Localization of fibroblast growth factor-2 (basic FGF) and FGF receptor-1 in adult human kidney

The Multiple Roles of Fibroblast Growth Factor in Diabetic Nephropathy

Diabetic nephropathy (DN) is a common microvascular complication in the late stages of diabetes. Currently, the etiology and pathogenesis of DN are not well understood. Even so, available evidence shows its development is associated with metabolism, oxidative stress, cytokine interaction, genetic factors, and renal microvascular disease. Diabetic nephropathy can lead to proteinuria, edema and hypertension, among other complications. In severe cases, it can cause life-threatening complications such as renal failure. Patients with type 1 diabetes, hypertension, high protein intake, and smokers have a higher risk of developing DN. Fibroblast growth factor (FGF) regulates several human processes essential for normal development. Even though FGF has been implicated in the pathological development of DN, the underlying mechanisms are not well understood. This review summarizes the role of FGF in the development of DN. Moreover, the association of FGF with metabolism, inflammation, oxidative stress and fibrosis in the context of DN is discussed. Findings of this review are expected to deepen our understanding of DN and generate ideas for developing effective prevention and treatments for the disease.

The potential role of mast cells and fibroblast growth factor-2 in the development of hypertension-induced renal damage

Hypertension-induced renal injury is a multifactorial process which plays a crucial role in the development of chronic kidney disease. Multiple studies have demonstrated that interstitial rather than glomerular changes correlate better with renal functional capacity. Recent evidence indicates that mast cells and cell signaling proteins such as fibroblast growth factor-2 may contribute to the progression of interstitial changes under hypertensive conditions. The aim of our study was to determine the localization of mast cells in the renal cortex and report on the changes in their number, to analyze the distribution of fibroblast growth factor-2, to assess the extent of renal fibrosis and to evaluate renal damage and correlate it with the changes in the number of mast cells in a model of hypertension-induced renal injury by comparing two age groups of spontaneously hypertensive rats. We used 6- and 12-month-old animals. A light microscopic study was conducted on sections stained with hematoxylin and eosin, periodic acid-Schiff stain, Mallory's trichrome method and toluidine blue. For the immunohistochemical study we used monoclonal antibodies against mast cell tryptase and fibroblast growth factor-2 and a polyclonal antibody against c-kit. The expression of fibroblast growth factor-2 was assessed semi-quantitatively. The number of mast cells was evaluated on toluidine blue-, tryptase- and c-kit-stained sections, as well as double-stained sections and a comparative statistical analysis with the Mann-Whitney test was conducted between the two age groups. Our results showed that mast cells were located mainly in the peritubular and perivascular areas and were absent in the region of the renal corpuscles. Their number increased significantly in 12-month-old animals. Immunostaining for tryptase, c-kit and double staining for both molecules yielded identical results. The immunohistochemical expression of fibroblast growth factor-2 increased in the kidneys of older animals, as did the percentage of collagen fibers. In addition, we described more severe renal damage in 12-month-old spontaneously hypertensive rats and noted a positive correlation in both age groups between the number of mast cells on the one hand and glomerular sclerosis index and tubulointerstitial damage index, on the other. The results obtained in the present study support the pivotal role of mast cells in the development of hypertension-induced kidney damage.

Microenvironment-Derived FGF-2 Stimulates Renal Cell Carcinoma Cell Proliferation through Modulation of p27Kip1: Implications for Spatial Niche Formation and Functional Intratumoral Heterogeneity

BACKGROUND/OBJECTIVE

Clear cell renal cell carcinoma (ccRCC) is characterized by a high degree of functional intratumoral heterogeneity (ITH). This is highlighted by the finding that tumor cell proliferation and intracellular signaling occur preferentially in the tumor periphery. The driving forces for such a spatial organization are largely unknown. Herein, we investigate the role of the tumor microenvironment in the control of tumor cell proliferation and functional ITH.

METHODS

Conditioned media (CM) derived from nonmalignant peritumoral kidney tissue were used to stimulate RCC cells in vitro. A neutralization assay was used to characterize the role of FGF-2 in the CM. The molecular mechanisms underlying the action of CM on RCC cells were investigated using immunoblotting, flow cytometry and immunofluorescence microscopy. Lastly, a series of ccRCCs were stained for Ki-67 and p27Kip1, and expression was analyzed in both tumor periphery and center.

RESULTS

We show that CM derived from nonmalignant kidney cells adjacent to an RCC can downregulate the expression of the CDK inhibitor p27Kip1 through enhanced protein degradation in an FGF-2-dependent fashion. FGF-2 functions mainly through the PI3K/AKT pathway downstream of its receptors, and RCC cells with constitutively high AKT activity show not only an enhanced degradation of p27Kip1 through the Emi1-Skp2 axis, but also a subcellular mislocalization of p27Kip1 to the cytoplasmic compartment. Such a mislocalization was also detected in the tumor periphery in vivo suggesting that p27Kip1 plays an important role in shaping this spatial niche.

CONCLUSIONS

Our results suggest that the tumor microenvironment is involved in shaping the tumor peripheral niche by stimulating the enhanced proliferation that is characteristic for this zone.

Cardiovascular Effects of Renal Distal Tubule Deletion of the FGF Receptor 1 Gene

The bone-derived hormone fibroblast growth factor-23 (FGF-23) activates complexes composed of FGF receptors (FGFRs), including FGFR1, and α-Klotho in the kidney distal tubule (DT), leading to increased sodium retention and hypertension. However, the role of FGFR1 in regulating renal processes linked to hypertension is unclear. Here, we investigated the effects of selective FGFR1 loss in the DT. Conditional knockout (cKO) of FGFR1 in the DT (FGFR1DT-cKO mice) resulted in left ventricular hypertrophy (LVH) and decreased kidney expression of α-Klotho in association with enhanced BP, decreased expression of angiotensin converting enzyme 2, and increased expression of the Na+-K+-2Cl- cotransporter. Notably, recombinant FGF-23 administration similarly decreased the kidney expression of α-Klotho and induced LVH in mice. Pharmacologic activation of FGFR1 with a monoclonal anti-FGFR1 antibody (R1MAb1) normalized BP and significantly attenuated LVH in the Hyp mouse model of excess FGF-23, but did not induce a response in FGFR1DT-cKO mice. The hearts of FGFR1DT-cKO mice showed increased expression of the transient receptor potential cation channel, subfamily C, member 6 (TRPC6), consistent with cardiac effects of soluble Klotho deficiency. Moreover, administration of recombinant soluble Klotho lowered BP in the Hyp mice. Thus, FGFR1 in the DT regulates systemic hemodynamic responses opposite to those predicted by the actions of FGF-23. These cardiovascular effects appear to be mediated by paracrine FGF control of kidney FGFR1 and subsequent regulation of soluble Klotho and TRPC6. FGFR1 in the kidney may provide a new molecular target for treating hypertension.

Role of Receptor Tyrosine Kinase Signaling in Renal Fibrosis

Renal fibrosis can be induced in different renal diseases, but ultimately progresses to end stage renal disease. Although the pathophysiologic process of renal fibrosis have not been fully elucidated, it is characterized by glomerulosclerosis and/or tubular interstitial fibrosis, and is believed to be caused by the proliferation of renal inherent cells, including glomerular epithelial cells, mesangial cells, and endothelial cells, along with defective kidney repair, renal interstitial fibroblasts activation, and extracellular matrix deposition. Receptor tyrosine kinases (RTKs) regulate a variety of cell physiological processes, including metabolism, growth, differentiation, and survival. Many studies from in vitro and animal models have provided evidence that RTKs play important roles in the pathogenic process of renal fibrosis. It is also showed that tyrosine kinases inhibitors (TKIs) have anti-fibrotic effects in basic research and clinical trials. In this review, we summarize the evidence for involvement of specific RTKs in renal fibrosis process and the employment of TKIs as a therapeutic approach for renal fibrosis.

Co-localization of LTBP-2 with FGF-2 in fibrotic human keloid and hypertrophic scar

We have recently shown that Latent transforming growth factor-beta-1 binding protein-2 (LTBP-2) has a single high-affinity binding site for fibroblast growth factor-2 (FGF-2) and that LTBP-2 blocks FGF-2 induced cell proliferation. Both proteins showed strong co-localisation within keloid skin from a single patient. In the current study, using confocal microscopy, we have investigated the distribution of the two proteins in normal and fibrotic skin samples including normal scar tissue, hypertrophic scars and keloids from multiple patients. Consistently, little staining for either protein was detected in normal adult skin and normal scar samples but extensive co-localisation of the two proteins was observed in multiple examples of hypertrophic scars and keloids. LTBP-2 and FGF-2 were co-localised to fine fibrous elements within the extracellular matrix identified as elastic fibres by immunostaining with anti-fibrillin-1 and anti-elastin antibodies. Furthermore, qPCR analysis of RNA samples from multiple patients confirmed dramatically increased expression of LTBP-2 and FGF-2, similar TGF-beta 1, in hypertrophic scar compared to normal skin and scar tissue. Overall the results suggest that elevated LTBP-2 may bind and sequester FGF-2 on elastic fibres in fibrotic tissues and modulate FGF-2's influence on the repair and healing processes.

Glypican-5 Increases Susceptibility to Nephrotic Damage in Diabetic Kidney

Type 2 diabetes mellitus is a leading health issue worldwide. Among cases of diabetes mellitus nephropathy (DN), the major complication of type 2 diabetes mellitus, the nephrotic phenotype is often intractable to clinical intervention and demonstrates the rapid decline of renal function to end-stage renal disease. We recently identified the gene for glypican-5 (GPC5), a cell-surface heparan sulfate proteoglycan, as conferring susceptibility for acquired nephrotic syndrome and additionally identified an association through a genome-wide association study between a variant in GPC5 and DN of type 2 diabetes mellitus. In vivo and in vitro data showed a progressive increase of GPC5 in type 2 DN along with severity; the excess was derived from glomerular mesangial cells. In this study, diabetic kidney showed that accumulation of fibroblast growth factor (Fgf)2 strikingly induced progressive proteinuria that was avoided in Gpc5 knockdown mice. The efficacy of Gpc5 inhibition was exerted through expression of the Fgf receptors 3 and 4 provoked in the diabetic kidney attributively. Extraglomerular Fgf2 was pathogenic in DN, and the deterrence of Gpc5 effectively inhibited the glomerular accumulation of Fgf2, the subsequent increase of mesangial extracellular matrix, and the podocytes' small GTPase activity. These findings elucidate the pivotal role of GPC5, identified as a susceptible gene in the genome-wide association study, in hyperglycemia-induced glomerulopathy.

Klotho suppresses renal tubulo-interstitial fibrosis by controlling basic fibroblast growth factor-2 signalling

Increased basic fibroblast growth factor-2 (FGF2) and reduced Klotho have both been reported to be closely associated with renal fibrosis. However, the relationship between Klotho and FGF2 remains unclear. We demonstrate that FGF2 induced tubulo-epithelial plasticity in cultured HK-2 cells, accompanied by a reduction in Klotho expression, whereas recombinant Klotho protein could inhibit the action of FGF2. The FGF2 effects required extracellular signal-regulated protein kinase 1/2 activation, which was suppressed by Klotho. Moreover, Klotho also restrained FGF2-induced fibroblast proliferation and activation. The inhibitory effect of Klotho on the activity of FGF2 was likely due to its potent ability to compete with FGF2 binding to FGF receptor 1. Unilateral ureteral obstruction (UUO)-induced renal fibrosis was associated with an increase in FGF2 and a reduction in Klotho expression in wild-type mice, whereas FGF2(-/-) mice largely preserved Klotho expression and developed only mild renal fibrosis after obstructive injury. Furthermore, administration of Klotho protein in UUO mice significantly reduced renal fibrosis, concomitant with a marked suppression of FGF2 production and signalling. These studies demonstrate a feedback loop between Klotho depletion and FGF2 activation in renal fibrosis. Our results also suggest that Klotho treatment reduces renal fibrosis, at least in part, by inhibiting FGF2 signalling.

Mathematical model of renal interstitial fibrosis

Lupus nephritis (LN) is an autoimmune disease that occurs when autoantibodies complex with self-antigen and form immune complexes that accumulate in the glomeruli. These immune complexes initiate an inflammatory response resulting in glomerular injury. LN often concomitantly affects the tubulointerstitial compartment of the kidney, leading first to interstitial inflammation and subsequently to interstitial fibrosis and atrophy of the renal tubules if not appropriately treated. Presently the only way to assess interstitial inflammation and fibrosis is through kidney biopsy, which is invasive and cannot be repeated frequently. Hence, monitoring of disease progression and response to therapy is suboptimal. In this paper we describe a mathematical model of the progress from tubulointerstitial inflammation to fibrosis. We demonstrate how the model can be used to monitor treatments for interstitial fibrosis in LN with drugs currently being developed or used for nonrenal fibrosis.

Peritubular capillary rarefaction: a new therapeutic target in chronic kidney disease

Chronic kidney disease (CKD) has reached worldwide epidemic proportions and desperately needs new therapies. Peritubular capillary (PTC) rarefaction, together with interstitial fibrosis and tubular atrophy, is one of the major hallmarks of CKD and predicts renal outcome in patients with CKD. PTC endothelial cells (ECs) undergo apoptosis during CKD, leading to capillary loss, tissue hypoxia, and oxidative stress. Although the mechanisms of PTC rarefaction are not well understood, the process of PTC rarefaction depends on multiple events that occur during CKD. These events, which lead to an antiangiogenic environment, include deprivation of EC survival factors, increased production of vascular growth inhibitors, malfunction of ECs, dysfunction of endothelial progenitor cells, and loss of EC integrity via pericyte detachment from the vasculature. In this review, we focus on major factors regulating angiogenesis and EC survival and describe the roles of these factors in PTC rarefaction during CKD and possible therapeutic applications.

Signal transduction in podocytes--spotlight on receptor tyrosine kinases

The mammalian kidney filtration barrier is a complex multicellular, multicomponent structure that maintains homeostasis by regulating electrolytes, acid-base balance, and blood pressure (via maintenance of salt and water balance). To perform these multiple functions, podocytes--an important component of the filtration apparatus--must process a series of intercellular signals. Integrating these signals with diverse cellular responses enables a coordinated response to various conditions. Although mature podocytes are terminally differentiated and cannot proliferate, they are able to respond to growth factors. It is possible that the initial response of podocytes to growth factors is beneficial and protective, and might include the induction of hypertrophic cell growth. However, extended and/or uncontrolled growth factor signalling might be maladaptive and could result in the induction of apoptosis and podocyte loss. Growth factors signal via the activation of receptor tyrosine kinases (RTKs) on their target cells and around a quarter of the 58 RTK family members that are encoded in the human genome have been identified in podocytes. Pharmacological inhibitors of many RTKs exist and are currently used in experimental and clinical cancer therapy. The identification of pathological RTK-mediated signal transduction pathways in podocytes could provide a starting point for the development of novel therapies for glomerular disorders.

The emergence of the glomerular parietal epithelial cell

Glomerular diseases are the leading causes of chronic and end-stage kidney disease. In the 1980s and 1990s, attention was focused on the biology and role of glomerular endothelial and mesangial cells. For the past two decades, seminal discoveries have been made in podocyte biology in health and disease. More recently, the glomerular parietal epithelial cell (PEC)-the fourth resident glomerular cell type-has been under active study, leading to a better understanding and definition of how these cells behave normally, and their potential roles in glomerular disease. Accordingly, this Review will focus on our current knowledge of PECs, in both health and disease. We discuss model systems to study PECs, how PECs might contribute to glomerulosclerosis, crescent and pseudocrescent formation and how PECs handle filtered albumin. These events have consequences on PEC structure and function, and PECs have potential roles as stem or progenitor cells for podocytes in glomerular regeneration, which will also be described.

The enigmatic parietal epithelial cell is finally getting noticed: a review

Although the normal glomerulus comprises four resident cell types, least is known about the parietal epithelial cells (PECs). This comprehensive review addresses the cellular origin of PECs, discusses the normal structure and protein makeup of PECs, describes PEC function, and defines the responses to injury in disease and how these events lead to clinical events. The data show that PECs have unique properties and that new functions are being recognized such as their role in differentiating into podocytes during disease.

Role of basic fibroblast growth factor (FGF-2) in diabetic nephropathy and mechanisms of its induction by hyperglycemia in human renal fibroblasts

Basic fibroblast growth factor (FGF-2) plays a role in renal fibrogenesis, although its potential implications for tubulointerstitial involvement in diabetic nephropathy are unknown. We evaluated the expression of FGF-2 in kidney biopsies from patients with diabetic nephropathy and studied the mechanisms of its induction in human renal fibroblasts under hyperglycemia. Tubulointerstitial expression of FGF-2 was significantly upregulated in diabetic nephropathy compared with control kidneys with a good correlation to the degree of the injury. Fibroblasts cultivated in high glucose displayed increased FGF-2 mRNA as well as protein synthesis and secretion compared with normal glucose. Proliferation rates under hyperglycemia were significantly higher and could be almost completely inhibited by addition of a neutralizing FGF-2 antibody. Alterations in proliferation were associated with changes in p27(kip1) expression. Hyperglycemia induced the expression of PKC-beta1 and PKC-beta2; however, only inhibition of PKC-beta1 but not PKC-beta2 led to a significant decrease of FGF-2 levels. Relevance of the culture findings and functional association was corroborated by colocalization of FGF-2 and PKC-beta in human diabetic kidneys in vivo. High glucose stimulated fibronectin synthesis and secretion, which could be substantially prevented by inhibition of PKC-beta1 and to a lesser extent by inhibiting the FGF-2. Expression of active phosphorylated form of p38 mitogen-activated protein kinase was upregulated under hyperglycemia; however, its inhibition had no effects on FGF-2 synthesis. Our results implicate a role of FGF-2 in high glucose-altered molecular signaling in pathogenesis of diabetic renal disease.

ERYTHROPOIETIN ENHANCES ANGIOGENESIS IN AN EXPERIMENTAL CYCLOSPORINE A-INDUCED NEPHROTOXICITY MODEL IN THE RAT

1. Erythropoietin (EPO) is a hormone regulating the proliferation and differentiation of erythroid precursor cells. The hypothesis that haematopoietic and endothelial cells share a common haemanglioblast progenitor among others is based on the finding that both cell lineages express cell surface antigens, such as CD31 and CD34. 2. In the present study, we investigated the angiogenic potential of recombinant human erythropoietin on cyclosporine A (CsA)-induced nephrotoxicity in the rat kidney and compared it with the effect of basic fibroblast growth factor (bFGF), a well-known angiogenic factor. 3. Rats were divided into five groups: A (control), B (EPO treated), C (CsA treated), D (CsA + EPO treated) and E (CsA + bFGF treated). Mouse anti-human CD31 and CD34 antibodies were used to evaluate the kidney vessels present in histological preparations. 4. Glomerular and peritubular capillaries in Group B (EPO) were increased compared with the control (Group A; P < 0.05). Reduction of the same kidney vessels (glomerular and peritubular capillaries) in Group C (CsA; P < 0.05) compared with controls was observed, whereas in Groups D (CsA + EPO treated) and E (CsA + bFGF treated), capillaries were increased compared with Group C (CsA; P < 0.05). 5. Erythropoietin has a significant angiogenic effect in rat kidney with CsA-induced nephrotoxicity, similar to the effect of the other angiogenic factor bFGF.

Different Effects of Growth Factors on Human Renal Early Distal Tubular Cells in vitro

BACKGROUND

In the kidney, recovery from tubular damage requires regenerative mechanisms leading to re-epithelialization of the injured tubules. Current evidence supports the para- or autocrine role of growth factors in repair and regeneration of ischemic or nephrotoxic experimental acute renal failure.

METHODS

We evaluated the effects of EGF, HGF, IGF-1, and bFGF on human renal thick ascending limb and distal convoluted cells (TALDC) in vitro. TALDC were isolated by immunomagnetic separation and cultured. Signal transduction of the growth factors was evaluated by Western blot of ERK1/2 MAP-K phosphorylation. Cell proliferation was measured by MTT assay and a fluorometric assay.

RESULTS

A significant, dose- and time-dependent phosphorylation of ERK1/2 could be detected exclusively after stimulation with EGF. No other growth factor induced a significant MAPK phosphorylation. In the same manner, proliferation assays showed a significant growth-promoting effect of EGF. Neither HGF, nor IGF-1 or bFGF showed a stimulative effect on TALDC proliferation.

CONCLUSION

The present study highlights the effects of growth factors on cultured TALDC and supports the hypothesis that in vivo EGF plays a para- or autocrine role during renal repair mechanisms.

Nonendothelial mesenchymal cell-derived MCP-1 is required for FGF-2-mediated therapeutic neovascularization: critical role of the inflammatory/arteriogenic pathway

OBJECTIVE

Monocyte chemoattractant protein-1 (MCP-1) is a C-C chemokine that is known as an inflammatory/arteriogenic factor. Angiogenesis contributes to the inflammatory process; however, the molecular and cellular mechanisms of the links among the inflammatory pathway, arteriogenesis, and angiogenesis have not been well elucidated.

METHODS AND RESULTS

Using murine models of fibroblast growth factor-2 (FGF-2)-mediated therapeutic neovascularization, we here show that FGF-2 targets nonendothelial mesenchymal cells (NEMCs) enhancing both angiogenic (vascular endothelial growth factor [VEGF]) and arteriogenic (MCP-1) signals via independent signal transduction pathways. Severe hindlimb ischemia stimulated MCP-1 expression that was strongly enhanced by FGF-2 gene transfer, and a blockade of MCP-1 activity via a dominant negative mutant as well as a deficiency of its functional receptor CCR2 resulted in the diminished recovery of blood flow attributable to adaptive and therapeutic neovascularization. Tumor necrosis factor (TNF)-alpha stimulated MCP-1 expression in all cell types tested, whereas FGF-2-mediated upregulation of MCP-1 was found only in NEMCs but not in others, a finding that was not affected by VEGF in vitro and in vivo.

CONCLUSIONS

These results indicate that FGF-2 targets NEMCs independently, enhancing both angiogenic (VEGF) as well as inflammatory/arteriogenic (MCP-1) pathways. Therefore, MCP-1/CCR2 plays a critical role in adaptive and FGF-2-mediated therapeutic neovascularization.

Lessons from studies on focal segmental glomerulosclerosis: an important role for parietal epithelial cells?

Glomerular diseases are caused by multiple mechanisms. Progressive glomerular injury is characterized by the development of segmental or global glomerulosclerosis independent of the nature of the underlying renal disease. Most studies on glomerular disease focus on the constituents of the filtration barrier (podocytes, glomerular basement membrane (GBM), endothelial cells) or the mesangial cells. Little attention is given to the epithelial cells lining Bowman's capsule, the so called parietal epithelial cells (PECs). This 'lack of attention' is partly explained by the presumed 'passive' function of PECs, which are large, flattened cells that cover Bowman's capsule in a single cell layer and form a barrier between the ultrafiltrate and the periglomerular interstitium, in normal glomerular physiology. A more important reason has been the lack of an established primary role for the parietal epithelium in glomerular diseases. However, in recent years, several studies have demonstrated that PECs are involved in extracapillary proliferation. In addition, PECs can become highly active, proliferating cells, expressing many growth factors, chemokines, cytokines, and their receptors. It was recently demonstrated that PECs also play a part in the development of focal segmental glomerulosclerosis (FSGS). This review summarises current knowledge of the PEC, with emphasis on the role of PECs in the development of FSGS.

The roles of specific genes implicated as circulating factors involved in normal and disordered phosphate homeostasis: frizzled related protein-4, matrix extracellular phosphoglycoprotein, and fibroblast growth factor 23

Normal serum phosphate (Pi) concentrations are relatively tightly controlled by endocrine mediators of Pi balance. Recent data involving several disorders of Pi homeostasis have shed new light on the regulation of serum Pi balance. It has been hypothesized that circulating phosphaturic factors, or phosphatonins, exist that, when present at high serum concentrations, directly act on the kidney to induce renal Pi wasting. This review will focus upon recently discovered factors that are overexpressed in tumors associated with tumor-induced osteomalacia and have reported activity consistent with effecting Pi balance in vivo. Currently, the best-characterized group of phosphatonin-like polypeptides includes secreted frizzled related protein-4, matrix extracellular phosphoglycoprotein, and fibroblast growth factor-23. Our understanding of these factors will, in the short term, aid us in understanding normal Pi balance and, in the future, help to design novel therapeutic strategies for disorders of Pi handling.

Immunolocalization of fibroblast growth factor-1 (FGF-1), its receptor (FGFR-1), and fibroblast-specific protein-1 (FSP-1) in inflammatory renal disease

BACKGROUND

The fibroblast growth factor (FGF) family has functions in development, cell proliferation, migration, and differentiation. While FGF-2 induces fibrosis, the role of FGF-1 in inflammation and fibrosis is less defined. We examined the expression of FGF-1 and FGF receptor (FGFR-1) to determine if renal diseases with varying etiologies of inflammation, including lupus nephritis (LN), acute interstitial nephritis (AIN) and acute rejection superimposed on chronic allograft nephropathy (CAN), showed varying patterns of expression. We also examined the expression of fibroblast-specific protein-1 (FSP-1), which has been linked to epithelial-mesenchymal transition (EMT) and fibrosis, to determine whether it was linked to potential profibrotic and inflammatory FGF-1 mechanisms.

METHODS

Proliferative LN (PLN) (N= 12), nonproliferative lupus nephritis (NPLN) (N= 5), AIN (N= 6), CAN (N= 4), and normal kidneys (N= 3) were studied. FGF, FGFR-1, and FSP-1 were localized by immunohistochemistry, and intensity scored on a 0 to 3+ scale. Double staining with CD68 and separate immunohistochemical staining for CD4 and CD8 with serial sections analysis were done to identify if T lymphocytes or macrophages showed staining for FGF-1 and FGFR-1 or FSP-1.

RESULTS

In normal kidneys, FGF-1 was expressed in mesangial cells (0.67 +/- 0.58), glomerular endothelial (0.67 +/- 0.58), visceral, and parietal epithelial cells (1.67 +/- 0.58). FGFR-1 showed a similar pattern of staining but also was expressed in tubular epithelium, and arterial endothelium and smooth muscle. Expression of FGF-1 was increased over normal in glomerular parenchymal cells only in CAN in podocytes (2.30 +/- 0.58 vs. 3.00 +/- 0.00) (P < 0.05) and parietal epithelial cells (1.67 +/- 0.58 vs. 2.25 +/- 0.50) (P < 0.05). Infiltrating glomerular and interstitial inflammatory cells in diseased glomeruli also expressed FGF-1 and FGFR-1. Tubular cells expressed slightly increased FGFR-1 in renal diseases vs. normal, whereas tubules remained negative for FGF-1 in diseased kidneys. FSP-1 expression was prominent in the interstitium in all kidneys with interstitial inflammation, and most prominent in CAN. Interstitial FSP-1+ cells were consistent with a myofibroblast-type morphology, and did not stain with CD-68. FSP-1 expression was closely associated with inflammatory cells expressing FGF-1 and FGFR-1. FSP-1 also showed positivity within crescents and occasional podocytes in PLN.

CONCLUSION

The expression of FGF-1 and FGFR-1 in infiltrating lymphocytes and macrophages, and of FGFR-1 in tubules, is supportive, but does not prove causality, of the possibility that FGF-1 might have both autocrine and paracrine functions in renal inflammation. However, the initial stimulus for renal inflammation, whether immune complex, hypersensitivity or rejection, did not alter expression patterns of FGF-1 or its receptor. The colocalization of inflammatory infiltrates with interstitial fibrosis supports the possibility of a contribution of FGF-1 for chemotaxis and associated fibrosis, further supported by interstitial FSP-1 expression closely associated with these inflammatory cells expressing FGF-1 and FGFR-1.

Fibroblast growth factor 23 and its receptors

Fibroblast growth factor 23 (FGF23) is a circulating factor that plays critical roles in phosphate and vitamin D metabolism, as evidenced by the fact that FGF23 missense mutations cause autosomal dominant hypophosphatemic rickets (ADHR). Autosomal dominant hypophosphatemic rickets is characterized by hypophosphatemia with inappropriately normal 1,25-dihydroxyvitamin D concentrations, as well as bone pain, fracture and rickets. This phenotype parallels that of patients with tumor induced osteomalacia (TIO), X-linked hypophosphatemic rickets (XLH), and fibrous dysplasia (FD), in whom elevated serum FGF23 levels are often observed. The fibroblast growth factor receptors (FGFR1-4) play key roles in skeletal development, as well as in normal metabolic processes. Several FGFR isoforms that potentially mediate the activity of FGF23 have been implicated. In the short term, these findings will lead to further understanding of FGF23 function, and potentially in the long term, to targeted therapies in disorders of hypo- and hyperphosphatemia that involve FGF23.

Gene profiling the effects of calcium deficiency versus 1,25-dihydroxyvitamin D induced hypercalcemia in rat kidney cortex

Determinants involved in the activation and repression of 1,25-dihydroxyvitamin D (1,25(OH)(2)D(3)) synthesis in renal cortex by changes in extracellular Ca were studied. Cortical kidney RNA isolated from hypocalcemic (LC) rats generated by a low Ca diet, and hypercalcemic (HC) rats generated by a normal Ca diet and two sequential 1 microg doses of 1,25(OH)(2)D(3). Among the genes up-regulated were 1alpha-OHase (4.6-fold) in the LC group and high differential gene expression of VDR (4.0-fold) and 24-OHase (10.4-fold) in the HC group. Moreover, the exposure of renal cortex to LC versus HC conditions revealed a high differential expression of a PKA-dominated pathway involving CBP interacting protein, GATA-1 and CREB transcription factors in the LC model. In the HC model, elevated renal cortex gene expression of several growth factors, peptide receptors, and intracellular signaling molecules depicts a role for CaSR activation and receptor tyrosine kinase signaling in 1,25(OH)(2)D(3)-mediated gene activation and repression of 1alpha-OHase.

Localization and functional characterization of glycosaminoglycan domains in the normal human kidney as revealed by phage display-derived single chain antibodies

Glycosaminoglycans (GAG) play an important role in renal homeostasis. They are strongly negatively charged polysaccharides that bind and modulate a myriad of proteins, including growth factors, cytokines, and enzymes. With the aid of specific phage display-derived antibodies, the distribution of heparan sulfate (HS) and chondroitin sulfate (CS) domains in the normal human kidney was studied. HS domains were specifically located in basement membranes and/or surfaces of renal cells and displayed a characteristic distribution over the nephron. A characteristic location in specific parts of the tubular system was also observed. CS showed mainly an interstitial location. Immunoelectron microscopy indicated specific ultrastructural location of domains. Only partial overlap with any of seven different proteoglycan core proteins was observed. Two HS domains, one highly sulfated (defined by antibody HS4C3) and one low sulfated (defined by antibody RB4Ea12), were studied for their cell biologic relevance with respect to the proliferative effect of FGF-2 on human mesangial cells in vitro. Fibroblast growth factor 2 (FGF-2) binding was HS dependent. Addition of purified HS4C3 antibody but not of the RB4Ea12 antibody counteracted the binding and the proliferative effect of FGF-2, indicating that the HS4C3 domain is involved in FGF-2 handling by mesangial cells. In conclusion, specific GAG domains are differentially distributed in the normal human kidney and are likely involved in binding of effector molecules such as FGF-2. The availability of tools to identify and study relevant GAG structures allows the development of glycomimetica to halt, for instance, mesangial proliferation and matrix production as seen in diabetic nephropathy.

Connective tissue growth factor participates in scar formation of crescentic glomerulonephritis

Glomerular crescents are a major determinant of progression in various renal diseases. Some types of growth factors are known to be involved in the evolution of crescents and the subsequent scar formation. Although glomerular parietal epithelial cells (PECs) are the major component of cellular crescents, the influence of growth factors on PECs is unknown. We performed immunohistochemical studies and in situ hybridization to examine alterations in connective tissue growth factor (CTGF) expression and to identify CTGF-synthesizing cells in crescents in the crescentic glomerulonephritis model of Wistar Kyoto rats. In addition, we examined the roles of fibroblast growth factor (FGF)-2, platelet-derived growth factor (PDGF)-BB, transforming growth factor (TGF)-beta, and CTGF in cell proliferation and matrix synthesis in an established rat PEC cell line (PEC line). In an acute phase of rat crescentic glomerulonephritis, a major component of the crescents were macrophages, which did not express CTGF mRNA. However, in the advanced phase, crescents strongly expressed CTGF mRNA and the epithelial marker pan-cadherin but did not express the macrophage marker ED1, suggesting that PECs synthesized the CTGF. In the PEC line, FGF-2 predominantly promoted [(3)H]thymidine incorporation compared with PDGF-BB. Both TGF-beta and PDGF-BB strongly stimulated extracellular matrix synthesis in association with up-regulation of endogenous CTGF, but TGF-beta showed a predominant role. FGF-2 had a minor effect on it. In addition, blockade of endogenous CTGF using an antisense oligodeoxynucleotide significantly attenuated both TGF-beta- and PDGF-BB-induced extracellular matrix synthesis. These results suggest that several growth factors promote cell proliferation and matrix production in PECs. CTGF-mediated matrix production via the TGF-beta or PDGF-BB pathway in PECs may, in part, play a role in the progression of scar formation in crescents.

Fibroblast growth factor receptors and their ligands in the adult rat kidney

BACKGROUND

Fibroblast growth factors (FGFs) are a family of at least 21 heparin-binding proteins involved in many biological processes, both during development and in the adult, including cell proliferation, differentiation, and angiogenesis. FGFs mediate their effects through high-affinity tyrosine kinase receptors (FGFRs), which are encoded by four genes. The aims of the present study were to localize FGFR-1 through FGFR-3 in the normal adult rat kidney and to determine which functional FGFR variants and FGFs were expressed.

METHODS

Avidin-biotin-enhanced horseradish peroxidase immunohistochemistry was used on paraffin sections of rat kidney to localize FGFR-1 through FGFR-3, whereas reverse transcriptase-polymerase chain reaction was used to examine expression of the receptor variants and also of FGF-1 through FGF-10 in cortex, outer medulla, and inner medulla.

RESULTS

By immunohistochemistry, each receptor was localized to distinct and overlapping nephron segments, such that one or more FGFRs were localized to all nephron and collecting duct epithelia. FGFR-1 and FGFR-3 were localized to glomeruli, FGFR-3 to proximal tubules and FGFR-1 to thin limbs. FGFR-1 through FGFR-3 were localized to distal straight tubules, with FGFR-1 and FGFR-3 localized to distal convoluted tubules. FGFR-1 and FGFR-3 were localized to medullary collecting ducts. In addition, FGFR-1 was localized to the smooth muscle of renal arteries. All seven FGFR variants were expressed in the cortex and outer medulla, with fewer FGFRs in the inner medulla. FGF-1, FGF-2, FGF-7, FGF-8, and FGF-9 were expressed in the kidney, with FGF-10 expression found only in the cortex.

CONCLUSIONS

Mapping of these receptors is critical to the determination of the effects of FGF ligands in discrete regions of the kidney. The distributions of the FGFRs in the normal adult kidney and the restricted expression of FGF ligands suggest that specific FGFs have distinct and important roles in the maintenance of normal kidney structure and function.

Osteogenic protein-1 prevents renal fibrogenesis associated with ureteral obstruction

Unilateral ureteral obstruction (UUO) is a model of renal injury characterized by progressive tubulointerstitial fibrosis and renal damage, while relatively sparing the glomerulus and not producing hypertension or abnormalities in lipid metabolism. Tubulointerstitial fibrosis is a major component of several kidney diseases associated with the progression to end-stage renal failure. Here we report that when a critical renal developmental morphogen, osteogenic protein-1 (OP-1; 100 or 300 microg/kg body wt), is administered at the time of UUO and every other day thereafter, interstitial inflammation and fibrogenesis are prevented, leading to preservation of renal function during the first 5 days after obstruction. Compared with angiotensin-converting enzyme inhibition with enalapril treatment, OP-1 was more effective in preventing tubulointerstitial fibrosis and in preserving renal function. The mechanism of OP-1- induced renal protection was associated with prevention of tubular atrophy, an effect not shared with enalapril, and was related to preservation of tubular epithelial integrity. OP-1 blocked the stimulation of epithelial cell apoptosis produced by UUO, which promoted maintenance of tubular epithelial integrity. OP-1 preserved renal blood flow (RBF) during UUO, but enalapril also stimulated RBF. Thus OP-1 treatment inhibited tubular epithelial disruption stimulated by the renal injury of UUO, preventing tubular atrophy and diminishing the activation of tubulointerstitial inflammation and fibrosis and preserving renal function.

Basic fibroblast growth factor expression is increased in human renal fibrogenesis and may mediate autocrine fibroblast proliferation

BACKGROUND

Interstitial fibroblasts play a critical role in renal fibrogenesis, and autocrine proliferation of these cells may account for continuous matrix synthesis. Basic fibroblast growth factor (FGF-2) is mitogenic for most cells and exerts intracrine, autocrine, and paracrine effects on epithelial and mesenchymal cells. The aims of the present studies were to localize and quantitate the expression of FGF-2 in normal and pathologic human kidneys and to study the in vitro effects of FGF-2 on proliferation, differentiation, and matrix production of isolated cortical kidney fibroblasts.

METHODS

FGF-2 protein expression was localized by immunofluoresence double labelings in normal and fibrotic human kidneys. Subsequently, interstitial FGF-2 labeling was determined semiquantitatively in 8 normal kidneys and 39 kidneys with variable degrees of interstitial fibrosis and was correlated with the morphometrically determined interstitial cortical volume. In addition, FGF-2 expression was quantitated by immunoblot analysis in three normal and six fibrotic kidneys. FGF-2 mRNA was localized by in situ hybridizations. Seven primary cortical fibroblast lines were established, and expression of FGF-2 and FGF receptor-1 (FGFR-1) were examined. The effects of FGF-2 on cell proliferation were determined by bromodeoxyuridine incorporation and cell counts, those on differentiation into myofibroblasts by staining for alpha-smooth muscle actin, and those on matrix synthesis by enzyme-linked immunosorbent assay for collagen type I and fibronectin. Finally, proliferative activity in vivo was evaluated by expression of MIB-1 (Ki-67 antigen).

RESULTS

In normal kidneys, FGF-2 expression was confined to glomerular, vascular, and a few tubular as well as interstitial fibroblast-like cells. The expression of FGF-2 protein was increased in human kidneys, with tubulointerstitial scarring correlating with the degree of interstitial fibrosis (r = 0.84, P < 0.01). Immunoblot analyses confirmed a significant increase in FGF-2 protein expression in kidneys with interstitial scarring. In situ hybridization studies demonstrated low-level detection of FGF-2 mRNA in normal kidneys. However, FGF-2 mRNA expression was robustly up-regulated in interstitial and tubular cells in end-stage kidneys, indicating that these cells are the source of excess FGF-2 protein. Primary cortical fibroblasts express FGF-2 and FGFR-1 in vitro. FGF-2 induced a robust growth response in these cells that could be blocked specifically by a neutralizing FGF-2 antibody. Interestingly, the addition of the neutralizing antibody alone did reduce basal proliferation up to 31.5%. In addition, FGF-2 induced expression of alpha-smooth muscle actin up to 1.6-fold, but no significant effect was observed on the synthesis of collagen type I and fibronectin. Finally, staining for MIB-1 revealed a good correlation of interstitial FGF-2 positivity with interstitial and tubular proliferative activity (r = 0.71, P < 0.01 for interstitial proliferation, N = 30).

CONCLUSIONS

Interstitial FGF-2 protein and mRNA expression correlate with interstitial scarring. FGF-2 is a strong mitogen for cortical kidney fibroblasts and may promote autocrine fibroblast growth. Expression of FGF-2 correlates with interstitial and tubular proliferation in vivo.