A preliminary study of possible fibrotic role of meprin metalloproteases in scleroderma patients

Objectives: This study aims to investigate the possible fibrotic role of meprin metalloproteases and possible fibrotic effects of activator protein-1 (AP-1) in scleroderma patients. Patients and methods: Between April 2018 and April 2019, a total of 85 scleroderma patients (9 males, 76 females; mean age: 54.9 years; range, 22 to 80 years) who met the 2013 American College of Rheumatology/European League Against Rheumatism criteria and 80 healthy control individuals (10 males, 70 females; mean age 42.9 years; range, 19 to 65 years) were included. Patients’ data and blood samples were collected. Messenger ribonucleic acid expressions of interleukin (IL)-6, AP-1 subunits, and tumor necrosis factor-alpha (TNF-α) were analyzed by quantitative real-time polymerase chain reaction. Serum meprin alpha and beta protein levels were analyzed using the enzyme-linked immunosorbent assay. Results: Meprin alpha and meprin beta protein levels increased in scleroderma patients. The AP-1 subunits (c-Fos, c-Jun), IL-6, and TNF-α increased in scleroderma patients, compared to controls. Conclusion: Our results provide evidence showing that increased meprins levels may be related to AP-1 levels and increased meprins levels may responsible for increased inflammatory TNF-α and IL-6 levels. All these data suggest meprins as promising therapeutic targets to restore the balance between inflammation and extracellular matrix deposition in scleroderma.

To be there when the picture is being painted

There is nothing quite like the excitement of discovery in science—of finding something no one else knew and seeing a story unfold. One has to be part of an emerging picture to feel the elation. These moments in a lifetime are few and far between, but they fuel enthusiasm and keep one going. They are embedded in struggles and joys of everyday life, years of establishing what Louis Pasteur called “the prepared mind,” working with mentors, trainees, and colleagues, failures and successes. This article recalls 1) how I got to be a biochemist; 2) my contributions as an educator and researcher, especially regarding meprin metalloproteases; and 3) my participation in communities of science. Perhaps my reflections will help an aspiring scientist see how fulfilling a career in science can be.

Undiagnosed Kidney Injury in Uninsured and Underinsured Diabetic African American Men and Putative Role of Meprin Metalloproteases in Diabetic Nephropathy

Diabetes is the leading cause of chronic kidney disease. African Americans are disproportionately burdened by diabetic kidney disease (DKD) and end stage renal disease (ESRD). Disparities in DKD have genetic and socioeconomic components, yet its prevalence in African Americans is not adequately studied. The current study used multiple biomarkers of DKD to evaluate undiagnosed DKD in uninsured and underinsured African American men in Greensboro, North Carolina. Participants consisted of three groups: nondiabetic controls, diabetic patients without known kidney disease, and diabetic patients with diagnosed DKD. Our data reveal undiagnosed kidney injury in a significant proportion of the diabetic patients, based on levels of both plasma and urinary biomarkers of kidney injury, namely, urinary albumin to creatinine ratio, kidney injury molecule-1, cystatin C, and neutrophil gelatinase-associated lipocalin. We also found that the urinary levels of meprin A, meprin B, and two kidney meprin targets (nidogen-1 and monocytes chemoattractant protein-1) increased with severity of kidney injury, suggesting a potential role for meprin metalloproteases in the pathophysiology of DKD in this subpopulation. The study also demonstrates a need for more aggressive tests to assess kidney injury in uninsured diabetic patients to facilitate early diagnosis and targeted interventions that could slow progression to ESRD.

Hypoxia Associated Proteolytic Processing of OS-9 by the Metalloproteinase Meprinβ

Meprin metalloproteases play a role in the pathology of ischemia/reperfusion- (IR-) induced renal injury. The endoplasmic reticulum-associated protein, osteosarcoma-9 (OS-9), has been shown to interact with the carboxyl-terminal tail of meprinβ. More importantly, OS-9 interacts with the hypoxia inducible factor-1α(HIF-1α) and the prolyl-hydroxylase, proteins which mediate the cell’s response to hypoxia. To determine if OS-9 is a meprin substrate, kidney proteins from meprinαβknockout mice (αβKO) (which lack endogenous meprins) and purified human OS-9 were incubated with activated forms of meprin A and meprin B, and Western blot analysis was used to evaluate proteolytic processing of OS-9. Fragmentation of OS-9 was observed in reactions with meprin B, but not meprin A. To determine whether meprin B cleaves OS-9in vivo, wild-type (WT) and meprinαβKO mice were subjected to IR-induced renal injury. Fragmentation of OS-9 was observed in kidney proteins from WT mice subjected to IR, but not in meprinαβKO counterparts. Transfection of kidney cells (MDCK and HEK293) with meprinβcDNA prevented accumulation of OS-9 following exposure to the hypoxia mimic, CoCl2. These data suggest that meprinβinteraction with OS-9 plays a role in the hypoxia response associated with IR-induced renal injury.

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.