Tweak/Fn14 system is involved in rhabdomyolysis-induced acute kidney injury

BACKGROUND

Rhabdomyolysis is a severe clinical syndrome associated to acute kidney injury (AKI) and chronic kidney disease (CKD). TWEAK/Fn14 signaling axis regulates renal inflammation and tubular cell death. However, the functional role of TWEAK/Fn14 in rhabdomyolysis remains unknown.

METHODS

Rhabdomyolysis was induced in wild-type, TWEAK- and Fn14-deficient mice or mice treated with TWEAK blocking antibody. Renal injury, inflammation, fibrosis and cell death were assessed. Additionally, we performed in vivo and in vitro studies to explore the possible signalling pathways involved in Fn14 regulation.

FINDINGS

Fn14 renal expression was increased in mice with rhabdomyolysis, correlating with decline of renal function. Mechanistically, myoglobin (Mb) induced Fn14 expression via ERK and p38 pathway, whereas Nrf2 activation diminished Mb-mediated Fn14 upregulation in cultured renal cells. TWEAK or Fn14 genetic depletion ameliorated rhabdomyolysis-associated loss of renal function, histological damage, tubular cell death, inflammation, and expression of both tubular and endothelial injury markers. Deficiency of TWEAK or Fn14 also decreased long-term renal inflammation and fibrosis in mice with rhabdomyolysis. Finally, pharmacological treatment with a blocking TWEAK antibody diminished the expression of acute renal injury markers and cell death and lessened residual kidney fibrosis and chronic inflammation in rhabdomyolysis.

INTERPRETATION

TWEAK/Fn14 axis participates in the pathogenesis of rhabdomyolysis-AKI and subsequent AKI-CKD transition. Blockade of this signaling pathway may represent a promising therapeutic strategy for reducing rhabdomyolysis-mediated renal injury.

FUNDING

Spanish Ministry of Science and Innovation, ISCIII and Junta de Andalucía.

Intravascular hemolysis triggers NAFLD characterized by a deregulation of lipid metabolism and lipophagy blockade

Intravascular hemolysis is a common feature of different clinical entities, including sickle cell disease and malaria. Chronic hemolytic disorders are associated with hepatic damage; however, it is unknown whether heme disturbs lipid metabolism and promotes liver steatosis, thereby favoring the progression to nonalcoholic fatty liver disease (NAFLD). Using an experimental model of acute intravascular hemolysis, we report here the presence of liver injury in association with microvesicular lipid droplet deposition. Hemolysis promoted serum hyperlipidemia and altered intrahepatic triglyceride fatty acid composition, with increments in oleic, palmitoleic, and palmitic acids. These findings were related to augmented expression of transporters involved in fatty acid uptake (CD36 and MSR1) and deregulation of LDL transport, as demonstrated by decreased levels of LDL receptor and increased PCSK9 expression. Hemolysis also upregulated hepatic enzymes associated with cholesterol biosynthesis (SREBP2, HMGC1, LCAT, SOAT1) and transcription factors regulating lipid metabolism (SREBP1). Increased LC3II/LC3I ratio and p62/SQSTM1 protein levels were reported in mice with intravascular hemolysis and hepatocytes stimulated with heme, indicating a blockade of lipophagy. In cultured hepatocytes, cell pretreatment with the autophagy inductor rapamycin diminished heme-mediated toxicity and accumulation of lipid droplets. In conclusion, intravascular hemolysis enhances liver damage by exacerbating lipid accumulation and blocking the lipophagy pathway, thereby promoting NAFLD. These new findings have a high translational potential as a novel NAFLD-promoting mechanism in individuals suffering from severe hemolysis episodes. © 2023 The Authors. The Journal of Pathology published by John Wiley & Sons Ltd on behalf of The Pathological Society of Great Britain and Ireland.

Indoxyl sulfate impairs erythropoiesis at BFU-E stage in chronic kidney disease

Chronic kidney disease (CKD) is a global health condition characterized by a progressive deterioration of kidney function. It is associated with high serum levels of uremic toxins (UT), such as Indoxyl Sulfate (IS), which may participate in the genesis of several uremic complications. Anemia is one of the major complications in CKD patients that contribute to cardiovascular disease, increase morbi-mortality, and is associated with a deterioration of kidney failure in these patients. Our study aimed to characterize the impact of IS on CKD-related erythropoiesis. Using cellular and pre-clinical models, we studied cellular and molecular effects of IS on the growth and differentiation of erythroid cells. First, we examined the effect of clinically relevant concentrations of IS (up to 250 μM) in the UT7/EPO cell line. IS at 250 μM increased apoptosis of UT7/EPO cells at 48 h compared to the control condition. We confirmed this apoptotic effect of IS in erythropoiesis in human primary CD34⁺ cells during the later stages of erythropoiesis. Then, in IS-treated human primary CD34⁺ cells and in a (5/6 Nx) mice model, a blockage at the burst-forming unit-erythroid (BFU-E) stage of erythropoiesis was also observed. Finally, IS deregulates a number of erythropoietic related genes such as GATA-1, Erythropoietin-Receptor (EPO-R), and β-globin. Our findings suggest that IS could affect cell viability and differentiation of erythroid progenitors by altering erythropoiesis and contributing to the development of anemia in CKD.

Role of Toll-like receptor 4 in intravascular hemolysis-mediated injury

Massive intravascular hemolysis is a common characteristic of several pathologies. It is associated with the release of large quantities of heme into the circulation, promoting injury in vulnerable organs, mainly kidney, liver, and spleen. Heme activates Toll-like receptor 4 (TLR4), a key regulator of the inflammatory response; however, the role of TLR4 in hemolysis and whether inhibition of this receptor may protect from heme-mediated injury are unknown. We induced intravascular hemolysis by injection of phenylhydrazine in wildtype and Tlr4-knockout mice. In this model, we analyzed physiological parameters, histological damage, inflammation and cell death in kidney, liver, and spleen. We also evaluated whether heme-mediated-inflammatory effects were prevented by TLR4 inhibition with the compound TAK-242, both in vivo and in vitro. Induction of massive hemolysis elicited acute kidney injury characterized by loss of renal function, morphological alterations of the tubular epithelium, cell death, and inflammation. These pathological effects were significantly ameliorated in the TLR4-deficient mice and in wildtype mice treated with TAK-242. In vitro studies showed that TAK-242 pretreatment reduced heme-mediated inflammation by inhibiting the TLR4/NF-κB (nuclear factor kappa B) axis. However, analysis in liver and spleen indicated that TLR4 deficiency did not protect against the toxic accumulation of heme in these organs. In conclusion, TLR4 is a key molecule involved in the renal inflammatory response triggered by massive intravascular hemolysis. TLR4 inhibition may be a potential therapeutic approach to prevent renal damage in patients suffering from hemolysis. © 2022 The Authors. The Journal of Pathology published by John Wiley & Sons Ltd on behalf of The Pathological Society of Great Britain and Ireland.

FC 037NEUTROPHILS PLAY A KEY ROLE IN THE INITIATION OF GLOMERULAR HEMATURIA IN A POSTINFECTIOUS IGAN EXPERIMENTAL MODEL

Background and Aims

Hematuria is a common finding in patients with IgA nephropathy (IgAN), occurring mainly after upper respiratory tract infections. Hematuria can lead to acute kidney injury and chronic loss of renal function in IgAN. However, the mechanisms involved in egression of erythrocytes from the glomerular capillaries into the urinary space are unknown. To answer this question, we developed an infection with Streptococcus pneumoniae (SP) in a humanized experimental IgAN model (α1KICD89tg mice) that resembles the pathological and clinical findings of disease (IgA1 and soluble CD89 mesangial deposits, complement activation, proteinuria and hematuria).

Method

α1KICD89tg mice (12 weeks old) received an intranasal instillation of SP (107 bacteria). Blood, urine and renal samples were obtained during 1 month after induction of respiratory infection. The presence of SP in lungs from these mice was confirmed by microbiological analysis. Hematuria was quantified in the urinary sediment and renal function was determined by biochemical analysis. Renal histological characteristics were evaluated by hematoxylin/eosin, masson's trichrome and PAS staining. IgA glomerular deposits, activation of complement system and infiltration of proinflammatory cells was examined by immunohistochemistry or immunofluorescence. Circulating leukocyte populations were studied on a hemocytometer. Renal inflammatory cytokines, metalloproteases, as well as markers of tubular and glomerular damage were determined in kidneys by RT-PCR and western-blot. To further validate the role of neutrophils in this pathological setting, we selective depleted these cells through a single injection of anti-Ly6G mAb (200 µg/kg i.p).

Results

SP-intranasal instillation in α1KICD89tg mice increased hematuria, microalbuminuria and proteinuria, peaking at 48h after induction of the respiratory infection. SP instillation caused disruption of the glomerular basement membrane, with decreased expression of the slit diaphragm proteins nephrin and synaptopodin, as well as higher glomerular accumulation of IgA and proteins of complement system (C3, MBL). Hematuria intensity was positively correlated with the presence of interstitial F4/80+ macrophages, matrix metalloproteinase 9 (MMP-9), inflammatory cytokines and chemokines (IL-1β, IL-6, TNF-α, CCL-2, CCL5 and CX3CL1/CX3CR1) as well as p65 NF-κB activation. Hematuria was negatively correlated with anti-inflammatory IL-10 mRNA expression, Factor H levels and collagen IV content. Notably, SP infection induced expression of the tubular injury markers N-GAL and KIM-1. Increased peripheral neutrophils levels were observed in the SP-infected α1KICD89tg mice. Mechanistically, anti-Ly6G-mediated neutrophil depletion reduced SP-mediated hematuria, proteinuria and albuminuria, prevented loss of synaptopodin and nephrin, decreased renal inflammation and MMP-9 expression in α1KICD89tg mice

Conclusion

In a humanized mouse model of IgAN, hematuria bouts following respiratory tract infections are caused by a neutrophil-mediated alteration of the glomerular filtration barrier (podocyte damage, complement deposits and loss of Collagen IV). These findings may help to unveil novel potential therapeutic approaches to combat one of the key elements in the progression of IgAN and related conditions.

Toll-Like Receptors in Acute Kidney Injury

Acute kidney injury (AKI) is an important health problem, affecting 13.3 million individuals/year. It is associated with increased mortality, mainly in low- and middle-income countries, where renal replacement therapy is limited. Moreover, survivors show adverse long-term outcomes, including increased risk of developing recurrent AKI bouts, cardiovascular events, and chronic kidney disease. However, there are no specific treatments to decrease the adverse consequences of AKI. Epidemiological and preclinical studies show the pathological role of inflammation in AKI, not only at the acute phase but also in the progression to chronic kidney disease. Toll-like receptors (TLRs) are key regulators of the inflammatory response and have been associated to many cellular processes activated during AKI. For that reason, a number of anti-inflammatory agents targeting TLRs have been analyzed in preclinical studies to decrease renal damage during AKI. In this review, we updated recent knowledge about the role of TLRs, mainly TLR4, in the initiation and development of AKI as well as novel compounds targeting these molecules to diminish kidney injury associated to this pathological condition.

Protective Role of Nrf2 in Renal Disease

Chronic kidney disease (CKD) is one of the fastest-growing causes of death and is predicted to become by 2040 the fifth global cause of death. CKD is characterized by increased oxidative stress and chronic inflammation. However, therapies to slow or prevent CKD progression remain an unmet need. Nrf2 (nuclear factor erythroid 2-related factor 2) is a transcription factor that plays a key role in protection against oxidative stress and regulation of the inflammatory response. Consequently, the use of compounds targeting Nrf2 has generated growing interest for nephrologists. Pre-clinical and clinical studies have demonstrated that Nrf2-inducing strategies prevent CKD progression and protect from acute kidney injury (AKI). In this article, we review current knowledge on the protective mechanisms mediated by Nrf2 against kidney injury, novel therapeutic strategies to induce Nrf2 activation, and the status of ongoing clinical trials targeting Nrf2 in renal diseases.

Podocyte and tubular involvement in AngioJet-induced kidney injury

The AngioJet technique combines localized thrombolysis and percutaneous mechanical thrombectomy (PMT). However, PMT may cause acute kidney injury (AKI), which has been ascribed to severe mechanical haemolysis, although no renal biopsies have been reported. We now report the first renal biopsy in a patient with AKI following PMT. There is histological evidence of haemoglobin (Hb)-induced tubular injury and podocyte stress characterized by intracellular Hb and staining for ferritin and hemo-oxygenase-1, suggestive of an adaptive response to oxidative stress. This confirms that Hb is involved in kidney cell injury and supports the existence of several different kidney cellular targets.

Nrf2 Plays a Protective Role Against Intravascular Hemolysis-Mediated Acute Kidney Injury

Massive intravascular hemolysis is associated with acute kidney injury (AKI). Nuclear factor erythroid-2-related factor 2 (Nrf2) plays a central role in the defense against oxidative stress by activating the expression of antioxidant proteins. We investigated the role of Nrf2 in intravascular hemolysis and whether Nrf2 activation protected against hemoglobin (Hb)/heme-mediated renal damage in vivo and in vitro. We observed renal Nrf2 activation in human hemolysis and in an experimental model of intravascular hemolysis promoted by phenylhydrazine intraperitoneal injection. In wild-type mice, Hb/heme released from intravascular hemolysis promoted AKI, resulting in decreased renal function, enhanced expression of tubular injury markers (KIM-1 and NGAL), oxidative and endoplasmic reticulum stress (ER), and cell death. These features were more severe in Nrf2-deficient mice, which showed decreased expression of Nrf2-related antioxidant enzymes, including heme oxygenase 1 (HO-1) and ferritin. Nrf2 activation with sulforaphane protected against Hb toxicity in mice and cultured tubular epithelial cells, ameliorating renal function and kidney injury and reducing cell stress and death. Nrf2 genotype or sulforaphane treatment did not influence the severity of hemolysis. In conclusion, our study identifies Nrf2 as a key molecule involved in protection against renal damage associated with hemolysis and opens novel therapeutic approaches to prevent renal damage in patients with severe hemolytic crisis. These findings provide new insights into novel aspects of Hb-mediated renal toxicity and may have important therapeutic implications for intravascular hemolysis-related diseases.

Curcumin reduces renal damage associated with rhabdomyolysis by decreasing ferroptosis-mediated cell death

Acute kidney injury is a common complication of rhabdomyolysis. A better understanding of this syndrome may be useful to identify novel therapeutic targets because there is no specific treatment so far. Ferroptosis is an iron-dependent form of regulated nonapoptotic cell death that is involved in renal injury. In this study, we investigated whether ferroptosis is associated with rhabdomyolysis-mediated renal damage, and we studied the therapeutic effect of curcumin, a powerful antioxidant with renoprotective properties. Induction of rhabdomyolysis in mice increased serum creatinine levels, endothelial damage, inflammatory chemokines, and cytokine expression, alteration of redox balance (increased lipid peroxidation and decreased antioxidant defenses), and tubular cell death. Treatment with curcumin initiated before or after rhabdomyolysis induction ameliorated all these pathologic and molecular alterations. Although apoptosis or receptor-interacting protein kinase (RIPK)3-mediated necroptosis were activated in rhabdomyolysis, our results suggest a key role of ferroptosis. Thus, treatment with ferrostatin 1, a ferroptosis inhibitor, improved renal function in glycerol-injected mice, whereas no beneficial effects were observed with the pan-caspase inhibitor carbobenzoxy-valyl-alanyl-aspartyl-(O-methyl)-fluoromethylketone or in RIPK3-deficient mice. In cultured renal tubular cells, myoglobin (Mb) induced ferroptosis-sensitive cell death that was also inhibited by curcumin. Mechanistic in vitro studies showed that curcumin reduced Mb-mediated inflammation and oxidative stress by inhibiting the TLR4/NF-κB axis and activating the cytoprotective enzyme heme oxygenase 1. Our findings are the first to demonstrate the involvement of ferroptosis in rhabdomyolysis-associated renal damage and its sensitivity to curcumin treatment. Therefore, curcumin may be a potential therapeutic approach for patients with this syndrome.-Guerrero-Hue, M., García-Caballero, C., Palomino-Antolín, A., Rubio-Navarro, A., Vázquez-Carballo, C., Herencia, C., Martín-Sanchez, D., Farré-Alins, V., Egea, J., Cannata, P., Praga, M., Ortiz, A., Egido, J., Sanz, A. B., Moreno, J. A. Curcumin reduces renal damage associated with rhabdomyolysis by decreasing ferroptosis-mediated cell death.

Photoreceptor preservation induced by intravitreal controlled delivery of GDNF and GDNF/melatonin in rhodopsin knockout mice

Purpose

To evaluate the potential of a poly(lactic-co-glycolic acid) (PLGA)-based slow release formulation of glial cell line-derived neurotrophic factor (GDNF) alone or in combination with melatonin to rescue photoreceptors in a mouse model of retinal degeneration.

Methods

GDNF and GDNF/melatonin-loaded PLGA microspheres (MSs) were prepared using a solid-in-oil-in-water emulsion solvent extraction-evaporation technique. A combination of PLGA and vitamin E (VitE) was used to create the microcarriers. The structure, particle size, encapsulation efficiency, and in vitro release profile of the microparticulate formulations were characterized. Microparticulate systems (non-loaded, GDNF, and GDNF/melatonin-loaded MSs) were administered intravitreally to 3-week-old rhodopsin knockout mice (rho (-/-); n=7). The functional neuroprotective effect was assessed with electroretinography at 6, 9, and 12 weeks old. The rescue of the structure was determined with photoreceptor quantification at 12 weeks (9 weeks after administration of MSs). Immunohistochemistry for photoreceptor, glial, and proliferative markers was also performed.

Results

The microspheres were able to deliver GDNF or to codeliver GDNF and melatonin in a sustained manner. Intravitreal injection of GDNF or GDNF/melatonin-loaded MSs led to partial functional and structural rescue of photoreceptors compared to blank microspheres or vehicle. No significant intraocular inflammatory reaction was observed after intravitreal injection of the microspheres.

Conclusions

A single intravitreal injection of GDNF or GDNF/melatonin-loaded microspheres in the PLGA/VitE combination promoted the rescue of the photoreceptors in rho (-/-) mice. These intraocular drug delivery systems enable the efficient codelivery of therapeutically active substances for the treatment of retinal diseases.

Podocytes are new cellular targets of haemoglobin-mediated renal damage

Recurrent and massive intravascular haemolysis induces proteinuria, glomerulosclerosis, and progressive impairment of renal function, suggesting podocyte injury. However, the effects of haemoglobin (Hb) on podocytes remain unexplored. Our results show that cultured human podocytes or podocytes isolated from murine glomeruli bound and endocytosed Hb through the megalin-cubilin receptor system, thus resulting in increased intracellular Hb catabolism, oxidative stress, activation of the intrinsic apoptosis pathway, and altered podocyte morphology, with decreased expression of the slit diaphragm proteins nephrin and synaptopodin. Hb uptake activated nuclear factor erythroid-2-related factor 2 (Nrf2) and induced expression of the Nrf2-related antioxidant proteins haem oxygenase-1 (HO-1) and ferritin. Nrf2 activation and Hb staining was observed in podocytes of mice with intravascular haemolysis. These mice developed proteinuria and showed podocyte injury, characterized by foot process effacement, decreased synaptopodin and nephrin expression, and podocyte apoptosis. These pathological effects were enhanced in Nrf2-deficient mice, whereas Nrf2 activation with sulphoraphane protected podocytes against Hb toxicity both in vivo and in vitro. Supporting the translational significance of our findings, we observed podocyte damage and podocytes stained for Hb, HO-1, ferritin and phosphorylated Nrf2 in renal sections and urinary sediments of patients with massive intravascular haemolysis, such as atypical haemolytic uraemic syndrome and paroxysmal nocturnal haemoglobinuria. In conclusion, podocytes take up Hb both in vitro and during intravascular haemolysis, promoting oxidative stress, podocyte dysfunction, and apoptosis. Nrf2 may be a potential therapeutic target to prevent loss of renal function in patients with intravascular haemolysis. Copyright © 2017 Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.