Olfactory-like chemosensory signaling occurs outside of the olfactory epithelium. We find that major components of olfaction, including olfactory receptors (ORs), olfactory-related adenylate cyclase (AC3) and the olfactory G protein (Golf), are expressed in the kidney. AC3 and Golf colocalize in renal tubules and in macula densa (MD) cells which modulate glomerular filtration rate (GFR). GFR is significantly reduced in AC3 ؊/؊ mice, suggesting that AC3 participates in GFR regulation. Although tubuloglomerular feedback is normal in these animals, they exhibit significantly reduced plasma renin levels despite up-regulation of COX-2 expression and nNOS activity in the MD. Furthermore, at least one member of the renal repertoire of ORs is expressed in a MD cell line. Thus, key components of olfaction are expressed in the renal distal nephron and may play a sensory role in the MD to modulate both renin secretion and GFR.adenylate cyclase 3 ͉ glomerular filtration rate ͉ Golf ͉ macula densa ͉ renin

Under these conditions, MDCK cells spontaneously formed either hollow spherical cysts or flat monolayer sheets, respectively. Microarray analysis of gene expression revealed a twofold or greater expression difference in 732 gene sets from MDCK cysts compared with monolayers (false discovery rate or FDR-adjusted P values Ͻ0.05). Interleukin-8 (IL-8) was reproducibly found to be among the genes whose expression was most dramatically upregulated, and this behavior was verified through real-time PCR analysis. The level of IL-8 protein expression was significantly increased in 3D MDCK cultures compared with that detected in cells in 2D culture. Hepatocyte growth factor (HGF) induces MDCK cells in 3D culture to form linear tubule-like structures. We found that HGF stimulation caused MDCK cells in 3D culture to decrease the expression of IL-8 at both the mRNA and protein levels. Furthermore, the addition of recombinant IL-8 to HGF-stimulated 3D MDCK cultures was sufficient to partially reverse the tubulogenic effects of HGF, resulting in the formation of cystic structures. These data suggest that IL-8 participates in the formation of cystic structures by MDCK cells in 3D culture and that HGF may stimulate tubulogenesis through the suppression of IL-8. renal epithelial cells; interleukin-8; hepatocyte growth factor; morphogenesis; Madin-Darby canine kidney IN TISSUES SUCH AS the lungs, intestines, and kidneys, epithelial cells form barriers between an organism and its external milieu. The surface membranes of these epithelial cells are exposed to disparate environments and are divided into discrete apical and basolateral domains (4,8,37,39). These membrane domains are established and maintained through the directed trafficking and selective retention of cellular components. In addition to this capacity to generate polarized plasma membrane domains with distinct biochemical and physiological properties, epithelial cells must also be able to organize themselves into complex multicellular architectures. The formation and maintenance of these structures is dependent both upon intercellular interactions between epithelial cells and upon cell-matrix interactions.Interactions between an individual cell and its surrounding environment are essential in the activation of signaling networks that subsequently regulate polarity and the determination of epithelial structural morphology (6,7,9,40,48). As epithelial cells establish polarity and interactions with their environment they can begin to function together to generate organized multicellular structures. This property is exemplified by comparing the behaviors of epithelial cell lines, such as Madin-Darby canine kidney (MDCK) cells, grown in twodimensional (2D) vs. three-dimensional (3D) culture conditions. MDCK cells form flat monolayer sheets when grown atop tissue culture plastic, permeable filter supports, and various extracellular matrix (ECM) substrates in traditional 2D culture conditions. When grown in 3D culture, in which cells are embedded within an ECM substrate, MDCK...

Recent work shows that olfactory receptors (ORs) are functionally expressed in non‐olfactory tissues. We find that key components of the OR signaling pathway, olfactory G protein (Golf) and the olfactory adenylyl cyclase (AC3), are detectable in the kidney by RT‐PCR and western blot. AC3 and Golf colocalize with one another and with markers of the distal convoluted tubule. Most notably, AC3 is expressed in the macula densa (MD). The MD regulates glomerular filtration rate (GFR) through both the tubuloglomerular feedback (TGF) and renin secretion pathways. Renal function studies using AC3−/− mice and wild‐type littermates demonstrated that GFR in AC3−/− mice is significantly decreased (AC3−/−:0.42 ± 0.08 ml/min/100g BW, n=8; AC3+/+: 0.87 ± 0.06, n=6, p<0.01). This is not due to alterations in TGF, as TGF assayed by micropuncture is normal in AC3−/−; however, AC3−/− have a ~50% reduction in plasma renin concentration (p<0.001). By RT‐PCR, we have identified six ORs in mouse kidney, suggesting that the chemosensors that participate in this pathway are also present in renal epithelia. These studies indicate that the olfaction machinery present in the kidney is necessary for proper control of GFR, presumably through modulation of renin secretion to regulate efferent arteriolar diameter. This OR machinery is found in the MD, an ideal localization for ORs to sense the chemical composition of the forming urine.

Recent studies have shown that olfactory receptors (ORs) are functionally expressed in non‐olfactory tissues. A potential role for ORs in the kidney, however, has yet to be investigated. We find that key components of the OR signaling pathway, olfactory G protein (Golf) and the olfactory‐related adenylyl cyclase (AC3), are detectable in the kidney by RT‐PCR as well as by western blot. AC3 and Golf are distinctly expressed in a subset of tubule segments where they colocalize with one another, as well as with markers of the distal convoluted tubule (NaCl cotransporter and calbindin). We have also observed AC3 staining in macula densa (MD) cells. MD cells are known to be important controllers of glomerular filtration rate (GFR). Renal function studies using AC3−/− mice and wild‐type littermates demonstrated that renal function in AC3−/− mice, as measured by GFR, is significantly decreased (0.42 ± 0.08 ml/min/100g BW, n=8 in AC3−/− vs. 0.87 ± 0.06, n=6 for AC3+/+; p<0.01). In order to identify which, if any, OR's are expressed in kidney we made use of a custom designed Affymetrics microarray in which the entire family of mouse OR genes (>1000) is represented. RNA was prepared from three normal mouse kidneys and the array was screened according to standard methods. We found that mouse kidney expresses approximately 80 ORs. These studies indicate that the machinery necessary for olfactory‐like signaling is present in the kidney. Intriguingly, this machinery is found in the MD/distal tubule, ideal localizations for ORs to serve as sensors of the chemical composition of the forming urine and regulators of GFR.