Tubular atrophy in the pathogenesis of chronic kidney disease progression

Advance on Chinese Medicine for Hypertensive Renal Damage: Focus on the Complex Molecular Mechanisms

Hypertensive renal damage (HRD) is a major cause of end-stage renal disease. Among the causes of end-stage renal disease, HRD accounts for nearly 34% of the total number of cases. Antihypertensive treatment is primarily drug-based, but therapeutic efficacy is less effective and can have serious side effects. Chinese medicine (CM) has significant advantages in the treatment of HRD. CM is rich in various active ingredients and has the property of targeting multiple targets and channels. Therefore, the regulatory network of CM on disease is complex. A large number of CM have been employed to treat HRD, either as single applications or as part of compound formulations. The key possible mechanisms of CM for HRD include regulation of the renin-angiotensin-aldosterone system, antioxidation, anti-inflammation, rescue of endothelial function, regulation of vasoactive substance secretion and obesity-related factors, etc. This review summarized and discussed the recent advance in the basic research mechanisms of CM interventions for HRD and pointed out the challenges and future prospects.

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.

Terpenes in the management of chronic kidney disease

Chronic kidney disease (CKD) is a chronic and progressive systemic condition that characterizes irreversible alterations in the kidneys' function and structure over an extended period, spanning months to years. CKD is the one of the major causes of mortality worldwide. However, very limited treatment options are available in the market for management of the CKD. Diabetes and hypertension are the key risk factors for the progression of CKD. It is majorly characterised by glomerulosclerosis, tubular atrophy, and interstitial fibrosis. Plants are considered safe and effective in treating various chronic conditions. A diverse group of phytoconstituents, including polyphenols, flavonoids, alkaloids, tannins, saponins, and terpenes, have found significant benefits in managing chronic ailments. Terpenes constitute a diverse group of plant compounds with various therapeutic benefits. Evidence-based pharmacological studies underscore the crucial role played by terpenes in preventing and managing CKD. These substances demonstrate the capacity to hinder detrimental pathways, such as oxidative stress, inflammation and fibrosis, thereby demonstrating benefit in renal dysfunction. This review offers a comprehensive overview of the roles and positive attributes of commonly occurring terpenes in managing the causes and risk factors of CKD and the associated conditions.

X-Ray-Based 3D Histopathology of the Kidney Using Cryogenic Contrast-Enhanced MicroCT

The kidney's microstructure, which comprises a highly convoluted tubular and vascular network, can only be partially revealed using classical 2D histology. Considering that the kidney's microstructure is closely related to its function and is often affected by pathologies, there is a need for powerful and high-resolution 3D imaging techniques to visualize the microstructure. Here, we present how cryogenic contrast-enhanced microCT (cryo-CECT) allowed 3D visualization of glomeruli, tubuli, and vasculature. By comparing different contrast-enhancing staining agents and freezing protocols, we found that the preferred sample preparation protocol was the combination of staining with 1:2 hafnium(IV)-substituted Wells-Dawson polyoxometalate and freezing by submersion in isopentane at -78°C. This optimized protocol showed to be highly sensitive, allowing to detect small pathology-induced microstructural changes in a mouse model of mild trauma-related acute kidney injury after thorax trauma and hemorrhagic shock. In summary, we demonstrated that cryo-CECT is an effective 3D histopathological tool that allows to enhance our understanding of kidney tissue microstructure and their related function.

Astragaloside IV attenuates renal tubule injury in DKD rats via suppression of CD36-mediated NLRP3 inflammasome activation

Background

In recent years, diabetic kidney disease (DKD) has emerged as a prominent factor contributing to end-stage renal disease. Tubulointerstitial inflammation and lipid accumulation have been identified as key factors in the development of DKD. Earlier research indicated that Astragaloside IV (AS-IV) reduces inflammation and oxidative stress, controls lipid accumulation, and provides protection to the kidneys. Nevertheless, the mechanisms responsible for its protective effects against DKD have not yet been completely elucidated.

Purpose

The primary objective of this research was to examine the protective properties of AS-IV against DKD and investigate the underlying mechanism, which involves CD36, reactive oxygen species (ROS), NLR family pyrin domain containing 3 (NLRP3), and interleukin-1β (IL-1β).

Methods

The DKD rat model was created by administering streptozotocin along with a high-fat diet. Subsequently, the DKD rats and palmitic acid (PA)-induced HK-2 cells were treated with AS-IV. Atorvastatin was used as the positive control. To assess the therapeutic effects of AS-IV on DKD, various tests including blood sugar levels, the lipid profile, renal function, and histopathological examinations were conducted. The levels of CD36, ROS, NLRP3, Caspase-1, and IL-1β were detected using western blot analysis, PCR, and flow cytometry. Furthermore, adenovirus-mediated CD36 overexpression was applied to explore the underlying mechanisms through in vitro experiments.

Results

In vivo experiments demonstrated that AS-IV significantly reduced hyperglycemia, dyslipidemia, urinary albumin excretion, and serum creatinine levels in DKD rats. Additionally, it improved renal structural abnormalities and suppressed the expression of CD36, NLRP3, IL-1β, TNF-α, and MCP-1. In vitro experiments showed that AS-IV decreased CD36 expression, lipid accumulation, and lipid ROS production while inhibiting NLRP3 activation and IL-1β secretion in PA-induced HK-2 cells.

Conclusion

AS-IV alleviated renal tubule interstitial inflammation and tubule epithelial cell apoptosis in DKD rats by inhibiting CD36-mediated lipid accumulation and NLRP3 inflammasome activation.

Hirudin in the Treatment of Chronic Kidney Disease

Chronic kidney disease (CKD) is a common public health concern. The global burden of CKD is increasing due to the high morbidity and mortality associated with it, indicating the shortcomings of therapeutic drugs at present. Renal fibrosis is the common pathology of CKD, which is characterized by glomerulosclerosis, renal tubular atrophy, and renal interstitial fibrosis. Natural hirudin is an active ingredient extracted from Hirudo medicinalis, which has been found to be the strongest natural specific inhibitor of thrombin. Evidence based on pharmacological data has shown that hirudin has important protective effects in CKD against diabetic nephrology, nephrotic syndrome, and renal interstitial fibrosis. The mechanisms of hirudin in treating CKD are mainly related to inhibiting the inflammatory response, preventing apoptosis of intrinsic renal cells, and inhibiting the interactions between thrombin and protease-activated receptors. In this review, we summarize the function and beneficial properties of hirudin for the treatment of CKD, and its underlying mechanisms.

Does Hypertension Affect the Recovery of Renal Functions after Reversal of Unilateral Ureteric Obstruction?

Research has demonstrated that hypertension can lead to an exaggeration in the renal functional and histological changes caused by ureteral obstruction. These changes were particularly observed shortly after the release of a relatively brief period of unilateral ureteral obstruction (UUO). However, the long-term impact of hypertension on the recovery of renal functions has not been investigated beyond the immediate period after UUO reversal. In order to investigate this effect, a group of spontaneously hypertensive rats (G-SHR, n = 11) and a group of normotensive Wistar Kyoto rats (G-NTR, n = 11) were subjected to a 48 h reversible left UUO. The impact of UUO was then examined 45 days after the reversal of obstruction. The glomerular filtration rate, renal blood flow, and the fractional excretion of sodium in the post-obstructed left kidney (POK) showed similarities to the non-obstructed right kidney (NOK) in both groups. However, the changes in the albumin creatinine ratio, renal injury markers, pro-apoptotic markers, and histological changes in the G-SHR were much more pronounced compared to the G-NTR. We conclude that hypertension continues to have a significant impact on various aspects of renal injury and function, even several weeks after UUO reversal.

Based on functional and histopathological correlations: is diffusion kurtosis imaging valuable for noninvasive assessment of renal damage in early-stage of chronic kidney disease?

PURPOSE

To evaluate the potential of 3 T magnetic resonance diffusion kurtosis imaging (DKI) in assessing the renal damage in early-stage of chronic kidney disease (CKD) patients with normal or slightly changed functional index, using histopathology as reference standard.

METHODS

49 CKD patients and 18 healthy volunteers were recruited in this study. CKD patients were divided into two groups based on estimated glomerular filtration rate (eGFR): Study group I (eGFR ≥ 90 ml/min/1.73 m2 [n = 20]) and Study group II (eGFR < 90 ml/min/1.73 m2 [n = 29]). DKI was performed in all participants. The DKI parameters (mean kurtosis [MK], mean diffusivity [MD], fractional anisotropy [FA]) of renal cortex and medulla were measured. The differences of parenchymal MD, MK and FA values among the different groups were compared. The correlations between DKI parameters and clinicopathological characteristics were assessed. Diagnostic performance of DKI to assess renal damage in early-stage of CKD was analyzed.

RESULTS

The cortex MD and MK showed significant difference among three groups (P < 0.05): trend of cortex MD: Study group II < Study group I < control group; trend of cortex MK: control group < Study group I < Study group II. The cortex MD and MK and medulla FA were correlated with eGFR and Interstitial fibrosis/Tubular atrophy score (0.3 < r < 0.5). Cortex MD and MK yielded an AUC of 0.752 for differentiating healthy volunteers from CKD patients with eGFR ≥ 90 ml/min/1.73 m2.

CONCLUSION

DKI shows potential in non-invasive and multi-parameter quantitative assessment of renal damage in early-stage of CKD patients and provide additional information for changes in renal function and histopathology.

Renal Epithelial Mitochondria: Implications for Hypertensive Kidney Disease

According to the Centers for Disease Control and Prevention, 1 in 2 U.S. adults have hypertension, and more than 1 in 7 chronic kidney disease. In fact, hypertension is the second leading cause of kidney failure in the United States; it is a complex disease characterized by, leading to, and caused by renal dysfunction. It is well-established that hypertensive renal damage is accompanied by mitochondrial damage and oxidative stress, which are differentially regulated and manifested along the nephron due to the diverse structure and functions of renal cells. This article provides a summary of the relevant knowledge of mitochondrial bioenergetics and metabolism, focuses on renal mitochondrial function, and discusses the evidence that has been accumulated regarding the role of epithelial mitochondrial bioenergetics in the development of renal tissue dysfunction in hypertension. © 2024 American Physiological Society. Compr Physiol 14:5225-5242, 2024.

LncRNA HOX transcript antisense RNA mediates hyperglycemic-induced injury in the renal tubular epithelial cell via the miR-126-5pAkt axis

OBJECTIVE

To investigate the involvement of HOX transcript antisense RNA (HOTAIR) in the injury of renal tubular epithelial cells induced by high glucose. Results: In high glucose-induced HK-2 cells, the expression of HOTAIR was upregulated, resulting in suppressed cell proliferation. Meanwhile, HOTAIR upregulates the expression of pro-apoptotic proteins Bax and cleaved caspase-3, while downregulating the expression of the anti-apoptotic protein Bcl-2. Luciferase reporter assays revealed that HOTAIR could target miR-126-5p. Additionally, it was found that the PI3K/Akt signaling pathway serves as a downstream target of miR-126-5p. Knockdown of HOTAIR relieved apoptosis, whereas further inhibition of miR-126-5p led to apoptosis in HK-2 cells. Conclusions: HOTAIR plays a regulatory role in mediating high glucose-induced injuries in HK-2 cells, specifically affecting apoptosis and cell viability, via the miR-126-5p/PI3K/Akt signaling pathway.

Long-term follow-up of IgA nephropathy: clinicopathological features and predictors of outcomes

Background

The establishment of the Oxford classification and newly developed prediction models have improved the prognostic information for immunoglobulin A nephropathy (IgAN). Considering new treatment options, optimizing prognostic information and improving existing prediction models are favorable.

Methods

We used random forest survival analysis to select possible predictors of end-stage kidney disease among 37 candidate variables in a cohort of 232 patients with biopsy-proven IgAN retrieved from the Norwegian Kidney Biopsy Registry. The predictive value of variables with relative importance >5% was assessed using concordance statistics and the Akaike information criterion. Pearson's correlation coefficient was used to identify correlations between the selected variables.

Results

The median follow-up period was 13.7 years. An isolated analysis of histological variables identified six variables with relative importance >5%: T %, segmental glomerular sclerosis without characteristics associated with other subtypes (not otherwise specified, NOS), normal glomeruli, global sclerotic glomeruli, segmental adherence and perihilar glomerular sclerosis. When histopathological and clinical variables were combined, estimated glomerular filtration rate (eGFR), proteinuria and serum albumin were added to the list. T % showed a better prognostic value than tubular atrophy/interstitial fibrosis (T) lesions with C-indices at 0.74 and 0.67 and was highly correlated with eGFR. Analysis of the subtypes of segmental glomerulosclerosis (S) lesions revealed that NOS and perihilar glomerular sclerosis were associated with adverse outcomes.

Conclusions

Reporting T lesions as a continuous variable, normal glomeruli and subtypes of S lesions could provide clinicians with additional prognostic information and contribute to the improved performance of the Oxford classification and prognostic tools.

The AKI-to-CKD Transition: The Role of Uremic Toxins

After acute kidney injury (AKI), renal function continues to deteriorate in some patients. In a pro-inflammatory and profibrotic environment, the proximal tubules are subject to maladaptive repair. In the AKI-to-CKD transition, impaired recovery from AKI reduces tubular and glomerular filtration and leads to chronic kidney disease (CKD). Reduced kidney secretion capacity is characterized by the plasma accumulation of biologically active molecules, referred to as uremic toxins (UTs). These toxins have a role in the development of neurological, cardiovascular, bone, and renal complications of CKD. However, UTs might also cause CKD as well as be the consequence. Recent studies have shown that these molecules accumulate early in AKI and contribute to the establishment of this pro-inflammatory and profibrotic environment in the kidney. The objective of the present work was to review the mechanisms of UT toxicity that potentially contribute to the AKI-to-CKD transition in each renal compartment.

Palmitoyltransferase DHHC9 and acyl protein thioesterase APT1 modulate renal fibrosis through regulating β-catenin palmitoylation

palmitoylation, a reversible post-translational modification, is initiated by the DHHC family of palmitoyltransferases and reversed by several acyl protein thioesterases. However, the role and mechanisms for protein palmitoylation in renal fibrosis have not been elucidated. Here we show protein palmitoylation and DHHC9 were downregulated in the fibrotic kidneys of mouse models and chronic kidney disease (CKD) patients. Ablating DHHC9 in tubular cells aggravated, while inducing DHHC9 overexpression with adeno-DHHC9 transfection or iproniazid treatment protected against kidney fibrosis in male mouse models. Mechanistically, DHHC9 palmitoylated β-catenin, thereby promoted its ubiquitination and degradation. Additionally, acyl protein thioesterase 1 (APT1) was induced in the fibrotic kidneys, which depalmitoylated β-catenin, increased its abundance and nuclear translocation. Ablating tubular APT1 or inhibiting APT1 with ML348 markedly protected against unilateral ureter obstruction (UUO) or ischemia/reperfusion injury (IRI)-induced kidney fibrosis in male mice. This study reveals the regulatory mechanism of protein palmitoylation in kidney fibrosis.

Renal Histopathology Associated With Kidney Failure and Mortality in Patients With Lupus Nephritis: A Long-Term Real-World Data Study

OBJECTIVE

Lupus nephritis (LN), a common manifestation of systemic lupus erythematosus, is associated with a higher risk of kidney failure and death. The renal pathology of LN helps elucidate the severity of inflammation and the extent of irreversible damage. We aimed to identify histologic variables that correlate with risks of kidney failure and mortality.

METHODS

Between 2006 and 2019, a total of 526 patients with LN were enrolled. Renal pathology was classified according to the International Society of Nephrology/Renal Pathology Society classification. Components of activity and chronicity indices were analyzed to determine which variables correlated with an increased risk of kidney failure and death, with the adjustment of potential confounders.

RESULTS

During the follow-up period (median 7.5, IQR 3.5-10.7 years), 58 patients progressed to kidney failure and 64 died. In the multivariate Cox regression analysis, tubular atrophy (hazard ratio [HR] 2.28, 95% CI 1.66-3.14) and tubulointerstitial inflammation (HR 3.13, 95% CI 1.34-7.33) predicted kidney failure. The renal outcome was even worse if tubular atrophy and tubulointerstitial inflammation coexisted (10-year kidney survival rate: 63.22%). The presence of cellular crescents was associated with an increased risk of death in male patients with LN (HR 1.91, 95% CI 1.02-3.57), whereas the presence of fibrous crescents predicted death in female patients with LN (HR 5.70, 95% CI 1.61-20.25).

CONCLUSION

Histologic variables of renal biopsy in LN could be regarded as prognostic indicators for kidney failure and mortality.

Redox regulation in diabetic kidney disease

Diabetic kidney disease (DKD) is one of the most devastating complications of diabetes mellitus, where currently there is no cure available. Several important mechanisms contribute to the pathogenesis of this complication, with oxidative stress being one of the key factors. The past decades have seen a large number of publications with various aspects of this topic; however, the specific details of redox regulation in DKD are still unclear. This is partly because redox biology is very complex, coupled with a complex and heterogeneous organ with numerous cell types. Furthermore, often times terms such as "oxidative stress" or reactive oxygen species are used as a general term to cover a wide and rich variety of reactive species and their differing reactions. However, no reactive species are the same, and not all of them are capable of biologically relevant reactions or "redox signaling." The goal of this review is to provide a biochemical background for an array of specific reactive oxygen species types with varying reactivity and specificity in the kidney as well as highlight some of the advances in redox biology that are paving the way to a better understanding of DKD development and risk.

Renal mitochondrial restoration by gymnemic acid in gentamicin-mediated experimental nephrotoxicity: evidence from serum, kidney and histopathological alterations

Background: Nephrotoxicity refers to the toxigenic impact of compounds and medications on kidney function. There are a variety of drug formulations, and some medicines that may affect renal function in multiple ways via nephrotoxins production. Nephrotoxins are substances that are harmful to the kidneys. Purpose: This investigation examines the renoprotective effect of gymnemic acid (GA) on Wistar rats in gentamicin-induced nephrotoxicity by analyzing serum, kidney, and histopathological markers. Study-design/methods: The current study investigated the protective effect of GA at doses of 20, 40, and 60 mg/kg against gentamicin-induced nephrotoxicity in rats. Vitamin E was administered to compare the antioxidant capacity and efficacy of GA. In addition to the treatment groups, 100 mg/kg of gentamicin was administered intraperitoneal for 14 days. At the end of the study protocol, kidney homogenate, blood, and serum were evaluated biochemically. Serum creatinine, blood urea, glomerular filtration rate (GFR), mitochondrial dysfunctions, inflammatory cytokines, and renal oxidative stress were examined to assess gentamicin-induced nephrotoxicity. In addition, the impact of GA on the above-mentioned nephrotoxic markers were evaluated and further confirmed by histological analysis. Results: This study establishes a correlation between antibiotic use, especifically aminoglycosides and acute renal failure. The research demonstrates the nephrotoxic effects of aminoglycosides, inducing mitochondrial ETC-complex dysfunction, and renal tissue inflammation in experimental rats. GA's antioxidant properties restored renal oxidative stress markers, reducing kidney inflammation and injury. Histopathological analysis revealed a significant reduction in renal injury with GA treatment. Additionally, GA demonstrated greater efficacy than Vitamin E in restoring antioxidant potential and mitochondrial enzymes. Conclusion: Consequently, our findings imply that long-term use of GA may be a suitable therapeutic strategy for reducing aminoglycoside toxicity. The current study suggests GA's potential in treating gentamicin-induced nephrotoxicity and acute renal failure, meriting further investigation using advanced techniques.

Recent Advances in Sodium Magnetic Resonance Imaging and Its Future Role in Kidney Disease

Sodium imbalance is a hallmark of chronic kidney disease (CKD). Excess tissue sodium in CKD is associated with hypertension, inflammation, and cardiorenal disease. Sodium magnetic resonance imaging (23Na MRI) has been increasingly utilized in CKD clinical trials especially in the past few years. These studies have demonstrated the association of excess sodium tissue accumulation with declining renal function across whole CKD spectrum (early- to end-stage), biomarkers of systemic inflammation, and cardiovascular dysfunction. In this article, we review recent advances of 23Na MRI in CKD and discuss its future role with a focus on the skin, the heart, and the kidney itself.

Novel Model of Oxalate Diet-Induced Chronic Kidney Disease in Dahl-Salt-Sensitive Rats

Diet-induced models of chronic kidney disease (CKD) offer several advantages, including clinical relevance and animal welfare, compared with surgical models. Oxalate is a plant-based, terminal toxic metabolite that is eliminated by the kidneys through glomerular filtration and tubular secretion. An increased load of dietary oxalate leads to supersaturation, calcium oxalate crystal formation, renal tubular obstruction, and eventually CKD. Dahl-Salt-Sensitive (SS) rats are a common strain used to study hypertensive renal disease; however, the characterization of other diet-induced models on this background would allow for comparative studies of CKD within the same strain. In the present study, we hypothesized that SS rats on a low-salt, oxalate rich diet would have increased renal injury and serve as novel, clinically relevant and reproducible CKD rat models. Ten-week-old male SS rats were fed either 0.2% salt normal chow (SS-NC) or a 0.2% salt diet containing 0.67% sodium oxalate (SS-OX) for five weeks.Real-time PCR demonstrated an increased expression of inflammatory marker interleukin-6 (IL-6) (p < 0.0001) and fibrotic marker Timp-1 metalloproteinase (p < 0.0001) in the renal cortex of SS-OX rat kidneys compared with SS-NC. The immunohistochemistry of kidney tissue demonstrated an increase in CD-68 levels, a marker of macrophage infiltration in SS-OX rats (p < 0.001). In addition, SS-OX rats displayed increased 24 h urinary protein excretion (UPE) (p < 0.01) as well as significant elevations in plasma Cystatin C (p < 0.01). Furthermore, the oxalate diet induced hypertension (p < 0.05). A renin-angiotensin-aldosterone system (RAAS) profiling (via liquid chromatography-mass spectrometry; LC-MS) in the SS-OX plasma showed significant (p < 0.05) increases in multiple RAAS metabolites including angiotensin (1-5), angiotensin (1-7), and aldosterone. The oxalate diet induces significant renal inflammation, fibrosis, and renal dysfunction as well as RAAS activation and hypertension in SS rats compared with a normal chow diet. This study introduces a novel diet-induced model to study hypertension and CKD that is more clinically translatable and reproducible than the currently available models.

Chilling injury in human kidney tubule cells after subzero storage is not mitigated by antifreeze protein addition

By preventing freezing, antifreeze proteins (AFPs) can permit cells and organs to be stored at subzero temperatures. As metabolic rates decrease with decreasing temperature, subzero static cold storage (SZ-SCS) could provide more time for tissue matching and potentially lead to fewer discarded organs. Human kidneys are generally stored for under 24 h and the tubule epithelium is known to be particularly sensitive to static cold storage (SCS). Here, telomerase-immortalized proximal-tubule epithelial cells from humans, which closely resemble their progenitors, were used as a proxy to assess the potential benefit of SZ-SCS for kidneys. The effects of hyperactive AFPs from a beetle and Cryostasis Storage Solution were compared to University of Wisconsin Solution at standard SCS temperatures (4 °C) and at -6 °C for up to six days. Although the AFPs helped guard against freezing, lower storage temperatures under these conditions were not beneficial. Compared to cells at 4 °C, those stored at -6 °C showed decreased viability as well as increased lactate dehydrogenase release and apoptosis. This suggests that this kidney cell type might be prone to chilling injury and that the addition of AFPs to enable SZ-SCS may not be effective for increasing storage times.

Polynucleotide phosphorylase protects against renal tubular injury via blocking mt-dsRNA-PKR-eIF2α axis

Renal tubular atrophy is a hallmark of chronic kidney disease. The cause of tubular atrophy, however, remains elusive. Here we report that reduction of renal tubular cell polynucleotide phosphorylase (PNPT1) causes renal tubular translation arrest and atrophy. Analysis of tubular atrophic tissues from renal dysfunction patients and male mice with ischemia-reperfusion injuries (IRI) or unilateral ureteral obstruction (UUO) treatment shows that renal tubular PNPT1 is markedly downregulated under atrophic conditions. PNPT1 reduction leads to leakage of mitochondrial double-stranded RNA (mt-dsRNA) into the cytoplasm where it activates protein kinase R (PKR), followed by phosphorylation of eukaryotic initiation factor 2α (eIF2α) and protein translational termination. Increasing renal PNPT1 expression or inhibiting PKR activity largely rescues IRI- or UUO-induced mouse renal tubular injury. Moreover, tubular-specific PNPT1-knockout mice display Fanconi syndrome-like phenotypes with impaired reabsorption and significant renal tubular injury. Our results reveal that PNPT1 protects renal tubules by blocking the mt-dsRNA-PKR-eIF2α axis.

Intestinal microbiome diversity of diabetic and non-diabetic kidney disease: Current status and future perspective

A significant portion of the health burden of diabetic kidney disease (DKD) is caused by both type 1 and type 2 diabetes which leads to morbidity and mortality globally. It is one of the most common diabetic complications characterized by loss of renal function with high prevalence, often leading to acute kidney disease (AKD). Inflammation triggered by gut microbiota is commonly associated with the development of DKD. Interactions between the gut microbiota and the host are correlated in maintaining metabolic and inflammatory homeostasis. However, the fundamental processes through which the gut microbiota affects the onset and progression of DKD are mainly unknown. In this narrative review, we summarised the potential role of the gut microbiome, their pathogenicity between diabetic and non-diabetic kidney disease (NDKD), and their impact on host immunity. A well-established association has already been seen between gut microbiota, diabetes and kidney disease. The gut-kidney interrelationship is confirmed by mounting evidence linking gut dysbiosis to DKD, however, it is still unclear what is the real cause of gut dysbiosis, the development of DKD, and its progression. In addition, we also try to distinguish novel biomarkers for early detection of DKD and the possible therapies that can be used to regulate the gut microbiota and improve the host immune response. This early detection and new therapies will help clinicians for better management of the disease and help improve patient outcomes.

Multi-Parameter Detection of Urine Based on Electropolymerized PANI: PSS/AuNPs/SPCE

Urine analysis is widely used in clinical practice to indicate human heathy status and is important for diagnosing chronic kidney disease (CKD). Ammonium ions (NH₄⁺), urea, and creatinine metabolites are main clinical indicators in urine analysis of CKD patients. In this paper, NH₄⁺ selective electrodes were prepared using electropolymerized polyaniline-polystyrene sulfonate (PANI: PSS), and urea- and creatinine-sensing electrodes were prepared by modifying urease and creatinine deiminase, respectively. First, PANI: PSS was modified on the surface of an AuNPs-modified screen-printed electrode, as a NH₄⁺-sensitive film. The experimental results showed that the detection range of the NH₄⁺ selective electrode was 0.5~40 mM, and the sensitivity reached 192.6 mA M^-1 cm^-2 with good selectivity, consistency, and stability. Based on the NH₄⁺-sensitive film, urease and creatinine deaminase were modified by enzyme immobilization technology to achieve urea and creatinine detection, respectively. Finally, we further integrated NH₄⁺, urea, and creatinine electrodes into a paper-based device and tested real human urine samples. In summary, this multi-parameter urine testing device offers the potential for point-of-care testing of urine and benefits the efficient chronic kidney disease management.

Evaluating the renal mild tubulointerstitial damage and renal function in IgAN patients: a comparative study based on diffusion kurtosis imaging and diffusion tensor imaging

OBJECTIVE

To compare the performance of 3.0 T magnetic resonance diffusion kurtosis imaging (DKI) and diffusion tensor imaging (DTI) in evaluation of the degree of tubulointerstitial damage and renal function in Immunoglobulin A Nephropathy (IgAN) patients.

METHODS

Both DKI and DTI were performed in 40 IgAN patients and 17 healthy volunteers. IgAN patients were divided into two groups according to tubulointerstitial lesion score: Mild injury group, n = 24; Moderate-severe injury group, n = 16. DKI characteristic parameters [mean kurtosis (MK), axial kurtosis (Ka), radial kurtosis (Kr)] and DTI parameters [fractional anisotropy (FA), mean diffusivity (MD), axial diffusivity (Da), radial diffusivity (Dr)] of renal cortex and medulla were measured and compared among different groups. Correlations between DKI, DTI parameters and clinicopathological characteristics were assessed. Diagnostic performance of DKI and DTI to evaluate tubulointerstitial damage of IgAN was compared.

RESULTS

Cortical MK, Kr, Da and parenchymal Ka significantly differed among three groups (P < 0.05). Cortical MK, Kr, Ka were negatively correlated with estimated glomerular filtration rate (eGFR) (MK: r = - 0.613; Kr: r = - 0.539; Ka: r = - 0.664) and positively correlated with tubulointerstitial lesion score (MK: r = 0.655; Kr: r = 0.577; Ka: r = 0.661) (all P < 0.001). Lower correlation coefficient was found among cortical FA, MD, Dr and eGFR, tubulointerstitial lesion score (all|r|< 0.350). The AUCs of DKI and DTI parameters for differentiating Mild injury group from control group were (cortical MK 0.822, cortical Ka 0.816; cortical FA 0.515, cortical MD 0.714) and for differentiating Mild injury group from Moderate-severe injury group were (cortical MK 0.813, cortical Ka 0.831; medulla FA 0.784, medulla MD 0.586).

CONCLUSION

Compared with DTI, DKI was more sensitive and accurate to probe the renal function and the tubulointerstitial damage of IgAN, especially the mild tubulointerstitial damage.

Pre-Implantation Kidney Biopsies in Extended Criteria Donors: From On Call to Expert Pathologist, from Conventional Microscope to Digital Pathology

The number of patients awaiting a kidney transplant is constantly rising but lack of organs leads kidneys from extended criteria donors (ECD) to be used to increase the donor pool. Pre-transplant biopsies are routinely evaluated through the Karpinski-Remuzzi score but consensus on its correlation with graft survival is controversial. This study aims to test a new diagnostic model relying on digital pathology to evaluate pre-transplant biopsies and to correlate it with graft outcomes. Pre-transplant biopsies from 78 ECD utilized as single kidney transplantation were scanned, converted to whole-slide images (WSIs), and reassessed by two expert nephropathologists using the Remuzzi-Karpinski score. The correlation between graft survival at 36 months median follow-up and parameters assigned by either WSI or glass slide score (GSL) by on-call pathologists was evaluated, as well as the agreement between the GSL and the WSIs score. No relation was found between the GSL assessed by on-call pathologists and graft survival (P = 0.413). Conversely, the WSI score assigned by the two nephropathologists strongly correlated with graft loss probability, as confirmed by the ROC curves analysis (DeLong test P = 0.046). Digital pathology allows to share expertise in the transplant urgent setting, ensuring higher accuracy and favoring standardization of the process. Its employment may significantly increase the predictive capability of the pre-transplant biopsy evaluation for ECD, improving the quality of allocation and patient safety.

Human kidney organoids model of Esculentoside A nephrotoxicity to investigate the role of epithelial-mesenchymal transition via STING signaling

Radix Phytolaccae (RP) has a long medicinal history and is commonly used to treat systemic edema and ascites in Asia. Although RP is known to cause nephrotoxicity, the role of its main constituent, Esculentoside A (EsA), in nephrotoxicity remains undetermined. We used kidney organoids derived from human inducible pluripotent stem cells (iPSCs) to model EsA nephrotoxicity accurately. Kidney organoids were differentiated and treated with EsA at doses of 0, 15, 30, or 60 μM for 48 h. The in vitro model was compared to a mouse model of EsA nephrotoxicity (intraperitoneally injected, 25 mg·kg^-1). The mechanisms were investigated. Cell viability decreased dose-dependently after treatment with EsA. As polarity was lost, tubular cells decreased, similar to mouse EsA nephrotoxicity with upregulated vimentin expression and a stimulator of the interferon gene (STING). Furthermore, 60 μM EsA could induce endothelial inflammation, lead to mitochondrial damage and activate STING by translocating mtDNA into the cytoplasm to develop an inflammatory cascade and destroy renal endothelial cells with interstitial changes. The data suggest that kidney organoids derived from iPSCs are promising for investigating nephrotoxicity. EsA nephrotoxicity involves the epithelial-mesenchymal transition via STING signaling.

The Contribution of Lipotoxicity to Diabetic Kidney Disease

Lipotoxicity is a fundamental pathophysiologic mechanism in diabetes and non-alcoholic fatty liver disease and is now increasingly recognized in diabetic kidney disease (DKD) pathogenesis. This review highlights lipotoxicity pathways in the podocyte and proximal tubule cell, which are arguably the two most critical sites in the nephron for DKD. The discussion focuses on membrane transporters and lipid droplets, which represent potential therapeutic targets, as well as current and developing pharmacologic approaches to reduce renal lipotoxicity.

Ion channels as a therapeutic target for renal fibrosis

Renal ion channel transport and electrolyte disturbances play an important role in the process of functional impairment and fibrosis in the kidney. It is well known that there are limited effective drugs for the treatment of renal fibrosis, and since a large number of ion channels are involved in the renal fibrosis process, understanding the mechanisms of ion channel transport and the complex network of signaling cascades between them is essential to identify potential therapeutic approaches to slow down renal fibrosis. This review summarizes the current work of ion channels in renal fibrosis. We pay close attention to the effect of cystic fibrosis transmembrane conductance regulator (CFTR), transmembrane Member 16A (TMEM16A) and other Cl− channel mediated signaling pathways and ion concentrations on fibrosis, as well as the various complex mechanisms for the action of Ca2+ handling channels including Ca2+-release-activated Ca2+ channel (CRAC), purinergic receptor, and transient receptor potential (TRP) channels. Furthermore, we also focus on the contribution of Na+ transport such as epithelial sodium channel (ENaC), Na+, K+-ATPase, Na+-H+ exchangers, and K+ channels like Ca2+-activated K+ channels, voltage-dependent K+ channel, ATP-sensitive K+ channels on renal fibrosis. Proposed potential therapeutic approaches through further dissection of these mechanisms may provide new therapeutic opportunities to reduce the burden of chronic kidney disease.

SARS-CoV-2 infection in hamsters and humans results in lasting and unique systemic perturbations after recovery

The host response to severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection can result in prolonged pathologies collectively referred to as post-acute sequalae of COVID-19 (PASC) or long COVID. To better understand the mechanism underlying long COVID biology, we compared the short- and long-term systemic responses in the golden hamster after either SARS-CoV-2 or influenza A virus (IAV) infection. Results demonstrated that SARS-CoV-2 exceeded IAV in its capacity to cause permanent injury to the lung and kidney and uniquely affected the olfactory bulb (OB) and olfactory epithelium (OE). Despite a lack of detectable infectious virus, the OB and OE demonstrated myeloid and T cell activation, proinflammatory cytokine production, and an interferon response that correlated with behavioral changes extending a month after viral clearance. These sustained transcriptional changes could also be corroborated from tissue isolated from individuals who recovered from COVID-19. These data highlight a molecular mechanism for persistent COVID-19 symptomology and provide a small animal model to explore future therapeutics.

Nephroprotective potential of eugenol in a rat experimental model of chronic kidney injury; targeting NOX, TGF-β, and Akt signaling

Chronic kidney disease is a crucial health problem associated with high morbidity and mortality. Eugenol is a natural phenolic plant compound with various pharmacological activities including antioxidant and anti-inflammatory properties. This study was designed to evaluate the possible protective effect of different eugenol doses in an experimental model of chronic CCl₄-induced renal damage and investigate various mechanisms that underlie this postulated effect. Eugenol treatment (100 mg/kg) ameliorated kidney damage induced by CCl₄ and rectified the distorted kidney function parameters and renal histological structure. Additionally, eugenol at a dose of 100 mg/kg suppressed the upregulated oxidative stress, inflammation and apoptosis in CCl₄-treated rats as evident by down regulations of NADPH oxidase (NOX2 and NOX4), proinflammatory markers (IL-6 and TNF-α) and proapoptotic markers (cyt c and caspase-3), respectively. Importantly, eugenol co-administration in rats challenged with CCl₄ downregulated the renal protein expressions of both TGF-β as well as pAkt compared with CCl₄ group. In conclusion, eugenol showed a potent nephroprotective effect against CCl₄-induced renal damage through its antioxidant, anti-inflammatory and anti-fibrotic activities.

Acute kidney injury and the compensation of kidney function after nephrectomy in living donation

Acute kidney injury (AKI) incidence is growing rapidly, and AKI is one of the predictors of inpatient mortality. After nephrectomy, all the patients have decreased kidney function with AKI and recover from AKI. However, the characteristic and behavior of AKI is different from usual AKI and compensatory kidney function has been well known in the postoperative setting, especially in living donors. In this review, we have focused on the compensation of kidney function after nephrectomy in living donors. We discuss factors that have been identified as being associated with kidney recovery in donors including age, sex, body mass index, remnant kidney volume, estimated glomerular filtration rate, and various comorbidities.

Correlation between Tubulointerstitial Lesion and Blood Pressure in Lupus Nephritis Patients: A Pathological, Retrospective Study

OBJECTIVE

The objective was to study the influence of pathological factors of glomerular lesion (GL), tubulointerstitial lesion (TIL), and arteriosclerotic lesion on the blood pressure (BP) of lupus nephritis (LN).

METHODS

The pathological data and clinical characteristics of 69 LN patients who underwent their first renal biopsy in Chengdu Second People's Hospital from 2012 to 2018 were retrospectively analyzed. The revised 2018 ISN/RPS classification criteria of LN were used to assess the GL and TIL. The lesion index of interlobar/arcuate artery and arteriolar was calculated. Multiple linear regressions were used to analyze the effects of GL, TIL, and vascular lesion (VL) on estimated glomerular filtration rate, systolic BP (SBP), and proteinuria.

RESULTS

TIL and VL scores were different between the various grades of BP (p = 0.009, 0.019). After adjusting for gender and age, multiple linear regression showed that only TIL was linearly correlated with SBP (p = 0.022).

CONCLUSION

After adjusting for gender and age, TIL is related to SBP and has a linear relationship with them.

Intact mitochondrial substrate efflux is essential for prevention of tubular injury in a sex-dependent manner

The importance of healthy mitochondrial function is implicated in the prevention of chronic kidney disease (CKD) and diabetic kidney disease (DKD). Sex differences also play important roles in DKD. Our previous studies revealed that mitochondrial substrate overload (modeled by homozygous deletion of carnitine acetyl-transferase [CrAT]) in proximal tubules causes renal injury. Here, we demonstrate the importance of intact mitochondrial substrate efflux by titrating the amount of overload through the generation of a heterozygous CrAT-KO model (PT-CrATHET mouse). Intriguingly, these animals developed renal injury similarly to their homozygous counterparts. Mitochondria were structurally and functionally impaired in both sexes. Transcriptomic analyses, however, revealed striking sex differences. Male mice shut down fatty acid oxidation and several other metabolism-related pathways. Female mice had a significantly weaker transcriptional response in metabolism, but activation of inflammatory pathways was prominent. Proximal tubular cells from PT-CrATHET mice of both sexes exhibited a shift toward a more glycolytic phenotype, but female mice were still able to oxidize fatty acid-based substrates. Our results demonstrate that maintaining mitochondrial substrate metabolism balance is crucial to satisfying proximal tubular energy demand. Our findings have potentially broad implications, as both the glycolytic shift and the sexual dimorphisms discovered herein offer potentially new modalities for future interventions for treating kidney disease.

Flavonoids in Treatment of Chronic Kidney Disease

Chronic kidney disease (CKD) is a progressive systemic disease, which changes the function and structure of the kidneys irreversibly over months or years. The final common pathological manifestation of chronic kidney disease is renal fibrosis and is characterized by glomerulosclerosis, tubular atrophy, and interstitial fibrosis. In recent years, numerous studies have reported the therapeutic benefits of natural products against modern diseases. Substantial attention has been focused on the biological role of polyphenols, in particular flavonoids, presenting broadly in plants and diets, referring to thousands of plant compounds with a common basic structure. Evidence-based pharmacological data have shown that flavonoids play an important role in preventing and managing CKD and renal fibrosis. These compounds can prevent renal dysfunction and improve renal function by blocking or suppressing deleterious pathways such as oxidative stress and inflammation. In this review, we summarize the function and beneficial properties of common flavonoids for the treatment of CKD and the relative risk factors of CKD.

Qingda Granule Attenuates Angiotensin II-Induced Renal Apoptosis and Activation of the p53 Pathway

Background: Qingda granules (QDG) exhibit antihypertension and multiple-target-organ protection. However, the therapeutic potential of QDG on hypertensive renal injury remains unknown. Therefore, the main objective of the current study is to explore the effects and underlying mechanisms of QDG treatment on renal injury in angiotensin (Ang) II-infused mice. Methods and results: Mice were infused with Ang II (500 ng/kg/min) or saline for 4 weeks with subcutaneously implanted osmotic pumps. After infusion, mice in the Ang II + QDG group were intragastrically administrated with QDG daily (1.145 g/kg/day), whereas the control group and Ang II group were intragastrically administrated with the same amount of double-distilled water. Blood pressure of the mice monitored using the CODA™ noninvasive blood pressure system revealed that QDG treatment significantly attenuated elevated blood pressure. Moreover, hematoxylin-eosin staining indicated that QDG treatment ameliorated Ang II-induced renal morphological changes, including glomerular sclerosis and atrophy, epithelial cell atrophy, and tubular dilatation. RNA-sequencing (RNA-seq) identified 662 differentially expressed transcripts (DETs) in renal tissues of Ang II-infused mice, which were reversed after QDG treatment. Kyoto Encyclopedia of Genes and Genomes (KEGG) analysis based on DETs in both comparisons of Ang II vs. Control and Ang II + QDG vs. Ang II identified multiple enriched pathways, including apoptosis and p53 pathways. Consistently, terminal deoxynucleotidyl transferase (TdT) dUTP nick-end labeling (TUNEL) staining and Annexin V staining revealed that QDG treatment significantly attenuated Ang II-induced cell apoptosis in renal tissues and cultured renal tubular epithelial cell lines (NRK-52E). Furthermore, western blot analysis indicated that Ang II infusion significantly upregulated the protein expression of p53, BCL2-associated X (BAX), cle-caspase-9, and cle-caspase-3, while downregulating the protein expression of BCL-2 in renal tissues, which were attenuated after QDG treatment. Conclusion: Collectively, QDG treatment significantly attenuated hypertensive renal injury, partially by attenuating renal apoptosis and suppressing p53 pathways, which might be the underlying mechanisms.

Cell types of origin of the cell-free transcriptome

Cell-free RNA from liquid biopsies can be analyzed to determine disease tissue of origin. We extend this concept to identify cell types of origin using the Tabula Sapiens transcriptomic cell atlas as well as individual tissue transcriptomic cell atlases in combination with the Human Protein Atlas RNA consensus dataset. We define cell type signature scores, which allow the inference of cell types that contribute to cell-free RNA for a variety of diseases.

Cell types affected by various diseases are inferred from cell-free RNA.

Multi modular toxicity assessment of nephrotoxicity in podophyllotoxin exposure rats on account of toxicological evidence chain (TEC) concept

Early diagnosis of kidney injuries caused by herbs is necessary to enable effective treatments, prevent kidney failure and promote the internationalization and modernization of herbal medicine. Whereas the toxic assessment evidence has not integrated yet, and the evaluation method has not been unanimously agreed. For example, the gold standard assessing toxicity in animals remains to be histopathology, but serum biochemical indexes are the primary measures for monitoring organs dysfunction in humans. In this study, using Sprague Dawley rats, we investigated whether integrated analyses of transcriptomic and metabolomic data with toxicological evidence chain (TEC) concept could identify indicators of injury and provide new insights into the mechanisms of nephrotoxicity. Firstly, the objective phenotype of the animals was observed in detail and the toxicity performance was collected after administration. Subsequently, histopathological examination and serum biochemical toxicity evidence were collected. Next, we obtained concurrent measurements of transcriptomic changes in kidneys, and changes along with metabolic profiles in serum, after exposure to PT(Podophyllotoxin) to acquire evidence at the molecular level. Last but not least, the GTEA (Grades of Toxicological Evidence Assessment) based on GRADE(Grading of Recommendations Assessment, Development, and Evaluation) system was used to evaluate toxic evidence which can be assigned to a toxic level. The orally gavaged rats with PT have been confirmed with dose-dependent kidney damage from 5 to 15 mg/kg after 4 d. Our findings suggest that the main pathological changes occurred in Glycerophosphatidylcholine metabolism, Arachidonic acid metabolism, Energy metabolism, Tyrosine metabolism, Tryptophan metabolism and so on.Moreover, the alteration of the potential metabolites lipid (i.e. LPC, palmitic acid) and sulfate could serve as plausible markers of PT-induced kidney injury. Our approach provides a mechanistic framework for the refinement of the grading standard of toxicity evidence, which is applicable to other toxicants originated from herbal medicine based on multi-omics data.

Molecular Mechanisms of Kidney Injury and Repair

Chronic kidney disease (CKD) will become the fifth global cause of death by 2040, thus emphasizing the need to better understand the molecular mechanisms of damage and regeneration in the kidney. CKD predisposes to acute kidney injury (AKI) which, in turn, promotes CKD progression. This implies that CKD or the AKI-to-CKD transition are associated with dysfunctional kidney repair mechanisms. Current therapeutic options slow CKD progression but fail to treat or accelerate recovery from AKI and are unable to promote kidney regeneration. Unraveling the cellular and molecular mechanisms involved in kidney injury and repair, including the failure of this process, may provide novel biomarkers and therapeutic tools. We now review the contribution of different molecular and cellular events to the AKI-to-CKD transition, focusing on the role of macrophages in kidney injury, the different forms of regulated cell death and necroinflammation, cellular senescence and the senescence-associated secretory phenotype (SAPS), polyploidization, and podocyte injury and activation of parietal epithelial cells. Next, we discuss key contributors to repair of kidney injury and opportunities for their therapeutic manipulation, with a focus on resident renal progenitor cells, stem cells and their reparative secretome, certain macrophage subphenotypes within the M2 phenotype and senescent cell clearance.

Shifting Paradigms for Suppressing Fibrosis in Kidney Transplants: Supplementing Perfusion Solutions With Anti-fibrotic Drugs

Great efforts have been made toward addressing the demand for donor kidneys. One of the most promising approaches is to use kidneys from donation after circulatory death donors. These kidneys, however, suffer from more severe ischemia and reperfusion injury than those obtained via donation after brain death and are thus more prone to develop interstitial fibrosis and tubular atrophy. Even though machine perfusion is increasingly used to reduce ischemia and reperfusion injury, there are no effective treatments available to ameliorate interstitial fibrosis and tubular atrophy, forcing patients to resume dialysis, undergo re-transplantation, or suffer from premature death. Safe and effective anti-fibrotic therapies are therefore greatly desired. We propose a new therapeutic approach in which machine perfusion solutions are supplemented with anti-fibrotic compounds. This allows the use of higher concentrations than those used in humans whilst eliminating side effects in other organs. To the authors' knowledge, no one has reviewed whether such an approach could reduce interstitial fibrosis and tubular atrophy; we therefore set out to explore its merit. In this review, we first provide background information on ischemia and reperfusion injury as well as interstitial fibrosis and tubular atrophy, after which we describe currently available approaches for preserving donor kidneys. We then present an evaluation of selected compounds. To identify promising compounds, we analyzed publications describing the effects of anti-fibrotic molecules in precision-cut kidneys slices, which are viable explants that can be cultured ex vivo for up to a few days whilst retaining functional and structural features. LY2109761, galunisertib, imatinib, nintedanib, and butaprost were shown to exert anti-fibrotic effects in slices within a relatively short timeframe (<48 h) and are therefore considered to be excellent candidates for follow-up ex vivo machine perfusion studies.

Renoprotective Roles of Curcumin

The use of herb-based therapies is increasing over the past decades. These agents have been reported to provide many beneficial effects in many experimental and clinical studies. Curcumin is one of these agents which has potent pharmacological effects enabling it for the prevent and treatment of many diseases and pathologies such as renal disorders, hyperglycemia, oxidative stress, hypertension, and dyslipidemia. However, the exact molecular mechanisms mediating these renoprotective effects of curcumin are not well established. So, in the current study, we surveyed for possible renoprotective roles of curcumin and concluded how curcumin protects against renal injuries.

Tubule-derived INHBB promotes interstitial fibroblast activation and renal fibrosis

Upstream stimuli for myofibroblast activation are of considerable interest for understanding the mechanisms underlying renal fibrosis. Activin B, a member of the TGF-β family, exists as a homodimer of inhibin subunit beta B (INHBB), but its role in renal fibrosis remains unknown. We found that INHBB expression was significantly increased in various renal fibrosis models and human chronic kidney disease specimens with renal fibrosis. Notably, the increase of INHBB occurred mainly in the tubular epithelial cells (TECs). In vivo, inhibiting INHBB blocked the activation of interstitial fibroblasts and ameliorated the renal fibrosis induced by unilateral ureteral obstruction or ischemia-reperfusion injury, while ectopic expression of INHBB in the TECs was able to activate interstitial fibroblasts and initiate interstitial fibrosis. In vitro, overexpression of INHBB in TECs led to the secretion of activin B, thereby promoting the proliferation and activation of interstitial fibroblasts through activin B/Smad signaling. Furthermore, inhibition of activin B/Smad signaling attenuated the fibrotic response caused by tubular INHBB. Mechanistically, the upregulation of INHBB depended on the transcription factor Sox9 in the injured TECs. Clinical analyses also identified a positive correlation between Sox9 and INHBB expression in human specimens, suggesting the Sox9/INHBB axis as a positive regulator of renal fibrosis. In conclusion, tubule-derived INHBB is implicated in the pathogenesis of renal fibrosis by activating the surrounding fibroblasts in a paracrine manner, thereby exhibiting as a potential therapeutic target. © 2021 The Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.

Identification of Galectin-3 as Potential Biomarkers for Renal Fibrosis by RNA-Sequencing and Clinicopathologic Findings of Kidney Biopsy

Background: Galectin-3 (Gal-3) is a multifunctional glycan-binding protein shown to be linked to chronic inflammation and fibrogenesis. Plasma Gal-3 is associated with proteinuria and renal dysfunction, but its role has never been confirmed with kidney biopsy results. In our study, we aimed to explore the expression of Gal-3 in biopsy-proven patients, and we tested the hypothesis that chronic kidney disease (CKD) leads to upregulation of plasma Gal-3 expression in corresponding biopsy findings and RNA sequencing analysis. Method: In 249 patients (male/female: 155/94, age: 57.2 ± 16.3 years) who underwent kidney biopsy, plasma levels of Gal-3 were measured to estimate the association of renal fibrosis. Relationships between plasma Gal-3 levels, estimated glomerular filtration rate (eGFR) and renal histology findings were also assessed. We further examined the gene expression of Gal-3 in RNA-sequencing analysis in biopsy-proven patients. Results: Compared to patients without CKD, CKD patients had higher levels of plasma Gal-3 (1,016.3 ± 628.1 pg/mL vs. 811.6 ± 369.6 pg/ml; P = 0.010). Plasma Gal-3 was inversely correlated with eGFR (P = 0.005) but not with proteinuria. Higher Gal-3 levels were associated with interstitial fibrosis, tubular atrophy and vascular intimal fibrosis. RNA-sequencing analysis showed the upregulation of Gal-3 in fibrotic kidney biopsy samples, and the differentially expressed genes were mainly enhanced in immune cell activation and the regulation of cell-cell adhesion. Conclusions: Plasma Gal-3 levels are inverse correlated with eGFR but positively correlated with renal fibrosis, which may be involved in the immune response and associated pathways. These findings support the role of Gal-3 as a predictive marker of renal fibrosis.

Lipotoxic Proximal Tubular Injury: A Primary Event in Diabetic Kidney Disease

The pathogenesis of diabetic nephropathy is a complex process that has a great relationship with lipotoxicity. Since the concept of “nephrotoxicity” was proposed, many studies have confirmed that lipotoxicity plays a significant role in the progression of diabetic nephropathy and causes various renal dysfunction. This review will make a brief summary of renal injury caused by lipotoxicity that occurs primarily and predominantly in renal tubules during diabetic progression, further leading to glomerular dysfunction. The latest research suggests that lipotoxicity-mediated tubular injury may be a major event in diabetic nephropathy.

Comparison of two different toxin-induced kidney fibrosis models in terms of inflammatory responses

Chronic kidney disease (CKD) is characterized by persistent abnormalities in kidney function, accompanied by structural changes. Interstitial fibrosis, characterized by the accumulation of extracellular matrix (ECM) proteins, is frequently detected during CKD development. Given the multiple underlying causes of CKD, numerous animal models have been developed to advance our understanding of human nephropathy. Herein, we compared two reliable toxin-induced mouse kidney fibrosis models in terms of fibrosis and inflammation. Administration of folic acid (250 mg/kg, intraperitoneal injection) or an adenine diet (0.25 % for three weeks) afforded similar effects on kidney function, as detected by increased serum nitrogen levels. In addition, the kidneys exhibited a similar extent of tubule dilation and kidney damage. The degree of fibrosis was compared using various biological methods. Although both models developed a significant fibrotic phenotype, the adenine diet-fed model showed a marginally higher increase in fibrosis than the folic acid model, as reflected by increased kidney ECM gene and protein levels. We further compared inflammatory responses in the kidneys. Interestingly, pro-inflammatory responses, including cytokine expression and immune cell infiltration, were significantly increased in adenine diet-fed kidneys. Furthermore, collagen expression was identified in the macrophage-infiltrated region, implying the importance of inflammation in fibrogenesis. Collectively, we observed that the adenine diet-fed kidney fibrosis model presented a higher inflammatory response with increased fibrosis when compared with the folic acid-induced kidney fibrosis model, indicating the importance of the inflammatory response in fibrosis development.

Proximal tubule cyclophilin D mediates kidney fibrogenesis in obstructive nephropathy

The proximal tubule (PT) is highly vulnerable to acute injury, including ischemic insult and nephrotoxins, and chronic kidney injury. It has been established that PT injury is a primary cause of the development of chronic kidney disease, but the underlying molecular mechanism remains to be defined. Here, we tested whether PT cyclophilin D (CypD), a mitochondrial matrix protein, is a critical factor to cause kidney fibrosis progression. To define the role of CypD in kidney fibrosis, we used an established mouse model for kidney fibrosis: the unilateral ureteral obstruction (UUO) model in global and PT-specific CypD knockout (KO). Global CypD KO blunted kidney fibrosis progression with inhibition of myofibroblast activation and fibrosis. UUO-induced tubular atrophy was suppressed in kidneys of global CypD KO but not tubular dilation or apoptotic cell death. PT cell cycle arrest was highly increased in wild-type UUO kidneys but was markedly attenuated in global CypD KO UUO kidneys. The number of macrophages and neutrophils was less in UUO kidneys of global CypD KO than those of wild-type kidneys. Proinflammatory and profibrotic factors were all inhibited in global CypD KO. In line with those of global CypD KO, PT-specific CypD KO also blunted kidney fibrosis progression, along with less tubular atrophy, renal parenchymal loss, cell cycle arrest in PT, and inflammation, indicating a critical role for PT CypD in fibrogenesis. Collectively, our data demonstrate that CypD in the PT is a critical factor contributing to kidney fibrosis in UUO, providing a new paradigm for mitochondria-targeted therapeutics of fibrotic diseases.NEW & NOTEWORTHY It has been established that renal proximal tubule (PT) injury is a primary cause of the development of chronic kidney disease, but the underlying molecular mechanism remains to be defined. Here, we show that cyclophilin D, a mitochondrial matrix protein, in the PT causes kidney fibrogenesis in obstructive nephropathy. Our data suggest that targeting PT cyclophilin D could be beneficial to prevent fibrosis progression.

Acute kidney injury and aging

Our aging population is growing and developing treatments for age-related diseases such as Alzheimer's and Parkinson's disease has taken on an increasing urgency and is accompanied by high public awareness. The already high and rising incidence of acute kidney injury (AKI) in the elderly, however, has received relatively little attention despite the potentially fatal outcomes associated with an episode of AKI in this age group. When discussing AKI and aging, one should consider two aspects: first, elderly patients have an increased susceptibility to an AKI episode, and second, they have decreased kidney repair after AKI given the high incidence of progression to chronic kidney disease (CKD). It is unclear if the same factors that drive the increased susceptibility to AKI could be playing a role in the decreased repair capacity or if they are totally different and unrelated. This review will examine current knowledge on the risk factors for the increased susceptibility to AKI in the elderly and will also explore potential aspects that might contribute to a decreased kidney repair response in this age group.

Histopathological features of low-dose organophosphate exposure

Organophosphate (OP) use remains largely available worldwide despite more strict regulatory measures, in agriculture, parks or households, leading to a daily low-dose exposure. The systemic dysfunction appears partly due to acetylcholinesterase inhibition, exhibiting a primary toxic effect on the endocrine system but also on the liver and kidneys, which are responsible for products metabolization and elimination. Prolonged OP exposure can be responsible for histopathological (HP) changes that can either evolve or worsen pre-existing conditions. We conducted an experimental study including six male Wistar rats divided into two groups (four rats in the study group and two in the control group). The subjects in the first group were administered 100 mg/kg Chlorpyrifos half median lethal dose (LD₅₀) at baseline and at 48 hours, under general anesthesia. Organ harvesting was achieved after one week. HP modifications were discovered in all kidney samples, with dystrophic changes and vacuolization of mesangial cells, dilation of renal tubules and epithelial atrophy. Congestion of vascular structures also occurred. The liver samples showed severe alteration in both vessels and hepatocytes. Adrenal gland impairment was confirmed through an increase in vacuole number in all areas, while a decrease in colloid content was noted in the thyroid gland simultaneously with a modified foamy aspect. This study is the first to certify the extent of organ injury induced by OP exposure, describing both glomerular and tubular involvement in the kidneys, liver necrosis and endocrine disturbances.

Defining therapeutic targets for renal fibrosis: Exploiting the biology of pathogenesis

Renal fibrosis is a failed wound-healing process of the kidney tissue after chronic, sustained injury, which is a common pathway and pathological marker of virtually every type of chronic kidney disease (CKD), regardless of cause. However, there is a lack of effective treatment specifically targeting against renal fibrosis per se to date. The main pathological feature of renal fibrosis is the massive activation and proliferation of renal fibroblasts and the excessive synthesis and secretion of extracellular matrix (ECM) deposited in the renal interstitium, leading to structural damage, impairment of renal function, and eventually end-stage renal disease. In this review, we summarize recent advancements regarding the participation and interaction of many types of kidney residents and infiltrated cells during renal fibrosis, attempt to comprehensively discuss the mechanism of renal fibrosis from the cellular level and conclude by highlighting novel therapeutic targets and approaches for development of new treatments for patients with renal fibrosis.

Dysregulations of miR-503-5p and Wnt/β-catenin pathway coordinate in mediating cadmium-induced kidney fibrosis

Cadmium is a severe environmental pollutant that mainly targets kidney and causes kidney disease in the end. However, the mechanism of cadmium-induced kidney disease is still unclear. In this study, we treated SD rats, kidney epithelial or fibroblast cells with cadmium, and examined the renal fibrosis process and underlying cellular and molecular mechanism. Rats received daily (Monday-Friday) subcutaneous injections of CdCl2, 0.6 mg/kg, for 6 weeks or 12 weeks, and NRK-52E cells were treated with CdCl2 of 8 μM for 24 h. Sirius red staining and immunohistochemistry assay showed that sub-chronic exposure to cadmium caused interstitial fibrosis in rat kidneys. Cell experiments showed that cadmium treatment in NRK-52E cells only changed levels of α-SMA, vimentin and E-cadherin, but not collagen1, indicating that cells other than EMT cells might be responsible for the extracellular matrix production. By contrast, co-culture of NRK-49F cells with cadmium-treated NRK-52E cells produced collagen1. Assays of supernatant of NRK-52E cell culture showed that the secreted Wnt1, Wnt4 were increased, while miR-503-5p was decreased by cadmium treatment. RT-QPCR assay found that miR-503-5p was downregulated in both kidney of rats and NRK-52E cells exposed to cadmium. miR-503-5p was further shown to be competent in hindering epithelial-mesenchymal transition and fibroblast activation. Given the well established involvement of Wnt/β-catenin pathway in fibrosis, this study suggested that dysregulations of Wnts and miR-503-5p coordinate in mediating cadmium-induced kidney fibrosis. Our findings might provide new insight in the cellular and molecular mechanisms of kidney interstitial fibrosis and novel therapeutic targets for cadmium-induced kidney disease.

The potential renal toxicity of silver nanoparticles after repeated oral exposure and its underlying mechanisms

BACKGROUND

Silver nanoparticles (AgNPs) can accumulate in various organs after oral exposure. The main objective of the current study is to evaluate the renal toxicity induced by AgNPs after repeated oral exposure and to determine the relevant molecular mechanisms.

METHODS

In this study, 40 male Wistar rats were treated with solutions containing 30, 125, 300, and 700 mg/kg of AgNPs. After 28 days of exposure, histopathological changes were assessed using hematoxylin-eosin (H&E), Masson's trichrome, and periodic acid-Schiff (PAS) staining. Apoptosis was quantified by TUNEL and immunohistochemistry of caspase-3, and the level of expression of the mRNAs of growth factors was determined using RT-PCR.

RESULTS

Histopathologic examination revealed degenerative changes in the glomeruli, loss of tubular architecture, loss of brush border, and interrupted tubular basal laminae. These changes were more noticeable in groups treated with 30 and 125 mg/kg. The collagen intensity increased in the group treated with 30 mg/kg in both the cortex and the medulla. Apoptosis was much more evident in middle-dose groups (i.e., 125 and 300 mg/kg). The results of RT-PCR indicated that Bcl-2 and Bax mRNAs upregulated in the treated groups (p < 0.05). Moreover, the data related to EGF, TNF-α, and TGF-β1 revealed that AgNPs induced significant changes in gene expression in the groups treated with 30 and 700 mg/kg compared to the control group.

CONCLUSION

Our observations showed that AgNPs played a critical role in in vivo renal toxicity.

Correlation between renal distribution of leptospires during the acute phase and chronic renal dysfunction in a hamster model of infection with Leptospira interrogans

BACKGROUND

Leptospirosis has been described as a biphasic disease consisting of hematogenous dissemination to major organs in the acute phase and asymptomatic renal colonization in the chronic phase. Several observational studies have suggested an association between leptospirosis and chronic kidney disease (CKD). We investigated the dynamics of leptospires and histopathological changes in the kidney to understand the relationship between them, and also investigated the extent of renal dysfunction in the acute and chronic phases of leptospirosis using a hamster model.

FINDINGS

Hamsters (n = 68) were subcutaneously infected with 1 × 104 cells of the Leptospira interrogans serovar Manilae strain UP-MMC-SM. A total of 53 infected hamsters developed fatal acute leptospirosis, and the remaining 15 hamsters recovered from the acute phase, 13 of which showed Leptospira colonization in the kidneys in the chronic phase. Five asymptomatic hamsters also had renal colonization in the chronic phase. Immunofluorescence staining showed that leptospires were locally distributed in the renal interstitium in the early acute phase and then spread continuously into the surrounding interstitium. The kidneys of the surviving hamsters in the chronic phase showed patchy lesions of atrophic tubules, a finding of chronic tubulointerstitial nephritis, which were substantially consistent with the distribution of leptospires in the renal interstitium. The degree of atrophic tubules in kidney sections correlated statistically with the serum creatinine level in the chronic phase (rs = 0.78, p = 0.01).

CONCLUSION

Subcutaneous infection with pathogenic leptospires could cause acute death or chronic leptospirosis in hamsters after surviving the acute phase. We suggest that the renal distribution of leptospires during the acute phase probably affected the extent of tubular atrophy, leading to CKD.