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

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

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

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

Targeting of regulated necrosis in kidney disease

The term acute tubular necrosis was thought to represent a misnomer derived from morphological studies of human necropsies and necrosis was thought to represent an unregulated passive form of cell death which was not amenable to therapeutic manipulation. Recent advances have improved our understanding of cell death in acute kidney injury. First, apoptosis results in cell loss, but does not trigger an inflammatory response. However, clumsy attempts at interfering with apoptosis (e.g. certain caspase inhibitors) may trigger necrosis and, thus, inflammation-mediated kidney injury. Second, and most revolutionary, the concept of regulated necrosis emerged. Several modalities of regulated necrosis were described, such as necroptosis, ferroptosis, pyroptosis and mitochondria permeability transition regulated necrosis. Similar to apoptosis, regulated necrosis is modulated by specific molecules that behave as therapeutic targets. Contrary to apoptosis, regulated necrosis may be extremely pro-inflammatory and, importantly for kidney transplantation, immunogenic. Furthermore, regulated necrosis may trigger synchronized necrosis, in which all cells within a given tubule die in a synchronized manner. We now review the different modalities of regulated necrosis, the evidence for a role in diverse forms of kidney injury and the new opportunities for therapeutic intervention. Resumen: La idea de que el término necrosis tubular aguda supone una denominación inapropiada se deriva de estudios morfológicos de necropsias humanas. La opinión generalizada ha sido que la necrosis representa una forma pasiva de muerte celular no regulada que no es susceptible de manipulación terapéutica. Los recientes avances han mejorado nuestra comprensión de la muerte celular en la lesión renal aguda. En primer lugar, la apoptosis origina una pérdida celular, pero no desencadena una respuesta inflamatoria. Sin embargo, los intentos rudimentarios de interferir en la apoptosis (p. ej., con determinados inhibidores de la caspasa) pueden desencadenar una necrosis y, por lo tanto, una lesión renal mediada por inflamación. En segundo lugar, y lo que es más revolucionario, ha surgido el concepto de necrosis regulada. Se han descrito varias modalidades de necrosis regulada como necroptosis, ferroptosis, piroptosis y necrosis regulada por transición de permeabilidad mitocondrial. De forma análoga a la apoptosis, la necrosis regulada se modula a través de moléculas específicas que actúan como dianas terapéuticas. Al contrario que la apoptosis, la necrosis regulada puede ser extremadamente proinflamatoria y, lo que es importante para el trasplante renal, inmunogénica. Además, la necrosis regulada puede desencadenar una necrosis sincronizada, en la que todas las células del interior de un túbulo concreto mueren de manera sincronizada. Revisaremos las diferentes modalidades de necrosis regulada, la evidencia de una función en las diversas formas de lesión renal y las nuevas oportunidades de intervención terapéutica. Keywords: Apoptosis, Ferroptosis, Necroptosis, Kidney, Acute kidney injury, Chronic kidney disease, Transplantation, Acute rejection, Delayed graft function, Palabras clave: Apoptosis, Ferroptosis, Necroptosis, Riñón, Lesión renal aguda, Enfermedad renal crónica, Trasplante, Rechazo agudo, Función retardada del injert