Role of the Cytokine of Macrophage Migration Inhibitory Factor (MIF) in Inner Ear Neuronal and Sensory Cell Development.

Spiral ganglion neuron (SGN) loss is a major cause of deafness. Cochlear implants (CI) are presently the only known "cure" for many forms of deafness. Nevertheless, successful function of a CI depends on the preservation of SGNs. In the early developing inner ear, the otocyst secretes a factor called Otocyst Derived Factor (ODF). ODF promotes directional neurite outgrowth and neuronal survival of the statoacoustic ganglion (SAG), the precursor of the auditory portion of the SAG that eventually forms the SG. Cytokine arrays and proteomic studies demonstrated that the bioactive components of ODF include Macrophage Migration Inhibitory Factor (MIF). Based on its known roles and our preliminary data, we hypothesized that MIF plays a key instructional role in inner ear development. The goal of this dissertation project is to determine the role of MIF in inner ear neuronal development as well as the possibility of using this developmental information to study and to enhance inner ear neuronal regeneration. We found that, at low concentrations, recombinant MIF alone supports SAG directional neurite outgrowth and neuronal survival and evokes a neuronal phenotype from mouse embryonic stem cells, while at higher concentrations, MIF inhibits these functions. We also found that MIF is expressed in supporting cells (SC) of the inner ear and its receptor, CD74 is expressed on both SAG and SGN. In the MIF knock-out (KO) mice, abnormal development of both SC and hair cells (HC) as well as a significant hearing impairment in the high frequency region of the cochlea are seen with concomitant loss of SGN in this region of the cochlea. Additionally, we observed that the neurites from SG explants extend directionally toward the wild-type (WT) Organ of Corti (OC), but not in the MIF KO OC. Finally, we found that blockade of either MIF or its receptor suppresses SAG neurite outgrowth and survival. Our study indicates that MIF functions as an essential component of normal inner ear neuronal development and innervation and could potentially be used for SGN retention or re-growth as well as to potentiate the function of a CI in the injured or diseased mammalian inner ear.Ph.D.NeuroscienceUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/78980/1/febisu_1.pd

Effects of mouse utricle stromal tissues on hair cell induction from induced pluripotent stem cells

BACKGROUND: Hair cells are important for maintaining our sense of hearing and balance. However, they are difficult to regenerate in mammals once they are lost. Clarification of the molecular mechanisms underlying inner ear disorders is also impeded by the anatomical limitation of experimental access to the human inner ear. Therefore, the generation of hair cells, possibly from induced pluripotent stem (iPS) cells, is important for regenerative therapy and studies of inner ear diseases. RESULTS: We generated hair cells from mouse iPS cells using an established stepwise induction protocol. First, iPS cells were differentiated into the ectodermal lineage by floating culture. Next, they were treated with basic fibroblast growth factor to induce otic progenitor cells. Finally, the cells were co-cultured with three kinds of mouse utricle tissues: stromal tissue, stromal tissue + sensory epithelium, and the extracellular matrix of stromal tissue. Hair cell-like cells were successfully generated from iPS cells using mouse utricle stromal tissues. However, no hair cell-like cells with hair bundle-like structures were formed using other tissues. CONCLUSIONS: Hair cell-like cells were induced from mouse iPS cells using mouse utricle stromal tissues. Certain soluble factors from mouse utricle stromal cells might be important for induction of hair cells from iPS cells

A mouse embryonic stem cell model of Schwann cell differentiation for studies of the role of neurofibromatosis type 1 in Schwann cell development and tumor formation

The neurofibromatosis Type 1 (NF1) gene functions as a tumor suppressor gene. One known function of neurofibromin, the NF1 protein product, is to accelerate the slow intrinsic GTPase activity of Ras to increase the production of inactive rasGDP, with wide-ranging effects on p21ras pathways. Loss of neurofibromin in the autosomal dominant disorder NF1 is associated with tumors of the peripheral nervous system, particularly neurofibromas, benign lesions in which the major affected cell type is the Schwann cell (SC). NF1 is the most common cancer predisposition syndrome affecting the nervous system. We have developed an in vitro system for differentiating mouse embryonic stem cells (mESC) that are NF1 wild type (+/+), heterozygous (+/−), or null (−/−) into SC-like cells to study the role of NF1 in SC development and tumor formation. These mES-generated SC-like cells, regardless of their NF1 status, express SC markers correlated with their stage of maturation, including myelin proteins. They also support and preferentially direct neurite outgrowth from primary neurons. NF1 null and heterozygous SC-like cells proliferate at an accelerated rate compared to NF1 wild type; this growth advantage can be reverted to wild type levels using an inhibitor of MAP kinase kinase (Mek). The mESC of all NF1 types can also be differentiated into neuron-like cells. This novel model system provides an ideal paradigm for studies of the role of NF1 in cell growth and differentiation of the different cell types affected by NF1 in cells with differing levels of neurofibromin that are neither transformed nor malignant. © 2007 Wiley-Liss, Inc.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/56140/1/20534_ftp.pd

Macrophage migration inhibitory factor acts as a neurotrophin in the developing inner ear

This study is the first to demonstrate that macrophage migration inhibitory factor (MIF), an immune system ‘inflammatory’ cytokine that is released by the developing otocyst, plays a role in regulating early innervation of the mouse and chick inner ear. We demonstrate that MIF is a major bioactive component of the previously uncharacterized otocyst-derived factor, which directs initial neurite outgrowth from the statoacoustic ganglion (SAG) to the developing inner ear. Recombinant MIF acts as a neurotrophin in promoting both SAG directional neurite outgrowth and neuronal survival and is expressed in both the developing and mature inner ear of chick and mouse. A MIF receptor, CD74, is found on both embryonic SAG neurons and adult mouse spiral ganglion neurons. Mif knockout mice are hearing impaired and demonstrate altered innervation to the organ of Corti, as well as fewer sensory hair cells. Furthermore, mouse embryonic stem cells become neuron-like when exposed to picomolar levels of MIF, suggesting the general importance of this cytokine in neural development