Improved renal ischemia tolerance in females influences kidney transplantation outcomes

Double-negative T cells have a reparative role after experimental severe ischemic acute kidney injury

T cells mediate organ injury and repair. A proportion of unconventional kidney T cells called double-negative (DN) T cells (TCR+ CD4- CD8-), with anti-inflammatory properties, were previously demonstrated to protect from early injury in moderate experimental acute kidney injury (AKI). However, their role in repair after AKI has not been studied. We hypothesized that DN T cells mediate repair after severe AKI. C57B6 mice underwent severe (40 min) unilateral ischemia-reperfusion injury (IRI). Kidney DN T cells were studied by flow cytometry and compared with gold-standard anti-inflammatory CD4+ regulatory T cells (Tregs). In vitro effects of DN T cells and Tregs on renal tubular epithelial cell (RTEC) repair after injury were quantified with live-cell analysis. DN T cells, Tregs, CD4, or vehicle were adoptively transferred after severe AKI. Glomerular filtration rate (GFR) was measured using fluorescein isothiocyanate (FITC)-sinistrin. Fibrosis was assessed with Masson's trichrome staining. Profibrotic genes were measured with qRT-PCR. Percentages and the numbers of DN T cells substantially decreased during repair phase after severe AKI, as well as their activation and proliferation. Both DN T cells and Tregs accelerated RTEC cell repair in vitro. Post-AKI transfer of DN T cells reduced kidney fibrosis and improved GFR, as did Treg transfer. DN T cell transfer lowered transforming growth factor (TGF)β1 and α-smooth muscle actin (αSMA) expression. DN T cells reduced effector-memory CD4+ T cells and IL-17 expression. DN T cells undergo quantitative and phenotypical changes after severe AKI, accelerate RTEC repair in vitro as well as improve GFR and renal fibrosis in vivo. DN T cells have potential as immunotherapy to accelerate repair after AKI.NEW & NOTEWORTHY Double-negative (DN) T cells (CD4- CD8-) are unconventional kidney T cells with regulatory abilities. Their role in repair from acute kidney injury (AKI) is unknown. Kidney DN T cell population decreased during repair after ischemic AKI, in contrast to regulatory T cells (Tregs) which increased. DN T cell administration accelerated tubular repair in vitro, while after severe in vivo ischemic injury reduced kidney fibrosis and increased glomerular filtration rate (GFR). DN T cell infusion is a potential therapeutic agent to improve outcome from severe AKI.

Gucy1α1 specifically marks kidney, heart, lung and liver fibroblasts

Fibrosis is a common outcome of numerous pathologies, including chronic kidney disease (CKD), a progressive renal function deterioration. Current approaches to target activated fibroblasts, key effector contributors to fibrotic tissue remodeling, lack specificity. Here, we report Gucy1α1 as a specific kidney fibroblast marker. Gucy1α1 levels significantly increased over the course of two clinically relevant murine CKD models and directly correlated with established fibrosis markers. Immunofluorescent (IF) imaging showed that Gucy1α1 comprehensively labelled cortical and medullary quiescent and activated fibroblasts in the control kidney and throughout injury progression, respectively. Unlike traditionally used markers platelet derived growth factor receptor beta (Pdgfrβ) and vimentin (Vim), Gucy1α1 did not overlap with off-target populations such as podocytes. Notably, Gucy1α1 labelled kidney fibroblasts in both male and female mice. Furthermore, we observed elevated GUCY1α1 expression in the human fibrotic kidney and lung. Studies in the murine models of cardiac and liver fibrosis revealed Gucy1α1 elevation in activated Pdgfrβ-, Vim- and alpha smooth muscle actin (αSma)-expressing fibroblasts paralleling injury progression and resolution. Overall, we demonstrate Gucy1α1 as an exclusive fibroblast marker in both sexes. Due to its multiorgan translational potential, GUCY1α1 might provide a novel promising strategy to specifically target and mechanistically examine fibroblasts.

Quinolinic acid links kidney injury to brain toxicity

Kidney dysfunction often leads to neurological impairment, yet the complex kidney-brain relationship remains elusive. We employed spatial and bulk metabolomics to investigate a mouse model of rapid kidney failure induced by mouse double minute 2 ( Mdm2) conditional deletion in the kidney tubules to interrogate kidney and brain metabolism. Pathway enrichment analysis of focused plasma metabolomics panel pinpointed tryptophan metabolism as the most altered pathway with kidney failure. Spatial metabolomics showed toxic tryptophan metabolites in the kidneys and brains, revealing a novel connection between advanced kidney disease and accelerated kynurenine degradation. In particular, the excitotoxic metabolite quinolinic acid was localized in ependymal cells adjacent to the ventricle in the setting of kidney failure. These findings were associated with brain inflammation and cell death. A separate mouse model of acute kidney injury also had an increase in circulating toxic tryptophan metabolites along with altered brain inflammation. Patients with advanced CKD similarly demonstrated elevated plasma kynurenine metabolites and quinolinic acid was uniquely correlated with fatigue and reduced quality of life in humans. Overall, our study identifies the kynurenine pathway as a bridge between kidney decline, systemic inflammation, and brain toxicity, offering potential avenues for diagnosis and treatment of neurological issues in kidney disease.

Proton pump inhibitors use is associated with a higher prevalence of kidney stones: NHANES 2007-2018

BACKGROUND

Proton pump inhibitors (PPIs) are widely used throughout the world as an effective gastrointestinal drug. Nevertheless, according to the existing literature, PPIs can reduce the excretion of magnesium, calcium and other components in urine, which may promote the formation of kidney stones. We used the National Health and Nutrition Examination Survey (NHANES) database to further investigate the association between the use of PPIs and the prevalence of kidney stones.

METHODS

We performed a cross-sectional analysis using data from 2007 to 2018 NHANES. PPIs use information of 29,910 participants was obtained by using prescription medications in the preceding month, and kidney stones were presented by a standard questionnaire. Multiple regression analysis and stratified analysis were used to estimate the association between PPIs use and kidney stones after an adjustment for potential confounders.

RESULTS

The multiple logistic regression indicated that the PPIs exposure group (P1) had a significantly higher risk of nephrolithiasis than the PPIs non-exposure group (P0) in Model 3 (OR 1.24, 95% CI 1.10-1.39, P < 0.001). The stratified analyses indicated there were significant statistical differences between PPIs use and kidney stones among females (OR 1.36, 95% CI 1.15-1.62, P < 0.001), non-Hispanic whites (OR 1.27, 95% CI 1.09-1.48, P = 0.002), individuals with an education level than 11th grade (OR 1.41, 95% CI 1.13-1.76, P = 0.002) and individuals with an annual family income of $0 to $19,999 (OR 1.32, 95% CI 1.06-1.65, P = 0.014) and $20,000 to $44,999 (OR 1.25, 95% CI 1.02-1.54, P = 0.033) in Model 3.

CONCLUSIONS

Our study revealed that PPIs use is associated with a higher prevalence of kidney stones for the US population, primarily among women, non-Hispanic whites, individuals with low education levels and individuals with low household income levels. Further studies are required to confirm our findings.

The immunoregulatory roles of non-haematopoietic cells in the kidney

The deposition of immune complexes, activation of complement and infiltration of the kidney by cells of the adaptive and innate immune systems have long been considered responsible for the induction of kidney damage in autoimmune, alloimmune and other inflammatory kidney diseases. However, emerging findings have highlighted the contribution of resident immune cells and of immune molecules expressed by kidney-resident parenchymal cells to disease processes. Several types of kidney parenchymal cells seem to express a variety of immune molecules with a distinct topographic distribution, which may reflect the exposure of these cells to different pathogenic threats or microenvironments. A growing body of literature suggests that these cells can stimulate the infiltration of immune cells that provide protection against infections or contribute to inflammation - a process that is also regulated by draining kidney lymph nodes. Moreover, components of the immune system, such as autoantibodies, cytokines and immune cells, can influence the metabolic profile of kidney parenchymal cells in the kidney, highlighting the importance of crosstalk in pathogenic processes. The development of targeted nanomedicine approaches that modulate the immune response or control inflammation and damage directly within the kidney has the potential to eliminate the need for systemically acting drugs.

Sex-related differences in SIRT3-mediated mitochondrial dynamics in renal ischemia/reperfusion injury

The prevalence of renal ischemia/reperfusion injury (IRI) in premenopausal women is considerably lower than that in age-matched men. This suggests that sex-related differences in mitochondrial function and homeostasis may contribute to sexual dimorphism in renal injury, though the mechanism remains unclear. Mouse model of unilateral left renal IRI with contralateral kidney enucleation, Ovariectomy in female mice, and a human embryonic kidney (HEK) cell model of hypoxia-reoxygenation were used to study how estrogen affects the sexual dimorphism of renal IRI through SIRT3 in vitro and in vivo, respectively. Here, we demonstrate differential expression of renal SIRT3 may induce sexual dimorphism in IRI using the renal IRI model. Higher SIRT3 level in female mice was associated with E2-induced protection of renal tubular epithelium, reduced mitochondrial reactive oxygen species (ROS), and IRI resistance. In hypoxia-reoxygenated HEK cells, SIRT3 knockdown increased oxidative stress, shifted the interconnected mitochondrial network toward fission, exacerbated hypoxia/reoxygenation-induced endoplasmic reticulum stress (ERS), and abolished the protective effects of E2 on IRI. Mechanistically, the SIRT3 level is E2-dependent and that E2 increases the SIRT3 protein level via estrogen receptor. SIRT3 targeted an i-AAA protease, yeast mitochondrial AAA metalloprotease (YME1L1), and hydrolyzed long optic atrophy 1 (L-OPA) to short-OPA1 (S-OPA1) by deacetylating YME1L1, regulating mitochondrial dynamics toward fusion to reduce oxidative stress and ERS. These findings explored the mechanism by how estrogen alleviates renal IRI and providing a basis for potential therapeutic interventions targeting SIRT3.

Influence of donor sex and age on graft outcome in kidney transplantation

BACKGROUND

There is a known recipient sex-dependent association between donor sex and kidney transplant survival. We hypothesized that donor age also modifies the association between donor sex and graft survival.

METHODS

First, deceased donor kidney transplant recipients (1988-2019, n = 461 364) recorded in the Scientific Registry of Transplant Recipients, the Australia and New Zealand Dialysis and Transplant Registry and the Collaborative Transplant Study were analyzed. We used multivariable Cox regression models to estimate the association between donor sex and death censored graft loss, accounting for the modifying effects of recipient sex and donor age; donor age was categorized as 5-19, 20-34, 35-49, 50-59 and ≥60 years. Results from cohort-specific Cox models were combined using individual patient data meta-analysis.

RESULTS

Among female recipients of donors aged <60 years, graft loss hazards did not differ by donor sex; recipients of female donors ≥60 years showed significantly lower graft loss hazards than recipients of male donors of the same age [combined adjusted hazard ratio (aHR) 0.90, 95% CI 0.86-0.94]. Among male recipients, female donors aged <50 years were associated with significantly higher graft loss hazards than same-aged male donors (5-19 years: aHR 1.11, 95% CI 1.02-1.21; 20-34 years: aHR 1.08, 95% CI 1.02-1.15; 35-49 years: aHR 1.07, 95% CI 1.04-1.10). There were no significant differences in graft loss by donor sex among male recipients of donors aged ≥50 years.

CONCLUSION

Donor age modifies the association between donor sex and graft survival. Older female donors were associated with similar or lower hazards of graft failure than older male donors in both male and female recipients, suggesting a better functional reserve of older female donor kidneys.

Interleukin-2/anti-interleukin-2 immune complex attenuates cold ischemia-reperfusion injury after kidney transplantation by increasing renal regulatory T cells

BACKGROUND

Cold ischemia-reperfusion injury (IRI) is an unavoidable complication of kidney transplantation. We investigated the role of regulatory T cells (Treg) in cold IRI and whether the interleukin (IL)-2/anti-IL-2 antibody complex (IL-2C) can ameliorate cold IRI.

METHODS

We developed a cold IRI mouse model using kidney transplantation and analyzed the IL-2C impact on cold IRI in acute, subacute and chronic phases.

RESULTS

Treg transfer attenuated cold IRI, while Treg depletion aggravated cold IRI. Next, IL-2C administration prior to IRI mitigated acute renal function decline, renal tissue damage and apoptosis and inhibited infiltration of effector cells into kidneys and pro-inflammatory cytokine expression on day 1 after IRI. On day 7 after IRI, IL-2C promoted renal regeneration and reduced subacute renal damage. Furthermore, on day 28 following IRI, IL-2C inhibited chronic fibrosis. IL-2C decreased reactive oxygen species-mediated injury and improved antioxidant function. When IL-2C was administered following IRI, it also increased renal regeneration with Treg infiltration and suppressed renal fibrosis. In contrast, Treg depletion in the presence of IL-2C eliminated the positive effects of IL-2C on IRI.

CONCLUSION

Tregs protect kidneys from cold IRI and IL-2C inhibited cold IRI by increasing the renal Tregs, suggesting a potential of IL-2C in treating cold IRI.

KEY POINTS

Interleukin (IL)-2/anti-IL-2 antibody complex attenuated acute renal injury, facilitated subacute renal regeneration and suppressed chronic renal fibrosis after cold ischemia-reperfusion injury (IRI) by increasing the renal Tregs. IL-2/anti-IL-2 antibody complex decreased reactive oxygen species-mediated injury and improved antioxidant function. This study suggests the therapeutic potential of the IL-2/anti-IL-2 antibody complex in kidney transplantation-associated cold IR.

Pre-Transplant Hyperparathyroidism and Graft or Patient Outcomes After Kidney Transplantation

The impact of pre-transplant parathyroid hormone (PTH) levels on early or long-term kidney function after kidney transplantation is subject of debate. We assessed whether severe hyperparathyroidism is associated with delayed graft function (DGF), death-censored graft failure (DCGF), or all-cause mortality. In this single-center cohort study, we studied the relationship between PTH and other parameters related to bone and mineral metabolism, including serum alkaline phosphatase (ALP) at time of transplantation with the subsequent risk of DGF, DCGF and all-cause mortality using multivariable logistic and Cox regression analyses. In 1,576 kidney transplant recipients (51.6 ± 14.0 years, 57.3% male), severe hyperparathyroidism characterized by pre-transplant PTH ≥771 pg/mL (>9 times the upper limit) was present in 121 patients. During 5.2 [0.2-30.0] years follow-up, 278 (15.7%) patients developed DGF, 150 (9.9%) DCGF and 432 (28.6%) died. A higher pre-transplant PTH was not associated with DGF (HR 1.06 [0.90-1.25]), DCGF (HR 0.98 [0.87-1.13]), or all-cause mortality (HR 1.02 [0.93-1.11]). Results were consistent in sensitivity analyses. The same applied to other parameters related to bone and mineral metabolism, including ALP. Severe pre-transplant hyperparathyroidism was not associated with an increased risk of DGF, DCGF or all-cause mortality, not supporting the need of correction before kidney transplantation to improve graft or patient survival.

Short-term hypercaloric carbohydrate loading increases surgical stress resilience by inducing FGF21

Dietary restriction promotes resistance to surgical stress in multiple organisms. Counterintuitively, current medical protocols recommend short-term carbohydrate-rich drinks (carbohydrate loading) prior to surgery, part of a multimodal perioperative care pathway designed to enhance surgical recovery. Despite widespread clinical use, preclinical and mechanistic studies on carbohydrate loading in surgical contexts are lacking. Here we demonstrate in ad libitum-fed mice that liquid carbohydrate loading for one week drives reductions in solid food intake, while nearly doubling total caloric intake. Similarly, in humans, simple carbohydrate intake is inversely correlated with dietary protein intake. Carbohydrate loading-induced protein dilution increases expression of hepatic fibroblast growth factor 21 (FGF21) independent of caloric intake, resulting in protection in two models of surgical stress: renal and hepatic ischemia-reperfusion injury. The protection is consistent across male, female, and aged mice. In vivo, amino acid add-back or genetic FGF21 deletion blocks carbohydrate loading-mediated protection from ischemia-reperfusion injury. Finally, carbohydrate loading induction of FGF21 is associated with the induction of the canonical integrated stress response (ATF3/4, NF-kB), and oxidative metabolism (PPARγ). Together, these data support carbohydrate loading drinks prior to surgery and reveal an essential role of protein dilution via FGF21.

Sex differences in blood pressure regulation and hypertension: renal, hemodynamic, and hormonal mechanisms

The teleology of sex differences has been argued since at least as early as Aristotle's controversial Generation of Animals more than 300 years BC, which reflects the sex bias of the time to contemporary readers. Although the question "why are the sexes different" remains a topic of debate in the present day in metaphysics, the recent emphasis on sex comparison in research studies has led to the question "how are the sexes different" being addressed in health science through numerous observational studies in both health and disease susceptibility, including blood pressure regulation and hypertension. These efforts have resulted in better understanding of differences in males and females at the molecular level that partially explain their differences in vascular function and renal sodium handling and hence blood pressure and the consequential cardiovascular and kidney disease risks in hypertension. This review focuses on clinical studies comparing differences between men and women in blood pressure over the life span and response to dietary sodium and highlights experimental models investigating sexual dimorphism in the renin-angiotensin-aldosterone, vascular, sympathetic nervous, and immune systems, endothelin, the major renal sodium transporters/exchangers/channels, and the impact of sex hormones on these systems in blood pressure homeostasis. Understanding the mechanisms governing sex differences in blood pressure regulation could guide novel therapeutic approaches in a sex-specific manner to lower cardiovascular risks in hypertension and advance personalized medicine.

Sex and Gender Differences in AKI

Sex differences in AKI continue to be identified. Generally, women are protected from AKI when compared to men. Much of the protection exhibited in women is diminished after menopause. These sex and age effects have also been noted in animal models of AKI. Gonadal hormones, as modifiers of incidence, severity, and progression of AKI, have been offered as likely contributors to this sex and age effect. In animal models of AKI, estrogen and testosterone seem to modulate susceptibility. Questions remain however regarding cellular and molecular changes that are initiated by modulation of these hormones because both estrogen and testosterone have effects across cell types that play a role in AKI. Although findings have largely been informed by studies in males, molecular pathways that are involved in the initiation and progression of AKI may be modulated by gonadal hormones. Compounding the hormone-receptor effects are developmental effects of sex chromosomal complement and epigenetic influences that may confer sex-based baseline differences in gene and protein expression, and gene dosage effects of X inactivation and escape on molecular pathways. Elucidation of sex-based protection may afford a more complete view of AKI and potential therapeutic interventions. Furthermore, the effect on susceptibility to AKI in transgender patients, who receive life-altering and essential gender-affirming hormone therapy, requires greater attention. In this review, several potential contributors to the sex differences observed in humans and animal models are discussed.

Effects of the environment on the evolution of the vertebrate urinary tract

Evolution of the vertebrate urinary system occurs in response to numerous selective pressures, which have been incompletely characterized. Developing research into urinary evolution led to the occurrence of clinical applications and insights in paediatric urology, reproductive medicine, urolithiasis and other domains. Each nephron segment and urinary organ has functions that can be contextualized within an evolutionary framework. For example, the structure and function of the glomerulus and proximal tubule are highly conserved, enabling blood cells and proteins to be retained, and facilitating the elimination of oceanic Ca+ and Mg+. Urea emerged as an osmotic mediator during evolution, as cells of large organisms required increased precision in the internal regulation of salinity and solutes. As the first vertebrates moved from water to land, acid-base regulation was shifted from gills to skin and kidneys in amphibians. In reptiles and birds, solute regulation no longer occurred through the skin but through nasal salt glands and post-renally, within the cloaca and the rectum. In placental mammals, nasal salt glands are absent and the rectum and urinary tracts became separate, which limited post-renal urine concentration and led to the necessity of a kidney capable of high urine concentration. Considering the evolutionary and environmental selective pressures that have contributed to renal evolution can help to gain an increased understanding of renal physiology.

Sex as a biological variable in acute kidney injury

PURPOSE OF REVIEW

The purpose of this review is to provide an overview of the preclinical and clinical studies investigating sex as a biological variable, as well as the impact of gender, on the development of and progression of acute kidney injury (AKI).

RECENT FINDINGS

Despite a matched degree of ischemia-reperfusion AKI based on measured glomerular filtration rates, male and female mice demonstrated important sex biases in cardiorenal outcomes (1). Although the 2012 Kidney Disease Improving Global Outcomes (KDIGO) Clinical Practice Guideline for AKI reported that female sex is associated with increased rates of hospital acquired AKI, subsequent meta-analyses do not show increased risk of AKI in women. Recent large scale, multicenter epidemiologic studies suggest males have higher rates of hospital acquired AKI. However, women have been consistently shown to have worse renal outcomes after AKI. There may be also be gender-based differences in presentation to care and management.

SUMMARY

Sex is an important biological variable in animal models of acute kidney injury. The impact of sex on AKI likely varies based on the etiology of AKI. Preclinical studies demonstrate the nuances of sex chromosomes, sex hormones and epigenetic factors on AKI, however these have not been well studied in humans. Gender may also impact processes of care, treatment and clinical outcomes related to AKI. The scientific rigor and reproducibility of translational studies benefit from the consideration of sex and gender.

Delayed graft function post renal transplantation: a review on animal models and therapeutics

The incidence of end-stage renal disease (ESRD) has been increasing worldwide. Its treatment involves renal replacement therapy, either by dialyses or renal transplantation from a living or deceased donor. Although the initial mortality rates for patients on dialysis are comparable with kidney transplant recipients, the quality of life and long-term prognosis are greatly improved in transplanted patients. However, there is a large gap between availability and need for donor kidneys. This has led to the increase in the use of expanded kidney donor criteria. Allograft dysfunction immediately after transplant sets it up for many complications, such as acute rejection and shorter allograft survival. Delayed graft function (DGF) is one of the immediate posttransplant insults to the kidney allograft, which is increasing in prevalence due to efforts to maximize the available donor pool for kidneys and use of expanded kidney donor criteria. In this review, we discuss the risk factors for DGF, its implications for long-term allograft survival, animal models of DGF, and the therapeutic options currently under evaluation for prevention and management of DGF.

Direct androgen receptor control of sexually dimorphic gene expression in the mammalian kidney

Mammalian organs exhibit distinct physiology, disease susceptibility, and injury responses between the sexes. In the mouse kidney, sexually dimorphic gene activity maps predominantly to proximal tubule (PT) segments. Bulk RNA sequencing (RNA-seq) data demonstrated that sex differences were established from 4 and 8 weeks after birth under gonadal control. Hormone injection studies and genetic removal of androgen and estrogen receptors demonstrated androgen receptor (AR)-mediated regulation of gene activity in PT cells as the regulatory mechanism. Interestingly, caloric restriction feminizes the male kidney. Single-nuclear multiomic analysis identified putative cis-regulatory regions and cooperating factors mediating PT responses to AR activity in the mouse kidney. In the human kidney, a limited set of genes showed conserved sex-linked regulation, whereas analysis of the mouse liver underscored organ-specific differences in the regulation of sexually dimorphic gene expression. These findings raise interesting questions on the evolution, physiological significance, disease, and metabolic linkage of sexually dimorphic gene activity.

Sex as a biological variable: Mechanistic insights and clinical relevance in solid organ transplantation

Biological sex affects immunity broadly, with recognized effects on the incidence and severity of autoimmune diseases, infections, and malignancies. Consequences of sex on alloimmunity and outcomes in solid organ transplantation are less well defined. Clinical studies have shown that donor and recipient sex independently impact transplant outcomes, which are further modified by aging. Potential mechanisms have thus far not been detailed and may include hormonal, genetic, and epigenetic components. Here, we summarize relevant findings in immunity in addition to studies in clinical and experimental organ transplantation detailing the effects of biological sex on alloimmunity. Understanding both clinical impact and mechanisms is expected to provide critical insights on the complexity of alloimmune responses, with the potential to fine-tune treatment and allocation while providing a rationale to include both sexes in transplant research.

Sex differences in obesity-induced renal lipid accumulation revealed by lipidomics: a role of adiponectin/AMPK axis

BACKGROUND

Sex differences have been observed in the development of obesity-related complications in patients, as well as in animal models. Accumulating evidence suggests that sex-dependent regulation of lipid metabolism contributes to sex-specific physiopathology. Lipid accumulation in the renal tissue has been shown to play a major role in the pathogenesis of obesity-induced kidney injury. Unlike in males, the physiopathology of the disease has been poorly described in females, particularly regarding the lipid metabolism adaptation.

METHODS

Here, we compared the lipid profile changes in the kidneys of female and male mice fed a high-fat diet (HFD) or low-fat diet (LFD) by lipidomics and correlated them with pathophysiological changes.

RESULTS

We showed that HFD-fed female mice were protected from insulin resistance and hepatic steatosis compared to males, despite similar body weight gains. Females were particularly protected from renal dysfunction, oxidative stress, and tubular lipid accumulation. Both HFD-fed male and female mice presented dyslipidemia, but lipidomic analysis highlighted differential renal lipid profiles. While both sexes presented similar neutral lipid accumulation with obesity, only males showed increased levels of ceramides and phospholipids. Remarkably, protection against renal lipotoxicity in females was associated with enhanced renal adiponectin and AMP-activated protein kinase (AMPK) signaling. Circulating adiponectin and its renal receptor levels were significantly lower in obese males, but were maintained in females. This observation correlated with the maintained basal AMPK activity in obese female mice compared to males.

CONCLUSIONS

Collectively, our findings suggest that female mice are protected from obesity-induced renal dysfunction and lipotoxicity associated with enhanced adiponectin and AMPK signaling compared to males.

The Utility of Spatial Transcriptomics for Solid Organ Transplantation

Spatial transcriptomics (ST) measures and maps transcripts within intact tissue sections, allowing the visualization of gene activity within the spatial organization of complex biological systems. This review outlines advances in genomic sequencing technologies focusing on in situ sequencing-based ST, including applications in transplant and relevant nontransplant settings. We describe the experimental and analytical pipelines that underpin the current generation of spatial technologies. This context is important for understanding the potential role ST may play in expanding our knowledge, including in organ transplantation, and the important caveats/limitations when interpreting the vast data output generated by such methodological platforms.

Direct androgen receptor regulation of sexually dimorphic gene expression in the mammalian kidney

Mammalian organs exhibit distinct physiology, disease susceptibility and injury responses between the sexes. In the mouse kidney, sexually dimorphic gene activity maps predominantly to proximal tubule (PT) segments. Bulk RNA-seq data demonstrated sex differences were established from 4 and 8 weeks after birth under gonadal control. Hormone injection studies and genetic removal of androgen and estrogen receptors demonstrated androgen receptor (AR) mediated regulation of gene activity in PT cells as the regulatory mechanism. Interestingly, caloric restriction feminizes the male kidney. Single-nuclear multiomic analysis identified putative cis-regulatory regions and cooperating factors mediating PT responses to AR activity in the mouse kidney. In the human kidney, a limited set of genes showed conserved sex-linked regulation while analysis of the mouse liver underscored organ-specific differences in the regulation of sexually dimorphic gene expression. These findings raise interesting questions on the evolution, physiological significance, and disease and metabolic linkage, of sexually dimorphic gene activity.

Multiomics Analyses Reveal Sex Differences in Mouse Renal Proximal Subsegments

SIGNIFICANCE STATEMENT

Sex-dependent differences in kidney function are recognized but the underlying molecular mechanisms are largely unexplored. Advances in genomics and proteomic technologies now allow extensive characterization of differences between the same cell types of males and females. Multiomics integrating RNA-seq, ATAC-seq, and proteomics data to investigate differences in gene expression, chromatin accessibility, and protein expression in proximal tubules of male and female mice identified many sex-biased genes and proteins associated with kidney functions, including metabolic and transport processes. Sex differences may also arise from variations of the interaction between transcription factors and accessible chromatin regions. A comprehensive web resource is provided to advance understanding of sex differences in cells of the proximal tubule.

BACKGROUND

Sex differences have been increasingly recognized as important in kidney physiology and pathophysiology, but limited resources are available for comprehensive interrogation of sex differences.

METHODS

RNA-seq and ATAC-seq of microdissected mouse proximal tubules and protein mass spectrometry of homogenized perfused mouse kidneys reveal differences in proximal tubule cells of males and females.

RESULTS

The transcriptomic data indicated that the major differences in the proximal tubules between the sexes were in the S2/S3 segments, and most of the sex-biased transcripts mapped to autosomes rather than to the sex chromosomes. Many of the transcripts exhibiting sex-biased expression are involved in monocarboxylic acid metabolic processes, organic anion transport, and organic acid transport. The ATAC-seq method on microdissected tubules captured chromatin accessibility. Many of the more than 7000 differentially accessible DNA regions identified were in distal regions. Motif analyses revealed a lack of direct involvement of estrogen receptors or the androgen receptor (absence of canonical hormone response elements), suggesting an indirect regulatory role of sex hormones. Instead, analyses identified several transcription factors (TFs) ( Tead1 , Nfia/b , and Pou3f3 ) whose interplay with proximal tubule-specific TFs ( e.g. , Hnf1b , Hnf4a ) may contribute to sex differences. Finally, the whole-kidney proteome was correlated with the transcriptome, and many sex-biased proteins ( e.g. , Cyp2e1, Acsm2/3) were identified.

CONCLUSIONS

Sex-dependent cis-regulatory elements interact with TFs in ways that lead to sex-biased gene expression in proximal tubule cells. These data are provided as a user-friendly web page at https://esbl.nhlbi.nih.gov/MRECA/PT/ .

Organ Protection by Caloric Restriction Depends on Activation of the De Novo NAD+ Synthesis Pathway

SIGNIFICANCE STATEMENT

AKI is a major clinical complication leading to high mortality, but intensive research over the past decades has not led to targeted preventive or therapeutic measures. In rodent models, caloric restriction (CR) and transient hypoxia significantly prevent AKI and a recent comparative transcriptome analysis of murine kidneys identified kynureninase (KYNU) as a shared downstream target. The present work shows that KYNU strongly contributes to CR-mediated protection as a key player in the de novo nicotinamide adenine dinucleotide biosynthesis pathway. Importantly, the link between CR and NAD+ biosynthesis could be recapitulated in a human cohort.

BACKGROUND

Clinical practice lacks strategies to treat AKI. Interestingly, preconditioning by hypoxia and caloric restriction (CR) is highly protective in rodent AKI models. However, the underlying molecular mechanisms of this process are unknown.

METHODS

Kynureninase (KYNU) knockout mice were generated by Clustered Regularly Interspaced Short Palindromic Repeats (CRISPR) and comparative transcriptome, proteome and metabolite analyses of murine kidneys pre- and post-ischemia-reperfusion injury in the context of CR or ad libitum diet were performed. In addition, acetyl-lysin enrichment and mass spectrometry were used to assess protein acetylation.

RESULTS

We identified KYNU as a downstream target of CR and show that KYNU strongly contributes to the protective effect of CR. The KYNU-dependent de novo nicotinamide adenine dinucleotide (NAD+) biosynthesis pathway is necessary for CR-associated maintenance of NAD+ levels. This finding is associated with reduced protein acetylation in CR-treated animals, specifically affecting enzymes in energy metabolism. Importantly, the effect of CR on de novo NAD+ biosynthesis pathway metabolites can be recapitulated in humans.

CONCLUSIONS

CR induces the de novo NAD+ synthesis pathway in the context of IRI and is essential for its full nephroprotective potential. Differential protein acetylation may be the molecular mechanism underlying the relationship of NAD+, CR, and nephroprotection.

Development of a risk prediction score and equation for chronic kidney disease: a retrospective cohort study

Chronic kidney disease (CKD) is a risk factor for end-stage renal disease and contributes to increased risk of cardiovascular disease morbidity and mortality. We aimed to develop a risk prediction score and equation for future CKD using health checkup data. This study included 58,423 Japanese participants aged 30-69 years, who were randomly assigned to derivation and validation cohorts at a ratio of 2:1. The predictors were anthropometric indices, life style, and blood sampling data. In derivation cohort, we performed multivariable logistic regression analysis and obtained the standardized beta coefficient of each factor that was significantly associated with new-onset CKD and assigned scores to each factor. We created a score and an equation to predict CKD after 5 years and applied them to validation cohort to assess their reproducibility. The risk score ranged 0-16, consisting of age, sex, hypertension, dyslipidemia, diabetes, hyperuricemia, and estimated glomerular filtration rate (eGFR), with area under the curve (AUC) of 0.78 for the derivation cohort and 0.79 for the validation cohort. The CKD incidence gradually and constantly increased as the score increased from ≤ 6 to ≥ 14. The equation consisted of the seven indices described above, with AUC of 0.88 for the derivation cohort and 0.89 for the validation cohort. We developed a risk score and equation to predict CKD incidence after 5 years in Japanese population under 70 years of age. These models had reasonably high predictivity, and their reproducibility was confirmed through internal validation.

Cytoplasmic HMGB1 induces renal tubular ferroptosis after ischemia/reperfusion

As a damage-associated molecular pattern molecule, high-mobility group box 1 (HMGB1) is well-studied and is released from injured tubular epithelial cells to trigger cell death. However, the role of intracellular HMGB1 induced cell death during acute kidney injury (AKI) is poorly understood. We showed that cytosolic HMGB1 induced ferroptosis by binding to acyl-CoA synthetase long-chain family member 4 (ACSL4), the driver of ferroptosis, following renal ischemia/reperfusion (I/R). Both mouse and human kidneys with acute tubular injury were characterized by nucleocytoplasmic translocation of HMGB1in tubular cells. Pharmacological inhibition of HMGB1 nucleocytoplasmic translocation and deletion of HMGB1 in tubular epithelial cells in mice inhibited I/R-induced AKI, tubular ferroptosis, and inflammation compared to those in controls. Co-immunoprecipitation and serial section staining confirmed the interaction between HMGB1 and ACSL4. Taken together, our results demonstrated that cytoplasmic HMGB1 is essential for exacerbating inflammation-associated cellular injury by activating renal tubular ferroptosis via ACSL4 after I/R injury. These findings indicate that cytoplasmic HMGB1 is a regulator of ferroptosis and a promising therapeutic target for AKI.

Single-cell profiling of healthy human kidney reveals features of sex-based transcriptional programs and tissue-specific immunity

Knowledge of the transcriptional programs underpinning the functions of human kidney cell populations at homeostasis is limited. We present a single-cell perspective of healthy human kidney from 19 living donors, with equal contribution from males and females, profiling the transcriptome of 27677 cells to map human kidney at high resolution. Sex-based differences in gene expression within proximal tubular cells were observed, specifically, increased anti-oxidant metallothionein genes in females and aerobic metabolism-related genes in males. Functional differences in metabolism were confirmed in proximal tubular cells, with male cells exhibiting higher oxidative phosphorylation and higher levels of energy precursor metabolites. We identified kidney-specific lymphocyte populations with unique transcriptional profiles indicative of kidney-adapted functions. Significant heterogeneity in myeloid cells was observed, with a MRC1⁺LYVE1⁺FOLR2⁺C1QC⁺ population representing a predominant population in healthy kidney. This study provides a detailed cellular map of healthy human kidney, and explores the complexity of parenchymal and kidney-resident immune cells.

Sex and gender disparity in kidney transplantation: Historical and future perspectives

Sex and gender disparity exist in various stages of kidney transplantation. Females were found to be less likely to be referred for kidney transplant, complete pre-transplant evaluation, be placed on the waitlist, and receive a kidney transplant compared to their male counterparts. Interestingly, females comprise the majority of living kidney donors. This review explores the biological and psychosocial factors that contribute to sex and gender disparity in kidney transplantation and proposes ways to address the disparity.

Sex differences in resilience to ferroptosis underlie sexual dimorphism in kidney injury and repair

In both humans and mice, repair of acute kidney injury is worse in males than in females. Here, we provide evidence that this sexual dimorphism results from sex differences in ferroptosis, an iron-dependent, lipid-peroxidation-driven regulated cell death. Using genetic and single-cell transcriptomic approaches in mice, we report that female sex confers striking protection against ferroptosis, which was experimentally induced in proximal tubular (PT) cells by deleting glutathione peroxidase 4 (Gpx4). Single-cell transcriptomic analyses further identify the NFE2-related factor 2 (NRF2) antioxidant protective pathway as a female resilience mechanism against ferroptosis. Genetic inhibition and pharmacological activation studies show that NRF2 controls PT cell fate and plasticity by regulating ferroptosis. Importantly, pharmacological NRF2 activation protects male PT cells from ferroptosis and improves cellular plasticity as in females. Our data highlight NRF2 as a potential therapeutic target to prevent failed renal repair after acute kidney injury in both sexes by modulating cellular plasticity.

Dietary selenium intake and the risk of kidney stones in adults, an analysis of 2007-2018 National Health and Nutrition Examination Survey, a cross-sectional study

Purpose

To evaluate the association between dietary selenium intake and the risk of kidney stones in adults.

Materials and methods

We performed a cross-sectional analysis using data from 2007 to 2018 National Health and Nutrition Examination Survey (NHANES). Dietary intake information of 30,184 participants was obtained using first 24-h dietary recall interview, and kidney stones were presented by a standard questionnaire. The quartile analysis, stratified analysis and non-linearity analysis were used to estimate the association between dietary selenium intake and kidney stones after an adjustment for potential confounders.

Results

The multiple logistic regression indicated that the fourth quantile (Q4) of dietary selenium intake had a lower risk of kidney stones than the first quantile (Q1) in Model 3 (OR 0.82, P < 0.05). The stratified analyses indicated there were statistical differences between dietary selenium intake and kidney stones among younger (age < 50) (OR 0.65, P < 0.01), male (OR 0.73, P < 0.01) and overweight/obese (BMI ≥ 25.0) (OR 0.80, P < 0.05) individuals in Model 3. The non-linear relationship was founded between dietary selenium intake and kidney stones in all participants, younger, male and overweight/obese individuals after adjusting for confounding factors.

Conclusion

Our study revealed an inverse relation between the level of dietary selenium intake and the risk of kidney stones for the United States population, especially for younger (age < 50), male and overweight/obese (BMI ≥ 25.0) individuals. The study provides preliminary guidance on dietary selenium intake for the prevention of kidney stones in different populations. Further studies are required to confirm our findings and clarified the biological mechanisms.

Donor characteristics and their impact on kidney transplantation outcomes: Results from two nationwide instrumental variable analyses based on outcomes of donor kidney pairs accepted for transplantation

BACKGROUND

Donor-characteristics and donor characteristics-based decision algorithms are being progressively used in the decision process whether or not to accept an available donor kidney graft for transplantation. While this may improve outcomes, the performance characteristics of the algorithms remains moderate. To estimate the impact of donor factors of grafts accepted for transplantation on transplant outcomes, and to test whether implementation of donor-characteristics-based algorithms in clinical decision-making is justified, we applied an instrumental variable analysis to outcomes for kidney donor pairs transplanted in different individuals.

METHODS

This analysis used (dis)congruent outcomes of kidney donor pairs as an instrument and was based on national transplantation registry data for all donor kidney pairs transplanted in separate individuals in the Netherlands (1990-2018, 2,845 donor pairs), and the United Kingdom (UK, 2000-2018, 11,450 pairs). Incident early graft loss (EGL) was used as the primary discriminatory factor. It was reasoned that a scenario with a dominant impact of donor variables on transplantation outcomes would result in high concordance of EGL in both recipients, whilst dominance of asymmetrical outcomes could indicate a more complex scenario, involving an interaction of donor, procedural and recipient factors.

FINDINGS

Incidences of congruent EGL (Netherlands: 1·2%, UK: 0·7%) were slightly lower than the arithmetical (stochastic) incidences, suggesting that once a graft has been accepted for transplantation, donor factors minimally contribute to incident EGL. A long-term impact of donor factors was explored by comparing outcomes for functional grafts from donor pairs with asymmetrical vs. symmetrical outcomes. Recipient survival was similar for both groups, but a slightly compromised graft survival was observed for grafts with asymmetrical outcomes in the UK cohort: (10-years Hazard Ratio for graft loss: 1·18 [1·03-1·35] p<0·018); and 5 years eGFR (48·6 [48·3-49·0] vs. 46·0 [44·5-47·6] ml/min in the symmetrical outcome group, p<0·001).

INTERPRETATION

Our results suggest that donor factors for kidney grafts deemed acceptable for transplantation impact minimally on transplantation outcomes. A strong reliance on donor factors and/or donor-characteristics-based decision algorithms could result in unjustified rejection of grafts. Future efforts to optimize transplant outcomes should focus on a better understanding of the recipient factors underlying transplant outcomes.

FUNDING

None.

Sex-specific differences in early renal impairment associated with arsenic, lead, and cadmium exposure among young adults in Taiwan

Exposure to a single metal has been reported to damage renal function in humans. However, information regarding the association between multiple-metal exposure and markers for early renal impairment in different sexes among the young adult Taiwanese population is scarce. We assessed the association between exposure to arsenic (As), cadmium (Cd), and lead (Pb), and early renal impairment markers using urinary microalbumin (MA), β2-microglobulin (β2MG), and N-acetyl-beta-D-glucosaminidase (NAG) by analyzing 157 young adults aged 20‒29 years, in Taiwan. Inductively coupled plasma mass spectrometry was used to determine urinary As, Cd, and Pb levels. Regression models were applied to different sex groups. The results showed that after adjusting for potential confounding factors and each metal, urinary Cd levels were significantly positively associated with urinary MA (β = 0.523, 95% CI: 0.147-0.899) and β2MG (β = 1.502, 95% CI: 0.635-2.370) in males. However, the urinary Cd level was significantly positively associated with only urinary NAG (β = 0.161, 95% CI: 0.027-0.296) in females. This study thus indicates that the effect of exposure to metals (especially Cd) on early renal impairment among young adults in Taiwan is sex-specific. Our study results could contribute toward developing early intervention programs for decreasing the incidence of renal dysfunction. Further studies are warranted to confirm our findings and clarify the potential mechanisms involved.

The Selective Estrogen Receptor Modulator, Raloxifene, Is Protective Against Renal Ischemia-Reperfusion Injury

BACKGROUND

There is increasing evidence that estrogen is responsible for improved outcomes in female kidney transplant recipients. Although the exact mechanism is not yet known, estrogen appears to exert its protective effects by ameliorating ischemia-reperfusion injury (IRI). In this study, we have examined whether the beneficial effects of exogenous estrogen in renal IRI are replicated by therapy with any one of several selective estrogen receptor modulators.

METHODS

C57BL/6 adult mice underwent standardized warm renal ischemia for 28 min after being injected with the selective estrogen receptor modulators, raloxifene, lasofoxifene, tamoxifen, bazedoxifene, or control vehicle (dimethyl sulfoxide), at 16 and 1 h before IRI. Plasma concentrations of blood urea nitrogen and creatinine were assessed 24, 48, 72, and 96 h post-IRI. Tissue was collected 30 d postischemia for fibrosis analysis using Sirius Red staining.

RESULTS

Raloxifene treatment in female mice resulted in significantly lower blood urea nitrogen and creatinine after IRI and significantly lower fibrosis 30 d following IRI.

CONCLUSIONS

Raloxifene is protective against both acute kidney injury and fibrosis resulting from renal IRI in a mouse model.

A systematic analysis of diet-induced nephroprotection reveals overlapping changes in cysteine catabolism

Caloric Restriction (CR) extends lifespan and augments cellular stress-resistance from yeast to primates, making CR an attractive strategy for organ protection in the clinic. Translation of CR to patients is complex, due to problems regarding adherence, feasibility, and safety concerns in frail patients. Novel tailored dietary regimens, which modulate the dietary composition of macro- and micronutrients rather than reducing calorie intake promise similar protective effects and increased translatability. However, a direct head-to-head comparison to identify the most potent approach for organ protection, as well as overlapping metabolic consequences have not been performed. We systematically analyzed six dietary preconditioning protocols - fasting mimicking diet (FMD), ketogenic diet (KD), dietary restriction of branched chained amino acids (BCAA), two dietary regimens restricting sulfur-containing amino acids (SR80/100) and CR - in a rodent model of renal ischemia-reperfusion injury (IRI) to quantify diet-induced resilience in kidneys. Of the administered diets, FMD, SR80/100 and CR efficiently protect from kidney damage after IRI. Interestingly, these approaches show overlapping changes in oxidative and hydrogen sulfide (H₂S)-dependent cysteine catabolism as a potential common mechanism of organ protection.

Caloric restriction reduces the pro-inflammatory eicosanoid 20- hydroxyeicosatetraenoic acid to protect from acute kidney injury

Acute kidney injury is a frequent complication in the clinical setting and associated with significant morbidity and mortality. Preconditioning with short-term caloric restriction is highly protective against kidney injury in rodent ischemia reperfusion injury models. However, the underlying mechanisms are unknown hampering clinical translation. Here, we examined the molecular basis of caloric restriction-mediated protection to elucidate the principles of kidney stress resistance. Analysis of an RNAseq dataset after caloric restriction identified Cyp4a12a, a cytochrome exclusively expressed in male mice, to be strongly downregulated after caloric restriction. Kidney ischemia reperfusion injury robustly induced acute kidney injury in male mice and this damage could be markedly attenuated by pretreatment with caloric restriction. In females, damage was significantly less pronounced and preconditioning with caloric restriction had only little effect. Tissue concentrations of the metabolic product of Cyp4a12a, 20-hydroxyeicosatetraenoic acid (20-HETE), were found to be significantly reduced by caloric restriction. Conversely, intraperitoneal supplementation of 20-HETE in preconditioned males partly abrogated the protective potential of caloric restriction. Interestingly, this effect was accompanied by a partial reversal of caloric restriction-induced changes in protein but not RNA expression pointing towards inflammation, endoplasmic reticulum stress and lipid metabolism. Thus, our findings provide an insight into the mechanisms underlying kidney protection by caloric restriction. Hence, understanding the mediators of preconditioning is an important pre-requisite for moving towards translation to the clinical setting.

Persistent vascular congestion in male spontaneously hypertensive rats contributes to delayed recovery of renal function following ischemia-reperfusion compared to females

Acute kidney injury (AKI) is a serious and frequent clinical complication with mortality rates up to 80%. Vascular congestion in the renal outer medulla occurs early after ischemia reperfusion (IR) injury, and congestion has been linked to worsened outcomes following IR. There is evidence implicating both male sex and preexisting hypertension as risk factors for poor outcomes following IR. The present study tested the hypothesis that male spontaneously hypertensive rats (SHR) have greater vascular congestion and impaired renal recovery following renal IR vs. female SHR and normotensive male Sprague-Dawley rats (SD). 13 wk old male and female SHR and SD were subjected to sham surgery or 30 minutes of warm bilateral ischemia followed by reperfusion. Rats were euthanized 24 hours or 7 days post-IR. IR increased renal injury in all groups vs. sham controls at 24 hours. At 7 days post-IR, injury remained elevated only in male SHR. Histological examination of SD and SHR kidneys 24 hours post-IR showed vascular congestion in males and females. Vascular congestion was sustained only in male SHR 7 days post-IR. To assess the role of vascular congestion on impaired recovery following IR, additional male and female SHR were pretreated with heparin (200 U/kg) prior to IR. Heparin pre-treatment reduced IR-induced congestion and improved renal function in male SHR 7 days post-IR. Interestingly, preventing increases in BP in male SHR did not alter sustained vascular congestion. Our data demonstrate that IR-induced vascular congestion is a major driving factor for impaired renal recovery in male SHR.

Estradiol Ameliorates Acute Kidney Ischemia-Reperfusion Injury by Inhibiting the TGF-βRI-SMAD Pathway

Renal ischemia–reperfusion injury (IRI) is less extensive in females than males in both animals and humans; however, this protection diminishes after menopause, suggesting that estrogen plays a pivotal role in IRI, but the underlying mechanism remains largely unknown. Our study found that 45 min of warm ischemia was sufficient to induce significant pathological changes without causing death in model animals. Compared with male rats, female rats exhibited less extensive apoptosis, kidney injury, and fibrosis; these effects were worsened in ovariectomized (OVX) rats and ameliorated upon estradiol (E₂) supplementation. Furthermore, the levels of TGF-βRI, but not TGF-βRII or TGF-β1, were significantly increased in OVX rats, accompanied by phosphorylated SMAD2/3 activation. Interestingly, the alteration trend of the nuclear ERα level was opposite that of TGF-βRI. Furthermore, dual luciferase reporter and chromatin immunoprecipitation assays showed that ERα could bind to the promoter region of TGF-βRI and negatively regulate its mRNA expression. Moreover, an in vitro study using NRK-52E cells showed that ERα knockdown blocked E₂-mediated protection, while TGF-βRI knockdown protected cells against hypoxic insult. The findings of this study suggest that renal IRI is closely related to the TGF-βRI-SMAD pathway in females and that E₂ exert its protective effect via the ERα-mediated transcriptional inhibition of TGF-βRI expression.

Does Gender Affirming Hormone Therapy Increase the Risk of Kidney Disease?

Kidney health and manifestation of disease in transgender men, women, and nonbinary individuals are not well understood. Transgender individuals commonly receive gender-affirming hormone therapy (GAHT) to align their outward appearance with their gender. Recent attention to the differences in fundamental kidney parameters has identified that transgender individuals may manifest levels of these biomarkers differently than their cisgender counterparts. Improving understanding of the differences in biomarkers and in the development of kidney disease is essential to providing appropriate kidney care to this vulnerable population. In this review, we introduce the current information related to GAHT and kidney health and highlight the significant gaps in our understanding of how GAHT may affect kidney physiology and pathophysiology.

A Reproducible Mouse Model of Moderate CKD With Early Manifestations of Osteoblastic Transition of Cardiovascular System

Chronic kidney disease (CKD) is a significant public health challenge with a substantial associated risk of mortality, morbidity, and health care expenditure. Culprits that lead to development and progression of CKD are multifaceted and heterogenous in nature. This notion underscores the need for diversification of animal models to investigate its pathophysiology, related complications, and to subsequently enable discovery of novel therapeutics. Importantly, animal models that could recapitulate complications of CKD in both genders are desperately needed. Cardiovascular disease is the most common cause of death in CKD patients that may be due in part to high prevalence of vascular calcification (VC). Using DBA/2 mice that are susceptible to development of VC, we sought to investigate the feasibility and reproducibility of a unilateral ischemia-reperfusion model followed by contralateral nephrectomy (UIRI/Nx) to induce CKD and its related complications in female and male mice. Our results demonstrate that irrespective of gender, mice faithfully displayed complications of moderate CKD following UIRI/Nx as evidenced by significant rise in serum creatinine, albuminuria, higher degree of collagen deposition, elevated expression of classic fibrotic markers, higher circulating levels of FGF-23, PTH and hepcidin. Moreover, we corroborate the osteoblastic transition of aortic smooth muscle cells and cardiomyocytes based on higher levels of osteoblastic markers namely, Cbfa-1, osteopontin, osteocalcin, and osterix. Our data confirms a viable, and consistent model of moderate CKD and its associated complications in both male and female mice. Furthermore, early evidence of osteoblastic transition of cardiovascular system in this model confirms its suitability for studying and implementing potential preventive and/or therapeutic approaches that are urgently needed in this field.

Sex and Gender Differences in Kidney Transplantation

Sex and gender often are used interchangeably, but are two distinct entities, with sex being the biological attribute and gender including the social, psychological, and cultural aspects of one's identity. Kidney transplantation has been proven to be the best treatment for end-stage kidney disease, improving both quality of life and life-expectancy for most patients. However, gender disparities in access to and outcomes of kidney transplantation remain despite the plethora of evidence showing the advantages of kidney transplantation to our patients. Data have shown that women are less likely to be waitlisted for a kidney transplant and to receive a deceased donor or a living donor kidney. On the other hand, women are more likely than men to become living kidney donors. Although some state the latter is the result of the female gender to nurture and care for loved ones, others believe this observation is because women often are incompatible with their spouse or child because pregnancy is a strong sensitizing event, which stems from the biological rather than the social differences between the sexes. Influence of sex and gender is not limited to access to kidney transplantation, but rather exist in other areas of transplant medicine, such as the difference observed in transplant outcomes between the sexes, variability in immunosuppression metabolism, and even in more contemporary areas such as recent data showing sex-based differences in outcomes of kidney transplant recipients with coronavirus disease-2019, with males having an increased incidence of acute kidney injury and death.

Experimental models of acute kidney injury for translational research

Preclinical models of human disease provide powerful tools for therapeutic discovery but have limitations. This problem is especially apparent in the field of acute kidney injury (AKI), in which clinical trial failures have been attributed to inaccurate modelling performed largely in rodents. Multidisciplinary efforts such as the Kidney Precision Medicine Project are now starting to identify molecular subtypes of human AKI. In addition, over the past decade, there have been developments in human pluripotent stem cell-derived kidney organoids as well as zebrafish, rodent and large animal models of AKI. These organoid and AKI models are being deployed at different stages of preclinical therapeutic development. However, the traditionally siloed, preclinical investigator-driven approaches that have been used to evaluate AKI therapeutics to date rarely account for the limitations of the model systems used and have given rise to false expectations of clinical efficacy in patients with different AKI pathophysiologies. To address this problem, there is a need to develop more flexible and integrated approaches, involving teams of investigators with expertise in a range of different model systems, working closely with clinical investigators, to develop robust preclinical evidence to support more focused interventions in patients with AKI.

The Neglected Price of Pediatric Acute Kidney Injury: Non-renal Implications

Preclinical models and emerging translational data suggest that acute kidney injury (AKI) has far reaching effects on all other major organ systems in the body. Common in critically ill children and adults, AKI is independently associated with worse short and long term morbidity, as well as mortality, in these vulnerable populations. Evidence exists in adult populations regarding the impact AKI has on life course. Recently, non-renal organ effects of AKI have been highlighted in pediatric AKI survivors. Given the unique pediatric considerations related to somatic growth and neurodevelopmental consequences, pediatric AKI has the potential to fundamentally alter life course outcomes. In this article, we highlight the challenging and complex interplay between AKI and the brain, heart, lungs, immune system, growth, functional status, and longitudinal outcomes. Specifically, we discuss the biologic basis for how AKI may contribute to neurologic injury and neurodevelopment, cardiac dysfunction, acute lung injury, immunoparalysis and increased risk of infections, diminished somatic growth, worsened functional status and health related quality of life, and finally the impact on young adult health and life course outcomes.

Thermoneutral Regulation and Acute Injury: Implications for Acute Kidney Injury

Acute kidney injury (AKI) has demonstrated sex differences as illustrated in clinical and preclinical studies. In most cases, females show a significant resistance to AKI as manifested by renal indicators of injury, and thus much of the literature is derived from studies exclusively in males. Thermoneutral housing alters sex differences in acute injury of the liver, but has not been studied in the kidney. Thermoneutrality, the ambient temperature at which additional energy is not needed to maintain core body temperature, is regulated by mechanisms residing in mitochondria. Importantly, mitochondrial function plays an important role in induction and recovery of AKI. Mechanisms that regulate thermoneutrality include uncoupling proteins (UCPs) and one of its upstream regulators peroxisome proliferator-activated receptor gamma coactivator-1α (PGC-1α). PGC-1α has been extensively studied in AKI in males. UCP-2, a UCP expressed in the kidney, has been minimally studied in AKI in males. Expression of other UCPs in the kidney has not been well defined. No studies of either PGC-1α or UCPs have interrogated for a sex difference nor have they been investigated at thermoneutrality in the kidney. In this brief review, pathways of importance in thermoneutrality are described and related to pathways of importance in modulating susceptibility to AKI. Clarity in the understanding of the impact of thermoneutrality on AKI in altering susceptibility in females may expand our understanding of the critical role of mitochondrial function in this setting. Unique utilization of mitochondrial-based molecular pathways in females may then inform potential therapies.

The impact of donor and recipient sex on kidney allograft survival in pediatric transplant recipients

BACKGROUND

Transplantation is widely considered the gold standard method of kidney replacement therapy. Despite compelling evidence for biological sexual dimorphisms, the role of donor and recipient sex matching in transplantation is undefined.

METHODS

The UK historical cohort study explores the impact of donor and recipient sex on allograft survival, in children receiving their first deceased donor transplant. Nationwide registry data were collected for 1316 transplant procedures performed from January 1, 1999, to December 31, 2019.

RESULTS

Male donor-male recipient transplantation occurred most frequently (35%), followed by female donor-male recipient (23%), male donor-female recipient (22%), and female donor-female recipient (20%). The median follow-up time was 7.03 years (IQR: 2.89-12.4 years), with a total of 10,326 person-years. Male donor-male recipients were associated with the highest 10-year kidney allograft survival (72.8% [95% CI 68.3-77.8]) and male donor-female recipients with the lowest (64% [95% CI 57.7-71.1]). Multivariable Cox regression demonstrated for male donor transplantation, the risk of kidney allograft failure was 1.46 times greater for female (compared to male) recipients, after adjusting for acquired recipient age, recipient/donor age at transplantation, mismatched HLA A/B/DR, waitlist time, cold ischemia time, CMV seropositivity, donor hypertension, and donor diabetes (HR 1.46 [95% CI. 1.06-2.01], p = 0.02). There was no evidence for an independent effect of donor or recipient sex in other combinations.

CONCLUSION

This study highlights the complex relationship between donor and recipient sex and pediatric kidney allograft survival, which require further mechanistic evaluation.

Estrogen alleviates hepatocyte necroptosis depending on GPER in hepatic ischemia reperfusion injury

Hepatic ischemia reperfusion injury (IRI) occurs in liver transplantation, complex liver resection, and hemorrhagic shock, which causes donor organ shortage and hepatic damage. The burst of reactive oxygen species (ROS) during reperfusion leads to cell apoptosis and necroptosis. It has been reported that estrogen could attenuate hepatic IRI. G protein estrogen receptor (GPER) mediates estrogen effects via nonclassic receptor systems. Here, we investigate whether estrogen protecting liver from hepatic IRI depends on GPER and the influence of GPER activation on hepatocyte necroptosis. We proved that estrogen had a protective effect on both hepatocyte hypoxia re-oxygen (H/R) challenge and mouse hepatic ischemia reperfusion model. However, the application of GPER specific antagonist G15 before estrogen inhibited this beneficial effect. The results of mitochondria functional measurement revealed that estrogen improved hepatocyte mitochondria function by activating GPER, which might benefit from the increased expression of connexin 43 (Cx43) in mitochondria. To investigate the relationship between GPER activation and necroptosis, we used caspase-3/7 inhibitor benzyloxycarbonyl-Asp(OMe)-Glu(OMe)-Val-Asp(OMe)-chloromethylketone (Z-DEVD-FMK) to eliminate the interference of apoptosis. Estrogen showed a protective effect on hepatic IRI after using Z-DEVD-FMK, which could be suppressed by G15. GPER activation decreased the level of receptor interacting protein kinase (RIPK) 3, phosphorylated (p-) RIPK1, and p-mixed lineage kinase domain-like (MLKL). The co-immunoprecipitation result indicated that GPER could bind with RIPK3. GPER is indispensable in estrogen protecting liver from IRI. GPER activation attenuates hepatocyte necroptosis by decreasing the level of RIPK3, p-RIPK1, and p-MLKL.

Measurement of glomerular filtration rate reveals that subcapsular injection of shear-thinning hyaluronic acid hydrogels does not impair kidney function in mice

The continued development of minimally invasive therapeutic implants, such as injectable hydrogels, necessitates the concurrent advancement of methods to best assess their biocompatibility via functional outcomes in vivo. Biomaterial implants have been studied to treat kidney disease; however, assessment of biocompatibility has been limited to biomarker and histological assessments. Techniques now exist to measure kidney function serially in vivo in murine studies via transcutaneous measurements of glomerular filtration rate (tGFR). In this study, adult male and female wild-type BalbC mice underwent right unilateral nephrectomy. The remaining solitary left kidney was allowed 4 weeks to recover via compensatory hypertrophy, after which subcapsular injection of either saline or shear-thinning hyaluronic acid hydrogel was performed. Serial tGFR measurements before and after treatment were used to assess the effect of hydrogel injection on kidney filtration. Urine and serum biomarkers of kidney function, and kidney histology were also quantified. Hydrogel injection did not affect kidney function, as assessed by tGFR. Results were in agreement with standard metrics of serum and urine biomarkers of injury as well as histological assessment of inflammation. The model developed provides a direct functional assessment of implant compatibility for the treatment of kidney disease and impact on kidney function.

Sirtuin-3 mediates sex differences in kidney ischemia-reperfusion injury

Studies suggest that biological sex influences susceptibility to kidney diseases with males demonstrating greater risk for developing ischemic acute kidney injury (AKI). Sex-related differences in mitochondrial function and homeostasis exist, likely contributing to sexual dimorphism in kidney injury, but the mechanisms are not well characterized. Our observations reveal lower baseline expression of Sirtuin-3 (Sirt3, a major mitochondrial acetyltransferase) in the kidneys of male mice versus females. We tested the hypothesis that differential expression of kidney Sirt3 may mediate sexual dimorphism in AKI using a bilateral kidney ischemia-reperfusion injury (IRI) model and three transgenic mouse models: (1) mice with global transgenic overexpression of Sirt3; (2) mice with inducible, kidney tubule-specific Sirt3 knockdown (iKD); and (3) mice with global Sirt3 knockout. Low mitochondrial Sirt3 (mtSirt3) in males versus females is associated with development of kidney tubular epithelium vacuoles, increased mitochondrial ROS and susceptibility to IRI. Transgenic overexpression of Sirt3 in males protects against kidney IRI and development of tubular epithelium vacuoles. In both sexes, mice with partial kidney tubular epithelium-specific Sirt3 knockdown display intermediate - while global Sirt3 knockout mice display the highest susceptibility to IRI. Female Sirt3 iKD mice demonstrate decreased survival and kidney function after IRI indistinguishable from control males, abolishing the protective effects observed in females. Mechanistically, observed differences in kidney mtSirt3 are sex hormone-dependent; estradiol increases - while testosterone decreases mtSirt3 protein. Our results demonstrate that Sirt3 is an important contributor to the observed sex-related differences in IRI susceptibility, and a potential therapeutic target in the clinical management of AKI.

Associations of Estimated Glomerular Filtration Rate with All-Cause Mortality and Cardiovascular Mortality in Patients with Diabetic Foot Osteomyelitis

Aim

The purpose of this study was to explore the association between estimated glomerular filtration rate (eGFR) and clinical outcomes in patients with diabetic foot osteomyelitis (DFO).

Methods

This was a retrospective observational study. A total of 199 patients with DFO were recruited and divided into three groups by eGFR: normal kidney function group (eGFR ≥ 90), mildly decreased kidney function group (eGFR 60–89) and moderately to severely decreased kidney function group (eGFR < 60). The patients were followed-up for a median of 36 months, and the study outcomes were all-cause mortality and major cardiovascular adverse events (MACE). Cox proportional hazard models were used to assess the association between eGFR and the outcomes, and a stratified analysis by sex was conducted.

Results

During follow-up, all-cause mortality occurred in 51 (25.63%) patients among 199 participants, 54 (28.72%) had MACE in 188 participants and 26 (48.15%) of them died. After fully adjusting for potential confounders, compared to eGFR < 90 mL/min/1.73 m², eGFR ≥ 90 mL/min/1.73 m² had lower incidence of all-cause mortality (HR = 0.43, 95% CI: 0.22–0.85; P = 0.015) and MACE (HR = 0.51, 95% CI: 0.27–0.96; P = 0.038). Additionally, compared to eGFR < 90 mL/min/1.73 m², eGFR ≥ 90 mL/min/1.73 m² was independently associated with decreased risk of all-cause mortality (HR = 0.33; 95% CI 0.14–0.76, P = 0.010) and MACE (HR = 0.27; 95% CI 0.11–0.65, P = 0.004) in male, but not in female.

Conclusion

In conclusion, decreased eGFR is a risk factor for all-cause mortality and MACE in individuals with DFO. Additionally, male with decreased eGFR had a higher risk of all-cause mortality and MACE, but female did not.

Targeting P2RX1 alleviates renal ischemia/reperfusion injury by preserving mitochondrial dynamics

Renal ischemia/reperfusion injury (IRI) is the major cause of acute kidney injury. However, mechanisms underlying the sudden loss in kidney function and tissue injury remain to be fully elucidated. Here, we performed RNA sequencing to systematically compare the transcriptome differences between IR injured kidneys and sham kidneys. We observed that mitochondrial dynamics was destructed in renal IRI. Expression of mitochondrial fusion-associated genes was reduced, whereas expression of mitochondrial fission-related genes was increased in renal IRI, and these findings were further confirmed by mitochondrial morphological observations. By screening 19 purinergic receptors, we noticed that P2RX1 expression was markedly upregulated in renal IRI. RNA sequencing and mitochondrial morphological observations revealed that mitochondrial dynamics was preserved in P2RX1 genetic knockout (P2rx1-/-) mice. Neutrophil extracellular traps (NETs) were reported to be essential for tissue injury in renal IRI, but the detailed mechanism remained unclear. In the present study, we found that P2RX1 favored the formation of neutrophil extracellular traps (NETs) in IRI, and NETs was essential for the impairment of mitochondrial dynamics. Mechanistically, P2RX1-involved metabolic interaction between platelets and neutrophils supported NETs formation. Activation of P2RX1 promoted platelets ATP release, which subsequently contributed to neutrophil glycolytic metabolism and NETs generation.

Counter Regulation of Spic by NF-κB and STAT Signaling Controls Inflammation and Iron Metabolism in Macrophages

Activated macrophages must carefully calibrate their inflammatory responses to balance efficient pathogen control with inflammation-mediated tissue damage, but the molecular underpinnings of this "balancing act" remain unclear. Using genetically engineered mouse models and primary macrophage cultures, we show that Toll-like receptor (TLR) signaling induces the expression of the transcription factor Spic selectively in patrolling monocytes and tissue macrophages by a nuclear factor κB (NF-κB)-dependent mechanism. Functionally, Spic downregulates pro-inflammatory cytokines and promotes iron efflux by regulating ferroportin expression in activated macrophages. Notably, interferon-gamma blocks Spic expression in a STAT1-dependent manner. High levels of interferon-gamma are indicative of ongoing infection, and in its absence, activated macrophages appear to engage a "default" Spic-dependent anti-inflammatory pathway. We also provide evidence for the engagement of this pathway in sterile inflammation. Taken together, our findings uncover a pathway wherein counter-regulation of Spic by NF-κB and STATs attune inflammatory responses and iron metabolism in macrophages.

HDAC2 targeting stabilizes the CoREST complex in renal tubular cells and protects against renal ischemia/reperfusion injury

Histone/protein deacetylases (HDAC) 1 and 2 are typically viewed as structurally and functionally similar enzymes present within various co-regulatory complexes. We tested differential effects of these isoforms in renal ischemia reperfusion injury (IRI) using inducible knockout mice and found no significant change in ischemic tolerance with HDAC1 deletion, but mitigation of ischemic injury with HDAC2 deletion. Restriction of HDAC2 deletion to the kidney via transplantation or PAX8-controlled proximal renal tubule-specific Cre resulted in renal IRI protection. Pharmacologic inhibition of HDAC2 increased histone acetylation in the kidney but did not extend renal protection. Protein analysis demonstrated increased HDAC1-associated CoREST protein in HDAC2-/- versus WT cells, suggesting that in the absence of HDAC2, increased CoREST complex occupancy of HDAC1 can stabilize this complex. In vivo administration of a CoREST inhibitor exacerbated renal injury in WT mice and eliminated the benefit of HDAC2 deletion. Gene expression analysis of endothelin showed decreased endothelin levels in HDAC2 deletion. These data demonstrate that contrasting effects of HDAC1 and 2 on CoREST complex stability within renal tubules can affect outcomes of renal IRI and implicate endothelin as a potential downstream mediator.

Greater high-mobility group box 1 in male compared with female spontaneously hypertensive rats worsens renal ischemia-reperfusion injury

Renal ischemia is the most common cause of acute kidney injury. Damage-associated molecular patterns (DAMPs) initiate an inflammatory response and contribute to ischemia-reperfusion (IR) injury in males, yet the contribution of DAMPs to IR injury in females is unknown. The goal of the current study was to test the hypothesis that males have greater increases in the DAMP high-mobility group box 1 (HMGB1), worsening injury compared with females. Thirteen-week-old male and female spontaneously hypertensive rats (SHR) were subjected to sham or 45-min warm bilateral ischemia followed by 24 h of reperfusion before measurement of HMGB1 and renal function. Additional SHR were pre-treated with control (IgG) or HMGB1 neutralizing antibody (300 µg/rat) 1 h prior to renal ischemia. Blood, urine and kidneys were harvested 24 h post-IR for histological and Western blot analyses. Initial studies confirmed that IR resulted in greater increases in renal HMGB1 in male SHR compared with females. Greater renal HMGB1 in male SHR post-IR resulted in greater increases in serum TNF-α and renal IL-1β, neutrophil infiltration and tubular cell death. Neutralization of HMGB1 attenuated IR-induced increases in plasma creatinine, blood urea nitrogen (BUN), inflammation, tubular damage and tubular cell death only in male SHR. In conclusion, our data demonstrate that there is a sex difference in the contribution of HMGB1 to IR-induced injury, where males exhibit greater increases in HMGB1-mediated renal injury in response to IR compared with females.