Tyrosine kinase dependent expression of TGF-beta induced by stretch in mesangial cells

Upregulation of Piezo2 in the mesangial, renin, and perivascular mesenchymal cells of the kidney of Dahl salt-sensitive hypertensive rats and its reversal by esaxerenone

The recent discovery of mechanosensitive ion channels has promoted mechanobiological research in the field of hypertension and nephrology. We previously reported Piezo2 expression in mouse mesangial and juxtaglomerular renin-producing cells, and its modulation by dehydration. This study aimed to investigate how Piezo2 expression is altered in hypertensive nephropathy. The effects of the nonsteroidal mineralocorticoid receptor blocker, esaxerenone, were also analyzed. Four-week-old Dahl salt-sensitive rats were randomly assigned to three groups: rats fed a 0.3% NaCl diet (DSN), rats fed a high 8% NaCl diet (DSH), and rats fed a high salt diet supplemented with esaxerenone (DSH + E). After six weeks, DSH rats developed hypertension, albuminuria, glomerular and vascular injuries, and perivascular fibrosis. Esaxerenone effectively decreased blood pressure and ameliorated renal damage. In DSN rats, Piezo2 was expressed in Pdgfrb-positive mesangial and Ren1-positive cells. Piezo2 expression in these cells was enhanced in DSH rats. Moreover, Piezo2-positive cells accumulated in the adventitial layer of intrarenal small arteries and arterioles in DSH rats. These cells were positive for Pdgfrb, Col1a1, and Col3a1, but negative for Acta2 (αSMA), indicating that they were perivascular mesenchymal cells different from myofibroblasts. Piezo2 upregulation was reversed by esaxerenone treatment. Furthermore, Piezo2 inhibition by siRNA in the cultured mesangial cells resulted in upregulation of Tgfb1 expression. Cyclic stretch also upregulated Tgfb1 in both transfections of control siRNA and Piezo2 siRNA. Our findings suggest that Piezo2 may have a contributory role in modulating the pathogenesis of hypertensive nephrosclerosis and have also highlighted the therapeutic effects of esaxerenone on salt-induced hypertensive nephropathy. Mechanochannel Piezo2 is known to be expressed in the mouse mesangial cells and juxtaglomerular renin-producing cells, and this was confirmed in normotensive Dahl-S rats. In salt-induced hypertensive Dahl-S rats, Piezo2 upregulation was observed in the mesangial cells, renin cells, and notably, perivascular mesenchymal cells, suggesting its involvement in kidney fibrosis.

Effects of Genistein on Common Kidney Diseases

Genistein is a naturally occurring phytoestrogen (soy or soybean products) that is classified as an isoflavone, and its structure is similar to that of endogenous estrogens; therefore, genistein can exert an estrogen-like effect via estrogen receptors. Additionally, genistein is a tyrosine kinase inhibitor, which enables it to block abnormal cell growth and proliferation signals through the inhibition of tyrosine kinase. Genistein is also an angiogenesis inhibitor and an antioxidant. Genistein has effects on kidney cells, some of the kidney’s physiological functions, and a variety of kidney diseases. First, genistein exerts a protective effect on normal cells by reducing the inflammatory response, inhibiting apoptosis, inhibiting oxidative stress, inhibiting remodeling, etc., but after cell injury, the protective effect of genistein decreases or even has the opposite effect. Second, genistein can regulate renin intake to maintain blood pressure balance, regulate calcium uptake to regulate Ca²⁺ and Pi balances, and reduce vasodilation to promote diuresis. Third, genistein has beneficial effects on a variety of kidney diseases (including acute kidney disease, kidney cancer, and different chronic kidney diseases), such as reducing symptoms, delaying disease progression, and improving prognosis. Therefore, this paper reviews animal and human studies on the protective effects of genistein on the kidney in vivo and in vitro to provide a reference for clinical research in the future.

Piezo2 expression and its alteration by mechanical forces in mouse mesangial cells and renin-producing cells

The kidney plays a central role in body fluid homeostasis. Cells in the glomeruli and juxtaglomerular apparatus sense mechanical forces and modulate glomerular filtration and renin release. However, details of mechanosensory systems in these cells are unclear. Piezo2 is a recently identified mechanically activated ion channel found in various tissues, especially sensory neurons. Herein, we examined Piezo2 expression and regulation in mouse kidneys. RNAscope in situ hybridization revealed that Piezo2 expression was highly localized in mesangial cells and juxtaglomerular renin-producing cells. Immunofluorescence assays detected GFP signals in mesangial cells and juxtaglomerular renin-producing cells of Piezo2^GFP reporter mice. Piezo2 transcripts were observed in the Foxd1-positive stromal progenitor cells of the metanephric mesenchyme in the developing mouse kidney, which are precursors of mesangial cells and renin-producing cells. In a mouse model of dehydration, Piezo2 expression was downregulated in mesangial cells and upregulated in juxtaglomerular renin-producing cells, along with the overproduction of renin and enlargement of the area of renin-producing cells. Furthermore, the expression of the renin coding gene Ren1 was reduced by Piezo2 knockdown in cultured juxtaglomerular As4.1 cells under static and stretched conditions. These data suggest pivotal roles for Piezo2 in the regulation of glomerular filtration and body fluid balance.

Long-Term Impact of Bariatric Surgery on Renal Outcomes at a Community-Based Publicly Funded Bariatric Program: The Regina Bariatric Study

Background:

Obesity is recognized as an independent risk factor for chronic kidney disease through multiple direct and indirect biological pathways. Bariatric surgery is a proven, effective method for sustained weight loss. However, there is a relative paucity of data on the impact of bariatric surgery on renal outcomes.

Objective:

The primary objective was to evaluate the change in urine albumin/creatinine ratio (ACR) in patients undergoing bariatric surgery, at 12 months after the procedure. Secondary objectives were to determine the changes in ACR at (6 and 24 months), estimated glomerular filtration rate (eGFR; 6, 12, and 24 months), and hemoglobin A1c (HbA1c); 12 and 24 months) after the procedure.

Design:

This observational retrospective cohort study included consecutive obese patients who underwent bariatric surgery.

Setting:

Provincial Bariatric Surgery Clinic at the Regina General Hospital, Saskatchewan.

Patients:

This study includes 471 consecutive obese adult patients who underwent bariatric surgery between 2008 and 2015.

Measurements:

We studied the impact of bariatric surgery on body mass index (BMI), renal outcomes (urine ACR and eGFR) and metabolic outcomes (fasting glucose, total cholesterol, low-density lipoprotein, triglycerides, and HbA1c) in 471 patients.

Methods:

Patients were followed for 2 years postsurgery in the bariatric clinic. Mixed linear models that accounted for the repeated nature of the data were used to access changes in outcomes over time.

Results:

Patients were predominantly female (81%) with a mean age (±SD) of 46 ± 10 years. Most patients (87%) had a BMI > 40 kg/m² and 81% of the patients underwent Roux-en-Y gastric bypass. The mean BMI decreased from 47.7 ± 7.8 kg/m² at baseline to 37.1 ± 7.9 kg/m² at 6 months and 34.8 ± 8.8 kg/m² at 12 months. In a subcohort of patients with microalbuminuria, ACR showed an improvement from a median [interquartile] value of 5.1 [3.7-7.5] mg/mmol at baseline to 2.3 [1.2-3.6] mg/mmol at 6 months (P = .007), to 1.4 [0.9-3.7] mg/mmol at 2-year follow-up (P < .001). Similarly, eGFR increased in patients with microalbuminuria from 109 ± 10 mL/min/1.73 m² at baseline to 120 ± 36 mL/min/1.73 m² at 2-year follow-up (P = .013). There were statistically significant reductions in triglycerides, fasting glucose, and HbA1c.

Limitations:

This was a retrospective chart review, with the lack of a control group. Patients with eGFR less than 60 mL/min/1.73 m² were not considered for surgery, and we had to measure renal outcomes predominantly on the presence of proteinuria.

Conclusions:

Our results suggest bariatric surgery significantly decreased weight and consequently improved renal and metabolic outcomes (eGFR, ACR, fasting glucose, cholesterol, and triglycerides) in patients with elevated BMI.

Intermittent cyclic mechanical tension-induced down-regulation of ectonucleotide pyrophosphatase phosphodiesterase 1 gene expression is mainly dependent on TGF-β1 in end-plate chondrocytes

OBJECTIVE

To investigate the relationship between ectonucleotide pyrophosphatase phosphodiesterase-1(ENPP-1) expression and transforming growth factor beta 1 (TGF-β1) of end-plate chondrocytes after stimulation with intermittent cyclic mechanical tension (ICMT) by using an FX-4000T Flexercell Tension Plus unit.

METHODS

Rat end-plate chondrocytes were cultured and ICMT (strain at 0.5 Hz sinusoidal curve at 10% elongation) applied for 7 days for 4 h/day and cultured for a further 2 days. End-plate chondrocytes were also exposed to 10 ng/mL of TGF-β1. Then, using small interfering RNA technology, small interfering TGF-β1 (siTGF-β1) was transfected. Expression of ENPP-1 and TGF-β1 was measured by real-time reverse-transcriptase polymerase chain reaction (RT-PCR) and western blotting.

RESULTS

Expression of both ENPP-1 and TGF-β1 was up-regulated after ICMT. Both RT-PCR and western blot showed that ENPP-1 expression decreases with siRNA TGF-β1 after 3% elongation 40 min, and cultured for an additional 2 days.

CONCLUSION

It was found that down-regulation of ENPP-1 gene expression induced by ICMT is likely dependent on TGF-β1 in end-plate chondrocytes.

The role of obesity in kidney disease: recent findings and potential mechanisms

Obesity epidemic is in rise in almost every industrialized country and continues to be a growing problem worldwide. In fact, obesity per se has been recognized as a chronic disease. Consequently, there has been a cascade of metabolic changes initiated by the markedly risen prevalence that contributes to the increased incidence of diabetes, hypertension, and cardiovascular disease. Moreover, obesity is also associated with an increased risk of chronic kidney disease (CKD). The majority of the studies indicate a direct relationship between body mass index (BMI) and CKD risk. Moreover, current evidence emphasized the fact that central obesity measurements, such as waist circumference, could be a better predictor of CKD progression and mortality than BMI. The detrimental effects of obesity on kidney outcome have been recognized in nondialysis-dependent (NDD)-CKD patients. However, survival in overweight or obese CKD patients undergoing maintenance hemodialysis is paradoxically opposed compared with the general population. This "reverse epidemiology," however, is valid mainly for the inflammated end-stage renal disease (ESRD) patients. In fact, renal transplant recipients with higher BMI have inferior patient and graft survival compared to patients with lower BMI. This review also provides perspectives concerning the mechanisms associated with obesity, such as the renin-angiotensin-aldosterone system (RAAS) activation, and the role of leptin, adiponectin, fetuin-A, and adipose tissue, as factors that contribute to the development of CKD. Prevention strategies for CKD patients are also discussed and should be considered by clinicians.

MicroRNA-24 regulates the processing of latent TGFβ1 during cyclic mechanical stress in human trabecular meshwork cells through direct targeting of FURIN

Cyclic mechanical stress (CMS) leads to alterations of cellular functions in the trabecular meshwork (TM), including the up-regulation of transforming growth factor beta 1 (TGFβ1), that can potentially contribute to the pathogenesis of glaucoma. Although microRNAs (miRNAs) are known to play important roles in many biological functions, little is known about their potential involvement in the cellular responses elicited by mechanical stress. Here we analyzed changes in miRNA expression induced by CMS, and examined the possible role of miR-24 in the response of human TM cells to CMS. CMS induced the expression of miR-24 that led to the down regulation of the subtilisin-like proprotein convertase FURIN, which is known to play a major role in the processing of TGFβ1. FURIN was confirmed as a novel target of miR-24 by 3' UTR luciferase assay and western blot. Overexpression of miR-24 resulted in a significant decrease in activated TGFβ1. This effect was mimicked by down regulation of FURIN by siRNA. Conversely, inhibition of miR-24 expression with a specific antagomir led to a small but significant increase in TGFβ1. Furthermore, the increase in active TGFβ1 induced by CMS in HTM cells was prevented by miR-24. Altogether, our results suggest that miRNAs might contribute to the regulation of responses to CMS in TM cells. Specifically, miR-24 might play an important role in modulating the induction of TGFβ1 mediated by CMS through direct targeting of FURIN.

Mechanical stretch-induced RhoA activation is mediated by the RhoGEF Vav2 in mesangial cells

Increased intraglomerular pressure is an important hemodynamic determinant of glomerulosclerosis, and can be modelled in vitro by exposing mesangial cells (MC) to cyclic mechanical stretch. We have previously shown that the GTPase RhoA mediates stretch-induced fibronectin production. Here we investigate the role of the RhoGEF Vav2 in the activation of RhoA by stretch. Primary rat MC were exposed to 1 Hz cyclic stretch, previously shown to induce maximal RhoA activation at 1 min. Total Vav2 tyrosine phosphorylation and specific phosphorylation on Y172, required for activation, were increased by 1 min of stretch. Overexpression of dominant-negative Vav2 Y172/159F in COS-1 cells or downregulation of Vav2 by siRNA in MC prevented stretch-induced RhoA activation. Vav2 is known to be activated in response to growth factors, and we have previously shown the epidermal growth factor receptor (EGFR) to be transactivated by stretch in MC. Both Vav2 Y172 phosphorylation and RhoA activation were blocked by the EGFR inhibitor AG1478 and prevented in MC overexpressing kinase inactive EGFR. Stretch led to physical association between the EGFR and Vav2, and this was dependent on EGFR activation. EGFR Y992 phosphorylation, required for growth factor-induced Vav2 phosphorylation, was also induced by stretch. Activation of both Src and PI3K were necessary upstream mediators of stretch-induced Vav2 Y172 phosphorylation and RhoA activation. In summary, stretch-induced RhoA activation is dependent on transactivation of the EGFR and activation of the RhoGEF Vav2. Src and PI3K are both required upstream of Vav2 and RhoA activation.

Monocyte chemoattractant protein-1 has prosclerotic effects both in a mouse model of experimental diabetes and in vitro in human mesangial cells

AIMS/HYPOTHESIS

Diabetic nephropathy is characterised by mesangial extracellular matrix accumulation. Monocyte chemoattractant protein-1 (MCP-1), a chemokine promoting monocyte infiltration, is upregulated in the diabetic glomerulus. We performed in vitro and in vivo studies to examine whether MCP-1 may have prosclerotic actions in the setting of diabetes, presumably via its receptor, chemokine (C-C motif) receptor 2 (CCR2), which has been described in mesangial cells.

METHODS

Human mesangial cells were exposed to recombinant human (rh)-MCP-1 (100 ng/ml) for 12, 24 and 48 h and to rh-MCP-1 (10, 100 and 200 ng/ml) for 24 h. Fibronectin, collagen IV and transforming growth factor, beta 1 (TGF-beta1) protein levels were measured by ELISA and pericellular polymeric fibronectin levels by western blotting. The intracellular mechanisms were investigated using specific inhibitors for CCR2, nuclear factor kappa B (NF-kappaB), p38 mitogen-activated protein kinase and protein kinase C, and an anti-TGF-beta1 blocking antibody. In both non-diabetic and streptozotocin-induced diabetic mice that were deficient or not in MCP-1, glomerular fibronectin accumulation was examined by immunohistochemistry, while cortical Tgf-beta1 (also known as Tgfb1) and fibronectin mRNA and protein levels were examined by real-time PCR and western blotting.

RESULTS

In mesangial cells, MCP-1 binding to CCR2 induced a 2.5-fold increase in fibronectin protein levels at 24 h followed by a rise in pericellular fibronectin, whereas no changes were seen in collagen IV production. MCP-1-induced fibronectin production was TGF-beta1- and NF-kappaB-dependent. In diabetic mice, loss of MCP-1 diminished glomerular fibronectin protein production and both renal cortical Tgf-beta1 and fibronectin mRNA and protein levels.

CONCLUSIONS/INTERPRETATION

Our in vitro and in vivo findings indicate a role for the MCP-1/CCR2 system in fibronectin deposition in the diabetic glomerulus, providing a new therapeutic target for diabetic nephropathy.

Tissue stretch decreases soluble TGF-beta1 and type-1 procollagen in mouse subcutaneous connective tissue: evidence from ex vivo and in vivo models

Transforming growth factor beta 1 (TGF-beta1) plays a key role in connective tissue remodeling, scarring, and fibrosis. The effects of mechanical forces on TGF-beta1 and collagen deposition are not well understood. We tested the hypothesis that brief (10 min) static tissue stretch attenuates TGF-beta1-mediated new collagen deposition in response to injury. We used two different models: (1) an ex vivo model in which excised mouse subcutaneous tissue (N = 44 animals) was kept in organ culture for 4 days and either stretched (20% strain for 10 min 1 day after excision) or not stretched; culture media was assayed by ELISA for TGF-beta1; (2) an in vivo model in which mice (N = 22 animals) underwent unilateral subcutaneous microsurgical injury on the back, then were randomized to stretch (20-30% strain for 10 min twice a day for 7 days) or no stretch; subcutaneous tissues of the back were immunohistochemically stained for Type-1 procollagen. In the ex vivo model, TGF-beta1 protein was lower in stretched versus non-stretched tissue (repeated measures ANOVA, P < 0.01). In the in vivo model, microinjury resulted in a significant increase in Type-1 procollagen in the absence of stretch (P < 0.001), but not in the presence of stretch (P = 0.21). Thus, brief tissue stretch attenuated the increase in both soluble TGF-beta1 (ex vivo) and Type-1 procollagen (in vivo) following tissue injury. These results have potential relevance to the mechanisms of treatments applying brief mechanical stretch to tissues (e.g., physical therapy, respiratory therapy, mechanical ventilation, massage, yoga, acupuncture).

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.

RhoA Activation in Mesangial Cells by Mechanical Strain Depends on Caveolae and Caveolin-1 Interaction

Increased intraglomerular pressure is an important hemodynamic determinant of glomerulosclerosis and can be modeled in vitro by exposing mesangial cells to cyclic mechanical strain. A previous study showed that RhoA mediates strain-induced production of fibronectin; herein is investigated the role of caveolae in RhoA activation. Cyclodextrin and filipin, agents that disrupt caveolae, abrogated strain-induced RhoA activation in mesangial cells. Caveolin-1 (cav-1), the defining protein of caveolae, was Y14 phosphorylated by strain, and this was inhibited by PP1, showing Src dependence. Strain also induced c-SrcY416 phosphorylation and hence activation. Strain increased RhoA association with cav-1, which was blocked by PP1. Cyclodextrin and filipin inhibited the strain-induced RhoA/cav-1 association, indicating dependence on caveolar structural integrity. Restoration of caveolae by coincubation of cyclodextrin with cholesterol rescued both RhoA activation and RhoA/cav-1 association in response to strain. Sucrose gradient detected a significant portion of RhoA in caveolae, with Src located exclusively in these domains. Finally, in cells that were infected with retrovirus that encodes the nonphosphorylatable cav-1 Y14A, RhoA/cav-1 association, RhoA activation, and fibronectin secretion in response to strain were abrogated. It is concluded that strain-induced RhoA activation depends on the integrity of caveolae and on physical association of cav-1 and RhoA. The phosphorylation of cav-1 at Y14 by Src kinases is required for this to occur. These studies define a novel function for cav-1 and caveolae as positive effectors of RhoA activation. Targeting caveolae thus may provide a new therapeutic option for glomerular sclerosis that is associated with elevated intraglomerular pressure.

Isoflavones made simple - genistein's agonist activity for the beta-type estrogen receptor mediates their health benefits

Soy isoflavones, the focus of much research and controversy, are often referred to as "weak estrogens". In fact, genistein is a relatively potent agonist for the recently characterized beta isoform of the estrogen receptor (ERbeta). The low nanomolar serum concentrations of unconjugated free genistein achieved with high-nutritional intakes of soy isoflavones are near the binding affinity of genistein for this receptor, but are about an order of magnitude lower than genistein's affinity for the "classical" alpha isoform of the estrogen receptor (ERalpha). Moreover, these concentrations are far too low to inhibit tyrosine kinases or topoisomerase II, in vitro activities of genistein often cited as potential mediators of its physiological effects. The thesis that these physiological effects are in fact mediated by ERbeta activation provides a satisfying rationale for genistein's clinical activities. Hepatocytes do not express ERbeta; this explains why soy isoflavones, unlike oral estrogen, neither modify serum lipids nor provoke the prothrombotic effects associated with increased risk for thromboembolic disorders. The lack of uterotrophic activity of soy isoflavones reflects the fact that ERalpha is the exclusive mediator of estrogen's impact in this regard. Vascular endothelium expresses both ERalpha and ERbeta, each of which has the potential to induce and activate nitric oxide synthase; this may account for the favorable influence of soy isoflavones on endothelial function in postmenopausal women and ovariectomized rats. The ERbeta expressed in osteoblasts may mediate the reported beneficial impact of soy isoflavones on bone metabolism. Suggestive evidence that soy-rich diets decrease prostate cancer risk, accords well with the observation that ERbeta appears to play an antiproliferative role in healthy prostate. In the breast, ERalpha promotes epithelial proliferation, whereas ERbeta has a restraining influence in this regard - consistent with the emerging view that soy isoflavones do not increase breast cancer risk, and possibly may diminish it. Premenopausal women enjoy a relative protection from kidney failure; since ERbeta is an antagonist of TGF-beta signaling in mesangial cells, soy isoflavones may have nephroprotective potential. Estrogen also appears to protect women from left ventricular hypertrophy, and recent evidence suggests that this effect is mediated by ERbeta. In conjunction with reports that isoflavones may have a modestly beneficial impact on menopausal symptoms - perhaps reflecting the presence of ERbeta in the hypothalamus - these considerations suggest that soy isoflavone regimens of sufficient potency may represent a safe and moderately effective alternative to HRT in postmenopausal women. Further clinical research is required to characterize the impact of optimal genistein intakes on endothelial and bone function in men. Studies with ERbeta-knockout mice could be helpful for clarifying whether ERbeta does indeed mediate the chief physiological effects of low nanomolar genistein. S-equol, a bacterial metabolite of daidzein, has an affinity for ERbeta nearly as high as that of genistein; whether this compound contributes meaningfully to the physiological efficacy of soy isoflavones in some individuals is still unclear.

Molecular pathways mediating mechanical signaling in bone

Bone tissue has the capacity to adapt to its functional environment such that its morphology is "optimized" for the mechanical demand. The adaptive nature of the skeleton poses an interesting set of biological questions (e.g., how does bone sense mechanical signals, what cells are the sensing system, what are the mechanical signals that drive the system, what receptors are responsible for transducing the mechanical signal, what are the molecular responses to the mechanical stimuli). Studies of the characteristics of the mechanical environment at the cellular level, the forces that bone cells recognize, and the integrated cellular responses are providing new information at an accelerating speed. This review first considers the mechanical factors that are generated by loading in the skeleton, including strain, stress and pressure. Mechanosensitive cells placed to recognize these forces in the skeleton, osteoblasts, osteoclasts, osteocytes and cells of the vasculature are reviewed. The identity of the mechanoreceptor(s) is approached, with consideration of ion channels, integrins, connexins, the lipid membrane including caveolar and non-caveolar lipid rafts and the possibility that altering cell shape at the membrane or cytoskeleton alters integral signaling protein associations. The distal intracellular signaling systems on-line after the mechanoreceptor is activated are reviewed, including those emanating from G-proteins (e.g., intracellular calcium shifts), MAPKs, and nitric oxide. The ability to harness mechanical signals to improve bone health through devices and exercise is broached. Increased appreciation of the importance of the mechanical environment in regulating and determining the structural efficacy of the skeleton makes this an exciting time for further exploration of this area.

Pathomechanism of ligamentum flavum hypertrophy: a multidisciplinary investigation based on clinical, biomechanical, histologic, and biologic assessments

STUDY DESIGN

A multidisciplinary study involving clinical, histologic, biomechanical, biologic, and immunohistologic approaches. OBJECTIVE.: To clarify the pathomechanism of hypertrophy of the ligamentum flavum.

SUMMARY OF BACKGROUND DATA

The most common spinal disorder in elderly patients is lumbar spinal canal stenosis, causing low back and leg pain, and paresis. Canal narrowing, in part, results from hypertrophy of the ligamentum flavum. Although histologic and biologic literature on this topic is available, the pathomechanism of ligamentum flavum hypertrophy is still unknown.

METHODS

The thickness of 308 ligamenta flava at L2/3, L3/4, L4/5, and L5/S1 levels of 77 patients was measured using magnetic resonance imaging. The relationships between thickness, age, and level were evaluated. Histologic evaluation was performed on 20 ligamentum flavum samples, which were collected during surgery. Trichrome and Verhoeff-van Gieson elastic stains were performed for each ligamentum flavum to understand the degree of fibrosis and elastic fiber status, respectively. To understand the mechanical stresses in various layers of ligamentum flavum, a 3-dimensional finite element model was used. Von Mises stresses were computed, and values between dural and dorsal layers were compared. There were 10 ligamenta flava collected for biologic assessment. Using real-time reverse transcriptase polymerase chain reaction, transforming growth factor (TGF)-beta messenger ribonucleic acid expression was quantitatively measured. The cellular location of TGF-beta was also confirmed from 18 ligamenta flava using immunohistologic techniques.

RESULTS

The ligamentum flavum thickness increased with age, however, the increment at L4/5 and L3/4 levels was larger than at L2/3 and L5/S1 levels. Histology showed that as the ligamentum flavum thickness increased, fibrosis increased and elastic fibers decreased. This tendency was more predominant along the dorsal side. Von Misses stresses revealed that the dorsal fibers of ligamentum flavum were subjected to higher stress than the dural fibers. This was most remarkably observed at L4/5. The largest increase in ratio observed between the dorsal and dural layer was approximately 5-fold in flexion at L4/5 in flexion. Expression of TGF-beta was observed in all ligamenta flava, however, the expression decreased as the ligamentum flavum thickness increased. Immunohistochemistry showed that TGF-beta was released by the endothelial cells, not by fibroblasts.

CONCLUSIONS

Fibrosis is the main cause of ligamentum flavum hypertrophy, and fibrosis is caused by the accumulation of mechanical stress with the aging process, especially along the dorsal aspect of the ligamentum flavum. TGF-beta released by the endothelial cells may stimulate fibrosis, especially during the early phase of hypertrophy.

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.

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.

Increased urinary TGF-beta1 and cortical renal GLUT1 and GLUT2 levels: additive effects of hypertension and diabetes

BACKGROUND/AIM

Diabetes and mesangial stretch caused by hypertension increase mesangial matrix deposition which is induced by local production of transforming growth factor beta 1 (TGF-beta1). Both conditions are associated with cortical GLUT1 overexpression. We evaluated the effect of genetically determined hypertension and its association with diabetes on urinary TGF-beta1 and cortical GLUT1 and GLUT2 expression.

METHODS

We studied Wistar-Kyoto rats (controls, C) and spontaneously hypertensive rats (SHR), weighing approximately 210 g, 30 days after the injection of streptozotocin (diabetic, D) or citrate buffer (10 C, 9 SHR, 12 C-D and 15 SHR-D). Twenty-four-hour urine was collected for glucose, albumin, and TGF-beta1 determinations. Catheters were implanted into the femoral artery to measure the arterial blood pressure in conscious animals 1 day later. Then GLUT1 and GLUT2 protein levels (Western blotting) in renal cortex and medulla were evaluated.

RESULTS

The cortical GLUT1 levels were 5, 2, and 7 times higher in SHR, C-D, and SHR-D groups versus C group (p < 0.05); the GLUT2 contents were 1.5, 1.8, and 2.3 times higher in SHR, C-D and SHR-D groups versus C group (p < 0.05). The urinary TGF-beta1 level was elevated by diabetes and diabetes and hypertension, but not by hypertension alone: 1.39 +/- 0.2, 2.34 +/- 0.6, 18.2 +/- 3.2, and 28.8 +/- 7.6 ng/24 h, respectively, in C, SHR, C-D, and SHR-D groups (p < 0.05).

CONCLUSIONS

Diabetes, hypertension, and especially their association increase the renal cortical GLUT1 and GLUT2 levels. The magnitude of GLUT1 overexpression caused by hypertension is higher than that induced by diabetes alone. The impact on urinary TGF-beta1 occurs when diabetes and hypertension are associated, suggesting an effect that is triggered in the presence of GLUT1 overexpression and hyperglycemia.

Akt mediates mechanical strain-induced collagen production by mesangial cells

Increased glomerular hydrostatic pressure is an important determinant of glomerulosclerosis and can be modeled by in vitro exposure of mesangial cells to cyclic mechanical strain. Stretched mesangial cells increase extracellular matrix protein production, the hallmark of glomerulosclerosis. Recent data indicate that the serine/threonine kinase Akt may be involved in matrix modulation. Thus, Akt activation and matrix synthesis in stretched mesangial cells were studied. Exposure of mesangial cells to 1 Hz cyclic strain led to prompt Akt activation, which was biphasic to 24 h. Activation was dependent on signaling through phosphatidylinositol-3-kinase and required EGF receptor transactivation. Inhibition of signaling through the PDGF receptor, Src kinase, or cytoskeletal disruption failed to prevent strain-induced Akt activation. Collagen type 1A1 transcript expression, promoter activation, and protein secretion were increased by stretch at 24 h and were dependent on phosphatidylinositol-3 kinase. Overexpression of dominant-negative Akt inhibited strain-induced collagen 1A1 production. Conversely, overexpression of constitutively active Akt led to increased collagen 1A1 upregulation and secretion. Finally, Akt activation was observed in the glomeruli of remnant rat kidneys, a model marked by increased intraglomerular pressure. The authors conclude that mechanical strain induces Akt activation in mesangial cells through a mechanism requiring phosphatidylinositol-3-kinase and EGF receptor transactivation. Type 1 collagen production is dependent on Akt and can be induced by Akt overexpression. Akt activation is observed in remnant kidneys in vivo. Thus, the role of Akt in progression of chronic hemodynamic glomerular disease is worthy of further exploration.

Effect of IgA aggregates on transforming growth factor-beta1 production in human mesangial cells and the intraglomerular expression of transforming growth factor-beta1 in patients with IgA nephropathy

BACKGROUND

Transforming growth factor-beta (TGF-beta) stimulates renal fibrosis in various renal diseases including IgA nephropathy.

METHODS

We examined whether immunoglobulin A (IgA) stimulated TGF-beta1 synthesis in human mesangial cells (MCs), and whether this effect was mediated through the protein kinase C (PKC) pathway. We measured the intraglomerular TGF-beta1 mRNA expression by using competitive RT-PCR, and this was compared with various parameters in IgA nephropathy patients.

RESULTS

The IgA aggregate increased the TGF-beta1 mRNA expression in MCs, while this expression was not affected by the culture media or IgG aggregate. Phorbol 12-myristate 13-acetate and calphostin C did not influence the TGF-beta1 mRNA expression that was increased by the IgA aggregate. Intraglomerular TGF-beta1 mRNA expression was significantly correlated with creatinine clearance (r = -0.764, p = 0.027), daily proteinuria (r = 0.781, p = 0.022), serum creatinine (r = 0.884, p = 0.004), and tubulointerstitial changes (r = 0.809, p = 0.015). Glomerular TGF-beta1 mRNA expression was associated with an increased tendency for glomerulosclerosis (r = 0.646, p = 0.084). After 4 years, patients with a high expression of intraglomerular TGF-beta1 mRNA showed a tendency for an decrease of their renal function.

CONCLUSION

The IgA aggregate increased TGF-beta1 mRNA expression in MCs, and this was independent of the PKC pathway. The evaluation of intraglomerular TGF-beta1 mRNA expression could be useful in predicting the progression of IgA nephropathy.

Mechanical stretch induces TGF-beta synthesis in hepatic stellate cells

BACKGROUND

It is known that mechanical stress induces extracellular matrix via transforming growth factor-beta (TGF-beta) synthesis in vascular smooth muscle cells. Activated hepatic stellate cells (HSCs) are an important source of TGF-beta in the liver. However, it remains unclear whether mechanical stress induces TGF-beta in HSCs. The Rho small GTP-binding protein (Rho) has recently emerged as an important regulator of actin and cytoskeleton. We examined whether TGF-beta is expressed in stretched HSCs and whether Rho is involved in stretch-induced TGF-beta synthesis.

MATERIALS AND METHODS

A cultured human HSC cell line, LI90, was used for this study. Hepatic stellate cells were cyclically stretched using the Flexercell(R) strain unit. Concentration of TGF-beta in the conditioned medium was estimated by a bioassay using mink lung epithelial cells transfected with a plasminogen activator inhibitor-1 promoter-luciferase construct. Transforming growth factor-beta mRNA expression of HSCs was estimated by a reverse-transcription polymerase chain reaction. Replication-defective adenoviral vectors expressing a dominant negative type of Rho was utilized to suppress its effect on HSCs.

RESULTS

Transforming growth factor-beta concentration of the conditioned media of stretched HSCs showed time-dependent increases as compared to nonstretched HSCs from 2 h to 24 h. Transforming growth factor-beta mRNA expression in stretched HSCs was increased compared with that in nonstretched HSCs. Transfection of dominant negative Rho inhibited the stretch-induced TGF-beta synthesis.

CONCLUSIONS

Mechanical stretch enhanced TGF-beta expression on mRNA and protein level in HSCs. Rho was closely related to stretch-induced TGF-beta synthesis in HSCs.

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

GLUT-1 overexpression: Link between hemodynamic and metabolic factors in glomerular injury?

Mesangial matrix deposition is the hallmark of hypertensive and diabetic glomerulopathy. At similar levels of systemic hypertension, Dahl salt-sensitive but not spontaneously hypertensive rats (SHR) develop glomerular hypertension, which is accompanied by upregulation of transforming growth factor beta1 (TGF-beta1), mesangial matrix expansion, and sclerosis. GLUT-1 is ubiquitously expressed and is the predominant glucose transporter in mesangial cells. In mesangial cells in vitro, GLUT-1 overexpression increases basal glucose transport, resulting in excess fibronectin and collagen production. TGF-beta1 has been shown to upregulate GLUT-1 expression. We demonstrated that in hypertensive Dahl salt-sensitive (S) rats fed 4% NaCl (systolic blood pressure [SBP]: 236+/-9 mm Hg), but not in similarly hypertensive SHR (SBP: 230+/-10 mm Hg) or their normotensive counterparts (Dahl S fed 0.5% NaCl, SBP: 145+/-5 mm Hg; and Wistar-Kyoto, SBP: 137+/-3 mm Hg), there was an 80% upregulation of glomerular GLUT-1 protein expression (P< or =0.03). This was accompanied by a 2.7-fold upregulation of TGF-beta1 protein expression in glomeruli of DSH compared with DSN rats (P=0.02). TGF-beta1 expression was not upregulated and did not differ in the glomeruli of Wistar-Kyoto and SHR rats. As an in vitro surrogate of the in vivo hemodynamic stress imposed by glomerular hypertension, we used mechanical stretching of human and rat mesangial cells. We found that after 33 hours of stretching, mesangial cells overexpressed GLUT-1 (40%) and showed an increase in basal glucose transport of similar magnitude (both P< or =0.01), which could be blocked with an anti TGF-beta1-neutralizing antibody. These studies suggest a novel link between hemodynamic and metabolic factors that may cooperate in inducing progressive glomerular injury in conditions characterized by glomerular hypertension.

The effects of weight loss on renal function in patients with severe obesity

Severe obesity is associated with increased renal plasma flow (RPF) and glomerular filtration rate (GFR). The aim of the present study was to examine whether weight loss may reverse glomerular dysfunction in obese subjects without overt renal disease. Renal glomerular function was studied in eight subjects with severe obesity (body mass index [BMI] 48.0 +/- 2.4) before and after weight loss. Nine healthy subjects served as controls. GFR and RPF were determined by measuring inulin and PAH clearance. In the obese group, GFR (145 +/- 14 ml/min) and RPF (803 +/- 39 ml/min) exceeded the control value by 61% (90 +/- 5 ml/min, P = 0.001) and 32% (610 +/- 41 ml/min, P < 0.005), respectively. Consequently, filtration fraction was increased. Mean arterial pressure, although normal, was higher than in the control group (101 +/- 4 versus 86 +/- 2 mmHg, P < 0.01). After weight loss, BMI decreased by 32 +/- 4%, to 32.1 +/- 1.5 (P = 0.001). GFR and RPF decreased to 110 +/- 7 ml/min (P = 0.01) and 698 +/- 42 ml/min (P < 0.02), respectively. Albumin excretion rate decreased from 16 microg/min (range, 4 to 152 microg/min) to 5 microg/min (range, 3 to 37 microg/min) (P < 0.01). Fractional clearance of albumin decreased from 3.2 x 10(-6) (range, 1.1 to 23 x 10(-6)) to 1.2 x 10(-6) (range, 0.5 to 6.8 x 10(-6)) (P < 0.02). This study shows that obesity-related glomerular hyperfiltration ameliorates after weight loss. The improvement in hyperfiltration may prevent the development of overt obesity-related glomerulopathy.

Impact of renal denervation on renal content of GLUT1, albuminuria and urinary TGF-beta1 in streptozotocin-induced diabetic rats

In long-term diabetes mellitus, the progression of nephropathy has been related to the occurrence of autonomic neuropathy. This study was designed to evaluate the effects of bilateral denervation of the kidneys of streptozotocin-diabetic rats, an experimental model that presents diabetic nephropathy with increased abundance of cortical GLUT1 in the kidney and increased urinary excretion of albumin and transforming growth factor-beta1 (TGF-beta1). Twenty-four-hour urinary TGF-beta1 (ELISA), urinary albumin (electroimmunoassay) and GLUT1 protein levels (Western blotting) in the renal cortex and medulla were evaluated in diabetic (n=13) and control (n=13) rats 45 days after streptozotocin injection, submitted or not to surgical renal denervation. Evaluations were performed 15 days after the surgery. The effects of renal denervation were confirmed by intra-renal decrease of norepinephrine levels. Mean arterial pressure did not differ between diabetic and control rats, whether they underwent renal denervation or not. Renal denervation increased cortical (6905+/-287, 3506+/-193, 4144+/-246 and 5204+/-516 AU in renal-denervated controls, controls, renal-denervated diabetics and diabetics, respectively) and medullar GLUT1 protein in control rats, but reverted the cortical GLUT1 protein rise determined by diabetes. Although kidney denervation in diabetic rats induced a decrease in cortical GLUT1 abundance toward normal levels, these levels did not reach those of normal animals. However, renal denervation did not determine any changes in urinary albumin and urinary TGF-beta1 in both diabetic (127.3+/-12 microg/24 h and 111.8+/-24 ng mg(-1) creatinine, respectively) and control rats (45.9+/-3 microg/24 h and 13.4+/-4 ng mg(-1) creatinine, respectively). In conclusion, early-phase renal denervation in streptozotocin-diabetic rats produces a normalisation of previously elevated cortical GLUT1 protein content, but is not enough for reverting the increased urinary TGF-beta1 and albuminuria of diabetes.

The effect of ramipril on albumin excretion in diabetes and hypertension: the role of increased lysosomal activity and decreased transforming growth factor-beta expression

OBJECTIVES

Albumin excretion is modulated post-filtration by lysosomal processing that produces a spectrum of albumin-derived material in urine, much of which is not detected by conventional immunoassays. This study aimed to determine the efficacy of ramipril treatment (+ RAM) after 24 weeks on total albumin excretion (intact plus albumin-derived peptides) in spontaneously hypertensive rats (SHR) and Wistar-Kyoto (WKY) rats with (d) and without (c) diabetes.

METHODS

Intact albumin excretion was analysed by radioimmunoassay and total albumin excretion was analysed by measuring radioactivity derived from circulating [ C]albumin. Renal lysosomal activity was determined by urinary [ H]dextran sulphate desulphation. Renal transforming growth factor-beta 1 (TGF-beta 1), TGF-beta inducible gene-h3 (beta ig-h3) and angiotensinogen mRNA production were analysed by real time reverse transcriptase-polymerase chain reaction.

RESULTS

Hypertension (SHR-c and SHR-d) resulted in a significant increase in intact albumin excretion, which was significantly reduced by ramipril treatment (P < 0.05 for SHR-c + RAM and 0.001 for SHR-d + RAM compared to non-treated). This was accompanied by a significant decrease in blood pressure (P < 0.001 for SHR-c + RAM and SHR-d + RAM), renal beta ig-h3 mRNA production (P < 0.05 for SHR-c + RAM and SHR-d + RAM), and an increase in lysosomal activity. Diabetes (WKY-d and SHR-d) primarily caused a significant increase in total albumin excretion, predominantly in the form of albumin-derived fragments in the WKY-d group and intact albumin in the SHR-d group. Ramipril treatment reduced total albumin excretion in the WKY-d + RAM group (P < 0.001).

CONCLUSIONS

Ramipril prevents increases in both intact albumin and total albumin excretion in hypertensive and diabetic states, respectively.

Mechanical stretching force promotes collagen synthesis by cultured cells from human ligamentum flavum via transforming growth factor-beta1

Although mechanical stress as a result of spinal instability is known to cause hypertrophy of the ligamentum flavum resulting in degenerative spinal canal stenosis, the mechanism of the ligament hypertrophy is not well understood. In the present study, we investigated the effect of mechanical stretching force on collagen synthesis and transforming growth factor-beta1 (TGF-beta1) production using ligament cells isolated from human ligamentum flavum in vitro. Ligamentum flavum cells (LFCs) were isolated from human ligamentum flavum obtained from patients who underwent lumbar spine surgery. The LFCs were subjected to a mechanical stretching force using a commercially available stretching device that physically deformed the cells. Collagen synthesis and TGF-beta1 production levels in the LFCs were then examined. Notable increases were observed in the gene expressions of collagen types I, III, and V in LFCs subjected to mechanical stretching force. The increase in collagen gene expression of LFCs was inhibited in the presence of anti-TGF-beta1 antibodies. Production of TGF-beta1 by the LFCs also increased significantly by the mechanical stretching force. Exogenous application of TGF-beta1 was confirmed to increase collagen synthesis of the LFCs. This data indicated that mechanical stretching force can promote TGF-beta1 production by LFCs, resulting in hypertrophy of the ligament.

Haemodynamics in microvascular complications in type 1 diabetes

Type 1 diabetes is commonly associated with microvascular complications. Most of the microvascular blood vessels are involved but those in the kidney, retina and large nerves exhibit the more significant pathology. Haemodynamic and metabolic factors both alone and through the activation of a common pathway contribute to the characteristic dysfunction observed in diabetic vasculopathy. The haemodynamic abnormalities in type 1 diabetes are characterized by increased systemic blood pressure and altered blood flow with subsequent activation of various vasoactive factors, which can contribute to the maintenance of the haemodynamic alterations and to the development and progression of the microvascular complications. These vasoactive factors include vasoconstrictors such as angiotensin II, and endothelin, as well as vasodilators such as nitric oxide (NO). Systemic hypertension and vasoactive factors independently and in interaction with the metabolic pathway activate intracellular second messengers, nuclear transcription factors and various growth factors which lead to the typical functional and structural alterations of diabetic microvascular complications. Therapeutic strategies involved in the management and prevention of diabetic complications currently include antihypertensive agents, particularly those that interrupt the renin-angiotensin system. Further understanding of the interactions among the vasoactive factors, the intracellular second messengers and the growth factors may help to identify novel strategies to influence the action of the vasoactive factors. These novel therapies, together with specific inhibitors of the metabolic pathway or the common pathway, may provide the possibility of preventing or even reversing the progression of diabetic microvascular complications.

Effects of stenting on adjacent vascular distensibility and neointima formation: role of nitric oxide

Intravascular stents increase long-term patency but their effects on the vascular mechanics of adjacent segments have not been studied. In this study, stents were deployed in the rabbit abdominal aorta after 1 week of normal diet, 1% cholesterol diet or 1% cholesterol diet with L-nitro arginine (L-NA 60 mg/l water). Intravascular ultrasound showed a small distal decrease in vessel distensibility (area/pressure * 100) before stenting. Distensibility was almost abolished by stenting (0.12 +/- 0.01, p < 0.001), but was increased proximal to the stent and decreased distal to the stent both acutely (proximal: 1.18 +/- 0.10 vs distal: 0.65 +/- 0.06, p < 0.001), and at 4 weeks (proximal: 1.05 +/- 0.08 vs distal: 0.37 +/- 0.07, p < 0.001). Nitric oxide (NO) activity was enhanced proximal to and within the stent, and remained constant distal to the stent, (versus control, proximal: 57 +/- 23%, stent: 136 +/- 35%, distal: 2 +/- 12%, p < 0.01). The I/M ratio was significantly higher proximal to and within the stent than in the distal segment (proximal: 0.40 +/- 0.10, stent: 0.37 +/- 0.12, distal: 0.12 +/- 0.11, p < 0.01). NO blockade with L-NA prevented hyperdistensibility proximally, and significantly increased the I/M ratio within the stent and distally (stent: 0.81 +/- 0.19, distal: 0.30 +/- 0.10, p < 0.05) but not proximally (0.38 +/- 0.09). In conclusion, aortic stenting increases proximal vascular distensibility and intimal lesion formation. Nitric oxide blockade augments intimal growth within but not proximal to the stent.

Renal handling of albumin: a critical review of basic concepts and perspective

Biochemical and physiological processes that underlie the mechanism of albuminuria are completely reassessed in this article in view of recent discoveries that filtered proteins undergo rapid degradation during renal passage and the resulting excreted peptide fragments are not detected by conventional urine protein assays. This means that filtered protein and/or albumin levels in urine have been seriously underestimated. The concept that albuminuria is a result of changes in glomerular permeability is questioned in light of these findings and also in terms of a critical examination of charge selectivity, shunts, or large-pore formation and hemodynamic effects. The glomerulus appears to function merely in terms of size selectivity alone, and for albumin, this does not change significantly in disease states. Intensive albumin processing by a living kidney occurs through cellular processes distal to the glomerular basement membrane. Failure of this cellular processing primarily leads to albuminuria. This review brings together recent data about urinary albumin clearance and current knowledge of receptors known to process albumin in both health and disease states. We conclude with a discussion of topical and controversial issues associated with the proposed new understanding of renal handling of albumin.

Cyclic AMP inhibits stretch-induced overexpression of fibronectin in glomerular mesangial cells

Glomerular hypertension is proposed to play an important role in the progression of various glomerular diseases. Glomerular mesangial cells are considered to be exposed to the stretch stress due to glomerular hypertension and are found to produce the excess amount of extracellular matrix (ECM) proteins including fibronectin when exposed to the mechanical stretch. Herein, we provide the evidence that cAMP-generating agents inhibit the stretch-induced overexpression of fibronectin through the inhibition of the stretch-induced activation of mitogen-activated protein kinases (MAPKs) in protein kinase-A-dependent manner. We also found that the mechanical stretch enhanced the binding of nuclear extracts to activator protein-1 (AP-1)-like sequences in the promoter region of rat fibronectin gene and this enhancement was also prevented by the cAMP-generating agent. These results indicate that the agents, which activate cAMP/protein kinase-A axis, may work protectively against the injury from glomerular hypertension in mesangial cells.

Modulation of membrane traffic by mechanical stimuli

All cells experience and respond to mechanical stimuli, such as changes in plasma membrane tension, shear stress, hydrostatic pressure, and compression. This review is an examination of the changes in membrane traffic that occur in response to mechanical forces. The plasma membrane has an associated tension that modulates both exocytosis and endocytosis. As membrane tension increases, exocytosis is stimulated, which acts to decrease membrane tension. In contrast, increased membrane tension slows endocytosis, whereas decreased tension stimulates internalization. In most cases, secretion is stimulated by external mechanical stimuli. However, in some cells mechanical forces block secretion. External stimuli also enhance membrane and fluid endocytosis in several cell types. Transduction of mechanical stimuli into changes in exocytosis/endocytosis may involve the cytoskeleton, stretch-activated channels, integrins, phospholipases, tyrosine kinases, and cAMP.

Albuminuria in hypertension is linked to altered lysosomal activity and TGF-beta1 expression

Increased intraglomerular pressure is considered a major factor for increased albumin excretion in hypertension. However, other factors should also be considered because recent studies in both humans and rats have demonstrated that proteins undergoing filtration and renal passage are extensively modified by renal cell lysosomal processing; >95% of albumin is degraded to peptides that are not detected by routine immunochemical assays. Changes in postglomerular lysosomal processing may therefore be responsible for the increased intact albumin excreted in hypertension-related kidney disease. We hypothesize that transforming growth factor-beta, which is known to decrease lysosomal activity, may be upregulated in hypertension and may play a role in increased intact albumin excretion. The aims of this study were to determine the effect that hypertension has on (1) renal cell lysosomal processing of albumin and dextran sulfate, (2) glomerular permeability, and (3) renal transforming growth factor-beta(1) expression. Spontaneously hypertensive rats and Wistar-Kyoto rats were used at 8, 16, and 24 weeks. We demonstrate that albuminuria in hypertension is linked to an inhibition of lysosomal processing as determined by (1) size exclusion chromatography analysis of urinary [(14)C]albumin structural integrity and (2) ion exchange analysis of urinary [(3)H]dextran sulfate. This inhibition gives rise to an increased proportion of radioimmunoassay detectable (intact) albumin and intact dextran sulfate independent of changes in glomerular capillary wall permeability as determined by the fractional clearance of [(3)H]Ficolls of various radii. These changes may be correlated with increased renal transforming growth factor-beta(1) expression.

Potentiation of glucose-mediated glomerular injury by mechanical strain

1. The glomerular injury of diabetes is characterized by the progressive accumulation of extracellular matrix in the mesangial regions, ultimately resulting in glomerulosclerosis. 2. The excessive glomerular extracellular matrix formation associated with the haemodynamic alteration of diabetes is the result of mesangial mechanical strain. 3. The increased synthesis and deposition of extracellular matrix is augmented by the presence of high glucose concentrations. 4. Both mechanical strain and high glucose share many of the mechanisms mediating their metabolic effects, including the stimulation of prosclerotic growth factors. 5. Little is known about factors that may influence the long-term effects of mechanical strain, but the preservation of the F-actin cytoskeleton is likely an important modulator of the resulting injury.

Dietary phytoestrogens: a possible role in renal disease protection

There is growing evidence that dietary phytoestrogens have a beneficial role in chronic renal disease. This review summarizes the recent findings from dietary intervention studies performed in animals and humans suggesting that consumption of soy-based protein rich in isoflavones and flaxseed rich in lignans retards the development and progression of chronic renal disease. In several animal models of renal disease, both soy protein and flaxseed have been shown to limit or reduce proteinuria and renal pathological lesions associated with progressive renal failure. In studies of human subjects with different types of chronic renal disease, soy protein and flaxseed also appear to moderate proteinuria and preserve renal function. However, most of these clinical trials were of relatively short duration and involved a small number of patients. Furthermore, it is not clear whether the renal protective effects of soy protein and flaxseed are caused by the isoflavones (daidzein and genistein) and lignans (matairesinol and secoisolariciresinol) or some other component. The biochemistry, metabolism, and mechanisms of actions of isoflavones and lignans are discussed. Isoflavones and lignans appear to act through various mechanisms that modulate cell growth and proliferation, extracellular matrix synthesis, inflammation, and oxidative stress. Some of these actions have been shown in vitro, but studies of the mechanisms operative in vivo are lacking. The diversity of cellular actions of isoflavones and lignans supports their protective effects in a variety of experimental and human types of chronic renal disease. Further investigations are needed to evaluate their long-term effects on renal disease progression in patients with chronic renal failure.

Angiotensin II and the pathophysiology of cardiovascular remodeling

Hypertension is associated with a number of adverse morphologic and functional changes in the cardiovascular system. These include remodeling of the left ventricle, alterations in the morphology and mechanical properties of the vasculature, and the development of endothelial dysfunction. Recent studies have shown that angiotensin II is capable of mediating these changes via its interaction with the angiotensin II type 1 receptor. These nonhemodynamic effects of angiotensin II are independent of its effect on blood pressure. Thus, elevated levels of angiotensin II may lead directly to many hypertension-associated pathologies. Recent evidence that mechanical strain, oxidized low-density lipoprotein cholesterol, and aldosterone can cause upregulation of angiotensin II type 1 receptors indicates that activation of the renin-angiotensin system is not necessary for the actions of angiotensin II to be amplified. Because the strain on the vessel wall may be increased under conditions of hypertension, increased arterial pressure may amplify the actions of angiotensin II without a discernible increase in plasma angiotensin II levels. In both the myocardium and the peripheral vasculature, fibrosis is a major component of the remodeling that occurs in hypertension. There is substantial evidence that transforming growth factor beta-1 (TGF-beta(1)) mediates angiotensin-II-induced fibrosis in patients with hypertension and in those with a variety of nephropathies. Mechanical strain also induces fibrosis in a mechanism mediated by TGF-beta(1). This cytokine thus represents a common pathway by which angiotensin II and increased arterial pressure may induce cardiovascular fibrosis.

Podocytes respond to mechanical stress in vitro

Glomerular capillary pressure is thought to affect the structure and function of glomerular cells. However, it is unknown whether podocytes are intrinsically sensitive to mechanical forces. In the present study, differentiated mouse podocytes were cultured on flexible silicone membranes. Biaxial cyclic stress (0.5 Hz and 5% linear strain) was applied to the membranes for up to 3 d. Mechanical stress reduced the size of podocyte cell bodies, and processes became thin and elongated. Podocytes did not align in the inhomogeneous force field. Whereas the network of microtubules and that of the intermediate filament vimentin exhibited no major changes, mechanical stress induced a reversible reorganization of the actin cytoskeleton: transversal stress fibers (SF) disappeared and radial SF that were connected to an actin-rich center (ARC) formed. Epithelial and fibroblast cell lines did not exhibit a comparable stress-induced reorganization of the F-actin. Confocal and electron microscopy revealed an ellipsoidal and dense filamentous structure of the ARC. Myosin II, alpha-actinin, and the podocyte-specific protein synaptopodin were present in radial SF, but, opposite to F-actin, they were not enriched in the ARC. The formation of the ARC and of radial SF in response to mechanical stress was inhibited by nonspecific blockade of Ca(2+) influx with Ni(2+) (1 mM), by Rho kinase inhibition with Y-27632 (10 microM), but not by inhibition of stretch-activated cation channels with Gd(3+) (50 microM). In summary, mechanical stress induces a unique reorganization of the actin cytoskeleton in podocytes, featuring radial SF and an ARC, which differ in protein composition. The F-actin reorganization in response to mechanical stress depends on Ca(2+) influx and Rho kinase. The present study provides the first direct evidence that podocytes are mechanosensitive.

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.

Pulsatile stretch-induced extracellular signal-regulated kinase 1/2 activation in organ culture of rabbit aorta involves reactive oxygen species

Increased steady intraluminal pressure in blood vessels activates the extracellular signal-regulated kinase (ERK)1/2 pathway. However, signal transduction of pulsatile stretch has not been elucidated. Using an organ culture model of rabbit aorta, we studied ERK1/2 activation by pulsatility in vessels maintained at 80 mm Hg for 24 hours. ERK1/2 activity was evaluated by in-gel kinase assays and by Western blot. Compared with control aortas without pulsatility, aortas submitted to a pulsatile 10% variation in vessel diameter displayed a significant increase in ERK1/2 activity (207+/-12%, P<0.001), which remained high after removal of the endothelium. Unlike steady overstretch, pulsatile stretch-induced activation of ERK1/2 was not modified by herbimycin A, a Src family tyrosine kinase inhibitor, but was reduced by other tyrosine kinase inhibitors, tyrphostin A48 and genistein (162+/-27% and 144+/-14%, respectively). Conversely, ERK1/2 activity was markedly decreased in pulsatile vessels treated with staurosporine (114+/-18%) although neither of the more specific protein kinase C inhibitors, Ro-31-8220 or Gö-6976, blocked ERK1/2 activation (209+/-24% and 238+/-34%, respectively), whereas staurosporine had no effect on steady overstretch-induced ERK1/2 activation. Pulsatility induced superoxide anion generation, which was prevented by the NADPH oxidase inhibitor diphenyleneiodonium. Furthermore, polyethylene glycol-superoxide dismutase completely abolished ERK1/2 activation by pulsatility (114+/-12%). Finally, ERK1/2 and O(2)(-) levels in freshly isolated vessels were equivalent to the levels found in pulsatile vessels. In conclusion, pulsatile stretch activates ERK1/2 in the arterial wall via pathways different from those induced by steady overstretch. Pulsatility might be considered a physiological stimulus that maintains a certain degree of ERK1/2 activation via oxygen-derived free radical production.

Expression of LOX-1, an oxidized low-density lipoprotein receptor, in experimental hypertensive glomerulosclerosis

Oxidized low-density lipoprotein (OxLDL) has been implicated in atherosclerosis and glomerulosclerosis. LOX-1 is a recently identified OxLDL receptor that is abundantly expressed in vascular endothelial cells. The aim of the present study was to investigate LOX-1 expression in the kidneys of hypertensive rats. Dahl salt-sensitive (DS) and salt-resistant (DR) rats were fed a 0.3% or 8% NaCl diet. Some DS 8% rats were treated with manidipine or hydralazine. LOX-1 gene expression was markedly elevated in the kidneys and glomeruli of hypertensive DS 8% rats compared with those of normotensive DR and DS 0.3% rats. Prolonged salt loading further increased the renal LOX-1 expression in DS rats. The LOX-1 upregulation in DS 8% rats was accompanied by renal overexpression of transforming growth factor-beta 1 and type I collagen, impaired renal function, and histologic glomerulosclerotic changes, all of which were ameliorated by antihypertensive treatment. LOX-1 was indeed expressed in the glomeruli in vivo and in cultured glomerular cells in vitro. However, LOX-1 expression was elevated in the aorta but not the kidneys of spontaneously hypertensive rats, which exhibited hypertension but minor glomerulosclerotic changes. In conclusion, the LOX-1 upregulation in the kidney of DS 8% rats was parallel to glomerulosclerotic changes and renal dysfunction, suggesting a possible pathogenetic role for renal LOX-1 in the progression to hypertensive glomerulosclerosis.

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.