Protease nexin-1, tPA, and PAI-1 are upregulated in cryoglobulinemic membranoproliferative glomerulonephritis

Integrative transcriptome analysis reveals Serpine2 promotes glomerular mesangial cell proliferation and extracellular matrix accumulation via activating ERK1/2 signalling pathway in diabetic nephropathy

BACKGROUND

Diabetic nephropathy (DN) is one of the main causes of end-stage renal disease (ESRD), but its mechanism has not been clearly studied. We utilized integrative transcriptome analysis to explore the pathogenesis of DN.

METHODS

We conducted an analysis by combining bulk dataset and single-cell transcriptome dataset. Through this approach, we identified that Serpine2 may regulate the 'collagen-containing extracellular matrix' pathway involved in DN. Subsequently, we established DN animal and cell models using db/db mice and mesangial cells (MCs) to validate the role of Serpine2 in DN. In the animal model, we detected the expression level of Serpine2 in DN using western blotting (WB) and immunofluorescence (IF) assays. To further clarify the molecular mechanism of Serpine2 in DN, we knocked down Serpine2 and observed its effects on MCs proliferation and extracellular matrix (ECM) accumulation.

RESULTS

Our single-cell analysis of DN models highlighted a pivotal role for MCs in the disease's initiation. Next, through Cytoscape analysis of differentially expressed genes (DEGs) in MCs, we identified the following 10 hub genes: Acta2, Angpt2, Ccn1, Col4a1, Col4a2, Col8a1, Kdr, Thbs1, Tpm4 and Serpine2. Subsequently, we identified that Serpine2 and Kdr were also significantly DEGs in the bulk analysis of glomeruli. Additionally, our integrated gene set enrichment analysis of bulk dataset and single-cell RNA dataset revealed that the 'collagen-containing extracellular matrix' was a key pathway in DN progression. Serpine2 was one of the crucial genes involved in regulating this pathway. Therefore, we speculated that the regulation of the 'collagen-containing extracellular matrix' pathway by Serpine2 was an important mechanism. Importantly, WB and IF staining confirmed that Serpine2 expression was upregulated in the MCs of diabetic mice. Knockdown of Serpine2 in cultured MCs alleviated high-glucose-induced excessive MCs proliferation and ECM accumulation. Finally, we found that ERK agonist Ro 67-7476 eliminated the effect of Serpine2 siRNA.

CONCLUSIONS

In summary, Serpine2 regulates MCs proliferation and ECM synthesis through activation of the ERK1/2 pathway, which is an important pathogenesis mechanism of DN. These findings offer fresh perspectives on the mechanisms of glomerulosclerosis in DN pathogenesis and may provide new targets for treating DN.

Regression of diabetic nephropathy by treatment with empagliflozin in BTBR ob/ob mice

BACKGROUND

The SGLT2 inhibitor empagliflozin lowers blood glucose via reduced tubular reabsorption of filtered glucose and is an important new therapy for diabetic nephropathy (DN). This study tested whether treatment with empagliflozin would ameliorate proteinuria and the pathologic alterations of DN including podocyte number and integrity in the leptin deficient BTBR ob/ob mouse model of DN.

METHODS

Study cohorts included wild type BTBR mice, untreated diabetic BTBR ob/ob mice, and mice treated with empagliflozin for six weeks after development of established DN at 18 weeks of age.

RESULTS

Hyperglycemia, proteinuria, serum creatinine, accumulation of mesangial matrix and the extent of mesangiolysis were reversed with empagliflozin treatment. Treatment with empagliflozin resulted in increased podocyte number and podocyte density, improvement in the degree of podocyte foot process effacement and parietal epithelial cell activation. SGLT2 inhibition reduced renal oxidative stress, measured by urinary excretion of markers of RNA/DNA damage and in situ demonstration of decreased carbonyl oxidation. There was no discernable difference in accumulations of advanced glycation endproducts by immunohistochemistry.

CONCLUSION

The structural improvements seen in BTBR ob/ob mice treated with empagliflozin provide insight into potential long term benefits for humans with DN, for whom there is no comparable biopsy information to identify structural changes effected by SGLT2 inhibition. The findings suggest SGLT2 inhibition may ameliorate diabetic nephropathy through glucose lowering-dependent and -independent mechanisms that lead to podocyte restoration and delay or reversal of the disease progress.

Genetic Association of Hepatitis C-Related Mixed Cryoglobulinemia: A 10-Year Prospective Study of Asians Treated with Antivirals

Genetic profiles of hepatitis C virus (HCV)-associated mixed cryoglobulinemia (MC) in Asians remain elusive. A 10-year prospective cohort study was conducted with 1043 consecutive HCV Ab-positive Taiwanese surveyed with 13 single nucleotide polymorphisms (SNPs). Of 1043, 589 (56.5%) had baseline MC, 934 (89.5%) had positive HCV RNA, 796 completed anti-HCV therapy, and 715 had sustained virological responses (SVRs). SNP associations were surveyed withgenotypic, allelic, trend, permutation and multivariate analyses. At baseline, higher male sex and MC rates were noted in HCV RNA-positive than RNA-negative patients; higher female sex and positive HCV RNA rates but lower HCV RNA levels were noted in patients with than those without MC. Baseline associations were: HLA II-rs9461776 A allele, IFNL3-rs12979860 T allele, SERPINE1-rs6976053 C allele and MC with HCV RNA positivity; IFNL3-rs12979860 C allele, ARNTL-rs6486122 T allele and HCV RNA positivity with baseline MC. In SVR patients, RETN-rs1423096 C allele and SERPINE1-rs6976053 T allele were associated with 24-week and 10-year post-therapy MC, respectively. Conclusions: HCV RNA, IFNL3-rs12979860 and ARNTL-rs6486122 were associated with baseline MC; RETN-rs1423096 and SERPINE1-rs6976053 were associated with short- and long-term post-therapy MC in SVR patients, respectively. Links with HCV RNA and immune-associated SNPs suggest MC an immune reaction to expel HCV.

Beneficial effect on podocyte number in experimental diabetic nephropathy resulting from combined atrasentan and RAAS inhibition therapy

Podocyte loss and proteinuria are both key features of human diabetic nephropathy (DN). The leptin-deficient BTBR mouse strain with the ob/ob mutation develops progressive weight gain, type 2 diabetes, and diabetic nephropathy that has many features of advanced human DN, including increased mesangial matrix, mesangiolysis, podocyte loss, and proteinuria. Selective antagonism of the endothelin-1 type A receptor (ET_AR) by atrasentan treatment in combination with renin-angiotensin-aldosterone system inhibition with losartan has been shown to have the therapeutic benefit of lowering proteinuria in patients with DN, but the underlying mechanism for this benefit is not well understood. Using a similar therapeutic approach in diabetic BTBR ob/ob mice, this treatment regimen significantly increased glomerular podocyte number compared with diabetic BTBR ob/ob controls and suggested that parietal epithelial cells were a source for podocyte restoration. Atrasentan treatment alone also increased podocyte number but to a lesser degree. Mice treated with atrasentan demonstrated a reduction in proteinuria, matching the functional improvement reported in humans. This is a first demonstration that treatment with the highly selective ET_AR antagonist atrasentan can lead to restoration of the diminished podocyte number characteristic of DN in humans and thereby underlies the reduction in proteinuria in patients with diabetes undergoing similar treatment. The benefit of ET_AR antagonism in DN extended to a decrease in mesangial matrix as measured by a reduction in accumulations of collagen type IV in both the atrasentan and atrasentan + losartan-treated groups compared with untreated controls.

Application of long-acting VLHL PAI-1 during sutureless partial nephrectomy in mice reduces bleeding

PAI-1 prevents lysis of blood clot by inhibiting the urokinase and tPA induced conversion of plasminogen to plasmin. VLHL PAI-1 protein mutant was created to extend half-life over 700 hours. The objective of this paper was to test VLHL PAI-1 effects on bleeding during partial nephrectomy in mice. All animals had a left partial nephrectomy after intravenous infusion of saline or tPA. The animals were divided into four groups. Group 1 was infused with saline and kidney was exposed to saline too; Group 2 was infused with saline and kidney was exposed to PAI-1. Group 3 was infused with tPA and kidney was exposed to saline, while Group 4 was infused with tPA and kidney was exposed to PAI-1. Preweighed gauze containing PAI-1 or saline was then applied to the kidney for 30 minutes. The gauze was afterward weighed and blood loss was measured by subtracting the preweight of gauze from the final weight. We have observed a statistically significant (P ≤ 0.05) reduction of bleeding in PAI-1-treated group in comparison to saline and tPA-treated groups. Based on these results we propose that VLHL PAI-1 can be used therapeutically in limiting the flow of blood from renal wounds.

Reversibility of structural and functional damage in a model of advanced diabetic nephropathy

The reversibility of diabetic nephropathy remains controversial. Here, we tested whether replacing leptin could reverse the advanced diabetic nephropathy modeled by the leptin-deficient BTBR ob/ob mouse. Leptin replacement, but not inhibition of the renin-angiotensin-aldosterone system (RAAS), resulted in near-complete reversal of both structural (mesangial matrix expansion, mesangiolysis, basement membrane thickening, podocyte loss) and functional (proteinuria, accumulation of reactive oxygen species) measures of advanced diabetic nephropathy. Immunohistochemical labeling with the podocyte markers Wilms tumor 1 and p57 identified parietal epithelial cells as a possible source of regenerating podocytes. Thus, the leptin-deficient BTBR ob/ob mouse provides a model of advanced but reversible diabetic nephropathy for further study. These results also suggest that restoration of lost podocytes is possible but is not induced by RAAS inhibition, possibly explaining the limited efficacy of RAAS inhibitors in promoting repair of diabetic nephropathy.

Eicosapentaenoic acid restores diabetic tubular injury through regulating oxidative stress and mitochondrial apoptosis

The present study was designed to elucidate a possible mechanism of hyperglycemia-induced tubular injury and to examine a therapeutic potential of dietary eicosapentaenoic acid (EPA) for the prevention of diabetic kidney disease. Utilizing streptozotocin-induced diabetic mice, the extents of albuminuria and histological injuries were monitored at 2 wk after diabetic induction. Reactive oxygen species (ROS) production, apoptosis, and hypoxia in the kidney were evaluated by immunohistochemistry and Western blotting. An in vitro study was performed using rat proximal tubular cells (NRK-52E) to confirm the protective effect of EPA for methylglyoxal (MG)-induced ROS generation and staurosporine (STS)-induced mitochondrial apoptosis. The extents of albuminuria and histological tubular injuries were significantly lower in EPA-treated diabetic mice compared with untreated diabetic mice. The levels of lipid peroxidation product (4-hydroxy-2-nonenal), oxidative DNA damage (8-hydoxy-deoxyguanosine), and mitochondrial apoptosis (TUNEL, caspase-9, cleaved caspase-3, and cytochrome c release) in the tubular cells were also significantly lower in EPA-treated diabetic mice. Furthermore, hypoxia-inducible factor (HIF)-1α expression was significantly upregulated in the kidney tissues from EPA-treated mice compared with untreated diabetic mice. MG-induced ROS overproduction and STS-induced mitochondrial apoptosis in NRK-52E cells were significantly reduced by EPA treatment in vitro. These results indicated that the ROS generation and mitochondrial apoptosis were involved in hyperglycemia-induced tubular injury and EPA had a beneficial effect by suppressing ROS generation and mitochondrial apoptosis partly through augmentation of an HIF-1α response in diabetic kidney disease.

Serine proteases, inhibitors and receptors in renal fibrosis

Chronic kidney disease (CKD) is estimated to affect one in eight adults. Their kidney function progressively deteriorates as inflammatory and fibrotic processes damage nephrons. New therapies to prevent renal functional decline must build on basic research studies that identify critical cellular and molecular mediators. Plasminogen activator inhibitor-1 (PAI-1), a potent fibrosis-promoting glycoprotein, is one promising candidate. Absent from normal kidneys, PAI-1 is frequently expressed in injured kidneys. Studies in genetically engineered mice have demonstrated its potency as a pro-fibrotic molecule. Somewhat surprising, its ability to inhibit serine protease activity does not appear to be its primary pro-fibrotic effect in CKD. Both tissue-type plasminogen activator and plasminogen deficiency significantly reduced renal fibrosis severity after ureteral obstruction, while genetic urokinase (uPA) deficiency had no effect. PAI-1 expression is associated with enhanced recruitment of key cellular effectors of renal fibrosis - interstitial macrophages and myofibroblasts. The ability of PAI-1 to promote cell migration involves interactions with the low-density lipoprotein receptor-associate protein-1 and also complex interactions with uPA bound to its receptor (uPAR) and several leukocyte and matrix integrins that associate with uPAR as co-receptors. uPAR is expressed by several cell types in damaged kidneys, and studies in uPAR-deficient mice have shown that its serves a protective role. uPAR mediates additional anti-fibrotic effects - it interacts with specific co-receptors to degrade PAI-1 and extracellular collagens, and soluble uPAR has leukocyte chemoattractant properties. Molecular pathways activated by serine proteases and their inhibitor, PAI-1, are promising targets for future anti-fibrotic therapeutic agents.

Cryoglobulinemia and renal disease

PURPOSE OF REVIEW

Cryoglobulinemia occurs in a variety of clinical settings including lymphoproliferative disorders, infection and autoimmune disease. The worldwide pandemic of hepatitis C virus infection has resulted in a significant increase in its extrahepatic complications including cryoglobulinemia and renal disease. Here we review the types of cryoglobulins, mechanisms of cryoglobulin formation, links between hepatitis C virus and renal disease, and current approaches to therapy.

RECENT FINDINGS

The prevalence of cryoglobulinemia in hepatitis C virus-infected individuals is surprisingly large and may be found in more than 50% of some infected subpopulations. Most of these patients will not have overt renal disease, but there is a population of unknown size of patients with subclinical glomerular disease that has the potential to become clinically significant. In cases of hepatitis C virus-associated cryoglobulinemia, treatment remains focused on eradication of viremia, but interventions directed at B lymphocytes are increasingly utilized. The mechanisms of cryoglobulin formation and renal injury remain largely obscure, but recent evidence implicates the innate immune system in the initiation of disease.

SUMMARY

The most common renal injury associated with hepatitis C virus infection, in patients both with and without evidence of cryoglobulinemia, is membranoproliferative glomerulonephritis. There has been increasing focus on defining the mechanisms that link these processes and the evolution of renal injury in all clinical settings of cryoglobulinemia.