Mechanical stretch/relaxation of cultured rat mesangial cells induces protooncogenes and cyclooxygenase

Direction of epithelial folding defines impact of mechanical forces on epithelial state

Cell shape dynamics during development is tightly regulated and coordinated with cell fate determination. Triggered by an interplay between biochemical and mechanical signals, epithelia form complex tissues by undergoing coordinated cell shape changes, but how such spatiotemporal coordination is controlled remains an open question. To dissect biochemical signaling from purely mechanical cues, we developed a microfluidic system that experimentally triggers epithelial folding to recapitulate stereotypic deformations observed in vivo. Using this system, we observe that the apical or basal direction of folding results in strikingly different mechanical states at the fold boundary, where the balance between tissue tension and torque (arising from the imposed curvature) controls the spread of folding-induced calcium waves at a short timescale and induces spatial patterns of gene expression at longer timescales. Our work uncovers that folding-associated gradients of cell shape and their resulting mechanical stresses direct spatially distinct biochemical responses within the monolayer.

The Blockade of TACE-Dependent EGF Receptor Activation by Losartan-Erlotinib Combination Attenuates Renal Fibrosis Formation in 5/6-Nephrectomized Rats Under Vitamin D Deficiency

Chronic kidney disease (CKD) has been considered a major public health issue. In addition to cardiovascular diseases and infections, hypovitaminosis D has been considered a non-traditional aggravating factor for CKD progression. Interstitial fibrosis is a hallmark of CKD strongly correlated with deterioration of renal function. Transforming growth factor β (TGF-β) is the major regulatory profibrotic cytokine in CKD. Many injurious stimuli converge on the TGF-β pathway, which has context-dependent pleiotropic effects and interacts with several related renal fibrosis formation (RFF) pathways. Epidermal growth factor receptor (EGFR) is critically involved in CKD progression, exerting a pathogenic role in RFF associated with TGF-β-related fibrogenesis. Among others, EGFR pathway can be activated by a disintegrin and a metalloproteinase known as tumor necrosis factor α-converting enzyme (TACE). Currently no effective therapy is available to completely arrest RFF and slow the progression of CKD. Therefore, we investigated the effects of a double treatment with losartan potassium (L), an AT1R antagonist, and the tyrosine kinase inhibitor erlotinib (E) on the alternative pathway of RFF related to TACE-dependent EGFR activation in 5/6-nephrectomized rats under vitamin D deficiency (D). During the 90-day protocol, male Wistar rats under D, were submitted to 5/6 nephrectomy (N) on day 30 and randomized into four groups: N+D, no treatment; N+D+L, received losartan (50 mg/kg/day); N+D+E, received erlotinib (6 mg/kg/day); N+D+L+E received losartan+erlotinib treatment. N+D+L+E data demonstrated that the double treatment with losartan+erlotinib not only blocked the TACE-dependent EGF receptor activation but also prevented the expression of TGF-β, protecting against RFF. This renoprotection by losartan+erlotinib was corroborated by a lower expression of ECM proteins and markers of phenotypic alteration as well as a lesser inflammatory cell infiltrate. Although erlotinib alone has been emerging as a renoprotective drug, its association with losartan should be considered as a potential therapeutic strategy on the modulation of RFF.

Low dose of flurbiprofen axetil decrease the rate of acute kidney injury after operation: a retrospective clinical data analysis of 9915 cases

Background

Flurbiprofen axetil (FA) is a commonly prescribed agent to relieve perioperative pain, but the relationship between FA and postoperative acute kidney injury (AKI) remains unclear. This study attempted to evaluate the effects of different dose of perioperative FA on postoperative AKI.

Methods

A total of 9915 patients were enrolled for this retrospective study. The clinical characteristics and the prevalence of postoperative AKI among patients non-using, using low dose (50-100 mg), middle dose (100-250 mg) and large dose (≧250 mg) of FA were analyzed respectively. The impact of different dose of FA on postoperative AKI was analyzed using univariable and multivariate logistic regression analysis.

Results

The prevalence of postoperative AKI was 6.7% in the overall subjects and 5.1% in 2446 cases who used FA. The incidence of AKI in low dose group was significantly less than that of non use group (4.5% vs 7.2%, P < 0.001), but the incidence of AKI in large dose group was significantly higher than that in the non-use group (18.8% vs 7.2%, P < 0.001). However, there was no significant difference between patients without using FA and subjects using middle dose of FA (7.2% vs 5.6%, p = 0.355). Multivariate logistic regression analysis showed that low dose of FA was a protective factor for postoperative AKI (OR = 0.75, p = 0.0188), and large dose of FA was a risk factor for postoperative AKI (OR = 4.8, p < 0.0001).

Conclusions

The impact of FA on postoperative AKI was dose-dependent, using of low dose FA (50-100 mg) perioperatively may effectively reduce the incidence of postoperative AKI.

Comparative analysis of gene expression in normal and degenerative human tendon cells: effects of cyclic strain

BACKGROUND

Tendinopathy is a clinical problem for which treatment shows mixed results and treatment options are limited. Gene expression signatures early in the mechanotransduction pathway can accurately predict risk and correlate with different clinical outcomes. Studies aimed at elucidating the molecular mechanisms of tendinopathy have focused on small cohorts of genes that show an incomplete picture of the degeneration process. This study compared the effect of cyclic strain on gene expression in tendon cells from normal tendon and chronically painful areas of tendinopathy in 3 patients.

METHODS

We measured a panel of mechanotransduction genes and cytoskeletal tensional balance with and without cyclic strain, which disrupts connective tissue synthetic-degradative equilibrium. Normal and degenerative tendons were obtained from patients undergoing surgery to treat chronic painful tendinopathy. A cyclic strain model was established to measure cytoskeletal tensional homeostasis.

RESULTS

Prior to cyclic strain, the normal tendon cells exhibited varying patterns of elevated expression of 7 genes compared with degenerative tendon cells. In response to cyclic strain, gene expression of COL1A1, ITGA6, CTNNA1, and CLEC3B was up-regulated in normal tendon cells. Cyclic strain had no effect on degenerative tendon cells. Cyclic strain exacerbated the inhibition of protein synthesis in both cell types, especially in the degenerative tendon cells.

CONCLUSION

Alterations in the pattern of gene expression are suggestive of a dynamic equilibrium between synthesis and degradation, whereby cell adhesion molecules are predominantly up-regulated to facilitate cellular reorientation in response to their altered functional environment.

CLINICAL RELEVANCE

These data might have future applications, including the identification of markers for early diagnosis, targets for drug design, and indicators for treatment responsiveness and prognosis.

Pathophysiology of the diabetic kidney

Diabetes mellitus contributes greatly to morbidity, mortality, and overall health care costs. In major part, these outcomes derive from the high incidence of progressive kidney dysfunction in patients with diabetes making diabetic nephropathy a leading cause of end-stage renal disease. A better understanding of the molecular mechanism involved and of the early dysfunctions observed in the diabetic kidney may permit the development of new strategies to prevent diabetic nephropathy. Here we review the pathophysiological changes that occur in the kidney in response to hyperglycemia, including the cellular responses to high glucose and the responses in vascular, glomerular, podocyte, and tubular function. The molecular basis, characteristics, and consequences of the unique growth phenotypes observed in the diabetic kidney, including glomerular structures and tubular segments, are outlined. We delineate mechanisms of early diabetic glomerular hyperfiltration including primary vascular events as well as the primary role of tubular growth, hyperreabsorption, and tubuloglomerular communication as part of a "tubulocentric" concept of early diabetic kidney function. The latter also explains the "salt paradox" of the early diabetic kidney, that is, a unique and inverse relationship between glomerular filtration rate and dietary salt intake. The mechanisms and consequences of the intrarenal activation of the renin-angiotensin system and of diabetes-induced tubular glycogen accumulation are discussed. Moreover, we aim to link the changes that occur early in the diabetic kidney including the growth phenotype, oxidative stress, hypoxia, and formation of advanced glycation end products to mechanisms involved in progressive kidney disease.

Increased cyclooxygenase-2 expression and prostaglandin E2 production in pressurized renal medullary interstitial cells

Renal medullary interstitial cells (RMICs) are subjected to osmotic, inflammatory, and mechanical stress as a result of ureteral obstruction, which may influence the expression and activity of cyclooxygenase type 2 (COX-2). Inflammatory stress strongly induces COX-2 in RMICs. To explore the direct effect of mechanical stress on the expression and activity of COX-2, cultured RMICs were subjected to varying amounts of pressure over time using a novel pressure apparatus. COX-2 mRNA and protein were induced following 60 mmHg pressure for 4 and 6 h, respectively. COX-1 mRNA and protein levels were unchanged. PGE(2) production in the RMICs was increased when cells were subjected to 60 mmHg pressure for 6 h and was prevented by a selective COX-2 inhibitor. Pharmacological inhibition indicating that pressure-induced COX-2 expression is dependent on p38 MAPK and biochemical knockdown experiments showed that NF-kappaB might be involved in the COX-2 induction by pressure. Importantly, terminal deoxyneucleotidyl transferase-mediated dUTP nick-end labeling and methylthiazoletetetrazolium assay studies showed that subjecting RMICs to 60 mmHg pressure for 6 h does not affect cell viability, apoptosis, and proliferation. To further examine the regulation of COX-2 in vivo, rats were subjected to unilateral ureteral obstruction (UUO) for 6 and 12 h. COX-2 mRNA and protein level was increased in inner medulla in response to 6- and 12-h UUO. COX-1 mRNA and protein levels were unchanged. These findings suggest that in vitro application of pressure recapitulates the effects on RMICs found after in vivo UUO. This directly implicates pressure as an important regulator of renal COX-2 expression.

Early growth response protein 1 acts as an activator of SOX18 promoter

Sex-determining region Y box 18 (Sox18/SOX18) gene is an important regulator of vascular development playing a role in endothelial cell specification or differentiation, angiogenesis and atherogenesis. The aim of this study was to perform comprehensive functional characterization of the human SOX18 promoter, including determination of transcription start point (tsp) and identification of control elements involved in the regulation of SOX18 gene expression, with an emphasis on angiogenesis-related transcription factors. Analyses were performed in HeLa cells, representing a tumor cell line, and in EA.hy926 cells used as an endothelial model system. We have determined unique tsp of SOX18 gene, located 172 nucleotides upstream from ATG codon. Further, we have shown that SOX18 promoter region, -726 to -89 bp relative to tsp, contains positive cis-regulatory element(s) that stimulates SOX18 promoter activity, while region -89 to+166 represents the minimal promoter. Within this region we have recognized the presence of essential element(s), positioned from -89 to +29, which harbors cluster of three putative early growth response 1 (EGR1) binding sites. By in vitro binding assays and functional analyses we have shown that these three putative binding sites are functionally relevant and sufficient for EGR1-induced SOX18 transcription. Mutations of these binding sites significantly impaired activity of the SOX18 promoter, particularly in EA.hy926 cells, indicating the importance of these regulatory elements for SOX18 promoter activity in endothelial setting. By data presented in this study, we have established SOX18 as a novel target gene regulated by EGR1 transcription factor, thus providing the first functional link between two transcription factors previously shown to be involved in the control of angiogenesis.

Differential effects of shear stress and cyclic strain on Sp1 phosphorylation by protein kinase Czeta modulates membrane type 1-matrix metalloproteinase in endothelial cells

Membrane type 1-matrix metalloproteinase (MT1-MMP) plays a key role in extracellular matrix remodeling, endothelial cell (EC) migration, and angiogenesis. Whereas cyclic strain (CS) increases MT1-MMP expression, shear stress (SS) decreases MT1-MMP expression. The aim of this study was to determine if changes in levels of Sp1 phosphorylation induced by protein kinase Czeta (PKCzeta) in ECs exposed to SS but not CS are important for MT1-MMP expression. The results showed that SS increased Sp1 phosphorylation, which could be inhibited by pretreatment with PKCzeta inhibitors. In the presence of PKCzeta inhibitors, the SS-mediated decrease in MT1-MMP protein expression was also abolished. These data demonstrate that increased affinity of Sp1 for MT1-MMP's promoter site occurs as a consequence of PKCzeta-induced phosphorylation of Sp1 in response to SS, increasing Sp1 binding affinity for the promoter site, preventing Egr-1 binding, and consequently decreasing MT1-MMP expression.

Mechanical stretch promotes proliferation of rat bone marrow mesenchymal stem cells

Tissues and cells in the body are continuously exposed to a complex mechanical environment. Mechanical stimulations are critical to morphological, developmental and functional states of living cells, and the fashion of the mechanical stimulation applied to the cells is supposed to be extremely important for the induced cell response and function. In this study, we investigated whether mechanical stretch regulates and promotes proliferation of rat bone marrow mesenchymal stem cells (rMSCs) in vitro. rMSCs from rat bone marrow were isolated, purified and subjected to a cyclic equiaxial stretch treatment, and then MTT assay was adopted and expression of c-fos gene was measured by RT-PCR to access cell proliferation. The results demonstrated that OD values of rMSCs increased in a time-dependent and magnitude-dependent manner after exposure to 1 Hz stretch within 15-60 min and 2-8% strain. Expression of c-fos gene in rMSCs subjected to stretch treatment (1 Hz, 8% strain and 60 min) is significantly higher than that of unstimulated control cells. These results suggest that mechanical stretch plays an important role in regulating the cell growth and proliferation, and an appropriate mechanical stretch treatment could promote proliferating capacity of rMSCs.

Exacerbation of albuminuria and renal fibrosis in subtotal renal ablation model of adiponectin-knockout mice

OBJECTIVE

Obesity is recognized increasingly as a major risk factor for kidney disease. We reported previously that plasma adiponectin levels were decreased in obesity, and that adiponectin had defensive properties against type 2 diabetes and hypertension. In this study, we investigated the role of adiponectin for kidney disease in a subtotal nephrectomized mouse model.

METHODS AND RESULTS

Subtotal (5/6) nephrectomy was performed in adiponectin-knockout (APN-KO) and wild-type (WT) mice. The procedure resulted in significant accumulation of adiponectin in glomeruli and interstitium in the remnant kidney. Urinary albumin excretion, glomerular hypertrophy, and tubulointerstitial fibrosis were significantly worse in APN-KO mice compared with WT mice. Intraglomerular macrophage infiltration and mRNA levels of vascular cell adhesion molecule (VCAM)-1, MCP-1, tumor necrosis factor (TNF)-alpha, transforming growth factor (TGF)-beta1, collagen type I/III, and NADPH oxidase components were significantly increased in KO mice compared with WT mice. Treatment of APN-KO mice with adenovirus-mediated adiponectin resulted in amelioration of albuminuria, glomerular hypertrophy, and tubulointerstitial fibrosis and reduced the elevated levels of VCAM-1, MCP-1, TNF-alpha, TGF-beta1, collagen type I/III, and NADPH oxidase components mRNAs to the same levels as those in WT mice.

CONCLUSIONS

Adiponectin accumulates to the injured kidney, and prevents glomerular and tubulointerstitial injury through modulating inflammation and oxidative stress.

Cyclic straining of cell-seeded synthetic ligament scaffolds: development of apparatus and methodology

Cyclic tensile strains acting along a ligament implant are known to stimulate cells that colonize it to proliferate and to synthesize an extracellular matrix (ECM), which will then remodel and form a new ligament structure. However, this process of tissue induction is poorly understood. As a first step toward elucidating this process, we aimed to investigate the effect of cyclic tensile strain on the proliferation of, and possible ECM synthesis by, cells colonizing ligament scaffolds. Because there was no commercially available apparatus to undertake such investigation the objectives of this study were to develop an apparatus for the application of cyclic tensile strains on cell-seeded synthetic ligament scaffolds and to develop and validate (through preliminary data obtained using the apparatus) methodology for studying the effect of cyclic strain on cell proliferation. We designed a multi-station test apparatus that operated inside an incubator. It allowed the application of tensile cyclic strains of between 0.5% and 5% at a frequency of 1 Hz on cell-seeded polyester ligament scaffolds immersed in culture medium. Test stations with windows in their bases could be easily de-coupled from the apparatus. This allowed monitoring of cell proliferation and morphology, with inverted light microscopy, through the transparent glass bases of the culture wells. Preliminary experiments lasting for 1 day or 9 weeks examined the effect of selected aspects of the cyclic strain on proliferation of cells seeded onto ligament scaffolds. Tests lasting for 1 day showed that the application of cyclic tensile strain of 5% for 4 h increased cell proliferation 24% above that observed in unstrained controls (p < .05). Scanning electron microscopy data from tests lasting for 9 weeks demonstrated further the dependency of cell proliferation and possible ECM synthesis on the magnitude of the strain. The larger the amplitude, the greater was the coverage of the scaffold with cells and ECM. Transmission electron microscopy of the ECM observed at 9 weeks showed evidence of collagen fibrils aligned in the direction of load in strained scaffolds, whereas the tissue on the control scaffolds was random.

Losartan-hydrochlorothiazide association promotes lasting blood pressure normalization and completely arrests long-term renal injury in the 5/6 ablation model

The possible long-term renoprotective effects of treatment with thiazides, either as monotherapy or associated with renin-angiotensin suppressors, have not been assessed. We investigated the effect of hydrochlorothiazide (H), alone or combined with losartan (L), in the 5/6 renal ablation model (Nx). Adult male Munich-Wistar rats underwent Nx, remaining untreated for 1 mo. At this time, functional and morphological studies were performed in 21 rats (group Nx(pre)). The remaining rats were distributed among groups: Nx, no treatment; Nx+L, receiving L, 50 mg kg(-1) day(-1) in the drinking water; Nx+H, receiving H, 6 mg kg(-1) day(-1) in drinking water; and Nx+L+H, receiving both L and H as described. At 30 days of treatment, systemic and glomerular pressures were markedly elevated in group Nx. Both H and L attenuated hypertension, whereas combined L+H treatment completely normalized both pressures. Eight months after Nx, mortality approached 70% in untreated rats, whereas severe albuminuria, hypertension, glomerulosclerosis, and interstitial expansion were observed. H and L attenuated, but did not prevent, mortality, hypertension, and renal injury. Combined L+H treatment completely prevented mortality, normalized albuminuria and blood pressure, and arrested renal injury at levels found 1 mo after ablation, despite the unusually long period of observation. Combined L+H treatment may represent an effective therapeutic alternative to prevent progression of chronic nephropathies.

Protein kinase C beta/early growth response-1 pathway: a key player in ischemia, atherosclerosis, and restenosis

Atherosclerosis, restenosis, and the consequences of ischemia are the major causes of morbidity and mortality worldwide. Elucidation of key contributing pathways in animal models of ischemia-reperfusion injury, atherosclerosis, and restenosis consequent to vascular injury may lead to great interest in determining if blocking these pathways could prevent vascular disease in human subjects. This review details the evidence that the protein kinase C (PKC) beta/early growth response-1 axis plays a central role in the response to both acute and chronic vascular stresses in animal models and also indicates the clinical implications of a specific inhibitor of PKCbeta, ruboxistaurin (LY333531).

Short-term nitric oxide inhibition induces progressive nephropathy after regression of initial renal injury

Chronic nitric oxide (NO) inhibition and salt overload (HS) promote severe hypertension and renal injury, which regress quickly, although not completely, on treatment withdrawal. We investigated whether renal function and structure remain stable 6 mo after cessation of these treatments. Adult male Munich-Wistar rats were distributed among three groups: HS, receiving 3.1% Na diet; HS+N, receiving HS and the NO inhibitor N(omega)-nitro-l-arginine methyl ester (l-NAME; 30 mg.kg(-1).day(-1) orally); and HS+N+L, receiving HS+N and the ANG II blocker losartan (L; 50 mg.kg(-1).day(-1) orally). In studies performed after 20 days of treatment (protocol 1), HS+N rats exhibited severe glomerular and systemic hypertension, massive albuminuria, glomerular and interstitial injury, and infiltration by macrophages and cells expressing ANG II. These abnormalities were largely prevented in the HS+N+L group. A second cohort (protocol 2) received HS+N for 20 days, followed by a conventional (0.5% Na) diet and no l-NAME treatment during the subsequent 30 days. At this time, systemic and glomerular pressure, along with parameters of renal injury and inflammation, were still higher than in HS or HS+N+L rats, although differences were much smaller than in protocol 1. Six months after 20-day l-NAME/salt overload treatment was ceased (protocol 3), severe albuminuria, hypertension, and renal injury developed in HS+N rats. Again, losartan prevented most of these changes. We conclude 1) short-term HS+N treatment triggers the autonomous development of progressive glomerulosclerosis; 2) this process may involve activation of the AT(1) receptor; and 3) temporary HS+N treatment may represent a new model of slowly progressive chronic nephropathy.

Stretch-induced myoblast proliferation is dependent on the COX2 pathway

Skeletal muscle increases in size due to weight bearing loads or passive stretch. This growth response is dependent in part upon myoblast proliferation. Although skeletal muscles are responsive to mechanical forces, the effect on myoblast proliferation remains unknown. To investigate the effects of mechanical stretch on myoblast proliferation, primary myoblasts isolated from Balb/c mice were subjected to 25% cyclical uniaxial stretch for 5 h at 0.5 Hz. Stretch stimulated myoblast proliferation by 32% and increased cell number by 41% 24 and 48 h after stretch, respectively. COX2 mRNA increased 3.5-fold immediately poststretch. Prostaglandin E2 and F2alpha increased 2.4- and 1.6-fold 6 h after stretch, respectively. Because COX2 has been implicated in regulating muscle growth and regeneration, we hypothesized that stretched myoblasts may proliferate via a COX2-dependent mechanism. We employed two different models to disrupt COX2 activity: (1) treatment with a COX2-selective drug, and (2) transgenic mice null for COX2. Treating myoblasts with a COX2-specific inhibitor blocked stretch-induced proliferation. Likewise, stretched COX2-/- myoblasts failed to proliferate compared to controls. However, supplementing stretched, COX2-/- myoblasts with prostaglandin E2 or fluprostenol increased proliferation. These data suggest that the COX2 pathway is critical for myoblast proliferation in response to stretch.

An extremely high dose of losartan affords superior renoprotection in the remnant model

BACKGROUND

Rats subjected to 5/6 renal ablation (NX) exhibit large renal amounts of angiotensin II (Ang II) and of its main receptor, AT-1R. At previously used doses, AT-1R blockers (ARB) offer only partial renal protection. A possible explanation for this limited effect is that these doses are insufficient to block most of the abnormally expressed AT-1R. We investigated whether extremely high doses of the ARB, losartan (L), offer better protection than conventional doses in the NX model.

METHODS

Thirty days after NX, tail-cuff pressure (TCP), albuminuria (U(alb)V, mg/day), glomerulosclerosis index (GSI), fractional interstitial area (%INT), and macrophage infiltration (MO) were evaluated in a separate group (NX(pre)). The remaining rats were then subdivided among 4 groups: NX+V, receiving vehicle; NX+L50, treated with L, at the "conventional" dose of 50 mg/kg/day; NX+L500, receiving L, 500 mg/kg/day; and NX+HH, receiving hydrochlorothiazide and hydralazine to lower blood pressure to a similar extent as in group L500.

RESULTS

After a month of treatment, blood pressure and renal vascular resistance were lowest in group L500. Glomerular pressure was lowered by a similar extent by L50 and L500, while GFR was similar among groups. U(alb)V, TCP, and renal injury were only partially reduced by L50 120 days after renal ablation. By contrast, L500 arrested renal inflammation and glomerular/interstitial injury at pretreatment levels, and promoted regression of hypertension and U(alb)V, causing no apparent untoward effects.

CONCLUSION

The renal protection afforded by ARB in NX is dose dependent. Maximal protection may require doses several fold higher than those currently employed.

Effect of cyclic tensile strain on proliferation of synovial cells seeded onto synthetic ligament scaffolds--an in vitro simulation

OBJECTIVE

Cyclic tensile strain is pivotal to the remodeling of tissue induced in implants used in reconstruction of anterior cruciate ligaments whether these implants were of autogenous tissues or synthetic materials. However, this process is poorly understood. The objective of this study was to investigate the short and medium-term effect of cyclic tensile strain on the proliferation of synovial cells seeded on ligament scaffolds.

METHODS

206 ligament scaffolds made from plasma treated polyester with an ultimate tensile strength of 320 N were used in this study. Synovial cells were obtained from the metatarsophalangeal joints of 2 years old bovines. After expansion of these, they were seeded onto the scaffolds which were subjected, in a specialized apparatus, to a cyclic tensile strain of 4.5% at a frequency of 1 Hz. Initially, the strain was applied for a period of 4 h, which was subsequently reduced in further experiments to 1.0 h and 0.5 h. In further tests, strains of approximately 2.5%, 1% and 0.6% were applied for 1 h at the same frequency. In all the above tests, which were short-term tests (lasting for approximately 1 day), cell proliferation was investigated by the uptake of thymidine with which cells were labeled according to prescribed protocols. Cell proliferation was further examined with light microscopy after 5 weeks and the degree of fill of inter-yarn spaces was quantified for strain amplitudes of 1, 2.5 and 4.5%. Equal number of control (not strained) specimens was used at each time point.

RESULTS

In the 1-day experiments, for all durations of application of cyclic strain (exercise), the effect of strain on cell proliferation was inhibitory during the period of exercise and up to 18 h from its commencement, but was stimulatory 22-24 h afterwards. This stimulatory effect was maximal at an exercise period of 1 h. The study has also shown that there is a threshold for the amplitude of the strain (1%), at and below which cell proliferation was not significantly different from that observed in control specimens (P was <0.05 for all data). After 5 weeks of cyclic strain application, it was shown that the higher the amplitude of strain the larger was the area occupied by cells of the intra-yarn space.

CONCLUSION

Both the amplitude of cyclic strain and duration of its application affect the proliferation of synovial cells seeded on ligament scaffolds. The data should be useful when selecting or designing an implant, and when prescribing a postoperative exercise regime.

Activation of mesangial cell MAPK in responseto homocysteine

BACKGROUND

Alteration in mesangial cell function is central to the progression of glomerular disease in numerous models of chronic renal failure (CRF). Animal models of chronic glomerular disease are characterized by mesangial cell proliferation and elaboration of extracellular matrix protein (ECM), resulting in glomerulosclerosis. Elevated plasma levels of homocysteine (Hcy) are seen in both animal models and humans with CRF, and have been proposed to contribute to the high prevalence of vascular disease in this group. Some of the pathogenetic effects of Hcy are thought to be mediated via the induction of endoplasmic reticulum stress. Thus, Hcy effects on mesangial cells could contribute to the progression of CRF. Previous work has shown Hcy- mediated induction of Erk mitogen-activated protein kinase (MAPK) in vascular smooth muscle cells (VSMCs). Erk induces increases in activator protein-1 (AP-1) transcription factor activity which may augment mesangial cell proliferation and ECM protein production. Consequently, we studied the effect of Hcy on mesangial cell Erk signaling.

METHODS

Mesangial cells were exposed to Hcy after 24 hours of serum starvation and Erk activity assessed. Nuclear translocation of phospho-Erk was visualized by confocal microscopy. AP-1 nuclear protein binding was measured in response to Hcy by mobility shift assay. Hcy-induced mesangial cell calcium flux was measured in Fura-2 loaded cells. Mesangial cell DNA synthesis in response to Hcy was assessed by [3H]-thymidine incorporation and proliferation by Western blotting for proliferating cell nuclear antigen (PCNA). Expression of endoplasmic reticulum stress response genes were determined by Northern and Western analysis.

RESULTS

Hcy led to an increase in Erk activity that was maximal at 50 micromol/L and 20 minutes of treatment. Subsequent experiments used this concentration and time point. Erk activity in response to Hcy was insensitive to n-acetylcysteine and catalase, indicating oxidative stress did not play a role. However, Hcy50 micromol/L induced a brief increase in intracellular mesangial cell calcium within 5 minutes, and the calcium ionophores A23187 and ionomycin increased Erk activity while chelation of intracellular calcium with BAPTA-AM abrogated the Erk response to Hcy. Confocal microscopy of activated Erk nuclear translocation mirrored these results as did mesangial cell nuclear protein binding to AP-1 consensus sequences. Hcy- induced increases in thymidine incorporation and PCNA expression at 24 hours were Erk dependent. The expression of endoplasmic reticulum stress response genes was significantly elevated by Hcy in an Erk-dependent manner.

CONCLUSION

Hcy increases Erk activity in mesangial cells via a calcium-dependent mechanism, resulting in increased AP-1 nuclear protein binding, cell DNA synthesis and proliferation and induction of endoplasmic reticulum stress. These observations suggest potential mechanisms by which Hcy may contribute to progressive glomerular injury.

p38 MAP kinase mediates mechanically induced COX-2 and PG EP4receptor expression in podocytes: implications for the actin cytoskeleton

A dynamic cytoskeleton allows podocytes to withstand significant mechanical stress on elevation of intraglomerular capillary pressure (Pgc). However, vasoactive hormones, such as prostaglandin E2(PGE2), may challenge the integrity of the actin cytoskeleton, alter podocyte morphology, and compromise glomerular permeability. PGE2synthesis correlates with the onset of proteinuria and increased Pgcfollowing reduced nephron mass. We investigated the interplay among mechanical stress, cyclooxygenase (COX), E-prostanoid (EP) receptor expression, and the actin cytoskeleton, using an in vitro model of cell stretch. Immortalized mouse podocytes grown on flexible silicone membranes were cyclically stretched (5% elongation, 0.5 Hz) for 2 h. EP4and COX-2 mRNA increased three- and sevenfold above nonstretched controls, whereas EP1and COX-1 levels were unchanged. Six hours of stretch resulted in a threefold increase in PGE2-stimulated cAMP accumulation, a measure of EP4receptor function, and an increase in COX-2 protein. The stretch-induced effects on COX-2/EP4expression and EP4-induced cAMP production were attributable to p38 MAP kinase, as blockade of this pathway, but not of ERK or JNK, abrogated the response. These stretch-induced changes in expression were transcriptionally dependent as they were actinomycin D sensitive. Finally, we investigated the influence of enhanced EP4signaling on the actin cytoskeleton. Addition of PGE2resulted in actin filament depolymerization observable only in stretched cells. Our results indicate that key components of the eicosanoid pathway are upregulated by mechanically stimulated p38 MAP kinase in podocytes. Enhanced EP4receptor signaling may undermine podocyte cytoskeletal dynamics and thereby compromise filtration barrier function under conditions of increased Pgc.

Renal expression of COX-2, ANG II, and AT1 receptor in remnant kidney: strong renoprotection by therapy with losartan and a nonsteroidal anti-inflammatory

Chronic renal injury can be mediated by angiotensin II (ANG II) and prostanoids through hemodynamic and inflammatory mechanisms and attenuated by individual suppression of these mediators. In rats with (5/6) renal ablation (Nx), we investigated 1) the intrarenal distribution of COX-2, ANG II, and the AT(1) receptor (AT(1)R); 2) the renoprotective and antiinflammatory effects of an association between the AT(1)R blocker, losartan (Los), and the gastric sparing anti-inflammatory nitroflurbiprofen (NOF). Adult male Munich-Wistar rats underwent Nx or sham operation (S), remaining untreated for 30 days, after which renal structure was examined in 12 Nx rats (Nx(pre)). The remaining rats were followed during an additional 90 days, distributed among 4 treatment groups: Nx(V) (vehicle), Nx(Los) (Los), Nx(NOF) (NOF), and Nx(Los/NOF) (Los/NOF). Nx(pre) rats exhibited marked albuminuria, hypertension, glomerulosclerosis, interstitial expansion, and macrophage infiltration, accompanied by abnormal glomerular, vascular, and interstitial COX-2 expression. ANG II appeared in interstitial cells, in contrast to S, in which ANG II was virtually confined to afferent arterioles. Intrarenal AT(1)R distribution shifted from mostly tubular in S to predominantly interstitial in Nx(pre). All these changes were aggravated at 120 days and attenuated by Los and NOF monotherapies. Los/NOF treatment arrested renal structural injury and ANG II expression and reversed hypertension, albuminuria, and renal inflammation. In conclusion, abnormal expression of COX-2, ANG II, and AT(1)R may be key to development of renal injury in Nx. Concomitant COX-2 inhibition and AT(1)R blockade arrested renal injury and may represent a useful strategy in the treatment of chronic nephropathies.

Nitric Oxide Inhibits Stretch-Induced MAPK Activation in Mesangial Cells Through RhoA Inactivation

ABSTRACT. Glomerular capillary hypertension is an important determinant of glomerulosclerosis in rats with subtotal renal ablation. Dietary supplementation withl-arginine increases renal nitric oxide (NO) production and limits glomerular injury in this model, and early benefits are seen without altered glomerular capillary pressure. In anin vitromodel of hemodynamically mediated signaling, the authors have reported that subjecting MC to cyclic stretch/relaxation activates the mitogen-activated protein kinase p42/44 (Erk) cascade and that NO and cyclic GMP abrogate stretch-induced Erk activation by inducing actin cytoskeletal disassembly. The actin cytoskeleton is regulated by the Rho family of GTPases, including RhoA; therefore, the authors examined the role of RhoA in stretch-induced Erk activation and as an NO target. In primary rat MC subjected to cyclic mechanical strain, RhoA activity was maximally increased (2.4-fold) after 1 min of stretch, and Erk activation temporally followed. The Rho-kinase inhibitor Y-27632 attenuated Erk activation in a dose-dependent manner and prevented stretch-induced actin stress fiber formation. The NO donors S-nitroso-N-acetylpenicillamine and cGMP both inhibited stretch-induced RhoA and Erk activation and stress fiber formation. Infection of MC with the RhoA mutant RhoA-Ala188, which is resistant to NO-dependent phosphorylation, abrogated the effects of NO and cGMP on stretch-induced Erk activation and stress fiber formation. The authors conclude that the early activation of RhoA is essential for stretch-induced actin stress fiber formation and Erk activation in MC, events which are prevented by NO and cGMP through their action on RhoA. Inhibition of RhoA may thus be a new approach to the prevention of hemodynamically mediated glomerular injury. E-mail: krepinj@mcmaster.ca

Synergistic effects of nitric oxide and prostaglandins on renal escape from vasopressin-induced antidiuresis

Recent results from our laboratories indicate that renal escape from AVP-induced antidiuresis is accompanied by marked downregulation of kidney aquaporin-2 (AQP2) and AVP V2 receptors. The present studies evaluated the effect of nitric oxide (NO) and PG synthesis blockade on escape from antidiuresis. dDAVP-infused rats were water loaded (WL) for 5 days. l-NAME, an NO synthesis inhibitor, or diclofenac, a cyclooxygenase inhibitor, was infused subcutaneously beginning 1 day before WL. As early as 2 days after WL, urine volume increased and urine osmolality decreased, indicating the onset of escape. Endogenous NO synthesis, measured as urinary NO2 + NO3 excretion, was significantly increased in the WL group compared with the non-WL controls during all 5 days of WL. l-NAME (20 mg. kg(-1). day(-1)) markedly decreased urine volume on days 4 and 5 of WL, indicating inhibition of the escape phenomenon. Kidney AQP2 protein was significantly increased by this dose of l-NAME as well. A lower dose of l-NAME (10 mg. kg(-1). day(-1)) or diclofenac (2.5 mg. kg(-1). day(-1)) did not significantly affect the escape phenomenon by itself, but the combination of l-NAME and diclofenac showed a marked inhibitory effect on the escape phenomenon, which was also accompanied by a significant increase in kidney AQP2 expression. These results therefore suggest that renal NO and PG both play important roles in escape from AVP-induced antidiuresis by acting synergistically to downregulate kidney AQP2 expression.

Effects of cyclooxygenase-2 (COX-2) inhibition on plasma and renal renin in diabetes

COX-2-derived prostaglandins (PG) have been suggested to be important modulators of renin release and expression. However, the role of COX-2 in various high-renin states is still being debated. In the present studies we explored the role of COX-2-derived PG on basal and angiotensin converting enzyme inhibitor (ACEI)-stimulated plasma and renal renin concentrations (PRC and RRC, RIA), and mRNA expression (RmRNA, RNAse protection assay) in experimental diabetes (DM). Groups of moderately hyperglycemic (n = 5, approximately 350 mg/dl), streptozotocin-diabetic rats (D) after 3 weeks of DM were treated with a selective COX-2 inhibitor, MF-tricyclic (MF, 5 mg/kg/day for 10 days in food), the combination of MF and the ACEI enalapril (3 mg/kg/day), enalapril alone, or vehicle (MF-free chow), for 10 days. Non-diabetic control rats, fed MF-free chow, were also studied. All groups of diabetic rats demonstrated similar glycemic control. Treatment with ACEI resulted in significant elevations in PRC, RRC and RmRNA as compared to non-ACEI treated groups of diabetic and control rats. A similar rise in these parameters was observed in the rats treated with the combination of ACEI and MF. Furthermore, in diabetic rats treated with MF alone, PRC and RRC were similar to vehicle-treated animals. Diabetic rats demonstrated higher urinary PG as compared to controls. MF-treated rats demonstrated a significant reduction in urinary PG excretion. In summary, selective COX-2 inhibition influenced neither basal renin status nor ACEI-induced renin release and expression in diabetic rats. These findings do not support a significant role for COX-2 in mediating renin status in diabetes.

Pulmonary epithelial liquid absorption, expressed in relation to alveolar surface area, is reduced in fetal lambs following in utero tracheal occlusion

We examined the effect of accelerated lung growth, induced by in utero tracheal occlusion (TO), on lung liquid uptake in near-term fetal sheep. In utero TO was performed in five fetal sheep at 110 days of gestation (term, approximately 145 days); six SHAM operated fetuses served as controls. The rate of liquid movement across the pulmonary epithelium was measured, using a previously established technique, in anesthetized fetal sheep between 133-137 days of gestation during a 2-hr adrenaline infusion (0.50 microg/min/kg, I.V.) and while lung luminal pressure was maintained at 5 mmHg. The rate of fetal lung liquid uptake was linear in all fetuses (mean r(2) < 0.97, n = 11). Mean values of lung liquid uptake expressed in relation to dry lung weight and luminal surface area of the right lung were significantly lower in TO fetuses (1.8 +/- 0.3 mL/hr/g and 1.0 +/- 0.2 mL/hr/m(2)) than in SHAM fetuses (2.6 +/- 0.2 mL/hr/g and 1.8 +/- 0.1 mL/hr/m(2)); surface area of the right lung was 140% greater in TO fetuses than in SHAM fetuses. There was a linear relationship between lung liquid uptake and pulmonary epithelial surface area in SHAM animals, but not in TO fetuses. We hypothesize that loss of alveolar epithelial type-II cells induced by increased levels of fetal lung expansion may impair alveolar liquid clearance in the perinatal period.

Molecular control of capillary growth in skeletal muscle

Angiogenesis, the growth of new capillaries, enhances the oxygen delivery capacity of an existing vascular network. This adaptation is a well-documented occurrence in exercising skeletal muscle. The purpose of this review is to summarize our current understanding of the various stimuli that are involved in the initiation of capillary growth in skeletal muscle. The roles of humoral and mechanical signals in the cellular regulation of several key angiogenic players, vascular endothelial cell growth factor and matrix metalloproteinases, will be discussed. Evidence will be presented supporting the existence of angiogenesis processes that are distinct from the "classically" defined process. Determining how specific angiogenic stimuli can initiate unique patterns of capillary growth will provide insight into the complex task of developing effective pro-angiogenic therapies.

Cyclic strain stimulates early growth response gene product 1-mediated expression of membrane type 1 matrix metalloproteinase in endothelium

SUMMARY

Matrix metalloproteinases (MMPs) are hypothesized to be involved in the processes of endothelial cell (EC) migration and matrix remodeling during angiogenesis. Although hemodynamic forces (such as blood pressure, wall tension, and shear stress) are considered to be strong stimuli for angiogenesis, the role of hemodynamic forces on the regulation of MMPs including membrane type 1 matrix metalloproteinase (MT1-MMP) has not been fully elucidated. To study this, rat microvascular EC were exposed to 60 cycles/minute of 24% maximum strain for up to 24 hours. MT1-MMP mRNA and protein increased in a time-dependent manner through 24 hours of exposure to cyclic strain. Cyclic strain induced early growth response gene product (Egr-1) mRNA and protein within 1 hour. A specific nucleoprotein complex was formed when an oligonucleotide containing binding sites for Sp1 and Egr-1 was incubated with nuclear extracts from EC exposed to 1 hour of cyclic strain. Antibodies to Egr-1 completely supershifted this complex. Increased binding of Egr-1 by cyclic strain to the MT1-MMP promoter correlated with enhanced transcriptional activity. These results suggest that cyclic strain up-regulates the Egr-1-mediated expression of MT1-MMP in rat microvascular EC, emphasizing the importance of hemodynamic forces in the regulation of MT1-MMP in vivo.

Immunohistochemical study of myofibroblasts in normal colonic mucosa, hyperplastic polyps, and adenomatous colorectal polyps

CONTEXT

Myofibroblasts are distinct cells with characteristics of both smooth muscle cells and fibroblasts. Through their ability to secrete cytokines, chemokines, prostaglandins, growth factors, and matrix components, they are thought to play critical roles in inflammation, growth, repair, and neoplasia.

OBJECTIVE

The goal of this study was to identify the distinct cell populations of the lamina propria of normal colon and colorectal polyps.

DESIGN

We studied the expression of alpha-smooth muscle actin (alphaSMA), smooth muscle myosin (SMM), desmin, vimentin, and c-kit by intestinal mesenchymal (stromal) cells in the normal colonic mucosa (n = 5), as well as in hyperplastic polyps (n = 5), sporadic colorectal adenomas (n = 47), and adenomas from patients with familial polyposis (n = 36).

RESULTS

In the normal colonic mucosa, the pericryptal stromal cells were alphaSMA+, SMM+, desmin-, and vimentin+, defining them as myofibroblasts. In contrast, cells of the muscularis mucosae were alphaSMA+, SMM+, desmin+, and vimentin-, defining them as smooth muscle cells. alpha-Smooth muscle actin also highlighted direct connections between the muscularis mucosae and the pericryptal myofibroblasts, and vimentin immunostaining showed a network of connections between the alphaSMA+ pericryptal myofibroblasts and the alphaSMA- fibroblasts in the interstitium. In all hyperplastic polyps and adenomatous polyps, the interstitial stromal cells (fibroblasts) now also express alphaSMA and form a syncytium of alphaSMA+ networklike connections throughout the lamina propria. Stromal cells of sporadic adenomas demonstrated the same immunohistochemical staining characteristics displayed by adenomas from patients with familial polyposis and by hyperplastic polyps. Conclusions.-These findings indicate that in normal colon, alphaSMA- fibroblasts are the predominant cell type in the lamina propria. However, the pericryptal (subepithelial) stromal cells are a distinct cell type (alphaSMA+ myofibroblast) that is immunophenotypically different from muscularis mucosae smooth muscle cells and are connected to the interstitial, nonpericryptal fibroblasts with which they exist as a network throughout the lamina propria of the normal colon. Furthermore, in both hyperplastic and neoplastic polyps, there are changes in nonpericryptal fibroblasts from vimentin+, alphaSMA-, and SMM- to vimentin+, alphaSMA+, and SMM+; thus, the interstitial fibroblasts are replaced by myofibroblasts. The factors that cause these changes and the origin of the myofibroblasts need to be determined to clarify the biology of colorectal tumorigenesis.

Activation of extracellular signal-regulated kinases is essential for pressure-induced proliferation of vascular smooth muscle cells

In hypertension, increased transmural pressure directly influences vascular smooth muscle cells and causes cell proliferation. However, the mechanisms of transmural pressure-induced proliferation of vascular smooth muscle cells are unknown. We investigated the role of various protein kinases in pressure-induced proliferation of vascular smooth muscle cells. Pressure was applied to quiescent rat vascular smooth muscle cells in culture by compressed helium gas in a loading apparatus. Pressure application increased [3H]thymidine incorporation in a time- and pressure-dependent manner and significantly increased the cell number. The pressor response was significantly suppressed by various protein kinase inhibitors for protein kinase C (bisindolylmaleimide I), tyrosine kinase (genistein), extracellular signal-regulated kinase kinase (PD98059; 2'-amino-3'-methoxyflavone) and p38 mitogen-activated protein kinases (MAPK) (SB203580; 4-(4-fluorophenyl)-2-(4-methylsulfinylphenyl)-5-(4-pyridyl)1H-imidazole). Pressure rapidly increased the phosphorylation and activity of extracellular signal-regulated kinases (ERK). Pressure also caused increment of phosphorylation level of p38 MAPK but not that of c-JUN N-terminal protein kinase (JNK). In ERK-deficient cells prepared by transfection of an antisense oligonucleotide for ERK, pressure-induced DNA synthesis was almost abolished. Our results suggest that activation of ERK is essential for pressure-induced DNA synthesis in rat vascular smooth muscle cells, in addition to activation of protein kinase C, tyrosine kinase and p38 MAPK. These processes could be involved in the pathogenesis of hypertension-related atherosclerosis.

Regulation of c-fos expression by static stretch in rat myometrial smooth muscle cells

OBJECTIVE

We investigated whether mechanical stretch stimulates expression of the immediate early gene c-fos messenger RNA in rat myometrial smooth muscle cells.

STUDY DESIGN

Freshly isolated myometrial smooth muscle cells (from virgin rats) were plated on flexible culture plates that were coated with either collagen I, laminin, elastin, or pronectin and were subjected to a static stretch with a computerized strain unit. Immunocytochemistry was used to define smooth muscle cell phenotype, and c-fos expression levels were assessed by Northern blotting.

RESULTS

Myometrial smooth muscle cells maintained their phenotype for at least 7 days in culture. Stretch induced a dramatic increase in levels of c-fos messenger RNA, which peaked after 30 minutes. Stimulation of c-fos gene expression was dependent on the degree of stretch (maximum induction at 25% elongation). Interestingly, as little as 1 minute of stretch was sufficient to induce maximal c-fos expression at 30 minutes. The most dramatic induction of c-fos was observed in smooth muscle cells that were stretched on collagen I-coated plates.

CONCLUSION

Myometrial smooth muscle cells can directly respond to mechanical stretch with a strength- and matrix component-dependent increase in c-fos messenger RNA. The time delay between the initial stimulus and the cumulative elevation of c-fos messenger RNA suggests a complex regulation from mechanoreception to c-fos gene expression.

Angiotensin II stimulates cyclooxygenase-2 mRNA expression in renal tissue from rats with kidney failure

We have shown increased cyclooxygenase-2 (COX-2) expression in rats with kidney failure. Increased angiotensin II concentration, hypertension, and renal mass reduction have been described during development of kidney failure. Thus we explored each of these mechanisms, because any one of them could be responsible for COX-2 induction. Kidney failure increased systolic blood pressure from 104 +/- 5 to 138 +/- 2 mmHg, urinary PGE(2) from 74 +/- 17 to 185 +/- 25 ng/24 h, and COX-2 expression from 0.06 +/- 0.04 to 0.17 +/- 0.03 arbitraty units (AU). Treatment of the rats with ramipril or losartan prevented the increase in blood pressure, urinary PGE(2), and COX-2 expression in the rats with kidney failure. Infusion of angiotensin II increased blood pressure from 101 +/- 6 to 132 +/- 6 mm Hg, urinary PGE(2) excretion from 62 +/- 15 to 155 +/- 17 ng/24 h, and COX-2 expression from 0.23 +/- 0.01 to 1.6 +/- 0.3 AU. When the angiotensin II-infused rats were treated with nitrendipine, blood pressure decreased from 132 +/- 6 to 115 +/- 2 mm Hg, and urinary PGE(2) excretion decreased from 152 +/- 18 to 97 +/- 12 ng/24 h, whereas COX-2 expression was 1.6 +/- 0.7 and 1.7 +/- 0.5 AU for rats with and without nitrendipine. Blood pressure of the rats with renal pole resection was similar to that in sham rats (97 +/- 7 and 91 +/- 4 mmHg, respectively), whereas COX-2 expression was increased in rats with renal pole resection, from 0.06 +/- 0.04 to 0.12 +/- 0.03 AU. We suggest that in kidney failure, the increase in angiotensin II concentration regulates COX-2 expression, thereby increasing prostaglandin synthesis, which contributes to the development of kidney failure.

17beta -Estradiol modulates mechanical strain-induced MAPK activation in mesangial cells

Gender is an important determinant of clinical outcome across a broad spectrum of kidney diseases, but the mechanism(s) responsible for the protective effect of female gender have not been fully elucidated. Remnant kidney glomerular injury is limited in female rats compared with male rats despite similar elevations in glomerular capillary pressure. In vitro, mechanical strain leads to the activation of p44/42 mitogen-activated kinase (p44/42 MAPK) and Jun N-terminal kinase/stress-activated protein kinase (SAPK) in glomerular mesangial cells (MC). Accordingly, we studied the effect of 17beta-estradiol on mechanical strain-induced signal transduction in MC. Exposure of MC to mechanical strain increased p44/42 MAPK activation (3-fold) and SAPK activation (2.5-fold), and kinase activation was inhibited by pretreatment with 17beta-estradiol (10(minus sign8) to 10(minus sign11) m) for 24 h in a dose-dependent manner. Mechanical strain-induced nuclear translocation of p44/42 MAPK and SAPK and nuclear protein binding to AP-1 were also attenuated by 17beta-estradiol. The inhibitory effects of 17beta-estradiol were not reproduced by the cell-impermeable estrogen, BSA/17beta-estradiol, nor did preincubation with 17beta-estradiol lead to actin cytoskeleton disassembly or impaired stress fiber formation. However, 17beta-estradiol did increase base-line levels of the dual specificity phosphatase MKP-1. The inhibitory effects of 17beta-estradiol on p44/42 MAPK activation and SAPK activation, translocation, and AP-1 binding were all abrogated by the estrogen receptor antagonist, ICI-182,780. We conclude that attenuation of mechanical strain-induced MAPK activation by 17beta-estradiol is dependent on intracellular estrogen receptor. The attenuation of stretch-induced kinase activation may be due, at least in part, to an effect of 17beta-estradiol on MKP-1 expression. Together, these findings add insight into the protective effect of gender on renal disease progression.

Renal and cardiovascular effects of selective cyclooxygenase-2 inhibitors

Selective inhibition of cyclooxygenase-2 (COX-2) was proposed as a novel anti-inflammatory and analgesic treatment with a reduced profile of gastrointestinal side effects compared with conventional nonsteroidal anti-inflammatory drugs (NSAIDs). Although perceived as an inducible enzyme by inflammatory and other stimuli, COX-2 is constitutively expressed in the kidney. In this review, we focus on renal and cardiovascular (CV) physiological and pathophysiological characteristics of COX-2 and renal and CV aspects of treatment with selective COX-2 inhibitors. Both clinical and experimental studies have shown that renal and CV effects of COX-2 inhibitors are similar to those of NSAIDs. These effects include sodium, potassium, and water retention and decreases in renal function, as well as mild to modest increases in blood pressure (BP) and edema. These deleterious effects are amplified in patients with volume and/or sodium depletion. The concomitant administration of COX-2 inhibitors may destabilize BP control in hypertensive patients treated with antihypertensive agents. In contrast to the normal kidney, which could constitute a target for adverse actions of COX-2 inhibitors, recent experimental studies showed increased renal COX-2 expression in several models of renal injury, such as the remnant kidney, renovascular hypertension, and diabetes, and implicated COX-2 in the progression of renal failure. This suggests that COX-2 inhibitors may confer a renoprotective effect in diverse renal disorders. These intriguing formulations must be delineated further in appropriately designed prospective clinical trials.

The transcription factor Egr-1: a potential drug in wound healing and tissue repair

In the United States, between 40 and 90 million hospital days are lost per year as a result of trauma and surgical procedures which result in the loss of functional tissue. This is estimated to cost the economy and healthcare providers in excess of US$ 500 billion, a figure that is increasing because of extending population lifespan. Tissue engineering and gene therapies are radical new treatments that are aimed at tissue regeneration ranging from dermal, osteal and occular repair to the replacement of failing tissue with entire biosynthetic organs. Over the last decade, numerous proteins have been identified that are able to direct the synthesis of new tissue. Such proteins include growth factors, cytokines and, more recently, transcription factors.

Endothelin-1 induces cyclooxygenase-2 expression via nuclear factor of activated T-cell transcription factor in glomerular mesangial cells

Nuclear factor of activated T cells (NFAT) originally was identified as a T-cell-specific transcription factor whose activity is regulated by calcineurin, one of the serine-threonine phosphatases. Recent studies have shown that NFAT also is expressed in nonlymphoid cells and plays an important role in various cell functions. It is widely known that treatment with cyclosporin A (CsA), which can inhibit calcineurin/NFAT signaling, results in glomerular dysfunction characterized by a decrease of GFR or glomerulosclerosis, suggesting that NFAT might regulate the glomerular function. However, the precise function of NFAT in glomerular cells remains to be clarified. Herein, evidence has been produced that NFAT2/NFATc, one of five known NFAT isoforms, is expressed in glomerular mesangial cells. Stimulation of mesangial cells with endothelin-1 caused translocation of NFAT2 into the nucleus with a concomitant increase in NFAT2 DNA-binding activity, both of which were inhibited by CsA. Furthermore, CsA inhibited endothelin-1-induced cyclooxygenase-2 (COX-2) expression in mesangial cells. NFAT2 bound directly to the GGAAA sequence, which is the minimal consensus sequence for NFAT binding, in a promoter region of rat COX-2 gene, and it enhanced the reporter activity of rat COX-2 promoter in mesangial cells. These findings provide the first evidence that NFAT2 is expressed and regulates COX-2 gene expression in mesangial cells. These results will contribute to evaluation of the precise roles of NFAT in glomerular functions and the CsA-induced nephrotoxicity.

The transcriptional corepressor NAB2 blocks Egr-1-mediated growth factor activation and angiogenesis

Effective tissue repair results from a rapid, temporally orchestrated series of events. At the site of local tissue injury, the production of many growth factors and cytokines is, in part, stimulated by the early growth response transcription factors such as Egr-1. Egr-1 protein binds to a family of corepressor proteins called NAB which function to block or limit Egr-1 trans-activation of cognate target genes. NAB2 blocks Egr-1 activation of the tissue factor (TF) promoter, Egr-1 stimulated production of PDGF-AB, HGF, TGFbeta(1), and VEGF and the endogenous expression of PDGF-AB and TGFbeta(1). Expression of a wild-type NAB2 but not a dominant negative NAB2 mutant abrogates Egr-1 driven TF promoter activity and tubule formation in an in vitro model of angiogenesis. These findings may have importance in any tissue that is subject to scarring after acute or chronic injury.

Immunohistochemical and functional correlations of renal cyclooxygenase-2 in experimental diabetes

Prostaglandins (PGs) generated by the enzyme cyclooxygenase (COX) have been implicated in the pathological renal hemodynamics and structural alterations in diabetes mellitus, but the role of individual COX isoenzymes in diabetic nephropathy remains unknown. We explored COX-1 and COX-2 expression and hemodynamic responses to the COX-1 inhibitor valeryl salicylate (VS) or the COX-2 inhibitor NS398 in moderately hyperglycemic, streptozotocin-diabetic (D) and control (C) rats. Immunoreactive COX-2 was increased in D rats compared with C rats and normalized by improved glycemic control. Acute systemic administration of NS398 induced no significant changes in mean arterial pressure and renal plasma flow in either C or D rats but reduced glomerular filtration rate in D rats, resulting in a decrease in filtration fraction. VS had no effect on renal hemodynamics in D rats. Both inhibitors decreased urinary excretion of PGE(2). However, only NS398 reduced excretion of thromboxane A(2). In conclusion, we documented an increase in renal cortical COX-2 protein expression associated with a different renal hemodynamic response to selective systemic COX-2 inhibition in D as compared with C animals, indicating a role of COX-2-derived PG in pathological renal hemodynamic changes in diabetes.

Early streptozotocin-diabetes mellitus downregulates rat kidney AT2 receptors

The interaction of ANG II with intrarenal AT1 receptors has been implicated in the progression of diabetic nephropathy, but the role of intrarenal AT2 receptors is unknown. The present studies determined the effect of early diabetes on components of the glomerular renin-angiotensin system and on expression of kidney AT2 receptors. Three groups of rats were studied after 2 wk: 1) control (C), 2) streptozotocin (STZ)-induced diabetic (D), and 3) STZ-induced diabetic with insulin implant (D+I), to maintain normoglycemia. By competitive RT-PCR, early diabetes had no significant effect on glomerular mRNA expression for renin, angiotensinogen, or angiotensin-converting enzyme (ACE). In isolated glomeruli, nonglycosylated (41-kDa) AT1 receptor protein expression (AT1A and AT1B) was increased in D rats, with no change in glycosylated (53-kDa) AT1 receptor protein or in AT1 receptor mRNA. By contrast, STZ diabetes caused a significant decrease in glomerular AT2 receptor protein expression (47.0 +/- 6.5% of C; P < 0.001; n = 6), with partial reversal in D+I rats. In normal rat kidney, AT2 receptor immunostaining was localized to glomerular endothelial cells and tubular epithelial cells in the cortex, interstitial, and tubular cells in the outer medulla, and inner medullary collecting duct cells. STZ diabetes caused a significant decrease in AT2 receptor immunostaining in all kidney regions, an effect partially reversed in D+I rats. In summary, early diabetes has no effect on glomerular mRNA expression for renin, angiotensinogen, or ACE. AT2 receptors are present in glomeruli and are downregulated in early diabetes, as are all kidney AT2 receptors. Our data suggest that alterations in the balance of kidney AT1 and AT2 receptor expression may contribute to ANG II-mediated glomerular injury in progressive diabetic nephropathy.

Cyclic stretching of mesangial cells up-regulates intercellular adhesion molecule-1 and leukocyte adherence: a possible new mechanism for glomerulosclerosis

Intraglomerular hypertension is a primary causal factor in the progressive glomerulosclerosis that characterizes diabetic nephropathy or severe renal ablation. However, inflammation of the glomerular mesangium also participates in at least the early phase of these diseases. In glomerulonephritis, where inflammation is thought to be the predominant causal factor, intraglomerular hypertension is also often present. Mesangial cells (MCs) are critical in orchestrating key functions of the glomerulus including extracellular matrix metabolism, cytokine production, and interaction with leukocytes. Because MCs are subject to increased stretching when intraglomerular hypertension is present, and in glomerulonephritis MC/leukocyte interactions seem to be mediated primarily via the up-regulation of intercellular adhesion molecule-1 (ICAM-1), we examine the possibility that cyclic stretching is a stimulus for increased MC ICAM-1 activity. We demonstrate that the normal low levels of MC ICAM-1 mRNA and protein are dramatically up-regulated by even short intervals of cyclic stretch. This effect is dose- and time-dependent, and requires little amplitude and a brief period of elongation for significant induction. Stretch-induced MC ICAM-1 also leads to a marked elevation in phagocytic leukocyte adherence. This stimulated adherence is equal or greater than that induced by the inflammatory cytokine tumor necrosis factor-alpha, whereas an additive effect occurs when both are applied in combination. Our results indicate that stretch-induced ICAM-1 may provide a direct link between hypertension and inflammation in the progression of injury and glomerulosclerosis in diabetes, renal ablation, and other forms of glomerulonephritis.

NO inhibits stretch-induced MAPK activity by cytoskeletal disruption

Mesangial cells (MC) grown on extracellular matrix protein-coated plates and exposed to cyclic strain/relaxation proliferate and produce extracellular matrix protein, providing an in vitro model of signaling in stretched MC. Intracellular transduction of mechanical strain involves mitogen-activated protein kinases, and we have shown that p42/44 mitogen-activated protein kinase (extracellular signal-regulated kinase (ERK)) is activated by cyclic strain in MC. In vivo studies show that increased production of nitric oxide (NO) in the remnant kidney limits glomerular injury without reducing glomerular capillary pressure, and we have observed that NO attenuates stretch-induced ERK activity in MC via generation of cyclic guanosine monophosphate (cGMP). Accordingly, we sought to determine whether NO affects strain-induced ERK activity after strain and how this is mediated. Strain-induced ERK activity was dependent on time and magnitude of stretch and was maximal after 10 min at -27 kilopascals. Actin cytoskeleton disruption with cytochalasin D abrogated this. The non-metabolizable cGMP analogue 8-bromo cyclic GMP (8-Br-cGMP) dose-dependently attenuated strain-induced ERK activity. Cytoskeletal stabilization with jasplakinolide prevented this inhibitory effect of 8-Br-cGMP. Cyclic strain increased nuclear translocation of phospho-ERK by immunofluorescent microscopy, again attenuated by 8-Br-cGMP. Jasplakinolide prevented the inhibitory effect of 8-Br-cGMP on activated ERK nuclear translocation after strain. Strain increased ERK-dependent AP-1 nuclear protein binding, which was attenuated by cytochalasin D and 8-Br-cGMP. These data indicate that cGMP can inhibit cyclic strain-induced ERK activity, nuclear translocation, and AP-1 nuclear protein binding. Cytoskeletal disruption leads to the same effect, whereas cytoskeleton stabilization reverses the effect of 8-Br-cGMP. Thus, NO inhibits strain-induced ERK activity by cytoskeletal destabilization.

The proliferative response of isolated human tendon fibroblasts to cyclic biaxial mechanical strain

At the cellular level, dynamic strain plays a key role in cell stimulation and organization of the extracellular matrix. Although positive effects of physical strain on tendon tissue are well known, little knowledge exists on how mechanical strain affects tendon cells. In this study, human tendon fibroblasts from patellar tendon were cultured on silicone dishes. Subsequently, cyclic biaxial mechanical strain was applied to the dishes for 15, 30, and 60 minutes using a specially developed cell stretching system. After the fibroblasts were strained, cells were tested for proliferation at 6, 12, and 24 hours. As a control, cells were grown on silicone dishes but did not receive any strain. A biphasic response in proliferation was observed for the 15- and 60-minute strain periods: at 6 hours and 24 hours there was more proliferation than at 12 hours. After a strain duration time of 30 minutes, a lower proliferation rate was measured compared with control levels. This study shows that application of mechanical stress to tendon fibroblasts resulted in an alteration of cellular proliferation depending on the stress time. Our results may implicate future modifications in the treatment of ligament and tendon injuries.

Tissue repair with a therapeutic transcription factor

The healing of tissue involves a wide range of molecular, cellular, and physiological events that are coordinated in a temporally specific manner. The cellular transcription factor early growth response factor 1 (Egr-1) is expressed minutes after acute injury and serves to stimulate the production of a class of growth factors whose role is to promote tissue repair. We have studied the effects of Egr-1 expression at the site of dermal wounding in rodents. We find that Egr-1 promotes angiogenesis in vitro and in vivo, increases collagen production, and accelerates wound closure. These results show that Egr-1 gene therapy accelerates the normal healing process and raises the potential use of this therapeutic transcription factor for any aspect of tissue repair.

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

Cyclic mechanical stretch of bladder smooth muscle cells (SMC) increases rates of DNA synthesis and stimulates transcription of the gene for heparin-binding epidermal growth factor-like growth factor (HB-EGF), an ErbB1/EGF receptor ligand that has been linked to hypertrophic bladder growth. In this study we sought to clarify the signaling pathways responsible for mechanotransduction of the stretch stimulus. HB-EGF mRNA levels, DNA synthesis, and AP-1/Ets DNA binding activities were induced by repetitive stretch of primary culture rat bladder SMC. Inhibitors of the p38 SAPK2 pathway, the angiotensin receptor type 1 (AT1), and the ErbB2 tyrosine kinase reduced each of these activities, while an inhibitor of the extracellular signal-regulated kinase mitogen-activated protein kinase (Erk-MAPK) pathway had no effect. Stretch rapidly activated stress-activated protein kinase 2 (p38 SAPK2) and Jun NH(2)-terminal kinase (JNK)/SAPK pathways but not the Erk-MAPK pathway and induced ErbB2 but not ErbB1 phosphorylation. Angiotensin II (ANG II) a bladder SMC mitogen previously linked to the stretch response, did not activate ErbB2, and ErbB2 activation occurred in response to stretch in the presence of an ANG receptor inhibitor, indicating that activation of the AT1-mediated pathway and the ErbB2-dependent pathway occurs by independent mechanisms. p38 SAPK2 and JNK/SAPK signaling also appeared to be independent of the ErbB2 and AT1 pathways. These findings indicate that stretch-stimulated DNA synthesis and gene expression in normal bladder SMC occur via multiple independent receptor systems (e.g., AT1 and ErbB2) and at least one MAPK pathway (p38 SAPK2). Further, we show that the Erk-MAPK pathway, which in most systems is linked to receptor-dependent cell growth responses, is not involved in progression to DNA synthesis or in the response of the HB-EGF gene to mechanical forces.

Stretch-induced mesangial cell ERK1/ERK2 activation is enhanced in high glucose by decreased dephosphorylation

Glomerular hypertension and hyperglycemia are major determinants of diabetic nephropathy. We sought to identify the mechanisms whereby stretch-induced activation of mesangial cell extracellular signal-regulated kinase 1 and 2 (ERK1/ERK2) is enhanced in high glucose (HG). Mesangial cells cultured on fibronectin Flex I plates in normal glucose (NG; 5.6 mM) or HG (30 mM), were stretched by 15% elongation at 60 cycles/min for up to 60 min. In HG, a 5-min stretch increased ERK1/ERK2 phosphorylation by 6.4 +/- 0.4/4.3 +/- 0.3-fold (P < 0.05 vs. NG stretch). In contrast, p38 phosphorylation was increased identically by stretch in NG and HG. Unlike many effects of HG, augmentation of ERK activity by HG was not dependent on protein kinase C (PKC) as indicated by downregulation of PKC with 24-h phorbol ester or inhibition with bisindolylmaleimide IV. In both NG and HG, pretreatment with arginine-glycine-aspartic acid peptide (0.5 mg/ml) to inhibit integrin binding or with cytochalasin D (100 ng/ml) to disassemble filamentous (F) actin, significantly reduced phosphorylation of ERK1/ERK2 and p38. To determine whether the rate of mitogen-activated protein kinase dephosphorylation is affected by HG, cellular kinase activity was inhibited by depleting ATP. Post-ATP depletion, phosphorylation of ERK1/ERK2 was reduced to 36 +/- 9/51 +/- 14% vs. 9 +/- 5/7 +/- 6% in NG (P < 0.05, n = 5). Thus stretch-induced ERK1/ERK2 and p38 activation in both NG and HG is beta(1)-integrin and F-actin dependent. Stretch-induced ERK1/ERK2 is enhanced in high glucose by diminished dephosphorylation, suggesting reduced phosphatase activity in the diabetic milieu. Enhanced mesangial cell ERK1/ERK2 signaling in response to the combined effects of mechanical stretch and HG may contribute to the pathogenesis of diabetic nephropathy.

Stretch activation of jun N-terminal kinase/stress-activated protein kinase in mesangial cells

BACKGROUND

Mesangial cells (MCs) grown on extracellular matrix (ECM)-coated plates and exposed to cyclic stretch/relaxation proliferate and produce ECM protein, suggesting that this may be a useful in vitro model for MC behavior in response to increased physical forces. The induction of c-fos in response to MC stretch has been shown. Stimuli that lead to c-fos induction pass through mitogen-activated protein (MAP) kinase pathways. We have seen early activation of jun N-terminal kinase/stress-activated protein kinase (SAPK/JNK) in MCs exposed to cyclic stretch. Accordingly, we studied SAPK/JNK activation in stretched MCs and the downstream consequences of this signaling.

METHODS

MCs (passages 5 to 10) cultured on type 1 collagen-coated, flexible-bottom plates were exposed to 2 to 60 minutes of cyclic strain (60 cycles per minute) by generation of vacuums of -10 to -27 kPa, inducing approximately 16 to 28% maximum elongation in the diameter of the surfaces. Control MCs were grown on coated rigid bottom plates. Protein levels (by Western blot) and activity assays for SAPK/JNK were performed under these conditions. We observed marked activation at -18 kPa and above and at two minutes, and then we studied activation mechanisms under these conditions. Nuclear protein binding to activator protein-1 (AP-1) consensus sequences was also examined. The role of calcium was studied with EGTA and BAPTA-AM to chelate extra- and intracellular calcium, respectively. Protein kinase C (PKC) was down-regulated by incubation with phorbol ester (PMA) for 24 hours prior to stretch. In unstretched MCs, A23187 was used as a calcium ionophore, and PKC was up-regulated with PMA application for 30 minutes to determine the effects on SAPK/JNK. Nuclear protein binding to AP-1 was also determined under these conditions. The effects of stretch, acute PMA, and A23187 on fibronectin mRNA levels were studied using reverse transcriptase-polymerase chain reaction (RT-PCR).

RESULTS

Cyclic strain/relaxation led to increased SAPK/JNK activity only at two minutes and -18 kPa and above. The activation of SAPK/JNK was dependent on intracellular calcium, with BAPTA-AM almost completely abrogating the response to stretch. EGTA was without effect. Down-regulation of PKC also led to a diminution of activity. In static cells, the calcium ionophore A23187 increased SAPK/JNK activity, and this was potentiated by acute PMA. Stretch, acute PMA, and A23187 all increased nuclear protein binding to AP-1 consensus sequences. mRNA levels for fibronectin were increased by stretch in MCs and by PMA and A23187 in static MCs. No change was observed in the amount of SAPK/JNK protein present in stretched MCs by Western blot.

CONCLUSIONS

Stretch leads to early activation of SAPK/JNK in MCs. This is dependent on intracellular calcium and PKC and can be replicated by activation of these stimuli in static MCs. A downstream induction of nuclear protein binding to AP-1 consensus sequences was seen in a pattern that was completely concordant with the SAPK/JNK induction.

Angiotensin II and its receptors in the diabetic kidney

Studies using either angiotensin-converting enzyme inhibitors or type 1 (AT(1)) angiotensin II (ANG II)-receptor blockers indicate that ANG II is a mediator of progressive injury in diabetic nephropathy. However, suppression of the systemic renin-angiotensin system (RAS) generally has been shown in diabetes mellitus. Evidence suggests that intrarenal RASs within glomeruli and proximal tubules may be activated with hyperglycemia, leading to stimulation of local ANG II production, which may exert feedback inhibition of systemic renin release. Once formed, intrarenal ANG II exerts most of its well-described effects through binding to AT(1) receptors that are abundantly present in cells of the glomeruli, tubules, vasculature, and interstitium. Thus, AT(1)-receptor activation increases vascular resistance, reduces renal blood flow, and stimulates production of extracellular matrix in the mesangium and tubulointerstitium. Recent studies suggest that the adult kidney also expresses type 2 (AT(2)) ANG II receptors in glomeruli, tubular segments, and vasculature. AT(2)-receptor activation is associated with increased intrarenal nitric oxide production, stimulation of natriuresis, and inhibition of cell growth and matrix synthesis, effects that oppose those of kidney AT(1) receptors. A number of studies have shown a reduction in kidney AT(1)-receptor expression in diabetic nephropathy, suggesting that the balance between AT(1)- and AT(2)-receptor-mediated cell-signaling events may be a determinant of progression rate in diabetic nephropathy and that unopposed stimulation of AT(2) receptors by ANG II with use of AT(1)-receptor blockers may contribute to the beneficial properties of these agents. Determination of the expression pattern of AT(2) receptors in diabetes and further definition of the role of AT(2) receptors in opposing the detrimental effects of AT(1) receptors may lead to more selective targeting of the RAS in diabetic nephropathy.

Full promoter sequence of human early growth response factor-1 (Egr-1): demonstration of a fifth functional serum response element

The early growth response factor-1 (Egr-1) gene encodes a zinc finger transcription factor which is critical for cell proliferation and differentiation. The human Egr-1 promoter comprises regulatory elements including two Sp1 sites, an AP1 site, two cAMP response elements and an Egr-1 binding site. In addition to these transcription factor binding sites, the promoter harbours five serum response elements (SREs) and associated binding sites for the Ets transcription factor family, previously identified from partial sequence data (Sakamoto et al, Oncogene 6; 867-871, 1991). We now report the full sequence of the human Egr-1 promoter and confirm the presence of a fifth serum response element. This element is functionally active in a minimal promoter vector in response to the MAP kinase kinase MEK1.

Nitric oxide modulates mechanical strain-induced activation of p38 MAPK in mesangial cells

Mesangial cells (MC), grown on extracellular matrix (ECM) protein-coated plates and stretched, proliferate and produce ECM, recapitulating in vivo responses to increased glomerular capillary pressure (Pgc). Transduction of strain involves mitogen-activated protein kinases (MAPK), and we have shown that p38 MAPK is activated by strain in MC. Because in vivo studies show that nitric oxide (NO) in the remnant kidney limits glomerular injury without reducing Pgc, we studied whether NO attenuated stretch-induced p38 activation in MC. Increasing p38 activation occurred with increasing stretch, maximally at 10 min at -27-kPa vacuum. Cyclic strain increased nuclear translocation of phosphorylated p38 by immunofluorescent microscopy and nuclear protein binding to nuclear factor-kappaB (NF-kappaB) consensus sequences by mobility shift assay. Both events were largely abrogated by the p38 inhibitor SB-203580. The NO donors 3-morpholinosydnonimine, S-nitroso-N-acetylpenicillamine, and 8-bromoguanosine 3',5'-cyclic monophosphate, a stable cGMP analog, prevented p38 activation and nuclear translocation. Thus strain induces p38 activity and translocation to the nucleus and p38-dependent increases in nuclear protein binding to NF-kappaB. This pathway is attenuated by the NO donors or a cGMP analog.