Osteopontin as a Biomarker in Chronic Kidney Disease

A bioprinted and scalable model of human tubulo-interstitial kidney fibrosis

Chronic kidney disease (CKD) affects more than 10% of the global population. As kidney function negatively correlates with the presence of interstitial fibrosis, the development of new anti-fibrotic therapies holds promise to stabilize functional decline in CKD patients. The goal of the study was to generate a scalable bioprinted 3-dimensional kidney tubulo-interstitial disease model of kidney fibrosis. We have generated novel human PDGFRβ+ pericytes, CD10+ epithelial and CD31+ endothelial cell lines and compared their transcriptomic signature to their in vivo counterpart using bulk RNA sequencing in comparison to human kidney single cell RNA-sequencing datasets. This comparison indicated that the novel cell lines still expressed kidney cell specific genes and shared many features with their native cell-state. PDGFRβ+ pericytes showed three-lineage differentiation capacity and differentiated towards myofibroblasts following TGFβ treatment. We utilized a fibrinogen/gelatin-based hydrogel as bioink and confirmed a good survival rate of all cell types within the bioink after printing. We then combined all three cells in a bioprinted model using separately printed compartments for tubule epithelium, and interstitial endothelium and pericytes. We confirmed that this 3D printed model allows to recapitulate key disease driving epithelial-mesenchymal crosstalk mechanisms of kidney fibrosis since injury of epithelial cells prior to bioprinting resulted in myofibroblast differentiation and fibrosis driven by pericytes after bioprinting. The bioprinted model was also scalable up to a 96-well format.

Single-cell analysis of proximal tubular cells with different DNA content reveals functional heterogeneity in the acute kidney injury to chronic kidney disease transition

INTRODUCTION

Proximal tubular epithelial cells with different DNA contents emerge after acute kidney injury (AKI). However, their heterogeneity and roles in the acute kidney injury-to-chronic kidney disease (AKI-to-CKD) transition remain incompletely understood.

METHODS

Proximal tubular epithelial cells with different DNA contents were isolated at days 3 and 14 post-AKI following ischemia reperfusion injury for single-cell RNA sequencing.

RESULTS

Here, we found that proximal tubular epithelial cells with different DNA contents have existing and distinct bulk transcriptome profiles, especially those cells over 4N (polyploid cells with more than four chromosome sets) with upregulated profibrotic signatures. Heterogeneity existed within four distinct functional clusters. In particular, the polyploid cells demonstrated a preferential enrichment within specific proinflammatory and profibrotic clusters post-AKI. Polyploid cells within these specific clusters displayed the profibrotic trajectory, accompanied by increased fibrosis-driving regulon activity and very strong cell-cell interactions. This suggests polyploidy cells have an intrinsic role in promoting the AKI-to-CKD transition. Furthermore, we identified that secreted phosphoprotein 1 (SPP1) as the pivotal hub of polyploid cells and may be involved in various profibrotic signaling pathways. Genetic knockdown of SPP1 in the proximal tubule in vivo dramatically ameliorated kidney fibrosis.

CONCLUSIONS

Overall, our findings reveal the heterogeneity of proximal tubular epithelial cells with different DNA contents and identify intrinsic factors of polyploid cells such as SPP1 expression in promoting kidney fibrosis. Our study provides novel insights into potential therapeutic target of preventing the AKI-to-CKD transition.

The role of osteopontin in chronic kidney disease-mineral bone disorder

PURPOSE OF REVIEW

Chronic kidney disease-mineral bone disorder (CKD-MBD) is associated with several adverse outcomes, including bone fragility and sarcopenia. Identification of new agents mitigating systemic damage related to uremia is critical and needed to unveil pathways implicated in CKD-MBD.

RECENT FINDINGS

Osteopontin (OPN) is involved in different physiological and pathological processes and works as a bridge connecting several systems. It may serve as a biomarker for many diseases, including human cancers, neurodegenerative disorders and autoimmune diseases. OPN has been implicated in disturbances of bone mineralization and remodeling, and has an interplay with parathyroid hormone and FGF23 in experimental models. In patients with CKD and severe hyperparathyroidism, OPN expression in muscle tissue has been linked to worse functionality and local inflammation, which is partially reverted after parathyroidectomy.

SUMMARY

Future studies could confirm the role of OPN as a biomarker in nephrology. Greater understanding of its role in CKD-MBD will help us define a better therapeutic strategy in patients with CKD.

Nfil3 contributes to renal fibrosis by activating fibroblasts through directly promoting the expression of Spp1

The activation of fibroblasts into myofibroblasts and the expansion of myofibroblasts are key processes contributing to renal fibrosis; however, the precise underlying mechanisms remain largely unclear. In this study, we found that nuclear factor, interleukin 3 regulated (Nfil3), a basic leucine zipper transcription factor, was significantly upregulated in fibroblasts in kidney tissues from mouse models of unilateral ureteral obstruction (UUO)-induced renal fibrosis and kidney biopsies from patients with renal fibrosis. Conditional knockout of Nfil3 in fibroblasts (Nfil3flox/floxS100a4Cre) and global knockout of Nfil3 reduced UUO-induced accumulation of myofibroblasts and the severity of renal fibrosis in mice, whereas ectopic expression of Nfil3 in fibroblasts activated renal interstitial fibroblasts and initiated renal fibrosis. Overexpression of Nfil3 significantly induced the expression of secreted phosphoprotein 1 (Spp1). Mechanistically, Nfil3 mediated the upregulation of Spp1 in renal fibroblasts by interacting with a conserved sequence in the promoter of Spp1 to regulate its transcription. Furthermore, transforming growth factor beta 1 (Tgfb1) was found to induce the upregulation of Nfil3 in renal fibroblasts. Knockdown of Nfil3 attenuated Tgfb1-induced expression of extracellular matrix proteins and the proliferation of fibroblasts by downregulating Spp1. Altogether, these results suggest that Nfil3 plays an important role in the activation and expansion of fibroblasts, thereby contributing to renal fibrosis.

The Identification of Novel Anti-Inflammatory Effects of Cannabigerol in the Kidney Tissue of Rats Subjected to a High-Fat High-Sucrose Diet

The inflammatory state is a significant factor associated with diabetic kidney disease (DKD), making it one of the significant causes of chronic kidney disease. Despite the availability of data, there is a lack of targeted treatment strategies for diabetes-related kidney disorders. The aim of our study was to determine the impact of cannabigerol (CBG) on lipid precursors for inflammatory mediators during DKD development. A six-week experiment was conducted on male Wistar rats fed standard (Control) or high-fat high-sucrose (HFHS) diets. For the last 14 days of the experiment (5th and 6th weeks), half of the rats from the Control and HFHS groups intragastrically received CBG solution. Gas-liquid chromatography (GLC) was used to measure the activities of n-6 and n-3 polyunsaturated fatty acid (PUFA) metabolic pathways and the concentrations of arachidonic acid (AA), eicosapentaenoic acid (EPA), and docosahexaenoic acid (DHA) in selected lipid fractions. Immunoblotting was performed to assess the expression of proteins involved in the regulation of the inflammatory state. A multiplex immunoassay kit was used to determine kidney toxicity biomarker levels. Our results revealed that CBG administration to rats fed an HFHS diet decreased n-6 PUFA biosynthetic pathway activity in phospholipid (PL) and triacylglycerol (TAG) and increased n-3 PUFA biosynthetic pathway activity in TAG and free fatty acid (FFA). We also observed a reduction in the AA concentration in PL, FFA, and diacylglycerol (DAG). CBG supplementation reduced the level of kidney damage biomarkers, such as osteopontin (OPN). Our observations confirm that CBG has potential anti-inflammatory properties and may be successfully used for further research to seek targeted therapies of inflammatory disorders, including diabetic kidney disease progression.

Biomarkers in Contrast-Induced Nephropathy: Advances in Early Detection, Risk Assessment, and Prevention Strategies

Contrast-induced nephropathy (CIN) represents a significant complication associated with the use of iodinated contrast media (ICM), especially in individuals with preexisting renal impairment. The pathophysiology of CIN encompasses oxidative stress, inflammation, endothelial dysfunction, and hemodynamic disturbances, resulting in acute kidney injury (AKI). Early detection is essential for effective management; however, conventional markers like serum creatinine (sCr) and estimated glomerular filtration rate (eGFR) exhibit limitations in sensitivity and timeliness. This review emphasizes the increasing significance of novel biomarkers in enhancing early detection and risk stratification of contrast-induced nephropathy (CIN). Recent advancements in artificial intelligence and computational analytics have improved the predictive capabilities of these biomarkers, enabling personalized risk assessment and precision medicine strategies. Additionally, we discuss mitigation strategies, including hydration protocols, pharmacological interventions, and procedural modifications, aimed at reducing CIN incidence. Incorporating biomarker-driven assessments into clinical decision-making can enhance patient management and outcomes. Future research must prioritize the standardization of biomarker assays, the validation of predictive models across diverse patient populations, and the exploration of novel therapeutic targets. Utilizing advancements in biomarkers and risk mitigation strategies allows clinicians to improve the safety of contrast-enhanced imaging and reduce the likelihood of renal injury.

Osteopontin in rheumatic diseases: A systematic review and meta-analysis

Osteopontin (OPN), a glycoprotein involved in immune regulation and inflammation, is a potential candidate biomarker for rheumatic diseases (RDs). However, variability across studies limits its clinical utility. This meta-analysis evaluated OPN concentrations in RD patients compared to healthy controls and explored sources of heterogeneity. A systematic search identified 37 studies (43 comparator groups) including 3,201 RD patients and 2,543 controls. Standardized mean differences (SMDs) were calculated, and subgroup and meta-regression analyses examined the modulating role of demographic and clinical variables. Publication bias was assessed using Begg's and Egger's tests. OPN concentrations were significantly higher in RD patients than controls (SMD = 1.54, 95 % CI: 1.17-1.90, p < 0.001). Subgroup analysis revealed consistent elevations in systemic lupus erythematosus (SLE, SMD = 0.97, I2 = 0 %) and rheumatoid arthritis (RA, SMD = 0.70, I2 = 92.5 %), with osteoarthritis showing the largest effect size (SMD = 4.02). Age significantly moderated OPN concentrations (p = 0.030). Although publication bias was detected (p < 0.05), removing seven studies eliminated bias and maintained significant between-group differences (SMD = 0.78, 95 % CI: 0.62-0.93; p < 0.001). The high concentrations of OPN support its possible use as a candidate biomarker for RDs, particularly in SLE and RA. Resolution of heterogeneity and standardization may improve its clinical utility.

The immune duality of osteopontin and its therapeutic implications for kidney transplantation

Osteopontin (OPN) is a multifunctional glycoprotein with various structural domains that enable it to perform diverse functions in both physiological and pathological states. This review comprehensively examines OPN from multiple perspectives, including its protein structure, interactions with receptors, interactions with immune cells, and roles in kidney diseases and transplantation. This review explores the immunological duality of OPN and its significance and value as a biomarker and therapeutic target in kidney transplantation. In cancer, OPN typically promotes tumor evasion by suppressing the immune system. Conversely, in immune-related kidney diseases, particularly kidney transplantation, OPN activates the immune system by enhancing the migration and activation of immune cells, thereby exacerbating kidney damage. This immunological duality may stem from different OPN splice variants and the exposure, after cleavage, of different structural domains, which play distinct biological roles in cellular interactions. Additionally, OPN has a significant biological impact posttransplantation and on chronic kidney disease and, highlighting its importance as a biomarker and potential therapeutic target. Future research should further explore the specific mechanisms of OPN in kidney transplantation to improve treatment strategies and enhance patient quality of life.

Telomere Length, Oxidative Stress, and Kidney Damage Biomarkers in Fabry Nephropathy

Fabry nephropathy is a life-threatening complication of Fabry disease characterized by complex and incompletely understood pathophysiological processes possibly linked to premature aging. We aimed to investigate leukocyte telomere length (LTL), oxidative stress, and kidney damage biomarkers in relation to kidney function. The study included 35 Fabry patients and 35 age and sex-matched control subjects. Based on the estimated slope of the glomerular filtration rate, the patients were divided into two groups. Relative LTL was quantified by qPCR, urinary biomarkers 8-hydroxy-2'-deoxyguanosine (8-OHdG) and malondialdehyde (MDA) by UHPLC-MS/MS, and kidney damage biomarkers by flow cytometry. There was no statistically significant difference in LTL between Fabry patients and controls. However, a significant difference was observed in male patients compared to their matched control subjects (p = 0.013). Oxidative stress biomarkers showed no differences between patients and controls, while significant differences were observed in urinary IGFBP7, EGF, and OPN levels between Fabry patients with stable kidney function and those with progressive nephropathy (FDR = 0.021, 0.002, and 0.013, respectively). Significant differences were also observed in plasma levels of cystatin C, TFF3, and uromodulin between patients with progressive nephropathy and controls (all FDR = 0.039). Along with these biomarkers (FDR = 0.007, 0.017, and 0.010, respectively), NGAL also exhibited a significant difference between the two patient groups (FDR = 0.017). This study indicates accelerated telomere attrition, which may be related to disease burden in males. Furthermore, analyses of urinary oxidative stress markers revealed no notable disparities between the different kidney function groups, indicating their limited utility. However, promising differences were found in some biomarkers of kidney damage in urine and plasma.

Mechanisms, Biomarkers, and Treatment Approaches for Diabetic Kidney Disease: Current Insights and Future Perspectives

Diabetic Kidney Disease (DKD) is the leading cause of end-stage renal disease (ESRD) worldwide. Among individuals with type 1 diabetes mellitus (T1DM), 30-40% are at risk of developing DKD. This review focuses on the mechanistic processes, available and emerging biomarkers for diagnosing, monitoring, and preventing DKD, as well as treatment options targeted at DKD patients. A literature search was conducted on PubMed and Scopus using specific keywords. Inclusion and exclusion criteria were applied to select the articles used for this review. The literature highlights various mechanisms involved in the progression of DKD to more severe stages. Additionally, several biomarkers have been identified, which aid in diagnosing and monitoring the disease. Furthermore, numerous treatment approaches are being explored to address the underlying causes of DKD. Advanced research is exploring new medications to aid in DKD remission; sodium-glucose cotransport (SGLT2) inhibitors and finerenone, in particular, are gaining attention for their novel renoprotective effects. DKD is a major complication of diabetes, marked by complex and multifactorial mechanisms. Thus, understanding these processes is essential for developing targeted therapies to potentially reverse DKD progression. Biomarkers show promise for early diagnosis and monitoring of disease progression, while current treatment strategies underscore the importance of a multifaceted approach.

Investigating the Role of Osteopontin (OPN) in the Progression of Breast, Prostate, Renal and Skin Cancers

Background/Objectives: Cancer is caused by disruptions in the homeostatic state of normal cells, which results in dysregulation of the cell cycle, and uncontrolled growth and proliferation in affected cells to form tumors. Successful development of tumorous cells proceeds through the activation of pathways promoting cell development and functionality, as well as the suppression of immune signaling pathways; thereby providing these cells with proliferative advantages, which subsequently metastasize into surrounding tissues. These effects are primarily caused by the upregulation of oncogenes, of which SPP1 (secreted phosphoprotein 1), a non-collagenous bone matrix protein, is one of the most well-known. Methods: In this study, we conducted a further examination of the transcriptomic expression profile of SPP1 (Osteopontin) during the progression of cancer in four human tissues, breast, prostate, renal and skin, in order to understand the circumstances conducive to its activation and dysregulation, the biological pathways and other mechanisms involved as well as differences in its splicing patterns influencing its expression and functionality. Results: A significant overexpression of SPP1, as well as a set of other highly correlated genes, was seen in most of these tissues, indicating their extensive implication in cancer. Increased expression was observed with higher tumor stages, especially in renal and skin cancer, while applying therapeutic modalities targeting these genes dampened this effect in breast, prostate and skin cancer. Pathway analyses showed gene signatures related to cell growth and development enriched in tumorigenic conditions and earlier cancer stages, while later stages of cancer showed pathways associated with weakened immune response, in all cancers studied. Moreover, the utilization of therapeutic methods showed the activation of immunogenic pathways in breast, prostate and skin cancer, thereby confirming their viability. Further analyses of differential transcript expression levels in these oncogenes showed their exonic regions to be selectively overexpressed similarly in tumorigenic samples in all cancers studied, while also displaying significant differences in exon selectivity between constituent transcripts, providing a basis for their high degree of multifunctionality in cancer. Conclusions: Overall, this study corroborates the entrenched role of SPP1 in the progression of these four types of cancer, as confirmed by its overexpression and activation of related oncogenes, their co-involvement in key cellular pathways, and predisposition to exhibit differential splicing between their transcripts, while the above effects were found to be highly inhibitable through treatment methods, thereby highlighting its promising role in therapeutic development.

Lack of renoprotective effects by long-term PCSK9 and SGLT2 inhibition using alirocumab and empagliflozin in obese ZSF1 rats

Chronic kidney disease (CKD) is associated with an increased risk of cardiovascular disease (CVD). Despite the entry of sodium glucose cotransporter 2 (SGLT2) inhibitors, CKD persists as a medical challenge. Proprotein convertase subtilisin/kexin type 9 (PCSK9) inhibition reduces low-density lipoprotein (LDL)-cholesterol, a major risk factor of CVD. Interestingly, studies indicate that PCSK9 inhibition decreases proteinuria in kidney disease, complementing the reduced CVD risk. This study aimed to validate obese ZSF1 rats as a model for the renoprotective effects of PCSK9 and SGLT2 inhibition using alirocumab and empagliflozin for 15 wk. Obese rats revealed a significant reduction in measured glomerular filtration rate (mGFR) and increased urine albumin/creatinine ratio (UACR) during follow-up compared with lean controls. Alirocumab treatment resulted in a decline in mGFR and increased UACR compared with vehicle-treated obese rats. Immunohistochemistry showed increased fibrosis and inflammation in kidney tissue from obese rats treated with empagliflozin or alirocumab, whereas hepatic cholesterol and triglyceride levels were lowered compared with vehicle-treated obese rats. Although alirocumab lowered circulating free cholesterol levels throughout the treatment period, certain cholesteryl esters were increased at the end of the study, resulting in no overall difference in total cholesterol levels in the alirocumab group. Correspondingly, only a trend toward increased hepatic LDL-receptor levels was observed. In conclusion, these findings suggest that alirocumab treatment aggravates kidney dysfunction in obese ZSF1 rats. Moreover, in contrast to the renoprotective properties of empagliflozin observed in patients with CKD, empagliflozin did not ameliorate kidney disease progression in the obese ZSF1 rat.NEW & NOTEWORTHY New treatments to slow kidney disease progression and reduce cardiovascular disease risk are needed for chronic kidney disease (CKD). We investigated the cholesterol-lowering PCSK9 inhibitor alirocumab as a new treatment for proteinuric CKD and the effect of SGLT2 inhibition using empagliflozin in obese ZSF1 rats. Regarding renoprotection, our findings were contradictory with previous preclinical studies and clinical data, suggesting that different pathophysiological mechanisms may apply to this rat model.

The Bone-Vascular Axis: A Key Player in Chronic Kidney Disease Associated Vascular Calcification

Background

The bone-vascular axis plays a key role in the pathogenesis of vascular calcification (VC) in patients with chronic kidney disease (CKD). Understanding and managing the role of the bone-vascular axis in CKD-mineral and bone disorder (CKD-MBD) is critical for preventing and treating associated complications, including osteoporosis, arterial calcification, and cardiovascular diseases. This study aimed to comprehensively summarize the role of bone metabolism markers in uremic VC.

Summary

The skeleton, as an endocrine organ, can regulate systemic metabolic processes by secreting various bioactive substances. These molecules can induce the transdifferentiation of vascular smooth muscle cells, promoting their transition to other functional states, thereby affecting vascular growth and remodeling.

Key Messages

The prevalence of VC in individuals with CKD is notably high. CKD-associated VC is characterized by the widespread accumulation of hydroxyapatite within the arterial media, which occurs as a result of the transformation of smooth muscle cells into osteoblastic smooth muscle cells under the influence of uremic toxins. Osteoblasts and osteoclasts in bone tissue secrete mineral metabolic proteins, which can influence neighboring cells, primarily vascular smooth muscle cells, through paracrine signaling. Both circulating and osteocytic sclerostin can exert a protective effect by inhibiting wingless/integrated (WNT)-induced calcification. The therapeutic goal for CKD-MBD is to reduce production of sclerostin by decreasing the osteogenic transdifferentiation of vascular smooth muscle cells. Calciprotein particles act as a physiological agent for delivering calcium-phosphate the bone and inducing fibroblast growth factor-23 expression in osteoblasts.

Senescence Biomarkers and Trajectories of Frailty and Physical Function After Kidney Transplantation

Cellular senescence is a biological mechanism of aging and age-related diseases. The aim of this study was to examine whether senescence biomarkers are associated with frailty and physical function trajectories in patients undergoing kidney transplantation (KT). We also discussed the relationship between senescence biomarkers and KT function. In this multicenter study, we prospectively assessed plasma levels of senescence biomarkers, frailty as measured by the Physical Frailty Phenotype, and physical function as measured by the Short Physical Performance Battery prior to KT. Frailty, physical function, and KT function were also measured 1 year after KT. Variable associations were assessed using Cox and relaxed least absolute shrinkage and selection operation regression. The cohort consisted of 197 participants (mean age 53 ± 13 years, 61.4% male, and 80.2% White race). Higher pre-KT levels of macrophage-derived chemokine (MDC/CCL22) and growth differentiation factor-15 (GDF-15) were independently associated with less improvement in frailty and/or physical function during the first year after KT. Higher pre-KT levels tumor necrosis factor receptor superfamily member 6 (FAS) and MMP-9 levels were independently associated with lower KT function one year after KT. Pre-KT cellular senescence may contribute to frailty, physical function, and kidney function trajectories during the first year after KT.

Molecular characterization of PANoptosis-related genes in chronic kidney disease

Chronic kidney disease (CKD) is characterized by fibrosis and inflammation in renal tissues. Several types of cell death have been implicated in CKD onset and progression. Unlike traditional forms of cell death, PANoptosis is characterized by the crosstalk among programmed cell death pathways. However, the interaction between PANoptosis and CKD remains unclear. Here, we used bioinformatics methods to identify differentially expressed genes and differentially expressed PANoptosis-related genes (DE-PRGs) using data from the GSE37171 dataset. Following this, we further performed gene ontology (GO), Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment analysis, and gene set enrichment analysis using the data. We adopted a combined approach to select hub genes, using the STRING database and CytoHubba plug-in, and we used the GSE66494 as a validation dataset. In addition, we constructed ceRNA, transcription factor (TF)-gene, and drug-gene networks using Cytoscape. Lastly, we conducted immunohistochemical analysis and western blotting to validate the hub genes. We identified 57 PANoptosis-associated genes as DE-PRGs. We screened nine hub genes from the 57 DE-PRGs. We identified two hub genes (FOS and PTGS2) using the GSE66494 database, Nephroseq, immunohistochemistry, and western blotting. A common miRNA (Hsa-miR-101-3p) and three TFs (CREB1, E2F1, and RELA) may play a crucial role in the onset and progression of PANoptosis-related CKD. In our analysis of the drug-gene network, we identified eight drugs targeting FOS and 52 drugs targeting PTGS2.

Cellular dynamics in pig-to-human kidney xenotransplantation

BACKGROUND

Xenotransplantation of genetically engineered porcine organs has the potential to address the challenge of organ donor shortage. Two cases of porcine-to-human kidney xenotransplantation were performed, yet the physiological effects on the xenografts and the recipients' immune responses remain largely uncharacterized.

METHODS

We performed single-cell RNA sequencing (scRNA-seq) and longitudinal RNA-seq analyses of the porcine kidneys to dissect xenotransplantation-associated cellular dynamics and xenograft-recipient interactions. We additionally performed longitudinal scRNA-seq of the peripheral blood mononuclear cells (PBMCs) to detect recipient immune responses across time.

FINDINGS

Although no hyperacute rejection signals were detected, scRNA-seq analyses of the xenografts found evidence of endothelial cell and immune response activation, indicating early signs of antibody-mediated rejection. Tracing the cells' species origin, we found human immune cell infiltration in both xenografts. Human transcripts in the longitudinal bulk RNA-seq revealed that human immune cell infiltration and the activation of interferon-gamma-induced chemokine expression occurred by 12 and 48 h post-xenotransplantation, respectively. Concordantly, longitudinal scRNA-seq of PBMCs also revealed two phases of the recipients' immune responses at 12 and 48-53 h. Lastly, we observed global expression signatures of xenotransplantation-associated kidney tissue damage in the xenografts. Surprisingly, we detected a rapid increase of proliferative cells in both xenografts, indicating the activation of the porcine tissue repair program.

CONCLUSIONS

Longitudinal and single-cell transcriptomic analyses of porcine kidneys and the recipient's PBMCs revealed time-resolved cellular dynamics of xenograft-recipient interactions during xenotransplantation. These cues can be leveraged for designing gene edits and immunosuppression regimens to optimize xenotransplantation outcomes.

FUNDING

This work was supported by NIH RM1HG009491 and DP5OD033430.

Drug-induced kidney injury: challenges and opportunities

Drug-induced kidney injury (DIKI) is a frequently reported adverse event, associated with acute kidney injury, chronic kidney disease, and end-stage renal failure. Prospective cohort studies on acute injuries suggest a frequency of around 14%-26% in adult populations and a significant concern in pediatrics with a frequency of 16% being attributed to a drug. In drug discovery and development, renal injury accounts for 8 and 9% of preclinical and clinical failures, respectively, impacting multiple therapeutic areas. Currently, the standard biomarkers for identifying DIKI are serum creatinine and blood urea nitrogen. However, both markers lack the sensitivity and specificity to detect nephrotoxicity prior to a significant loss of renal function. Consequently, there is a pressing need for the development of alternative methods to reliably predict drug-induced kidney injury (DIKI) in early drug discovery. In this article, we discuss various aspects of DIKI and how it is assessed in preclinical models and in the clinical setting, including the challenges posed by translating animal data to humans. We then examine the urinary biomarkers accepted by both the US Food and Drug Administration (FDA) and the European Medicines Agency for monitoring DIKI in preclinical studies and on a case-by-case basis in clinical trials. We also review new approach methodologies (NAMs) and how they may assist in developing novel biomarkers for DIKI that can be used earlier in drug discovery and development.

Osteopontin: A Versatile Biomarker-Insights and Innovations from Three Decades of Research

This second Biomedicines Special Issue-"30 Years of osteopontin (OPN) Milestones and Future Avenues 2 [...].

Proteomic Changes Induced by the Immunosuppressant Everolimus in Human Podocytes

mTOR inhibitors (mTOR-Is) may induce proteinuria in kidney transplant recipients through podocyte damage. However, the mechanism has only been partially defined. Total cell lysates and supernatants of immortalized human podocytes treated with different doses of everolimus (EVE) (10, 100, 200, and 500 nM) for 24 h were subjected to mass spectrometry-based proteomics. Support vector machine and partial least squares discriminant analysis were used for data analysis. The results were validated in urine samples from 28 kidney transplant recipients receiving EVE as part of their immunosuppressive therapy. We identified more than 7000 differentially expressed proteins involved in several pathways, including kinases, cell cycle regulation, epithelial-mesenchymal transition, and protein synthesis, according to gene ontology. Among these, after statistical analysis, 65 showed an expression level significantly and directly correlated with EVE dosage. Polo-Like Kinase 1 (PLK1) content was increased, whereas osteopontin (SPP1) content was reduced in podocytes and supernatants in a dose-dependent manner and significantly correlated with EVE dose (p < 0.0001, FDR < 5%). Similar results were obtained in the urine of kidney transplant patients. This study analyzed the impact of different doses of mTOR-Is on podocytes, helping to understand not only the biological basis of their therapeutic effects but also the possible mechanisms underlying proteinuria.

Identification of ligand and receptor interactions in CKD and MASH through the integration of single cell and spatial transcriptomics

BACKGROUND

Chronic Kidney Disease (CKD) and Metabolic dysfunction-associated steatohepatitis (MASH) are metabolic fibroinflammatory diseases. Combining single-cell (scRNAseq) and spatial transcriptomics (ST) could give unprecedented molecular disease understanding at single-cell resolution. A more comprehensive analysis of the cell-specific ligand-receptor (L-R) interactions could provide pivotal information about signaling pathways in CKD and MASH. To achieve this, we created an integrative analysis framework in CKD and MASH from two available human cohorts.

RESULTS

The analytical framework identified L-R pairs involved in cellular crosstalk in CKD and MASH. Interactions between cell types identified using scRNAseq data were validated by checking the spatial co-presence using the ST data and the co-expression of the communicating targets. Multiple L-R protein pairs identified are known key players in CKD and MASH, while others are novel potential targets previously observed only in animal models.

CONCLUSION

Our study highlights the importance of integrating different modalities of transcriptomic data for a better understanding of the molecular mechanisms. The combination of single-cell resolution from scRNAseq data, combined with tissue slide investigations and visualization of cell-cell interactions obtained through ST, paves the way for the identification of future potential therapeutic targets and developing effective therapies.

Nontargeted Plasma Proteomic Analysis of Renal Disease and Pulmonary Hypertension in Patients with Sickle Cell Disease

Sickle cell disease (SCD) is characterized by red blood cell sickling, vaso-occlusion, hemolytic anemia, damage to multiple organ systems, and, as a result, shortened life expectancy. Sickle cell disease nephropathy (SCDN) and pulmonary hypertension (pHTN) are common and frequently co-occurring complications of SCD; both are associated with markedly accelerated mortality. To identify candidate circulating biomarkers of SCDN and pHTN, we used mass spectrometry to quantify the relative abundance of >1000 proteins in plasma samples from 189 adults with SCD from the Outcome Modifying Genes in SCD (OMG-SCD) cohort (ProteomeXchange identifier PXD048716). Forty-four proteins were differentially abundant in SCDN, most significantly cystatin-C and collagen α-1(XVIII) chain (COIA1), and 55 proteins were dysregulated in patients with SCDN and pHTN, most significantly insulin-like growth factor-binding protein 6 (IBP6). Network analysis identified a module of 133 coregulated proteins significantly associated with SCDN, that was enriched for extracellular matrix proteins, insulin-like growth factor binding proteins, cell adhesion proteins, EGF-like calcium binding proteins, and several cadherin family members. Collectively, these data provide a comprehensive understanding of plasma protein changes in SCDN and pHTN which validate numerous studies of chronic kidney disease and suggest shared profiles of protein disruption in kidney dysfunction and pHTN among SCD patients.

The Role of Osteopontin in Atherosclerosis and Its Clinical Manifestations (Atherosclerotic Cardiovascular Diseases)-A Narrative Review

Atherosclerotic cardiovascular diseases (ASCVDs) are the most common and severe public health problem nowadays. Osteopontin (OPN) is a multifunctional glycoprotein highly expressed at atherosclerotic plaque, which has emerged as a potential biomarker of ASCVDs. OPN may act as an inflammatory mediator and/or a vascular calcification (VC) mediator, contributing to atherosclerosis progression and eventual plaque destabilization. In this article, we discuss the complex role of OPN in ASCVD pathophysiology, since many in vitro and in vivo experimental data indicate that OPN contributes to macrophage activation and differentiation, monocyte infiltration, vascular smooth muscle cell (VSMC) migration and proliferation and lipid core formation within atherosclerotic plaques. Most but not all studies reported that OPN may inhibit atherosclerotic plaque calcification, making it "vulnerable". Regarding clinical evidence, serum OPN levels may become a biomarker of coronary artery disease (CAD) presence and severity. Significantly higher OPN levels have been found in patients with acute coronary syndromes than those with stable CAD. In limited studies of patients with peripheral artery disease, circulating OPN concentrations may be predictive of future major adverse cardiovascular events. Overall, the current literature search suggests the contribution of OPN to atherosclerosis development and progression, but more robust evidence is required.

Pathomechanisms of Diabetic Kidney Disease

The worldwide occurrence of diabetic kidney disease (DKD) is swiftly rising, primarily attributed to the growing population of individuals affected by type 2 diabetes. This surge has been transformed into a substantial global concern, placing additional strain on healthcare systems already grappling with significant demands. The pathogenesis of DKD is intricate, originating with hyperglycemia, which triggers various mechanisms and pathways: metabolic, hemodynamic, inflammatory, and fibrotic which ultimately lead to renal damage. Within each pathway, several mediators contribute to the development of renal structural and functional changes. Some of these mediators, such as inflammatory cytokines, reactive oxygen species, and transforming growth factor β are shared among the different pathways, leading to significant overlap and interaction between them. While current treatment options for DKD have shown advancement over previous strategies, their effectiveness remains somewhat constrained as patients still experience residual risk of disease progression. Therefore, a comprehensive grasp of the molecular mechanisms underlying the onset and progression of DKD is imperative for the continued creation of novel and groundbreaking therapies for this condition. In this review, we discuss the current achievements in fundamental research, with a particular emphasis on individual factors and recent developments in DKD treatment.

Obesity and Bone Mineral Density Protection Paradox in Chronic Kidney Disease: Secreted Protein Acidic and Rich in Cysteine as a Piece of the Puzzle?

Obesity is a health condition that represents a risk factor for numerous diseases and complications. However, obesity might also have-to some extent-some "benefits" in certain situations. This includes potential bone protection in patients suffering from chronic kidney disease. In an attempt to explain such a paradox, we highlight secreted protein acidic and rich in cysteine (SPARC) as a hypothetical mediator of this protection. Indeed, SPARC properties provide a logical rationale to describe such bone protection via its overexpression combined with its calcium-binding and collagen-binding properties. We believe that exploring such hypotheses could open new doors to elucidate unknown pathways towards developing a new generation of molecular therapies.

Fibroblast Growth Factor 23 Neutralizing Antibody Ameliorates Abnormal Renal Phosphate Handling in Sickle Cell Disease Mice

We assessed the involvement of fibroblast growth factor 23 (FGF23) in phosphaturia in sickle cell disease (SCD) mice. Control and SCD mice were treated with FGF23 neutralizing antibody (FGF23Ab) for 24 hours. Serum ferritin was significantly increased in SCD mice and was significantly reduced in female but not male SCD mice by FGF23Ab. FGF23Ab significantly reduced increased erythropoietin in SCD kidneys. Serum intact FGF23 was significantly increased in SCD female mice and was markedly increased in SCD male mice; however, FGF23Ab significantly reduced serum intact FGF23 in both genotypes and sexes. Serum carboxy-terminal-fragment FGF23 (cFGF23) was significantly reduced in SCD IgG male mice and was markedly but not significantly reduced in SCD IgG female mice. FGF23Ab significantly increased cFGF23 in both sexes and genotypes. Serum 1,25-dihydroxyvitamin D3 was significantly increased in SCD IgG and was further significantly increased by FGF23Ab in both sexes and genotypes. Significantly increased blood urea nitrogen in SCD was not reduced by FGF23Ab. The urine phosphate (Pi)/creatinine ratio was significantly increased in SCD in both sexes and was significantly reduced by FGF23Ab. Increased SCD kidney damage marker kidney injury molecule 1 was rescued, but sclerotic glomeruli, increased macrophages, and lymphocytes were not rescued by short-term FGF23Ab. FGF23Ab significantly reduced increased phospho-fibroblast growth factor receptor 1, αKlotho, phosphorylated extracellular signal-regulated kinase, phosphorylated serum/glucocorticoid-regulated kinase 1, phosphorylated sodium-hydrogen exchanger regulatory factor-1, phosphorylated janus kinase 3, and phosphorylated transducer and activator of transcription-3 in SCD kidneys. The type II sodium Pi cotransporter (NPT2a) and sodium-dependent Pi transporter PiT-2 proteins were significantly reduced in SCD kidneys and were increased by FGF23Ab. We conclude that increased FGF23/FGF receptor 1/αKlotho signaling promotes Pi wasting in SCD by downregulating NPT2a and PIT2 via modulation of multiple signaling pathways that could be rescued by FGF23Ab.

Toxicity induced by orellanine from the mushroom Cortinarius orellanus in primary renal tubular proximal epithelial cells (RPTEC): Novel mechanisms of action

The toxicity of Orellanine (OR), a significant factor in mushroom poisoning, has severe effects on the kidneys, particularly the proximal tubules. This study investigated the acute toxicity of OR from the Cortinarius orellanus mushroom in human Primary Renal Tubular Proximal Epithelial Cells (RPTEC). Additionally, the half maximal inhibitory concentration (IC50) of OR in MCF-7 cells was established. RPTEC were subjected to a 6.25 μg/ml dose of orellanine for 24 h, while Control cells were exposed to 0.05% DMSO (vehicle). The RT2 Profiler™ PCR Array Human Nephrotoxicity was utilized to identify genes that were upregulated or downregulated. Western blotting confirmed the protein product of some significantly regulated genes compared to control cells. The IC50 of OR was found to be 319.2 μg/ml. The mechanism of OR toxicity involved several pathways including apoptosis, metal ion binding, cell proliferation, tissue remodeling, xenobiotic metabolism, transporters, extracellular matrix molecules, and cytoskeleton pathways. Other genes from non-specific pathways were also identified. These findings enhance our understanding of OR nephrotoxicity and pave the way for future research into potential treatments or antidotes for natural mushroom poisoning.