PDE6D dependent G_olf subunit trafficking in olfactory epithelium

Abstract

Purpose : PDE6D functions as a prenyl-binding protein and is expressed ubiquitously. In photoreceptors it mediates trafficking of GRK1 and PDE6. Pde6d null alleles in mouse are associated with recessive cone rod dystrophy, and in human with Joubert Syndrome. Here we explore whether PDE6D plays a role in the Gβ₁/Gγ₁₃ trafficking to the cilia of olfactory sensory neurons.

Methods : We used the Pde6d^-/- line as described previously by our lab (Zhang et al, 2007). We weighed mice at P21 to determine if there was a weight reduction in knockouts (KOs) versus heterozygous controls. We performed IHC staining against PDE6D, G_olfα, Gγ₁₃, ACIII and CNGA2. We performed electro-olfactograms (EOGs) to measure potential differences in the olfactory epithelium in response to odor stimulation. An odor habituation task was used to assess behavioral measures of deficits in olfactory discrimination.

Results : We observed an average of 7-16% reduction in body weight between KO and controls, with extreme values of up to 30% reduced. PDE6D was present in the olfactory epithelium in wildtype controls. In heterotrimeric G_olf consisting of G_olfα , Gβ₁ and Gγ₁₃, only Gγ₁₃ is prenylated by geranylgeranylation. G_olf subunits were not present in the olfactory epithelium in the KO compared to controls. ACIII and CNGA2, downstream proteins in the olfactory signal transduction cascade, localized normally to the olfactory epithelium in KO and controls. EOG response was diminished in KOs compared to controls. Behaviorally, the KOs showed decreased discrimination compared to controls.

Conclusions : Pde6d^-/- mice show impaired olfaction, similar to the visual impairment shown in photoreceptors. The slight weight reduction in the first few weeks may be due to impaired olfaction in the KOs. Electrophysiological and behavioral data indicate dysosmia, but not anosmia. Therefore, the Pde6d^-/- mouse is a syndromic ciliopathy model, with visual and olfactory sensory deficits.

Funding: EY08123, EY019298; EY014800-039003; T32 EY024234; P30EY014800, Retina Research Foundation (Houston).

This is an abstract that was submitted for the 2018 ARVO Annual Meeting, held in Honolulu, Hawaii, April 29 - May 3, 2018.