The contribution of histone crotonylation to tissue health and disease: focus on kidney health

Acute kidney injury (AKI) and chronic kidney disease (CKD) are the most severe consequences of kidney injury. They are interconnected syndromes as CKD predisposes to AKI and AKI may accelerate CKD progression. Despite their growing impact on the global burden of disease, there is no satisfactory treatment for AKI and current therapeutic approaches to CKD remain suboptimal. Recent research has focused on the therapeutic target potential of epigenetic regulation of gene expression, including non-coding RNAs and the covalent modifications of histones and DNA. Indeed, several drugs targeting histone modifications are in clinical use or undergoing clinical trials. Acyllysine histone modifications (e.g. methylation, acetylation, and crotonylation) have modulated experimental kidney injury. Most recently, increased histone lysine crotonylation (Kcr) was observed during experimental AKI and could be reproduced in cultured tubular cells exposed to inflammatory stress triggered by the cytokine TWEAK. The degree of kidney histone crotonylation was modulated by crotonate availability and crotonate supplementation protected from nephrotoxic AKI. We now review the functional relevance of histone crotonylation in kidney disease and other pathophysiological contexts, as well as the implications for the development of novel therapeutic approaches. These studies provide insights into the overall role of histone crotonylation in health and diseaseSources of support: FIS/FEDER funds (PI15/00298, CP14/00133, PI16/02057, PI16/01900, PI18/01386, PI19/00588, PI19/00815, DTS18/00032, ERA-PerMed-JTC2018 (KIDNEY ATTACK AC18/00064 and PERSTIGAN AC18/00071), ISCIII-RETIC REDinREN RD016/0009), Sociedad Española de Nefrología, FRIAT, Comunidad de Madrid en Biomedicina B2017/BMD- 3686 CIFRA2-CM. Salary support: ISCIII Miguel Servet and to AS and MS-N, ISCIII Sara Borrell to JM-M and Comunidad de Madrid (B2017/BMD-3686 CIFRA2-CM) to MF-B and DM-S

Molecular pathways driving omeprazole nephrotoxicity

Omeprazole, a proton pump inhibitor used to treat peptic ulcer and gastroesophageal reflux disease, has been associated to chronic kidney disease and acute interstitial nephritis. However, whether omeprazole is toxic to renal cells is unknown. Omeprazole has a lethal effect over some cancer cells, and cell death is a key process in kidney disease. Thus, we evaluated the potential lethal effect of omeprazole over tubular cells. Omeprazole induced dose-dependent cell death in human and murine proximal tubular cell lines and in human primary proximal tubular cell cultures. Increased cell death was observed at the high concentrations used in cancer cell studies and also at lower concentrations similar to those in peptic ulcer patient serum. Cell death induced by omeprazole had features of necrosis such as annexin V/7-AAD staining, LDH release, vacuolization and irregular chromatin condensation. Weak activation of caspase-3 was observed but inhibitors of caspases (zVAD), necroptosis (Necrostatin-1) or ferroptosis (Ferrostatin-1) did not prevent omeprazole-induced death. However, omeprazole promoted a strong oxidative stress response affecting mitochondria and lysosomes and the antioxidant N-acetyl-cysteine reduced oxidative stress and cell death. By contrast, iron overload increased cell death. An adaptive increase in the antiapoptotic protein BclxL failed to protect cells. In mice, parenteral omeprazole increased tubular cell death and the expression of NGAL and HO-1, markers of renal injury and oxidative stress, respectively. In conclusion, omeprazole nephrotoxicity may be related to induction of oxidative stress and renal tubular cell deathSupported by FIS CP12/03262, CP14/00133, PI16/02057, PI16/ 01900, PI18/01366, PI19/00588, PI19/00815, DTS18/00032, ERAPerMed-JTC2018 (KIDNEY ATTACK AC18/00064 and PERSTIGAN AC18/00071, ISCIII-RETIC REDinREN RD016/0009 FEDER funds, Sociedad Española de Nefrología, Fundacion Renal Iñigo Álvarez de Toledo (FRIAT), ISCIII Miguel Servet (ABS, MDS-N), ISCIII Sara Borrell (JMM-M), Comunidad de Madrid CIFRA2 B2017/BMD-3686 (MF-B and DM-S

The role of PGC-1α and mitochondrial biogenesis in kidney diseases

Chronic kidney disease (CKD) is one of the fastest growing causes of death worldwide, emphasizing the need to develop novel therapeutic approaches. CKD predisposes to acute kidney injury (AKI) and AKI favors CKD progression. Mitochondrial derangements are common features of both AKI and CKD and mitochondria-targeting therapies are under study as nephroprotective agents. PGC-1α is a master regulator of mitochondrial biogenesis and an attractive therapeutic target. Low PGC-1α levels and decreased transcription of its gene targets have been observed in both preclinical AKI (nephrotoxic, endotoxemia, and ischemia-reperfusion) and in experimental and human CKD, most notably diabetic nephropathy. In mice, PGC-1α deficiency was associated with subclinical CKD and predisposition to AKI while PGC-1α overexpression in tubular cells protected from AKI of diverse causes. Several therapeutic strategies may increase kidney PGC-1α activity and have been successfully tested in animal models. These include AMP-activated protein kinase (AMPK) activators, phosphodiesterase (PDE) inhibitors, and anti-TWEAK antibodies. In conclusion, low PGC-1α activity appears to be a common feature of AKI and CKD and recent characterization of nephroprotective approaches that increase PGC-1α activity may pave the way for nephroprotective strategies potentially effective in both AKI and CKD.Supported by ISCIII-FIS, FEDER funds, CP14/00133, PI16/02057, PI16/01900, PI18/01366, PI19/00588, PI19/00815, DTS18/00032, ERA-PerMed-JTC2018 (KIDNEY ATTACK AC18/00064 and PERSTIGAN AC18/00071, ISCIII-RETIC REDinREN RD016/0009, Sociedad Española de Nefrología, Fundacion Renal Iñigo Álvarez de Toledo (FRIAT), ISCIII Miguel Servet (A.B.S., M.D.S.-N.), ISCIII Sara Borrell (J.M.M.-M.), Comunidad de Madrid CIFRA2 B2017/BMD-3686 (M.F.-B. and D.M.-S.

Urinary cyclophilin A as marker of tubular cell death and kidney injury

Background: Despite the term acute kidney injury (AKI), clinical biomarkers for AKI re-flect function rather than injury and independent markers of injury are needed. Tubular cell death, including necroptotic cell death, is a key feature of AKI. Cyclophilin A (CypA) is an intracellular protein that has been reported to be released during necroptosis. We have now explored CypA as a potential marker for kidney injury in cultured tubular cells and in clinical settings of ischemia-reperfusion injury (IRI), characterized by limitations of current diagnostic criteria for AKI. Meth-ods: CypA was analyzed in cultured human and murine proximal tubular epithelial cells exposed to chemical hypoxia, hypoxia/reoxygenation (H/R) or other cell death (apoptosis, necroptosis, fer-roptosis) inducers. Urinary levels of CypA (uCypA) were analyzed in patients after nephron sparing surgery (NSS) in which the contralateral kidney is not disturbed and kidney grafts with initial function. Results: Intracellular CypA remained unchanged while supernatant CypA increased in parallel to cell death induction. uCypA levels were higher in NSS patients with renal artery clamping (that is, with NSS-IRI) than in no clamping (NSS-no IRI), and in kidney transplantation (KT) recipients (KT-IRI) even in the presence of preserved or improving kidney function, while this was not the case for urinary Neutrophil gelatinase-associated lipocalin (NGAL). Furthermore, higher uCypA levels in NSS patients were associated with longer surgery duration and the incidence of AKI increased from 10% when using serum creatinine (sCr) or urinary output criteria to 36% when using high uCypA levels in NNS clamping patients. Conclusions: CypA is released by kidney tubular cells during different forms of cell death, and uCypA increased during IRI-induced clinical kidney injury independently from kidney function parameters. Thus, uCypA is a potential bi-omarker of kidney injury, which is independent from decreased kidney functionResearch by the authors was funded by FIS/ FEDER funds (PI17/00257, PI18/01386, PI19/00588, PI19/00815, DTS18/00032, ERA-PerMed-JTC2018 (KIDNEY ATTACK AC18/00064 and PERSTIGAN AC18/00071, ISCIII-RETIC REDinREN RD016/0009), Sociedad Española de Nefrología, FRIAT, Comunidad de Madrid en Biomedicina B2017/BMD-3686 CIFRA2-CM. Salary support: ISCIII Miguel Servet to A.B.S., MICIN Ramon y Cajal to M.D.S.-N., REDinREN RD016/0009 to M.F.-B.,SENEFRO to D.M.-S. and Consejería de Educación, Juventud y Deporte (Comunidad de Madrid/FSE) to A.M.L.-

Epigenetic modifiers as potential therapeutic targets in diabetic kidney disease

Diabetic kidney disease is one of the fastest growing causes of death worldwide. Epigenetic regulators control gene expression and are potential therapeutic targets. There is functional interventional evidence for a role of DNA methylation and the histone post-translational modifications—histone methylation, acetylation and crotonylation—in the pathogenesis of kidney disease, including diabetic kidney disease. Readers of epigenetic marks, such as bromodomain and extra terminal (BET) proteins, are also therapeutic targets. Thus, the BD2 selective BET inhibitor apabetalone was the first epigenetic regulator to undergo phase-3 clinical trials in diabetic kidney disease with an endpoint of kidney function. The direct therapeutic modulation of epigenetic features is possible through pharmacological modulators of the specific enzymes involved and through the therapeutic use of the required substrates. Of further interest is the characterization of potential indirect effects of nephroprotective drugs on epigenetic regulation. Thus, SGLT2 inhibitors increase the circulating and tissue levels of β-hydroxybutyrate, a molecule that generates a specific histone modification, β-hydroxybutyrylation, which has been associated with the beneficial health effects of fasting. To what extent this impact on epigenetic regulation may underlie or contribute to the so-far unclear molecular mechanisms of cardio-and nephroprotection offered by SGLT2 inhibitors merits further in-depth studies.This research was funded by FIS/FEDER funds (PI15/00298, CP14/00133, PI16/01900, PI18/01386, PI18/0133, PI19/00588, PI19/00815, DTS18/00032, ERA-PerMed-JTC2018 (KIDNEY ATTACK AC18/00064 and PERSTIGAN AC18/00071), ISCIII-RETIC REDinREN RD016/0009), Sociedad Española de Nefrología, FRIAT, Comunidad de Madrid en Biomedicina B2017/BMD- 3686 CIFRA2-CM. Salary support: ISCIII Miguel Servet to ABS and MDS-N, ISCIII Sara Borrell to JM-MM, REDinREN RD016/0009 to MF-B, and MICIU to JG-M

RICORS2040 : The need for collaborative research in chronic kidney disease

Chronic kidney disease (CKD) is a silent and poorly known killer. The current concept of CKD is relatively young and uptake by the public, physicians and health authorities is not widespread. Physicians still confuse CKD with chronic kidney insufficiency or failure. For the wider public and health authorities, CKD evokes kidney replacement therapy (KRT). In Spain, the prevalence of KRT is 0.13%. Thus health authorities may consider CKD a non-issue: very few persons eventually need KRT and, for those in whom kidneys fail, the problem is 'solved' by dialysis or kidney transplantation. However, KRT is the tip of the iceberg in the burden of CKD. The main burden of CKD is accelerated ageing and premature death. The cut-off points for kidney function and kidney damage indexes that define CKD also mark an increased risk for all-cause premature death. CKD is the most prevalent risk factor for lethal coronavirus disease 2019 (COVID-19) and the factor that most increases the risk of death in COVID-19, after old age. Men and women undergoing KRT still have an annual mortality that is 10- to 100-fold higher than similar-age peers, and life expectancy is shortened by ~40 years for young persons on dialysis and by 15 years for young persons with a functioning kidney graft. CKD is expected to become the fifth greatest global cause of death by 2040 and the second greatest cause of death in Spain before the end of the century, a time when one in four Spaniards will have CKD. However, by 2022, CKD will become the only top-15 global predicted cause of death that is not supported by a dedicated well-funded Centres for Biomedical Research (CIBER) network structure in Spain. Realizing the underestimation of the CKD burden of disease by health authorities, the Decade of the Kidney initiative for 2020-2030 was launched by the American Association of Kidney Patients and the European Kidney Health Alliance. Leading Spanish kidney researchers grouped in the kidney collaborative research network Red de Investigación Renal have now applied for the Redes de Investigación Cooperativa Orientadas a Resultados en Salud (RICORS) call for collaborative research in Spain with the support of the Spanish Society of Nephrology, Federación Nacional de Asociaciones para la Lucha Contra las Enfermedades del Riñón and ONT: RICORS2040 aims to prevent the dire predictions for the global 2040 burden of CKD from becoming true

Los reguladores transcripcionales PGC-1(alfa) y RUNX1 en el fracaso renal agudo

Tesis Doctoral inédita leída en la Universidad Autónoma de Madrid, Facultad de Medicina, Departamento de Medicina. Fecha de Lectura: 27-05-2022Esta tesis tiene embargado el acceso al texto completo hasta el 27-11-2023El fracaso renal agudo (FRA) es un síndrome clínico caracterizado por una rápida pérdida de la función renal. El FRA no tiene tratamiento satisfactorio y la mortalidad es alta. Por ello, es necesaria la búsqueda de nuevas dianas terapéuticas. En esta tesis doctoral, hemos identificado mediante transcriptómica renal dos reguladores transcripcionales diferencialmente expresados en el FRA, PGC-1α y RUNX1, y hemos caracterizado su función en células tubulares cultivadas y durante el FRA experimental. PGC-1α (del inglés peroxisome proliferator-activated receptor γ coactivator-1α) es un coactivador transcripcional que regula la expresión de genes relacionados con el metabolismo y la biogénesis mitocondrial. Un análisis funcional de un array transcriptómico de riñones de ratones de genotipo salvaje con FRA nefrotóxico inducido por sobredosis de ácido fólico (AF-FRA) mostró que PGC-1α era el regulador con actividad transcripcional más reducida. Además, su expresión estaba reducida en biopsias de pacientes con FRA. Los ratones deficientes en PGC-1α (Pgc-1α-/-) tenían inflamación renal espontánea y daño renal subclínico. En el AF-FRA, la deficiencia de PGC-1α redujo la supervivencia, aumentó la gravedad del FRA y disminuyó la biogénesis y la masa mitocondrial. Además, los ratones Pgc-1α-/- con AF-FRA tenían una inflamación más acentuada que los de ratones de genotipo salvaje, con un defecto de la polarización de macrófagos desde el fenotipo M1 o proinflamatorio al fenotipo M2 o reparador. El silenciamiento de la expresión de PGC-1α en células tubulares proximales (MCTs) cultivadas favoreció la muerte celular y una respuesta proinflamatoria exacerbada. RUNX1 (del inglés Runt-related transcription factor 1) es un factor de transcripción implicado en la proliferación y diferenciación de múltiples linajes celulares, destacando sus funciones en la regulación de la hematopoyesis. La expresión renal de RUNX1 aumentó en dos modelos de FRA experimental, el AF-FRA y el FRA endotoxémico inducido por la administración de LPS (LPS-FRA), en biopsias de pacientes con FRA y en MCTs estimuladas con la citoquina proinflamatoria TWEAK o la endotoxina LPS. La inhibición de RUNX1 en MCTs con Ro5-3335 o con un ARN de interferencia específico mostró que RUNX1 modulaba la expresión de citoquinas inflamatorias inducida por TWEAK o LPS. En concreto, RUNX1 se unía directamente al promotor del gen Il-6 y aumentaba su expresión. p21 es un inhibidor de quinasas dependientes de ciclina que regula la parada del ciclo celular y que está sobrexpresado en el AF-FRA y el LPS-FRA. Tanto TWEAK como LPS inducían la expresión de p21 a través de RUNX1 en MCTs. La inhibición de RUNX1 in vivo con Ro5-3335 protegió del AF-FRA y del LPS-FRA, mejorando la función renal y reduciendo la muerte celular, la inflamación la parada del ciclo celular y disminuyendo la expresión de p21. En resumen, hemos identificado nuevos mecanismos de daño renal en el FRA que implican una menor actividad del regulador transcripcional PGC-1α y una mayor actividad de RUNX1, causando una disminución de la biogénesis mitocondrial, y un aumento de la inflamación y de la parada del ciclo celular. La traslación clínica de estos hallazgos vendrá de la mano de la identificación de aproximaciones terapéuticas que permitan mantener o aumentar la actividad renal de PGC-1α o inhibir RUNX1 de forma segura en humano

Tubular Mitochondrial Dysfunction, Oxidative Stress, and Progression of Chronic Kidney Disease

Acute kidney injury (AKI) and chronic kidney disease (CKD) are interconnected conditions, and CKD is projected to become the fifth leading global cause of death by 2040. New therapeutic approaches are needed. Mitochondrial dysfunction and oxidative stress have emerged as drivers of kidney injury in acute and chronic settings, promoting the AKI-to-CKD transition. In this work, we review the role of mitochondrial dysfunction and oxidative stress in AKI and CKD progression and discuss novel therapeutic approaches. Specifically, evidence for mitochondrial dysfunction in diverse models of AKI (nephrotoxicity, cytokine storm, and ischemia-reperfusion injury) and CKD (diabetic kidney disease, glomerulopathies) is discussed; the clinical implications of novel information on the key role of mitochondria-related transcriptional regulators peroxisome proliferator-activated receptor gamma coactivator 1-alpha, transcription factor EB (PGC-1α, TFEB), and carnitine palmitoyl-transferase 1A (CPT1A) in kidney disease are addressed; the current status of the clinical development of therapeutic approaches targeting mitochondria are updated; and barriers to the clinical development of mitochondria-targeted interventions are discussed, including the lack of clinical diagnostic tests that allow us to categorize the baseline renal mitochondrial dysfunction/mitochondrial oxidative stress and to monitor its response to therapeutic intervention. Finally, key milestones for further research are proposed

RIPK3 and kidney disease

Receptor interacting protein kinase 3 (RIPK3) is an intracellular kinase at the crossroads of cell death and inflammation. RIPK3 contains a RIP homotypic interaction motif (RHIM) domain which allows interactions with other RHIM-containing proteins and a kinase domain that allows phosphorylation of target proteins. RIPK3 may be activated through interaction with RHIM-containing proteins such as RIPK1, TRIF and DAI (ZBP1, DLM-1) or through RHIM-independent mechanisms in an alkaline intracellular pH. RIPK3 mediates necroptosis and promotes inflammation, independently of necroptosis, through either activation of NFκB or the inflammasome. There is in vivo preclinical evidence of the contribution of RIPK3 to both acute kidney injury (AKI) and chronic kidney disease (CKD) and to the AKI-to-CKD transition derived from RIPK3 deficient mice or the use of small molecule RIPK3 inhibitors. In these studies, RIPK3 targeting decreased inflammation but kidney injury improved only in some contexts. Clinical translation of these findings has been delayed by the potential of some small molecule inhibitors of RIPK3 kinase activity to trigger apoptotic cell death by inducing conformational changes of the protein. A better understanding of the conformational changes in RIPK3 that trigger apoptosis, dual RIPK3/RIPK1 inhibitors or repurposing of multiple kinase inhibitors such as dabrafenib may facilitate clinical development of the RIPK3 inhibition concept for diverse inflammatory diseases, including kidney diseases. Resumen: La proteína quinasa 3 que interactúa con el receptor (RIPK3) es una quinasa intracelular que se encuentra a medio camino entre la muerte celular y la inflamación. La RIPK3 contiene un dominio motivo de interacción homotípica de RIP (RHIM), que permite las interacciones con otras proteínas que contienen RHIM, y un dominio de quinasa que permite la fosforilación de las proteínas diana. La RIPK3 puede ser activada a través de la interacción con las proteínas que contienen RHIM tales como RIPK1, TRIF y DAI (ZBP1, DLM-1), o a través de mecanismos independientes de RHIM en un pH intracelular alcalino. La RIPK3 media en la necroptosis y promueve la inflamación, independientemente de la necroptosis, bien a través de la activación de NFκB, o del inflamasoma. Existe evidencia preclínica in vivo de la contribución de RIPK3 a la insuficiencia renal aguda (IRA) y la enfermedad renal crónica (ERC), así como a la transición IRA-ERC derivada de ratones con deficiencia de RIPK3 o del uso de pequeñas moléculas inhibidoras de RIPK3. En dichos estudios, el tener a RIPK3 como objetivo redujo la inflamación, pero la nefropatía mejoró solo en algunos contextos. La traducción clínica de estos hallazgos se ha demorado debido al potencial de ciertas pequeñas moléculas inhibidoras de la actividad de la quinasa RIPK3 para activar la muerte celular induciendo cambios conformacionales de la proteína. Comprender mejor los cambios conformacionales de RIPK3 activadores de la apoptosis, los inhibidores duales RIPK3/RIPK1 o la reconversión de múltiples inhibidores de la quinasa tales como dabrafenib podría facilitar el desarrollo clínico del concepto de la inhibición de RIPK3 para diversas enfermedades inflamatorias, incluyendo las enfermedades renales

The Urinary Level of Injury Biomarkers Is Not Univocally Reflective of the Extent of Toxic Renal Tubular Injury in Rats

Nephrotoxicity is a major cause of intrinsic acute kidney injury (AKI). Because renal tissue damage may occur independently of a reduction in glomerular filtration rate and of elevations in plasma creatinine concentration, so-called injury biomarkers have been proposed to form part of diagnostic criteria as reflective of tubular damage independently of renal function status. We studied whether the urinary level of NGAL, KIM-1, GM2AP, t-gelsolin, and REGIIIb informed on the extent of tubular damage in rat models of nephrotoxicity, regardless of the etiology, moment of observation, and underlying pathophysiology. At a time of overt AKI, urinary biomarkers were measured by Western blot or ELISA, and tubular necrosis was scored from histological specimens stained with hematoxylin and eosin. Correlation and regression studies revealed that only weak relations existed between biomarkers and tubular damage. Due to high interindividual variability in the extent of damage for any given biomarker level, urinary injury biomarkers did not necessarily reflect the extent of the underlying tissue injury in individual rats. We contended, in this work, that further pathophysiological contextualization is necessary to understand the diagnostic significance of injury biomarkers before they can be used for renal tubular damage severity stratification in the context of nephrotoxic and, in general, intrinsic AKI