Renal Olfactory Receptor 90 (Olfr90) Responds to Fungal Metabolites

In recent years, olfactory receptors (ORs) have been shown to play a variety of roles outside of the nose, acting as chemosensors to aid in muscle migration and sperm chemotaxis. In 2009, we reported that individual ORs, including Olfr90, are expressed in kidney. Olfr90 is an orphan receptor (i.e. no known ligands). Identifying Olfr90 ligands is a key and necessary step in unraveling the physiological role of Olfr90 in the kidney. To this end, we employed a cAMP‐dependent luciferase reporter assay for ligand screening. We used four initial strategies to identify chemicals to screen. First, we used mixes of chemicals with like functional groups (thiols mix, ketones mix, etc), but found that no mix activated Olfr90. Second, we tested “sibling ligands”, taking advantage of the fact that ORs in the same subfamily (“siblings”) often have ligands in common. Olfr90 is a member of the MOR256 subfamily; 6 ORs in this subfamily have been deorphanized, responding to a total of 121 chemicals. Of these 121, we tested the 13 ligands that were common to 2 or more MOR256 family members, of which 2 activated Olfr90 (cinnamaldehyde; lyral; p<0.05 vs control media). As Olfr90 is a renal OR, our third approach was to use the Human Metabolome Database (HMDB; www.hmdb.ca ) to determine if any of the 121 sibling ligands are present in biofluids likely to contact the kidney. 43 of the 121 ligands are listed as present in biofluids in the HMDB; these 43 were tested and 3 yielded a response for Olfr90 (1‐octanol, allylbenzene, 2‐pentylfuran; p<0.05). Finally, another search of the HMDB was performed to identify chemicals classified as ‘odorants’, yielding 8 chemicals, 4 of which activated Olfr90 (2‐methyl‐4‐propyl‐1,3‐oxithiane (MPOT), 1‐octen‐3‐ol, 1‐octen‐3‐one, 1,3‐dimethylbenzene; p<0.05). Thus, the compilation of all 4 strategies yielded 9 ligands. Typically OR ligands for the same receptor are structurally related; however, Olfr90 ligands had little in common in terms of functional groups or molecular weight. Intriguingly, however, 4 of the 9 were of fungal origin. To determine if Olfr90 might be generally reactive to fungal‐derived ligands, we performed a literature search to identify additional fungal metabolites for testing (n=13), and found that 7 of the 13 chemicals activated Olfr90 (linalool, 2‐octanone, 3‐octanone, benzyl cyanide, 2,5‐dimethylfuran, 2‐octen‐1‐ol, 3‐octanol, trans ‐2‐octenal; p<0.05). Thus, in total we identified 16 ligands (11 fungal) that activate Olfr90 in a dose dependent manner. EC 50 values (a measure of activation) for the strongest ligands were MPOT, EC 50 =0.53 mM; 1‐octen‐3‐ol (fungal), EC 50 =0.50 mM; linalool (fungal), EC 50 =0.39 mM. In sum, we have found that Olfr90 senses chemicals reported to be present in biofluids, the majority of which are not produced by the host – rather, they are metabolites produced by fungi. Recent studies have shown that host receptors respond to bacterial metabolites to modulate host physiology; however, few studies have examined interactions between fungal metabolites and host receptors. Through our studies of this novel signaling pathway, we hope to expand our understanding of host‐microbe interactions and to uncover novel roles for ORs in renal physiology. Support or Funding Information F31 DK104454‐01A1