Mechanisms of Regulation of Olfactory Transduction and Adaptation in the Olfactory Cilium

Abstract

Olfactory adaptation is a fundamental process for the functioning of the olfactory system, but the underlying mechanisms regulating its occurrence in intact olfactory sensory neurons (OSNs) are not fully understood. In this work, we have combined stochastic computational modeling and a systematic pharmacological study of different signaling pathways to investigate their impact during short-term adaptation (STA). We used odorant stimulation and electroolfactogram (EOG) recordings of the olfactory epithelium treated with pharmacological blockers to study the molecular mechanisms regulating the occurrence of adaptation in OSNs. EOG responses to paired-pulses of odorants showed that inhibition of phosphodiesterases (PDEs) and phosphatases enhanced the levels of STA in the olfactory epithelium, and this effect was mimicked by blocking vesicle exocytosis and reduced by blocking cyclic adenosine monophosphate (cAMP)-dependent protein kinase (PKA) and vesicle endocytosis. These results suggest that G-coupled receptors (GPCRs) cycling is involved with the occurrence of STA. To gain insights on the dynamical aspects of this process, we developed a stochastic computational model. The model consists of the olfactory transduction currents mediated by the cyclic nucleotide gated (CNG) channels and calcium ion (Ca2+)-activated chloride (CAC) channels, and the dynamics of their respective ligands, cAMP and Ca2+, and it simulates the EOG results obtained under different experimental conditions through changes in the amplitude and duration of cAMP and Ca2+ response, two second messengers implicated with STA occurrence. The model reproduced the experimental data for each pharmacological treatment and provided a mechanistic explanation for the action of GPCR cycling in the levels of second messengers modulating the levels of STA. All together, these experimental and theoretical results indicate the existence of a mechanism of regulation of STA by signaling pathways that control GPCR cycling and tune the levels of second messengers in OSNs, and not only by CNG channel desensitization as previously thought.

Modelling intracellular competition for calcium: kinetic and thermodynamic control of different molecular modes of signal decoding

“…The n Hill and K 1/2 obtained by fitting the dose-response curve of activation of CaM as a function of free [Ca 2+ ] ([Ca 2+ ] free ) ( Fig. 1C ) were in accordance with published values 22 .…”

“…To reproduce physiological changes of [Ca 2+ ], two buffers were simulated, an unspecific buffer (UB) and CaM. We simulated CaM according to its structure composed by two distinct domains, each one containing a pair of Ca 2+ -binding sites 22 . We validated the model of association of Ca 2+ to CaM by fitting a dose-response curve with the Hill equation:…”

Whole-genome sequencing of a Brazilian naturalized horse breed resistant to arid climate for identifying single nucleotide variants and insertions/deletions

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The cilium: a cellular antenna with an influence on obesity risk

“…From there, the signal is sent on to the hypothalamus and other regions in the brain. Experiments in the mouse have indicated that fluctuations in the level of secondary messengers, which in part are controlled by cyclases and phosphodiesterases, influence the way in which signals from odour-binding receptors are transferred (178) . Cilia-based olfactory defects may also relate to changes in the grey matter of the brain as shown by Braun et al (167) .…”