An old enzyme with a new function: purification and characterization of a distinct matrix-degrading metalloproteinase in rat kidney cortex and its identification as meprin

Meprin β expression modulates the interleukin-6 mediated JAK2-STAT3 signaling pathway in ischemia/reperfusion-induced kidney injury

Meprin metalloproteinases have been implicated in the pathophysiology of ischemia/reperfusion (IR)-induced kidney injury. Previous in vitro data showed that meprin β proteolytically processes interleukin-6 (IL-6) resulting in its inactivation. Recently, meprin-β was also shown to cleave the IL-6 receptor. The goal of this study was to determine how meprin β expression impacts IL-6 and downstream modulators of the JAK2-STAT3-mediated signaling pathway in IR-induced kidney injury. IR was induced in 12-week-old male wild-type (WT) and meprin β knockout (βKO) mice and kidneys obtained at 24 h post-IR. Real-time PCR, western blot, and immunostaining/microscopy approaches were used to quantify mRNA and protein levels respectively, and immunofluorescence counterstaining with proximal tubule (PT) markers to determine protein localization. The mRNA levels for IL-6, CASP3 and BCL-2 increased significantly in both genotypes. Interestingly, western blot data showed increases in protein levels for IL-6, CASP3, and BCL-2 in the βKO but not in WT kidneys. However, immunohistochemical data showed increases in IL-6, CASP3, and BCL-2 proteins in select kidney tubules in both genotypes, shown to be PTs by immunofluorescence counterstaining. IR-induced increases in p-STAT-3 and p-JAK-2 in βKO at a global level but immunoflourescence counterstaining demonstrated p-JAK2 and p-STAT3 increases in select PT for both genotypes. BCL-2 increased only in the renal corpuscle of WT kidneys, suggesting a role for meprins expressed in leukocytes. Immunohistochemical analysis confirmed higher levels of leukocyte infiltration in WT kidneys when compared to βKO kidneys. The present data demonstrate that meprin β modulates IR-induced kidney injury in part via IL-6/JAK2/STAT3-mediated signaling.

Regulation of meprin metalloproteases in mucosal homeostasis

Mucus is covering the entire epithelium of the gastrointestinal tract (GIT), building the interface for the symbiosis between microorganisms and their host. Hence, a disrupted mucosal barrier or alterations of proper mucus composition, including the gut microbiota, can cause severe infection and inflammation. Meprin metalloproteases are well-known to cleave various pro-inflammatory molecules, contributing to the onset and progression of pathological conditions including sepsis, pulmonary hypertension or inflammatory bowel disease (IBD). Moreover, meprins have an impact on migration and infiltration of immune cells like monocytes or leukocytes during intestinal inflammation by cleaving tight junction proteins or cell adhesion molecules, thereby disrupting epithelial cell barrier and promoting transendothelial cell migration. Interestingly, both meprin α and meprin β are susceptibility genes for IBD. However, both genes are significantly downregulated in inflamed intestinal tissue in contrast to healthy donors. Therefore, a detailed understanding of the underlying molecular mechanisms is the basis for developing new and effective therapies against manifold pathologies like IBD. This review focuses on the regulation of meprin metalloproteases and its impact on physiological and pathological conditions related to mucosal homeostasis.

Meprin-β activity modulates the β-catalytic subunit of protein kinase A in ischemia-reperfusion-induced acute kidney injury

Meprin metalloproteases have been implicated in the progression of kidney injury. Previous work from our group has shown that meprins proteolytically process the catalytic subunit of protein kinase A (PKA-C), resulting in decreased PKA-C kinase activity. The goal of the present study was to determine the PKA-C isoforms impacted by meprin-β and whether meprin-β expression affects downstream mediators of the PKA signaling pathway in ischemia-reperfusion (IR)-induced kidney injury. IR was induced in 12-wk-old male wild-type (WT) and meprin-β knockout (βKO) mice. Madin-Darby canine kidney cells transfected with meprin-β cDNA were also subjected to 2 h of hypoxia. Western blot analysis was used to evaluate levels of total PKA-C, PKA-Cα, PKA-Cβ, phosphorylated (p-)PKA-C, and p-ERK1/2. Meprin-β expression enhanced kidney injury as indicated by levels of neutrophil gelatinase-associated lipocalin and cystatin C. IR-associated decreases were observed in levels of p-PKA-C in kidney tissue from WT mice but not βKO mice, suggesting that meprin-β expression/activity is responsible for the in vivo reduction in kinase activity. Significant increases in levels of PKA-Cβ were observed in kidney lysates for WT mice but not βKO mice at 6 h post-IR. Proximal tubule PKA-Cβ increases in WT but not βKO kidneys were demonstrated by fluorescent microscopy. Furthermore, IR-induced injury was associated with significant increases in p-ERK levels for both genotypes. The present data demonstrate that meprin-β enhances IR-induced kidney injury in part by modulating mediators of the PKA-Cβ signaling pathway.

LC-MS-based metabolomics analysis to identify meprin-β-associated changes in kidney tissue from mice with STZ-induced type 1 diabetes and diabetic kidney injury

Meprin metalloproteases have been implicated in the pathophysiology of diabetic kidney disease (DKD). Single-nucleotide polymorphisms in the meprin-β gene have been associated with DKD in Pima Indians, a Native American ethnic group with an extremely high prevalence of DKD. In African American men with diabetes, urinary meprin excretion positively correlated with the severity of kidney injury. In mice, meprin activity decreased at the onset of diabetic kidney injury. Several studies have identified meprin targets in the kidney. However, it is not known how proteolytic processing of the targets by meprins impacts the metabolite milieu in kidneys. In the present study, global metabolomics analysis identified differentiating metabolites in kidney tissues from wild-type and meprin-β knockout mice with streptozotocin (STZ)-induced type 1 diabetes. Kidney tissues were harvested at 8 wk post-STZ and analyzed by hydrophilic interaction liquid chromatography ultra-performance liquid chromatography-quadrupole time-of-flight mass spectrometry. Principal component analysis identified >200 peaks associated with diabetes. Meprin expression-associated metabolites with strong variable importance of projection scores were indoxyl sulfate, N-γ-l-glutamyl-l-aspartic acid, N-methyl-4-pyridone-3-carboxamide, inosine, and cis-5-decenedioic acid. N-methyl-4-pyridone-3-carboxamide has been previously implicated in kidney injury, and its isomers, 4-PY and 2-PY, are markers of peroxisome proliferation and inflammation that correlate with creatinine clearance and glucose tolerance. Meprin deficiency-associated differentiating metabolites with high variable importance of projection scores were cortisol, hydroxymethoxyphenylcarboxylic acid-O-sulfate, and isovaleryalanine. The data suggest that meprin-β activity enhances diabetic kidney injury in part by altering the metabolite balance in kidneys, favoring high levels of uremic toxins such as indoxyl sulfate and N-methyl-pyridone-carboxamide.

An integrated in silico approach to understand protein-protein interactions: human meprin-β with fetuin-A

Human meprin-β, a zinc metalloprotease belonging to the astacin family, have been found to be associated with many pathological conditions like inflammatory bowel disease, fibrosis and neurodegenerative disease. The inhibition of meprin-β by various inhibitors, both macromolecular and small molecules, is crucial in the control of several diseases. Human fetuin-A, a negative acute phase protein involved in inflammatory disease, has recently been identified as an endogenous inhibitor for meprin-β. In this computational study, an integrated in silico approach was performed using existing structural information of meprin-β coupled with ab initio modelling of human fetuin-A to predict a rational model of the complex through protein-protein docking. Further, the models were optimized and validated to generate an ensemble of conformations through extensive molecular dynamics simulation. Virtual alanine scanning mutagenesis was explored to identify hotspot residues on both proteins significant for protein-protein interaction (PPI). The results of the study provide structural insight into PPI between meprin-β and fetuin-A which can be useful in designing molecules to modulate meprin-β activity. Communicated by Ramaswamy H. Sarma.

Meprin β metalloproteases associated with differential metabolite profiles in the plasma and urine of mice with type 1 diabetes and diabetic nephropathy

Background

Meprin metalloproteases are abundantly expressed in the brush border membranes of kidney proximal tubules and small intestines. Meprins are also expressed in podocytes and leukocytes (monocytes and macrophages). Meprins are implicated in the pathophysiology of diabetic nephropathy (DN) but underlying mechanisms are not fully understood. Single nucleotide polymophisms (SNPs) in the meprin β gene were associated with DKD in human subjects. Furthermore, meprin α and β double deficiency resulted in more severe kidney injury and higher mortality rates in mice with Streptozotocin (STZ)-induced type 1 diabetes. Identification of meprin substrates has provided insights on how meprins could modulate kidney injury. Meprin targets in the kidney include extracellular matrix (ECM) proteins, modulators of inflammation, and proteins involved in the protein kinase A (PKA) and PKC signaling pathways. The current study used a global metabolomics approach to determine how meprin β expression impacts the metabolite milieu in diabetes and DKD.

Methods

Low dose STZ was used to induce type 1 diabetes in 8-week old wild-type (WT) and meprin β knockout (βKO) mice. Blood and urine samples were obtained at 4 and 8 weeks post-STZ injection. Assays for albumin, creatinine, neutrophil gelatinase-associated lipocalin (NGAL), kidney injury molecule − 1 (KIM-1), and cystatin C were used for biochemical assessment of kidney injury. Data for biomarkers of kidney injury utilized two-way ANOVA. Metabolomics data analysis utilized UPLC-QTOF MS and multivariate statistics.

Results

The number of metabolites with diabetes-associated changes in levels were significantly higher in the WT mice when compared to meprin βKO counterparts. Annotated meprin β expression-associated metabolites with strong variable importance in projection (VIP) scores play roles in lipid metabolism (LysoPC(16:1(9Z)), taurocholic acid), amino acid metabolism (indoxyl sulfate, hippuric acid), and neurotransmitter/stress hormone synthesis (cortisol, 3-methoxy-4-hydroxyphenylethylene glycolsulfate, homovanillic acid sulfate). Metabolites that associated with meprin β deficiency include; 3,5-dihydroxy-3′,4′-dimethoxy-6,7-methylenedioxyflavone 3-glucuronide, pantothenic acid, and indoxyl glucuronide (all decreased in plasma).

Conclusion

Taken together, the annotated metabolites suggest that meprin β impacts complications of diabetes such as DKD by altering distinct metabolite profiles.

Electronic supplementary material

The online version of this article (10.1186/s12882-019-1313-2) contains supplementary material, which is available to authorized users.

Role of meprin metalloproteinases in cytokine processing and inflammation

Meprin metalloendopeptidases, comprising α and β isoforms, are widely expressed in mammalian cells and organs including kidney, intestines, lungs, skin, and bladder, and in a variety of immune cells and cancer cells. Meprins proteolytically process many inflammatory mediators, including cytokines, chemokines, and other bioactive proteins and peptides that control the function of immune cells. The knowledge of meprin-mediated processing of inflammatory mediators and other target substrates provides a pathophysiologic link for the involvement of meprins in the pathogenesis of many inflammatory disorders. Meprins are now known to play important roles in inflammatory diseases including acute kidney injury, sepsis, urinary tract infections, bladder inflammation, and inflammatory bowel disease. The proteolysis of epithelial and endothelial barriers including cell junctional proteins by meprins promotes leukocyte influx into areas of tissue damage to result in inflammation. Meprins degrade extracellular matrix proteins; this ability of meprins is implicated in the cell migration of leukocytes and the invasion of tumor cells that express meprins. Proteolytic processing and maturation of procollagens provides evidence that meprins are involved in collagen maturation and deposition in the fibrotic processes involved in the formation of keloids and hypertrophic scars and lung fibrosis. This review highlights recent progress in understanding the role of meprins in inflammatory disorders in both human and mouse models.

Meprin Metalloprotease Deficiency Associated with Higher Mortality Rates and More Severe Diabetic Kidney Injury in Mice with STZ-Induced Type 1 Diabetes

Meprins are membrane-bound and secreted metalloproteinases consisting of α and/or β subunits that are highly expressed in kidney epithelial cells and are differentially expressed in podocytes and leukocytes (macrophages and monocytes). Several studies have implicated meprins in the progression of diabetic nephropathy (DN) and fibrosis-associated kidney disease. However, the mechanisms by which meprins modulate DN are not understood. To delineate the role of meprins in DN, we subjected meprin αβ knockout (αβKO) mice and their wild-type (WT) counterparts to streptozotocin-induced type 1 diabetes. The 18-week survival rates were significantly lower for diabetic meprin αβKO mice when compared to those for their WT counterparts. There were significant decreases in mRNA and protein levels for both meprin α and β in diabetic WT kidneys. Furthermore, the blood urea nitrogen levels and urine albumin/creatinine ratios increased in diabetic meprin αβKO but not in diabetic WT mice, indicating that meprins may be protective against diabetic kidney injury. The brush border membrane levels of villin, a meprin target, significantly decreased in diabetic WT but not in diabetic meprin αβKO kidneys. In contrast, isoform-specific increases in cytosolic levels of the catalytic subunit of PKA, another meprin target, were demonstrated for both WT and meprin αβKO kidneys.

Proteolytic processing and inactivation of CCL2/MCP-1 by meprins

Monocyte chemotactic protein 1 (CCL2/MCP-1) is a small chemokine involved in the recruitment and trafficking of mononuclear immune cells to inflammation sites. Our studies demonstrate that the metalloendopeptidases meprin A (purified from kidney cortex), recombinant meprin α, and recombinant meprin β can all process CCL2/MCP-1. The cleavage sites were determined by amino acid sequencing and mass spectrometry analysis of the generated products, and the biological activity of the products was evaluated by chemotactic migration assay using THP-1 cells. The cleavage sites generated by the meprin isoforms revealed that meprin A and meprin α cleaved the N-terminal domain of mouse CCL2/MCP-1 at the Asn⁶ and Ala⁷ bond, resulting in significant reduction in the chemotactic activity of the cleaved CCL2/MCP-1. Meprin β was unable to cleave the N-terminus of mouse CCL2/MCP-1 but cleaved the C-terminal region between Ser⁷⁴ and Glu⁷⁵. Human CCL2/MCP-1 that lacks the murine C-terminal region was also cleaved by meprin α at the N-terminus resulting in significant loss of CCL2/MCP-1 biological activity, whereas meprin β did not affect the biological activity. These studies suggest that meprin α and meprin β may play important roles in regulating the CCL2/MCP-1 chemokine activity during inflammation.

Basement membrane protein nidogen-1 is a target of meprin β in cisplatin nephrotoxicity

Meprins are oligomeric metalloproteinases that are abundantly expressed in the brush-border membranes of renal proximal tubules. During acute kidney injury (AKI) induced by cisplatin or ischemia-reperfusion, membrane-bound meprins are shed and their localization is altered from the apical membranes toward the basolateral surface of the proximal tubules. Meprins are capable of cleaving basement membrane proteins in vitro, however, it is not known whether meprins are able to degrade extracellular matrix proteins under pathophysiological conditions in vivo. The present study demonstrates that a basement membrane protein, nidogen-1, is cleaved and excreted in the urine of mice subjected to cisplatin-induced nephrotoxicity, a model of AKI. Cleaved nidogen-1 was not detected in the urine of untreated mice, but during the progression of cisplatin nephrotoxicity, the excretion of cleaved nidogen-1 increased in a time-dependent manner. The meprin inhibitor actinonin markedly prevented urinary excretion of the cleaved nidogen-1. In addition, meprin β-deficient mice, but not meprin α-deficient mice, subjected to cisplatin nephrotoxicity significantly suppressed excretion of cleaved nidogen-1, further suggesting that meprin β is involved in the cleavage of nidogen-1. These studies provide strong evidence for a pathophysiological link between meprin β and urinary excretion of cleaved nidogen-1 during cisplatin-induced AKI.

Isoform-specific interactions between meprin metalloproteases and the catalytic subunit of protein kinase A: significance in acute and chronic kidney injury

Meprin metalloproteases are abundantly expressed in the brush-border membranes of kidney proximal tubules. Meprins are implicated in ischemia-reperfusion (IR)-induced renal injury and diabetic nephropathy. The protein kinase A (PKA) signaling pathway modulates extracellular matrix metabolism in diabetic kidneys. The present study evaluated isoform-specific interactions between the catalytic subunit of PKA (PKA C) and meprins. To this end, cytosolic-enriched kidney proteins from meprin αβ double knockout mice, and purified forms of recombinant mouse PKA Cα, Cβ1, and Cβ2, were incubated with activated forms of either homomeric meprin A or meprin B. The cleaved protein products were subjected to SDS-PAGE and analyzed by Coomassie staining and Western blot analysis. While meprin A only cleaved PKA Cβ1, meprin B cleaved all three PKA C isoforms. Analysis of the proteolytic fragments by mass spectrometry revealed that meprin A and B cleave the PKA C isoforms at defined sites, resulting in unique cleavage products. Michaelis-Menten enzyme kinetics demonstrated that meprin B-mediated cleavage of PKA Cα occurs at a rate consistent with that of other physiologically relevant meprin substrates. Meprin cleavage decreased the kinase activity of PKA Cα, Cβ1, and Cβ2. PKA C levels were higher in diabetic kidneys, with evidence of in vivo fragmentation in wild-type diabetic kidneys. Confocal microscopy showed localization of meprin A in the glomeruli of diabetic kidneys. At 3 h post-IR, PKA C levels in proximal tubules decreased compared with distal tubules, which lack meprins. These data suggest that meprins may impact kidney injury, in part, via modulation of PKA signaling pathways.

ADAM10 is the major sheddase responsible for the release of membrane-associated meprin A

Meprin A, composed of α and β subunits, is a membrane-bound metalloproteinase in renal proximal tubules. Meprin A plays an important role in tubular epithelial cell injury during acute kidney injury (AKI). The present study demonstrated that during ischemia-reperfusion-induced AKI, meprin A was shed from proximal tubule membranes, as evident from its redistribution toward the basolateral side, proteolytic processing in the membranes, and excretion in the urine. To identify the proteolytic enzyme responsible for shedding of meprin A, we generated stable HEK cell lines expressing meprin β alone and both meprin α and meprin β for the expression of meprin A. Phorbol 12-myristate 13-acetate and ionomycin stimulated ectodomain shedding of meprin β and meprin A. Among the inhibitors of various proteases, the broad spectrum inhibitor of the ADAM family of proteases, tumor necrosis factor-α protease inhibitor (TAPI-1), was most effective in preventing constitutive, phorbol 12-myristate 13-acetate-, and ionomycin-stimulated shedding of meprin β and meprin A in the medium of both transfectants. The use of differential inhibitors for ADAM10 and ADAM17 indicated that ADAM10 inhibition is sufficient to block shedding. In agreement with these results, small interfering RNA to ADAM10 but not to ADAM9 or ADAM17 inhibited meprin β and meprin A shedding. Furthermore, overexpression of ADAM10 resulted in enhanced shedding of meprin β from both transfectants. Our studies demonstrate that ADAM10 is the major ADAM metalloproteinase responsible for the constitutive and stimulated shedding of meprin β and meprin A. These studies further suggest that inhibiting ADAM 10 activity could be of therapeutic benefit in AKI.

The metalloproteases meprin α and meprin β: unique enzymes in inflammation, neurodegeneration, cancer and fibrosis

The metalloproteases meprin α and meprin β exhibit structural and functional features that are unique among all extracellular proteases. Although meprins were discovered more than 30 years ago, their precise substrates and physiological roles have been elusive. Both enzymes were originally found to be highly expressed in kidney and intestine, which focused research on these particular tissues and associated pathologies. Only recently it has become evident that meprins exhibit a much broader expression pattern, implicating functions in angiogenesis, cancer, inflammation, fibrosis and neurodegenerative diseases. Different animal models, as well as proteomics approaches for the identification of protease substrates, have helped to reveal more precise molecular signalling events mediated by meprin activity, such as activation and release of pro-inflammatory cytokines. APP (amyloid precursor protein) is cleaved by meprin β in vivo, reminiscent of the β-secretase BACE1 (β-site APP-cleaving enzyme 1). The subsequent release of Aβ (amyloid β) peptides is thought to be the major cause of the neurodegenerative Alzheimer's disease. On the other hand, ADAM10 (a disintegrin and metalloprotease domain 10), which is the constitutive α-secretase, was shown to be activated by meprin β, which is itself shed from the cell surface by ADAM10. In skin, both meprins are overexpressed in fibrotic tumours, characterized by massive accumulation of fibrillar collagens. Indeed, procollagen III is processed to its mature form by meprin α and meprin β, an essential step in collagen fibril assembly. The recently solved crystal structure of meprin β and the unique cleavage specificity of these proteases identified by proteomics will help to generate specific inhibitors that could be used as therapeutics to target meprins under certain pathological conditions.

Meprin A metalloproteinase and its role in acute kidney injury

Meprin A, composed of α- and β-subunits, is a membrane-associated neutral metalloendoprotease that belongs to the astacin family of zinc endopeptidases. It was first discovered as an azocasein and benzoyl-l-tyrosyl-p-aminobenzoic acid hydrolase in the brush-border membranes of proximal tubules and intestines. Meprin isoforms are now found to be widely distributed in various organs (kidney, intestines, leukocytes, skin, bladder, and a variety of cancer cells) and are capable of hydrolyzing and processing a large number of substrates, including extracellular matrix proteins, cytokines, adherens junction proteins, hormones, bioactive peptides, and cell surface proteins. The ability of meprin A to cleave various substrates sheds new light on the functional properties of this enzyme, including matrix remodeling, inflammation, and cell-cell and cell-matrix processes. Following ischemia-reperfusion (IR)- and cisplatin-induced acute kidney injury (AKI), meprin A is redistributed toward the basolateral plasma membrane, and the cleaved form of meprin A is excreted in the urine. These studies suggest that altered localization and shedding of meprin A in places other than the apical membranes may be deleterious in vivo in acute tubular injury. These studies also provide new insight into the importance of a sheddase involved in the release of membrane-associated meprin A under pathological conditions. Meprin A is injurious to the kidney during AKI, as meprin A-knockout mice and meprin inhibition provide protective roles and improve renal function. Meprin A, therefore, plays an important role in AKI and potentially is a unique target for therapeutic intervention during AKI.

Pharmacological targets in the renal peritubular microenvironment: implications for therapy for sepsis-induced acute kidney injury

One of the most frequent and serious complications to develop in septic patients is acute kidney injury (AKI), a disorder characterized by a rapid failure of the kidneys to adequately filter the blood, regulate ion and water balance, and generate urine. AKI greatly worsens the already poor prognosis of sepsis and increases cost of care. To date, therapies have been mostly supportive; consequently there has been little change in the mortality rates over the last decade. This is due, at least in part, to the delay in establishing clinical evidence of an infection and the associated presence of the systemic inflammatory response syndrome and thus, a delay in initiating therapy. A second reason is a lack of understanding regarding the mechanisms leading to renal injury, which has hindered the development of more targeted therapies. In this review, we summarize recent studies, which have examined the development of renal injury during sepsis and propose how changes in the peritubular capillary microenvironment lead to and then perpetuate microcirculatory failure and tubular epithelial cell injury. We also discuss a number of potential therapeutic targets in the renal peritubular microenvironment, which may prevent or lessen injury and/or promote recovery.

Enhanced activity of meprin-α, a pro-migratory and pro-angiogenic protease, in colorectal cancer

Meprin-α is a metalloprotease overexpressed in cancer cells, leading to the accumulation of this protease in a subset of colorectal tumors. The impact of increased meprin-α levels on tumor progression is not known. We investigated the effect of this protease on cell migration and angiogenesis in vitro and studied the expression of meprin-α mRNA, protein and proteolytic activity in primary tumors at progressive stages and in liver metastases of patients with colorectal cancer, as well as inhibitory activity towards meprin-α in sera of cancer patient as compared to healthy controls. We found that the hepatocyte growth factor (HGF)- induced migratory response of meprin-transfected epithelial cells was increased compared to wild-type cells in the presence of plasminogen, and that the angiogenic response in organ-cultured rat aortic explants was enhanced in the presence of exogenous human meprin-α. In patients, meprin-α mRNA was expressed in colonic adenomas, primary tumors UICC (International Union Against Cancer) stage I, II, III and IV, as well as in liver metastases. In contrast, the corresponding protein accumulated only in primary tumors and liver metastases, but not in adenomas. However, liver metastases lacked meprin-α activity despite increased expression of the corresponding protein, which correlated with inefficient zymogen activation. Sera from cancer patients exhibited reduced meprin-α inhibition compared to healthy controls. In conclusion, meprin-α activity is regulated differently in primary tumors and metastases, leading to high proteolytic activity in primary tumors and low activity in liver metastases. By virtue of its pro-migratory and pro-angiogenic activity, meprin-α may promote tumor progression in colorectal cancer.

Role of interaction of mannan-binding protein with meprins at the initial step of complement activation in ischemia/reperfusion injury to mouse kidney

Ischemia/reperfusion (I/R) is an important cause of acute renal failure. Recent studies have shown that the complement system mediated by the mannan-binding protein (MBP), which is a C-type serum lectin recognizing mannose, fucose and N-acetylglucosamine residues, plays a critical role in the pathogenesis of ischemic acute renal failure. MBP causes complement activation through the MBP lectin pathway and a resulting complement component, C3b, is accumulated on the brush borders of kidney proximal tubules in a renal I/R-operated mouse kidney. However, the initial step of the complement activation has not been studied extensively. We previously identified both meprins α and β, highly glycosylated zinc metalloproteases, localized on kidney proximal tubules as endogenous MBP ligands. In the present study, we demonstrated that serum-type MBP (S-MBP) and C3b were co-localized with meprins on both the cortex and the medulla in the renal I/R-operated mouse kidney. S-MBP was indicated to interact with meprins in vivo in the I/R-operated mouse kidney and was shown to initiate the complement activation through the interaction with meprins in vitro. Taken together, the present study strongly suggested that the binding of S-MBP to meprins triggers the complement activation through the lectin pathway and may cause the acute renal failure due to I/R on kidney transplantation and hemorrhagic shock.

Villin and actin in the mouse kidney brush-border membrane bind to and are degraded by meprins, an interaction that contributes to injury in ischemia-reperfusion

Meprins, metalloproteinases abundantly expressed in the brush-border membranes (BBMs) of rodent proximal kidney tubules, have been implicated in the pathology of renal injury induced by ischemia-reperfusion (IR). Disruption of the meprin β gene and actinonin, a meprin inhibitor, both decrease kidney injury resulting from IR. To date, the in vivo kidney substrates for meprins are unknown. The studies herein implicate villin and actin as meprin substrates. Villin and actin bind to the cytoplasmic tail of meprin β, and both meprin A and B are capable of degrading villin and actin present in kidney proteins as well as purified recombinant forms of these proteins. The products resulting from degradation of villin and actin were unique to each meprin isoform. The meprin B cleavage site in villin was Glu(744)-Val(745). Recombinant forms of rat meprin B and homomeric mouse meprin A had K(m) values for villin and actin of ∼1 μM (0.6-1.2 μM). The k(cat) values varied substantially (0.6-128 s(-1)), resulting in different efficiencies for cleavage, with meprin B having the highest k(cat)/K(m) values (128 M(-1)·s(-1) × 10(6)). Following IR, meprins and villin redistributed from the BBM to the cytosol. A 37-kDa actin fragment was detected in protein fractions from wild-type, but not in comparable preparations from meprin knockout mice. The levels of the 37-kDa actin fragment were significantly higher in kidneys subjected to IR. The data establish that meprins interact with and cleave villin and actin, and these cytoskeletal proteins are substrates for meprins.

Actinonin, a meprin A inhibitor, protects the renal microcirculation during sepsis

Sepsis-induced acute kidney injury occurs in 20% to 50% of septic patients and nearly doubles the mortality rate of sepsis. Because treatment in the septic patient is usually begun only after the onset of symptoms, therapy that is effective even when delayed would have the greatest impact on patient survival. The metalloproteinase meprin A, an oligomeric complex made of α- and β-subunits, is highly expressed at the brush-border membranes of the kidney and capable of degrading numerous substrates including extracellular matrix proteins and cytokines. The goal of the present study was to compare the therapeutic potential of actinonin, an inhibitor of meprin A, when administered before and after the onset of sepsis. Mice were treated with actinonin at 30 min before or 7 h after induction of sepsis by cecal ligation and puncture (CLP). Intravital videomicroscopy was used to image renal peritubular capillary perfusion and reactive nitrogen species. Actinonin treatment 30 min before CLP reduced IL-1β levels and prevented the fall in renal capillary perfusion at 7 and 18 h. Actinonin also prevented the fall in renal capillary perfusion even when administered at 7 h after CLP. In addition, even late administration of actinonin preserved renal morphology and lowered blood urea nitrogen and serum creatinine concentrations. These data suggest that agents such as actinonin should be evaluated further as possible therapeutic agents because targeting both the early systemic and later organ-damaging effects of sepsis should have the highest likelihood of success.

Specific processing of tenascin-C by the metalloprotease meprinbeta neutralizes its inhibition of cell spreading

The metalloprotease meprin has been implicated in tissue remodelling due to its capability to degrade extracellular matrix components. Here, we investigated the susceptibility of tenascin-C to cleavage by meprinbeta and the functional properties of its proteolytic fragments. A set of monoclonal antibodies against chicken and human tenascin-C allowed the mapping of proteolytic fragments generated by meprinbeta. In chicken tenascin-C, meprinbeta processed all three major splicing variants by removal of 10kDa N-terminal and 38kDa C-terminal peptides, leaving a large central part of subunits intact. A similar cleavage pattern was found for large human tenascin-C variant where two N-terminal peptides (10 or 15kDa) and two C-terminal fragments (40 and 55kDa) were removed from the intact subunit. N-terminal sequencing revealed the exact amino acid positions of cleavage sites. In both chicken and human tenascin-C N-terminal cleavages occurred just before and/or after the heptad repeats involved in subunit oligomerization. In the human protein, an additional cleavage site was identified in the alternative fibronectin type III repeat D. Whereas all these sites are known to be attacked by several other proteases, a unique cleavage by meprinbeta was located to the 7th constant fibronectin type III repeat in both chicken and human tenascin-C, thereby removing the C-terminal domain involved in its anti-adhesive activity. In cell adhesion assays meprinbeta-digested human tenascin-C was not able to interfere with fibronectin-mediated cell spreading, confirming cleavage in the anti-adhesive domain. Whereas the expression of meprinbeta and tenascin-C does not overlap in normal colon tissue, inflamed lesions of the mucosa from patients with Crohn's disease exhibited many meprinbeta-positive leukocytes in regions where tenascin-C was strongly induced. Our data indicate that, at least under pathological conditions, meprinbeta might attack specific functional sites in tenascin-C that are important for its oligomerization and anti-adhesive activity.

Disruption of the meprin alpha and beta genes in mice alters homeostasis of monocytes and natural killer cells

Meprin metalloproteases are implicated in inflammatory bowel disease, which involves dysfunction of immune cells. However, the roles of meprins in the immune and hematological system remain uncharacterized. In this report, we demonstrate that meprins were expressed in the hematological system, and meprin alpha/beta null (alpha(-/-)/beta(-/-)) mice had decreased prevalence of resident monocytes and natural killer (NK) cells in blood, with a concomitant accumulation of inflammatory monocytes and NK cells in bone marrow. In contrast, T and B lymphocytes were not affected by meprin deficiency. In response to acute inflammation induced by intraperitoneal injection of thioglycollate, meprin-deficient mice exhibited higher body temperature than wild-type mice, which was correlated with retention of inflammatory monocytes, but persistent low prevalence of NK cells in blood. These results indicate that meprin metalloproteases play important roles in the homeostasis of monocytes and NK cells, and possibly are involved in egress of these two type cells from bone marrow and homing to the periphery. Our findings are the first report to demonstrate that metalloproteases affect homeostasis of leukocytes, which have important implications for understanding physiology of and pathogenesis in the hematological system.

Meprin A and meprin alpha generate biologically functional IL-1beta from pro-IL-1beta

The present study demonstrates that both oligomeric metalloendopeptidase meprin A purified from kidney cortex and recombinant meprin alpha are capable of generating biologically active IL-1beta from its precursor pro-IL-1beta. Amino-acid sequencing analysis reveals that meprin A and meprin alpha cleave pro-IL-1beta at the His(115)-Asp(116) bond, which is one amino acid N-terminal to the caspase-1 cleavage site and five amino acids C-terminal to the meprin beta site. The biological activity of the pro-IL-1beta cleaved product produced by meprin A, determined by proliferative response of helper T-cells, was 3-fold higher to that of the IL-1beta product produced by meprin beta or caspase-1. In a mouse model of sepsis induced by cecal ligation puncture that results in elevated levels of serum IL-1beta, meprin inhibitor actinonin significantly reduces levels of serum IL-1beta. Meprin A and meprin alpha may therefore play a critical role in the production of active IL-1beta during inflammation and tissue injury.

Dynamic changes in messenger RNA profiles of bovine endometrium during the oestrous cycle

During the oestrous cycle, the bovine endometrium exhibits characteristic morphological and functional changes, which are mainly induced by progesterone (P(4)), oestrogens and oxytocin. We studied the response of the endometrium to this changing hormonal environment at the transcriptome level using a custom-made cDNA microarray. Endometrium samples were recovered from Simmental heifers on days 0 (oestrus), 3.5 (metoestrus), 12 (dioestrus) and 18. The latter group was divided into animals with high (late dioestrus) and low P(4) levels (preoestrus). Significance analysis of microarrays revealed 269 genes exhibiting significant changes in their transcript levels during the oestrous cycle in distinct temporal patterns. Two major types of expression profiles were observed, which showed the highest mRNA levels during the oestrus phase or the highest levels during the luteal phase respectively. A minor group of genes exhibited the highest mRNA levels on day 3.5. Gene ontology (GO) analyses revealed GO categories related to extracellular matrix remodelling, transport, and cell growth and morphogenesis enriched at oestrus, whereas immune response and particular metabolic pathways were overrepresented at dioestrus. Generation of gene interaction networks uncovered the genes possibly involved in endometrial remodelling (e.g. collagen genes, TNC, SPARC, MMP2, MEP1B, TIMP1, TIMP2, HTRA1), regulation of angiogenesis (e.g. ANGPTL2, TEK, NPY, AGT, EPAS1, KLF5 ), regulation of invasive growth (e.g. PCSK5, tight junction proteins, GRP, LGALS1, ANXA2, NOV, PLAT, MET, TDGF1, CST6, ITGB4), cell adhesion (e.g. MUC16, LGALS3BP) and embryo feeding (e.g. SLC1A1, SLC11A2, SLC16A1, SEPP1, ENPP1). Localisation of mRNA expression in the endometrium was analysed for CLDN4, CLDN10, TJP1, PCSK5, MAGED1, and LGALS1.

Meprins, membrane-bound and secreted astacin metalloproteinases

The astacins are a subfamily of the metzincin superfamily of metalloproteinases. The first to be characterized was the crayfish enzyme astacin. To date more than 200 members of this family have been identified in species ranging from bacteria to humans. Astacins are involved in developmental morphogenesis, matrix assembly, tissue differentiation and digestion. Family members include the procollagen C-proteinase (BMP1, bone morphogenetic protein 1), tolloid and mammalian tolloid-like, HMP (Hydra vulgaris metalloproteinase), sea urchin BP10 (blastula protein) and SPAN (Strongylocentrotus purpuratus astacin), the 'hatching' subfamily comprising alveolin, ovastacin, LCE, HCE ('low' and 'high' choriolytic enzymes), nephrosin (from carp head kidney), UVS.2 from frog, and the meprins. In the human and mouse genomes, there are six astacin family genes (two meprins, three BMP1/tolloid-like, one ovastacin), but in Caenorhabditis elegans there are 40. Meprins are the only astacin proteinases that function on the membrane and extracellularly by virtue of the fact that they can be membrane-bound or secreted. They are unique in their domain structure and covalent subunit dimerization, oligomerization propensities, and expression patterns. They are normally highly regulated at the transcriptional and post-translational levels, localize to specific membranes or extracellular spaces, and can hydrolyse biologically active peptides, cytokines, extracellular matrix (ECM) proteins and cell-surface proteins. The in vivo substrates of meprins are unknown, but the abundant expression of these proteinases in the epithelial cells of the intestine, kidney and skin provide clues to their functions.

A novel 2D-based approach to the discovery of candidate substrates for the metalloendopeptidase meprin

In the past, protease-substrate finding proved to be rather haphazard and was executed by in vitro cleavage assays using singly selected targets. In the present study, we report the first protease proteomic approach applied to meprin, an astacin-like metalloendopeptidase, to determine physiological substrates in a cell-based system of Madin-Darby canine kidney epithelial cells. A simple 2D IEF/SDS/PAGE-based image analysis procedure was designed to find candidate substrates in conditioned media of Madin-Darby canine kidney cells expressing meprin in zymogen or in active form. The method enabled the discovery of hitherto unknown meprin substrates with shortened (non-trypsin-generated) N- and C-terminally truncated cleavage products in peptide fragments upon LC-MS/MS analysis. Of 22 (17 nonredundant) candidate substrates identified, the proteolytic processing of vinculin, lysyl oxidase, collagen type V and annexin A1 was analysed by means of immunoblotting validation experiments. The classification of substrates into functional groups may propose new functions for meprins in the regulation of cell homeostasis and the extracellular environment, and in innate immunity, respectively.

Downregulated expression in high IgA (HIGA) mice and the renal protective role of meprinbeta

This study discusses the critical role of the metalloproteinase meprinbeta in the progression of glomerulonephritis. Using a microarray technique, the gene expression profiles in glomeruli isolated from high serum IgA (HIGA) mice with a purity of 97% or greater were examined. HIGA mice are a valid model of human IgA nephropathy (IgAN), with the typical pathological features of this condition, including a consistently high serum IgA level as well as dominant mesangial IgA deposition and mesangial enlargement. Among the many upregulated/downregulated genes after the development of IgAN, the downregulation of meprinbeta was intriguing. The expression level of the meprinbeta gene at 40 weeks of age was 52% of that observed at 8 weeks of age (prior to the development of IgAN), although in the control BALB/c mice, a 2.19-fold elevation was seen. These results were also confirmed by semi-quantitative RT-PCR and immunostaining analyses. As meprinbeta is a subunit of metalloproteinase meprins (meprin A, meprin B) and meprins are capable of proteolytically degrading extracellular matrix (ECM) components and proteolytically processing bioactive peptides, the downregulation of meprinbeta may contribute to the progression of glomerulonephritis and the eventual glomerular scarring. This working hypothesis was examined using an in vivo meprinbeta inhibition study. The inhibition of meprins by actinonin exacerbated some parameters of renal injury in mice afflicted with anti-glomerular basement membrane (anti-GBM) antibody-associated nephritis. These in vitro and in vivo results suggest that meprinbeta may play a protective role against the progression of renal injury through the degradation of ECM and bioactive peptides.

Actinonin, a meprin inhibitor, protects ischemic acute kidney injury in male but not in female rats

We investigated the effects of actinonin, an inhibitor of a matrix-degrading enzyme meprin, on ischemic acute kidney injury in male and female rats, and these were compared with the effects of verapamil, a Ca(2+) channel blocker. Ischemic acute kidney injury was induced by occlusion of the left renal artery and vein for 45 min followed by reperfusion, 2 weeks after contralateral nephrectomy. At 24 h after reperfusion, renal function and histology of both males and females showed significant deterioration. The degrees of renal dysfunction and histological damage were much more severe in males than in females. Pre-ischemic treatment with actinonin (10 or 30 mg/kg, i.v.) dose-dependently attenuated the ischemia/reperfusion-induced renal injury in male rats, but failed to improve the renal injury in female rats. On the other hand, verapamil (1 mg/kg, i.v.) could efficiently prevent the ischemic acute kidney injury in female rats, as well as male rats. These results indicate that the renoprotective effect of actinonin is male-specific, thereby suggesting that meprin is involved in exacerbation of ischemia/reperfusion-induced renal injury in male rats. The possibility that meprin is a key factor involved in the sex difference in the pathogenesis of ischemic acute kidney injury, warrants further attention.

Two alpha subunits and one beta subunit of meprin zinc-endopeptidases are differentially expressed in the zebrafish Danio rerio

Meprins are members of the astacin family of metalloproteases expressed in epithelial tissues, intestinal leukocytes and certain cancer cells. In mammals, there are two homologous subunits, which form complex glycosylated disulfide-bonded homo- and heterooligomers. Both human meprin alpha and meprin beta cleave several basement membrane components, suggesting a role in epithelial differentiation and cell migration. There is also evidence that meprin beta is involved in immune defence owing to its capability of activating interleukin-1beta and the diminished mobility of intestinal leukocytes in meprin beta-knockout mice. Here we show for the first time by reverse transcription PCR, immunoblotting and immunofluorescence analyses that meprins are expressed not only in mammals, but also in the zebrafish Danio rerio. In contrast to the human, mouse and rat enzymes, zebrafish meprins are encoded by three genes, corresponding to two homologous alpha subunits and one beta subunit. Observations at both the mRNA and protein level indicate a broad distribution of meprins in zebrafish. However, there are strikingly different expression patterns of the three subunits, which is consistent with meprin expression in mammals. Hence, D. rerio appears to be a suitable model to gain insight into the basic physiological functions of meprin metalloproteases.

Role of meprin A in renal tubular epithelial cell injury

Meprins are zinc-dependent metalloproteinases that are highly expressed in the brush-border membranes of both the kidney and the intestines. Meprins are capable of proteolytically degrading extracellular matrix proteins, proteolytically processing bioactive proteins, and play a role in inflammatory processes. In this study, the function of meprin A in the acute kidney injury (AKI) model of cisplatin nephrotoxicity was examined. Normal linear localization of meprin A in the brush border membranes of proximal tubules was altered in AKI. The meprin A alpha-subunit was detected in the urine of both control and cisplatin-treated mice. A cleaved product of the meprin A beta-subunit, undetected in the urine of control mice, was found to be significantly increased in the urine during the progression of cisplatin nephrotoxicity. The excretion of this beta-fragment was found to be before the rise in serum creatinine and blood urea nitrogen (BUN) suggesting usefulness as a biomarker for AKI. Pretreatment of mice with a meprin A inhibitor afforded protection from cisplatin nephrotoxicity as reflected by significant decreases in serum creatinine, BUN, and the excretion of kidney injury molecule-1. These decreases in serum and urine biomarkers were accompanied by significant decreases in histologic markers such as leukocyte infiltration and apoptosis. Meprin A appears to be an important therapeutic target and urinary excretion appears to be a potential biomarker of AKI.

The evolution of the vertebrate metzincins; insights from Ciona intestinalis and Danio rerio

BACKGROUND

The metzincins are a large gene superfamily of proteases characterized by the presence of a zinc protease domain, and include the ADAM, ADAMTS, BMP1/TLL, meprin and MMP genes. Metzincins are involved in the proteolysis of a wide variety of proteins, including those of the extracellular matrix. The metzincin gene superfamily comprises eighty proteins in the human genome and ninety-three in the mouse. When and how the level of complexity apparent in the vertebrate metzincin gene superfamily arose has not been determined in detail. Here we present a comprehensive analysis of vertebrate metzincins using genes from both Ciona intestinalis and Danio rerio to provide new insights into the complex evolution of this gene superfamily.

RESULTS

We have identified 19 metzincin genes in the ciona genome and 83 in the zebrafish genome. Phylogenetic analyses reveal that the expansion of the metzincin gene superfamily in vertebrates has occurred predominantly by the simple duplication of pre-existing genes rather than by the appearance and subsequent expansion of new metzincin subtypes (the only example of which is the meprin gene family). Despite the number of zebrafish metzincin genes being relatively similar to that of tetrapods (e.g. man and mouse), the pattern of gene retention and loss within these lineages is markedly different. In addition, we have studied the evolution of the related TIMP gene family and identify a single ciona and four zebrafish TIMP genes.

CONCLUSION

The complexity seen in the vertebrate metzincin gene families was mainly acquired during vertebrate evolution. The metzincin gene repertoire in protostomes and invertebrate deuterostomes has remained relatively stable. The expanded metzincin gene repertoire of extant tetrapods, such as man, has resulted largely from duplication events associated with early vertebrate evolution, prior to the sarcopterygian-actinopterygian split. The teleost repertoire of metzincin genes in part parallels that of tetrapods but has been significantly modified, perhaps as a consequence of a teleost-specific duplication event.

The alpha and beta subunits of the metalloprotease meprin are expressed in separate layers of human epidermis, revealing different functions in keratinocyte proliferation and differentiation

The zinc endopeptidase meprin (EC 3.4.24.18) is expressed in brush border membranes of intestine and kidney tubules, intestinal leukocytes, and certain cancer cells, suggesting a role in epithelial differentiation and cell migration. Here we show by RT-PCR and immunoblotting that meprin is also expressed in human skin. As visualized by immunohistochemistry, the two meprin subunits are localized in separate cell layers of the human epidermis. Meprin alpha is expressed in the stratum basale, whereas meprin beta is found in cells of the stratum granulosum just beneath the stratum corneum. In hyperproliferative epidermis such as in psoriasis vulgaris, meprin alpha showed a marked shift of expression from the basal to the uppermost layers of the epidermis. The expression patterns suggest distinct functions for the two subunits in skin. This assumption is supported by diverse effects of recombinant meprin alpha and beta on human adult low-calcium high-temperature keratinocytes. Here, beta induced a dramatic change in cell morphology and reduced the cell number, indicating a function in terminal differentiation, whereas meprin alpha did not affect cell viability, and may play a role in basal keratinocyte proliferation.

Compartmentalised expression of meprin in small intestinal mucosa: enhanced expression in lamina propria in coeliac disease

Epithelial cells in the human small intestine express meprin, an astacin-like metalloprotease, which accumulates normally at the brush border membrane and in the gut lumen. Therefore, meprin is targeted towards luminal components. In coeliac disease patients, peptides from ingested cereals trigger mucosal inflammation in the small intestine, disrupting epithelial cell differentiation and function. Using in situ hybridisation on duodenal tissue sections, we observed a marked shift of meprin mRNA expression from epithelial cells, the predominant expression site in normal mucosa, to lamina propria leukocytes in coeliac disease. Meprin thereby gains access to the substrate repertoire present beneath the epithelium.

Embryo-induced transcriptome changes in bovine endometrium reveal species-specific and common molecular markers of uterine receptivity

The endometrium plays a central role among the reproductive tissues in the context of early embryo–maternal communication and pregnancy. This study investigated transcriptome profiles of endometrium samples from day 18 pregnant vs non-pregnant heifers to get insight into the molecular mechanisms involved in conditioning the endometrium for embryo attachment and implantation. Using a combination of subtracted cDNA libraries and cDNA array hybridisation, 109 mRNAs with at least twofold higher abundance in endometrium of pregnant animals and 70 mRNAs with higher levels in the control group were identified. Among the mRNAs with higher abundance in pregnant animals, at least 41 are already described as induced by interferons. In addition, transcript levels of many new candidate genes involved in the regulation of transcription, cell adhesion, modulation of the maternal immune system and endometrial remodelling were found to be increased. The different expression level was confirmed with real-time PCR for nine genes. Localisation of mRNA expression in the endometrium was shown byin situhybridisation forAGRN,LGALS3BP,LGALS9,USP18,PARP12andBST2. A comparison with similar studies in humans, mice, and revealed species-specific and common molecular markers of uterine receptivity.

Differential regulation of metzincins in experimental chronic renal allograft rejection: Potential markers and novel therapeutic targets

Chronic renal allograft rejection is characterized by alterations in the extracellular matrix compartment and in the proliferation of various cell types. These features are controlled, in part by the metzincin superfamily of metallo-endopeptidases, including matrix metalloproteinases (MMPs), a disintegrin and metalloproteinase (ADAM) and meprin. Therefore, we investigated the regulation of metzincins in the established Fisher to Lewis rat kidney transplant model. Studies were performed using frozen homogenates and paraffin sections of rat kidneys at day 0 (healthy controls) and during periods of chronic rejection at day +60 and day +100 following transplantation. The messenger RNA (mRNA) expression was examined by Affymetrix Rat Expression Array 230A GeneChip and by real-time Taqman polymerase chain reaction analyses. Protein expression was studied by zymography, Western blot analyses, and immunohistology. mRNA levels of MMPs (MMP-2/-11/-12/-14), of their inhibitors (tissue inhibitors of metalloproteinase (TIMP)-1/-2), ADAM-17 and transforming growth factor (TGF)-beta1 significantly increased during chronic renal allograft rejection. MMP-2 activity and immunohistological staining were augmented accordingly. The most important mRNA elevation was observed in the case of MMP-12. As expected, Western blot analyses also demonstrated increased production of MMP-12, MMP-14, and TIMP-2 (in the latter two cases as individual proteins and as complexes). In contrast, mRNA levels of MMP-9/-24 and meprin alpha/beta had decreased. Accordingly, MMP-9 protein levels and meprin alpha/beta synthesis and activity were downregulated significantly. Members of metzincin families (MMP, ADAM, and meprin) and of TIMPs are differentially regulated in chronic renal allograft rejection. Thus, an altered pattern of metzincins may represent novel diagnostic markers and possibly may provide novel targets for future therapeutic interventions.

Meprin-α in chronic diabetic nephropathy: interaction with the renin-angiotensin axis

Meprin (MEP) A is a metalloendopeptidase that is present in the renal proximal tubule brush-border membrane (BBM) and that colocalizes with angiotensin-converting enzyme (ACE). The MEP β-chain gene locus on chromosome 18 has been linked to a heightened risk of diabetic nephropathy (DN) in patients with type 2 diabetes. This study evaluated 1) whether MEP-α and MEP-β gene and protein expression are altered in db/db mice before the onset of DN and 2) the role of MEP-α in the pathogenesis of DN and the impact of the renin-angiotensin system on this interaction in two experimental models of diabetes. MEP-α and MEP-β gene and protein expression were evaluated in db/db mice, 13–14 wk of age, compared with lean C57BLKS/J littermate animals. A treatment study was then performed in which db/db mice and controls were assigned to one of three groups: control (C) water, no therapy; ACE inhibitor therapy, enalapril (EN)-treated water, 50 mg/l; ANG II receptor type 1 blocker (ARB) therapy, losartan (LOS)-treated water, 500 mg/l. Treatment was started at 8 wk of age and continued for 52 wk. Male Sprague-Dawley rats with diabetes for 52 wk following a single dose of streptozocin (STZ; 60 mg/kg) were also studied. At 13.5 wk of age, MEP-α and MEP-β kidney mRNA abundance and protein expression were significantly lower in db/db mice compared with lean controls, with greater changes in MEP-β ( P < 0.05). In the treatment study, EN ameliorated and LOS exacerbated DN in db/db mice. BBM MEP A enzymatic activity and MEP-α protein content were lower in db/db mice vs. control nonobese mice at 52 wk ( P < 0.02). EN-treated db/db mice showed increased MEP A activity, MEP-α content in BBM, decreased urinary MEP-α excretion, and enhanced BBM staining for MEP-α protein vs. C and LOS-treated db/db mice. In nonobese mice, EN and LOS treatment had no effect on MEP-α expression. In rats with STZ-induced diabetes for 52 wk, urinary MEP-α excretion was increased and MEP A activity and MEP-α protein content per milligram of BBM protein were decreased compared with age-matched control animals ( P < 0.05). These results indicate that db/db mice manifest decreased MEP-α and MEP-β gene and protein expression, before the development of overt kidney disease. Moreover, in db/db mice with DN and rats with STZ-diabetes, there was an inverse relationship between renal MEP-α content and the severity of the renal injury. Treatment with an ACE inhibitor was more effective than ARB in ameliorating DN in db/db mice, a change that correlated with alterations in urinary excretion and BBM content of MEP-α. MEP-α may play a role in the pathogenesis of DN and the benefits of ACE inhibitor therapy on the progression of diabetic kidney disease may be related, in part, to its impact on renal MEP-α expression.

Mannan-Binding Protein Blocks the Activation of Metalloproteases Meprin α and β

Mannan-binding protein (MBP) is a C-type serum lectin that is known to be a host defense factor involved in innate immunity, and recognizes mannose, fucose, and N-acetylglucosamine residues. Although some exogenous MBP ligands have been reported, little is known about its endogenous ligands. In the present study, we found that endogenous MBP ligands are highly expressed in the brush border epithelial cells of kidney-proximal tubules by immunohistochemistry, and both meprin alpha and beta (meprins), as novel endogenous MBP ligands, have been identified through affinity chromatography and mass spectrometry. Meprins are membrane-bound and secreted zinc metalloproteases extensively glycosylated and highly expressed in kidney and small intestinal epithelial cells, leukocytes, and certain cancer cells. Meprins are capable of cleaving growth factors, extracellular matrix proteins, and biologically active peptides. Deglycosylation experiments indicated that the MBP ligands on meprins are high mannose- or complex-type N-glycans. The interaction of MBP with meprins resulted in significant decreases in the proteolytic activity and matrix-degrading ability of meprins. Our results suggest that core N-linked oligosaccharides on meprins are associated with the optimal enzymatic activity and that MBP is an important regulator for modulation of the localized meprin proteolytic activity via N-glycan binding. Because meprins are known to be some of the major matrix-degrading metalloproteases in the kidney and intestine, MBP, which functions as a natural and effective inhibitor of meprins, may contribute, as a potential therapeutic target, to tumor progression by facilitating the migration, intravasation, and metastasis of carcinoma cells, and to acute renal failure and inflammatory bowel diseases.

Human meprin alpha and beta homo-oligomers: cleavage of basement membrane proteins and sensitivity to metalloprotease inhibitors

Meprin is a zinc endopeptidase of the astacin family, which is expressed as a membrane-bound or secreted protein in mammalian epithelial cells, in intestinal leucocytes and in certain cancer cells. There are two types of meprin subunits, alpha and beta, which form disulphide-bonded homo- and hetero-oligomers. Here we report on the cleavage of matrix proteins by hmeprin (human meprin) alpha and beta homo-oligomers, and on the interactions of these enzymes with inhibitors. Despite their completely different cleavage specificities, both hmeprin alpha and beta are able to hydrolyse basement membrane components such as collagen IV, nidogen-1 and fibronectin. However, they are inactive against intact collagen I. Hence the matrix-cleaving activity of hmeprin resembles that of gelatinases rather than collagenases. Hmeprin is inhibited by hydroxamic acid derivatives such as batimastat, galardin and Pro-Leu-Gly-hydroxamate, by TAPI-0 (tumour necrosis factor alpha protease inhibitor-0) and TAPI-2, and by thiol-based compounds such as captopril. Therapeutic targets for these inhibitors are MMPs (matrix metalloproteases), TACE (tumour necrosis factor alpha-converting enzyme) and angiotensin-converting enzyme respectively. The most effective inhibitor of hmeprin alpha in the present study was the naturally occurring hydroxamate actinonin ( K(i)=20 nM). The marked variance in the cleavage specificities of hmeprin alpha and beta is reflected by their interaction with the TACE inhibitor Ro 32-7315, whose affinity for the beta subunit (IC50=1.6 mM) is weaker by three orders of magnitude than that for the alpha subunit ( K(i)=1.6 microM). MMP inhibitors such as the pyrimidine-2,4,6-trione derivative Ro 28-2653 that are more specific for gelatinases do not bind to hmeprin, presumably due to the subtle differences in the mode of zinc binding and active-site structure between the astacins and the MMPs.

Phorbol 12-myristate 13-acetate-induced ectodomain shedding and phosphorylation of the human meprinbeta metalloprotease

Shedding of proteins localized at the cell surface is an important regulatory step in the function of many of these proteins. Human meprin (N-benzoyl-l-tyrosyl-p-aminobenzoic acid hydrolase, PPH, EC 3.4.24.18) a zinc-metalloendopeptidase of the astacin family is an oligomeric protein complex of alpha- and beta-subunits and is expressed abundantly in the intestine and kidney as well as in leukocytes of the lamina propria and in cancer cells. In transfected cells intracellular proteolytic removal of the membrane anchor results in the secretion of the meprin alpha-subunit. In rats and mice, the beta-subunit exists in a membrane-anchored form. In contrast, human meprinbeta is constitutively converted into a secretable form. We now show that phorbol 12-myristate 13-acetate (PMA) stimulates an increased release of hmeprinbeta from transfected COS-1 cells, whereas hmeprinalpha secretion is not influenced. This stimulatory effect is inhibited by the protein kinase C (PKC) inhibitor staurosporine, suggesting that activation of PKC mediates PMA-induced hmeprinbeta shedding. The use of different protease inhibitors shows that two different metalloprotease activities are responsible for the constitutive and the PMA-stimulated hmeprinbeta shedding. We identified tumor necrosis factor alpha-converting enzyme (TACE or ADAM17) as the protease that mediates the PMA-induced release. We also demonstrate that hmeprinbeta is phosphorylated by PMA treatment on Ser687 within a PKC consensus sequence in the cytosolic domain of the protein. This phosphorylation of hmeprinbeta is not, however, implicated in the enhanced secretion by PMA treatment.

Differences in the activation mechanism between the alpha and beta subunits of human meprin

Meprins are zinc-endopeptidases of the astacin family, which are expressed as membrane-bound or secreted forms in renal and intestinal brush-border membranes of mouse, rat and man. There are two types of meprin subunits, alpha and beta, which form disulfide-bonded homo- and heterodimers; further oligomerization is mediated by non-covalent interactions. Both subunits are translated as proenzymes that have to be activated by removal of an N-terminal propeptide. In the gut, the most probable activator is trypsin. In addition, plasmin has been shown to activate the human alpha subunit in colorectal cancer tissue. In the present study we have overexpressed the human meprin alpha subunit and a His-tagged soluble tail-switch-mutant of meprin beta in Baculovirus-infected insect cells. The recombinant homo-oligomeric proteins were purified by gel filtration and affinity chromatography with yields of up to 10 mg/l cell culture medium and analyzed with regard to their activation mechanism. While both alpha and beta homo-oligomers are activated by trypsin, only meprin alpha homo-oligomers are processed to their mature form by plasmin. These results indicate a different accessibility of the propeptide in meprin homo-oligomers and suggest an explanation for the appearance of meprin hetero-oligomers consisting of active alpha, but latent beta subunits.

Targeted disruption of the meprin beta gene in mice leads to underrepresentation of knockout mice and changes in renal gene expression profiles

Meprins are multidomain zinc metalloproteases that are highly expressed in mammalian kidney and intestinal brush border membranes and in leukocytes and certain cancer cells. Mature meprins are oligomers of evolutionarily related, separately encoded alpha and/or beta subunits. Homooligomers of meprin alpha are secreted; oligomers containing meprin beta are plasma membrane associated. Meprin substrates include bioactive peptides and extracellular matrix proteins. Meprins have been implicated in cancer and intestinal inflammation. Additionally, meprin beta is a candidate gene for diabetic nephropathy. To elucidate in vivo functions of these metalloproteases, meprin beta null mice were generated by targeted disruption of the meprin beta gene on mouse chromosome 18q12. Analyses of meprin beta knockout mice indicated that (i) 50% fewer null mice are born than the Mendelian distribution predicts, (ii) null mice that survive develop normally and are viable and fertile, (iii) meprin beta knockout mice lack membrane-associated meprin alpha in kidney and intestine, and (iv) null mice have changes in renal gene expression profiles compared to wild-type mice as assessed by microarray analyses. Thus, disruption of the meprin beta allele in mice affects embryonic viability, birth weight, renal gene expression profiles, and the distribution of meprin alpha in kidney and intestine.

Activation of human meprin-alpha in a cell culture model of colorectal cancer is triggered by the plasminogen-activating system

The activation of latent proenzymes is an important mechanism for the regulation of localized proteolytic activity. Human meprin-alpha, an astacin-like zinc metalloprotease expressed in normal colon epithelial cells, is secreted as a zymogen into the intestinal lumen. Here, meprin is activated after propeptide cleavage by trypsin. In contrast, colorectal cancer cells secrete meprin-alpha in a non-polarized way, leading to accumulation and increased activity of meprin-alpha in the tumor stroma. We have analyzed the activation mechanism of promeprin-alpha in colorectal cancer using a co-culture model of the intestinal mucosa composed of colorectal adenocarcinoma cells (Caco-2) cultivated on filter supports and intestinal fibroblasts grown in the companion dish. We provide evidence that meprin-alpha is activated by plasmin and show that the presence of plasminogen in the basolateral compartment of the co-cultures is sufficient for promeprin-alpha activation. Analysis of the plasminogen-activating system in the co-cultures revealed that plasminogen activators produced and secreted by fibroblasts converted plasminogen to active plasmin, which in turn generated active meprin-alpha. This activation mechanism offers an explanation for the observed meprin-alpha activity in the tumor stroma, a prerequisite for a potential role of this protease in colorectal cancer.

Probing the active sites and mechanisms of rat metalloproteases meprin A and B

Meprin A and B are highly regulated, secreted and cell-surface homo- and hetero-oligomeric enzymes. Meprins are abundantly expressed in kidney and intestine. The multidomain alpha and beta subunits have high sequence identity, however they have very different substrate specificities, oligomerization potentials and are differentially regulated. Here we describe that meprin subunit activities are modulated differently by physico-chemical factors. Homo-oligomeric meprin B had an acidic pH optimum. The low pH protonation indicated the existence of at least two ionizable groups. An additional ionizable group generated a shoulder in the basic pH range. Homo-oligomeric meprin A had a neutral pH optimum and the activity curve revealed that two ionizable groups might be protonated at acidic pH similar to meprin B. Increasing the concentration of salt generally inhibited meprin B activity. Meprin A was inhibited at low salt concentrations but activated as salt was increased. This work has important implications in the elucidation of the catalytic mechanisms of meprins and other metalloproteases. In addition, the activity of meprin oligomers that arise in tissues will be affected by variations in pH and NaCl. This could have profound implications because meprins are exposed to a range of conditions in the extracellular milieu of renal and intestinal tissues and in inflammation and cancer.

Meprin, a brush-border enzyme, plays an important role in hypoxic/ischemic acute renal tubular injury in rats

BACKGROUND

It has been shown that non-congenic mice strains with lower levels of renal meprin develop less renal injury following renal ischemia and reperfusion. We have demonstrated that following ischemia-reperfusion renal injury, there is a rapid shift of meprin localization and intensity from the brush border to the cytoplasmic compartment, tubular lumens and the tubular basement membranes. Radical shifts in the localization of an activated enzyme to potentially sensitive areas of the tubule suggest a toxic role for meprin in ischemia-reperfusion injury. Though meprin degrades extracellular matrix components and other substrates, to our knowledge meprin cytotoxicity has never been examined. Therefore, the first objective of this study was to determine if meprin is directly cytotoxic to renal cells in vitro. The second objective was to determine if inhibition of meprin is protective against hypoxia-reoxygenation injury in vitro and ischemia-reperfusion injury in vivo.

METHODS

The immortalized porcine epithelial cell line (LLC-PK1) and Madin-Darby canine kidney (MDCK) cells in culture were exposed to meprin in various concentrations and for various times. Cell death was determined by Trypan Blue exclusion, lactate dehydrogenase (LDH) release and the 3-[4,5] dimethylthiazol-2,5-diphenyltetrazolium bromide (MTT) assay. Renal slices were used to examine the effect of the meprin inhibitor, actinonin, on hypoxic injury in vitro. Male Sprague-Dawley rats were used in ischemia-reperfusion injury studies to determine the effect of actinonin on renal function as measured by plasma urea nitrogen, creatinine and renal histology.

RESULTS

Meprin is cytotoxic to LLC-PK1 and MDCK cells in a concentration and time dependent manner. The meprin inhibitor 1,10-phenanthroline completely abolished the cytotoxic effect. Renal slices exposed to hypoxia and hypoxia followed by reoxygenation showed marked cell death. Pre-treatment with the actinonin was markedly protective while not interfering with the hypoxia-induced fall in adenosine 5'-triphosphate (ATP) levels. In in vivo studies, rats exposed to ischemia/reperfusion injury were markedly protected against acute renal failure by IP treatment with actinonin.

CONCLUSIONS

Meprin is cytotoxic to cultured renal tubular epithelial cells in vitro. Renal slices are protected from hypoxia-reoxygenation injury in vitro by the meprin inhibitor actinonin. Meprin inhibition is protective against rat renal hypoxia-reoxygenation injury. These data strongly support the concept that meprin is cytotoxic and may play a key role in renal ischemia-reperfusion induced renal injury.

Developmental expression of meprin metalloprotease subunits in ICR and C3H/He mouse kidney and intestine in the embryo, postnatally and after weaning

Meprins are secreted and membrane-bound metalloendopeptidases highly expressed in kidney and intestinal epithelial cells. They are oligomeric glycoproteins composed of evolutionarily related alpha and/or beta subunits. The present work revealed that the messages for both meprin subunits were expressed in intestine and kidney in ICR and C3H/He mouse embryos (as early as day 11), indicating developmental functions for both subunits. During the first 2 weeks after birth, the mRNA levels for both subunits increased in ICR mice, but between 10 days and 3 weeks (time of weaning) the alpha subunit level in the intestine fell markedly. In adult ICR mice, meprin beta mRNA was consistently expressed in both kidney and intestine, whereas meprin alpha mRNA was highly expressed in kidney but only present at low levels in intestine. In C3H/He mice, the pattern of meprin alpha and beta subunit mRNA expression was similar to that of ICR mice, except that meprin alpha was barely detectable in kidney after birth. The results of postnatal studies indicate that the meprin alpha subunit has a role in the intestine during suckling but is not essential after weaning, and that the beta homooligomer is the major meprin form after weaning in both kidney and intestine.

Acute rejection-associated tubular basement membrane defects and chronic allograft nephropathy

BACKGROUND

Acute rejection is a major risk factor for chronic allograft nephropathy, although the link(s) between these events is not understood. The hypothesis of this study is that alterations in tubular basement membranes (TBMs) that occur during acute rejection may be irreversible and thereby play a role in the development of chronic allograft nephropathy.

METHODS

Fourteen renal transplant patients were selected, each having had two or more biopsies performed (42 total). All biopsies were scored for acute and chronic rejection using Banff 1997 criteria. The initial biopsy showed only acute interstitial rejection (type I rejection). No biopsies contained significant chronic arterial lesions of chronic vascular rejection. The entire cortex was examined on Jones methenamine silver-stained sections at x400 for interruption in TBM staining. The number of tubules with TBM abnormalities was counted, and the renal cortical area was measured by image analysis. Periodic acid-Schiff/immunoperoxidase stain was performed on 12 acute rejection biopsies stained for laminin, cytokeratin 7, CD3, CD20, and CD68. Controls consisted of 11 biopsies (8 negative for rejection and 3 acute tubular necrosis).

RESULTS

Numerous TBM alterations in silver staining were identified as being associated with acute rejection and tubulitis, consisting of abrupt TBM discontinuities and/or extreme attenuation with segmental or complete absence of TBM. A loss of TBM matrix proteins was confirmed by absent laminin staining in areas of acute rejection and tubulitis. There was herniation of tubular cells into the interstitium through TBM defects confirmed by cytokeratin staining. The TBM defects were spatially associated with inflammatory cells, particularly macrophages. When the biopsies were divided into two groups, <10 and> 10 TBM breaks/mm2, there were statistically significant morphologic and clinical correlations. The number of TBM disruptions correlated with the serum creatinine at the time of biopsy, a combined Banff t + i score, the difference in tubular atrophy between the initial and most recent biopsy and the difference between the nadir creatinine and most recent creatinine.

CONCLUSION

Damage to TBM develops in acute rejection as a consequence of interstitial inflammation and tubulitis. These lytic events correlate with the later development of clinical and morphologic evidence of chronic injury in the absence of arterial injury of chronic rejection. We suggest that chronic allograft nephropathy may have an inflammatory interstitial origin.

Structure and expression of the human MEP1A gene encoding the alpha subunit of metalloendopeptidase meprin A

The human genome contains several sequences that are similar to the MEP1A gene encoding the alpha subunit of metalloendopeptidase meprin A. We now report the first genomic structure for the human MEP1A gene that maps to chromosome 6p21. The gene spans approximately 45 kb and consists of 14 exons and 13 introns. Overall, about 6.7% (3 kb) of the MEP1A gene corresponds to the exon sequences. Tissue specificity of the MEP1A gene expression was examined by dot blot analysis of poly(A) RNA from 50 different human tissues. The MEP1A mRNA was detected for the first time in kidney and appendix in addition to colon and small intestine previously known to express the gene. The elucidated gene structure and tissue-specific expression of the MEP1A gene set the stage for investigating regulation and function of the gene and related sequences in the human genome.