دانلود رایگان مقاله قطعات سیگنالینگ بویایی و گیرنده بویایی در سلول توبول کلیه انسان

Abstract

Cells of the renal tubule system are in direct contact with compounds dissolved in the urine, such as short chain fatty acids (SCFA). Murine OR78, a member of the olfactory receptor (OR) family, is involved in SCFA-related regulation of renal blood pressure in mice. It is still unclear whether OR signaling has an impact on human renal physiology. In our study, we showed that OR51E1 and OR11H7, both of which can be activated by the SCFA isovaleric acid, are expressed in the HK-2 human proximal tubule cell line. We observed a transient increase in intracellular Ca2+ when isovaleric acid and 4-methylvaleric acid were added to HK-2 cells. The isovaleric acid-induced response was dependent on extracellular Ca2+ and adenylyl cyclase (AC) activation. Furthermore, we demonstrated that the canonical olfactory signaling components Gαolf and ACIII are co-localized with OR51E1. The number of cells responding to isovaleric acid correlated with the presence of primary cilia on HK-2 cells. OR51E1 protein expression was confirmed in the tubule system of human kidney tissue. Our study is the first to show the expression of ORs and olfactory signaling components in human kidney cells. Additionally, we discuss ORs as potential modulators of the renal physiology.

4. Discussion

In this study, we demonstrated the activation of HK-2 cells by an odorant mixture containing three different fatty acids; two of which, IVA and 4-MVA, led to Ca2þ responses when applied to HK- 2 cells. IVA and 4-MVA are both known agonists for human OR51E1 [18,21]. In general, OR51E1 seems to play a crucial role in sensing fatty acids. In addition to the aforementioned ligands, nonanoic acid, 3-methylvaleric acid, and butyric acid are also described as agonists for heterogeneously expressed OR51E1 [18,22,23]. The expression of the pig orthologue to human OR51E1 has already been described in cells of the gastrointestinal tract and is believed to be involved in detecting bacterial metabolites [24]. IVA can also activate the receptors OR11H4, OR11H6, and OR11H7. OR11H7 expression is considered an important sensor for the detection of the “sweaty feet” odor [20]. Additionally, IVA is a metabolite of the leucine metabolism, and pathogenesis can lead to the autosomal recessive disorder isovaleric acidemia, which causes an increased concentration of IVA in the urine [15]. We verified the expression of OR51E1 and OR11H7 in HK-2 cells at the transcript level by quantitative PCR experiments. OR11H7 presents as an intact form and a non-functional form. Nonfunctional OR11H7 results from a nonsense mutation caused by a single nucleotide polymorphism (SNP) at the nucleotide position 679 that leads to a stop codon and a short defect [20].