Endothelin is a potent inhibitor of matrix metalloproteinase-2 secretion and activation in rat mesangial cells

Matrix Metalloproteinases in Diabetic Kidney Disease

Around the world diabetic kidney disease (DKD) is the main cause of chronic kidney disease (CKD), which is characterized by mesangial expansion, glomerulosclerosis, tubular atrophy, and interstitial fibrosis. The hallmark of the pathogenesis of DKD is an increased extracellular matrix (ECM) accumulation causing thickening of the glomerular and tubular basement membranes, mesangial expansion, sclerosis, and tubulointerstitial fibrosis. The matrix metalloproteases (MMPs) family are composed of zinc-dependent enzymes involved in the degradation and hydrolysis of ECM components. Several MMPs are expressed in the kidney; nephron compartments, vasculature and connective tissue. Given their important role in DKD, several studies have been performed in patients with DKD proposing that the measurement of their activity in serum or in urine may become in the future markers of early DKD. Studies from diabetic nephropathy experimental models suggest that a balance between MMPs levels and their inhibitors is needed to maintain renal homeostasis. This review focuses in the importance of the MMPs within the kidney and their modifications at the circulation, kidney and urine in patients with DKD. We also cover the most important studies performed in experimental models of diabetes in terms of MMPs levels, renal expression and its down-regulation effect.

Endothelin-1 down-regulates matrix metalloproteinase 14 and 15 expression in human first trimester trophoblasts via endothelin receptor type B

STUDY QUESTION

Does endothelin-1 (ET-1) regulate matrix metalloproteinase (MMP) 14 and 15 production and invasion of human first trimester trophoblasts?

SUMMARY ANSWER

ET-1 in pathophysiological concentrations down-regulates MMP14 and MMP15 expression via endothelin receptor (ETR) type B and decreases trophoblast migration and invasion.

WHAT IS KNOWN ALREADY

MMP14 and MMP15 are involved in trophoblast invasion. Impairment of invasion has been linked to pregnancy complications such as pre-eclampsia (PE). ET-1 is up-regulated in PE.

STUDY DESIGN, SIZE, DURATION

In vitro study using primary human trophoblasts from 50 first trimester placentas (gestational week 7-12).

PARTICIPANTS/MATERIALS, SETTING, METHODS

Trophoblasts were cultured in the absence or presence of 10-100 nM ET-1. MMP14 and MMP15 mRNA and protein were quantified by RT-qPCR and Western blotting, respectively. Selective antagonists for ETRA (BQ-123) or ETRB (BQ-788) were used to identify ETR subtypes involved. Functional ET-1 effects were tested in first trimester chorionic villous explants and transwell invasion assays. The roles of tumor necrosis factor (TNF)-α (25 ng/ml) and oxygen (1%) in ET-1 regulation of MMP14 and 15 expression were assessed by Western blotting.

MAIN RESULTS AND THE ROLE OF CHANCE

ET-1 down-regulated MMP14 and MMP15 mRNA (-21% and -26%, respectively, P < 0.05) and protein levels (-18% and -22%, respectively, P < 0.05). This effect was mediated via ETRB. ET-1 decreased trophoblast outgrowth in placental explants (-24%, P < 0.05) and trophoblast invasion (-26%, P ≤ 0.01). TNF-α enhanced ET-1 mediated MMP15 down-regulation (by 10%, P < 0.05), whereas hypoxia abolished the effect of ET-1 on both MMPs.

LARGE SCALE DATA

N/A.

LIMITATIONS, REASONS FOR CAUTION

Only primary trophoblasts were used in this study. Since trophoblast yield from first trimester placental material is limited, further aspects of MMP14 and 15 regulation could not be characterized. Other anti-invasive factors may be altered by ET-1 in trophoblasts and, thus, contribute to the reduced invasion, but have not been investigated. Oxygen levels similar to those found in the decidua (5-8% O₂) were not analyzed in this study.

WIDER IMPLICATIONS OF THE FINDINGS

ET-1 modifies placental function already during the first trimester of pregnancy, the time-window when the placental changes implicated in PE occur. Thus, our results improve the understanding of the placental mechanisms underlying trophoblast invasion and PE.

STUDY FUNDING/COMPETING INTERESTS

The study was funded by the Oesterreichische Nationalbank (Anniversary Fund, project number: 14796) and the Herzfelder'sche Familienstiftung (to J.P.; number: 00685). AMM received funding from the Austrian Science Fund FWF (W1241) and the Medical University Graz through the PhD Program Molecular Fundamentals of Inflammation (DK-MOLIN). The authors have no conflict of interest.

High glucose-induced hypertrophy of mesangial cells is reversed by connexin43 overexpression via PTEN/Akt/mTOR signaling

BACKGROUND

Hypertrophy of glomerular mesangial cells (GMC) is one of the earliest pathological abnormalities in diabetic nephropathy, which correlates with eventual glomerulosclerosis. We have previously proved that this hypertrophy is mediated by downregulation of connexin43 (Cx43) and dysfunction of gap junctional intercellular communication, but the mechanism involved is still unclear. This study aims to investigate whether PTEN/Akt/mammalian target of rapamycin (mTOR) was involved as the downstream molecular signaling of Cx43 in regulating high glucose-induced GMC hypertrophy.

METHODS

GMC were isolated from male Wistar rats at the age of 3 months. Gene transfer technique was used to upregulate Cx43 in GMC, which was validated by western blot and immunofluorescent staining. Forward scatter of flow cytometry and total protein/cell number were examined to testify GMC hypertrophy induced by high glucose (30 mM) and the influence of Cx43 overexpression; western blot was performed to demonstrate the changes of Cx43 and signal protein level and flow cytometry and MTT test were carried out to check cell cycle and proliferation rate, respectively.

RESULTS

GMC exposed to a high concentration of glucose presented decreased Cx43, inhibited PTEN, triggered Akt phosphorylation and activated downstream mTOR, leading to stagnancy of cell cycle, decline of proliferation rate and occurrence of hypertrophy. Cx43 overexpression could prevent PTEN inhibition, Akt and mTOR phosphorylation, resulting in restoration of cell cycle and proliferation ability and reversion of GMC hypertrophy. GMC with Cx43 inhibition showed similar PTEN/Akt/mTOR change as stimulated by high glucose.

CONCLUSION

PTEN/Akt/mTOR signaling stimulated by high concentration of glucose is regulated by Cx43 overexpression, which unveils part of the molecular mechanism of Cx43 in regulating hyperglycemia-induced hypertrophy.

Hypoxia down-regulates secretion of MMP-2, MMP-9 in porcine pulmonary artery endothelial and smooth muscle cells and the role of HIF-1

Primary cell culture, techniques of gene transfection, gelatin zymography, and Western blot were used to investigate the effect of hypoxia on the secretion of MMP-2 and MMP-9 in pulmonary artery endothelial cells (PAEC) and smooth muscle cells (PASMC), and the role of HIF-1. Our results showed that (1) after exposure to hypoxia for 24 h, the protein content and activity of MMP-2 in the PAEC medium as well as these of MMP-2 and MMP-9 in PASMC medium (P < 0. 01) decreased significantly in contrast to those in normoxic group (P < 0.05); (2) after transfection of wild type EPO3'-enhancer, a HIF-1 decoy, the content and activity of MMP-2 and MMP-9 in hypoxic mediums became higher than those in normoxic group (P < 0.01), while transfection of mutant EPO3'-enhancer didn't affect the hypoxia-induced down-regulation. It is concluded that hypoxia could inhibit the secretion and activity of MMP-2 and MMP-9 in PAEC and PASMC, which could be mitigated by the transfection of EPO3'-enhancer and that HIF-1 pathway might contribute to hypoxia-induced down-regulation of MMP-2 and MMP-9.

Lysophosphatidic acid down-regulates stress fibers and up-regulates pro-matrix metalloproteinase-2 activation in ovarian cancer cells

Epithelial ovarian cancer (EOC) is asymptomatic at early stages and is often diagnosed late when tumor cells are highly metastatic. Lysophosphatidic acid (LPA) has been implicated in ovarian oncogenesis as levels of this lipid are elevated in patient ascites and plasma. Because the underlying mechanism governing LPA regulation of matrix metalloproteinase-2 (MMP-2) activation remains undefined, we investigated the relationship between LPA-induced changes in actin microfilament organization and MMP-2 enzymatic activity. We report that when cells were cultured at a high density, LPA mediated stress fiber and focal adhesion disassembly and significantly repressed RhoA activity in EOC cells. Inhibition of Rho-kinase/ROCK enhanced both LPA-stimulated loss of stress fibers and pro-MMP-2 activation. In contrast, expression of the constitutively active RhoA(G14V) mutant diminished LPA-induced pro-MMP-2 activation. LPA had no effects on membrane type 1-MMP or tissue inhibitor of metalloproteinase-2 expression, but up-regulated MMP-2 levels, contributing to the induction of MMP-2 activation. Interestingly, when cells were cultured at a low density, stress fibers were present after LPA stimulation, and ROCK activity was required for EOC cell migration. Collectively, these results were consistent with a model in which LPA stimulates the metastatic dissemination of EOC cells by initiating loss of adhesion and metalloproteinase activation.

Clinical outcomes of bosentan in pulmonary arterial hypertension do not correlate with levels of TIMPs

BACKGROUND

Matrix metalloproteinases (MMP) and their inhibitors, tissue inhibitors of metalloproteinases (TIMP), are involved in tissue inflammation and fibrotic processes. Treatment with bosentan has been shown to improve the clinical outcome of patients with pulmonary arterial hypertension (PAH) with and without association with systemic sclerosis (SSc), and also to modulate the serum levels of matrix metalloproteases-9. We measured TIMP-1 and TIMP-2 in the serum of patients with SSc with and without PAH treated with long-term bosentan compared with healthy donors (HD).

MATERIALS AND METHODS

Serum samples from HD (n = 16) and patients with SSc (n = 35), including patients with SSc without PAH (n = 23) and patients with PAH (n = 12), were analyzed using enzyme-linked immunosorbent assays (ELISAs) for total TIMP-1 and TIMP-2.

RESULTS

Both mean TIMP-1 and TIMP-2 levels were significantly increased in patients with SSc compared with HD, but no differences were observed between patients with SSc with and without PAH. In the eight bosentan-treated patients, TIMP-1 and TIMP-2 levels did not change during 1 year of treatment, while bosentan increased the 6-min walking distance by 136 meters after 1 year, as well as clinical outcomes.

CONCLUSIONS

Increased levels of TIMP-1 and TIMP-2 in patients with SSc compared with HD suggest that the inhibition of proteolysis allows the accumulation of ECM proteins. As bosentan does not stimulate TIMPs, it appears to favour proteolytic imbalance and to increase the turnover of ECM proteins.

Essential role of Ca2+ release channels in angiotensin II-induced Ca2+ oscillations and mesangial cell contraction

The increased resistance of the glomerulus as a result of contractile dysfunction of mesangial cells (MCs) is associated with reduction of glomerular filtration rate and development of glomerulosclerosis. Evidences show MCs contraction changes with intracellular Ca(2+) concentration ([Ca(2+)](i)). Here, we explore the mechanism of angiotensin II (AngII)-induced Ca(2+) oscillations and MCs contraction. Primary MCs from 3-month-old and 28-month-old rats were used for detection of Ca(2+) oscillations and MC planar area with confocal microscopy. AngII could induce typical Ca(2+) oscillations and contraction of MCs. This process was abolished by thapsigargin, 2-aminoethoxydiphenyl borate, or 1-O-octadecyl-2-O-methyl-sn-glycero-3-phosphorylcholine, and partially inhibited by ryanodine, but could not be inhibited in the absence of extracellular Ca(2+). Ryanodine receptors (RyRs) and inositol 1,4,5-trisphosphate (InsP(3)) receptors displayed a strong colocalization, which may contribute to the amplification of Ca(2+) response. MLC(20) phosphorylation and MC planar area were associated with AngII-induced Ca(2+) oscillations. The frequency of Ca(2+) oscillations was dependent on the AngII concentration and correlated with the MCs' contractive extent, which could be attenuated by KN-93. The amplitude reduction of oscillations correlated with the decrease in aging-related contraction. In conclusion, [Ca(2+)](i) response of MCs to AngII is characterized by repetitive spikes through the following repetitive cycles: Ca(2+) release by phospholipase C -InsP(3) pathway, Ca(2+) amplification by Ca(2+)-activated RyRs and Ca(2+) reuptake by the endoplasmic reticulum. MCs contraction can be modulated by oscillations not only in an AngII-induced frequency-dependent mode but also in an aging-related, amplitude-dependent mode.

Endothelin antagonism prevents early EGFR transactivation but not increased matrix metalloproteinase activity in diabetes

Although past studies have demonstrated decreased renal matrix metalloproteinase (MMP) activity in type 1 diabetes and in mesangial cells grown under high glucose conditions, renal MMP expression and activity in type 2 diabetes and the regulation of MMPs by profibrotic factors involved in diabetic renal complications such as endothelin-1 (ET-1) remained unknown. The renal expression and activity of MMPs in type 2 diabetic Goto-Kakizaki (GK) rats treated with vehicle or ET(A) receptor selective antagonist ABT-627 for 4 wk were assessed by gelatin zymography, fluorogenic gelatinase assay, and immunoblotting. In addition, expression and phosphorylation of epidermal growth factor receptor (EGFR) and connective tissue growth factor were evaluated by immunoblotting. Renal sections stained with Masson trichrome were used to investigate kidney structure. MMP-2 activity and protein levels were significantly increased in both cortical and medullary regions in the GK rats. Membrane-bound MMP (MT1-MMP), MMP-9, and fibronectin levels were also increased, and ABT-627 treatment did not have an effect on MMP activity and expression. Histological analysis of kidneys did not reveal any structural changes. Phosphorylation of EGFR was significantly increased in the diabetic animals, and ABT-627 treatment prevented this increase, suggesting ET-1-mediated transactivation of EGFR. These results suggest that there is early upregulation of renal MMPs in the absence of any kidney damage. Although the ET(A) receptor subtype is not involved in the early activation of MMPs in type 2 diabetes, ET-1 contributes to transactivation of growth-promoting and profibrotic EGFR.

From hyperglycemia to diabetic kidney disease: the role of metabolic, hemodynamic, intracellular factors and growth factors/cytokines

At present, diabetic kidney disease affects about 15-25% of type 1 and 30-40% of type 2 diabetic patients. Several decades of extensive research has elucidated various pathways to be implicated in the development of diabetic kidney disease. This review focuses on the metabolic factors beyond blood glucose that are involved in the pathogenesis of diabetic kidney disease, i.e., advanced glycation end-products and the aldose reductase system. Furthermore, the contribution of hemodynamic factors, the renin-angiotensin system, the endothelin system, and the nitric oxide system, as well as the prominent role of the intracellular signaling molecule protein kinase C are discussed. Finally, the respective roles of TGF-beta, GH and IGFs, vascular endothelial growth factor, and platelet-derived growth factor are covered. The complex interplay between these different pathways will be highlighted. A brief introduction to each system and description of its expression in the normal kidney is followed by in vitro, experimental, and clinical evidence addressing the role of the system in diabetic kidney disease. Finally, well-known and potential therapeutic strategies targeting each system are discussed, ending with an overall conclusion.

Physiology and pathology of endothelin-1 in renal mesangium

Mesangial cells (MCs) play a central role in the physiology and pathophysiology of endothelin-1 (ET-1) in the kidney. MCs release ET-1 in response to a variety of factors, many of which are elevated in glomerular injury. MCs also express ET receptors, activation of which leads to a complex signaling cascade with resultant stimulation of MC hypertrophy, proliferation, contraction, and extracellular matrix accumulation. MC ET-1 interacts with other important regulatory factors, including arachidonate metabolites, nitric oxide, and angiotensin II. Excessive stimulation of ET-1 production by, and activity in, MC is likely of pathogenic importance in glomerular damage in the setting of diabetes, hypertension, and glomerulonephritis. The recent introduction of ET antagonists, and possibly ET-converting enzyme inhibitors, into the clinical arena establishes the potential for new therapies for those diseases characterized by increased MC ET-1 actions. This review will examine our present understanding of how ET-1 is involved in mesangial function in health and disease. In addition, we will discuss the status of clinical trials using ET antagonists, which have only been conducted in nonrenal disease, as a background for advocating their use in diseases characterized by excessive MC-derived ET-1.

Cytoskeletal rearrangement and signal transduction in TGF-beta1-stimulated mesangial cell collagen accumulation

TGF-beta1 has been implicated in glomerular extracellular matrix accumulation, although the precise cellular mechanism(s) by which this occurs is not fully understood. The authors have previously shown that the Smad signaling pathway is present and functional in human glomerular mesangial cells and plays a role in activating type I collagen gene expression. It also was determined that TGF-beta1 activates ERK mitogen-activated protein kinase in mesangial cells to enhance Smad activation and collagen expression. Here, it was shown that TGF-beta1 rapidly induces cytoskeletal rearrangement in human mesangial cells, stimulating smooth muscle alpha-actin detection in stress fibers and promoting focal adhesion complex assembly and redistribution. Disrupting the actin cytoskeleton with cytochalasin D (Cyto D) selectively decreased basal and TGF-beta1-induced cell-layer collagen I and IV accumulation. The balance of matrix metalloproteinases (MMP) and inhibitors was altered by Cyto D or TGF-beta1 alone, increasing MMP activity, increasing MMP-1 expression, and decreasing tissue inhibitor of matrix metalloproteinase-2 expression. Cyto D also decreased basal and TGF-beta1-stimulated alpha1(I) collagen mRNA but did not inhibit TGF-beta-stimulated alpha1(IV) mRNA expression. A similar decrease in alpha1(I) mRNA expression caused by the actin polymerization inhibitor latrunculin B was partially blocked by the addition of jasplakinolide, which promotes actin assembly. The Rho-family GTPase inhibitor C. difficile toxin B or the Rho-associated kinase inhibitor Y-27632 also blocked TGF-beta1-stimulated alpha1(I) mRNA expression. Cytoskeletal disruption reduced Smad2 phosphorylation but had little effect on mRNA stability, TGF-beta receptor number, or receptor affinity. Thus, TGF-beta1-mediated collagen I accumulation is associated with cytoskeletal rearrangement and Rho-GTPase signaling.

Coordination of mesangial cell contraction by gap junction--mediated intercellular Ca(2+) wave

Gap junction intercellular communication (GJIC) plays a fundamental role in mediating intercellular signals and coordinating multicellular behavior in various tissues and organs. Glomerular mesangial cells (MC) are rich in GJ, but the functional associations of these intercellular channels are still unclear. This study examines the potential role of GJ in the transmission of intercellular Ca(2+) signals and in the coordination of MC contraction. First, the presence of GJ protein Cx43 and functional GJIC was confirmed in MC by using immunochemical staining or transfer of Lucifer yellow (LY) after a single cell injection, respectively. Second, mechanical stimulation of a single MC initiated propagation of an intercellular Ca(2+) wave, which was preventable by the GJ inhibitor heptanol but was not altered by pretreatment of MC with ATP or addition of apyrase into the assay system. Third, the phospholipase C (PLC) inhibitor U73122 could largely eliminate the mechanically elicited propagation of intercellular Ca(2+) waves, suggesting a possibly mediating role of inositol trisphosphate (IP(3)) in the initiation and transmission of intercellular Ca(2+) signaling. Fourth, injection of IP(3) into a single cell caused contraction, not only in the targeted cell, but also in the adjacent cells, as indicated by the reduction of cellular planar area. Fifth, addition of two structurally unrelated GJ inhibitors, heptanol and alpha-glycyrrhetinic acid (GA), into MC embedded in collagen gels significantly attenuated the reduction of gel areas after exposure to serum. This study provides the first functional evidence supporting the critical role of GJIC in the synchronization of MC behaviors.