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

[This corrects the article DOI: 10.1155/2017/9035038.].

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 ß 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 αß knockout (αßKO) mice and their wild-type (WT) counterparts to streptozotocin-induced type 1 diabetes. The 18-week survival rates were significantly lower for diabetic meprin αßKO mice when compared to those for their WT counterparts. There were significant decreases in mRNA and protein levels for both meprin α and ß in diabetic WT kidneys. Furthermore, the blood urea nitrogen levels and urine albumin/creatinine ratios increased in diabetic meprin αßKO 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 αßKO 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 αßKO kidneys.

Human and mouse homo-oligomeric meprin A metalloendopeptidase: substrate and inhibitor specificities.

Meprin metalloproteinases have been implicated in the susceptibility to and progression of diabetic nephropathy and inflammatory bowel diseases. Our studies with experimental models of these diseases in mice are congruent with the conclusion that meprins modulate the inflammatory responses and tissue damage. To determine whether the mouse and human enzymes differ, recombinant forms of meprin A from the two species were compared with respect to structure, substrates and inhibitors. Human homo-oligomeric meprin A formed oligomers ranging from 950,000 to 1,500,000 Da vs. 900,000 Da for mouse meprin A. Human and mouse meprin A exhibited similar activity against azocasein, fibronectin, collagen IV, and peptides such as parathyroid hormone, ghrelin, and gastrin-releasing peptide. The human enzyme had lower activity against gelatin, bradykinin, alpha-melanocyte-stimulating hormone and neurotensin, and higher activity against secretin and orcokinin. Human meprin A showed a preference for acidic residues in the P1' position of the substrate, unlike mouse meprin A. Several metalloproteinase inhibitors had IC(50) values in the nanomolar range, but potency ranged from similar values to a difference of several orders of magnitude for meprins from the two species. This work provides valuable data to improve predictability for human systems based on meprin functions in mouse models.

Meprin-alpha 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 beta-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-alpha and MEP-beta gene and protein expression are altered in db/db mice before the onset of DN and 2) the role of MEP-alpha in the pathogenesis of DN and the impact of the renin-angiotensin system on this interaction in two experimental models of diabetes. MEP-alpha and MEP-beta 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-alpha and MEP-beta kidney mRNA abundance and protein expression were significantly lower in db/db mice compared with lean controls, with greater changes in MEP-beta (P < 0.05). In the treatment study, EN ameliorated and LOS exacerbated DN in db/db mice. BBM MEP A enzymatic activity and MEP-alpha 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-alpha content in BBM, decreased urinary MEP-alpha excretion, and enhanced BBM staining for MEP-alpha protein vs. C and LOS-treated db/db mice. In nonobese mice, EN and LOS treatment had no effect on MEP-alpha expression. In rats with STZ-induced diabetes for 52 wk, urinary MEP-alpha excretion was increased and MEP A activity and MEP-alpha 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-alpha and MEP-beta 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-alpha 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-alpha. MEP-alpha 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-alpha expression.

Meprin proteolytic complexes at the cell surface and in extracellular spaces.

Meprins are metalloproteinases of the astacin family and metzincin superfamily that are composed of evolutionarily related alpha and beta subunits, which exist as homo- and hetero-oligomeric complexes. These complexes are abundant at the brush border membranes of kidney proximal tubule cells and epithelial cells of the intestine, and are also expressed in certain leucocytes and cancer cells. Meprins cleave bioactive peptides such as gastrin, cholecystokinin and parathyroid hormone, cytokines such as osteopontin and monocyte chemotactic peptide-1, as well as proteins such as gelatin, collagen IV, fibronectin and casein. Database predictions and initial data indicate that meprins are also capable of shedding proteins, including itself, from the cell surface. Membrane-bound meprin subunits are composed of dimeric meprin beta subunits or tetrameric hetero-oligomeric alpha beta complexes of approx. 200-400 kDa, and can be activated at the cell surface; secreted forms of homo-oligomeric meprin alpha are zymogens that form high-molecular-mass complexes of 1-6 MDa. These are among the largest extracellular proteases identified thus far. The latent (self-associating) homo-oligomeric complexes can move through extracellular spaces in a non-destructive manner, and deliver a concentrated form of the metalloproteinase to sites that have activating proteases, such as sites of inflammation, infection or cancerous growth. Meprins provide examples of novel ways of concentrating proteolytic activity at the cell surface and in the extracellular milieu, which may be critical to proteolytic function.