Regulated Vesicular Trafficking of Specific PCDH15 and VLGR1 Variants in Auditory Hair Cells

Abstract

Usher syndrome is a genetically heterogeneous disorder characterized by hearing and balance dysfunction and progressive retinitis pigmentosa. Mouse models carrying mutations for the nine Usher-associated genes have splayed stereocilia and some show delayed maturation of ribbon synapses suggesting these proteins may play different roles in terminal differentiation of auditory hair cells. The presence of the Usher proteins at the basal and apical aspects of the neurosensory epithelia suggests the existence of regulated trafficking through specific transport proteins and routes. Immature mouse cochleae and UB/OC-1 cells were used in this work to address whether specific variants of PCDH15 and VLGR1 are being selectively transported to opposite poles of the hair cells. Confocal co-localization studies between apical and basal vesicular markers and the different PCDH15 and VLGR1 variants along with sucrose density gradients and the use of vesicle trafficking inhibitors show the existence of Usher protein complexes in at least two vesicular sub-pools. The apically trafficked pool co-localized with the early endosomal vesicle marker, rab5, while the basally trafficked pool associates with membrane microdomains and SNAP25. Moreover, co-immunoprecipitation experiments between SNAP25 and VLGR1 show a physical interaction of these two proteins in organ of Corti and brain. Collectively, these findings establish the existence of a differential vesicular trafficking mechanism for specific Usher protein variants in mouse cochlear hair cells, with the apical variants playing a potential role in endosomal recycling and stereocilia development/maintenance and the basolateral variants involved in vesicle docking and/or fusion through SNAP25-mediated interactions.

International Union of Basic and Clinical Pharmacology. XCIV. Adhesion G Protein–Coupled Receptors

“…Similarly, several isoforms of ADGRV1 (VLGR1) were reported to be widely expressed in a spatiotemporally regulated manner (reviewed in McMillan and White, 2010). This receptor shows a particularly strong expression in sensory cells of the eye and the inner ear, as well as in the brain (van Wijk et al, 2006;Maerker et al, 2008;Zallocchi et al, 2012;Shin et al, 2013).…”

“…In photoreceptor cells, ADGRV1 (VLGR1) is a component of a periciliary USH protein network, which is crucial for the transport of cargo from the inner to the outer segment (Maerker et al, 2008). In addition, ADGRV1 (VLGR1) is found at synapses of cochlear and retinal cells (Reiners et al, 2005;Specht et al, 2009;Zallocchi et al, 2012); however, its synaptic function remains to be elucidated.…”

Constitutive Gαi Coupling Activity of Very Large G Protein-coupled Receptor 1 (VLGR1) and Its Regulation by PDZD7 Protein

“…We thus overexpressed three known VLGR1 C terminus-interacting partners, Harmonin, Whirlin, and PDZD7, all of which are involved in Usher syndrome, to investigate their effects on VLGR1-mediated AC inhibition (33,34). Interestingly, although overexpression of Harmonin or Whirlin had no effect on VLGR1-mediated AC inhibition, overexpression of the other Usher syndrome-related protein, PDZD7, inhibited both V gain -and V ␤ -mediated AC inhibition (Fig.…”

In vitro and in vivo effects of lutein against cisplatin-induced ototoxicity

“…Most variants in both organs have the same molecular weights, which portends to similar functional roles for these proteins in the cochlea and the retina. Recent biochemical analysis documents a number of protein variants for VLGR1, cadherin 23, and protocadherin 15 in the cochlea and the retina (Lagziel et al, 2009;Zallocchi et al, 2012). Due to the involvement of ROS generation and inflammation mediators in cisplatin toxicity (Casares et al, 2012), and these common characteristics, there is a strong rationale for testing lutein as a protective agent against cisplatin-induced damage due to its antioxidant and anti-inflammatory activity.…”