Browsing by Author "Maass, Juan"
Now showing 1 - 6 of 6
Results Per Page
Sort Options
Item Analysis of FGF-dependent and FGF-independent pathways in otic placode induction(PLoS, 2013) Yang, Lu; O’Neill, Paul; Martin, Kareen; Maass, Juan; Vassilev, Vassil; Ladher, Raj; Groves, AndrewThe inner ear develops from a patch of thickened cranial ectoderm adjacent to the hindbrain called the otic placode. Studies in a number of vertebrate species suggest that the initial steps in induction of the otic placode are regulated by members of the Fibroblast Growth Factor (FGF) family, and that inhibition of FGF signaling can prevent otic placode formation. To better understand the genetic pathways activated by FGF signaling during otic placode induction, we performed microarray experiments to estimate the proportion of chicken otic placode genes that can be up-regulated by the FGF pathway in a simple culture model of otic placode induction. Surprisingly, we find that FGF is only sufficient to induce about 15% of chick otic placode-specific genes in our experimental system. However, pharmacological blockade of the FGF pathway in cultured chick embryos showed that although FGF signaling was not sufficient to induce the majority of otic placode-specific genes, it was still necessary for their expression in vivo. These inhibitor experiments further suggest that the early steps in otic placode induction regulated by FGF signaling occur through the MAP kinase pathway. Although our work suggests that FGF signaling is necessary for otic placode induction, it demonstrates that other unidentified signaling pathways are required to co-operate with FGF signaling to induce the full otic placode program.Item Changes in the regulation of the Notch signaling pathway are temporally correlated with regenerative failure in the mouse cochlea(Frontiers Research Foundation, 2015) Maass, Juan; Gu, Rende; Basch, Martin; Waldhaus, Joerg; Lopez, Eduardo; Xia, Anping; Oghalai, John; Heller, Stefan; Groves, AndrewSensorineural hearing loss is most commonly caused by the death of hair cells in the organ of Corti, and once lost, mammalian hair cells do not regenerate. In contrast, other vertebrates such as birds can regenerate hair cells by stimulating division and differentiation of neighboring supporting cells. We currently know little of the genetic networks which become active in supporting cells when hair cells die and that are activated in experimental models of hair cell regeneration. Several studies have shown that neonatal mammalian cochlear supporting cells are able to trans-differentiate into hair cells when cultured in conditions in which the Notch signaling pathway is blocked. We now show that the ability of cochlear supporting cells to trans-differentiate declines precipitously after birth, such that supporting cells from six-day-old mouse cochlea are entirely unresponsive to a blockade of the Notch pathway. We show that this trend is seen regardless of whether the Notch pathway is blocked with gamma secretase inhibitors, or by antibodies against the Notch1 receptor, suggesting that the action of gamma secretase inhibitors on neonatal supporting cells is likely to be by inhibiting Notch receptor cleavage. The loss of responsiveness to inhibition of the Notch pathway in the first postnatal week is due in part to a down-regulation of Notch receptors and ligands, and we show that this down-regulation persists in the adult animal, even under conditions of noise damage. Our data suggest that the Notch pathway is used to establish the repeating pattern of hair cells and supporting cells in the organ of Corti, but is not required to maintain this cellular mosaic once the production of hair cells and supporting cells is completed. Our results have implications for the proposed used of Notch pathway inhibitors in hearing restoration therapies.Publication Color Dependence Analysis in a CNN-Based Computer-Aided Diagnosis System for Middle and External Ear Diseases(2022) Viscaino, Michelle; Talamilla, Matias; Maass, Juan; Henríquez, Pablo; Délano, Paul; Auat, Cecilia; Auat, FernandoArtificial intelligence-assisted otologic diagnosis has been of growing interest in the scientific community, where middle and external ear disorders are the most frequent diseases in daily ENT practice. There are some efforts focused on reducing medical errors and enhancing physician capabilities using conventional artificial vision systems. However, approaches with multispectral analysis have not yet been addressed. Tissues of the tympanic membrane possess optical properties that define their characteristics in specific light spectra. This work explores color wavelengths dependence in a model that classifies four middle and external ear conditions: normal, chronic otitis media, otitis media with effusion, and earwax plug. The model is constructed under a computer-aided diagnosis system that uses a convolutional neural network architecture. We trained several models using different single-channel images by taking each color wavelength separately. The results showed that a single green channel model achieves the best overall performance in terms of accuracy (92%), sensitivity (85%), specificity (95%), precision (86%), and F1-score (85%). Our findings can be a suitable alternative for artificial intelligence diagnosis systems compared to the 50% of overall misdiagnosis of a non-specialist physician.Publication Inteligencia artificial en otorrinolaringología: estado actual y perspectivas a futuro(2022) Talamilla P., Matías; Ignacio Vargas V., Ignacio; Cisternas P., Irma; Viscaíno S., Michelle; Auat-Cheein, Fernando; Délano R., Paul; Maass, JuanLa inteligencia artificial posee una larga historia, llena de innovaciones que han dado como resultado diferentes recursos diagnósticos de alto rendimiento, que se encuentran disponibles actualmente. En este artículo se presenta una revisión sobre la inteligencia artificial y sus aplicaciones en medicina. El trabajo se centra en la especialidad de otorrinolaringología con el objetivo de informar a la comunidad médica la importancia y las aplicaciones más destacadas en los diferentes procesos diagnósticos dentro de la especialidad. Incluimos una sección para el análisis del estado actual de la inteligencia artificial en otorrinolaringología en Chile, así como los desafíos a enfrentar a futuro para utilizar la inteligencia artificial en la práctica médica diaria.Item p27 Kip1 down-regulation as achieved by two clinically feasible means did not induce proliferation of supporting cells in the rat neonatal cochlea in vivo(2019) Silva, Sebastián A.; Maass, JuanIn mammals, the cochlear sensory epithelium becomes quiescent early during development. After the first postnatal week, there is no cell replacement or proliferation, and severe damage leads to permanent deafness. Supporting cells’ trans-differentiation has been suggested as a way to regenerate cochlear hair cells after damage. However, they are also needed for proper functionality. Cdkn1b (p27Kip1) participates in the cochlear terminal mitosis state achieved during development. Its expression is maintained in adult supporting cells and its postnatal deletion has induced cochlear proliferation in vitro and in vivo. Therefore, its manipulation has been proposed as a feasible way to induce proliferation of supporting cells after birth. Nevertheless, the literature is scarce regarding feasible methods to directly decrease p27Kip1 in the clinical domain. The effects of p27Kip1 knockdown using viral vectors are not completely elucidated and no pharmacological approaches to decrease p27Kip1 in the cochlea have been tested in vivo before. This study explores the ability of p27Kip1 messenger knockdown and pharmacological transcriptional inhibition to induce proliferation of supporting cells in the P0 neonatal rat cochlea in vivo. Respectively, lentiviral vectors transducing shRNA against p27Kip1 were administered into the scala media or Alsterpaullone 2-Cyanoethyl into the round window niche. Cell markers and gene expression were assessed through immunostaining and qRT-PCR. Despite both methods significantly decreasing p27Kip1 expression in vivo, signs of toxicity in the organ of Corti were not found; however, relevant proliferation was not found either. Finally, cochlear damage was added to increase the response in vitro, achieving only a mild to moderate proliferation induction. We conclude that our approaches were not able to stimulate the recall of supporting cell proliferation despite significantly decreased p27Kip1 levels in vivo. Considering the evaluation of the cochlea at a very responsive stage, we propose that the level of isolated modification of p27Kip1 expression in living mammals achievable through these approaches is insufficient to induce proliferation of supporting cells. Future proliferation induction experiments in the cochlea should study other methods and genes.Item p27Kip1 knockdown induces proliferation in the organ of Corti in culture after efficient shRNA lentiviral transduction(Springer, 2013) Maass, Juan; Berndt, Andrés; Cánovas, José; Kukuljan, ManuelThe cells in the organ of Corti do not exhibit spontaneous cell regeneration; hair cells that die after damage are not replaced. Supporting cells can be induced to transdifferentiate into hair cells, but that would deplete their numbers, therefore impairing epithelium physiology. The loss of p27Kip1 function induces proliferation in the organ of Corti, which raises the possibility to integrate it to the strategies to achieve regeneration. Nevertheless, it is not known if the extent of this proliferative potential, as well as its maintenance in postnatal stages, is compatible with providing a basis for eventual therapeutic manipulation. This is due in part to the limited success of approaches to deliver tools to modify gene expression in the auditory epithelium. We tested the hypothesis that the organ of Corti can undergo significant proliferation when efficient manipulation of the expression of regulators of the cell cycle is achieved. Lentiviral vectors were used to transduce all cochlear cell types, with efficiencies around 4 % for hair cells, 43 % in the overall supporting cell population, and 74 % within lesser epithelial ridge (LER) cells. Expression of short hairpin RNA targeting p27Kip1 encoded by the lentiviral vectors led to measurable proliferation in the organ of Corti and increase in LER cells number but not hair cell regeneration. Our results revalidate the use of lentiviral vectors in the study and in the potential therapeutic approaches for inner ear diseases, as well as demonstrate that efficient manipulation of p27Kip1 is sufficient to induce significant proliferation in the postnatal cochlea.