Insulin-like growth factor I induces mesangial proliferation and increases mRNA and secretion of collagen

Klotho Supplementation Reverses Renal Dysfunction and Interstitial Fibrosis in Remnant Kidney

INTRODUCTION

While recent investigations show that klotho exerts renoprotective actions, it has not been fully addressed whether klotho protein supplementation reverses renal damage.

METHODS

The impacts of subcutaneous klotho supplementation on rats with subtotal nephrectomy were examined. Animals were divided into 3 groups: group 1 (short remnant [SR]): remnant kidney for 4 weeks, group 2 (long remnant [LR]): remnant kidney for 12 weeks, and group 3 (klotho supplementation [KL]): klotho protein (20 μg/kg/day) supplementation on the remnant kidney. Blood pressure, blood and urine compositions with conventional methods such as enzyme-linked immunosorbent assay and radioimmunoassay, kidney histology, and renal expressions of various genes were analyzed. In vitro studies were also performed to support in vivo findings.

RESULTS

Klotho protein supplementation decreased albuminuria (-43%), systolic blood pressure (-16%), fibroblast growth factor (FGF) 23 (-51%) and serum phosphate levels (-19%), renal angiotensin II concentration (-43%), fibrosis index (-70%), renal expressions of collagen I (-55%), and transforming growth factor β (-59%) (p < 0.05 for all). Klotho supplementation enhanced fractional excretion of phosphate (+45%), glomerular filtration rate (+76%), renal expressions of klotho (+148%), superoxide dismutase (+124%), and bone morphogenetic protein (BMP) 7 (+174%) (p < 0.05 for all).

CONCLUSION

Our data indicated that klotho protein supplementation inactivated renal renin-angiotensin system, reducing blood pressure and albuminuria in remnant kidney. Furthermore, exogenous klotho protein supplementation elevated endogenous klotho expression to increase phosphate excretion with resultant reductions in FGF23 and serum phosphate. Finally, klotho supplementation reversed renal dysfunction and fibrosis in association with improved BMP7 in remnant kidney.

Klotho supplementation attenuates blood pressure and albuminuria in murine model of IgA nephropathy

BACKGROUND

Klotho interacts with various membrane proteins, such as transforming growth factor-β (TGFβ) and insulin-like growth factor (IGF) receptors. The renal expression of klotho is diminished in chronic kidney disease.

METHOD

In this study, we assessed the effects of klotho supplementation on a murine model of IgA nephropathy. Twenty-four-week-old hyper serum IgA (HIGA) mice were subcutaneously injected daily with recombinant human klotho protein (20 μg/kg per day) or the vehicle. After 2 months, the mice were killed using an anesthesia overdose and their kidneys were harvested for analysis.

RESULTS

Supplementation of exogenous klotho protein reduced SBP, albuminuria, 8-epi-prostaglandin F2α excretion, glomerular filtration rate, renal angiotensin II concentration, and angiotensinogen expression in HIGA mice. Additionally, it enhanced renal expression of superoxide dismutase (SOD) and renal klotho itself. The findings using laser-manipulated microdissection demonstrated that klotho supplementation reduced the glomerular expression of TGFβ, fibronectin, and IGF, and increased the glomerular expression of connexin (Cx) 40.

CONCLUSION

These results indicate that klotho supplementation reduces blood pressure by suppressing the renin--angiotensin system in HIGA mice. Klotho inhibits IGF signaling to preserve glomerular Cx40 levels, ameliorating albuminuria in HIGA mice. Klotho protein supplementation attenuates mesangial expansion by inhibiting TGFβ signaling in HIGA mice.

Acromegaly accompanied by diabetes mellitus and polycystic kidney disease

Acromegaly is characterized by autonomous excessive growth hormone (GH) secretion, generally due to GH-producing pituitary adenoma, and is associated with various systemic comorbidities including diabetes mellitus. Polycystic kidney disease (PKD) is characterized by the growth of numerous cysts in the kidneys that deteriorate renal function. While possible renal effects of excessive GH exposure have been a current issue in experimental medicine, only five cases of coexisting acromegaly and PKD have been reported previously, and little is known regarding the influence of acromegaly on renal disease. We treated a 50-year-old male with diabetes mellitus who showed a sudden and rapid decline of renal function along with increasing proteinuria, which led to diagnoses of PKD and acromegaly. His urinary protein levels were increased together with excessive GH secretion and worsening glycemic control. An increase of total kidney volume was also noted. Transsphenoidal surgery for the pituitary adenoma was successfully performed. Marked improvement of hyperglycemia and proteinuria were observed after the surgery, but renal function was unchanged. The patient's clinical course suggested common aspects of excessive GH secretion as an accelerating factor of the progression of diabetic nephropathy and PKD via direct and indirect pathways. Although coexisting acromegaly and PKD is clinically rare, vigilance for early diagnosis of acromegaly is appropriate in patients with diabetes and/or PKD, especially in those showing unexpected exacerbation of renal dysfunction.

Renal hypoxia in kidney disease: Cause or consequence?

Tissue hypoxia has been proposed as an important factor in the pathophysiology of both chronic kidney disease (CKD) and acute kidney injury (AKI), initiating and propagating a vicious cycle of tubular injury, vascular rarefaction, and fibrosis and thus exacerbation of hypoxia. Here, we critically evaluate this proposition by systematically reviewing the literature relevant to the following six questions: (i) Is kidney disease always associated with tissue hypoxia? (ii) Does tissue hypoxia drive signalling cascades that lead to tissue damage and dysfunction? (iii) Does tissue hypoxia per se lead to kidney disease? (iv) Does tissue hypoxia precede pathology? (v) Does tissue hypoxia colocalize with pathology? (vi) Does prevention of tissue hypoxia prevent kidney disease? We conclude that tissue hypoxia is a common feature of both AKI and CKD. Furthermore, at least under in vitro conditions, renal tissue hypoxia drives signalling cascades that lead to tissue damage and dysfunction. Tissue hypoxia itself can lead to renal pathology, independent of other known risk factors for kidney disease. There is also some evidence that tissue hypoxia precedes renal pathology, at least in some forms of kidney disease. However, we have made relatively little progress in determining the spatial relationships between tissue hypoxia and pathological processes (i.e. colocalization) or whether therapies targeted to reduce tissue hypoxia can prevent or delay the progression of renal disease. Thus, the hypothesis that tissue hypoxia is a "common pathway" to both AKI and CKD still remains to be adequately tested.

Rs1520220 and Rs2195239 Polymorphisms of IGF-1 Gene Associated with Histopathological Grades in IgA Nephropathy in Northwestern Chinese Han Population

BACKGROUND/AIMS

Insulin-like growth factor-1 (IGF-1) plays important roles in cellular proliferation, differentiation, and growth. Previous studies showed that single-nucleotide polymorphisms (SNPs) of IGF-1 are associated with various diseases. This case-control study aimed to examine the relationship between IGF-1 polymorphisms and IgA nephropathy (IgAN) risk in a Chinese Han population.

METHODS

We recruited 351 IgAN patients and 310 healthy controls from Northwestern China. Sequenom MassARRAY was utilized to examine the genotypes of two common IGF-1 SNPs (rs1520220 and rs2195239). Odds ratios (ORs) and 95% confidence intervals (95% CIs) were calculated by the Chi square test to evaluate the associations between IGF-1 and IgAN.

RESULTS

Our study demonstrated that IGF-1 gene rs1520220 and rs2195239 polymorphisms did not confer susceptibility to IgAN. We found no correlation between gender, blood pressure, proteinuria, eGFR, and IgAN in both SNPs. However, the rs1520220 and rs2195239 variants were correlated with M1 and E1 in patients with IgAN (M0/M1: CC vs. CG+GG: OR = 1.62, P = 0.04; E0/E1: CC vs. CG+GG: OR = 1.95, P = 0.004; GG vs. GC+CC: OR = 1.90, P = 0.004, respectively).

CONCLUSION

These results indicate that IGF-1 gene polymorphisms play crucial roles in the histopathological progression of IgAN in the Chinese Han population.

Nephrotoxicity Induced by Cisplatin Intake in Experimental Rats and Therapeutic Approach of Using Mesenchymal Stem Cells and Spironolactone

Chronic kidney disease may lead to subsequent tissue fibrosis. However, many factors can combat injurious stimuli in these tissues aiming to repair, heal, and alleviate any disturbance. Chemokines release, migration of inflammatory cells to the affected site, and activation of fibroblasts for the production of extracellular matrix are commonly observed in this disease. In the last years, many studies have focused on spironolactone (SPL), a mineralocorticoid receptor antagonist, and its pharmacological effects. In the present study, SPL was selected as an anti-inflammatory agent to combat nephrotoxicity and renal fibrosis induced by cisplatin. Mesenchymal stem cells (MSCs) were also selected in addition as a referring agent. Renal fibrosis induced by cisplatin intake significantly increased creatinine, urea, nuclear factor kappa B, insulin-like growth factor-1, fibroblast growth factor-23, and kidney malondialdehyde (MDA) content. Hepatocyte growth factor and renal content of reduced glutathione demonstrated a significant decrease. Histopathological examination of kidney tissues demonstrated marked cellular changes which are correlated with the biochemical results. Oral SPL intake (20 mg/kg/body weight) daily for 4 weeks and MSCs administration (3 × 10⁶ cell/rat) intravenous to the experimental rats resulted in a significant improvement of both the biomarkers studied and the histopathological profile of the renal tissue. Individual administration of spironolactone and MSCs exhibited a marked anti-inflammatory potential and alleviated to a great extent the nephrotoxicity and renal fibrotic pattern induced by cisplatin.

PAPP-A in normal human mesangial cells: effect of inflammation and factors related to diabetic nephropathy

Insulin-like growth factors (IGFs) are implicated in the development of diabetic nephropathy (DN) and are shown to increase proliferation and extracellular matrix production in mesangial cells. The IGF system is complex and is composed of ligands, receptors, six binding proteins (IGF BPs) and a novel zinc metalloproteinase - pregnancy-associated plasma protein (PAPP)-A. PAPP-A increases the local bioavailability of IGF through the cleavage of IGF BP-4. Mesangial expansion is a major component of DN, and PAPP-A is shown to be increased in the glomeruli of patients with DN. Therefore, we determined the expression of PAPP-A and components of the IGF system in normal human mesangial cells (HMCs) and their regulation by factors known to be involved in DN. Under basal conditions, HMCs expressed PAPP-A, IGF1 receptor and all six IGF BPs. Interleukin (IL)-1β was the most potent stimulus for PAPP-A expression (5-fold) followed by tumor necrosis factor (TNF)-α (2.5-fold). This PAPP-A was secreted, cell associated and proteolytically active. IL1β also increased IGF BP-1expression (3-fold) with either reduction or no effect on other IGF BPs. Generally, TNF-α treatment decreased IGF BP expression. No treatment effect on PAPP-A or IGF BPs was seen with IL6, IGFs, advanced glycation end products or prolonged hyperglycemia. In addition, stimulation of HMCs with IGF1 alone or IGF1 complexed to wild-type, but not protease-resistant, IGF BP-4 led to increased [(3)H]-thymidine incorporation. In conclusion, these novel findings of PAPP-A and its regulation by proinflammatory cytokines, as well as the comprehensive analysis of the IGF system regulation in HMCs, suggest a mechanism by which inflammatory states such as DN can impact IGF activity in the kidney.

Anti-dsDNA antibodies and resident renal cells - Their putative roles in pathogenesis of renal lesions in lupus nephritis

Lupus nephritis affects up to 70% of patients with systemic lupus erythematosus and is an important treatable cause of kidney failure. Cardinal features of lupus nephritis include loss of self-tolerance, production of autoantibodies, immune complex deposition and immune-mediated injury to the kidney, resulting in increased cell proliferation, apoptosis, and induction of inflammatory and fibrotic processes that destroy normal nephrons. The production anti-dsDNA antibodies is a cardinal feature in lupus and their level correlates with disease activity. In addition to the formation of immune complexes thereby triggering complement activation, how anti-dsDNA antibodies home to the kidney and induce pathological processes in the renal parenchyma remain to be fully elucidated. Data from our laboratory and other investigators show that the properties of anti-dsDNA antibodies vary between patients and change over time, and that anti-dsDNA antibodies could bind directly to integral cell surface molecules such as annexin II or α-actinin, or indirectly through chromatin material deposited on the cell surface. The binding of anti-dsDNA antibodies to mesangial cells and proximal renal tubular epithelial cells triggers downstream inflammatory and fibrotic pathways, which include the activation of the PKC and MAPK signaling pathways, increased secretion of pro-inflammatory cytokines and matrix protein deposition that contribute to pathological processes in the renal parenchyma.

Low Insulin-Like Growth Factor-1 Level in Obesity Nephropathy: A New Risk Factor?

Introduction

IGF-1 (insulin-like growth factor-1) is a hormone involved in cell growth and other important processes. In the kidney, IGF-1 has a stimulating effect, increasing the blood flow and glomerular filtration rate. Although many experimental animal studies regarding the role of IGF-1 in the kidney have been conducted, few human studies are available in the literature. Obesity is a cause of renal failure, and several glomerular lesions associated with obesity have been described. However, no studies regarding the levels of IGF-1 in morbidly obese patients with renal injury associated with obesity have been conducted.

Aim

To determine the serum IGF-1 concentrations in morbidly obese patients with normal renal function but with different types of early obesity-related glomerular lesions and to evaluate the possible relationship between IGF-1 and the presence of renal lesions.

Methods

Eighty morbidly obese patients with renal biopsy, including 11 patients with no evidence of renal lesion, 17 patients with single glomerulomegaly, 21 patients with single podocyte hypertrophy, 10 patients with glomerulomegaly and podocyte hypertrophy, 5 patients with focal segmental hyalinosis, and 16 patients with increased mesangial matrix and/or mesangial proliferation, participated in this study. Biological parameters, including serum IGF-1 concentrations with the standard deviation score for age (SDS-IGF-1), were determined for all patients.

Results

Eighty patients (50 women and 30 men) with a mean BMI of 52.63 ± 8.71 and a mean age of 42.40 ± 9.45 years were included in this study. IGF-1, IGF-1 SDS and IGF-1BP3 levels according to the renal injury were compared (normal glomeruli: IGF-1 = 190.17 ± 72.46; glomerulomegaly: IGF-1 = 122.3 ± 50.05; podocyte hypertrophy: IGF-1 = 119.81 ± 60.34; focal segmental hyalinosis: IGF-1 170.98 ± 100.83, increased mesangial matrix and/or mesangial proliferation: IGF-1 117.73 ± 63.87). Statistically significant differences were observed between serum levels of IGF-1 and between the levels of SDS-IGF-1 by comparing the group without glomerular lesion with the group formed by patients with any type of glomerular injury. Logistic regression analysis was performed, with the dependent variable defined as the glomerular injury. In the multivariate analysis, only SDS-IGF-1 was associated with glomerular injury, and low levels of IGF-1 SDS were a risk factor for kidney injury.

Conclusions

Our study demonstrates that low IGF-1 serum levels are associated with renal lesions in morbidly obese patients without overt clinical renal manifestations.

Assessment of Urine Proteomics in Type 1 Primary Hyperoxaluria

BACKGROUND

Primary hyperoxaluria type 1 (PH1) and idiopathic hypercalciuria (IHC) are stone-forming diseases that may result in the formation of calcium (Ca) oxalate (Ox) stones, nephrocalcinosis, and progressive chronic kidney disease (CKD). Poorer clinical outcome in PH1 is segregated by the highest urine (Ur)-Ox (UrOx), while IHC outcomes are not predictable by UrCa. We hypothesized that differences would be found in selected Ur-protein (PRO) patterns in PH1 and IHC, compared to healthy intra-familial sibling controls (C) of PH1 patients. We also hypothesized that the PRO patterns associated with higher UrOx levels would reflect injury, inflammation, biomineralization, and abnormal tissue repair processes in PH1.

METHODS

Twenty four-hour Ur samples were obtained from 3 cohorts: PH1 (n = 47); IHC (n = 35) and C (n = 13) and were analyzed using targeted platform-based multi-analyte profile immunoassays and for UrOx and UrCa by biochemical measurements.

RESULTS

Known stone matrix constituents, osteopontin, calbindin, and vitronectin were lowest in PH1 (C > IHC > PH1; p < 0.05). Ur-interleukin-10; chromogranin A; epidermal growth factor (EGF); insulin-like growth factor-1 (IGF-1), and macrophage inflammatory PRO-1α (MIP-1α) were higher in PH1 > C (p = 0.03 to p < 0.05). Fetuin A; IGF-1, MIP-1α, and vascular cell adhesion molecule-1 were highest in PH1 > IHC (p < 0.001 to p = 0.005).

CONCLUSION

PH1 Ur-PROs reflected overt inflammation, chemotaxis, oxidative stress, growth factors (including EGF), and pro-angiogenic and calcification regulation/inhibition compared to the C and IHC cohorts. Many of the up- and downregulated PH1-PROs found in this study are also found in CKD, acute kidney injury, stone formers, and/or stone matrices. Further data analyses may provide evidence for PH1 unique PROs or demonstrate a poorer clinical outcome.

Growth Hormone and Craniofacial Tissues. An update

Growth hormone is an important regulator of bone homeostasis. In childhood, it determines the longitudinal bone growth, skeletal maturation, and acquisition of bone mass. In adulthood, it is necessary to maintain bone mass throughout life. Although an association between craniofacial and somatic development has been clearly established, craniofacial growth involves complex interactions of genes, hormones and environment. Moreover, as an anabolic hormone seems to have an important role in the regulation of bone remodeling, muscle enhancement and tooth development. In this paper the influence of growth hormone on oral tissues is reviewed.

Cross-talk between integrin receptor and insulin-like growth factor receptor in regulation of collagen biosynthesis in cultured fibroblasts

PURPOSE

Cellular processes are regulated by signals generated by adhesion receptors and growth factor receptors. IGFbinding protein 1 (IGFBP-1) is a molecule which may affect the both signaling pathways through inactivation of IGF-I (ligand for IGF-IR) and binding to RGD region of integrin receptors. Whether this phenomenon is important in communication between insulin-like growth factor receptor (IGF-IR) and β1-integrin receptor in regulation of prolidase activity and collagen biosynthesis is the aim of this study.

MATERIAL AND METHOD

We studied the effects of IGFBP-1, IGF-I, thrombin (integrin activator), echistatin (disintegrin), phosphatidylinositol 3-kinase inhibitor (LY-294002) and ERK 1/2 inhibitors (PD98059 and UO126) on prolidase activity, collagen biosynthesis and expression of proteins participating in pathways generated by these receptors.

RESULTS

Stimulation of β1-integrin and IGF-I receptors by standard ligands was proved to up-regulate collagen synthesis in cultured fibroblasts. IGFBP-1, similarly as echistatin and studied inhibitors, contributed to down-regulation of ERK1/2, Akt, mTOR expression and up-regulation of NFκB. It was accompanied by parallel decrease in prolidase activity and collagen biosynthesis.

CONCLUSION

The data suggest that "cross talk" between IGF-I receptor and integrin receptor may play important role in regulation of prolidase activity and collagen biosynthesis.

Growth hormone, insulin-like growth factor-1, and the kidney: pathophysiological and clinical implications

Besides their growth-promoting properties, GH and IGF-1 regulate a broad spectrum of biological functions in several organs, including the kidney. This review focuses on the renal actions of GH and IGF-1, taking into account major advances in renal physiology and hormone biology made over the last 20 years, allowing us to move our understanding of GH/IGF-1 regulation of renal functions from a cellular to a molecular level. The main purpose of this review was to analyze how GH and IGF-1 regulate renal development, glomerular functions, and tubular handling of sodium, calcium, phosphate, and glucose. Whenever possible, the relative contributions, the nephronic topology, and the underlying molecular mechanisms of GH and IGF-1 actions were addressed. Beyond the physiological aspects of GH/IGF-1 action on the kidney, the review describes the impact of GH excess and deficiency on renal architecture and functions. It reports in particular new insights into the pathophysiological mechanism of body fluid retention and of changes in phospho-calcium metabolism in acromegaly as well as of the reciprocal changes in sodium, calcium, and phosphate homeostasis observed in GH deficiency. The second aim of this review was to analyze how the GH/IGF-1 axis contributes to major renal diseases such as diabetic nephropathy, renal failure, renal carcinoma, and polycystic renal disease. It summarizes the consequences of chronic renal failure and glucocorticoid therapy after renal transplantation on GH secretion and action and questions the interest of GH therapy in these conditions.

Uremic toxins impair human bone marrow-derived mesenchymal stem cells functionality in vitro

Mesenchymal stem cells (MSCs) are becoming therapeutic agents of interest in many areas of medicine, including renal diseases and kidney transplantations. However, the effect of uremia on cell properties is still unclear. Therefore, we examined the in vitro influence of uremic toxins, p-cresol (PC) and indoxyl sulfate (IS), on human bone marrow-derived MSC functionality. Cultured MSCs were treated with PC and IS at concentrations corresponding to subsequent stages of chronic kidney disease. Cell viability was characterized by metabolic activity (MTT assay) and proliferation rate (BrdU assay). Apoptosis (Annexin V test) and cell membrane damage (LDH assay) were also tested. MSC secretory properties were determined by measuring cytokine/growth factor levels in media from toxin-treated cells (ELISA). Uremic concentrations of PC and IS resulted in significant inhibition of MSC metabolic activity and proliferation. Toxins did not induce apoptosis, but damaged cell membranes. MSC paracrine activity was also altered - a decrease of VEGF and TGF-β1 levels and an increase in IGF-1 and IL-8 secretion was detected. Presented data indicate a negative influence of uremic toxins on functional characteristics of human bone marrow-derived MSCs. Therefore, their use as autologous therapeutic agents for kidney disease may be questionable and requires further investigations. The observed phenomenon may be attributable to many other MSC therapies, because of the high prevalence of chronic kidney disease in adult population.

The insulin-like growth factor system in chronic kidney disease: Pathophysiology and therapeutic opportunities

The growth hormone-insulin-like growth factor-insulin-like growth factor binding protein (GH-IGF-IGFBP) axis plays a critical role in the maintenance of normal renal function and the pathogenesis and progression of chronic kidney disease (CKD). Serum IGF-I and IGFBPs are altered with different stages of CKD, the speed of onset, the amount of proteinuria, and the potential of remission. Recent studies demonstrate that growth failure in children with CKD is due to a relative GH insensitivity and functional IGF deficiency. The functional IGF deficiency in CKD results from either IGF resistance due to increased circulating levels of IGFBPs or IGF deficiency due to increased urinary excretion of serum IGF-IGFBP complexes. In addition, not only GH and IGFs in circulation, but locally produced IGFs, the high-affinity IGFBPs, and low-affinity insulin-like growth factor binding protein-related proteins (IGFBP-rPs) may also affect the kidney. With respect to diabetic kidney disease, there is growing evidence suggesting that GH, IGF-I, and IGFBPs are involved in the pathogenesis of diabetic nephropathy (DN). Thus, prevention of GH action by blockade either at the receptor level or along its signal transduction pathway offers the potential for effective therapeutic opportunities. Similarly, interrupting IGF-I and IGFBP actions also may offer a way to inhibit the development or progression of DN. Furthermore, it is well accepted that the systemic inflammatory response is a key player for progression of CKD, and how to prevent and treat this response is currently of great interest. Recent studies demonstrate existence of IGF-independent actions of high-affinity and low-affinity-IGFBPs, in particular, antiinflammatory action of IGFBP-3 and profibrotic action of IGFBP-rP2/CTGF. These findings reinforce the concept in support of the clinical significance of the IGF-independent action of IGFBPs in the assessment of pathophysiology of kidney disease and its therapeutic potential for CKD. Further understanding of GH-IGF-IGFBP etiopathophysiology in CKD may lead to the development of therapeutic strategies for this devastating disease. It would hold promise to use of GH, somatostatin analogs, IGFs, IGF agonists, GHR and insulin-like growth factor-I receptor (IGF-IR) antagonists, IGFBP displacer, and IGFBP antagonists as well as a combination treatment as therapeutic agents for CKD.

Expression and localization of insulin-like growth factor binding proteins in normal and proteinuric kidney glomeruli

AIM

Insulin-like growth factor I (IGF-I) acts on target cells in an endocrine and/or local manner through the IGF-I receptor (IGF-IR), and its actions are modulated by multiple IGF binding proteins (IGFBP). To elucidate the roles of local IGFBP in kidney glomeruli, the expression and localization of their genes were examined and compared with normal and proteinuric kidney glomeruli.

METHODS

A cDNA microarray database (MAd-761) was constructed using human kidney glomeruli and cortices. The gene expression levels of IGF-I, IGF-1R and IGFBP (1-10) were examined in glomeruli and cortices by polymerase chain reaction (PCR) and in situ hybridization (ISH), and the expression levels of IGFBP that were abundantly found in the glomerulus were compared between normal and proteinuric kidneys in rats and humans.

RESULTS

IGFBP-2, -7 and -8 were demonstrated to be abundantly and preferentially expressed in the glomerulus. In PCR, the expression levels of the IGFBP-2, -7, -8 and -10 genes in glomeruli were shown to have more than doubled compared with their levels in the cortices. In ISH, the IGFBP-2, -7, -8 and -10 genes were found to be localized in glomerular cells including podocytes, and their increased expression was observed in inflammatory glomeruli. IGF-I gene expression was localized in glomerular podocytes, whereas the IGF-IR gene was expressed in glomerular podocytes and cortical tubular cells. In nephrotic rats, the expression of the IGFBP-10 gene was increased in glomerular podocytes; however, the expression levels of IGFBP-2, -7 and -8 did not change.

CONCLUSION

IGFBP-2, -7, -8 and -10 are produced by normal and injured glomerular podocytes and may regulate local IGF-I actions in podocytes and/or cortical tubular cells in the kidney.

Association between IGF-1 and chronic kidney disease among US adults

BACKGROUND

Insulin-like growth factor (IGF-1) has been associated with cardiovascular disease, hypertension and diabetes in previous studies. However, the association between IGF-1 and chronic kidney disease (CKD) has not been previously studied. Therefore, we examined the association between serum IGF-1 and CKD in a representative sample of US adults.

METHODS

We conducted a cross-sectional study of 5388 Third National Health and Nutrition Examination Survey (NHANES III) participants aged ≥20 years of age (55.2% women). Serum IGF-1 was categorized into quartiles for the analysis. CKD (n = 241) was defined as an estimated glomerular filtration rate of <60 mL/min/1.73/m(2).

RESULTS AND CONCLUSION

Higher serum IGF-1 levels were positively associated with CKD after adjusting for age, sex, race/ethnicity, education levels, smoking, alcohol intake, body mass index, diabetes, hypertension and serum cholesterol. Compared to quartile 1 of IGF-1 (referent), the odds ratio (95% confidence interval) of CKD associated with quartile 4 was 2.66 (1.18-5.99); p trend = 0.008. Subgroup analysis that examined the relation between IGF-1 and CKD by gender showed a consistent positive association. In summary, increasing levels of serum IGF-1 were positively associated with CKD in a representative sample of US adults. Our results suggest that IGF-1 might be a predictor of CKD in Western populations.

IGF-1 increases laminin, cyclin D1, and p21Cip1 expression in glomerular mesangial cells: an investigation of the intracellular signaling pathway and cell-cycle progression

Insulin-like growth factor (IGF)-1 is accumulated in the diabetic kidney and is considered to be involved in the development of glomerular sclerosis. Here, we investigate IGF-1 regulation of laminin, an extracellular matrix (ECM) component, and cyclin D1 and p21Cip1, cell-cycle progression factor, expressions in glomerular mesangial cells. We show that IGF-1 increases the level of laminin gamma1 and beta1 subunits approximately 1.5- and 2.5-fold, respectively, in a time-dependent manner. IGF-1 also stimulates protein kinase Akt/PKB phosphorylation at Thr 308, which correlates with its activity, up to 24 h. The Akt activation is coupled with Ser 9 phosphorylation of its downstream target, glycogen synthase kinase-3beta (GSK-3beta), which inhibits its kinase activity. Laminin beta1 is reduced significantly (P < 0.03) by inhibitors of Akt and p38MAPK whereas laminin gamma1 is not affected. Surprisingly, IGF-1 activates the expression of both cyclin D1 and cell-cycle arrest factor, p21Cip1 parallely. Pharmacological inhibition of calcineurin by cyclosporin A blocks IGF-1-induced cyclin D1 and p21Cip1expression significantly (P < 0.05). IGF-1 enhances cellular metabolic activity and viability of rat mesangial cells; however, they are arrested at the G1 phase of cell cycle as revealed by the FACS analysis. These results indicate that IGF-1 mediates mesangial cell-cycle progression, hypertrophy, and ECM protein synthesis. The Akt/GSK-3beta, p38MAPK, and calcineurin pathways may play an important role in IGF-1 signaling, cell-cycle regulation, and matrix gene expression in mesangial cells leading to the development of diabetic glomerulopathy.

The growth hormone-insulin-like growth factor-I axis in chronic kidney disease

Growth hormone (GH) and insulin-like growth factor-I (IGF-I) are important physiologic regulators of growth, body composition, and kidney function. Perturbations in the GH-IGF-I axis are responsible for many important complications seen in chronic kidney disease (CKD), such as growth retardation and cachectic wasting, as well as disease progression. Recent evidence suggests that CKD is characterized by abnormalities in GH and IGF-I signal transduction and the interaction of these pathways with those that involve other molecules such as ghrelin, myostatin, and the suppressor of cytokine signaling (SOCS) family. Further understanding of GH/IGF pathophysiology in CKD may lead to the development of therapeutic strategies for these devastating complications, which are associated with high rates of mortality and morbidity.

Angiotensin II- and glucose-stimulated extracellular matrix production: mediation by the insulin-like growth factor (IGF) axis in a murine mesangial cell line

In diabetic nephropathy, glomerular mesangial cells exhibit aberrant anabolic activity that includes excessive production of extracellular matrix (ECM) proteins, leading to crowding of filtration surface areas and possible renal failure. In the present study, a murine mesangial cell line (MES-13 cells) was studied to determine the roles of the renin-angiotensin system (RAS) and the insulin-like growth factor (IGF) axis in the anabolic response to elevated glucose levels. Culture of MES-13 cells in medium containing supra-physiological glucose concentrations (>5.5 mmol/l) resulted in increased production of ECM proteins including laminin, fibronectin, and heparan sulfate proteoglycan with concurrent increases in IGF-binding protein (IGFBP)-2 production. These responses were blocked by the angiotensin receptor antagonists saralasin and losartan, while exogenous angiotensin II (Ang II) treatment directly stimulated increases in ECM and IGFBP-2. In all experiments, IGFBP-2 levels were correlated with anabolic activity implicating IGFBP-2 as a possible mediator in cellular responses to high glucose and Ang II. Such mediation appears to involve IGFBP-2 modulation of IGF-I signaling, since all responses to high glucose or Ang II were blocked by immuno-neutralization of IGF-I. These data suggest alterations in the IGF axis as key mechanisms underlying nephropathic responses of mesangial cells to Ang II and high glucose.

Engineering of Biologically Active Living Heart Valve Leaflets Using Human Umbilical Cord–Derived Progenitor Cells

This study demonstrates the engineering of biologically active heart valve leaflets using prenatally available human umbilical cord-derived progenitor cells as the only cell source. Wharton's Jelly-derived cells and umbilical cord blood-derived endothelial progenitor cells were subsequently seeded on biodegradable scaffolds and cultured in a biomimetic system under biochemical or mechanical stimulation or both. Depending on the stimulation, leaflets showed mature layered tissue formation with functional endothelia and extracellular matrix production comparable with that of native tissues. This demonstrates the feasibility of heart valve leaflet fabrication from prenatal umbilical cord-derived progenitor cells as a further step in overcoming the lack of living autologous replacements with growth and regeneration potential for the repair of congenital malformation.

Effects of Blocking the Renin-Angiotensin System on Expression and Translocation of Protein Kinase C Isoforms in the Kidney of Diabetic Rats

BACKGROUND

High glucose and angiotensin II (Ang II) can activate protein kinase C (PKC) in diabetes mellitus. However, it is not clear which isoform of PKC is activated by glucose or Ang II. Our study focused on the effects of angiotensin blockade, using the angiotensin-converting enzyme inhibitor fosinopril, the Ang II receptor blocker irbesartan and their combination, on the expression and translocation of PKC isoforms alpha and betaII in the renal cortex and medulla in diabetes.

METHODS

Hyperglycemia was induced with streptozotocin and diabetic rats were randomized to 4 groups: diabetic control, irbesartan group (40 mg/kg daily), fosinopril group (40 mg/kg daily) and combination group (irbesartan plus fosinopril, 20 mg/kg daily, respectively); age-matched normal rats served as normal control. After 4 weeks, expression and translocation of PKC-alpha and -betaII in the renal cortex and medulla were assessed by immunohistochemistry and Western immunoblotting.

RESULTS

The expression of PKC-alpha in the membrane and cytosol fractions from the renal cortex was significantly higher in diabetic rats (276.83 +/- 32.44% in membrane, 149.04 +/- 23.42% in cytosol) than that in normal ones. The expression of PKC-betaII in the renal cortex of diabetic rats decreased significantly in the membrane (50.00 +/- 11.68%, p < 0.05) and remained unchanged in the cytosol (94.51 +/- 11.69%, p > 0.05) compared with normal controls. Treatment with irbesartan, fosinopril and their combination partially corrected the abnormalities mentioned above. For the expression of PKC-alpha and -betaII in the medulla, no difference was detected among the 5 groups.

CONCLUSION

The renin-angiotensin system was implicated in the pathogenesis of diabetic nephropathy by regulating the activation of PKC isoforms.

Increased expression of insulin-like growth factors in progressive glomerulonephritis of the MRL/lpr mouse

Glomerulonephritis is an important complication of systemic lupus erythematosus (SLE). The tissue distribution and exact role of the insulin-like growth factors (IGFs) in the development of lupus nephritis in the MRL/lpr mouse model have not been established. The present study was undertaken to evaluate the changes over time in mRNA and peptide expression of IGF-I and IGFBP-2 in the MRL/lpr mouse. Using in situ hybridization and immunocytochemistry techniques, the expression of IGF-I and IGFBP-2 in MRL/lpr mouse was examined and compared to their congenic normal MRL-++ mouse counterparts from nine to 24 weeks of age. In the MRL-++ and MRL/lpr mouse kidneys, IGF-I and IGFBP-2 mRNA expression was limited to the cortical and medullary collecting ducts, while their immunoreactivity (IR) was localized to the cortical and medullary collecting ducts, loop of Henle, glomeruli and proximal tubules. Over time, and with progression of disease, the MRL/lpr mice displayed a significant increase in IGF-I IR and a modest increase in IGFBP-2 IR within the outer cortical glomeruli, which was associated with a significant increase in glomerulosclerosis and glomerular cell proliferation and with a significant decrease in renal function. In conclusion, this overexpression of IGF-I and IGFBP-2 within the glomeruli of the MRL/lpr mouse kidney supports their potential role in the alterations in renal function and morphology that accompany lupus nephritis.

The physiological and pathophysiological roles of the GH/IGF-axis in the kidney: lessons from experimental rodent models

The growth hormone (GH)/insulin-like growth factor (IGF) system plays an important role in renal development, growth, function and pathophysiology. IGF-I has been associated with renal/glomerular hypertrophy and compensatory renal growth. Potential effects on glomerular size are of interest, since an increase in glomerular size may be permissive for the development of glomerulosclerosis. In an effort to abolish the decline of renal function and possibly to restore the renal structure, different approaches have been tested in experimental models of nephropathy, focusing mainly on early renal changes. The involvement of the GH/IGF system in renal pathophysiology has been studied in much detail in the rat. In view of the growing interest in murine physiology, occurring in large part by genetically modified animals, this review examines those aspects of GH, IGFs, their receptors and binding proteins that relate both to mouse kidney physiology and to a number of conditions characterized by pathophysiological renal changes. A deeper understanding of the role of the GH/IGF system in renal dysfunction may stimulate the development of novel therapeutic approaches aiming at preventing or retarding various kidney diseases.

Role of interleukin-10 in rat mesangioproliferative glomerulonephritis

Interleukin-10 (IL-10) has been recognized as a growth factor for rat mesangial cells in vitro; however, its role in mesangioproliferative glomerulonephritis is unknown. We studied the expression of IL-10 mRNA in the rat anti-Thy-1 model of mesangioproliferative glomerulonephritis (experiment 1) and, subsequently, the effects of blocking IL-10 during anti-Thy-1 nephritis using the IL-10 inhibitor, AS101 (experiment 2). In experiment 1, PCR analysis failed to detect IL-10 mRNA in normal rat kidney, however, a clear signal for IL-10 mRNA was evident on day 6 of anti-Thy-1 nephritis. In situ hybridization showed IL-10 mRNA expression in focal glomerular areas in anti-Thy-1 nephritis. Combined in situ hybridization and immunohistochemistry showed that glomerular IL-10 mRNA was expressed by both macrophages and mesangial cells. In experiment 2, treatment with AS101 significantly downregulated renal IL-10 gene expression, as demonstrated by semiquantitative PCR. However, the induction of glomerular hypercellularity, mesangial proliferation (PCNA+ cells), mesangial cell activation (alpha-SMA expression) and macrophage accumulation (ED1+ cells) seen in saline-treated anti-Thy-1 nephritis was unaffected by AS101 treatment. In conclusion, renal IL-10 gene expression is upregulated during pathological mesangial cell proliferation in rats with anti-Thy-1 nephritis. However, the inability of IL-10 suppression with AS101 to prevent anti-Thy-1 disease suggests that IL-10 is not essential for pathological mesangial cell proliferation.

Effects of chemokines on proliferation and apoptosis of human mesangial cells

Background

Proliferation and apoptosis of mesangial cells (MC) are important mechanisms during nephrogenesis, for the maintenance of glomerular homeostasis as well as in renal disease and glomerular regeneration. Expression of chemokines and chemokine receptors by intrinsic renal cells, e.g. SLC/CCL21 on podocytes and CCR7 on MC is suggested to play a pivotal role during these processes. Therefore the effect of selected chemokines on MC proliferation and apoptosis was studied.

Methods

Proliferation assays, cell death assays including cell cycle analysis, hoechst stain and measurement of caspase-3 activity were performed.

Results

A dose-dependent, mesangioproliferative effect of the chemokine SLC/CCL21, which is constitutively expressed on human podocytes was seen via activation of the chemokine receptor CCR7, which is constitutively expressed on MC. In addition, in cultured MC SLC/CCL21 had a protective effect on cell survival in Fas-mediated apoptosis. The CXCR3 ligands IP-10/CXCL10 and Mig/CXCL9 revealed a proproliferative effect but did not influence apoptosis of MC. Both the CCR1 ligand RANTES/CCL5 and the amino-terminally modified RANTES analogue Met-RANTES which blocks CCR1 signalling had no effect on proliferation and apoptosis.

Conclusions

The different effects of chemokines and their respective receptors on proliferation and apoptosis of MC suggest highly regulated, novel biological functions of chemokine/chemokine receptor pairs in processes involved in renal inflammation, regeneration and glomerular homeostasis.

Nephroprotective effect of bosentan in diabetic rats

Previous studies have suggested that endothelins could be involved in the pathogenesis of target organ damage in diabetes. The aim of this study was to evaluate the possible protective effect of Bosentan, an antagonist of endothelin receptor, on the kidney of diabetic rats. The study comprised a control group of 10 WKY rats and a group of 22 WKY rats in which diabetes was induced by streptozotocin i.v.; 10 rats were the control group. Diabetic rats received insulin and mean blood glucose was approximately mS 400 mg/dl throughout the study; they were divided into two groups: 11 rats received Bosentan 100 mg/kg/die by gastric gavage and 11 received vehicle for 1 month. Twenty-four hour urine collection was performed before and at the end of the study. Urinary protein excretion rate was expressed as microg urinary protein/mg urinary creatinine. The renal collagen I, fibronectin, and TGFbeta were evaluated by means of immunochemistry. The statistical analysis of the results demonstrates that Bosentan has prevented the increase in urinary protein excretion and that of renal immunoreactive collagen I, fibronectin, and TGFbeta induced by diabetes without reducing blood pressure. This study suggests a new clinical application for the antagonists of endothelin receptors.

Connective tissue growth factor and igf-I are produced by human renal fibroblasts and cooperate in the induction of collagen production by high glucose

Tubulointerstitial fibrosis is an important component in the development of diabetic nephropathy. Various renal cell types, including fibroblasts, contribute to the excessive matrix deposition in the kidney. Although transforming growth factor-beta (TGF-beta) has been thought to play a major role during fibrosis, other growth factors are also involved. Here we examined the effects of connective tissue growth factor (CTGF) and IGF-I on collagen type I and III production by human renal fibroblasts and their involvement in glucose-induced matrix accumulation. We have demonstrated that both CTGF and IGF-I expressions were increased in renal fibroblasts under hyperglycemic conditions, also in the absence of TGF-beta signaling. Although CTGF alone had no effect on collagen secretion, combined stimulation with IGF-I enhanced collagen accumulation. Furthermore, IGF-I also had a synergistic effect with glucose on the induction of collagens. Moreover, we observed a partial inhibition in glucose-induced collagen secretion with neutralizing anti-CTGF antibodies, thereby demonstrating for the first time the involvement of endogenous CTGF in glucose-induced effects in human renal fibroblasts. Therefore, the cooperation between CTGF and IGF-I might be involved in glucose-induced matrix accumulation in tubulointerstitial fibrosis and might contribute to the pathogenesis of diabetic nephropathy.

Regulation of growth-hormone-receptor gene expression by growth hormone and pegvisomant in human mesangial cells

BACKGROUND

Mice transgenic for growth hormone develop mesangial proliferation, glomerular hypertrophy, and progressive glomerular sclerosis suggesting that the growth hormone-insulin-like growth factor I (IGF-I) pathway plays an important role. Therefore, we studied the impact of variable concentrations of 22 kD, 20 kD growth hormone, as well as of the growth hormone receptor antagonist pegvisomant (B2036-PEG), on both the growth hormone receptor (GHR/GHBP) gene expression and growth hormone binding protein (GHBP) formation in a human glomerular mesangial cell line. Further, the impact on collagen, IGF-I and IGF binding protein-1 (IGFBP-1) formation was studied.

METHODS

In order to assess transcription, quantitative reverse transcription-polymerase chain reaction (RT-PCR) was used.

RESULTS

Physiologic doses of 22 kD or 20 kD growth hormone caused a dose-dependent and significant (P < 0.01) up-regulation of GHR/GHBP gene transcription, whereas supraphysiologic doses (50 and 500 ng/mL) resulted in down-regulation (P < 0.001). Whenever pegvisomant was used, there was no increase in GHR/GHBP expression. These data were confirmed using run-on experiments. Further, the assessment of GHBP presented a constant, dose-dependent increase, which was completely abolished in the experiments where pegvisomant was used.

CONCLUSION

We present data showing that growth hormone has a direct impact on GHR/GHPB gene transcription and that pegvisomant is a potent growth hormone receptor antagonist in human mesangial cells. In addition, although the GHR/GHBP gene transcription is down-regulated by supraphysiologic growth hormone concentrations, this effect was not found when GHBP levels were measured. This finding may reflect a self-inhibitory effect of growth hormone on the level of GHR/GHBP gene transcription, which does not involve the regulation of the shedding of GHBP and may, therefore, be of physiologic interest.

Expression of IGF-binding protein-1 phosphoisoforms in fasted rat skin and its role in regulation of collagen biosynthesis

Insulin-like growth factor-I (IGF-I) is an important stimulator of collagen and glycosaminoglycan (GAG) biosynthesis in tissues. IGF-I activity is modulated by a family of IGF-binding proteins (IGFBPs) with different IGF-I binding affinities. At least IGFBP-1 and IGFBP-2 are known as inhibitors of IGF functions. Some IGFBPs (IGFBP-1, IGFBP-3 and IGFBP-5) may undergo phosphorylation that dramatically increase their affinity for IGF. During fasting of animals there is a significant decrease of the collagen and GAG content of the skin, accompanied by a reduction of plasma IGF-I levels. However, in previous studies we showed that in the skin of fasted rats IGF-I as well as IGFBP-1 and IGFBP-2 expressions were not different, compared to control rat skin, although collagen content was significantly decreased. In the present study we show that fasted rat skin contains similar amounts of IGF-I, IGFBP-3 and IGFBP-1, although extract from fasted rat skin induced inhibition of collagen biosynthesis in cultured fibroblasts, compared to control rat skin extract. Western immunoblot analysis of control and fasted rat skin extracts, using anti-phosphoserine antibodies for immunoprecipitated IGFBP-1 and IGFBP-3, revealed that both proteins are present in phosphorylated form. Although no differences were found in the expression of phosphorylated IGFBP-3 between control and fasted rat skins, that of phosphorylated IGFBP-1 in fasted rat skin extract was higher than in control one. We suggest that there is an increased level of IGFBP-1 phosphoisoform in fasted rat skin, associated with increased affinity for IGF-I. The increase of phosphorylated IGFBP-1 in fasted rat skin tissue may augment IGF-I binding affinity for IGF and decrease its bioavailability for receptor interaction. This mechanism may prevent IGF-I dependent stimulation of fibroblasts to produce extracellular matrix components. The specific expression of IGFBPs and their phosphoisoforms in tissues may play an important role in regulation of IGF-I action during physiologic and pathologic responses.

Type Ialpha collagen is an IGFBP-3 binding protein

Insulin-like growth factor (IGF) binding protein-3 (IGFBP-3) possesses both growth-inhibitory and -potentiating effects on cells, which are independent of IGF action and mediated through specific IGFBP-3 binding proteins/receptors located at the cell membrane, cytosol, or nuclear compartments as well as in the extracellular matrix. We here characterized type Ialpha collagen as one of these IGFBP-3 binding proteins. Human serum was fractionated over an IGFBP-3 affinity column, and bands at 70-100 kDa were eluted as IGFBP-3 ligands. The 100-kDa band was extracted, subjected to N-terminal amino acid sequencing, and identified through database searching as the N-terminal chain of type Ialpha collagen protein. In a separate screening approach, using a yeast two-hybrid system, we cloned the type Ialpha collagen cDNA from a human liver cDNA library as an IGFBP-3 protein partner. Anti-IGFBP-3 antibodies co-immunoprecipitated type Ialpha collagen and IGFBP-3 from the conditioned media of human fibroblasts and vice versa. We demonstrated through ligand dot blot analysis that type Ialpha collagen binds IGFBP-3. IGFBP-3 mutants, with altered sequence at the nuclear localization sequence, bound type Ialpha collagen poorly. Western immunoblot showed that type Ialpha collagen binds only IGFBP-3 but not IGF-I, suggesting an IGF-I-independent mechanism of this interaction. Physiological effects of IGFBP-3-collagen interactions may include modulation of cell adhesion and migration.

SPARC regulates cell cycle progression in mesangial cells via its inhibition of IGF-dependent signaling

Glomerular mesangial cells both synthesize and respond to insulin-like growth factor-1 (IGF-1). Increased activity of the IGF signaling pathway has been implicated as a major contributor to renal enlargement and subsequent development of diabetic nephropathy. Secreted protein acidic and rich in cysteine (SPARC), a matricellular protein, has been shown to modulate the interaction of cells with growth factors and extracellular matrix. We have reported that primary glomerular mesangial cells derived from SPARC-null mice exhibit an accelerated rate of proliferation and produce substantially decreased levels of transforming growth factor beta1 (TGF-beta1) in comparison to their wild-type counterparts (Francki et al. [1999] J. Biol. Chem. 274: 32145-32152). Herein we present evidence that SPARC modulates IGF-dependent signaling in glomerular mesangial cells. SPARC-null mesangial cells produce increased amounts of IGF-1 and -2, as well as IGF-1 receptor (IGF-1R) in comparison to wild-type cells. Addition of recombinant SPARC to SPARC-null cells inhibited IGF-1-stimulated mitogen activated protein kinase (MAPK) activation and DNA synthesis. We also show that the observed accelerated rate of basal and IGF-1-stimulated proliferation in mesangial cells derived from SPARC-null animals is due, at least in part, to markedly diminished levels of cyclin D1 and the cyclin-dependent kinase (cdk) inhibitors p21 and p27. Since expression of SPARC in the glomerulus is especially prominent during renal injury, our findings substantiate previous claims that SPARC is involved in glomerular remodeling and repair, a process commonly associated with mesangioproliferative glomerulonephritis and diabetic nephropathy.

Bradykinin reduces growth factor-induced glomerular ERK1/2 phosphorylation

Several experimental data report both mitogenic and antimitogenic effects of bradykinin (BK). To conciliate these apparent opposite effects, we hypothesized that, depending on cell context activation, BK could reduce the mitogenic effect of growth factors. Therefore, in the present study we assessed the existence of possible negative cross talk between BK and potential pathogenic growth factors in freshly isolated rat glomeruli (IG). Next, we determined whether this cross talk could be pharmacologically recruited during angiotensin-converting enzyme (ACE) inhibition in the diabetic rat. In IG from normal rats, BK, via activation of the B(2) kinin receptor (B(2)R), causes a transient stimulation of ERK1/2 phosphorylation, whereas it inhibits ERK1/2 phosphorylation induced by IGF-1, PDGF-BB, VEGF, or basic FGF. The reduction of growth factor-induced ERK1/2 phosphorylation is abolished by an inhibitor of tyrosine phosphatase. In glomeruli from diabetic rats, hyperglycemia increased the phosphorylation level of ERK-1/2 as well as oxidative stress. The reversal of these events by ACE inhibition is mediated via B(2)R activation. These observations are consistent with a potential therapeutic role of BK and B(2)R during glomerulosclerosis.

IGF-1-induced lipid accumulation impairs mesangial cell migration and contractile function

BACKGROUND

Chronic treatment of mesangial cells with insulin-like growth factor-1 (IGF-1) results in intracellular lipid accumulation. These mesangial cells resemble foam cells.

METHODS

To determine whether this phenotype affects cell function, lipid-laden mesangial cells were tested for their ability to migrate in response to IGF-binding protein-5 (IGFBP-5) and to contract in response to angiotensin II (Ang II). IGFBP-5 binding and subsequent activation of the signal transduction cascade for migration were examined. To confirm that lipid accumulation was responsible for impaired contractility, lipid was removed from lipid-laden mesangial cells and the cells were re-tested for contractile response to Ang II.

RESULTS

In comparison to control mesangial cells, lipid-laden cells failed to migrate in response to IGFBP-5. Although cellular binding of IGFBP-5 was not altered by lipid accumulation, IGFBP-5 failed to activate cdc42, a Rho GTPase required for IGFBP-5-mediated mesangial cell migration. These data indicate that lipid accumulation within the mesangial cell interferes with the signal transduction response to IGFBP-5. In addition, mesangial cells treated with IGF-1 had reduced contraction to Ang II. When lipid accumulation was exaggerated by adding cholesteryl esters to the culture medium, mesangial cells failed to contract in response to Ang II. Following removal of excess lipid from these mesangial cells, the contractile response to Ang II was restored.

CONCLUSIONS

IGF-1 induces lipid accumulation in mesangial cells, which impairs their ability to respond to specific migratory and contractile stimuli. These observations are relevant to understanding functional abnormalities in diseases where mesangial foam cells occur, such as focal and segmental glomerulosclerosis and diabetic nephropathy.

Inhibition of IGF-I-induced Erk 1 and 2 activation and mitogenesis in mesangial cells by bradykinin

BACKGROUND

The beneficial effects of therapeutic angiotensin-converting enzyme (ACE) inhibitor treatment against the worsening of glomerulosclerosis during the course of diabetic nephropathy have been widely documented. ACE inhibitors inhibit both angiotensin II formation and bradykinin (BK) degradation, thereby reducing angiotensin II type 1 (AT1) receptor activity and favoring B2-kinin receptor (B2 receptor) activation. Since the involvement of growth factors such as insulin-like growth factor (IGF-I) has been implicated in the early steps of diabetic nephropathy, we investigated the effect of BK on Erk 1 and 2 activation and cell proliferation by IGF-I.

METHODS

The activation of Erk 1 and 2 in mesangial cells (MCs) and isolated glomeruli (IG) was investigated by immunoprecipitation and Western blotting during activation of the IGF-I receptor in the presence or absence of BK and of protein kinase C (PKC), tyrosine-kinase and phosphatase selective inhibitors. Mesangial cell proliferation was assessed in vitro by cell counting.

RESULTS

In untreated MCs and IG, when added separately, BK and IGF-I both activated Erk 1 and 2. In contrast, in MCs and IG pretreated with BK, the IGF-I-induced Erk 1 and 2 activation was dose-dependently reduced. The inhibitory effect of BK on IGF-I-induced activation of Erk 1 and 2 was completely abolished by addition of a B2 antagonist, by chelation of intracellular calcium and by tyrosine phosphatase inhibition. Additionally, BK reduced MC proliferation induced by IGF-I.

CONCLUSIONS

A new inhibitory pathway of the early steps of IGF-I signaling by the B2 receptor is found both in cultured MCs and in IG, which involves a calcium-dependent tyrosine phosphatase activity. Recruitment of this mechanism may account for the beneficial effects of ACE inhibitor treatment on glomerulosclerosis associated with diabetic nephropathies.

An expression of IGF-binding proteins in normal and pre-eclamptic human umbilical cord serum and tissues

Pre-eclampsia, is the most common, pregnancy-associated pathological syndrome accompanied by a significant increase in collagen and sulphated glycosaminoglycans (GAGs) contents in the umbilical cord arteries (UCAs). Insulin-like growth factor-I (IGF-I) is expressed in most foetal tissues and it is involved in anabolic effects. It stimulates protein (mainly collagen) and GAG biosynthesis, cell proliferation and differentiation. Previously, we have found that pre-eclampsia is associated with an increase of IGF-I concentration in the umbilical cord blood. A family of IGF-I-binding proteins (BPs) modulates the activity of IGF-I. We demonstrated qualitative differences between BPs of normal and pre-eclamptic human umbilical cord (UC) serum and UC-tissues (UCA-wall and Wharton's jelly) by Western immunoblot analysis. All examined sera and tissues contained BP-1 and BP-5 as well lower molecular weight materials. The BP-2 was recovered from both control and pre-eclamptic sera, while it was not detected in the UC-tissues. Instead, lower molecular weight forms of BP-2 were found as judged by the anti-BP-2 antibody. The BP-3 was detected in sera, UCA and Wharton's jelly. The most distinct expression of BP-3 was found in the UCA. The pre-eclamptic UCA and Wharton's jelly contained additional BP-3-reactive material of lower molecular weight. The BP-4 was strongly expressed in pre-eclamptic UC-serum and the expression was decreased in pre-eclamptic UC-tissues, compared to respective controls. Ligand binding assay revealed that most of IGF-I was bound to 46 kDa region (typical for BP-3) in both control and pre-eclamptic sera and tissues. However, distinctly less IGF-I was bound in pre-eclamptic serum, distinctly more in pre-eclamptic UCA and no differences were found in pre-eclamptic Wharton's jelly, compared to controls. We demonstrated that both normal and pre-eclamptic UC-sera and tissues are able to degrade 46 kDa IGF-I-BP. The degradation may result in a decrease of IGF-I binding, contributing to increase in free IGF-I that may stimulate the cells to produce extracellular matrix (ECM) components. The specific BPs and their proteolytic modification in UC tissues may be important modulators of IGF-I action during foetal development.

Transforming growth factor-beta induces renal epithelial jagged-1 expression in fibrotic disease

For elucidation of the mechanisms by which growth factors and cytokines affect renal epithelial cells, gene array analysis of renal cells cultured in the presence of transforming growth factor-beta1 (TGF-beta1) was performed. Many genes that were not previously considered to be involved in renal cell biologic processes were affected, one of which was jagged-1. The jagged ligand/notch receptor family controls the formation of boundaries between groups of cells and regulates cell fates. On the basis of the array analysis, jagged-1 expression was further evaluated in cultured cells and in C57BL/6 mice with a model of unilateral ureteral obstruction (UUO). Recombinant human TGF-beta1 increased jagged-1 mRNA levels at concentrations between 10(-11) and 10(-10) M. There was a commensurate increase in jagged-1 protein levels, as assessed by Western blotting. The expression of jagged-1 mRNA and protein was observed to be significantly increased in the kidneys of C57BL/6 mice with obstructed ureters, compared with the contralateral kidneys, at 7 and 14 d of UUO. Immunohistochemical analyses demonstrated jagged-1 expression in distal tubules of kidneys from normal mice or contralateral kidneys from mice with UUO. Jagged-1 protein expression was increased in tubules not yet in apparent atrophy in the kidneys with an obstructed ureter. Jagged-1 expression was significantly increased in the kidneys of normal mice treated with TGF-beta1 and was decreased in the kidneys of mice with UUO treated with a TGF-beta receptor II-Fc chimera. These results suggest that jagged-1 is expressed in normal kidneys and that this expression is upregulated during renal disease, in a TGF-beta-dependent manner.

Roles of SLC/CCL21 and CCR7 in human kidney for mesangial proliferation, migration, apoptosis, and tissue homeostasis

The release of chemokines by intrinsic renal cells is an important mechanism for the regulation of leukocyte trafficking during renal inflammation. The expression of chemokine receptors by intrinsic renal cells such as mesangial cells (MC) suggests an expanded role for chemokine-chemokine receptor biology in local immunomodulation and potentially glomerular homeostasis. By immunohistochemistry we found the chemokine receptor CCR7 expressed in a mesangial pattern while the CCR7 ligand SLC/CCL21 showed a podocyte-specific expression. CCR7 expression was further characterized by RT-PCR, RNase protection assays, and FACS analysis of cultured human MC, and was found to be constitutively present. Real-time PCR of microdissected glomeruli confirmed the expression of SLC/CCL21. A functional role for CCR7 was demonstrated for human MC migration and proliferation. A protective effect of SLC/CCL21 was shown for MC survival in Fas Ab-induced apoptosis. Finally, "wound healing" was enhanced in the presence of SLC/CCL21 in an in vitro injury model. The constitutive glomerular expression of CCR7 and its ligand SLC/CCL21 in adjacent cell types of the human kidney suggests novel biological functions of this chemokine/chemokine receptor pair and a potential role in processes involved in glomerular homeostasis and regeneration.

Induction of B1 receptors in streptozotocin diabetic rats: possible involvement in the control of hyperglycemia-induced glomerular Erk 1 and 2 phosphorylation

We investigated the effects of a 3-week treatment with various combinations of angiotensin-converting enzyme inhibitor (ACEI) and B1 and B2 bradykinin receptor (B1R and B2R) antagonists (B1A and B2A) and AT1 receptor antagonist on ERK 1 and 2 phosphorylation in isolated glomeruli from streptozotocin-treated diabetic rats (STZ rats). Body weight, glycemia, and blood pressure were monitored. The rats were divided into nine groups: (1) control; and groups 2-9 were STZ treated with (3) insulin, (4) ACEI, (5) ACEI + B1A, (6) ACEI + B2A, (7) B2A, (8) B1A, (9) AT1 antagonist. ERK 1 and 2 phosphorylation and expression of B1R and B2R were assessed by Western blot analysis. ERK 1 and 2 phosphorylation was higher in STZ rats; this activation was normalized by insulin and reduced by ACEI but not by AT1 antagonist. The reduction of ERK 1 and 2 phosphorylation by the ACEI was reversed by B1A and B2A. The induction of B1R was confirmed by increased expression of mRNA and B1 receptor protein. Since ERK 1 and 2 phosphorylation is an early event in the induction of matrix secretion and hyperproliferation associated with diabetic nephropathy, activation of B1R and B2R appears to be a useful pharmacological target in the management of this pathology.

Insulin is a potent survival factor in mesangial cells: role of the PI3-kinase/Akt pathway

BACKGROUND

Elucidating the mechanisms of apoptosis is important for understanding the molecular mechanisms underlying glomerular disease. The phosphatidylinositol 3 kinase (PI3-kinase)/Akt pathway is essential for survival signaling in non-renal cells. However, little is known about the anti-apoptotic effect of insulin and the role of the PI3-kinase/Akt pathway in mesangial cells (MC) apoptosis.

METHODS

Apoptosis was induced in wild type, p27Kip1 (p27) -/- and p21Cip1/Waf1 (p21) -/- mouse MC by survival factor withdrawal, actinomycin D, ultraviolet (UV)-B irradiation and cycloheximide in the presence or absence of insulin (1 micromol/L) or insulin-like growth factor-I (IGF-I; 100 ng/mL). The activation and levels of Akt, extracellular signal regulated kinase (ERK) and specific cell cycle proteins were determined by Western blot analysis.

RESULTS

Insulin and IGF-I inhibited wild-type MC apoptosis induced by survival factor withdrawal, actinomycin D, ultraviolet-B irradiation and cycloheximide and in p27 -/- MC when apoptosis was induced by survival factor withdrawal. Akt was activated by insulin and IGF-I during apoptosis. Blocking PI3-kinase with LY294002 reduced Akt activation and abrogated the anti-apoptotic effect of insulin. ERK was activated during apoptosis and blocking ERK activation with U0126 or PD98059 partially rescued MC from apoptosis. Moreover, insulin also suppressed ERK activation during apoptosis. Our results also showed that the CDK-inhibitor p21 was increased by insulin and that p21 up-regulation was PI3-kinase/Akt pathway dependent. Furthermore, p21 -/- MC apoptosis induced by survival factor withdrawal was not rescued by insulin in contrast to the wild-type and p27 -/- MC. These data suggest that p21 may have a critical role in the anti-apoptotic effect of insulin.

CONCLUSIONS

Insulin is a potent survival factor for MC in response to a number of different apoptotic triggers, and this effect is mediated through the PI3-kinase/Akt pathway. Moreover, ERK and p21 may be involved in anti-apoptotic effect of insulin in MC.

IGF-1 induces foam cell formation in rat glomerular mesangial cells

When rat glomerular mesangial cells (MCs) are cultured with IGF-1 they accumulate intracellular lipid and take on foam cell morphology. These changes were characterized by electron microscopy and Nile red staining. To define the mechanism responsible for IGF-1-mediated lipid uptake, MCs were evaluated for endocytosis, scavenger receptor activity, and receptor-mediated uptake by the LDL receptor. Lipid accumulation was markedly increased when MCs were cultured with IGF. The primary route of uptake was through enhanced endocytosis. Lipid-laden MCs have decreased phagocytic capacity and disrupted cytoskeletons. These data show that IGF-1 induces MC to take on a foam cell morphology and that lipid-laden MCs have impaired phagocytic function.

Insulin-like growth factor-I induces renal cell hypertrophy via a calcineurin-dependent mechanism

Insulin-like growth factor-I (IGF-I) may play an important role in the development of renal hypertrophy. In this study we determined the effect of IGF-I on cultured mesangial cells (MCs) and examined activation of key signaling pathways. IGF-I induced hypertrophy as determined by an increase in cell size and an increase in protein to DNA ratio and increased accumulation of extracellular matrix (ECM) proteins. IGF-I also activated both Erk1/Erk2 MAPK and phosphatidylinositol 3-kinase (PI3K) in MCs. Inhibition of either MAPK or PI3K, however, had no effect on IGF-I-induced hypertrophy or ECM production. Next, we examined the effect of IGF-I on activation of the calcium-dependent phosphatase calcineurin. IGF-I treatment stimulated calcineurin activity and increased the protein levels of calcineurin and the calcineurin binding protein, calmodulin. Cyclosporin A, an inhibitor of calcineurin, blocked both IGF-I-mediated hypertrophy and up-regulation of ECM. In addition, calcineurin resulted in sustained Akt activation, indicating possible cross-talk with other signaling pathways. Finally, IGF-I treatment resulted in the calcineurindependent nuclear localization of NFATc1. Therefore, IGF-I induces hypertrophy and increases ECM accumulation in MCs. IGF-I-mediated hypertrophy is associated with activation of Erk1/Erk2 MAPK and PI3K but does not require either of these pathways. Instead, IGF-I mediates hypertrophy via a calcineurin-dependent pathway.

Stimulation of collagen biosynthesis by the umbilical cord serum of newborns delivered by mothers with EPH-gestosis (preeclampsia)

Edema, proteinuria, hypertension (EPH)-gestosis, known also as preeclampsia, is the most common, pregnancy-associated pathological syndrome. It is accompanied by a significant increase in collagen content in the umbilical cord arteries and premature replacement of hyaluronic acid by sulfated glycosaminoglycans both in these arteries and in Wharton's jelly. This remodelling of the umbilical cord tissues is accompanied by a distinct increase in insulin-like growth factor-I (IGF-I) concentration in the umbilical cord serum. Such a serum introduced into the culture medium of fibroblasts growing in vitro strongly stimulated the incorporation of radioactive proline into collagen (hydroxyproline-containing and collagenase-sensitive protein). Biosynthesis of noncollagenous proteins was not stimulated. Since IGF-I is known as a stimulator of collagen and sulfated glycosaminoglycan biosynthesis, the high concentration of this growth factor in the umbilical cord plasma may be an agent responsible for preeclampsia-associated remodelling of the umbilical cord, which results in dysfunction in fetal circulation.

Inhibition of collagen biosynthesis and increases in low molecular weight IGF-I binding proteins in the skin of fasted rats

Insulin-like growth factor-I (IGF-I) is an important stimulator of collagen biosynthesis and prolidase activity in connective tissue cells. The disturbances in skin collagen metabolism (reflected by significant decrease in skin collagen content, collagen biosynthesis and prolidase activity) in fasted rats were accompanied by decrease in serum IGF-I level. Fasted rat serum was found to contain about 58% of IGF-I (101.6 +/- 15.4 ng/ml) as compared to control rat serum (175.7 +/- 19.8 ng/ml), while the skin of control and fasted rats contained similar concentrations of IGF-I (about 77 ng/g tissue). The insulin-like growth factor binding proteins (IGFBPs) of sera and tissue extracts (known to regulate IGF-I activity) were analysed by ligand blotting. In the serum of control rats one IGFBP band of about 46 kDa (corresponding to the acid-dissociated IGFBP-3) was detected. In the serum of fasted rats the 46 kDa IGFBP was not observed, however, an other IGFBP of about 30 kDa (corresponding to low molecular weight IGFBPs, e.g. IGFBP-1 or IGFBP-2) was found. The intensity of IGF-I binding to the 30 kDa IGFBP was much higher than that of IGFBP-3, found in control rat serum. Control and fasted rat skin contained similar IGFBPs, however their IGF-I binding abilities were much lower, compared to their serum counterparts. It was found that 46 kDa and 30 kDa proteins, observed in ligand blotting represent IGFBP-3 and IGFBP-1 or IGFBP-2. respectively as demonstrated by western immunoblot analysis. An increase in IGF-binding to 30 kDa IGFBP-1 and/or IGFBP-2 (known as an inhibitors of IGF-dependent functions) in the skin of fasted rats may explain the mechanism of reduced collagen biosynthesis and deposition in tissues during fasting.