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The Effect of Round Window Sealants on Delayed Hearing Loss in a Guinea Pig Model of Cochlear Implantation.
Related Articles The Effect of Round Window Sealants on Delayed Hearing Loss in a Guinea Pig Model of Cochlear Implantation. Otol Neurotol. 2016 Sep;37(8):1024-31 Authors: Rowe D, Chambers S, Hampson A, Eastwood H, O'Leary S Abstract AIM: To determine whether the type of material used to seal the cochlea after round window cochlear implantation influences delayed hearing loss. BACKGROUND: Cochlear implants are now prescribed to patients with residual, low-frequency hearing. This hearing-which provides perceptual benefits for the implanted ear-is frequently lost for unknown reasons weeks to months after surgery in a proportion of patients. A post-surgical change in cochlear mechanics, related to the material used to seal the cochlea after round window implantation, may contribute to this loss. METHODS: An electrode array was implanted in guinea pigs via the round window, which was then sealed with muscle, periosteum, or fibrin glue. Auditory brainstem responses (ABRs) to pure tones (2, 8, 16, 24, and 32 kHz) were recorded before surgery and 1, 4, and 12 weeks after surgery, with subjects then euthanized and their cochleae harvested for histological analysis. RESULTS: Muscle and periosteum, but not fibrin glue, exhibited delayed threshold rises at 2 kHz. Twelve weeks after implantation, 2 kHz threshold shifts differed significantly between muscle (mean, 27.1 dB) and fibrin glue (9.3 dB), but not between these groups and periosteum (19.3 dB). Muscle was sometimes associated with much greater tissue reactions than the other sealants. Most cochleae had injuries to the basilar membrane and/or osseous spiral lamina, regardless of sealant. Hair cell counts did not differ significantly among sealants. CONCLUSION: Delayed, low-frequency hearing loss was observed when cochleae were sealed with muscle or periosteum, but not when cochleae were sealed with fibrin glue. PMID: 27525617 [PubMed - indexed for MEDLINE]Read more...
Applying Neurotrophins to the Round Window Rescues Auditory Function and Reduces Inner Hair Cell Synaptopathy After Noise-induced Hearing Loss.
Related Articles Applying Neurotrophins to the Round Window Rescues Auditory Function and Reduces Inner Hair Cell Synaptopathy After Noise-induced Hearing Loss. Otol Neurotol. 2016 Oct;37(9):1223-30 Authors: Sly DJ, Campbell L, Uschakov A, Saief ST, Lam M, O'Leary SJ Abstract HYPOTHESIS: Applying neurotrophins to the round window immediately after a single noise exposure will prevent noise-induced hidden hearing loss. BACKGROUND: Loud noise can eliminate neural connections between inner hair cells and their afferent neurons (thereby diminishing sound perception) without causing a detectable change on audiogram. This phenomenon is termed hidden hearing loss. METHODS: Guinea pigs were exposed for 2 hours to 4 to 8 kHz noise at either 95 or 105 dB SPL. Immediately afterward a 4 μl bolus of neurotrophins (brain-derived neurotrophic factor 1 μg/μl, and neurotrophin-3 1 μg/μl) was delivered to the round window of one ear, and saline to the other. Auditory brainstem responses to pure-tone pips were acquired preoperatively, and at 1 and 2 weeks' postexposure. Cochleae were removed and whole mounted for immunohistochemical analysis, with presynaptic ribbons of inner hair cells and associated postsynaptic glutamatergic AMPA receptors identified using CtBP2 and GluA2 antibodies respectively. RESULTS: After exposure to 105 dB noise, threshold did not change, but the amplitude growth of the auditory brainstem response was significantly reduced in control ears in response to 16 and 32 kHz tones. The amplitude growth was also reduced neurotrophin ears, but to a lesser degree and the reduction was not significant. Similar results were obtained from control ears exposed to 95 dB, but amplitude growth recovered in neurotrophin-treated ears, this reaching statistical significance in response to 16 kHz tones. There were significantly more presynaptic ribbons, postsynaptic glutamate receptors, and colocalized ribbons after neurotrophin treatment. CONCLUSION: A single dose of neurotrophins delivered to the round window reduced synaptopathy and recovered high-frequency hearing in ears exposed to 95 dB noise. These findings suggest that hidden hearing loss may be reduced by providing trophic support to the cochlea after injury. PMID: 27631825 [PubMed - indexed for MEDLINE]Read more...
Transmission of auditory sensory information decreases in rate and temporal precision at the endbulb of Held synapse during age-related hearing loss.
Related Articles Transmission of auditory sensory information decreases in rate and temporal precision at the endbulb of Held synapse during age-related hearing loss. J Neurophysiol. 2016 Dec 01;116(6):2695-2705 Authors: Xie R Abstract Age-related hearing loss (ARHL) is largely attributed to structural changes and functional declines in the peripheral auditory system, which include synaptopathy at the inner hair cell/spiral ganglion cell (SGC) connection and the loss of SGCs. However, functional changes at the central terminals of SGCs, namely the auditory nerve synapses in the cochlear nucleus, are not yet fully understood during ARHL. With the use of young (1-3 mo) and old (25-30 mo) CBA/CaJ mice, this study evaluated the intrinsic properties of the bushy neurons postsynaptic to the endbulb of Held synapses, and the firing properties of these neurons to direct current injections as well as to synaptic inputs from the auditory nerve. Results showed that bushy neurons in old mice are more excitable and are able to fire spikes at similar rate and timing to direct current injections as those in young mice. In response to synaptic inputs, however, bushy neurons from old mice fired spikes with significantly decreased rate and reduced temporal precision to stimulus trains at 100 and 400 Hz, with the drop in firing probability more profound at 400 Hz. It suggests that transmission of auditory information at the endbulb is declined in both rate and timing during aging, which signifies the loss of sensory inputs to the central auditory system under ARHL. The study proposes that, in addition to damages at the peripheral terminals of SGCs as well as the loss of SGCs, functional decline at the central terminals of surviving SGCs is also an essential component of ARHL. PMID: 27683884 [PubMed - indexed for MEDLINE]Read more...
Related Articles Adipose-derived stromal cell in regenerative medicine: A review. World J Stem Cells. 2017 Aug 26;9(8):107-117 Authors: Tabatabaei Qomi R, Sheykhhasan M Abstract The application of appropriate cell origin for utilizing in regenerative medicine is the major issue. Various kinds of stem cells have been used for the tissue engineering and regenerative medicine. Such as, several stromal cells have been employed as treat option for regenerative medicine. For example, human bone marrow-derived stromal cells and adipose-derived stromal cells (ADSCs) are used in cell-based therapy. Data relating to the stem cell therapy and processes associated with ADSC has developed remarkably in the past 10 years. As medical options, both the stromal vascular and ADSC suggests good opportunity as marvelous cell-based therapeutics. The some biological features are the main factors that impact the regenerative activity of ADSCs, including the modulation of the cellular immune system properties and secretion of bioactive proteins such as cytokines, chemokines and growth factors, as well as their intrinsic anti-ulcer and anti-inflammatory potential. A variety of diseases have been treated by ADSCs, and it is not surprising that there has been great interest in the possibility that ADSCs might be used as therapeutic strategy to improve a wider range of diseases. This is especially important when it is remembered that routine therapeutic methods are not completely effective in treat of diseases. Here, it was discuss about applications of ADSC to colitis, liver failure, diabetes mellitus, multiple sclerosis, orthopaedic disorders, hair loss, fertility problems, and salivary gland damage. PMID: 28928907 [PubMed]Read more...
WNT Proteins and Noggin Proteins
From Rockefeller University
Rockefeller scientists identify 'natural' proteins that push stem cells to produce hair, not skin
The clearest picture to date of how two proteins determine the destiny of a stem cell that is genetically programmed to develop into either hair or skin epidermis is emerging with mouse embryos as models for human biology from the Howard Hughes Medical Institute at Rockefeller University. The scientists' latest results are reported in this week's (March 20) issue of the journal Nature.
The proteins, called Wnt and noggin, act in concert to set the stage for the stem cell's developmental pathway into a hair follicle rather than skin, says HHMI investigator Elaine Fuchs, Ph.D., professor and head of the Laboratory of Mammalian Cell Biology and Development at Rockefeller.
These two proteins help change the stem cell's shape so that it can separate from adjoining cells and move downward -- a developmental step that is essential for a hair follicle to form from a stem cell.
Because the Wnt and noggin proteins occur naturally in humans, the research of Fuchs and her research team may enhance understanding of stem cells in humans. "These results might prove to be clinically relevant," Fuchs adds.
The Wnt pathway involved in hair growth has already been implicated in the spread of some cancers, such as colon and breast cancer. In addition, the same process that leads to the separation of a stem cell from other cells may shed insight into how a cancer cell metastasizes, or spreads, from its host tumor, Fuchs explains.
The research may also prove relevant to a much less serious but more common condition, baldness.
"Skin turns over every two weeks, so there is an enormous reservoir of stem cells there," Fuchs notes. "To understand the biology and development of stem cells in general, we are trying to answer the question of whether we can coax some 'skin' stem cells to become hair. These findings reveal some of the natural signals that promote the process of forming hair follicles."
While at the University of Chicago, before joining Rockefeller University in 2002, Fuchs and her research team created an extraordinarily hairy mouse by altering its genes to grow hair follicles out of skin. The hairy mouse demonstrated that the researchers had identified elements of the molecular pathway that leads to hair follicle growth.
The latest study, at Rockefeller University, identifies the external signals that are naturally present in developing skin and that stimulate the production of hair follicles.
Additionally, on a basic science level, the study provides further support to the idea that cell parts known as adherens junctions, once thought useful only as the glue that holds cells of a tissue together actually play an important role in controlling when certain genes are turned on or off, thus transforming the essential nature of the cell.
The study also describes in detail how external protein growth factors produced outside of the stem cells work to activate genetic changes within the cells that prompt hair follicle formation.
"Before this, we didn't know how multiple growth factors collaborated to cause changes within the cell," says the first author, Colin Jamora, Ph.D., a postdoctoral researcher in the Fuchs lab. "Now we know how two of the known ones target a specific gene to change the cell's function."
In the beginning…
In a developing mouse embryo, a sheet of tightly adhering epithelial stem cells form on the body surface. Beginning at embryonic day 13, some of these stem cells receive "growth signals" that tell them to unlink from neighboring stem cells and move downward to form a pocket that will become a hair follicle. Surrounding cells that don't receive these messages continue to develop into the skin cells that form the epidermis, the body's waterproof outer coat. While stem cells at the body surface are forming either skin epidermis or hair, other stem cells in the embryo are differentiating in a similar way, migrating away from that sheet of cells to form teeth, lungs and other organs.
Stem cells that create epidermis or hair have become a model system to study, because they are plentiful in adult skin and they can be maintained in a Petri dish in the laboratory, says Fuchs. The skin epidermis is a multi-layered tissue, and at the innermost or basal layer, stem cells give rise to progeny that divide several times before they are pushed upward and differentiate to produce the body's barrier to keep harmful microbes out and fluids in. The cells that reach the skin surface are dead, and sloughed off, continually replaced by inner layer cells moving outward. "Every two weeks, the epidermis is nearly brand new," she says.
Adult stem cells taken from both humans and mice can be maintained in laboratory culture, and continually propagated. In that way, Fuchs says, researchers can study the genes and proteins involved in turning stem cells into epidermis or hair follicles.
Fuchs and her research team previously discovered that a protein called beta-catenin is a key player in formation of hair. This finding has contributed to the recognition that accumulation of this protein in certain specific cells may be a critical, early step in selecting the developmental pathway of a number of stem cells in the body.
The Rockefeller scientists also found that beta-catenin works in concert with a transcription factor known as Lef-1 (lymphoid enhancer factor). A transcription factor is a protein that can combine with other proteins (in this case, beta-catenin) so that it can turn certain genes in the cell's DNA on or off. The Fuchs lab found that in mice, Lef-1 is expressed (produced) in stem cells that become hair follicles, but not in stem cells that develop into skin epidermis.
In other words, stem cells destined to become hair contain two nuclear proteins -- beta-catenin and Lef-1 -- that are not found in stem cells fated to become skin epidermis. The Rockefeller scientists suspected that beta-catenin and Lef-1 worked together to produce changes in the stem cell that pushed it to "morph" into hair, but they didn't know how, at that time.
Proof of their findings came when the scientists altered genes in experimental mice to over produce beta-catenin and Lef-1. Skin cells on the mice produced luxuriant hair.
However, these same genetic changes form benign tumors around the new hair follicles because the beta-catenin continually pushes new stem cells to form hair. "Such genetic manipulation is obviously not an answer to human hair woes," Fuchs says. v The Rockefeller researchers then searched for the natural triggers that cause both beta-catenin and Lef-1 to form hair without genetic manipulation of the stem cells.
Proteins that cause the cell to change shape
The new research summed up in the Nature paper now paints a more complete picture of the molecular changes involved in hair follicle formation, says Jamora. The Fuchs research team found that proteins that help the cell maintain its shape, collectively called the cytoskeleton, are involved in the decision to change that shape to form hair follicles.
Before stem cells differentiate, they are locked together in tight sheets, zipped to one another. The protein that forms the "teeth" of these zippers is known as E-cadherin; it sticks outside the membrane of each stem cell, and zips together with other E-cadherins in nearby stem cells. E-cadherins are called "adhesion" proteins because they stick like Velcro to each other to help maintain both the shape of the cell and its link to other cells.
"When the process of forming this sheet of stem cells begins, cells touch each other and maintain contact by joining single E-cadherin proteins together on adjacent cells," says Jamora. "This triggers the structural proteins inside the cell to start linking to the actin cytoskeleton. "
That allows the cell to change shape, so that they can zip up tight, locking together through all the many E-cadherin proteins found on the outside of the cell, he says.
Any extra beta-catenin produced within these cells that is not used to link E-cadherin to the actin cytoskeleton is quickly gobbled up by special enzyme "machinery" within the cell body, the researchers say. These stem cells become skin.
Fuchs and her team then clarified what happens when that same cell receives growth signals to change shape and become a hair follicle. After years of research using a series of knockout mice and lab experimentation with their stem cell cultures, the researchers found that both the Wnt and noggin growth factors are needed as simultaneous input to the stem cell.
First, noggin signals the cells to make the Lef-1 transcription factor. Then, the Wnt protein prompts a cascade of signals that turn off the machinery that degrades excess beta-catenin. This allows beta-catenin proteins to build up inside the stem cell. This excess beta-catenin binds to Lef-1.
Once in the nucleus of the stem cell, the beta-catenin/Lef-1 complex reduces the transcription of the gene that produces E-cadherin. By reducing the ongoing synthesis of the E-cadherin protein that is constantly needed to keep cells stuck together, the cell can loosen from others around it. Without as much E-cadherin there to bind to the beta-catenin-actin cytoskeleton complex, the structure of the cell changes, allowing it to migrate down between the other stem cells, Fuchs says.
Using mice genetically altered not to produce noggin, the researchers showed that the Lef-1 transcription factor was not being produced. Experiments in which the level of E-cadherin was kept high blocked production of hair follicles, because E-cadherin production must be reduced in order for stem cells to loosen and reorganize to form follicles. Together these experiments verified the importance of the beta-catenin/Lef-1 pathway in hair follicle formation.
The finding that the beta-catenin/Lef-1 transcription complex turns down the expression of the gene that makes E-cadherin is completely novel, says Jamora, since this complex was only known to turn genes on.
Hair, cancer, and more
The description of how Wnt and noggin produce structural changes in a stem cell may ultimately shed light on several developmental and disease processes, Fuchs says. Mutations in E-cadherin and problems in the Wnt signaling pathway have already been linked to some cancers, says Fuchs. "The reason why tumor cells don't interact properly with other cells may be that their levels of adherens junction proteins are not maintained," she says. "For example, squamous cell skin cancers are large masses of cells that invaginate downward."
Too much, or too little, E-cadherin is "a bad thing," Fuchs says. With too much, hair can't develop. With too little, cancer may result.
The study was funded by a grant from the National Institutes of Health.
Founded by John D. Rockefeller in 1901, The Rockefeller University was this nation's first biomedical research university. Today it is internationally renowned for research and graduate education in the biomedical sciences, chemistry, bioinformatics and physics. A total of 22 scientists associated with the university have received the Nobel Prize in medicine and physiology or chemistry, 18 Rockefeller scientists have received Lasker Awards, have been named MacArthur Fellows, and 11 have garnered the National Medical of Science. More than a third of the current faculty are elected members of the National Academy of Sciences.