Transient receptor potential channels have recently been implicated in physiological functions in a urogenital system. In this study, we investigated the role of transient receptor potential vanilloid 4 (TRPV4) channels in a stretch sensing mechanism in mouse primary urothelial cell cultures. The selective TRPV4 agonist, 4␣-phorbol 12,13-didecanoate (4␣-PDD) evoked Ca 2؉ influx in wild-type (WT) urothelial cells, but not in TRPV4-deficient (TRPV4KO) cells. We established a cellstretch system to investigate stretch-evoked changes in intracellular Ca 2؉ concentration and ATP release. Stretch stimulation evoked intracellular Ca 2؉ increases in a stretch speed-and distance-dependent manner in WT and TRPV4KO cells. In TRPV4KO urothelial cells, however, the intracellular Ca 2؉ increase in response to stretch stimulation was significantly attenuated compared with that in WT cells. Stretch-evoked Ca 2؉ increases in WT urothelium were partially reduced in the presence of ruthenium red, a broad TRP channel blocker, whereas that in TRPV4KO cells did not show such reduction. Potent ATP release occurred following stretch stimulation or 4␣-PDD administration in WT urothelial cells, which was dramatically suppressed in TRPV4KO cells. Stretch-dependent ATP release was almost completely eliminated in the presence of ruthenium red or in the absence of extracellular Ca 2؉ . These results suggest that TRPV4 senses distension of the bladder urothelium, which is converted to an ATP signal in the micturition reflex pathway during urine storage. Transient receptor potential vanilloid 4 (TRPV4),3 a member of the TRP superfamily of cation channels, is a Ca 2ϩ -permeable channel activated by a wide variety of physical and chemical stimuli (1, 2). TRPV4 was originally viewed as an osmo-or mechano-sensor, because the channel opens in response to hypotonicity-induced cell swelling (3-5) and shear stress (6). Alternatively, TRPV4 can be activated by diverse chemical stimuli such as synthetic phorbol ester 4␣-phorbol 12,13-didecanoate (4␣-PDD) (7), a botanical agent (bisandrographolide A), anandamide metabolites such as arachidonic acid and epoxyeicosatrienoic acids, as well as moderate warmth (Ͼ27°C) (8 -10). TRPV4 is widely expressed throughout the body, including renal epithelium, auditory hair cells, skin keratinocytes, hippocampus neurons, endothelial cells, and urinary bladder epithelium, thereby contributing to numerous physiological processes such as osmoregulation (11, 12), hearing (13), thermal and mechanical hyperalgesia (14, 15), neural activity in the brain (16), skin barrier recovery (17), and cell volume regulation (18). Therefore, the TRPV4 channel is now considered a multimodal transducer in various tissues and cells.Non-neuronal cells within the urinary bladder wall (notably the transitional epithelial cells (urothelial cells)) function as a barrier against ions, solutes, and infection and also participate in the detection of physical and chemical stimuli (19 -21). The urothelium expresses various sensory receptors and channe...

Proliferation, differentiation, and tube formation by endothelial progenitor cells in response to shear stress. Endothelial progenitor cells (EPCs), circulating in peripheral blood, migrate toward target tissue, differentiate, and contribute to the formation of new vessels. In this study, we report that shear stress generated by blood flow or tissue fluid flow can accelerate the proliferation, differentiation, and capillary-like tube formation of EPCs. When EPCs cultured from human peripheral blood were subjected to laminar shear stress, the cells elongated and oriented their long axes in the direction of flow. The cell density of the EPCs exposed to shear stress was higher, and a larger percentage of these cells were in the G 2-M phase of the cell cycle, compared with EPCs cultured under static conditions. Shear stress markedly increased the EPC expression of two vascular endothelial growth factor receptors, kinase insert domain-containing receptor and fms-like tyrosine kinase-1, and an intercellular adhesion molecule, vascular endothelial-cadherin, at both the protein and mRNA levels. Assays for tube formation in the collagen gels showed that the shear-stressed EPCs formed tubelike structures and developed an extensive tubular network significantly faster than the static controls. These findings suggest that EPCs are sensitive to shear stress and that their vasculogenic activities may be modulated by shear stress. blood vessels; angiogenesis; neovascularization; mechanical stress; vascular endothelial growth factor THE FORMATION OF NEW BLOOD vessels in postnatal life has generally been considered to be mediated by the sprouting of endothelial cells (ECs) from preexisting vessels, a process referred to as angiogenesis. However, recent studies have indicated that a vasculogenesis process involving the in situ differentiation of endothelial precursor cells and their subsequent organization into new vessels is also responsible for postnatal neovascularization (10, 22, 27). The existence of bone marrow-derived endothelial progenitor cells (EPCs) circulating in the peripheral blood has been demonstrated in adult humans (6, 26). EPCs have the capacity to circulate, proliferate, and differentiate into mature ECs in response to a variety of growth factors, including VEGF, and other cytokines (7, 16, 18). Transplantation studies have revealed that EPCs can be incorporated into sites of active neovascularization in ischemic hindlimbs and myocardium and contribute to both tumor growth and the formation of new blood vessels (5,20,40). However, the role of EPCs in supporting postnatal vasculogenesis is under intensive investigation, and the factors regulating the migration, proliferation, differentiation, and vessel formation of EPCs are not yet known.During the process of EPC incorporation into tissues and neovascularization, the cells are exposed to fluid shear stress, a mechanical force generated by blood flow or interstitial fluid flow (42). Ample evidence has shown that shear stress modulates mature EC function and gene...

The structure and function of blood vessels adapt to environmental changes such as physical development and exercise. This phenomenon is based on the ability of the endothelial cells to sense and respond to blood flow; however, the underlying mechanisms remain unclear. Here we show that the ATP-gated P2X4 ion channel, expressed on endothelial cells and encoded by P2rx4 in mice, has a key role in the response of endothelial cells to changes in blood flow. P2rx4(-/-) mice do not have normal endothelial cell responses to flow, such as influx of Ca(2+) and subsequent production of the potent vasodilator nitric oxide (NO). Additionally, vessel dilation induced by acute increases in blood flow is markedly suppressed in P2rx4(-/-) mice. Furthermore, P2rx4(-/-) mice have higher blood pressure and excrete smaller amounts of NO products in their urine than do wild-type mice. Moreover, no adaptive vascular remodeling, that is, a decrease in vessel size in response to a chronic decrease in blood flow, was observed in P2rx4(-/-) mice. Thus, endothelial P2X4 channels are crucial to flow-sensitive mechanisms that regulate blood pressure and vascular remodeling.

Pluripotent embryonic stem (ES) cells are capable of differentiating into all cell lineages, but the molecular mechanisms that regulate ES cell differentiation have not been sufficiently explored. In this study, we report that shear stress, a mechanical force generated by fluid flow, can induce ES cell differentiation. When Flk-1-positive (Flk-1(+)) mouse ES cells were subjected to shear stress, their cell density increased markedly, and a larger percentage of the cells were in the S and G(2)-M phases of the cell cycle than Flk-1(+) ES cells cultured under static conditions. Shear stress significantly increased the expression of the vascular endothelial cell-specific markers Flk-1, Flt-1, vascular endothelial cadherin, and PECAM-1 at both the protein level and the mRNA level, but it had no effect on expression of the mural cell marker smooth muscle alpha-actin, blood cell marker CD3, or the epithelial cell marker keratin. These findings indicate that shear stress selectively promotes the differentiation of Flk-1(+) ES cells into the endothelial cell lineage. The shear stressed Flk-1(+) ES cells formed tubelike structures in collagen gel and developed an extensive tubular network significantly faster than the static controls. Shear stress induced tyrosine phosphorylation of Flk-1 in Flk-1(+) ES cells that was blocked by a Flk-1 kinase inhibitor, SU1498, but not by a neutralizing antibody against VEGF. SU1498 also abolished the shear stress-induced proliferation and differentiation of Flk-1(+) ES cells, indicating that a ligand-independent activation of Flk-1 plays an important role in the shear stress-mediated proliferation and differentiation by Flk-1(+) ES cells.

Transient receptor potential V3 (TRPV3) and TRPV4 are heat-activated cation channels expressed in keratinocytes. It has been proposed that heat-activation of TRPV3 and/or TRPV4 in the skin may release diffusible molecules which would then activate termini of neighboring dorsal root ganglion (DRG) neurons. Here we show that adenosine triphosphate (ATP) is such a candidate molecule released from keratinocytes upon heating in the co-culture systems. Using TRPV1-deficient DRG neurons, we found that increase in cytosolic Ca 2+ -concentration in DRG neurons upon heating was observed only when neurons were co-cultured with keratinocytes, and this increase was blocked by P2 purinoreceptor antagonists, PPADS and suramin. In a co-culture of keratinocytes with HEK293 cells (transfected with P2X 2 cDNA to serve as a biosensor), we observed that heat-activated keratinocytes secretes ATP, and that ATP release is compromised in keratinocytes from TRPV3-deficient mice. This study provides evidence that ATP is a messenger molecule for mainly TRPV3-mediated thermotransduction in skin.

Transient receptor potential vanilloid 4 (TRPV4) channel is a physiological sensor for hypo-osmolarity, mechanical deformation, and warm temperature. The channel activation leads to various cellular effects involving Ca 2؉ dynamics. We found that TRPV4 interacts with ␤-catenin, a crucial component linking adherens junctions and the actin cytoskeleton, thereby enhancing cell-cell junction development and formation of the tight barrier between skin keratinocytes. TRPV4-deficient mice displayed impairment of the intercellular junction-dependent barrier function in the skin. In TRPV4-deficient keratinocytes, extracellular Ca 2؉ -induced actin rearrangement and stratification were delayed following significant reduction in cytosolic Ca 2؉ increase and small GTPase Rho activation. TRPV4 protein located where the cell-cell junctions are formed, and the channel deficiency caused abnormal cell-cell junction structures, resulting in higher intercellular permeability in vitro. Our results suggest a novel role for TRPV4 in the development and maturation of cell-cell junctions in epithelia of the skin. Transient receptor potential vanilloid 4 (TRPV4),3 a member of the TRP superfamily of cation channels, is a Ca 2ϩ -permeable channel expressed in both neuronal and non-neuronal cells. Channel activation allows cation influx into cells, leading to various Ca 2ϩ -dependent processes (1, 2). TRPV4 can be activated by a variety of chemical and physical stimuli such as synthetic phorbol ester 4␣-phorbol 12,13-didecanoate (4␣-PDD) (3), a botanical agent (bisandrographolide A) (4), anandamide metabolites including arachidonic acid and epoxyeicosatrienoic acids (5), hypo-osmotic stimulation (6, 7), shear stress (8), mechanical stretch (9), and moderate warmth (27-35°C) (7, 10). Therefore, the TRPV4 channel functions as a multimodal transducer in various tissues and cells.Keratinocytes in the skin epidermis express TRPV4 (10, 11), and it has been proposed that the channel is involved in the detection of warm temperature (12). Skin keratinocytes express another warm temperature-sensitive TRP channel, TRPV3 (activated by temperature above 32°C), which is also implicated in temperature sensation in mice (13). Because both TRPV3 and TRPV4 are expressed in keratinocytes and are activated by a similar range of temperatures, these channels likely have distinct functions in the skin. Consistent with this idea, a recent report provided evidence that TRPV3, rather than TRPV4, mainly participates in transmission of warm temperature information from keratinocytes to adjacent nerve endings through ATP release (14). It has also been reported that mutation of TRPV3 is linked to defective hair growth and dermatitis in rodents (15, 16), although the involvement of TRPV4 has not been confirmed.The skin constitutes an interface between the external environment and the body, serving as a hydrophobic barrier essential for protection against infection from the outside and dehydration from the inside. The skin barrier function is achieved by keratinocytes in...

The mechanisms by which flow-imposed shear stress elevates intracellular Ca2+ in cultured endothelial cells (ECs) are not fully understood. Here we report finding that endogenously released ATP contributes to shear stress-induced Ca2+ responses. Application of flow of Hanks' balanced solution to human pulmonary artery ECs (HPAECs) elicited shear stress-dependent increases in Ca2+ concentrations. Chelation of extracellular Ca2+ with EGTA completely abolished the Ca2+ responses, whereas the phospholipase C inhibitor U-73122 or the Ca2+-ATPase inhibitor thapsigargin had no effect, which thereby indicates that the response was due to the influx of extracellular Ca2+. The Ca2+ influx was significantly suppressed by apyrase, which degrades ATP, or antisense oligonucleotide targeted to P2X4 purinoceptors. A luciferase luminometric assay showed that shear stress induced dose-dependent release of ATP. When the ATP release was inhibited by the ATP synthase inhibitors angiostatin or oligomycin, the Ca2+ influx was markedly suppressed but was restored by removal of these inhibitors or addition of extracellular ATP. These results suggest that shear stress stimulates HPAECs to release ATP, which activates Ca2+ influx via P2X4 receptors.

Members of the transient receptor potential (TRP) family are temperature sensors, and TRPV1, V3, and V4 are expressed in epidermal keratinocytes. To evaluate the influence of these receptors on epidermal permeability barrier homeostasis, we kept both hairless mouse skin and human skin at various temperatures immediately after tape stripping. At temperatures from 36 to 40 degrees C, barrier recovery was accelerated in both cases compared with the area at 34 degrees C. At 34 or 42 degrees C, barrier recovery was delayed compared with the un-occluded area. 4Alpha-phorbol 12,13-didecanone, an activator of TRPV4, accelerated barrier recovery, whereas ruthenium red, a blocker of TRPV4, delayed barrier recovery. Capsaicin, an activator of TRPV1, delayed barrier recovery, whereas capsazepin, an antagonist of TRPV1, blocked this delay. 2-Aminoethoxydiphenyl borate and camphor, TRPV3 activators, did not affect the barrier recovery rate. As TRPV4 is activated at about 35 degrees C and above, whereas TRPV1 is activated at about 42 degrees C and above, these results suggest that both TRPV1 and TRPV4 play important roles in skin permeability barrier homeostasis. Previous reports suggest the existence of a water flux sensor in the epidermis, and as TRPV4 is known to be activated by osmotic pressure, our results indicate that it might be this sensor.