Our previous work demonstrated a protective role of protein S in early diabetic kidney disease (DKD). Protein S exerts antiinflammatory and antiapoptotic effects through the activation of TYRO3, AXL, and MER (TAM) receptors. Among the 3 TAM receptors, we showed that the biological effects of protein S were mediated largely by TYRO3 in diabetic kidneys. Our data now show that TYRO3 mRNA expression is highly enriched in human glomeruli and that TYRO3 protein is expressed in podocytes. Interestingly, glomerular TYRO3 mRNA expression increased in mild DKD but was suppressed in progressive DKD, as well as in focal segmental glomerulosclerosis (FSGS). Functionally, morpholino-mediated knockdown of tyro3 altered glomerular filtration barrier development in zebrafish larvae, and genetic ablation of Tyro3 in murine models of DKD and Adriamycin-induced nephropathy (ADRN) worsened albuminuria and glomerular injury. Conversely, the induction of TYRO3 overexpression specifically in podocytes significantly attenuated albuminuria and kidney injury in mice with DKD, ADRN, and HIV-associated nephropathy (HIVAN). Mechanistically, TYRO3 expression was suppressed by activation of TNF-α/NF-κB pathway, which may contribute to decreased TYRO3 expression in progressive DKD and FSGS, and TYRO3 signaling conferred antiapoptotic effects through the activation of AKT in podocytes. In conclusion, TYRO3 plays a critical role in maintaining normal podocyte function and may be a potential new drug target to treat glomerular diseases.
Fang Zhong, Zhaohong Chen, Liwen Zhang, Yifan Xie, Viji Nair, Wenjun Ju, Matthias Kretzler, Robert G. Nelson, Zhengzhe Li, Hongyu Chen, Yongjun Wang, Aihua Zhang, Kyung Lee, Zhihong Liu, John Cijiang He
TGF-β signals through a receptor complex composed of 2 type I and 2 type II (TGF-βRII) subunits. We investigated the role of macrophage TGF-β signaling in fibrosis after AKI in mice with selective monocyte/macrophage TGF-βRII deletion (macrophage TGF-βRII–/– mice). Four weeks after injury, renal TGF-β1 expression and fibrosis were higher in WT mice than macrophage TGF-βRII–/– mice, which had decreased renal macrophages. The in vitro chemotactic response to f-Met-Leu-Phe was comparable between bone marrow–derived monocytes (BMMs) from WT and macrophage TGF-βRII–/– mice, but TGF-βRII–/– BMMs did not respond to TGF-β. We then implanted Matrigel plugs suffused with either f-Met-Leu-Phe or TGF-β1 into WT or macrophage TGF-βRII–/– mice. After 6 days, f-Met-Leu-Phe induced similar macrophage infiltration into the Matrigel plugs of WT and macrophage TGF-βRII–/– mice, but TGF-β induced infiltration only in WT mice. We further determined the number of labeled WT or TGF-βRII–/– BMMs infiltrating into WT kidneys 20 days after ischemic injury. There were more labeled WT BMMs than TGF-βRII–/– BMMs. Therefore, macrophage TGF-βRII deletion protects against the development of tubulointerstitial fibrosis following severe ischemic renal injury. Chemoattraction of macrophages to the injured kidney through a TGF-β/TGF-βRII axis is a heretofore undescribed mechanism by which TGF-β can mediate renal fibrosis during progressive renal injury.
Sungjin Chung, Jessica M. Overstreet, Yan Li, Yinqiu Wang, Aolei Niu, Suwan Wang, Xiaofeng Fan, Kensuke Sasaki, Guan-Nan Jin, Stellor Nlandu Khodo, Leslie Gewin, Ming-Zhi Zhang, Raymond C. Harris
Gut microbiota–derived metabolites play important roles in health and disease. D–amino acids and their L-forms are metabolites of gut microbiota with distinct functions. In this study, we show the pathophysiologic role of D–amino acids in association with gut microbiota in humans and mice with acute kidney injury (AKI). In a mouse kidney ischemia/reperfusion model, the gut microbiota protected against tubular injury. AKI-induced gut dysbiosis contributed to the altered metabolism of D–amino acids. Among the D–amino acids, only D-serine was detectable in the kidney. In injured kidneys, the activity of D–amino acid oxidase was decreased. Conversely, the activity of serine racemase was increased. The oral administration of D-serine mitigated the kidney injury in B6 mice and D-serine–depleted mice. D-serine suppressed hypoxia-induced tubular damage and promoted posthypoxic tubular cell proliferation. Finally, the D-serine levels in circulation were significantly correlated with the decrease in kidney function in AKI patients. These results demonstrate the renoprotective effects of gut-derived D-serine in AKI, shed light on the interactions between the gut microbiota and the kidney in both health and AKI, and highlight D-serine as a potential new therapeutic target and biomarker for AKI.
Yusuke Nakade, Yasunori Iwata, Kengo Furuichi, Masashi Mita, Kenji Hamase, Ryuichi Konno, Taito Miyake, Norihiko Sakai, Shinji Kitajima, Tadashi Toyama, Yasuyuki Shinozaki, Akihiro Sagara, Taro Miyagawa, Akinori Hara, Miho Shimizu, Yasutaka Kamikawa, Kouichi Sato, Megumi Oshima, Shiori Yoneda-Nakagawa, Yuta Yamamura, Shuichi Kaneko, Tetsuya Miyamoto, Masumi Katane, Hiroshi Homma, Hidetoshi Morita, Wataru Suda, Masahira Hattori, Takashi Wada
Chronic obstructive pulmonary disease (COPD), associated with cigarette smoke–induced (CS-induced) emphysema, contributes significantly to the global health care burden of disease. Although chronic kidney disease (CKD) may occur in patients with COPD, the relationship between COPD and CKD remains unclear. Using a murine model of experimental COPD, we show that chronic CS exposure resulted in marked kidney injury and fibrosis, as evidenced by histological and ultrastructural changes, altered macrophage subpopulations, and expression of tissue injury, fibrosis, and oxidative stress markers. CS induced mitochondrial dysfunction, and increased autophagic flux in kidney tissues and in kidney tubular epithelial (HK-2) cells, as determined by LC3B turnover assays. Mice heterozygous for Beclin-1 (Becn1+/–) were protected from the development of kidney tissue injury and renal fibrosis in response to CS exposure, and displayed impaired basal and inducible mitochondrial turnover by mitophagy. Interestingly, CS caused a reduction of Beclin-1 expression in mouse kidneys and kidney tubular epithelial cells, attributed to increased autophagy-dependent turnover of Beclin-1. These results suggest that Beclin-1 is required for CS-induced kidney injury and that reduced levels of Beclin-1 may confer renoprotection. These results identify the kidney as a target for CS-induced injury in COPD and the Beclin-1–dependent autophagy pathway as a potential therapeutic target in CKD.
Maria A. Pabón, Edwin Patino, Divya Bhatia, Jocelyn Quintero, Kevin C. Ma, Eli J. Finkelsztein, Juan C. Osorio, Faryal Malick, Francesca Polverino, Caroline A. Owen, Stefan W. Ryter, Augustine M.K. Choi, Suzanne M. Cloonan, Mary E. Choi
Lipocalin-2 is not only a sensitive biomarker, but it also contributes to the pathogenesis of renal injuries. The present study demonstrates that adipose tissue–derived lipocalin-2 plays a critical role in causing both chronic and acute renal injuries. Four-week treatment with aldosterone and high salt after uninephrectomy (ANS) significantly increased both circulating and urinary lipocalin-2, and it induced glomerular and tubular injuries in kidneys of WT mice. Despite increased renal expression of lcn2 and urinary excretion of lipocalin-2, mice with selective deletion of lcn2 alleles in adipose tissue (Adipo-LKO) are protected from ANS- or aldosterone-induced renal injuries. By contrast, selective deletion of lcn2 alleles in kidney did not prevent aldosterone- or ANS-induced renal injuries. Transplantation of fat pads from WT donors increased the sensitivity of mice with complete deletion of Lcn2 alleles (LKO) to aldosterone-induced renal injuries. Aldosterone promoted the urinary excretion of a human lipocalin-2 variant, R81E, in turn causing renal injuries in LKO mice. Chronic treatment with R81E triggered significant renal injuries in LKO, resembling those observed in WT mice following ANS challenge. Taken in conjunction, the present results demonstrate that lipocalin-2 derived from adipose tissue causes acute and chronic renal injuries, largely independent of local lcn2 expression in kidney.
Wai Yan Sun, Bo Bai, Cuiting Luo, Kangmin Yang, Dahui Li, Donghai Wu, Michel Félétou, Nicole Villeneuve, Yang Zhou, Junwei Yang, Aimin Xu, Paul M. Vanhoutte, Yu Wang
Chronic kidney disease (CKD) leads to decreased sensitivity to the metabolic effects of insulin, contributing to protein energy wasting and muscle atrophy. Targeted metabolomics profiling during hyperinsulinemic-euglycemic insulin clamp testing may help identify aberrant metabolic pathways contributing to insulin resistance in CKD. Using targeted metabolomics profiling, we examined the plasma metabolome in 95 adults without diabetes in the fasted state (58 with CKD, 37 with normal glomerular filtration rate [GFR]) who underwent hyperinsulinemic-euglycemic clamp. We assessed heterogeneity in fasting metabolites and the response to insulin to identify potential metabolic pathways linking CKD with insulin resistance. Baseline differences and effect modification by CKD status on changes with insulin clamp testing were adjusted for confounders. Mean GFR among participants with CKD was 37.3 compared with 89.3 ml/min per 1.73 m2 among controls. Fasted-state differences between CKD and controls included abnormalities in tryptophan metabolism, ubiquinone biosynthesis, and the TCA cycle. Insulin infusion markedly decreased metabolite levels, predominantly amino acids and their metabolites. CKD was associated with attenuated insulin-induced changes in nicotinamide, arachidonic acid, and glutamine/glutamate metabolic pathways. Metabolomics profiling suggests disruption in amino acid metabolism and mitochondrial function as putative manifestations or mechanisms of the impaired anabolic effects of insulin in CKD.
Baback Roshanravan, Leila R. Zelnick, Daniel Djucovic, Haiwei Gu, Jessica A. Alvarez, Thomas R. Ziegler, Jorge L. Gamboa, Kristina Utzschneider, Bryan Kestenbaum, Jonathan Himmelfarb, Steven E. Kahn, Daniel Raftery, Ian H. de Boer
Although the cause of hypertension among individuals with obesity and insulin resistance is unknown, increased plasma insulin, acting in the kidney to increase sodium reabsorption, has been proposed as a potential mechanism. Insulin may also stimulate glucose uptake, but the contributions of tubular insulin signaling to sodium or glucose transport in the setting of insulin resistance is unknown. To directly study the role of insulin signaling in the kidney, we generated inducible renal tubule–specific insulin receptor–KO mice and used high-fat feeding and mineralocorticoids to model obesity and insulin resistance. Insulin receptor deletion did not alter blood pressure or sodium excretion in mice on a high-fat diet alone, but it mildly attenuated the increase in blood pressure with mineralocorticoid supplementation. Under these conditions, KO mice developed profound glucosuria. Insulin receptor deletion significantly reduced SGLT2 expression and increased urinary glucose excretion and urine flow. These data demonstrate a direct role for insulin receptor–stimulated sodium and glucose transport and a functional interaction of insulin signaling with mineralocorticoids in vivo. These studies uncover a potential mechanistic link between preserved insulin sensitivity and renal glucose handling in obesity and insulin resistance.
Jonathan M. Nizar, Blythe D. Shepard, Vianna T. Vo, Vivek Bhalla
Sodium-glucose cotransporter 2 (SGLT2) inhibitors have pleiotropic properties beyond blood glucose–lowering effects and modify important nonglycemic pathways, leading to end-organ protection. SGLT2 inhibitors display renoprotective effects in diabetic kidney disease, which creates a rationale for testing the therapeutic potential of this drug class in nondiabetic chronic kidney disease. Here, we have shown that dapagliflozin provided glomerular protection in mice with protein-overload proteinuria induced by bovine serum albumin (BSA), to a similar extent as an ACE inhibitor used as standard therapy for comparison. Dapagliflozin limited proteinuria, glomerular lesions, and podocyte dysfunction and loss. We provide the observation that SGLT2 was expressed in podocytes and upregulated after BSA injections. Through in vitro studies with cultured podocytes loaded with albumin we have identified what we believe to be a novel mechanism of action for SGLT2 inhibitor that directly targets podocytes and relies on the maintenance of actin cytoskeleton architecture. Whether SGLT2 inhibitors represent a possible future therapeutic option for some patients with proteinuric glomerular disease who do not have as yet an effective treatment will require ad hoc clinical studies.
Paola Cassis, Monica Locatelli, Domenico Cerullo, Daniela Corna, Simona Buelli, Cristina Zanchi, Sebastian Villa, Marina Morigi, Giuseppe Remuzzi, Ariela Benigni, Carlamaria Zoja
Different nephron tubule segments perform distinct physiological functions, collectively acting as a blood filtration unit. Dysfunction of the proximal tubule segment can lead to Fanconi renotubular syndrome (FRTS), with major symptoms such as excess excretion of water, glucose, and phosphate in the urine. It has been shown that a mutation in HNF4A is associated with FRTS in humans and that Hnf4a is expressed specifically in proximal tubules in adult rat nephrons. However, little is known about the role of Hnf4a in nephrogenesis. Here, we found that Hnf4a is expressed in both presumptive and differentiated proximal tubules in the developing mouse kidney. We show that Hnf4a is required for the formation of differentiated proximal tubules but is dispensable for the formation of presumptive proximal tubules. Furthermore, we show that loss of Hnf4a decreased the expression of proximal tubule–specific genes. Adult Hnf4a mutant mice presented with FRTS-like symptoms, including polyuria, polydipsia, glycosuria, and phosphaturia. Analysis of the adult Hnf4a mutant kidney also showed proximal tubule dysgenesis and nephrocalcinosis. Our results demonstrate the critical role of Hnf4a in proximal tubule development and provide mechanistic insight into the etiology of FRTS.
Sierra S. Marable, Eunah Chung, Mike Adam, S. Steven Potter, Joo-Seop Park
BACKGROUND. The prevalence of chronic kidney disease (CKD) is increasing worldwide. The identification of factors contributing to its progression is important for designing preventive measures. Previous studies have suggested that chronically high vasopressin is deleterious to renal function. Here, we evaluated the association of plasma copeptin, a surrogate of vasopressin, with the incidence of CKD in the general population. METHODS. We studied 3 European cohorts: DESIR (n = 5,047; France), MDCS-CC (n = 3,643; Sweden), and PREVEND (n = 7,684; the Netherlands). Median follow-up was 8.5, 16.5, and 11.3 years, respectively. Pooled data were analyzed at an individual level for 4 endpoints during follow-up: incidence of stage 3 CKD (estimated glomerular filtration rate [eGFR] < 60 ml/min/1.73 m2); the KDIGO criterion “certain drop in eGFR”; rapid kidney function decline (eGFR slope steeper than –3 ml/min/1.73 m2/yr); and incidence of microalbuminuria. RESULTS. The upper tertile of plasma copeptin was significantly and independently associated with a 49% higher risk for stage 3 CKD (P < 0.0001); a 64% higher risk for kidney function decline, as defined by the KDIGO criterion (P < 0.0001); a 79% higher risk for rapid kidney function decline (P < 0.0001); and a 24% higher risk for microalbuminuria (P = 0.008). CONCLUSIONS. High copeptin levels are associated with the development and the progression of CKD in the general population. Intervention studies are needed to assess the potential beneficial effect on kidney health in the general population of reducing vasopressin secretion or action. FUNDING. INSERM and Danone Research Centre for Specialized Nutrition.
Ray El Boustany, Irina Tasevska, Esther Meijer, Lyanne M. Kieneker, Sofia Enhörning, Guillaume Lefèvre, Kamel Mohammedi, Michel Marre, Frédéric Fumeron, Beverley Balkau, Nadine Bouby, Lise Bankir, Stephan J.L. Bakker, Ronan Roussel, Olle Melander, Ron T. Gansevoort, Gilberto Velho
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