Fibroblast Growth Factor 23 and Klotho in AKI

The clinical efficacy of cGMP-specific sildenafil on mitochondrial biogenesis induction and renal damage in cats with acute on chronic kidney disease

BACKGROUND

Mitochondrial biogenesis (MB) induction has recently emerged as potential therapeutic approaches in kidney pathology and the mitochondria-targeted therapies should be investigated to improve treatment of animals with kidney diseases. This study aimed to investigate the effects of MB induction with sildenafil citrate on the cGMP/NO pathway, glomerular filtration, and reduction of kidney damage and fibrosis (TGF-β/SMAD pathway) in cats with acute on chronic kidney disease (ACKD). Thirty-three cats were divided into the non-azotemic (healthy) group (n:8) and the ACKD group (n:25), comprising different breeds, sexes, and ages. Sildenafil citrate was administered to the non-azotemic and ACKD groups (2.5 mg/kg, PO, q12 hours) for 30 days. Serum and urine NO, MDA, NGAL, KIM-1, TGF-β1, IL-18, FGF 23, PGC-1α and cGMP concentrations were measured.

RESULTS

Serum cGMP concentrations increased (P < 0.05) in the non-azotemic group during the 2nd (median 475.99 pmol/mL) and 3rd (median 405.01 pmol/mL) weeks of the study, whereas serum cGMP concentrations decreased in the ACKD group during the 4th(median 188.52 pmol/mL) week compared to the non-azotemic group (P < 0.05). No difference was observed in serum biomarker concentrations except NO, which increased in the 4th week (P < 0.05). The urinary concentrations of NO, MDA, PGC-1α, TGF-β1, NGAL, KIM-1, IL-18, and FGF 23 in the ACKD group were found to be higher compared to those in the non-azotemic group from the 1st to the 4th week (P  < 0.05). In the ACKD group, the urine PGC-1α concentration in the 2nd (median 6.10 ng/mL) week was lower compared to that in the 0 and 1st (median 7.65 and 7.21 ng/mL, respectively) week, and the NO concentration in the 3rd (median 28.94 µmol/mL) week was lower than that in the 0th (median 37.43 µmol/mL) week (P < 0.05).

CONCLUSIONS

While sildenafil citrate has been determined to induce a low level of MB and to have a beneficial effect on glomerular filtration, it is observed to be ineffective in mitigating renal damage and fibrosis via the TGF-β/SMAD pathway in cats with ACKD.

An overview of circulating and urinary biomarkers capable of predicting the transition of acute kidney injury to chronic kidney disease

INTRODUCTION

Acute kidney injury (AKI) defined by a substantial decrease in kidney function within hours to days and is often irreversible with higher risk to chronic kidney disease (CKD) transition.

AREAS COVERED

The authors discuss the diagnostic and predictive utilities of serum and urinary biomarkers on AKI and on the risk of AKI-to-CKD progression. The authors focus on the relevant literature covering evidence of circulating and urinary biomarkers' capability to predict the transition of AKI to CKD.

EXPERT OPINION

Based on the different modalities of serum and urinary biomarkers, multiple biomarker panel seems to be potentially useful to distinguish between various types of AKI, to detect the severity and the risk of AKI progression, to predict the clinical outcome and evaluate response to the therapy. Serum/urinary neutrophil gelatinase-associated lipocalin (NGAL), serum/urinary uromodulin, serum extracellular high mobility group box-1 (HMGB-1), serum cystatin C and urinary liver-type fatty acid-binding protein (L-FABP) were the most effective in the prediction of AKI-to-CKD transition regardless of etiology and the presence of critical state in patients. The current clinical evidence on the risk assessments of AKI progression is mainly based on the utility of combination of functional, injury and stress biomarkers, mainly NGAL, L-FABP, HMGB-1 and cystatin C.

From premature birth to premature kidney disease: does accelerated aging play a role?

As the limits of fetal viability have increased over the past 30 years, there has been a growing body of evidence supporting the idea that chronic disease should be taken into greater consideration in addition to survival after preterm birth. Accumulating evidence also suggests there is early onset of biologic aging after preterm birth. Similarly, chronic kidney disease (CKD) is also associated with a phenotype of advanced biologic age which exceeds chronologic age. Yet, significant knowledge gaps remain regarding the link between premature biologic age after preterm birth and kidney disease. This review summarizes the four broad pillars of aging, the evidence of premature aging following preterm birth, and in the setting of CKD. The aim is to provide additional plausible biologic mechanisms to explore the link between preterm birth and CKD. There is a need for more research to further elucidate the biologic mechanisms of the premature aging paradigm and kidney disease after preterm birth. Given the emerging research on therapies for premature aging, this paradigm could create pathways for prevention of advanced CKD.

Preoperative inflammatory biomarkers reveal renal involvement in postsurgical mortality in hip fracture patients: an exploratory study

Background

Hip fractures in frail patients result in excess mortality not accounted for by age or comorbidities. The mechanisms behind the high risk of mortality remain undetermined but are hypothesized to be related to the inflammatory status of frail patients.

Methods

In a prospective observational exploratory cohort study of hospitalized frail hip fracture patients, 92 inflammatory markers were tested in pre-operative serum samples and markers were tested against 6-month survival post-hip fracture surgery and incidence of acute kidney injury (AKI). After correcting for multiple testing, adjustments for comorbidities and demographics were performed on the statistically significant markers.

Results

Of the 92 markers tested, circulating levels of fibroblast growth factor 23 (FGF-23) and interleukin-15 receptor alpha (IL15RA), both involved in renal disease, were significantly correlated with 6-month mortality (27.5% overall) after correcting for multiple testing. The incidence of postoperative AKI (25.4%) was strongly associated with 6-month mortality, odds ratio = 10.57; 95% CI [2.76-40.51], and with both markers plus estimated glomerular filtration rate (eGFR)- cystatin C (CYSC) but not eGFR-CRE. The effect of these markers on mortality was significantly mediated by their effect on postoperative AKI.

Conclusion

High postoperative mortality in frail hip fracture patients is highly correlated with preoperative biomarkers of renal function in this pilot study. The effect of preoperative circulating levels of FGF-23, IL15RA, and eGFR-CYSC on 6-month mortality is in part mediated by their effect on postoperative AKI. Creatinine-derived preoperative renal function measures were very poorly correlated with postoperative outcomes in this group.

ERRγ-inducible FGF23 promotes alcoholic liver injury through enhancing CYP2E1 mediated hepatic oxidative stress

Fibroblast growth factor 23 (FGF23) is a member of endocrine FGF family, along with FGF15/19 and FGF21. Recent reports showed that under pathological conditions, liver produces FGF23, although the role of hepatic FGF23 remains nebulous. Here, we investigated the role of hepatic FGF23 in alcoholic liver disease (ALD) and delineated the underlying molecular mechanism. FGF23 expression was compared in livers from alcoholic hepatitis patients and healthy controls. The role of FGF23 was examined in hepatocyte-specific knock-out (LKO) mice of cannabinoid receptor type 1 (CB1R), estrogen related receptor γ (ERRγ), or FGF23. Animals were fed with an alcohol-containing liquid diet alone or in combination with ERRγ inverse agonist. FGF23 is mainly expressed in hepatocytes in the human liver, and it is upregulated in ALD patients. In mice, chronic alcohol feeding leads to liver damage and induced FGF23 in liver, but not in other organs. FGF23 is transcriptionally regulated by ERRγ in response to alcohol-mediated activation of the CB1R. Alcohol induced upregulation of hepatic FGF23 and plasma FGF23 levels is lost in ERRγ-LKO mice, and an inverse agonist mediated inhibition of ERRγ transactivation significantly improved alcoholic liver damage. Moreover, hepatic CYP2E1 induction in response to alcohol is FGF23 dependent. In line, FGF23-LKO mice display decreased hepatic CYP2E1 expression and improved ALD through reduced hepatocyte apoptosis and oxidative stress. We recognized CBIR-ERRγ-FGF23 axis in facilitating ALD pathology through hepatic CYP2E1 induction. Thus, we propose FGF23 as a potential therapeutic target to treat ALD.

Bone and bone derived factors in kidney disease

Purpose of review: Mineral and bone disorder (MBD) is a prevalent complication in chronic kidney disease (CKD), significantly impacting overall health with multifaceted implications including fractures, cardiovascular events, and mortality. Despite its pervasive nature, effective treatments for CKD-MBD are lacking, emphasizing the urgency to advance understanding and therapeutic interventions. Bone metabolism intricacies, influenced by factors like 1,25 dihydroxy vitamin D, parathyroid hormone (PTH), and fibroblast growth factor 23 (FGF23), along with intrinsic osseous mechanisms, play pivotal roles in CKD. Skeletal abnormalities precede hormonal changes, persisting even with normalized systemic mineral parameters, necessitating a comprehensive approach to address both aspects. Recent findings: In this review, we explore novel pathways involved in the regulation of systemic mineral bone disease factors, specifically examining anemia, inflammation, and metabolic pathways. Special emphasis is placed on internal bone mechanisms, such as hepatocyte nuclear factor 4α, transforming growth factor-β1, and sclerostin, which play crucial roles in the progression of renal osteodystrophy. Summary: Despite advancements, effective treatments addressing CKD-MBD morbidity and mortality are lacking, necessitating ongoing research for novel therapeutic targets.

Acute Kidney Injury and Subsequent Cardiovascular Disease: Epidemiology, Pathophysiology, and Treatment

Cardiovascular disease poses a significant threat to individuals with kidney disease, including those affected by acute kidney injury (AKI). In the short term, AKI has several physiological consequences that can impact the cardiovascular system. These include fluid and sodium overload, activation of the renin-angiotensin-aldosterone system and sympathetic nervous system, and inflammation along with metabolic complications of AKI (acidosis, electrolyte imbalance, buildup of uremic toxins). Recent studies highlight the role of AKI in elevating long-term risks of hypertension, thromboembolism, stroke, and major adverse cardiovascular events, though some of this increased risk may be due to the impact of AKI on the course of chronic kidney disease. Current management strategies involve avoiding nephrotoxic agents, optimizing hemodynamics and fluid balance, and considering renin-angiotensin-aldosterone system inhibition or sodium-glucose cotransporter 2 inhibitors. However, future research is imperative to advance preventive and therapeutic strategies for cardiovascular complications in AKI. This review explores the existing knowledge on the cardiovascular consequences of AKI, delving into epidemiology, pathophysiology, and treatment of various cardiovascular complications following AKI.

Interorgan communication networks in the kidney-lung axis

The homeostasis and health of an organism depend on the coordinated interaction of specialized organs, which is regulated by interorgan communication networks of circulating soluble molecules and neuronal connections. Many diseases that seemingly affect one primary organ are really multiorgan diseases, with substantial secondary remote organ complications that underlie a large part of their morbidity and mortality. Acute kidney injury (AKI) frequently occurs in critically ill patients with multiorgan failure and is associated with high mortality, particularly when it occurs together with respiratory failure. Inflammatory lung lesions in patients with kidney failure that could be distinguished from pulmonary oedema due to volume overload were first reported in the 1930s, but have been largely overlooked in clinical settings. A series of studies over the past two decades have elucidated acute and chronic kidney-lung and lung-kidney interorgan communication networks involving various circulating inflammatory cytokines and chemokines, metabolites, uraemic toxins, immune cells and neuro-immune pathways. Further investigations are warranted to understand these clinical entities of high morbidity and mortality, and to develop effective treatments.

Exogenous Klotho Extends Survival in COVID-19 Model Mice

A striking feature of COVID-19 disease is the broad spectrum of risk factors associated with case severity, as well as the diversity of clinical manifestations. While no central agent has been able to explain the pathogenesis of SARS-CoV-2 infection, the factors that most robustly correlate with severity are risk factors linked to aging. Low serum levels of Klotho, an anti-aging protein, strongly correlate with the pathogenesis of the same risk factors and manifestations of conditions similar to those expressed in severe COVID-19 cases. The current manuscript presents original research on the effects of the exogenous application of Klotho, an anti-aging protein, in COVID-19 model mice. Klotho supplementation resulted in a statistically significant survival benefit in parametric and non-parametric models. Further research is required to elucidate the mechanistic role Klotho plays in COVID-19 pathogenesis as well as the possible modulation SARS-CoV-2 may have on the biological aging process.

A Combined Biomarker That Includes Plasma Fibroblast Growth Factor 23, Erythropoietin, and Klotho Predicts Short- and Long-Term Morbimortality and Development of Chronic Kidney Disease in Critical Care Patients with Sepsis: A Prospective Cohort

Acute Kidney Injury (AKI) is a frequent complication in intensive care unit (ICU) patients that increases mortality and chronic kidney disease (CKD) development. AKI is associated with elevated plasma fibroblast growth factor 23 (FGF23), which can be modulated by erythropoietin (EPO) and Klotho. We aimed to evaluate whether a combined biomarker that includes these molecules predicted short-/long-term outcomes. We performed a prospective cohort of ICU patients with sepsis and previously normal renal function. They were followed during their inpatient stay and for one year after admission. We measured plasma FGF23, EPO, and Klotho levels at admission and calculated a combined biomarker (FEK). A total of 164 patients were recruited. Of these, 50 (30.5%) had AKI at admission, and 55 (33.5%) developed AKI within 48 h. Patients with AKI at admission and those who developed AKI within 48 h had 12- and 5-fold higher FEK values than non-AKI patients, respectively. Additionally, patients with higher FEK values had increased 1-year mortality (41.9% vs. 18.6%, p = 0.003) and CKD progression (26.2% vs. 8.3%, p = 0.023). Our data suggest that the FEK indicator predicts the risk of AKI, short-/long-term mortality, and CKD progression in ICU patients with sepsis. This new indicator can improve clinical outcome prediction and guide early therapeutic strategies.

Fibroblast Growth Factor 23 and Muscle Wasting: A Metabolic Point of View

Protein energy wasting (PEW), mostly characterized by decreased body stores of protein and energy sources, particularly in the skeletal muscle compartment, is highly prevalent in patients with moderate to advanced chronic kidney disease (CKD). Fibroblast growth factor 23 (FGF23) is an endocrine hormone secreted from bone and has systemic actions on skeletal muscle. In CKD, FGF23 is elevated and its coreceptor α-klotho is suppressed. Multiple lines of evidence suggest that FGF23 is interconnected with various mechanisms of skeletal muscle wasting in CKD, including systemic and local inflammation, exaggerated oxidative stress, insulin resistance (IR), and abnormalities in adipocytokine metabolism. Investigation of metabolic actions of FGF23 on muscle tissue could provide new insights into metabolic and nutritional abnormalities observed in patients with CKD.

α-Klotho: An Early Risk-Predictive Biomarker for Acute Kidney Injury in Patients with Acute Myocardial Infarction

Background

Acute kidney injury (AKI) was a common and serious complication in patients with acute myocardial infarction (AMI). Novel biomarkers and therapies were deficient and imperative for AKI's early diagnosis and therapy after AMI. α-Klotho was considered as an early biomarker and potential therapy for AKI recently. Previous studies reported that the expression of α-Klotho was decreased in AKI rodents, and supplement of α-Klotho alleviated kidney injury. Nevertheless, its effect has not been studied in patients presenting with AMI.

Methods

A total of 155 consecutive diagnosed with AMI at emergency department whose eGFR >60 ml/min ∗ 1.73 m2 were enrolled in this prospective observational cohort study which conducted between May 2016 and April 2019 in Peking University People's Hospital. AKI was defined according to the KDIGO criteria in 2012. At admission, the clinical data of patients were collected and serum α-Klotho was tested by ELISA. The relationship between α-Klotho, serum creatinine, eGFR, systolic pressure, BNP, LVEF, and Hgb of AKI were analyzed and their discrimination performances were compared. The association variables were calculated (adjusted odds ratio) with a confidence interval (CI) of 95% by binary logistic regression. And, we followed up the incidence of CKD and rehospitalization after patients' discharge in one year. Our study was approved by the ethics committee (no. 2016PHB042-01).

Results

AKI incidence was 17.4% (27/155) during hospitalization. Compared to patients without AKI, the AKI group had obviously higher mortality and was more female and had higher incidence of chronic kidney disease, worse cardiac function, more cardiac complications, larger doses of diuretics, and less use of angiotensin-converting enzyme inhibitors/angiotensin receptor blocker. By contrary to previous animal experiments, we found serum α-Klotho levels were increased significantly in AKI patients (740.2 ± 306.8 vs. 419.0 ± 272.6 pg/mL, p < 0.001). And, the areas under the receiver operating curves indicated serum α-Klotho levels had a superior discriminative power for predicting AKI after AMI compared with other risk factors (0.792, 95% CI, 0.706-0.878, p < 0.001). Meanwhile, logistic regression model indicates extensive anterior myocardial infarction, Killip classification ≥2 grade, α-Klotho ≥516.9 pg/mL, eGFR (decrease per 10 ml/min ∗ 1.73 m2), Hgb, and nonuse of ACEI/ARB were the risk factors of AKI after AMI. Moreover, one-year follow-up presented AMI patients developed CKD had higher α-Klotho levels (739.7 ± 315.2 vs. 443.8 ± 292.5 pg/mL, p = 0.001), but no significant difference in rehospitalization. And, patients with α-Klotho ≥516.9 pg/ml was 6.699 times more likely to develop CKD than those with α-Klotho <516.9 pg/ml (relative risk 6.699, 95% CI 1.631-27.519, p = 0.007).

Conclusion

Compared with traditional cardiac and renal biomarkers, serum α-Klotho could be a more appropriate predict biomarker for AKI after AMI in patients' eGFR >60 ml/min ∗ 1.73 m2. Higher α-Klotho levels are related to the development of AKI during hospitalization and suggest a higher prevalence of CKD after discharge. By contrary to animal experiments, whether the increased expression of α-Klotho could be a protective factor secreted by AKI after AMI, is remained to be further studied.

FGF23 functions and disease

The main function of fibroblast growth factor 23 (FGF23) is the regulation of phosphate metabolism through its action on the sodium-dependent phosphate cotransporters in the proximal renal tubules. Additionally, FGF23 interacts with vitamin D and parathyroid hormone in a complex metabolic pathway whose detailed mechanisms are still not clear in human physiology and disease. More recently, research has also focused on the understanding of mechanisms of FGF23 action on organs and system other than the kidneys and bone, as well as on its interaction with other metabolic pathways. Collectively, the new evidence are successfully used for the clinical evaluation and management of FGF23-related disorders, for which new therapies with many potential applications are now available.

Klotho restoration via ACE2 activation: A potential therapeutic strategy against acute kidney injury-diabetes comorbidity

Acute kidney injury (AKI) is a collection of clinical syndromes with persistent increases in morbidity and mortality rates. Hyperglycemia is a risk factor for AKI development. Renin-angiotensin-aldosterone system (RAS) disequilibrium and Klotho downregulation also play a pivotal role in the pathogenesis of AKI. Moreover, the relationship between Klotho and ACE2 (a component of non-conventional RAS) regulation in AKI remains an unexplored area of research. Hence, in this study, we investigated ACE2 and Klotho regulation in AKI using ischemic Wistar rats and NRK52E cells under normal and hyperglycemic conditions. Our findings suggested that hyperglycemia exacerbates renal ischemia-reperfusion injury (IRI)/hypoxia-reperfusion injury (HRI) induced AKI. Systemic and renal Klotho deficiency is a novel hallmark of AKI. Additionally, ACE2 is a protective component of the RAS, and its inhibition/deficiency leads to inflammation, apoptosis, Klotho downregulation, and thus AKI development. However, ACE2 activation resulted in the amelioration of AKI. Importantly, ACE2 plays an important role in Klotho upregulation, which might act as an intermediate for ACE2-mediated reno-protection. In conclusion, ACE2 activator i.e. DIZE restored endogenous ACE2-Ang-(1-7)-Klotho level, inhibited apoptosis and inflammation, and ameliorates IRI/HRI induced AKI under diabetic and non-diabetic conditions. Hence, in future, targeting ACE2-Ang-(1-7)-Klotho axis may prove a novel therapeutic strategy against AKI, where further preclinical and clinical investigations are required to verify the clinical potential of this finding.

New developments in the biology of fibroblast growth factors

The fibroblast growth factor (FGF) family is composed of 18 secreted signaling proteins consisting of canonical FGFs and endocrine FGFs that activate four receptor tyrosine kinases (FGFRs 1-4) and four intracellular proteins (intracellular FGFs or iFGFs) that primarily function to regulate the activity of voltage-gated sodium channels and other molecules. The canonical FGFs, endocrine FGFs, and iFGFs have been reviewed extensively by us and others. In this review, we briefly summarize past reviews and then focus on new developments in the FGF field since our last review in 2015. Some of the highlights in the past 6 years include the use of optogenetic tools, viral vectors, and inducible transgenes to experimentally modulate FGF signaling, the clinical use of small molecule FGFR inhibitors, an expanded understanding of endocrine FGF signaling, functions for FGF signaling in stem cell pluripotency and differentiation, roles for FGF signaling in tissue homeostasis and regeneration, a continuing elaboration of mechanisms of FGF signaling in development, and an expanding appreciation of roles for FGF signaling in neuropsychiatric diseases. This article is categorized under: Cardiovascular Diseases > Molecular and Cellular Physiology Neurological Diseases > Molecular and Cellular Physiology Congenital Diseases > Stem Cells and Development Cancer > Stem Cells and Development.

The Role of Alterations in Alpha-Klotho and FGF-23 in Kidney Transplantation and Kidney Donation

Cardiovascular disease and mineral bone disorders are major contributors to morbidity and mortality among patients with chronic kidney disease and often persist after renal transplantation. Ongoing hormonal imbalances after kidney transplant (KT) are associated with loss of graft function and poor outcomes. Fibroblast growth factor 23 (FGF-23) and its co-receptor, α-Klotho, are key factors in the underlying mechanisms that integrate accelerated atherosclerosis, vascular calcification, mineral disorders, and osteodystrophy. On the other hand, kidney donation is also associated with endocrine and metabolic adaptations that include transient increases in circulating FGF-23 and decreases in α-Klotho levels. However, the long-term impact of these alterations and their clinical relevance have not yet been determined. This manuscript aims to review and summarize current data on the role of FGF-23 and α-Klotho in the endocrine response to KT and living kidney donation, and importantly, underscore specific areas of research that may enhance diagnostics and therapeutics in the growing population of KT recipients and kidney donors.

Interplay between mineral bone disorder and cardiac damage in acute kidney injury: from Ca2+ mishandling and preventive role of Klotho in mice to its potential mortality prediction in human

Biomarkers of mineral bone disorders (MBD) including phosphorus, fibroblast growth factor (FGF)-23 and Klotho are strongly altered in patients with acute kidney injury (AKI) who have high cardiac outcomes and mortality rates. However, the crosslink between MBD and cardiac damage after an AKI episode still remains unclear. We tested MBD and cardiac biomarkers in an experimental AKI model after 24 or 72 hours of folic acid injection and we analyzed structural cardiac remodeling, intracellular calcium (Ca²⁺) dynamics in cardiomyocytes and cardiac rhythm. AKI mice presented high levels of FGF-23, phosphorus and cardiac troponin T and exhibited a cardiac hypertrophy phenotype accompanied by an increase in systolic Ca²⁺ release 24 hours after AKI. Ca²⁺ transients and contractile dysfunction were reduced 72 hours after AKI while diastolic sarcoplasmic reticulum Ca²⁺ leak, pro-arrhythmogenic Ca²⁺ events and ventricular arrhythmias were increased. These cardiac events were linked to the activation of the calcium/calmodulin-dependent kinase II pathway through the increased phosphorylation of ryanodine receptors and phospholamban specific sites after AKI. Cardiac hypertrophy and the altered intracellular Ca²⁺ dynamics were prevented in transgenic mice overexpressing Klotho after AKI induction. In a translational retrospective longitudinal clinical study, we determined that combining FGF-23 and phosphorus with cardiac troponin T levels achieved a better prediction of mortality in AKI patients at hospital admission. Thus, monitoring MBD and cardiac damage biomarkers could be crucial to prevent mortality in AKI patients. In this setting, Klotho might be considered as a new cardioprotective therapeutic tool to prevent deleterious cardiac events in AKI conditions.

Serum cystatin C, kidney injury molecule-1, neutrophil gelatinase-associated lipocalin, klotho and fibroblast growth factor-23 in the early prediction of acute kidney injury associated with sepsis in a Chinese emergency cohort study

Background

Acute kidney injury (AKI) is a common and critical complication of sepsis, and is associated with unacceptable morbidity and mortality. Current diagnostic criteria for AKI was insensitive for early detection. Novel biomarkers including cystatin C, kidney injury molecule-1 (KIM-1), neutrophil gelatinase-associated lipocalin (NGAL), klotho and fibroblast growth factor-23 (FGF-23) can predict AKI earlier and allow immediate interventions. We aimed to determine the diagnostic performance of these biomarkers for detecting AKI in sepsis patients.

Methods

This prospective observational study was conducted between May 2018 and November 2020, enrolling 162 sepsis patients eventually. The AKI was defined in accordance with 2012 KDIGO criteria and we divided patients into non-AKI (n = 102) and AKI (n = 60) groups. Serum levels of several AKI biomarkers were detected by ELISA. The relationship between biomarker levels on admission of AKI was analyzed and discrimination performances comparison were performed.

Results

AKI incidence was up to 37.0% (60/162) during hospitalization. Compared with non-AKI group, both serum cystatin C, KIM-1, NGAL and FGF-23 were significantly elevated at admission in septic AKI patients. The areas under the receiver operating curves demonstrated that serum cystatin C had modest discriminative powers for predicting AKI after sepsis, and cystatin C combined with serum creatinine in the prediction of septic AKI increased the diagnostic sensitivity prominently.

Conclusion

Serum cystatin C, KIM-1, NGAL and FGF-23 levels were both increased in septic AKI patients. Our study provided reliable evidence that cystatin C solely and combined with serum creatinine may accurately and sensitively predict septic AKI of patients on admission.

S-Klotho level and physiological markers of cardiometabolic risk in healthy adult men

S-Klotho is perceived as a biomarker of healthy aging that has been shown to be inversely associated with cardiometabolic risk in elderly individuals. The aim of this study was to test if s-Klotho level is associated with cardiometabolic risk markers in younger healthy men in order to verify the possible role of s-Klotho level as an early marker of cardiometabolic risk. A cross-sectional study was conducted among 186 healthy men (M_age=35.33, SD_age=3.47) from a Western urban population. Serum basal levels of s-Klotho, lipid profile, homocysteine, glycemia markers, C-reactive protein, liver transaminases and creatinine were evaluated. Also, blood pressure was measured and cardiometabolic risk score and homeostatic model assessment for insulin resistance (HOMA-IR) were calculated. Testosterone and cortisol levels, self-reported psychological stress, physical activity, smoking in the past, alcohol use and body adiposity were controlled for. We found no relationship between levels of s-Klotho and physiological markers of cardiometabolic risk in the studied population. The results were similar when controlled for adiposity, testosterone level, physical activity, alcohol use and smoking in the past. We suggest that s-Klotho level is not an early marker of cardiometabolic risk in younger middle-aged healthy men.

Calpain Inhibitor Calpeptin Alleviates Ischemia/Reperfusion-Induced Acute Kidney Injury via Suppressing AIM2 Inflammasome and Upregulating Klotho Protein

Renal ischemia/reperfusion injury is a major contributor of acute kidney injury (AKI), leading to renal cell necrosis, apoptosis, and inflammation. Calpains, a family of Ca²⁺-dependent cysteine proteases, play a pivotal role in the pathogenesis of renal diseases. Several studies have reported calpain inhibitors showing remarkable reno-protective effects against proteinuria and α-klotho deficiency-induced renal aging symptoms, particularly against glomerulus injury. However, little is known about the role of the calpain inhibitor calpeptin in acute kidney injury. The present study aims to investigate the potential mechanism of downregulation of Calpain 1 and 2 activity by calpeptin in the ischemia/reperfusion (IR)-induced AKI model. Firstly, we observed that the contents of Calpain 1 and 2 were significantly increased in the renal biopsy of clinical AKI patients, especially in the diseased tubules space. To investigate the impacts of calpain activity inhibition, we further pretreated with calpeptin in both the IR mouse model and in the HK-2 cells hypoxia model. We found that the calpain inhibitor calpeptin improved renal functional deterioration, attenuated pathological structure damage, and decreased tubular cell apoptosis in the IR injury-induced AKI mice model. Mechanistically, calpeptin significantly suppressed the AIM2 (absent in melanoma 2) and NLRP3 (NOD-like receptor protein 3) inflammasome signaling pathways and increased Klotho protein levels. Furthermore, immunofluorescence assays demonstrated that the application of calpeptin effectively inhibited Calpain 1 activation and gasdermin D (GSDMD) cleavage in the renal tubules of IR mice. Taken together, our both in vivo and in vitro experiments suggest that calpeptin conveyed reno-protection in AKI might be mediated by the inhibition of AIM2 inflammasome activation and upregulation of Klotho protein. As such, we provide new evidence that Calpain 1 and 2 activation may be closely associated with the pathogenesis of clinical AKI. The calpain-mediated AIM2 inflammasome signaling pathway and distinct interaction between calpain and Klotho may provide a potential novel preventative and therapeutic target for acute kidney injury.

Interorgan crosstalk mechanisms in disease: the case of acute kidney injury-induced remote lung injury

Homeostasis and health of multicellular organisms with multiple organs depends on interorgan communication. Tissue injury in one organ disturbs this homeostasis and can lead to disease in multiple organs, or multiorgan failure. Many routes of interorgan crosstalk during homeostasis are relatively well known, but interorgan crosstalk in disease still lacks understanding. In particular, how tissue injury in one organ can drive injury at remote sites and trigger multiorgan failure with high mortality is poorly understood. As examples, acute kidney injury can trigger acute lung injury and cardiovascular dysfunction; pneumonia, sepsis or liver failure conversely can cause kidney failure; lung transplantation very frequently triggers acute kidney injury. Mechanistically, interorgan crosstalk after tissue injury could involve soluble mediators and their target receptors, cellular mediators, in particular immune cells, as well as newly identified neuro-immune connections. In this review, I will focus the discussion of deleterious interorgan crosstalk and its mechanistic concepts on one example, acute kidney injury-induced remote lung injury.

Hypophosphatemia in acute liver failure of a broad range of etiologies is associated with phosphaturia without kidney damage or phosphatonin elevation

Hypophosphatemia is a common and dangerous complication of acute liver failure (ALF) of various etiologies. While various mechanisms for ALF-associated hypophosphatemia have been proposed including high phosphate uptake into regenerating hepatocytes, acetaminophen (APAP)-associated hypophosphatemia was linked to renal phosphate wasting, and APAP-induced renal tubular injury was proposed as underlying mechanism. We studied 30 normophosphatemic and 46 hypophosphatemic (serum phosphate < 2.5 mg/dL) patients from the Acute Liver Failure Study Group registry with APAP- or non-APAP-induced ALF. Since kidney injury affects phosphate excretion, patients with elevated serum creatinine (>1.2 mg/dL) were excluded. Maximal amount of renal tubular phosphate reabsorption per filtered volume (TmP/GFR) was calculated from simultaneous serum and urine phosphate and creatinine levels to assess renal phosphate handling. Instead of enhanced renal phosphate reabsorption as would be expected during hypophosphatemia of non-renal causes, serum phosphate was positively correlated with TmP/GFR in both APAP- and non-APAP-induced ALF patients (R2 = 0.66 and 0.46, respectively; both P < 0.0001), indicating renal phosphate wasting. Surprisingly, there was no evidence of kidney damage based on urinary markers including neutrophil gelatinase-associated lipocalin and cystatin C even in the APAP group. Additionally, there was no evidence that the known serum phosphatonins parathyroid hormone, fibroblast growth factor 23, and α-Klotho contribute to the observed hypophosphatemia. We conclude that the observed hypophosphatemia with renal phosphate wasting in both APAP- and non-APAP-mediated ALF is likely the result of renal tubular phosphate leak from yet-to-be identified factor(s) with no evidence for proximal tubular damage or contribution of known phosphatonins.

Soluble Klotho and Incident Hypertension

BACKGROUND AND OBJECTIVES

Hypertension is associated with significant morbidity and mortality despite effective antihypertensive therapies. Soluble klotho is a circulating protein that in preclinical studies is protective against the development of hypertension. There are limited studies of klotho and blood pressure in humans.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

Within the Health, Aging, and Body Composition Study, a cohort of well-functioning older adults, soluble klotho was measured in serum. We evaluated the cross-sectional and longitudinal association between klotho and blood pressure, prevalent hypertension, incident hypertension, and BP trajectories. Analyses were adjusted for demographics, cardiovascular disease and kidney disease risk factors, and measures of mineral metabolism including calcium, phosphate, parathyroid hormone, 25(OH) vitamin D, and fibroblast growth factor 23.

RESULTS

The median klotho concentration was 630 pg/ml (478-816, 25th to 75th percentile). Within the cohort, 2093 (76%) of 2774 participants had prevalent hypertension and 476 (70%) of the remaining 681 developed incident hypertension. There was no association between klotho and prevalent hypertension or baseline systolic BP, but higher klotho was associated with higher baseline diastolic BP (fully adjusted β=0.92 mmHg, 95% confidence interval, 0.24 to 1.60 mmHg, higher per two-fold higher klotho). Higher baseline serum klotho levels were significantly associated with a lower rate of incident hypertension (fully adjusted hazard ratio, 0.80; 95% confidence interval, 0.69 to 0.93 for every two-fold higher klotho). Higher klotho was also associated with lower subsequent systolic BP and diastolic BP (-0.16, 95% confidence interval, -0.31 to -0.01, mmHg lower systolic BP per year and -0.10, 95% confidence interval, -0.18 to -0.02, mmHg lower diastolic BP per year, for each two-fold higher klotho).

CONCLUSIONS

Higher klotho is associated with higher baseline diastolic but not systolic BP, a lower risk of incident hypertension, and lower BP trajectories during follow-up.

Epigenetic and senescence markers indicate an accelerated ageing-like state in women with preeclamptic pregnancies

Background

Preeclampsia is a pregnancy-specific hypertensive disorder characterized by proteinuria and/or multisystem involvement. Disease-specific therapy has yet to be developed due to the lack of understanding of underlying mechanism(s). We postulate that accelerated ageing in general, and particularly cellular senescence, play a role in its pathophysiology.

Methods

We compared women with preeclampsia vs. normotensive pregnancies with respect to epigenetic markers of ageing and markers of senescence in tissues/organs affected by preeclampsia (blood, urine, adipose tissue, and kidney).

Findings

We demonstrate that preeclamptic compared to normotensive pregnant women: (i) undergo accelerated epigenetic ageing during pregnancy, as demonstrated by an “epigenetic clock”; (ii) exhibit higher levels/expression of senescence-associated secretory phenotype factors in blood and adipose tissue; (iii) display increased expression of p16^INK4A in adipose tissue and renal sections, and (iv) demonstrate decreased levels of urinary α-Klotho (an anti-ageing protein) at the time of delivery. Finally, we provide data indicating that pre-treatment with dasatinib, a senolytic agent, rescues the angiogenic potential of mesenchymal stem cells (MSC) obtained from preeclamptic pregnancies, and promotes angiogenesis, even under pro-inflammatory conditions.

Interpretation

Taken together, our results identify senescence as one of the mechanisms underpinning the pathophysiology of preeclampsia. Therapeutic strategies that target senescent cells may offer novel mechanism-based treatments for preeclampsia.

Funding

This work was supported by NIH grants, R01 HL136348, R37 AG013925, P01 AG062413, R01 DK11916, generous gifts from the Connor Fund, Robert J. and Theresa W. Ryan and from The George G. Beasley family, the Noaber Foundation, and the Henry and Emma Meyer Professorship in Molecular Genetics.

Significance of serum FGF-23 for risk assessment of contrast-associated acute kidney injury and clinical outcomes in patients undergoing coronary angiography

Background

Fibroblast growth factor (FGF)-23 levels rise as kidney function declines. Whether elevated FGF-23 levels are associated with an increased risk for contrast-associated acute kidney injury (CA-AKI) and major adverse cardiovascular events (MACE) in patients undergoing coronary angiography remain uncertain.

Methods

In total, 492 patients receiving coronary angiography were enrolled. Their serum FGF-23 levels were measured before administration of contrast media. The occurrence of CA-AKI was defined as a rise in serum creatinine of 0.5 mg/dL or a 25% increase from the baseline value within 48 h after the procedure. All patients were followed up for at least 1 year or until the occurrence of MACE including death, nonfatal myocardial infarction (MI), and ischemic stroke.

Results

Overall, CA-AKI occurred in 41 (8.3%) patients. During a median follow-up of 2.6 years, there were 24 deaths, 3 nonfatal MIs, and 7 ischemic strokes. Compared with those in the lowest FGF-23 tertile, individuals in the highest FGF-23 tertile had a significantly higher incidence of CA-AKI (P < 0.001) and lower incidence of MACE-free survival (P = 0.001). In multivariate regression analysis, higher FGF-23 level was found to be independently associated with a graded risk for CA-AKI (OR per doubling, 1.90; 95% CI 1.48–2.44) and MACE (HR per doubling, 1.25; 95% CI 1.02–1.52).

Conclusions

Elevated FGF-23 levels were associated with an increased risk for CA-AKI and future MACE among patients undergoing coronary angiography. FGF-23 may play a role in early diagnosis of CA-AKI and predicting clinical outcomes after coronary angiography.

Nanobodies: new avenue to treat kidney disease

Current therapeutic options for renal diseases are limited, and the search for disease-specific treatments is ongoing. Nanobodies, single-domain antibodies with many advantages over conventional antibodies, provide flexible, easy-to-format biologicals with many possible applications. Here, we discuss the potential use of nanobodies for renal diseases.

Orphan nuclear receptor ERR-γ regulates hepatic FGF23 production in acute kidney injury

Bone is the main source of fibroblast growth factor 23 (FGF23), which is important for phosphate and vitamin D homeostasis. In acute kidney injury (AKI), high blood levels of FGF23 are positively correlated with disease progression and increased risk of mortality. Reducing adverse plasma FGF23 levels in AKI patients is favorable. We showed here that hepatocytes are the major source of circulating FGF23, and orphan nuclear receptor ERR-γ is a novel transcriptional regulator of hepatic FGF23 production in AKI. Liver-specific depletion of ERR-γ or ERR-γ inverse agonist, GSK5182, significantly reduced plasma levels of FGF23 in AKI. This study reveals liver is the source of FGF23 and a therapeutic strategy to control pathologically adverse plasma FGF23 levels in AKI.

Orphan nuclear receptor ERR-γ regulates hepatic FGF23 production in acute kidney injury

Fibroblast growth factor 23 (FGF23), a hormone generally derived from bone, is important in phosphate and vitamin D homeostasis. In acute kidney injury (AKI) patients, high-circulating FGF23 levels are associated with disease progression and mortality. However, the organ and cell type of FGF23 production in AKI and the molecular mechanism of its excessive production are still unidentified. For insight, we investigated folic acid (FA)-induced AKI in mice. Interestingly, simultaneous with FGF23, orphan nuclear receptor ERR-γ expression is increased in the liver of FA-treated mice, and ectopic overexpression of ERR-γ was sufficient to induce hepatic FGF23 production. In patients and in mice, AKI is accompanied by up-regulated systemic IL-6, which was previously identified as an upstream regulator of ERR-γ expression in the liver. Administration of IL-6 neutralizing antibody to FA-treated mice or of recombinant IL-6 to healthy mice confirms IL-6 as an upstream regulator of hepatic ERR-γ-mediated FGF23 production. A significant (P < 0.001) interconnection between high IL-6 and FGF23 levels as a predictor of AKI in patients that underwent cardiac surgery was also found, suggesting the clinical relevance of the finding. Finally, liver-specific depletion of ERR-γ or treatment with an inverse ERR-γ agonist decreased hepatic FGF23 expression and plasma FGF23 levels in mice with FA-induced AKI. Thus, inverse agonist of ERR-γ may represent a therapeutic strategy to reduce adverse plasma FGF23 levels in AKI.

Epigenetic modifications of Klotho expression in kidney diseases

Developments of many renal diseases are substantially influenced by epigenetic modifications of numerous genes, mainly mediated by DNA methylations, histone modifications, and microRNA interference; however, not all gene modifications causally affect the disease onset or progression. Klotho is a critical gene whose repressions in various pathological conditions reportedly involve epigenetic regulatory mechanisms. Klotho is almost unexceptionally repressed early after acute or chronic renal injuries and its levels inversely correlated with the disease progression and severity. Moreover, the strategies of Klotho derepression via epigenetic modulations beneficially change the pathological courses both in vitro and in vivo. Hence, Klotho is not only considered a biomarker of the renal disease but also a potential or even an ideal target of therapeutic epigenetic intervention. Here, we summarize and discuss studies that investigate the Klotho repression and intervention in renal diseases from an epigenetic point of view. These information might shed new sights into the effective therapeutic strategies to prevent and treat various renal disorders.

Renohepatic crosstalk: a review of the effects of acute kidney injury on the liver

Several theories regarding acute kidney injury (AKI)-related mortality have been entertained, although mounting evidence supports the paradigm that impaired kidney function directly and adversely affects the function of several remote organs. The kidneys and liver are fundamental to human metabolism and detoxification, and it is therefore hardly surprising that critical illness complicated by hepatorenal dysfunction portends a poor prognosis. Several diseases can simultaneously impact the proper functioning of the liver and kidneys, although this review will address the impact of AKI on liver function. While evidence for this relationship in humans remains sparse, we present supportive studies and then discuss the most likely mechanisms by which AKI can cause liver dysfunction. These include 'traditional' complications of AKI (uremia, volume overload and acute metabolic acidosis, among others) as well as systemic inflammation, hepatic leukocyte infiltration, cytokine-mediated liver injury and hepatic oxidative stress. We conclude by addressing the therapeutic implications of these findings to clinical medicine.

Epigenetic and non-epigenetic regulation of Klotho in kidney disease

Klotho is a novel renoprotective anti-aging protein available in membrane-bound or soluble form. Klotho is expressed in brain, pancreas, and other solid organs but shows highest expression levels in the kidney. Klotho sustains normal kidney physiology but Klotho regulation also contributes to the progression of kidney disease. Systemic and intrarenal levels of Klotho fall drastically during acute kidney injury, kidney fibrosis, diabetic nephropathy, and other forms of chronic kidney disease, etc. Moreover, exogenous supplementation or overexpression of endogenous Klotho attenuates kidney disease. The regulation of endogenous Klotho expression involves epigenetic as well as non-epigenetic mechanisms. The epigenetic modifications such as DNA methylation, post-translational histone modifications, miRNAs regulate the change in Klotho expression in kidney disease. Non-epigenetic mechanisms such as ER stress, Wnt signaling, activation of the renin angiotensin system (RAS), excessive reactive oxygen species and cytokine generation, albumin overload, and PPAR-γ signaling also contribute to Klotho regulation. Evolving evidence highlight the capacity of natural products to regulate Klotho expression in kidney disease. All these preclinical data suggest that Klotho could be a novel biomarker as well as therapeutic target. Here we review the different mechanisms of Klotho regulation in the context of Klotho as a biomarker and potential therapeutic agent.

Serum Cystatin C, Klotho, and Neutrophil Gelatinase-Associated Lipocalin in the Risk Prediction of Acute Kidney Injury after Acute Myocardial Infarction

BACKGROUND

Patients with acute myocardial infarction (AMI) are at high risk for acute kidney injury (AKI). Novel biomarkers that can predict AKI after AMI may facilitate immediate interventions. Recently, cystatin C, neutrophil gelatinase-associated lipocalin (NGAL), and klotho have been established as novel AKI biomarkers. However, their effects have not been studied in patients presenting with AMI. In this study, we will measure the serum levels of these three biomarkers to find reliable biomarkers for early diagnosis of AKI in AMI patients.

METHODS

This prospective observational cohort study was conducted between May 2016 and November 2017. A total of 285 consecutive patients with AMI were enrolled. The study was approved by the institutional review board of Peking University People's Hospital (No. 2016PHB 042-01). AKI was defined according to the KDIGO criteria in 2012. At admission, the clinical data of patients was collected and serum levels of several AKI biomarkers, including cystatin C, NGAL, and klotho, were measured by ELISA. The relationship between biomarker levels of AKI were analyzed and their discrimination performances were compared.

RESULTS

AKI incidence was 17.5% (50/285) during hospitalization. Compared to patients without AKI, the AKI group had higher mortality (20.0% vs. 0.4%, p < 0.001) and tended to be older, had higher incidence of chronic kidney disease, severe cardiac function, more cardiac complications, larger doses of diuretics, and less use of angiotensin-converting enzyme inhibitors/angiotensin receptor blocker and statins. Moreover, AKI patients experienced an increase in serum cystatin C (3,709.2 ± 2,281.5 vs. 1,918.5 ± 1,140.6 ng/mL, p < 0.001), NGAL (118.0 ± 70.3 vs. 91.8 ± 52.3 ng/mL, p = 0.003), and klotho (742.2 ± 497.4 vs. 470.3 ± 257.2 pg/mL, p <0.001). Furthermore, the areas under the receiver operating curves demonstrated that serum cystatin C levels at admission had modest discriminative powers for predicting AKI after AMI compared with serum creatinine (0.899, 95% CI, 0.855-0.944 vs. 0.734, 95% CI, 0.649-0.819, p <0.001). There was no difference between the discrimination performances of serum creatinine, NGAL, and klotho.

CONCLUSION

Elevated cystatin C levels are associated with AKI in patients with AMI. This study provides reliable evidence that cystatin C levels may be superior to serum creatinine for predicting AKI after AMI at admission.

Effects of Klotho supplementation on hyperoxia-induced renal injury in a rodent model of postnatal nephrogenesis

BACKGROUND

Hyperoxia (HO) causes kidney injury in preterm infants; however, whether these effects are modifiable is unknown. We hypothesized that administration of exogenous soluble Klotho, a kidney-derived antioxidant, would attenuate HO-induced kidney injury during postnatal nephrogenesis in rats.

METHODS

Sprague Dawley neonatal rats assigned to normoxia (21% O₂) or HO (85% O₂) groups from postnatal day (P) 1 to 21 were randomly assigned to receive alternate day intraperitoneal injections of recombinant Klotho or placebo for 3 weeks. They were recovered in normoxia for an additional 3 weeks and sacrificed at 6 weeks. Renal artery resistance and pulsatility indices, tubular injury scores, glomerular area, and renal antioxidant capacity were assessed.

RESULTS

Rodents exposed to HO during postnatal nephrogenesis had reduced kidney Klotho expression, glomerulomegaly, and higher tubular injury scores. Exogenous Klotho administration improved renal perfusion as indicated by decreases in both resistance and pulsatility indices and increased antioxidant enzyme expression.

CONCLUSIONS

HO exposure during postnatal nephrogenesis in rodents results in a decline in kidney Klotho expression, decreased renal perfusion, enlarged glomerular size, and tubular injury. The exogenous administration of Klotho attenuated HO-induced kidney injury and augmented antioxidant capacity.

Fibroblast Growth Factor 23 and αKlotho in Acute Kidney Injury: Current Status in Diagnostic and Therapeutic Applications

Fibroblast growth factor (FGF) 23 and αKlotho are circulating mineral regulatory substances that also have a very diverse range of actions. Acute kidney injury (AKI) is a state of high FGF23 and low αKlotho. Clinical association data for FGF23 are strong, but the basic pathobiology of FGF23 in AKI is rather sparse. Conversely, preclinical data supporting a pathogenic role of αKlotho in AKI are strong, but the human data are still being generated. This pair of substances can potentially serve as diagnostic and prognostic biomarkers. FGF23 blockade and αKlotho restoration can have prophylactic and therapeutic utility in AKI. The literature to date is briefly reviewed in this article.

Klotho is regulated by transcription factor Sp1 in renal tubular epithelial cells

BACKGROUND

Klotho is a multifunctional protein, which exists both in a membrane bound and a soluble form. In renal tubules, Klotho is involved in cell senescence, anti-oxidant response, and renal fibrosis, thus regulation of its expression is critical to understand its roles in renal diseases. Indeed, reduced expression was observed in various renal disease. However, the mechanisms underlying transcriptional regulation of the human klotho gene (KL) largely remain unknown.

RESULTS

Here we demonstrated that the Klotho expression in human renal tubular epithelial cells (RTECs) was enhanced by overexpression of the transcription factor Sp1. On the contrary, Klotho expression was decreased by Sp1 knockdown. Besides, increased expression of Sp1 alleviated TGF-β1-induced fibrosis in HK-2 cells by inducing Klotho expression. Luciferase reporter assays and chromatin immunoprecipitation assays further identified the binding site of Sp1 was located in - 394 to - 289 nt of the KL promoter, which was further confirmed by mutation analysis.

CONCLUSIONS

These data demonstrate that KL is a transcriptional target of Sp1 and TGF-β1-induced fibrosis was alleviated by Sp1 in human RTECs by directly modulating Klotho expression, which help to further understand the transcriptional regulation of Klotho in renal disease models.

Serum Klotho in Living Kidney Donors and Kidney Transplant Recipients: A Meta-Analysis

α-Klotho is a known anti-aging protein that exerts diverse physiological effects, including phosphate homeostasis. Klotho expression occurs predominantly in the kidney and is significantly decreased in patients with chronic kidney disease. However, changes in serum klotho levels and impacts of klotho on outcomes among kidney transplant (KTx) recipients and kidney donors remain unclear. A literature search was conducted using MEDLINE, EMBASE, and Cochrane Database from inception through October 2019 to identify studies evaluating serum klotho levels and impacts of klotho on outcomes among KTx recipients and kidney donors. Study results were pooled and analyzed utilizing a random-effects model. Ten cohort studies with a total of 431 KTx recipients and 5 cohort studies with a total of 108 living kidney donors and were identified. After KTx, recipients had a significant increase in serum klotho levels (at 4 to 13 months post-KTx) with a mean difference (MD) of 243.11 pg/mL (three studies; 95% CI 67.41 to 418.81 pg/mL). Although KTx recipients had a lower serum klotho level with a MD of = -234.50 pg/mL (five studies; 95% CI -444.84 to -24.16 pg/mL) compared to healthy unmatched volunteers, one study demonstrated comparable klotho levels between KTx recipients and eGFR-matched controls. Among kidney donors, there was a significant decrease in serum klotho levels post-nephrectomy (day 3 to day 5) with a mean difference (MD) of -232.24 pg/mL (three studies; 95% CI -299.41 to -165.07 pg/mL). At one year following kidney donation, serum klotho levels remained lower than baseline before nephrectomy with a MD of = -110.80 pg/mL (two studies; 95% CI 166.35 to 55.24 pg/mL). Compared to healthy volunteers, living kidney donors had lower serum klotho levels with a MD of = -92.41 pg/mL (two studies; 95% CI -180.53 to -4.29 pg/mL). There is a significant reduction in serum klotho levels after living kidney donation and an increase in serum klotho levels after KTx. Future prospective studies are needed to assess the impact of changes in klotho on clinical outcomes in KTx recipients and living kidney donors.

Fibroblast Growth Factors in the Management of Acute Kidney Injury Following Ischemia-Reperfusion

Ischemia-reperfusion injury (IRI), which is triggered by a transient reduction or cessation of blood flow followed by reperfusion, is a significant cause of acute kidney injury (AKI). IRI can lead to acute cell death, tissue injury, and even permanent organ dysfunction. In the clinic, IRI contributes to a higher morbidity and mortality and is associated with an unfavorable prognosis in AKI patients. Unfortunately, effective clinical drugs to protect patients against the imminent risk of renal IRI or treat already existing AKI are still lacking. Fibroblast growth factors (FGFs) are important regulators of key biological and pathological processes, such as embryonic development, metabolic homeostasis and tumorigenesis through the regulation of cell differentiation, migration, proliferation and survival. Accumulating evidence suggests that altered expression of endogenous FGFs is associated with IRI and could be instrumental in mediating the repair process. Therefore, FGFs have been proposed as potential biomarkers in the clinic. More importantly, exogenous FGF ligands have been reported to protect against renal IRI and display promising features for therapy. In this review, we summarize the evidence and mechanisms of AKI following IRI with a focus on the therapeutic capacity of several members of the FGF family to treat AKI after IRI.

Glycerol-3-phosphate is an FGF23 regulator derived from the injured kidney

Fibroblast growth factor 23 (FGF23) is a bone-derived hormone that controls blood phosphate levels by increasing renal phosphate excretion and reducing 1,25-dihydroxyvitamin D3 [1,25(OH)2D] production. Disorders of FGF23 homeostasis are associated with significant morbidity and mortality, but a fundamental understanding of what regulates FGF23 production is lacking. Because the kidney is the major end organ of FGF23 action, we hypothesized that it releases a factor that regulates FGF23 synthesis. Using aptamer-based proteomics and liquid chromatography-mass spectrometry-based (LC-MS-based) metabolomics, we profiled more than 1600 molecules in renal venous plasma obtained from human subjects. Renal vein glycerol-3-phosphate (G-3-P) had the strongest correlation with circulating FGF23. In mice, exogenous G-3-P stimulated bone and bone marrow FGF23 production through local G-3-P acyltransferase-mediated (GPAT-mediated) lysophosphatidic acid (LPA) synthesis. Further, the stimulatory effect of G-3-P and LPA on FGF23 required LPA receptor 1 (LPAR1). Acute kidney injury (AKI), which increases FGF23 levels, rapidly increased circulating G-3-P in humans and mice, and the effect of AKI on FGF23 was abrogated by GPAT inhibition or Lpar1 deletion. Together, our findings establish a role for kidney-derived G-3-P in mineral metabolism and outline potential targets to modulate FGF23 production during kidney injury.

Potential targeted therapy and diagnosis based on novel insight into growth factors, receptors, and downstream effectors in acute kidney injury and acute kidney injury-chronic kidney disease progression

Acute kidney injury (AKI) is defined as a rapid decline in renal function and is characterized by excessive renal inflammation and programmed death of resident cells. AKI shows high morbidity and mortality, and severe or repeated AKI can transition to chronic kidney disease (CKD) or even end-stage renal disease (ESRD); however, very few effective and specific therapies are available, except for supportive treatment. Growth factors, such as epidermal growth factor (EGF), insulin-like growth factor (IGF), and transforming growth factor-β (TGF-β), are significantly altered in AKI models and have been suggested to play critical roles in the repair process of AKI because of their roles in cell regeneration and renal repair. In recent years, a series of studies have shown evidence that growth factors, receptors, and downstream effectors may be highly involved in the mechanism of AKI and may function in the early stage of AKI in response to stimuli by regulating inflammation and programmed cell death. Moreover, certain growth factors or correlated proteins act as biomarkers for AKI due to their sensitivity and specificity. Furthermore, growth factors originating from mesenchymal stem cells (MSCs) via paracrine signaling or extracellular vesicles recruit leukocytes or repair intrinsic cells and may participate in AKI repair or the AKI-CKD transition. In addition, growth factor-modified MSCs show superior therapeutic potential compared to that of unmodified controls. In this review, we summarized the current therapeutic and diagnostic strategies targeting growth factors to treat AKI in clinical trials. We also evaluated the possibilities of other growth factor-correlated molecules as therapeutic targets in the treatment of AKI and the AKI-CKD transition.

Acute Kidney Injury and Pediatric Bone Health

Acute kidney injury (AKI) has been associated with deleterious impacts on a variety of body systems. While AKI is often accompanied by dysregulation of mineral metabolism-including alterations in calcium, phosphate, vitamin D, parathyroid hormone, fibroblast growth factor 23, and klotho-its direct effects on the skeletal system of children and adolescents remain largely unexplored. In this review, the pathophysiology of dysregulated mineral metabolism in AKI and its potential effects on skeletal health are discussed, including data associating AKI with fracture risk.