Chemical Exposure-Induced Changes in the Expression of Neurotrophins and Their Receptors in the Main Olfactory System of Mice Lacking TRPM5-Expressing Microvillous Cells

Abstract

Functional maintenance of the mammalian main olfactory epithelium (MOE) is challenging because of its direct exposure to a wide spectrum of environmental chemicals. We previously reported that transient receptor potential channel M5-expressing microvillous cells (TRPM5-MCs) in the MOE play an important role in olfactory maintenance. To investigate the underpinning mechanisms, we exposed transcription factor Skn-1a knockout (Skn-1a−/−) mice lacking TRPM5-MCs, and TRPM5-GFP mice to either vehicle (water) or a mixture of odorous chemicals and chitin for two weeks and analyzed the expression of olfactory signaling proteins using immunolabeling and neurotrophin (NT) and NT receptor (NTR) gene transcripts using real-time quantitative PCR. The chemical exposure did not significantly attenuate the immunolabeling of olfactory signaling proteins. Vehicle-exposed Skn-1a−/− and TRPM5-GFP mice expressed similar levels of NT and NTR gene transcripts in the MOE and olfactory bulb. Chemical exposure significantly increased MOE expression of p75NTR in Skn-1a−/− mice, while p75NTR expression was reduced in TRPM5-GFP mice, as compared to vehicle-exposed mice. Additionally, our RNA in situ hybridization analysis and immunolabeling confirmed MOE expression of most NTs and NTRs. Together, these results indicate that TRPM5-MCs and chemical exposure influence expression of some NTs and NTRs in the MOE and olfactory bulb (OB).

TRPM5+microvillous tuft cells regulate neuroepithelial intrinsic olfactory stem cell proliferation

“…They are thus able to respond to environmental signals with de novo generation of mediators, prominently acetylcholine and eicosanoids. The function of olfactory tuft cells (previously called TRPM5 + MVCs) has proven enigmatic; their genetic ablation leads to aberrant neurotrophin expression (92) and impaired olfactory-guided behaviors, albeit only after extended exposure to strong odorants (12). Tuft cell activation through chemical (strong odorants or bacterial lysate) or thermal (cold temperatures) stimulation leads to acetylcholine-mediated calcium flux in olfactory sustentacular cells and modulates the responses to xenobiotic substances in the olfactory mucosa (11, 13).…”

Estradiol Replacement at the Critical Period Protects Hippocampal Neural Stem Cells to Improve Cognition in APP/PS1 Mice

“…A 1 μl 20-fold diluted cDNA (each sample in triplicate) was then used for each run. The primer sets used for p75 NTR , GAPDH , TERT , and β- actin were designed according to the previous publications (AlMatrouk et al, 2018 ; Zhang et al, 2019 ). PCR conditions for TERT and β- actin were 30 cycles of denaturation at 94°C for 45 s, annealing at 65°C for 45 s, and extension at 72°C for 45 s. PCR product of TERT was resolved by 1.5% agarose gel electrophoresis and visualized by ethidium bromide staining.…”