Cyclic stretch activates p38 SAPK2-, ErbB2-, and AT1-dependent signaling in bladder smooth muscle cells

High Hydrostatic Pressure Exacerbates Bladder Fibrosis through Activating Piezo1

OBJECTIVE

Bladder outlet obstruction (BOO) results in significant fibrosis in the chronic stage and elevated bladder pressure. Piezo1 is a type of mechanosensitive (MS) channel that directly responds to mechanical stimuli. To identify new targets for intervention in the treatment of BOO-induced fibrosis, this study investigated the impact of high hydrostatic pressure (HHP) on Piezo1 activity and the progression of bladder fibrosis.

METHODS

Immunofluorescence staining was conducted to assess the protein abundance of Piezo1 in fibroblasts from obstructed rat bladders. Bladder fibroblasts were cultured under normal atmospheric conditions (0 cmH2O) or exposed to HHP (50 cmH2O or 100 cmH2O). Agonists or inhibitors of Piezo1, YAP1, and ROCK1 were used to determine the underlying mechanism.

RESULTS

The Piezo1 protein levels in fibroblasts from the obstructed bladder exhibited an elevation compared to the control group. HHP significantly promoted the expression of various pro-fibrotic factors and induced proliferation of fibroblasts. Additionally, the protein expression levels of Piezo1, YAP1, ROCK1 were elevated, and calcium influx was increased as the pressure increased. These effects were attenuated by the Piezo1 inhibitor Dooku1. The Piezo1 activator Yoda1 induced the expression of pro-fibrotic factors and the proliferation of fibroblasts, and elevated the protein levels of YAP1 and ROCK1 under normal atmospheric conditions in vitro. However, these effects could be partially inhibited by YAP1 or ROCK inhibitors.

CONCLUSION

The study suggests that HHP may exacerbate bladder fibrosis through activating Piezo1.

Stable hydrogel adhesion to polydimethylsiloxane enables cyclic mechanical stimulation of 3D-bioprinted smooth muscle constructs

During normal urination, smooth muscle cells (SMCs) in the lower urinary tract (LUT) are exposed to mechanical signals that have a critical impact on tissue structure and function. Nevertheless, the mechanisms underlying the maintenance of the contractile phenotype of SMCs remain poorly understood. This is due, in part, to a lack of studies that have examined the effects of mechanical loading using three-dimensional (3D) models. In this study, surface modifications of polydimethylsiloxane (PDMS) membrane were evaluated to investigate the effects of cyclic mechanical stimulation on SMC maturation in 3D constructs. Commercially available cell stretching plates were modified with amino or methacrylate groups to promote adhesion of 3D constructs fabricated by bioprinting. After 6 days of stimulation, the effects of mechanical stimulation on the expression of contractile markers at the mRNA and protein levels were analyzed. Methacrylate-modified surfaces supported stable adhesion of the 3D constructs to the membrane and facilitated cyclic mechanical stimulation, which significantly increased the expression of contractile markers at the mRNA and protein levels. These effects were found to be mediated by activation of the p38 MAPK pathway, as inhibition of this pathway abolished the effects of stimulation in a dose-dependent manner. These results provide valuable insights into the role of mechanical signaling in maintaining the contractile phenotype of bladder SMCs, which has important implications for the development of future treatments for LUT diseases.

Phosphorylation of the small heat shock protein HspB1 regulates cytoskeletal recruitment and cell motility

The small heat shock protein HspB1, also known as Hsp25/27, is a ubiquitously expressed molecular chaperone that responds to mechanical cues. Uniaxial cyclic stretch activates the p38 mitogen-activated protein kinase (MAPK) signaling cascade and increases the phosphorylation of HspB1. Similar to the mechanosensitive cytoskeletal regulator zyxin, phospho-HspB1 is recruited to features of the stretch-stimulated actin cytoskeleton. To evaluate the role of HspB1 and its phosphoregulation in modulating cell function, we utilized CRISPR/Cas9-edited HspB1-null cells and determined they were altered in behaviors such as actin cytoskeletal remodeling, cell spreading, and cell motility. In our model system, expression of WT HspB1, but not nonphosphorylatable HspB1, rescued certain characteristics of the HspB1-null cells including the enhanced cell motility of HspB1-null cells and the deficient actin reinforcement of stretch-stimulated HspB1-null cells. The recruitment of HspB1 to high-tension structures in geometrically constrained cells, such as actin comet tails emanating from focal adhesions, also required a phosphorylatable HspB1. We show that mechanical signals activate posttranslational regulation of the molecular chaperone, HspB1, and are required for normal cell behaviors including actin cytoskeletal remodeling, cell spreading, and cell migration.

Loss of muscleblind splicing factor shortens Caenorhabditis elegans lifespan by reducing the activity of p38 MAPK/PMK-1 and transcription factors ATF-7 and Nrf/SKN-1

Muscleblind-like splicing regulators (MBNLs) are RNA-binding factors that have an important role in developmental processes. Dysfunction of these factors is a key contributor of different neuromuscular degenerative disorders, including Myotonic Dystrophy type 1 (DM1). Since DM1 is a multisystemic disease characterized by symptoms resembling accelerated aging, we asked which cellular processes do MBNLs regulate that make them necessary for normal lifespan. By utilizing the model organism Caenorhabditis elegans, we found that loss of MBL-1 (the sole ortholog of mammalian MBNLs), which is known to be required for normal lifespan, shortens lifespan by decreasing the activity of p38 MAPK/PMK-1 as well as the function of transcription factors ATF-7 and SKN-1. Furthermore, we show that mitochondrial stress caused by the knockdown of mitochondrial electron transport chain components promotes the longevity of mbl-1 mutants in a partially PMK-1-dependent manner. Together, the data establish a mechanism of how DM1-associated loss of muscleblind affects lifespan. Furthermore, this study suggests that mitochondrial stress could alleviate symptoms caused by the dysfunction of muscleblind splicing factor, creating a potential approach to investigate for therapy.

Matrix mechanotransduction mediated by thrombospondin-1/integrin/YAP in the vascular remodeling

The extracellular matrix (ECM) initiates mechanical cues that activate intracellular signaling through matrix-cell interactions. In blood vessels, additional mechanical cues derived from the pulsatile blood flow and pressure play a pivotal role in homeostasis and disease development. Currently, the nature of the cues from the ECM and their interaction with the mechanical microenvironment in large blood vessels to maintain the integrity of the vessel wall are not fully understood. Here, we identified the matricellular protein thrombospondin-1 (Thbs1) as an extracellular mediator of matrix mechanotransduction that acts via integrin αvβ1 to establish focal adhesions and promotes nuclear shuttling of Yes-associated protein (YAP) in response to high strain of cyclic stretch. Thbs1-mediated YAP activation depends on the small GTPase Rap2 and Hippo pathway and is not influenced by alteration of actin fibers. Deletion of Thbs1 in mice inhibited Thbs1/integrin β1/YAP signaling, leading to maladaptive remodeling of the aorta in response to pressure overload and inhibition of neointima formation upon carotid artery ligation, exerting context-dependent effects on the vessel wall. We thus propose a mechanism of matrix mechanotransduction centered on Thbs1, connecting mechanical stimuli to YAP signaling during vascular remodeling in vivo.

Use of Mechanical Stretching to Treat Skin Graft Contracture

After transplantation, skin grafts contract to different degrees, thus affecting the appearance and function of the skin graft sites. The exact mechanism of contracture after skin grafting remains unclear, and reliable treatment measures are lacking; therefore, new treatment methods must be identified. Many types of centripetal contraction forces affect skin graft operation, thus leading to centripetal contracture. Therefore, antagonizing the centripetal contraction of skin grafts may be a feasible method to intervene in skin contracture. Here, the authors propose the first reported mechanical stretching method to address contracture after skin grafting. A full-thickness skin graft model was established on the backs of SD rats. The skin in the experimental group was stretched unilaterally or bidirectionally with a self-made elastic stretching device, whereas the skin was non-stretched in the control group. The rats were sacrificed 2 weeks after stretching. The area, length, and width of the skin were measured. The grafts were cut and fixed with formalin. Routine paraffin sections were stained with hematoxylin-eosin, picric acid-Sirius red, Victoria blue, and anti-alpha-smooth muscle actin (SMA). Mechanical stretching made the graft lengthen in the direction of the stress and had an important influence on collagen deposition and alpha-SMA expression in the graft. This method warrants further in-depth study to provide a basis for clinical application.

TRPV4 Protects the Lung from Bacterial Pneumonia via MAPK Molecular Pathway Switching

Mechanical cell-matrix interactions can drive the innate immune responses to infection; however, the molecular underpinnings of these responses remain elusive. This study was undertaken to understand the molecular mechanism by which the mechanosensitive cation channel, transient receptor potential vanilloid 4 (TRPV4), alters the in vivo response to lung infection. For the first time, to our knowledge, we show that TRPV4 protects the lung from injury upon intratracheal Pseudomonas aeruginosa in mice. TRPV4 functions to enhance macrophage bacterial clearance and downregulate proinflammatory cytokine secretion. TRPV4 mediates these effects through a novel mechanism of molecular switching of LPS signaling from predominant activation of the MAPK, JNK, to that of p38. This is accomplished through the activation of the master regulator of inflammation, dual-specificity phosphatase 1. Further, TRPV4's modulation of the LPS signal is mechanosensitive in that both upstream activation of p38 and its downstream biological consequences depend on pathophysiological range extracellular matrix stiffness. We further show the importance of TRPV4 on LPS-induced activation of macrophages from healthy human controls. These data are the first, to our knowledge, to demonstrate new roles for macrophage TRPV4 in regulating innate immunity in a mechanosensitive manner through the modulation of dual-specificity phosphatase 1 expression to mediate MAPK activation switching.

Increased expression of desmin and vimentin reduces bladder smooth muscle contractility via JNK2

Bladder dysfunction is associated with the overexpression of the intermediate filament (IF) proteins desmin and vimentin in obstructed bladder smooth muscle (BSM). However, the mechanisms by which these proteins contribute to BSM dysfunction are not known. Previous studies have shown that desmin and vimentin directly participate in signal transduction. In this study, we hypothesized that BSM dysfunction associated with overexpression of desmin or vimentin is mediated via c-Jun N-terminal kinase (JNK). We employed a model of murine BSM tissue in which increased expression of desmin or vimentin was induced by adenoviral transduction to examine the sufficiency of increased IF protein expression to reduce BSM contraction. Murine BSM strips overexpressing desmin or vimentin generated less force in response to KCl and carbachol relative to the levels in control murine BSM strips, an effect associated with increased JNK2 phosphorylation and reduced myosin light chain (MLC₂₀ ) phosphorylation. Furthermore, desmin and vimentin overexpressions did not alter BSM contractility and MLC₂₀ phosphorylation in strips isolated from JNK2 knockout mice. Pharmacological JNK2 inhibition produced results qualitatively similar to those caused by JNK2 knockout. These findings suggest that inhibition of JNK2 may improve diminished BSM contractility associated with obstructive bladder disease.

MicroRNA-101 protects bladder of BOO from hypoxia-induced fibrosis by attenuating TGF-β-smad2/3 signaling

Bladder outlet obstruction is a common disease, which always evokes urinary bladder wall remodeling significantly. It has been suggested that bladder outlet obstruction can make the bladder progression from inflammation to fibrosis, and hypoxia may play a vital role. It has been found the expression of microRNA-101 varied in bladder after BOO. But what role microRNA-101 and hypoxia play in bladder is not well known. This study is to investigate the mechanism of microRNA-101 and hypoxia in fibrosis of bladder after BOO. We found the expression of microRNA-101 and hif-1α increased in bladder after BOO. Hypoxia could promote the expression of extracellular matrix subtypes and microRNA-101 in BSMCs. When microRNA-101b was translated into BSMCs, the smad2/3 signaling pathway was found to repress. Dual luciferase reporter detected that microRNA-101b attenuated the TGF-β signaling pathway by inhibiting the expression of TGFβR1. Then, we conclude microRNA-101b is induced by hypoxia and represses fibrosis of BSMCs by inhibiting the expression of TGFβR1 through TGF-β signaling pathway, and it may be an anti-fibrotic miRNA for therapy. © 2018 IUBMB Life, 71(1):235-243, 2019.

Mechanical signals activate p38 MAPK pathway-dependent reinforcement of actin via mechanosensitive HspB1

Mechanical force induces protein phosphorylations, subcellular redistributions, and actin remodeling. We show that mechanical activation of the p38 MAPK pathway leads to phosphorylation of HspB1 (hsp25/27), which redistributes to cytoskeletal structures, and contributes to the actin cytoskeletal remodeling induced by mechanical stimulation.

Despite the importance of a cell’s ability to sense and respond to mechanical force, the molecular mechanisms by which physical cues are converted to cell-instructive chemical information to influence cell behaviors remain to be elucidated. Exposure of cultured fibroblasts to uniaxial cyclic stretch results in an actin stress fiber reinforcement response that stabilizes the actin cytoskeleton. p38 MAPK signaling is activated in response to stretch, and inhibition of p38 MAPK abrogates stretch-induced cytoskeletal reorganization. Here we show that the small heat shock protein HspB1 (hsp25/27) is phosphorylated in stretch-stimulated mouse fibroblasts via a p38 MAPK-dependent mechanism. Phosphorylated HspB1 is recruited to the actin cytoskeleton, displaying prominent accumulation on actin “comet tails” that emanate from focal adhesions in stretch-stimulated cells. Site-directed mutagenesis to block HspB1 phosphorylation inhibits the protein’s cytoskeletal recruitment in response to mechanical stimulation. HspB1-null cells, generated by CRISPR/Cas9 nuclease genome editing, display an abrogated stretch-stimulated actin reinforcement response and increased cell migration. HspB1 is recruited to sites of increased traction force in cells geometrically constrained on micropatterned substrates. Our findings elucidate a molecular pathway by which a mechanical signal is transduced via activation of p38 MAPK to influence actin remodeling and cell migration via a zyxin-independent process.

Urothelium update: how the bladder mucosa measures bladder filling

AIM

This review critically evaluates the evidence on mechanoreceptors and pathways in the bladder urothelium that are involved in normal bladder filling signalling.

METHODS

Evidence from in vitro and in vivo studies on (i) signalling pathways like the adenosine triphosphate pathway, cholinergic pathway and nitric oxide and adrenergic pathway, and (ii) different urothelial receptors that are involved in bladder filling signalling like purinergic receptors, sodium channels and TRP channels will be evaluated. Other potential pathways and receptors will also be discussed.

RESULTS

Bladder filling results in continuous changes in bladder wall stretch and exposure to urine. Both barrier and afferent signalling functions in the urothelium are constantly adapting to cope with these dynamics. Current evidence shows that the bladder mucosa hosts essential pathways and receptors that mediate bladder filling signalling. Intracellular calcium ion increase is a dominant factor in this signalling process. However, there is still no complete understanding how interacting receptors and pathways create a bladder filling signal. Currently, there are still novel receptors investigated that could also be participating in bladder filling signalling.

CONCLUSIONS

Normal bladder filling sensation is dependent on multiple interacting mechanoreceptors and signalling pathways. Research efforts need to focus on how these pathways and receptors interact to fully understand normal bladder filling signalling.

Mechanical Strain Delivers Anti-apoptotic and Proliferative Signals to Gingival Fibroblasts

Physical forces play a critical role in the survival and proliferation of many cell types, including fibroblasts. Gingival fibroblasts are exposed to mechanical stress during mastication, orthodontic tooth movement, and wound healing following periodontal surgery. The aim of this study was to examine the effect of mechanical strain on human gingival fibroblasts (hGF). Cells were subjected to short-term (up to 60 min) and long-term (up to 48 hrs) 20% average elongation at 0.1 Hz. We monitored survival signaling by evaluating the phosphorylation status and localization of Forkhead box (FoxO) family members, which are mediators of apoptosis. We also examined strain-induced proliferation by measuring the level of proliferating cell nuclear antigen (PCNA). We observed that cyclic strain caused the phosphorylation and retention in the cytoplasm of FoxO family members. Moreover, mechanical strain resulted in increased ERK kinase phosphorylation and PCNA expression. In conclusion, cyclic strain delivers anti-apoptotic and proliferative stimuli to hGF.

Angiotensin II receptors and peritoneal dialysis-induced peritoneal fibrosis

The vasoactive hormone angiotensin II initiates its major hemodynamic effects through interaction with AT1 receptors, a member of the class of G protein-coupled receptors. Acting through its AT1R, angiotensin II regulates blood pressure and renal salt and water balance. Recent evidence points to additional pathological influences of activation of AT1R, in particular inflammation, fibrosis and atherosclerosis. The transcription factor nuclear factor κB, a key mediator in inflammation and atherosclerosis, can be activated by angiotensin II through a mechanism that may involve arrestin-dependent AT1 receptor internalization. Peritoneal dialysis is a therapeutic modality for treating patients with end-stage kidney disease. The effectiveness of peritoneal dialysis at removing waste from the circulation is compromised over time as a consequence of peritoneal dialysis-induced peritoneal fibrosis. The non-physiological dialysis solution used in peritoneal dialysis, i.e. highly concentrated, hyperosmotic glucose, acidic pH as well as large volumes infused into the peritoneal cavity, contributes to the development of fibrosis. Numerous trials have been conducted altering certain components of the peritoneal dialysis fluid in hopes of preventing or delaying the fibrotic response with limited success. We hypothesize that structural activation of AT1R by hyperosmotic peritoneal dialysis fluid activates the internalization process and subsequent signaling through the transcription factor nuclear factor κB, resulting in the generation of pro-fibrotic/pro-inflammatory mediators producing peritoneal fibrosis.

Uni-axial stretch induces actin stress fiber reorganization and activates c-Jun NH2 terminal kinase via RhoA and Rho kinase in human bladder smooth muscle cells

Background

Excessive mechanical overload may be involved in bladder wall remodelling. Since the activity of Rho kinase is known to be upregulated in the obstructed bladder, we investigate the roles of the RhoA/Rho kinase pathway in mechanical overloaded bladder smooth muscle cells.

Methods

Human bladder smooth muscle cells were stimulated on silicon culture plates by 15 % elongated uni-axial cyclic stretch at 1 Hz. The activity of c-Jun NH₂-terminal kinase was measured by western blotting and actin stress fibers were observed by stained with phallotoxin conjugated with Alexa-Fluor 594.

Results

The activity of c-Jun NH₂-terminal kinase 1 peaked at 30 min (4.7-fold increase vs. before stretch) and this activity was partially abrogated by the RhoA inhibitor, C3 exoenzoyme or by the Rho kinase inhibitor, Y-27632. Stretch induced the strong formation of actin stress fibers and these fibers re-orientated in a direction that was perpendicular to the stretch direction. The average angle of the fibers from the perpendicular to the direction of stretch was significantly different between before, and 4 h after, stretch. Actin stress fibers reorganization was also suppressed by the C3 exoenzyme or Y-27632.

Conclusions

Bladder smooth muscle cells appear to have elaborate mechanisms for sensing mechanical stress and for adapting to mechanical stress overload by cytoskeletal remodeling and by activating cell growth signals such as c-Jun NH₂-terminal kinase via RhoA/Rho kinase pathways.

Dynamic reciprocity in cell-scaffold interactions

Tissue engineering in urology has shown considerable promise. However, there is still much to understand, particularly regarding the interactions between scaffolds and their host environment, how these interactions regulate regeneration and how they may be enhanced for optimal tissue repair. In this review, we discuss the concept of dynamic reciprocity as applied to tissue engineering, i.e. how bi-directional signaling between implanted scaffolds and host tissues such as the bladder drives the process of constructive remodeling to ensure successful graft integration and tissue repair. The impact of scaffold content and configuration, the contribution of endogenous and exogenous bioactive factors, the influence of the host immune response and the functional interaction with mechanical stimulation are all considered. In addition, the temporal relationships of host tissue ingrowth, bioactive factor mobilization, scaffold degradation and immune cell infiltration, as well as the reciprocal signaling between discrete cell types and scaffolds are discussed. Improved understanding of these aspects of tissue repair will identify opportunities for optimization of repair that could be exploited to enhance regenerative medicine strategies for urology in future studies.

Gastrointestinal motility and its enteric actors in mechanosensitivity: past and present

Coordinated contractions of the smooth muscle layers of the gastrointestinal (GI) tract are required to produce motor patterns that ensure normal GI motility. The crucial role of the enteric nervous system (ENS), the intrinsic ganglionated network located within the GI wall, has long been recognized in the generation of the main motor patterns. However, devising an appropriate motility requires the integration of informations emanating from the lumen of the GI tract. As already found more than half a century ago, the ability of the GI tract to respond to mechanical forces such as stretch is not restricted to neuronal mechanisms. Instead, mechanosensitivity is now recognized as a property of several non-neuronal cell types, the excitability of which is probably involved in shaping the motor patterns. This brief review gives an overview on how mechanosensitivity of different cell types in the GI tract has been established and, whenever available, on what ionic conductances are involved in mechanotransduction and their potential impact on normal GI motility.

Integration of proteomic and transcriptomic profiles identifies a novel PDGF-MYC network in human smooth muscle cells

Background

Platelet-derived growth factor-BB (PDGF-BB) has been implicated in the proliferation, migration and synthetic activities of smooth muscle cells that characterize physiologic and pathologic tissue remodeling in hollow organs. However, neither the molecular basis of PDGFR-regulated signaling webs, nor the extent to which specific components within these networks could be exploited for therapeutic benefit has been fully elucidated.

Results

Expression profiling and quantitative proteomics analysis of PDGF-treated primary human bladder smooth muscle cells identified 1,695 genes and 241 proteins as differentially expressed versus non-treated cells. Analysis of gene expression data revealed MYC, JUN, EGR1, MYB, RUNX1, as the transcription factors most significantly networked with up-regulated genes. Forty targets were significantly altered at both the mRNA and protein levels. Proliferation, migration and angiogenesis were the biological processes most significantly associated with this signature, and MYC was the most highly networked master regulator. Alterations in master regulators and gene targets were validated in PDGF-stimulated smooth muscle cells in vitro and in a model of bladder injury in vivo. Pharmacologic inhibition of MYC and JUN confirmed their role in SMC proliferation and migration. Network analysis identified the diaphanous-related formin 3 as a novel PDGF target regulated by MYC and JUN, which was necessary for PDGF-stimulated lamellipodium formation.

Conclusions

These findings provide the first systems-level analysis of the PDGF-regulated transcriptome and proteome in normal smooth muscle cells. The analyses revealed an extensive cohort of PDGF-dependent biological processes and connected key transcriptional effectors to their regulation, significantly expanding current knowledge of PDGF-stimulated signaling cascades. These observations also implicate MYC as a novel target for pharmacological intervention in fibroproliferative expansion of smooth muscle, and potentially in cancers in which PDGFR-dependent signaling or MYC activation promote tumor progression.

Blockade of renin-angiotensin system prevents micturition dysfunction in renovascular hypertensive rats

Association between hypertension and bladder symptoms has been described. We hypothesized that micturition dysfunction may be associated with renin-angiotensin system (RAS) acting in urethra. The effects of the anti-hypertensive drugs losartan (AT1 antagonist) and captopril (angiotensin-converting enzyme inhibitor) in comparison with atenolol (β1-adrenoceptor antagonist independently of RAS blockade) have been investigated in bladder and urethral dysfunctions during renovascular hypertension in rats. Two kidney-1 clip (2K-1C) rats were treated with losartan (30 mg/kg/day), captopril (50mg/kg/day) or atenolol (90 mg/kg/day) for eight weeks. Cystometric study, bladder and urethra smooth muscle reactivities, measurement of cAMP levels and p38 MAPK phosphorylation in urinary tract were determined. Losartan and captopril markedly reduced blood pressure in 2K-1C rats. The increases in non-voiding contractions, voiding frequency and bladder capacity in 2K-1C rats were prevented by treatments with both drugs. Likewise, losartan and captopril prevented the enhanced bladder contractions to electrical-field stimulation (EFS) and carbachol, along with the impaired relaxations to β-adrenergic-cAMP stimulation. Enhanced neurogenic contractions and impaired nitrergic relaxations were observed in urethra from 2K-1C rats. Angiotensin II also produced greater urethral contractions that were accompanied by higher phosphorylation of p38 MAPK in urethral tissues of 2K-1C rats. Losartan and captopril normalized the urethral dysfunctions in 2K-1C rats. In contrast, atenolol treatment largely reduced the blood pressure in 2K-1C rats but failed to affect the urinary tract smooth muscle dysfunction. The urinary tract smooth muscle dysfunction in 2K-1C rats takes place by local RAS activation irrespective of levels of arterial blood pressure.

Expression and proliferation profiles of PKC, JNK and p38MAPK in physiologically stretched human bladder smooth muscle cells

OBJECTIVE

To determine protein kinase C (PKC), c-Jun NH2-Terminal Kinase (JNK) and P38 mitogen-activated protein kinases (p38MAPK) expression levels and effects of their respective inhibitors on proliferation of human bladder smooth muscle cells (HBSMCs) when physiologically stretched in vitro.

MATERIALS AND METHODS

HBSMCs were grown on silicone membrane and stretch was applied under varying conditions; (equibiaxial elongation: 2.5%, 5%, 10%, 15%, 20%, 25%), (frequency: 0.05, 0.1, 0.2, 0.5, 1Hz). Optimal physiological stretch was established by assessing proliferation with 5-Bromo-2-deoxyuridine (BrdU) assay and flow cytometry. PKC, JNK and p38 expression levels were analyzed by Western blot. Specificity was maintained by employing specific inhibitors; (GF109203X for PKC, SP600125 for JNK and SB203580 for p38MAPK), in some experiments.

RESULTS

Optimum proliferation was observed at 5% equibiaxial stretch (BrdU: 0.837±0.026 (control) to 1.462±0.023)%, (P<0.05) and apoptotic cell death rate decreased from 16.4±0.21% (control) to 4.5±0.13% (P<0.05) applied at 0.1Hz. Expression of PKC was upregulated with slight increase in JNK and no change in p38MAPK after application of stretch. Inhibition had effects on proliferation (1.075±0.024, P<0.05 GF109203X); (1.418±0.021, P>0.05 SP600125) and (1.461±0.01, P>0.05 SB203580). These findings show that mechanical stretch can promote magnitude-dependent proliferative modulation through PKC and possibly JNK but not via p38MAPK in hBSMCs.

The purinergic component of human bladder smooth muscle cells' proliferation and contraction under physiological stretch

OBJECTIVE

To investigate whether cyclic stretch induces proliferation and contraction of human smooth muscle cells (HBSMCs), mediated by P2X purinoceptor 1 and 2 and the signal transduction mechanisms of this process.

METHODS

HBSMCs were seeded on silicone membrane and stretched under varying parameters; (equibiaxial elongation: 2.5%, 5%, 10%, 15%, 20%, 25%), (Frequency: 0.05Hz, 0.1Hz, 0.2Hz, 0.5Hz, 1Hz). 5-Bromo-2-deoxyuridine assay was employed for proliferative studies. Contractility of the cells was determined using collagen gel contraction assay. After optimal physiological stretch was established; P2X1 and P2X2 were analyzed by real time polymerase chain reaction and Western Blot. Specificity of purinoceptors was maintained by employing specific inhibitors; (NF023 for P2X1, and A317491for P2X2), in some experiments.

RESULTS

Optimum proliferation and contractility were observed at 5% and 10% equibiaxial stretching respectively, applied at a frequency of 0.1Hz; At 5% stretch, proliferation increased from 0.837±0.026 (control) to 1.462±0.023%, p<0.05. Mean contraction at 10% stretching increased from 31.7±2.3%, (control) to 78.28 ±1.45%, p< 0.05. Expression of P2X1 and P2X2 was upregulated after application of stretch. Inhibition had effects on proliferation (1.232±0.051, p<0.05 NF023) and (1.302±0.021, p<0.05 A314791) while contractility was markedly reduced (68.24±2.31, p<0.05 NF023) and (73.2±2.87, p<0.05 A314791). These findings shows that mechanical stretch can promote magnitude-dependent proliferative and contractile modulation of HBSMCs in vitro, and P2X1 and 2 are at least partially responsible in this process.

Effect of cyclic hydrodynamic pressure-induced proliferation of human bladder smooth muscle through Ras-related C3 botulinum toxin substrate 1, mitogen-activated protein kinase kinase 1/2 and extracellular regulated protein kinases 1/2

OBJECTIVES

To examine the role of Ras-related C3 botulinum toxin substrate 1, mitogen-activated protein kinase kinase 1/2 and extracellular regulated protein kinases 1/2 in the cyclic hydrodynamic pressure-induced proliferation of human bladder smooth muscle cells.

METHODS

Human bladder smooth muscle cells were exposed to cyclic hydrodynamic pressures in vitro with defined parameters (static, 100 cmH(2) O, 200 cmH(2) O and 300 cmH(2) O pressure) for 24 h. The proliferation of cells was assessed by flow cytometry. Ras-related C3 botulinum toxin substrate 1, mitogen-activated protein kinase kinase 1/2 and extracellular regulated protein kinases 1/2 messenger ribonucleic acid, and protein expression was analyzed by real-time polymerase chain reaction and Western blot. Specificity of the Rac1 was determined with real-time polymerase chain reaction and Western blot technique with small interfering ribonucleic acid transfection and Rac1 inhibitor (NSC23766).

RESULTS

The proliferation of human bladder smooth muscle cells was increased. Ras-related C3 botulinum toxin substrate 1, mitogen-activated protein kinase kinase 1/2 and extracellular regulated protein kinases 1/2 were activated by 200 and 300 cmH(2) O cyclic hydrodynamic pressure compared with static and 100 cmH(2) O pressure. The "knockdown" of activation of Rac1 using target small interfering ribonucleic acid transfection and Rac1 inhibitor (NSC23766) decreased proliferation of human bladder smooth muscle cells, and downregulated mitogen-activated protein kinase kinase 1/2, extracellular regulated protein kinases 1/2.

CONCLUSION

The Rac1 pathway is activated in mechanotransduction and regulation of human bladder smooth muscle cell proliferation in response to cyclic hydrodynamic pressure.

Integrin-dependent activation of the JNK signaling pathway by mechanical stress

Mechanical force is known to modulate the activity of the Jun N-terminal kinase (JNK) signaling cascade. However, the effect of mechanical stresses on JNK signaling activation has previously only been analyzed by in vitro detection methods. It still remains unknown how living cells activate the JNK signaling cascade in response to mechanical stress and what its functions are in stretched cells.

We assessed in real-time the activity of the JNK pathway in Drosophila cells by Fluorescence Lifetime Imaging Microscopy (FLIM), using an intramolecular phosphorylation-dependent dJun-FRET (Fluorescence Resonance Energy Transfer) biosensor. We found that quantitative FRET-FLIM analysis and confocal microscopy revealed sustained dJun-FRET biosensor activation and stable morphology changes in response to mechanical stretch for Drosophila S2R+ cells. Further, these cells plated on different substrates showed distinct levels of JNK activity that associate with differences in cell morphology, integrin expression and focal adhesion organization.

These data imply that alterations in the cytoskeleton and matrix attachments may act as regulators of JNK signaling, and that JNK activity might feed back to modulate the cytoskeleton and cell adhesion. We found that this dynamic system is highly plastic; at rest, integrins at focal adhesions and talin are key factors suppressing JNK activity, while multidirectional static stretch leads to integrin-dependent, and probably talin-independent, Jun sensor activation. Further, our data suggest that JNK activity has to coordinate with other signaling elements for the regulation of the cytoskeleton and cell shape remodeling associated with stretch.

FosB regulates stretch-induced expression of extracellular matrix proteins in smooth muscle

Fibroproliferative remodeling in smooth muscle-rich hollow organs is associated with aberrant extracellular matrix (ECM) production. Although mechanical stimuli regulate ECM protein expression, the transcriptional mediators of this process remain poorly defined. Previously, we implicated AP-1 as a mediator of smooth muscle cell (SMC) mechanotransduction; however, its role in stretch-induced ECM regulation has not been explored. Herein, we identify a novel role for the AP-1 subunit FosB in stretch-induced ECM expression in SMCs. The DNA-binding activity of AP-1 increased after stretch stimulation of SMCs in vitro. In contrast to c-Jun and c-fos, which are also activated by the SMC mitogen platelet-derived growth factor, FosB was only activated by stretch. FosB silencing attenuated the expression of the profibrotic factors tenascin C (TNC) and connective tissue growth factor (CTGF), whereas forced expression of Jun~FosB stimulated TNC and CTGF promoter activity. Chromatin immunoprecipitation revealed enrichment of AP-1 at the TNC and CTGF promoters. Bladder distension in vivo enhanced nuclear localization of c-jun and FosB. Finally, the distension-induced expression of TNC and CTGF in the detrusor smooth muscle of bladders from wild-type mice was significantly attenuated in FosB-null mice. Together, these findings identify FosB as a mechanosensitive regulator of ECM production in smooth muscle.

An Akt- and Fra-1-dependent pathway mediates platelet-derived growth factor-induced expression of thrombomodulin, a novel regulator of smooth muscle cell migration

Overdistension of hollow organs evokes pathological changes characterized by smooth muscle remodeling. Mechanical stimuli induce smooth muscle cell (SMC) growth through acute activation of signaling cascades and by increased expression of soluble mitogens. Physical forces have also been implicated in ligand-independent activation of receptor tyrosine kinases, including the platelet-derived growth factor (PDGF) receptor, although the extent to which this occurs in intact tissue is unknown. Previously, we implicated Akt and activator protein-1 (AP-1) as mediators of growth and gene expression in SMC exposed to cyclic stretch or PDGF. Here we show that bladder wall distension leads to PDGFR activation and identify thrombomodulin (TM) as an Akt and AP-1 target in SMC. We demonstrate that TM, also induced by bladder stretch injury, is regulated at the transcriptional level by the AP-1 components c-jun and Fra1. Mutation of an AP-1 motif at -2010/-2004 abolished both AP-1 binding and PDGF responsiveness of the TM promoter. Fra1 silencing diminished PDGF-induced TM expression and SMC cell cycle transit. In contrast, TM knockdown did not affect cell growth but attenuated PDGF-stimulated SMC migration. Taken together, these results reveal new facets of TM regulation in SMC and provide the first demonstration of a role for endogenous TM in PDGF-induced cell migration. Moreover, TM induction on bladder injury suggests that it may be a biomarker for pathological smooth muscle remodeling.

Mammalian target of rapamycin (mTOR) induces proliferation and de-differentiation responses to three coordinate pathophysiologic stimuli (mechanical strain, hypoxia, and extracellular matrix remodeling) in rat bladder smooth muscle

Maladaptive bladder muscle overgrowth and de-differentiation in human bladder obstructive conditions is instigated by coordinate responses to three stimuli: mechanical strain, tissue hypoxia, and extracellular matrix remodeling.( 1,2) Pathway analysis of genes induced by obstructive models of injury in bladder smooth muscle cells (BSMCs) identified a mammalian target of rapamycin (mTOR)-specific inhibitor as a potential pharmacological inhibitor. Strain-induced mTOR-specific S6K activation segregated differently from ERK1/2 activation in intact bladder ex vivo. Though rapamycin's antiproliferative effects in vascular smooth muscle cells are well known, its effects on BSMCs were previously unknown. Rapamycin significantly inhibited proliferation of BSMCs in response to mechanical strain, hypoxia, and denatured collagen. Rapamycin inhibited S6K at mTOR-sensitive phosphorylation sites in response to strain and hypoxia. Rapamycin also supported smooth muscle actin expression in response to strain or hypoxia-induced de-differentiation. Importantly, strain plus hypoxia synergistically augmented mTOR-dependent S6K activation, Mmp7 expression and proliferation. Forced expression of wild-type and constitutively active S6K resulted in loss of smooth muscle actin expression. Decreased smooth muscle actin, increased Mmp7 levels and mTOR pathway activation during in vivo partial bladder obstruction paralleled our in vitro studies. These results point to a coordinate role for mTOR in BSMCs responses to the three stimuli and a potential new therapeutic target for myopathic bladder disease.

The green tea polyphenol EGCG potentiates the antiproliferative activity of c-Met and epidermal growth factor receptor inhibitors in non-small cell lung cancer cells

PURPOSE

Activation of the c-Met and epidermal growth factor receptors (EGFR) promotes the growth and survival of non-small cell lung cancer (NSCLC). Specific receptor antagonists have shown efficacy in the clinic, but tumors often become resistant to these therapies. We investigated the ability of (-)-epigallocatechin-3-gallate (EGCG) to inhibit cell proliferation, and c-Met receptor and EGFR kinase activation in several NSCLC cell lines.

EXPERIMENTAL DESIGN

NSCLC cell lines with variable sensitivity to the EGFR antagonist erlotinib were studied. Cell growth was evaluated using proliferation and colony formation assays. Kinase activation was assessed via Western blot analysis. Experiments were conducted with EGCG, the EGFR antagonist erlotinib, and the c-Met inhibitor SU11274. The antagonists were also tested in a xenograft model using SCID mice.

RESULTS

EGCG inhibited cell proliferation in erlotinib-sensitive and -resistant cell lines, including those with c-Met overexpression, and acquired resistance to erlotinib. The combination of erlotinib and EGCG resulted in greater inhibition of cell proliferation and colony formation than either agent alone. EGCG also completely inhibited ligand-induced c-Met phosphorylation and partially inhibited EGFR phosphorylation. The triple combination of EGCG/erlotinib/SU11274 resulted in a greater inhibition of proliferation than EGCG with erlotinib. Finally, the combination of EGCG and erlotinib significantly slowed the growth rate of H460 xenografts.

CONCLUSION

EGCG is a potent inhibitor of cell proliferation, independent of EGFR inhibition, in several NSCLC cell lines, including those resistant to both EGFR kinase inhibitors and those overexpressing c-Met. Therefore, EGCG might be a useful agent to study as an adjunct to other anticancer agents.

Sartan-AT1 receptor interactions: in vitro evidence for insurmountable antagonism and inverse agonism

Sartans are non-peptide AT(1) receptor antagonists used to treat hypertension and related pathologies. Their effects on the G protein-dependent responses of angiotensin II (Ang II) were the same in vascular tissues and in isolated cell systems. All are competitive but, when pre-incubated, they act surmountably (only rightward shift of the Ang II concentration-response curve) or insurmountably (also decreasing the maximal response). Insurmountable behaviour reflects the formation of tight sartan-receptor complexes; it is often partial due to the co-existence of tight and loose complexes. Their ratio positively correlates with the dissociation half-life of the tight complexes and depends on the sartan: i.e. candesartan>olmesartan>telmisartan approximately equal EXP3174>valsartan>irbesartan>>losartan. When AT(1) receptors display sufficient basal activity (in case of receptor over-expression, mutation and, especially, tissue stretching) sartans may also act as inverse agonists. This rather affects long-term, G protein-independent hypertrophic responses leading to cardiovascular remodelling.

Biomechanical regulation of cell orientation and fate

Biomechanical regulation of tumor phenotypes have been noted for several decades, yet the function of mechanics in the co-evolution of the tumor epithelium and altered cancer extracellular matrix has not been appreciated until fairly recently. In this review, we examine the dynamic interaction between the developing epithelia and the extracellular matrix, and discuss how similar interactions are exploited by the genetically modified epithelium during tumor progression. We emphasize the process of mechanoreciprocity, which is a phenomenon observed during epithelial transformation, in which tension generated within the extracellular microenvironment induce and cooperate with opposing reactive forces within transformed epithelium to drive tumor progression and metastasis. We highlight the importance of matrix remodeling, and present a new, emerging paradigm that underscores the importance of tissue morphology as a key regulator of epithelial cell invasion and metastasis.

Role of desmin in active force transmission and maintenance of structure during growth of urinary bladder

Role of the intermediate filament protein desmin in hypertrophy of smooth muscle was examined in desmin-deficient mice (Des(-/-)). A partial obstruction of the urethra was created, and after 9-19 days bladder weight increased approximately threefold in both Des(-/-) and wild type (Des(+/+)) animals. Bladder growth was associated with the synthesis of actin and myosin. In the hypertrophic Des(+/+) bladder, the relative content of desmin increased. In Des(-/-)mice, desmin was absent. No alterations in the amount of vimentin were observed. Although Des(-/-) obstructed bladders were capable of growth, they had structural changes with a partial disruption of the wall. Des(-/-)bladders had slightly lower passive stress and significantly lower active stress compared with Des(+/+). Des(-/-)preparations had lower shortening velocity. During hypertrophy, these structural and mechanical alterations in the Des(-/-)urinary bladder became more pronounced. In conclusion, desmin in the bladder smooth muscle is not needed for growth but has a role in active force transmission and maintenance of wall structure.

Cyclic stretch-induced nuclear localization of transcription factors results in increased nuclear targeting of plasmids in alveolar epithelial cells

BACKGROUND

We have shown previously that cyclic stretch corresponding to that experienced by the pulmonary epithelium during normal breathing enhances nonviral gene transfer and expression in alveolar epithelial cells by increasing plasmid intracellular trafficking. Although reorganization of the microtubule and actin cytoskeletons by cyclic stretch is necessary for increased plasmid trafficking, the role of nuclear entry in this enhanced trafficking has not been elucidated.

METHODS

Alveolar epithelial cells were subjected to biaxial cyclic stretch (10% change in surface area at 0.5 Hz) and assayed for RNA expression, nuclear localization and activation of key transcription factors. Stretched epithelial cells were transfected with plasmids via electroporation and exposed to inhibitors of transcription factor activation.

RESULTS

When assayed by in situ hybridization, more plasmids were localized to the nuclei of cells that were stretched following electroporation compared to unstretched cells. Cyclic stretch also increases the nuclear localization of multiple transcription factors thought to be involved in plasmid nuclear entry, including AP1, AP2, NF-kappaB and NF1. Specific inhibition of the nuclear import of AP1 and/or NF-kappaB abolishes the enhanced plasmid nuclear localization seen with stretch.

CONCLUSIONS

Nuclear entry of plasmids is thought to be mediated by the binding of proteins that chaperone the DNA through the nuclear pore. Stretch-enhanced nuclear localization of transcription factors increases nuclear targeting of plasmids, whereas inhibition of the nuclear import of specific transcription factors abrogated stretch-enhanced plasmid nuclear localization. Taken together, these results suggest that cyclic stretch increases gene trafficking in the cytoplasm and at the nuclear envelope.

Mechanotransduction of keratinocytes in culture and in the epidermis

The epidermis, like many other tissues, reacts to mechanical stress by increasing cell proliferation. Mechanically stressed skin regions often develop thicker skin and hyperkeratosis. Interestingly, a large number of skin diseases are accompanied by epidermal proliferation and hyperkeratosis even under normal mechanical stress conditions. Although, some of the molecular pathways of mechanical signaling involving integrins, the epidermal growth factor receptor and mitogen-activated protein kinases are known it is still unclear, how mechanical force is sensed and transformed into the molecular signals that induce cell proliferation. This review focuses on the molecules and pathways known to play a role in mechanotransduction in epidermal keratinocytes and discusses the pathways identified in other well-studied cell types.

Cyclic Pressure Stimulates DNA Synthesis through the PI3K/Akt Signaling Pathway in Rat Bladder Smooth Muscle Cells

Previous studies demonstrated that the bladder exhibited severe tissue remodeling following spinal cord injury. In such pathological bladders, uninhibited non-voiding contractions subject bladder cells to cyclic oscillations of intravesical pressure. We hypothesize that cyclic pressure is a potential trigger for tissue remodeling in overactive bladder. Using a custom-made setup, rat bladder smooth muscle cells (SMC) in vitro were exposed to cyclic hydrostatic pressure (40 cm H2O) at either 0.1 Hz or 0.02 Hz frequency for up to 24 h. When compared to static control and cells exposed to 0.02-Hz cyclic pressure, SMC exposed to 0.1-Hz cyclic pressure contained significantly (p < 0.05) higher amounts of DNA. We confirmed that the increase in DNA was due to increased cell proliferation, indicated by increased BrdU incorporation, but not due to decreased apoptosis rates in response to cyclic pressure. In addition, significant (p < 0.05) elevation of Akt phosphorylation in SMC following exposure to cyclic pressure and lack of pressure-induced SMC hyperplasia in the presence of PI3K inhibitors, wortmannin and LY294002, indicated the involvement of the PI3K/Akt pathway in the proliferative response of SMC to cyclic pressure. We concluded that chronic exposure to intravesical pressure oscillation may be a potential trigger for bladder tissue remodeling.

Changing concepts of bladder regeneration

During the last decade, there has been a dramatic increase in studies aimed at regeneration of the urinary bladder. Many studies employed animal-derived or synthetic materials as grafts for experimental bladder augmentation models, with or without additional measures to promote regeneration, such as autologous cell transplantation or growth factor loading. However, in spite of encouraging results in several reports, few methodologies have shown proven definitive clinical utility. One major problem in these studies is the lack of a clear distinction between native and regenerated bladder in total bladder function after augmentation. Another crucial problem is the absorption and shrinkage of larger grafts, which may result from insufficient vascular supply and smooth muscle regeneration. In contrast, researchers have recently attempted to establish alternative regenerative strategies for treating bladder diseases, and have employed far more diverse approaches according to the various pathological conditions to be treated. For total replacement of the bladder after cystectomy for invasive bladder cancer, urothelium-covered neobladder with non-urinary tract backbone remains a viable choice. In addition, functional bladder diseases such as urinary incontinence, weak detrusor, or non-compliant fibrotic bladder have also been major targets for many leading research groups in this field. These conditions are studied much more from different therapeutic standpoints, aiming at the prevention or reversal of pathological conditions in muscle remodeling or neural control. Such altered research direction would inevitably lead to less surgically based basic biological research, and also would include a far wider spectrum of adult and pediatric bladder diseases, from overactive bladder to dysfunctional voiding.

Apical epidermal growth factor receptor signaling: regulation of stretch-dependent exocytosis in bladder umbrella cells

The apical surface of polarized epithelial cells receives input from mediators, growth factors, and mechanical stimuli. How these stimuli are coordinated to regulate complex cellular functions such as polarized membrane traffic is not understood. We analyzed the requirement for growth factor signaling and mechanical stimuli in umbrella cells, which line the mucosal surface of the bladder and dynamically insert and remove apical membrane in response to stretch. We observed that stretch-stimulated exocytosis required apical epidermal growth factor (EGF) receptor activation and that activation occurred in an autocrine manner downstream of heparin-binding EGF-like growth factor precursor cleavage. Long-term changes in apical exocytosis depended on protein synthesis, which occurred upon EGF receptor-dependent activation of mitogen-activated protein kinase signaling. Our results indicate a novel physiological role for the EGF receptor that couples upstream mechanical stimuli to downstream apical EGF receptor activation that may regulate apical surface area changes during bladder filling.

Inhibition of EGFR signaling abrogates smooth muscle proliferation resulting from sustained distension of the urinary bladder

Urinary bladder outlet obstruction results in sustained stretch of the detrusor muscle and can lead to pathological smooth muscle hyperplasia and hypertrophy. The epidermal growth factor receptor (EGFR) is a cognate receptor for mitogens implicated in bladder hyperplasia/hypertrophy. Here, we investigated the potential for modulation of this pathway by pharmacologic targeting with a clinically available EGFR antagonist using an organ culture model of bladder stretch injury as a test system. Urinary bladders from adult female rats were distended in vivo with medium containing the EGFR inhibitor ZD1839 (gefitinib, Iressa). The bladders were excised and incubated in ex vivo organ culture for 4-24 h. EGFR phosphorylation, DNA proliferation, and the extent of apoptosis in the cultured tissues were assessed. To verify that the smooth muscle cells (SMC) are a target of the EGFR inhibitor, primary culture human and rat bladder SMC were subjected to cyclic mechanical stretch in vitro in the presence of ZD1839. Levels of phosphorylated EGFR were significantly increased in the detrusor muscle with 12 h of stretch in the organ cultures. This activation coincided with a subsequent 23-fold increase in DNA synthesis and a 30-fold decrease in apoptosis in the muscle compartment at 24 h. In the presence of ZD1839, DNA synthesis was reduced to basal levels without an increase in the rate of apoptosis under ex vivo conditions. Mechanical stretch of bladder SMC in vitro resulted in a significant increase in DNA synthesis, which was completely abrogated by treatment with ZD1839 but not by AG825, an inhibitor of the related receptor, ErbB2. Our results indicate that the EGFR pathway is a physiologically relevant signaling mechanism in hypertrophic bladder disease resulting from mechanical distension and may be amenable to pharmacologic intervention.

Matrix metalloproteinase-7 and epidermal growth factor receptor mediate hypoxia-induced extracellular signal-regulated kinase 1/2 mitogen-activated protein kinase activation and subsequent proliferation in bladder smooth muscle cells

Low oxygen tension (hypoxia) has been implicated in proliferation of vascular smooth muscle cells (SMCs) of the lung. Tissue hypoxia also occurs in the obstructed bladder. The extracellular-regulated kinase mitogen-activated protein kinase 1/2 (Erk1/2) pathway is induced in many cell types during hypoxia. We examined whether hypoxia (3% O2), compared with normoxia (21% O2), induces proliferation responses and activation of the Erk1/2 pathways in primary rat bladder smooth muscle cells (BSMCs). We show that hypoxia induces proliferation of BSMCs at 18 h and, although reduced at 22 h, still remained above normoxic levels. Hypoxia induced a strikingly transient activation of Erk1/2 that lasted only 10-30 min. However, inhibition of the transient Erk1/2 activity with a specific mitogen-activated protein kinase kinase 1 (MEK-1) inhibitor PD 98059 prevented subsequent hypoxia-induced proliferation at 18 h. Interestingly, inhibition of general matrix metalloproteinase (MMP) activity, using either doxycycline or GM 6001, prevented both transient Erk1/2 activity and subsequent proliferation in response to hypoxia. Furthermore, MMP-7 (matrilysin) is activated in the conditioned medium (CM) of BSMCs at 10-20 min of hypoxia. In addition, MMP-7 was also transcriptionally induced at 6 h of hypoxia in an Erk1/2-dependent manner. Moreover, transient Erk1/2 activation and BSMC proliferation were both dependent on epidermal growth factor receptor (EGFR/HER1) but not neu receptor (HER2/ERB2) autophosphorylation. We conclude that hypoxia leads to Erk1/2 activation, which appears to modulate BSMC proliferation through MMP-7-and EGFR-mediated mechanisms.

EGFR-activated signaling and actin remodeling regulate cyclic stretch-induced NRF2-ARE activation

Cyclic stretch (CS) associated with mechanical ventilation (MV) can cause excessive alveolar and endothelial distention, resulting in lung injury and inflammation. Antioxidant enzymes (AOEs) play a major role in suppressing these effects. The transcription factor Nrf2, via the antioxidant response element (ARE), alleviates pulmonary toxicant- and oxidant-induced oxidative stress by up-regulating the expression of several AOEs. Although gene expression profiling has revealed the induction of AOEs in the lungs of rodents exposed to MV, the mechanisms by which mechanical forces, such as CS, regulate the activation of Nrf2-dependent ARE-transcriptional responses are poorly understood. To mimic mechanical stress associated with MV, we have cultured pulmonary alveolar epithelial and endothelial cells on collagen I-coated BioFlex plates and subjected them to CS. CS exposure stimulated ARE-driven transcriptional responses and subsequent AOE expression. Ectopic expression of a dominant-negative Nrf2 suppressed the CS-stimulated ARE-driven responses. Our findings suggest that actin remodeling is necessary but not sufficient for high-level CS-induced ARE activation in both epithelial and endothelial cells. We also found that inhibition of EGFR activity by a pharmacologic agent ablated the CS-induced ARE transcriptional response in both cell types. Additional studies revealed that amphiregulin, an EGFR ligand, regulates this process. We further demonstrated that the PI3K-Akt pathway acts as the downstream effector of EGFR and regulates CS-induced ARE-activation in an oxidative stress-dependent manner. Collectively, these novel findings suggest that EGFR-activated signaling and actin remodeling act in concert to regulate the CS-induced Nrf2-ARE transcriptional response and subsequent AOE expression.

Mechanotransduction of extracellular signal-regulated kinases 1 and 2 mitogen-activated protein kinase activity in smooth muscle is dependent on the extracellular matrix and regulated by matrix metalloproteinases

Excessive wall stretch of distensible hollow organs in cardiovascular and urinary systems can activate matrix metalloproteinases (MMPs), thereby releasing matrix neoepitopes and growth factor ligands, leading to ERK1/2 activation. However, the role of MMPs in mechanotransduction of ERK1/2 signaling in the bladder is unknown. We examined bladders undergoing sustained distension over time, which provides a novel platform for smooth muscle mechanotransduction studies. Bladder distension ex vivo caused increased proliferation and MMP activity. Conditioned medium from distended compared with undistended bladders induced proliferation in bladder smooth muscle cells (BSMCs). When conditioned medium from distended bladders was used to proteolyze collagen type I matrices, matrices augmented BSMC proliferation, which was inhibited if bladders were distended in presence of broad-spectrum MMP inhibitors. Distension of ex vivo bladders also induced ERK1/2 phosphorylation in situ, which was dependent on MMP activity in the intact bladder. Similarly, stretching BSMCs in vitro induced increases in ERK1/2 activation and ERK1/2-dependent proliferation under discrete mechanical conditions, and distension conditioned medium itself induced MMP-dependent ERK1/2 activation in BSMCs. Overall, stretch-induced proliferation and ERK1/2 signaling in bladder tissue and BSMCs likely depend on secreted MMP activity. Identification of intermediaries between MMPs and ERK1/2 may elaborate novel mechanisms underlying mechanotransduction in bladder smooth muscle.

Role of signal transducer and activator of transcription 3 (STAT3) in stretch injury to bladder smooth muscle cells

Excessive stretch of the bladder can lead to wall thickening including the growth of bladder smooth muscle cells (BSMC). Only three phospho-proteins (JNK, p38, and PI3K) have been previously shown to participate in stretch-induced BSMC growth. CD1 mouse bladders were hyper- or non-distended by our ex vivo bladder distention model and screened, by a commercial screening method, for phosphorylated signaling proteins. This uncovered a factor previously unexamined for its role in bladder stretch injury: signal transducer and activator of transcription 3 (STAT3). STAT3 was assessed for its role in mitogen- and stretch-induced BSMC proliferation. Proliferation was assessed by 3H-thymidine incorporation/cell counting in response to mitogenic stimulation or to stretch on silastic collagen or carboxyl-coated membranes. JAK2, upstream of STAT3, was inhibited by AG490 (2 microM). Ex vivo distention of bladders activated a discrete number of kinases, including two MAPK pathways (JNK and ERK2) and STAT3. STAT3 signaling was activated during hyperdistention of intact bladder and by stretch and mitogenic treatments of BSMC in vitro. JAK2/STAT3 inhibition by AG490 blocked mitogen- and stretch-induced BSMC proliferation. Thus, BSMC stretch responses may involve the recruitment of both growth factor and mechanically induced BSMC growth responses integrated by a common signaling pathway, STAT3.

Oxidant driven signaling pathways during diabetes: role of Rac1 and modulation of protein kinase activity in mouse urinary bladder

BACKGROUND

Urinary bladder dysfunction is a complication in diabetes but the mechanisms involved are undefined. Here, we investigated roles of oxidative stress and oxidant driven signaling pathways in a murine model of diabetes, with an emphasis on urothelial vs. smooth muscle regional changes.

METHODS

Mice were dosed with streptozotocin (150 mg/kg) or vehicle and studied at 5 weeks. Functional changes were assessed by in vitro cystometry. Immunohistochemical methods and automated digital imaging was used for morphometric and histochemical analysis of bladder tissue regions.

RESULTS

We detected significant increases in protein 3-nitrotyrosine in both urothelium and smooth muscle regions during diabetes, demonstrating an increased prevalence of reactive nitrogen species. In light of nitric oxide synthase (NOS) isoforms as potential contributors to increased protein nitration, all three NOS isoforms were studied; region specific increases in NOS1 (urothelium and smooth muscle), NOS2 (urothelium only) but no alterations in NOS3 isoform were detected during diabetes. In contrast, p21-Rac1 (coordinating protein of NADPH oxidase) was significantly increased only in smooth muscle (diabetic vs. controls). We also investigated phosphorylation of ERK, JNK, p38 and Akt using immunohistochemical techniques; each of these was increased during diabetes but with different distributions in the two major regions of bladder tissues viz the smooth muscle and urothelium.

CONCLUSIONS

The STZ mouse model of diabetes exhibits bladder dysfunction and structural changes similar to human. Reactive nitrogen species formation occurs in this setting and region specific assessments also revealed that urothelial changes and smooth muscle changes are discrete with respect to mechanisms of reactive nitrogen species (increased production of NO vs. superoxide anion) and activation of oxidant related stress signaling pathways.

Recent insights into the cell biology of bladder smooth muscle

Much of current biomedical research is focused on the development of 'targeted therapies' based on detailed knowledge about the signals that mediate aberrant cellular behavior in a given disease. Although this concept has been used most widely in cancer treatment, the same strategy applies to nonmalignant conditions such as pathologic tissue expansion in the genitourinary tract. A rigorous understanding of the key molecular events and pathways that underlie normal and pathologic activity of the bladder would allow us to identify potential targets for rational drug design. In this review, I will summarize our current understanding of cell signaling in bladder smooth muscle and highlight potential targets for drug-based treatment of tissue remodeling in the lower urinary tract.