cap. The primary RNA substrate for RAN translation of C9ORF72 sense repeats is shown to be the spliced first intron, following its excision from the initial pre-mRNA and transport to the cytoplasm. Cap-independent RAN translation is shown to be upregulated by various stress stimuli through phosphorylation of the α subunit of eukaryotic initiation factor-2 (eIF2α), the core event of an integrated stress response (ISR). Compounds inhibiting phospho-eIF2α-signaling pathways are shown to suppress RAN translation. Since the poly-dipeptides can themselves induce stress, these findings support a feedforward loop with initial repeat-mediated toxicity enhancing RAN translation and subsequent production of additional poly-dipeptides through ISR, thereby promoting progressive disease.

The periductal channels of the endolymphatic duct, hydrodynamic implications.

OBJECTIVE: To describe the anatomy of a small network of channels surrounding the human endolymphatic duct. STUDY DESIGN: Archival temporal bone sections and a surgical specimen were studied using a variety of techniques. SETTING: Temporal bone laboratory of the House Research Institute. SUBJECTS AND METHODS: Archival temporal bone sections were examined by light microscopy, 3D reconstruction, and immunohistochemical labeling. A surgical specimen was examined using electron microscopy. Sections from temporal bones with blocked endolymphatic ducts or amputated sacs were examined for the manifestations of endolymphatic hydrops. RESULTS: Peri-endolymphatic duct channels were found to extend from the proximal cisternal part of the endolymphatic sac to the supporting tissue of the saccule and utricle. Tissue in the channels, as seen by conventional and electron microscopy, is continuous with and identical with the tissue surrounding the endolymphatic duct. Tissue in the channels labels with the S100 antibody similar to the spiral ligament and supporting tissue of the vestibular end organs and suggests a neural crest origin, as did the presence of melanocytes. Obstruction of the endolymphatic duct resulted in endolymphatic hydrops whereas amputation of the sac did not. CONCLUSION: Endolymph is probably absorbed in the endolymphatic duct. The peri-endolymphatic duct channels that extend from the proximal sac to the supporting tissue of the saccule label with the S100 antibody and contain melanocytes suggest a neural crest origin and involvement in fluid and potassium hydrodynamics similar to those described for the similarly staining spiral ligament of the cochlea.

Endolymphatic pseudohydrops of the cochlear apex.

OBJECTIVE: To demonstrate that what appears to be endolymphatic hydrops of the apical scala media is normal anatomy. STUDY DESIGN: Computer-generated three-dimensional reconstruction of the cochlear apex and tabulation of the number of cases with arched Reissner's membranes (pseudohydrops) versus flat membranes. SETTING: Temporal bone laboratory consisting of 809 documented pairs of temporal bones. SUBJECTS AND METHODS: Archival temporal bone sections from 107 bones (65 patients) were used to determine the percentage of arched (pseudohydrops) versus flat Reissner's membranes. Two bones, one of each membrane shape, were randomly selected for computer-generated three-dimensional reconstructions showing the cochlear apical anatomy. RESULTS: An arched Reissner's membrane was found in 48.6 percent of bones. In the cochlear apex, Reissner's membrane appears to be distended, simulating hydrops, due to its transition from a conical structure to a triangle bounded by the basilar membrane with the organ of Corti, the stria vascularis, and Reissner's membrane. Membrane findings were similar in both ears in 73.8 percent of the bilateral cases studied. There were no significant relationships between membrane type and clinical characteristics. CONCLUSION: What appears to be endolymphatic hydrops of the cochlear apex is the transition area of the cochlear duct from a conical shape at the extreme apex to the triangular shape found in the rest of the cochlea. The appearance of distension is dependent upon the cochlear length and the level of the microscopic section.

Histopathologic assessment of fibrosis and new bone formation in implanted human temporal bones using 3D reconstruction.

OBJECTIVE: To evaluate new bone formation and fibrosis in implanted human temporal bones and relate that to neurosensory elements preservation. STUDY DESIGN: Human temporal bone histopathology study. SETTING: Temporal bone laboratory. SUBJECTS AND METHODS: Ten human temporal bones from eight patients with multichannel cochlear implants and one single-electrode implant were examined under light microscopy and reconstructed with AMIRA 4.1 3D reconstruction software. Volumes of new bone formation, fibrosis, and patent area were calculated in each bone. RESULTS: The amount of fibrosis and new bone formation postimplantation varied among bones. There were no statistically significant relationships between age at implantation or duration of implantation and the overall amount of new tissue in the implanted ear. There was a relationship between total amount of new tissue and preservation of neurosensory elements only in segment I of the cochlea (Rho=-0.75, P