Autoimmune hearing loss (AHL) is a poorly understood disorder that can lead to profound and permanent hearing loss. Inner ear damage in AHL can be antibody mediated or cell mediated. We have focused on antibody mediated hearing loss in which the inner ear target is a multi-transmembrane protein called choline transporter-like protein 2 (CTL2) or solute carrier protein 44A2 (SLC44A2)(hereafter referred to as CTL2). CTL2 is prominently expressed on supporting cells within the organ of Corti. Binding of antibodies to this protein in the inner ear in vivo is accompanied by loss of inner ear hair cells and hearing loss in experimental animals. Thus, CTL2 has a necessary function that is disrupted by antibodies. Patients with clinical AHL who have antibodies that bind to inner ear supporting cells with the same pattern as CTL2 antibodies are three times more likely to respond to corticosteroid treatment. In preliminary studies antibodies from these patients also bind to recombinant human (rHu) CTL2 protein on western blots. The overall objectives of this study are: 1. To investigate the association of anti-CTL2 antibodies with AHL and to develop a sensitive and high through-put assay with a secondary objective to determine if the assay has value to diagnose and manage treatment of autoimmune CTL2 antibody mediated hearing loss. 2. To determine the function of CTL2 using proven in vitro approaches that have demonstrated the transporter function of numerous SLC family members and to deduce how this function is related to inner ear homeostasis, hearing and balance. 3. To investigate the in vivo role of CTL2 in inner ear development and function in a conditional CTL2 knock out in transgenic mice. To accomplish these objectives we propose the following:
In Aim 1 we will develop an ELISA assay that will present rHuCTL2 in different conformations so that all of the highly antigenic epitopes will be displayed. Sera from patients and from rHuCTL2 immunized mice will be tested to determine if there is a single immunodominant epitope or if all of the major highly antigenic domains must be displayed to detect anti-CTL2 antibodies from different individuals. Using this information we will develop a high through-put ELISA that can be used to test large numbers of sera from patients and from control individuals. We expect to learn what proportion of AHL patients and what proportion of control individuals have antibodies to CTL2. We will also determine if controls and patients differ in the titer of antibody and if there is a predilection for antibodies to a particular epitope that is associated with development of hearing problems. CTL2 is a member of the transporter family, but its function is not known.
In Aim 2 we will determine the transporter function of CTL2. We will also use the data developed from the transporter function experiments to determine if antibodies to various CTL2 epitopes will block CTL2 function in vitro.
In Aim 3 we will study inner ear development, hearing, and balance in transgenic mice with defective CTL2.
Autoimmune hearing loss is devastating to affected individuals. The studies proposed in this application will result in a clear understanding of the role of anti-CTL2 antibodies in inner ear disease, and a better understanding of the function of CTL2 in the inner ear as well as its role in ear development and function. It will lead to better diagnostic tests, better treatment through novel strategies based on knowledge, better surveillance of affected individuals and control of a process that destroys a person's ability to communicate.
|Tilburg, Julia; Adili, Reheman; Nair, Thankam S et al. (2018) Characterization of hemostasis in mice lacking the novel thrombosis susceptibility gene Slc44a2. Thromb Res 171:155-159|
|Nair, Thankam S; Kommareddi, Pavan K; Galano, Maria M et al. (2016) SLC44A2 single nucleotide polymorphisms, isoforms, and expression: Association with severity of Meniere's disease? Genomics 108:201-208|
|Kommareddi, Pavan; Nair, Thankam; Kakaraparthi, Bala Naveen et al. (2015) Hair Cell Loss, Spiral Ganglion Degeneration, and Progressive Sensorineural Hearing Loss in Mice with Targeted Deletion of Slc44a2/Ctl2. J Assoc Res Otolaryngol 16:695-712|
|Beyer, Lisa A; Galano, Maria M; Nair, Thankam S et al. (2011) Age-related changes in expression of CTL2/SLC44A2 and its isoforms in the mouse inner ear. Hear Res 282:63-8|
|Kommareddi, P K; Nair, T S; Thang, L V et al. (2010) Isoforms, expression, glycosylation, and tissue distribution of CTL2/SLC44A2. Protein J 29:417-26|
|Kommareddi, Pavan K; Nair, Thankam S; Vallurupalli, Mounica et al. (2009) Autoantibodies to recombinant human CTL2 in autoimmune hearing loss. Laryngoscope 119:924-32|
|Kommareddi, P K; Nair, T S; Raphael, Y et al. (2007) Cochlin isoforms and their interaction with CTL2 (SLC44A2) in the inner ear. J Assoc Res Otolaryngol 8:435-46|
|Zeitoun, Hisham; Beckman, Jennifer Gray; Arts, H Alexander et al. (2005) Corticosteroid response and supporting cell antibody in autoimmune hearing loss. Arch Otolaryngol Head Neck Surg 131:665-72|
|Nair, Thankam S; Kozma, Kelley E; Hoefling, Nickoleta L et al. (2004) Identification and characterization of choline transporter-like protein 2, an inner ear glycoprotein of 68 and 72 kDa that is the target of antibody-induced hearing loss. J Neurosci 24:1772-9|
|Yeom, Kristen; Gray, J; Nair, T S et al. (2003) Antibodies to HSP-70 in normal donors and autoimmune hearing loss patients. Laryngoscope 113:1770-6|