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Ca 2؉ enters the stereocilia of hair cells through mechanoelectrical transduction channels opened by the deflection of the hair bundle and is exported back to endolymph by an unusual splicing isoform (w/a) of plasma-membrane calcium-pump isoform 2 (PMCA2). Ablation or missense mutations of the pump cause deafness, as described for the G283S mutation in the deafwaddler (dfw) mouse. A deafness-inducing missense mutation of PMCA2 (G293S) has been identified in a human family. The family also was screened for mutations in cadherin 23, which accentuated hearing loss in a previously described human family with a PMCA2 mutation. A T1999S substitution was detected in the cadherin 23 gene of the healthy father and affected son but not in that of the unaffected mother, who presented instead the PMCA2 mutation. The w/a isoform was overexpressed in CHO cells. At variance with the other PMCA2 isoforms, it became activated only marginally when exposed to a Ca 2؉ pulse. The G293S and G283S mutations delayed the dissipation of Ca 2؉ transients induced in CHO cells by InsP3. In organotypic cultures, Ca 2؉ imaging of vestibular hair cells showed that the dissipation of stereociliary Ca 2؉ transients induced by Ca 2؉ uncaging was compromised in the dfw and PMCA2 knockout mice, as was the sensitivity of the mechanoelectrical transduction channels to hair bundle displacement in cochlear hair cells.hereditary hearing loss ͉ mutations ͉ calcium homeostasis ͉ calcium transport T he receptive organelle of sensory hair cells in the mammalian cochlea, the stereocilia bundle, protrudes from the cell's apical surface. Inner hair cells transduce mechanical vibrations into electrical signals that are eventually transmitted to the brain to be transformed into hearing signals (1), whereas outer hair cells (OHCs) (2) amplify the vibrations of the basilar membrane (3). Mechanical stimuli that are detected as excitatory deflect a hair bundle, thus increasing tension in the tip link, a filament stretched between the tops of stereocilia. This tension is conveyed to mechanosensitive transduction (MET) channels that open to allow ions into the cell (4). The apical surface of hair cells is bathed in endolymph, which is rich in K ϩ but low in Na ϩ and Ca 2ϩ (5). K ϩ carries most the transduction current, but MET channels are Ca 2ϩ selective, i.e., Ca 2ϩ influx is significant even at the low Ca 2ϩ levels of the endolymph, which are much lower than those of other extracellular fluids (6-10): 20-23 M in the rodent cochlea (11, 12), 200-250 M in the vestibular system, possibly because of the presence there of calcium carbonate crystals (13,14). Approximately 10% of the MET current may actually be carried by Ca 2ϩ ions (15). Ca 2ϩ entering through MET channels is rapidly sequestered by buffers in the stereocilia (16,17) and is shuttled back to endolymph by the plasma membrane Ca 2ϩ pump (PMCA) (18,19), which is very concentrated in the stereocilia membrane (Ϸ2,000 per squared micrometer) (15, 19-21). The PMCA is assumed to increase Ca 2ϩ in the immediate pro...

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SUMMARYMyelination is a complex process that requires coordinated Schwann cell-axon interactions during development and regeneration. Positive and negative regulators of myelination have been recently described, and can belong either to Schwann cells or neurons. Vimentin is a fibrous component present in both Schwann cell and neuron cytoskeleton, the expression of which is timely and spatially regulated during development and regeneration. We now report that vimentin negatively regulates myelination, as loss of vimentin results in peripheral nerve hypermyelination, owing to increased myelin thickness in vivo, in transgenic mice and in vitro in a myelinating co-culture system. We also show that this is due to a neuron-autonomous increase in the levels of axonal neuregulin 1 (NRG1) type III. Accordingly, genetic reduction of NRG1 type III in vimentin-null mice rescues hypermyelination. Finally, we demonstrate that vimentin acts synergistically with TACE, a negative regulator of NRG1 type III activity, as shown by hypermyelination of double Vim/Tace heterozygous mice. Our results reveal a novel role for the intermediate filament vimentin in myelination, and indicate vimentin as a regulator of NRG1 type III function.

Background and purpose This study was undertaken to determine the diagnostic and prognostic value of a panel of serum biomarkers and to correlate their concentrations with several clinical parameters in a large cohort of patients with amyotrophic lateral sclerosis (ALS). Methods One hundred forty‐three consecutive patients with ALS and a control cohort consisting of 70 patients with other neurodegenerative disorders (DEG), 70 patients with ALS mimic disorders (ALSmd), and 45 healthy controls (HC) were included. Serum neurofilament light chain (NfL), ubiquitin carboxyl‐terminal hydrolase isozyme L1 (UCHL1), glial fibrillary acidic protein (GFAP), and total tau protein levels were measured using ultrasensitive single molecule array. Results NfL correlated with disease progression rate (p < 0.001) and with the measures of upper motor neuron burden (p < 0.001). NfL was higher in the ALS patients with classic and pyramidal phenotype. GFAP was raised in ALS with cognitive–behavioral impairment compared with ALS with normal cognition. NfL displayed the best diagnostic performance in discriminating ALS from HC (area under the curve [AUC] = 0.990), DEG (AUC = 0.946), and ALSmd (AUC = 0.850). UCHL1 performed well in distinguishing ALS from HC (AUC = 0.761), whereas it was not helpful in differentiating ALS from DEG and ALSmd. In multivariate analysis, NfL (p < 0.001) and UCHL1 (p = 0.038) were independent prognostic factors. Survival analysis combining NfL and UCHL1 effectively stratified patients with lower NfL levels (p < 0.001). Conclusions NfL is a useful biomarker for the diagnosis of ALS and the strongest predictor of survival. UCHL1 is an independent prognostic factor helpful in stratifying survival in patients with low NfL levels, likely to have slowly progressive disease. GFAP reflects extramotor involvement, namely cognitive impairment or frontotemporal dementia.