Relationship of matrix Gla protein and vitamin K with vascular calcification in hemodialysis patients

Objective: This study evaluated associations of serum matrix Gla protein (MGP), plasma vitamin K1, and plasma vitamin K2 with coronary artery calcium score (CACS) and cardiovascular disease (CVD) in maintenance hemodialysis (MHD) patients. Methods: Subjects comprised 112 MHD patients aged 30-60 years and 40 age-matched healthy subjects. Total MGP, vitamin K1, vitamin K2, and lipid profile were examined in all subjects; other clinical data, medication use, and CACS were assessed only in MHD patients. Determinants of MGP in all subjects were identified by regression analysis. Factors associated with CACS and CVD in MHD patients were identified by regression analysis and logistic analysis, respectively. Results: Lower plasma levels of vitamin K1 corrected for triglycerides [0.39 (0.24-0.70) vs. 0.77 (0.48-1.34) ng/mg, p < 0.001], higher frequency of plasma vitamin K2 ≤ 0.05 ng/ml (p = 0.23), and higher serum total MGP (288.4 ± 44.2 vs. 159.7 ± 40.6 ng/ml, p < 0.0001) were observed in MHD patients than in healthy controls. Total MGP level was significantly associated with levels of vitamin K1 corrected for triglycerides (p <0 .001) and vitamin K2 ≤ 0.05 ng/ml (p < 0.05) in all subjects. Total MGP level was significantly associated with presence of CVD (p <0 .05), but not CACS, in MHD patients. Conclusion: The end-stage renal disease on hemodialysis is a deficiency state of vitamin K. Total MGP was significantly higher in MHD patients compared to healthy subjects and total MGP was associated with the presence of CVD, but not CACS, in MHD patients.

High-normal albuminuria is associated with subclinical atherosclerosis in male population with estimated glomerular filtration rate ≥60 mL/min/1.73 m2: A cross-sectional study

Background

Low-grade albuminuria has been considered a predictor of cardiovascular mortality. We investigated the relationship between high-normal albuminuria and subclinical atherosclerosis in non-diabetic men with estimated glomerular filtration rate (eGFR) ≥60 mL/min/1.73 m².

Methods

In this cross-sectional study, 1,756 men with eGFR ≥60 mL/min/1.73 m² and urine albumin-to-creatinine ratio (UACR) <30 mg/g, who attended general health checkups between April 2012 and March 2015, underwent blood sampling, urinalysis, and carotid ultrasonography. We excluded the subjects who were diabetic and/or received an anti-hypertensive drug. Carotid intima-media thickness (IMT) and the number of focal atheromatous plaques were used as indicators of subclinical atherosclerosis. Multiple linear regression analysis was performed to identify clinical factors associated with carotid IMT. Poisson regression analysis was used to assess the determinants of the carotid plaque number.

Results

Median UACR was 4.8 mg/g (interquartile range, 3.6–6.9 mg/g). Compared with subjects with low-normal UACR (<10.0 mg/g), subjects with high-normal UACR (10.0–29.8 mg/g) had greater IMT and higher carotid plaque number. High-normal UACR was independently associated with thickened IMT in the model adjusted for conventional cardiovascular disease risk factors. Moreover, participants with high-normal UACR were also more likely to be associated with increased plaque count (prevalence ratio: 1.06; 95% confidence interval: 1.01–1.14) after adjustment for conventional cardiovascular disease risk factors.

Conclusions

Our results indicate that high-normal albuminuria is associated with both carotid IMT and plaque formation in the non-diabetic male population with eGFR ≥60 mL/min/1.73 m².

Inhibition of the H3K4 methyltransferase MLL1/WDR5 complex attenuates renal senescence in ischemia reperfusion mice by reduction of p16INK4a

Renal function declines with aging and is pathologically characterized by chronic inflammation and fibrosis. Renal senescence is induced not only by aging but also by various stimuli, including ischemia reperfusion injury. Recently, the accumulation of p16^INK4a-positive cells in the kidney has been considered a molecular feature of renal senescence, with the p16^INK4a gene reportedly regulated by mixed-lineage leukemia 1 (MLL1)/WD-40 repeat protein 5 (WDR5)-mediated histone 3 lysine 4 trimethylation (H3K4me3). Here, we determined whether inhibition of MLL1/WDR5 activity attenuates renal senescence, inflammation, and fibrosis in mice with ischemia reperfusion injury and in cultured rat renal fibroblasts. MM-102 or OICR-9429, both MLL1/WDR5 protein-protein interaction inhibitors, and small interfering RNA (siRNA) for MLL1 or WDR5 suppressed the expression of p16^INK4a in mice with ischemia reperfusion injury, accompanied by downregulation of H3K4me3 expression. MM-102 attenuated renal fibrosis and inflammation in the kidney of mice with ischemia reperfusion injury. Moreover, in vitro study showed that transforming growth factor-β1 induced the expression of MLL1, WDR5, H3K4me3, and p16^INK4a. Finally, chromatin immunoprecipitation identified the p16^INK4a promoter at an H3K4me3 site in renal fibroblasts. Thus, our findings show that H3K4me3 inhibition ameliorates ischemia reperfusion-induced renal senescence along with fibrosis and inflammation.

Calnexin promotes the folding of mutant iduronate 2-sulfatase related to mucopolysaccharidosis type II

Mucopolysaccharidosis type II (MPS II) is one of the most common mucopolysaccharidoses, which is caused by mutation of the gene encoding iduronate 2-sulfatase (IDS). The loss of function of IDS leads to the accumulation of heparan sulfate and dermatan sulfate of glycosaminoglycans throughout the body, resulting in skeletal deformities, mental retardation, rigid joints, and thick skin. Recently, enzyme replacement therapy has become a common strategy for treating this condition. However, its effectiveness on the central nervous system (CNS) is limited because intravenously administered recombinant IDS (rIDS) cannot pass through the blood brain barrier. Therefore, several methods for delivering rIDS to the CNS, using anti-human transferrin receptor antibody and adeno-associated virus 9, have been explored. To investigate additional approaches for treatment, more cognition about the intracellular dynamics of mutant IDS is essential. We have already found that mutant IDS accumulated in the endoplasmic reticulum (ER) and was degraded by ER-associated degradation (ERAD). Although the dynamics of degradation of mutant IDS was revealed, the molecular mechanism related to the folding of mutant IDS in the ER remained unclear. In this research, we confirmed that mutant IDS retained in the ER would be folded by binding with calnexin (CNX). Thus, knockdown of CNX reduced the translocation of mutant IDS from ER to lysosome and its enzyme activity, indicating that the correct folding of this protein via interaction with CNX ensures its functional activity. These findings reveal the possibility that modifying the interaction of mutant IDS and CNX could contribute to alternative therapeutic strategies for MPS II.

Renal medullary tonicity regulates RNF183 expression in the collecting ducts via NFAT5

Nuclear factor of activated T-cells 5 (NFAT5) directly binds to the promoter of the RING finger protein 183 (RNF183) gene and induces its transcription under hypertonic conditions in mouse inner-medullary collecting duct (mIMCD-3) cells. However, there is no specific anti-RNF183 antibody for immunostaining; therefore, it is unclear whether NFAT5 regulates RNF183 expression in vivo and where RNF183 is localized in the kidney. This study investigated NFAT5-regulated in vivo RNF183 expression and localization using CRISPR/Cas9-mediated RNF183-green fluorescent protein (RNF183-GFP) knock-in mice. GFP with linker sequences was introduced upstream of an RNF183 open reading frame in exon 3 by homologous recombination through a donor plasmid. Immunofluorescence staining using GFP antibody revealed that GFP signals gradually increase from the outer medulla down to the inner medulla and colocalize with aquaporin-2. Furosemide treatment dramatically decreased RNF183 expression in the renal medulla, consistent with the decrease in NFAT5 protein and target gene mRNA expression. Furosemide treatment of mIMCD-3 cells did not affect mRNA expression and RNF183 promoter activities. These results indicated that RNF183 is predominantly expressed in the renal medullary collecting ducts, and that decreased renal medullary tonicity by furosemide treatment decreases RNF183 expression by NFAT5 downregulation.

Iliopsoas Abscess in Hemodialysis Patients With End-Stage Kidney Disease

Iliopsoas abscess in HD patients is rare. We examined nine HD patients with iliopsoas abscess (six men and five diabetes mellitus cases) treated between 2005 and 2015. Mean age and dialysis vintage at onset were 72 years and 109 months, respectively. Of the nine patients, four had lumbar orthopedic diseases, and two had all components of the classic triad of iliopsoas abscess at onset. All nine patients underwent percutaneous drainage, while seven underwent antimicrobial therapy. The most common pathogenic bacterium was methicillin-resistantStaphylococcus aureus(MRSA) (n = 5). Four patients had multilocular recurrence on the same side as the initial abscess and did not undergo CT before drainage catheter removal. Five patients died in the hospital, in which three died due to infectious diseases by MRSA. We suggest percutaneous drainage as the first-line therapy for HD patients with iliopsoas abscess and recommend combining antimicrobial therapy for MRSA, because of poor prognosis.

Hypomagnesemia is not an independent risk factor for mortality in Japanese maintenance hemodialysis patients

PURPOSE

It is unclear whether hypomagnesemia is an independent risk factor or innocent bystander for mortality in maintenance hemodialysis (MHD) patients. Thus, we studied associations between hypomagnesemia and all-cause as well as cardiovascular (CV) mortality in MHD patients.

METHODS

Baseline clinical characteristics and coronary artery calcium score (CACS) of 353 Japanese MHD patients were reviewed. Three-year survival rate and mortality risk factors were assessed.

RESULTS

Median (interquartile range) age, dialysis vintage, serum magnesium (Mg), serum albumin and CACS of the subjects were 68 (60-78) years, 75 (32-151) months, 2.4 (2.2-2.7) mg/dl, 3.6 (3.3-3.8) g/dl, and 1181 (278-3190), respectively. During the 3-year period, 91 patients died. Kaplan-Meier overall 3-year survival rates were 59.0% in in patients with Mg < 2.4 mg/dl (n = 136) and 82.3% in patients with Mg ≥ 2.4 mg/dl (n = 217), (P < 0.0001). In Cox regression models not incorporating serum albumin, Mg < 2.4 mg/dl was significantly associated with 3-year all-cause death, independent of age, dialysis vintage, average ultrafiltration, Log (CACS + 1), warfarin use, serum potassium, high-sensitivity C-reactive protein (hsCRP), phosphate, uric acid, and intact parathyroid hormone [Hazard ratio (HR) 95% confidence interval (CI): 2.82 (1.31-6.29), P = 0.0078], and CV death, independent of age, dialysis vintage, Log (CACS + 1), warfarin use, serum hsCRP, and uric acid [HR (95% CI): 4.47 (1.45-16.76), P = 0.0086]. Nevertheless, associations of Mg < 2.4 mg/dl with all-cause and CV mortality were all absent in models that included serum albumin.

CONCLUSIONS

Hypomagnesemia is not an independent risk factor for mortality but is associated with malnutrition in MHD patients.

Novel Asp511Thr mutation in McArdle disease with acute kidney injury caused by rhabdomyolysis

McArdle disease (glycogen storage disease type V) is a rare hereditary metabolic myopathy. It can be overlooked clinically because it often presents as chronic asymptomatic hypercreatine phosphokinasemia (hyperCKemia). However, vigorous exercise or infections can trigger severe rhabdomyolysis. We present the case of a patient with long-term idiopathic hyperCKemia who, after contracting an upper respiratory tract infection, developed severe rhabdomyolysis and acute kidney injury. Upon hemodialysis, his renal function recovered and CK levels fell to below baseline, and maintenance therapy with vitamin B6 was also started. A molecular diagnosis of McArdle disease was subsequently made. Whole-exome sequencing revealed homozygous c1538delG (p.Asp511Thr fs*28) mutations in the PYGM gene, which was a novel mutation. Therefore, when investigating idiopathic hyperCKemia, glycogen storage disorders should also be considered.

Possible involvement of normalized Pin1 expression level and AMPK activation in the molecular mechanisms underlying renal protective effects of SGLT2 inhibitors in mice

BACKGROUND

Recently, clinical studies have shown the protective effects of sodium glucose co-transporter2 (SGLT2) inhibitors against progression of diabetic nephropathy, but the underlying molecular mechanisms remain unclear.

METHODS

Diabetic mice were prepared by injecting nicotinamide and streptozotocin, followed by high-sucrose diet feeding (NA/STZ/Suc mice). The SGLT2 inhibitor canagliflozin was administered as a 0.03% (w/w) mixture in the diet for 4 weeks. Then, various parameters and effects of canagliflozin on diabetic nephropathy were investigated.

RESULTS

Canagliflozin administration to NA/STZ/Suc mice normalized hyperglycemia as well as elevated renal mRNA of collagen 1a1, 1a2, CTGF, TNFα and MCP-1. Microscopic observation revealed reduced fibrotic deposition in the kidneys of canagliflozin-treated NA/STZ/Suc mice. Interestingly, the protein level of Pin1, reportedly involved in the inflammation and fibrosis affecting several tissues, was markedly increased in the NA/STZ/Suc mouse kidney, but this was normalized with canagliflozin treatment. The cells showing increased Pin1 expression in the kidney were mainly mesangial cells, along with podocytes, based on immunohistochemical analysis. Furthermore, it was revealed that canagliflozin induced AMP-activated kinase (AMPK) activation concentration-dependently in CRL1927 mesangial as well as THP-1 macrophage cell lines. AMPK activation was speculated to suppress mesangial cell proliferation and exert anti-inflammatory effects in hematopoietic cells.

CONCLUSION

Therefore, we can reasonably suggest that normalized Pin1 expression and AMPK activation contribute to the molecular mechanisms underlying SGLT2 inhibitor-induced suppression of diabetic nephropathy, possibly at least in part by reducing inflammation and fibrotic change.

The Xanthine Oxidase Inhibitor Febuxostat Suppresses the Progression of IgA Nephropathy, Possibly via Its Anti-Inflammatory and Anti-Fibrotic Effects in the gddY Mouse Model

Recent clinical studies have demonstrated the protective effect of xanthine oxidase (XO) inhibitors against chronic kidney diseases, although the underlying molecular mechanisms remain unclear. However, to date, neither clinical nor basic research has been carried out to elucidate the efficacy of XO inhibitor administration for IgA nephropathy. We thus investigated whether febuxostat, an XO inhibitor, exerts a protective effect against the development of IgA nephropathy, using gddY mice as an IgA nephropathy rodent model. Eight-week-old gddY mice were provided drinking water with (15 μg/mL) or without febuxostat for nine weeks and then subjected to experimentation. Elevated serum creatinine and degrees of glomerular sclerosis and fibrosis, judged by microscopic observations, were significantly milder in the febuxostat-treated than in the untreated gddY mice, while body weights and serum IgA concentrations did not differ between the two groups. In addition, elevated mRNA levels of inflammatory cytokines such as TNFα, MCP-1, IL-1β, and IL-6, collagen isoforms and chemokines in the gddY mouse kidneys were clearly normalized by the administration of febuxostat. These data suggest a protective effect of XO inhibitors against the development of IgA nephropathy, possibly via suppression of inflammation and its resultant fibrotic changes, without affecting the serum IgA concentration.

Long-term maintenance of hemoglobin levels in hemodialysis patients treated with bi-weekly epoetin beta pegol switched from darbepoetin alfa: a single-center, 12-month observational study in Japan

Recent evidence on maintenance administration of epoetin beta pegol, a continuous erythropoiesis receptor activator (CERA), in dialysis patients shows the clinical benefit of bi-weekly administration (Q2W) in improving hematopoiesis and iron use efficiency. We undertook a single-center observational study of 33 Japanese maintenance dialysis patients, whose anemia had been kept stable through weekly administration (Q1W) of darbepoetin (DA), to evaluate the effectiveness of CERA Q2W switched from DA in maintaining hemoglobin (Hb) levels over a 12-month period. The target Hb level was 10.0-12.0 g/dL. Throughout the 12-month period, the mean Hb was stably maintained at 10.5-10.8 g/dL, 69.7-87.9% of the patients achieving the target Hb level. The mean CERA dose was within the range of 62.9-78.8 µg/2 weeks. The average CERA dose adjustment frequency after switching was low at 0.42-0.67 times/3 months. In both subgroups stratified by the DA dose prior to the switch, Hb levels were kept stable during CERA administration; however, in the low-dose group (10-20 µg/week of DA), the CERA and iron doses decreased over time, whereas in the high-dose group (30-60 µg/week of DA) they remained unchanged. CERA Q2W achieved long-term successful anemia management in Japanese maintenance dialysis patients after switching from DA Q1W. CERA dose was adjusted based on an overall consideration of past changes in Hb levels, erythropoiesis-stimulating agent and iron doses. Subgroup analysis showed the CERA dose in the low-dose group decreased continuously, due possibly to a long-term improvement in iron use efficiency.

NFAT5 up-regulates expression of the kidney-specific ubiquitin ligase gene Rnf183 under hypertonic conditions in inner-medullary collecting duct cells

We previously reported that among the 37 RING finger protein (RNF) family members, RNF183 mRNA is specifically expressed in the kidney under normal conditions. However, the mechanism supporting its kidney-specific expression pattern remains unclear. In this study, we elucidated the mechanism of the transcriptional activation of murine Rnf183 in inner-medullary collecting duct cells. Experiments with anti-RNF183 antibody revealed that RNF183 is predominantly expressed in the renal medulla. Among the 37 RNF family members, Rnf183 mRNA expression was specifically increased in hypertonic conditions, a hallmark of the renal medulla. RNF183 up-regulation was consistent with the activation of nuclear factor of activated T cells 5 (NFAT5), a transcription factor essential for adaptation to hypertonic conditions. Accordingly, siRNA-mediated knockdown of NFAT5 down-regulated RNF183 expression. Furthermore, the -3,466 to -3,136-bp region upstream of the mouse Rnf183 promoter containing the NFAT5-binding motif is conserved among mammals. A luciferase-based reporter vector containing the NFAT5-binding site was activated in response to hypertonic stress, but was inhibited by a mutation at the NFAT5-binding site. ChIP assays revealed that the binding of NFAT5 to this DNA site is enhanced by hypertonic stress. Of note, siRNA-mediated RNF183 knockdown increased hypertonicity-induced caspase-3 activation and decreased viability of mIMCD-3 cells. These results indicate that (i) RNF183 is predominantly expressed in the normal renal medulla, (ii) NFAT5 stimulates transcriptional activation of Rnf183 by binding to its cognate binding motif in the Rnf183 promoter, and (iii) RNF183 protects renal medullary cells from hypertonicity-induced apoptosis.

Serum-Free Medium Enhances the Immunosuppressive and Antifibrotic Abilities of Mesenchymal Stem Cells Utilized in Experimental Renal Fibrosis

Serum used in culture medium brings risks of immune reactions or infections and thus may hinder using ex vivo expanded mesenchymal stem cells (MSCs) for medical treatment. Here, we cultured MSCs in a serum-free medium (SF-MSCs) and in a medium containing 10% fetal bovine serum (10%MSCs) and investigated their effects on inflammation and fibrosis. MSC-conditioned medium suppressed transforming growth factor-β1-induced phosphorylation of Smad2 in HK-2 cells, with no significant difference between the two MSCs. This finding suggests that the direct antifibrotic effect of SF-MSCs is similar to that of 10%MSCs. However, immunohistochemistry revealed that renal fibrosis induced by unilateral ureteral obstruction in rats was more significantly ameliorated by the administration of SF-MSCs than by that of 10%MSCs. Coculture of MSCs and monocytic THP-1 cell-derived macrophages using a Transwell system showed that SF-MSCs significantly induced polarization from the proinflammatory M1 to the immunosuppressive M2 phenotype macrophages, suggesting that SF-MSCs strongly suppress the persistence of inflammation. Furthermore, the gene expression of tumor necrosis factor-α-induced protein 6 (TSG-6), which inhibits the recruitment of inflammatory cells, was higher in SF-MSCs than in 10%MSCs, and TSG-6 knockdown in SF-MSCs attenuated the anti-inflammatory responses in unilateral ureteral obstruction rats. These findings imply that SF culture conditions can enhance the immunosuppressive and antifibrotic abilities of MSCs and the administration of ex vivo expanded SF-MSCs has the potential to be a useful therapy for preventing the progression of renal fibrosis. Stem Cells Translational Medicine 2018;7:893-905.

TGF-β1 promotes expression of fibrosis-related genes through the induction of histone variant H3.3 and histone chaperone HIRA

Renal fibrosis is a histological manifestation that occurs in almost every type of chronic kidney disease. Histone variant H3.3 and its chaperone, histone cell cycle regulation defective homolog A (HIRA), serve as epigenetic marks that regulate transcriptional activity. In this study, we assessed the roles of histone H3.3 and HIRA in unilateral ureteral-obstruction (UUO) mice. In UUO mice, the levels of histone H3.3 and HIRA were significantly upregulated in the kidneys. These upregulated levels were decreased by a TGF-β1 neutralizing antibody. TGF-β1 induced histone H3.3 and HIRA expression in vitro via a Smad3-dependent pathway in normal rat kidney (NRK)-52E cells. Additionally, knockdown of HIRA expression decreased histone H3.3 expression and fibrogenesis in NRK-52E cells after TGF-β1 stimulation. Chromatin immunoprecipitation analysis revealed that promoters of fibrosis-related genes were immunoprecipitated with both histone H3.3 and HIRA in NRK-52E cells. Lastly, in human kidney biopsies from patients diagnosed with IgA nephropathy, histone H3.3 and HIRA immunostaining correlated positively with areas of fibrosis and estimated glomerular filtration rate. In conclusion, TGF-β1 induces expression of histone H3.3 and HIRA, which regulates expression of fibrosis-related genes.